Date of Award

2023

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Rebecca G. Ong

Committee Member 1

David R. Shonnard

Committee Member 2

Michael R. Gretz

Committee Member 3

Smitha Rao Hatti

Abstract

Renewable fuels from lignocellulosic biomass are an appealing option because they can seamlessly integrate into the existing fuel distribution infrastructure. Lignocellulosic biomass constitutes nonedible plant material obtained from plant cell walls. The natural recalcitrance of lignocellulosic biomass poses a challenge in accessing the cell wall carbohydrates during biochemical conversion. Despite various approaches, enzymatic hydrolysis of lignocellulosic biomass remains economically impractical due to incomplete knowledge about biomass recalcitrance and the influence of environmental factors on biomass quality.

The first goal of this dissertation was to construct a microfluidic imaging reactor to better understand the tissue-specific deconstruction of plant materials. Confocal laser scanning microscopy was conducted on thin sections (60 mm thickness) of corn stems at different time points during dilute acid and dilute alkali pretreatment. The digestibility of the acid and alkali-pretreated biomass sections during enzymatic hydrolysis were evaluated using brightfield imaging. Corn stem parenchyma cells were more susceptible to deconstruction than vascular bundles in both pretreatment and enzymatic hydrolysis. After 48 hours of enzymatic hydrolysis, only the protoxylem remained undegraded.

The second goal was to investigate how increasing stem solidness impacts enzymatic digestibility in wheat straw using the microfluidic imaging reactor. This was based on the rationale that the pith parenchyma cells are more digestible than the other vascular cell types. During the pretreatment and enzymatic hydrolysis, the solid stemmed samples showed considerably greater amenability to degradation than the hollow and semisolid cultivars, which based on the imaging was largely due to the greater digestibility of the pith parenchyma cells.

The third goal was to develop a high-throughput, moderate-scale enzymatic hydrolysis method at high-solids loading to study the impact of drought and extreme weather conditions on biomass deconstruction. At the laboratory scale, high solids loading results in improper mixing and low saccharification due to low water availability. This was overcome using horizontal mixing on a laboratory scale roller to improve enzyme accessibility and obtain higher sugar yields. The saccharification for the roller bottle method was about 25-50% higher than the traditional shake flask method. This was evaluated for a variety of AFEX-pretreated feedstocks, including corn stover, sorghum, miscanthus, native prairie, and switchgrass.

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