Date of Award

January 2020

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

First Advisor

Wayne Seames

Abstract

Depletion of petroleum-based resources requires the development of high-valued chemicals from renewable sources. Previous work at the University of North Dakota demonstrated that four building block chemical acids, namely lactic, levulinic, acetic, and formic acids, can be generated by transforming cellulose into glucose followed the catalytic decomposition into the target acids. The most important of these chemicals is lactic acid, which can be used as a building block to produce a variety of biodegradable plastics. Traditional fermentation methods for lactic acid synthesis have proven costly, making it difficult for its subsequent products to compete economically. Alternatively, the use of a Lewis acidic heterogeneous catalyst, Sn-Beta, can be used to produce lactic acid in less time and more economically. Levulinic acid is emerging as an important chemical intermediate which can be transformed into a number of more valuable products, including biodegradable polyesters.

In the present study, Sn-Beta catalyst was used to convert the two most abundant sugars in lignocellulosic biomass, glucose and xylose, to lactic acid at yields of 13 wt% and 19 wt% of inlet carbon, respectively with yields of levulinic acid of 18 wt% and 0.8 wt%, respectively. However, the addition of CaSO4 to the aqueous reaction solvent resulted in increased lactic acid yields of 68 wt% and 50 wt% of inlet carbon for glucose and xylose, respectively. Application of this reaction system to sugars extracted from corn stover had a comparable lactic acid yield of 60 wt% while microalgae extracted sugars decomposition appeared to be inhibited leading to a yield of only 8.2 wt% of inlet carbon. The addition of CaSO4 to the aqueous reaction solvent neutralizes the Brønsted acid sites on the surface of Sn-Beta, decreasing the formation of unwanted dehydration products, and adds an additional Lewis acid, increasing the formation of lactic acid.

In a second study, the purification of lactic, levulinic, acetic, and formic acids produced from Sn-Beta was examined. The target acids were reacted with a basic tertiary amine, trioctylamine (TOA), to form an organic soluble ion-pair. Two active alcohol diluents, isoamyl alcohol and 1-octanol, were examined based on their ability to efficiently solvate the produced ion-pair. For each diluent, optimum acid composition, organic/aqueous phase ratio and TOA composition were determined using a central composite design. At optimal conditions isoamyl alcohol was observed to have 50% higher efficiency at extracting lactic acid and levulinic acid. Despite this advantage, similar boiling points between isoamyl and the short chain acids – acetic and formic – decreased the downstream separation efficiency, leading to the conclusion that 1-octanol is the more economical diluent.

Finally, a comparative scoping study was performed to determine the technological and economic feasibility of a world scale processing plant for the Sn-Beta conversion of corn stover-derived sugars. Two separate processes were developed, one based upon the preliminary Sn-Beta yields that produces higher levels of levulinic acid while the other was based upon the addition of calcium sulfate, yielding primarily lactic acid. AACE Class 4 cost estimates and economic analyses were conducted for each process. Net present values @ 20% were estimated as $26 million ± 40% and $250 million ± 40% for the base Sn-Beta and Sn-Beta + CaSO4 alternatives, respectively.

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