Syngas Mass Transfer Delivers Fermentation Potential

Bacterial conversion of CO and H₂ from synthesis gas opens a potential supply of energy and chemicals from renewable biomass and waste feedstocks.  This potential is being tested in commercial scale plants that use vegetative wastes and industrial waste gases for production of ethanol.  Commercial success will hinge on efficiency, selectivity, productivity and stability of the process deployed.  The microorganisms that perform the syngas fermentation use the Wood-Ljungdahl biochemical pathway to obtain energy as electrons and protons from the oxidation of CO and H₂ on enzymes inside the cell.  The transfer of the substrates CO and H₂ from the gas phase into the cell determines the electrochemical potential inside the cell, and thus the reaction kinetics and the thermodynamic ratio of products.  As such, the application of gas/liquid mass transfer is the most important parameter for control of the syngas fermentation process.  Analysis of syngas fermentation that employs mass transfer, reaction kinetics, thermodynamics and mass balance derived from the pathway provides a basis for successful control and equipment design in syngas fermentation.  Control of mass transfer can be used to effect high energy conservation, high selectivity for desired product and high productivity in stable continuous fermentation.