Butanol recovery from synthetic fermentation broth by vacuum distillation in a rotating packed bed

Abstract

The present study was performed to investigate feasibility of butanol recuperation from a synthetic fermentation broth via vacuum distillation in a rotating packed bed (RPB). Unlike in stationary columns, the packing element rotates generating a centrifugal field which exceeds gravity by orders of magnitude. Thereby, the RPB improves the gas–liquid mass transfer by factors of 10 up to 1000, resulting in more efficient compounds separation. The process was performed under reduced pressure to allow temperatures getting closer to the typical fermentation temperature, which is usually between 35 and 37 °C. Therefore, the butanol recuperation can be carried out in-line without bacteria deactivation.The complex mixture used in this study was based on a real fermentation broth obtained during fermentation of cellulosic fraction of lignocellulosic biomass by butanol-tolerant mixed culture. Consequently, the composition of the synthetic fermentation broth as liquid feed stream was as following (g/L): 20 of butanol, 7 of ethanol, 2.5 of acetic acid, 3 of propionic acid, 5.5 of valeric acid, 2.0 of caproic acid, and 3.5 of furfural. Experiments under total reflux and stripping experiments using 5% of steam relative to the fermentation broth feed were performed. In the first case, butanol recuperation in the light phase of the top product reached concentration of 521.6 g/L. For stripping experiments, butanol concentration achieved the concentration at the level of 126.9 g/L in the top product. Ethanol and furfural were also recuperated at high concentrations at 39 and 13 g/L, respectively during stripping experiments. The experiments demonstrated that vacuum distillation in an RPB allows not only for separation of butanol from complex mixture but also for ethanol and furfural recuperation. Nevertheless, a further purification step is needed to achieve a pure product which can be used as an alternative fuel or feedstock substitute for the fossil components.