An electrically driven gas-liquid-liquid contactor for bioreactor and other applications

An electrically driven gas-liquid-liquid bioreactor is described here, in w hich an aqueous medium containing a biocatalyst is introduced as a disconti nuous phase into an organic-continuous liquid phase containing a substrate to be converted by the biocatalyst. A gas discontinuous phase, which may be needed to provide oxygen or a gaseous substrate to the biocatalyst, is als o introduced into the bioreactor. In contrast to previous work on electrica lly driven contactors, it was found that the electroconvection generated by the electric field between parallel-plate electrodes may be employed to in crease the volume fraction of the discontinuous gas phase in the bioreactor , providing the means for enhanced mass transfer. The electrically driven b ioreactor was utilized for oil, desulfurization experiments with Rhodococcu s sp. IGTS8 bacteria as the biocatalyst. The organic phase used in the expe riments was hexadecane containing dibenzothiophene, a model sulfur compound , that is oxidatively desulfurized to 2-hydroxybiphenyl (2-HBP) by the bact eria in the presence of air or oxygen. The gas volume fraction was increase d by 60% by the application of a pulsed electric field, thus providing a me ans for increased transport of oxygen needed for oxidative desulfurization. The velocity of droplets and bubbles was measured by a phase Doppler veloc imeter. The average rising velocity of bubbles was decreased from 13 to les s than 3 cm/s and the average horizontal velocity was increased from 0 to 5 cm/s as the field strength was increased from 0 to 4 kV/cm. Desulfurizatio n rates ranged from 1.0 to 5.0 mg of 2-HBP/g of dry cells/h. The desulfuriz ation rate with aeration was doubled under the electric field as compared t o the zero-field desulfurization under the same conditions.