September 11-16, 2016
Biofuels are an alternative to more traditional fuels, such as those derived from crude oil. Bioalcohols, including bioethanol and biobutanol, are produced from biomass through sugar fermentation and purification processes and thus they are a more sustainable alternative to reducing the CO2 footprint of transportation and mitigating climate change. In the short term they will find it difficult to replace hydrocarbon fuels due to direct competition with the food supply chain, although as new alternative raw materials and production processes are developed this hurdle will be overcome. The recovery of bioalcohols from fermentation broths includes a series of very challenging steps that need more attention. In this regard, membrane-based technologies with lower energy consumption, such as pervaporation (PV), have emerged as potential candidates for the replacement of energy intensive distillation operations. In this work we present the development of novel organophilic membranes based on polymers of intrinsic microporosity (PIMs) and graphene for the separation of ethanol and butanol from aqueous solutions.
PIM-1 is one of the few polymers that offer selectivity for organic compounds over water [1-3]. However, excessive swelling limits its performance and the addition of graphene nanoparticles can have a positive effect in preventing it [4,5]. For the preparation of mixed matrix membranes (MMMs) PIM-1 and graphene were first synthesized. Graphene oxide (GO) was obtained from natural flake graphite via a modified Hummer’s method, functionalized with octylamine (OA) and octadecylamine (ODA), 8 and 18 carbons, respectively and subsequently reduced with hydrazine monohydrate. PIM-1 was prepared by the polycondensation of monomers 3,3,3’,3’-tetramethyl-1,1’’-spirobisindane-5,5’,6’,6’-tetrol with 2,3,5,6-tetrafluorophthalonitrile with a molecular ratio of 1:1 . The preparation of freestanding membranes was done via a casting-evaporation technique using chloroform as solvent (one of the very few that dissolve PIM-1). The functionalization of GO with OA or ODA allowed its dispersion in chloroform and therefore a homogeneous casting solution was obtained.
Membranes of thicknesses up to 40 µm with loadings of graphene from 0.01 to 0.5 wt.% were prepared and characterized via contact angle measurements, FTIR, TGA, and SEM. PV tests of aqueous feed solutions containing 5wt% of alcohol were performed at 65 ˚C and a pressure of 10 mbar on the permeate side of the membrane. An increase in the separation factor of ethanol and butanol over water was achieved for both amine-functionalized GO with maximum values of 7 and 40, respectively. The maximum flux achieved of ~ 2 kg m-2 h1 was obtained for membranes with graphene loadings of 0.5 wt.%.
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Patricia Gorgojo, Monica Alberto, Jose Miguel Luque-Alled, Lei Gao, Maria Illut, Aravind Vijayaraghavan, and Peter Budd, "PIM-1/graphene pervaporation membranes for bioalcohol recovery" in "Advanced Membrane Technology VII", Isabel C. Escobar, Professor, University of Kentucky, USA Jamie Hestekin, Associate Professor, University of Arkansas, USA Eds, ECI Symposium Series, (2016). https://dc.engconfintl.org/membrane_technology_vii/5