Ammonolysis process

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%. 

Ammonolysis of PET involves the reaction of PET with ammonia at temperatures of 70-180°C, usually under pressure in EG. The ammonolysis of PET postconsumer bottles has been canied out at temperatures in the range of 120-180°C and a pressure of ca. 2 MPa for 1-7 h. The TPA diamide formed may be converted to terephthalonitrile. Terephthalonitrile may be hydrogenated to form p-xylylenediamine and l,4-bis(aminomethyl)cyclohexane.12 A low-pressure PET ammonolysis process in EG has been developed. The process is catalyzed by 0.5 wt% zinc acetate at a temperature of 70°C and a PET-NH3 ratio of 1 6 (w/w). The yield of TPA diamide was 87%. 

Quantitative conversion Scheme 7.3 Example of an ammonolysis process using an ionic liquid-like solvent. 

The enzymatic resolution of esters via aminolysis or ammonolysis processes represents an efficient alternative to the resolution of substrates by transesterification... 

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 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. 

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. 

Thus, a number of researchers have chosen ammonolysis as a route to phase and chemically pure Si3N433-37. This process involves removal of excess free C and displacement of carbon in Si—C bonds with Si—N bonds. The process is assumed to involve free radical reactions. There is no apparent relationship between precursor structure or functionality and the extent of carbon removal33. During the ammonolysis process, the carbon leaves as toxic HCN, thus care should be used in this approach38. 

Other aspects of the ammonolysis process have been discussed. ... 

An interesting ammonolysis process has recently been developed93 based on the reaction of polyurethane with ammonia under supercritical conditions, which favours both the degradation reactions and separation of the polyols produced. The flow diagram of this process is shown in Figure 2.6. 

The typical reaction parameters of an ammonolysis process are temperature of 139°C, pressure of 140 bar, and reaction time of 120 min. The ammonolysis reaction transforms derivatives of carbonic acid... 

Figure 7,15 The DuPont Ammonolysis process for PA 6 and PA 66 (courtesy DuPont de Nemours).

The ammonolysis process is scheduled to reach commercial-scale operations in North America before the year 2000. Current recycling cost estimates give a material price that is 10-15 per cent higher than that of a normal PA production plant which would mean a material price of 5.5-5.75 SFr/kg. The total cost of the material will of course depend on the cost and quality of the feedstock. Large quantities of solid waste carmot be purged economically from the process. Fillers or modifiers would have to be removed from the feedstock before recycling to achieve high quality. 

Bordrero et al. [40] utilized a two-step ami/ammonolysis process to depoly-merize nylon 6,6. The first step is based on an aminolysis treatment of nylon 6.6 by n-butylamine at a temperature of 300°C and a pressure of 45 atm. Free HMDA and AA -dibutyladipamide are generated. The second step is ammonolysis of AA -dibutyladipamide at a temperature of 285°C and a pressure of 50 atm. The end product is adiponitrile (ADN). It is estimated that the yields could be about 48% for ADN and about 100% for HMDA at optimized reaction conditions. 

Bodrero S., Canivenc E. and CanseU F. (1999), Chemical Recycling of Polyamide 6.6 and Polyamide 6 through a Two Step Ami-/Ammonolysis Process , 4th Annual Corfer-ence on Recycling of Fibrous Textile and Carpet Waste, Dalton, GA, May 17-18. Schut J. H. (1993), A Recycling First Carpets , Plastic Technology, 22-25, April. 

In 1994, DuPont [18] patented the ammonolysis process, in which PA6 and PA66 react with ammonia in the presence of a catalyst (ammonium phosphate) and as a result the corresponding monomers can be obtained. A high purity of the waste polyamides (98%) is required. The process conditions are 300-350°C and pressure of 68.9 MPa [18,40,41]. 

Berthold H and Hagen R (1994) Recovery of polyamides, European Patent 603,434. Bodrero S, Canivenc E and Cansell F (1998) Chemical recycling of polyamide 6,6 and polyamide 6 through a two step AMI-/ammonolysis process, Abstr Pap ACS 16 395-Poly Part 3 Aug 23. 

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