Polymer Testing (Apr 2023)
ZIF/PA thin film nano-composite (TFN) total heat exchange membranes (THEMs): Preparation, performance and integrated online testing
Abstract
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 CO2 and moisture exchange rates as well as energy recovery efficiencies. ZIF PTs added in water phase improved the CO2 barrier property of the THEMs due to their good dispersion in water, the coordination of the excess cations on their surfaces with the –NH2 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 CO2 barrier property of the THEMs depending on their dispersion, structure rigidity, and interaction with the PA polymer matrix. Adding 0.01 g/144 cm2 of ZIF-67 in aqueous phase and 0.02 g/144 cm2 of ZIF-9 in organic phase could form TFN membranes with improved CO2 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 CO2 exchange rates of 1.7%. The newly obtained online CO2 exchange rates (hCO2) were found to have good correlation with the off-line CO2 permeance values (PERCO2), ηCO2 = ln (PERCO2)%-0.005, with a high Pearson's R value of 0.9914. There was also a linear correlation between the permeation selectivity obtained online (DSH2O/CO2) and calculated offline (ISH2O/CO2), ISH2O/CO2 = 0.289*DSH2O/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.
