Browsing by Author "Wallace, Joshua"
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- ItemEnzymatic hydrolysis of steam pretreated bagasse : Enzyme preparations for efficient cellulose conversion and evaluation of physiochemical changes during hydrolysis(Stellenbosch : Stellenbosch University, 2013-03) Wallace, Joshua; Gorgens, Johann F.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH ABSTRACT: Biomass recalcitrance represents the major technical obstacle in 2nd generation bio-ethanol production, as it impedes efficient enzyme action. Elucidating how the recalcitrant nature of lignocellulosic biomass inhibits the enzymatic degradation of cell wall polysaccharides could help to overcome these obstacles. This decrease in overall enzymatic hydrolysis performance in the industry, calls for the addition of different enzymes that work synergistically to alleviate slow cellulose to glucose conversion rates and low final glucose yields. Furthermore, high enzyme dosages (greater than 25FPU/g cellulose ~ approximately 75g enzyme/ kg cellulose) are required for rapid biomass conversion rates and complete hydrolysis, which have a negative effect on the viability of the process, as enzyme addition is a cost intensive part of biomass derived bio-ethanol production. In this regard, this study strived to improve the 2nd generation bio-ethanol industry by elucidating the slowdown phenomenon related to biomass recalcitrance during enzymatic hydrolysis. The substrate and enzyme properties that affect enzymatic hydrolysis rate and yield were investigated. Additionally, screening and optimization of a commercially available enzyme cocktail for bio-ethanol production from steam pretreated sugarcane bagasse (SB) was performed. Therefore, in the present study, sugarcane bagasse was steam pretreated and subjected to enzymatic hydrolysis (Spezyme + Novozym 188) whereafter the kinetic of the conversion was studied. Furthermore, new commercially available cocktails (Cellic CTec2, Optiflow) were compared, and the dosage of the preferred cocktail (Cellic CTec2) optimized for the production of bio-ethanol from steam pretreated sugarcane bagasse. Additionally, xylanase (Cellic HTec2 and Multifect Xylanase), pectinase (Pectinex Ultra) and surfactant (Tween 80) supplementation was investigated for positive effects on glucose and xylose release, and on ethanol production. Three distinctive phases of cellulose conversion rates were observed in succession of each other: (1) initial fast phase, (2) intermediate, slower phase, and (3) the slowest recalcitrant phase. The material was characterised by physicochemical analysis during each of the stages during enzymatic hydrolysis. The results indicated that the slowdown was caused by an increased lignin/cellulose ratio combined with changes in accessible surface area for enzymatic action (determined by Simons‘ staining). Xylanase supplementation was the only significant factor improving the cellulase cocktails. The positive effect of xylanase on glucose and xylose release (rate and yield) was probably due to synergism between xylanases and cellulases, as well as the increased accessible surface area due to hemicellulose removal. Decreased solid loadings % (w/v) were also favorable for maximal cellulose conversion yield and rate with all enzymes studied. The optimized cocktail (0.15ml/g WIS Cellic CTec2 + 0.213ml/g WIS HTec2) resulted in 79.2% ethanol yield compared with 55% for the control cocktail, at equivalent volumetric dosages. The increased ethanol production yield and rate with the optimized cocktail was due to the presence of greater amounts of cellulase, xylanase, β-glucosidase and oxidative enzymes (GH61s). These enzymes possibly increased the accessible surface area for cellulose degradation vs. the control cocktail. Altogether, the recalcitrance caused by increasing lignin/cellulose ratio with subsequent decreases in accessible surface area was the most important factors slowing down enzymatic hydrolysis rate and yield. However, it seems that newer generations of enzymes, such as CTec2, were less susceptible to the increasing biomass recalcitrance during enzymatic hydrolysis of lignocellulose resulting in higher product formation.