Method for improving reaction stability for synthesizing xylene through toluene and methanol alkylation

Abstract

The invention relates to a method for improving reaction stability for synthesizing xylene through toluene and methanol alkylation. The method is used for realizing preparation of the xylene through the toluene and methanol alkylation via molecular sieve catalysis under the condition that carbon dioxide or water vapor is used as a reaction medium. The method comprises the following steps of: taking mixture of the toluene and the methanol according to a ratio of the toluene to the methanol which is equal to 1.0-4.0 (mol / mol) as a raw material under the condition that carbon dioxide or water vapor is used as the reaction medium; keeping toluene reaction air speed at 0.1-3.5 h<-1> at reaction temperature of 380-540 DEG C; keeping pressure of the reaction medium at 1.0-6.0 MPa; keeping the ratio of the carbon dioxide to hydrocarbon at 0.5-5.0 (mol / mol) or the ratio of the water to the hydrocarbon at 1.0-4.0 (mol / mol); and realizing synthesis of the xylene through the toluene and methanol alkylation via the molecular sieve shape-selective catalyst containing a metal auxiliary agent. According to the method, a large amount of redundant greenhouse gas carbon dioxide is used as the reaction medium, and the problem of poor reaction stability in the conventional toluene and methanol alkylation process is solved while the xylene is prepared at high yield, so that the reaction stability reaches the standard of industrial application.

Description

technical field [0001] The invention relates to a continuous and stable reaction method for synthesizing xylene by improving the alkylation of toluene and methanol. Background technique [0002] at present, As the most important raw material for the synthesis of terephthalic acid and dimethyl terephthalate, xylene has been increasing in demand, and its main industrial production methods are xylene isomerization separation and toluene shape-selective disproportionation , respectively have the problems of low yield of xylene and low utilization rate of raw materials. The synthesis of xylene from toluene and methanol through molecular sieve-catalyzed alkylation has always been considered as a production method that can replace the above two traditional processes, but the problem of poor reaction stability limits its large-scale industrialization. US7060864 (A. K. Ghosh et al.) claimed that the introduction of water during the alkylation reaction of toluene and methanol can ef...

AI Technical Summary

Problems solved by technology

US7453018B2 (J. M. Dakka et al.) reported that Rh and Si co-modified ZSM-5 molecular sieve catalysts were used for the alkylation reaction of toluene and methanol, the selectivity of p-xylene in xylene was greater than 90%, and the conversion rate of toluene was continuously reacted for 300 hours Stable, but the single-pass conversion rate is not high, the yield of p-xylene is low, and a large amount of toluene needs to be recycled, resulting in a large energy consumption of the entire production device

Y. Zhao et al. reported that Pt, P and Si co-modified nanocrystalline ZSM-5 catalyst, which catalyzed the alkylation of toluene methanol for 500 hours in H2 medium, had good stability. The conversion rate of toluene is greater than 20%, and the selectivity of p-xylene in xylene is greater than 98%, but a large amount of hydrogen is consumed, which makes the production and operation cost higher

Recently, CN102701899A (H. Dong et al.) reported a p-xylene production process combining reaction and separation, which achieves energy saving and environmental protection through thermal power integration, rectification and melting crystallization coupling operation, etc. However, the requirements for reaction and separation equipment are high, the investment in production equipment is huge and the cost of maintenance is high, so it is difficult for practical application

Images