Measurement and prediction of mass transfer coefficients for syngas constituents in a hollow fiber reactor.

Syngas fermentation for producing biofuels and other products suffers from mass transfer limitations due to low CO and H2 solubility in liquid medium. Therefore, it is critical to characterize mass transfer rates of these gases to guide bioreactor design and optimization. This work presents a novel technique to measure the volumetric mass transfer coefficients (kia) for H2 and CO using gas chromatography in a non-porous hollow fiber reactor (HFR). The largest measured kia for H2 and CO were 840 and 420 h-1, respectively. A model was developed to predict kia for H2 and CO that agreed well with experimental data. This study is the first to measure, compare, and model both H2 and CO mass transfer coefficients in an HFR. Based on model predictions, HFRs have the potential to be a reactor of choice for syngas fermentation as a result of high mass transfer that can support high cell densities.

A comparison of mass transfer coefficients between trickle-bed, hollow fiber membrane and stirred tank reactors.

Trickle-bed reactor (TBR), hollow fiber membrane reactor (HFR) and stirred tank reactor (STR) can be used in fermentation of sparingly soluble gasses such as CO and H2 to produce biofuels and bio-based chemicals. Gas fermenting reactors must provide high mass transfer capabilities that match the kinetic requirements of the microorganisms used. The present study compared the volumetric mass transfer coefficient (K(tot)A/V(L)) of three reactor types; the TBR with 3 mm and 6 mm beads, five different modules of HFRs, and the STR. The analysis was performed using O2 as the gaseous mass transfer agent. The non-porous polydimethylsiloxane (PDMS) HFR provided the highest K(tot)A/V(L) (1062 h(-1)), followed by the TBR with 6mm beads (421 h(-1)), and then the STR (114 h(-1)). The mass transfer characteristics in each reactor were affected by agitation speed, and gas and liquid flow rates. Furthermore, issues regarding the comparison of mass transfer coefficients are discussed.