Caprolactam From phenol

Processes for producing caprolactam from phenol and cyclohexane... 

Some other phenol derivatives are somewhat local in appHcation. Eor example, aniline is produced from phenol at only two plants, one in Japan and one in the United States. Likewise, phenol is used in the production of nylon, via caprolactam (qv) or adipic acid (qv) by only one United States producer and one European producer. These markets, like the phenoHc resin and polycarbonate markets, are quite cycHcal. Thus, the entire phenol market tends to be cycHcal and closely tied to the housing and automotive markets. 

AH commercial processes for the manufacture of caprolactam ate based on either toluene or benzene, each of which occurs in refinery BTX-extract streams (see BTX processing). Alkylation of benzene with propylene yields cumene (qv), which is a source of phenol and acetone ca 10% of U.S. phenol is converted to caprolactam. Purified benzene can be hydrogenated over platinum catalyst to cyclohexane nearly aH of the latter is used in the manufacture of nylon-6 and nylon-6,6 chemical intermediates. A block diagram of the five main process routes to caprolactam from basic taw materials, eg, hydrogen (which is usuaHy prepared from natural gas) and sulfur, is given in Eigute 2. 

About half of the nylon made in the world is made from the polymerization of caprolactam. Although the cyclohexanone needed to make caprolactam can be made from cyclohexane as shown above, most of it is made from phenol. 

About Half the caprolactam is made from phenol. (The other half comes from cyclohexane.) Caprolactam is an intermediate step in making Nylon 6. 

Table 11.2 outlines the uses of phenol. We will consider the details of phenol uses in later chapters. Phenol-formaldehyde polymers (phenolics) have a primary use as the adhesive in plywood formulations. We have already studied the synthesis of bisphenol A from phenol and acetone. Phenol s use in detergent synthesis to make alkylphenols will be discussed later. Caprolactam and aniline are mentioned in the following sections in this chapter. 

The common name caprolactam comes from the original name for the Ce carboxylic acid, caproic acid. Caprolactam is the cyclic amide (lactam) of 6-aminocaproic acid. Its manufacture is from cyclohexanone, made usually from cyclohexane (58%), but also available from phenol (42%). Some of the cyclohexanol in cyclohexanone/cyclohexanol mixtures can be converted to cyclohexanone by a ZnO catalyst at 400°C. Then the cyclohexanone is converted into the oxime with hydroxylamine. The oxime undergoes a very famous acid-catalyzed reaction called the Beckmann rearrangement to give caprolactam. Sulfuric acid at 100-120°C is common but phosphoric acid is also used, since after treatment with ammonia the by-product becomes... 

Pyrrolidone is a lactone used for the production of nylon-4. This reactant may be produced by the reduction ammoniation of maleic anhydride. s-Caprolactam, used in the production of nylon-6, may be produced by the Beckman rearrangement of cyclohexanone oxime (structure 17.11). The oxime may be produced by the catalytic hydrogenation of nitrobenzene, the photolytic nitrosylation of cyclohexane (structure 17.9), or the reaction of cyclohexanone and hydroxylamine (structure 17.10). Nearly one-half of the production of caprolactam is derived from phenol. 

In addition to the construction industry, phenol has many other applications. It is used in pharmaceuticals, in herbicides and pesticides, and as a germicide in paints. It can be used to produce caprolactam, which is the monomer used in the production of nylon 6. Another important industrial compound produced from phenol is bisphenol A, which is made from phenol and acetone. Bisphenol A is used in the manufacture of polycarbonate resins. Polycarbonate resins are manufactured into structural parts used in the manufacture of various products such as automobile parts, electrical products, and consumer appliances. Items such as compact discs, reading glasses, sunglasses, and water bottles are made from polycarbonates. 

Caprolactam can be made by the Beckmann rearrangement of the oxime f of cyclohexanone. (Check that you can draw the mechanisms, of both these reactions and look at Chapters 14 and 37 if you find you can t.) Cyclohexanone used to be made by the oxidation of cyclohexane with molecular oxygen until the explosion at Fiixborough in Lincolnshire on 1 June 1974 that killed 28 people. Now cyclohexanone is made from phenol. 

Polycaproamide via caprolactam, which is derived from phenol or benzene (Nylon 6). 

The most common starting materials for preparations of caprolactam are phenol, cyclohexane, and toluene. Some caprolactam is also made from aniline. In these synthetic processes, the key material is cyclohexanone oxime. The route based on phenol can be shown as follows ... 

Cyclohexanol and cyclohexanone are produced from phenol as intermediates for synthetic fibers (Nylon 66, Nylon 6) obtained via adipic acid and caprolactam respectively. 

Frentzen Y. H., ThijertM. P. andZwart R. L. (1997), ProcessfortheRecovery of Caprolactam from Waste Containing Nylon by Extraction with Alkyl Phenol , World Patent 9703 04. 

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). 

Usually, the cyclohexanone intermediate is made from the oxidation of cyclohexane. However, cyclohexanone is also made from phenol (Honeywell) or toluene (BASF, DSM). With the new processes, ammonia is oxidized to nitrous oxide (NjO), which is hydrogenated in the presence of sulfuric acid into hydroxylamine sulfate, which in turn is reacted with cyclohexanone to form cyclohexanone oxime. This chemical product is subjected to a Beckmann rearrangement with oleum to produce caprolactam. 

Ammonia is used in the fibers and plastic industry as the source of nitrogen for the production of caprolactam, the monomer for nylon 6. Oxidation of propylene with ammonia gives acrylonitrile (qv), used for the manufacture of acryHc fibers, resins, and elastomers. Hexamethylenetetramine (HMTA), produced from ammonia and formaldehyde, is used in the manufacture of phenoHc thermosetting resins (see Phenolic resins). Toluene 2,4-cHisocyanate (TDI), employed in the production of polyurethane foam, indirectly consumes ammonia because nitric acid is a raw material in the TDI manufacturing process (see Amines Isocyanates). Urea, which is produced from ammonia, is used in the manufacture of urea—formaldehyde synthetic resins (see Amino resins). Melamine is produced by polymerization of dicyanodiamine and high pressure, high temperature pyrolysis of urea, both in the presence of ammonia (see Cyanamides). 

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]. 

Caprolactam [105-60-2] (2-oxohexamethyleiiiiriiQe, liexaliydro-2J -a2epin-2-one) is one of the most widely used chemical intermediates. However, almost all of the aimual production of 3.0 x 10 t is consumed as the monomer for nylon-6 fibers and plastics (see Fibers survey Polyamides, plastics). Cyclohexanone, which is the most common organic precursor of caprolactam, is made from benzene by either phenol hydrogenation or cyclohexane oxidation (see Cyclohexanoland cyclohexanone). Reaction with ammonia-derived hydroxjlamine forms cyclohexanone oxime, which undergoes molecular rearrangement to the seven-membered ring S-caprolactam. 

Until the mid-1950s the main raw material source for the European plastics industry was coal. On destructive distillation coal yields four products coal tar, coke, coal gas and ammonia. Coal tar was an important source of aromatic chemicals such as benzene, toluene, phenol, naphthalene and related products. From these materials other chemicals such as adipic acid, hexamethylenedia-mine, caprolactam and phthalic anhydride could be produced, leading to such important plastics as the phenolic resins, polystyrene and the nylons. 

The major aromatics (organics having at least one ring structure with six carbon atoms) manufactured include benzene, toluene, xylene, and naphthalene. Other aromatics manufactured include phenol, chlorobenzene, styrene, phthalic and maleic anhydride, nitrobenzene, and aniline. Benzene is generally recovered from cracker streams at petrochemical plants and is used for the manufacture of phenol, styrene, aniline, nitrobenzene, sulfonated detergents, pesticides such as hexachlorobenzene, cyclohexane (an important intermediate in synthetic fiber manufacture), and caprolactam, used in the manufacture of nylon. Benzene is also used as a general purpose solvent. 

There are nine chemicals in the top 50 that are manufactured from benzene. These are listed in Table 11.1. Two of these, ethylbenzene and styrene, have already been discussed in Chapter 9, Sections 5 and 6, since they are also derivatives of ethylene. Three others—cumene, acetone, and bisphenol A— were covered in Chapter 10, Sections 3-5, when propylene derivatives were studied. Although the three carbons of acetone do not formally come from benzene, its primary manufacturing method is from cumene, which is made by reaction of benzene and propylene. These compounds need not be discussed further at this point. That leaves phenol, cyclohexane, adipic acid, and nitrobenzene. Figure 11.1 summarizes the synthesis of important chemicals made from benzene. Caprolactam is the monomer for nylon 6 and is included because of it importance. 

Copolymers. Copolymers from mixtures of different bisphenols or from mixtures of dichlorosulfone and dichlorobenzophenone have been reported in the patent literature. Bifunctional hydroxyl-terminated polyethersulfone oligomers are prepared readily by the polyetherification reaction simply by providing a suitable excess of the bisphenol. Block copolymers are obtained by reaction of the oligomers with other polymers having end groups capable of reacting with the phenol. Multiblock copolymers of BPA-polysulfone with polysiloxane have been made in this way by reaction with dimethyl amino-terminated polydimethylsiloxane the products are effective impact modifiers for the polyethersulfone (79). Block copolymers with nylon-6 are obtained when chlorine-terminated oligomers, which are prepared by polyetherification with excess dihalosulfone, are used as initiators for polymerization of caprolactam (80). 

N20 emission at chemical plants and the methods of its abatement have been considered in several reviews [185-187]. The major emission is related to the preparation of nitric add and its use in oxidation processes, like those involved in the production of adipic acid, caprolactam, glyoxal, acrylonitrile, and so forth. Of them, the biggest emission is the offgases of adipic acid about 1 M MT N 20 per year with a concentration of 30-40%. Recovery and purification of N20 from these offgases for use in the oxidation of benzene to phenol are described by Uriarte [188], Some companies use these off-gases to obtain medical-grade nitrous oxide. 

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