Polymer inclusion membranes containing ionic liquids for the recovery of n-butanol from ABE solutions by pervaporation

Making economically competitive technologies for using biofuels as alternatives to move towards a low carbon economy has recently increased the interest of researchers and industry. Biobutanol has a good potential due to its attractive physicochemical properties. It can be produced through the ABE process (acetone-butanol-ethanol) by Clostridium bacteria. However, severe product inhibition, leading to low productivity and low final concentration in the broth, the butanol toxicity to the microorganisms and the high energy consumption are still the main challenges. Pervaporation (PV) is proposed as an efficient alternative to the current separation methods. In PV, the properties of the membrane material dictate the separation of the process for the recovery of butanol. Different polymers and additives are being studied for different membrane characteristics. This work focuses on the fabrication of composite membranes with different polymer/ionic liquid (PEBA/HMImFAP) compositions by the temperature-induced phase-inversion technique (TIPS) to be used in a PV unit to recover butanol from ABE synthetic mixtures. Modeling of mass transfer through the membrane using the resistances-in-series approach was used to find the liquid and membrane resistances. It was seen that the overall resistance decreases as the flow rate increases; regarding the liquid side resistance, it becomes important at smaller flow rates and is almost negligible for flowrates above 4.5 L min-1. The resistance that exerted the composite polymeric membrane followed this trend acetone > water > ethanol > butanol. Increasing the IL content favours the selective separation towards butanol because of the smaller membrane resistance. Also, adding IL to the membrane at concentration above 20% leads to a worse separation of the components (in terms of separation factor) because of the formation of defects in the polymeric matrix allowing the water to pass through. Finally, running PV experiments under the same operating conditions allowed the comparison of the PSI of the self-made membranes with a commercial membrane, concluding a better performance of the former membranes.

This research has been funded by the by the projects CTQ2016-75158-R (AEI/FEDER) and RTI2018-093310-B-I00 (MINECO/AEI/FEDER). Carla Arregoitia also thanks for a FPI research scholarship (BES-2017-081708).