Pervaporation and vapour permeation of methanol - dimethyl carbonate mixtures through PIM-1 membranes

The separation of dimethyl carbonate (DMC) from its mixtures with methanol was studied using pervaporation (PV) and vapour permeation (VP) through thick (similar to 0.5 mm) PIM-1 membranes; PV characteristics of PDMS and PTMSP membranes are provided for comparison. DMC is a "green" chemical with numerous applications in chemistry, but its production is energy- and cost-intensive. As their azeotrope contains 82 mol.% of methanol at 40 degrees C, DMC-selective rather than common methanol-selective membranes can allow for energy efficient separation and thus production of this "green chemical". PV of the azeotropic mixture through the PIM-1 membrane showed a separation factor of 2.3, which is comparable to that observed for PV through the PDMS membrane; the PTMSP membrane showed practically no separation. The total PV fluxes followed the order: PTMSP >> PIM-1 > PDMS. When the PIM-1 membrane was operated in the VP mode, a separation factor of up to 5.1 was reached for the vapours having the azeotropic composition, while total fluxes dropped ca 50-times compared to PV. The highest observed separation factor of 6.5 was found for VP of DMC-rich vapour mixtures highly diluted with inert gas. To our knowledge, VP through PIM-1 membranes enables to date the most selective membrane-based removal of DMC from its azeotrope with methanol.