Gas separation characteristic of mixed matrix membrane prepared by MOF-5 including different metals

Abstract

In this study mixed matrix membranes (MMMs) were manufactured by introducing metal organic frameworks (MOFs) within polyimide (PI) in order to investigate their separation performances for H2, CO2 and CH4 gases. MOF-5, Cu, Co and Ni doped MOF-5 and CuCo, CuNi and NiCo doped MOF-5 particles have been produced and used as fillers for the manufacturing MMMs. MOFs and membranes have been characterized by using SEM, FTIR, XRD, TGA, DTG and DSC analysis. It has been evidenced that MOF particles have the similar shape, and XRD and FTIR analysis showed all metals exist in the MOFs. MOF particles and PI showed generally a good compatibility, but MMMs were brittle and comprised some nonselective fissures in case of loading above 5w.% MOFs including triple metals. MMM manufactured by using Cu doped MOFs showed higher gas permeation, and Cu also made positive effect on gas permeation of MMMs which were manufactured initially using Co doped MOF-5 or Ni doped MOF-5. Permeation rate of gases through MMMs enhanced gradually with increasing the loading rate of MOFs (5w.%, 10w.%, 15w.%) and transmembrane pressure (100–500 kPa) at room temperature. 5w.% of MOF-5 incorporation within PI increased its H2, CO2 and CH4 permeabilities as 20.35%, 31.41% and 23.98%, respectively. But, introducing 5w.% of Cu doped MOF-5 (CuMOF-5) within PI increased its H2, CO2 and CH4 permeabilities as 62.86%, 94.00% and 121.27%, respectively. This higher interest of MOFs to CO2 and CH4 reduced the H2/CO2 and H2/CH4 selectivities. There was no a linear relationship between gas adsorption capacities of MOFs and permeation rate of these gases through the MMMs. The more adsorbed gas (H2) permeated slowly through MMMs. Feed pressure increased the permeability of gases and reduced selectivities of the membranes. MMMs manufactured by using MOFs can be used for H2 separation from CO2, and enrichment of CH4 from natural or biogas.