چكيده به لاتين
The scope of this work is synthesis and modification of ZIF-8 nanoparticles and their incorporation as the filler particles into PEBAX-1074 for mixed matrix membranes (MMMs) preparation and application for natural gas's CO2 and H2S removal. Since gas transport mechanism through the MMMs is a combination of the solution diffusion and molecular sieving mechanisms, it is necessitate to investigate behaviors of the polymer matrix and the incorporated nanoparticles in their exposure to the acid gas molecules. Modification and size reduction of the ZIF-8 nanoparticles were selected as two scenarios of acid gases solution and sieving facilitation through the MMMs. The measured adsorption isotherms of CH4, CO2 and H2S, showed that the synthesized WS-ZIF-8, EDM-ZIF-8 and ED-ZIF-8 are the best nanoparticles for preparation of MMMs. H2S and CO2 adsorption breakthrough times for the as-synthesized WS-ZIF-8 nanoparticles from mixed feed gas of CH4/CO2/H2S /He (88.8 / 7.3 / 3 / 1 mol. %) at 25 °C and 2 bar were found as ~ 190 and 308 s, respectively, while those for modified ED-ZIF-8 nanoparticles were considerably improved as ~ 400 and 531 s, respectively. In next step of this work, DS-ZIF-8 and EDD-ZIF-8 nanoparticles were applied for preparation of two series of MMMs and also WS-ZIF-8, ED-ZIF-8 and EDM-ZIF-8 nanoparticles were used to prepare another three of series of MMMs, all with 5, 10, 20 and 30 Wt. % loading of the nanoparticle for synthetic natural gas accompanying CO2 and H2S removal. Pure CO2 and CH4 permeabilities through MMMs were evaluated at room temperature and different transmembrane pressures. CO2 permeability and CO2/CH4 selectivity through the 30 Wt.% loaded WS-ZIF-8, EDM-ZIF-8 and ED-ZIF-8 nanoparticles loaded MMMs were found as ~ 194, 499, and 530 Barrer and 20.22, 30.18 and 39.56, respectively, revealed significant improvement in the mixed gas CO2 permeabilities and CO2/CH4 selectivity by 2, 1.5, and 4.5, 2.2, 5.4 and 3 times enhancement compared with those of the neat membrane. The MMMs results also showed significant improvement in their CO2 permeabilities and real CO2/CH4 selectivities for mixed gas feed of CO2/CH4 (50/50 by mol) as 169, 320, 395 Barrer and 13.8, 26.77 and 34.7 at 30 Wt. % of the modified ZIF-8 loading. Real permeabilities through the best MMM’s (PZ30TM and PZ30TT) in this study were evaluated with mixed gas of CH4/CO2/H2S (89.7 / 7.3 / 3 mol. %) at 25 °C and 15 bar as 523 and 590 for H2S and 224 and 268 for CO2. Their selectivities were measured as 23.4 and 28.5 for CO2/CH4 and 54.0 and 62.8 for H2S/CH4, respectively, which revel their comparable separation performance with those of commercial membrane type as Torlon with H2S/CH4 selectivity of 14.8.
