Investigation and Modeling of Gas-Liquid Mass Transfer in a Sparged and Non-Sparged Continuous Stirred Tank Reactor with Potential Application in Syngas Fermentation

Syngas (mixture of CO, H-2 and CO2) fermentation suffers from mass transfer limitation due to low solubility of CO and H-2 in the liquid medium. Therefore, it is critical to characterize the mass transfer in syngas fermentation reactors to guide in delivery of syngas to the microorganisms. The objective of this study is to measure and predict the overall volumetric mass transfer coefficient, k(L)a for O-2 at various operating conditions in a 7-L sparged and non-sparged continuous stirred-tank reactor (CSTR). Measurements indicated that the k(L)a for O-2 increased with an increase in air flow rate and agitation speed. However, k(L)a for O-2 decreased with the increase in the headspace pressure. The highest k(L)a for O-2 with air sparged in the CSTR was 116 h(-1) at 600 sccm, 900 rpm, 101 kPa, and 3 L working volume. Backmixing of the headspace N-2 in the sparged CSTR reduced the observed k(L)a. The mass transfer model predicted the k(L)a for O-2 within 10% of the experimental values. The model was extended to predict the k(L)a for syngas components CO, CO2 and H-2, which will guide in selecting operating conditions that minimize power input to the bioreactor and maximize the syngas conversion efficiency.