Hexamethylenediamine, from adiponitrile

Figure 10.3 Manufacture of adiponitrile and hexamethylenediamine from 1,3-butadiene.

Hexamethylenediamine is discussed in Chapter 10, Sections 1 and 8. It is produced from adiponitrile by hydrogenation. Adiponitrile comes from electrodimerization of acrylonitrile (32%) or from anti-Markovnikov addition of 2 moles of hydrogen cyanide to butadiene (68%). 

Adiponitrile (hexanedinttrile, dicyanobutane, ADN), NC(CH2)4CN is manufactured mainly for use as an intermediate for hexamethylenediamine (1,6-diaminohexane), which is a principal ingredient for nylon-6,6. BASF has announced the development of a process to make caprolactam from adiponitrile. Caprolactam is used to produce nylon-6,... 

Extraction and distillation is necessary to obtain pure adiponitrile. Even then the hexamethylenediamine made by hydrogenation of adiponitrile must also be distilled through seven columns to purify it before polymerization to nylon. Hexamethylenediamine is produced from adiponitrile by hydrogenation. 

Adipic Acid. Nylon 66, produced from adipic acid and hexamethylenediamine (HMDA), currently is the largest-volume domestic nylon. About 90 percent of all adipic acid goes to make nylon 66 fibers and resins. Although HMDA can be made from adipic acid, a major source is from adiponitrile. The commercial synthesis of adipic acid is a two-step reaction starting with either cyclohexane or phenol. In both cases, a cyclohexanone/cyclohexanol mixture is formed as an intermediate. This mixture then is catalytically oxidized with nitric acid to the adipic product. It also can be manufactured as a by-product of the caprolactam process. 

Hexamethylenediamine may be conveniently prepared from adipic acid via adiponitrile... 

In a typical process adiponitrile is formed by the interaction of adipic acid and gaseous ammonia in the presence of a boron phosphate catalyst at 305-350°C. The adiponitrile is purified and then subjected to continuous hydrogenation at 130°C and 4000 Ibf/in (28 MPa) pressure in the presence of excess ammonia and a cobalt catalyst. By-products such as hexamethyleneimine are formed but the quantity produced is minimized by the use of excess ammonia. Pure hexamethylenediamine (boiling point 90-92°C at 14mmHg pressure, melting point 39°C) is obtained by distillation, Hexamethylenediamine is also prepared commercially from butadience. The butadiene feedstock is of relatively low cost but it does use substantial quantities of hydrogen cyanide. The process developed by Du Pont may be given schematically as ... 

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. 

Adiponitrile is readily hydrogenated catalytically to hexamethylenediamine, which is an important starting material for the prodnction of nylons and other plastics. The electrochemical production of adiponitrile was started in the United States in 1965 at present its volume is about 200 kilotons per year. The reaction occurs at lead or cadmium cathodes with current densities of np to 200 mA/cm in phosphate buffer solutions of pH 8.5 to 9. Salts of tetrabntylammonium [N(C4H9)4] are added to the solution this cation is specihcally adsorbed on the cathode and displaces water molecules from the first solution layer at the snrface. Therefore, the concentration of proton donors is drastically rednced in the reaction zone, and the reaction follows the scheme of (15.36) rather than that of (15.35), which wonld yield propi-onitrile. 

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. 

A process for the hydrogenation of adiponitrile and 6-aminocapronitrile to hexamethylenediamine in streams of depolymerized Nylon-6,6 or a blend of Nylon-6 and Nylon-6,6 has been described. Semi-batch and continuous hydrogenation reactions of depolymerized (ammonolysis) products were performed to study the efficacy of Raney Ni 2400 and Raney Co 2724 catalysts. The study showed signs of deactivation of Raney Ni 2400 even in the presence of caustic, whereas little or no deactivation of Raney Co 2724 was observed for the hydrogenation of the ammonolysis product. The hydrogenation products from the continuous run using Raney Co 2724 were subsequently distilled and the recycled hexamethylenediamine (HMD) monomer was polymerized with adipic acid. The properties of the polymer prepared from recycled HMD were found to be identical to that obtained from virgin HMD. 

Hexamethylenediamine (HMD) and adiponitrile (ADN) are formed from Nylon-6,6, while 6-aminocapronitrile (ACN) and caprolactam (CL) are formed from Nylon-6. The ammonolysis product, which also contains many minor byproduct components, is fractionated by distillation with the HMD, ACN, ADN, and CL in one fraction. This fraction is subsequently hydrogenated to form HMD. Caprolactam remains intact during the hydrogenation reaction. 

Another derivative of butadiene, hexamethylenediamine (HMDA), is used in the synthesis of nylon. We have already met this compound earlier in this chapter since it is made from acrylonitrile through adiponitrile. 

The manufacture of hexamethylenediamine [124-09-1], a key comonomer in nylon-6,6 production proceeds by a two-step HCN addition reaction to produce adiponitrile [111 -69-3], NCCH2CH2CH2CH2CN. The adiponitrile is then hydrogenated to produce the desired diamine. The other half of nylon-6,6, adipic acid (qv), can also be produced from butadiene by means of either of two similar routes involving the addition of CO. Reaction between the diamine and adipic acid [124-04-5] produces nylon-6,6. 

Currently the global production of hexamethylenediamine exceeds 1.2 Mt/a and production (e.g. ICI, BASF and Rhone-Poulenc in Europe) is based on the hydrogenation of adiponitrile, largely obtained by catalytic addition of HCN to butadiene. Celanese produced hexamethylenediamine by reaction of ammonia with hexane-1,6-diol, coming from the hydrogenation of adipic acid. However, production by this method was abandoned in 1984. 

Alternatively, adiponitrile may also be made from 1,3-butadiene via chlorination, folloAved by treatment with sodium cyanide. Catalytic reduction of adiponitrile with hydrogen then produces hexamethylenediamine (b.p. 205°C, Eq. 19.60). 

In 1965, the Monsanto Company started production of adiponitrile from acrylonitrile via an electrochemical route [Equation (26.113)]. Adiponitrile was then converted to either adipic acid or hexamethylenediamine by chemical means these two compounds are reactants in the production of nylon 66. 

The same set of data is plotted vs. ADN conversion in Figure 2. The diagonal line indicates theoretical 100% selectivity of conversion of adiponitrile to aminocapronitrile. Data points corresponding to concentration of ACN in the reaction mixture show increasing deviation from this line with increasing conversion of ADN. A steep increase in hexamethylenediamine concentration is seen above ca. 90% conversion of ADN. ... 

Nylon 66 is a polymer manufactured by the condensation of adipic acid with hexamethylcnediamine, and in excess of I million ton year are manufactured in the USA atone. Adiponitrile is a convenient intermediate for the production of both hexamethylenediamine and adipic acid, the former by hydrogenation and the Latter by hydrolysis. In addition, acrylonitrile is available from the gas phase, catalytic oxy-amination of propylene. Hence, to complete the manufacture of nylon from propylene and ammonia, a procedure for the conversion of acrylonitrile to adiponitrile is required (Fig. 6.1). 

Fig. 6.1 A route for the manufacture of nylon from basic feedstocks. In practice, there are probably cheaper routes to adipic acid and all the adiponitrile is now converted to hexamethylenediamine.

The modified process is summarized in Fig. 6.5 and employs an emulsion of acrylonitrile and 15% disodium hydrogen phosphate in water containing a low concentration of quaternary ammonium salt (0.4%). Thus, the concentration of the starting material in the aqueous phase is 7% (i.e. saturated) and the adiponitrile will extract back into the acrylonitrile within the cell. The quaternary ammonium ion used is hexamethylene-i /s(ethyldibutylammonium) it is prepared on the site by quaternization of hexamethylenediamine, an intermediate between adiponitrile and the nylon. It is therefore cheap but it is also convenient because traces are readily washed from the organic phase with water. Hence, the product isolation is straightforward and the aqueous and organic phases can be treated separately. The organic phase is merely washed with water and distilled. 

The manufacture of hexamethylenediamine is usually a two stage process. In the first stage, adiponitrile is produced, and in the second stage, adiponitrile is hydrogenated to hexamethylenediamine. Adiponitrile has been manufactured, in the main, from three feedstocks, and these will be described briefly in tixm. 

---