Caprolactam from benzoic acid

Benzoic Acid. Ben2oic acid is manufactured from toluene by oxidation in the liquid phase using air and a cobalt catalyst. Typical conditions are 308—790 kPa (30—100 psi) and 130—160°C. The cmde product is purified by distillation, crystallization, or both. Yields are generally >90 mol%, and product purity is generally >99%. Kalama Chemical Company, the largest producer, converts about half of its production to phenol, but most producers consider the most economic process for phenol to be peroxidation of cumene. Other uses of benzoic acid are for the manufacture of benzoyl chloride, of plasticizers such as butyl benzoate, and of sodium benzoate for use in preservatives. In Italy, Snia Viscosa uses benzoic acid as raw material for the production of caprolactam, and subsequendy nylon-6, by the sequence shown below. 

In the Hquid-phase process, both benzaldehyde and benzoic acid are recovered. This process was iatroduced and developed ia the late 1950s by the Dow Chemical Company, as a part of their toluene-to-phenol process, and by Snia Viscosa for their toluene-to-caprolactam process. The benzaldehyde recovered from the Hquid-phase air oxidation of toluene may be purified by either batch or continuous distillation. Liquid-phase air oxidation of toluene is covered more fully (see Benzoic acid). 

Caprolactam. At the same time that Dow was constmcting toluene to phenol plants, Snia Viscosa (28—30) introduced two processes for the manufacture of caprolactam (qv) from benzoic acid. The earlier process produced ammonium sulfate as a by-product, but the latter process did not. In either process benzoic acid is hydrogenated to cyclohexanecarboxyHc acid [98-89-5] which then reacts with nitrosylsulfuric acid to form caprolactam [105-60-2]. 

The first step in producing caprolactam from benzoic acid is its hydrogenation to cyclohexane carboxylic acid at approximately 170°C and 16 atmospheres over a palladium catalyst ... 

Nitrosylsulfuric acid is used in making caprolactam from benzoic acid and in preparing many disperse azo dyes. Other apphcations are bleaching, maturing, dough-conditioning cereal products, and in preparing crystalline diazonium sulfates. 

Caprolactam is also manufactured from toluene (Fig. 2) by oxidation of toluene (with air) to benzoic acid at 160°C and 10 atm pressure. The benzoic acid is then hydrogenated under pressure (16 atm) and 170°C in a series of continuous stirred tank reactors. The cyclohexane carboxylic acid is blended with oleum and fed to a multistage reactor, where it is converted to caprolactam by reaction with nitrosyl sulfuric acid. 

The catalytic effect of e-caprolactam in the production of benzoyl chloride from phosgene and benzoic acid has been explained in terms of the following scheme [1495] ... 

Until 2005, DSM produced about 130 kt/a of phenol, used as a raw material to produce caprolactam from cyclohexanone. Phenol was produced by a copper-catalysed oxidation of benzoic acid. The raw material, benzoic acid, was produced in the same plant by the cobalt-catalysed oxidation of toluene, which also produced significant amounts of benzaldehyde (Fig. 16.19). 

The benzoic acid is now hydrogenated to cyclohexane eaiboxylie acid with a palladium/carbon catalyst at 170°C and 10-19 bar, whereas originally a nickel catalyst was used. Reaction with nitrosyl sulfuric acid in olenm solntion at 80°C then gives e-caprolactam. In the original Snia-Viscosa process, abont 25% more ammonium sulfate was formed than in the conventional proeess. However, solvent extraction of the eaprolactam from the add solntion nsing alkyl phenols does avoid the prodnetion of the ammonium salt. 

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