Aqueous ionic liquid pretreatment of straw

Pretreatment of wastepaper with an aqueous solution of amino acid-derived ionic liquid for biochar production as adsorbent

The carbonization of lignocellulosic biomass with ionic liquids (ILs) are considered as an advantageous approach for the preparation of carbonaceous materials. The commonly used imidazolium and pyridinium based ILs have drawbacks such as toxicity, resistance to biodegradation, high cost and viscosity. These issues can be mitigated by diluting ILs with water, although excessive water content above 1 wt% can reduce the solubility of biomass. This research aims to investigate the potential of pretreating wastepaper with a "fully green" ILs, amino acid-based IL with high water content, followed by pyrolysis without IL, in enhancing the properties of biochar. For this purpose, the paper was treated with an aqueous solution of IL cysteine nitrate ([Cys][NO3]), and the IL was not involved in the pyrolysis process to prevent the formation of secondary gaseous pollutants. The findings revealed that the hemicellulose and mineral filler in the paper were eliminated during pretreatment, leading to higher carbon content but lower oxygen content. As a result, the biochar exhibited micropores of 0.42 cm3g-1 and a specific surface area of 1011.21 m2 g-1. The biochar demonstrated high adsorption capacities for Cd2+, enrofloxacin, bisphenol A, ciprofloxacin, and tetracycline, with values of 45.20 mg g-1, 49.82 mg g-1, 49.90 mg g-1, 49.88 mg g-1, and 49.65 mg g-1, respectively. The proposed mechanism for the adsorption of enrofloxacin by the biochar primarily involves physical adsorption such as pore filling and electrostatic interactions, along with chemical adsorption facilitated by graphitic nitrogen.

A green pathway for lignin valorization: Enzymatic lignin depolymerization in biocompatible ionic liquids and deep eutectic solvents

Lignin depolymerization, which enables the breakdown of a complex and heterogeneous aromatic polymer into relatively uniform derivatives, serves as a critical process in valorization of lignin. Enzymatic lignin depolymerization has become a promising biological strategy to overcome the heterogeneity of lignin, due to its mild reaction conditions and high specificity. However, the low solubility of lignin compounds in aqueous environments prevents efficient lignin depolymerization by lignin-degrading enzymes. The employment of biocompatible ionic liquids (ILs) and deep eutectic solvents (DESs) in lignin fractionation has created a promising pathway to enzymatically depolymerize lignin within these green solvents to increase lignin solubility. In this review, recent research progress on enzymatic lignin depolymerization, particularly in a consolidated process involving ILs/DESs is summarized. In addition, the interactions between lignin-degrading enzymes and solvent systems are explored, and potential protein engineering methodology to improve the performance of lignin-degrading enzymes is discussed. Consolidation of enzymatic lignin depolymerization and biocompatible ILs/DESs paves a sustainable, efficient, and synergistic way to convert lignin into value-added products.

Revolutionizing lignocellulosic biomass: A review of harnessing the power of ionic liquids for sustainable utilization and extraction

The potential for the transformation of lignocellulosic biomass into valuable commodities is rapidly growing through an environmentally sustainable approach to harness its abundance, cost-effectiveness, biodegradability, and environmentally friendly nature. Ionic liquids (ILs) have received considerable and widespread attention as a promising solution for efficiently dissolving lignocellulosic biomass. The fact that ILs can act as solvents and reagents contributes to their widespread recognition. In particular, ILs are desirable because they are inert, non-toxic, non-flammable, miscible in water, recyclable, thermally and chemically stable, and have low melting points and outstanding ionic conductivity. With these characteristics, ILs can serve as a reliable replacement for traditional biomass conversion methods in various applications. Thus, this comprehensive analysis explores the conversion of lignocellulosic biomass using ILs, focusing on main components such as cellulose, hemicellulose, and lignin. In addition, the effect of multiple parameters on the separation of lignocellulosic biomass using ILs is discussed to emphasize their potential to produce high-value products from this abundant and renewable resource. This work contributes to the advancement of green technologies, offering a promising avenue for the future of biomass conversion and sustainable resource management.

Enzymatic hydrolysis of low temperature alkali pretreated wheat straw using immobilized β-xylanase nanoparticles

A low temperature alkali (LTA) pretreatment method was used to treat wheat straw. In order to obtain good results, different factors like temperature, incubation time, NaOH concentration and solid to liquid ratio for the pretreatment process were optimized. Wheat straw is a potential biomass for the production of monomeric sugars. The objective of the current study was to observe the saccharification (%) of wheat straw with immobilized magnetic nanoparticles (MNPs). For this purpose, immobilized MNPs of purified β-xylanase enzyme was used for hydrolysis of pretreated wheat straw. Wheat straw was pretreated using the LTA method and analyzed by SEM analysis. After completion of the saccharification process, saccharification% was calculated by using a DNS method. Scanning electron micrographs revealed that the hemicellulose, cellulose and lignin were partially removed and changes in the cell wall structure of the wheat straw had caused it to become deformed, increasing the specific surface area, so more fibers of the wheat straw were exposed to the immobilized β-xylanase enzyme after alkali pretreatment. The maximum saccharification potential of wheat straw was about 20.61% obtained after pretreatment with optimized conditions of 6% NaOH, 1/10 S/L, 30 °C and 72 hours. Our results indicate the reusability of the β-xylanase enzyme immobilized magnetic nanoparticles and showed a 15% residual activity after the 11th cycle. HPLC analysis of the enzyme-hydrolyzed filtrate also revealed the presence of sugars like xylose, arabinose, xylobiose, xylotriose and xylotetrose. The time duration of the pretreatment has an important effect on thermal energy consumption for the low-temperature alkali method.

Deep Eutectic Solvent Pretreatment of Water Hyacinth for Improved Holocellulosic Saccharification and Fermentative Co-Production of Xylitol and Lipids Using Rhodosporidium toruloides NCIM 3547

In this study, delignification of water hyacinth (WH) using a mild ionic liquid-like chemical deep eutectic solvent (DES) synthesized using choline chloride and urea was conducted and the process parameters were optimized by Box–Behnken design (BBD)-based response surface methodology (RSM). From the results, a delignification of 64.32 ± 4.08% (w/w) was obtained under 1:12.5 (biomass:DES ratio), 4.63 h (time) and 87 °C (temperature). Further, a dilute sulphuric acid (2%, v/v) hydrolysis was carried out to destabilize the hemicellulose that resulted in 23.7 ± 0.50 g/L of xylose. Fermentation of the obtained xylose was carried out using a red oleaginous yeast, Rhodosporidium toruloides NCIM 3547, with free and Ca2+-alginate-immobilized cells for xylitol production under microaerophilic conditions and obtained yields of 4.73 ± 0.40 g/L (168 h) and 9.18 ± 0.10 g/L (packed bed reactor with a retention time of 18 h), respectively. Further, when the same fermentation was performed under aerobic conditions about 40.93 ± 0.73% lipid accumulation was observed with free cells. For saccharification, Aspergillus-niger-derived cellulase was used and this resulted in a yield of 27.45 ± 0.04 g/L of glucose. The glucose-enriched hydrolysate was supplemented for fermentation under nitrogen starved conditions from which 46.81 ± 2.60% (w/w) lipid content was obtained.

Enhanced activity of hyperthermostable Pyrococcus horikoshii endoglucanase in superbase ionic liquids

Objectives

Ionic liquids (ILs) that dissolve biomass are harmful to the enzymes that degrade lignocellulose. Enzyme hyperthermostability promotes a tolerance to ILs. Therefore, the limits of hyperthemophilic Pyrococcus horikoschii endoglucanase (PhEG) to tolerate 11 superbase ILs were explored.

Results

PhEG was found to be most tolerant to 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) in soluble 1% carboxymethylcellulose (CMC) and insoluble 1% Avicel substrates. At 35% concentration, this IL caused an increase in enzyme activity (up to 1.5-fold) with CMC. Several ILs were more enzyme inhibiting with insoluble Avicel than with soluble CMC. K_m increased greatly in the presence ILs, indicating significant competitive inhibition. Increased hydrophobicity of the IL cation or anion was associated with the strongest enzyme inhibition and activation. Surprisingly, PhEG activity was increased 2.0–2.5-fold by several ILs in 4% substrate. Cations exerted the main role in competitive inhibition of the enzyme as revealed by their greater binding energy to the active site.

Conclusions

These results reveal new ways to design a beneficial combination of ILs and enzymes for the hydrolysis of lignocellulose, and the strong potential of PhEG in industrial, high substrate concentrations in aqueous IL solutions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10529-022-03268-5.

Effect of microwave/hydrothermal combined ionic liquid pretreatment on straw: Rumen anaerobic fermentation and enzyme hydrolysis

To explore green technology for wheat straw pretreatment, this study combined the microwave or hydrothermal with ionic liquid ([Bmim][OAc]) on wheat straw followed by rumen fermentation. The optimal conditions of microwave assisted ionic liquids pretreatment (M-I) and hydrothermal assisted ionic liquids pretreatment (H-I) treatment were 360 W and 200 °C, and the corresponding lignin removal rates reached 35.3% and 25.4%, respectively. Rumen fermentation showed that the highest volatile fatty acid (VFA) yield was found in M-I group, followed by H-I group at 234 and 180 mg/g, respectively. As for enzymatic hydrolysis, the saccharification rates at 3 days of M-I (360 W) and H-I (200 °C) were determined to be 393 and 320 mg/g. The optimal ionic liquid dosage was determined to be 30% in consideration of cost and VFA conversion rate. M-I pretreatment plus the rumen fermentation enjoyed the benefit of no enzyme addition and high product recovery, which was worth further investigating.

Efficient saccharification of ionic liquid-pretreated rice straw in a one-pot system using novel metagenomics derived cellulases

Ionic liquids (ILs)-resistant cellulase enzymes can facilitate the saccharification of IL- pretreated biomass in a one-pot wash-free method. Using a bioinformatics approach, two cellulases, Persicel7 and Persicel8, with convincing evidence for ionic liquid tolerance were identified. Subsequently, these enzymes were heterologously expressed and biochemically characterized. Persicel7 and Persicel8 exhibited endo-β-1, 4-glucanase activity and were resistant to inhibitors and several organic solvents. Their activity in 10% (v/v) 1-ethyl-3-methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride were 130% higher compared with IL-free control. The half-life of cellulases was improved up to 11-fold when incubated with 20% (v/v) solution of ion liquids. In addition, a one-pot IL-pretreatment and enzymatic saccharification of rice straw enhanced the saccharification rate by 33% compared to the untreated reaction. The Persicel7 and Persicel8 unique properties make them attractive candidates for industrial applications, particularly hydrolyzing ion liquid activated biomass in a one-pot system.

Current understanding and optimization strategies for efficient lignin-enzyme interaction: A review

From energy perspective, with abundant polysaccharides (45-85%), the renewable lignocellulosic is recognized as the 2nd generation feedstock for bioethanol and bio-based products production. Enzymatic hydrolysis is a critical pathway to yield fermentable monosaccharides from pretreated substrates of lignocellulose. Nevertheless, the lignin presence in lignocellulosic substrates leads to the low substrate enzymatic digestibility ascribed to the nonproductive adsorption. It has been reported that the water-soluble lignin (low molecular weight, sulfonated/sulfomethylated and graft polymer) enhance the rate of enzymatic digestibility, however, the catalytic mechanism of lignin-enzyme interaction remains elusive. In this review, optimization strategies for enzymatic hydrolysis based on the lignin structural modification, enzyme engineering, and different additives are critically reviewed. Lignin-enzyme interaction mechanism is also discussed (lignin and various cellulases). In addition, the mathematical models and simulation of lignin, cellulose and enzyme aims for promoting an integrated biomass-conversion process for sustainable production of value-added biofuels.

Identifying Advanced Biotechnologies to Generate Biofertilizers and Biofuels From the World's Worst Aquatic Weed

Water hyacinth (Eichhornia crassipes L.) was introduced as an invasive plant in freshwater bodies more particularly in Asia and Africa. This invasive plant grows rapidly and then occupies a huge layer of freshwater bodies. Hence, challenges are facing many countries for implementing suitable approaches for the valorization of the world's worst aquatic weed, and water hyacinth (WH). A critical and up-to-date review article has been conducted for more than 1 year, based on more than 100 scientific journal articles, case studies, and other scientific reports. Worldwide distribution of WH and the associated social, economic, and environmental impacts were described. In addition, an extensive evaluation of the most widely used and innovative valorization biotechnologies, leading to the production of biofertilizer and bioenergy from WH, and was dressed. Furthermore, an integrated search was used in order to examine the related advantages and drawbacks of each bioprocess, and future perspectives stated. Aerobic and anaerobic processes have their specific basic parameters, ensuring their standard performances. Composting was mostly used even at a large scale, for producing biofertilizers from WH. Nevertheless, this review explored some critical points to better optimize the conditions (presence of pollutants, inoculation, and duration) of composting. WH has a high potential for biofuel production, especially by implementing several pretreatment approaches. This review highlighted the combined pretreatment (physical-chemical-biological) as a promising approach to increase biofuel production. WH valorization must be in large quantities to tackle its fast proliferation and to ensure the generation of bio-based products with significant revenue. So, a road map for future researches and applications based on an advanced statistical study was conducted. Several recommendations were explored in terms of the choice of co-substrates, initial basic parameters, and pretreatment conditions and all crucial conditions for the production of biofuels from WH. These recommendations will be of a great interest to generate biofertilizers and bioenergy from WH, especially within the framework of a circular economy.

One-Pot Ionic Liquid-Mediated Bioprocess for Pretreatment and Enzymatic Hydrolysis of Rice Straw with Ionic Liquid-Tolerance Bacterial Cellulase

Ionic liquid (IL) pretreatment of lignocellulose is an efficient method for the enhancement of enzymatic saccharification. However, the remaining residues of ILs deactivate cellulase, therefore making intensive biomass washing after pretreatment necessary. This study aimed to develop the one-pot process combining IL pretreatment and enzymatic saccharification by using low-toxic choline acetate ([Ch][OAc]) and IL-tolerant bacterial cellulases. Crude cellulases produced from saline soil inhabited Bacillus sp. CBD2 and Brevibacillus sp. CBD3 were tested under the influence of 0.5–2.0 M [Ch][OAc], which showed that their activities retained at more than 95%. However, [Ch][OAc] had toxicity to CBD2 and CBD3 cultures, in which only 32.85% and 12.88% were alive at 0.5 M [Ch][OAc]. Based on the specific enzyme activities, the sugar amounts produced from one-pot processes using 1 mg of CBD2 and CBD3 were higher than that of Celluclast 1.5 L by 2.0 and 4.5 times, respectively, suggesting their potential for further application in the biorefining process of value-added products.

BAILs mediated Catalytic Thermo Liquefaction (CTL) process to convert municipal solid waste into carbon densified liquid (CTL-Oil)

Continual increase in municipal solid waste (MSW) posing global environmental challenge which directed focus towards the waste to energy to achieve dual goal of waste minimization and energy generation. The present manuscript introducing Bronsted acid ionic liquids (BAILs) mediated Catalytic Thermo Liquefaction (CTL) process for conversion of MSW into carbon densified liquid (CTL-Oil) which can be used for multiple energy and fuel applications. BAILs with different counter ions were synthesized and tested for CTL of wet organic biodegradable MSW. The exploration of BAILs provides significant benefits in terms of operating conditions (120 °C, 90 min) with zero char and gases. Of the synthesized catalysts [Benz-SO₃HIm]⁺[H₂PO₄]^-,[Benz-SO₃Him]⁺[HSO₄]^-_,[Benz-SO₃HIm]⁺[TsO]^-and [BenzSO₃HIm]⁺[TfO]^-, BAIL with [HSO₄]^-counter ion showed a profound effect on CTL. The intensified CTL process resulted in > 85% MSW conversion with > 80% yield of CTL-Oil without any char and gas formation. Use of BAILs assisted the ease of dissolution and hydrolysis of biomass to produce CTL-Oil via hydrolysis, condensation, cyclization and dehydration reactions. The plausible mechanism for CTL has been proposed. The physicochemical analysis of CTL-Oil was conducted by using elemental analysis, Bomb calorimeter, GC-MS and ATR-FTIR. It was found that the CTL-Oil was rich source of C (48-55%), H (6-8%), O (30-41%) containing compounds such as long-chain hydrocarbons, carboxylic acids, heterocyclic compounds, aldehydes, ketones and esters, etc. Furthermore, the calorific value of CTL-Oil was found to be 20-23 MJ/kg, thus it can be explored for multiple energy and fuel applications. However, the CTL process also adds several environmental and process economic benefits over the conventional waste liquefaction/disposal processes.

Exploring the Effect of Water Content and Anion on the Pretreatment of Poplar with Three 1-Ethyl-3-methylimidazolium Ionic Liquids

We report on the pretreatment of poplar wood with three different 1-ethyl-3-methylimidazolium ionic liquids, [EMim][OAc], [EMim][MeSO3], and [EMim][HSO4], at varying water contents from 0-40 wt% at 100 °C. The performance was evaluated by observing the lignin and hemicellulose removal, as well as enzymatic saccharification and lignin yield. The mechanism of pretreatment varied between the ionic liquids studied, with the hydrogen sulfate ionic liquid performing delignification and hemicellulose hydrolysis more effectively than the other solvents across the investigated water content range. The acetate ionic liquid produced superior glucose yield at low water contents, while the hydrogen sulfate ionic liquid performed better at higher water contents and produced a recoverable lignin. The methanesulfonate ionic liquid did not introduce significant fractionation or enhancement of saccharification yield under the conditions used. These findings help distinguish the roles of anion hydrogen bonding, solvent acidity, and water content on ionic liquid pretreatment and can aid with anion and water content selections for different applications.

A Review on the Partial and Complete Dissolution and Fractionation of Wood and Lignocelluloses Using Imidazolium Ionic Liquids

Ionic liquids have shown great potential in the last two decades as solvents, catalysts, reaction media, additives, lubricants, and in many applications such as electrochemical systems, hydrometallurgy, chromatography, CO2 capture, etc. As solvents, the unlimited combinations of cations and anions have given ionic liquids a remarkably wide range of solvation power covering a variety of organic and inorganic materials. Ionic liquids are also considered "green" solvents due to their negligible vapor pressure, which means no emission of volatile organic compounds. Due to these interesting properties, ionic liquids have been explored as promising solvents for the dissolution and fractionation of wood and cellulose for biofuel production, pulping, extraction of nanocellulose, and for processing all-wood and all-cellulose composites. This review describes, at first, the potential of ionic liquids and the impact of the cation/anion combination on their physiochemical properties and on their solvation power and selectivity to wood polymers. It also elaborates on how the dissolution conditions influence these parameters. It then discusses the different approaches, which are followed for the homogeneous and heterogeneous dissolution and fractionation of wood and cellulose using ionic liquids and categorize them based on the target application. It finally highlights the challenges of using ionic liquids for wood and cellulose dissolution and processing, including side reactions, viscosity, recyclability, and price.

Wheat Bran Pretreatment by Room Temperature Ionic Liquid-Water Mixture: Optimization of Process Conditions by PLS-Surface Response Design

Room Temperature Ionic Liquids (RTILs) pretreatment are well-recognized to improve the enzymatic production of platform molecules such as sugar monomers from lignocellulosic biomass (LCB). The conditions for implementing this key step requires henceforth optimization to reach a satisfactory compromise between energy saving, required RTIL amount and hydrolysis yields. Wheat bran (WB) and destarched wheat bran (DWB), which constitute relevant sugar-rich feedstocks were selected for this present study. Pretreatments of these two distinct biomasses with various 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc])-water mixtures prior to hydrolysis catalyzed by hemicellulolytic cocktail (Cellic CTec2) were finely investigated. The main operating conditions such as pretreatment temperature (25–150°C), time (40–180 min), WB and DWB loading (2–5% w/v) and concentration of [C2mim][OAc] in water [10–100% (v/v)] were screened through glucose and xylose yields and then optimized through a Partial Least Square (PLS)—Second Order Design. In an innovative way, the PLS results showed that the four factors and their interactions could be well-fitted by a second-order model (p < 0.05). The quadratic PLS models were used to predict optimal pretreatment conditions. Thus, maximum glucose (83%) and xylose (95%) yields were obtained from enzymatic hydrolysis of WB pretreated at 150°C for 40 min with 10% of [C2mim][OAc] in water and 5% of WB loading. For DWB, maximum glucose (100%) and xylose (57%) yields were achieved for pretreatment temperatures of 150°C and 25°C, respectively. The required duration was still 40 min, with 20% of [C2mim][OAc] in water and a 5% DWB loading. Then, Multiple Response Optimization (MRO) performed by Nelder-Mead Simplex Method displayed sugar yields similar to those obtained by individual PLS optimization. This complete statistical study confirmed that the established models were appropriate to predict the sugar yields achieved after different pretreatment conditions from WB and DWB biomasses. Finally, Scanning Electron microscopy (SEM) studies allowed us to establish clearer link between structural changes induced by pretreatment and the best enzymatic performances obtained.

Comparison of Bioethanol Preparation from Triticale Straw Using the Ionic Liquid and Sulfate Methods

Triticale straw constitutes a potential raw material for biofuel production found in Poland in considerable quantities. Thus far, production of bioethanol has been based on food raw materials such as cereal seeds, sugar beets or potatoes, and the biofuel production methods developed for these lignocellulose raw materials can threaten the environment and are inefficient. Therefore, this study aimed to compare of methods for pretreatment of triticale straw using 1-ethyl-3-methylimidazolium acetate and the sulfate method in the aspect of ethanol production intended for fuel. Based on the conducted experiments it has been determined that the use of 1-ethyl-3-methylimidazolium acetate for the pretreatment of triticale straw resulted in an increase of reducing sugars after enzymatic hydrolysis and ethyl alcohol after alcoholic fermentation. Furthermore, the study compared the efficiency of enzymatic hydrolysis of triticale straw without pretreatment, after processing with ionic liquid, recycled ionic liquid and using sulfate method, allowing a comparison of these methods. The more favorable method of lignocellulose material purification was the use of ionic liquid, due to the lower amount of toxic byproducts formed during the process, and the efficiency test results of bioethanol production using pretreatment with ionic liquid and sulfate method were similar. Ionic liquid recycling after pretreatment of rye straw using lyophilization allowed us to reuse this solvent to purify rye straw, yet the efficiency of this method remained at a low level. As a result of the conducted study it was determined that the use of ionic liquid-1-ethyl-3-methylimidazolium acetate enhanced the yield of bioethanol from triticale straw from 1.60 g/dm3 after processing without pre-treatment to 10.64 g/dm3 after pre-treatment.

Extraction of lignin, structural characterization and bioconversion of sugarcane bagasse after ionic liquid assisted pretreatment

The primary focus of this work was to recover lignin and investigate the structural changes in sugarcane bagasse after pretreatment with ionic liquid 1-ethyl-3-methylimidazolium acetate ([EMIM]oAc). 90% lignin recovery was achieved while bagasse was treated with [EMIM]oAc at 140 °C, 120 min reaction time and 1:20 bagasse to the ionic liquid ratio (w/w). The impact of ionic liquid pretreatment on bagasse was confirmed by qualitative analysis of untreated and pretreated bagasse. Scanning electron microscopy analysis exhibited the porous and irregular structure of bagasse after pretreatment. X-ray powder diffraction analysis verified a decrease in crystallinity as a result of the pretreatment process by showing a 14.7% reduction of Crystallinity index after ionic liquid treatment. The efficacy of [EMIM]oAc on bagasse treatment was also examined by enzymatic hydrolysis which manifested an increase in reducing sugar yield as a result of pretreatment. Maximum yield of 54.3% reducing sugar was obtained after 72 h enzymatic hydrolysis of pretreated bagasse. Recovered lignin was analyzed qualitatively. 1D NMR spectroscopy of lignin revealed the presence of essential functional groups whereas 2D NMR spectroscopy showed the dominance of etherified syringyl unit. Further ionic liquid recovery and reuse were substantiated by Gel permeation chromatography analysis of lignin. Weight average molecular weight (M_w) of lignin extracted by fresh [EMIM]oAc was obtained as 1769 g/mol (in the previous study) while lignin recovered by recycled [EMIM]oAc showed almost equal M_w 1765 g/mol in this study. Thus, the current investigation corroborated satisfactory performance of [EMIM]oAc in lignocellulose processing which further enhanced enzymatic hydrolysis in the subsequent step.

Pretreatment of corn straw using the alkaline solution of ionic liquids

In the present work, the pretreatment of corn stalk with the solution of 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) ionic liquid containing NaOH was explored for its lignin removal. The effects of reaction temperature, reaction time, and solid-liquid ratio on the lignin removal efficiency were determined by the response surface methodology (RSM). The pretreatment conditions were optimized by the Box-Behnken design and the comparative study of the composition and structure of corn straw before and after the pretreatment to be: reaction temperature 98.5 °C, reaction time 1.31 h, and solid-liquid ratio 1:8.7. Under the optimized conditions, the cellulose and hemicellulose contents of the corn straw were increased to 85.69% and 9.1%, respectively, and the lignin content was reduced to 2.27% with the lignin removal efficiency up to 87.4%.

Enhancement of anaerobic digestion of grass by pretreatment with imidazolium-based ionic liquids

In this work, the toxicity of imidazolium-based ionic liquids (ILs) and the enhancement of high-solid anaerobic digestion by pretreatment were studied. Compared with [Bmim]Cl, [Bmim]OAc and [Bmim]BF₄, [Bmim]PF₆ had the highest toxicity. When the mass ratio of [Bmim]PF₆ to grass was higher than 1:10, biogas was not produced within 30 days. The ability to remove lignin and hemicellulose followed the sequence of [Bmim]OAc, [Bmim]Cl, [Bmim]BF₄ and [Bmim]PF₆. The crystallinity index of grass pretreated with [Bmim]OAc, [Bmim]Cl, [Bmim]BF₄ and [Bmim]PF₆ reduced by 73.83%, 54.44%, 17.52% and 7.47%, respectively. The pretreatment with ILs enhanced the methane yield of grass by reducing crystallinity and particle size. The grass pretreated with [Bmim]OAc had the highest methane yield, about 221 mL/g volatile solids, due to its good lignin removal ability and relative low toxicity. After 10 times recycling, the cumulative methane yield of grass pretreated by recycled [Bmim]OAc decreased by 11.95%.

Ternary ionic liquid-water pretreatment systems of an agave bagasse and municipal solid waste blend

BACKGROUND

Pretreatment is necessary to reduce biomass recalcitrance and enhance the efficiency of enzymatic saccharification for biofuel production. Ionic liquid (IL) pretreatment has gained a significant interest as a pretreatment process that can reduce cellulose crystallinity and remove lignin, key factors that govern enzyme accessibility. There are several challenges that need to be addressed for IL pretreatment to become viable for commercialization, including IL cost and recyclability. In addition, it is unclear whether ILs can maintain process performance when utilizing low-cost, low-quality biomass feedstocks such as the paper fraction of municipal solid waste (MSW), which are readily available in high quantities. One approach to potentially reduce IL cost is to use a blend of ILs at different concentrations in aqueous mixtures. Herein, we describe 14 IL-water systems with mixtures of 1-ethyl-3-ethylimidazolium acetate ([C₂C₁Im][OAc]), 1-butyl-3-ethylimidazolium acetate ([C₄C₁Im][OAc]), and water that were used to pretreat MSW blended with agave bagasse (AGB). The detailed analysis of IL recycling in terms of sugar yields of pretreated biomass and IL stability was examined.

RESULTS

Both biomass types (AGB and MSW) were efficiently disrupted by IL pretreatment. The pretreatment efficiency of [C₂C₁Im][OAc] and [C₄C₁Im][OAc] decreased when mixed with water above 40%. The AGB/MSW (1:1) blend demonstrated a glucan conversion of 94.1 and 83.0% using IL systems with ~10 and ~40% water content, respectively. Chemical structures of fresh ILs and recycle ILs presented strong similarities observed by FTIR and ¹H-NMR spectroscopy. The glucan and xylan hydrolysis yields obtained from recycled IL exhibited a slight decrease in pretreatment efficiency (less than 10% in terms of hydrolysis yields compared to that of fresh IL), and a decrease in cellulose crystallinity was observed.

CONCLUSIONS

Our results demonstrated that mixing ILs such as [C₂C₁Im][OAc] and [C₄C₁Im][OAc] and blending the paper fraction of MSW with agricultural residues, such as AGB, may contribute to lower the production costs while maintaining high sugar yields. Recycled IL-water mixtures provided comparable results to that of fresh ILs. Both of these results offer the potential of reducing the production costs of sugars and biofuels at biorefineries as compared to more conventional IL conversion technologies.Graphical abstractSchematic of ionic liquid (IL) pretreatment of agave bagasse (AB) and paper-rich fraction of municipal solid waste (MSW).

Ionic liquids and deep eutectic solvents for lignocellulosic biomass fractionation

State of the art overview of the fractionation of lignocellulosic biomass with ionic liquids and deep eutectic solvents.

Ionic liquids as efficient pretreatment solvents for lignocellulosic biomass

Ionic liquid (IL)-assisted pretreatment of lignocellulosic biomass has been extensively studied.

Green methods of lignocellulose pretreatment for biorefinery development

Lignocellulosic biomass is the most abundant, low-cost, bio-renewable resource that holds enormous importance as alternative source for production of biofuels and other biochemicals that can be utilized as building blocks for production of new materials. Enzymatic hydrolysis is an essential step involved in the bioconversion of lignocellulose to produce fermentable monosaccharides. However, to allow the enzymatic hydrolysis, a pretreatment step is needed in order to remove the lignin barrier and break down the crystalline structure of cellulose. The present manuscript is dedicated to reviewing the most commonly applied "green" pretreatment processes used in bioconversion of lignocellulosic biomasses within the "biorefinery" concept. In this frame, the effects of different pretreatment methods on lignocellulosic biomass are described along with an in-depth discussion on the benefits and drawbacks of each method, including generation of potentially inhibitory compounds for enzymatic hydrolysis, effect on cellulose digestibility, and generation of compounds toxic for the environment, and energy and economic demand.

Liberation of fermentable sugars from soybean hull biomass using ionic liquid 1-butyl-3-methylimidazolium acetate and their bioconversion to ethanol

Optimized hydrolysis of lignocellulosic waste biomass is essential to achieve the liberation of sugars to be used in fermentation process. Ionic liquids (ILs), a new class of solvents, have been tested in the pretreatment of cellulosic materials to improve the subsequent enzymatic hydrolysis of the biomass. Optimized application of ILs on biomass is important to advance the use of this technology. In this research, we investigated the effects of using 1-butyl-3-methylimidazolium acetate ([bmim][Ac]) on the decomposition of soybean hull, an abundant cellulosic industrial waste. Reaction aspects of temperature, incubation time, IL concentration, and solid load were optimized before carrying out the enzymatic hydrolysis of this residue to liberate fermentable glucose. Optimal conditions were found to be 75°C, 165 min incubation time, 57% (mass fraction) of [bmim][Ac], and 12.5% solid loading. Pretreated soybean hull lost its crystallinity, which eased enzymatic hydrolysis, confirmed by Fourier Transform Infrared analysis. The enzymatic hydrolysis of the biomass using an enzyme complex from Penicillium echinulatum liberated 92% of glucose from the cellulose matrix. The hydrolysate was free of any toxic compounds, such as hydroxymethylfurfural and furfural. The obtained hydrolysate was tested for fermentation using Candida shehatae HM 52.2, which was able to convert glucose to ethanol at yields of 0.31. These results suggest the possible use of ILs for the pretreatment of some lignocellulosic waste materials, avoiding the formation of toxic compounds, to be used in second-generation ethanol production and other fermentation processes. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 32:312-320, 2016.

Facile isothermal solid acid catalyzed ionic liquid pretreatments to enhance the combined sugars production from Arundo donax Linn

BACKGROUND

Solid acid catalyzed inexpensive ionic liquid (IL) pretreatment is promising because of its effectiveness at decreasing biomass recalcitrance to subsequent enzymatic hydrolysis or in situ hydrolysis of carbohydrate oligomers. However, the conventional strategy was limited by the complex non-isothermal process and considering only one aspect of sugar recovery. In this study, facile isothermal pretreatments using Amberlyst 35DRY catalyzed 1-n-butyl-3-methylimidazolium chloride ([C4mim]Cl) at mild conditions were developed on bioenergy crop Arundo donax Linn. to enhance the combined sugars released. The physicochemical differences, enzymatic digestibility, and sugars released in situ were evaluated and compared to define the best set of conditions.

RESULTS

The optimized isothermal pretreatment (110 °C, IL for 3 h, Amberlyst for 1 h) resulted in significant enhancement in combined sugars released (58.4 g/100 g raw materials), recovering 85.0 % of the total reducing glycan in the raw biomass. This remarkable improvement could be correlated to cellulose crystallinity reduction, crystalline conversion, and partial removal of the main chemical components caused by the pretreatment. Particularly, solubilization of hemicelluloses and partial depolymerization of cellulose contributed to the synergetic improvement of sugars production in enzymatic hydrolysis and in situ. Irrespective of the generous differences in mass recovery, the highest cellulose digestibility of 90.2 % and sugar released of 43.0 % (based on initial materials) in the pretreatment liquor were obtained. Interestingly, lignin (0.8-6.1 %) and sugars derived lactic acid (4.70-5.94 %) were produced without any notable deleterious effects.

CONCLUSIONS

Isothermal [C4mim]Cl-Amberlyst pretreatment was a highly effective, simple, and convenient process that produced high yields of fermentable sugars from recalcitrant biomass by in situ hydrolysis of soluble biomass and enhancement of cellulose digestibility of the regenerated biomass. Relatively high amount of new revenues beyond sugars of this pretreatment could promote the commercial viability.

Advances in improving the performance of cellulase in ionic liquids for lignocellulose biorefinery

Ionic liquids (ILs) have been considered as a class of promising solvents that can dissolve lignocellulosic biomass and then provide enzymatic hydrolyzable holocellulose. However, most of available cellulases are completely or partially inactivated in the presence of even low concentrations of ILs. To more fully exploit the benefits of ILs to lignocellulose biorefinery, it is critical to improve the compatibility between cellulase and ILs. Various attempts have been made to screen natural IL-tolerant cellulases from different microhabitats. Several physical and chemical methods for stabilizing cellulases in ILs were also developed. Moreover, recent advances in protein engineering have greatly facilitated the rational engineering of cellulases by site-directed mutagenesis for the IL stability. This review is aimed to provide the first detailed overview of the current advances in improving the performance of cellulase in non-natural IL environments. New ideas from the most representative progresses and technical challenges will be summarized and discussed.

Understanding lignin treatment in dialkylimidazolium-based ionic liquid-water mixtures

The treatment of enzymatically hydrolyzed lignin (EHL) in dialkylimidazolium-based ionic liquid (IL)-water mixtures (50-100wt% IL content) was investigated at 150°C for 3h. pH, IL type, and IL content were found to greatly influence the degradation of lignin and the structure of regenerated lignin. 1-Butyl-3-methylimidazolium methylsulfonate-water mixtures with low pH facilitated lignin depolymerization but destroyed the regenerated lignin substructure. Regenerated lignin with low molecular weight and narrow polydispersity index (2.2-7.7) was obtained using a 1-butyl-3-methylimidazolium acetate-based system. Water addition inhibited lignin depolymerization at 50-100wt% IL content, except for 70wt% 1-butyl-3-methylimidazolium chloride-water mixture. Compared with pure IL treatment, obvious differences were observed in the breakdown of inter-unit linkages and ratio of syringyl to guaiacyl units in regenerated lignin with IL-water treatment.

Enhancement of enzymatic saccharification of corn stover with sequential Fenton pretreatment and dilute NaOH extraction

In this study, an effective method by the sequential Fenton pretreatment and dilute NaOH extraction (FT-AE) was chosen for pretreating corn stover. Before dilute NaOH (0.75 wt%) extraction at 90 °C for 1h, Fenton reagent (0.95 g/L of FeSO4 and 29.8 g/L of H2O2) was employed to pretreat CS at a solid/liquid ratio of 1/20 (w/w) at 35 °C for 30 min. The changes in the cellulose structural characteristics (porosity, morphology, and crystallinity) of the pretreated solid residue were correlated with the enhancement of enzymatic saccharification. After being enzymatically hydrolyzed for 72 h, the reducing sugars and glucose from the hydrolysis of 60 g/L FT-AE-CS pretreated could be obtained at 40.96 and 23.61 g/L, respectively. Finally, the recovered hydrolyzates containing glucose had no inhibitory effects on the ethanol fermenting microorganism. In conclusion, the sequential Fenton pretreatment and dilute NaOH extraction has high potential application in future.

Deep eutectic solvent pretreatment and subsequent saccharification of corncob

Ionic liquid (ILs) pretreatment of lignocellulosic biomass has attracted broad scientific interest, despite high costs, possible toxicity and energy intensive recycling. An alternative group of ionic solvents with similar physicochemical properties are deep eutectic solvents (DESs). Corncob residues were pretreated with three different DES systems: choline chloride and glycerol, choline chloride and imidazole, choline chloride and urea. The pretreated biomass was characterised in terms of lignin content, sugars concentration, enzymatic digestibility and crystallinity index. A reduction of lignin and hemicellulose content resulted in increased crystallinity of the pretreated biomass while the crystallinity of the cellulose fraction could be reduced, depending on DES system and operating conditions. The subsequent enzymatic saccharification was enhanced in terms of rate and extent. A total of 41 g fermentable sugars (27 g glucose and 14 g xylose) could be recovered from 100g corncob, representing 76% (86% and 63%) of the initially available carbohydrates.

Effects of glycerol on enzymatic hydrolysis and ethanol production using sugarcane bagasse pretreated by acidified glycerol solution

In this study, for the first time the effects of glycerol on enzymatic hydrolysis and ethanol fermentation were investigated. Enzymatic hydrolysis was inhibited slightly with 2.0 wt% glycerol, leading to reduction in glucan digestibility from 84.9% without glycerol to 82.9% (72 h). With 5.0 wt% and 10.0 wt% glycerol, glucan digestibility was reduced by 4.5% and 11.0%, respectively. However, glycerol did not irreversibly inhibit cellulase enzymes. Ethanol fermentation was not affected by glycerol up to 5.0 wt%, but was inhibited slightly at 10.0 wt% glycerol, resulting in reduction in ethanol yield from 86.0% in the absence of glycerol to 83.7% (20 h). Based on the results of laboratory and pilot-scale experiments, it was estimated that 0.142 kg ethanol can be produced from 1.0 kg dry bagasse (a glucan content of 38.0%) after pretreatment with acidified glycerol solution.