Comparison of Stirred and Immobilized Cell Reactors For Ethanol Production

Biomass can be converted to sugars by hydrolysis with enzymes or mineral acids. These sugars can be converted into a number of chemical intermediates in biological reactors. Biological reactions are generally slow and selection of the most efficient reactor is important in these applications. Immobilized cell reactors allow high cell densities and high throughput by attaching microorganisms to a fixed support. This paper compares the rate of production of ethanol from glucose by Saccharomyces Cerevisiae in a packed column and a stirred reactor. Continuous stirred reactor studies showed a washout rate of .27 hr-1. The optimum rate of alcohol production of 1.75 g/l-hr occurred at a dilution rate of .182 hr-1. In a 36 immobilized cell reactor, rates were found to be 7.4 g/l-hr, or about 4.2 times better than the stirred reactor. Sustained periods of operation of this type column are possible by removal of cell overgrowth with a gas purge. Immobilized cell reactors should also be more stable and should require lower power input than the mixed reactor