Removal of CO 2 from natural gas is necessary to purify the gas and to enhance its calorific value. Membrane technology is an efficient technique for CO 2 removal due to its ease of operation and low cost. Polymeric membranes exhibit excellent separation performance which is affected by plasticization and swelling in the membrane. Recent technological advancements and major problems in polymeric membranes are reported in this review. Separation performance of polymeric membranes is highlighted in terms of permeability and selectivity. Moreover, techniques to overcome the major problems in polymeric membranes are reviewed. Commonly, cross-linking and thermal treatment are used to minimize the effect of plasticization and swelling in the membrane. For future perspectives, there is a need to find more efficient methods to overcome these problems.

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Asymmetric polysulfone (PSF) membrane was developed and modified to PSF/polydimethylsiloxane (PSF/PDMS) composite membrane by dip coating technique. Effect of PDMS coating time on membrane properties was examined by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, attenuated total reflectance-Fourier transform infrared, and water contact angle. The increase in PDMS coating time resulted in a decrement in the thermal strength of PSF membrane. Surface contact angle values revealed that increase in PDMS coating time had increased the surface hydrophobicity in membranes. CO 2 /CH 4 separation performance of membranes was evaluated, and an increase in CO 2 /CH 4 ideal selectivity was observed with the increase of PDMS coating time. At feed pressure of 10 bar, the selectivity of PSF has increased up to 65% after dip coating with PDMS for 30 min. Modification of polymeric membrane into composite membrane provided a way forward towards the enhancement of gas separation performance in polymeric membranes.

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Generation of biogas from organic substances is an attractive evolution of energy generation from fossil-based energy supply to renewable resources.

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A PSF/PDMS composite membrane was developed by film casting of polydimethylsiloxane (PDMS) over polysulphone (PSF) support. The CO 2 /CH 4 separation performance of membranes was evaluated under dry and wet conditions to evaluate the influence of water swelling on the separation performance of the developed membrane. Gas permeance in developed pure and composite membranes was theoretically predicted considering the effect of swelling on gas permeation in the membrane. Swelling in the membrane was confirmed by comparing the cross-sectional morphology of the developed membranes before and after wet tests. Water swelling in the membrane affected the separation performance of PSF, and CO 2 permeance decreased from 48.79 to 2.37 GPU at 1000 kPa. However, the PSF/PDMS composite membrane resisted the effect of water swelling, and CO 2 permeance increased from 39.9 to 40.87 GPU at 1000 kPa. CO 2 and CH 4 permeation were fitted with the dual mode model to predict the permeation in developed membranes theoretically. Permeation under wet feed conditions was not well-explained by the existing dual mode model. Thus, a modified dual mode model was presented with the best prediction of gas permeation under the effect of water swelling in the membrane.