Preparation and characterization of SAPO-34 nanoparticles-mixed matrix membranes (MMM) via combined phase separation method for CO_2/CH_4 gas separation application

摘要

Phase separation is one of the common methods for fabrication of polymeric membrane, which classifies into the categories of Thermally Induced Phase Separation (TIPS) and Nonsolvent Induced Phase Separation (NIPS), i.e. heat and mass transfer induced phase separation, respectively. NIPS has been applied more commonly than TIPS, but the membranes which have resulted from this technique have macro finger-like voids, weak mechanical strength and not high separation ability in comparison with the TIPS. In contrast, membranes produced by the TIPS method have micro scale pores, high mechanical strength and also high separation capability, however, polymeric solutions prepared at high temperatures may ruin the polymer and consume high amount of energy. In this regard, combined method has the valuable advantages of both TIPS and NIPS techniques and it is suitable for MMM application. The present study, elucidates the feasibility of MMM's fabrication via the combined method. Mixed matrix membranes (MMM) comprising of SAPO-34 zeolite nanoparticles in polyethersulfone (PES) matrix were fabricated via combined phase separation method and characterized. The performance of the membranes was tested for separation of CO_2 from CH_4. The method of the MMM fabrication is a key factor to achieve the desired structure of mixed matrix membrane with high separation performance. In MMM structures only zeolite particles contribute to the separation properties of the membrane. Polyethersulfone (PES) flat-sheet membranes were successfully prepared by the combined TIPS/NIPS method in which the membrane forming solution consisted of PES, N-methyl-2-pyrrolidone (NMP) as solvent and phenyl benzoate as diluent. The morphology of these membranes were investigated using scanning electron microscopy (SEM) to find the optimum conditions for fabrication of the desired MMM for gas separation applications. SAPO-34 zeolite particles were dispersed in the polymeric matrix, which was produced under the optimum condition. In addition to SEM, the morphology of membranes was characterized by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). MMM's characterization tests revealed that the desired structure was obtained by the combined TIPS/NIPS phase separation method. Gas permeation tests showed that the fabricated MMM had ideal selectivity of CO_2/ CH_4 of 80.37 in the best condition, in comparison with ideal selectivity of pure polyethersulfone membrane of 25.08 at 2 bar, more than tripled.