Kinetics Analysis of the Syngas Fermentation to Produce Acetic Acid from Cardoon Residual Biomass

Abstract

Lignocellulosic biomass can be converted to biofuels and biochemicals through several process pathways: pretreatment and sugars fermentation, thermochemical conversion (pyrolysis, gasification) and syngas synthesis. A promising syngas valorization process consists of the syngas fermentation, able to maximize the biomass fraction used for the fermentation. The limits of this process are the need for high-quality syngas, fermentation rate optimization and the two-phase bioreactor design. This work aims to analyze the two effects (fermentation and gas to liquid mass transfer) distinctly. A syngas fermentation kinetics was modeled in order to optimize the fermentation conditions in terms of substrate and microorganism concentrations maximizing the acetic acid yield. Under the hypothesis of constant CO and H2 concentration, the gas-liquid mass transfer coefficients were estimated considering a syngas composition coming from the Cynara cardunculus L. residual biomass gasification. Results presented identify the optimal CO and H2 concentrations 0.01 and 0.1 mmol/L respectively, with an initial microorganism concentration equal to 2 g/L, obtaining a maximum acetic acid yield and an acetic acid maximum concentration of 12.5 % and 4.2 g/L respectively.