Cellulose Recovery Research Articles

High-efficient cellulosic butanol production from deep eutectic solvent pretreated corn stover without detoxification

Biobutanol is one of the most promising renewable biofuels, which can be produced from lignocellulosic biomass by Clostridium. However, due to the dense structure of lignin, biomass is difficult to be hydrolyzed into fermentable sugars. This study has developed a short time (90 min) and low energy consumption (120 °C) pretreatment process using deep eutectic solvent (DES). Importantly, the cellulose recovery of treated corn stover (CS) after DES pretreatment at 120 °C was 99.24 %, while the removal of xylan and lignin reached 57.58 % and 61.40 %, respectively. The total sugars released from treated CS at 120 °C reached 37.94 g L−1 (glucose: 30.59 g L−1; xylose: 7.35 g L−1) at a low enzyme loading of 7.5 filter paper unit (FPU) g−1 pretreated CS. Furthermore, the DES treated CS hydrolysate was successfully used to produce butanol by Clostridium beijerinckii P260 without any detoxification and sterilization, thus producing 13.65 g L-1 total acetone-butanol-ethanol (ABE) with a high productivity (0.68 g L-1 h−1) and yield (0.38 g g−1). Overall, the present work provides a new insight into the efficient application of DES systems in lignocellulose biomass biorefinery.

Alternative Lime Pretreatment of Corn Stover for Second-Generation Bioethanol Production

In this work, a delignification process, using lime (Ca(OH)2) as an alternative alkali, was evaluated to improve enzymatic saccharification of corn stover cellulose, with the final goal of obtaining second-generation bioethanol. For that, an experimental design was conducted in order to assay the effect of temperature, lime loading, and time on the corn stover fractionation and enzymatic susceptibility of cellulose. Under conditions evaluated, lime pretreatment was selective for the recovery of cellulose (average of 91%) and xylan (average of 75.3%) in the solid phase. In addition, operating in mild conditions, a delignification up to 40% was also attained. On the other hand, a maximal cellulose-to-glucose conversion (CGCMAX) of 89.5% was achieved using the solid, resulting from the treatment carried out at 90 °C for 5 h and lime loading of 0.4 g of Ca(OH)2/g of corn stover. Finally, under selected conditions of pretreatment, 28.7 g/L (or 3.6% v/v) of bioethanol was produced (corresponding to 72.4% of ethanol conversion) by simultaneous saccharification and fermentation. Hence, the process, based on an alternative alkali proposed in this work, allowed the successful production of biofuel from the important and abundant agro-industrial residue of corn stover.

Sequential pretreatment of sugarcane bagasse by alkali and organosolv for improved delignification and cellulose saccharification by chimera and cellobiohydrolase for bioethanol production.

The online version contains supplementary material available at 10.1007/s13205-020-02600-y.

Development of non-derivatizing hydrate salt pre-treatment solvent for pre-treatment and fractionation of corn cob

Major concern in beneficiating lignocellulose is overcoming biomass recalcitrance through pre-treatment. Molten hydrate salts (MHS) is a green solvent with ability to swell and dissolve cellulose and biomass in a non-derivatizing way. Over the last decade, MHSs have been used for isolated cellulose dissolution, however very few studies have been reported on their effectiveness in pre-treating lignocellulosic biomass. Therefore, effectiveness of their application as solvent for pre-treating and fractionating corn cob is presented in this article. In this study, seven molten hydrate salt pre-treatment solvent systems such as unary, binary and ternary mixtures of ZnCl2.4H2O, LiClO4.3H2O and Urea were investigated for their ability to pre-treat and fractionate biomass. The pre-treatment experiments were carried out in a shaking incubator at 70°C for 60 minutes at a biomass: solvent ratio of 1:10. The surface chemistry of the biomass was checked before and after pre-treatment using Fourier Transform infrared spectroscopy. X-ray diffraction and scanning electron microscopy were employed to check the crystallinity and surface morphology of the biomass. Physicochemical analysis consistently indicated a disruption in the structure of corncob due to removal of lignin and hemicellulose during the pre-treatment process. Additionally, results showed a decrease in crystallinity and a change in surface morphology after the pre-treatment using all the seven solvent systems (MHS solvents). The use of ZnCl2.4H2O/ Urea solvent displayed 100% recovery of cellulose, 42% recovery of hemicellulose and 44% recovery of lignin from the corn-cob when compared to the performance of the other proposed solvent systems in this study.

OBTAINING AN ANALYTICAL DEPENDENCE OF THE STRENGTH PROPERTIES OF PAPER ON THE PAPER-FORMING PARAMETERS OF THE FIBROUS MASS

Wood is of great practical importance as a starting material for the recovery of cellulose. Wood plays not only an important economic role as a building and finishing material, but is also one of the cheapest and most widely used raw materials for the industrial production of cellulose vines. In turn, the grinding equipment serves to divide the cellulosic materials into fibers, from the grinding of the fibers and imparting certain properties to them. One of the most important properties of paper is mechanical strength. The standard provides for certain requirements for different types of paper, depending on the consumer conditions for the use of finished products. Durability of paper is determined by various indicators characterizing: paper resistance to a gap, breakdown, tear, an anguish, lengthening to a gap. In this work, the role of milling of fibrous materials in the general preparatory cycle of pulp and paper production is considered, the advantages of knife-free milling are presented, the factors determining the strength of paper are considered, functional dependencies of the main physical and mechanical characteristics of the finished product on the complex parameter of the quality of pulp milling and the complex parameter of the machine are obtained. Numerical value of complex parameter of grinding quality is determined depending on duration of grinding.

Effect of sequential pretreatment combinations on the composition and enzymatic hydrolysis of hazelnut shells

Hazelnut shells, a high lignin containing biomass, were subjected to individual and sequential liquid hot water (LHW), alkaline (AP) and dilute acid pretreatments (DAP). Among the single pretreatments, LHW demonstrated the highest cellulose recovery of 98.1%, DAP resulted in the highest hemicellulose solubilization of 56.0%, and AP of the highest lignin removal of 49.6%. Employing two-step pretreatment on hazelnut shells, in general, demonstrated an enhanced action of the second pretreatment; therefore, the sequence of the pretreatment methods had a significant impact on both substrate characteristics and enzymatic hydrolysis efficiency of biomass. In terms of delignification, AP-LHW achieved 60.7% lignin removal, while LHW-DAP showed the highest hemicellulose removal of 93.8% and DAP-LHW resulted in the highest cellulose recovery of 94.0%. Structural properties of raw and pretreated hazelnut shells were observed by FTIR. The maximum glucose recovery of 54.9% was observed in DAP-LHW pretreated samples. For this pretreatment combination, almost 1.8 MJ total energy was required to recover 10.2 g glucose. The findings indicated that complete removal of the physical barrier of lignin and hemicellulose might not be essential; partial relocation of lignin and alteration of cellulose structure may also be efficient in increasing the sugar recovery from the lignocellulosic biomass.

Implementation of Auto-Hydrolysis Process for the Recovery of Antioxidants and Cellulose from Wheat Straw

Wheat straw is an easily affordable, cost-effective and natural source of antioxidants and cellulose, but its full potential is not yet utilized. In the present investigation, an auto-hydrolytic process was applied to recover both antioxidant phenolic compounds and cellulose from wheat straw. Two three-step acid/alkaline fractionation processes were applied differing for the first step: a conventional mild acid hydrolysis or an auto-hydrolysis. The liquors from the first step were analyzed for the recovery of antioxidants, while the final residues from the whole process were analyzed for cellulose yield and purity. The auto-hydrolysis process led to a higher yield in antioxidants but also in sugars (glucose and xylose) and sugar degradation products (5-HMF, 5-MF, furfural) than the acid hydrolysis process. The overall cellulose recovery (about 45% g/100 gcellulose wheat straw dm) and purity was comparable in the two processes; therefore, the auto-hydrolysis-based process could be recommended as a potentially more environmentally friendly process to recover antioxidants and cellulose from wheat straw for different applications. Finally, a first study on the optimization of hydrolysis step was provided from the point of view of improving the cellulose yield, monitoring the sugars release during both the acid hydrolysis and the auto-hydrolysis process.

Water-Soluble Sugars of Pedigreed Sorghum Mutant Stalks and Their Recovery after Pretreatment

Chemical composition of biomass, especially carbohydrate content, is a critical indicator of a biomass source’s potential for biofuel applications. This study characterized physico-chemical properties of stalks from 16 representative pedigreed sorghum mutant lines. The objectives of this study were to evaluate the recovery of sucrose and its hydrolysis products, glucose and fructose, during dilute sulfuric acid pretreatment at conditions typically used for lignocellulosic biomass, and to determine the relationship between water-extractive contents and sugar recovery after pretreatment. Dilute acid-pretreated sorghum stalks had enzymatic saccharification of >82.4% glucose yield for all treated samples with more than 82.3% cellulose recovery and 85% hemicellulose removal. A single-step, one-pot process was recommended for sorghum mutant stalks with low water-extractive content (<35%, w/w) to reduce processing cost and minimize wastewater disposal since the majority of sugars will be recovered after dilute acid pretreatment with minimal degradation products. However, for sorghum mutant stalks with high water-extractive content (>35%, w/w), a pre-washing step is beneficial to recover the water-soluble sugars before subjecting to the pretreatment process in order to avoid sugar losses during the pretreatment stage. Thus, different processing technologies should be applied to lignocellulosic biomass with various water-extractive contents and water-soluble sugar concentrations.

Rapid fractionation of various lignocellulosic biomass using gamma-valerolactone

Organosolv fractionation of eucalyptus sawdust using γ-valerolactone (GVL) was optimised to maximise cellulose recovery and enhance the economics of the process. Results showed a pretreated biomass (PB) of 88.3% w/w cellulose could be achieved within 10 min using 56% w/w GVL at 167 °C. To assess potential correlation between the lignocellulosic material composition and effectiveness of the rapid GVL pretreatment, six lignocellulosic biomass, including two sawdust, forestry waste, garden waste, wheat straw and rice straw, were pretreated. The fractionation process favoured sawdust compared to other biomass, where sawdust, forestry waste, garden waste and straws resulted in PB of cellulose content of 81.9–85.8%, 76.4%, 71.9% and 55.5–66.3% w/w, respectively. This trend indicated cellulose recovery correlated with the initial cellulose to lignin (C/L) ratio. PB produced using GVL fractionation had increased cellulose crystallinity. Organosolv using GVL demonstrated high potential for rapid fractionation of sawdust, producing PB of high cellulose content.

Multivariate analysis as a tool for selecting the vine pruning pretreatment towards the highest enzymatic hydrolysis yield

Lignocellulosic materials require pretreatment to remove lignin enabling the enzyme access to the cellulose. This work used multivariate analysis to investigate the acid and alkali pretreatments of vine pruning followed by enzymatic hydrolysis. The best acid pretreatment conditions were H2SO4 1.5%, 120 °C for 30 min, removing 68.7% of hemicellulose, enabling 95.8% of cellulose recovery. However, this treatment was not enough to allow the enzyme hydrolysis. A second step of treatment with NaOH 3.0% at 120 °C without agitation for 60 min led to a material with 75.0% of cellulose and 25.0% of lignin. However, the lowest glucose yield (80.86% and 32.26 g L−1 of glucose) was obtained after the enzyme hydrolysis of this material. The highest glucose yield (98.72% with 35.06 g L−1) was obtained using a pretreated material containing 68.1% of cellulose and 31.9% of lignin obtained after a milder condition (NaOH 2% at 100 °C), thus showing that not all the lignin need to be removed to obtain a high saccharification yield. A less severe pretreatment with no adverse effect on the glucose yield with the advantage of preserving the non-cellulose biomass fractions was effective for vine prune valorization.

OxiOrganosolv: A novel acid free oxidative organosolv fractionation for lignocellulose fine sugar streams

The valorization of lignocellulosic biomass towards the production of value-added products requires an efficient pretreatment/fractionation step. In this work we present a novel, acid-free, mildly oxidative organosolv delignification process -OxiOrganosolv- which employs oxygen gas to depolymerize and remove lignin. The results demonstrate that the OxiOrganosolv process achieved lignin removal as high as 97% in a single stage, with a variety of solvents; it was also efficient in delignifying both beechwood (hardwood) and pine (softwood), a task in which organosolv pretreatments have failed in the past. Minimal amounts of sugar degradation products were detected, while cellulose recovery was ~100% in the solid pulp. Enzymatic hydrolysis of pulps showed >80 wt% cellulose conversion to glucose. Overall, the OxiOrganosolv pretreatment has significant advantages, including high delignification efficiency of hardwood and softwood biomass, absence of acid homogeneous catalysis and all corresponding challenges involved, and close to zero losses of sugars to degradation products.

Ultrasound-assisted alkaline pre-treatment and its sequential combination with microwave for fractionation of pistachio shell

Ultrasound-assisted alkaline pre-treatment (UAAP) and its sequential combination with microwave (SUMAAP) were performed for fractionation of pistachio shell and compared with conventional alkaline pre-treatment (CAP). The pre-treatment conditions were investigated and optimized using Box-Behnken design for maximum hemicellulose and cellulose recoveries. Under optimum conditions, the hemicellulose and cellulose recoveries were 57.67% and 94.05% for UAAP and 66.14% and 90.78% for SUMAAP, while these values were 16.28% and 98.70% after CAP, respectively. The compositional analysis showed that the xylo-oligosaccharides were the main components in liquid phases, while the solid phases were enriched in cellulose. Furthermore, a significant increase in enzymatic hydrolysis yield of pre-treated solids was obtained compared to the raw pistachio shell. Thus, the UAAP was proved to be a reliable and efficient process for pistachio shell pre-treatment and its sequential combination with microwave provide further increase in pre-treatment efficiency while reducing the processing time and alkali requirement.

Recovery of High Purity Lignin and Digestible Cellulose from Oil Palm Empty Fruit Bunch Using Low Acid-Catalyzed Organosolv Pretreatment

The lignocellulosic residue from the palm oil industry, oil palm empty fruit bunch (OPEFB), represents a challenge to both producing industries and environment due to its disposal difficulties. Alternatively, OPEFB can be used for the production of valuable products if pretreatment methods, which overcome OPEFB recalcitrance and allow tailored valorization of all its carbohydrates and lignin, are developed. Specifically, high-value applications for lignin, to increase its contribution to the feasibility of lignocellulosic biorefineries, demand high-purity fractions. In this study, acid-catalyzed organosolv using ethanol as a solvent was used for the recovery of high-purity lignin and digestible cellulose. Factors including catalyst type and its concentration, temperature, retention time, and solid-to-liquid (S/L) ratio were found to influence lignin purity and recovery. At the best conditions (0.07% H2SO4, 210 °C, 90 min, and S/L ratio of 1:10), a lignin purity and recovery of 70.6 ± 4.9% and 64.94 ± 1.09%, respectively, were obtained in addition to the glucan-rich fraction. The glucan-rich fraction showed 94.06 ± 4.71% digestibility within 18 h at an enzyme loading of 30 filter paper units (FPU) /g glucan. Therefore, ethanol organosolv can be used for fractionating OPEFB into three high-quality fractions (glucan, lignin, and hemicellulosic compounds) for further tailored biorefining using low acid concentrations. Especially, the use of ethanol opens the possibility for integration of 1st and 2nd generation ethanol benefiting from the separation of high-purity lignin.

A Preliminary Study of Catalytic Hydrothermal Conversion of Cellulose to Lactic Acid: Effects of Reaction Temperature and Metal Ion Catalyst

Cellulose biopolymer was converted to lactic acid by catalytic hydrothermal method. The conversion was studied under various temperatures (120 to 190 °C) and types of metal ion catalyst (Pb2+ and Al3+), while the reaction period remained fixed at 3 h. Following the reaction, the recovery of untreated cellulose and the mass loss were determined by gravimetric means. Meanwhile, the resultant liquid products were analysed by high performance liquid chromatography (HPLC) for detecting the targeted products: lactic acid, glucose, and fructose. The study reveals useful insights; elevating the reaction temperature was found to increase the mass loss, so did the yield of the targeted products. On the other hand, using a metal ion catalyst, possessing stronger Lewis acidity character, further enhanced lactic acid production.

Enhancement, production, and immobilization of beta-glucosidase from Zobellella denitrificans VIT SB117 and its utilization in bioethanol production from lignocellulosic feedstock

β-Glucosidase from novel bacteria Zobellella denitrificans VIT SB117 was isolated, and to increase the production of the enzyme, various growth parameters of the bacteria were optimized. Plackett–Burman design and response surface methodology helped determine the most significant parameters (fructose, temperature, and culture volume) resulting in a 10-fold increase in enzyme activity. The enzyme was purified and kinetics study for free and immobilized enzyme revealed Km of 4.76 mM and 8.39 mM, Kcat of 255.02 s−1 and 114.02 s−1, and Vmax of 4.33 mg/s and 1.25 mg/s, respectively. Enzyme characterization determined optimum substrate concentration and incubation time as 3.5 mM and 10 min respectively for the free enzyme, and 4 mM and 20 min respectively for the immobilized enzyme for maximum activity. pH 5, 45 °C incubation temperature and addition of Mg2+ and Mn2+ ions exhibited similar stimulatory effects on free and immobilized enzyme activities while Hg2+ ions showed strong inhibitory effects. The immobilized enzyme had negligible loss of activity after a month’s storage at 2–4 °C in acetate buffer and ~ 27.76% residual activity after 17 continuous cycles. These optimized parameters were employed for bioethanol production from lignocellulosic wastes. A total cellulose recovery of 52.77% was achieved after pretreatment. Release of ~ 57 mg/g substrate reducing sugars was achieved by enzymatic hydrolysis using immobilized cellulase enzyme complex that produced ~ 5.46 mg/ml bioethanol after 144 h of fermentation using yeast.

Simulation and optimization of combined acid pretreatment and enzymatic saccharification of medical cotton waste

The purpose of the present study was to develop an efficient, cost-effective process towards the valorization of medical cotton waste (MCW). Application of dilute acid pretreatment as an initial step partially degrades the cotton cellulosic fibers rendering the material more amenable to enzymatic hydrolysis towards the production of glucose. MCW was treated with sulfuric acid, in a batch autoclave, at various temperature conditions. An experimental design was set up and applied to study cotton’s behavior to acid hydrolysis. The pretreatment process variables included temperature, time, and sulfuric acid concentration targeting maximal cellulose recovery and enzymatic saccharification yields. The results showed a maximum cellulose conversion to glucose of 95.6% wt. after pretreatment at 220 °C with 22.5 mM acid concentration. To the best of our knowledge, this is the first report in the literature suggesting a treatment process for the utilization of MCW as a source of fermentable sugars.

Thermochemical pretreatment enhanced bioconversion of elephant grass (Pennisetum purpureum): insight on the production of sugars and lignin

Pennisetum purpureum, commonly known as elephant grass, possesses an immense ability to be recognized as bioenergy crop due to its high carbohydrate content and ample availability in the northeastern states of India. In the present study, an alkaline treatment was conducted using NaOH of different concentrations (1%, 2% and 3% (w/v)) at varying reaction periods of 30, 60 and 90 min with an aspiration of maximum delignification and an enhanced recovery of carbohydrates from biomass. A maximum delignification of 81.0% (w/w) was obtained when the biomass was pretreated with 2% (w/v) of NaOH for 60 min while in the presence of 3% (w/v) of NaOH, the highest cellulose recovery of 72.3% (w/w) was accounted at 90 min of reaction time. During saccharification of biomass, a maximum 18.4 g/L of glucose was produced using 20 filter paper unit of commercial cellulase after 48 h of enzymatic reaction with a cellulose conversion of more than 46%. Furthermore, product inhibition study showed the significant inhibitory effect on enzymatic production of sugars even in the presence of 2 g/L glucose and xylose in the reaction system. The severity of alkaline treatment of the untreated and treated biomass was evaluated using different physiochemical analyses. Moreover, the extracted lignin obtained after acid precipitation of alkaline filtrate was characterised using UV-Visible spectrophotometer. Finally, two-way ANOVA revealed a significant variation in the production of glucose and xylose from biomass even when glucose was added at a fixed concentration (P value = 0.00044 << 0.05) into the reaction system. On the other hand, xylose shows significant inhibition in glucose and xylose production from biomass at both of a particular (P value = 9.05 × 10−7 << 0.05) and different (P value = 0.0078 << 0.05) concentrations of extraneous addition.

Artificial neural network and response surface methodology: a comparative analysis for optimizing rice straw pretreatment and saccharification

The present study demonstrates a comparative analysis between the artificial neural network (ANN) and response surface methodology (RSM) as optimization tools for pretreatment and enzymatic hydrolysis of lignocellulosic rice straw. The efficacy for both the processes, that is, pretreatment and enzymatic hydrolysis was evaluated using correlation coefficient (R2) & mean squared error (MSE). The values of R2 obtained by ANN after training, validation, and testing were 1, 0.9005, and 0.997 for pretreatment and 0.962, 0.923, and 0.9941 for enzymatic saccharification, respectively. On the other hand, the R2 values obtained with RSM were 0.9965 for cellulose recovery and 0.9994 for saccharification efficiency. Thus, ANN and RSM together successfully identify the substantial process conditions for rice straw pretreatment and enzymatic saccharification. The percentage of error for ANN and RSM were 0.009 and 0.01 for cellulose recovery and for 0.004 and 0.005 for saccharification efficiency, respectively, which showed the authority of ANN in exemplifying the non-linear behavior of the system.

Effects of organosolv pretreatment using ethylene glycol on degraded empty fruit bunch for delignification and fractionation

Malaysia and Indonesia are the largest palm oil producers worldwide. In palm oil production, approximately one tonne of empty fruit bunch (EFB) will be generated as waste for every one tonne of palm oil produced. Currently, these fresh EFB are still underutilised and generally disposed under open environment. The fresh EFB are more susceptible to microbial attack under natural environment when exposed even for short period and become degraded empty fruit bunch (DEFB) which have lower quality. Consequently, disposal of DEFB becomes an enormous challenge as well as its following environmental problems including soil pollution and emission of greenhouse gases such as methane. However, DEFB remain as a promising lignocellulosic biomass feedstock with huge potential for production of high value added products entailing biofuels, bio-polymer and membrane with appropriate pretreatment. Therefore, DEFB was subjected to organosolv pretreatment in this research to recover its cellulose content. DEFB was discovered to possess higher cellulose content, lignin content and lower hemicellulose content as compared to fresh EFB. Organosolv pretreatment successfully fractionated DEFB to recover the cellulose portion by removing the lignin and hemicellulose content. Pretreatment with 50 v/v% ethylene glycol in the presence of 3 v/v% NaOH removed 75.1 wt.% lignin and 81.5 wt.% hemicellulose with 90.4 wt.% cellulose recovery. Furthermore, the cellulose purity of treated DEFB was improved drastically from 55.9% to 84.5%. For pretreatment liquor, the recoverable lignin was amounted to 74.6 % at pH 2.0. This study proved that organosolv pretreated DEFB exhibited the desirable properties for subsequent processes such as hydrolysis to synthesise the biomass waste into other high value added bio-products.

Characterization of Eucalyptus nitens Lignins Obtained by Biorefinery Methods Based on Ionic Liquids.

Eucalyptus nitens wood samples were subjected to consecutive stages of hydrothermal processing for hemicellulose solubilization and delignification with an ionic liquid, i.e., either 1-butyl-3-methylimidazolium hydrogen sulfate or triethylammonium hydrogen sulfate. Delignification experiments were carried out a 170 °C for 10–50 min. The solid phases from treatments, i.e., cellulose-enriched solids, were recovered by centrifugation, and lignin was separated from the ionic liquid by water precipitation. The best delignification conditions were identified on the basis of the results determined for delignification percentage, lignin recovery yield, and cellulose recovery in solid phase. The lignins obtained under selected conditions were characterized in deep by 31P-NMR, 13C-NMR, HSQC, and gel permeation chromatography. The major structural features of the lignins were discussed in comparison with the results determined for a model Ionosolv lignin.