Recovery of n-butanol using ionic liquid-based pervaporation membranes

Abstract Biobutanol ( n -butanol) offers the possibility of expanding the production of bulk chemicals and fuels based on renewable resources. A drawback in the microbial production of n -butanol is the energy-intensive product recovery process, making biobutanol expensive. One method for overcoming this limitation is the application of supported ionic liquid membranes (SILMs) for continuous product removal. In this work, the pervaporation performance of SILMs with tetracyanoborate and tris(pentafluoroethyl)trifluorophosphate ionic liquids (ILs) was investigated. Pervaporation was carried out at 37 °C using binary mixtures of n -butanol and water with n -butanol concentrations lower than 5 wt.%. Two concepts for immobilisation of ILs were tested using nylon or polypropylene as support material. ILs were immobilised by inclusion between silicone layers or by dissolution in poly(ether block amide). It was observed that a higher affinity of the IL for n -butanol increases the permeability of the membrane for more than three times, whereas no changes in the selectivity occurred. Furthermore it was shown, that fluxes increased with an increasing IL content in the membrane. The maximum permeate flux achieved was 560 g/(m 2  h), and the highest concentrations of n -butanol in the permeate was found to be 55 wt.%. In future thickness of SILMs needs to be reduced to make these membranes competitive with respect to conventional pervaporation membranes.