Evaluation of Gas Mass Transfer in Reactor for Syngas Fermentation

The low mass transfer rate of less soluble gas CO and H-2 to liquid has been considered as the major bottleneck of syngas fermentation. Gas mass transfer rate depends on many factors, including the reactor type, gas flow rate and agitation speed. This paper presents the evaluation of the mass transfer coefficient (k(L)a) for the hollow fiber membrane (HFM) reactor as the new proposed configuration reactor to be used in syngas fermentation, in which an external microporous HFM module was used as the gas diffuser and gas-liquid contactor to enhance gas-liquid mass transfer. Experiments were conducted at various agitation speed, gas flow rate and liquid recirculation rate. Similar experiments were also conducted for the stirred-tank reactor (STR) as the most common type of fermenter. The k(L)a value was determined with a dynamic method, in which the change in oxygen concentration in the liquid phase is measured with time. The k(L)a of CO or H-2 were inferred from equations developed based on penetration theory using O-2 k(L)a value. The maximum value of CO k(L)a (300.5 h(-1)) was achieved in HFM supported reactor at the specific CO flow rate of 1.05 vvm and liquid recirculation rate of 120 ml/min. The result of this study would be used for designing configuration of syngas fermentation in the future.