Enhancing Biofuel Pellet Quality using Combined Torrefaction and Co-pelletization Processes of Palm Kernel Shell and Empty Fruit Bunch

Enhancing Biofuel Pellet Quality using Combined Torrefaction and Co-pelletization Processes of Palm Kernel Shell and Empty Fruit Bunch | 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 Enhancing Biofuel Pellet Quality using Combined Torrefaction and Co-pelletization Processes of Palm Kernel Shell and Empty Fruit Bunch Chang Siaw Sang, Noor Asma Fazli Abdul Samad, Suriyati Binti Saleh This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3864756/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Jan, 2025 Read the published version in Environmental Science and Pollution Research → Version 1 posted 6 You are reading this latest preprint version Abstract Palm kernel shell (PKS) and empty fruit bunch (EFB) are potential biomass resources for producing solid biofuel for energy applications. However, raw EFB and PKS are not uniform in size and pose rotting behavior. Torrefaction and co-pelletization are both effective methods to improve their combustion and mechanical characteristics. This study aims to investigate the effect of torrefaction temperature and the blending ratio of PKS and EFB on the mechanical and combustion characteristics of co-pellets. Initially, PKS and EFB underwent torrefaction process for 30 minutes at three different temperatures (210°C, 240°C, and 270°C). Then, both torrefied PKS and EFB were blended at five different ratios (0:100, 25:75, 50:50, 75:25, 100:0) with carboxymethyl cellulose as a binder (10% by weight). The results showed that a higher torrefaction temperature resulted in an increment of the higher heating value (HHV) but weaker mechanical strength. Pellets with a blending ratio of PKS to EFB (75:25) torrefied at 240°C showed the comparatively best pellet quality in terms of HHV (17.94 MJ/kg), high compressive strength (3.5 MPa), low ash content (3.97 wt%), and the lowest density changes (0.66%), which satisfy the requirements set in standard EN ISO 17255-6 for good quality pellets, indicating that a high quality biofuel pellet can be produced using the combined approach of torrefaction and co-pelletization. Torrefaction Pelletization Biofuel Pellet quality Palm kernel shell Empty fruit bunch Figures Figure 1 Figure 2 1. Introduction Biomass waste has been widely used for producing biofuel as an alternative source to replace depleted fossil fuels, especially in European Union countries. However, it is rarely used in developing countries like Thailand, Indonesia, and Malaysia (Malek et al. 2020 ). In fact, Malaysia has abundant amounts of biomass waste, especially from the palm oil industry. Palm kernel shell (PKS) and empty fruit bunch (EFB) are examples of biomass waste generated from palm oil mills. Current practices show that EFB is commonly utilized as fertilizer since it is abundant in minerals such as phosphorus, magnesium, potassium, nitrogen, and carbon. These minerals are beneficial for soil pH increments, soil erosion reduction, and soil moisture conservation (Sukiran et al. 2017 ). Hence, EFB is transformed into chemical fertilizers through the incineration process. However, this method is not environmentally friendly because it produces high amounts of white smoke and fly ash throughout the process, resulting in air pollution (Loh 2017 ). Meanwhile, PKS has been commonly utilized as solid fuel for a steam boiler in the milling plant since PKS has a comparatively higher heating value compared to other lignocellulosic biomass. However, current practice has limited the potential of biomass usage and the commercial value of EFB and PKS, and most practices contribute to the degradation of environmental conditions. The limited application of both EFB and PKS is due to their inferior characteristics such as low bulk density, hygroscopic nature, and low energy density, which ultimately contributes to inconveniences during handling, transportation, and storage processes, as well as reduced combustion efficiency as a solid fuel (Kumar et al. 2017 ). In fact, both EFB and PKS have high potential to be utilized as an energy commodity by upgrading their characteristics through suitable pre-treatment methods. Torrefaction and pelletization are widely used pre-treatment methods for improving the fuel quality of biomass, which eventually enhances their commercialized value as solid biofuel. The main reasons for using pre-treatment methods are to enhance the heating value, inhibit rotting behavior, as well as improve the bulk and energy density of biomass waste (Sukiran et al. 2017 ; Pradhan et al. 2018 ; Mostafa et al. 2019 ). Theoretically, the torrefaction process is a thermochemical pre-treatment method that occurs in a mild temperature range (200°C to 300°C) under atmospheric conditions without oxygen supply (Mostafa et al. 2019 ; Siyal et al. 2020 ). The torrefaction process transforms biomass waste with a hygroscopic nature into hydrophobic by destroying hydroxyl groups in biomass (Manouchehrinejad et al. 2021 ). Furthermore, the torrefaction process improves the heating value of biomass waste, reducing moisture content while increasing the fixed carbon content of biomass waste (Kanwal et al. 2019 ). However, the main challenge in employing torrefied biomass as solid biofuel is related to the delicate and brittle properties of torrefied biomass, which are unfavorable for handling, transportation, and storage processes (Larsson et al. 2013 ). Hence, biomass needs to be transformed into a uniform particle size with enhanced mechanical strength to reduce losses due to fracture and breakage during handling, transportation, and storage processes. This limitation can be overcome by using pelletization, where this physical pre-treatment method can compact biomass waste into uniform-sized particles with increased bulk density (Sukiran et al. 2017 ; Picchio et al. 2020 ; Sambeth et al. 2022 ). In addition, pelletization is an effective method that enables easier and more efficient handling, transportation, and storage processes. However, the limitation of pelletization is that this method does not improve the combustion properties of raw biomass waste. As a solution, torrefaction and pelletization processes must be combined to enhance both the combustion and physical characteristics of biomass waste. The combination of torrefaction and pelletization approaches is able to produce biomass pellets with better high heating value, hydrophobicity, a compact structure, and uniform size (Bach and Skreiberg 2016 ). However, suitable operating conditions for torrefaction and pelletization must be considered to produce the desired quality of biomass pellets. For example, residence time and torrefaction temperature are two significant operating conditions in the torrefaction process. Torrefaction temperature is a more significant operating condition compared to residence time because residence time shows a less substantial effect on enhancing the characteristics of biomass waste. Additionally, torrefaction temperature is the most significant variable that affects the higher heating value (HHV) of the pellet formed and the binding mechanisms of biomass waste during the pelletization process. This is due to the fact that a higher torrefaction temperature results in more severe degradation of lignocellulosic components, which naturally act as a natural binder. Usually, lignocellulosic components form solid bridges between biomass particles and improve their cohesive strength. Several research works have been conducted to investigate the impacts of torrefaction temperature on the binding mechanisms of biomass waste during the pelletization process, and the effect varies depending on the properties of the biomass employed. For example, biomass processed at high torrefaction temperatures produces more fragile and brittle pellets, and more energy is consumed during the co-pelletization process (Bach and Skreiberg 2016 ; Rudolfsson et al. 2017 ). Although a high HHV of torrefied biomass can be obtained at higher torrefaction temperatures, a low compression strength of the pellet is expected, suggesting that biomass undergoing severe torrefactions (275°C to 300°C) tends to have low quality in terms of mechanical properties (Stelte et al. 2013 ). Thus, torrefaction and pelletization present an ideal approach to transform EFB and PKS wastes into pellet products for energy-related applications. Based on the availability of oil palm solid wastes in Malaysia, around 18.88 million tonnes per year of EFB has been generated compared to only 4.72 million tonnes per year of PKS waste (Sukiran et al. 2017 ). This indicates that EFB has abundant resources compared to PKS. However, EFB has a calorific value of 18.88 MJ/kg, which is lower than the calorific value of PKS, which is around 20.09 MJ/kg (Loh 2017 ). In addition, PKS contains a high lignin content, around 50.7 wt%, which is preferable to produce stronger and more compact pellets (Siyal et al. 2020 ). High lignin content can strengthen solid bridges between particles, preventing pellet fracture and breakage during handling, transport, and storage processes. This theoretically shows that PKS will produce better pellets in terms of energy content compared to EFB. The main drawback is that EFB is the main priority for sustainable energy production in Malaysia due to a significant amount of waste. Therefore, blending EFB with PKS through co-pelletization provides another approach to produce high-quality pellets. Previous studies show that a better quality pellet can be obtained using a combination of different biomass materials. For example, oil palm trunk bark was blended with corncob at different mixing ratios, and the blended pellet exhibited better quality in terms of heating values, ash content, and compression strength (Kpalo et al. 2020 ). Torrefied canola meal and canola hull were blended using a mixer at five different ratios (100:0, 80:20, 60:40, 40:60, 100:0), and the blended pellet with more than 40 wt% of torrefied canola hull possessed better heating value and mechanical strength than the pure torrefied pellet (Faizal et al. 2018 ). Currently, research found in literature involving EFB and PKS is focusing only on the torrefaction process, and in some cases, working on pelleting raw EFB and PKS. Based on our knowledge, no work has been conducted on the influence of torrefaction and the blending ratio of raw and torrefied EFB and PKS on the co-pelletization process. Hence, the aim of this study is to investigate the effect of torrefaction temperature (210°C, 240°C, 270°C) and the blending ratio of PKS to EFB (0:100, 25:75, 50:50, 75:25, 100:0) on the physical and combustion characteristics of biomass pellets. The combustion properties such as HHV, moisture and ash content, as well as physical properties such as compression strength, pellet density, density changes, and dimensional stability, were measured to evaluate the quality of co-pellets. Moreover, univariate analysis of variance (UANOVA) was conducted to investigate the impact of the studied parameters (torrefaction temperature and blending ratio) themselves, as well as the interaction effects of the studied parameters on the combustion and physical characteristics of co-pellets produced. 2. Materials and Methods 2.1 Biomass collection, preparation and torrefaction Raw EFB and PKS samples were collected from Lepar Hilir Palm Oil Mill, Kuantan, Pahang, Malaysia. The collected biomass samples were air-dried for a few days before being oven-dried for 4 hours. The dried biomass samples were ground and sieved, where biomass with particle sizes in the range between 0.5 mm and 1 mm was used to facilitate feedstock loading and heat transfer rate (Sukiran et al. 2017 ). In terms of the torrefaction experiment, approximately 10 g of biomass samples were loaded into a vertical tubular reactor with dimensions of 39.7 cm in length and an internal diameter of 1.9 cm, respectively. Afterwards, a flow of 10 ml/min of nitrogen was used to flush the reactor for 5 minutes. The biomass samples were torrefied at temperatures of 210°C, 240°C, and 270°C for a 30-minute residence time. A residence time of 30 mins was chosen as no significant improvement has been observed in biomass undergoing torrefaction for more than 30 mins (Wahid et al. 2017 ; Wattana et al. 2017 ). Finally, the torrefied samples were stored in a desiccator. 2.2 Biomass characterization The proximate analysis of raw EFB and PKS was determined based on standard procedures of ASTM E872-82 for volatile matter, ASTM 1755-01 for ash content, and a moisture analyzer (Model MS-70, A&D Company Ltd., Tokyo, Japan) for moisture content. The higher heating value (HHV) of raw EFB and PKS was measured using a bomb calorimeter (C200, IKA® Works (Asia) Sdn Bhd). Chemical analyses were conducted following NREL procedures (Azargohar et al. 2019 ). 2.3 Pelletization process The pelletization process was conducted at a fixed temperature (130°C) and pressure (12 MPa) for 20 minutes using a hot press machine. Firstly, raw and torrefied EFB and PKS samples were blended based on the ratios shown in Table 1 . The blended samples were then mixed with carboxymethyl cellulose (CMC) as a binder (10% by weight of the sample) to further strengthen the solid bridges of the pellets. For example, the 50PKS/50EFB sample refers to equal amounts of PKS and EFB blended together with an additional approximately 10 wt% of CMC. Then, the blended samples were filled into pellet molds and transferred into the hot press machine for compressing the pellets. All pellet samples were produced in a cylindrical shape with specifications of 1.5 cm for diameter and a height of 2.0 cm. Table 1 Blending ratio of raw and torrefied pellet samples. Sample Name Ratio of PKS Ratio of EFB 100EFB 0 100 25PKS/75EFB 25 75 50PKS/50EFB 50 50 75PKS/25EFB 75 25 100PKS 100 0 Table 1 2.4 Pellet characterization HHV of each pellet sample was determined using a bomb calorimeter (C200, IKA® Works (Asia) Sdn Bhd). Each HHV measurement was replicated three times, and the average value of HHV was presented. The density of the pellet was determined by dividing its mass by its volume. Two different pellet densities were measured, where the initial density of the pellet was measured directly after the pelletization process, and the final density of the pellet was taken after 14 days of storage in an open-air area (Emadi et al. 2017 ). Density changes and dimensional stability were determined after 14 days of storage. Dimensional stability was divided into two: longitudinal dimension (changes in pellet length) and radial dimensions (changes in diameter). The dimensional stability of the pellet was calculated by subtracting longitudinal and radial dimensions from 100%. The compression strength of the pellet was measured using a universal testing machine (AGs-X series, Shidmadzu Corporation). The pelletized sample was placed on a stainless-steel base platen vertically. Then, a 5 kN load cell was applied to the samples at a 2 mm/min crosshead speed until the pellet began to crush. The maximum load the samples were able to withstand is known as the fracture load. The compression strength of the pellets is calculated based on Eq. ( 1 ): $$Compression Strength \left(MPa\right)= \frac{2 \times Fracture Load \left(N\right)}{\pi {\times Pellet Diameter \left(mm\right)}^{2}}$$ 1 Ash content is another important property for determining the quality of pellets. The ash content of the pellets was determined based on ASTM 1755-01. Each measurement was performed three times, and the average values are presented in this work. 2.5 Statistical analysis All data obtained during torrefaction and co-pelletization studies were analyzed to investigate the influence of torrefaction temperature and blending ratio on the pellet characteristics (HHV, initial density, final density, compression strength, moisture, and ash content) based on the principles of UANOVA. The Tukey test was used to study the statistically significant differences between the mean values of different pellet properties (Moreira et al. 2020 ). 3. Results and Discussion 3.1 Proximate and chemical analysis of raw PKS and EFB Proximate analysis can be used to evaluate the combustion properties of biomass waste. Fixed carbon content is the combustible residue that can improve the combustion performance of burning materials, whereas ash content is the non-combustible content that can lead to equipment corrosion and cause air pollution due to its non-combustible characteristics (Sukiran et al. 2017 ). PKS has a higher fixed carbon content but lower ash content compared to EFB, as shown in Table 2 . This indicates that PKS is a better solid biofuel than EFB, as it exhibits better combustion performance and generates lower ash during the combustion process. Additionally, PKS has a higher energy content than EFB, as indicated by its higher HHV. The lignocellulosic components (hemicellulose, cellulose, and lignin) have a significant impact on forming pellets with high quality, as they serve as a natural binder between biomass particles. PKS showed a higher lignin content than EFB, which can form solid bridges between particles, as shown in Table 2 . High lignin content is significant for producing more durable pellets since it acts as a natural binder when heat is applied during the pelletization process (Siyal et al. 2020 ). Table 2 Proximate and chemical analysis of EFB and PKS. Analysis PKS EFB Proximate analysis (dry basis wt%) Ash 1.03 3.15 Volatile matter 71.83 74.37 Moisture 4.30 6.20 Fixed carbon 22.84 16.28 Chemical analysis (wt%) Hemicellulose 21.80 36.80 Cellulose 19.05 30.16 Lignin 50.40 21.50 Ash 3.85 5.58 Extractives 4.90 5.96 HHV (MJ/kg) 19.79 17.48 Table 2 3.2 Higher heating value (HHV) HHV is a vital characteristic in evaluating the combustion performance of biofuel co-pellets as it shows the maximum energy content of the biofuel. The HHV of biofuel co-pellets observed in this study is presented in Fig. 1 . Both torrefaction temperature and the blending ratio of EFB and PKS show a significant effect (p < 0.05) on the HHV of biofuel pellets, as shown in Supplementary Material. The findings reveal that the rise in torrefaction temperature substantially improved the HHV of the biofuel pellets. This result may be explained by the fact that carbonization of both EFB and PKS during the torrefaction process increases the fixed carbon content of EFB and PKS (Siyal et al. 2020 ). Additionally, the rise in torrefaction temperature significantly enhanced the HHV of the pellets due to the removal of a hydroxyl group from hemicellulose during torrefaction, leading to an enhancement in the energy content of the torrefied sample (Bach and Skreiberg 2016 ). Torrefied pellets formed at a torrefaction temperature of 270°C showed the highest enhancement in HHV, particularly 100PKS, where around a 1.12 HHV enhancement has been observed. Figure 1 3.3 Dimensional stability Pellet density is a significant factor that affects the combustion properties and handling cost of biofuel co-pellets. Normally, denser pellets require a longer burning time but need less storage space and exhibit higher efficiency in transportation (Campbell et al. 2019 ). Table 3 shows the density, density changes, and dimensional stability of pellet samples. Initial density indicates the density of pellets measured immediately after the pelletization process, and the final density was taken after two weeks of storage at room conditions. As shown in Table 3 , the final density for all pellets decreased from the initial density, which is due to the relaxation of grinds in the pellet after pressure release (Emadi et al. 2017 ). Raw pellets showed lower initial and final density compared to the torrefied pellets, indicating that torrefaction improves the density of biomass pellets. The rise in torrefaction temperature improves the initial and final pellet density, indicating a significant effect of torrefaction temperature on the initial and final density of the pellets (p < 0.05). In addition, the density change for pellets was reduced when the torrefaction temperature was increased up to 240°C, but the density change increased for pellets formed from torrefied samples at 270°C. This indicates that this temperature is considered a severe torrefaction condition, which produces more fine suspended particles contributing to the further reduction of final pellet density. As a consequence, pellets formed from torrefied samples at 240°C are stable and can be safely handled, transported, and stored. In terms of dimensional stability, all pellets obtained close to 100% longitudinal and radial changes, indicating they experience minimal changes in mass, diameter, and length in a 14-day storage time. This shows that less air pollution is expected due to the low generation of fine particles from the pellets (Emadi et al. 2017 ). Table 3 Density, density changes and dimensional stability of pellet samples. Torrefaction Temperature (°C) Samples Density (kg/m 3 ) Density change (%) Dimensional stability (%) Initial Final Longitudinal Radial 100EFB 536.82 ± 5.26 511.34 ± 2.42 4.75 99.44 99.68 25PKS/75EFB 648.31 ± 5.46 628.36 ± 2.58 3.08 99.52 99.72 Raw 50PKS/50EFB 750.16 ± 2.17 728.35 ± 2.72 2.91 99.54 99.72 75PKS/25EFB 981.23 ± 7.15 968.56 ± 4.67 1.29 99.65 99.78 100PKS 970.75 ± 2.57 950.47 ± 3.91 2.09 99.62 99.76 100EFB 555.67 ± 3.47 535.81 ± 5.24 3.57 99.48 99.72 25PKS/75EFB 673.25 ± 3.81 658.78 ± 5.16 2.15 99.58 99.74 210 50PKS/50EFB 790.31 ± 2.05 774.68 ± 2.63 1.98 99.61 99.75 75PKS/25EFB 1015.46 ± 3.63 999.16 ± 4.45 1.61 99.61 99.76 100PKS 988.26 ± 5.84 964.61 ± 3.85 2.39 99.56 99.74 100EFB 604.34 ± 5.28 588.45 ± 2.44 2.63 99.55 99.74 25PKS/75EFB 731.21 ± 3.67 717.82 ± 3.26 1.83 99.61 99.75 240 50PKS/50EFB 835.45 ± 3.10 825.36 ± 2.46 1.21 99.67 99.78 75PKS/25EFB 1105.72 ± 3.90 1098.42 ± 3.11 0.66 99.74 99.8 100PKS 1050.72 ± 4.64 1030.32 ± 3.33 1.94 99.69 99.82 100EFB 596.36 ± 5.21 580.45 ± 4.41 2.67 99.5 99.68 25PKS/75EFB 711.38 ± 5.26 697.92 ± 2.42 1.89 99.6 99.74 270 50PKS/50EFB 798.72. ±1.41 787.55 ± 1.89 1.40 99.62 99.74 75PKS/25EFB 1031.43 ± 4.10 1017.74 ± 3.62 1.33 99.61 99.76 100PKS 1023.28 ± 4.39 1004.16 ± 2.91 1.87 99.64 99.78 The blending ratio of the pellet also showed a significant effect on pellet density (p < 0.05), as shown in Supplementary Material. The 75PKS/25EFB pellet produced from a torrefaction temperature of 240°C showed the highest final and initial density compared to other pellets. It obtained the lowest density changes and the highest dimensional stability. This is due to the fact that the intertwined fibers of EFB strengthened the interlocking bonding of the pellets formed, resulting in lower density change and better dimensional stability, whereas PKS filled in the void space between the EFB fibers, forming pellets with higher density (Sambeth et al. 2022 ). Torrefaction temperature and blending ratio showed an interaction effect on the initial and final density of pellets (p < 0.05) because torrefaction temperature and blending ratio affect the compactness of the pellet formed. Overall, only the 75PKS/25EFB and 100PKS torrefied at temperatures of 240 and 270°C achieved pellet density within the acceptable standard range of 1000–1400 kg/m 3 , where the torrefied pellet at 240°C with a blending ratio of 75PKS/25EFB shows the highest density and dimensional stability, contributing to the low fine generation and less air pollution expected during handling, transportation, and storage processes. Table 3 3.4 Compression strength Compression strength is a vital property of biofuel pellets, revealing the hardness of the pellets for handling, packing, and transportation. Table 4 shows the fracture load and compression strength of the pellets produced from EFB and PKS. It is evident that the blending ratio of 75PKS/25EFB torrefied at 240°C shows the highest fracture load (1025.23 ± 15.5 N) and compression strength (3.5 ± 0.25 MPa), whereas 100EFB without torrefaction pretreatment shows the lowest fracture load (280.18 ± 10.25 N) and compression strength (0.25 ± 0.03 MPa). Torrefaction temperature showed significant effects on the fracture load and compression strength of the pellet (p < 0.05), as shown in Supplementary Material. This can be observed in Table 4 , where torrefied pellet samples exhibit better fracture load and compression strength compared to raw pellets. The enhancement in fracture load and compression strength of the torrefied pellets was achieved because the torrefaction process causes a change in plastic and viscoelastic behavior, resulting in harder biomass (Emadi et al. 2017 ). However, severe torrefaction conditions result in a reduction of fracture load and compression strength of the pellet, as observed for torrefied pellets at a temperature of 270°C. This is due to the degradation of lignocellulosic components (lignin, hemicellulose, and cellulose), which are responsible for forming solid bridges between particles during the pelletization process. The decrement in fracture load and compression strength is also related to the glass transition point of lignin, contributing to a strong binding force between particles (Emadi et al. 2017 ). Due to the severity of torrefaction, plasticization between particles may occur since it is already beyond the glass transition point of lignin, lowering the modulus of elasticity of biomass particles and forming empty spaces between them (Mostafa et al. 2019 ). Hence, fracture load and compression strength are reduced when biomass undergoes torrefaction at high temperatures. Table 4 Fracture load and compression strength of pellet samples. Torrefaction Temperature (°C) Samples Fracture load (N) Compression strength (MPa) 100EFB 280.18 ± 10.25 0.25 ± 0.03 25PKS/75EFB 404.15 ± 2.84 0.38 ± 0.03 Raw 50PKS/50EFB 657.81 ± 8.18 1.22 ± 0.61 75PKS/25EFB 726.52 ± 11.56 1.83 ± 0.91 100PKS 441.44 ± 11.15 0.46 ± 0.11 100EFB 465.35 ± 9.62 0.55 ± 0.07 25PKS/75EFB 596.47 ± 5.43 0.83 ± 0.08 210 50PKS/50EFB 822.18 ± 10.36 2.25 ± 0.28 75PKS/25EFB 914.26 ± 11.04 2.85 ± 0.49 100PKS 664.19 ± 10.65 1.25 ± 0.32 100EFB 580.27 ± 10.85 0.72 ± 0.05 25PKS/75EFB 708.23 ± 4.53 1.65 ± 0.12 240 50PKS/50EFB 955.68 ± 13.28 3.15 ± 0.11 75PKS/25EFB 1025.23 ± 15.50 3.50 ± 0.25 100PKS 772.85 ± 10.14 2.07 ± 0.21 100EFB 555.64 ± 7.27 0.70 ± 0.10 25PKS/75EFB 686.82 ± 6.13 1.43 ± 0.01 270 50PKS/50EFB 910.46 ± 12.54 2.85 ± 0.68 75PKS/25EFB 977.55 ± 6.61 3.20 ± 0.34 100PKS 783.48 ± 3.41 2.12 ± 0.11 Table 4 Furthermore, the blending ratio of EFB and PKS also shows a significant effect on the fracture load and compression strength of the pellet (p < 0.05), as illustrated in Supplementary Material. This result may be due to the fact that different biomass consists of different natural binders that can form strong solid bridges between particles in the pelletization process (Mostafa et al. 2019 ). The increase in the amount of PKS in the blending ratio, particularly for the 50PKS/50EFB and 75PKS/25EFB samples, contributes to the increase in fracture load and compression strength compared to pure 100EFB and 100PKS pellets, respectively. This result may be explained by the fact that the intertwined fiber structures of EFB increased the contact area between particles and formed solid bridges. This finding is in accordance with the co-pelletization of oil cake and sawdust where cedarwood, consisting of more intertwined fiber, formed stronger solid bridges with castor bean cake compared to camphorwood (Huang et al. 2016 ). Therefore, co-pelletization significantly improves fracture load and compression strength compared to pure biomass pellets, making handling, transport, and storage processes more economically friendly. Torrefaction temperature and blending ratio of biomass samples show a significant interaction effect on the fracture load and compression strength of pellets (p < 0.05), as depicted in Supplementary Material. Lignocellulosic components of EFB and PKS may exhibit different decomposition rates at different torrefaction temperatures. The decomposition of the lignocellulosic components will affect the binding mechanisms of EFB and PKS because lignocellulosic components act as natural binding agents during the pelletization process (Mostafa et al. 2019 ). There is no standard limit for the fracture load and tensile strength of a commercialized pellet. However, the ideal fracture load for the pellet based on previous studies was 216 N (Mostafa et al. 2019 ). All of the pellets formed in this work satisfy the ideal fracture load, with the pellet formed based on the blending ratio of 75PKS/25EFB torrefied at 240°C showing the highest fracture load and compression strength. 3.5 Ash content Ash is a non-combustible product of the combustion process, which may shorten the lifetime of the boiler due to the occurrence of slagging and fouling (Kambo and Dutta 2014 ). Figure 2 illustrates the ash content of pellets formed from different blending ratios of EFB and PKS for raw and different torrefaction temperatures. It is apparent that raw pellets showed lower ash content compared to torrefied pellets. Moreover, ash contents show a positive correlation with the torrefaction temperature and are significantly affected by the torrefaction temperature (p < 0.05), as shown in Supplementary Material. This is due to the build-up of metallic elements such as magnesium, silicon, potassium, calcium, and iron in the torrefaction process (Xue et al. 2014 ). Besides that, an increase in ash content is mainly affected by the torrefaction process compared to the pelletization process. This is due to the fact that the release of volatile matter becomes more substantial at higher torrefaction temperatures, leading to an increase in the ash content of biomass pellets, even though the processes are in the opposite direction (pelletization before torrefaction) (Faizal et al. 2018 ; Siyal et al. 2020 ). Figure 2 On the other hand, the blending ratio of pellets also affects the ash content of the pellets formed (p < 0.05), as indicated in Supplementary Material. Pellets with a blend of PKS and EFB showed higher ash contents compared to the pure PKS pellets. This is due to the fact that PKS contains lower ash content (3.85 wt.%) compared to EFB (5.58%), indicating that higher ash content is harder to burn and evaporate. Both torrefaction temperature and blending ratios of pellets show a significant effect on the ash contents of the pellets formed (p < 0.05). This may be due to the increase in ash formation with the rise in torrefaction temperature and the difference in ash contents in different biomass waste. Overall, all the ash content pellets formed were less than 5%, meeting the requirement stated in standard EN ISO 17255-6 (≤ 6%) (Moreira et al. 2020 ; Picchio et al. 2020 ). Hence, the pellets generated are environmentally friendly and have a high potential to replace fossil fuel. 4. Conclusions The blending of torrefied EFB and PKS has significantly improved the commercial value of raw EFB and PKS. Both torrefaction temperature and the blending ratio of the sample show a significant influence on the combustion and physical characteristics of pellet samples. The production of pellets from torrefied EFB and PKS with enhanced chemical and physical properties becomes an attractive option as solid renewable biofuel. Additionally, torrefied co-pellets produced from blended EFB and PKS showed higher compression strength, lesser density changes, and higher dimensional stability, contributing to more cost-effective handling, transportation, and storage processes. The ash content of pellet samples produced meets the currently available standard, EN ISO-17255-6, for non-woody pellets for commercial purposes. Overall, 75PKS/25EFB pellets produced from EFB and PKS torrefied at 240°C possess comparatively higher quality compared to other pellets. Competitive characteristics of pellets produced from EFB and PKS, including high heating value, high dimensional stability, low ash content, and high compression strength, have been achieved and justified in this study. Hence, the combination of torrefaction and co-pelletization is a promising and effective approach to produce solid biofuel. The use of EFB and PKS as alternative sources of energy is necessary to eradicate environmental pollution and the depletion of fossil fuels. Transforming EFB and PKS into biofuel pellets will also contribute to economic growth, especially in Malaysia, due to the growing demand for biopellets globally. Declarations Acknowledgements The authors would like to thank the Ministry of Higher Education Malaysia for supporting this work and Universiti Malaysia Pahang Al-Sultan Abdullah (UMPSA) for providing laboratory facilities and scholarship under Master Research Scheme. Funding This work is financially supported through Fundamental Research Grant Scheme (FRGS) No. FRGS/1/2019/TK02/UMP/02/10 (University reference RDU1901137) under Ministry of Higher Education Malaysia and Universiti Malaysia Pahang Al-Sultan Abdullah (UMPSA). Competing Interests The authors have no relevant financial or non-financial interests to disclose. Author Contributions All authors contributed to the study conception and experimental planning. Biomass materials preparation, experimental works, data collection and analysis were performed by Chang Siaw Sang, Noor Asma Fazli Abdul Samad and Suriyati Saleh. The first draft of the manuscript was written by Chang Siaw Sang and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Ethical Approval This study does not require ethical approval because no human participants and biological materials are involved. Consent to Participate This study does not require any consent to participate. Consent to Publish This study does not require any consent to publish. 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Appl Energy 191: 414–424. https://doi.org/10.1016/j.apenergy.2017.01.035 Sambeth SK, Chang SS, Samad NAFA, Saleh S (2022) Pelletization of torrefied palm kernel shell by using different binding agents. Mater Today: Proc 57: 1116-1122. https://doi.org/10.1016/j.matpr.2021.09.490 Siyal AA, Mao X, Liu Y, Ran C, Fu J, Kang Q, Ao W, Zhang R, Dai J, Liu G (2020) Torrefaction subsequent to pelletization: Characterization and analysis of furfural residue and sawdust pellets. Waste Manag 113: 210–224. https://doi.org/10.1016/j.wasman.2020.05.037 Stelte W, Nielsen NPK, Hansen HO, Dahl J, Shang L, Sanadi AR (2013) Pelletizing properties of torrefied wheat straw. Biomass Bioenerg 49: 214–221. https://doi.org/10.1016/j.biombioe.2012.12.025 Sukiran MA, Abnisa F, Daud WMAW, Bakar NA, Loh SK (2017) A review of torrefaction of oil palm solid wastes for biofuel production. Energy Convers Manag 149: 101–120. https://doi.org/10.1016/j.enconman.2017.07.011 Wahid FRAA, Harun NHHM, Rashid SRM, Samad NAFA, Saleh S (2017) Physicochemical property changes and volatile analysis for torrefaction of oil palm frond. Chem Eng Trans 56: 199–204. DOI: 10.3303/CET1756034 Wattana W, Phetklung S, Jakaew W, Chumuthai S, Sriam P, Chanurai N (2017) Characterization of mixed biomass pellet made from oil palm and para-rubber tree residues. Energy Procedia 138: 1128–1133. https://doi.org/10.1016/j.egypro.2017.10.218 Xue G, Kwapinska M, Kwapinski W, Czajka KM, Kennedy J, Leahy JJ (2014) Impact of torrefaction on properties of miscanthus x giganteus relevant to gasification. Fuel 121: 189–197. https://doi.org/10.1016/j.fuel.2013.12.022 Supplementary Files SupplementaryMaterial.docx Cite Share Download PDF Status: Published Journal Publication published 14 Jan, 2025 Read the published version in Environmental Science and Pollution Research → Version 1 posted Editorial decision: Major Revision 26 Aug, 2024 Reviewers agreed at journal 19 Jun, 2024 Reviewers invited by journal 19 Jun, 2024 Editor invited by journal 21 Feb, 2024 Editor assigned by journal 04 Feb, 2024 First submitted to journal 26 Jan, 2024 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-3864756","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":316416297,"identity":"0a03aa3d-bbcd-4b2a-b84b-d5313a0d111f","order_by":0,"name":"Chang Siaw Sang","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Chang","middleName":"Siaw","lastName":"Sang","suffix":""},{"id":316416298,"identity":"fdbebf2b-4e4b-47f0-a5d1-15b5515b8930","order_by":1,"name":"Noor Asma Fazli Abdul Samad","email":"","orcid":"","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":false,"prefix":"","firstName":"Noor","middleName":"Asma Fazli Abdul","lastName":"Samad","suffix":""},{"id":316416299,"identity":"7333584e-55e8-4ead-b7d6-870a50fddb8d","order_by":2,"name":"Suriyati Binti Saleh","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA60lEQVRIiWNgGAWjYJCCA0DMw4/CJUKLAY9kAylagMCAwQCukpAW+Rm5Dw/z1PyRMb6RnfbwRw2DHN+NBNbNPPiMv5FucJjnmAGP2Y3c7cY8xxiMJW8ksN3Gq0UijeEwDxtYyzZpBjaGxA2EtMjPAGn5Z8BjPCN3m+SPfwz1BLUw3ABq4W0z4DGQyN0mwdvGkGBA0GFnnjEcnNtnzCNx5u12Y94+CcOZZx623ZyDz2Htacwf3nyTs+dvz9328Mc3G3m+48nHbrzB5zAgYII6gw2IJYCYsYEJr19ASn4gtKCKjIJRMApGwSgAAQCCnk6GuWuoPgAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-2571-4099","institution":"Universiti Malaysia Pahang Al-Sultan Abdullah","correspondingAuthor":true,"prefix":"","firstName":"Suriyati","middleName":"Binti","lastName":"Saleh","suffix":""}],"badges":[],"createdAt":"2024-01-14 23:22:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3864756/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3864756/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11356-025-35901-x","type":"published","date":"2025-01-14T15:57:53+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":59824457,"identity":"c6c175ac-40b3-492c-a428-695c47d1fdd5","added_by":"auto","created_at":"2024-07-08 05:20:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":126175,"visible":true,"origin":"","legend":"\u003cp\u003eHigher heating value of co-pellet samples.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3864756/v1/9bc6e4ae48187d0a77032559.png"},{"id":59824836,"identity":"e4813cdb-7e06-4a8b-8430-6745580fe850","added_by":"auto","created_at":"2024-07-08 05:28:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":103528,"visible":true,"origin":"","legend":"\u003cp\u003eAsh content of pellet samples.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3864756/v1/3fa893b506eaa5fa786ed549.png"},{"id":74284672,"identity":"4782e7a6-8c6e-4c7a-bd94-0923e768873e","added_by":"auto","created_at":"2025-01-20 16:10:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1090563,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3864756/v1/1478210e-da37-477b-891d-e0a0eda0e238.pdf"},{"id":59824459,"identity":"f29679a8-0905-48d2-ad9a-cd9aad646b38","added_by":"auto","created_at":"2024-07-08 05:20:17","extension":"docx","order_by":7,"title":"","display":"","copyAsset":false,"role":"supplement","size":16699,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryMaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-3864756/v1/8c97c2e3408764fe67b62b3d.docx"}],"financialInterests":"","formattedTitle":"Enhancing Biofuel Pellet Quality using Combined Torrefaction and Co-pelletization Processes of Palm Kernel Shell and Empty Fruit Bunch","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eBiomass waste has been widely used for producing biofuel as an alternative source to replace depleted fossil fuels, especially in European Union countries. However, it is rarely used in developing countries like Thailand, Indonesia, and Malaysia (Malek et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In fact, Malaysia has abundant amounts of biomass waste, especially from the palm oil industry. Palm kernel shell (PKS) and empty fruit bunch (EFB) are examples of biomass waste generated from palm oil mills. Current practices show that EFB is commonly utilized as fertilizer since it is abundant in minerals such as phosphorus, magnesium, potassium, nitrogen, and carbon. These minerals are beneficial for soil pH increments, soil erosion reduction, and soil moisture conservation (Sukiran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Hence, EFB is transformed into chemical fertilizers through the incineration process. However, this method is not environmentally friendly because it produces high amounts of white smoke and fly ash throughout the process, resulting in air pollution (Loh \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Meanwhile, PKS has been commonly utilized as solid fuel for a steam boiler in the milling plant since PKS has a comparatively higher heating value compared to other lignocellulosic biomass. However, current practice has limited the potential of biomass usage and the commercial value of EFB and PKS, and most practices contribute to the degradation of environmental conditions. The limited application of both EFB and PKS is due to their inferior characteristics such as low bulk density, hygroscopic nature, and low energy density, which ultimately contributes to inconveniences during handling, transportation, and storage processes, as well as reduced combustion efficiency as a solid fuel (Kumar et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In fact, both EFB and PKS have high potential to be utilized as an energy commodity by upgrading their characteristics through suitable pre-treatment methods.\u003c/p\u003e \u003cp\u003eTorrefaction and pelletization are widely used pre-treatment methods for improving the fuel quality of biomass, which eventually enhances their commercialized value as solid biofuel. The main reasons for using pre-treatment methods are to enhance the heating value, inhibit rotting behavior, as well as improve the bulk and energy density of biomass waste (Sukiran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Pradhan et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Mostafa et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Theoretically, the torrefaction process is a thermochemical pre-treatment method that occurs in a mild temperature range (200\u0026deg;C to 300\u0026deg;C) under atmospheric conditions without oxygen supply (Mostafa et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Siyal et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The torrefaction process transforms biomass waste with a hygroscopic nature into hydrophobic by destroying hydroxyl groups in biomass (Manouchehrinejad et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Furthermore, the torrefaction process improves the heating value of biomass waste, reducing moisture content while increasing the fixed carbon content of biomass waste (Kanwal et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, the main challenge in employing torrefied biomass as solid biofuel is related to the delicate and brittle properties of torrefied biomass, which are unfavorable for handling, transportation, and storage processes (Larsson et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Hence, biomass needs to be transformed into a uniform particle size with enhanced mechanical strength to reduce losses due to fracture and breakage during handling, transportation, and storage processes. This limitation can be overcome by using pelletization, where this physical pre-treatment method can compact biomass waste into uniform-sized particles with increased bulk density (Sukiran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Picchio et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sambeth et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In addition, pelletization is an effective method that enables easier and more efficient handling, transportation, and storage processes. However, the limitation of pelletization is that this method does not improve the combustion properties of raw biomass waste. As a solution, torrefaction and pelletization processes must be combined to enhance both the combustion and physical characteristics of biomass waste.\u003c/p\u003e \u003cp\u003eThe combination of torrefaction and pelletization approaches is able to produce biomass pellets with better high heating value, hydrophobicity, a compact structure, and uniform size (Bach and Skreiberg \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, suitable operating conditions for torrefaction and pelletization must be considered to produce the desired quality of biomass pellets. For example, residence time and torrefaction temperature are two significant operating conditions in the torrefaction process. Torrefaction temperature is a more significant operating condition compared to residence time because residence time shows a less substantial effect on enhancing the characteristics of biomass waste. Additionally, torrefaction temperature is the most significant variable that affects the higher heating value (HHV) of the pellet formed and the binding mechanisms of biomass waste during the pelletization process. This is due to the fact that a higher torrefaction temperature results in more severe degradation of lignocellulosic components, which naturally act as a natural binder. Usually, lignocellulosic components form solid bridges between biomass particles and improve their cohesive strength. Several research works have been conducted to investigate the impacts of torrefaction temperature on the binding mechanisms of biomass waste during the pelletization process, and the effect varies depending on the properties of the biomass employed. For example, biomass processed at high torrefaction temperatures produces more fragile and brittle pellets, and more energy is consumed during the co-pelletization process (Bach and Skreiberg \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Rudolfsson et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Although a high HHV of torrefied biomass can be obtained at higher torrefaction temperatures, a low compression strength of the pellet is expected, suggesting that biomass undergoing severe torrefactions (275\u0026deg;C to 300\u0026deg;C) tends to have low quality in terms of mechanical properties (Stelte et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThus, torrefaction and pelletization present an ideal approach to transform EFB and PKS wastes into pellet products for energy-related applications. Based on the availability of oil palm solid wastes in Malaysia, around 18.88\u0026nbsp;million tonnes per year of EFB has been generated compared to only 4.72\u0026nbsp;million tonnes per year of PKS waste (Sukiran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This indicates that EFB has abundant resources compared to PKS. However, EFB has a calorific value of 18.88 MJ/kg, which is lower than the calorific value of PKS, which is around 20.09 MJ/kg (Loh \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In addition, PKS contains a high lignin content, around 50.7 wt%, which is preferable to produce stronger and more compact pellets (Siyal et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). High lignin content can strengthen solid bridges between particles, preventing pellet fracture and breakage during handling, transport, and storage processes. This theoretically shows that PKS will produce better pellets in terms of energy content compared to EFB. The main drawback is that EFB is the main priority for sustainable energy production in Malaysia due to a significant amount of waste. Therefore, blending EFB with PKS through co-pelletization provides another approach to produce high-quality pellets. Previous studies show that a better quality pellet can be obtained using a combination of different biomass materials. For example, oil palm trunk bark was blended with corncob at different mixing ratios, and the blended pellet exhibited better quality in terms of heating values, ash content, and compression strength (Kpalo et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Torrefied canola meal and canola hull were blended using a mixer at five different ratios (100:0, 80:20, 60:40, 40:60, 100:0), and the blended pellet with more than 40 wt% of torrefied canola hull possessed better heating value and mechanical strength than the pure torrefied pellet (Faizal et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCurrently, research found in literature involving EFB and PKS is focusing only on the torrefaction process, and in some cases, working on pelleting raw EFB and PKS. Based on our knowledge, no work has been conducted on the influence of torrefaction and the blending ratio of raw and torrefied EFB and PKS on the co-pelletization process. Hence, the aim of this study is to investigate the effect of torrefaction temperature (210\u0026deg;C, 240\u0026deg;C, 270\u0026deg;C) and the blending ratio of PKS to EFB (0:100, 25:75, 50:50, 75:25, 100:0) on the physical and combustion characteristics of biomass pellets. The combustion properties such as HHV, moisture and ash content, as well as physical properties such as compression strength, pellet density, density changes, and dimensional stability, were measured to evaluate the quality of co-pellets. Moreover, univariate analysis of variance (UANOVA) was conducted to investigate the impact of the studied parameters (torrefaction temperature and blending ratio) themselves, as well as the interaction effects of the studied parameters on the combustion and physical characteristics of co-pellets produced.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Biomass collection, preparation and torrefaction\u003c/h2\u003e \u003cp\u003eRaw EFB and PKS samples were collected from Lepar Hilir Palm Oil Mill, Kuantan, Pahang, Malaysia. The collected biomass samples were air-dried for a few days before being oven-dried for 4 hours. The dried biomass samples were ground and sieved, where biomass with particle sizes in the range between 0.5 mm and 1 mm was used to facilitate feedstock loading and heat transfer rate (Sukiran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). In terms of the torrefaction experiment, approximately 10 g of biomass samples were loaded into a vertical tubular reactor with dimensions of 39.7 cm in length and an internal diameter of 1.9 cm, respectively. Afterwards, a flow of 10 ml/min of nitrogen was used to flush the reactor for 5 minutes. The biomass samples were torrefied at temperatures of 210\u0026deg;C, 240\u0026deg;C, and 270\u0026deg;C for a 30-minute residence time. A residence time of 30 mins was chosen as no significant improvement has been observed in biomass undergoing torrefaction for more than 30 mins (Wahid et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Wattana et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Finally, the torrefied samples were stored in a desiccator.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Biomass characterization\u003c/h2\u003e \u003cp\u003eThe proximate analysis of raw EFB and PKS was determined based on standard procedures of ASTM E872-82 for volatile matter, ASTM 1755-01 for ash content, and a moisture analyzer (Model MS-70, A\u0026amp;D Company Ltd., Tokyo, Japan) for moisture content. The higher heating value (HHV) of raw EFB and PKS was measured using a bomb calorimeter (C200, IKA\u0026reg; Works (Asia) Sdn Bhd). Chemical analyses were conducted following NREL procedures (Azargohar et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Pelletization process\u003c/h2\u003e \u003cp\u003eThe pelletization process was conducted at a fixed temperature (130\u0026deg;C) and pressure (12 MPa) for 20 minutes using a hot press machine. Firstly, raw and torrefied EFB and PKS samples were blended based on the ratios shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The blended samples were then mixed with carboxymethyl cellulose (CMC) as a binder (10% by weight of the sample) to further strengthen the solid bridges of the pellets. For example, the 50PKS/50EFB sample refers to equal amounts of PKS and EFB blended together with an additional approximately 10 wt% of CMC. Then, the blended samples were filled into pellet molds and transferred into the hot press machine for compressing the pellets. All pellet samples were produced in a cylindrical shape with specifications of 1.5 cm for diameter and a height of 2.0 cm.\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\u003eBlending ratio of raw and torrefied pellet samples.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample Name\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRatio of PKS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRatio of EFB\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\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\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Pellet characterization\u003c/h2\u003e \u003cp\u003eHHV of each pellet sample was determined using a bomb calorimeter (C200, IKA\u0026reg; Works (Asia) Sdn Bhd). Each HHV measurement was replicated three times, and the average value of HHV was presented. The density of the pellet was determined by dividing its mass by its volume. Two different pellet densities were measured, where the initial density of the pellet was measured directly after the pelletization process, and the final density of the pellet was taken after 14 days of storage in an open-air area (Emadi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Density changes and dimensional stability were determined after 14 days of storage. Dimensional stability was divided into two: longitudinal dimension (changes in pellet length) and radial dimensions (changes in diameter). The dimensional stability of the pellet was calculated by subtracting longitudinal and radial dimensions from 100%.\u003c/p\u003e \u003cp\u003eThe compression strength of the pellet was measured using a universal testing machine (AGs-X series, Shidmadzu Corporation). The pelletized sample was placed on a stainless-steel base platen vertically. Then, a 5 kN load cell was applied to the samples at a 2 mm/min crosshead speed until the pellet began to crush. The maximum load the samples were able to withstand is known as the fracture load. The compression strength of the pellets is calculated based on Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$Compression Strength \\left(MPa\\right)= \\frac{2 \\times Fracture Load \\left(N\\right)}{\\pi {\\times Pellet Diameter \\left(mm\\right)}^{2}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eAsh content is another important property for determining the quality of pellets. The ash content of the pellets was determined based on ASTM 1755-01. Each measurement was performed three times, and the average values are presented in this work.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eAll data obtained during torrefaction and co-pelletization studies were analyzed to investigate the influence of torrefaction temperature and blending ratio on the pellet characteristics (HHV, initial density, final density, compression strength, moisture, and ash content) based on the principles of UANOVA. The Tukey test was used to study the statistically significant differences between the mean values of different pellet properties (Moreira et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Proximate and chemical analysis of raw PKS and EFB\u003c/h2\u003e \u003cp\u003eProximate analysis can be used to evaluate the combustion properties of biomass waste. Fixed carbon content is the combustible residue that can improve the combustion performance of burning materials, whereas ash content is the non-combustible content that can lead to equipment corrosion and cause air pollution due to its non-combustible characteristics (Sukiran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). PKS has a higher fixed carbon content but lower ash content compared to EFB, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. This indicates that PKS is a better solid biofuel than EFB, as it exhibits better combustion performance and generates lower ash during the combustion process. Additionally, PKS has a higher energy content than EFB, as indicated by its higher HHV. The lignocellulosic components (hemicellulose, cellulose, and lignin) have a significant impact on forming pellets with high quality, as they serve as a natural binder between biomass particles. PKS showed a higher lignin content than EFB, which can form solid bridges between particles, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. High lignin content is significant for producing more durable pellets since it acts as a natural binder when heat is applied during the pelletization process (Siyal et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\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\u003eProximate and chemical analysis of EFB and PKS.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnalysis\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePKS\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEFB\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProximate analysis (dry basis wt%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAsh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVolatile matter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e71.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e74.37\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMoisture\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e6.20\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFixed carbon\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e22.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e16.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemical analysis (wt%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHemicellulose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e21.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e36.80\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCellulose\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e30.16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLignin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e50.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e21.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAsh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eExtractives\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHHV (MJ/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e19.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.48\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=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Higher heating value (HHV)\u003c/h2\u003e \u003cp\u003eHHV is a vital characteristic in evaluating the combustion performance of biofuel co-pellets as it shows the maximum energy content of the biofuel. The HHV of biofuel co-pellets observed in this study is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Both torrefaction temperature and the blending ratio of EFB and PKS show a significant effect (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) on the HHV of biofuel pellets, as shown in Supplementary Material. The findings reveal that the rise in torrefaction temperature substantially improved the HHV of the biofuel pellets. This result may be explained by the fact that carbonization of both EFB and PKS during the torrefaction process increases the fixed carbon content of EFB and PKS (Siyal et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Additionally, the rise in torrefaction temperature significantly enhanced the HHV of the pellets due to the removal of a hydroxyl group from hemicellulose during torrefaction, leading to an enhancement in the energy content of the torrefied sample (Bach and Skreiberg \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Torrefied pellets formed at a torrefaction temperature of 270\u0026deg;C showed the highest enhancement in HHV, particularly 100PKS, where around a 1.12 HHV enhancement has been observed.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e1\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Dimensional stability\u003c/h2\u003e \u003cp\u003ePellet density is a significant factor that affects the combustion properties and handling cost of biofuel co-pellets. Normally, denser pellets require a longer burning time but need less storage space and exhibit higher efficiency in transportation (Campbell et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the density, density changes, and dimensional stability of pellet samples. Initial density indicates the density of pellets measured immediately after the pelletization process, and the final density was taken after two weeks of storage at room conditions. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the final density for all pellets decreased from the initial density, which is due to the relaxation of grinds in the pellet after pressure release (Emadi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Raw pellets showed lower initial and final density compared to the torrefied pellets, indicating that torrefaction improves the density of biomass pellets. The rise in torrefaction temperature improves the initial and final pellet density, indicating a significant effect of torrefaction temperature on the initial and final density of the pellets (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). In addition, the density change for pellets was reduced when the torrefaction temperature was increased up to 240\u0026deg;C, but the density change increased for pellets formed from torrefied samples at 270\u0026deg;C. This indicates that this temperature is considered a severe torrefaction condition, which produces more fine suspended particles contributing to the further reduction of final pellet density. As a consequence, pellets formed from torrefied samples at 240\u0026deg;C are stable and can be safely handled, transported, and stored. In terms of dimensional stability, all pellets obtained close to 100% longitudinal and radial changes, indicating they experience minimal changes in mass, diameter, and length in a 14-day storage time. This shows that less air pollution is expected due to the low generation of fine particles from the pellets (Emadi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\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\u003eDensity, density changes and dimensional stability of pellet samples.\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTorrefaction Temperature (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eDensity (kg/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eDensity change (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eDimensional stability (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eInitial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFinal\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLongitudinal\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRadial\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e536.82\u0026thinsp;\u0026plusmn;\u0026thinsp;5.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e511.34\u0026thinsp;\u0026plusmn;\u0026thinsp;2.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e648.31\u0026thinsp;\u0026plusmn;\u0026thinsp;5.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e628.36\u0026thinsp;\u0026plusmn;\u0026thinsp;2.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRaw\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e750.16\u0026thinsp;\u0026plusmn;\u0026thinsp;2.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e728.35\u0026thinsp;\u0026plusmn;\u0026thinsp;2.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e981.23\u0026thinsp;\u0026plusmn;\u0026thinsp;7.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e968.56\u0026thinsp;\u0026plusmn;\u0026thinsp;4.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.78\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e970.75\u0026thinsp;\u0026plusmn;\u0026thinsp;2.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e950.47\u0026thinsp;\u0026plusmn;\u0026thinsp;3.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e555.67\u0026thinsp;\u0026plusmn;\u0026thinsp;3.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e535.81\u0026thinsp;\u0026plusmn;\u0026thinsp;5.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e3.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e673.25\u0026thinsp;\u0026plusmn;\u0026thinsp;3.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e658.78\u0026thinsp;\u0026plusmn;\u0026thinsp;5.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.58\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e210\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e790.31\u0026thinsp;\u0026plusmn;\u0026thinsp;2.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e774.68\u0026thinsp;\u0026plusmn;\u0026thinsp;2.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1015.46\u0026thinsp;\u0026plusmn;\u0026thinsp;3.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e999.16\u0026thinsp;\u0026plusmn;\u0026thinsp;4.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e988.26\u0026thinsp;\u0026plusmn;\u0026thinsp;5.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e964.61\u0026thinsp;\u0026plusmn;\u0026thinsp;3.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e604.34\u0026thinsp;\u0026plusmn;\u0026thinsp;5.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e588.45\u0026thinsp;\u0026plusmn;\u0026thinsp;2.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e731.21\u0026thinsp;\u0026plusmn;\u0026thinsp;3.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e717.82\u0026thinsp;\u0026plusmn;\u0026thinsp;3.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.75\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e835.45\u0026thinsp;\u0026plusmn;\u0026thinsp;3.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e825.36\u0026thinsp;\u0026plusmn;\u0026thinsp;2.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.78\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1105.72\u0026thinsp;\u0026plusmn;\u0026thinsp;3.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1098.42\u0026thinsp;\u0026plusmn;\u0026thinsp;3.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1050.72\u0026thinsp;\u0026plusmn;\u0026thinsp;4.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1030.32\u0026thinsp;\u0026plusmn;\u0026thinsp;3.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.82\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e596.36\u0026thinsp;\u0026plusmn;\u0026thinsp;5.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e580.45\u0026thinsp;\u0026plusmn;\u0026thinsp;4.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e2.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e711.38\u0026thinsp;\u0026plusmn;\u0026thinsp;5.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e697.92\u0026thinsp;\u0026plusmn;\u0026thinsp;2.42\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e270\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e798.72. \u0026plusmn;1.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e787.55\u0026thinsp;\u0026plusmn;\u0026thinsp;1.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1031.43\u0026thinsp;\u0026plusmn;\u0026thinsp;4.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1017.74\u0026thinsp;\u0026plusmn;\u0026thinsp;3.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1023.28\u0026thinsp;\u0026plusmn;\u0026thinsp;4.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1004.16\u0026thinsp;\u0026plusmn;\u0026thinsp;2.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e99.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e99.78\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\u003eThe blending ratio of the pellet also showed a significant effect on pellet density (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as shown in Supplementary Material. The 75PKS/25EFB pellet produced from a torrefaction temperature of 240\u0026deg;C showed the highest final and initial density compared to other pellets. It obtained the lowest density changes and the highest dimensional stability. This is due to the fact that the intertwined fibers of EFB strengthened the interlocking bonding of the pellets formed, resulting in lower density change and better dimensional stability, whereas PKS filled in the void space between the EFB fibers, forming pellets with higher density (Sambeth et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Torrefaction temperature and blending ratio showed an interaction effect on the initial and final density of pellets (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) because torrefaction temperature and blending ratio affect the compactness of the pellet formed. Overall, only the 75PKS/25EFB and 100PKS torrefied at temperatures of 240 and 270\u0026deg;C achieved pellet density within the acceptable standard range of 1000\u0026ndash;1400 kg/m\u003csup\u003e3\u003c/sup\u003e, where the torrefied pellet at 240\u0026deg;C with a blending ratio of 75PKS/25EFB shows the highest density and dimensional stability, contributing to the low fine generation and less air pollution expected during handling, transportation, and storage processes.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Compression strength\u003c/h2\u003e \u003cp\u003eCompression strength is a vital property of biofuel pellets, revealing the hardness of the pellets for handling, packing, and transportation. Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the fracture load and compression strength of the pellets produced from EFB and PKS. It is evident that the blending ratio of 75PKS/25EFB torrefied at 240\u0026deg;C shows the highest fracture load (1025.23\u0026thinsp;\u0026plusmn;\u0026thinsp;15.5 N) and compression strength (3.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25 MPa), whereas 100EFB without torrefaction pretreatment shows the lowest fracture load (280.18\u0026thinsp;\u0026plusmn;\u0026thinsp;10.25 N) and compression strength (0.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 MPa). Torrefaction temperature showed significant effects on the fracture load and compression strength of the pellet (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as shown in Supplementary Material. This can be observed in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, where torrefied pellet samples exhibit better fracture load and compression strength compared to raw pellets. The enhancement in fracture load and compression strength of the torrefied pellets was achieved because the torrefaction process causes a change in plastic and viscoelastic behavior, resulting in harder biomass (Emadi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, severe torrefaction conditions result in a reduction of fracture load and compression strength of the pellet, as observed for torrefied pellets at a temperature of 270\u0026deg;C. This is due to the degradation of lignocellulosic components (lignin, hemicellulose, and cellulose), which are responsible for forming solid bridges between particles during the pelletization process. The decrement in fracture load and compression strength is also related to the glass transition point of lignin, contributing to a strong binding force between particles (Emadi et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Due to the severity of torrefaction, plasticization between particles may occur since it is already beyond the glass transition point of lignin, lowering the modulus of elasticity of biomass particles and forming empty spaces between them (Mostafa et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Hence, fracture load and compression strength are reduced when biomass undergoes torrefaction at high temperatures.\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\u003eFracture load and compression strength of pellet samples.\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=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTorrefaction Temperature (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSamples\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFracture load (N)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCompression strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e280.18\u0026thinsp;\u0026plusmn;\u0026thinsp;10.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e404.15\u0026thinsp;\u0026plusmn;\u0026thinsp;2.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRaw\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e657.81\u0026thinsp;\u0026plusmn;\u0026thinsp;8.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e726.52\u0026thinsp;\u0026plusmn;\u0026thinsp;11.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e441.44\u0026thinsp;\u0026plusmn;\u0026thinsp;11.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e465.35\u0026thinsp;\u0026plusmn;\u0026thinsp;9.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e596.47\u0026thinsp;\u0026plusmn;\u0026thinsp;5.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e210\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e822.18\u0026thinsp;\u0026plusmn;\u0026thinsp;10.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e914.26\u0026thinsp;\u0026plusmn;\u0026thinsp;11.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e664.19\u0026thinsp;\u0026plusmn;\u0026thinsp;10.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e580.27\u0026thinsp;\u0026plusmn;\u0026thinsp;10.85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e708.23\u0026thinsp;\u0026plusmn;\u0026thinsp;4.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e955.68\u0026thinsp;\u0026plusmn;\u0026thinsp;13.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e1025.23\u0026thinsp;\u0026plusmn;\u0026thinsp;15.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e772.85\u0026thinsp;\u0026plusmn;\u0026thinsp;10.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e555.64\u0026thinsp;\u0026plusmn;\u0026thinsp;7.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25PKS/75EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e686.82\u0026thinsp;\u0026plusmn;\u0026thinsp;6.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e1.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e270\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50PKS/50EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e910.46\u0026thinsp;\u0026plusmn;\u0026thinsp;12.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e75PKS/25EFB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e977.55\u0026thinsp;\u0026plusmn;\u0026thinsp;6.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e3.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100PKS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e783.48\u0026thinsp;\u0026plusmn;\u0026thinsp;3.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e2.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\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=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u003c/p\u003e \u003cp\u003eFurthermore, the blending ratio of EFB and PKS also shows a significant effect on the fracture load and compression strength of the pellet (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as illustrated in Supplementary Material. This result may be due to the fact that different biomass consists of different natural binders that can form strong solid bridges between particles in the pelletization process (Mostafa et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The increase in the amount of PKS in the blending ratio, particularly for the 50PKS/50EFB and 75PKS/25EFB samples, contributes to the increase in fracture load and compression strength compared to pure 100EFB and 100PKS pellets, respectively. This result may be explained by the fact that the intertwined fiber structures of EFB increased the contact area between particles and formed solid bridges. This finding is in accordance with the co-pelletization of oil cake and sawdust where cedarwood, consisting of more intertwined fiber, formed stronger solid bridges with castor bean cake compared to camphorwood (Huang et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Therefore, co-pelletization significantly improves fracture load and compression strength compared to pure biomass pellets, making handling, transport, and storage processes more economically friendly.\u003c/p\u003e \u003cp\u003eTorrefaction temperature and blending ratio of biomass samples show a significant interaction effect on the fracture load and compression strength of pellets (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as depicted in Supplementary Material. Lignocellulosic components of EFB and PKS may exhibit different decomposition rates at different torrefaction temperatures. The decomposition of the lignocellulosic components will affect the binding mechanisms of EFB and PKS because lignocellulosic components act as natural binding agents during the pelletization process (Mostafa et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). There is no standard limit for the fracture load and tensile strength of a commercialized pellet. However, the ideal fracture load for the pellet based on previous studies was 216 N (Mostafa et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). All of the pellets formed in this work satisfy the ideal fracture load, with the pellet formed based on the blending ratio of 75PKS/25EFB torrefied at 240\u0026deg;C showing the highest fracture load and compression strength.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Ash content\u003c/h2\u003e \u003cp\u003eAsh is a non-combustible product of the combustion process, which may shorten the lifetime of the boiler due to the occurrence of slagging and fouling (Kambo and Dutta \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the ash content of pellets formed from different blending ratios of EFB and PKS for raw and different torrefaction temperatures. It is apparent that raw pellets showed lower ash content compared to torrefied pellets. Moreover, ash contents show a positive correlation with the torrefaction temperature and are significantly affected by the torrefaction temperature (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as shown in Supplementary Material. This is due to the build-up of metallic elements such as magnesium, silicon, potassium, calcium, and iron in the torrefaction process (Xue et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Besides that, an increase in ash content is mainly affected by the torrefaction process compared to the pelletization process. This is due to the fact that the release of volatile matter becomes more substantial at higher torrefaction temperatures, leading to an increase in the ash content of biomass pellets, even though the processes are in the opposite direction (pelletization before torrefaction) (Faizal et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Siyal et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003cp\u003eOn the other hand, the blending ratio of pellets also affects the ash content of the pellets formed (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05), as indicated in Supplementary Material. Pellets with a blend of PKS and EFB showed higher ash contents compared to the pure PKS pellets. This is due to the fact that PKS contains lower ash content (3.85 wt.%) compared to EFB (5.58%), indicating that higher ash content is harder to burn and evaporate. Both torrefaction temperature and blending ratios of pellets show a significant effect on the ash contents of the pellets formed (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). This may be due to the increase in ash formation with the rise in torrefaction temperature and the difference in ash contents in different biomass waste. Overall, all the ash content pellets formed were less than 5%, meeting the requirement stated in standard EN ISO 17255-6 (\u0026le;\u0026thinsp;6%) (Moreira et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Picchio et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Hence, the pellets generated are environmentally friendly and have a high potential to replace fossil fuel.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe blending of torrefied EFB and PKS has significantly improved the commercial value of raw EFB and PKS. Both torrefaction temperature and the blending ratio of the sample show a significant influence on the combustion and physical characteristics of pellet samples. The production of pellets from torrefied EFB and PKS with enhanced chemical and physical properties becomes an attractive option as solid renewable biofuel. Additionally, torrefied co-pellets produced from blended EFB and PKS showed higher compression strength, lesser density changes, and higher dimensional stability, contributing to more cost-effective handling, transportation, and storage processes. The ash content of pellet samples produced meets the currently available standard, EN ISO-17255-6, for non-woody pellets for commercial purposes. Overall, 75PKS/25EFB pellets produced from EFB and PKS torrefied at 240\u0026deg;C possess comparatively higher quality compared to other pellets. Competitive characteristics of pellets produced from EFB and PKS, including high heating value, high dimensional stability, low ash content, and high compression strength, have been achieved and justified in this study. Hence, the combination of torrefaction and co-pelletization is a promising and effective approach to produce solid biofuel. The use of EFB and PKS as alternative sources of energy is necessary to eradicate environmental pollution and the depletion of fossil fuels. Transforming EFB and PKS into biofuel pellets will also contribute to economic growth, especially in Malaysia, due to the growing demand for biopellets globally.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to thank the Ministry of Higher Education Malaysia for supporting this work and Universiti Malaysia Pahang Al-Sultan Abdullah (UMPSA) for providing laboratory facilities and scholarship under Master Research Scheme.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work is financially supported through Fundamental Research Grant Scheme (FRGS) No. FRGS/1/2019/TK02/UMP/02/10 (University reference RDU1901137) under Ministry of Higher Education Malaysia and Universiti Malaysia Pahang Al-Sultan Abdullah (UMPSA).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and experimental planning. Biomass materials preparation, experimental works, data collection and analysis were performed by Chang Siaw Sang, Noor Asma Fazli Abdul Samad and Suriyati Saleh. The first draft of the manuscript was written by Chang Siaw Sang and \u003cem\u003eall authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/em\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study does not require ethical approval because no human participants and biological materials are involved.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study does not require any consent to participate.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent to Publish\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study does not require any consent to publish.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAzargohar R, Soleimani M, Nosran S, Bond T, Karunakaran C, Dalai AK, Tabil LG (2019) Thermo-physical characterization of torrefied fuel pellet from co-pelletization of canola hulls and meal. 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DOI: 10.3303/CET1756034\u003c/li\u003e\n\u003cli\u003eWattana W, Phetklung S, Jakaew W, Chumuthai S, Sriam P, Chanurai N (2017) Characterization of mixed biomass pellet made from oil palm and para-rubber tree residues. Energy Procedia 138: 1128\u0026ndash;1133. https://doi.org/10.1016/j.egypro.2017.10.218\u003c/li\u003e\n\u003cli\u003eXue G, Kwapinska M, Kwapinski W, Czajka KM, Kennedy J, Leahy JJ (2014) Impact of torrefaction on properties of miscanthus x giganteus relevant to gasification. Fuel 121: 189\u0026ndash;197. https://doi.org/10.1016/j.fuel.2013.12.022\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":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Torrefaction, Pelletization, Biofuel, Pellet quality, Palm kernel shell, Empty fruit bunch","lastPublishedDoi":"10.21203/rs.3.rs-3864756/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3864756/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003ePalm kernel shell (PKS) and empty fruit bunch (EFB) are potential biomass resources for producing solid biofuel for energy applications. However, raw EFB and PKS are not uniform in size and pose rotting behavior. Torrefaction and co-pelletization are both effective methods to improve their combustion and mechanical characteristics. This study aims to investigate the effect of torrefaction temperature and the blending ratio of PKS and EFB on the mechanical and combustion characteristics of co-pellets. Initially, PKS and EFB underwent torrefaction process for 30 minutes at three different temperatures (210\u0026deg;C, 240\u0026deg;C, and 270\u0026deg;C). Then, both torrefied PKS and EFB were blended at five different ratios (0:100, 25:75, 50:50, 75:25, 100:0) with carboxymethyl cellulose as a binder (10% by weight). The results showed that a higher torrefaction temperature resulted in an increment of the higher heating value (HHV) but weaker mechanical strength. Pellets with a blending ratio of PKS to EFB (75:25) torrefied at 240\u0026deg;C showed the comparatively best pellet quality in terms of HHV (17.94 MJ/kg), high compressive strength (3.5 MPa), low ash content (3.97 wt%), and the lowest density changes (0.66%), which satisfy the requirements set in standard EN ISO 17255-6 for good quality pellets, indicating that a high quality biofuel pellet can be produced using the combined approach of torrefaction and co-pelletization.\u003c/p\u003e","manuscriptTitle":"Enhancing Biofuel Pellet Quality using Combined Torrefaction and Co-pelletization Processes of Palm Kernel Shell and Empty Fruit Bunch","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-08 05:20:12","doi":"10.21203/rs.3.rs-3864756/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2024-08-26T11:11:42+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-06-19T15:14:18+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-06-19T13:01:46+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2024-02-21T18:22:20+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-02-05T04:52:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2024-01-26T13:49:19+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a6067f94-6ad6-4244-813f-88914667ba6a","owner":[],"postedDate":"July 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-01-20T16:03:58+00:00","versionOfRecord":{"articleIdentity":"rs-3864756","link":"https://doi.org/10.1007/s11356-025-35901-x","journal":{"identity":"environmental-science-and-pollution-research","isVorOnly":false,"title":"Environmental Science and Pollution Research"},"publishedOn":"2025-01-14 15:57:53","publishedOnDateReadable":"January 14th, 2025"},"versionCreatedAt":"2024-07-08 05:20:12","video":"","vorDoi":"10.1007/s11356-025-35901-x","vorDoiUrl":"https://doi.org/10.1007/s11356-025-35901-x","workflowStages":[]},"version":"v1","identity":"rs-3864756","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3864756","identity":"rs-3864756","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}