Purification Of Ethylene From Multicomponent Gas By Bidentate Chelating Ligand MOFs

Ethylene is an important raw material for petrochemical industry and is widely used in the production of synthetic plastics/fiber/rubber.However,it often appears in the form of mixing of low-carbon hydrocarbons with similar properties,such as acetylene（C₂H₂）and ethane（C₂H₆）.The efficient separation of low-carbon hydrocarbons is one of the key processes for the sustainable development of petrochemical industry,and faces many challenges at the same time.As a new porous material,metal organic framework（MOF）has good designability,adjustability and modifiability in composition,topology,pore size and surface.It can be used as porous adsorbent to achieve high-efficiency adsorption and separation through selective reverse adsorption and multicomponent separation.Therefore,MOF can be used to purify important hydrocarbons in industry such as ethylene.Based on this,this paper takes the purification of ethylene in multicomponent low-carbon hydrocarbons as the application direction,integrates the structural design of new MOF and the post modification of known MOF,studies the application potential of MOF in multicomponent gas separation,and further explores the relationship between MOF structure and ethylene purification performance in multicomponent environment.The specific work is as follows:Firstly,two novel binuclear nickel cluster MOFs,BUT-150 and BUT-151,were developed using tetracarboxyl ligands containing chelated bipyridyl units.The two MOF pore surfaces have open metal sites,which show selective C₂H₂ and C₂H₆adsorption properties relative to C₂H₄,and have the application potential of separating and purifying ethylene from ternary C2 mixed gas system.In particular,the C₂H₂/C₂H₄selectivity and C₂H₆/C₂H₄ selectivity of BUT-151 containing o-phenanthroline units on the ligand are 2.31 and 1.36 at 273 K,which are similar to the reported reference materials.The overall good separation performance of BUT-151 can be attributed to the appropriate electron absorption of open metal sites,which improves the affinity of the material for acetylene,but is not enough to form electrostatic interaction with ethylene.At the same time,because some exposed oxygen atoms of the carboxylate group of the ligand are not coordinated with the metal,it forms a moderate C-H···O interaction with ethane molecules.The column penetration experiment confirmed that BUT-151 has good separation performance for binary or ternary C2 mixture under dynamic conditions.In addition,the adsorption properties of a cationic MOF（ITC-2）,before and after anion exchange modification were studied.After modification,the selective adsorption capacity of ethane was improved.The single component adsorption isotherm test showed that under 298 K and 1 bar conditions,the C₂H₂/C₂H₄ adsorption selectivity of ITC-2 increased from 1.36 before modification to 1.51 after modification and the acetylene adsorption capacity did not decrease significantly.The post modification method of anion exchange is simple and easy,and can effectively improve the selective adsorption capacity of the MOF material for ethane.It may also be a potential method for other types of MOF to improve the selective adsorption.