Continuous Butanol Production Using an Immobilized Cell Bioreactor and Online Gas Stripping

Renewable liquid fuels will be a future necessity following the end of the shale gas boom. Of the renewable liquid fuel options, butanol is a promising candidate due to its similar physical and chemical properties when compared to gasoline, though biological options of large scale production are limited due to the toxicity of butanol. This study looks at the production of butanol using immobilized Clostridium acetobutylicum for acetone, butanol and ethanol (ABE) fermentation when combined with a gas stripping recovery process. The effect of internal and external diffusion limitations on ABE production is examined, mathematical models are developed to determine the productivity of these bioreactors, and large scale butanol production and recovery are examined through simulation and optimization. It has been found that internal and external mass limitations can be lessened using immobilization bead sizes less than 2 mm. In addition, it is shown that continuous immobilized bioreactors can approach productivities of batch systems. Finally, optimimal Aspen simulations show that gas stripping can be used achieve a 90% butanol recovery and an 86.60% ABE recovery overall. The process is then analyzed for total cost and sensitivity of the butanol recovery.