Because of the growing demand for renewable fuels, the production of butanol through acetone-butanol-ethanol (ABE) fermentation of lignocellulosic biomasses has been recently attracting an increasing research interest.The major limit for an industrial-scale production of bio-butanol is the high separation cost, due to the presence of other fermentation products and to its low final concentration in the broth. In fact, the microorganism used in the ABE fermentation suffers from product inhibition leading to a low ABE final concentration in a batch process. The application of an integrated product recovery technique able to remove butanol during fermentation is a viable solution to solve the problem and to improve the economics of the ABE fermentation.
In this context, gas stripping has been proven to be an effective separation technique, able to reduce the inhibition of the microorganism and, therefore, to increase the process productivity.
However, gas stripping usually removes a large amount of water together with butanol and requires a higher energy input, because of its lower butanol selectivity, in comparison with other separation techniques. To improve the performances of the integrated fermentation-gas stripping process for butanol production, optimization of gas stripping and fermenter conditions, and a better understanding of its effects on the ABE fermentation is needed.
This study deals with the synthesis of a process configuration for the integrated recovery of butanol from a fermentation unit operated in a fed-batch mode, in which the product is recovered from the fermentation broth by means of nitrogen gas stripping and is, subsequently, fractionated in a distillation train. For the studied configuration, a detailed simulation of the integrated recovery process including the fed-batch fermenter and the downstream separation train has been performed. The simulation results have been used to evaluate the effect of the integrated product recovery on the process productivity and on the total energy consumption, which has been quantified through the net equivalent fuel approach. Finally, the performances of the integrated process have been compared with the ones obtained with a traditional batch fermentation, in order to assess the potential of the proposed process solution.