Comparative assessment of hydrocarbon separation performance of bulky poly(urethane-urea)s toward rubbery membranes

In the present study, two seriess of poly (urethane urea)s (PUUs) membranes containing aromatic and aliphatic side chains with different sizes were used for separation of higher hydrocarbons from methane. Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetery (DSC), fractional free volume (FFV) estimation, and gas permeation measurements (CH4, C2H6, C3H8) were done to characterize the membranes. Bulkier or longer side chains in aromatic and aliphatic substituted PUUs provided enhanced phase separation, lower glass transition temperature and higher gas permeability. Fractional free volume (FFV) as a significant factor controlling gas separation had a reverse trend in both series by increasing the size of side chains. The main findings confirmed the capability of higher phase separated PUUs for hydrocarbon separation. The highest permeability and selectivity was obtained by the longest side chain based PUU with propane permeability of 186 barrer and propane/methane selectivity of 6.51.

Automated summary

The present study investigated the use of poly(urethane urea)s membranes with aromatic and aliphatic side chains of different sizes for the separation of higher hydrocarbons from methane. The results indicated that the membranes with bulkier or longer side chains exhibited enhanced phase separation, lower glass transition temperature, and higher gas permeability. The fractional free volume (FFV) was found to be a significant factor in controlling gas separation, and its trend reversed when the size of side chains increased. The membranes with the longest side chain achieved the highest permeability and selectivity.