Paracetamol Production from Nitrobenzene

The process under analysis comprises four major sections: (1) Nitrobenzene reduction; (2) PAP separation and purification; (3) PAP acetylation; and (4) Paracetamol purification

Nitrobenzene reduction. The nitrobenzene (NB) is reacted with hydrogen in the presence of sulfuric acid and a platinum on activated carbon catalyst to produce p-aminophenol (PAP). Besides PAP, o-aminophenol, aniline and 4,4'-diaminodiphenyl ether are also generated as by-products. The reaction is stopped before depletion of NB so two phases are present at the end. An organic phase, comprised of unreacted NB and the catalyst, which is recycled back to the reactor, and an aqueous phase containing PAP and by-products.

PAP separation and purification. The aqueous phase is fed to the middle of an extraction column. An aniline-toluene mixture is used to extract the 4,4'-diaminodiphenyl ether. An aqueous sulfuric acid solution is fed at the top of the column to recover PAP extracted. Toluene is fed to the bottom of the column to extract the aniline from the aqueous PAP solution. Aniline is recovered from the top organic stream to be sold as by-product. The bottom aqueous stream is fed to a crystallizer, to purify the PAP, which is then centrifuged and dried.

PAP acetylation. The PAP is dissolved in an acetic acid solution and fed to a reactor along with acetic anhydride. An acetylation reaction is carried out by heating the mixture of PAP with acetic anhydride, yielding crude Paracetamol.

Paracetamol purification. The crude Paracetamol is treated with decolorizing charcoal. The product is further purified by crystallization/centrifugation steps, and subsequently dried, ground under a dry air atmosphere, packed and stored. The liquor separated during centrifugation is sent to extraction step to recover acetic acid, as by-product.