Functionalized Zeolitic-Imidazole Frameworks-8 Based Poly(ether-b-amide) Nanocomposite Membrane for Carbon Dioxide/Methane Gas Separation: Synthesis and Characterization

Hypothesis: The separation of carbon dioxide from methane is an important process in chemical industry and gas refineries from both economic and environmental perspectives. The conventional method for natural gas sweetening involves physical absorption by amines, but it has high operational cost. In this study, dual-layer mixed-matrix membranes based on poly(ether-b-amide), with trade name Pebax, containing zeolitic imidazolate frameworks-8 (ZIF-8) nanoparticles were synthesized and dispersed within the polymer matrix for separation of carbon dioxide/methane gas mixtures
To improve the distribution and compatibility of the nanoparticles in the polymeric matrix, the particles were modified by (3-aminopropyl) triethoxysilane (APTES). The modified nanoparticles were characterized and examined using XRD, FTIR, and BET. The supporting polyether sulphone (PES) sublayer was synthesized by solution casting and wet phase separation methods. The optimum thickness of this layer in the casting solution stage was found to be 200 μm. The selective Pebax/ZIF-8 layer was subsequently formed by dry phase separation method. To compare and evaluate the effect of nanoparticles on gas separation performance, some mixed matrix membranes were synthesized with different nanoparticles loadings. The permeability test was performed toward carbon dioxide and methane gases.
Findings: The mobility of polymer chain increased with the presence of ZIF-8 particle. With increasing ZIF-8 loading in the mixed matrix up to 40 wt%, the selectivity and gas permeability changed to 10.6 and 169 Barrer, respectively. APTES-modified particles showed the best performance. The bond between silane agent and the particle surface led to higher compatibility of particles in the polymeric matrix. The presence of APTES-modified particles also increased the selectivity and permeability at the same time. At 40% wt loading, the permeability and selectivity of carbon dioxide significantly increased to 925 Barrer and 16, respectively. Also, the selectivity reduction was about 34% in a 1:1 molar mixture of carbon dioxide and methane.