Preparation Of Flexible PDMS Composite Membranes And Gas Separation Performance For C₃/N₂ Mixture

Light hydrocarbon has been the raw materials during many industrial processes with high cost. They can do damage to environment via photochemical pollution and form liquid drop inside pipes, which is dangerous for transportation. Therefore, it is well worth recycling light hydrocarbon. It has been realized that membrane process is an innovative technology successfully used in hydrocarbon recycle. Rubbery polydimethylsiloxane (PDMS), which is a solubility-dominated material, is the most commonly used for separation of higher hydrocarbon from permanent gases. It is important to investigate PDMS membrane with new structure for promoting the fields of hydrocarbon recycle.In the present work, PDMS composite membrane embedded to the flexible stainless steel mesh as support was fabricated by dip-coating method. The effects of PDMS, supports, preparation condition and testing condition were investigated for the separation of C3 hydrocarbon/N2.Meantime, the micro-morphology, micro-structure and thermal stability of PDMS composite membranes were characterized by SEM, ATR-FTIR, XRD and TG.Compared to PDMS homogeneous membrane, the PDMS composite membranes embedded to flexible support exhibited a significantly increase of gas permeation rate with similar high gas selectivity, excellent flexibility and mechanical property. The size and structure of supports affected the gas separation performance of derived composite membranes. It is demonstrated that incompact structure showed a higher gas separation performance.Effects of preparation condition including the two component ratio, curing time, the concentration of PDMS and dip coating time made a huge influence to gas performance. The gas separation performances of PDMS composite membrane fabricated under the optimum conditions were PN2=8 GPU, PC3H8=106 GPU, PC3H6=178 GPU, ?C3H8/N2=12 and ?C3H8/N2=21.PDMS homogeneous membrane showed shrink and mass loss after low temperature pyrolysis, while PDMS composite membrane kept stability and mechanical strength due to the constraint of steel mesh. Meanwhile, it is turned out that composite membrane had thermal stability owning to good gas performance after pyrolysis.PDMS composite membrane measured in different testing condition led to different performance. It is indicated that with the increase of C3 component in mixtures, the permeation rate of C3 increased. Low temperature was in favour of C3 solubility and high pressure was good for solubility and diffusivity of C3 due to the swelling of C3 hydrocarbon to PDMS matrix. It is demonstrated that the prepared PDMS composite membrane exhibited long-time permeating stability and durability with broad application prospect.