Polymer blend based mixed matrix gas separation membranes

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Chemical Engineering, Turkey

Approval Date: 2015




Polymer blending and mixed matrix membranes are two methods suggested to improve performance of gas separation membranes. Dense and asymmetric membranes of PES/PI blends with different compositions were prepared and the effect of blend composition on gas separation performances was investigated. In addition, PES/PI/ZIF-8 blend based mixed matrix membranes were prepared in order to investigate the effect of nano-porous filler addition to polymer blends. ZIF-8 particles with size of 83 nm were synthesized. Particles were characterized through scanning electron microscopy (SEM), X-Ray diffractometer (XRD), and thermogravimetric analysis (TGA). Dense PES/PI blend membranes were prepared in DMF with PI composition in range of 5 to 95%. Membranes were characterized through SEM, TGA, and differential scanning calorimetry (DSC). Glass transition temperatures of the blend membranes were in between the values of pristine membranes. Gas permeation test were conducted for H2, CO2, and CH4 at 3 bar feed pressure. It was determined that no phase separation occurred based on SEM or DSC characterization. The permeability of all gases increased as the amount of the PI in the blend increased. H2/CO2, CO2/CH4, and H2/CH4 selectivity values increased with increasing PI composition. PES/PI 20/80 membranes performed best for all gas pairs among the blend membranes. Polymer blend based dense, mixed matrix membranes were prepared by addition of 10 wt% ZIF-8 particles into the PES/PI 20/80 matrix. Membranes were characterized through TGA, SEM, and DSC. The decomposition temperature of PES/PI/ZIF-8 membrane was found below PES/PI 20/80 membranes. ZIF-8 particles were dispersed in the polymer matrix homogeneously and formed sieve-in-cage structure. ZIF-8 addition improved the permeability of the membranes due to high porosity of the particles, while selectivity values remained almost same for all gas pairs, compared to PES/PI 20/80 blend membranes. Furthermore, CO2/CH4 separation performance of PES/PI/ZIF-8 membrane was found better than PI/ZIF-8 membranes. PES/PI 20/80 asymmetric blend membranes were prepared by immersing polymer blend/DMF solution casted on a glass plate into DMF/IPA mixture. Thermal characters of the asymmetric membranes were improved very little in terms of the decomposition temperature and weight losses. According to the SEM micrographs, membranes have thin, nanoporous skin layer on sponge-like microporous support layer. The permeances of the asymmetric membranes were significantly higher than the dense membranes, due to the high porous structure. Besides, H2/CO2 and H2/CH4 selectivity values were improved by preparation of asymmetric membranes, relative to dense membranes.