Natural zeolite membranes for gas and liquid separations

Synthetic zeolitic membranes have received much research attention over the past several decades but few studies have examined the potential application of natural zeolites for membrane separations. In this study two separate high density natural zeolite deposits were identified, characterized and experiments were performed separating gases and liquids using these robust membranes.;As-mined, raw clinoptilolite membranes showed industrially relevant permeances and selectivities of hydrogen over carbon dioxide and light hydrocarbons above Knudsen selectivity. This is indicative of activated diffusion through zeolitic pores. A simple alkaline membrane pre-treatment increases thermal stability and further increases hydrogen selectivity to well above Knudsen selectivity.;Desalination of a synthetic seawater and purification of a synthetic process water was also performed. High ion rejection and efficient fluxes were found for pervaporative desalination experiments. The synthetic process water showed similar results while also exhibiting high rejection to a model organic compound.;Further investigations are required before industrial application can be considered but these studies clearly indicate that natural zeolite membranes are not only feasible but show great potential as alternatives to their synthetic analogs.