Gas separation properties of polymer nanocomposite membranes containing metal organic framework (MOF) and zeolitic imidazolate framework (ZIF)

The number of researches conducted today on production materials which have outstanding qualities have increased upon the expansion of usage areas of these materials and most importantly the developments in membrane technology. Many procedures including selective removal of CO2, enrichment of nitrogen and oxygen from air, separation of hydrogen from nitrogen, and removal of volatile compounds from air for a variety of applications such as improvement of natural gas quality, landfill gas recovery, enhanced oil recovery and prevention of global warming have been among a few interesting issues of membrane technology applications. In this point, researchers have long been carrying out researches on mixed matrix membranes (MMMs) commonly used for economic and effective applications of gas separation. In these researches carried out it is ensured that polymer membranes have both high permeability and high selectivity with nano-fillers such as zeolitic imidazole frameworks (ZIFs) and metal organic frameworks (MOFs). ZIFs are a new class of porous materials and used as nano-fillers by being synthesised in a wide spectrum of pore sizes. ZIFs attract a great deal of attention due to their outstanding chemical and thermal stabilities among a large number of MOFs and ability to be easily synthesised at low prices and they are promising materials for a variety of important applications such as gas storage, chemical sensor and separation process due to these properties. Also MOFs used as fillers for MMMs indicated positive results in various reports. While only a few types of zeolites are successfully applied in MMMs, MOFs can offer almost unlimited porous structures and compounds. In this study, firstly, the nano-fillers Ni-10-MOF-5 and Ni-50-MOF-5 were synthesised to be incorporated into the PEI (polyetherimide, Ultem®1000) polymer which were composed through nickel (Ni) loading of 10% and 50% in mole into the MOF-5 nano-filler and ZIF-7, ZIF-8 and MOF-5 nanoparticles. In the second step, the H2, CH4 and CO2 gas permeability tests were conducted for the membranes prepared with these fillers at 35 °C and 3.1 bar and their ideal selectivities (α H2/CH4, α H2/CO2 and α CO2/CH4) were calculated. Various characterisation analyses including particularly scanning electron microscope (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, X-Ray Diffraction (XRD) analysis were done for these membranes whose diffusion and solubility coefficients were also calculated. According to the test results, as the rate of the ZIF-7 and ZIF-8 nanoparticles incorporated into the pure PEI membrane increased, there was an improvement in the values of gas permeability and diffusion and solubility coefficients of the membranes, however the selectivities of the ideal membranes decreased in the reverse direction of this increase. When the membranes prepared with the nano-fillers Ni-50-MOF-5 and Ni-10-MOF-5 are compared to each other, we can say that the incorporation of Ni-50-MOF-5 improves all of the values of gas permeability of the PEI membranes. Also it was seen that the H2/CH4 and CO2/CH4 ideal selectivities of the membranes PEI/Ni-50-MOF-5 increased from 89.4 to 93.96 and from 15.57 to 20.47 in comparison with the pure PEI membrane, respectively.