Methane purification by adsorptive processes on MIL-53(Al)

Abstract

The main polluting compound in natural gas and biogas is CO2. Therefore, the removal of CO2 from these fuels is a major process in the industry for upgrading their energy content. The separation by Pressure Swing Adsorption (PSA) is energy-wise efficient and the porous aluminium terephthalate – MIL-53(Al) MOF has been pointed out as a promising adsorbent to carry out this separation. In this work, MIL-53(Al) tablets (Basolite® A100) provided by BASF are evaluated to carry out CO2/CH4 separation by adsorption. The adsorption capacity of CO2 and CH4 was assessed by dynamic experiments in a fixed-bed reactor, carried out at 303K and pressures up to 3.5bar. The evaluated material presents an adsorption capacity of 4.3molkg−1 at 3.5bar for CO2. Fixed-bed experiments adsorption and desorption in helium flow revealed high selectivity of MIL-53(Al) material for CO2, with a separation factor of 4.1 at 303K and pressures of 0.1–3.5bar, thus showing to be promising for a PSA process. The measured single and binary breakthrough curves were simulated with a mathematical model for fixed bed column. Two VSA cycles, both with 4-steps but with different pressurization types were designed to produce 96.5% CH4 from a 40:60 CO2/CH4 mixture; experimental validation confirms a good model prediction. Two industrial-scale PSA processes were designed and optimized by simulations, a case similar to natural gas upgrade (but lower inlet pressure) and biogas upgrade. The CH4 recoveries were determined as 92.8% and 72.9%. The productivities were estimated as 2.09 and 2.78molkgads−1h−1 and the power consumptions as 17.0 and 5.1Whmol−1CH4. The obtained purity values allow the distribution via pipelines of upgraded CH4.