Manufacturing process nylon

Enzymatic hydrolysis is also used for the preparation of L-amino acids. Racemic D- and L-amino acids and their acyl-derivatives obtained chemically can be resolved enzymatically to yield their natural L-forms. Aminoacylases such as that from Pispergillus OTj e specifically hydrolyze L-enantiomers of acyl-DL-amino acids. The resulting L-amino acid can be separated readily from the unchanged acyl-D form which is racemized and subjected to further hydrolysis. Several L-amino acids, eg, methionine [63-68-3], phenylalanine [63-91-2], tryptophan [73-22-3], and valine [72-18-4] have been manufactured by this process in Japan and production costs have been reduced by 40% through the appHcation of immobilized cell technology (75). Cyclohexane chloride, which is a by-product in nylon manufacture, is chemically converted to DL-amino-S-caprolactam [105-60-2] (23) which is resolved and/or racemized to (24)... 

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). 

Hydrocarbon Oxidation. The oxidation of hydrocarbons (qv) and hydrocarbon derivatives can be significantly altered by boron compounds. Several large-scale commercial processes, such as the oxidation of cyclohexane to a cyclohexanol—cyclohexanone mixture in nylon manufacture, are based on boron compounds (see Cylcohexanoland cyclohexanone Eibers, polyamide). A number of patents have been issued on the use of borate esters and boroxines in hydrocarbon oxidation reactions, but commercial processes apparently use boric acid as the preferred boron source. The Hterature in this field has been covered through 1967 (47). Since that time the Hterature consists of foreign patents, but no significant appHcations have been reported for borate esters. 

The most important use of cyclohexanone is as a chemical intermediate in nylon manufacture 97% of all cyclohexanone output is used either to make caprolactam for nylon-6, or adipic acid for nylon-6,6. In the caprolactam process cyclohexanone is converted to cyclohexanone oxime (mp,... 

Some of the common types of plastics that ate used ate thermoplastics, such as poly(phenylene sulfide) (PPS) (see Polymers containing sulfur), nylons, Hquid crystal polymer (LCP), the polyesters (qv) such as polyesters that ate 30% glass-fiber reinforced, and poly(ethylene terephthalate) (PET), and polyetherimide (PEI) and thermosets such as diaHyl phthalate and phenoHc resins (qv). Because of the wide variety of manufacturing processes and usage requirements, these materials ate available in several variations which have a range of physical properties. 

Most of the benzene used in chemical applications ends up in the manufacturing processes for styrene (covered in Chapter 8), cumene (covered in Chapter 7), and cyclohexane (covered in Chapter 4), Polymers and all sorts of plastics are produced from styrene. Cumene is the precursor to phenol, which ultimately ends up in resins and adhesives, mostly for gluing plywood together. The production of styrene and phenol account for. about 70% of the benzene produced. Cyclohexane, used to make Nylon 6 and Nylon 66, is the next biggest application of benzene. 

Dyeing Mechanism. Nylon i.s. similar in its general chemical structure to the natural fiber wool, and therefore all the previously described processes lor wool are applicable to dyeing nylon with acid, metallized, and other dyes. There are. however, significant differences. Nylon is synthetic, it has delined chemical structure depending on the manufacturing process, and it is hydrophobic. 

In one process for nylon manufacture, the feedstock is nitration-grade toluene, air, hydrogen, anhydrous ammonia (NH3), and sulfuric acid (H2S04). The toluene is oxidized to yield a 30% solution of benzoic acid, plus intermediates and by-products. Pure benzoic acid, after fractionation, is hydrogenated with a palladium catalyst in stirred reactors operated at about 170°C under a pressure of 147 psi (1013 kPa). The product, cyclohexanecarboxylic acid, is mixed with sulfuric acid and then reacted with nitrosylsulfuric acid to yield caprolactam. 

Other materials in waste that is thermally processed also were studied by pyrolytic techniques, typically with the purpose of regenerating the monomers or of obtaining other useful small molecules. For example, pyrolytic studies were performed for the evaluation of the possibilities for re-utilization of nylon carpet waste [7], the recycling of thermoset polymeric composites [8], the recovery of methyl methacrylate from poly(methyl methacrylate) waste [9], as well as for other raw material recovery from pyrolysis of plastic waste [10]. The results of incineration of various other types of waste also were studied at model scale [11, 12). These studies were applied to specific waste materials associated with the manufacturing process or to municipal solid waste [13-15)... 

Solution Dyed Nylon (now a product of Invista, which DuPont sold to Koch Industries in 2004). Historically, DuPont s nylon customers purchased raw product and dyed it themselves. More recently, DuPont has offered these customers nylon that is dyed to their specifications in the manufacturing process. This has a number of benefits to the customer including the steadfastness and consistency of the colors. For the environment, this process means more of the overall dying process happens in a centralized location with high environmental controls. From the DuPont business perspective, this adds more value to their customers and raises the cost of switching to another material supplier. 

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