Ethanol fermentation by immobilized cells in a trickle bed reactor

Abstract

A modified discontinuous packed bed reactor with CO₂ ventilation ports, resembling a trickle bed reactor was employed to overcome gas holdup and bed compaction problems which are commonly encountered in cell immobilized packed bed reactors for ethanol fermentation. The reactor consisting of yeast cells entrapped in alginate matrix was operated by varying the substrate concentration, bed volume and inlet flow rates. The number of recirculation cycles (passes) and total stages were dependent upon the liquid flow rate, though the total contact time for complete conversion remains the same for a particular initial substrate level. The total contact time was 1.5, 3 and 4.5 h for initial substrate concentrations of 0.555, 0.933 and 1.3 kmol/m³ respectively. The number of cycles and in turn stages increased with the increase in initial sugar level. A graphical method for predicting the number of stages required for complete conversion was proposed based on material balance equation and evaluated for the operating variables of the present study. The reactor was operated continuously for 30 days producing 1.05– 1.15 kmol/m³.