Date of Award

8-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Biosystems Engineering

Committee Member

Dr. Caye Drapcho, Committee Chair

Committee Member

Dr. John Nghiem

Committee Member

Dr. Terry Walker

Abstract

Sorghum has been proposed to be a complement to corn for ethanol production. Several advantages have been identified while using sorghum in agricultural and technological aspects. One of the differences between sorghum and corn is the presence of tannins. These compounds are well known for binding proteins and especially affecting enzymatic activity. This is the main disadvantage that sorghum has for ethanol production. High tannin sorghum hybrid XM217 was used to analyze the effect of tannin removal by alkaline pretreatment of sorghum for ethanol production. In this process, 87.6% of the tannins of sorghum were removed. A laboratory-scale dry milling process was used to generate the mashes to be fermented with Saccharomyces cerevisiae. Several ratios of corn and treated sorghum were tested, which included 0, 25, 50, 75 and 100% treated sorghum. A fermentation experiment using 100% untreated sorghum also was performed to obtain base-line results. The use of alkaline tannin removal generated a significant increase on the ethanol production compared to the untreated sorghum. The average theoretical yield increased from 68.2 ± 1.5% to 78.5 ± 2.5%, also average ethanol concentrations increased from 8.02 ± 0.15 to 9.39 ± 0.26 % w/v. Mixtures of 25, 50 and 75 and 100% treated sorghum produced the highest ethanol compared to the use of only corn or untreated sorghum. Cellulase was added to a similar set of experiments to determine the feasibility of the tannin removal treatment as a pretreatment method for cellulosic ethanol production. When using alkaline tannin removal with cellulase, a significantly higher ethanol production can be found compared to non-cellulase experiments. For 100% treated and 100% untreated sorghum trials, the average theoretical yield increased from 69.8 ± 1.7% to 94.6 ± 1.9%, also average ethanol concentrations improved from 8.77 ± 0.18 to 11.29 ± 0.21 % w/v.

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