Masters Theses

Date of Award

5-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Chemical Engineering

Major Professor

Brian H. Davison

Committee Members

Paul D. Frymier,Cynthia B. Peterson

Abstract

Since the early 1980s, work in the area of nonaqueous bioprocessing has revolutionized the field of biocatalysis. Once thought to function only in aqueous environments, enzymes have been proven to be catalytically active in organic solvents as well as in completely gaseous systems. Gas phase enzymatic systems are advantageous for several reasons, including reduced mass transfer limitations and increased thermal stability. In such systems, some water remains bound to the enzyme and can also be present in the form of relative humidity. This water plays a dual role; it is necessary for catalytic activity, but at the same time its presence facilitates thermal inactivation of the enzyme.

In order to provide a more fundamental understanding of the dual role of water in gas ' phase enzyme catalysis, the effects of relative humidity and temperature on several lipase catalyzed, gas phase transesterification reactions were investigated. Several different reactor configurations were used including single pass, continuous recycle, and batch reactor modes. Temperature and relative humidity were controlled both inside reactors and throughout the course of the reaction in an attempt to account for and optimize their effects.

Results indicated that, at low relative humidity, reaction rates increase with temperature up to a point. However, when relative humidity was increased, a similar increase in temperature resulted in the loss of nearly all enzyme activity. These results are consistent with the idea that dryer enzymes are more thermally stable. Furthermore, at constant ambient temperatures, production increased dramatically with an increase in relative humidity, confirming the idea that an increase in water increases catalytic activity.

A mass balance performed on reactors at higher relative humidity revealed that hydrolysis (rather than transesterification) of the ester was occurring. These hydrolysis rates should be determined separately from transesterification rates at all combinations of temperature and relative humidity. This would allow for the determination of transesterification rates independent of hydrolysis and enable more accurate comparisons. An optimal combination of temperature and relative humidity for this reaction system could then be determined.

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