Mass Transfer and Bioethanol Production in an External-Loop Liquid-Lift Bioreactor

Abstract

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 aqueous, fermentation media. The overall ethanol mass-transfer coefficient (K C a) was found to vary between 7.0 × 10-7 and 3.0 × 10-4 s-1. K C a increased with the sparger spinning speed, oleic acid flow rate, and ethanol concentration in the aqueous phase. Oleic acid holdup (φL) in the bioreactor increased in a similar manner for each of these independent variables. Both K C a and φL were empirically fit to extensive experimental data sets using power-law models. Two batch fermentation experiments demonstrated improved production of bioethanol when oleic acid was used to remove high concentrations of ethanol from the fermentation broth.

In situ extractive ethanol fermentation in a drop column bioreactor

“…The use of extractive fermentation resulted in substrate consumption in shorter times, compared with the conventional fermentation, hence increasing the ethanol volumetric productivity. The same behavior was observed by Stang et al . using a spinning‐sparger, external‐loop, liquid‐lift bioreactor (ELLB) to enhance the production of ethanol.…”

“…This process starts with screening for biocompatible solvents, followed by experimental assays using selected solvents in order to characterize the best one in terms of its ethanol extraction capacity . Oleic acid, a solvent that is nontoxic towards Saccharomyces cerevisiae , has already been used for ethanol extraction in different processes and configurations . However, it has not yet been used in extractive ethanol fermentation employing a drop column bioreactor (DCB) with recirculation of the solvent.…”

“…Furthermore, the development of a mathematical model for prediction of the behaviors of extractive fermentation processes employing organic solvents would enable the use of simulations in order to analyze different operating modes and support scaling up studies. Process models can be valuable tools for facilitating the implementation of these processes, avoiding the expense of numerous tests and focusing on promising extractive agents , , . These models can be used to investigate the applicability and cost of a real process.…”

“…[13][14][15][16] Oleic acid, a solvent that is nontoxic towards Saccharomyces cerevisiae, has already been used for ethanol extraction in different processes and configurations. [17][18][19][20][21][22] However, it has not yet been used in extractive ethanol fermentation employing a drop column bioreactor (DCB) with recirculation of the solvent.…”

“…Process models can be valuable tools for facilitating the implementation of these processes, avoiding the expense of numerous tests and focusing on promising extractive agents. 18,19,23 These models can be used to investigate the applicability and cost of a real process. They can also be used to predict substrate, microorganism, and product concentrations, enabling definition of the operating conditions for an optimized process and guiding selection of the best extractive agents.…”