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Document Type

Dissertation - University Access Only

Award Date

2012

Degree Name

Doctor of Philosophy (PhD)

Department

Agricultural and Biosystems Engineering

First Advisor

James L. Julson

Abstract

Lignocellulosic materials are considered the future of the biofuels and biobased products industry, thus creating a chance for petroleum independence. Due to its widespread availability and low cost of production, lignocellulose has huge potential to be a renewable and sustainable energy source. However, because of its complex and rigid structure, lignocellulose requires an effective pretreatment method prior to any further processing.
This dissertation focuses on clean fractionation, which is organosolv treatment applied to raw and extruded prairie cordgrass, switchgrass and com stover. The goal of these experiments was to examine the clean fractionation process as a pretreatment method for lignocellulosic biomass and its effectiveness in production of highly digestible cellulose pulp, hemicellulose and lignin fractions. The purpose of using two types of biomass (raw and extruded) was to investigate possible benefits of a two-step pretreatment process (extension and clean fractionation) in terms of enzymatic hydrolysis glucose yield and percent lignin and hemicellulose extraction. Statistical analyses and optimizations were performed for each of the feedstocks using Response Surface Methodology.
Raw prairie cordgrass (PCG), switchgrass (SG) and com stover (CS) were subjected to clean fractionation with the purpose of obtaining the highest glucose yields. Following clean fractionation (CF) processing, the lignocellulosic biomass was fractionated into its three main building blocks: cellulose, hemicellulose and lignin. Effects of processing factors such as time, (16-50 min), temperature (104-160°C), catalyst concentration (0.12-0.93% w/w) and organic solvent mixture composition (3-44% MIBK w/w) were evaluated. The organic solvent mixture contained methyl isobutyl ketone (MIBK), ethanol and water in different proportions. Sulfuric acid was used as a catalyst. In order to evaluate the effectiveness of pre-treatment, enzymatic saccharification was employed on the cellulose fraction obtained from the CF process. Response surface methodology was used for process optimization and statistical analysis. High rates of lignin and xylan removal from biomass were obtained, leaving solid pulp rich in glucan in all three feedstocks examined. High enzymatic hydrolysis glucoseyields (>90%) were obtained for selected optimal conditions. Additionally, relatively high separation of xylose and lignin fractions suggests the applicability of clean fractionation technology in a biorefinery concept.
All three feedstocks (PCG, SG and CS) were also pretreated by sequential extrusion and clean fractionation (CF) processing. Previous research optimized conditions, for each type of feedstock, were used for extrusion. Following CF, biomass was fractionated into cellulose-, hemicellulose-, and lignin-rich fractions. Cellulose pulp was then enzymatically hydrolyzed, producing glucose. The main purpose of this research was to produce the highest glucose yield possible. The effects of time, temperature, catalyst concentration and solvent mixture composition on the fractionation of pre-extruded biomasses were tested. Different proportions of methyl isobutyl ketone (MIBK), ethanol and water with sulfuric acid as a catalyst were evaluated. A central composite design was used for process optimization. Results showed high lignin and xylan removal from all three extruded feedstocks, leaving solid pulp rich in glucan. High enzymatic hydrolysis glucose yields (>90%) were obtained for selected optimal conditions.
In general, pairwise comparison between the clean fractionation of raw biomass and extruded biomass revealed no difference in glucose yields. However, xylan and AIT. removal were higher in the case of clean fractionation of the pre-extruded PCG, and xylan removal and xylose separation to the aqueous fraction was higher in the case of clean fractionation of the pre-extruded CS, whereas delignification was higher in the case of clean fractionation of raw CS and raw SG.

Library of Congress Subject Headings

lignocellulose
biomass conversion
biomass energy
extrusion process

Description

Includes bibliographical references (207-214)

Format

application/pdf

Number of Pages

230

Publisher

South Dakota State University

Rights

Copyright © 2012 Grzegorz Brudecki. All rights reserved

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