Preparation And Application Of Modified Zeolite Catalysts In Synthesis Of MTBE

With the continuous increase in the scale of the ethylene production,the increase in raw materials of catalytic cracking and the expansion of their deep processing,the source of carbon tetra（C4）is gradually becoming abundant.At present,the mature technologies of utilizing C4at home and abroad are focused on both of butadiene and isobutylene.Among them,isobutylene is mainly used for the synthesis of methyl tertiary butyl ether（MTBE）used in gasoline additives（To improve the octane number of gasoline）.Cation exchange resin with macroporous and strong acid is traditionally used as the catalyst for the synthesis of MTBE from isobutylene.The advantages of this type of catalyst are higher catalytic activity and higher selectivity of MTBE,but there are also some disadvantages in catalyst-poor thermal stability-easy falling off of sulfonic acid groups-resulting in the declining in the catalyst activity,corroding the equipment and polluting the product,lower selectivity of the MTBE affected easily by the acidity,and difficult to load and easy to crush.In order to overcome these shortcomings,the hot spots of the researches at home and abroad have focused on the selection of molecular sieve catalysts as the alternatives.Molecular sieve catalysts have the advantages of good thermal stability,high reaction selectivity,long service life,and no pollution to the environment,but the general problem is that the activity of the catalyst is relatively low.Because properties between molecular sieve and cationic resin are different in the surface acidity and acid density distribution as well as the diffusion of the material on the surface,the molecular sieve used as a catalyst for the etherification reaction needs to be improved to increase its catalytic activity and selectivity.The synthesis of MTBE from methanol and isobutene has been carried out in a fixed bed reactor under conditions of constant pressure in gas phase.The influence of the molar ratio methanol to isobutene,the reaction temperature and the weight hourly space velocity（WHSV）on the conversion of isobutene and the selectivity of MTBE are studied.The optimum conditions for the evaluation of the catalyst are as follows:the gasification temperature of methanol of 110℃,the reaction temperature of 70⁸5℃,the WHSV of 0.9¹.1h^-1,and the molar ratio of methanol to isobutene of 4⁵.Under suitable conditions,the catalytic activities and selectivities of cationic resin catalyst for industrial production,HZSM-5 and Hβzeolites with different SiO₂/Al₂O₃ ratio are evaluated,and their microstructure and physicochemical properties of the catalyst are characterized and analyzed.The catalytic activities of HZSM-5 zeolite catalyst with 38 of SiO₂/Al₂O₃ ratio and Hβzeolite catalyst with 25 of SiO₂/Al₂O₃ ratio are the best according to experiments.The catalytic activities of Hβare much higher than that of the HZSM-5,The selectivity of MTBE is up to97%.But the catalytic activities of the zeolites are lower than cationic resin catalystModifications of catalysts are studied in this research.The effects of zeolite catalysts modified by means of acid depositions are not ideal.Among hydrothermal modification of Hβcatalyst treated by hydrothermal at 180℃for 6 hours,Hβcatalyst（SiO₂/Al₂O₃ ratio is 25）is the best in catalytic activities because of its content increasing of weak acid and the strong acid and acid strength increasing,and because of amplifying of the mesoporous pore size of zeolite resulting from dealuminum to improve diffusion of reactant molecules.Under the suitable reaction conditions,the conversion of isobutene was up to 88%,which reached the level of catalytic activity of cationic resin for industrial use.The best Hβzeolite catalyst modified by hydrothermal treatment at 180℃is also evaluated in the pressurized liquid phase reaction device,in which conversion of isobutene and the selectivity of MTBE are slightly higher than those of cationic resin catalysts for industrial application.Undergoing 500h continuous evaluation,the catalyst remained stable in performance and could meet the requirements of industrial production.