ZIF/PA thin film nano-composite (TFN) total heat exchange membranes (THEMs): Preparation, performance and integrated online testing

Thin film nano-composite polyamide (TFN PA) total heat exchange membranes (THEMs) containing ZIF-7, ZIF-8, ZIF-9 and ZIF-67 particles (PTs) introduced during interface polymerization process were prepared. A novel integrated online testing system was established to simultaneously evaluate their CO 2 and moisture exchange rates as well as energy recovery efficiencies. ZIF PTs added in water phase improved the CO 2 barrier property of the THEMs due to their good dispersion in water, the coordination of the excess cations on their surfaces with the –NH 2 groups of MPD from the PA matrix and partially by increasing the PA layer thickness. Addition of ZIF PTs in organic phase showed variety of effects on the CO 2 barrier property of the THEMs depending on their dispersion, structure rigidity, and interaction with the PA polymer matrix. Adding 0.01 g/144 cm 2 of ZIF-67 in aqueous phase and 0.02 g/144 cm 2 of ZIF-9 in organic phase could form TFN membranes with improved CO 2 barrier property without sacrificing energy recovery efficiencies. ZIF-9 addition in organic phase formed ZIF/PA TFN THEMs with the highest total heat recovery rates of 72% and lowest on-line CO 2 exchange rates of 1.7%. The newly obtained online CO 2 exchange rates (h CO2 ) were found to have good correlation with the off-line CO 2 permeance values (PER CO2 ), ηCO 2  = ln (PER CO2 )%-0.005, with a high Pearson's R value of 0.9914. There was also a linear correlation between the permeation selectivity obtained online (DS H2O/CO2 ) and calculated offline (IS H2O/CO2 ), IS H2O/CO2  = 0.289*DS H2O/CO2 +14.4, with an excellent Pearson's R values of 0.9942. The integrated testing system could give more realistic evaluation for novel THEMs with a lot less efforts.