CNT@Cu₃(BTC)₂ and Metal–Organic Frameworks for Separation of CO₂/CH₄ Mixture

Effectively separating CO₂ from the natural gas, which is one of alternative “friendly” fuels, is a very important issue. A hybrid material CNT@Cu₃(BTC)₂ has been prepared to separate CO₂ from the CO₂/CH₄ mixture. For comparison of separation efficiency, a series of representative metal–organic frameworks (MOF-177, UMCM-1, ZIF-8, MIL-53 (Al), and Cu₃(BTC)₂) have also been synthesized by the solvothermal method. Adsorption isotherms of CO₂ and CH₄ pure gases are measured by Hiden Isochema Intelligent Gravimetric Analyzer (IGA-003). The dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict adsorption of each component in the CO₂/CH₄ mixture. The IAST-predicted results show that the hybrid material CNT@Cu₃(BTC)₂ exhibits the greatest selectivity among the six materials, and its selectivity keeps in the range of 5.5 to 7.0 for equimolar CO₂/CH₄ mixture at 1 < p < 20 bar, which is higher than activated carbons. Moreover, the selectivity of CNT@Cu₃(BTC)₂ for the CO₂/CH₄ mixture keeps almost no change with the composition of CH₄, which is one of the excellent properties as a promising separation material. In short, this hybrid material CNT@Cu₃(BTC)₂ shows great potential in separation and purification of CO₂ from various CO₂/CH₄ mixtures by adsorptive processes in important industrial systems.