Pretreatment And Fractionation Of Biomass For Biological Production Of Transportation Fuels And Value Added Chemicals

Lignocellulosic biomass is an abundant renewable material from hardwood, softwood, grasses and agricultural residues for ethanol production. Pretreatment of lignocellulosic materials has been a main technical challenge to a cellulosic ethanol production process. The purpose of this thesis is to investigate four pretreatment methods and conduct comparative analyses among pretreatment methods, chemicals used and biomass species to determine the best process in terms of glucan to ethanol conversion efficiencies. The separation of hemicellulose fractions to be used as precursors for the production of high value chemicals after pretreatment of biomass samples is also investigated. Pretreatment methods including Accelerated Solvent Extraction (ASE), Reactive Screw Extrusion (RSE), Continuous Stirred Tank Reactor (CSTR) and Ambient Storage Tank (AST) were used along with abrasive chemicals including 10% acetic acid, 10% ammonium hydroxide (NH4OH), 10% calcium hydroxide (Ca(OH)2), 30% ethanol solution and deionized water at different conditions for the fractionation of biomass into monomeric sugars for ethanol fermentation in a Simultaneous Saccharification and Fermentation (SSF) process. Separation of hemicellulose fractions after pretreatment was done via a liquid-liquid extraction procedure in a mass ratio of biomass extract to 95.5% ethanol solution at 1:4. xviii ASE pretreatment of biomass samples with 10% acetic acid solution at 180oC resulted in 100% solvation of hemicellulose fractions into the liquid extract stream for all biomass samples treated. Pretreatment of corn stover with a 10% ammonium hydroxide aqueous solution in the CSTR resulted in the glucose to ethanol conversion efficiency of 85.2%. Alkali (Ca(OH)2 and NH4OH) pretreatment of biomass in the AST resulted in the highest glucose to ethanol conversion yields of 30.4%, 23.0%, 38.2% and 47.4% for switch grass, corn stover wheat straw and sweet sorghum bagasse pretreated with 10% NH4OH respectively; 29.2%, 24.1%, 40.3% and 37.6% for switch grass, corn stover wheat straw and sweet sorghum bagasse pretreated with 10% Ca(OH)2 respectively over acetic acid and deionized water used in the AST. RSE pretreatment of switch grass using 10% Ca(OH)2 at 180oC resulted in a 75.5% glucose to ethanol conversion efficiency. Ammonium hydroxide pretreatment of biomass resulted in the highest hemicellulose fractions after liquid-liquid extraction with 95.5% ethanol solution