Preparation And Performance Of Low-temperature Pyrolysis PDMS Composite Membrane

Silicon rubber (PDMS), one of the membrane materials with the highest gas permeability, is widely used to prepare dense or composite membranes. It is also inexpensive and has good cohesiveness and membrane-forming property. Composite membrane is composed of dense selective layer and porous support layer prepared with two or more kinds of membrane materials separately. There are a lot of composite membranes’studies since they can combine properties of different materials and can obtain better gas performance.In this paper, PDMS composite membranes were prepared using PDMS as membrane material, steel sieve and spiral-wound carbon membrane as supports. Effects of preparing conditions on PDMS membrane’s intrinsic gas performance were studied. Based on the studies of PDMS membrane, low-temperature pyrolysis PDMS membrane was prepared. Effects of pyrolysis technique on permselectivity on the pyrolytic membrane was also studied. The chemical structure and microstructure changes of PDMS membranes through the pyrolysis process were analyzed by TG, FT-IR, XRD and SEM. The conclusions of this paper are as follows:PDMS membrane was prepared by dip-coating method, using steel sieve as support. Effects of preparing conditions such as PDMS concentration, the two components ratio, dip-coating time, dip-coating times, solvent evaporation time, curing temperature and curing time on the gas performance of PDMS membrane were studied. The optimum gas performance of PDMS membrane was that O2permeance of18.85GPU and O2/N2selectivity of2.4.During the low-temperature pyrolysis process of PDMS membrane,-CH3was partial removed from the polymer matrix, increasing the free volume of polymer and left channels in the polymer matrix. Therefore, the pyrolytic membranes obtained higher gas permeance. The gas performance were that O2permeance of25GPU and O2/N2selectivity of2.1when the pyrolysis temperature was470℃. The pyrolytic membrane has good mechanical strength and flexibility which is provided by the steel sieve support. Therefore, the pyrolytic membrane has good application prospect.In this paper, PDMS and spiral-wound carbon membrane were used as coating material and substrate separately to prepare defect-free PDMS/C composite membrane by dip-coating method. Effects of membrane preparing conditions on its gas permselectivity were discussed in detail. The results showed that the optimum condition was PDMS concentration of15wt.%, two components ratio of10:1, dip-coating twice with each time5s and curing at180℃for1h. The optimum gas performance of PDMS/C composite membrane were that O2permeance of1.3GPU and O2/N2selectivity of4.9. In order to improve gas permeability of the composite membrane, pyrolysis treatment at400-500℃was conducted. Membrane had good gas performance when pyrolysis temperature was450℃on which condition O2permeability was2.0GPU and O2/N2selectivity was3.8.