Separation of methane from ethane and propane by selective adsorption and diffusion in MOF Cu-BTC: A molecular simulation study.

Pure methane is an alternative source of cleaner energy. Although, natural gas contains around 90% of methane, there are other heavier alkanes such as ethane and propane. Presence of these heavier hydrocarbons affects the reusability of an adsorbed natural gas system (ANG). Thus, separation of these higher alkanes from methane is important. In the present study, we employed molecular simulation techniques to assess the performance of MOF Cu-BTC for separation of methane from ethane and propane at 298 K and for a range of pressure. The assessment was carried out on the basis of variety of performance metrics suitable for adsorption based separation. The performance metrics that we relied upon are adsorption selectivity, working capacity, regenerability (R%), adsorption performance score (APS), diffusion selectivity, and membrane selectivity. We investigated the performance for two equimolar binary mixtures - methane/ethane and methane/propane, and two ternary mixtures - one equimolar mixture and the other containing 90% methane, 7% ethane, and 3% propane. The adsorption selectivity of ethane over methane and propane over methane are really attractive indicating good performance of the MOF in separating the two binary mixtures. We also investigated the effect of the presence of ethane and propane on the mobility of methane. The diffusivities of methane, although, reduces by some factor in presence of ethane and propane, are sufficiently higher at all the pressures and at different compositions with ethane and propane. Finally, we assessed the performance of Cu-BTC as a membrane for separation of methane from ethane and propane.