Simultaneous hydrolysis and extractive fermentation in aqueous and non-aqueous environments

• Main Author: Tsui, Ana Cristina May
• Format: Others
• Language: English
• Published: 2009
• Online Access: http://hdl.handle.net/2429/7870

In nature, many enzyme-catalyzed reactions occur in environments where water activity, solvent effects, interfacial forces, electrostatic effects and steric influences provide an environment which is decidedly different from that which is designed in conventional experimental catalytic reactions. The fact that most process industries make use of reaction conditions which are extreme from a biological perspective, continues to limit the use of biotechnology in mainstream processes. This thesis proposes to examine some of the fundamental physical factors which will impact upon enzyme activity in nonconventional environments. As a model reaction system, simultaneous hydrolysis and fermentation of cellulose, in combination with non-aqueous biocatalysis, will be used. A screening protocol instituted to identify suitable extracting solvents showed that oleyl alcohol and lauryl alcohol exhibited the most favourable characteristics in terms of partition behaviour, biocompatibility with the fermenting organism and the enzymes, immiscibility with water and volatility. Efforts to characterize the interfacial and mass transport effects were partly successful. The presence of inactivated yeast cells did seem to affect the sugar yield from hydrolysis (20% reduction in sugar produced). In an attempt to accelerate interfacial denaturation of cellulose, Versal 850, a high surface area colloid was used. The addition of Versal did not seem to exert a significant influence on enzyme activity although it was seen that enzyme adsorbs onto the surface of Versal. The presence of a second, non-aqueous phase to remove ethanol was analyzed. Fermenting matrices with oleyl alcohol and lauryl alcohol as extractants produced 38% and 48% more ethanol than conventional fermentation, respectively. However, addition of extracting solvents did not seem to improve ethanol production in simultaneous hydrolysis and extractive fermentation reactions. An attempt to determine the effect of decreasing aqueous content in reaction matrices containing organic solvent showed that it was possible to reduce aqueous content to 1 - 4% without affecting conversion. Primary clarifier sludge, as a cellulosic substrate, has shown to result in 45% and 55% conversion, based on total weight, in presence of oleyl alcohol and lauryl alcohol, respectively. === Applied Science, Faculty of === Chemical and Biological Engineering, Department of === Graduate