Adsorption And Separation Of Hexane Isomers In Metal-Organic Frameworks

Separation of n-alkane and isoparaffin is an important means to utilize naphtha resources to enhance the economical efficiency of steam cracking and catalytic reforming as well as to increase the octane number of gasoline.The content of hexane in naphtha is high,so the separation of n-hexane and isohexane is particularly important.In industry,the adsorption separation technology for C6 alkane isomerization is based on the shape-selective adsorption by molecular sieves,and 5A zeolites are used as adsorbent,which have the disadvantages of low adsorption capacity and difficulty in functionalization.MOFs emerged in recent years have many advantages and have broad application prospects in the field of adsorption and separation.Computational calculations and adsorption experiments were combined to investigate the adsorption behaviors of two kinds of MOF materials:ZIFs and Ui O-66-R.The factors affecting the adsorption performance were analyzed and the MOF materials with excellent adsorption performance were screened out.Firstly,the interactions between organic ligands of MOFs and C6 isomers were studied by DFT method,and the microscopic mechanism was explored.Secondly,the adsorption behaviors of pure and mixed components of C6 isomers in ZIFs and Ui O-66-R were studied by means of molecular simulation,and the adsorption capacity and selectivity were compared.Finally,the adsorption results of pure component simulation of Ui O-66 and Ui O-66-NH₂ were verified by adsorption experiments.The results show that ZIF-67 has a large adsorption capacity of alkanes but a low selectivity.Compared with ZIF-68,ZIF-78 and ZIF-81 have a large adsorption capacity for n-hexane and a good selectivity.Ui O-66-R materials show reverse shape selectivity during the adsorption of the mixed components,preferentially adsorbing the di-branched alkane,and the selectivity of dibranched alkane in Ui O-66-NH₂ and Ui O-66-OH are high.ZIF-78 and ZIF-81 have the ability to preferentially separate n-hexane from a mixture of C6 isomers,and the selectivity factor of 3MP over n HEX is 6;Ui O-66-NH₂ and Ui O-66-OH have the ability to preferentially separate the di-branched alkanes in the adsorption separation of the mixed components,and the selectivity factor of 22DMB over n HEX is 15.The four MOF materials are highly effective adsorption separation materials,which have guiding significance for the screening of MOF materials.