Improvement of enzymatic hydrolysis and ethanol production from corn stalk by alkali and N-methylmorpholine-N-oxide pretreatments

Sugar Production from Hybrid Poplar Sawdust: Optimization of Enzymatic Hydrolysis and Wet Explosion Pretreatment

Wet explosion pretreatment of hybrid poplar sawdust (PSD) for the production of fermentable sugar was carried out in the pilot-scale. The effects of pretreatment conditions, such as temperature (170-190 °C), oxygen dosage (0.5-7.5% of dry matter (DM), w/w), residence time (10-30 min), on cellulose and hemicellulose digestibility after enzymatic hydrolysis were ascertained with a central composite design of the experiment. Further, enzymatic hydrolysis was optimized in terms of temperature, pH, and a mixture of CTec2 and HTec2 enzymes (Novozymes). Predictive modeling showed that cellulose and hemicellulose digestibility of 75.1% and 83.1%, respectively, could be achieved with a pretreatment at 177 °C with 7.5% O2 and a retention time of 30 min. An increased cellulose digestibility of 87.1% ± 0.1 could be achieved by pretreating at 190 °C; however, the hemicellulose yield would be significantly reduced. It was evident that more severe conditions were required for maximal cellulose digestibility than that of hemicellulose digestibility and that an optimal sugar yield demanded a set of conditions, which overall resulted in the maximum sugar yield.

Pretreatment of wheat straw leads to structural changes and improved enzymatic hydrolysis

Wheat straw (WS) is a potential biomass for production of monomeric sugars. However, the enzymatic hydrolysis ratio of cellulose in WS is relatively low due to the presence of lignin and hemicellulose. To enhance the enzymatic conversion of WS, we tested the impact of three different pretreatments, e.g. sulfuric acid (H₂SO₄), sodium hydroxide (NaOH), and hot water pretreatments to the enzymatic digestions. Among the three pretreatments, the highest cellulose conversion rate was obtained with the 4% NaOH pretreatment at 121 °C (87.2%). In addition, NaOH pretreatment was mainly effective in removing lignin, whereas the H₂SO₄ pretreatment efficiently removed hemicellulose. To investigate results of pretreated process for enhancement of enzyme-hydolysis to the WS, we used scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy to analyze structural changes of raw and treated materials. The structural analysis indicated that after H₂SO₄ and NaOH pretreatments, most of the amorphous cellulose and partial crystalline cellulose were hydrolyzed during enzymatic hydrolysis. The findings of the present study indicate that WS could be ideal materials for production of monomeric sugars with proper pretreatments and effective enzymatic base hydrolysis.

Insight into the efficient catalytic conversion of biomass to EG and 1,2-PG over W–Ni bimetallic catalyst

In this work, a mesoporous silica microsphere (MSM) was selected as a support to prepare a bimetallic supported catalyst (15% W–5% Ni/MSM) by a co-impregnation method that was simple and easy to conduct. We wished to improve the capability of catalytic conversion of biomass into ethylene glycol (EG) and 1,2-propylene glycol (1,2-PG). 15% W–5% Ni/MSM was examined on microcrystalline cellulose (cellulose) and corn stalks in a one-pot catalytic process, and total yields of EG and 1,2-PG reached up to 82.40 wt% and 62.60 wt%, respectively. This remarkable catalytic performance of W–Ni/MSM catalyst could be attributed to the synergistic effect between the active sites of Ni and W and the unique structure of MSM, which was suitable for mass transfer and metal loading. Based on physicochemical characterizations, the metal component was well-distributed on the surface of the MSM, and the metallic Ni, W and WO₃ of the fresh catalyst were converted mainly into NiWO₄ during the catalytic conversion of cellulose. To shed light on the reaction mechanism of the catalyzed hydrogenation of biomass, a possible process involving the formation of H_xWO₃ homogeneous catalysts, cellulose hydrolysis, C–C cleavage and hydrogenation conversion to 1,2-PG and EG was illustrated. Furthermore, the reusability of W–Ni/MSM catalyst was tested and we explored the cause of decreased diols yields. In summary, this work provides important guidance to rationally design effective catalysts for biomass conversion.

Bimetallic supported catalyst (W-Ni/MSM) was proposed to improve capability of catalytic conversion and investigated reaction pathway of lignocellulose into ethylene glycol and 1,2-propylene glycol.

Ionic-liquid pretreatment of cassava residues for the cogeneration of fermentative hydrogen and methane

An ionic liquid of N-methylmorpholine-N-oxide (NMMO) was used to effectively pretreat cassava residues for the efficient enzymatical hydrolysis and cogeneration of fermentative hydrogen and methane. The reducing sugar yield of enzymolysed cassava residues with NMMO pretreatment improved from 36 to 42g/100g cassava residues. Scanning electron microscopy images revealed the formation of deep grooves (∼4μm wide) and numerous pores in the cassava residues pretreated with NMMO. X-ray diffraction patterns showed that the crystallinity coefficient of NMMO-pretreated cassava residues decreased from 40 to 34. Fourier transform infrared spectra indicated that crystal cellulose I was partially transformed to amorphous cellulose II in the NMMO-pretreated cassava residues. This transformation resulted in a reduced crystallinity index from 0.85 to 0.77. Hydrogen yield from the enzymolysed cassava residues pretreated with NMMO increased from 92.3 to 126mL/gTVS, and the sequential methane yield correspondingly increased from 79.4 to 101.6mL/g TVS.

Cobalt-60 gamma-ray irradiation pretreatment and sludge protein for enhancing enzymatic saccharification of hybrid poplar sawdust

In order to improve the enzymatic saccharification of hybrid poplar sawdust, gamma irradiation pretreatment and enzymatic hydrolysis in the presence of sludge protein were investigated. The cellulose crystallinity index were significantly decreased after irradiation pretreatment, and adding sludge protein improved enzyme activity and increased the reducing sugar yield. The conditions of irradiation pretreatment and enzymatic hydrolysis in the presence of sludge protein were systematically examined. The maximum reducing sugar yield was 519mg/g under an irradiation dose of 300kGy, a sludge protein dosage of 2mg/mL, an enzymatic hydrolysis temperature of 45°C, an enzymatic hydrolysis time of 84h, and a 90FPU/g enzyme loading. This work indicated that the combined method of gamma irradiation pretreatment and enzymatic hydrolysis in the presence of sludge protein was a promising potential for the saccharification of hybrid poplar sawdust.