Highly selective zeolite T membranes with different ERI stacking faults for pervaporative dehydration of ethanol

Abstract The effect of stacking arrangements of ERI into OFF structure on the separation performance of zeolite T membrane, which was obtained from a modified gel containing a small number of fluoride ions for ethanol dehydration, was investigated for the first time. The addition of fluoride ions and water content largely influenced the zeolite framework structure, the content of ERI stacking, and separation performance. The membrane M3 with MF(NaF: KF = 3:1)/SiO2 and H2O/SiO2 ratio of 0.15 and 35 respectively showed high crystallinity of zeolite T and ordered intergrowth of ERI with the content of about 50–60% estimated by comparing the simulated and observed ratios of (201) and (211) ERI odd lines. The M7 with an H2O/SiO2 ratio of 25 exhibited disordered stacking of ERI in the T membrane. Further increasing MF/SiO2 ratio to 0.20 and 0.25 (M4-M5) or H2O/SiO2 ratio to 45 and 55 (M8-M9) led to the formation of zeolite T membrane with impurity of PHI or CHA structure. The membrane M3 and M7 showed the highest separation index among the reported T membranes for ethanol dehydration with water flux of 2.68 and 1.94 kg·m-2·h-1 and separation factors of 9163 and 10000, respectively. The optimized membrane also exhibited good hydrothermal stability and reproducibility.