SNIA Viscosa

E. Dodgen, "Continuous Nitration of Cellulose SNIA Viscosa Process," in Symposium on Processing Propellants, Explosives and Ingredients, ADPA, Washington, D.C., 1977, p. 4.2-1. 

Erom 1920 to 1931, after the expiration of the viscose patents, world output increased from 14,000 to 225,000 t per year, as more than 100 companies entered the ceUulose fiber field. In Europe, Vereinigte Glanstoff Eabriken (VGE, Germany), Enka (HoUand), I. G. Earben (Germany), Snia Viscosa (Italy), Comptoir des Textiles Artificiels (CTA, Erance), Rhodiaceta (Erance), Tubize (Belgium), and ChatiUon (Italy) were among the new starters. 

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). 

In the United States all other processes have been completely phased out and virtually all benzoic acid is manufactured by the continuous hquid-phase air oxidation of toluene. In the late 1950s and the early 1960s both Dow Chemical and Snia Viscosa constmcted faciUties for Hquid-phase toluene oxidation because of large requirements for benzoic acid in the production of phenol and caprolactam. Benzoic acid, its salts, and esters are very useful and find appHcation in medicinals, food and industrial preservatives, cosmetics, resins, plasticizers, dyestuffs, and fibers. 

Ben2oic acid is almost exclusively manufactured by the cobalt cataly2ed Hquid-phase air oxidation of toluene [108-88-3]. Large-scale plants have been built for ben2oic acid to be used as an intermediate in the production of phenol (by Dow Chemical) and in the production of caprolactam (by Snia Viscosa) (6-11). 

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]. 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

Section A. - Explosives and Propellants 1) B.P.D. (Bombrini-Parodi-Delfino), now SNIA VISCOSA factory in Colleferro, near Rome (Production of TNT, Propellants, Hunting Powder and Missiles)... 

Prof. Gino Dall Asta, SNIA VISCOSA — Centro Studi Chimico, Colleferro (Roma), Italia... 

SNIA Viscosa developed a toluene-based process to produce caprolactam in 1960. The steps in the SNIA process are listed below and shown in Figure... 

In a newer process revision, caprolactam is extracted from the sulfuric acid solution with alkylphenols and then stripped with water. In this way the Snia Viscosa route can be a salt-free process. With a 50% conversion of cyclohexanecarboxylic acid, the selectivity to caprolactam is 90%46. 

Prof. Gino Dall ASTA, SNIA VISCOSA - Centro Studi Chimico, Colleferto (Roma), Italia Prof. Karel DuSek, Institute of Macromolecular Chemistry, Czechoslovak Academy of Sciences, 16206 Prague 616, CSSR... 

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