Development of Carbon Monoxide Fermentation Process for Value-Added Chemical Production

Abstract

Carbon monoxide (CO) is discharged as a waste gas from steel mill, thermal power plant, and chemical processes, or produced by gasification of waste biomass and coal. Owing to a huge amount of CO discharged, gas-to-liquid conversion process using C-1 compound such as CO is being highlighted as green technology to replace a portion of conventional chemical production based on petrochemical plant. Among the various gas conversion technologies, biological process called gas fermentation has been being studied to eco-friendly convert syngas including CO into value-added chemicals such as carboxylic acids and organic alcohols. However, the chemical productivity of gas fermentation is limited due to the poor mass transfer performance of a bioreactor and absence of optimized process and operating method. In this work, the attempt has been done to develop gas fermentation process with high mass transfer and productivity, to convert CO into acetate using the model strain, Clostridium autoethanogenum. First, ceramic membrane-integrated bubble column was designed for high CO-water mass transfer. The dimensionless mass transfer model was newly proposed using superficial gas velocity and membrane gas supply area as a new variable. The effect of chemical components on mass transfer increase was investigated. Then, the model to correct mass transfer coefficient of CO in a fermentation medium was newly proposed for bubble column. The CO specific parameter for gas solubility prediction model was determined based on the experimental data set tested in various solutions. Second, CO fermentation process was developed for high volumetric productivity with long-term operational stability. A variety of CO fermentation processes such as vial, batch, cell wash-out, cell-recycled and two-stage were designed and tested to investigate the fermentation profiles. The importance of internal gas circulation was confirmed in resolving kinetic limitations during gas CO fermentation. The nutrients requirements of C. autoethanogenum was precisely investigated to develop an optimized medium composition that can support cellular growth and be applied to industrial process. Through the aforementioned findings, two-stage CO fermentation process, that can produce around 30 g/L acetate with total volumetric productivity over 0.4 g/L/hr, was developed. Third, the design and operating condition were optimized to maximize the economic feasibility of the proposed CO fermentation process. An integration of acetate-to-high value compound conversion process was suggested in order to further increase net profit of the CO fermentation process currently developed.