Ethanol dehydration performance of three types of commercial-grade zeolite permselective membranes.

Abstract

Many organic solvents form difficult-to-separate mixtures with water and have an affinity for water, making drying a potential reuse prerequisite. Pervaporation (PV) and vapor permeation (VP) membrane technologies hold promise for energy-efficient solvent drying. Several water-selective membrane materials are commercially available, but performance data is limited, particularly for two recently commercialized membrane materials: chabazite (CHA) and T-type zeolites. In this work, commercial-grade samples of CHA and T-type membranes, along with a NaA zeolite membrane, were evaluated for the removal of water from ethanol. The CHA sample had the highest initial PV water permeance (6820 GPU) and water permselectivity (3430) with 5 wt% water in ethanol at 50 °C. Initial NaA membrane performance was slightly lower (6060 GPU and 3260), while the T-type membrane had the lowest initial permeance and selectivity (4260 GPU and 1090). Performance declined over time, most notably for the NaA membrane, for which water permeance fell over 50% through 39 days of testing. The T-type membrane exhibited the steadiest PV water permeance, but the most variable ethanol permeance. The PV performance of the three membranes largely overlapped the predicted range for T-type membranes. That performance generally exceeds the anticipated ethanol drying performance of non-zeolitic PV membranes but is less than that predicted for NaA and CHA membranes. The present CHA membrane results, along with other recent reports, refine earlier predictions of the ethanol dehydration performance of that type of zeolite. The changing performance with time should be understood to properly design a solvent dehydration system.