Nylon cyclohexane oxidation

Benzene is hydrogenated to cyclohexane. Cyclohexane is then oxidized to cyclohexanol, cyclohexanone, or adipic acid (qv). Adipic acid is used to produce nylon. Cyclohexane manufacture was responsible for about 14% of benzene consumption in 1988. 

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. 

Adipic acid is an important intermediate extensively used for the manufacture of nylon 66. It is currently produced from cyclohexane oxidation by a two steps process [1]. During the first step, oxidation of cyclohexane by air in the liquid phase forms cyclohexanol and cyclohexanone. Further oxidation of this mixture by nitric acid gives adipic acid. In addition to its cost, the use of nitric acid generates corrosion risks and requires recovery of the nitrogen oxides effluents. 

Nylon intermediates by cyclohexane oxidation , British Chem. Engng, Process SuppL (Nov. 1967). 

Within the scope of its program aimed at process improvements, the Corporate Department for Research and Patents of DSM is now seeking ways of optimizing the cyclohexane oxidation route towards cyclohexanone (anone) and cyclohexanol (anol). These products are Intermediates in the preparation of caprolactam. Caprolactam is polymerised to nylon-6. As DSM has a great interest in the world production of caprolactam, much effort is put into research and optimization of the various process steps. 

Adipic acid is a commodity used primarily in the synthesis of nylon-6,6. Annual global production of adipic acid is approximately 2 x 10 kg. o Although a number of new, creative routes have been elaborated for synthesis of adipic acid, most adipic acid manufacture (Figure 12.6) begins with hydrogenation of benzene to cyclohexane. Oxidation of cyclohexane affords a mixture of cyclohexanol and cyclohexanone. This mixture is then further oxidized to afford adipic acid. The nitrous oxide (N2O),... 

Gold catalysts can be used in a solventless liquid-phase system to oxidize cyclohexane to cyclo-hexanol and cyclohexanone using oxygen. Almost all the cyclohexane produced (4.4 million tonnes per annum, and expected to grow at ca. 3%) is converted to cyclohexanol and cyclohexanone, the intermediates in the production of caprolactam and adipic acid, used in the manufacture of nylon-6 and nylon-66 polymers, respectively. The present commercial process for cyclohexane oxidation is carried out at around 423 K and 1-2 MPa over a catalyst such as cobalt naphthenate with approximately 4% conversion and 70-85% selectivity to cyclohexanol and cyclohexanone [66,67,93]. 

Since adipic acid has been produced in commercial quantities for almost 50 years, it is not surprising that many variations and improvements have been made to the basic cyclohexane process. In general, however, the commercially important processes stiU employ two major reaction stages. The first reaction stage is the production of the intermediates cyclohexanone [108-94-1] and cyclohexanol [108-93-0], usuaHy abbreviated as KA, KA oil, ol-one, or anone-anol. The KA (ketone, alcohol), after separation from unreacted cyclohexane (which is recycled) and reaction by-products, is then converted to adipic acid by oxidation with nitric acid. An important alternative to this use of KA is its use as an intermediate in the manufacture of caprolactam, the monomer for production of nylon-6 [25038-54-4]. The latter use of KA predominates by a substantial margin on a worldwide basis, but not in the United States. 

Cyclohexane. The LPO of cyclohexane [110-82-7] suppUes much of the raw materials needed for nylon-6 and nylon-6,6 production. Cyclohexanol (A) and cyclohexanone (K) maybe produced selectively by using alow conversion process with multiple stages (228—232). The reasons for low conversion and multiple stages (an approach to plug-flow operation) are apparent from Eigure 2. Several catalysts have been reported. The selectivity to A as well as the overall process efficiency can be improved by using boric acid (2,232,233). K/A mixtures are usually oxidized by nitric acid in a second step to adipic acid (233) (see Cyclohexanol and cyclohexanone). 

Adipic acid (qv) has a wide variety of commercial uses besides the manufacture of nylon-6,6, and thus is a common industrial chemical. Many routes to its manufacture have been developed over the years but most processes in commercial use proceed through a two-step oxidation of cyclohexane [110-83-8] or one of its derivatives. In the first step, cyclohexane is oxidized with air at elevated temperatures usually in the presence of a suitable catalyst to produce a mixture of cyclohexanone [108-94-1] and cyclohexanol [108-93-0] commonly abbreviated KA (ketone—alcohol) or KA oil ... 

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. 

Essentially, all cyclohexane is oxidized either to a cyclohexanone-cyclohexanol mixture used for making caprolactam or to adipic acid. These are monomers for making nylon 6 and nylon 6/6. 

C04-0063. One starting material for the preparation of nylon is adipic acid. Adipic acid is produced from the oxidation of cyclohexane ... 

Adipic acid (1,4-butanedicarboxylic acid) is used for the production of nylon-6,6 and may be produced from the oxidation of cyclohexane as shown in structure 17.1. Cyclohexane is obtained by the Raney nickel catalytic hydrogenation of benzene. Both the cyclohexanol and cyclohexanone are oxidized to adipic acid by heating with nitric acid. 

One of the best known explosion disasters took place in Flixborough, England, in 1974. Nypro Limited manufactured 70,000 tons/year of caprolactam as intermediate for the manufacturing of nylon. This is done by air oxidation of cyclohexane to cyclo-hexanol, with the help of a number of catalysts in the reactors. At that time, cracks developed in the reactor combined with pipe rupture, which released 30 tons of cyclohexane in a cloud. It was ignited by an unknown source and exploded, which resulted in 28 deaths and 36 injured, and the fire burned for 10 days. This disaster was also devastating to the future of the company. 

Nitric acid is used for nitrating numerous other compounds to produce nitrates. Nitric acid is used to produce adipic acid (C6H4O10), which is used in the production of nylon (see Nylon). In this process, cyclohexane is oxidized to a cyclohexanol-cyclohexanone mixture. Cyclohexanol and cyclohexanone are then oxidized with nitric acid to adipic acid. 

Cyclohexane is an essential intermediate for the synthesis of nylon-6,6. The purity level required for the use of cyclohexane, especially for its oxidation, is higher than 99%. This purity can be obtained by the benzene hydrogenation technique. The conversion is highly exothermic and is favored by low temperature, and high hydrogen partial pressure. 

Adipic acid [124-04-9] - [ALKYD RESINS] (Vol 2) - [DICARBOXYLIC ACIDS] (Vol 8) - [FOOD ADDITIVES] (Vol 11) - (ELECTROCHEMICALPROCESSDTG - ORGANIC] (Vol 9) -barrier polymers from [BARRIERPOLYMERS] (Vol 3) -from cyclohexane [HYDROCARBONS - C1-C6] (Vol 13) -from cyclohexane [HYDROCARBON OXIDATION] (Vol 13) -from cyclohexanol [CYCLOHEXANOL AND CYCLOHEXANONE] (Vol 7) -as food additive [FOOD ADDITIVES] (Vol 11) -nylon from [POLYAMIDES - FIBERS] (Vol 19) -nylon-6,6 from [POLYAMIDES - GENERAL] (Vol 19) -nylon-6,6 from [POLYAMIDES - PLASTICS] (Vol 19) -m polyester production [COMPOSITE MATERIALS - POLYMER-MATRIX - THERMOSETS] (Vol 7) -m polyester resins [POLYESTERS, UNSATURATED] (Vol 19) -soda preservatives [CARBONATED BEVERAGES] (Vol 5)... 

The reaction is very important because cyclohexane is used widely as a solvent and also is oxidized to cyclohexanone, an important intermediate in the synthesis of hexanedioic (adipic) and azacycloheptan-2-one (caprolactam), which are used in the preparation of nylon (Section 24-3C). 

The starting materials for nylon 66 can be made in many ways. Apparently, the best route to hexanedioic acid is by air oxidation of cyclohexane by way of cyclohexanone ... 

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... 

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