Method for eliminating acidity of external surface of ZSM-5 molecular sieve catalyst

Abstract

The invention provides a method for eliminating acidity of an external surface of a ZSM-5 molecular sieve catalyst. The method comprises the following steps that 3,5-dimethylbromobenzene, a magnesium rod, iodine and tetrahydrofuran as raw materials undergo a reaction without water and oxygen to produce a 3,5-dimethylphenylmagnesium bromide Grignard reagent; the 3,5-dimethylphenylmagnesium bromide Grignard reagent is added with a molecular sieve n-hexane turbid liquid in a nitrogen atmosphere; the mixed solution is subjected to reflux at a temperature of 80 DEG C for 4 hours and then is dried by evaporation; and a sample obtained by the previous step is calcinated at a temperature in air to form a MgO-modified ZSM-5 molecular sieve catalyst. The MgO-modified ZSM-5 molecular sieve catalyst obtained by the method can be used for reactions such as a toluene disproportionation reaction, an ethylbenzene disproportionation reaction, a toluene carbonylation reaction and an ethylbenzene carbonylation reaction, wherein the reactions can selectively produce a certain product because of shape selectivity. The method has simple processes, a low cost and a wide application prospect.

Description

technical field [0001] The invention relates to a method for removing acidity on the outer surface of a molecular sieve catalyst. Specifically, it relates to a method for preparing a catalyst for preparing p-diethylbenzene. Background technique [0002] ZSM-5 molecular sieve is an acidic catalyst with a specific pore structure. It has been widely valued due to its excellent shape-selective catalytic performance. Its shape-selective ability is closely related to the diffusion performance of reactant and product molecules in the molecular sieve channels. The diffusion properties of reactants and products mainly depend on the pore size and channel depth of molecular sieves. For example, for the disproportionation of ethylbenzene, macromolecular products such as o-diethylbenzene and m-diethylbenzene have a slow diffusion rate due to the limitation of molecular sieve channels, while p-diethylbenzene with less steric hindrance is easier to diffuse out. The acidic sites on the ou...

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Problems solved by technology

MgO and other basic oxides are also often used alone for the modification of molecular sieves, but because the modified reagents used (such as magnesium nitrate in Chinese patent 90101436, magnesium acetate in Chinese patent 95118372, etc.) are usually molecular size Smaller, while MgO changes the acidity of the outer surface, it also tends to change the acidity of the inner surface, thereby affecting the activity of the catalyst

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