Economic comparison of a continuous ABE fermentation with and without the integration of an in situ vacuum separation unit
The development of renewable fuels has achieved enormous progress motivated by the rapid decline in petroleum resources and their oscillating price. After a wave of interest in bioethanol and biodiesel, biobutanol has been intensely investigated over the last decade and is considered a suitable renewable fuel. Biobutanol is most often produced through the Acetone-Butanol-Ethanol (ABE) bacterial fermentation process. This process is plagued, however, with high recovery costs because of the low final butanol concentration (∼0.01 g/g, 1 wt %) due to product inhibition on the microorganisms. To partly alleviate this problem and increase productivity, in situ butanol recovery techniques from the fermentation broth were proposed. These integrated methods increase the final concentration of butanol, and as a result improve the separation efficiency of the process. This paper compares the economic feasibility of a large-scale continuous ABE fermentation process with and without integrating a vacuum separation unit. It is illustrated that based on the current market price of butanol, only the integrated fermentation process is economically feasible for discount rates up to ∼45 %. Adding an in situ butanol recovery technique made this process profitable compared to the conventional fermentation process analyzed under two different scenarios: constant fermenter volume and constant butanol production rate. The net present values (NPV) of the conventional process were found to be negative for both scenarios, whereas the integrated vacuum process had a NPV of US$ 87 000 000 at the end of 10 years of operation based on a discount rate of 10 %.