Effect of gas transfer on the performance of microbial water gas shift reaction by hyperthermophilic archaea

Abstract

In this study, we investigated the effect of CO transfer on the performance of syngas fermentation. A series of batch fermentations of Thermococcus onnurineus NA1 using a model LDG (Linz Donawitz Gas) containing 60% of CO was carried out at 80 oC in a stirred tank reactor with Rushton turbine impeller. T. onnurineus NA1 is a carboxydotrophic hyperthermophilic archaeon, which is able to produce hydrogen from CO via microbial water gas shift reaction. It was reported that the hydrogen productivity of T. onnurineus NA1 on CO is outstanding compared to other carboxydotrophic strains, demonstrating its possibility for replacing conventional water gas shift processes based on metal catalysts. Reactor performance with various agitation speeds and CO flow rate was compared in terms of cell growth and hydrogen productivity. After the lag period depending on agitation speed and CO flow rate, T. onnurineus NA1 produced hydrogen with growth-associated kinetics, governed by Luedeking-Piret model. However, within several hours after inoculation, severe mass transfer was occurred and hydrogen productivity remained constant while cell mass increased. From mass transfer coefficient of CO, determined using the hydrogen productivity in the mass transfer limiting stage, we derived a correlation equation between CO transfer and reaction conditions. Also, the CO metabolism by T. onnurineus NA1 could be modeled well with substrate-inhibiti 80 oC in a stirred tank reactor with Rushton turbine impeller. T. onnurineus NA1 is a carboxydotrophic hyperthermophilic archaeon, which is able to produce hydrogen from CO via microbial water gas shift reaction. It was reported that the hydrogen productivity of T. onnurineus NA1 on CO is outstanding compared to other carboxydotrophic strains, demonstrating its possibility for replacing conventional water gas shift processes based on metal catalysts. Reactor performance with various agitation speeds and CO flow rate was compared in terms of cell growth and hydrogen productivity. After the lag period depending on agitation speed and CO flow rate, T. onnurineus NA1 produced hydrogen with growth-associated kinetics, governed by Luedeking-Piret model. However, within several hours after inoculation, severe mass transfer was occurred and hydrogen productivity remained constant while cell mass increased. From mass transfer coefficient of CO, determined using the hydrogen productivity in the mass transfer limiting stage, we derived a correlation equation between CO transfer and reaction conditions. Also, the CO metabolism by T. onnurineus NA1 could be modeled well with substrate-inhibiti