Cyclohexanol manufacture

Colourless liquid with a strong peppermintlike odour b.p. 155" C. Manufactured by passing cyclohexanol vapour over a heated copper catalyst. Volatile in steam. Oxidized to adipic acid. Used in the manufacture of caprolactam. Nylon, adipic acid, nitrocellulose lacquers, celluloid, artificial leather and printing inks. 

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. 

Reactions. The most important commercial reaction of cyclohexane is its oxidation (ia Hquid phase) with air ia the presence of soluble cobalt catalyst or boric acid to produce cyclohexanol and cyclohexanone (see Hydrocarbon oxidation Cyclohexanoland cyclohexanone). Cyclohexanol is dehydrogenated with 2iac or copper catalysts to cyclohexanone which is used to manufacture caprolactam (qv). 

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 ... 

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. 

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. 

One principal use of cyclohexanol has been in the manufacture of esters for use as plasticizers (qv), ie, cyclohexyl and dicyclohexyl phthalates. In the finishes industry, cyclohexanol is used as a solvent for lacquers, shellacs, and varnishes. Its low volatiUty helps to improve secondary flow and to prevent blushing. It also improves the miscibility of cellulose nitrate and resin solutions and helps maintain homogeneity during drying of lacquers. Reaction of cyclohexanol with ammonia produces cyclohexylamine [108-91-8], a corrosion inhibitor. Cyclohexanol is used as a stabilizer and homogenizer for soaps and synthetic detergent emulsions. It is used also by the textile industry as a dye solvent and kier-boiling assistant (see Dye carriers). 

The plant was a stage in the production of nylon. It manufactured a mixture of cyclohexanone and cyclohexanol (known as KA, for the ketone/alcohol naixture) by oxidizing... 

Nearly all the adipic acid manufactured, 98%, is made from cyclohexane by oxidation. Air oxidation of cyclohexane with a cobalt or manganese (II) naphthenate or acetate catalyst at 125-160°C and 50-250 psi pressures gives a mixture of cyclohexanone and cyclohexanol. Benzoyl peroxide is another... 

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... 

Cyclohexanol and cyclohexanone are made by the air oxidation of cyclohexane (81%) with a cobalt(II) naphthenate or acetate or benzoyl peroxide catalyst at 125-160°C and 50-250 psi. Also used in the manufacture of this mixture is the hydrogenation of phenol at elevated temperatures and pressures, in either the liquid or vapor phase (19%). The ratio of alcohol to ketone varies with the conditions and catalysts. 

Mixed oil is used for the manufacture of caprolactam (53%, for nylon 6) and adipic acid (44%, for nylon 6,6). Cyclohexanol is favored if the use is for adipic acid cyclohexanone is favored if the mixture is to be made into caprolactam. 

Oxidation of Cyclohexane. The synthesis of cyclohexanol and cyclohexanone is the first step in the transformation of cyclohexane to adipic acid, an important compound in the manufacture of fibers and plastics. Cyclohexane is oxidized industrially by air in the liquid phase to a mixture of cyclohexanol and cyclohexanone.866 872-877 Cobalt salts (naphthenate, oleate, stearate) produce mainly cyclohexanone at about 100°C and 10 atm. The conversion is limited to about 10% to avoid further oxidation by controlling the oxygen content of the reaction mixture. Combined yields of cyclohexanol and cyclohexanone are about 60-70%. 

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... 

No atoms are lost in the cleavage reaction so that cheap cyclohexene 6 is used to make adipic acid 7 for nylon manufacture. Any of the oxidative cleavage methods from the last chapter could be used Vogel1 has a recipe using concentrated nitric acid on cyclohexanol 8 that presumably goes by dehydration to the alkene 6 followed by oxidation, and other methods are probably used industrially. 

Cyclohexane, the six-carbon ring hydrocarbon with the molecular formula C6H12, is the most significant of the cyclic alkanes. Under ambient conditions it is a clear, volatile, highly flammable liquid. It is manufactured by the hydrogenation of benzene and is used primarily as a raw material for the synthesis of cyclohexanol and cyclohexanone through a liquid-phase oxidation with air in the presence of a dissolved cobalt catalyst. 

Adipic acid (melting point 152.1°C, density 1.344) is manufactured predominantly by the oxidation of cyclohexane followed by oxidation of the cyclohexanol/cyclohexanone mixture with nitric acid (Figs. 1 and 2) ... 

Caprolactam is usually manufactured from cyclohexanone, made by the oxidation of cyclohexane or by the hydrogenation/oxidation of phenol (Fig. 1), although the manufacture can be an integrated process with several starting materials (Fig. 2). The cyclohexanol that is also produced with the cyclohexanone can be converted to cyclohexanone by a zinc oxide (ZnO) catalyst at 400°C. The cyclohexanone is converted into the oxime with hydroxylamine, which then undergoes rearrangement to give caprolactam. 

The hydrogenation of phenol at elevated temperatures and pressures, in either the liquid or vapor phase and with a nickel catalyst, is also used in the manufacture of cyclohexanol. 

Amongst hydrocarbon oxidations, the liquid phase oxidation of cyclohexane is of immediate interest. It is a typical example of this class of reactions and has considerable industrial importance, especially in the nylon industry. The oxidation of cyclohexane produces cyclohexanol, cyclohexanone and adipic acid, the raw materials for the manufacture of nylon 6 and nylon 6,6. Problems normally encountered in this reaction are those of selectivity. Single stage conversion has to be kept low to avoid over-oxidation and the production of large quantities of unwanted by-products. 

The main industrial routes for cyclohexanone manufacture have as starting points cyclohexane and phenol, by oxidation and hydrogenation, respectively. Another interesting method is based on the hydration of cyclohexene obtained by selective hydrogenation of benzene. The intermediate cyclohexanol is further dehydrogenated or separated if desired. 

Today the main route for cyclohexanone manufacturing is liquid-phase oxidation of cyclohexane. The synthesis involves the formation of cyclohexyl-hydroperoxide, further converted to cyclohexanone, cyclohexanol and byproducts, as illustrated by the following scheme ... 

Figure 5.1 illustrates the key reactions implied in the manufacturing of cyclohexanone by phenol hydrogenation. The reactions are of consecutive type, in which the desired product is an intermediate. Small amounts of cyclohexene might appear at higher temperature by cyclohexanol dehydration. Additional reactions can lead to heavies by polymerization or benzene and cyclohexane by disproportionation. 

The case study of cyclohexanone manufacturing by phenol hydrogenation illustrates the basic principles of the conceptual development of a process flowsheet. For more complexity we consider a two-step process. Firstly, phenol is submitted to hydrogenation, in which both cyclohexanone and cyclohexanol... 

An important goal is, therefore, to develop effective methods for catalytic oxidations with dioxygen, under mild conditions in the liquid phase. Two substrates which are often chosen as models for alkane oxidations are cyclohexane and adamantane. Cyclohexane is of immense industrial importance as its oxidation products - cyclohexanone and adipic acid - are the raw materials for the manufacture of nylon-6 and nylon-6,6. Adamantane is an interesting substrate as the ratio of oxidation at the secondary versus the tertiary C-H bonds is used as a measure of radical versus nonradical oxidation pathways. Industrial processes for the oxidation of cyclohexane, to a mixture of cyclohexanol and cyclohexanone, generally involve low conversions (under 10%). Even at such low conversions, selectivities are modest (70-80%) and substantial amounts of overoxidation products, mostly dicarboxylic acids, are formed. 

Fig. 12.14. Flow diagram for the manufacture of nylon 66 yarn (1) air (2) cyclohexane from petroleum (3) reactor (4) recycle cyclohexane (5) still (6) cyclohexanol-cyclohexanone (7) nitric acid (8) converter (9) adipic acid solution (10) still (11) impurities (12) crystallizer (13) centrifuge (14) impurities (15) adipic acid crystals (16) dryer (17) vaporizer (18) ammonia (19) converter (20) crude adiponitrile (21) still (22) impurities (23) hydrogen (24) converter (25) crude diamine (26) still (27) impurities (28) nylon salt solution (29) reactor (30) stabilizer (31) calandria (32) evaporator (33) excess water (34) autoclave (35) delustrant (36) water sprays (37) casting wheel (38) polymer ribbon (39) grinder (40) polymer flake (41) spinning machine (42) heating cells (43) spinnerette (44) air (45) draw twisting (46) inspection (47) nylon bobbin. (Note Whenever the demand for liquid polymer at a spinnerette is large, as, for example, in the spinning of tire yarn, it is pumped directly from the autoclave.)...

Phenol Hydrogenation. In principle, appropriate lignin deconstruction processes will provide a stream of mixed phenols. Reduction of these phenols will lead to a new source of cyclic aliphatic alcohols of potential use in the manufacture of adipic acid derivatives. Several catalytic processes for these types of reductions have appeared for phenol and should be applicable to lignin-derived mixed phenols. Phenol itself is reduced to cyclohexanol in the presence of various heterogeneous catalysts based on Pd.530-535... 

As mentioned earlier, soluble salts of cobalt and manganese catalyze oxidation of cyclohexane by oxygen to cyclohexanol and cyclohexanone. Cyclohexanol and cyclohexanone are oxidized by nitric acid to give adipic acid. The oxidation by nitric acid is carried out in the presence of V5+ and Cu2+ ions. These reactions are shown by Eq. 8.8. Adipic acid is used in the manufacture of nylon 6,6. 

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. 

Adipic acid is used in the manufacture of nylon 6,6. It is made by hydrogenation of phenol to a mixture of cyclohexanol and cyclohexanone (known as KA oil-ketone... 

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