Date of Award

Spring 5-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Joan G Lynam

Abstract

Secondary agriculture residues have the potential to be major contributors as resources for energy and sustainably sourced materials production. Separating secondary agricultural residues, which have already been transported to processing centers, into individual biomass components could convert these wastes into bioproducts. Many types of pretreatments to achieve this separation involve chemicals that are hazardous for the environment. Several deep eutectic solvents (DES) that are biocompatible have been investigated for their ability to deconstruct rice hulls and sugarcane bagasse. Mass yield, enzymatic hydrolysis of the pretreated biomass, fiber analysis, and Fourier transform infrared spectroscopy have confirmed that the DES formic acid:choline chloride, lactic acid:choline chloride, and acetic acid:choline chloride are effective in removing lignin, thus concentrating cellulose in the pretreated biomass. Addition of water precipitated lignin from the spent DES, as confirmed by the above analyses. However, the DES lactic acid:betaine and lactic acid:proline had little effect on rice hulls or sugarcane bagasse. Formic acid:choline chloride was the most effective of the DES tested in preparing the biomass for enzymatic saccharification.

Rice hulls, a widely-available secondary agricultural residue, was pretreated with formic acid and choline chloride in a 2:1 mole ratio (FA:CC) using conductive heating and microwave heating. Enzymatic hydrolysis data indicated that pretreated biomass using either heating technique gave higher glucose yield compared to raw rice hulls. FTIR analysis showed similar findings for both heating techniques. For biomass pretreatment using DES, microwave heating required less than half of the energy compared to conductive heating. Conductive heating required a higher residence time for the biomass in the pretreatment process. Thus, this work shows the potential benefits of a microwave heating technique for deconstruction of biomass using DESs.

Using waste agriculture and power plant byproducts to replace materials that are energy-intensive to produce can make these materials more "green." Improved compressive strength can be obtained when rice husk ash (RHA) partially replaces ordinary Portland cement, a substance potentially hazardous and energy-intensive to make. When RHA is combined with other nano-particles to replace ordinary Portland cement (OPC), strength can be further enhanced. The microstructure of cement binders with replacement of OPC by combinations of coal fly ash, silica fume, RHA, nano-silica, and metakaolin were investigated using X-ray diffraction, back scattered electron imaging with energy dispersive spectrum analysis, X-ray photoelectron spectroscopy, and nitrogen sorptiometry. A combination of sustainable, renewable RHA and the waste product coal fly ash was found to synergistically improve cement binder strength. Analyses suggested the enhanced strength was due to RHA increasing amorphous reactive silica and coal fly ash contributing alumina to form Calcium-Silicate-Hydrate (C-S-H) gel along with calcium-aluminum-silicate-hydrate (C-A-S-H). Thus, this work shows the potential benefits of merging residual wastes from the agricultural sector with wastes from coal in combustion-based power plants.

Food product preparation generates large quantities of wastes that are concentrated in central processing facilities, meaning that the wastes do not require energy-intensive transporting from the fields. If these waste biomass are landfilled, they pollute the environment both physically and in transportation to the landfill. A chemically simple process, hydrothermal carbonization (HTC) requires only biomass and water to generate a solid fuel and a sugar-laden liquid. HTC processing of coffee silverskins increased the energy density of the solid product, with higher temperatures increasing energy density more. The concentrations of glucose, galactose, and arabinose in the liquid HTC product decreased with higher HTC temperatures. HTC processing temperature could thus be chosen to optimize either the solid or the liquid product. If monomeric sugars are desired, a lower HTC temperature should be employed.

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