Development Of Rare Earth Ionic Liquids For The Resource Recovery Of Ethylene In Refinery Dry Gas

As a basic chemical raw material,ethylene(C2H4)has promoted the development of world industry.Its production capacity and scale also reflect a country’s industrial development level.With the rapid development of the petroleum refining industry,a large amount of dry gas will be produced in the petroleum refining process,mainly ethylene,ethane(C2H6)and other small molecule hydrocarbon mixtures.But without mature technical conditions,current refinery dry gas is usually directly drained or burned treatment,adds huge carbon reduction pressure to the petrochemical industry.Therefore,the effective resource utilization of ethylene in the refinery dry gas by a highefficiency,energy-saving and environmentally friendly way,that is,the separation and recovery of high-purity ethylene from the ethylene/ethane mixture in refinery dry gas,is of great significance to improve resource utilization and protect the environment.In recent years,ionic liquids(ILs)have been widely used in ethylene/ethane(C2H4/C2H6)separation due to their advantages of low saturated vapor pressure and high gas solubility.For the separation of C2H4/C2H6,conventional ionic liquids and functionalized ionic liquids have problems such as complex synthesis steps,high viscosity,and low separation selectivity,while metal-containing ionic liquids can greatly improve the separation selectivity of C2H4/C2H6 due to the complexation effect between metal and C2H4.Therefore,metal-containing ionic liquids are considered as one of the most promising and efficient absorption solvents for C2H4/C2H6 separation.However,the low solubility of metal salts in ionic liquids and the inactivation of absorbers containing monovalent metal ions Ag+and Cu+also limit their development.Due to their special electronic configuration and much electron energy level,rare earth metal elements have the potential to become one of the effective complexation absorption carriers for separation of C2H4/C2H6.Based on the above background,this paper first studies the design and synthesis of rare earth metal-containing ionic liquids(hereinafter referred to as REMILs)suitable for C2H4/C2H6 separation.The REMILs absorbents with[Bmim]+as cation,[TFO]-and[NO3]-as anions,and Er3+ as rare earth metal ions were chosen and synthesized.These ionic liquids have the characteristics of stable properties,non-volatile and high gas solubility.Then,the absorption performance of C2H4/C2H6 in quaternary phosphine REMILs containing different metal ions and imidazole REMILs containing Er3+was determined.The results showed that the absorption of C2H4 by REMILs containing Er3+was 5.72 mg C2H4/mg IL.[Bmim][Er(NO3)4]had the highest selectivity of C2H4/C2H6 among REMILs and some conventional ionic liquids,because REMILs have almost no absorption of C2H6 at 30℃ and 0.1 MPa.At the same time,the results of five absorption-desorption cycles show that the absorption performance of[Bmim][Er(NO3)4]is reduced by only about 3%,which has good regeneration performance.Finally,in order to further improve the absorption and separation performance of C2H4/C2H6,a new low-viscosity absorbent REMILs-DMF was designed and synthesized by using REMILs and N,N dimethylformamide(DMF)as raw materials for the first time.The separation performance and absorption mechanism of the absorbents for C2H4/C2H6 separation was analyzed by infrared spectroscopy,Raman spectroscopy and quantum chemical calculations.Among the absorbents,[Bmim][TFO]/Er(TFO)3+20 wt%DMF had the highest absorption selectivity,reaching at 10(at 303 K,0.1 MPa),which was significantly higher than that of traditional conventional imidazole ILs and some metal ionic liquid absorbents.Finally,in the experiment of the absorption-desorption cycles,the absorption performance of[Bmim][Er(NO3)4]decreases by only about 2%,and fully reversible regeneration can be achieved.In summary,a new strategy for the design of rare earth ionic liquid absorbent for separating C2H4/C2H6 is proposed.These absorbents in this study can provide a reference for C2H4/C2H6 separation by using REMILs as efficient and reversible absorbents,which provides a new idea for expanding the application of ionic liquids in gas absorption and separation industry.And it is of great significance to the utilization of refinery dry gas resources and environmental protection.