Energy requirements for the in-situ recovery of biobutanol via gas stripping

Biobutanol has been accepted as the preferred renewable, bio-based additive or replacement for petroleum based fuels. The production of biobutanol has, however, encountered low productivity and titres due to a high toxicity of butanol to the bacteria. This leads to an energy intensive distillation step. Gas stripping has been presented as a method of good potential because of its simplicity and clean operation, with the ability to concentrate the product by several fold. However, these investigations have lacked rigorous analysis of energy requirements, with the energy required at best being estimated using simplified assumptions. A detailed assessment of the energy requirements for gas stripping is presented in this work. This includes a rigorous analysis of the key operating variables of 21 experimental mass balance data sets from 16 investigations in the literature. Higher butanol concentrations in the culture and higher stripping temperatures are shown to be the two most significant parameters influencing the energy efficiency of the process. Gas stripping with distillation consumes 34.2 to 380 MJ/kg butanol and is 41-370% less energy efficient than the use of distillation only for product recovery. Hence an integrated analysis of the production and separation steps is essential to determine overall process benefits.