Application of molecular sieve catalyst in fine chemical industry

The alkylation reaction of long-chain olefins and benzene produces linear alkyl benzene which is an important raw material for synthetic detergents. The catalysts used are generally toxic and corrosive strong acids, which are difficult to adapt to the increasing environmental protection requirements. Therefore, the study of solid acid alkylation catalysts has attracted people's attention. In the early 1990s, UOP Company of the United States and Petresa Company of Spain jointly developed a new solid acid alkylation catalyst Detal and a new alkylation process. In recent years, my country has also done a lot of research on solid acid alkylation catalysts. The results show that Y-type molecular sieves modified with alkaline earth or rare earth metal ions have good catalytic activity and selectivity, and the reaction temperature can be greatly reduced. The linearity of base benzene is improved, and it is an ideal alkyl benzene catalyst.

     In the study of shape-selective catalysis, people are very interested in the 4,4'-alkylation of biphenyl. Biphenyl and propylene undergo alkylation reaction on HY, HM and HL zeolites. The conversion and selectivity given by HY and HL zeolites are similar to those of amorphous silicon and aluminum, but the oval pore structure of HM can make the selectivity improve. US DOW Chemical Company uses highly dealuminated HM zeolite as a shape-selective catalyst for the liquid-phase alkylation of biphenyl and propylene, achieving a biphenyl conversion rate of 98% and a 4,4'-dialkylbenzene selectivity of 73.5%. Dealumination reduces the acidity of the catalyst and increases the pore volume. As a result, side reactions such as coking and polymerization are reduced.

    2,6-Diisopropylnaphthalene is the raw material for preparing high-performance polyester. It is difficult to synthesize with general alkylation technology because of the numerous substitutions. In the reaction of naphthalene with propylene or isopropanol, the use of acidic zeolite allows 2,6-alkylation to be preferentially formed over other isomers. HM zeolite has the best effect in the selective alkylation of 2,6-diisopropylnaphthalene. Compared with HM and HY zeolite, HZSM-5 zeolite has a lower conversion rate, but it is a more effective shape-selective catalyst.

    The alkylation of phenol can be carried out on the carbon atom of the benzene ring (C-alkylation) or on the oxygen atom (O-alkylation). Since the beta acid site of Pentasil zeolite is higher than that of faujasite, the former is beneficial to the formation of C-alkylate, and the latter is beneficial to the formation of O-alkylate. The catalyst prepared by combining chemical dealumination and hydrothermal treatment on HY molecular sieve has a developed secondary pore structure, and there are more strong acid centers on the surface of the secondary pores, which is beneficial to increase the alkylation of phenol and long-chain olefins. The conversion rate and selectivity of the reaction, the conversion rate reached 87%, and the para-selectivity was greater than 98%. α-Methylbenzylphenol is an antioxidant widely used in the rubber and plastic industries. Using HY zeolite as a catalyst for its synthesis reaction, due to its high activity and good selectivity, many disadvantages of using liquid acid catalysts can be avoided. Heteropolyacid H3PW12O40 (PW) supported on mesoporous molecular sieve MCM-41, used in the alkylation reaction of p-tert-butylphenol with isobutylene and styrene, shows higher catalytic activity than H2SO4 or PW. Compared with PW supported on amorphous silica gel, it shows superior shape-selective catalytic performance