Pervaporation studies of n-hexane, benzene, mesitylene and their mixtures on zeolitic imidazolate framework-8 membranes

The metal–organic framework (MOF) ZIF-8 (ZIF-8 = zeolitic imidazolate framework-8) was evaluated as molecular sieve membrane in the pervaporation of the two liquid mixtures n-hexane/benzene and n-hexane/mesitylene. Though it is known from permeation studies of light gases that ZIF-8 membranes show no sharp separation cut-off at the estimated crystallographic pore size of 3.4 Å, highly branched or aromatic hydrocarbons > C5 could be expected therefore to become rejected by the ZIF-8 pores thus remaining in the retentate. However, the ZIF-8 membrane shows for n-hexane and benzene remarkable fluxes. Under consideration of the leakage of the apparatus, we can state that n-hexane and benzene can pass the ZIF-8 membrane. Benzene had a lower flux than n-hexane, whereas for mesitylene we could only observe a very small leakage rate through the O-ring gasket. Correspondingly, medium mixture separation factors have been found for the pervaporation separation of a liquid n-hexane/benzene mixture. Additional mixed gas hydrogen/methane separations, adsorption experiments and leak rate measurements were carried out to evaluate the results.

Figure optionsDownload as PowerPoint slideHighlights
► ZIF-8 membranes were evaluated by separating n-hexane/benzene and n-hexane/mesitylene.
► Sharp separation could not be found experimentally for n-hexane/benzene.
► Simple liquid adsorption experiments show that benzene becomes adsorbed by ZIF-8.
► Mesitylene becomes not adsorbed by ZIF-8.