Organic vapour permeation in amorphous and semi-crystalline rubbery membranes: Experimental data versus prediction by solubility parameters

The applicability of Hansen and Hoftyzer and van Krevelen solubility parameters for the prediction of potential VOC/N separation efficiency was analysed with both new experiments and literature data. It was found that Hansen solubility parameters can be successfully applied for the prediction of permeability order of some types of volatile organic compounds (VOC). The results show limited predictability of solubility parameters for a cyclic hydrocarbon. The principle was tested with the low-permeable polyethylene representing an organophilic membrane material with very similar Hansen solubility parameters as polydimethylsiloxane (PDMS). PDMS was selected as a commercially used membrane material in VOC/N separation with high permeability, above 20,500 Barrer for hexane, 13,500 Barrer for cyclohexane, 12,900 Barrer for 2,2,4-trimethylpentane and 11,100 Barrer for ethanol vapours, respectively. The analysis was extended to two polyether-polyamide block-copolymers (Pebax® 2533 and Pebax® 1657) to cover different polymeric materials in the whole Hansen database. The analysis showed a deviating trend for Pebax® 2533, caused by its anisotropic microstructure, in which the transport is dominated by the flexible poly (tetramethylene oxide) phase. This suggests the need for a revised model, including parameters that describe the microstructure for this type of copolymer. Further tuning of the model is needed to improve the predictions for cyclic and aromatic compounds, for instance by introducing properties that correlate with diffusivity.