Pretreatment Of Lignocellulosic Materials Research Articles

Bacterial metabolic engineering for the production of second-generation (2G) bioethanol and biobutanol; a review.

The second generation (2G) biofuels were introduced to solve the issues associated with first-generation biofuel (dependency on food materials) and fossil fuels such as reservoirs diminution, high demand, price fluctuation, and lethal greenhouse gases emission. Butanol and ethanol are the main 2G biofuels. They are used as a disinfectant, antiseptic, and chemical solvent in pharmaceutical, plastic, textiles, cosmetics, and fuel industries. Currently, their bacterial biological production from lignocellulosic material at the industrial level with primitive microorganisms is under development and not economical and qualitative compatible as compared to that of fossil origin, due to slow growth rate, low titer, recalcitrant nature of lignocellulose, strain intolerance to a higher amount of butanol and ethanol, and strain inability to tolerate inhibitors accumulated during pretreatment of lignocellulosic materials. Therefore, metabolic engineering strategies such as redirection of carbon flux, knocking out competing pathways, enhancing strain robustness and wide range of substrate utilization ability, and overexpression of enzymes involved in their biological synthesis have been applied to bacteria for enhancing their ability for 2G ethanol and butanol production in a highly cost-effective amount from lignocellulosic materials. Herein, we summarized and reviewed the progress in metabolic engineering of bacterial species such as clostridium spp, E. coli, and Z. moibilis for the synthesis of 2G butanol and ethanol, especially from lignocellulosic materials.

Pre-treatment of lignocellulosic materials by enzymatic mixture to enhance biogas production

Abstract The aim of this study was to evaluate the effect of an enzymatic mixture on the increase of biogas production from lignocellulosic materials as rapeseed straw, maize waste, and wheat straw. For efficient application of the enzymatic mixture, conditions of its use were optimized regarding 50 °C, pH 7 and an enzyme dose of 0.25 % w/v. Biogas potential test confirmed positive effect of the enzymatic mixture on anaerobic digestion of already thermally and alkali pre-treated lignocellulosic materials, as significantly higher biogas production was observed after the enzymatic mixture addition for all monitored substrates. Addition of the enzymatic mixture to the most used substrate at biogas plants — maize silage, had also positive effect on biogas production during the biogas potential test. This fact was not proven during long-term operations of the reactors as the values of total cumulative biogas productions for the whole monitored period from reactors for anaerobic digestion of maize silage with and without addition of enzymatic mixture did not differ significantly.

Comparison of the Deep Euteutic Solvent (DES) Solvent for Extracting Lignin from the Lignocellulosic Material of Pineapple Leaves

Background: Lignocellulosic biomass is one of the materials that has the potential to produce cellulose. Lignocellulose material consists of lignin, hemicellulose and cellulose so that the three materials must be separated first to get pure cellulose. The main problem faced in the process of separating cellulose is the difficulty of separating lignin. One of the processes in separating lignin is by pretreatment of lignocellulosic material. Methods: In this study, Deep Euteutic Solvent (DES) choline (ChCl) as a hydrogen bond acceptor was synthesized and eight hydrogen bond donors (HBD) were mixed. Eight types of DESs, i.e. , choline chloride-acetic acid (ChCl-AA), ChCl: formic acid (ChCl-FA). ), choline chloride: Lactic acid (ChCl-LA), choline chloride:Citric acid (ChCl-SA), choline chloride: Glycerol (ChCl-G), choline chloride: Ethylenglycol (ChCl-EG), choline chloride: Sorbitol (ChCl-S), and choline chloride: Urea (ChCl -U) with a ratio of 1: 2 were investigated. Each. DES solvent was applied as a pretreatment for the lignocellulosic material of pineapple leaves. The results of the pretreatment formed were characterized by the Infra Red spectroscopic method to determine the typical functional groups. Result: The results showed that the pretreatment process using DES solvent resulted in a decrease in lignin levels in pineapple leaf powder, the highest in DES with linear saturated acid-based HBD, formic acid at 32.05%, glycerol at 30.18% and then in alpha hydroxy-based HBD, acetic acid at 29.90%. Meanwhile, the FT-IR results show that ChCl-FA has a high delignification ability during pretreatment. Pineapple leaves that have been pretreted with DES solvent can be a potential raw material for the next conversion process. This study presents DES as an effective and easy pretreatment method for lignin extraction.

Increasing the Biogas Potential of Rapeseed Straw Using Pulsed Electric Field Pre-Treatment

Due to the high availability of lignocellulosic biomass, which can be obtained from terrestrial plants, agricultural waste biomass, and the agro-food, paper or wood industries, its use for energy production by methane fermentation is economically and environmentally justified. However, due to their complex structures, lignocellulosic substrates have a low conversion factor to biogas. Therefore, scientists are still working on the development of new methods of the pre-treatment of lignocellulosic materials that will increase the biogas productivity from lignocellulosic biomass. The presented research focuses on the use of a pulsed electric field (PEF) to disintegrate rapeseed straw prior to the methane fermentation process. Scanning electron microscopy observation showed that, in the disintegrated sample, the extent of damage to the plant tissue was more severe than in the control sample. In the sample disintegrated for 7 min, the chemical oxygen demand increased from 4146 ± 75 mg/L to 4920 ± 60 mg/L. The best result was achieved with a 5-min PEF pre-treatment. The methane production reached 290.8 ± 12.1 NmL CH4/g VS, and the biogas production was 478.0 ± 27.5 NmL/g VS; it was 14% and 15% higher, respectively, compared to the control sample.

Enhancing biogas production from agroindustrial waste pre-treated with filamentous fungi.

Biogas is the product of anaerobic digestion (AD) of organic waste and is considered to be one of the most valuable natural renewable energy carriers. Plant biomass represents the most abundant eco-friendly energy reservoir on Earth. However, the tenacious and heterogeneous structure of the lignocellulose-rich elements makes it difficult for the involved microbes to digest the recalcitrant substrates. Both the degradation process and the biogas production yield can be enhanced by appropriate pre-treatment of lignocellulosic materials. Filamentous fungi have been known as proficient colonizers of lignocellulosic plant tissues and have been recognized as producers of exceptionally rich and diverse hydrolytic enzymes. We tested Aspergillus nidulans, Trichoderma reesei, Rhizomucor miehei and Gilbertella persicaria filamentous fungal strains for pre-treatment of various agricultural lignocellulosic wastes. During the pre-treatment phase, the β-glucosidase and endoglucanase activity was measured spectrophotometrically. In the AD step, methane production was monitored by gas chromatography. The preliminary results showed that all the applied strains (Aspergillus nidulans, Trichoderma reesei, Rhizomucor miehei and Gilbertella persicaria) were highly effective in producing both β-glucosidase and endo-(1,4)-β-D-glucanase enzymes, which might explain the greatly improved AD results. Pre-treatment with the above-mentioned filamentous fungi positively affected the biogas production, although the effect strongly depended on the selection of the fungal partner for any given biomass substrate. Depending on the used substrate and the pre-treatment strain, overall methane yields were elevated two-fold relative to the controls.

Analysis of the response of the cell membrane of Saccharomyces cerevisiae during the detoxification of common lignocellulosic inhibitors

Gaining an in-depth understanding of the response of Saccharomyces cerevisiae to the different inhibitors generated during the pretreatment of lignocellulosic material is driving the development of new strains with higher inhibitor tolerances. The objective of this study is to assess, using flow cytometry, how three common inhibitors (vanillin, furfural, and acetic acid) affect the membrane potential, the membrane permeability and the concentration of reactive oxygen species (ROS) during the different fermentations. The membrane potential decreased during the detoxification phase and reflected on the different mechanisms of the toxicity of the inhibitors. While vanillin and furfural caused a metabolic inhibition and a gradual depolarization, acetic acid toxicity was related to fast acidification of the cytosol, causing an immediate depolarization. In the absence of acetic acid, ethanol increased membrane permeability, indicating a possible acquired tolerance to ethanol due to an adaptive response to acetic acid. The intracellular ROS concentration also increased in the presence of the inhibitors, indicating oxidative stress. Measuring these features with flow cytometry allows a real-time assessment of the stress of a cell culture, which can be used in the development of new yeast strains and to design new propagation strategies to pre-adapt the cell cultures to the inhibitors.

Ethanol Production from Wheat Straw Hydrolysate by Issatchenkia Orientalis Isolated from Waste Cooking Oil

The interest in using non-conventional yeasts to produce value-added compounds from low cost substrates, such as lignocellulosic materials, has increased in recent years. Setting out to discover novel microbial strains that can be used in biorefineries, an Issatchenkia orientalis strain was isolated from waste cooking oil (WCO) and its capability to produce ethanol from wheat straw hydrolysate (WSHL) was analyzed. As with previously isolated I. orientalis strains, WCO-isolated I. orientalis KJ27-7 is thermotolerant. It grows well at elevated temperatures up to 42 °C. Furthermore, spot drop tests showed that it is tolerant to various chemical fermentation inhibitors that are derived from the pre-treatment of lignocellulosic materials. I. orientalis KJ27-7 is particularly tolerant to acetic acid (up to 75 mM) and tolerates 10 mM formic acid, 5 mM furfural and 10 mM hydroxymethylfurfural. Important for biotechnological cellulosic ethanol production, I. orientalis KJ27-7 grows well on plates containing up to 10% ethanol and media containing up to 90% WSHL. As observed in shake flask fermentations, the specific ethanol productivity correlates with WSHL concentrations. In 90% WSHL media, I. orientalis KJ27-7 produced 10.3 g L−1 ethanol within 24 h. This corresponds to a product yield of 0.50 g g−1 glucose (97% of the theoretical maximum) and a volumetric productivity of 0.43 g L−1 h−1. Therefore, I. orientalis KJ27-7 is an efficient producer of lignocellulosic ethanol from WSHL.

Compositional and microstructural changes in compressed hot water pretreated corn stalk

Lignocellulosic materials are currently the most economic and environmental friendly precursors for production of fuel and biochemical. Understanding the intricate effect of pretreatment on the lignocellulosic composition would be an advantage to predict their proper utilization for biochemical production. Compressed Hot-Water (CHW) pretreatment was used to disrupt Corn stalk (CS) cell walls at temperature range 100–200 ​°C for reaction time 10 ​min. Highest glucose recovery was recorded in CS pretreated at 180 ​°C while furfural, 5-Hydroxymethylfurfural (5-HMF) and total phenolics concentrations were highest in 200 ​°C. Crystallinity Index (CrI) of the pretreated CS increased with increase in severity of the Pretreatment Temperature (PT); while Fourier-Transform Infrared (FTIR) spectroscopic images showed changes in the functional groups of CS as the PT was gradually intensified. Cumulatively, changes in chemical and structural profile of pretreated lignocellulosic material could be determining factor for its utilization in the production of biofuels and biochemicals.

Dilute acid hydrolysis pretreatment for sugar and organic acid production from pineapple residues

Pineapple residue which is pineapple leaves composed of about 80% of carbohydrate containing lignin, cellulose and hemicellulose was utilised for the production of fermentable sugars. However, pretreatment of lignocellulosic material is required to remove hemicellulose and lignin and reducing crystallinity of cellulose to enhance hydrolysis. This paper presents an experimental study of acid hydrolysis pretreatment in pineapple residue to produce sugar and organic acid using sulphuric acid. The effect of different acid concentration (4%, 8% and 12% v/v), solid-to-liquid ratio (10%, 15% and 20% w/v) and reaction time (40, 80, and 120 minutes) of acid hydrolysis pretreatment on pineapple residue at temperature of 100°C were studied to produce high yield of sugar and low organic acid production. As a result, the highest of sugar concentration simultaneously with the lowest of organic acids concentration from pineapple residue were 2.68 ± 0.12 g/L (xylose), 8.84 ± 0.11 g/L (glucose), 1.62 ± 0.20 g/L (formic acid) and 3.28 ± 0.26 g/L (acetic acid); recorded at conditions of 12% acid concentration (v/v), 20% solid-to-liquid ratio and 80 minutes of reaction time. In conclusion, dilute acid hydrolysis pretreatment was a great approach in order to produce high sugar at the same time with low organic acids yield from pineapple residue at mild conditions.

Physical techniques shed light on the differences in sugarcane bagasse structure subjected to steam explosion pretreatments at equivalent combined severity factors

Significant improvements in pretreatments and a deeper understanding of changes in the physical structure and chemical composition of pretreated lignocellulosic materials are required to guarantee the technical and economic sustainability of second-generation ethanol technologies. In present work, several biophysical techniques were applied to characterize sugarcane bagasse samples that have been subjected to autocatalytic, phosphoric acid and sulfuric acid catalyzed steam explosion under equivalent combined severity factors (CSF). Confocal laser scanning microscopy and fluorescence lifetime imaging studies demonstrated unequal changes in lignin distribution in the plant cell wall that could be nicely correlated with substrate susceptibility to enzymatic hydrolysis. Furthermore, solid state nuclear magnetic resonance corroborated these observations by showing the differences in biomass composition primarily associated with hemicellulose removal, whereas X-ray diffraction analysis revealed changes in crystallinity indexes and average crystallite sizes. Thus, the impact of pretreatment temperature on the physical structure and chemical composition of CSF-equivalent steam-exploded sugarcane bagasse was identified as the key factor for developing substrate accessibility. This calls for caution in using combined severity factor as a chief parameter for comparison of different pretreatment conditions.

A Cellulolytic Streptomyces Sp. Isolated from a Highly Oligotrophic Niche Shows Potential for Hydrolyzing Agricultural Wastes

Cellulases from Streptomyces species can be used as auxiliary agents in the pretreatment of lignocellulosic materials, but little work has been done on this topic. Besides, Streptomyces strains have been identified from Cuatro Cienegas basin, but their potential in the treatment of agricultural wastes has not been demonstrated. In this work a Streptomyces sp., strain CC48 isolated from the oligotrophic environment, shows high levels of cellulolytic activity (0.76 U/ mL at pH 7.0, 60 °C) in minimum medium supplemented with carboxymethyl cellulose compared with other Streptomyces strains and isolates in a bacterial collection. At least three putative cellulases (~30, 40, and 45 kDa) were identified in Streptomyces sp. CC48 extracts. The addition of Mg2+ increased cellulase activity by 23%, whereas other cations resulted in decreased catalysis. Residual cellulolytic activities after 4 and 8 h of incubation at 60 °C were ~ 73 and 65%, respectively, and ~ 98% at 50 °C after 8 h. Corn cob and wheat straw pretreated with an alkaline method showed saccharification values of 320 and 330 mg/g of reducing sugars per gram of dry substrate, respectively. The significance of this work lies in the fact that data provided here show that Streptomyces sp. strain CC48 is capable of hydrolyzing both maize and wheat substrates, suggesting the potential of this bacterium to hydrolyze agricultural wastes. Also, Cuatro Cienegas Basin may represent a source for efficient cellulolytic microorganisms.

Steam explosion pretreatment to obtain eco-friendly building blocks from oil palm mesocarp fiber

The pretreatment of lignocellulosic material via steam explosion process can be used to decrease the energy and chemical consumption during pulping to obtain environmentally friendly building blocks and improve the quality of materials by reducing the hemicellulose content. The objective of this work was to optimize the extraction of building blocks (lignin and cellulose) from oil palm mesocarp fibers using steam explosion pretreatment, followed by acetosolv and bleaching. The experimental central composite design 22 was used to optimize the steam explosion procedure prior to the acetosolv and bleaching processes. Although steam explosion increased the cellulose pulp yield by 47 % compared to without pretreatment (25 % vs 17 %), at 210 °C for 3 min, these conditions were not favorable for lignin extraction, which decreased from 56 % without pretreatment to 46 %. Pretreated cellulosic pulp had a higher purity, thermal stability, and crystallinity. Lignin with or without pretreatment showed similar characteristics. Our findings demonstrate that steam explosion is an efficient pretreatment for improving the characteristics of cellulosic pulp without affecting the quality of lignin, highlighting the potential use of these building blocks in the production of cellulose nanoparticles such as crystals and fibrils, as well as in the substitution of non-renewable phenols in resins.

Strategies for Increasing the Biohydrogen Yield in Anaerobic Fermentation of Xylose

The pretreatment of lignocellulosic materials to obtain cellulose generates a residual stream with hemicellulosic composition, mainly containing xylose. This C5 fraction is not directly fermentable by microorganisms traditionally used to produce ethanol. Hence, more promising alternatives for the C5 fraction have been studied, and acidogenic fermentation proves to be an attractive option for the production of biohydrogen, due to the possibility of using hemicellulose fractions and mixed anaerobic cultures. To reduce the activity of hydrogen-consuming microorganisms when mixed cultures are employed as inoculum to produce hydrogen by anaerobic fermentation, thermal pretreatment was selected. However, such pretreatment method also affects the activity of hydrogen-producing acidogenic bacteria, and strategies should be studied to enrich the inoculum for these bacteria and to increase hydrogen yields. Thus, this study evaluated the effect of some strategies on the biohydrogen production from xylose. The strategies adopted were thermal pretreatment of the sludge, maintenance of the incubation temperature at 35 °C, adaptation of the sludge by successive contacts with the xylose solution, and increasing inoculum to substrate ratio (I/S) from 1 to 2. This approach improved hydrogen yield approximately 30 times, from 0.03 to 0.93 mmol H2/mmol xylose. However, this yield was only 56% of the theoretical value and can still be improved.

Pretreatment of Lignocellulosic Materials as Substrates for Fermentation Processes.

Lignocellulosic biomass is an abundant and renewable resource that potentially contains large amounts of energy. It is an interesting alternative for fossil fuels, allowing the production of biofuels and other organic compounds. In this paper, a review devoted to the processing of lignocellulosic materials as substrates for fermentation processes is presented. The review focuses on physical, chemical, physicochemical, enzymatic, and microbiologic methods of biomass pretreatment. In addition to the evaluation of the mentioned methods, the aim of the paper is to understand the possibilities of the biomass pretreatment and their influence on the efficiency of biofuels and organic compounds production. The effects of different pretreatment methods on the lignocellulosic biomass structure are described along with a discussion of the benefits and drawbacks of each method, including the potential generation of inhibitory compounds for enzymatic hydrolysis, the effect on cellulose digestibility, the generation of compounds that are toxic for the environment, and energy and economic demand. The results of the investigations imply that only the stepwise pretreatment procedure may ensure effective fermentation of the lignocellulosic biomass. Pretreatment step is still a challenge for obtaining cost-effective and competitive technology for large-scale conversion of lignocellulosic biomass into fermentable sugars with low inhibitory concentration.

Temperature and pH effect on glucose production from pretreated bagasse by a novel species of Citrobacter and other bacteria

Cellulolytic bacteria that produce cellulases, which are active over a range of pH and temperatures, can be used to catalyze hydrolysis of pretreated lignocellulosic material. This is important in the production of second generation biofuels among other biotechnological applications. In this investigation, bacteria isolated from sugarcane bagasse were identified as strains of Enterobacter xiangfangensis, Serratia rubidaea, Klebsiella pneumoniae and a novel species of Citrobacter designated Citrobacter sp. UWIBGS10. The glucose production potential of these strains was studied on thermally and solvent pretreated sugarcane bagasse. This was performed at 24-hour intervals up to 168 hours in the range of pH 5–9 and temperature range 25–40 °C. Maximal concentrations of glucose for Citrobacter sp. UWIBGS10 occurred at pH 6 and 25 °C. For E. xiangfangensis, S. rubidaea, K. pneumoniae glucose concentrations were consistent across the pH and temperature ranges examined. From these results it could be concluded that the bacteria demonstrated ability for lignocellulolytic hydrolysis for the production of glucose and could be further explored for the characterization of commercial cellulolytic enzymes.

Water retention value predicts biomass recalcitrance for pretreated lignocellulosic materials across feedstocks and pretreatment methods

Understanding the causes of lignocellulosic biomass recalcitrance is necessary for developing robust biomass conversion processes for fuels and chemicals. A key factor in biomass recalcitrance is the physical and chemical relationship between biomass and water. Water is known to be important for enzymatic hydrolysis both because it is a co-substrate for cellulose hydrolysis, but also because it acts as a swelling agent that allows enzymes access to the substrate. It has been shown that the water retention value, and water constraint as measured by spin–spin low field NMR (T2 LFNMR) techniques, correlated to biomass recalcitrance for similar lignocellulosic materials pretreated at different severities. In this work, water retention and water constraint was measured across species and pretreatment methods and compared to the enzymatic digestibility of the cellulose fraction. There is an overall positive correlation between the water retention value and glucose hydrolysis yields. Average water constraint in the samples (as represented by monocomponent T2 decay times) could not be correlated to biomass recalcitrance; however a relationship was found between the relative amount of more highly constrained water measured and hydrolysis performance. Feedstock heterogeneity and differences in sample morphology may account for the variation in the sample set. Further research is needed to develop these predictive methods, but can be applied with good accuracy on specific feedstock types or for specific pretreatment methods.

Acid, alkali and peroxide pretreatments increase the cellulose accessibility and glucose yield of banana pseudostem

Lignocellulosic biomasses such as banana pseudostem are attractive cellulose sources for bioenergy production, and for the use in biorefinery processes. However, pretreatment of lignocellulosic material is required to remove hemicellulose and lignin, while increasing cellulose accessibility to enzymatic hydrolysis (i.e., decreasing biomass recalcitrance). The effect of different concentrations of acid (H2SO4), alkaline (NaOH) and peroxide (H2O2) pretreatments on the chemical composition, cellulose accessibility, and enzymatic digestibility of banana pseudostem were studied. The water insoluble solids (WIS) recovery was low (∼30%) for the severe pretreatment conditions applied, indicating high material solubilization. Acid pretreatment completely removed the hemicellulose content, whereas alkaline and peroxide pretreatments reduced its amount to 4.38 and 8.68%, respectively. In contrast, the lignin content increased (from 17.26 to 39.99%) after severe acid pretreatment, while alkaline and peroxide pretreatments reduced the lignin content to 7.65% and 7.17%, respectively. In line with hemicellulose and lignin removal, the cellulose content increased from 60.84 to 75.48 and 74.37%, respectively for alkaline and peroxide pretreatments, with no alteration for acid. Dye adsorption assays showed that alkaline and acid pretreatments resulted in high internal and external specific surface areas – indicative of high cellulose accessibility – when compared with peroxide pretreatments. Overall, alkaline and acid pretreatments resulted in the highest glucose yields from enzymatic hydrolysis of banana pseudostem, compared with peroxide pretreatment. In conclusion, concentrations of each pretreatment that led to the highest glucose yields was identified, confirming that the banana pseudostem is a great source of fermentable sugars, with high potential for biofuel production.

Inhibition of enzymatic hydrolysis of pretreated corn stover and sugar cane straw by laccases

Laccase detoxification has been proposed to enhance the enzymatic hydrolysis of lignocellulosics by reducing the effect of inhibitors formed during the pretreatment step. Herein, we investigated the effect of the laccase treatment on the enzymatic hydrolysis of two lignocellulosic materials pretreated by diluted acid/steam explosion through two strategies. Simultaneous laccase treatment and enzymatic hydrolysis of pretreated corn stover (PCS) and sugar cane straw (PSCS) led to a significant reduction of the concentration of glucose released from 67.7 down to 39.2 g/Kg and from 69 down to 53.5 g/Kg. Laccase treatment prior to hydrolysis of both substrates showed the same inhibitory effect. After hydrolysis of PCS and PSCS, the glucose concentration decreased by approximately 44 and 21% compared to the control assays, respectively. Therefore, these results do not support the use of laccases to detoxify pretreated lignocellulosic materials for improving the bioethanol production.

Municipal solid waste as a suitable substrate for butanol production as an advanced biofuel

The biodegradable fraction of municipal solid waste (BMSW), dominantly composed of starchy and lignocellulosic materials, has high potential to be used for liquid biofuel production. Hot water or dilute acid treatment at high temperature was utilized for the solubilization or hydrolysis of the starch fraction and pretreatment of the lignocellulosic fraction. The treatment liquor, which was rich in sugars and starch, was evaluated for acetone, butanol, and ethanol (ABE) production by Clostridium acetobutylicum, and it was found that phenolic compounds, especially tannins, critically inhibited the butanol production. To improve ABE production, the extraction of phenolic compounds prior to hot water or dilute acid treatment was evaluated. Among the evaluated extractants, i.e., acetone, ethanol, butanol, and water, ethanol showed the highest amount of tannin extraction, resulting in an 87% reduction in tannin content. Dilute acid treatment of the ethanol extracted BMSW at 140 °C for 60 min resulted in a liquor containing 23 g/L glucose and 41 g/L soluble starch, which was fermented to the highest ABE concentration of 17 g/L with productivity of 0.24 g/L/h. The fermentation of liquor obtained by dilute acid treatment of butanol, acetone, and water-extracted BMSW was accompanied by 9, 6, and 4 g/L ABE production. Even by hot water treatment, the liquor obtained from ethanol extracted BMSW was fermented to the highest ABE concentration of 8 g/L. In addition to the liquor, the pretreated lignocellulosic material was subjected to enzymatic hydrolysis and ABE fermentation, leading to production of 5–6 g/L ABE. This process resulted in the production of 83.9 g butanol, 36.6 g acetone, and 20.8 g ethanol from each kg of BMSW. Moreover, the co-production of ethanol by ABE fermentation reduced concerns about organic extractor loss in the extraction process, which was inescapable in the tannin extraction process.

Physical and Chemical Characterization of Agave tequilana Bagasse Pretreated with the Ionic Liquid 1-Ethyl-3-Methylimidazolium Acetate

Pretreatment of lignocellulosic biomass remains a bottleneck for the production of second-generation bioethanol. Conventional pretreatments have had moderated success in meeting the criteria to be considered cost and energy efficient; however, ionic liquids have shown promising results. 1-ethyl-3-methylimidazolium acetate is one of the most successful ionic liquids used for biomass dissolution. The physical and chemical changes of ionic liquid pretreated lignocellulosic materials must be thoroughly studied to maximize the benefits of this technology. Agave tequilana bagasse (a major source of residual lignocellulosic biomass in Mexico) was pretreated using ionic liquid at four different temperatures: 40, 80, 120 and 160 °C. Untreated and pretreated samples were chemically characterized, and their physical properties were studied using X-ray diffraction, thermogravimetric analysis, attenuated total reflection Fourier-transform infrared spectroscopy, scanning electron microscopy, and surface area analysis using a BET model. Positive effects in the physical characteristics of the bagasse were obtained: an increase in surface area, decrease in cellulose crystallinity, and lignin content were observed at temperatures up to 120 °C. Higher temperatures were detrimental for these characteristics.