Nylon toluene oxidation

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. 

Homolytic liquid-phase processes are generally well suited to the synthesis of carboxylic acids, viz. acetic, benzoic or terephthalic acids which are resistant to further oxidation. These processes operate at high temperature (150-250°C) and generally use soluble cobalt or manganese salts as the main catalyst components. High conversions and selectivities are usually obtained with methyl-substituted aromatic hydrocarbons such as toluene and xylenes.95,96 The cobalt-catalyzed oxidation of cyclohexane by air to a cyclohexanol-cyclohexanone mixture is a very important industrial process since these products are intermediates in the manufacture of adipic acid (for nylon 6,6) and caprolactam (nylon 6). However, the conversion is limited to ca. 10% in order to prevent consecutive oxidations, with roughly 70% selectivity.97... 

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. 

Escherichia coli (see Draths and Frost, 1994). Hydroquinone is a very practical intermediate in the manufacture of polymeric materials—almost 2 billion kg of adipic acid are produced from it and used annually in the manufacture of nylon 66. Most commercial syntheses of adipic acid utilize benzene as the starting material, derived from the benzene/toluene/xylene (BTX) fraction of petroleum refining. Benzene is hydrogenated over a metal catalyst to form cyclohexane, which is then oxidized over another catalyst that produces both cyclohexanone and cyclohexanol. See Figure 12.6. These molecules are catalytically oxidized in the presence of nitric acid to form adipic acid. 

Air oxidation of toluene gives predominantly benzoic acid. This is used in perfumery for the preparation of benzoate esters, benzo-phenone and various other compounds, but this use is dwarfed by the other industrial uses of benzoic acid. It is used in many different ways, for instance, as a precursor for nylon monomers. Crude benzoic acid contains a small amount of benzaldehyde, which is easily extracted from it. In view of the huge volume of benzoic acid produced, the volume of benzaldehyde recovered makes a substantial contribution to that used by the perfumery industry. 

Nitrous oxide is produced as a byproduct in multimillion Ib/year quantities in nylon manufacture worldwide. Currently, there is a great interest toward the utilization of NjO due to the environmentally hazardous nature of this gas with respect to the greenhouse effect and ozone layer depletion. In addition to their ability to utilize dioxygen for catalytic hydrocarbon oxidations, ruthenium porphyrins have been shown to activate nitrous oxide which is an extremely inert molecule and a poor ligand. Groves and Roman have found that N O reacted with Ru"(TMP)(THF)2 in toluene to produce Ru (TMP)(0)2 . trans-dioxoRu(VI) complex can in turn epoxidize a suitable substrate such as tra/js-p-methyl styrene. This system was subsequently shown to be catalytic under appropriate conditions . 

Brassylic acid, a 13-caihon saturated dibasic acid, can be derived from the oxidative cleavage of erucic acid and used as a feedstock for the production of nylon (Scheme 1). Brassylic acid is made by ozonolytic cleavage of erucic acid in acetic acid followed by oxidation of the resultant aldehyde by oxygen at elevated temperatures (100°C) to give the diacid. Crystallization from toluene gives a polymer-grade brassylic acid (6). Pilot-scale production of nylon-1313 (7) as well as nylon-613 was found to have exceptionally low sensitivity to moisture, excellent dimensional stability. and dielectric properties. Long-chain nylons of this type have found niche markets in automotive parts. 

Other chemical products, often referred to as connnodity chemicals, are required in large quantities. These are often intermediates in the manufacture of specialty chemicals and industrial and consumer products. These include ethylene, propylene, butadiene, methanol, ethanol, ethylene oxide, ethylene glycol, ammonia, nylon, and caprolactam (for carpets), together with solvents like benzene, toluene, phenol, methyl chloride, and tetrahydrofuran, and fuels like gasoline, kerosene, and diesel fuel. These are manufactured in large-scale processes that produce billions of pounds annually in continuous operation. Since they usually involve small well-defined molecules, the focus of the design is on the process to produce these chemicals from various raw materials. 

Several other companies oxidize toluene to benzoic acid, as above. Except for Dow and Snia Viscosa (nylon-6), outlets are mainly into speciality uses. Benzaldehyde is often recovered as a by-product, while Rhone-Poulenc and others oxidize toluene to give mainly benzaldehyde and benzyl alcohol (phenylmethanol). However, many derivatives, including the major benzyl esters, are produced via the side-chain chlorination of toluene. 

Baling Petrochemical Co is an affiliate of Sinopec. The company s annual outputs of PP and epoxy resins are 131 600 tonnes and 25 000 tonnes, respectively. In addition, it produces piolystyrene, PBT, unsaturated polyester resin, nylon-6 and polyester chip. Other main products include hydrochloric acid, caustic soda, hydrogen, peroxide, sulphur, commercial liquefied chlorine, ammonia, ammonium sulphate, urea, aqueous ammonia, nitrogenous fertilizer, propylene, propylene oxide, butadiene, benzene, toluene, mixed xylene, styrene, bisphenol-A, cyclohexanone,... 

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