Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Supervisor

Rehmann, Lars

Abstract

Lignocellulosic biomass, such as agricultural and forestry residues, can be transformed into valuable fuels and chemicals. However, the high cost of feedstock handling and the complex nature of cellulosic biomass processing and conversion remain two major challenges in biorefineries. This thesis aims to tackle these challenges by assessing the transformation of multi-feedstock using autohydrolysis pretreatment.

Corn cobs and stover (residues from corn processing), poplar chips (forestry residue), bagasse and wheat straw (agricultural residues) are abundant and often under-utilized cellulosic residues. These feedstocks were used to investigate the effects of biomass characteristics on the composition of the autohydrolysis pretreatment products. Moreover, biomass mixtures were used to improve the feedstock characteristics and increase their conversion into value-added compounds.

It was found that the relative abundance of xylan, Klason lignin, and acetate correlate with a feedstock’s susceptibility to hydrolysis, therefore affecting the autohydrolysis products. These structural compounds were used to develop the C5-Hydrolysis Index (C5HI) of each feedstock. The C5HI was then analyzed for the production of xylo-oligosaccharides (XOS), for solvents production by ABE (Acetone-Butanol-Ethanol) fermentation, and to assess the potential for ethanol production. Furthermore, the C5HI of individual feedstocks were used to select mixtures and study how the change in the feedstock C5HI affects the autohydrolysate.

Results show that feedstocks presenting high C5HI (poplar and corn cob) result in high xylan hydrolysis and high XOS production, while low C5HI (bagasse) leads to low XOS amounts and low total xylan recovery. Mixing feedstocks either improved or maintained a linear relationship for XOS production compared to the individual components. Additionally, higher solvents (acetone-butanol-ethanol) production by ABE fermentation were obtained when feedstocks with low C5HI were present in the mixture, attributed to the lower presence of sugar degradation products that inhibit fermentation. The pretreatment of mixed feedstocks also presented higher xylan solubilization and higher monomeric xylose, which increased enzymatic hydrolysis of the cellulose and could potentially decrease the need for oligosaccharides hydrolysis prior to ethanol fermentation. Therefore, the autohydrolysis of mixed biomass is presented as an alternative to improve feedstock logistics and pretreatment products.

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