Enhanced hydrolysis of bamboo biomass by chitosan based solid acid catalyst with surfactant addition in ionic liquid

Simultaneous saccharification of hemicellulose and cellulose of corncob in a one-pot system using catalysis of carbon based solid acid from lignosulfonate

The drive towards sustainable chemistry has inspired the development of active solid acids as catalysts and ionic liquids as solvents for an efficient release of sugars from lignocellulosic biomass for future biorefinery practices. Carbon-based solid acid (SI-C-S-H2O2) prepared from sodium lignosulfonate, a waste of the paper industry, was used with water or ionic liquid to hydrolyze corncob in this study. The effects of various reaction parameters were investigated in different solvent systems. The highest xylose yield of 83.4% and hemicellulose removal rate of 90.6% were obtained in an aqueous system at 130 °C for 14 h. After the pretreatment, cellulase was used for the hydrolysis of residue and the enzymatic digestibility of 92.6% was obtained. Following these two hydrolysis steps in the aqueous systems, the highest yield of total reducing sugar (TRS) was obtained at 88.1%. Further, one-step depolymerization and saccharification of corncob hemicellulose and cellulose to reducing sugars in an IL-water system catalyzed by SI-C-S-H2O2 was conducted at 130 °C for 10 h, with a high TRS yield of 75.1% obtained directly. After recycling five times, the solid acid catalyst still showed a high catalytic activity for sugar yield in different systems, providing a green and effective method for lignocellulose degradation.

Construction of an enzymatic shuttling compartment based on reverse micellar for bamboo biomass hydrolysis in ionic liquids

The enzymatic saccharification of regenerated lignocellulose must occur separately due to the toxicity of ionic liquids to cellulase. Therefore, it is important to develop a biocompatible IL-cellulase system which effectively achieves activation and saccharification of lignocellulose. For this purpose, a dual-phase "enzyme-shuttling compartment" was constructed in this study. Tween 80 was found to form reverse micelles in the isooctane-IL two-liquid phase, acting as a microenvironment that maintains the energetic conformation of the reactive cellulase. The activated bamboo biomass was enzymatically hydrolyzed in 20% (w/v) 1-ethyl-3-methylimidazolium dimethyl phosphate and 50 mM citrate buffer at 50 °C, achieving a high total reducing sugar yield of 71.2% and maintaining an enzymatic activity of 91.2% after 24 h. Thus, an efficient system with the simultaneous activation and saccharification of natural biomass was successfully developed in a one-pot procedure at low temperatures, ensuring large-scale biomass conversion into biofuels and biological products.

Efficient and Selective Catalytic Conversion of Hemicellulose in Rice Straw by Metal Catalyst under Mild Conditions

Rice straw is an abundant material with the potential to be converted into a sustainable energy resource. Transition-metal catalysis activated the C–O bond in the hemicellulose of raw rice straw, cleaving it to form monosaccharides. The mechanism of rice straw catalytic conversion had a synergistic effect due to in situ acid catalysis and metal catalysis. The conditions for the hydrogenation of hemicellulose from rice straw were optimized: catalyst to rice straw solid/solid ratio of 3:10, stirring speed of 600 r/min, temperature of 160 °C, time of 3 h, solid/liquid ratio of 1:15, and H2 gas pressure of 1.5 MPa. An excellent hemicellulose conversion of 97.3% with the yields of xylose and arabinose at 53.0% and 17.3%, respectively, were obtained. The results from FTIR and SEM experiments also confirmed the destruction of the rigidity and reticulate structure of rice straw after the catalytic reaction.

Green biorefinery - the ultra-high hydrolysis rate and behavior of Populus tomentosa hemicellulose autohydrolysis under moderate subcritical water conditions

A high monosaccharide conversion rate of hemicellulose in a green solvent and under moderate reaction conditions for industrialization is one of the most important keys in a lignocellulosic biorefinery. The behavior of Populus tomentosa hemicellulose polysaccharides, crystallinity and the furfural formation in the autohydrolysis process under moderate subcritical water conditions (160-180 °C, 0.618-1.002 MPa) were studied. The results have shown that the hemicellulose was converted to corresponding monosaccharides at an ultra-high hydrolysis rate. Factor analysis indicates that the temperature is the most important factor affecting hemicellulose autohydrolysis. When the autohydrolysis temperature increased from 160 to 180 °C for 2 h, the hydrolysis rate of xylose, rhamnose, galactose, mannose, and glucose from hemicellulose increased from 70% to 91%, 71% to 100%, 82% to 95%, 42% to 58%, and 34% to 37%, respectively. Arabinose was completely dissolved in 30 min. The xylose, rhamnose, galactose, and arabinose from hemicellulose could be almost completely removed under the conditions. The hemicellulose removal rate obtained herein exceeded the values reported for most acid, alkali, ionic liquid, or deep eutectic solvent treatments. It is notable that almost all glucose in hemicellulose was dissolved and the glucose in cellulose was partially hydrolyzed. An analysis of the sugar composition and the crystallinity change in the process at 180 °C demonstrate that hydrolysis reaction started to shift from amorphous regions to crystalline regions, due to the partial hydrolysis of crystalline cellulose after 90 min at 180 °C. Overall, these results show that the moderate subcritical water autohydrolysis of hemicellulose in Populus tomentosa may be a potential bio-refinery process.

Selective removal of lignin to enhance the process of preparing fermentable sugars and platform chemicals from lignocellulosic biomass

The economic dependency on fossil fuels and the resulting effects on climate and environment have put more focus on finding alternative renewable sources (e.g. lignocellulose) for the production of fuels and chemicals. Nevertheless, the yield and quality of fermentable sugar and platform chemical produced by directly degradation of lignocellulose are severely restricted owing to the presence of lignin and its derivatives. Therefore, the present study was aimed to selective removal of lignin to enhance the process of preparing fermentable sugars and platform chemicals from lignocellulosic biomass. The results showed that the highest degree of delignification was 92.01%. Reducing sugar obtained by enzymatic hydrolysis of lignocellulose was suitable for L-lactic acid fermentation without appreciable inhibition. The highest cellulose digestibility and yield of 5-HMF were 90.67% and 61.02%, respectively. SO₄^2-/ZrO₂ could be reused at least 5 times without appreciable loss of catalytic performance, which shows an industrial application prospects in biorefinery.

Consolidated bioprocessing of surfactant-assisted ionic liquid-pretreated Parthenium hysterophorus L. biomass for bioethanol production

The current study presents the first ever report of surfactant (Tween-20) assisted ionic liquid IL, (1-ethyl-3-methylimidazolium methane sulphonate [Emim][MeSO₃]) pretreatment of Parthenium hysterophorus biomass, its saccharification by in-house developed enzyme cocktail from Aspergillus aculeatus PN14, and fermentation of sugars to bioethanol under consolidated bioprocess. Optimization of pretreatment process variables viz. biomass loading, temperature and time, resulted in enhanced sugar yield (40.1%) upon saccharification of pretreated biomass with IL-stable cellulase and xylanase enzymes from an IL-tolerant newly isolated fungus Aspergillus aculeatus PN14. Physicochemical analysis of surfactant assisted IL-pretreated biomass by SEM, FT-IR and XRD provided molecular insights into inter/intra molecular ultrastructural changes in the biomass that eased the saccharification. Thorough understanding of chemical/molecular structure of biomass may help developing customized pretreatment regimes of apt severity which might result in enhanced accessibility of enzymes to biomass, and hence more sugar content.

Fractionation of Lignocellulosic Biomass by Selective Precipitation from Ionic Liquid Dissolution

We propose the treatment of barley straw with 1-ethyl-3-methylimidazolium acetate [EMIMAcO] ionic liquids (ILs) and subsequent precipitation with antisolvent mixtures, thus allowing the separation of the sugar-rich fractions (cellulose and hemicellulose) from the lignin fraction. For this purpose, different concentration ranges of acetone:water antisolvent mixtures were studied. In all cases, a high recovery percentage and a high and effective separation of fractions was achieved for 1:1 acetone:water. The fractionated lignocellulosic compounds were studied by using infrared spectroscopy, scanning electron microscopy and 1H nuclear magnetic resonance characterization techniques. This method allows the possibility of reusing IL, confirming the versatility of the established method. The fraction rich in cellulose and hemicellulose was subjected to acid hydrolysis (0.2 mol/L H2SO4) for 5 h at 140 °C, obtaining a yield of total reducing sugars of approximately 80%, much higher than those obtained in non-pretreated samples.