Process for the Recovery of Epsilon-Caprolactam from Nylon 6 Carpet

Europaisches Patentamt European Patent Office © Publication number: 0 522 235 A1 Office europeen des brevets

EUROPEAN PATENT APPLICATION

© Priority: 24.06.91 US 718720 © Applicant: BASF CORPORATION 100 Cherry Hill Road @ Date of publication of application: Parsippany, NJ 07054(US) 13.01.93 Bulletin 93/02 @ Inventor: Corbin, Thomas F. © Designated Contracting States: 26 Braddock Way BE CH DE FR GB IT LI NL Asheville, NC 28803(US) Inventor: Davis, Edward A. P. O. Box 693 Candler, NC 28715(US) Inventor: Dellinger, Jack A. 5 Salem Acres Weaverville, NC 28787(US)

© Representative: Huber, Bernhard, Dipl.-Chem. et al Patentanwalte H. Weickmann, Dr. K. Fincke F.A. Weickmann, B. Huber Dr. H. Liska, Dr. J. Prechtel Kopernikusstrasse 9 Postfach 86 08 20 W-8000 Munchen 86(DE)

© A process for the continuous recovery of e- caprolactam provides a carpet made from nylon 6 fibers and having a backing to a separator to prepare scrap containing nylon 6 and waste. The scrap from the separator is fed to a depolymerizing reactor where the scrap is subjected to a depolymerization catalyst, temperatures of at least the melting point of nylon 6 and superheated steam to produce an e- caprolactam containing distillate and more waste. CM The e-caprolactam in the distillate is separated from other volatiles therein; and purified. CM CM m

Rank Xerox (UK) Business Services 1 EP 0 522 235 A1 2

FIELD OF THE INVENTION Although the motivation for reclaiming raw materials from waste polymer or spent polymeric pro- The present invention relates to a process for ducts is well recognized, some products do not reclaiming e-caprolactam. More particularly, the readily lend themselves to recycling. Especially, present invention relates to a process for reclaim- 5 items which are composites of several materials ing e-caprolactam from nylon 6 carpet. present problems. Along these lines, polymeric materials formed into carpets present an interesting BACKGROUND OF THE INVENTION reclamation problem This is due, in part, to the variety of materials present in traditional carpet and As landfills continue to reach capacity, raw io the manner in which they are intimately combined. materials are depleted and man recognizes that the In traditional carpets, the tufts are often nylon 6, earth's resources are limited, more and more ma- while the backing of a nylon 6 tufted carpet may terials need to be recycled. Synthetic polymers include jute, polypropylene and latex, among other have long presented problems in recycling due to things. Also, the latex may contain fillers such as their often being commingled with other materials 75 calcium carbonate, clay or hydrated aluminum. The and sometimes apparently irreversible polymeriza- chemical and physical nature of these materials is tion from which useful raw materials cannot be such that reclamation of e-caprolactam from nylon obtained easily. 6 carpets has traditionally been considered too Certain polyamides, however, are known to be complex, too expensive and cumbersome to be hydrolytically degradable and reusable. Especially, 20 practical. in the case of nylon 6, the monomeric starting materials are reclaimed from waste polymer and SUMMARY OF THE INVENTION used in the manufacture of man-made fibers. The literature reveals procedures for reclaiming such Accordingly, the present invention is a process monomers and polymers. L. A. Dmitrieva et al., 25 for recovering e-caprolactam from nylon 6 carpet, Regeneration of e-caprolactam from Wastes in the which is made from nylon 6 fibers and has a Manufacture of Polycaproamide Fibres and Yarns, backing. The carpet can be provided to a separator Fibre Chemistry, March 1986, pp. 229-241, de- to prepare scrap containing nylon 6 and a first scribes methods for reclaiming polycaprolactam waste portion. The scrap from the separator is fed (nylon 6) waste. 30 to a depolymerizing reactor where the scrap is There are generally two methods for reclaiming subjected to a depolymerization catalyst, tempera- nylon 6 waste. The first involves reprocessing the tures of at least the melting point of nylon 6 and waste nylon 6, for example, via extrusion to form superheated steam to produce an e-caprolactam useful articles. This concept is demonstrated in containing distillate and a second waste portion. U.S. Patent 4,143,001 to Raab et al. 35 The e-caprolactam in the distillate is separated from The second method involves chemical regen- other volatiles therein and purified after separating. eration through depolymerization. Processes for It is an object of the present invention to pro- depolymerizing solid polyamide waste are known. vide a process for reclaiming e-caprolactam from For example, U.S. Patent 2,343,174 to Edison et al. nylon 6 carpets.Traditional thought was that poly- shows general hydrolytic degradation using steam. 40 propylene or jute and especially latex would give U.S. Patent 3,988,406 to Nakamura et al. shows the impurities which would make purification so difficult recycling of polyamide waste by depolymerization. or the reclaimed yield so low as to render de- Among the polyamides depolymerized for repolymerization of carpets impractical. Moreover, use of the monomer is nylon 6. For example, U.S. the CaC03 usually present in the latex as filler Patent 4,107,160 to Dicoi et al. describes reclama- 45 would neutralize an equivalent amount of any acid tion of solid nylon 6 waste, accumulated during the depolymerization catalyst, such as H3PCv processing of nylon 6, low molecular weight Related objects and advantages will be readily oligomers and residual monomer from the polycon- apparent to one ordinarily skilled in the art after densation of caprolactam. considering the following. Other polymers are also recycled. An example 50 of a process for continuously degrading various BRIEF DESCRIPTION OF THE DRAWINGS plastics is provided m U.S. Patent 4,051,212 to Grigat et al. Grigat et al. shows a process for FIG. 1 is a schematic of the process of the continuously hydrolytically degrading plastics. The present invention. hydrolyzable material is introduced with water into 55 FIG. 2 is a schematic of an alternate process of a screw machine, where it is subjected to a tem- the present invention. perature of 100°C to 300 °C at a pressure of 5 to 100 bars for 2 to 100 minutes. DESCRIPTION OF THE PREFERRED EMBODI-

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MENTS reactor bottoms. Optionally, other nylon 6 solid waste (13), such To promote an understanding of the principles as yarn waste, chip waste or extruder slag, can be of the present invention, descriptions of specific combined with the nylon 6 feed from separator 10 embodiments of the invention follow, and specific 5 or with the carpet if the separator is not used. Also, language describes the same. It will nevertheless optionally, contaminated monomeric caprolactam or be understood that no limitation of the scope of the caprolactam oligomers, such as from nylon 6 wash invention is thereby intended, and that such alter- water, can be fed to depolymerization unit 20. If a ations and further modifications, and such further thin film evaporator is used as the CDR, then applications of the principles of the invention as io preferably the waste carpet material is molten prior discussed are contemplated, as would normally to feeding into the thin film evaporator. Total waste occur to one ordinarily skilled in the art to which feed 21 is fed through depolymerization unit 20. the invention pertains. One preferred manner of feeding waste 21 is by The present invention surprisingly produces means of an auger internal to CDR unit 20, but from nylon 6 carpets, e-caprolactam which contains is other means for feeding the waste, such as a only those impurities derived from nylon 6. Al- conveyor belt or gravity feed, should be readily though it is preferred that most of the poly- apparent. propylene and latex or other non-nylon materials In CDR unit 20, a depolymerization catalyst is are separated by mechanical means, it is not es- injected. Preferably, the catalyst is injected down- sential. Where mechanical means are used there is 20 stream from where waste 21 is fed into de- much less by-product from depolymerization and polymerization unit 20. One suitable depolymeriza- the reclamation of e-caprolactam is easier. tion catalyst is phosphoric acid, which is preferably The process of the present invention is sche- provided at a rate to make the acid concentration in matically illustrated in FIG. 1. Preferably, in the first the reactor from 1%-10%, more preferably from step, carpet in strips or pieces is fed to separator 25 5%-7%. Phosphoric acid can be recovered via the 10, in which the carpet is mechanically reduced to reactor waste. Other depolymerization catalysts can a smaller size. A large portion of any non-caprolac- also be used, such as boric acid and phosphate tam materials, including latex, jute and poly- salts. propylene may be removed in the separator by Superheated steam, preferably between about shredding, tearing, grinding, or other mechanical 30 1 00 to about 250 °C, is provided to CDR unit 20. action. Non-volatile waste 11 removed in separator Preferably, the steam is provided further down- 10 is separated from the nylon 6. Waste 11 is stream than the depolymerization catalyst to help routed away and may, optionally, be directed to distill lactam volatiles as they are formed. It may power house 15. At power house 15, the waste is be added at a rate to give a condensate of up to used to produce energy. Several separator compo- 35 about 20% lactam in the distillate. But more or less nents suitable for use in the present invention are steam can be added depending on the amount of available from Schirp Corporation as Type 75, auxiliary heat added to the CDR by other means, Type 38CIII, Type 58, Type 38CII, Type 66, Type e.g. electrical resistance heat to the wall of the 71, Type 66-L, Type 57, Type 57S500, Type 64, CDR. and Type 62C. 40 The depolymerization reactor is preferably Nylon 6 (12) obtained from separator 10 is then maintained at a temperature between about 230 ° C fed to a continuous depolymerization reactor (CDR) and about 325 ° C, more preferably between about unit 20. A thin film evaporator can be used for 250 °C to 280 °C. The superheated steam volatil- depolymerization. Luwa Corporation is one source izes caprolactam and other volatile compounds out for such evaporators. It is also possible to feed 45 of the melt as these compounds are formed to carpet directly to the CDR, bypassing the separator produce distillate 22. step. This is shown in FIG. 2 where carpet 24 is Distillate 22 is then passed through fractionat- fed directly to unit 20, optionally after combination ing column 25, where water and caprolactam are with solid waste 13. The rest of the process is fractionated from other non-aqueous volatile sub- substantially as shown in FIG. 1 so that the refer- 50 stances, for example, styrene. Nonvolatile residue ence numbers are the same. 23 from CDR unit 20 may, optionally, be routed to The following description of depolymerization power house 15 as a further fuel supply. Styrene relates to a CDR. However, the continuous de- produced from fractionating styrene and other non- polymerization reactor depolymerization process aqueous volatile distillates from water and aqueous can be carried out with a batch reactor or other 55 distillates such as e-caprolactam from the aqueous suitable non-continuous reactor. The continuous re- lactam are optionally routed to power house 15 for actor is preferred mostly because the process does fuel. Styrene may optionally be collected for pu- not have to be interrupted to remove nonvolatile rification and reused. Also, the residue from de-

3 5 EP 0 522 235 A1 6 polymerization will contain a high concentration of feed of a power generator. The emissions of the phosphoric acid when phosphoric acid is used as generator upon burning the solids contain P2O5, the reaction catalyst. The combustion from residue which is reacted with water to regenerate phos- 23 in power house 15 could allow recovery of the phoric acid. phosphoric acid for reuse. 5 The distillate is passed through a fractionating After fractionation, aqueous lactam-containing column where non-aqueous volatiles are removed stream 26 is subjected to oxidizing agent 30 to and routed to the power generator. The fractionated oxidize residual impurities which were not removed aqueous phase is treated with 1-2% KMnO+ at by the fractionation column to compounds which about 40-50 0 C. Water is removed by evaporation can be more easily separated in the subsequent 10 to concentrate the oxidized aqueous phase. After process steps. Oxidizing agent 30 is preferably vacuum distillation, nearly pure e-caprolactam is potassium permanganate, preferably provided at obtained which is suitable for blending with virgin ° ° ° about 25 to about 75 , preferably at about 40 C, lactam and repolymerization. but other oxidizing agents are also useful. For example, H2O2, K2Cr2 07, sodium or potassium 15 EXAMPLE 2 hypochlorites, perchlorites, and perboric acid are useful. When the oxidizing agent is potassium per- The procedure of Example 1 is followed except manganate, it is preferably supplied at about 1-5 that the Schirp separator is bypassed. The carpet wt. % of the caprolactam but more may be used containing nylon 6 is charged directly, after heat- depending on how impure the lactam may be. For 20 ing, to the thin film evaporator. Nearly pure e- example, more potassium permanganate is re- caprolactam is obtained which is suitable for reuse quired for more impure lactam. Manganese dioxide in making nylon 6. may be filtered out as a by-product of the oxidative treatment. EXAMPLE 3 The oxidized aqueous caprolactam is then con- 25 centrated when subjected to concentration step 31 . 108 grams of nylon 6 carpet, backed with Concentration is preferably accomplished by evap- CaC03 filled latex and polypropylene, is charged to oration at elevated temperature of the water, op- a 1000 ml three-neck round bottom flask with 6 ml tionally under reduced pressure. of 85% phosphoric acid. Superheated steam is After concentration, concentrated e-caprolactam 30 injected continuously during the 45-minute reac- stream 32 is fed to a vacuum distillation unit for tion. The vapor temperature of the reaction is additional purification The distillation preferably 250 °C - 300 °C. A distillate of 1065 ml is con- takes place at about 100°C to about 150°C under densed and collected. The distillate contains 1.9% a reduced pressure of less than about 20 mm Hg e-caprolactam. A small quantity of non-aqueous using a thin film evaporator. Epsilon-caprolactam 35 phase is separated from the distillate. The remain- 36 suitable for fiber production is provided after ing aqueous phase is treated with 2% KMnO+, at vacuum distillation Epsilon-caprolactam 36 is useful 40 0 C - 50 0 C for 2 hours. The water is removed by for all common uses of e-caprolactam, including evaporation to produce solid e-caprolactam. The repolymerization to form nylon carpet fiber. solid e-caprolactam is distilled under about 1 mm The invention will be described by referring to 40 Hg to yield nearly pure e-caprolactam. the following detailed examples. These examples are set forth by way of illustration and are not Claims intended to be limiting in scope. 1. A process for the recovery of e-caprolactam EXAMPLE 1 45 from nylon 6 carpet, comprising: a) providing a carpet made from nylon 6 108 grams of nylon carpet backed with poly- fibers and having a non-nylon 6 backing to propylene and latex are fed to a Schirp separator. a separator to prepare scrap containing ny- Much of the backing material is removed and lon 6 and a first waste portion; passed to the feed of a power generator. The nylon 50 b) feeding the scrap from the separator to a portion is charged to a thin film evaporator with depolymerizing reactor where the scrap is 30.0 mL of 85% phosphoric acid. Superheated subjected to a depolymerization catalyst, steam is injected continuously during the 45 minute temperatures of at least the melting point of reaction. The vapor temperature in the evaporator nylon 6 and superheated steam to produce is 250°C-300°C. The distillate collected (1000 mL) 55 an e-caprolactam containing distillate and a contains about 2.9% e-caprolactam (as determined second waste portion; by GC) and thus gives a crude yield of about 56%. c) separating e-caprolactam in the distillate The solids from the reactor are passed to the from other volatiles therein; and

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d) purifying the e-caprolactam obtained after about 230 ° C and 325 ° C to produce volatile separating. monomers and a first waste portion; d) separating the volatile monomers from 2. The process of claim 1 further comprising e) the first waste portion; and routing the first and second waste portions to a 5 e) fractionating the volatile monomers to power generating means as fuel for power yield e-caprolactam and a second waste production. portion.

3. The process of claim 1 wherein said separat- 9. The process of claim 8 further comprising using is by fractional distillation to obtain an w ing the first and second waste portions as feed aqueous fraction and a non-aqueous fraction for a power generating means.

4. The process of claim 3 further comprising h) sending the non-aqueous fraction to a power generating means. 15

5. The process of claim 1 wherein said purifying is by oxidizing the aqueous fraction, concen- trating the oxidized aqueous fraction and distill- ing the concentrated oxidized aqueous fraction. 20

6. The process of claim 1 wherein said feeding is carried out continuously.

7. A process for recovering e-caprolactam from 25 nylon 6 carpet comprising: a) providing a carpet made from nylon 6 fibers and having a backing to a separator to prepare scrap containing nylon 6 and a first waste portion; 30 b) feeding the scrap from the separator to a depolymerizing reactor where the scrap is subjected to a depolymerization catalyst, temperatures of at least the melting point of nylon 6 and superheated steam to produce 35 an e-caprolactam containing distillate and a second waste portion; c) separating e-caprolactam in the distillate from non-aqueous volatiles therein; d) purifying the e-caprolactam obtained after 40 separating; e) routing the first and second waste portions to a power generating means as fuel for power production; and f) sending the non-aqueous volatiles to the 45 power generating means.

8. A process for reclaiming e-caprolactam from nylon 6 carpet comprising: a) providing a carpet tufted with nylon 6 and 50 having a backing containing latex for recycling b) feeding the carpet to a depolymerization reactor; c) subjecting the carpet in the de- 55 polymerization reactor to a depolymerization catalyst present at about 1% to about 10% of the carpet weight at a temperature of

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CO Patent European EUROPEAN SEARCH REPORT )ffice [P 92 10 3184

DOCUMENTS CONSIDERED TO BE RELEVANT Citation of document with indication, where appropriate, Koevani Category] of relevant passages o chum UPPLICATION (Int. Q.S ) IE-A-518 416 (VEREINIGTE ,5,7,8 ILANZSTOFF-FABRIKEN) I08J11/14 the whole document * 7C08L77:00

IHEMICAL ABSTRACTS, vol. 77, no. 20, ,7,8 .3 November 1972, Columbus, Ohio, US; ibstract no. 127211, ;. PETRU ET AL. 'Recovery of caprolactam1 iage 12 ; ! abstract * , CS-A-143 502 IE-A-2 440 243 (DR. ILLING KG ,7,8 IAKR0M0LEKULARE CHEMIE) * ' page 2, line 6 - line 17; claim

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