Copper-exchanged LTA zeolite membranes with enhanced water flux for ethanol dehydration

LTA (Linde Type A) molecular sieve has widely used in adsorption and separation due to its regular pore structure, high thermal stability and chemical stability. Copper-exchanged LTA (Cu-LTA) zeolite membranes with enhanced water flux of ethanol dehydration were developed through copper ion exchange of Na-LTA zeolite membrane. In the first step, a thin and well intergrown Na-LTA zeolite membrane was prepared on macroporousα-Al2O3 tube which was modified by 3-aminopropyltriethox-ysilane (APTES). Afterwards, copper exchange of the as-synthesized Na-LTA zeolite membranes was done to prepare Cu-LTA zeolite membrane. According to characterizations of XRD, FESEM, and XPS, both the morphology and structure of the Cu-LTA zeolite membranes are identical to those of the Na-LTA zeolite membranes, and there are no cracks and pinholes are found in the membrane layer. Attributing to a wider pore diameter because two sodium ions of Na-LTA framework are replaced by one copper ion, the Cu-LTA zeolite membrane displays a higher water flux in the separation of ethanol/water mixture than Na-LTA membranes. At 75 °C, the water flux of the Cu-LTA zeolite membrane is 3.52 kg m^-2 h^-1 with water/ethanol separation factor of 3591, while the water flux of the Na-LTA zeolite membrane is only 1.65 kg m^-2 h^-1 with water/ethanol separation factor of 4082.

Facile preparation of compact LTA molecular sieve membranes on polyethyleneimine modified substrates

A facile preparation strategy was proposed for preparation of compact zeolite LTA membranes on polyethyleneimine(PEI)modified substrates without seeding.Through the functionalization of substrates by using PEI,compact LTA membranes can be formed on various kinds of substrates.A well-intergrown and phase-pure LTA membrane with a thickness of about 3.0μm is successfully prepared on the a-Al_(2)O_(3)disk after crystallization for 24 h at 60℃.Besides LTA membrane,wellintergrown zeolite FAU membranes can also be formed on PEI-modified a-Al_(2)O_(3)substrates,suggesting the universality of this strategy.The zeolite LTA membranes synthesized on PEI-modified a-Al_(2)O_(3)tubes were evaluated for the separation of alcohols/water mixture through pervaporation.The as-synthesized zeolite LTA membranes display high pervaporation performances.For the separation of 10 wt%isopropanol/water solution at 90℃,a high separation factor of44991 and a water flux of 1.73 kg m^(-2)h^(-1)are achieved.