Mechanical pretreatment of lignocellulosic biomass to increase the yield of enzymatic hydrolysis

摘要

Sugar is a core transitional biofeedstock produced in a biorefinery process that can be further converted into biofuels or chemicals thus offering a sustainable alternative to fossil fuel-based chemicals. However, one challenge of sugar production from lignocellulosic biomass is to develop an efficient pretreatment process to improve the efficiency of enzymatic hydrolysis, due to its unique lignocellulosic biomass recalcitrances.;Disk refiners usually used in mechanical pulping mills might have become idled industrial machines because of the low demand for traditional products. The disk refining technology has attracted attention for the lignocellulosic biomass pretreatment in a biochemical conversion process, since it can improve enzymatic digestibility by removing biomass recalcitrances. Also, using existing highly commercialized disk refining equipment into a biorefinery mill would significantly lower investment cost and reduce associated risks.;In this thesis, an existing disk refining system (pilot plant scale) utilized as a pretreatment process has been modified to obtain a high sugar yield by enzymatic hydrolysis with a low energy consumption for different lignocellulosic biomasses.;In the first phase, a thermal treatment with NaOH addition (5% w/w biomass) before disk refining was studied for hardwood chips. The residues were the feedstocks of the disk refining system at various disk refining gap sizes from 0.15 mm to 1.00 mm and consistency from 5% to 15%. The solid residues then were used for enzymatic hydrolysis. - The results showed that the thermal treatment (140?C) with NaOH addition can partially remove lignin and significantly increase sugar yield. It also reduces energy consumption of mechanical pretreatment. - Low consistency refining can reduce energy cost and slightly decrease sugar yield. Small refining gap size increases sugar yield while results in significantly higher energy cost. - The strategy of the thermochemical disk refining pretreatment (TCDRP) process consists of a two-step treatment: a thermochemical pretreatment (TCP) and a disk refining pretreatment (DRP). The optimum condition of TCDRP is NaOH addition of 5% (w/w dry biomass), steaming at 140?C for 30 minutes, refining consistency at 8% and refining gap at 0.80 mm. - Compared to a non-modified typical mechanical pulping process, the TCDRP pretreatment has higher sugar yield by 35% with an energy saving of 62%.;The second phase of this work focused on the investigation of the TCDRP on different lignocellulosic biomasses including white birch, black spruce, corn stover and alfalfa. It consists of the characterizations of chemical composition and physical structure, and analysis of energy consumption and sugar streams. - The results revealed that there is a removal of lignin and hemicelluloses by the TCDRP for all biomasses. The corn stover pretreated by the TCDRP had the lowest lignin content versus the other biomasses pretreated by the TCDRP. - At the same refining gap size, the TCPRP treated corn stover had the lowest fiber length while the TCDRP treated black spruce had the highest fiber length. According to energy consumption and sugar yield, this TCDRP had more effect on corn stover and alfalfa than on white birch and black spruce. In particular, the sugar yield of the TCDRP treated corn stover is the highest (97.3%) compared to other biomasses; its energy consumption is 196 kWh/ton.