Ethanol by continuous fermentation using a combination of immobilised yeast and liquid-liquid extraction

The ethanolic fermentation of glucose by yeast-in combination with liquid-liquid extraction of the product. ethanol using n-dodecanol as the solvent has been investigated in a continuous laboratory pilot plant. Severe emulsification problems occurred in initial experiments and the emulsification was found to be caused by free yeast cells in the aqueous/solvent mixtures. The emulsification problems were overcome by immobilisation of the yeast in calcium alginate beads. A number of continuous runs were made using fresh feed glucose concentrations between 10% wt and 45.8% wt. The duration of run was sufficient for the system to attain equilibrium and the run lengths at each glucose concentration were between 7 - 17 days. At all glucose concentrations the steady state ethanol concentration in the fermenter was between 2.8% wt and 3.8% wt ethanol with glucose to ethanol conversions between 70.9% and 95.7% and the corresponding overall yield of ethanol on glucose between 67.0% and 91.9%. The glycerol concentration in the fermenter increased from 0.27% to l.08% wt at the maximum glucose feed concentration. The dilution rates based on the fresh feed were between 0.06 - 0.27 h-1 The fermenter productivities varied between 10.2 - 14. b g ethanol l-lh -1. The use of 45.8% wt glucose feed would enable a 77.8% reduction in the volume of aqueous effluent from the process.