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[Chemical Knowledge]：Manufacturing method and process of salicylic acid

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The manufacturing method
of salicylic acid
salicylic acid, also known as o-hydroxybenzoic acid, is an important organic chemical raw material, widely used in medicine, pesticides, dyes, spices and other fields. There are two main methods for the production of salicylic acid, one is obtained by the reaction of phenol with sodium hydroxide, and the other is obtained by the nitration and hydrolysis of m-xylene. This article will detail these two manufacturing methods.

1. of sodium phenolate method

of sodium phenolate method is the main method for the production of salicylic acid, the process is as follows:

1. phenol mixed with sodium hydroxide solution, heated to a molten state, generating sodium phenolate.
2. Hydrochlorination of sodium phenolate to generate salicylic acid and sodium chloride.
3. Through crystallization, centrifugation, drying and other steps, high purity salicylic acid products were obtained.

The advantages of this method are easy to obtain raw materials, simple operation and good product quality. However, it should be noted that the temperature and pH value should be strictly controlled during the operation to avoid the formation of by-products and the decomposition of the product.

2. m-xylene nitration method

m-xylene nitration method is a more traditional method of producing salicylic acid, the process is as follows:

1. m-xylene and mixed acid (mixture of nitric acid and sulfuric acid) at low temperature nitration reaction, generating m-nitrotoluene.
2. m-nitrotoluene is hydrolyzed with sodium hydroxide solution to generate salicylic acid and sodium nitrate.
3. Through crystallization, centrifugation, drying and other steps, salicylic acid products are obtained.

The advantage of this method is that cheap m-xylene can be used as raw material, but the temperature and acidity need to be strictly controlled during the operation to ensure the purity and yield of the product. In addition, the wastewater produced by this method contains more sodium nitrate and needs to be treated to meet environmental requirements.

No matter which method is used to produce salicylic acid, it is necessary to strictly abide by safety production regulations to ensure product quality and the safety of the production process. At the same time, in order to improve the economic and environmental benefits of enterprises, it is also necessary to continuously optimize the production process, improve the utilization rate of raw materials and product yields, and reduce wastewater discharge.

In general, the manufacturing methods of salicylic acid mainly include sodium phenolate and m-xylene nitration. These two methods have their own advantages and disadvantages, and enterprises can choose the appropriate production method according to their own actual situation and needs. At the same time, with the continuous progress and application of science and technology, the production process of salicylic acid will continue to improve and perfect, and make greater contributions to the development of chemical production.

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