Intensification of helium separation from CH4 and N2 by size-reduced Cu-BTC particles in Matrimid matrix

Preparation of mixed matrix membranes (MMMs) with appropriate separation efficiency requires tenacious interfacial affinity between filler particles and polymer matrix. In this work, Cu-BTC particles with two structures of size-reduced and needle were successfully synthesized via the three-layer synthesis approach and combined with Matrimid to prepare MMMs for helium separation. Extensive characterization of particles (XRD, SEM, TGA, FTIR and N-2 sorption) and membranes (SEM, TGA, DSC and density-FFV measurements) were performed to gain insight in the membranes separation behavior. Then gas separation performance of membranes were examined for the single gases He, CH4 and N-2 and the gas mixtures He/CH4 and He/N-2. The combination of MOFs with Matrimid resulted in an increase in Tg, density and degradation behavior of MMMs indicating a good compatibility between the fillers and polymer, however this development is more pronounced for reduced particles. The MMMs containing size-reduced MOF had premiere gas separation performance in comparison with the needle particles and overcame the 1991 Robeson upper bond. The MMM at 40 wt% loading exhibited the best efficiency with He permeability of 66.4 Barrer which is about three times more than pure Matrimid. In addition, the improvements in He/CH4 and He/N-2 ideal selectivities were 181 and 169%, respectively. Mixed gas permeability measurements showed that helium permeability values and also selectivities decreased slightly compared to single gas data due to the competitive effects between large gases of CH4 and N-2 with small helium.