Nylon ammonolysis

Since the hydrogenation step of the Nylon ammonolysis process had not been studied extensively, it was deemed necessary to investigate the feasibility of a relatively low-pressure (less than 1000 psig) and low-temperature (less than 100°C) process for the hydrogenation of depolymerized Nylon-6,6 and/or a blend of Nylon-6 and -6,6 products. 

Peter Kassera is acknowledged for helpful discussions and leadership of the Nylon Ammonolysis program. Leon Scott is acknowledged for assistance in distillation work. Nancy Singletary is acknowledged for assistance in polymer preparation. 

If adipamide reacts with hexarnethylenediarnine, then nylon-6,6 can be prepared by aminolysis of the adipamide this could also be viewed as reverse ammonolysis. 

Lewis acids, such as the haUde salts of the alkaline-earth metals, Cu(I), Cu(II), 2inc, Fe(III), aluminum, etc, are effective catalysts for this reaction (63). The ammonolysis of polyamides obtained from post-consumer waste has been used to cleave the polymer chain as the first step in a recycle process in which mixtures of nylon-6,6 and nylon-6 can be reconverted to diamine (64). The advantage of this approach Hes in the fact that both the adipamide [628-94-4] and 6-aminohexanoamide can be converted to hexarnethylenediarnine via their respective nitriles in a conventional two-step process in the presence of the diamine formed in the original ammonolysis reaction, thus avoiding a difficult and cosdy separation process. In addition, the mixture of nylon-6,6 and nylon-6 appears to react faster than does either polyamide alone. 

Ammonolysis is the preferred route currently in use at the DuPont Company for the depolymerization of nylon-6,6 carpet waste. McKinney13 has described the reaction of nylon-6,6 and nylon-6 mixtures with ammonia at temperatures in the range of 300-350°C at a pressure of about 68 atm in the presence of an ammonium phosphate catalyst to form a mixture of nylon-6,6 and nylon-6 monomers (HMD A, A A, and s-caprolactam) and adiponitrile, 5-cyanovaleramide, 6-aminocapronitrile, and 6-aminocaproamide. 

In recent months, three nylon producers (DMS, DuPont, and Honeywell) have developed closed-loop recycling processes for nylon carpet,15 thereby joining companies like BASF, Allied, and Rhodia, which have been recycling nylon on a modest level for years. DuPont is building a demonstration plant in Maitland, Ontario, which will be dedicated to the chemical recycling of nylon-6,6 and nylon-6. The newly developed ammonolysis process invented by DuPont can be used to depolymerize both nylon-6 and nylon-6,6. However, the cost of recycled nylon is estimated to exceed that of virgin nylon by ca. 25%. 

Important solvolysis reactions for nylons are hydrolysis, methanolysis, glycolysis, aminolysis, ammonolysis, transamidation, and acidolysis.17 Hydrolysis of nylon-6 with steam in the presence of an acid catalyst to form caprolactam is tlie preferred depolymerization approach. However, when recycling carpet face fibers, file fillers in the polymer may react with file acid catalyst and lower the efficiency of the catalyst. 

In die case of nylon-6,6 waste recycled by ammonolysis, nylon is treated with ammonia in die presence of a phosphate catalyst. Reaction occurs at 330°C and 7 MPa. Distillation of die reaction mixture produces ammonia which is recycled and three fractions containing (a) caprolactam, (b) HMDA and aminocaproni-trile, and (c) adiponitrile. Aminocapronitrile and adiponitrile are hydrogenated to yield pure HMDA, and die caprolactam is eidier converted to aminocapronitrile by further ammonolysis or distilled to produce pure caprolactam. The HMDA produced by this process is extremely pure (>99.8).1 The main impurities are aminomediylcyclopentylaniiiie and tetrahydroazepine, which are expected to be removed more effectively in the larger distillation columns employed in the larger plants. 

Lewis acid-base mechanism, 233, 234 Lewis acid catalysts, 13, 546 Lewis-acid-catalyzed ammonolysis, of nylon, 571 Lewis acids, 224 catalysis by, 68-69 Lewis bases, 338... 

Nylon. See also Nylons PA entries Lewis-acid-catalyzed ammonolysis of, 571... 

Nylon-6,6, 2, 136, 530. See also PA-6,6 acid-catalyzed hydrolysis of, 568 acidolysis of, 568 alkaline hydrolysis of, 568-569 ammonolysis of, 555, 570 chemistry and catalysis of, 546 creation of, 1 hydrogen bonding in, 539 hydrolysis of, 531, 544, 552-555 phase-transfer-catalyzed alkaline hydrolysis of, 569-570... 

It is reported here that DuPont is planning to launch a pilot plant in 2000, to test a new, patented process for chemically recycling nylon 6/6 resin. Full details are given of the process, called ammonolysis. 

Large companies are taking a closer look at depolymerising nylon, polyester and PU produets that would otherwise end up in landfills. The most reeent project is a worldscale faeility to be built by DSM Chemicals North America and AlliedSignal that will produce about 100 million pounds of caprolactam per year by depolymerising nylon 6. The faeility will remove about 200 million pounds of earpet from landfills annually. DuPont says it has a proeess, ammonolysis, that ean depolymerise a combination of nylon 6 and 66. 

This paper describes DuPont s very successful progress in the chemical recycling of nylon carpets by a patented ammonolysis process. Each stage of the process is described, from the collection of old and dirty used carpets, right through to the production of high-purity monomers. 

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. 

A Nylon recycle based on depolymerization via ammonolysis has been shown to be a technically feasible route for the recovery of high purity Nylon intermediates (1-6). In the ammonolysis process, the secondary amides of the Nylon (-6 and / or -6,6) fibers/polymers react with ammonia to break the Nylon chain and form a primary amide and an amine (Figure 1). The primary amide can subsequently be dehydrated to form a nitrile group. The net result is that the ammonolysis product is predominantly a mixture of four major components. 

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. 

Figure 1 Ammonolysis of Nylon-6 and Nylon-6,6 leads to a variety of products. The ultimate products of ammonolysis and dehydration are ideally ACN, ADN and HMD, which can be converted to Recycle HMD via hydrogenation.

The crude recycled HMD and CL can be separated by distillation and subsequently refined to produce monomer grade HMD and CL, respectively. The caprolactam can be directly polymerized to Nylon-6 or it can be recycled back to the ammonolysis reactor, where it can be converted into ACN. 

Figure 3 Hydrogenation of recycled Nylon-6 and Nylon-6,6 ammonolysis feed in the presence of 5 g of Raney Co 2724 catalyst at a total pressure of 500 psig, and temperature of 85 to 90°C, at a feed flowrate of 12 ml/h. Hexamethylenediamine ( ), caprolactam (A), adiponitrile ( ), 6-...

The hydrogenation products from the continuous run using Raney Co 2724 were subsequently distilled and the product hexamethylenediamine monomer (i.e. recycled HMD ) 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, indicating that the continuous hydrogenation of ammonolysis product offers potential for the commercial production of recycled Nylon. 

The depolymerized Nylon used in the hydrogenation process was obtained by the ammonolysis of a mixture of Nylon-6 and Nylon-6,6 (described elsewhere, see reference 2). Hydrogenation reactions were conducted in 300 cc stirred pressure vessels. For semi-batch reactions hydrogen was constantly replenished to the reactor from a 1L reservoir to maintain a reactor pressure of 500 psig and all of the reactions were conducted with the same operating parameters and protocol. In continuous stirred tank studies hydrogen flow was controlled using... 

Adipic acid so obtained is both a reactant for the production of nylon and the raw material source for hexamethylenediamine, the other reactant. The adipic acid first is converted to adiponitrile by ammonolysis and then to hexamethylenediamine by hydrogenation ... 

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