Method for preparing dichloroaniline by continuously catalyzing and hydrogenating dichloronitrobenzene

Abstract

The invention discloses a method for preparing dichloroaniline by continuously catalyzing and hydrogenating dichloronitrobenzene. The method comprises the following steps: I, filling a fixed bed reactor with catalyst, and introducing reduction gas into the fixed bed reactor to reduce the catalyst; II, lowering the temperature of the fixed bed reactor to a reaction temperature, pumping an ammonia-ammonium chloride buffer solution, introducing the molten dichloronitrobenzene, and carrying out the catalytic hydrogenation reaction under the condition of the reaction temperature; and III, separating the material after the catalytic hydrogenation reaction by virtue of an oil-water separator to obtain an organic phase and a water phase, wherein the organic phase is the dichloroaniline. The conversion rate of the raw material dichloronitrobenzene is more than or equal to 99.5 percent, the mass concentration of a dechlorination byproduct is less than 0.2 percent, the mass purity of the dichloroaniline is more than or equal to 99.2 percent, the stability of the catalyst is stable, the catalytic hydrogenation reaction efficiency is high, and the process flow is capable of saving the resource and is environmentally friendly.

Description

Technical field [0001] The invention belongs to the technical field of catalytic hydrogenation, and specifically relates to a method for preparing dichloroaniline by continuous catalytic hydrogenation of dichloronitrobenzene. Background technique [0002] Dichloroaniline compounds are important intermediates used in medicines, dyes, pesticides and liquid crystal materials, with a wide range of uses. The traditional process adopts iron powder method or alkali sulfide method to reduce dichloronitrobenzene to dichloroaniline. These two methods cause great harm to the environment, so they have been gradually replaced by catalytic hydrogenation process. At present, large-scale industrial The use of a clean catalytic hydrogenation process requires the use of a precious metal catalyst with better performance. Due to the high activity of the precious metal catalyst, a certain degree of dechlorination side reactions will occur. Many companies are concerned about how to prevent dechlorinat...

AI Technical Summary

Problems solved by technology

The traditional process uses iron powder method or alkali sulfide method to reduce dichloronitrobenzene to dichloroaniline. These two methods cause great harm to the environment, so they have been gradually replaced by catalytic hydrogenation technology. At present, large-scale industrial The use of a clean catalytic hydrogenation process requires the use of noble metal catalysts with better performance. Due to the high activity of noble metal catalysts, a certain degree of dechlorination side reactions often occur. Many companies have questions about how to prevent dechlorination side reactions. A lot of research has been done, and it is found that adding a certain amount of dechlorination inhibitors to the reaction system can inhibit the occurrence of dechlorination side reactions to a certain extent, but the addition of dechlorination inhibitors not only increases the difficulty of subsequent product purification but also Increased the cost of the catalytic reaction

[0003] Chinese patent 200510015186.9 discloses the hydrogenation of chloronitrobenzene to synthesize chloroaniline-supported nickel catalyst and its preparation method. The tank reaction process is adopted. Under the optimal conditions, the conversion rate of chloronitrobenzene is greater than 99%, and the product selectivity is greater than 99%. %; Chinese patent 200710040456.0 describes a catalyst for the hydrogenation of dichloronitrobenzene to prepare dichloroaniline and a preparation method thereof. What is used is a noble metal Pd catalyst supported by activated carbon, and the Pd loading is 0.2% to 2%. Still catalytic hydrogenation process, systematically investigated the influence of precious metal loading, reaction temperature and reaction pressure on the catalytic reaction results, and achieved good results; Chinese patent 200610049942.4 discloses the preparation of 3,4-dichloronitrobenzene by hydrogenation The preparation method of the catalyst of 3,4-dichloroaniline also adopts the noble metal Pd catalyst supported by activated carbon. After careful research on the preparation method of the catalyst, it is found that the size of the Pd particles on the surface of the catalyst has a great influence on the The reaction of hydrogenation of chloronitrobenzene to prepare 3,4-dichloroaniline has a great influence. When the Pd particle size is around 25nm, the activity of the catalyst is optimal, the conversion rate of the catalytic reaction is high, and the selectivity is good; Chinese patent 201010132079.5 describes A preparation method for synthesizing 2,4-dichloroaniline with 2,4-dichloronitrobenzene, the method adopts autoclave reaction, the reaction temperature is low, but the reaction pressure is as high as 3MPa-30MPa, and the reaction time is 6h-16h , the mass purity of the product 2,4-dichloroaniline after the reaction is greater than 99%, and the solvent is added in the reaction, which may increase the difficulty of subsequent separation and purification

[0004] At present, the batch autoclave process is commonly used in industry. The catalysts are mainly noble metal carbon-supported catalysts, noble metal alumina or noble metal molecular sieve catalysts. Various dechlorination inhibitors are added during the reaction to prevent side reactions. More than 0.8MPa, increasing the pressure can speed up the catalytic reaction rate, and it is also conducive to the occurrence of dechlorination side reactions. If the pressure is too low, the reaction time will be too long. With the extension of the reaction time, dechlorination side reactions are also difficult to avoid , in addition, the batch reaction also has the problem of low production efficiency

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