Impact of nozzle operation on mass transfer in jet aerated loop reactors. Characterization and comparison to an aerated stirred tank reactor.

Abstract

The impact of mass transfer on productivity can become a crucial aspect in the fermentative production of bulk chemicals. For highly aerobic bioprocesses the oxygen transfer rate (OTR) and productivity are coupled. The achievable space time yields can often be correlated to the mass transfer performance of the respective bioreactor. The oxygen mass transfer capability of a jet aerated loop reactor is discussed in terms of the volumetric oxygen mass transfer coefficient kLa [h-1] and the energetic oxygen transfer efficiency E [kgO2kW-1h-1]. The jet aerated loop reactor (JLR) is compared to the frequently deployed aerated stirred tank reactor. In jet aerated reactors high local power densities in the mixing zone allow higher mass transfer rates, compared to aerated stirred tank reactors. When both reactors are operated at identical volumetric power input and aeration rates, local kLa values up to 1.5 times higher are possible with the JLR. High dispersion efficiencies in the JLR can be maintained even if the nozzle is supplied with pressurized gas. For increased oxygen demands (above 120 mmolL-1h-1) improved energetic oxygen transfer efficiencies of up to 100 % were found for a JLR compared to an aerated stirred tank reactor operating with Rushton turbines.