Degree Type

Dissertation

Date of Award

2010

Degree Name

Doctor of Philosophy

Department

Civil, Construction, and Environmental Engineering

First Advisor

Shihwu Sung

Abstract

Lignocellulosic biomass like straw, wood, and agritural residues are plentiful and inexpensive, and can serve as feedstock for fuels and commercial chemicals production. These lignocellulosic biomasses of abundant supply, consisting of cellulose, hemicelluloses and lignin, however have to be pretreated to form simple sugars for further conversion into alternative fuels and chemicals. One existing technology that could convert biomass into fuels is the hybrid thermochemical/biological approach for the potential commercialization necessary to the answer of fossil fuels replacement. The process starts with the gasification of biomass to produce synthesis gas (syngas) that is a gas mixture of carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2) and Nitrogen (N2). Then, syngas is served as microorganism substrates for several microbial metabolisms and produces for the synthesis of various valuable fuels including ethanol and butanol.

The low solubility of carbon monoxide and hydrogen into the aqueous fermentation broth for the microorganisms, however, limits the potential commercialization. The fermentor design for the improvement of synags-liquid mass transfer is, thus, the dominating key to determine the production of syngas fermentation. An innovative fermentor using hollow fiber membrane as a mean of gas delivery has demonstrated to be an effective method for eliminating the mass transfer limitation of syngas fermentation. The highest CO mass transfer rate of 1.49 s-1 which is over its counterpart (nonporous silicone HFM) and previous studies was obtained using the microporous polypropylene HFM. A model is calculated for commercialization of syngas fermentation.

Clostridium ljungdahlii, a gram-positive, motile, rod-shaped anaerobe, utilizes the CO in syngas to produce ethanol and acetate. Information is limited pertaining to the optimization of growth and production condition as well as the performance of the hollow fiber membrane fermentor. Clostridium ljungdahlii demonstrated its highest growth rate on PETC 1754 with 5 g*l-1 fructose and 1 g*l-1 yeast extract with pH between 6.5 and 7.5. pH at 5 in the production phase is recommended for the optimal ethanol production from C. ljungdahlii.

Growth and production conditions were optimized on the 40-ml hypovial test. The optimal conditions from the 40-ml hypovial test were applied to a 2-L hollow fiber membrane reactor for the optimization of ethanol production. The results demonstrated that the hollow fiber membrane reactor could produce ethanol to 6 g*L-1 by Clostridium ljungdahlii from the fructose-free medium and syngas with an ethanol to acetate ratio of 2.6 which was the highest ratio in compared with other previous studies.

DOI

https://doi.org/10.31274/etd-180810-236

Copyright Owner

Po-Heng Lee

Language

en

Date Available

2013-05-02

File Format

application/pdf

File Size

157 pages

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