Adipic acid from cyclohexane

Another reaction which enjoys much commercial interest is the production of adipic acid from cyclohexane oxidation. The two types of processes that are employed commercially are outlined in Figure 24. 

Liquid phase oxidation of hydrocarbons by molecular oxygen forms the basis for a wide variety of petrochemical processes,3 "16 including the manufacture of phenol and acetone from cumene, adipic acid from cyclohexane, terephthalic acid from p-xylene, acetaldehyde and vinyl acetate from ethylene, propylene oxide from propylene, and many others. The majority of these processes employ catalysis by transition metal complexes to attain maximum selectivity and efficiency. 

Adipic acid from cyclohexane Cu(II), V(V) salts, nitric acid... 

Fig. 28. Production of adipic acid from cyclohexane using MnAPO-36 catalyst. Metal-modified aluminophosphates are the most frequently used for this reaction, that is oxidation of cyclohexane.

Figure 9.12 Manufacture of adipic acid from cyclohexane...

Homogeneous catalysts are used for many large-scale oxidation processes. Some of the most important large-scale oxidation processes are acetaldehyde from ethylene, adipic acid from cyclohexane, tere-phthalic acid from p-xylene, and propylene oxide (PO) from propylene. The mechanisms of these reactions are very different and can be broadly classified into three categories. 

The entrapped complexes are known to catalyze selective oxidation or hydrogenation reactions, depending mainly on the complexed transition metal cation [4, 82, 84]. Recently, two exciting examples have been published describing the synthesis of adipic acid from cyclohexene [93] or even from cyclohexane [94], respectively (cf Figure 6). 

The production cycle of adipic acid from hydrocarbons — benzene or cyclohexane — is a two-stage process (i) the production of the raw material for the synthesis of adipic acid, consisting of cyclohexanol alone or, more often, a mixture of cyclohexanol and cyclohexanone (KA oil), and (ii) the production of adipic acid by nitric acid oxidation in the presence of copper and vanadium catalysts (see Figs. 13.2 and 13.3). 

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. 

Although many variations of the cyclohexane oxidation step have been developed or evaluated, technology for conversion of the intermediate ketone—alcohol mixture to adipic acid is fundamentally the same as originally developed by Du Pont in the early 1940s (98,99). This step is accomplished by oxidation with 40—60% nitric acid in the presence of copper and vanadium catalysts. The reaction proceeds at high rate, and is quite exothermic. Yield of adipic acid is 92—96%, the major by-products being the shorter chain dicarboxytic acids, glutaric and succinic acids,and CO2. Nitric acid is reduced to a combination of NO2, NO, N2O, and N2. Since essentially all commercial adipic acid production arises from nitric acid oxidation, the trace impurities patterns ate similar in the products of most manufacturers. 

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). 

The production of alcohols by the catalytic hydrogenation of carboxylic acids in gas-liquid-particle operation has been described. The process may be based on fixed-bed or on slurry-bed operation. It may be used, for example, for the production of hexane-1,6-diol by the reduction of an aqueous solution of adipic acid, and for the production of a mixture of hexane-1,6-diol, pentane-1,5-diol, and butane-1,4-diol by the reduction of a reaction mixture resulting from cyclohexane oxidation (CIO). 

Type 66 nylon is a polyamide first commercialized by DuPont just prior to World War II. At that time, the needed hexamethylenediamine was made from adipic acid by reaction with ammonia to adiponitrile followed by reaction with hydrogen. The adipic acid then, like now, was made from cyclohexane. The cyclohexane, however, was derived from benzene obtained from coal. The ammonia was made from nitrogen in the air by reaction with hydrogen from water obtained in the water-gas shift reaction with carbon monoxide from the coal. So, in the 1950s, nylon was honestly advertised by DuPont as being based on coal, air, and water. 

Hexamethylenediamine is now made by three different routes the original from adipic acid, the electrodimerization of acrylonitrile, and the addition of hydrogen cyanide to butadiene. Thus, the starting material can be cyclohexane, propylene, or butadiene. Currently, the cyclohexane-based route from adipic acid is the most costly and this process is being phased out. The butadiene route is patented by DuPont and requires hydrogen cyanide facilities. Recent new hexamethylenediamine plants, outside DuPont, are based on acrylonitrile from propylene, a readily available commodity. 

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

Hexamethylenediamine (HMDA), a monomer for the synthesis of polyamide-6,6, is produced by catalytic hydrogenation of adiponitrile. Three processes, each based on a different reactant, produce the latter coimnercially. The original Du Pont process, still used in a few plants, starts with adipic acid made from cyclohexane adipic acid then reacts with ammonia to yield the dinitrile. This process has been replaced in many plants by the catalytic hydrocyanation of butadiene. A third route to adiponitrile is the electrolytic dimerization of acrylonitrile, the latter produced by the ammoxidation of propene. 

Chemical/Physical. Gaseous products formed from the reaction of cyclohexene with ozone were (% yield) formic acid (12), carbon monoxide (18), carbon dioxide (42), ethylene (1), and valeraldehyde (17) (Hatakeyama et al., 1987). In a smog chamber experiment conducted in the dark at 25 °C, cyclohexane reacted with ozone. The following products and their respective molar yields were oxalic acid (6.16%), malonic acid (6.88%), succinic acid (0.63%), glutaric acid (5.89%), adipic acid (2.20%), 4-hydroxybutanal (2.60%), hydroxypentanoic acid (1.02%), hydroxyglutaric acid (2.33%), hydroxyadipic acid (1.19%), 4-oxobutanoic acid (6.90%), 4-oxopentanoic acid (4.52%), 6-oxohexanoic acid (4.16%), 1,4-butandial (0.53%), 1,5-pentanedial (0.44%), 1,6-hexanedial (1.64%), and pentanal (17.05%). 

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. 

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... 

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. 

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)... 

Adipic acid historically has been manufactured predominantly from cyclohexane and, to a lesser extent, phenol. During the 1970s and 1980s, however, much research has been directed to alternative feedstocks, especially butadiene and cyclohexene, as dictated by shifts in hydrocarbon markets. All current industrial processes use nitric acid in the final oxidation stage. Growing concern with air quality may exert further pressure for alternative routes as manufacturers seek to avoid NO, abatement costs, a necessary part of processes dial use nitric acid. 

Adipic acid is a most important petrochemical product which is mostly used for the synthesis of nylon 6.6 from its condensation with hexamethylenediamine. Cyclohexane is transformed to adipic acid in two steps (a) oxidation of cyclohexane to a cyclohexanol-cyclohexanone mixture (ol-one) via the formation of cyclohexyl hydroperoxide followed by (b) oxidation of the ol-one mixture to adipic acid by nitric acid (equation 239). 

In the Dupont process, cyclohexane is reacted with air at 150 °C and 10 atm pressure in the presence of a soluble cobalt(II) salt (naphthenate or stearate). The conversion is limited to 8-10% in order to prevent consecutive oxidation of the ol-one mixture. Nonconverted cyclohexane is recycled to the oxidation reactor. Combined yields of ol-one mixture are 70-80%.83,84,555 The ol-one mixture is sent to another oxidation reactor where oxidation by nitric acid is performed at 70-80 °C by nitric acid (45-50%) in the presence of a mixture of Cu(N03)2 and NH4V03 catalysts, which increase the selectivity of the reaction. The reaction is complete in a few minutes and adipic acid precipitates from the reaction medium. The adipic acid yield is about 90%. Nitric acid oxidation produces gaseous products, mainly nitric oxides, which are recycled to a nitric acid synthesis unit. Some nitric acid is lost to products such as N2 and N20 which are not recovered. 

---