Impact of lignin composition on enzymatic hydrolysis of cellulosic biomass Public Deposited

http://ir.library.oregonstate.edu/concern/undergraduate_thesis_or_projects/9w032503q

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  • Lignocellulosic biomass has potential as a renewable resource for global energy and bioproducts production. Biomass consists of three main polymers, cellulose, hemicellulose, and lignin. Cellulose is a homopolymer of glucose, while hemicellulose and lignin are heteropolymers. Lignin is primarily made of syringyl (S), guiacayl (G) and p-hydroxyphenyl (H) units. Pretreatment of biomass is a critical step to reduce recalcitrance and facilitate further enzymatic hydrolysis. Several studies have demonstrated that the S/G ratio of lignin has a significant effect on the effectiveness of pretreatment. Lignin is known to solubilize, redistribute, precipitate, and coalesce as droplets during conventional pretreatment processes used in production of ethanol from cellulosic biomass. These transformations vary based on the type of the pretreatment process, and are attributed to the differences in the chemical composition and distribution of lignin in biomass. The goal of this study was to quantify the distribution of lignin droplets in order to understand how the S/G ratios of lignin affects enzymatic hydrolysis. Lignin from three biomass sources was isolated using organosolv process to obtain lignins with three S/G ratios. Isolated lignins with different S/G ratios and pure cellulose filter paper were subjected to dilute acid pretreatments (0.75% w/w sulfuric acid concentration) at 120, 150, and 180°C. Imaging of the pretreated filter paper was done using Scanning Electron Microscopy (SEM) to visually observe the distribution of the lignin droplets. Wheat straw lignin (with S/G ratio range of 0.50 to 0.69) was observed to produce many large and small droplets of sizes ranging 5.0 μm to well below 0.10 μm in diameter with an increase in droplet amount relative to higher temperatures. Bagasse was coated in a layer of tiny droplets that gave the surface a textured appearance throughout each temperature. Mostly uniform small and large droplets formed on poplar with an increase in amount as temperature increased. Larger droplet size did not correlate to a greater amount of lignin or S/G ratio, however lignin droplets appeared to increase in amount as temperatures increased.
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