Polymeric membranes for dimethyl ether separation from methanol

Polymeric membranes have potential for dimethyl ether (DME) separation from the methanol dehydration process as a more energy efficient alternative to distillation. Various polymer classes were studied for their DME, methanol (CH 3 OH), and water (H 2 O) permeability and selectivity over a temperature range of 35 - 200°C. At 35°C, DME significantly plasticized the glassy polymers, with permeability increasing substantially with pressure. Polymers with high fractional free volume like Teflon AF 1600 and 6FDA-TMPDA exhibited the highest DME permeabilities around 1000 barrers. However, only the superhydrophobic PVDF-HFP and Teflon AF 1600 demonstrated DME/CH 3 OH separation factors greater than 1, making them suitable for separating DME. At elevated temperatures above DME's critical temperature, the plasticization effects diminished as DME transitioned from a vapor to gas phase. DME permeability increased with temperature following an Arrhenius relationship, with activation energies inversely related to the polymers’ fractional free volume. The DME/CH 3 OH separation factor improved at 200°C compared to 150°C for most polymers as DME's permeability increased. All membranes displayed selectivity for H 2 O over DME, indicative of H 2 O smaller kinetic diameter and greater condensation. The H 2 O/DME selectivity of the polymers ranged, from 2.4 to 10,100 at 35 o C, and decreased at higher temperatures due to reduced H 2 O solubility. For H 2 O/CH 3 OH separation, all polymers exhibited H 2 O/CH 3 OH separation factors between 10 and 1000 at 35°C, with values decreasing at higher temperatures due to reduced H 2 O solubility. Teflon AF 1600 demonstrated the most stable H 2 O/CH 3 OH separation performance across the temperatures studied. Overall, the results highlighted the potential of conventional gas separation membranes, particularly superhydrophobic perfluorinated polymers, to be utilised for sustainable DME production from methanol dehydration. • Characterised polymeric membranes for dimethyl ether permeability as a function of temperature and pressure. • Hydrophobic membranes displayed selectivity for dimethyl ether over methanol. • All membranes displayed selectivity for water over dimethyl ether. • Dimethyl ether permeability was strongly solubility controlled and plasticized most polymers. • Dimethyl ether permeability changed at elevated temperature due to the transition from vapor to gas.