SO2-ethanol-water Research Articles

Influence of spent liquor obtained from SO2–ethanol–water (SEW) fractionation of Eucalyptus on drifting sands stabilization

Abstract The utilization of mulch stands as a paramount approach in the management of wind erosion and the stabilization of soil and drifting sands. This study aimed to explore the impact of various concentrations of spent liquor (20 %, 30 %, and 50 % v/v) derived from SO2–ethanol–water (SEW) fractionation of Eucalyptus wood on the physical and mechanical properties of sand. These properties encompassed moisture content, thickness, temperature, electrical conductivity (EC), wind erodibility, penetration resistance, and seed germination. The findings revealed that the highest compressive strength (0.76 MPa) was attained with mulch consisting of 50 % SEW spent liquor, resulting in a 3.3-fold increase in penetration resistance compared to the control treatment. Furthermore, the 20 % concentration of spent liquor did not adversely affect the germination of black saxaul (Haloxylon ammodendron), whereas the lowest seed germination rate was associated with the 50 % concentration. Based on the measured parameters, the optimal mulch treatment for stabilizing drifting sands was identified as mulch with a 50 % (v/v) concentration. This study underscores the efficacy of SEW spent liquor in dust control and mitigating its environmental impacts, thus highlighting its potential in sustainable soil management practices.

Transforming non-wood feedstocks into dissolving pulp via organosolv pulping: An alternative strategy to boost the share of natural fibers in the textile industry.

This work evaluates wheat straw, switchgrass, and hemp hurd as potential alternatives for producing dissolving pulp using sulfur dioxide (SO2)-ethanol-water (SEW) pulping. The SEW process is described in detail for wheat straw, and the best pulping conditions for this feedstock were 130 °C, 4 h, and 10% SO2 concentration, comprised in a sulfur-ethanol-water ratio of 10-45-45. This resulted in a viscose-grade pulp with 93% α-cellulose, 2.0% hemicelluloses, <0.1% lignin, 0.2% ash content, and a viscosity of 4.7 cP. The best pulping conditions for wheat straw were applied to switchgrass and hemp hurd. Wheat straw and switchgrass had similar pulp quality, while hemp hurd pulp had a higher hemicellulose content and lower viscosity. This work suggests that non-wood feedstocks such as wheat straw and switchgrass can be promising alternatives for dissolving pulp production, which can help reduce the pressure on the textile industry to increase the use of natural fibers and mitigate the environmental impact of non-biodegradable synthetic fibers.

SO2-ethanol–water (SEW) and Kraft pulp and paper properties of Eldar pine (Pinus eldarica): a comparison study

SO2-ethanol–water (SEW) and Kraft pulp and paper properties of Eldar pine (Pinus eldarica): a comparison study

Production of dissolving grade pulp from tobacco stalk through SO2-ethanol-water fractionation, alkaline extraction, and bleaching processes

The objective of this study was to evaluate the possibility of producing dissolving grade pulp from tobacco stalk through combining SO2-ethanol-water (SEW) fractionation, alkaline extraction, and bleaching with oxygen (O), chlorine dioxide (D), alkaline extraction with hydrogen peroxide (Ep), and hydrogen peroxide (P) (OD0(Ep)D1P). The results showed that the optimum SEW cooking condition to remove the original xylan and lignin in tobacco stalk to an acceptable level was 6% SO2 charge (by weight) at 135 °C for 180 min. A bleachable pulp (Kappa number of 21.5) was produced from the SEW-treated tobacco stalk via a subsequent 1% NaOH extraction. After the OD0(Ep)D1P sequence bleaching, the bleached pulp showed a high brightness (88.1% ISO) and a high α-cellulose content (94.9%). The viscosity (15.8 cP) and the residual xylan content (4.4%) of the pulp were within acceptable levels for dissolving pulp production. Thus, tobacco stalk was shown to be a viable raw material for dissolving pulp production following a SEW treatment, alkaline extraction, and a conventional bleaching sequence.

How properties of cellulose acetate films are affected by conditions of iodine-catalyzed acetylation and type of pulp

The present study has been carried out to consider the effect of acetylation conditions and type of bleached pulps [Kraft and SO2–ethanol–water (SEW) pulps] on the properties of obtained cellulose acetates (CA) and their films. The acetylation reaction in the absence of solvent was performed by using acetic anhydride and iodine as a catalyst. The efficiency of acetylation and the degree of substitution, crystallinity, transparency, tensile strength, young modulus, differential scanning calorimetry, water vapor permeability (WVP), scanning electron microscope and atomic force microscopy images were studied. The results showed that the while the Young’s modulus and transparency increased by up to 8% of the catalyst due to the increase in iodine charge; higher iodine levels led to embrittlement of the film. The increase in the ratio of acetic anhydride to pulp (A:P) from 10:1 to 20:1 with 4% catalyst led to a reduction of the DS by 8–10%, the crystallinity by 25%, the Young’s modulus by 13–25%, and transparency by 1–34% of a CA obtained from SEW and Kraft pulp, respectively. With the use of higher amounts of the catalyst (8%) and a ratio of A:P equal to 20:1, all properties of CA were suitable for film preparation. WVP of films from Kraft pulp and SEW pulp showed a decrease of about 8.5% and 18% respectively when increasing the iodine amount from 4 to 8% in acetylation. The tensile strength of CA films was initially increased by enhancing the amount of iodine, but then reduced in a similar way to other properties. The condition of acetylation can be adjusted to produce a high-quality CA film according to the characteristics of the pulp used as raw material.

Influence of sulfur dioxide-ethanol-water pretreatment on the physicochemical properties and enzymatic digestibility of bamboo residues

SO2-ethanol-water (SEW) is a promising pretreatment for improving enzymatic digestibility of biomass through simultaneously removing hemicellulose and lignin. In this work, SEW pretreatment was performed at different cooking times (10 min–60 min) and different SO2 concentrations (0.5%–2%) to produce pretreated bamboo residues for enzymatic hydrolysis. Meanwhile, physicochemical features of the residual cellulose and lignin were analyzed to better understand how SEW improves enzymatic digestibility. Under optimized SEW pretreatment condition (1% SO2 concentration, 150 °C, 60 min), 81.7% of xylan and 80.3% of lignin were solubilized, along with 89.1% of cellulose preserved in pretreated solid. A good enzymatic digestibility (80.4%) was achieved at optimum SEW condition. Several compelling correlations (R2 > 0.7) were observable between enzymatic digestibility and physicochemical features, demonstrating the importance of SEW pretreatment abilities of hemicellulose and lignin removal, reducing cellulose’s degree of polymerization, and improving the amount of sulfonyl groups imparted to the original lignin structure.

SO2–ethanol–water (SEW) and kraft pulping of giant milkweed (Calotropis procera) for cellulose acetate film production

SO2–ethanol–water (SEW) fractionation and kraft pulping were applied to produce pulp from stem chips of Calotropis procera. The two pulps with different purities of cellulose were used for the production of cellulose acetate (CA) films. The motivation of this study was to investigate the possibility to produce high-quality cellulose CA films from low-grade pulp. The results showed that SEW pulping was more efficient in the selective removal of lignin and hemicelluloses from Calotropis procera wood as compared to kraft pulping. There, the pulping intensity was enhanced by increasing the H-factor to reach low lignin and hexenuronic acid (HexA) concentrations. However, a relatively high amount of alkali-insoluble xylan remained in the bleached kraft pulp and also the HexA content could not be fully removed during ECF-bleaching. In contrast, xylan was readily removed during SEW pulping and only a small amount of HexA (8.6 meq/kg) was observed in the pulp. High weight gains of about 55 and 63% were obtained during acetylation of kraft pulp and SEW pulp, respectively indicating a high degree of substitution (DS). The CA films prepared from both kraft and SEW pulps revealed higher transparency (88.0 and 88.5%), tensile stress (109 and 146 MPa) and modulus (4.6 and 5.6 GPa) as reported by previous studies. The results confirmed that CA films can be produced from SEW or kraft pulps through iodine catalysis showing similar properties than those obtained from high-purity dissolving pulps.

Heat Treatment of Spent Liquors to Recover Chemically Bound Xylose and Alcohol

SO2–ethanol–water (SEW) and SO2–isopropanol–water (SPW) spent liquors are obtained by fractionating sugarcane straw. The SEW and SPW liquors contain significant amounts of chemically bound xylose as ethyl xylosides (EX) and isopropyl xylosides (PX) respectively. The liquors are subjected to a constant temperature heat treatment to hydrolyze the alkyl xylosides to allow full recovery of xylose and alcohol. Complete hydrolysis of EX and PX is achieved at 121 °C in 70 and 30 min, respectively. The first-order kinetics of EX and PX hydrolysis are determined at temperatures from 100 to 121 °C. At full hydrolysis of the alkyl xylosides, the quantity of alcohol produced is greater than stoichiometric. Other sources of covalently bound alcohols in the spent liquors are identified to explain the excess alcohol produced.

Lignin and ash balances of sulfur dioxide-ethanol-water fractionation of sugarcane straw

Lignin and ash material balances of SO2-ethanol–water (AVAP®) fractionation of sugarcane (SC) straw were thoroughly studied at various conditions. Most of straw lignin and ash dissolve in the liquor and 40–80% of lignin is precipitated after ethanol removal as a pure (∼99%) and sulfur-lean (<2%) fraction. Most of the acid-soluble ash and its elements (Na, K, Fe, Al) as well as large portion of silica are removed from the fiber phase. Straw lignin behavior exhibited differences compared to wood lignin including high apparent content in fiber, higher degree of sulfonation of dissolved lignin, and dense char-like precipitate formation upon ethanol removal. Variation in fractionation conditions did not have significant effect on lignin properties, while post-sulfonation was capable of changing its form from char-like to colloidal precipitate.

Ethyl xylosides formation in SEW (AVAP®) fractionation of sugarcane straw; implications for ethanol and xylose recovery

Abstract High solvent recovery and monomeric sugar yield are essential for a viable biochemical conversion technology. The SO2-ethanol-water (SEW) or AVAP® process has great potential to produce easily fermentable pulp fibers and sugars dissolved in the spent liquor stream. The SEW fractionation process is evaluated for delignification, xylan removal and potential reactions between ethanol and sugarcane straw (SCS) carbohydrates. α-ethyl-xyloside (aEX) and β-ethyl-xyloside (bEX) formed by reaction of ethanol with xylose are quantified. The fractionation experiments are carried out at 135°C, 145°C, and 155°C for 20–120 min at fixed liquor composition (SO2/EtOH/H2O=12:44:44, w/w) and liquor to feedstock ratio (4 l kg−1). The results are interpreted in terms of combined severity factor (CSF). Maximum ethyl xylosides (EX, or sum of aEX and bEX) and monomeric xylose concentrations are observed at CSF of 2.4±0.1. The maximum amount of EX in spent liquor accounts for nearly 1.4% of EtOH (feedstock basis). The implications for downstream recovery of EtOH and sugars from the spent liquor are discussed.

Comparison of Reactive Distillation and Dual Extraction Processes for the Separation of Acetone, Butanol, and Ethanol from Fermentation Broth

Two processes, reactive distillation (RD) and dual extraction (DE), were presented and compared for the separation and purification of acetone, butanol, and ethanol (ABE) from fermentation broth. Reactive distillation produces all the extraction solvents needed from the fermentation products, while dual extraction utilizes extremely effective but nonbiocompatible solvents in extraction. In this work, these processes were simulated using Aspen Plus. The sugars consumed in the ABE fermentation were produced using SO2–ethanol–water (SEW) pulping from lignocellulosic biomass. According to the simulations, DE was more energy efficient of these two processes with energy consumption of 4.97 and 6.12 MJ kg–1 for all products and butanol, respectively. RD consumed 11.02 and 15.98 MJ kg–1 for all products and butanol, respectively. According to the economic analysis, the total investment costs were very similar for both of the processes. The DE process, with its slightly higher sales revenue, proved to be a more ec...

Genetic engineering of Clostridium acetobutylicum to enhance isopropanol-butanol-ethanol production with an integrated DNA-technology approach

Acetone being a non-fuel solvent produced during the traditional acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum; reduces the overall fuel alcohol yield. However, the conversion of acetone into isopropanol has been recommended to improve the process economy. The present study aims to develop an engineered C. acetobutylicum DSM 792 strain to convert acetone into isopropanol by introducing the secondary alcohol dehydrogenase gene from Clostridium beijerinckii NRRL B593 using the allele-coupled exchange approach. Batch and continuous fermentation experiments were carried out with a modified strain C. acetobutylicum DSM 792-ADH to improve the isopropanol yield and titer. The growth and production behavior of the modified strain in stationary flask culture and controlled batch culture was studied. Almost 50% of acetone was converted into isopropanol with highest total solvent yield to be 0.39 g g−1 glucose. The modified strain also utilized sugar mixture and SO2–ethanol–water spent liquor as a substrate to produce the solvents.

The effect of chemical and physical characteristics of spruce SEW pulps on enzymatic hydrolysis

Conifers, which are the most abundant biomass species in Nordic countries, USA, Canada and Russia, exhibit strong resistance towards depolymerization by cellulolytic enzymes. At present, it is still not possible to isolate a single structural feature which would govern the rate and degree of enzymatic hydrolysis. On the other hand, the forest residues alone represent an important potential for biochemical production of biofuels. In this study, the effect of substrate properties on the enzymatic hydrolysis of softwood was studied. Stem wood spruce chips were fractionated by SO2–ethanol–water (SEW) treatment to produce pulps of varying composition by applying different operating conditions. The SEW technology efficiently fractionates different types of lignocellulosic biomass by rapidly dissolving hemicelluloses and lignin. Cellulose remains fully in the solid residue which is then treated by enzymes to release glucose. The differences in enzymatic digestibility of the spruce SEW pulp fibers were interpreted in terms of their chemical and physical characteristics. A strong correlation between the residual lignin content of SEW pulp and enzymatic digestibility was observed whereas cellulose degree of polymerization and hemicellulose content of pulp were not as important. For the pulps containing about 1.5 % (w/w) lignin, 90 % enzymatic digestibility was achieved at 10 FPU enzyme charge and 24 h of hydrolysis time.

Enzymatic hydrolysis of hardwood and softwood harvest residue fibers released by sulfur dioxide–ethanol–water fractionation

The enzymatic hydrolysis of hardwood and softwood harvest residues treated by SO2–ethanol–water (SEW) fractionation was studied. The target was to convert these fibers with high yield into glucose monomers which could be further converted into biofuel by a subsequent fermentation stage. Hardwood biomass residues were efficiently digested at low enzyme dosage (5FPU/g cellulose) whereas the softwood residues required notably higher enzyme dosage (20FPU) for sufficient conversion. However, cellulase dosage of softwood could be reduced mannanase supplementation. Especially the high lignin content of softwood biomass pulps impairs the digestibility and thereby, improved delignification could notably enhance the hydrolysis yields. It was shown that inferior delignification of SW biomass is due to persistent polyphenolic acids present in coniferous bark, whereas no evidence of the negative effect of inorganics and acetone extractives was observed. Additionally, SW hydrolyzate was successfully converted into a mixture of butanol, acetone and ethanol through ABE fermentation.

The effect of bark on sulfur dioxide–ethanol–water fractionation and enzymatic hydrolysis of forest biomass

The focus of this study was to find out the effect of bark on SO2–ethanol–water (SEW) fractionation and enzymatic hydrolysis of forest biomass. Softwood bark was found to be more harmful than hardwood bark in both processes. For softwood, the amount of undigested wood in SEW fractionation increased with the increasing bark content, whereas the hardwood bark did not impair the fractionation of wood. The higher the softwood bark content was the lower were the yields in enzymatic hydrolysis likely due to the unproductive binding of enzymes on lignin and other compounds. Addition of surfactant Tween 20 (2% w/w on substrate) prior to enzyme more than doubled the sugar yield of bark-rich softwood pulp. Hardwood bark impaired enzymatic hydrolysis when its share was over 28%. According to a preliminary study, lignosulfonates from the carry-over liquor seem to improve the sugar yield in the enzymatic hydrolysis by acting as a surfactant.

A Kinetic Study of CO2 and Steam Gasification of Char from Lignin Produced in the SEW Process

The reaction kinetics of gasification are important for the design of gasifiers using biomass feedstocks, such as lignin, produced in biorefinery processes. Condensed and uncondensed lignin samples used in the present study were prepared using the SEW (SO2-ethanol-water) fractionation process applied to spruce wood chips: the dissolved lignin is precipitated during the recovery of SO2 and ethanol from the spent fractionation liquor. The gasification of char made from condensed and uncondensed SEW lignin was investigated using thermogravimetric analysis (TGA) at atmospheric pressure using either CO2 or steam. The main aim of this study was to quantify the reaction rate during the gasification process, which was found to be best described as zero-order. All experiments were performed at constant temperatures between 700 and 1050 °C to obtain the necessary information for describing the reaction rate equation in an Arrhenius form; the heating rate was 20 °C/min for both samples. The experiments led to almost similar results for both samples. The activation energies of CO2 gasification were approximately 160 kJ/mol and 170 kJ/mol for uncondensed and condensed lignin char, respectively. The activation energies of steam gasification were approximately 90 kJ/mol and 100 kJ/mol for uncondensed and condensed lignin char, respectively.

Effects of residual lignin and heteropolysaccharides on the bioconversion of softwood lignocellulose nanofibrils obtained by SO2–ethanol–water fractionation

The amount of residual lignin and hemicelluloses in softwood fibers was systematically varied by SO2-ethanol-water fractionation for integrated biorefinery with nanomaterial and biofuel production. On the basis of their low energy demand in mechanical processing, the fibers were deconstructed to lignocellulose nanofibrils (LCNF) and used as substrate for bioconversion. The effect of LCNF composition on saccharification via multicomponent enzymes was investigated at different loadings. LCNF digestibility was compared with the enzyme activity measured with a quartz crystal microbalance. LCNF hydrolysis rate gradually decreased with lignin and hemicellulose concentration, both of which limited enzyme accessibility. Enzyme inhibition resulted from non-productive binding of proteins onto lignin. Near complete LCNF hydrolysis was achieved, even at high lignin and hemicellulose content. Sugar yields for LCNF were higher than those for precursor SEW fibers, highlighting the benefits of high surface area in LCNF.

SO2–ethanol–water (SEW) fractionation process: production of dissolving pulp from spruce

SO2–ethanol–water (SEW) fractionation process is a highly attractive platform for future lignocellulosic Biorefineries. Its governing advantages include high flexibility in the selection of the raw material, simple and efficient recovery of fractionation chemicals, absence of carbohydrate degradation (both cellulose and hemicelluloses), and high reaction rates. The process is suitable for production of various carbohydrate- and lignin-based products including papermaking pulp, glucose, bioalcohols and lignosulfonates. The present paper addresses the possibility of producing dissolving pulp from spruce using SEW fractionation followed by ECF bleaching with and without hot caustic extraction. Comprehensive characterisation of chemical and macromolecular properties of the SEW dissolving pulps was complemented by determining the quality of viscose. The comparison with conventional viscose-grade acid sulfite pulps revealed close proximity in all properties. Therefore, considering the advantages of SEW process, it is suggested as a possible replacement for acid sulfite process in dissolving pulp manufacturing.

Kinetics of SO2–ethanol–water (SEW) fractionation of hardwood and softwood biomass

SO(2)-ethanol-water (SEW) fractionation of forest residues (tree tops, stumps, branches) was investigated to demonstrate the potential of this method for forest biorefineries. The effect of fractionation time on dissolution of wood components was studied. Total mass balances of fractionation show that lignin and hemicelluloses are rapidly dissolved in the spent fractionation liquor whereas cellulose is fully preserved in the solid residue throughout the fractionation treatment. Within 20min treatment at 150°C (SO(2):EtOH:H2O=12:43.5:44.5, by weight, L:W ratio 6Lkg(-1)), 89% of hardwood lignin and 74% of hemicelluloses are dissolved. The corresponding values for softwood biomass are 64% and 74%, respectively, indicating slower delignification but equal hemicellulose removal. Additionally, sulfur content of the feedstocks, solid fractionation residues and spent liquors were analyzed to determine the degree of lignin sulfonation. The obtained results are compared with the stem wood fractionation results.

SO2–ethanol–water (SEW) fractionation of spruce: kinetics and conditions for paper and viscose-grade dissolving pulps

The study describes SO2–ethanol–water fractionation of spruce as a promising basis for future Biorefineries. The dissolution kinetics of lignin and hemicelluloses as well as the depolymerisation kinetics of cellulose during the fractionation process are expressed in terms of the H-factor, a parameter combining fractionation temperature and duration. The raw material moisture content is shown to have a very small effect on the fractionation kinetics. The liquor-to-wood ratio has little effect on the process during the (delignification) bulk phase, while in the residual phase the effect becomes pronounced. During the latter phase, lower liquor-to-wood ratios lead to higher residual lignin content, lower residual hemicelluloses and pulp viscosity, but higher hemicelluloses removal selectivity. Higher delignification rates and selectivities are obtained at ethanol-to-water ratios close to 1 : 1 (w/w) and high SO2 concentrations (≥12 w/w%). Based on the presented data, the optimum fractionation conditions for the production of paper and viscose-grade dissolving pulps are quantified.