Process for converting scrap to PET 4-aminomethyl benzoic acid

Abstract: Scrap poly(ethyleneterephthalate) is converted to useful amine and diamine monomers such as para-xylylenediamine, 1,4-bis(aminomethyl)cyclo­ hexane and 4-aminomethyl benzoic acid for the production of various polyamides. The conversion of poly(ethyleneterephthalate) to diamine monomers is achieved by a three step process involving (a) ammonolysis of the poly(ethyleneterephthalate) to produce terephthalamide and ethylene glycol; (b) pyrolytic dehydration of the terephthalamide to produce terephthalonitrile; and (c) hydrogenation of the terephthalonitrile to produce the para-xylylene diamine and/or 1,4-bis(aminomethyl)cyclohexane. The conversion of poly(ethyleneterephthalate) to 4-aminomethyl benzoic acid involves the steps of (a) ammonolysis of the poly(ethyleneterephthalate) to produce terephthalamide; (b) partial pyrolytic dehydration of said terephthalamide to produce 4-cyanobenzoic acid; and (c) hydrogenation of said 4-cyanobenzoic acid to produce 4-aminomethylbenzoic acid. The process of the present invention permits the conversion of low value PET scrap such as beverage bottles, fibers and film to relatively high value and relatively pure diamine monomers and ethylene glycol.

Description: The present invention relates to production of useful monoamine monomers from poly(ethyleneterephthalate). More particularly, it relates to the conversion of poly(ethyleneterephthalate) scrap to 4-aminomethylbenzoic acid. Poly(ethyleneterephthalate) (PET) is a thermoplastic polyester which finds commercial utility in the production of disposable consumer items such as soft drink bottles, packaging films, and fibers for fabrics and the like. These PET consumer items are eventually discarded thereby either contributing to environmental pollution as trash or finding marginal utility as PET scrap for recycle as low grade PET. Attempts at reducing the amount of PET trash have included the aforementioned recycling of PET to low grade PET. Prior recycling of PET, however, has had a number of problems associated with it including that scrap PET items are often partially degraded and have colorants therein which means that recycled PET is not colorless and thus cannot be used for many commercial applications, for example as PET stock for soft drink bottles. Therefore, it is a principal objective of the present invention to provide a process for the conversion of scrap poly(ethyleneterephthalate) to valuable, substantially pure chemical products in high yields. It is also an objective to provide a process for converting a scrap PET to monomers useful for the production of various polyamides. DE-A-2216116 discloses a process for the preparation of terephthalic acid diamide by treating polyethylene terephthalate with ammonia containing not more than 15% by weight of water. Industrial and Engineering Chemistry, Product Research and Development, Vol 15, no 3, 1976 pages 186-189, Washington DC; H G Zengel et al discloses a process for the production of p-phenylenediamine from polyester waste in which the first stage is the ammonolysis of polyethylene terephthalate to terephthalic diamide which is converted to terephthalic bis(chloroamide) in the second stage which in the third stage of the process undergoes a rearrangement reaction to p-phenylenediamine. Chemical Abstracts 85 , no. 21, 1976, page 512, Abstract no. 159685d; and JP-A-7632536 discloses the catalytic hydrogenation of 4-cyanobenzoic acid to 4-aminomethylbenzoic acid in an alkaline solution, in the presence of a ruthenium catalyst. SUMMARY OF THE INVENTION Accordingly, this invention provides a method for converting a scrap poly(ethyleneterephthalate) to useful, substantially pure (aminomethyl) benzoic acid. The present process involves a process for producing 4-aminomethyl benzoic acid from poly(ethyleneterephthalate), said process comprising the steps of : (a) ammonolysis of said poly(ethyleneterephthalate) to produce terephthalamide; (b) partial pyrolytic dehydration of said terephthalamide to produce 4-cyanobenzoic acid; and (c) hydrogenation of said 4-cyanobenzoic acid to produce 4-aminomethylbenzoic acid. The scrap PET employed may initially include contaminates such as polyethylene bottom cups, paper labels, glues, metal caps and metal rings or the scrap PET employed may be pre-sorted from the above contaminates. The ammonolysis of the scrap poly(ethyleneterephthalate) involves contacting the PET dispersed in ethylene glycol with ammonia and applying pressure and heat thereto whereupon the PET reacts with the ammonia to produce terephthalamide and ethylene glycol. The initial ethylene glycol provides a reaction and heat exchange media as well as partial solvent for the PET. Preferably the contacted poly(ethyleneterephthalate), ammonia, and ethylene glycol are heated to a reaction temperature of from between about 120°C and about 180°C and are pressurized to a reaction pressure of 863 kPa (125 pounds per square inch (psi)) thereby resulting in a reaction which produces terephthalamide in a yield of greater than 90 percent and at a purity of greater than 99 percent. Ammonolysis may be carried out at reaction temperatures of from about 80°C to about 250°C. At temperatures below this range, the reaction is slow and at temperatures above this range undesirable side reactions occur too rapidly. The ammonolysis of scrap PET to produce terephthalamide appears substantially as follows: where n is the number of ethyleneterephthalate moieties in a given polymer chain of poly(ethyleneterephthalate). The reaction of a given ethyleneterephthalate moiety of PET with ammonia is represented by the following reaction: Commercially available PET scrap can be purchased which is substantially free from typical contaminates such as polyethylene bottoms from soft drink bottles, metal caps, and metal rings. These contaminates are often removed by known methods such as grinding the contaminated scrap followed by simple screening and density separation of the contaminates from the PET. Pursuant to the present process, PET is then subjected to substantial ammonolysis to yield terephthalamide and ethylene glycol. The terephthalamide which is insoluble in the ethylene glycol is then separated therefrom by simple filtration to yield terephthalamide in powdered form. Substantially pure terephthalamide can be obtained by washing and filtering the terephthalamide with deionized water and then drying the terephthalamide at elevated temperatures, for example 80°C, for a period of time, for example 1 hour, to produce terephthalamide at yields of greater than 90% and at purities of greater than 99%. The terephthalamide is then further processed by pyrolytic dehydration to produce terephthalonitrile. The ethylene glycol produced during ammonolysis can be sold as a chemical product for various purposes, including, for example, as a monomer for the production of poly(ethyleneterephthalate). Partial pyrolytic dehydration of the terephthalamide produces 4-cyanobenzoic acid, this reaction is represented as follows : The water generated reacts with this partial dehydration product to form the 4-cyanobenzoic acid: The conditions of dehydration are chosen to promote the formation of 4-cyanobenzoic acid since it represents a valuable raw material. When 4-cyanobenzoic acid is reduced (hydrogenated) the resultant product is 4-aminomethylbenzoic acid, an attractive bifunctional monomer for the production of polyamide resin. The hydrogenation of 4-cyanobenzoic acid to 4-aminomethylbenzoic acid is represented by the following reaction: From the above process steps it can be seen that high yields of high purity, high value, 4-aminomethylbenzoic acid can be obtained from scrap PET by the process of the present invention. The process is illustrated in the following example. Percent yield is defined as the moles of actual product produced as a percentage of the theoretically maximum number of moles of product producible from the starting material. Thus if 100 moles of starting material can theoretically produce a maximum of 100 moles of product but only 75 moles of product was actually produced then the yield was 75 percent. EXAMPLE Step (a): Ammonolysis of Poly(ethyleneterephthalate), PET 100 grams of PET pellets were placed into a 1 liter Parr bomb. 150 grams of ethylene glycol were added to the PET in the Parr bomb. The bomb was sealed and heated to 120°C. Ammonia (anhydrous, liquid) was introduced into the vessel until the pressure equalized with that of the ammonia cylinder (approximately 125 psi). The mixture was then stirred for 7 hrs at 120°C while maintaining a pressure of 125 psi by continued addition of ammonia. The insoluble terephthalamide was then filtered off from the ethylene glycol and was then washed with 50 mililiters of deionized water. The resulting powder was dried at 80°C for 1 hour and yielded 79.3 grams of terephthalamide (greater than 90% yield at greater than 99% purity). The results of a substantially identical run are set forth as reaction II of Table 1. Ammonolysis of PET scrap was also conducted in a process similar to the aforementioned ammonolysis of PET pellets. The PET scrap employed was obtained from PET beverage containers, the walls of which were cut into small strips. These strips of PET were then converted to terephthalamide by ammonolysis. The PET strips were converted to terephthalamide at a faster rate than were the pellets because the strips had greater surface area per gram of PET. Table I sets forth additional examples (Reactions I - IX) of the conversion of PET to terephthalamide by ammonolysis. The form of the PET, the reaction temperature and the the reaction time were varied to illustrate their impact on yield of terephthalamide. Step (b): Dehydration of Terephthalamide The following table (Table II) sets forth the amounts of reaction products obtained at various reaction temperatures, nitrogen flow rates, and reaction periods. Each of the reactions of Table II were conducted by heating the terephthalamide to the reaction temperature, passing nitrogen heated to the reaction temperature through the terephthalamide to remove volatile reaction products, and passing the nitrogen and volatile reaction products through a condenser to condense out the reaction products. Three predominate reaction products were obtained from the condensate. Those products were: and their respective mole percent yields are listed in the Table II. A sand bath was employed to obtain the desired temperatures. A stainless steel reaction vessel and a nitrogen inlet coil were submerged in the sand bath. Terephthalamide was placed on a filter in the reaction vessel. Nitrogen was fed into the coil wherein it was heated to the temperature of the sand bath, the heated nitrogen then entered into the bottom of the reaction vessel wherein it passed through the filter and through the terephthalamide, sweeping out the volatile reaction products. The nitrogen then carried the volatile products out the top of the reaction vessel and into a condenser wherein the volatile reaction products were condensed out from the nitrogen gas stream. Table II indicates the respective yields of products obtained in the condensate. Step (c): Hydrogenation of 4-Cyanobenzoic Acid 5g of 4-cyanobenzoic acid, 1g of Ni 5136P (nickel catalyst from Harshaw/Filtrol), 85g of ethanol and 5g of ammonia were charged to a 300cc stainless steel pressure vessel. After purging the vessel with nitrogen, it was pressurized to 6.9 MPa (1000 psi) with hydrogen. The temperature was then increased to 150°C over period of 30 minutes. The pressure was held at 6.9 MPa (1000 psi) and the temperature at 150°C for an additional 2.5 hours and then cooled. The product was recovered from the solid precipitate by hot water extraction. The filtered extract (catalyst removed) was evaporated to dryness to yield 3.85g (75% yield) of a white solid. The infrared spectrum of the white solid was identical to that of an authentic sample of 4-aminomethyl benzoic acid.

Claims: A process for producing 4-aminomethyl benzoic acid from poly (ethyleneterephthalate), said process comprising the steps of : (a) ammonolysis of said poly(ethyleneterephthalate) to produce terephthalamide; (b) partial pyrolytic dehydration of said terephthalamide to produce 4-cyanobenzoic acid; and (c) hydrogenation of said 4-cyanobenzoic acid to produce 4-aminomethylbenzoic acid.

Inventors: BLACKMON KENNETH PAUL, FOX DANIEL WAYNE, SHAFER SHELDON JAY, BLACKMON, KENNETH PAUL, FOX, DANIEL WAYNE, SHAFER, SHELDON JAY
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1989
Main classification: C07C209
IPC codes: C07C31, C07C255, C07C233, C07C253, C07C29, C07C209, C07C229, C07C231, C07C211, C07C27, C07C227