An effect of the seed species on the PV performance of the secondary synthesized MER zeolite membranes

Polycrystalline merlinoite (MER) zeolite membranes were synthesized using K-MER, K-CHA and Na-PHI seed crystals to clarify the effect of the seed species on the water/ethanol separation performance of the membranes. The powdered seed crystals of 2–4 g/m2 were implanted on the porous mullite tubular substrates. The secondary growth of MER membranes was carried out hydrothermally at 140 °C for 12 h. X-ray diffraction (XRD) patterns showed that the synthesized membranes have MER structures. Scanning electron microscope (SEM) observations revealed that the MER membranes comprised the block of the MER column particles with the densely packed nanoparticle zone near the substrate. Transmission electron microscopic (TEM) observation and electron diffraction patterns revealed that some of the nanoparticles still had the structures of the seed species. The MER membranes showed hydrophilic behavior in pervaporation (PV) measurements; however, in the measurement of single-component permeation, peculiarly high ethanol permeation was only observed in the case using Na-PHI-seeded membranes, which is likely due to the structural change of the PHI phase caused by dehydration. Therefore, we suggested that the ethanol permeation was affected by the bottom nanoparticle zone in the membrane, and the water selectivity was mainly due to the outer polycrystals zone. Since the CHA- and Na-PHI-seeded MER membrane showed higher performances at 40 °C (in spite of their roughness compared to the membrane using MER seed), it was suggested that the water permeation was strongly affected by adsorption, and the seeded zone plays the role of a molecular sieve.