Modified ZSM-5 catalyst for alkylation reactions, preparation method and applications thereof, and p-xylene preparation method

Abstract

The invention discloses a modified ZSM-5 catalyst for alkylation reactions, a preparation method and applications thereof, and a p-xylene preparation method. The modified ZSM-5 catalyst comprises a ZSM-5 molecular sieve core and an all-silicon molecular sieve shell formed on the outer surface of the core, wherein the pore channels of the shell are communicated to the pore channels of the core so as not to cover the pore channels of the ZSM-5 molecular sieve core by the all-silicon molecular sieve shell, the all-silicon molecular sieve shell has shape-selective effects on alkylation reactions and does not have reaction activity, a molar ratio of Si to Al in the ZSM-5 molecular sieve core is 100-500:1, and the all-silicon molecular sieve shell is formed by reducing the concentrations of a silicon source and a template agent through epitaxial growth. According to the present invention, the catalyst can operate at a high toluene concentration and high space velocity to obtain the high yield of p-xylene, and is suitable for large-scale production and industrial scale application.

Description

technical field [0001] The invention relates to the field of alkylation catalysts, in particular to a modified ZSM-5 catalyst used in an alkylation reaction, a preparation method and application thereof, and a preparation method of p-xylene. Background technique [0002] P-xylene (p-xylene, PX) is an important chemical raw material commonly used in industry, and most of p-xylene is used to produce terephthalic acid, which is then used to produce chemical products such as polyester fiber. The demand for p-xylene has been growing rapidly in recent years. In 2015, the domestic demand for PX was 24 million tons, while the national production capacity was only about 11 million tons. In recent years, the import volume has exceeded 50%. Although new PX projects have been put into production all over the country in recent years, the annual gap is still more than 5 million tons. [0003] At present, there are three production processes of p-xylene worldwide, disproportionation of to...

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Problems solved by technology

However, most of these modification methods adopt coverage or poisoning because they cover a large number of molecular sieve channels and active centers, which will greatly reduce the activity of molecular sieves while improving product selectivity.

[0006] The literature "Advanced Materials 2005,17,1985-1988" and the literature "Journal of Catalysis 2006,243,389-394" and CN102671694A all mentioned a kind of use Silicate-1 molecular sieve to ZSM-5 catalyst powder to carry out surface coverage modification to improve the The xylene selectivity method, although this method can effectively improve the p-xylene selectivity, but according to the SEM photos provided in the above literature, it can be judged that this surface coverage is not all-round, and the newly formed on the outer surface of the ZSM-5 crystal Silicate-1 with smaller grains will grow along the original orientation of the parent ZSM-5

However, there are dozens to hundreds of nanometers of ZSM-5 gaps exposed between different Silicate-1 small grains, which is enough to make the generated PX contact with it and undergo isomerization reaction, thereby reducing the selectivity of p-xylene; and, When Silicate-1 grows along the original orientation of these parent ZSM-5, it will block the original pores of ZSM-5, resulting in the covering of a large number of molecular sieve pores and active centers, resulting in low product selectivity

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