Topological isomer effect on one-step C2H4 purification from ternary C2 hydrocarbon mixture

Abstract

One-step separation of C2H4 from ternary C2H2/C2H4/C2H6 hydrocarbon mixtures is desirable yet challenging in the industry due to their similar sizes and physical properties. Herein, we investigate the topological isomer effect on the relationship of pore environments and one-step separation of C2H4. IAM-8 and NU-912 are topological isomers that are obtained with the identical molecular formula [Zr6(μ3-O)8(H2O)8(PPTBA)2)]·(solvents)x (H4PPTBA = 4,4′,4′',4′''-(pyrrolo[3,2-b]pyrrole-1,2,4,5-tetrayl) tetrabenzoic acid) but with different topologies, (4,8)-connected sqc and scu, respectively. Both IAM-8 and NU-912 exhibit inverse adsorption behaviors. The IAM-8 shows excellent C2H6/C2H4 (v/v = 10/90) selectivity of 2.1 and a large uptake ratio of 120% (78.70/65.78 cm3 g−1) at 298 K and 1 bar. The NU-912 exhibits relatively lower C2H6/C2H4 (v/v = 10/90) selectivity of 1.5 and adsorption capacity (63.00/47.00 cm3 g−1) at 298 K and 1 bar. GCMC and DFT simulations show that the higher adsorption capacity of IAM-8 relative to that of NU-912, as well as the C2H6/C2H4 selectivity of IAM-8 over NU-912, is due to pore size and shape matching. Dynamic breakthrough experiments demonstrate that polymer-grade C2H4 (>99.9%) can be harvested in one step from a ternary mixture of C2H2/C2H6/C2H4 (1/9/90, v/v/v) for both materials, but indeed showing a better performance for IAM-8. This work is the first case to demonstrate the topological isomer effect to fulfill the pore matching requirement in promoting the challenging one-step C2H4 separation.