Study On Adsorption Separation Of C8 Alkyl-aromatics In Liquid Phase By Metal-organic Frameworks

Owing to the demand of single isomer in most applications,the separation of C8alkyl-aromatics has attracted growing attention in recent years.However,the four components have similar physical and chemical properties,which makes their separation difficult.And this separation is considered to be one of seven separations changing the world.The main separation method used in industry is adsorption method.At present,the performance of the adsorbent used in industry is low,so it is impossible to separate C8 alkyl-aromatics efficiently.Metal–organic frameworks(MOFs),a rapidly expanding family of crystalline porous materials,have shown great promise to address various separation challenges.In this paper,the static separation performance of C8 alkyl-aromatics on MIL-53 with flexible framework was studied.The adsorption performance of MIL-53(Fe),MIL-53(Al)and MIL-53(Cr)were compared by static adsorption experiments.MIL-53(Cr)showed the best C8 alkyl-aromatics adsorption performance in the quaternary liquid-phase static adsorption experiments.The adsorption capacity of OX can reach228.38mg/g,and the selectivity data of OX/PX is about 5.6,which are higher than the adsorption performance of industrial adsorbents.Cell parameters,pore diameter data and cell volume change ratios of MIL-53 materials in different states were obtained through Rietveld refinement.The different adsorption properties of the three materials were explained.We also studied the adsorption mechanism of MIL-53(Cr).The adsorption process is the result of the combination of enthalpy effect and entropy effect.In this paper,the dynamic separation performance of C8 alkyl-aromatics of MIL-53(Cr)was studied by breakthrough experiment.The adsorption capacity of MIL-53(Cr)for OX,MX,PX,and EB is 1.89,0.53,0.41 and 0.23 mmol/g,respectively,at 25?.The total adsorption capacity is 3.05 mmol/g,which is far surpassed the state-of-the-art adsorption capacity of typical molecular sieve adsorbents used in industrial SMB separation of C8 alkyl-aromatics.The selectivity values of OX/EB,OX/PX,OX/MX,MX/PX are 8.3,4.6,3.6 and 1.3,respectively,which are higher than most C8 alkylaromatics adsorbents that have ever been investigated.The curve obtained by Aspen chromatography simulation is basically consistent with the experimental breakthrough curve,which proves that the simulation model can predict the effect of MIL-53(Cr)adsorption and separation of C8 alkyl-aromatics,and provide basic data for the simulation of SMB adsorption and separation of C8 alkyl-aromatics.In the stability experiment,after five cycles,adsorption capacity of MIL-53(Cr)basically unchanged,which proves that MIL-53(Cr)has excellent regeneration ability and good adsorption stability.In summary,MIL-53(Cr)is an excellent adsorptive separation material with high specific surface area,high adsorption capacity and selectivity,excellent regeneration ability and good thermostability,it has promising potential and broad application prospect for industrial adsorption and separation of C8 alkyl-aromatics.