Synthesis of oriented zeolite T membranes from clear solutions and their pervaporation properties

Zeolite T membranes were synthesized from clear solutions with a molar composition of SiO₂: Al₂O₃: Na₂O: K₂O: H₂O = 1: 0.015: 0.25: 0.08: 30 on seeded mullite tubes using nano-sized (∼100 nm) and micro-sized (∼4000 nm) zeolite T seeds, respectively. It was found that a crystal growth behavior was strongly dependent on synthesis temperature, seeding and silica source. Zeolite T crystals fast grew onto the nano-sized-zeolite-T seeded supports, leading to the formation of a (00l)&(h0l)-oriented top crystal layer at synthesis temperatures of 373 and 423 K, respectively. The same oriented crystal top layer was also formed on the micro-sized-zeolite T seeded mullite tube at 423 K. The oriented zeolite T membranes displayed good PV performance for water over organic mixtures. For example, the highest water/i-propanol separation factor of 13,000 with a high flux of 2.50 kg m^-2 h^-1 for a feed concentration of 10 wt% water at 348 K was obtained through the zeolite T membrane synthesized on the micro-sized-zeolite-T seeded tube at 423 K. Twelve membranes prepared under optimized synthesis conditions showed high flux and selectivity with low deviations, indicating the membrane synthesis had good reproducibility. The as-synthesized zeolite T membranes also revealed good hydrothermal and acidic (at pH = 3) stabilities.