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[Chemical Knowledge]：Production and manufacturing method and process flow of p-hydroxybenzoic acid

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Para-hydroxybenzoic acid (PHBA) is an important organic chemical raw material, which is widely used in medicine, pesticides, dyes, spices and other fields. The method for producing p-hydroxybenzoic acid will be described in detail below.

1. Phenol method

Phenol method is the main production method of p-hydroxybenzoic acid, the process route is as follows:

1. Phenol reacts with potassium hydroxide to generate potassium phenol salt;
2. Potassium phenol salt reacts with carbon dioxide to generate potassium p-hydroxybenzoate;
3. Potassium p-hydroxybenzoate is obtained by acidification, crystallization, drying and other steps.

The advantages of this method are easy to obtain raw materials, simple operation and high product purity. However, a large amount of waste water and waste gas will be produced in the production process of this method, which will cause certain pollution to the environment.

2. biological method

biological method is the use of microbial fermentation production of hydroxybenzoic acid method. The process route is as follows:

1. using phenol as carbon source and energy source, inoculating the production bacteria of p-hydroxybenzoic acid;
2. by controlling the fermentation conditions, the microbial metabolism produces p-hydroxybenzoic acid;
3. by separation and purification technology, high purity p-hydroxybenzoic acid is obtained. The advantage of

biological method is that the production process is more environmentally friendly and does not produce a large amount of waste water and waste gas. However, the production cycle of this method is long, the production efficiency is low, and the cost is high.

3. other methods

In addition to the above two methods, there are some other methods of producing p-hydroxybenzoic acid, such as:

1. Benzoic acid method: benzoic acid reacts with potassium hydroxide to generate potassium benzoate, and then carbon dioxide is introduced to carry out carboxylation reaction to generate potassium p-hydroxybenzoate, and then p-hydroxybenzoic acid is obtained through acidification, crystallization, drying and other steps.
2. Benzaldehyde method: the reaction of benzaldehyde and potassium hydroxide to generate potassium benzyl alcohol, and then carbon dioxide into the carboxylation reaction to generate potassium p-hydroxybenzaldehyde, and then after reduction, acidification, crystallization, drying and other steps to obtain p-hydroxybenzoic acid.
the advantage of
these methods is that the production cost can be reduced to a certain extent, but the operation process is more complicated, and the product purity may not be as good as the phenol method and the biological method.

In summary, there are many methods for manufacturing p-hydroxybenzoic acid, and the advantages and disadvantages and scope of application of different methods are different. When choosing a production method, it is necessary to consider comprehensively according to the specific situation to ensure the economy, environmental protection and sustainability of the production process.

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