Optimized pore environment for efficient high selective C2H2/C2H4 and C2H2/CO2 separation in a metal-organic framework

Abstract

Ethylene and acetylene are both important starting materials for the production of polyethylene, vinyl chloride, but-2-yne-1,4-diol, etc. To remove trace acetylene effectively from ethylene and the separation of acetylene from carbon dioxide are particularly challenging in the petrochemical industry. Although catalytic hydrogenation or cryogenic distillation for the separation of such light hydrocarbons is a very mature operation in the current petrochemical industry, it still requires huge capital and energy consumptions. Herein, a metal-organic framework (MOF), [Ni2(BTEC)(bipy)3] (H4BTEC = 1,2,4,5-benzene tetracarboxylic acid, bipy = 4,4′-bipyridine), has been developed for efficient adsorptive separation of C2H2 from C2H2/C2H4 or C2H2/CO2 mixtures. Ni2(BTEC)(bipy)3 exhibited extraordinary two-step adsorption for C2H2 with the adsorption capacity of 76.8 cm3/g at 298 K and 1 bar, significantly discriminating from C2H4 (7.9 cm3/g) and CO2 (13.0 cm3/g) in the same condition. The huge adsorption difference of Ni2(BTEC)(bipy)3 between C2H2 and C2H4/CO2 resulted in the record high uptake ratio for C2H2/C2H4 (9.7), C2H2/CO2 (5.9) and very high ideal adsorption solution selectivity (104, 33.5) in robust MOFs at 298 K and 1 atm. The excellent separation performance was verified by breakthrough experiments; this material could effectively separate C2H2/C2H4 or C2H2/CO2 mixtures directly to obtain high purity of C2H4 (>99.999%) and CO2 (>99.99%) in one separation cycle. Furthermore, this material could be easily scaled up to be synthesized at room temperature under mild conditions, indicating the great potential in actual industrial applications.