NaP1 zeolite membranes with high selectivity for water-alcohol pervaporation

Abstract

Membrane pervaporation is an emerging technique for the separation of water from alcohols, and zeolites with ordered ultramicropores (pore size <0.7 nm) have shown particular promise for use as membrane materials. This is the first paper to propose the use of NaP1 zeolite in membrane pervaporation. NaP1 zeolite has a GIS type topology with an 8-member ring that forms a pore limiting diameter of 3.0 Å, which is ideal for the separation of water from alcohols. NaP1 zeolite membranes with various Si/Al ratios (1.9, 3.3, and 3.9) were made via the seeded growth. Pervaporation tests were performed using an aqueous feed solution of 90 wt% ethanol or IPA at 348 K. The sample with a Si/Al ratio of 3.3 achieved separation factors surpassing most existing zeolite membranes: water/ethanol (200,000) and water/isopropanol (36,000). Nano-beam X-ray diffraction was used to map grain sizes in membrane samples, due to its role in surface hydrophilicity. State-of-the-art molecular simulations provided valuable insights into the diffusion and adsorption of water/alcohol molecules in NaP1 zeolite. From simulations, NaP1 zeolite presented a high water diffusivity and a high adsorption selectivity of water over ethanol or isopropanol. Experiment and computation results demonstrate the potential of NaP1 zeolite as a membrane material for alcohol dehydration.