Date of Award

Spring 5-10-2019

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Chemical Engineering (MSChE)

Department

Chemical Engineering

Advisor

Peter van Walsum

Second Committee Member

Thomas J. Schwartz

Third Committee Member

Jean D. MacRae

Abstract

Medium-chain fatty acids (MCFA, e.g., hexanoic, heptanoic and octanoic acid) are versatile chemical compounds that are suitable precursors for the production of high-carbon-number, value-added chemicals such as bio-based lubricants. Short-chain fatty acids (SCFA, e.g., acetic, propionic, butyric, valeric acid) and methane are the natural fermentation products of anaerobic digestion, however, they have a lower value compared to MCFAs. Our current investigation seeks to integrate the production of MCFAs through chain elongation fermentation of pretreated biomass with catalytic conversion of MCFAs to lubricant molecules. By adding reducing agents such as ethanol and lactic acid to the anaerobic digestion, and inhibiting methanogenesis, microorganisms can elongate SCFA to MCFA. At low ethanol concentration, the elongation reaction does not reach a high concentration of MCFA, whereas very high ethanol concentration has an inhibitory effect, and the fermentation ends before consuming all the ethanol. To maximize MCFA production, different ethanol concentrations and feeding schedules were investigated in the mixed-culture fermentation of pretreated hardwood, inoculated with a mixture of manure, beach sediments, and corn steep liquor. Addition of ethanol at the initiation of fermentation resulted in increased accumulation of MCFAs. Incremental addition of ethanol during the fermentation resulted in significantly higher titers of MCFAs. Another necessary step in the production of bio-lubricants is extraction of the produced acids from the fermentation medium. We have investigated the effect of different solvents such as Cyanex 923, Trioctylamine and Oleyl Alcohol on mixed acids with the purpose to find a low cost, selective and reusable extractant. In this study, we characterized the applicability of these solvents in the extraction of Hexanoic acid regarding pH and solvent ratio. Many extractions in controlled conditions were carried out and the method with the best result was tested on actual fermentation. The effects of the extraction on fermentation and acid production, conversion and selectivity were some of the major focuses.

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