In industry, toluene, o-xylene or naphthalene are commonly used as raw materials to prepare benzoic acid. The above raw materials can be obtained from coal tar or petroleum. In addition, benzoic acid can be co-produced when producing benzaldehyde from toluene [3]. .Industrial production methods of benzoic acid include toluene chlorination, phthalic acid desorption, carboxylation of toluene liquid-phase air oxidation, hypobenzyl trichlorohydrolysis and phthalic anhydride decarboxylation. The final product obtained by the decarboxylation of phthalic anhydride is not easy to be refined, and the production cost is high. It is only used in the manufacturing process of medicines and other products in small batches. Toluene chlorination products are not suitable for use in food. Benzoic acid has different specifications for industrial use, food use, and pharmaceutical use. The food grade should comply with GB1901-80, the content is above 99.5%, the melting point is 121-123°C, and the quality indicators such as easy oxides, easy carbides, chlorine-containing compounds, burning residue, heavy metals, arsenic content, etc. are stipulated.

The industrial production method commonly used at home and abroad is liquid-phase catalytic air oxidation method using toluene as raw material. Toluene and air with dissolved catalyst (cobalt naphthalate, cobalt naphthenate or cobalt acetate) are continuously pumped into the oxidation tower (or kettle), and then oxidized to benzoic acid under 140-165°C and 0.3-0.4MPa pressure The crude benzoic acid is obtained by distilling off unreacted toluene, and then distilled under reduced pressure to recrystallize to obtain the finished product.

The tail gas at the top of the tower is recovered by condensation and activated carbon adsorption and then vented; the reaction liquid of the tower kettle is often pre-pressed to recover unreacted toluene, benzyl alcohol and benzaldehyde and other light components, and then distilled under reduced pressure to obtain benzoic acid; Toluene is returned to the oxidation tower, and the single-pass conversion rate of toluene can be controlled above 35%. Domestic consumption of benzoic acid per ton is 1025-1500kg of toluene and cobalt naphthenate is about 4kg; toluene consumption abroad is 820kg per ton.