Modification Of TS-1 And Its Catalytic Performance Over Oxidative Hydration Of Ethylene To Ethylene Glycol

As one of the widely used catalyst material in industrial reaction,TS-1zeolite has a extensive application in petroleum industry production,for the outstanding catalytic performance,mild catalytic conditions and easy separation after the reaction.Ethylene glycol,an vital petrochemical raw material,is mainly used in the production of polyester.At present,the production of MEG in China is still dominated by petroleum ethylene route,including two-stage process:the epoxidation of ethylene and the hydration of ethylene oxide.However,there are many disadvantages such as different catalyst types in each stage of the process,long technological process and large energy consumption.Therefore,researchers hope to find a heterogeneous catalyst that can catalyze direct synthesis of MEG from ethylene to solve the above problems.Studies have found that the TS-1/H₂O₂catalytic system has superior catalytic performance in both ethylene epoxidation and hydration of EO.The reaction system is pollution-free and has been widely studied.However,the TS-1/H₂O₂catalytic system still has some problems,such as low effective utilization of H₂O₂,low selectivity of MEG and high water ratio,which need to be further studied.According to the above problems,in this paper,the catalytic performance of modified TS-1 molecular sieve in oxidative hydration of ethylene reaction were studied through metal-doped modification and hydrothermal acid treatment.On this foundation,the optimization of process conditions and catalytic stability study over oxidative hydration of ethylene reaction in batch reactor were completed.The main research contents are as follows:1.A series of TS-1 molecular sieves with different Ti/Si,TPAOH dosage and crystallization time were prepared by hydrothermal crystallization method.Characterization results of XRD and UV-vis demonstrate that when the molar ratio of Si:Ti:TPAOH is 1:0.03:0.18 and crystallized at 175℃for 72hours,the TS-1 molecular sieve has higher skeleton titanium content and lower amorphous non-skeleton titanium content,and has the best catalytic effect in the oxidative hydration of ethylene.The conversion of H₂O₂and selectivity of MEG can reach 95.01%and 59.62%,respectively.Moreover,the TS-1 doped with Ni has better catalytic performance than the unmodified TS-1in the oxidative hydration of ethylene reaction.When Ni loading is 0.13 wt%,the conversion of H₂O₂and selectivity of MEG can reach 96.47%and 80.63%,respectively.This is attributed to the fact that the doping of nickel species enhances the electrophilicity of skeleton Ti and"neutralizes"the surface acidity of TS-1 molecular sieve,which is conducive to the combination of Ti（Ⅳ）and H₂O₂to form Ti-OOH active intermediate,catalyzing the oxidative hydration of ethylene to form MEG and inhibiting the ineffective decomposition of H₂O₂.2.Through the high temperature hydrothermal acid treatment of TS-1molecular sieve,the amorphous non-skeleton titanium is effectively removed,and the effective utilization of H₂O₂and the selectivity of MEG of TS-1molecular sieve in oxidative hydration of ethylene reaction are improved.Combined with the characterization results of UV-vis,it is found that the removal difficulty of various Ti species by acid treatment is in the descending order of anatase Ti O₂,tetrahedral coordination skeleton titanium and amorphous non-skeleton titanium.The reaction evaluation results shows that the selectivity of MEG in oxidative hydration of ethylene over TS-1 molecular sieve can reach 85.43%when TS-1 is treated in 0.56 M HCl solution at 200℃for 12 hours.However,the conversion of H₂O₂will decrease to 86.54%.3.The optimum reaction conditions were determined by applying TS-1molecular sieve to the intermittent reaction process of oxidative hydration of ethylene:the reaction temperature is 70℃,the ethylene charging pressure is2.5 MPa,the concentration and feed rate of H₂O₂is 1.2 M（4.1 wt%）and 0.4m L/min,respectively,the quantity of catalyst is 0.25 g,that is,8.68 g catalyst per mole of hydrogen peroxide,and the stirring rate is 1250 r/min.Moreover,the catalytic stability study shows that the principal reason for the deactivation of the TS-1 catalyst is that a large amount of organic matter is accumulated on the surface and inside the pores of TS-1 zeolite during the reaction.The organic matter blocks in the pores or covers the skeleton titanium active sites to prevent the reaction.However,the deactivation is reversible that does not destroy the crystal structure and can be regenerated by high-temperature calcination.