p-Aminobenzoic acid is a dye and pharmaceutical intermediate. It is used in the production of reactive red M-80, M-10B, reactive red purple X-2P, cyanobenzoic acid, p-carboxybenzylamine, various esters and sunscreen.
Firstly, 400 kg glacial acetic acid, 350 kg p-nitrotoluene and 1.5 kg cobalt bromide were added to the autoclave. When the temperature was raised to 120 oC, the air was ventilated to keep the pressure below 600 kpa and the temperature at 135~165 oC. After 5 hours of reaction, it was cooled and filtered, then washed to neutral with acetic acid and hot water, and about 250 kg of p-nitrobenzoic acid was obtained after drying. The autoclave of the reaction device is lined with titanium and the vent pipe is made of titanium.
Water, sodium chloride and hydrochloric acid are added in turn in the reactor. Start stirring and heat up to 50~65 oC. Add iron powder, continue to heat up to 100 oC, heat preservation for 1 h. Stop heating, slowly add p-nitrobenzoic acid under 95 oC, add iron powder after adding, and keep it under 100 oC for 1h. After the end of the reaction, cool to 80 oC, adjust the pH value to 8.5-9 with 30% liquid alkali, filter under pressure, and wash with a small amount of water. The filtrate lotion is merged, put into the acid precipitation kettle, cooled to 30~35 oC, decolorized by adding insurance powder, and filtered. The pH value of the filtrate was adjusted to 3.5~4 by adding acid, and then cooled below 10 oC. The finished product was obtained by throwing water and drying.
Fig. 1 Process flow chart of p-nitrobenzoic acid
pressure reactor; B-washing filter; C-waste acid tank; D-waste water tank
Fig. 2 Process flow chart of p-aminobenzoic acid
reduction kettle; B-acid precipitation kettle; C-condenser; D, E-filter
