Enhancing enzymatic hydrolysis efficiency of crop straws via tetrahydrofuran/water co-solvent pretreatment.

Pretreatment and enzymatic hydrolysis are critical steps in bio-ethanol production from lignocellulose. The enhancement of enzymatic hydrolysis of several typical crop straws and the particle size adaptability of sorghum straw by tetrahydrofuran/water co-solvent pretreatment were studied. Efficient cellulose conversions (>83.2%) and adequate hemicellulose conversion (>40.7%) were obtained from pretreated rice straw, sorghum straw, wheat straw and corn stover in enzymatic hydrolysis, and the highest glucose yield and xylose yield were 274.0 and 26.3 mg/g dry solid, respectively. Glucose production of 140.4 mg/mL was obtained when the pretreated sorghum straw with mixed particle sizes was employed in enzymatic hydrolysis at 20% solid loading (8 FPU/g cellulose). When the enzyme loading reduced to 4 FPU/g cellulose, 221.7 mg/g dry solid glucose yield and 68.6% enzymatic hydrolysis efficiency could be still obtained with 15% solid loading, exhibiting high potential for bio-ethanol production.

The inhibition of p-hydroxyphenyl hydroxyl group in residual lignin on enzymatic hydrolysis of cellulose and its underlying mechanism.

The controlling factors of the inhibition on enzymatic hydrolysis caused by residual lignin were identified with molecular level understanding of the mechanism. Residual lignin samples with different properties were isolated, characterized and added into the enzymatic hydrolysis of Avicel. It was found that the phenolic hydroxyl group (OH) was the main inhibitor in residual lignin, and the p-hydroxyphenyl OH was the crucial sub-structure that exhibited the highest inhibition and non-productive adsorption, ascribing to its higher electrophilicity and lower steric hindrance. The H-bond interaction and π-π stacking between phenolic OH of lignin and phenolic OH of tyrosine on the planar face of carbohydrate binding module of cellulase were probably responsible for the non-productive adsorption. The binding sites of H-bonds may be the H in phenolic OH of lignin and the O in phenolic OH of tyrosine, respectively, and that of the π-π stacking may be the benzene rings of them.

Pretreatment of Wheat Straw with Phosphoric Acid and Hydrogen Peroxide to Simultaneously Facilitate Cellulose Digestibility and Modify Lignin as Adsorbents.

Effective valorization of lignin is crucial to achieve a sustainable, economic and competitive biorefinery of lignocellulosic biomass. In this work, an integrated process was proposed based on a concentrated phosphoric acid plus hydrogen peroxide (PHP) pretreatment to simultaneously facilitate cellulose digestibility and modify lignin as adsorbent. As a dominant constitutor of PHP pretreatment, H2O2 input and its influence on the overall fractionation/lignin modification performance was thoroughly investigated. Results indicated that wheat straw was fractionated more efficiently by increasing the H2O2 input. H2O2 input had a significant influence on the digestibility of the obtained cellulose-rich fraction whereby almost 100.0% cellulose-glucose conversion can be achieved even with only 0.88% H2O2 input. Besides, the adsorption capacity of lignin on MB was improved (74.3 to 210.1 mg g-1) due to the oxidative-modification in PHP pretreatment with H2O2 inputs. Regression analysis indicated that -COOH groups mainly governed the lignin adsorption (R2 = 0.946), which displayed the considerable adsorption capacities for typical cationic substances. This work shows a promising way to integrate the lignin modification concept into the emerging PHP pretreatment process with the dual goal of both cellulose utilization and lignin valorization.

Recycling solvent system in phosphoric acid plus hydrogen peroxide pretreatment towards a more sustainable lignocellulose biorefinery for bioethanol.

Pretreating lignocellulosic biomass by phosphoric acid plus hydrogen peroxide (PHP) was integrated with recovering concentrated phosphoric acid (CPA), lignin, and treating phosphorus (P) wastewater. Results indicated no significant effects on cellulose recovery was observed by promoting ethanol addition, but CPA and lignin recovery were improved to 80.0% and 23.3%, respectively. Increasing water addition did not greatly affect CPA recovery (80.0-80.4%), and lignin recovery (22.8-23.6%). Consequently, the ratio of 11:1 (ethanol/PHP solution) and 4:1 (water/de-ethanol liquor) were suggested for solid/liquid separation and lignin precipitation. Average 86.0% CPA was recycled for pretreatment (≥11 runs) with average 96.3% cellulose-glucose conversion. A specially-developed biochar from crab shell was efficient on P removal with maximal adsorption capacity of 261.6 mg/g. Pretreating 1.0 kg wheat straw by 1.1 kg CPA harvested 155.0 g ethanol, 45.0 g high purity lignin and 4.9 kg P-rich biochar fertilizer. Recovering CPA, biochar-fertilizer and lignin, and P wastewater treatment made PHP pretreatment towards more sustainable and cleaner.