Abstract
Thin pure-silica CHA-type zeolite (Si-CHA) membranes have been synthesized via secondary growth method on a porous silica support, to the best of our knowledge, for the first time The synthesis temperature was varied from 150 to 180℃ and the synthesis time was varied from 4 to 16 h. The obtained membranes were investigated for CO2 permeance and ideal and real CO2/CH4 selectivity. Higher synthesis temperatures have shown an increase in crystallization speed, whereas higher synthesis times had a positive effect in the separation layer’s crystallinity. However, although the increase of both variables resulted in a more selective and thicker zeolite layer, it was observed that, for membranes synthesized for over 4 h at temperatures of 160℃ and above, the silica from the substrate was considerably dissolved and separation layers could not be obtained. All membranes synthesized at 150℃ for 8 to 16 h have displayed a CO2/CH4 ideal selectivity of over 90. In a mixed gas permeance test with a CO2/CH4 mixture, the membrane synthesized at 150℃ for 16 h has shown a CO2 permeance rate of 4.2 × 10–7 mol m-2 s-1 Pa-1 and a real selectivity of 52. By fitting the experimental data to the Arrhenius equation, it was observed that the obtained membranes have shown not only molecular sieving as a permeation mechanism, but also surface diffusion of CO2. Since it is a novel technique for CHA zeolite membrane synthesis, these new results are satisfactory, although there is still much room for improvement.
