Effect of operating parameters on performance of additive/ zeolite/ polymer mixed matrix membranes

Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Turkey

Approval Date: 2011

Thesis Language: English

Student: Edibe Eda Oral



Membrane based separation techniques have been widely used and developed over decades. Generally polymeric membranes are used in membrane based gas separation; however their gas separation performances are not sufficient enough for industrial feasibility. On the other hand inorganic membranes have good separation performance but they have processing difficulties. As a consequence mixed matrix membranes (MMMs) which comprise of inorganic particles dispersed in organic matrices are developed. Moreover, to enhance the interaction between polymer and zeolite particles ternary mixed matrix membranes are introduced by using low molecular weight additives as third component and promising results were obtained at 35 °C. Better understanding on gas transport mechanism of these membranes could be achieved by studying the effect of preparation and operating parameters. This study investigates the effect of operation temperature and annealing time and temperature on gas separation performance of MMMs. The membranes used in this study consist of glassy polyethersulfone (PES) polymer, SAPO-34 particles and 2- v hidroxy 5-methyl aniline (HMA) as compatibilizer. The membranes fabricated in previous study were used and some membranes were used as synthesized while post annealing (at 120°C, 0.2atm, N2 atm, 7-30 days) applied to some membranes before they are tested. The temperature dependent gas transport properties of the membranes were characterized by single gas permeation measurements of H2, CO2, and CH4 gases between 35 °C-120 °C. The membranes also characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Annealing time and temperature affected the reproducibility and stability of the mixed matrix membranes and by applying post annealing step to mixed matrix membranes at higher temperatures and longer times, more stable membranes were obtained. For pure PES membranes thermally stable performances were obtained without any need of extra treatment. The permeabilities of all studied gases increased with increasing operation temperature. Also the selectivities of H2/CO2 were increased while CO2/CH4, H2/CH4 selectivities were decreased with temperature. The best separation performance belongs to PES/SAPO-34/HMA mixed matrix membrane at each temperature. When the temperature increased from 35 °C to 120 °C H2/CO2 selectivity for PES/SAPO- 34/HMA membrane was increased from 3.2 to 4.6 and H2 permeability increased from 8 Barrer to 26.50 Barrer. This results show that for H2/CO2 separation working at higher temperatures will be more advantageous. The activation energies were found in the order of; CH4 > H2> CO2 for all types of membranes. Activation energies were in the same order of magnitude for all membranes but the PES/SAPO-34 membrane activation energies were slightly lower than PES membrane. Furthermore, PES/SAPO-34/HMA membrane has activation energies higher than PES/SAPO-34 membrane and is very close to pure membrane which shows that HMA acts as a compatibilizer between two phases.