Mass transfer and bioethanol production in an external-loop liquid-lift bioreactor

A novel, spinning-sparger, external-loop, liquid-lift bioreactor (ELLB) has been studied for the purpose of enhancing the production of bioethanol by simultaneous mass transfer and fermentation. Oleic acid was used to produce circulatory fluid flow in the ELLB and also to absorb ethanol from the aqu eous, fermentation media. The overall ethanol mass-transfer coefficient (K( C)a) was found to vary between 7.0 x 10(-7) and 3.0 x 10(-4) s(-1). K(C)a. increased with the sparger spinning speed, oleic acid flow rate, and ethano l concentration in the aqueous phase. Oleic acid holdup (phi (L)) in the bi oreactor increased in a similar manner for each of these independent variab les. Both K(C)a and phi (L) were empirically fit to extensive experimental data sets using power-law models. Two batch fermentation experiments demons trated improved production of bioethanol when oleic acid was used to remove high concentrations of ethanol from the fermentation broth.