Addition of Green and Black Liquor in Kraft Pulping of Eucalyptus dunnii wood: Possible Solutions for the Problems with Kraft Pulping Caused by High Calcium Content

Addition of Green and Black Liquor in Kraft Pulping of Eucalyptus dunnii wood: Possible Solutions for the Problems with Kraft Pulping Caused by High Calcium Content | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Addition of Green and Black Liquor in Kraft Pulping of Eucalyptus dunnii wood: Possible Solutions for the Problems with Kraft Pulping Caused by High Calcium Content Vijaya Vegunta, Olena Sevastyanova, Raghu Deshpande, Pär A. Lindén, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3165099/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 20 Dec, 2023 Read the published version in Cellulose → Version 1 posted 7 You are reading this latest preprint version Abstract In our previous study, we demonstrated that Eucalyptus dunnii samples containing high calcium content show inferior pulping properties concerning delignification and polysaccharide degradation. This led us to investigate alternative methods for improving the pulping process of these samples. In the present work, we evaluated the effects of incorporating black and green liquors into the Eucalyptus dunnii chips before kraft pulping, aiming to enhance the pulping process and overcome the negative impact of high calcium content. The addition of both black and green liquors resulted in specific enhancements, with the green liquor having a more significant impact on the pulping process. Even wood samples with the highest calcium content demonstrated satisfactory pulping results when treated with green liquor. Delignification occurred more rapidly, and selectivity was higher for samples pre-treated with green liquor before kraft pulping. Moreover, calcium tended to follow the fiber under these conditions rather than being released into the black liquor, which may contribute to the improved pulping performance. Subsequent bleaching tests revealed that the bleachability of green liquor-treated pulp was nearly identical to that of a control pulp, while maintaining a higher viscosity. This suggests that incorporating green liquor into the pre-treatment process not only improves the pulping performance of Eucalyptus dunnii samples with high calcium content but also maintains desirable bleachability characteristics. To better understand the underlying mechanisms of these findings, we discuss the potential chemical explanations behind the observed improvements. Kraft pulping green liquor black liquor Eucalyptus dunnii Calcium Delignification Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Introduction For many years, kraft pulping has maintained its status as the most crucial method for processing wood, primarily due to its low operating costs, which can be attributed in part to efficient chemical recovery systems. Other factors contributing to its success include its relatively high selectivity of delignification and its broad tolerance for various raw materials (Ragnar et al. 2013 ). Despite this wide range of acceptable raw materials, not all wood types are pulped at the same rate. The lignin structure is a key factor, with softwood, and particularly compression wood, delignifying at a slower rate than hardwood. This slower rate is a result of a higher content of stable condensed bonds in the lignin (Gonzalo Epelde et al. 1998 ). In addition to lignin structure, covalent bonds between lignin and polysaccharides, known as "lignin carbohydrate complexes" (LCC), significantly influence delignification rates. These complexes, which exhibit variations between different tree species, serve as rate-limiting factors for delignification (Lawoko et al. 2004 ). One less studied aspect in the field of kraft pulping is the impact of inorganic content of wood on the kinetics of the process. An interesting example of this is the calcium oxalate content present in Eucalyptus dunnii wood; recent research has revealed that wood samples of this species with a higher calcium content exhibit suboptimal performance during kraft pulping. Specifically, these samples display slower delignification rates and a more significant degree of cellulose degradation (Vegunta et al. 2022 ). In laboratory-scale experiments, pulping samples with the highest calcium content, which reached levels of 4.7 grams of calcium per kilogram of wood, proved to be a challenge. This finding highlights the importance of considering the inorganic content of wood when optimizing kraft pulping processes. Interestingly, this issue was less pronounced, yet still significant, at the industrial scale. One possible explanation is that industrial white liquor may be "less pure" due to incomplete causticizing, meaning it contains carbonates. Alternatively, the addition of black liquor to fresh chips before pulping could partially alleviate the calcium-related challenges in some manner (Vegunta et al. 2022 ). Kraft pulping of wood chips using black or green liquor is a potential solution to address challenges associated with high calcium content in wood. Since green liquor is an intermediate in the chemical recovery system, it is readily available in the kraft mill alongside black liquor (Ragnar et al. 2013 ). Previous experiments with green liquor kraft pulping have demonstrated encouraging results, such as increased delignification rate, higher pulp yield, enhanced strength, improved selectivity, and reduced chemical consumption (Andrews and Chang H 1985; Ban et al. 2004 ; Klevinska and Treimanis 1997 ; Svedman and Tikka 1998 ). Nevertheless, the exact mechanisms behind these improvements remain elusive. In this study, we examine the impact of adding black and green liquor prior to kraft pulping on the delignification kinetics of E. dunnii wood with varying calcium contents including as high as of 4.7 g/kg – a quality that is difficult to pulp under normal conditions in laboratory (Vegunta et al. 2022 ). Materials and methods Materials Wood chips of standard kraft pulping size Eucalyptus dunnii with a calcium content of 3366 mg/kg were from Soriano farm at Bequilo district, Uruguay. E. dunnii , with a calcium content of 3756 mg/kg, was from Grecco farm and Los Cercos, District, Uruguay. E. dunnii , with a calcium content of 4668 mg/kg, was from Grecco farm and Los Cercos, District, Uruguay Sodium carbonate (99.5%) was from Sigma Aldrich, St. Louis, USA, Nitric acid (65%) is from Sigma Aldrich, Burlington, USA, hydrogen peroxide (30 at%H 2 O 2 ) was from Sigma Aldrich St. Louis, USA, Sulphuric acid (72%), was from Alfa Aesar, Kendel, Germany). Storage of the Samples: The black liquor obtained after pulping was stored in the refrigerator. Prior to analysis, the samples were left on the table to reach room temperature and thoroughly mixed. Methods Kraft Cooking Three sets of kraft pulping experiments were conducted, using E. dunnii wood chips with varying calcium content: the first with 3366 mg/kg, the second with 4668 mg/kg, and the third with 3756 mg/kg. In the first set of experiments, different kraft pulping process conditions were assessed, and the effects of black or green liquor additions on pulping efficiency were evaluated. The second set of experiments involved E. dunnii wood chips with a very high calcium content of 4668 mg/kg, which were challenging to pulp in the laboratory using a conventional protocol. Green liquor was used as both impregnation and cooking liquor in this case. The objective was to further examine and confirm the role of green liquor on the pulping performance of wood with very high calcium content. The third set of experiments utilized E. dunnii wood chips with a calcium content of 3756 mg/kg, similar to the wood chips in the first set. This study aimed to assess the effects of green liquor on the bleachability of the produced kraft pulp. Both batches had calcium content too high to achieve reasonable defibration in our laboratory using standard pulping techniques (Vegunta et al. 2022 ). The kraft pulping experiments were conducted using a 1000 ml steel autoclave multiunit digester system, with the process controlled by a computer system and an electric heater. Impregnation took place in steel autoclaves, where wood chips were degassed under vacuum for 30 minutes. Following this, the liquor was drawn into the autoclaves and positioned in a stream-heated glycol bath. It took 10 minutes for the required temperature to be reached, so the actual impregnation time commenced 10 minutes after placing the autoclaves in the electric heater. The impregnation and cooking liquor conditions were consistent across all kraft cooks in this study. Impregnation conditions included a temperature of 110°C and a duration of 90 minutes. As for the kraft cooking liquor conditions, they involved a liquid-to-wood ratio of 4:1, with effective alkali and sulfide charges set at 18% and 35%, respectively. Stock solutions of Na 2 S were prepared by dissolving technical-grade flakes of Na 2 S. Preparation of Black Liquor for impregnation experiment: Black liquor production was conducted in the laboratory for impregnation experiments, utilizing E. dunnii wood chips containing 3366 mg/kg of calcium. The kraft cooking conditions for producing black liquor included an impregnation temperature of 110°C for 90 minutes, 35% sulfide content, a 4:1 liquid-to-wood ratio, 18% effective alkali (EA), and kraft cooking at 145°C for 1 hour. Consequently, the laboratory-produced black liquor, containing hydroxyl and sulfide ions, closely resembles industrial black liquor. Preparation of Green Liquor: Green liquor preparation involved adding sodium carbonate with a concentration of 0.66M to the water, after adjusting the effective alkali (18%) and sulfide (35%) content in the white liquor. The liquid-to-wood ratio was maintained at 4:1. White liquor, a precursor to green liquor, is created from sodium hydroxide and sodium sulfide stock solutions. Kraft Cook Series 1: E. dunnii wood chips with a calcium content of 3366 mg/kg were used in this study. Kraft cooks were conducted using reference white liquor, a combination of black and white liquor, and green liquor. The impregnation and cooking chemicals were the same as previously described. Kraft cooking was performed at various H-factors, with a constant time of 210 minutes and temperatures ranging from 138°C to 170°C. Kraft Cook Series 2: E. dunnii wood chips containing 4668 mg/kg of calcium were used. Kraft cooking was performed using synthetic green liquor. The impregnation and cooking chemical conditions remained the same as previously described, followed by the kraft cook. The kraft cooking conditions were set at 145°C for 210 minutes. Kraft Cook Series 3: E. dunnii wood chips with a calcium content of 3768 mg/kg were used. Kraft cooking was conducted using reference white liquor, a combination of black and white liquor, and synthetic green liquor, aiming to achieve similar kappa numbers (13–14). The impregnation and cooking chemical conditions were consistent with prior descriptions, followed by the kraft cook. The kraft cooking conditions for the three cooking liquors were as follows: white liquor (170°C, 210 minutes), black and white liquor (170°C, 210 minutes), and green liquor (145°C, 210 minutes). Bleaching: A DEDED bleaching sequence was conducted on kraft pulp (with similar kappa numbers) obtained from E. dunnii wood using reference white liquor, a combination of black and white liquor, and synthetic green liquor. The drainability (ISO 5267-1), water retention value (WRV) for 100 mesh (ISO 23714), tensile index (ISO 1924-2), tensile stiffness (ISO 1924-2), and tear index (ISO 1974) were evaluated for both unbleached and bleached pulps. Table 1 Chemical composition details for DEDED bleaching sequence on kraft pulps. D0 E1 D1 E2 D2 Acid Reaction temperature (°C) 60 70 70 70 70 20–25 Reaction time (min) 60 90 120 90 120 15 pH target at the end 2-2.5 10.5–11 4-4.5 10.5–11 4-4.5 4.5-0 ClO 2 (%) 4.76 - 2.00 - 0.90 - NaOH (%) - 1.90 0.50 0.50 0.10 - Lignin Isolation : Concentrated sulfuric acid (97 to 98% H 2 SO 4 ) was added to 20 ml of impregnation liquor until the pH of the solution reached 2–3. The mixture was then centrifuged at 4800 rpm for ten-minute intervals, with 5-minute breaks in between. After centrifugation, the supernatant was separated from the precipitate, which was subsequently washed twice with a sulfuric acid solution at pH 2 and centrifuged again. The resulting pellet was dried in an oven overnight at 80°C, and the weight was recorded. The precipitation process was performed in duplicate. Analysis Determination of Oxalic Acid Using HPLC: Approximately 100 mg of dried black liquor samples were diluted with a dilution factor of 1000 using Milli-Q water. The diluted samples were filtered through a 0.25 µm nylon filter and transferred to HPLC vials. Oxalic acid content was determined using high-performance liquid chromatography (HPLC) with a Thermo Fischer Scientific system (USA) equipped with a ROA-organic acid column (Thermo Fischer Scientific, USA) and a refractive index detector. The mobile phase consisted of a sulfuric acid solution with a pH between 2 and 8 (0.45 M) at a flow rate of 0.5 ml/min. The oven temperature was set at 50°C. Determination of Dry Solid Content and Ash Content: Approximately 5 ml of black liquor was placed in a ceramic crucible and kept in an oven at a temperature of 105°C until a constant mass was achieved (typically within 12 to 15 hours). The mass was then recorded. Following this, the residue from the 105°C drying process was heated to 600°C for 6 hours in the oven, and the resulting weight, representing the ash content, was documented. Viscosity The viscosity of pulp samples was determined according to the (ISO 5351:2010) standard. Klason Lignin and Sugar Composition Analysis: All pulp samples were Wiley milled using a 40 mesh screen and then subjected to acid hydrolysis to determine lignin and sugar content. Initially, 3 ml of 72% H2SO4 was added to each sample, followed by placement in a vacuum desiccator for 1 hour and 20 minutes with occasional stirring. The mixtures were then diluted with 84 ml of Milli-Q water and autoclaved at 125°C for 1 hour. Subsequently, the samples were filtered through a glass fiber filter using a 3-piece filtration setup. The filtrates were diluted at a 1:10 ratio for sugar analysis and acid-soluble lignin determination. The insoluble (Klason lignin) fraction was dried in an oven at 105°C and weighed. Acid-soluble lignin was measured using a Shimadzu UV-2550 UV-VIS spectrophotometer at an absorbance of 205 nm. Carbohydrate content was determined using a Dionex ICS-3000 high-performance anion-exchange chromatography system with pulsed amperometric detection (HPAEC-PAD), featuring a CarboPac PA1 column (Thermo Scientific, USA), an injection volume of 25 µl, and a flow rate of 1 ml/min. External sugar standards based on the sample were used for calibration. The results were reported as anhydrous sugars and performed in duplicate. Metal Ion Content Analysis: The total metal ion content in the pulp samples was measured using ICP-OES (Thermo Scientific iCAP 7000 series). Before the ICP-OES measurements, approximately 100 mg of each sample was taken for analysis. Initially, 7 ml of aqua regia solution (2 ml H2O2 + 5 ml HNO3) was added to the samples. The tubes were sealed and then placed in an ultrasonic bath for several minutes. After this, the samples were left overnight for acid digestion. The samples were then filtered using filter paper and diluted to 50 ml with Milli-Q water. This solution was further diluted to a 1:50 ratio using 5% HNO3. Finally, 10 ml of the diluted sample was subjected to metal analysis using ICP-OES. Kappa number determination Kappa number of pulp samples was determined according to the ISO 302:2004 standard. Residual alkali determination The residual alkali of black liquor samples was determined according to the SCAN-N 33:94 standard. Results and discussion Kraft cooking with different cooking liquors Previous research has demonstrated that higher calcium content results in slower delignification and more severe cellulose degradation in E. dunnii with calcium contents of 705, 870, and 1500 mg/kg, and has proposed possible mechanisms for these effects (Vegunta et al. 2022 ). Even under harsh conditions, kraft pulping with lab-made white liquor proved to be practically challenging for samples containing more than 3000 mg/kg calcium. However, high calcium content had a lesser impact on industrial-scale pulping, although severe problems did arise. The difference between laboratory and industrial-scale pulping lies in the fact that black liquor is typically added to wood chips in a pulp mill (Ragnar et al. 2013 ), whereas white liquor may become contaminated with green liquor due to insufficient causticization. As a result, the composition of the liquors used for impregnation and kraft cooking in the pulp mill and a lab varies significantly. In this study, we conducted kraft pulping on a laboratory scale using white liquor, a combination of black and white liquor, and synthetic green liquor (prepared in our lab from pure chemicals). Further details on the composition can be found in the materials and methods section. Table 2 Details of kraft pulping experiments using different cooking liquors. E. dunnii wood chips with a calcium content of 3366 mg/kg were used. H-factor Total pulp yield Screened pulp yield (%) Rejects (%) Kappa number unbleached pulp White liquor (reference) 387.8 64 17 48 24 948.8 55 43 11.8 21 2237.3 54 50 3.3 20 3389.6 51 47 2 13 Black + white liquor 387.8 51 28 23.1 25 948.8 58 47 11.5 22 2237.3 57 53 4.2 20 3389.6 52 51 1.4 14 Green liquor (synthetic) 247.6 57 37 20.4 19 278.9 56 52 5 18 387.8 55 55 0 14 Table 1 shows the characteristics of kraft pulps produced using various cooking liquors at different H-factors. Kraft pulping was carried out with the aim of achieving a similar kappa number in the pulp. To achieve the desired kappa number, the cooking temperature was selected as a variable factor (H-factor). In this study, kraft pulping of E. dunnii wood chips with a calcium content of 3366 mg/kg was performed at temperatures ranging from 138°C to 140°C, 145°C, 155°C, 165°C, and 170°C. The rate of delignification of high calcium-content wood chips is significantly influenced by green liquor. Despite a lower H-factor for green liquor pulping, high calcium-containing wood chips could be pulped with fewer rejects to achieve a lower kappa (as shown in Figs. 1 ). Additionally, the kappa numbers were considerably lower for the pulps pulped with green liquor. In contrast, the addition of black liquor did not produce any significant effects (as illustrated in Figs. 1 and 2 ). E. dunnii wood chips with a calcium content of 3366 mg/kg were employed in this study. Additionally, the viscosity of the pulps generated using green liquor was higher at a given Kappa number (as depicted in Fig. 3 ). This indicates that green liquor, in some manner, protects cellulose from degradation during kraft pulping. These findings are consistent with previous studies demonstrating that green liquor has a significant impact on the delignification rate and pulp quality in kraft pulping (Andrews and Chang 1985 ; Ban et al. 2004 ; Klevinska and Treimanis 1997 ; Svedman and Tikka 1998 ). While earlier research suggested that green liquor could be used to increase the sulfur content in pulping, our experiments did not support this explanation since the sulfur content was not increased by the addition of green liquor. Instead, we propose that it is the carbonate ions in green liquor that are responsible for the positive effects by forming inert calcium carbonate crystals, thereby preventing the negative effects of calcium ions during pulping. Figure 5 provides a schematic representation of this hypothesis. However, if this hypothesis is correct, calcium must remain in the fiber even during kraft cooking and not be significantly transferred to the pulping liquor. The data in Fig. 6 support the hypothesis in Fig. 5 , indicating that green liquor-treated pulp contains considerably more calcium than white and black liquor-treated pulp. Table 3 presents the data on the residual alkali, oxalic acid, inorganic, organic, and lignin content of the black liquor collected after each kraft cook. The data indicate that black liquor always contains total dry solids (%) and lignin content (%), as well as inorganics. Additionally, a substantial amount of residual alkali was detected in the black liquor obtained using green liquor at a low kappa number, suggesting that kraft pulping selectivity is more favorable for this kraft cook at a low kappa number, particularly when compared to white liquor and black combined with white liquor. Table 3 Characterization of black liquor collected from kraft cooks performed using different cooking liquors. H-factor Dry solids (%) Ash content (%) Residual alkali (mol/l) Precipitated lignin (%) Oxalic acid White liquor (reference) 387.8 19 ± 0.09 62 ± 0.03 0.5 5.5 ± 0.02 1.7 948.8 15 ± 0.05 56 ± 0.04 0.2 3.9 ± 0.3 1.9 2237.3 14 ± 0.06 48 ± 0.2 0.3 3.3 ± 0.2 0.9 3389.6 16 ± 0.04 47 ± 0.03 0.2 3.4 ± 0.1 3.4 Black + white liquor 387.8 22 ± 0.5 57 ± 0.02 0.8 7.5 ± 0.06 1.6 948.8 22 ± 0.05 55 ± 0.04 0.3 8.2 ± 0.3 1.9 2237.3 21 ± 0.8 54 ± 0.03 0.4 4.8 ± 0.3 1.8 3389.6 22 ± 0.06 59 ± 0.02 0.2 5.5 ± 0.4 1.3 Green liquor (synthetic) 247.6 17 ± 0.9 56 ± 0.03 0.4 2.4 ± 0.2 1.7 278.9 18 ± 1 56 ± 0.05 0.5 3.3 ± 0.2 1.9 387.8 17 ± 1 47 ± 0.05 0.6 4.5 ± 0.3 1.9 Figure 5 illustrates a hypothetical interpretation of the chemistry of cooking liquors with regard to calcium oxalate ions in wood chips. Previous research has identified calcium oxalate in the lumen of wood, and during kraft pulping with strongly alkaline white liquor, oxalate and calcium ions can deteriorate into the cell wall. According to our previous study (Vegunta et al. 2022 ), these calcium ions can accelerate polysaccharide degradation while delaying delignification. If this hypothesis is correct, calcium must remain in the fiber during kraft cooking and should not be significantly transferred to the pulping liquor. The data presented in Fig. 6 support this hypothesis, as green liquor-treated pulp contains considerably more calcium than white and black liquor-treated pulp. Given the success of kraft pulping with high calcium content E. dunni wood, we tested pulping with wood containing even higher calcium content – 4668 mg/kg wood – a quality that had been virtually impossible to pulp in the laboratory with conventional white liquor pulping. As expected, pure white liquor pulping did not result in defibrillation under the conditions used (see materials and methods), but adding green liquor allowed for pulping to generate pulp with low rejects and acceptable kappa numbers (Table 3 ) Table 4 Details regarding pulp produced using high calcium-containing wood chips (4668mg/kg) using green liquor. Green liquor (synthetic) 100% (0.66M) Rejects (%) 0.1 Total yield (%) 52 Screened pulp yield (%) 52 Kappa number 18.6 Dry solids In Black liquor (%) 18 Ash content in black liquor (%) 59 Precipitated lignin (%) 4.7 Glucose (% on wood) 31.8 Xylose (% on wood) 9.4 Klason lignin (%) 3.97 Viscosity (ml/g) 1369 Calcium content in pulp sample (mg/kg) 4138 HEXA Unbleached pulp (µmol/g) 11.5 HEXA Bleached pulp(µmol/g) 11 Impact of Green Liquor on Bleaching of Pulp In order to assess the impact of green liquor on the bleaching of high calcium content wood chips, additional batches of pulp were prepared as controls and subjected to bleaching experiments. The pulp was produced at a specific kappa number (13–14) to investigate the effects on pulp quality and strength. Wood chips with a calcium content of 3758 mg/kg were used for these experiments, and three different impregnation liquors were employed in the kraft cooking process. These experiments were conducted to determine whether the enhanced mineral content from green liquor would have any adverse effects on pulp bleaching, due to coprecipitated transition metal ions, among other factors. Table 5 Characterization of kraft cooks subjected to bleaching experiments. White liquor (reference) Black + white liquor Green liquor (synthetic) Rejects (%) 1.3 0 0 Total yield (%) 45.7 46.3 51.5 Screened pulp yield (%) 44.4 46.3 51.5 Kappa number 17 16 16.1 Dry solids In Black liquor (%) 14 23 16 Ash content in black liquor (%) 59 60 59 Precipitated lignin (%) 5.1 9.2 5.7 Viscosity (ml/g) 882 896 1364 Calcium content in pulp sample (mg/kg) 1925 2362 2580 HexA Unbleached pulp (µmol/g) 22.5 31.3 13.5 Glucose (% on wood) 24.5 27.7 31 Xylose (% on wood) 5.5 7.2 7.7 Klason lignin (%) 2.5 2.3 4.9 Table 5 summarizes the properties of the pulp obtained through kraft pulping with different impregnation liquors. The green liquor impregnation resulted in higher pulp yield, faster delignification, and higher viscosity at the same kappa number, consistent with previous experiments using wood chips with a calcium content of 3366 mg/kg. All pulps were kraft pulped under identical chemical conditions with different H-factors to achieve a similar kappa number. The total yield increased by 5% when green liquor impregnation was used, compared to white and black + white liquor. The hexeneuronic acid content was slightly lower in the pulp obtained using green liquor impregnation. Table 5 displays the total inorganic metal content in unbleached pulp samples produced using different impregnation liquors. The unbleached pulp obtained from green liquor impregnation has a slightly higher calcium content compared to those obtained from black liquor + white liquor and white liquor (Table 5 ). This suggests that the calcium content follows the fiber line instead of being washed out with black liquor. However, the presence of calcium carbonate crystals in the pulp may trap transition metal ions and hinder the bleaching process. Hence, bleaching experiments with the sequence DEDED were conducted on pulps cooked with white and green liquors to comparable kappa numbers to assess the impact of green liquor on bleaching efficiency. The green liquor impregnated pulp samples had significantly higher intrinsic viscosity compared to those impregnated with white liquor and black + white liquor. This indicates an improvement in the mechanical properties of the pulp. The findings are consistent with the tensile strength and tear index results obtained from unbleached and bleached pulp samples (see Figs. 8 – 9 ). The viscosity (Fig. 7 ) of unbleached and bleached pulp generated with white liquor and black liquor + white liquor is lower at a given kappa number than that of green liquor impregnated pulp. The use of higher H-factor in pulp obtained from white liquor and black liquor + white liquor could be a reason for the lower viscosity. The benefits of the green liquor treatment in achieving high viscosity were mostly retained even after bleaching, as depicted in Fig. 7 . This is evident in the improved tensile index (Fig. 8 ) and tear index (Fig. 9 ) for the bleached pulps previously treated with green liquor. Refining of pulp fibers through PFI refining enhances the paper-making properties of pulp fibers, improving their binding ability and increasing their strength. As shown in Fig. 9 , both unbleached and bleached pulps processed with green liquor impregnation have higher mechanical and tear indices. The higher hemicellulose content on the fiber surfaces in green liquor-treated pulps may contribute to their improved strength properties. However, this increase in strength appears to cause an increase in drainage resistance (Fig. 10 ). The bleaching of green liquor-treated pulps was found to be equally effective in developing brightness as it was for the control samples. This, together with the data in Figs. 7 – 11 , suggests that calcium carbonate crystals in pulps should not significantly affect the bleaching process. Conclusions In this study, we have conducted a series of experiments researching high calcium-content wood chips that cannot pulp under conventional kraft cooking conditions using white liquor on a lab scale. Instead, we could pulp these highly impossible wood chips using green liquor kraft pulping at a lower H-factor. The bleaching of green-liquor cooked pulps was not affected. The following conclusions can be drawn from this work: Exceptionally low reject content and low kappa number at similar H-factor using green liquor impregnation can be achieved compared to reference white liquor and black + white liquor. Kappa number was lower at given H-factor for pulps of calcium rich wood when green liquor was added to the white liquor. The bleached pulps produced using green liquor impregnation have increased tensile, and tear index. The addition of green liquor to kraft pulping directs the calcium to stay with the fiber rather than to go with the black liquor. Kraft cooking with green liquor results in improved selectivity of the kraft pulping. Green liquor usage makes pulping of Eucalypts with even a very high calcium content possible. Green liquor-treated pulps could be bleached with good results, mainly keeping the advantages from the unbleached pulp. A hypothesis for the effects of green liquor based on the formation of calcium carbonate (Fig. 5 ) has been presented. Declarations Ethics approval and consent to participate Not applicable. Consent for publication Not applicable. Availability of data and materials All data generated or analysed during this work are included in this publication. Raw data for the figures are available from the corresponding author on request. Competing Interests The authors declare that they have no competing interests as defined by Springer, or other interests that might be perceived to influence the results and/or discussion reported in this paper. Funding For Vegunta, Garcia, Björk and Jansson, financial support from Stora Enso is gratefully acknowledged. For Lindén, support from the Knut and Alice Wallenberg Foundation (KAW) through the Wallenberg Wood Science Center, KAW 2015.0390, is gratefully acknowledged. Authors' contributions All authors contributed to the planning of the experiments. Most of the experimental work was performed by Vegunta with help from Lindén and Deshpande, except for the bleaching experiments and part of the pulp characterization which was performed by Björk with instructions from Jansson. Garcia and Jansson selected and procured the wood chips samples which were used in the experiments. Vegunta, Henriksson and Sevastyanova wrote the major part of the text, but all authors participated in reading and commenting on the text. Acknowledgements Monica Heberling, Montes del Plata Colonia Department, is gratefully acknowledged for her role in the sampling of the wood chips samples. References Andrews EK, Chang HM (1985) Extended delignification kraft pulping of softwoods effect of treatment on chips and pulp with sulfide containing liquors. J Wood Chem Technol 5:431-450. Ban W, Song J, Lucia LA (2004) Insight into the Chemical Behaviour of Softwood Carbohydrates during High-Sulfidity Green Liquor Pre-treatment. Ind Eng Chem Res 43:1366-1372. Ban W, Wang S, Lucia LA (2003) The relationship of pretreatment pulping parameters with respect to pulp qualities: optimization of green liquor pretreatment conditions for improved kraft pulping. Pap Puu 85(7):1-7. 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A practical approach to provide cost savings in Kraft mill’s pulping operation. Tappsa J (2):20–26. Johakimu JK, Sithole BB (2021) Wood chip impregnation with weak white liquor and its effect in mitigating operational costs and environmental impacts in Kraft pulp mills. Biofuels, Bioprod. Bioref 15(5):1360–1371. Johakimu J, Andrew J (2013) Hemicellulose extraction from south African eucalyptus using green liquor and its impact on kraft pulping efficiency and paper making properties. Bioresources 8(3):3490-3504. Klevinska V, Treimanis A (1997) Pretreatment of wood chips with green liquor and its effect upon kraft delignification. Cellulose Chem Technol 31:253-261. Kochetkov NK, Kudrjashov LI., Chlenov MA (1979) Radiation Chemistry of Carbohydrates. Pergamon Press, Oxford. ISBN 008022962X. Lawoko M, Berggren R, Berthold F, Henriksson G, Gellerstedt G (2004) Changes in the Lignin-Carbohydrate complex in softwood kraft pulp during kraft- and oxygen delignification. Lignin-polysaccharide networks II. Holzforchung 58(6):603-610. Maholanyiova M, Opalena E, Fiserova M (2013) Kraft pulping combined with green liquor pre-extraction of beech wood. Cellulose Chem and Technol 47(7):583-593. Norgren M, Lindström B, (2000) Physico-chemical characterization of a fractionated kraft lignin. Holzforschung 54(5):528-534. DOI: 10.1515/hf.2000.089. Ragnar M, Henriksson G, Lindström ME, Wimby M, Süttinger R (2013) Pulp. In: Ley C (ed) Ullman Encyclopedia of Industrial Chemistry, 7 th edn., Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, pp 1-89. Santiago ASVM (2008) Estratégias para o aumento da retenção de polissacarídeos durante a produção de pasta kraft de Eucalyptus globulus . Doctoral dissertation, Universidade de Aveiro, Portugal. Santiago AS, Neto CP (2008) Eucalyptus globulus kraft process modifications: Effect on pulping and bleaching performance and papermaking properties of bleached pulps. J Chem Technol Biotechnol 83(9):1298-1305. Svedman M, Tikka P (1998) The use of green liquor and its derivatives in improving kraft pulping. Tappi J (1998) 81:151-158. Schwartz JT, and Lawoko M (2010) Removal of acid-soluble lignin from biomass extracts using amber lite XAD-4 resin Acid soluble lignin. BioResources 5(4):2337-2347. Vegunta V, Sethikumar ER, Lindén P, Sevastyanova O, Vilaplana F, Garcia A, Björk M, Jansson U, Henriksson G, Lindström ME (2022) High calcium content of Eucalyptus dunnii wood affects delignification and polysaccharide degradation in kraft pulping. Nordic Pulp Paper Res J 37(2):338-348. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 20 Dec, 2023 Read the published version in Cellulose → Version 1 posted Editorial decision: Major revision 12 Aug, 2023 Reviews received at journal 10 Aug, 2023 Reviewers agreed at journal 05 Aug, 2023 Reviewers invited by journal 05 Aug, 2023 Editor assigned by journal 01 Aug, 2023 Submission checks completed at journal 01 Aug, 2023 First submitted to journal 12 Jul, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3165099","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":223208391,"identity":"cfa4909a-54c7-47ef-b4f4-30bfc69ac38b","order_by":0,"name":"Vijaya Vegunta","email":"","orcid":"","institution":"Department of Fiber and Polymer Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Royal Institute of Technology, KTH","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Vijaya","middleName":"","lastName":"Vegunta","suffix":""},{"id":223208392,"identity":"b5aa9350-1b66-456c-86ea-4fd05fa121f2","order_by":1,"name":"Olena Sevastyanova","email":"","orcid":"","institution":"Department of Fiber and Polymer Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Royal Institute of Technology, KTH","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Olena","middleName":"","lastName":"Sevastyanova","suffix":""},{"id":223208393,"identity":"27987945-ac66-4537-9268-ed204810a104","order_by":2,"name":"Raghu Deshpande","email":"","orcid":"","institution":"Department of Fiber and Polymer Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Royal Institute of Technology, KTH","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Raghu","middleName":"","lastName":"Deshpande","suffix":""},{"id":223208394,"identity":"2f20fb1e-7493-4c93-976f-8bf444ce7b0c","order_by":3,"name":"Pär A. Lindén","email":"","orcid":"","institution":"Wallenberg Wood Science Center, WWSC, Department of Fiber and Polymer Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Royal Institute of Technology, KTH","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Pär","middleName":"A.","lastName":"Lindén","suffix":""},{"id":223208395,"identity":"f766a9e5-2b32-453d-99a8-18d0beafaba9","order_by":4,"name":"Andres Garcia","email":"","orcid":"","institution":"Montes del Plata Colonia Department","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Andres","middleName":"","lastName":"Garcia","suffix":""},{"id":223208396,"identity":"54555fb7-af81-4c09-b1f5-ac7c7190fd62","order_by":5,"name":"Maria Björk","email":"","orcid":"","institution":"Stora Enso, Biomaterials division","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Maria","middleName":"","lastName":"Björk","suffix":""},{"id":223208397,"identity":"67ee9c58-88ab-4dc9-9735-a1cc70f92026","order_by":6,"name":"Ulla Jansson","email":"","orcid":"","institution":"Stora Enso, Biomaterials division","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ulla","middleName":"","lastName":"Jansson","suffix":""},{"id":223208398,"identity":"1e241df0-9cb7-4204-b355-5c2b983bfa37","order_by":7,"name":"Gunnar Henriksson","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtElEQVRIiWNgGAWjYDACCRBhkCAnwcBDohZjCTbStDAkJM4gWot8dPOxxxUFaekz5/ceYPxRQYQWwzvH0g3PGOTkzmbjS2DmOUOMlhk5ZpINBhW589h4DJgZ24jSkv8NpCVdDqiF8ec/IrTIS+SwAbXkJEgDtTDwNhChxUAiDeSwNMOZbTkGh3mOEWPLjORnkg1/kuUlDp8xfPijhhhbDiBxDuBQhGZLA1HKRsEoGAWjYEQDADF5L+50160BAAAAAElFTkSuQmCC","orcid":"","institution":"Department of Fiber and Polymer Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Royal Institute of Technology, KTH","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Gunnar","middleName":"","lastName":"Henriksson","suffix":""},{"id":223208399,"identity":"19388074-5aa2-4a34-9859-0337ab780c03","order_by":8,"name":"Mikael E. Lindström","email":"","orcid":"","institution":"Department of Fiber and Polymer Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Royal Institute of Technology, KTH","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mikael","middleName":"E.","lastName":"Lindström","suffix":""}],"badges":[],"createdAt":"2023-07-12 22:59:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3165099/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3165099/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s10570-023-05603-z","type":"published","date":"2023-12-20T15:00:50+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":41182010,"identity":"b010b70d-a64b-49c2-abb4-d5676af8b13a","added_by":"auto","created_at":"2023-08-07 13:54:49","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":180462,"visible":true,"origin":"","legend":"\u003cp\u003eReject (%) as a function of H-factor.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/0074ebfa4f1123ffb8a42134.png"},{"id":41182011,"identity":"22e8bf8b-2395-4ba4-b9a4-b6ec7550a857","added_by":"auto","created_at":"2023-08-07 13:54:49","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":173815,"visible":true,"origin":"","legend":"\u003cp\u003eKappa number as a function of H-factor.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/d9c68c43737ef9acef6ef081.png"},{"id":41182012,"identity":"9fe10f64-cba2-43e7-b33f-c2475af187a4","added_by":"auto","created_at":"2023-08-07 13:54:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":192598,"visible":true,"origin":"","legend":"\u003cp\u003eIntrinsic viscosity (ml/g) as a function of H-factor.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/67fdb8507a189d64a556c79b.png"},{"id":41180831,"identity":"cdfc95fa-fb52-4753-ade6-3424110f3f0c","added_by":"auto","created_at":"2023-08-07 13:46:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":192977,"visible":true,"origin":"","legend":"\u003cp\u003eIntrinsic viscosity (ml/g) as a function of kappa number.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/3015047e0197655692af1333.png"},{"id":41180830,"identity":"1a20a55a-5e3d-4896-8ede-81caf2f76b56","added_by":"auto","created_at":"2023-08-07 13:46:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":590019,"visible":true,"origin":"","legend":"\u003cp\u003eHypothetical explanation for the strong positive effect of green liquor impregnation.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/57d65cf21983a05095402b52.png"},{"id":41180836,"identity":"d53d3639-bd26-493b-814f-60063e383cd0","added_by":"auto","created_at":"2023-08-07 13:46:49","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":211170,"visible":true,"origin":"","legend":"\u003cp\u003eCalcium content in pulp (mg/kg) as a function of kappa number\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/9bd7681d5ce3916fea41351e.png"},{"id":41180833,"identity":"856a03b1-4bd4-45af-bdfb-bb765b58356f","added_by":"auto","created_at":"2023-08-07 13:46:49","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":453272,"visible":true,"origin":"","legend":"\u003cp\u003eIntrinsic viscosity (ml/g) after kraft cooking and after bleaching.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/0e370f589a4da347ab66a8e2.png"},{"id":41183108,"identity":"4d98e80d-b5b5-4ef2-b5f7-8840487492f0","added_by":"auto","created_at":"2023-08-07 14:02:49","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":187551,"visible":true,"origin":"","legend":"\u003cp\u003eTensile index (Nm/g) of pulps produced at targeted kappa number using different cooking liquor.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/eedb6692791944e094609290.png"},{"id":41180835,"identity":"3237b85d-ef61-4fd8-8021-5ca05c7a35ed","added_by":"auto","created_at":"2023-08-07 13:46:49","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":169494,"visible":true,"origin":"","legend":"\u003cp\u003eTear index (mNm\u003csup\u003e2\u003c/sup\u003e/g) of pulp pulps produced at targeted kappa number using different cooking liquor.\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/2dbd8e1b94df612166fecf82.png"},{"id":41182014,"identity":"6b39f47b-aa40-4cc6-acdf-d38fb73f3a39","added_by":"auto","created_at":"2023-08-07 13:54:49","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":201460,"visible":true,"origin":"","legend":"\u003cp\u003ePCC brightness of unbleached and bleached pulp\u003c/p\u003e","description":"","filename":"Figure10.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/1f75d9d4a9078bbe25c3b94f.png"},{"id":41183637,"identity":"fa9268f5-9199-4f5c-a79e-658b361dd61c","added_by":"auto","created_at":"2023-08-07 14:10:49","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":182807,"visible":true,"origin":"","legend":"\u003cp\u003eDrainage resistance of pulps produced at targeted kappa number using different cooking liquor.\u003c/p\u003e","description":"","filename":"Figure11.png","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/8b8ffc911cfce681c17709a2.png"},{"id":48776663,"identity":"0f361d66-c111-4018-9e0f-95ac2530d6c0","added_by":"auto","created_at":"2023-12-25 15:06:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2525441,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3165099/v1/0a2bab5c-4e6b-4506-bfd0-ac1452290fc1.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Addition of Green and Black Liquor in Kraft Pulping of Eucalyptus dunnii wood: Possible Solutions for the Problems with Kraft Pulping Caused by High Calcium Content","fulltext":[{"header":"Introduction","content":"\u003cp\u003eFor many years, kraft pulping has maintained its status as the most crucial method for processing wood, primarily due to its low operating costs, which can be attributed in part to efficient chemical recovery systems. Other factors contributing to its success include its relatively high selectivity of delignification and its broad tolerance for various raw materials (Ragnar et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Despite this wide range of acceptable raw materials, not all wood types are pulped at the same rate. The lignin structure is a key factor, with softwood, and particularly compression wood, delignifying at a slower rate than hardwood. This slower rate is a result of a higher content of stable condensed bonds in the lignin (Gonzalo Epelde et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1998\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn addition to lignin structure, covalent bonds between lignin and polysaccharides, known as \"lignin carbohydrate complexes\" (LCC), significantly influence delignification rates. These complexes, which exhibit variations between different tree species, serve as rate-limiting factors for delignification (Lawoko et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOne less studied aspect in the field of kraft pulping is the impact of inorganic content of wood on the kinetics of the process. An interesting example of this is the calcium oxalate content present in \u003cem\u003eEucalyptus dunnii\u003c/em\u003e wood; recent research has revealed that wood samples of this species with a higher calcium content exhibit suboptimal performance during kraft pulping. Specifically, these samples display slower delignification rates and a more significant degree of cellulose degradation (Vegunta et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In laboratory-scale experiments, pulping samples with the highest calcium content, which reached levels of 4.7 grams of calcium per kilogram of wood, proved to be a challenge. This finding highlights the importance of considering the inorganic content of wood when optimizing kraft pulping processes.\u003c/p\u003e \u003cp\u003eInterestingly, this issue was less pronounced, yet still significant, at the industrial scale. One possible explanation is that industrial white liquor may be \"less pure\" due to incomplete causticizing, meaning it contains carbonates. Alternatively, the addition of black liquor to fresh chips before pulping could partially alleviate the calcium-related challenges in some manner (Vegunta et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eKraft pulping of wood chips using black or green liquor is a potential solution to address challenges associated with high calcium content in wood. Since green liquor is an intermediate in the chemical recovery system, it is readily available in the kraft mill alongside black liquor (Ragnar et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePrevious experiments with green liquor kraft pulping have demonstrated encouraging results, such as increased delignification rate, higher pulp yield, enhanced strength, improved selectivity, and reduced chemical consumption (Andrews and Chang H 1985; Ban et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Klevinska and Treimanis \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Svedman and Tikka \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). Nevertheless, the exact mechanisms behind these improvements remain elusive.\u003c/p\u003e \u003cp\u003eIn this study, we examine the impact of adding black and green liquor prior to kraft pulping on the delignification kinetics of \u003cem\u003eE. dunnii\u003c/em\u003e wood with varying calcium contents including as high as of 4.7 g/kg \u0026ndash; a quality that is difficult to pulp under normal conditions in laboratory (Vegunta et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eMaterials\u003c/h2\u003e \u003cp\u003eWood chips of standard kraft pulping size \u003cem\u003eEucalyptus dunnii\u003c/em\u003e with a calcium content of 3366 mg/kg were from Soriano farm at Bequilo district, Uruguay. \u003cem\u003eE. dunnii\u003c/em\u003e, with a calcium content of 3756 mg/kg, was from Grecco farm and Los Cercos, District, Uruguay. \u003cem\u003eE. dunnii\u003c/em\u003e, with a calcium content of 4668 mg/kg, was from Grecco farm and Los Cercos, District, Uruguay Sodium carbonate (99.5%) was from Sigma Aldrich, St. Louis, USA, Nitric acid (65%) is from Sigma Aldrich, Burlington, USA, hydrogen peroxide (30 at%H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) was from Sigma Aldrich St. Louis, USA, Sulphuric acid (72%), was from Alfa Aesar, Kendel, Germany).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eStorage of the Samples:\u003c/h2\u003e \u003cp\u003eThe black liquor obtained after pulping was stored in the refrigerator. Prior to analysis, the samples were left on the table to reach room temperature and thoroughly mixed.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eMethods\u003c/h2\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003eKraft Cooking\u003c/h2\u003e \u003cp\u003eThree sets of kraft pulping experiments were conducted, using \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with varying calcium content: the first with 3366 mg/kg, the second with 4668 mg/kg, and the third with 3756 mg/kg. In the first set of experiments, different kraft pulping process conditions were assessed, and the effects of black or green liquor additions on pulping efficiency were evaluated. The second set of experiments involved \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a very high calcium content of 4668 mg/kg, which were challenging to pulp in the laboratory using a conventional protocol. Green liquor was used as both impregnation and cooking liquor in this case. The objective was to further examine and confirm the role of green liquor on the pulping performance of wood with very high calcium content. The third set of experiments utilized \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a calcium content of 3756 mg/kg, similar to the wood chips in the first set. This study aimed to assess the effects of green liquor on the bleachability of the produced kraft pulp. Both batches had calcium content too high to achieve reasonable defibration in our laboratory using standard pulping techniques (Vegunta et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe kraft pulping experiments were conducted using a 1000 ml steel autoclave multiunit digester system, with the process controlled by a computer system and an electric heater. Impregnation took place in steel autoclaves, where wood chips were degassed under vacuum for 30 minutes. Following this, the liquor was drawn into the autoclaves and positioned in a stream-heated glycol bath. It took 10 minutes for the required temperature to be reached, so the actual impregnation time commenced 10 minutes after placing the autoclaves in the electric heater. The impregnation and cooking liquor conditions were consistent across all kraft cooks in this study. Impregnation conditions included a temperature of 110\u0026deg;C and a duration of 90 minutes. As for the kraft cooking liquor conditions, they involved a liquid-to-wood ratio of 4:1, with effective alkali and sulfide charges set at 18% and 35%, respectively.\u003c/p\u003e \u003cp\u003eStock solutions of Na\u003csub\u003e2\u003c/sub\u003eS were prepared by dissolving technical-grade flakes of Na\u003csub\u003e2\u003c/sub\u003eS.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003ePreparation of Black Liquor for impregnation experiment:\u003c/h2\u003e \u003cp\u003eBlack liquor production was conducted in the laboratory for impregnation experiments, utilizing \u003cem\u003eE. dunnii\u003c/em\u003e wood chips containing 3366 mg/kg of calcium. The kraft cooking conditions for producing black liquor included an impregnation temperature of 110\u0026deg;C for 90 minutes, 35% sulfide content, a 4:1 liquid-to-wood ratio, 18% effective alkali (EA), and kraft cooking at 145\u0026deg;C for 1 hour. Consequently, the laboratory-produced black liquor, containing hydroxyl and sulfide ions, closely resembles industrial black liquor.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003ePreparation of Green Liquor:\u003c/h2\u003e \u003cp\u003eGreen liquor preparation involved adding sodium carbonate with a concentration of 0.66M to the water, after adjusting the effective alkali (18%) and sulfide (35%) content in the white liquor. The liquid-to-wood ratio was maintained at 4:1. White liquor, a precursor to green liquor, is created from sodium hydroxide and sodium sulfide stock solutions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003eKraft Cook Series 1:\u003c/h2\u003e \u003cp\u003e \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a calcium content of 3366 mg/kg were used in this study. Kraft cooks were conducted using reference white liquor, a combination of black and white liquor, and green liquor. The impregnation and cooking chemicals were the same as previously described. Kraft cooking was performed at various H-factors, with a constant time of 210 minutes and temperatures ranging from 138\u0026deg;C to 170\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eKraft Cook Series 2:\u003c/h2\u003e \u003cp\u003e \u003cem\u003eE. dunnii\u003c/em\u003e wood chips containing 4668 mg/kg of calcium were used. Kraft cooking was performed using synthetic green liquor. The impregnation and cooking chemical conditions remained the same as previously described, followed by the kraft cook. The kraft cooking conditions were set at 145\u0026deg;C for 210 minutes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eKraft Cook Series 3:\u003c/h2\u003e \u003cp\u003e \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a calcium content of 3768 mg/kg were used. Kraft cooking was conducted using reference white liquor, a combination of black and white liquor, and synthetic green liquor, aiming to achieve similar kappa numbers (13\u0026ndash;14). The impregnation and cooking chemical conditions were consistent with prior descriptions, followed by the kraft cook. The kraft cooking conditions for the three cooking liquors were as follows: white liquor (170\u0026deg;C, 210 minutes), black and white liquor (170\u0026deg;C, 210 minutes), and green liquor (145\u0026deg;C, 210 minutes).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eBleaching:\u003c/h2\u003e \u003cp\u003eA DEDED bleaching sequence was conducted on kraft pulp (with similar kappa numbers) obtained from E. dunnii wood using reference white liquor, a combination of black and white liquor, and synthetic green liquor. The drainability (ISO 5267-1), water retention value (WRV) for 100 mesh (ISO 23714), tensile index (ISO 1924-2), tensile stiffness (ISO 1924-2), and tear index (ISO 1974) were evaluated for both unbleached and bleached pulps.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition details for DEDED bleaching sequence on kraft pulps.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD0\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eE1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eD1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eE2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eD2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAcid\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eReaction temperature (\u0026deg;C)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e20\u0026ndash;25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eReaction time (min)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003epH target at the end\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2-2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.5\u0026ndash;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4-4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.5\u0026ndash;11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4-4.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e4.5-0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eClO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e \u003cb\u003e(%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNaOH (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003eLignin Isolation\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eConcentrated sulfuric acid (97 to 98% H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e) was added to 20 ml of impregnation liquor until the pH of the solution reached 2\u0026ndash;3. The mixture was then centrifuged at 4800 rpm for ten-minute intervals, with 5-minute breaks in between. After centrifugation, the supernatant was separated from the precipitate, which was subsequently washed twice with a sulfuric acid solution at pH 2 and centrifuged again. The resulting pellet was dried in an oven overnight at 80\u0026deg;C, and the weight was recorded. The precipitation process was performed in duplicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eAnalysis\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003eDetermination of Oxalic Acid Using HPLC:\u003c/h2\u003e \u003cp\u003eApproximately 100 mg of dried black liquor samples were diluted with a dilution factor of 1000 using Milli-Q water. The diluted samples were filtered through a 0.25 \u0026micro;m nylon filter and transferred to HPLC vials. Oxalic acid content was determined using high-performance liquid chromatography (HPLC) with a Thermo Fischer Scientific system (USA) equipped with a ROA-organic acid column (Thermo Fischer Scientific, USA) and a refractive index detector. The mobile phase consisted of a sulfuric acid solution with a pH between 2 and 8 (0.45 M) at a flow rate of 0.5 ml/min. The oven temperature was set at 50\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of Dry Solid Content and Ash Content:\u003c/h2\u003e \u003cp\u003eApproximately 5 ml of black liquor was placed in a ceramic crucible and kept in an oven at a temperature of 105\u0026deg;C until a constant mass was achieved (typically within 12 to 15 hours). The mass was then recorded. Following this, the residue from the 105\u0026deg;C drying process was heated to 600\u0026deg;C for 6 hours in the oven, and the resulting weight, representing the ash content, was documented.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eViscosity\u003c/h2\u003e \u003cp\u003eThe viscosity of pulp samples was determined according to the (ISO 5351:2010) standard.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eKlason Lignin and Sugar Composition Analysis:\u003c/h2\u003e \u003cp\u003eAll pulp samples were Wiley milled using a 40 mesh screen and then subjected to acid hydrolysis to determine lignin and sugar content. Initially, 3 ml of 72% H2SO4 was added to each sample, followed by placement in a vacuum desiccator for 1 hour and 20 minutes with occasional stirring. The mixtures were then diluted with 84 ml of Milli-Q water and autoclaved at 125\u0026deg;C for 1 hour. Subsequently, the samples were filtered through a glass fiber filter using a 3-piece filtration setup. The filtrates were diluted at a 1:10 ratio for sugar analysis and acid-soluble lignin determination. The insoluble (Klason lignin) fraction was dried in an oven at 105\u0026deg;C and weighed.\u003c/p\u003e \u003cp\u003eAcid-soluble lignin was measured using a Shimadzu UV-2550 UV-VIS spectrophotometer at an absorbance of 205 nm. Carbohydrate content was determined using a Dionex ICS-3000 high-performance anion-exchange chromatography system with pulsed amperometric detection (HPAEC-PAD), featuring a CarboPac PA1 column (Thermo Scientific, USA), an injection volume of 25 \u0026micro;l, and a flow rate of 1 ml/min. External sugar standards based on the sample were used for calibration. The results were reported as anhydrous sugars and performed in duplicate.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eMetal Ion Content Analysis:\u003c/h2\u003e \u003cp\u003eThe total metal ion content in the pulp samples was measured using ICP-OES (Thermo Scientific iCAP 7000 series). Before the ICP-OES measurements, approximately 100 mg of each sample was taken for analysis. Initially, 7 ml of aqua regia solution (2 ml H2O2\u0026thinsp;+\u0026thinsp;5 ml HNO3) was added to the samples. The tubes were sealed and then placed in an ultrasonic bath for several minutes. After this, the samples were left overnight for acid digestion. The samples were then filtered using filter paper and diluted to 50 ml with Milli-Q water. This solution was further diluted to a 1:50 ratio using 5% HNO3. Finally, 10 ml of the diluted sample was subjected to metal analysis using ICP-OES.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003eKappa number determination\u003c/h2\u003e \u003cp\u003eKappa number of pulp samples was determined according to the ISO 302:2004 standard.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003eResidual alkali determination\u003c/h2\u003e \u003cp\u003eThe residual alkali of black liquor samples was determined according to the SCAN-N 33:94 standard.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003eKraft cooking with different cooking liquors\u003c/h2\u003e \u003cp\u003ePrevious research has demonstrated that higher calcium content results in slower delignification and more severe cellulose degradation in \u003cem\u003eE. dunnii\u003c/em\u003e with calcium contents of 705, 870, and 1500 mg/kg, and has proposed possible mechanisms for these effects (Vegunta et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Even under harsh conditions, kraft pulping with lab-made white liquor proved to be practically challenging for samples containing more than 3000 mg/kg calcium. However, high calcium content had a lesser impact on industrial-scale pulping, although severe problems did arise. The difference between laboratory and industrial-scale pulping lies in the fact that black liquor is typically added to wood chips in a pulp mill (Ragnar et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), whereas white liquor may become contaminated with green liquor due to insufficient causticization. As a result, the composition of the liquors used for impregnation and kraft cooking in the pulp mill and a lab varies significantly. In this study, we conducted kraft pulping on a laboratory scale using white liquor, a combination of black and white liquor, and synthetic green liquor (prepared in our lab from pure chemicals). Further details on the composition can be found in the \u003cspan refid=\"Sec2\" class=\"InternalRef\"\u003ematerials and methods\u003c/span\u003e section.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetails of kraft pulping experiments using different cooking liquors. \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a calcium content of 3366 mg/kg were used.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH-factor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTotal pulp yield\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eScreened pulp yield (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRejects (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eKappa number unbleached pulp\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003eWhite liquor (reference)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e387.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e948.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2237.3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e3389.6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBlack\u0026thinsp;+\u0026thinsp;white liquor\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e387.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e948.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2237.3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e3389.6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGreen liquor (synthetic)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e247.6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e278.9\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e387.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the characteristics of kraft pulps produced using various cooking liquors at different H-factors. Kraft pulping was carried out with the aim of achieving a similar kappa number in the pulp. To achieve the desired kappa number, the cooking temperature was selected as a variable factor (H-factor). In this study, kraft pulping of \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a calcium content of 3366 mg/kg was performed at temperatures ranging from 138\u0026deg;C to 140\u0026deg;C, 145\u0026deg;C, 155\u0026deg;C, 165\u0026deg;C, and 170\u0026deg;C.\u003c/p\u003e \u003cp\u003eThe rate of delignification of high calcium-content wood chips is significantly influenced by green liquor. Despite a lower H-factor for green liquor pulping, high calcium-containing wood chips could be pulped with fewer rejects to achieve a lower kappa (as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Additionally, the kappa numbers were considerably lower for the pulps pulped with green liquor. In contrast, the addition of black liquor did not produce any significant effects (as illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cem\u003eE. dunnii\u003c/em\u003e wood chips with a calcium content of 3366 mg/kg were employed in this study. Additionally, the viscosity of the pulps generated using green liquor was higher at a given Kappa number (as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This indicates that green liquor, in some manner, protects cellulose from degradation during kraft pulping.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese findings are consistent with previous studies demonstrating that green liquor has a significant impact on the delignification rate and pulp quality in kraft pulping (Andrews and Chang \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Ban et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Klevinska and Treimanis \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Svedman and Tikka \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1998\u003c/span\u003e). While earlier research suggested that green liquor could be used to increase the sulfur content in pulping, our experiments did not support this explanation since the sulfur content was not increased by the addition of green liquor. Instead, we propose that it is the carbonate ions in green liquor that are responsible for the positive effects by forming inert calcium carbonate crystals, thereby preventing the negative effects of calcium ions during pulping. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e provides a schematic representation of this hypothesis.\u003c/p\u003e \u003cp\u003eHowever, if this hypothesis is correct, calcium must remain in the fiber even during kraft cooking and not be significantly transferred to the pulping liquor. The data in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e support the hypothesis in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, indicating that green liquor-treated pulp contains considerably more calcium than white and black liquor-treated pulp.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e presents the data on the residual alkali, oxalic acid, inorganic, organic, and lignin content of the black liquor collected after each kraft cook. The data indicate that black liquor always contains total dry solids (%) and lignin content (%), as well as inorganics. Additionally, a substantial amount of residual alkali was detected in the black liquor obtained using green liquor at a low kappa number, suggesting that kraft pulping selectivity is more favorable for this kraft cook at a low kappa number, particularly when compared to white liquor and black combined with white liquor.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacterization of black liquor collected from kraft cooks performed using different cooking liquors.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH-factor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDry solids (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAsh content (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eResidual alkali (mol/l)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ePrecipitated lignin (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eOxalic acid\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eWhite liquor (reference)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e387.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e948.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2237.3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e3389.6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBlack\u0026thinsp;+\u0026thinsp;white liquor\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e387.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e948.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e2237.3\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e3389.6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e59\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGreen liquor (synthetic)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e247.6\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e278.9\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e387.8\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates a hypothetical interpretation of the chemistry of cooking liquors with regard to calcium oxalate ions in wood chips. Previous research has identified calcium oxalate in the lumen of wood, and during kraft pulping with strongly alkaline white liquor, oxalate and calcium ions can deteriorate into the cell wall. According to our previous study (Vegunta et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), these calcium ions can accelerate polysaccharide degradation while delaying delignification. If this hypothesis is correct, calcium must remain in the fiber during kraft cooking and should not be significantly transferred to the pulping liquor. The data presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e support this hypothesis, as green liquor-treated pulp contains considerably more calcium than white and black liquor-treated pulp.\u003c/p\u003e \u003cp\u003eGiven the success of kraft pulping with high calcium content \u003cem\u003eE. dunni\u003c/em\u003e wood, we tested pulping with wood containing even higher calcium content \u0026ndash; 4668 mg/kg wood \u0026ndash; a quality that had been virtually impossible to pulp in the laboratory with conventional white liquor pulping. As expected, pure white liquor pulping did not result in defibrillation under the conditions used (see materials and methods), but adding green liquor allowed for pulping to generate pulp with low rejects and acceptable kappa numbers (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e)\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDetails regarding pulp produced using high calcium-containing wood chips (4668mg/kg) using green liquor.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eGreen liquor (synthetic) 100% (0.66M)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRejects (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal yield (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eScreened pulp yield (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eKappa number\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDry solids In Black liquor (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAsh content in black liquor (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePrecipitated lignin (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGlucose (% on wood)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e31.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eXylose (% on wood)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e9.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eKlason lignin (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.97\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eViscosity (ml/g)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1369\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCalcium content in pulp sample (mg/kg)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4138\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHEXA Unbleached pulp (\u0026micro;mol/g)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHEXA Bleached pulp(\u0026micro;mol/g)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eImpact of Green Liquor on Bleaching of Pulp\u003c/h2\u003e \u003cp\u003eIn order to assess the impact of green liquor on the bleaching of high calcium content wood chips, additional batches of pulp were prepared as controls and subjected to bleaching experiments. The pulp was produced at a specific kappa number (13\u0026ndash;14) to investigate the effects on pulp quality and strength. Wood chips with a calcium content of 3758 mg/kg were used for these experiments, and three different impregnation liquors were employed in the kraft cooking process. These experiments were conducted to determine whether the enhanced mineral content from green liquor would have any adverse effects on pulp bleaching, due to coprecipitated transition metal ions, among other factors.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacterization of kraft cooks subjected to bleaching experiments.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWhite liquor (reference)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eBlack\u0026thinsp;+\u0026thinsp;white liquor\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGreen liquor (synthetic)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRejects (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eTotal yield (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e45.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e46.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e51.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eScreened pulp yield (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e44.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e46.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e51.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eKappa number\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16.1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDry solids In Black liquor (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAsh content in black liquor (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePrecipitated lignin (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eViscosity (ml/g)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e882\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e896\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1364\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCalcium content in pulp sample (mg/kg)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1925\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2362\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2580\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHexA Unbleached pulp (\u0026micro;mol/g)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e22.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eGlucose (% on wood)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e24.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e27.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eXylose (% on wood)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e7.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eKlason lignin (%)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e summarizes the properties of the pulp obtained through kraft pulping with different impregnation liquors. The green liquor impregnation resulted in higher pulp yield, faster delignification, and higher viscosity at the same kappa number, consistent with previous experiments using wood chips with a calcium content of 3366 mg/kg. All pulps were kraft pulped under identical chemical conditions with different H-factors to achieve a similar kappa number. The total yield increased by 5% when green liquor impregnation was used, compared to white and black\u0026thinsp;+\u0026thinsp;white liquor. The hexeneuronic acid content was slightly lower in the pulp obtained using green liquor impregnation.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays the total inorganic metal content in unbleached pulp samples produced using different impregnation liquors. The unbleached pulp obtained from green liquor impregnation has a slightly higher calcium content compared to those obtained from black liquor\u0026thinsp;+\u0026thinsp;white liquor and white liquor (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This suggests that the calcium content follows the fiber line instead of being washed out with black liquor. However, the presence of calcium carbonate crystals in the pulp may trap transition metal ions and hinder the bleaching process. Hence, bleaching experiments with the sequence DEDED were conducted on pulps cooked with white and green liquors to comparable kappa numbers to assess the impact of green liquor on bleaching efficiency. The green liquor impregnated pulp samples had significantly higher intrinsic viscosity compared to those impregnated with white liquor and black\u0026thinsp;+\u0026thinsp;white liquor. This indicates an improvement in the mechanical properties of the pulp. The findings are consistent with the tensile strength and tear index results obtained from unbleached and bleached pulp samples (see Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). The viscosity (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e) of unbleached and bleached pulp generated with white liquor and black liquor\u0026thinsp;+\u0026thinsp;white liquor is lower at a given kappa number than that of green liquor impregnated pulp. The use of higher H-factor in pulp obtained from white liquor and black liquor\u0026thinsp;+\u0026thinsp;white liquor could be a reason for the lower viscosity.\u003c/p\u003e\u003cp\u003eThe benefits of the green liquor treatment in achieving high viscosity were mostly retained even after bleaching, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. This is evident in the improved tensile index (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) and tear index (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e) for the bleached pulps previously treated with green liquor.\u003c/p\u003e \u003cp\u003eRefining of pulp fibers through PFI refining enhances the paper-making properties of pulp fibers, improving their binding ability and increasing their strength. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, both unbleached and bleached pulps processed with green liquor impregnation have higher mechanical and tear indices. The higher hemicellulose content on the fiber surfaces in green liquor-treated pulps may contribute to their improved strength properties. However, this increase in strength appears to cause an increase in drainage resistance (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e). The bleaching of green liquor-treated pulps was found to be equally effective in developing brightness as it was for the control samples. This, together with the data in Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, suggests that calcium carbonate crystals in pulps should not significantly affect the bleaching process.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn this study, we have conducted a series of experiments researching high calcium-content wood chips that cannot pulp under conventional kraft cooking conditions using white liquor on a lab scale. Instead, we could pulp these highly impossible wood chips using green liquor kraft pulping at a lower H-factor. The bleaching of green-liquor cooked pulps was not affected. The following conclusions can be drawn from this work:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eExceptionally low reject content and low kappa number at similar H-factor using green liquor impregnation can be achieved compared to reference white liquor and black\u0026thinsp;+\u0026thinsp;white liquor.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eKappa number was lower at given H-factor for pulps of calcium rich wood when green liquor was added to the white liquor.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe bleached pulps produced using green liquor impregnation have increased tensile, and tear index.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe addition of green liquor to kraft pulping directs the calcium to stay with the fiber rather than to go with the black liquor.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eKraft cooking with green liquor results in improved selectivity of the kraft pulping.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eGreen liquor usage makes pulping of \u003cem\u003eEucalypts\u003c/em\u003e with even a very high calcium content possible.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eGreen liquor-treated pulps could be bleached with good results, mainly keeping the advantages from the unbleached pulp.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eA hypothesis for the effects of green liquor based on the formation of calcium carbonate (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) has been presented.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll data generated or analysed during this work are included in this publication. Raw data for the figures are available from the corresponding author on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests as defined by Springer, or other interests that might be perceived to influence the results and/or discussion reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFor Vegunta, Garcia, Bj\u0026ouml;rk and Jansson, financial support from Stora Enso is gratefully acknowledged. For Lind\u0026eacute;n, support from the Knut and Alice Wallenberg Foundation (KAW) through the Wallenberg Wood Science Center, KAW 2015.0390, is gratefully acknowledged.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the planning of the experiments. Most of the experimental work was performed by Vegunta with help from Lind\u0026eacute;n and Deshpande, except for the bleaching experiments and part of the pulp characterization which was performed by Bj\u0026ouml;rk with instructions from Jansson. Garcia and Jansson selected and procured the wood chips samples which were used in the experiments. Vegunta, Henriksson and Sevastyanova wrote the major part of the text, but all authors participated in reading and commenting on the text.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMonica Heberling, Montes del Plata Colonia Department, is gratefully acknowledged for her role in the sampling of the wood chips samples.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAndrews EK, Chang HM (1985) Extended delignification kraft pulping of softwoods effect of treatment on chips and pulp with sulfide containing liquors. 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KGaA, Weinheim, pp 1-89. \u003c/li\u003e\n\u003cli\u003eSantiago ASVM (2008) Estrat\u0026eacute;gias para o aumento da reten\u0026ccedil;\u0026atilde;o de polissacar\u0026iacute;deos durante a produ\u0026ccedil;\u0026atilde;o de pasta kraft de \u003cem\u003eEucalyptus globulus\u003c/em\u003e. Doctoral dissertation, Universidade de Aveiro, Portugal.\u003c/li\u003e\n\u003cli\u003eSantiago AS, Neto CP (2008) \u003cem\u003eEucalyptus globulus\u003c/em\u003e kraft process modifications: Effect on pulping and bleaching performance and papermaking properties of bleached pulps. J Chem Technol Biotechnol 83(9):1298-1305.\u003c/li\u003e\n\u003cli\u003eSvedman M, Tikka P (1998) The use of green liquor and its derivatives in improving kraft pulping. Tappi J (1998) 81:151-158.\u003c/li\u003e\n\u003cli\u003eSchwartz JT, and Lawoko M (2010) Removal of acid-soluble lignin from biomass extracts using amber lite XAD-4 resin Acid soluble lignin. BioResources 5(4):2337-2347.\u003c/li\u003e\n\u003cli\u003eVegunta V, Sethikumar ER, Lind\u0026eacute;n P, Sevastyanova O, Vilaplana F, Garcia A, Bj\u0026ouml;rk M, Jansson U, Henriksson G, Lindstr\u0026ouml;m ME (2022) High calcium content of \u003cem\u003eEucalyptus dunnii\u003c/em\u003e wood affects delignification and polysaccharide degradation in kraft pulping. Nordic Pulp Paper Res J 37(2):338-348.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Kraft pulping, green liquor, black liquor, Eucalyptus dunnii, Calcium, Delignification","lastPublishedDoi":"10.21203/rs.3.rs-3165099/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3165099/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn our previous study, we demonstrated that \u003cem\u003eEucalyptus dunnii\u003c/em\u003e samples containing high calcium content show inferior pulping properties concerning delignification and polysaccharide degradation. This led us to investigate alternative methods for improving the pulping process of these samples. In the present work, we evaluated the effects of incorporating black and green liquors into the \u003cem\u003eEucalyptus dunnii\u003c/em\u003e chips before kraft pulping, aiming to enhance the pulping process and overcome the negative impact of high calcium content.\u003c/p\u003e \u003cp\u003eThe addition of both black and green liquors resulted in specific enhancements, with the green liquor having a more significant impact on the pulping process. Even wood samples with the highest calcium content demonstrated satisfactory pulping results when treated with green liquor. Delignification occurred more rapidly, and selectivity was higher for samples pre-treated with green liquor before kraft pulping. Moreover, calcium tended to follow the fiber under these conditions rather than being released into the black liquor, which may contribute to the improved pulping performance.\u003c/p\u003e \u003cp\u003eSubsequent bleaching tests revealed that the bleachability of green liquor-treated pulp was nearly identical to that of a control pulp, while maintaining a higher viscosity. This suggests that incorporating green liquor into the pre-treatment process not only improves the pulping performance of \u003cem\u003eEucalyptus dunnii\u003c/em\u003e samples with high calcium content but also maintains desirable bleachability characteristics.\u003c/p\u003e \u003cp\u003eTo better understand the underlying mechanisms of these findings, we discuss the potential chemical explanations behind the observed improvements.\u003c/p\u003e","manuscriptTitle":"Addition of Green and Black Liquor in Kraft Pulping of Eucalyptus dunnii wood: Possible Solutions for the Problems with Kraft Pulping Caused by High Calcium Content","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-08-07 13:46:44","doi":"10.21203/rs.3.rs-3165099/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major revision","date":"2023-08-12T05:09:57+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2023-08-10T07:05:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"3ed597ea-fb0a-4a37-bf36-beafb741ebf2","date":"2023-08-05T21:21:11+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2023-08-05T07:15:12+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-08-01T12:33:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2023-08-01T12:33:10+00:00","index":"","fulltext":""},{"type":"submitted","content":"Cellulose","date":"2023-07-12T22:54:06+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"cellulose","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"cels","sideBox":"Learn more about [Cellulose](https://www.springer.com/journal/10570)","snPcode":"10570","submissionUrl":"https://submission.nature.com/new-submission/10570/3","title":"Cellulose","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"7911078c-f342-4e2d-9d03-8bb20a5c5cc5","owner":[],"postedDate":"August 7th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-12-25T15:02:42+00:00","versionOfRecord":{"articleIdentity":"rs-3165099","link":"https://doi.org/10.1007/s10570-023-05603-z","journal":{"identity":"cellulose","isVorOnly":false,"title":"Cellulose"},"publishedOn":"2023-12-20 15:00:50","publishedOnDateReadable":"December 20th, 2023"},"versionCreatedAt":"2023-08-07 13:46:44","video":"","vorDoi":"10.1007/s10570-023-05603-z","vorDoiUrl":"https://doi.org/10.1007/s10570-023-05603-z","workflowStages":[]},"version":"v1","identity":"rs-3165099","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3165099","identity":"rs-3165099","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}