Amino-functionalized microporous hybrid silica membranes

The present study describes the effect of the incorporation of amino-functionalized terminating groups on the behaviour and performance of an organic-inorganic hybrid silica membrane. A primary amine, a mixed primary and secondary amine, and an imidazole functionality were selected. The molar ratio of the amino-functionalized precursors in the matrix forming 1,2-bis(triethoxysilyl)ethane (BTESE) precursor was varied in the range of 25-100 mol%. Strong water adsorption, which remains at temperatures up to 523 K, was found for all membranes. The observed low gas permeances and contrasting high water fluxes in pervaporation were explained in relation to the strong water adsorption. XPS measurements indicate a relation between the concentration of amino functional groups in the hybrid layers and the starting amine concentration of the sols. XPS measurements also revealed the existence of a maximum loading of the amino-functionalized precursor. Depending on the precursor, a maximum N/Si element ratio between 0.07 and 0.45 was found. At amine concentrations higher than a precursor dependent threshold value, membrane selectivity is constant over the range of amine concentrations. For alcohol/water (95/5 wt%) feed mixtures, the observed water concentrations in the permeate were over 90 wt% for EtOH and 95 wt% for n-BuOH dehydration.