DESIGN AND ANALYSIS OF AN IMMOBILIZED CELL REACTOR WITH SIMULTANEOUS PRODUCT SEPARATION: ETHANOL FROM WHEY LACTOSE
Abstract
The simultaneous separation of volatile fermentation products from product inhibited fermentations can increase the productivity of a bioreactor by reducing the product concentration in the bioreactor. In this work, a simultaneous tubular reactor separator is developed in which the volatile product is removed from the reacting broth by an inert gas phase. The immobilized cell reactor separator (ICRS) consists of two column reactors: a cocurrent enriching column followed by an countercurrent stripping column. The columns are four phase tubular reactors consisting of (1) an inert gas phase, (2) the liquid fermentation broth, (3) the solid column internal packing, and (4) the immobilized cells or biological catalyst. In the enricher the stripping gas moves cocurrently with the liquid broth, picking up the volatile product as it is formed. The gas phase leaving the enricher is condensed while the liquid phase (with about half of the substrate remaining) enters the stripping column where the remaining substrate is reacted while the product is stripped from the broth. The liquid phase leaving the stripper is depleted in both product and substrate, leaving only trace nutrients, by-products, salts, and cells. The gas phase is condensed to obtain a high concentration of pure product. The application of the ICRS concept to the ethanol from whey lactose fermentation was investigated using the yeast Kluyveromyces fragilis 2415. An equilibrium stage model of the ICRS was developed including a 'surface renewal' term for an adsorbed monolayer of reacting cells. This model demonstrated the effect of important operational parameters including temperature, pressure and gas flow rates. Experimental results using yeast adsorbed to 1/4" ceramic saddles were somewhat unsatisfactory but very high productivities, cell densities, and separation efficiency were obtained using an absorbant column packing in a gas continuous operating mode.
Degree
Ph.D.
Subject Area
Chemical engineering
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