Integration of mild acid hydrolysis in γ-valerolactone/water system for enhancement of enzymatic saccharification from cotton stalk

Enhancing the potential production of bioethanol with bamboo by γ-valerolactone/water pretreatment

In this study, the effect of the γ-valerolactone (GVL)/H2O pretreatment system on bamboo (Neosinocalamus affinis) for enzymatic hydrolysis and ethanol fermentation was investigated. The performance characterization of the pretreated bamboo substrates, including the chemical composition, the structural characteristics, and the ability to produce bioethanol, were evaluated. The recovered substrates were enzymatically hydrolyzed for 48 h and then fermented to bioethanol. For the cellulose in the raw bamboo material, the highest cellulose-to-glucose conversion yield (CGCY) was achieved at 140 °C for 2 h with GVL : H2O = 8 : 2, which was 73.39%, and the cellulose-to-ethanol conversion yield (CECY) was 67.00%. This indicated that 183.5 kg of bioethanol could be produced per ton of bamboo, which was 9.71-folds higher than that directly converted from the untreated raw bamboo powder. Under these conditions, 50.60% of the active lignin can be recovered and be used as a wood-derived feedstock for further high-valued utilization. Meanwhile, the maximum concentration of fermentation inhibitors formed after pretreatment was about 140.9 mmol L-1, and had weak inhibition to the subsequent reaction. It has been shown that the cellulose could be effectively separated from bamboo and converted into bioethanol through the GVL/H2O pretreatment system.

Valorization of Miscanthus × giganteus by γ-Valerolactone/H2O/FeCl3 system toward efficient conversion of cellulose and hemicelluloses

γ-Valerolactone (GVL), a biomass-derived green chemical, offers an environmentally responsible solvent for conversion of lignocellulose to high value-added chemicals. Herein, we report a two-step process for directly producing cellulosic residual, furfural and lignin from Miscanthus × giganteus (M. × giganteus) bypassing the isolation of xylose, which exhibits promising advantage in energy reduction. The optimized pretreatment (100 mM FeCl₃ at 160 °C for 60 min) induced significant xylan removal (98.4%), resulting in rugged fibre surface, thus leading to the peak cellulose conversion of 99.3%. Furfural yield in the second step reached to 76.6% after 100 mM FeCl₃ catalyzed GVL/H₂O treatment at 180 °C for 10 min without addition of any chemical. The extracted lignin showed representative structure (such as β-O-4', β-β' linkages) and medium molecular weight (4275.5 g/mol). 79.6% of furfural can be recovered by distillation. This study proposes a systematic and energy efficient approach for maximizing biomass utilization.

Ethylene glycol based acid pretreatment of corn stover for cellulose enzymatic hydrolysis

A highly efficient pretreatment strategy using ethylene glycol with dilute sulfuric acid was developed for the fractionation of lignocellulose. The pretreatment behaviors were related to the composition analysis and structure of the samples analyzed by SEM, XRD, FTIR and 2D HSQC NMR, resulting in 80.3% delignification and 84.7% retention of cellulose under the selected conditions (120 °C, 60 min, and 0.6 wt% H2SO4 (w/w)). The enzymatic hydrolysis sugar yield significantly increased from 24.1 to 70.6% (3 FPU g-1), which displayed immense improvement compared with untreated corn stover (24.1%), nearly 3-fold higher than its untreated counterparts. Besides, the regenerated lignin could be fitted to valorize renewable aromatic chemicals and alkane fuels. The present study shows that the pretreatment is a simple, efficient and promising process for corn stover biorefinery.

Structural and Morphological Analysis of Cellulose Pulp Produced from the Fractionation of Eucalyptus obliqua Sawdust Using γ-Valerolactone

Organic solvents offer promising methods for the fractionation of Eucalyptus obliqua lignocellulosic biomass. This study investigated the impact of γ-valerolactone (GVL) fractionation on the morphology of cellulose and its internal structure using scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy. The solubilized lignin precipitated on the macrofibril surface as lignin spheres. GVL fractionation significantly increased the crystallinity of the recovered pulps from 0.29 for the sawdust to an average of 0.53 and a maximum of 0.66. The main states of cellulose that were susceptible to hydrolysis during the fractionation were amorphous and surface cellulose, both of which were reduced significantly, while paracrystalline and pure crystalline fractions in the pulp increased. It was concluded that GVL fractionation can produce a crystalline cellulose pulp of high quality suitable for further processing.

Acid-Assisted Organosolv Pre-Treatment and Enzymatic Hydrolysis of Cynara cardunculus L. for Glucose Production

Lignocellulosic biomass is a non-edible feedstock that can be used in integrated biorefinery for the production of biochemicals and biofuel. Among lignocellulosic biomass, Cynara cardunculus L. (cardoon) is a promising crop thanks to its low water and fertilizer demand. Organosolv is a chemical treatment that uses numerous organic or aqueous solvent mixtures, and a small amount of acid catalyst, in order to solubilize the lignin and hemicellulose fractions, making the cellulose accessible to hydrolytic enzymes. Lignocellulosic residues of cardoon underwent a two-step treatment process to obtain fermentable glucose. In the first step, the milled biomass was subjected to microwave-assisted extraction using an acidified γ-valerolactone (GVL)/water mixture, yielding a solid cellulose pulp. In the second step, the pre-treated material was hydrolyzed by cellulolytic enzymes to glucose. The first step was optimized by means of a two-level full factorial design. The investigated factors were process temperature, acid catalyst concentration, and GVL/water ratio. A glucose production equal to 30.17 g per 100 g of raw material (89% of the maximum theoretical yield) was achieved after conducting the first step at 150 °C using an acidified water solution (1.96% H2SO4w/w).

Stepwise separation of poplar wood in oxalic acid/water and γ-valerolactone/water systems

A cost-efficient methodology was developed for a two-step removal of hemicellulose from lignocellulosic biomass, thereby yielding C5 sugars, further separated residue, and high purity cellulose as well as lignin. In the first step of the process, an oxalic acid (OA)-assisted hydrolysis pretreatment was conducted for the selective decomposition of hemicellulose to C5 sugars. The optimized process conditions were as follows: temperature: 160 °C, OA concentration: 1%, holding time: 10 min. Under these conditions, various monosaccharides and other intermediates were obtained and more than 98.32% of the hemicellulose was removed from the original poplar. In the second step of the process, to extract lignin, a low concentration of sulfuric acid was used as a catalyst during the treatment of samples in a γ-valerolactone/H₂O system; more than 91.57% lignin was removed, 82.99% cellulose was retained in the solid cellulose-rich substrates, and 94.45% (i.e., high-purity) cellulose was obtained. This method can be used for efficient fractionation of hemicellulose, cellulose, and lignin with the aim of achieving high value utilization of the entire biomass.

A combined treatment method of oxalic acid/H₂O and γ-valerolactone/H₂O can be used for efficient fractionation of hemicellulose, cellulose, and lignin.

In situ deep eutectic solvent pretreatment to improve lignin removal from garden wastes and enhance production of bio-methane and microbial lipids

Biomass pretreatment can improve the conversion efficiency of bioenergy production. Liquid hot water (LHW) pretreatment is a truly green pretreatment due to its zero chemical use, but has the disadvantages of low lignin removal and pseudo-lignin formation. A modified liquid hot water (MLHW) process based on in situ synthesis of deep eutectic solvent (DES) could efficiently improve delignification of Roystonea regia leaves (LR) and leaf sheaths (LSR). LSR was less recalcitrant than LR, and its characteristics of higher porosity (34.8%) and thinner cell walls (5.2 μm) for LSR contributed it higher lignin removal (53.6%) and lower choline chloride (ChCl) consumption (H₂O-ChCl mass ratio of 2:1) than those (44.6% and 1:2) from LR. Moreover, a great improvement of 309.0% in bio-methane yield was achieved for the MLHW-treated LSR. In addition, in situ DES in MLHW had good biocompatibility with cellulase, microalgae, and yeast.

Bioethanol potential of Eucalyptus obliqua sawdust using gamma-valerolactone fractionation

Optimisation of conditions for gamma-valerolactone (GVL) pretreatment of Australian eucalyptus sawdust for high cellulose biomass and bioethanol production was demonstrated. Pretreatment parameters investigated included GVL concentrations of 35-50% w/w, temperatures of 120-180 °C and reaction durations of 0.5-2.0 h. Optimum conditions were determined using the response surface method (RSM) and central composite face-centred design. Cellulose content increased from 39.9% to a maximum of 89.3% w/w using treatments with 50% GVL at 156 °C for 0.5 h. Temperature had the most significant effect (RSM p < .05) on cellulose content of residual biomass and reducing operational duration of < 0.5 h may be viable according to RSM. PSSF fermentations of optimised pretreated eucalyptus sawdust produced up to 94% theoretical ethanol yield, which corresponded to approximately 181 kg of ethanol per dry ton of eucalyptus sawdust. The compositions of both the residual biomass and pretreatment liquors show that GVL pretreatment is a promising solvent for lignocellulosic biorefining.

Treatment of supermarket vegetable wastes to be used as alternative substrates in bioprocesses

Fruits and vegetables have the highest wastage rates at retail and consumer levels. These wastes have promising potential for being used as substrates in bioprocesses. However, an effective hydrolysis of carbohydrates that form these residues has to be developed before the biotransformation. In this work, vegetable wastes from supermarket (tomatoes, green peppers and potatoes) have been separately treated by acid, thermal and enzymatic hydrolysis processes in order to maximise the concentration of fermentable sugars in the final broth. For all substrates, thermal and enzymatic processes have shown to be the most effective. A new combined hydrolysis procedure including these both treatments was also assayed and the enzymatic step was successfully modelled. With this combined hydrolysis, the percentage of reducing sugars extracted was increased, in comparison with the amount extracted from non-hydrolysed samples, approximately by 30% in the case of tomato and green peeper wastes. For potato wastes this percentage increased from values lower than 1% to 77%. In addition, very low values of fermentation inhibitors were found in the final broth.

Valorization of bamboo by γ-valerolactone/acid/water to produce digestible cellulose, degraded sugars and lignin

A novel pretreatment process was developed to achieve valorization of bamboo components into digestible cellulose, degraded sugars and lignin. In this case, bamboo was pretreated with 60% γ-valerolactone (GVL)/40% water containing 0.05mol/L H₂SO₄, yielding solid fraction rich in cellulose. The resulting liquor was further treated with the addition of NaCl and ultrasound, resulting in water phase rich in degraded sugars and GVL phase containing lignin, which was easy to recover. Results showed that the enzymatic hydrolysis was enhanced by 6.7-fold after treatment as compared to the control. The degraded sugars released in water phase contained monosaccharides (70.72-160.47g/kg) together with oligo- and polysaccharides (46.4-181.85g/kg). The lignin obtained had high purity, low molecular weight (1820-2970gmol^-1) and low polydispersity (1.93-1.98). The present study creates a novel pretreatment process for the conversion of Gramineae biomass into useful feedstocks with potential applications in the fields of fuels, chemicals and polymers.

Analysis of the Cybotactic Region of Two Renewable Lactone-Water Mixed-Solvent Systems that Exhibit Synergistic Kamlet-Taft Basicity

Kamlet-Taft solvatochromic parameters (polarity, basicity, acidity) of hydrogen bond donor (HBD)/acceptor (HBA) mixed-solvent systems, water (H2O)-γ-valerolactone (GVL), methanol (MeOH)-GVL, ethanol (EtOH)-GVL, H2O-γ-butyrolactone (GBL), MeOH-GBL, and EtOH-GBL, were measured over their entire composition region at 25 °C using UV-vis spectroscopy. Basicity of H2O-GVL and H2O-GBL systems exhibited positive deviation from ideality and synergism in the Kamlet-Taft basicity values. The cybotactic region around each indicator in the mixed-solvent systems was analyzed with the preferential solvation model. Both H2O-GVL and H2O-GBL mixed-solvent systems were found to be completely saturated with mutual complex molecules and to have higher basicity than pure water because water prefers to interact with GVL or GBL molecules rather than with itself. Formation of H2O-GVL and H2O-GBL complex molecules via specific hydrogen bond donor-acceptor interactions were confirmed by infrared spectroscopy. In MeOH-GVL or MeOH-GBL mixed-solvent systems, MeOH molecules prefer self-interaction over that with GVL or GBL so that synergistic basicity was not observed. Synergistic basicity and basicity increase for various functional groups of ten mixed-solvent (water-HBA solvent) systems can be quantitatively explained by considering electrostatic basicity and a ratio of the partial excess HBA solvent basicity with the HBA solvent molar volume that correlate linearly with the preferential solvation model complex molecular parameter (f12/1). Analysis of the cybotactic region of indicators in aqueous mixtures with the preferential solvation model allows one to estimate the trends of mixed-solvent basicity.

Efficient recovery and structural characterization of lignin from cotton stalk based on a biorefinery process using a γ-valerolactone/water system

Lignin component (35.7–64.7%) was recovered by the pretreatment using γ-valerolactone/water system under different ratios of GVL to water.