In-situ synthetic modified metal-organic framework (MZIF-8) as an interlayer of the composite membranes for ethanol dehydration

The Metal-organic frameworks (MOFs) have received extensive attention in membrane field due to their higher porosity, tunable structure and pores size. However, the weak hydrothermal or chemical stability limits their application in the separation of liquid mixtures. Here, a stable modified ZIF-8 (MZIF-8) as an interlayer of the composite membranes was designed using poly (4-styrenesulfonic acid) (PSS) to string together ZIF-8 nanoparticles. The membrane flux and separation factor increase with the increasing operation temperature, which echoes the higher active energy for permeation of water (EJ,W = 31.6 KJ/mol) than that of ethanol (EJ,E = 16.0 KJ/mol). Along with the decreasing ethanol feed concentration, the total flux increased from 0.81 kg/m2h to 4.47 kg/m2h while the separation factor decreased from 318 to 127. The selectivity of the polyamide/MZIF-8 (PA/MZIF-8) membranes for water-ethanol mixtures was found to be about five times higher than the ideal water-ethanol selectivity, demonstrating the ethanol permeance in membrane matrix was hindered by the preferential water adsorption of the PA/MZIF-8 membranes. The as-synthesized PA/MZIF-8 membranes not only exhibited excellent dehydrating performance for ethanol-water mixtures, but also operation stability under the higher temperature and acid conditions. Therefore, the PA/MZIF-8 membranes had great potential for industrial applications.