Keywords: single-step silica membranes, two-step silica membranes, permeation, permselectivity, energetics, exergetics, gas separation, microporous membranes, nanotechnology, porous molecular sieves, sol-gel method, ceramic substrates, energy modelling, exergy efficiency, performance evaluation, membrane performance
Energetics for gas separation in microporous membranes
Gas separation by inorganic membranes has proven to be effective at laboratory scales, but is now facing challenges in developing for industrial scales. A particular type of inorganic membrane is the class of porous molecular sieves formed by sol-gel method deposited on ceramic substrates. These molecular sieve silica (MSS) membranes are ideally suited to high temperature He, H2, CO2 and CH4 separation, but one of the major understandings lacking is energy modelling enabling industrial level simulations for technology potential forecasting. In this paper we report experimental results of high quality membranes and use as a basis for predicting the exergetic efficiency of mixture separation. A specifically exergetic analysis was derived and successfully implemented. The more selective two-step membrane offered better exergetic efficiency for widely different gas molecule pair sizes like He/CH4, but lower improvement to less different pair sizes like H2/CH4. For instance, at 10 bar pressure difference, He/CH4 exergetic efficiency was around 54% while being around 35% for H2/CH4. Likewise, the higher CO2/CH4 selectivity of the single-step membrane leads to better exergetic efficiency prediction. This technique has therefore provided a working method to evaluate membrane unit performance for optimal industrial outcomes. Permselectivities were shown to correlate to exergetic efficiencies leading to a practical analysis of membrane performance.