Microchannel based Multistage Solvent Extraction Studies for the Separation of Propionic Acid from its Aqueous Mixture using Hydrocarbon Solvents

Microchannel based Multistage Solvent Extraction Studies for the Separation of Propionic Acid from its Aqueous Mixture using Hydrocarbon Solvents | 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 Microchannel based Multistage Solvent Extraction Studies for the Separation of Propionic Acid from its Aqueous Mixture using Hydrocarbon Solvents Sudhanshu Singh, U K Arun Kumar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3786779/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Solvent extraction is an important industrial operation where several stages are needed for a desired separation. Microchannel based solvent extraction is widely reported for process intensification. However, all these works are confined to a single-stage extraction till date. For industrial application knowledge of multistage extraction is mandatory. This work focuses on the multistage microchannel extraction using a model mixture containing aqueous propionic acid. Four different single solvents were employed in this study hexane, toluene, heptane, and cyclohexanol. The Effect of flow rate, flow ratio on percentage extraction, extraction efficiency, and the required number of stages was investigated. The number of stages required for the maximum recovery of PA from the raffinate is 5 for hexane &heptane and 3 for toluene and 2 for cyclohexanol. The percentage extraction of solvents obtained overall through all the stages is, cyclohexanol, 57–89%, toluene, 35–50%, heptane, 27–51%, and hexane 19-31.3%. Cyclohexanol produced the maximum percentage extraction. The extraction efficiency and the volumetric mass transfer coefficient decreased with the stage numbers. The maximum extraction efficiency for all the solvents is in the range of 98-99.8%. A microchannel stack is found to reduce the total annual cost (TAC). Particularly, fabrication in India results in very less capital cost for the microchannels i.e.1.9–14.3% of TAC. The total annual cost analysis of toluene is the minimum than other solvents. Propionic acid solvent extraction Multistage Extraction liquid-liquid slug flow mass transfer coefficient Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 1.0 Introduction The separation of carboxylic acids from the fermentation broth is an important focus of research. Although these acids are presently produced on a large scale from petroleum-based raw materials, interest in producing them from renewable resources i.e., bio-based production is growing in recent days. Several organic acids like acetic, citric, lactic, succinic and itaconic acids are commercially produced by fermentation methods (López-Garzón, 2014). However, few acids like propionic acid are still in the development stage for their bio-based production commercially using strains like propionibacterium (Barbirato, et al., 1997, Boyaval and Corre, 1995, Suwannakham, 2005). Propionic acid has several uses, especially they are used as an antifungal agent, as a bacteriostatic agent used for conserving cereals. Its salts are used in the production of food and pharmaceutical products, surfactants, etc., (Kośmider et al., 2010, Wasewar, 2012, Reyhanitash et al., 2016, Kumar & Babu, 2006, Pan et al., 2019). Numerous separation techniques are available to separate propionic acid, however, economic isolation and purification method are in demand. Separation methods like solvent extraction, distillation, pervaporation, electrodialysis, reactive extraction and many others are the options for PA separation. The downstream processing (DSP) in these industries contributes to 30–40% of the total production cost ( 10 ). Any such separation techniques need to reduce this cost. Solvent extraction is one such unit operation that is simple in operation and less energy demanding. However, they need the help of distillation to recover the acid and the solvent from the extract. At present, conventional extractors are being used for conducting solvent extraction. Devices like mixer settler cascades, tray column, packed column in some cases, rotating disk contactors, centrifugal extractors and many others are included in them. The problems associated with this type of equipment include non-uniform size distribution of liquid/gas drops, poor mixing behaviour, low surface to volume ratio, low heat and mass transfer coefficients, and so on (López-Garzón & Straathof, 2014, Straathof et al., 2011, Gentry & Solazzo, 1995). Microchannels have been proved to be effective devices for conducting solvent extraction processes. It is also one of the means of process intensification. A very high specific surface area as much as 10,000–50,000 m 2 /m 3 can be achieved in microchannels in comparison to the conventional agitated vessel which yields a maximum value of about 1000 m 2 /m 3 (Straathof et al., 2011, Sprakel & Schuur, 2019, Wasewar et al., 2010, Raimondi et al. 2014, Assmann & von Rohr, 2011, Ponce-Ortega et al., 2012). Extensive reports on microchannel extraction are found in the literature. Few major works are highlighted here. Burns and Ramshaw (2001) investigated the titration of acetic acid in kerosene in a square microchannel having 0.38 mm width. Also, Khasid et al., (2007) conducted extraction studies for the separation of succinic acid, acetic acid and iodine in PTFE microchannel under slug flow conditions. They reported 90% separation in less than 20 seconds. Zhao et al., (2006) for the separation of succinic acid from aqueous solution using n-butanol in microchannels reported four times higher volumetric mass transfer coefficient higher than the traditional extractors. Likewise, Kamio et al., (2011) demonstrated the separation of docosahexaenoic acid ethyl ester from aqueous solution in T and Y junction microchannels in the emulsion and slug flow conditions. Both the flow patterns produced maximum separation. Similarly, Jovanovic et al., (2011) compared the extraction performance of slug and bubble flow and achieved 100% separation for the separation of 2-butanol from toluene in water in a fused silica microchannel. Tang et al., 2013 (2013) used vertical microchannels and separated 80% succinic acid from water in n-butanol under the droplet flow regime. Tsaoulidis et al., 2013 (2013) demonstrated the extraction of dioxouranium from the nitric acid aqueous mixture in a Teflon based microchannel and achieved extraction efficiency greater than 90%. Raimondi et al., (2014) reported the separation of acetone from toluene in solvent water in a square microchannel generating slug flow. They also validated a mass transfer coefficient correlation and obtained a value in the range of 0.72–8.44 s − 1 . Nandagopal et al., (2016), conducted phenol extraction from dodecane by several extraction methods, i.e., batch, ultrasonic extraction assisted by microwave, and microchannel extraction. However, they reported the maximum extraction in the microchannel, which is about 94%. Sahu et al., (2016) investigated the PA extraction from toluene using water in batch and microchannel extractor and reported the separation factor close to unity. Kumar and Mohan, (2018), in the same way, explored the aromatic extraction from alkanes in PTFE and glass microchannels. They obtained an extraction efficiency of nearly 97% using solvents furfural, propylene carbonate, etc. Sahu et al., (2016) separated propionic acid from toluene using water in a microchannel. The extraction efficiency of PA is reported to be 98%. Susanti et al. (2016) separated lactic acid by the solvent tri-n-octylamine in n-octanol by reactive extraction in a microchannel and achieved equilibrium in 90 seconds. Recently, Singh et al., (2020), evaluated the separation of propionic acid from its aqueous mixture by solvent extraction and used microchannel distillation to recover the same from the solvent. The literature indicates that all the microchannel extraction studies reported till the recent ones are confined to single microchannels. Multistage extraction studies in the microchannel are rarely reported. Estimation of the number of stages for the maximum recovery of propionic acid is essential for the design of a microchannel extraction unit. Hence this work focuses on the multistage solvent extraction of propionic acid in microchannels using solvents like hexane, heptane, toluene and cyclohexanol. The reason for choosing these solvents is that the first three solvents can be easily separated by distillation from the extract. This has been proven by Singh et al., (2020). 2.0 Materials and methods 2.1 Materials The chemicals used in the experimental work are given in Table 1 . All the chemicals used in this study had ≥ 0.97 purity (based on mass fraction). The purity of the chemicals was observed at 0.97, propionic acid 0.99, toluene 0.99, n-heptane 0.99, and cyclohexanol > .995. The Milli- Q water of conductivity < 0.07 µ siemens was used in the experiments. All the chemicals were used as it is without further purification. Their physical properties are given in the same table. Table 1 list of the chemicals used in experimental studies. Chemical used Source Purity in mass fraction Density (g/cm 3 ) Refractive index Viscosity (cP) Propionic Acid Sigma Aldrich > 0.99 0.990 1.3843 1.175 n-Hexane Merk > 0.97 0.672 1.3749 0.297 Toluene Loba Chem > 0.99 0.868 1.4960 0.5312 n-Heptane Loba Chem > 0.99 0.6795 1.3855 0.3891 Cyclohexanol Loba Chem > 0.995 0.962 1.4641 41.03 2.2 Fabrication of Microchannels A rectangular microchannel was fabricated on a PMMA plate having a width of 0.75 mm. The channel was designed by using coral draw suit X7 (2007) software. Fabrication was done by the CO 2 laser technique. The dimension of the channel is 0.75 mm in width, 240 mm long and 0.5 mm deep. The engraving was made on one of the PMMA plates and the other PMMA plate with no engraving was placed above the first plate and was fastened by using suitable nuts & bolts. A stainless-steel channel with a width of 0.75 mm, depth of 0.5 mm, and length of 90 mm was also designed and fabricated by mechanical engraving techniques for handling solvents of toluene and cyclohexanol, as these solvents damage the PMMA material. 2.3 Experimental setup The schematic diagram of the experimental setup is shown in Fig. 2.1. The experimental setup comprises two glass syringes, two syringe pumps, a micro-channel, a light source, PVC tubes for connections, a high-speed camera (part of Goniometer) and a collection flask. Yashtech India Pvt. Ltd., Nashik, India, supplied the syringe pumps. Syringe pumps were used to distribute the feed and the solvent into the microchannel. The flow range of the pump was 0.01 to 9.99 mL/min. The accuracy of the syringe pumps is ± 0.01 mL/min. Glass syringes were supplied by Top Syringes, Mumbai, Maharashtra. The syringes and the inlets of the microchannel were connected by the PVC tubes. The slug images inside the microchannel were captured using a high-speed camera, which is part of the Goniometer (DSA 25E) of Kruss GmbH make. The samples that exited from the microchannel were collected for analysis in a conical flask. 2.4 Experimental procedure A semi-batch type extraction was performed in this work. Aqueous solutions of 1M of propionic acid were used in this work. The feed mixtures were prepared by mixing the organic acid and the distilled water under extreme precaution using micropipettes (Sartorius Corporate Administration GmbH, Germany) accuracy of ± 0.001mL. A Sartorius make weighing balance with the accuracy ± 0.0001g was used for weighing the samples. N-hexane, n-heptane, toluene, and cyclohexanol were used as the solvents. Glass syringes were filled with the feed mixture and the solvent separately. The syringes were clipped to the pump carefully, ensuring that no air bubbles were present inside the syringes. The fluids were pumped into the channel at the desired flow rates. After the steady state was achieved, the samples were collected from the outlet of the channel in a collection beaker. The collected samples were analyzed. The acid concentration in both the raffinate and the extract phase was also confirmed by acid-base titration. All the experiments were conducted at 30 ℃. At the beginning of the extraction experiments, samples were collected using a phase separator and without it. This was done to find the difference in propionic acid concentration at the exit. Accordingly, no significant difference was found between the two methods (as described in our previous work by Singh et al., (2020). Hence the remaining experiments were conducted without using a phase separator. The samples were collected, and the analysis was done by titrating them with 0.1N NaOH solution. 2.5 Extraction performance parameters Percentage extraction (%) = \(\frac{\left({C}_{in}^{Aq}-{C}_{out}^{Aq}\right)}{{C}_{in}^{Aq}}\) (2.1) Where \({C}_{in}^{Aq}\) is the PA concentration in the feed (aqueous solution) inlet; \({C}_{out}^{Aq}\) is the PA concentration in the raffinate (feed outlet). The extraction efficiency is defined as the transported solute to the maximum transferable solute (Arun & Mohan, 2018, Susanti, 2016). The extraction efficiency was calculated by using Eq. (1) Extraction efficiency E (%) = \(\frac{{c}_{out}^{s}-{c}_{in}^{s}}{{c}_{s}^{*}-{c}_{in}^{s}}\) (2.2) where, c s in , c s out & c s * are the PA concentration in the solvent inlet, solvent outlet and the equilibrium concentration of PA in the solvent, respectively. The volumetric mass transfer coefficient (K L a) from Eq. (3) K L a= \({K}_{L}a=\frac{1}{t}{ln}\left(\frac{{c}_{s}^{*}- {c}_{in}^{s}}{{c}_{s}^{*}- {c}_{out}^{s}}\right)\) (2.3) In both equations 2 and 3, K L a is the volumetric mass transfer coefficient, s − 1 ; K L is the mass transfer coefficient, m/s; t is the residence time, s; c s in , c s out & c s * are the PA concentration in the solvent inlet, outlet and the equilibrium concentration of PA in the solvent respectively ( 6 , 8 ). 3.0 Results and discussion 3.1 Percentage Extraction In this section, the percentage extraction of all four solvents, hexane, heptane, toluene and cyclohexanol, are compared as a function of flow rate and flow ratio. Extraction with hexane and heptane was conducted in the PMMA microchannel. The feed flow rate was in the range of 0.1–1.2 mL/min, and the solvent flow rate was maintained in the range of 0.02–3.6 mL/min. The flow ratio varied from 0.25-3.0. The flow ratio is defined as the ratio of solvent to feed flow rate. The results of percentage extraction are shown in Fig. 3.1 and Fig. 3.2, respectively. At each flow ratio, the percentage extraction is observed to decrease with the increase in flow rate, as known. This may be because of the insufficient contact time between the solvent and the feed at higher flow rates. Next, the percentage extraction variation with respect to the flow ratio is seen from the same figures wherein the separation percentage increases with the flow ratio, which may be due to the proportionate increase in the solvent rate at the given conditions. A significant difference is observed at flow ratios 0.25 and 3. Although this seems to be advantageous, the flow ratio increase is not beneficial from the operations aspect as it would increase solvent consumption. Furthermore, the separation obtained at higher flow ratios is not very different. (vast difference). Overall, the percentage extraction of n-hexane is in the range of 12 to 22%. The extraction performance of heptane is nearly similar to that of hexane; however, not more than a 2% increase. The maximum percentage is obtained at the lowest feed rate, where the maximum contact time between the solvent and the feed is obtained. At flow ratio 1, the percentage extraction lies in the range of 21.2–16.2%. In the same way, the Effect of the flow ratio for heptane is seen to follow the same trend as n-hexane. At a flow ratio of 0.25, the percentage extraction is in the range of 19.1–16.1%. The same flow ratio 3 varies from 24 − 17%, which is the maximum at the given conditions. Such lower percentage separation suggests that a single-stage extraction is not adequate to completely remove the solute from the feed and needs many more stages. A good solvent requires to have more distribution coefficient and high selectivity, where it can dissolve more solute selectivity and thereby reduce the required number of stages. Extraction with toluene and cyclohexanol was conducted in a stainless steel microchannel as these solvents would damage the PMMA material. Hence for comparisons, the flow rates were adjusted such that their performance could be compared with hexane and heptane at equivalent residence times. In this case, the flow rate of the feed solutions was maintained from 0.04 to 0.45 mL/min, and the solvent was 0.01–1.35 mL/min. Similarly, the flow ratio varied from 0.25 to 3. The results of the percentage extraction of PA as a function of flow rate and flow ratio are shown in Fig. 3.3 and Fig. 3.4, respectively. The results indicate that the percentage extraction of toluene and cyclohexanol is twofold higher than the first two alkane solvents. At each flow ratio, the percentage extraction decreases with the increase in total flow rate, as expected. It should also be highlighted that at each flow ratio, there is about an 8–10% difference exists in the percentage separation. The overall percentage extraction of toluene changes from 26.1 to 41.2%. In cyclohexanol’s case, a relatively high separation is achieved then all the first three solvents. The overall percentage separation of cyclohexanol ranges from 56 to 60% with cyclohexanol. At each flow ratio, for the given flow rates, nearly 4 to 5% separation is achieved. Comparing all the solvents, hexane and heptane are observed to possess poor separation characteristics, while toluene and cyclohexanol exhibit relatively better performance. The extent of separation in terms of percentage separation implies that the solute is not completely removed from the feed in a single stage. This creates the need for several stages for the maximum removal of the solute. In the previous work, Singh et al., (2020) studied the extraction of PA with hexane & toluene and reported the highest percentage extraction of 36% and 19.4% for toluene and hexane, respectively at 0.1 mL/min total flow rate & flow ratio 1. 3.2. Extraction efficiency The next important parameter is extraction efficiency which determines the effectiveness of the extractor. In general, the extraction efficiency is very high, close to 100% in microchannels. In this work, extraction efficiency as a function of flow rate and flow ratio was evaluated for all the solvents. The results are shown in Fig. 3.5 to 3.8. The Effect of flow rate on extraction efficiency is more obvious which decreases with the former. This may be due to the insufficient contact time between the solvent and the feed. Similarly, the Effect of flow ratio on extraction efficiency is also seen. In all the cases, it is noticed that the increase in flow ratio does not favour the extraction efficiency. The maximum extraction efficiency is found at flow ratio 1.0 i.e. when the solvent and the feed flow rates are equal. Extraction efficiency at other flow ratios decreases with the latter’s increase correspondingly. At flow ratio 0.25, the efficiency is seen to be nearly less than the efficiency at flow ratio 1.0 which maybe because of the inadequate solvent quantity (flow rate). Likewise, way when the flow ratio is greater than 1.0, the extraction efficiency decreases. Here, even when the solvent rate is increased than the feed rate, the decrease in contact time results in poor separation efficiencies. Although the flow ratio increase leads to, Interestingly the Effect of the flow ratio concludes that the maximum extraction is achieved at a low S/F (flow) ratio. For the PA-hexane system, the maximum extraction efficiency is in the range of 97.5–87.1%. Similarly, the PA-heptane recorded 96.3–86.3% efficiency at the same conditions. For toluene and cyclohexanol, the separation efficiency is in the range of 97.7–87.5% and 99.8–93.8% respectively. In the literature, Kashid et al., (2007) recorded greater than 90% extraction efficiency for the succinic acid separation from its aqueous solution into butanol in SMC. Sahu et al., (2016) reported a separation efficiency of close to a hundred per cent to extract PA from water using toluene by slug flow pattern in a single microchannel. Recently, Singh et al., (2020), performed the extraction of the aqueous propionic acid with solvents hexane & toluene in stainless steel microchannel and reported the highest extraction efficiency 99.6% for PA-toluene mixture at 0.01 mL/min and 98.4% for the PA-hexane mixture, at the same conditions. This shows that our experimental results are in good agreement with the literature values. 3.3 Volumetric mass transfer coefficient The volumetric mass transfer coefficient for all four solvents is shown in Fig. 3.9 to 3.12 at different flow rates and flow ratios. It is seen from these figures that the volumetric mass transfer coefficient increases with the increase in flow rate. This increase in the mass transfer coefficient may be due to the rigorous internal mixing within each slug which is expected to enhance the convective transfer of mass. The increase in K L a values can also happen with the increase in surface area at higher velocities. The maximum K L a values were obtained at flow ratio 0.25 which for hexane it is in the range of 0.15–0.87 s − 1 , for heptane it is from 0.08 to 0.91 s − 1 , for toluene, it lies in the range is 0.17–1.12 s − 1 and finally, for cyclohexanol, it is the range of 0.16–1.23 s − 1 . The values are found to be higher than any conventional contactors. For instance, the K L a generated in a rotating disc contactor for the water-succinic acid-butanol mixture is close to 0.0057 s − 1 . Similarly, for the water-acetic acid-benzene mixture in a spray column, it is about 0.0017–0.0063 s − 1 (Kashid et al., 2007). (Comparison of the experimental K L a and the with the literature values, suggests that they are in good agreement). For example, the volumetric mass transfer coefficient reported by Kashid et al. 2007 for the water-succinic acid-kerosene system in microchannels, is in the range of 0.02–0.32 s − 1 . Sahu et al., (2016) reported K L a in the range of 0.005–0.009 s − 1 for 3.73wt% PA and 0.0067–0.007 s − 1 for 7.47 wt% PA. For the aromatic separation in microchannels, Kumar and Mohan, (2018) obtained K L a values falling in the range of 0.005–0.02 s − 1 . Recently Singh et al., (2020) obtained the volumetric mass transfer coefficient in the range of 0.01–0.1 s − 1 for PA-hexane and 0.01–0.25 s − 1 for PA-toluene systems respectively in a stainless steel microchannel. These comparisons confirm that the experimental K L a values are in good agreement with the literature data. Next, the Effect of flow ratio on volumetric mass transfer coefficient is seen to have less impact. The K L a values decrease with the increase in flow ratio however the changes are insignificant. In the same way, the experimental K L a and that in the literature for separation in microchannel suggested that they are in good agreement. 3.4 Number of Stages It was intended to estimate the number of stages required for the maximum removal of the solute PA from the aqueous solution (feed) using all four solvents. Accordingly, the feed and the solvent were fed into the first stage wherein the solvent with the solute called extract was collected separately and the leftover feed called the raffinate was collected separately while the raffinate was fed into the subsequent microchannels to recover the PA. In each stage, the pure solvent was used for extraction. The flow rates and the flow ratio were adjusted such that the percentage extraction & extraction efficiency was maximum. Hence, the flow rate of the feed and the solvent was maintained equal in the range of 0.1 to 1.2 mL/min. Figure 3.13 to 3.16 shows the Effect of flow rate on concentration change, percentage extraction, extraction efficiency, volumetric mass transfer coefficient and the number of stages. For the solvent hexane, Fig. 3.13(a) displays the Effect of multistage the change extraction in PA the raffinate and the extract. This plot displays the maximum separation obtained at equal flow rates of hexane and the feed at 0.1 mL/min. As expected, the concentration of PA in the raffinate decreases with each stage and reaches a constant value at the fifth stage and vice-versa in the extract. In each stage, nearly 20% extraction is achieved. Figure 3.13(b) shows the Effect of total flow rate on percentage extraction for each stage. As anticipated, the percentage extraction decreases with the flow rate. While it increases with each stage due to the increase in PA concentration difference in the successive stage, respectively. It should be noted that overall 74.3% solute is separated by hexane from the first to the fifth stage. In each stage, about 23% separation is achieved by hexane. Similarly, the extraction efficiency is plotted in Fig. 3.13(c). Similarly, the volumetric mass transfer coefficient is seen in Fig. 3.13(d). It is seen in the figures that efficiency decreases with each stage and the overall values lie between 97.96 and 90.66 at 0.2 mL/min. The maximum efficiency is obtained in stage 1, later the extraction efficiency decreases in each stage due to the decrease in concentration ratio (According to Eq. 2.2). In the same manner, the volumetric mass transfer coefficient is found to decrease with each stage because of the decrease in concentration difference between the saturated and the inlet PA concentration. The overall volumetric mass transfer coefficient is in the range of 0.45 to 0.88 s − 1 . Heptane exhibits an identical extraction performance like that of hexane. The extraction results of n-heptane are shown in Fig. 3.14(a-d). Here too, the PA concentration in the raffinate becomes stable at the fifth stage. The PA molarity in the extract is increased from range to 0.825 g/L. The overall PA separation by heptane is about 86.06% in five stages. The percentage extraction increases in each stage and the corresponding values are about 21% in the first two stages and from the third to the fifth stage, its value is in the following order 27.3%, 36.4%, 51.3% respectively. The maximum extraction efficiency obtained with heptane is about 98.9%. The extraction efficiency is found to decrease as well as with the stage, and the latter decreases with the flow rate as expected and also with each stage. The volumetric mass transfer coefficient also exhibits an opposite behaviour where the K L a increases with the increase in flow rate but decreases with each stage. The maximum range of K L a is obtained in stage 1 which is 0.16–0.91 s − 1 . The next solvent used was toluene. The extraction characteristics of toluene are shown in Fig. 3.15(a-d). The concentration profile for PA in toluene for both the raffinate and extract is shown in Fig. 3.15(a). It is seen that nearly 3 stages are required for the solute concentration in the raffinate to reach the minimum value of 0.05 M. The percentage extraction plot further increases in stage results, that the maximum percentage extraction is reached at stage 3 which is about 50% at 0.2 mL/min total flow rate. The respective percentage separation in each stage is about 35.5%, 46.1% and 62.2%. The overall separation percentage through the 3 stages is approximately 87.1% which is higher than the first two solvents. The corresponding extraction efficiency is nearly 100% in stage 1 and decreases further with the flow rate and stages. The maximum K L a value is obtained in stage 1, which is nearly in the range of 0.25-1.0 s − 1 . Finally, cyclohexanol was tested for determining the number of microchannel stages required to bring down the PA concentration in the raffinate to the lowest level. The extraction results of cyclohexanol are shown in Fig. 3.16(a-d). In this case, merely 2 stages are required by the solvent to achieve a PA concentration of 0.04 M in the raffinate where other solvents needed 3.5 stages for reaching the same molarity. The percentage of extraction of PA by cyclohexanol in the first stage is 57.2% while it is 89% in the second stage. The overall separation of the solute by cyclohexanol is about 95.3% which is very high than the other solvents. Likewise, the volumetric mass transfer coefficient for cyclohexanol is in the range of 0.2–1.2 s − 1 in the first stage which is the maximum. 3.5 Total annual Cost Analysis (TAC) The TAC (Total Annual Cost) comparison was performed for the propionic acid extraction for the solvent used. TAC was calculated using the below Eq. (30,31). TAC = Fixed cost + Operating cost (3.1) The fixed costs in Eq. (3.1) represent the cost of purchase and installation of microchannel stack extractor. The operating cost includes the cost of raw materials, solvents, labour and electricity. To calculate the TAC, a few assumptions were made for processing 1000Kg per day, which are as follows.350 days of the operation in the year, the dollar price 1 $ = 73.83 INR, the cost of the labour per day $ 3.88 and the cost of the electricity is about $ 0.092/unit. Although the maximum extraction efficiency of the solvents varies from 97.5–99.8%. An average efficiency value was adopted for the TAC calculation, which is 98.3%. Accordingly, the required number of microchannel units for a single stage is 4197, 3,723, 11,993, and 10,119 for the solvents hexane, heptane, toluene and cyclohexanol respectively. The capital cost per unit of the microchannel is found to be about $ 536 for hexane/heptane and $ 731 for toluene &cyclohexanol. Thus, for the above-mentioned repeating units and for the respective number of total stages the capital cost for hexane, heptane, toluene and cyclohexanol are in the following order $ 1,12,58,242, $ 1,10,19,504, $ 2,33,36,474, and $ 1,47,98,632 respectively. Thus, the capital cost calculation is about 86.2–94%, while the solvent cost contributes close to 2-12.4% of the TAC. These values suggest that repeating individual microchannels is not a feasible option. The second case of the TAC estimation was based on the microchannel stack by adopting Arora 2010, microchannel stack in place of single microchannels unit is expected to minimize the capital cost significantly, Arora (2010) had used such a method i.e., stacked microchannel distillation unit for separating methanol-water mixture from a bio-diesel plant by distillation. The actual stack had 204 repeating units each having 426 microchannels for processing 1409 kg/h mixture. Based on this information, the cost of capital cost for processing 1000 Kg/day capacity is $ 73,627 for one stage. Hence, applying the same design for extraction the total number of the repeating unit for a single stage for the following systems PA-hexane, Pa-heptane, PA-toluene, PA-cyclohexanol are 9.85, 8.7, 28.1 and 24 units respectively. For the overall stages, the total number of stacks required is, nearly 50 units are required for the solvent hexane, 43 units for heptane,75 units for toluene and 48 units for cyclohexanol. The results of the TAC analysis is shown in Fig. 3.17 and 3.18. According to the calculations, the overall capital cost for the total number of stages in the order of solvents is $ 36,26,129, $ 32,02,774and $ 62,06,756, $ 35,34,096 for hexane, heptane, toluene and cyclohexanol respectively. This corresponds to 69–93% of the TAC. In this design, the solvent cost contributes the major portion of the operation cost which is nearly 6 to 30% of the same. Accordingly, the total annual cost is $ 41,83,379.75, $ 45,96,971.50, $ 66,47,213.10 and $ 49,10,453.00 for the above solvents in the same order. In the third case, of TAC estimation, the cost of fabrication was based on the fabrication of the stacked microchannel units locally (in India). The cost of a stacked microchannel (consisting of 426 channels) for the hexane & heptane is $ 625, and for toluene & cyclohexanol, it is $ 876 respectively. Then the capital cost for the total number of stacked units (for overall stages) are $ 30,781.25, $ 27,187.5, $ 73,846.8 and $ 42,048forhexane, heptane, toluene & cyclohexanol respectively. Now the contribution of the capital cost is mere 1.9–14%of the TAC. On the other hand, now the TAC is dominated by the solvent cost only which corresponds to 81–97% of the TAC. In this new estimation, the total annual cost is $ 5,88,031, $ 14,21,384.5, $ 5,14,303.80 and $ 14,18,405.0 for the above order of solvents. It is seen that the overall annual cost is found to be less for toluene than all other solvents. Although cyclohexanol needs merely two stages the total annual cost is increased by its solvent cost. Thus, among the solvents, toluene seems to be a better option due to its relatively lowest TAC. If a suitable co-solvent can be employed with cyclohexanol the overall operation cost may significantly be reduced to a desirable value. Moreover, a solvent even more effective than these is expected to reduce the overall annual cost. For microchannel stack was calculated based on the local charges i.e. charges incurred in our region for the stack design. Conclusion Multistage extraction for the separation of propionic acid (7.04 wt%) from its aqueous solution by solvent extraction using n-hexane, heptane, toluene and cyclohexanol was conducted in microchannels. These solvents were chosen based on their ease of recovery by distillation except the last. The Effect of flow rate, flow ratio, stages on PA concentration in raffinate and extract, percentage extraction, extraction efficiency and volumetric mass transfer coefficient were studied. Besides, a total annual cost for the multistage extraction process was also made. The percentage extraction is found to decrease with the total flow rate for all the solvent. On the other hand, the same increased with the increase in flow ratio. The overall percentage extraction for hexane is in the range of 12 to 22%, for heptane it is in the range of 16–24%. The percentage separation of PA with toluene and cyclohexanol is in the range of 41.2 to 26% and 60.5 to 52%. Thus toluene and cyclohexanol are found to be better than the first two solvents considered. Percentage extraction increased with flow ratio in all the cases however the increment was not more than 1–3% in the case of hexane and heptane but with toluene and cyclohexanol, it was in the range of nearly 4–5%. The Effect of flow rate and flow ratio on extraction efficiency was studied. Extraction efficiency decreased with the total flow rate and reached the maximum at the lowest flow rate and flow ratio 1. The Effect of flow ratio indicated increased extraction efficiency with the flow ratio increase from 0.25 to 1.0 and the same decreased with further increase in flow ratio from 1.5 to 3.0. Extraction efficiency was also evaluated for the individual solvents. The maximum value obtained for hexane is in the range of 97.5–87.1%. Similarly, heptane is in the range of 96.3 to 86.3%. The highest extraction efficiency was obtained for toluene and cyclohexanol that is 97.7–87.5% and 99.8–93.8% respectively. The volumetric mass transfer coefficient was evaluated with respect to flow rate and flow ratio. It was found that the K L a increased with the increase in flow rate. The maximum K L a was obtained at flow ratio 0.25 which is for hexane in the range of 0.15–0.87 s − 1 , for heptane 0.08–0.91 s − 1 , for toluene it is 0.17–1.12 s − 1 and finally, for cyclohexanol, it is the range of 0.16–1.23 s − 1 The number of stages required for the maximum removal of PA from the feed was estimated. Also, the Effect of stages on percentage extraction, extraction efficiency and the volumetric mass transfer coefficient was studied. Consecutively, the required number of stages for hexane and heptane was 5 and for toluene, it is 3 and finally, for cyclohexanol, it is 2. The percentage extraction increased with each stage due to the increase in PA concentration difference. In the successive stages. Hexane recovered 74.3% of PA from the feed-in five stages. In each stage, about 23.7% of separation was achieved. Similarly, heptane removed nearly 86% of PA overall and in the first two stages about 22% separation was obtained and from the third to the fifth stage, it increased from 27 to 51.3%. Toluene required three extraction stages for separating 87.1% PA. The separation obtained in the three stages is around 35.5%, 45.1% and 62.2% respectively. In the same way, cyclohexanol required only 2 stages to separate nearly 95.3% PA overall. The separation obtained in the two stages is 57% and 89% respectively. The overall volumetric mass transfer coefficient decreased with each multiple extraction stage for all the solvents. The overall K L a values are in the range of 0.15-0.87s − 1 , 0.08-0.91s − 1 , 0.17–1.12 s − 1 and 0.16-1.23s − 1 for hexane, heptane, toluene and cyclohexanol respectively. The effect of stages on extraction efficiency was evaluated. Maximum efficiency was obtained in stage 1 for all the solvents. The extraction efficiency values for the above solvents (in the same order) are 97.9–86.3%, 98.9–86.2%, 99.7–89.5% and 99.8–93.8%, respectively. The extraction efficiency decreased with the increase in stage numbers; however, the change is not so significant, which is only 1–3%. The total cost analysis was made for the multistage extraction of propionic acid involving all the solvents. For processing 1000 Kg/day, 4197, 3723, 11,993 and 10,119 individual microchannels were required. In this design, the capital cost of the microchannels contributed about 86–96% of the TAC, while the solvent cost contributed 2–12% of the overall costs. In the second estimation technique, a microchannel stack design containing 426 microchannels was adopted from the literature to estimate TAC comparison. Accordingly, about 50, 84 and 48 total units were required for the solvents one to four listed at the beginning. In this design, the capital cost of the microchannel stack accounts for 8-33.9% and the solvent costs were increased to 45-81.5% of the overall TAC. The third case involved the TAC estimation based on the fabrication cost in India. The results indicated that the TAC is greatly reduced and the capital cost for the stacks accounts for only 1.2–14.3% of the TAC. The solvent cost, on the other hand, contributes 81–96% of the TAC. Overall, solvent toluene contributes the minimum TAC than the other solvents. Thus, it can be concluded that effective solvents can greatly reduce the number of stages required for the maximum recovery of PA from the feed. At the same time, the TAC of the process can be greatly reduced by employing a suitable, efficient solvent. Declarations Conflict of Interest Statement “The authors declare no competing financial interest.” References López-Garzón CS, Straathof AJJ (2014) Recovery of carboxylic acids produced by fermentation. Biotechnol Adv 32:873–904. 10.1016/j.biotechadv.2014.04.002 Barbirato F, Chedaille D, Bories A (1997) Propionic acid fermentation from glycerol: Comparison with conventional substrates. Appl Microbiol Biotechnol 47(4):441–446 Boyaval P, Corre C (1995) Production of propionic acid. Le Lait 75(4–5):453–461 Suwannakham S, Yang ST (2005) Enhanced propionic acid fermentation by Propionibacterium acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor. Biotechnol Bioeng 91(3):325–337 Kośmider A, Drozdzyńska A, Blaszka K, Leja K, Czaczyk K (2010) Propionic acid production by propionibacterium freudenreichii ssp. shermanii using crude glycerol and whey lactose industrial wastes. Pol J Environ Stud 19:1249–1253 Wasewar KL, Extraction R (2012) An intensifying approach for carboxylic acid separation. Int J Chem Eng Appl 3:249–255. 10.7763/IJCEA.2012.V3.195 Reyhanitash E, Zaalberg B, Kersten SRA, Schuur B (2016) Extraction of volatile fatty acids from fermented wastewater. Sep Purif Technol 161:61–68. 10.1016/j.seppur.2016.01.037 Kumar S, Babu BV (2006) A brief review on propionic acid: a renewal energy source, NCEC-2006. 4 459–464 Pan J, Li X, Zhang W, Cui W, Zhou Z, Liu D (2019) Isobaric vapour-liquid equilibrium for binary systems of ethyl iodide with ethanol, propionic acid and ethylpropionate at 101.3 kPa. J Chem Thermodyn 132:23–28. https://doi.org/10.1016/j.jct.2018.12.023 Straathof AJJ (2011) The proportion of downstream costs in fermentative production processes. In: Moo-Young (ed) Comprehensive biotechnology, 2nd edn. Elsevier, pp 811–814. https://doi.org/10.1016/B978-0-08-088504-9.00492-X . Gentry JC, Solazzo AJ (1995) Recovery of carboxylic acids from aqueous streams. Environ Prog 14:61–64. https://doi.org/10.1002/ep.670140123 Sprakel LMJ, Schuur B (2019) Solvent developments for liquid-liquid extraction of carboxylic acids in perspective. Sep Purif Tech 211:935–957 Wasewar KL, Keshav A, Seema (2010) Physical extraction of propionic acid. Int J Res Rev Appl Sci 3:290–302 Raimondi NDM, Prat L, Gourdon C, Tasselli J (2014) Experiments of mass transfer with liquid-liquid slug flow in square microchannels. Chem Eng Sci 105:169–178. https://doi.org/10.1016/j.ces.2013.11.009 Assmann N, von Rohr PR (2011) Extraction in microreactors: Intensification by adding an inert gas phase. Chem Eng Process Process Inten 50:822–827. https://doi.org/10.1016/j.cep.2011.05.009 Ponce-Ortega JM, Al-Thubaiti MM, El-Halwagi MM (2012) Process Intensification: New understanding and Systematic Approach. Chem Eng Process 53:63–75. https://doi.org/10.1016/j.cep.2011.12.010 Burns JR, Ramshaw C (2001) The intensification of rapid reactions in multiphase systems using slug flow in capillaries, Lab on a Chip. 1 10–15. 10.1039/b102818a Kashid MN, Harshe YM, Agar DW (2007) Liquid-liquid slug flow in a capillary: An alternative to suspended drop or film contactors. Ind Eng Chem Res 46:8420–8430. 10.1021/ie070077x Zhao Y, Chen G, Yuan Q (2006) Liquid-liquid two-phase flow patterns in a rectangular microchannel. AIChE J 52:4052–4060. http://doi:10.1002/aic Kamio E, Seike Y, Yoshizawa H, Matsuyama H, Ono T (2011) Microfluidic extraction of docosahexaenoic acid ethyl ester: comparison between slug flow and emulsion. Ind Eng Chem Res 50(11):6915–6924 Jovanovi´c J, Zhou W, Rebrov EV, Nijhuis TA, Hessel V, Schouten JC (2011) Liquid-liquid slug flow: Hydrodynamics and pressure drop. Chem Eng Sci 66:42–54. https://doi.org/10.1016/j.ces.2010.09.040 Tang J, Zhang X, Cai W, Wang F (2013) Liquid–liquid extraction based on droplet flow in a vertical microchannel. Exp Therm Fluid Sci 49:185–192 Tsaoulidis D, Dore V, Angeli P, Plechkova NV, Seddon KR (2013) Dioxouranium (VI) extraction in microchannels using ionic liquids. Chem Eng J 227:151–157 Nandagopal MG, Antony R, Selvaraju N (2016) Comparative study of liquid–liquid extraction in miniaturized channels over other conventional extraction methods. Microsyst Technol 22(2):349–356 Sahu AB, Vir LNS, Molleti S, Ramji S, Pushpavanam (2016) Comparison of liquid-liquid extraction in batch systems and micro-channels. Chem Eng Process Process Intensif 104:190–200. http://doi:10.1016/j.cep.2016.03.010 Arun Kumar UK, Mohan R (2018) Liquid-liquid extraction of aromatics from hydrocarbon mixtures in capillaries. Brazilian J Chem Eng 35:605–614. http://doi:10.1590/0104-6632.20180352s20160654 Susanti JGM, Winkelman B, Schuur HJ, Heeres J, Yue (2016) Lactic Acid Extraction and Mass Transfer Characteristics in Slug Flow Capillary Microreactors. Ind Eng Chem Res 55:4691–4702. https://doi.org/10.1021/acs.iecr.5b04917 Singh S, Mohan R, Gosu V, Kumar UKA (2020) Process Intensification of Propionic Acid Extraction and its Recovery by Distillation in Microchannel. Chem Eng Process 157:108150. http://doi:10.1016/j.cep.2020.108150 Garcia-Chavez LY, Schuur B, De Haan AB (2013) Conceptual process design and economic analysis of a process based on liquid-liquid extraction for the recovery of glycols from aqueous streams. Ind Eng Chem Res 52:4902–4910. https://doi.org/10.1021/ie303187x Li H, Na J, Cong H, Wu L, Zhao L, Li X, Gao X (2020) Thermodynamics Foundation and Separation Process Design for Production of Propionic Acid from Ethanol Carbonylation Catalyzed by Iodide. Ind Eng Chem Res 59:6090–6101. https://doi.org/10.1021/acs.iecr.9b06505 Arora R (2013) Distributive Distillation Enabled by Microchannel Process Technology, United States, https://doi.org/10.2172/1077001 Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 09 Feb, 2024 Reviewers invited by journal 08 Jan, 2024 Editor invited by journal 22 Dec, 2023 Editor assigned by journal 21 Dec, 2023 First submitted to journal 20 Dec, 2023 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3786779","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":266106881,"identity":"7954d8f0-83bc-4615-b38f-f9a6a01a3713","order_by":0,"name":"Sudhanshu Singh","email":"","orcid":"","institution":"Malaviya National Institute of Technology Jaipur","correspondingAuthor":false,"prefix":"","firstName":"Sudhanshu","middleName":"","lastName":"Singh","suffix":""},{"id":266106882,"identity":"7df65386-0907-4019-87d0-addf0aa948be","order_by":1,"name":"U K Arun 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12:03:02","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3786779/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3786779/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49454508,"identity":"5e638855-64bf-4ee6-bc05-35cdf6182f4f","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":114062,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 2.1– \u003c/strong\u003eSchematic diagram for the estimation of stages for complete extraction\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/35563ba68ff3b10a23a04be8.png"},{"id":49454504,"identity":"7d034234-b708-4b76-927b-d572298b7b40","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":21103,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.1 \u003c/strong\u003eEffect of total flow rate (solvent + feed) and flow ratio on percentage extraction for the aqueous PA-Hexane system.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/5350d2ec3a0ae9b69473b319.png"},{"id":49454507,"identity":"e1c72bf0-e5f7-4c4b-be2a-099753edd29d","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":19591,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.2 \u003c/strong\u003eEffect of total flow rate (solvent + feed) and flow ratio on percentage extraction for the aqueous PA-Heptane system.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/96da8192a345aa1ab2167312.png"},{"id":49455029,"identity":"a2d10e52-bff5-4cca-bf04-b5c709aaf4a1","added_by":"auto","created_at":"2024-01-11 06:15:21","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":17590,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.3\u003c/strong\u003e Effect of total flow rate (solvent + feed) and flow ratio on percentage extraction –PA-Toluene.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/6489b33f51fb42aed99295c0.png"},{"id":49454505,"identity":"28e711ac-ea89-43fd-b0c1-a75e8b76ea41","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":17911,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.4\u003c/strong\u003e Effect of total flow rate (solvent + feed) and flow ratio on percentage extraction PA-Cyclohexanol\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/8106b49e19531556d18009f4.png"},{"id":49455354,"identity":"164702d7-0167-44e0-96f7-c98dd08aab39","added_by":"auto","created_at":"2024-01-11 06:23:21","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":19657,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.5 \u003c/strong\u003eEffect of total flow rate and flow ratio on extraction efficiency 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8","display":"","copyAsset":false,"role":"figure","size":20748,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.6 \u003c/strong\u003eEffect of total flow rate and flow ratio on extraction efficiency PA-Toluene\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/38c2361a4ddf4e3ac556a6f9.png"},{"id":49456307,"identity":"deb2d16a-de26-4a27-aa28-fea950a7bb55","added_by":"auto","created_at":"2024-01-11 06:31:21","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":21008,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig.3.7 \u003c/strong\u003eEffect of total \u0026nbsp;\u0026nbsp;flow rate and flow ratio on extraction efficiency 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11","display":"","copyAsset":false,"role":"figure","size":27210,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 3.10\u003c/strong\u003e Effect of total flow rate on volumetric mass transfer coefficient PA-heptane\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/432d39ce8236224094cc7765.png"},{"id":49456313,"identity":"eec2a86d-5759-4623-9a21-a66220fa137b","added_by":"auto","created_at":"2024-01-11 06:31:21","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":29165,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 3.11 \u003c/strong\u003eEffect of total flow rate on volumetric mass transfer coefficient PA-Toluene\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/05a4f80968feb95fddfd05f6.png"},{"id":49455040,"identity":"bf9fb84a-ec75-4210-97d3-a48ada3e663f","added_by":"auto","created_at":"2024-01-11 06:15:21","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":28238,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 3.12\u003c/strong\u003e Effect of total flow rate on volumetric mass transfer coefficient PA-Cyclohexanol\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/2168a473fb5f605d11c0681b.png"},{"id":49454516,"identity":"94d206d5-5889-4840-845c-1aee75f158d5","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":62096,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.13\u003c/strong\u003eEffect of stages on, (a) percentage extraction, (b) extraction efficiency, (c) volumetric mass transfer coefficient and, (d) stages required for complete separation at flow ratio 1 for PA- hexane system\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/db0e527f42ed72c2eee5b348.png"},{"id":49454512,"identity":"39562773-262a-4980-a343-7fed23262d7c","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":50927,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig 3.14\u003c/strong\u003e – Effect of stages on (a) percentage extraction, (b) \u0026nbsp;\u0026nbsp;extraction efficiency, (c) volumetric mass transfer coefficient and (d) \u0026nbsp;\u0026nbsp;number of stages required for separation\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/a5e3dbe494368422f20cdae1.png"},{"id":49454521,"identity":"9b4ee8e8-c1fc-4954-a6fb-c9bcb701dccd","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":46642,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.15 \u003c/strong\u003eEffect of stages on (a) percentage extraction, (b) extraction efficiency, (c) volumetric mass transfer coefficient and (d) stages required for complete separation at flow ratio 1 for PA- toluene system\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/13f3fea50bfac18315047001.png"},{"id":49454522,"identity":"2202bd94-8a88-4b3f-869f-91832d2d047c","added_by":"auto","created_at":"2024-01-11 06:07:21","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":50829,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.16 \u003c/strong\u003eEffect of stages on (a) Percentage extraction (b) Extraction efficiency (c) Volumetric mass transfer coefficient and (d) Stages required for complete separation at flow ratio 1 for PA- cyclohexanol system\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/2abc97945105578b5a01542e.png"},{"id":49455358,"identity":"2751f872-d70b-44f1-8e79-e243c99a7a57","added_by":"auto","created_at":"2024-01-11 06:23:21","extension":"png","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":11772,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.17 The\u003c/strong\u003e total annual cost TAC comparison between different solvents at actual stages\u003c/p\u003e","description":"","filename":"18.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/8237a57e979ee8c008cd58f9.png"},{"id":49455361,"identity":"6a57b014-e8d2-4e82-ac3d-045a8e9fc8c3","added_by":"auto","created_at":"2024-01-11 06:23:23","extension":"png","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":24799,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. 3.18 \u003c/strong\u003eBreakup of the operating costs for all the extractors for actual stages\u003c/p\u003e","description":"","filename":"19.png","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/dfa77c86774940e293a385cc.png"},{"id":49992642,"identity":"be11801e-02b1-4358-9daf-c53140143482","added_by":"auto","created_at":"2024-01-22 18:57:51","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":908891,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3786779/v1/d3f8c49c-155c-4dd7-9d89-f26b977e9aca.pdf"}],"financialInterests":"","formattedTitle":"Microchannel based Multistage Solvent Extraction Studies for the Separation of Propionic Acid from its Aqueous Mixture using Hydrocarbon Solvents","fulltext":[{"header":"1.0 Introduction","content":"\u003cp\u003eThe separation of carboxylic acids from the fermentation broth is an important focus of research. Although these acids are presently produced on a large scale from petroleum-based raw materials, interest in producing them from renewable resources i.e., bio-based production is growing in recent days. Several organic acids like acetic, citric, lactic, succinic and itaconic acids are commercially produced by fermentation methods (L\u0026oacute;pez-Garz\u0026oacute;n, 2014). However, few acids like propionic acid are still in the development stage for their bio-based production commercially using strains like \u003cem\u003epropionibacterium\u003c/em\u003e (Barbirato, et al., 1997, Boyaval and Corre, 1995, Suwannakham, 2005). Propionic acid has several uses, especially they are used as an antifungal agent, as a bacteriostatic agent used for conserving cereals. Its salts are used in the production of food and pharmaceutical products, surfactants, etc., (Kośmider et al., 2010, Wasewar, 2012, Reyhanitash et al., 2016, Kumar \u0026amp; Babu, 2006, Pan et al., 2019). Numerous separation techniques are available to separate propionic acid, however, economic isolation and purification method are in demand. Separation methods like solvent extraction, distillation, pervaporation, electrodialysis, reactive extraction and many others are the options for PA separation. The downstream processing (DSP) in these industries contributes to 30\u0026ndash;40% of the total production cost (\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). Any such separation techniques need to reduce this cost. Solvent extraction is one such unit operation that is simple in operation and less energy demanding. However, they need the help of distillation to recover the acid and the solvent from the extract.\u003c/p\u003e \u003cp\u003eAt present, conventional extractors are being used for conducting solvent extraction. Devices like mixer settler cascades, tray column, packed column in some cases, rotating disk contactors, centrifugal extractors and many others are included in them. The problems associated with this type of equipment include non-uniform size distribution of liquid/gas drops, poor mixing behaviour, low surface to volume ratio, low heat and mass transfer coefficients, and so on (L\u0026oacute;pez-Garz\u0026oacute;n \u0026amp; Straathof, 2014, Straathof et al., 2011, Gentry \u0026amp; Solazzo, 1995). Microchannels have been proved to be effective devices for conducting solvent extraction processes. It is also one of the means of process intensification. A very high specific surface area as much as 10,000\u0026ndash;50,000 m\u003csup\u003e2\u003c/sup\u003e/m\u003csup\u003e3\u003c/sup\u003e can be achieved in microchannels in comparison to the conventional agitated vessel which yields a maximum value of about 1000 m\u003csup\u003e2\u003c/sup\u003e/m\u003csup\u003e3\u003c/sup\u003e(Straathof et al., 2011, Sprakel \u0026amp; Schuur, 2019, Wasewar et al., 2010, Raimondi et al. 2014, Assmann \u0026amp; von Rohr, 2011, Ponce-Ortega et al., 2012).\u003c/p\u003e \u003cp\u003eExtensive reports on microchannel extraction are found in the literature. Few major works are highlighted here. Burns and Ramshaw (2001) investigated the titration of acetic acid in kerosene in a square microchannel having 0.38 mm width. Also, Khasid et al., (2007) conducted extraction studies for the separation of succinic acid, acetic acid and iodine in PTFE microchannel under slug flow conditions. They reported 90% separation in less than 20 seconds. Zhao et al., (2006) for the separation of succinic acid from aqueous solution using n-butanol in microchannels reported four times higher volumetric mass transfer coefficient higher than the traditional extractors. Likewise, Kamio et al., (2011) demonstrated the separation of docosahexaenoic acid ethyl ester from aqueous solution in T and Y junction microchannels in the emulsion and slug flow conditions. Both the flow patterns produced maximum separation. Similarly, Jovanovic et al., (2011) compared the extraction performance of slug and bubble flow and achieved 100% separation for the separation of 2-butanol from toluene in water in a fused silica microchannel. Tang et al., 2013 (2013) used vertical microchannels and separated 80% succinic acid from water in n-butanol under the droplet flow regime. Tsaoulidis et al., 2013 (2013) demonstrated the extraction of dioxouranium from the nitric acid aqueous mixture in a Teflon based microchannel and achieved extraction efficiency greater than 90%. Raimondi et al., (2014) reported the separation of acetone from toluene in solvent water in a square microchannel generating slug flow. They also validated a mass transfer coefficient correlation and obtained a value in the range of 0.72\u0026ndash;8.44 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Nandagopal et al., (2016), conducted phenol extraction from dodecane by several extraction methods, i.e., batch, ultrasonic extraction assisted by microwave, and microchannel extraction. However, they reported the maximum extraction in the microchannel, which is about 94%.\u003c/p\u003e \u003cp\u003eSahu et al., (2016) investigated the PA extraction from toluene using water in batch and microchannel extractor and reported the separation factor close to unity. Kumar and Mohan, (2018), in the same way, explored the aromatic extraction from alkanes in PTFE and glass microchannels. They obtained an extraction efficiency of nearly 97% using solvents furfural, propylene carbonate, etc. Sahu et al., (2016) separated propionic acid from toluene using water in a microchannel. The extraction efficiency of PA is reported to be 98%. Susanti et al. (2016) separated lactic acid by the solvent tri-n-octylamine in n-octanol by reactive extraction in a microchannel and achieved equilibrium in 90 seconds.\u003c/p\u003e \u003cp\u003eRecently, Singh et al., (2020), evaluated the separation of propionic acid from its aqueous mixture by solvent extraction and used microchannel distillation to recover the same from the solvent. The literature indicates that all the microchannel extraction studies reported till the recent ones are confined to single microchannels. Multistage extraction studies in the microchannel are rarely reported. Estimation of the number of stages for the maximum recovery of propionic acid is essential for the design of a microchannel extraction unit. Hence this work focuses on the multistage solvent extraction of propionic acid in microchannels using solvents like hexane, heptane, toluene and cyclohexanol. The reason for choosing these solvents is that the first three solvents can be easily separated by distillation from the extract. This has been proven by Singh et al., (2020).\u003c/p\u003e"},{"header":"2.0 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eThe chemicals used in the experimental work are given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. All the chemicals used in this study had\u0026thinsp;\u0026ge;\u0026thinsp;0.97 purity (based on mass fraction). The purity of the chemicals was observed at 0.97, propionic acid 0.99, toluene 0.99, n-heptane 0.99, and cyclohexanol\u0026thinsp;\u0026gt;\u0026thinsp;.995. The Milli- Q water of conductivity\u0026thinsp;\u0026lt;\u0026thinsp;0.07 \u0026micro; siemens was used in the experiments. All the chemicals were used as it is without further purification. Their physical properties are given in the same table.\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\u003elist of the chemicals used in experimental studies.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemical used\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSource\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePurity in mass fraction\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDensity\u003c/p\u003e \u003cp\u003e(g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRefractive index\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eViscosity\u003c/p\u003e \u003cp\u003e(cP)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePropionic Acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSigma Aldrich\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.990\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.3843\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.175\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003en-Hexane\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMerk\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;0.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.672\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.3749\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.297\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eToluene\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLoba Chem\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.868\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.4960\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.5312\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003en-Heptane\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLoba Chem\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;0.99\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.6795\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.3855\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.3891\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCyclohexanol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLoba Chem\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026gt;\u0026thinsp;0.995\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.962\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.4641\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e41.03\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Fabrication of Microchannels\u003c/h2\u003e \u003cp\u003eA rectangular microchannel was fabricated on a PMMA plate having a width of 0.75 mm. The channel was designed by using coral draw suit X7 (2007) software. Fabrication was done by the CO\u003csub\u003e2\u003c/sub\u003e laser technique. The dimension of the channel is 0.75 mm in width, 240 mm long and 0.5 mm deep. The engraving was made on one of the PMMA plates and the other PMMA plate with no engraving was placed above the first plate and was fastened by using suitable nuts \u0026amp; bolts. A stainless-steel channel with a width of 0.75 mm, depth of 0.5 mm, and length of 90 mm was also designed and fabricated by mechanical engraving techniques for handling solvents of toluene and cyclohexanol, as these solvents damage the PMMA material.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Experimental setup\u003c/h2\u003e \u003cp\u003eThe schematic diagram of the experimental setup is shown in Fig.\u0026nbsp;2.1. The experimental setup comprises two glass syringes, two syringe pumps, a micro-channel, a light source, PVC tubes for connections, a high-speed camera (part of Goniometer) and a collection flask. Yashtech India Pvt. Ltd., Nashik, India, supplied the syringe pumps. Syringe pumps were used to distribute the feed and the solvent into the microchannel. The flow range of the pump was 0.01 to 9.99 mL/min. The accuracy of the syringe pumps is \u0026plusmn;\u0026thinsp;0.01 mL/min. Glass syringes were supplied by Top Syringes, Mumbai, Maharashtra. The syringes and the inlets of the microchannel were connected by the PVC tubes. The slug images inside the microchannel were captured using a high-speed camera, which is part of the Goniometer (DSA 25E) of Kruss GmbH make. The samples that exited from the microchannel were collected for analysis in a conical flask.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Experimental procedure\u003c/h2\u003e \u003cp\u003eA semi-batch type extraction was performed in this work. Aqueous solutions of 1M of propionic acid were used in this work. The feed mixtures were prepared by mixing the organic acid and the distilled water under extreme precaution using micropipettes (Sartorius Corporate Administration GmbH, Germany) accuracy of \u0026plusmn;\u0026thinsp;0.001mL. A Sartorius make weighing balance with the accuracy\u0026thinsp;\u0026plusmn;\u0026thinsp;0.0001g was used for weighing the samples. N-hexane, n-heptane, toluene, and cyclohexanol were used as the solvents. Glass syringes were filled with the feed mixture and the solvent separately. The syringes were clipped to the pump carefully, ensuring that no air bubbles were present inside the syringes. The fluids were pumped into the channel at the desired flow rates. After the steady state was achieved, the samples were collected from the outlet of the channel in a collection beaker. The collected samples were analyzed. The acid concentration in both the raffinate and the extract phase was also confirmed by acid-base titration. All the experiments were conducted at 30 ℃.\u003c/p\u003e \u003cp\u003eAt the beginning of the extraction experiments, samples were collected using a phase separator and without it. This was done to find the difference in propionic acid concentration at the exit. Accordingly, no significant difference was found between the two methods (as described in our previous work by Singh et al., (2020). Hence the remaining experiments were conducted without using a phase separator. The samples were collected, and the analysis was done by titrating them with 0.1N NaOH solution.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Extraction performance parameters\u003c/h2\u003e \u003cp\u003ePercentage extraction (%) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{\\left({C}_{in}^{Aq}-{C}_{out}^{Aq}\\right)}{{C}_{in}^{Aq}}\\)\u003c/span\u003e\u003c/span\u003e (2.1)\u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{in}^{Aq}\\)\u003c/span\u003e\u003c/span\u003eis the PA concentration in the feed (aqueous solution) inlet; \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({C}_{out}^{Aq}\\)\u003c/span\u003e\u003c/span\u003eis the PA concentration in the raffinate (feed outlet). The extraction efficiency is defined as the transported solute to the maximum transferable solute (Arun \u0026amp; Mohan, 2018, Susanti, 2016).\u003c/p\u003e \u003cp\u003eThe extraction efficiency was calculated by using Eq.\u0026nbsp;(1)\u003c/p\u003e \u003cp\u003eExtraction efficiency E (%) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{{c}_{out}^{s}-{c}_{in}^{s}}{{c}_{s}^{*}-{c}_{in}^{s}}\\)\u003c/span\u003e\u003c/span\u003e (2.2)\u003c/p\u003e \u003cp\u003ewhere, c\u003csup\u003es\u003c/sup\u003e\u003csub\u003ein\u003c/sub\u003e, c\u003csup\u003es\u003c/sup\u003e\u003csub\u003eout\u003c/sub\u003e \u0026amp; c\u003csub\u003es\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003e are the PA concentration in the solvent inlet, solvent outlet and the equilibrium concentration of PA in the solvent, respectively.\u003c/p\u003e \u003cp\u003eThe volumetric mass transfer coefficient (K\u003csub\u003eL\u003c/sub\u003ea) from Eq.\u0026nbsp;(3)\u003c/p\u003e \u003cp\u003eK\u003csub\u003eL\u003c/sub\u003ea=\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({K}_{L}a=\\frac{1}{t}{ln}\\left(\\frac{{c}_{s}^{*}- {c}_{in}^{s}}{{c}_{s}^{*}- {c}_{out}^{s}}\\right)\\)\u003c/span\u003e\u003c/span\u003e (2.3)\u003c/p\u003e \u003cp\u003eIn both equations 2 and 3, K\u003csub\u003eL\u003c/sub\u003ea is the volumetric mass transfer coefficient, s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; K\u003csub\u003eL\u003c/sub\u003e is the mass transfer coefficient, m/s; t is the residence time, s; c\u003csup\u003es\u003c/sup\u003e\u003csub\u003ein\u003c/sub\u003e, c\u003csup\u003es\u003c/sup\u003e\u003csub\u003eout\u003c/sub\u003e \u0026amp; c\u003csub\u003es\u003c/sub\u003e\u003csup\u003e*\u003c/sup\u003eare the PA concentration in the solvent inlet, outlet and the equilibrium concentration of PA in the solvent respectively (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3.0 Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Percentage Extraction\u003c/h2\u003e \u003cp\u003eIn this section, the percentage extraction of all four solvents, hexane, heptane, toluene and cyclohexanol, are compared as a function of flow rate and flow ratio. Extraction with hexane and heptane was conducted in the PMMA microchannel. The feed flow rate was in the range of 0.1\u0026ndash;1.2 mL/min, and the solvent flow rate was maintained in the range of 0.02\u0026ndash;3.6 mL/min. The flow ratio varied from 0.25-3.0. The flow ratio is defined as the ratio of solvent to feed flow rate. The results of percentage extraction are shown in Fig.\u0026nbsp;3.1 and Fig.\u0026nbsp;3.2, respectively. At each flow ratio, the percentage extraction is observed to decrease with the increase in flow rate, as known. This may be because of the insufficient contact time between the solvent and the feed at higher flow rates. Next, the percentage extraction variation with respect to the flow ratio is seen from the same figures wherein the separation percentage increases with the flow ratio, which may be due to the proportionate increase in the solvent rate at the given conditions. A significant difference is observed at flow ratios 0.25 and 3. Although this seems to be advantageous, the flow ratio increase is not beneficial from the operations aspect as it would increase solvent consumption. Furthermore, the separation obtained at higher flow ratios is not very different. (vast difference). Overall, the percentage extraction of n-hexane is in the range of 12 to 22%.\u003c/p\u003e \u003cp\u003eThe extraction performance of heptane is nearly similar to that of hexane; however, not more than a 2% increase. The maximum percentage is obtained at the lowest feed rate, where the maximum contact time between the solvent and the feed is obtained. At flow ratio 1, the percentage extraction lies in the range of 21.2\u0026ndash;16.2%. In the same way, the Effect of the flow ratio for heptane is seen to follow the same trend as n-hexane. At a flow ratio of 0.25, the percentage extraction is in the range of 19.1\u0026ndash;16.1%. The same flow ratio 3 varies from 24\u0026thinsp;\u0026minus;\u0026thinsp;17%, which is the maximum at the given conditions. Such lower percentage separation suggests that a single-stage extraction is not adequate to completely remove the solute from the feed and needs many more stages. A good solvent requires to have more distribution coefficient and high selectivity, where it can dissolve more solute selectivity and thereby reduce the required number of stages.\u003c/p\u003e \u003cp\u003eExtraction with toluene and cyclohexanol was conducted in a stainless steel microchannel as these solvents would damage the PMMA material. Hence for comparisons, the flow rates were adjusted such that their performance could be compared with hexane and heptane at equivalent residence times. In this case, the flow rate of the feed solutions was maintained from 0.04 to 0.45 mL/min, and the solvent was 0.01\u0026ndash;1.35 mL/min. Similarly, the flow ratio varied from 0.25 to 3. The results of the percentage extraction of PA as a function of flow rate and flow ratio are shown in Fig.\u0026nbsp;3.3 and Fig.\u0026nbsp;3.4, respectively. The results indicate that the percentage extraction of toluene and cyclohexanol is twofold higher than the first two alkane solvents. At each flow ratio, the percentage extraction decreases with the increase in total flow rate, as expected. It should also be highlighted that at each flow ratio, there is about an 8\u0026ndash;10% difference exists in the percentage separation. The overall percentage extraction of toluene changes from 26.1 to 41.2%. In cyclohexanol\u0026rsquo;s case, a relatively high separation is achieved then all the first three solvents. The overall percentage separation of cyclohexanol ranges from 56 to 60% with cyclohexanol. At each flow ratio, for the given flow rates, nearly 4 to 5% separation is achieved. Comparing all the solvents, hexane and heptane are observed to possess poor separation characteristics, while toluene and cyclohexanol exhibit relatively better performance. The extent of separation in terms of percentage separation implies that the solute is not completely removed from the feed in a single stage. This creates the need for several stages for the maximum removal of the solute. In the previous work, Singh et al., (2020) studied the extraction of PA with hexane \u0026amp; toluene and reported the highest percentage extraction of 36% and 19.4% for toluene and hexane, respectively at 0.1 mL/min total flow rate \u0026amp; flow ratio 1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Extraction efficiency\u003c/h2\u003e \u003cp\u003eThe next important parameter is extraction efficiency which determines the effectiveness of the extractor. In general, the extraction efficiency is very high, close to 100% in microchannels. In this work, extraction efficiency as a function of flow rate and flow ratio was evaluated for all the solvents. The results are shown in Fig.\u0026nbsp;3.5 to 3.8. The Effect of flow rate on extraction efficiency is more obvious which decreases with the former. This may be due to the insufficient contact time between the solvent and the feed. Similarly, the Effect of flow ratio on extraction efficiency is also seen. In all the cases, it is noticed that the increase in flow ratio does not favour the extraction efficiency. The maximum extraction efficiency is found at flow ratio 1.0 i.e. when the solvent and the feed flow rates are equal. Extraction efficiency at other flow ratios decreases with the latter\u0026rsquo;s increase correspondingly. At flow ratio 0.25, the efficiency is seen to be nearly less than the efficiency at flow ratio 1.0 which maybe because of the inadequate solvent quantity (flow rate). Likewise, way when the flow ratio is greater than 1.0, the extraction efficiency decreases. Here, even when the solvent rate is increased than the feed rate, the decrease in contact time results in poor separation efficiencies. Although the flow ratio increase leads to, Interestingly the Effect of the flow ratio concludes that the maximum extraction is achieved at a low S/F (flow) ratio. For the PA-hexane system, the maximum extraction efficiency is in the range of 97.5\u0026ndash;87.1%. Similarly, the PA-heptane recorded 96.3\u0026ndash;86.3% efficiency at the same conditions. For toluene and cyclohexanol, the separation efficiency is in the range of 97.7\u0026ndash;87.5% and 99.8\u0026ndash;93.8% respectively. In the literature, Kashid et al., (2007) recorded greater than 90% extraction efficiency for the succinic acid separation from its aqueous solution into butanol in SMC. Sahu et al., (2016) reported a separation efficiency of close to a hundred per cent to extract PA from water using toluene by slug flow pattern in a single microchannel. Recently, Singh et al., (2020), performed the extraction of the aqueous propionic acid with solvents hexane \u0026amp; toluene in stainless steel microchannel and reported the highest extraction efficiency 99.6% for PA-toluene mixture at 0.01 mL/min and 98.4% for the PA-hexane mixture, at the same conditions. This shows that our experimental results are in good agreement with the literature values.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Volumetric mass transfer coefficient\u003c/h2\u003e \u003cp\u003eThe volumetric mass transfer coefficient for all four solvents is shown in Fig.\u0026nbsp;3.9 to 3.12 at different flow rates and flow ratios. It is seen from these figures that the volumetric mass transfer coefficient increases with the increase in flow rate. This increase in the mass transfer coefficient may be due to the rigorous internal mixing within each slug which is expected to enhance the convective transfer of mass. The increase in K\u003csub\u003eL\u003c/sub\u003ea values can also happen with the increase in surface area at higher velocities. The maximum K\u003csub\u003eL\u003c/sub\u003ea values were obtained at flow ratio 0.25 which for hexane it is in the range of 0.15\u0026ndash;0.87 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, for heptane it is from 0.08 to 0.91 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, for toluene, it lies in the range is 0.17\u0026ndash;1.12 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and finally, for cyclohexanol, it is the range of 0.16\u0026ndash;1.23 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The values are found to be higher than any conventional contactors. For instance, the K\u003csub\u003eL\u003c/sub\u003ea generated in a rotating disc contactor for the water-succinic acid-butanol mixture is close to 0.0057 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Similarly, for the water-acetic acid-benzene mixture in a spray column, it is about 0.0017\u0026ndash;0.0063 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Kashid et al., 2007). (Comparison of the experimental K\u003csub\u003eL\u003c/sub\u003ea and the with the literature values, suggests that they are in good agreement). For example, the volumetric mass transfer coefficient reported by Kashid et al. 2007 for the water-succinic acid-kerosene system in microchannels, is in the range of 0.02\u0026ndash;0.32 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Sahu et al., (2016) reported K\u003csub\u003eL\u003c/sub\u003ea in the range of 0.005\u0026ndash;0.009 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 3.73wt% PA and 0.0067\u0026ndash;0.007 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for 7.47 wt% PA. For the aromatic separation in microchannels, Kumar and Mohan, (2018) obtained K\u003csub\u003eL\u003c/sub\u003ea values falling in the range of 0.005\u0026ndash;0.02 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Recently Singh et al., (2020) obtained the volumetric mass transfer coefficient in the range of 0.01\u0026ndash;0.1 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003efor PA-hexane and 0.01\u0026ndash;0.25 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for PA-toluene systems respectively in a stainless steel microchannel. These comparisons confirm that the experimental K\u003csub\u003eL\u003c/sub\u003ea values are in good agreement with the literature data. Next, the Effect of flow ratio on volumetric mass transfer coefficient is seen to have less impact. The K\u003csub\u003eL\u003c/sub\u003ea values decrease with the increase in flow ratio however the changes are insignificant. In the same way, the experimental K\u003csub\u003eL\u003c/sub\u003ea and that in the literature for separation in microchannel suggested that they are in good agreement.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Number of Stages\u003c/h2\u003e \u003cp\u003eIt was intended to estimate the number of stages required for the maximum removal of the solute PA from the aqueous solution (feed) using all four solvents. Accordingly, the feed and the solvent were fed into the first stage wherein the solvent with the solute called extract was collected separately and the leftover feed called the raffinate was collected separately while the raffinate was fed into the subsequent microchannels to recover the PA. In each stage, the pure solvent was used for extraction. The flow rates and the flow ratio were adjusted such that the percentage extraction \u0026amp; extraction efficiency was maximum. Hence, the flow rate of the feed and the solvent was maintained equal in the range of 0.1 to 1.2 mL/min. Figure\u0026nbsp;3.13 to 3.16 shows the Effect of flow rate on concentration change, percentage extraction, extraction efficiency, volumetric mass transfer coefficient and the number of stages.\u003c/p\u003e \u003cp\u003eFor the solvent hexane, Fig.\u0026nbsp;3.13(a) displays the Effect of multistage the change extraction in PA the raffinate and the extract. This plot displays the maximum separation obtained at equal flow rates of hexane and the feed at 0.1 mL/min. As expected, the concentration of PA in the raffinate decreases with each stage and reaches a constant value at the fifth stage and vice-versa in the extract. In each stage, nearly 20% extraction is achieved. Figure\u0026nbsp;3.13(b) shows the Effect of total flow rate on percentage extraction for each stage. As anticipated, the percentage extraction decreases with the flow rate. While it increases with each stage due to the increase in PA concentration difference in the successive stage, respectively. It should be noted that overall 74.3% solute is separated by hexane from the first to the fifth stage. In each stage, about 23% separation is achieved by hexane. Similarly, the extraction efficiency is plotted in Fig.\u0026nbsp;3.13(c). Similarly, the volumetric mass transfer coefficient is seen in Fig.\u0026nbsp;3.13(d). It is seen in the figures that efficiency decreases with each stage and the overall values lie between 97.96 and 90.66 at 0.2 mL/min. The maximum efficiency is obtained in stage 1, later the extraction efficiency decreases in each stage due to the decrease in concentration ratio (According to Eq.\u0026nbsp;2.2). In the same manner, the volumetric mass transfer coefficient is found to decrease with each stage because of the decrease in concentration difference between the saturated and the inlet PA concentration. The overall volumetric mass transfer coefficient is in the range of 0.45 to 0.88 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eHeptane exhibits an identical extraction performance like that of hexane. The extraction results of n-heptane are shown in Fig.\u0026nbsp;3.14(a-d). Here too, the PA concentration in the raffinate becomes stable at the fifth stage. The PA molarity in the extract is increased from range to 0.825 g/L. The overall PA separation by heptane is about 86.06% in five stages. The percentage extraction increases in each stage and the corresponding values are about 21% in the first two stages and from the third to the fifth stage, its value is in the following order 27.3%, 36.4%, 51.3% respectively. The maximum extraction efficiency obtained with heptane is about 98.9%. The extraction efficiency is found to decrease as well as with the stage, and the latter decreases with the flow rate as expected and also with each stage. The volumetric mass transfer coefficient also exhibits an opposite behaviour where the K\u003csub\u003eL\u003c/sub\u003ea increases with the increase in flow rate but decreases with each stage. The maximum range of K\u003csub\u003eL\u003c/sub\u003ea is obtained in stage 1 which is 0.16\u0026ndash;0.91 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The next solvent used was toluene. The extraction characteristics of toluene are shown in Fig.\u0026nbsp;3.15(a-d). The concentration profile for PA in toluene for both the raffinate and extract is shown in Fig.\u0026nbsp;3.15(a). It is seen that nearly 3 stages are required for the solute concentration in the raffinate to reach the minimum value of 0.05 M. The percentage extraction plot further increases in stage results, that the maximum percentage extraction is reached at stage 3 which is about 50% at 0.2 mL/min total flow rate. The respective percentage separation in each stage is about 35.5%, 46.1% and 62.2%. The overall separation percentage through the 3 stages is approximately 87.1% which is higher than the first two solvents. The corresponding extraction efficiency is nearly 100% in stage 1 and decreases further with the flow rate and stages. The maximum K\u003csub\u003eL\u003c/sub\u003ea value is obtained in stage 1, which is nearly in the range of 0.25-1.0 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Finally, cyclohexanol was tested for determining the number of microchannel stages required to bring down the PA concentration in the raffinate to the lowest level. The extraction results of cyclohexanol are shown in Fig.\u0026nbsp;3.16(a-d). In this case, merely 2 stages are required by the solvent to achieve a PA concentration of 0.04 M in the raffinate where other solvents needed 3.5 stages for reaching the same molarity. The percentage of extraction of PA by cyclohexanol in the first stage is 57.2% while it is 89% in the second stage. The overall separation of the solute by cyclohexanol is about 95.3% which is very high than the other solvents. Likewise, the volumetric mass transfer coefficient for cyclohexanol is in the range of 0.2\u0026ndash;1.2 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in the first stage which is the maximum.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Total annual Cost Analysis (TAC)\u003c/h2\u003e \u003cp\u003eThe TAC (Total Annual Cost) comparison was performed for the propionic acid extraction for the solvent used. TAC was calculated using the below Eq.\u0026nbsp;(30,31).\u003c/p\u003e \u003cp\u003eTAC\u0026thinsp;=\u0026thinsp;Fixed cost\u0026thinsp;+\u0026thinsp;Operating cost (3.1)\u003c/p\u003e \u003cp\u003eThe fixed costs in Eq.\u0026nbsp;(3.1) represent the cost of purchase and installation of microchannel stack extractor. The operating cost includes the cost of raw materials, solvents, labour and electricity. To calculate the TAC, a few assumptions were made for processing 1000Kg per day, which are as follows.350 days of the operation in the year, the dollar price 1\u003cspan\u003e$\u003c/span\u003e = 73.83 INR, the cost of the labour per day \u003cspan\u003e$\u003c/span\u003e3.88 and the cost of the electricity is about \u003cspan\u003e$\u003c/span\u003e0.092/unit. Although the maximum extraction efficiency of the solvents varies from 97.5\u0026ndash;99.8%. An average efficiency value was adopted for the TAC calculation, which is 98.3%. Accordingly, the required number of microchannel units for a single stage is 4197, 3,723, 11,993, and 10,119 for the solvents hexane, heptane, toluene and cyclohexanol respectively. The capital cost per unit of the microchannel is found to be about \u003cspan\u003e$\u003c/span\u003e536 for hexane/heptane and \u003cspan\u003e$\u003c/span\u003e731 for toluene \u0026amp;cyclohexanol. Thus, for the above-mentioned repeating units and for the respective number of total stages the capital cost for hexane, heptane, toluene and cyclohexanol are in the following order \u003cspan\u003e$\u003c/span\u003e1,12,58,242, \u003cspan\u003e$\u003c/span\u003e1,10,19,504, \u003cspan\u003e$\u003c/span\u003e2,33,36,474, and \u003cspan\u003e$\u003c/span\u003e1,47,98,632 respectively. Thus, the capital cost calculation is about 86.2\u0026ndash;94%, while the solvent cost contributes close to 2-12.4% of the TAC. These values suggest that repeating individual microchannels is not a feasible option.\u003c/p\u003e \u003cp\u003e The second case of the TAC estimation was based on the microchannel stack by adopting Arora 2010, microchannel stack in place of single microchannels unit is expected to minimize the capital cost significantly, Arora (2010) had used such a method i.e., stacked microchannel distillation unit for separating methanol-water mixture from a bio-diesel plant by distillation. The actual stack had 204 repeating units each having 426 microchannels for processing 1409 kg/h mixture. Based on this information, the cost of capital cost for processing 1000 Kg/day capacity is \u003cspan\u003e$\u003c/span\u003e73,627 for one stage. Hence, applying the same design for extraction the total number of the repeating unit for a single stage for the following systems PA-hexane, Pa-heptane, PA-toluene, PA-cyclohexanol are 9.85, 8.7, 28.1 and 24 units respectively. For the overall stages, the total number of stacks required is, nearly 50 units are required for the solvent hexane, 43 units for heptane,75 units for toluene and 48 units for cyclohexanol. The results of the TAC analysis is shown in Fig.\u0026nbsp;3.17 and 3.18. According to the calculations, the overall capital cost for the total number of stages in the order of solvents is \u003cspan\u003e$\u003c/span\u003e36,26,129, \u003cspan\u003e$\u003c/span\u003e32,02,774and \u003cspan\u003e$\u003c/span\u003e62,06,756, \u003cspan\u003e$\u003c/span\u003e35,34,096 for hexane, heptane, toluene and cyclohexanol respectively. This corresponds to 69\u0026ndash;93% of the TAC. In this design, the solvent cost contributes the major portion of the operation cost which is nearly 6 to 30% of the same. Accordingly, the total annual cost is \u003cspan\u003e$\u003c/span\u003e41,83,379.75, \u003cspan\u003e$\u003c/span\u003e45,96,971.50, \u003cspan\u003e$\u003c/span\u003e66,47,213.10 and \u003cspan\u003e$\u003c/span\u003e49,10,453.00 for the above solvents in the same order.\u003c/p\u003e \u003cp\u003eIn the third case, of TAC estimation, the cost of fabrication was based on the fabrication of the stacked microchannel units locally (in India). The cost of a stacked microchannel (consisting of 426 channels) for the hexane \u0026amp; heptane is \u003cspan\u003e$\u003c/span\u003e625, and for toluene \u0026amp; cyclohexanol, it is \u003cspan\u003e$\u003c/span\u003e876 respectively. Then the capital cost for the total number of stacked units (for overall stages) are \u003cspan\u003e$\u003c/span\u003e30,781.25, \u003cspan\u003e$\u003c/span\u003e27,187.5, \u003cspan\u003e$\u003c/span\u003e73,846.8 and \u003cspan\u003e$\u003c/span\u003e42,048forhexane, heptane, toluene \u0026amp; cyclohexanol respectively. Now the contribution of the capital cost is mere 1.9\u0026ndash;14%of the TAC. On the other hand, now the TAC is dominated by the solvent cost only which corresponds to 81\u0026ndash;97% of the TAC. In this new estimation, the total annual cost is \u003cspan\u003e$\u003c/span\u003e5,88,031, \u003cspan\u003e$\u003c/span\u003e14,21,384.5, \u003cspan\u003e$\u003c/span\u003e5,14,303.80 and \u003cspan\u003e$\u003c/span\u003e14,18,405.0 for the above order of solvents. It is seen that the overall annual cost is found to be less for toluene than all other solvents. Although cyclohexanol needs merely two stages the total annual cost is increased by its solvent cost. Thus, among the solvents, toluene seems to be a better option due to its relatively lowest TAC. If a suitable co-solvent can be employed with cyclohexanol the overall operation cost may significantly be reduced to a desirable value. Moreover, a solvent even more effective than these is expected to reduce the overall annual cost. For microchannel stack was calculated based on the local charges i.e. charges incurred in our region for the stack design.\u003c/p\u003e \u003cp\u003e \u003cb\u003eConclusion\u003c/b\u003e \u003c/p\u003e \u003cp\u003eMultistage extraction for the separation of propionic acid (7.04 wt%) from its aqueous solution by solvent extraction using n-hexane, heptane, toluene and cyclohexanol was conducted in microchannels. These solvents were chosen based on their ease of recovery by distillation except the last. The Effect of flow rate, flow ratio, stages on PA concentration in raffinate and extract, percentage extraction, extraction efficiency and volumetric mass transfer coefficient were studied. Besides, a total annual cost for the multistage extraction process was also made.\u003c/p\u003e \u003cp\u003eThe percentage extraction is found to decrease with the total flow rate for all the solvent. On the other hand, the same increased with the increase in flow ratio. The overall percentage extraction for hexane is in the range of 12 to 22%, for heptane it is in the range of 16\u0026ndash;24%. The percentage separation of PA with toluene and cyclohexanol is in the range of 41.2 to 26% and 60.5 to 52%. Thus toluene and cyclohexanol are found to be better than the first two solvents considered. Percentage extraction increased with flow ratio in all the cases however the increment was not more than 1\u0026ndash;3% in the case of hexane and heptane but with toluene and cyclohexanol, it was in the range of nearly 4\u0026ndash;5%.\u003c/p\u003e \u003cp\u003eThe Effect of flow rate and flow ratio on extraction efficiency was studied. Extraction efficiency decreased with the total flow rate and reached the maximum at the lowest flow rate and flow ratio 1. The Effect of flow ratio indicated increased extraction efficiency with the flow ratio increase from 0.25 to 1.0 and the same decreased with further increase in flow ratio from 1.5 to 3.0. Extraction efficiency was also evaluated for the individual solvents. The maximum value obtained for hexane is in the range of 97.5\u0026ndash;87.1%. Similarly, heptane is in the range of 96.3 to 86.3%. The highest extraction efficiency was obtained for toluene and cyclohexanol that is 97.7\u0026ndash;87.5% and 99.8\u0026ndash;93.8% respectively. The volumetric mass transfer coefficient was evaluated with respect to flow rate and flow ratio. It was found that the K\u003csub\u003eL\u003c/sub\u003ea increased with the increase in flow rate. The maximum K\u003csub\u003eL\u003c/sub\u003ea was obtained at flow ratio 0.25 which is for hexane in the range of 0.15\u0026ndash;0.87 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, for heptane 0.08\u0026ndash;0.91 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, for toluene it is 0.17\u0026ndash;1.12 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and finally, for cyclohexanol, it is the range of 0.16\u0026ndash;1.23 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eThe number of stages required for the maximum removal of PA from the feed was estimated. Also, the Effect of stages on percentage extraction, extraction efficiency and the volumetric mass transfer coefficient was studied. Consecutively, the required number of stages for hexane and heptane was 5 and for toluene, it is 3 and finally, for cyclohexanol, it is 2. The percentage extraction increased with each stage due to the increase in PA concentration difference. In the successive stages. Hexane recovered 74.3% of PA from the feed-in five stages. In each stage, about 23.7% of separation was achieved. Similarly, heptane removed nearly 86% of PA overall and in the first two stages about 22% separation was obtained and from the third to the fifth stage, it increased from 27 to 51.3%. Toluene required three extraction stages for separating 87.1% PA. The separation obtained in the three stages is around 35.5%, 45.1% and 62.2% respectively. In the same way, cyclohexanol required only 2 stages to separate nearly 95.3% PA overall. The separation obtained in the two stages is 57% and 89% respectively.\u003c/p\u003e \u003cp\u003eThe overall volumetric mass transfer coefficient decreased with each multiple extraction stage for all the solvents. The overall K\u003csub\u003eL\u003c/sub\u003ea values are in the range of 0.15-0.87s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 0.08-0.91s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 0.17\u0026ndash;1.12 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 0.16-1.23s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for hexane, heptane, toluene and cyclohexanol respectively. The effect of stages on extraction efficiency was evaluated. Maximum efficiency was obtained in stage 1 for all the solvents. The extraction efficiency values for the above solvents (in the same order) are 97.9\u0026ndash;86.3%, 98.9\u0026ndash;86.2%, 99.7\u0026ndash;89.5% and 99.8\u0026ndash;93.8%, respectively. The extraction efficiency decreased with the increase in stage numbers; however, the change is not so significant, which is only 1\u0026ndash;3%.\u003c/p\u003e \u003cp\u003eThe total cost analysis was made for the multistage extraction of propionic acid involving all the solvents. For processing 1000 Kg/day, 4197, 3723, 11,993 and 10,119 individual microchannels were required. In this design, the capital cost of the microchannels contributed about 86\u0026ndash;96% of the TAC, while the solvent cost contributed 2\u0026ndash;12% of the overall costs.\u003c/p\u003e \u003cp\u003eIn the second estimation technique, a microchannel stack design containing 426 microchannels was adopted from the literature to estimate TAC comparison. Accordingly, about 50, 84 and 48 total units were required for the solvents one to four listed at the beginning. In this design, the capital cost of the microchannel stack accounts for 8-33.9% and the solvent costs were increased to 45-81.5% of the overall TAC. The third case involved the TAC estimation based on the fabrication cost in India. The results indicated that the TAC is greatly reduced and the capital cost for the stacks accounts for only 1.2\u0026ndash;14.3% of the TAC. The solvent cost, on the other hand, contributes 81\u0026ndash;96% of the TAC. Overall, solvent toluene contributes the minimum TAC than the other solvents. Thus, it can be concluded that effective solvents can greatly reduce the number of stages required for the maximum recovery of PA from the feed. At the same time, the TAC of the process can be greatly reduced by employing a suitable, efficient solvent.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eConflict of Interest Statement\u003c/h2\u003e \u003cp\u003e\u0026ldquo;The authors declare no competing financial interest.\u0026rdquo;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eL\u0026oacute;pez-Garz\u0026oacute;n CS, Straathof AJJ (2014) Recovery of carboxylic acids produced by fermentation. Biotechnol Adv 32:873\u0026ndash;904. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.biotechadv.2014.04.002\u003c/span\u003e\u003cspan address=\"10.1016/j.biotechadv.2014.04.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBarbirato F, Chedaille D, Bories A (1997) Propionic acid fermentation from glycerol: Comparison with conventional substrates. Appl Microbiol Biotechnol 47(4):441\u0026ndash;446\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBoyaval P, Corre C (1995) Production of propionic acid. Le Lait 75(4\u0026ndash;5):453\u0026ndash;461\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuwannakham S, Yang ST (2005) Enhanced propionic acid fermentation by Propionibacterium acidipropionici mutant obtained by adaptation in a fibrous-bed bioreactor. Biotechnol Bioeng 91(3):325\u0026ndash;337\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKośmider A, Drozdzyńska A, Blaszka K, Leja K, Czaczyk K (2010) Propionic acid production by propionibacterium freudenreichii ssp. shermanii using crude glycerol and whey lactose industrial wastes. Pol J Environ Stud 19:1249\u0026ndash;1253\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWasewar KL, Extraction R (2012) An intensifying approach for carboxylic acid separation. Int J Chem Eng Appl 3:249\u0026ndash;255. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.7763/IJCEA.2012.V3.195\u003c/span\u003e\u003cspan address=\"10.7763/IJCEA.2012.V3.195\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReyhanitash E, Zaalberg B, Kersten SRA, Schuur B (2016) Extraction of volatile fatty acids from fermented wastewater. Sep Purif Technol 161:61\u0026ndash;68. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.seppur.2016.01.037\u003c/span\u003e\u003cspan address=\"10.1016/j.seppur.2016.01.037\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKumar S, Babu BV (2006) A brief review on propionic acid: a renewal energy source, NCEC-2006. 4 459\u0026ndash;464\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePan J, Li X, Zhang W, Cui W, Zhou Z, Liu D (2019) Isobaric vapour-liquid equilibrium for binary systems of ethyl iodide with ethanol, propionic acid and ethylpropionate at 101.3 kPa. J Chem Thermodyn 132:23\u0026ndash;28. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jct.2018.12.023\u003c/span\u003e\u003cspan address=\"10.1016/j.jct.2018.12.023\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStraathof AJJ (2011) The proportion of downstream costs in fermentative production processes. In: Moo-Young (ed) Comprehensive biotechnology, 2nd edn. Elsevier, pp 811\u0026ndash;814. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/B978-0-08-088504-9.00492-X\u003c/span\u003e\u003cspan address=\"10.1016/B978-0-08-088504-9.00492-X\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGentry JC, Solazzo AJ (1995) Recovery of carboxylic acids from aqueous streams. Environ Prog 14:61\u0026ndash;64. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/ep.670140123\u003c/span\u003e\u003cspan address=\"10.1002/ep.670140123\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSprakel LMJ, Schuur B (2019) Solvent developments for liquid-liquid extraction of carboxylic acids in perspective. Sep Purif Tech 211:935\u0026ndash;957\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWasewar KL, Keshav A, Seema (2010) Physical extraction of propionic acid. Int J Res Rev Appl Sci 3:290\u0026ndash;302\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRaimondi NDM, Prat L, Gourdon C, Tasselli J (2014) Experiments of mass transfer with liquid-liquid slug flow in square microchannels. Chem Eng Sci 105:169\u0026ndash;178. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ces.2013.11.009\u003c/span\u003e\u003cspan address=\"10.1016/j.ces.2013.11.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAssmann N, von Rohr PR (2011) Extraction in microreactors: Intensification by adding an inert gas phase. Chem Eng Process Process Inten 50:822\u0026ndash;827. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cep.2011.05.009\u003c/span\u003e\u003cspan address=\"10.1016/j.cep.2011.05.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePonce-Ortega JM, Al-Thubaiti MM, El-Halwagi MM (2012) Process Intensification: New understanding and Systematic Approach. Chem Eng Process 53:63\u0026ndash;75. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cep.2011.12.010\u003c/span\u003e\u003cspan address=\"10.1016/j.cep.2011.12.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBurns JR, Ramshaw C (2001) The intensification of rapid reactions in multiphase systems using slug flow in capillaries, Lab on a Chip. 1 10\u0026ndash;15. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1039/b102818a\u003c/span\u003e\u003cspan address=\"10.1039/b102818a\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKashid MN, Harshe YM, Agar DW (2007) Liquid-liquid slug flow in a capillary: An alternative to suspended drop or film contactors. Ind Eng Chem Res 46:8420\u0026ndash;8430. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1021/ie070077x\u003c/span\u003e\u003cspan address=\"10.1021/ie070077x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhao Y, Chen G, Yuan Q (2006) Liquid-liquid two-phase flow patterns in a rectangular microchannel. AIChE J 52:4052\u0026ndash;4060. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi:10.1002/aic\u003c/span\u003e\u003cspan address=\"http://doi:10.1002/aic\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKamio E, Seike Y, Yoshizawa H, Matsuyama H, Ono T (2011) Microfluidic extraction of docosahexaenoic acid ethyl ester: comparison between slug flow and emulsion. Ind Eng Chem Res 50(11):6915\u0026ndash;6924\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJovanovi\u0026acute;c J, Zhou W, Rebrov EV, Nijhuis TA, Hessel V, Schouten JC (2011) Liquid-liquid slug flow: Hydrodynamics and pressure drop. Chem Eng Sci 66:42\u0026ndash;54. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ces.2010.09.040\u003c/span\u003e\u003cspan address=\"10.1016/j.ces.2010.09.040\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTang J, Zhang X, Cai W, Wang F (2013) Liquid\u0026ndash;liquid extraction based on droplet flow in a vertical microchannel. Exp Therm Fluid Sci 49:185\u0026ndash;192\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTsaoulidis D, Dore V, Angeli P, Plechkova NV, Seddon KR (2013) Dioxouranium (VI) extraction in microchannels using ionic liquids. Chem Eng J 227:151\u0026ndash;157\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNandagopal MG, Antony R, Selvaraju N (2016) Comparative study of liquid\u0026ndash;liquid extraction in miniaturized channels over other conventional extraction methods. Microsyst Technol 22(2):349\u0026ndash;356\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSahu AB, Vir LNS, Molleti S, Ramji S, Pushpavanam (2016) Comparison of liquid-liquid extraction in batch systems and micro-channels. Chem Eng Process Process Intensif 104:190\u0026ndash;200. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi:10.1016/j.cep.2016.03.010\u003c/span\u003e\u003cspan address=\"http://doi:10.1016/j.cep.2016.03.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArun Kumar UK, Mohan R (2018) Liquid-liquid extraction of aromatics from hydrocarbon mixtures in capillaries. Brazilian J Chem Eng 35:605\u0026ndash;614. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi:10.1590/0104-6632.20180352s20160654\u003c/span\u003e\u003cspan address=\"http://doi:10.1590/0104-6632.20180352s20160654\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSusanti JGM, Winkelman B, Schuur HJ, Heeres J, Yue (2016) Lactic Acid Extraction and Mass Transfer Characteristics in Slug Flow Capillary Microreactors. Ind Eng Chem Res 55:4691\u0026ndash;4702. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acs.iecr.5b04917\u003c/span\u003e\u003cspan address=\"10.1021/acs.iecr.5b04917\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSingh S, Mohan R, Gosu V, Kumar UKA (2020) Process Intensification of Propionic Acid Extraction and its Recovery by Distillation in Microchannel. Chem Eng Process 157:108150. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi:10.1016/j.cep.2020.108150\u003c/span\u003e\u003cspan address=\"http://doi:10.1016/j.cep.2020.108150\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarcia-Chavez LY, Schuur B, De Haan AB (2013) Conceptual process design and economic analysis of a process based on liquid-liquid extraction for the recovery of glycols from aqueous streams. Ind Eng Chem Res 52:4902\u0026ndash;4910. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/ie303187x\u003c/span\u003e\u003cspan address=\"10.1021/ie303187x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi H, Na J, Cong H, Wu L, Zhao L, Li X, Gao X (2020) Thermodynamics Foundation and Separation Process Design for Production of Propionic Acid from Ethanol Carbonylation Catalyzed by Iodide. Ind Eng Chem Res 59:6090\u0026ndash;6101. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acs.iecr.9b06505\u003c/span\u003e\u003cspan address=\"10.1021/acs.iecr.9b06505\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArora R (2013) Distributive Distillation Enabled by Microchannel Process Technology, United States, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2172/1077001\u003c/span\u003e\u003cspan address=\"10.2172/1077001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"brazilian-journal-of-chemical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bjce","sideBox":"Learn more about [Brazilian Journal of Chemical Engineering](http://link.springer.com/journal/43153)","snPcode":"43153","submissionUrl":"https://www.editorialmanager.com/bjce/default2.aspx","title":"Brazilian Journal of Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Propionic acid, solvent extraction, Multistage Extraction, liquid-liquid slug flow, mass transfer coefficient","lastPublishedDoi":"10.21203/rs.3.rs-3786779/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3786779/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSolvent extraction is an important industrial operation where several stages are needed for a desired separation. Microchannel based solvent extraction is widely reported for process intensification. However, all these works are confined to a single-stage extraction till date. For industrial application knowledge of multistage extraction is mandatory. This work focuses on the multistage microchannel extraction using a model mixture containing aqueous propionic acid. Four different single solvents were employed in this study hexane, toluene, heptane, and cyclohexanol. The Effect of flow rate, flow ratio on percentage extraction, extraction efficiency, and the required number of stages was investigated. The number of stages required for the maximum recovery of PA from the raffinate is 5 for hexane \u0026amp;heptane and 3 for toluene and 2 for cyclohexanol. The percentage extraction of solvents obtained overall through all the stages is, cyclohexanol, 57\u0026ndash;89%, toluene, 35\u0026ndash;50%, heptane, 27\u0026ndash;51%, and hexane 19-31.3%. Cyclohexanol produced the maximum percentage extraction. The extraction efficiency and the volumetric mass transfer coefficient decreased with the stage numbers. The maximum extraction efficiency for all the solvents is in the range of 98-99.8%. A microchannel stack is found to reduce the total annual cost (TAC). Particularly, fabrication in India results in very less capital cost for the microchannels i.e.1.9\u0026ndash;14.3% of TAC. The total annual cost analysis of toluene is the minimum than other solvents.\u003c/p\u003e","manuscriptTitle":"Microchannel based Multistage Solvent Extraction Studies for the Separation of Propionic Acid from its Aqueous Mixture using Hydrocarbon Solvents","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-11 06:07:16","doi":"10.21203/rs.3.rs-3786779/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2024-02-09T14:19:58+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-01-08T18:59:58+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Brazilian Journal of Chemical Engineering","date":"2023-12-22T20:23:02+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2023-12-22T04:29:18+00:00","index":"","fulltext":""},{"type":"submitted","content":"Brazilian Journal of Chemical Engineering","date":"2023-12-20T05:30:54+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"brazilian-journal-of-chemical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bjce","sideBox":"Learn more about [Brazilian Journal of Chemical Engineering](http://link.springer.com/journal/43153)","snPcode":"43153","submissionUrl":"https://www.editorialmanager.com/bjce/default2.aspx","title":"Brazilian Journal of Chemical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"5a88f870-6009-4f9e-b636-12036cdeaf07","owner":[],"postedDate":"January 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2024-01-11T06:07:16+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-11 06:07:16","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3786779","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3786779","identity":"rs-3786779","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}