Enzymatic hydrolysis of several pretreated lignocellulosic biomasses: Fractal kinetic modelling.

Enzymatic hydrolysis of three pre-treated lignocellulosic biomasses -LCB- (wheat straw-WS-, corn stover-CSV- and cardoon stems -CS-) is studied. These biomasses were pre-treated by two methods: diluted sulfuric acid and acid ethanol-water extraction at six severity levels (H values). Pretreated solid fractions were hydrolyzed with commercial enzyme cocktails at standard conditions. A first-order kinetic fractal model was fitted to the experimental results. This model accurately describes the hydrolysis of all biomasses at all pre-treatment conditions studied. The results show that the formal first-order kinetic constant k depends on the biomass nature. The hydrolysis rate increases as the pre-treatment severity does, while the fractal exponent value h decreases. With these pre-treatments, and in terms of k and h, WS is highly reactive and, at medium H with EW pretreatment, highly accessible; CSV has a low reactivity and high accessibility and CS has the lowest reactivity and an increasing accessibility as severity rises.

Liquor re-use strategy in lignocellulosic biomass fractionation with ethanol-water mixtures.

Liquor recycle in lignocellulosic biomass fractionation with ethanol-water has been studied. Runs have been carried out in a 6 L tank reactor with liquor recirculation. The liquors obtained in six successive fractioning operations have been analyzed together with the solid phase remnant. Experimental results revealed that the number of re-uses reduces solids recovery (from 52.2 to 42.6%) and cellulose recovery (from 28.1 to 23.3%) with minor or no effect on the hemicelluloses and lignin removal. The more remarkable effect is an increase of the glucose yield (from 76.7 to 95.3% after enzymatic hydrolysis during 72 h). The accumulation of acetic acid in the spent liquors (until 1.3 g/L) seems to be responsible of the higher enzymatic hydrolysis yield, from 76.3 (first use) to 87.7% (fifth re-use). Liquor re-use is effective to improve the sustainability of the pre-treatment obtaining a cellulose-rich solid easy to hydrolysate to sugars reducing energy consumption.

Thermal and operational deactivation of Aspergillus fumigatus ß-glucosidase in ethanol/water pretreated wheat straw enzymatic hydrolysis.

The stabilization effects on a novel commercial ß-glucosidase preparation from Aspergillus fumigatus during saccharification of ethanol-water pretreated wheat straw were analysed in comparison to this enzyme stability during cellobiose hydrolysis. For this purpose, the kinetics of ß-glucosidase residual activity during cellobiose hydrolysis from 40 till 70 °C were studied, resulting in the fitting of a first-order partial deactivation model. Furthermore, a subsequent fitting of a kinetic model including this first-order deactivation equation and a Michaelis-Menten equation with double competitive inhibition by glucose and uncompetitive inhibition by cellobiose to released glucose was successful. Finally, global enzyme deactivation and prospective deactivation of enzyme remaining in the liquid phase were evaluated during wheat straw hydrolysis at 50 °C as a relevant saccharification process. Results suggest that the presence of a solid substrate dramatically reduces the global deactivation rate of the enzyme and, in addition, there is no loss the stability of the enzyme in the liquid phase along the saccharification process, even for 72 h.

Pre-treatment of corn stover, Cynara cardunculus L. stems and wheat straw by ethanol-water and diluted sulfuric acid: Comparison under different energy input conditions.

Ethanol-water (EW) and diluted sulfuric acid (DSA) pre-treatment have been studied for lignocellulosic biomass (corn stover, Cynara cardunculus L. stems and wheat straw). Both pre-treatments have been compared taken into account: solids recovery, glucans recovery, xylans removed, delignification and glucose yield. In all cases, the amount of energy involved has been taken as a criterion for sustainability. In general terms, EW is more efficient to remove lignin and DSA more appropriate to hydrolysate xylans. The combined effect of delignification and xylans removal is responsible for the improvement in the enzymatic cellulose hydrolysis. Under conditions of moderate-low energy inputs, EW pre-treatment yields better results than DSA with glucose yields in the range of 50-60% for EW pre-treated corn stover and cardoon stems; while wheat straw pulps reach up to 80%. So, multiple raw materials biorefinery needs a previous study to fit the type and conditions of the pre-treatment to each feedstock.

Wheat straw fractionation by ethanol-water mixture: Optimization of operating conditions and comparison with diluted sulfuric acid pre-treatment.

The fractionation of wheat straw by ethanol-water (EW) pre-treatment was studied regarding its main operating conditions: time, temperature, L/S ratio and ethanol percentage were optimized by using an orthogonal experimental design (Taguchi). Afterwards, diluted sulfuric acid (DSA) hydrolysis and EW treatments have been compared in terms of energy consumption and yield of a cellulosic solid residue able to be enzymatically hydrolyzed to glucose. Experimental results show that temperature is the only variable of EW with a significant effect on the quality of the pretreated solids. EW pre-treatment of wheat straw is more effective than DSA hydrolysis due to its higher capacity of delignification. Moreover, a high glucose yield (80%) can be obtained by enzymatic hydrolysis of a solid pretreated with a moderate energy input EW (160 °C, 45 min) while wheat straw needs of a higher energy input during DSA to produce a similar yield of glucose after saccharification.