MXPA98000423A - Procedure for the recovery of caprolactama from waste containing ny - Google Patents

Abstract

The present invention relates to a process for the recovery of caprolactam from waste containing nylon 6 a) by treating a first mixture comprising water comprising nylon 6 with water at a temperature between 200 ° C and 400 ° C to give a second mixture comprising depolymerized nylon 6 components, b) optionally, separating the second mixture from any insoluble waste (carpet) that is present, c) subjecting said second mixture to an extraction with an organic extraction agent to produce a third aqueous raffinate mixture and a fourth mixture of organic phase comprising caprolactam and said extraction agent, d) recovering the caprolactam of said fourth organic phase mixture by distillation, e) recirculating said third aqueous raffinate mixture to step (a), further characterized in that the Caprolactam concentration in the second mixture is 5-35% by weight and that the extraction agent used in an alkyl phenol that has a melting point that is greater than that of caprolacta

Description

PROCEDURE PORO Lfl RECOVERY OF CflPROLflCTfÍflfl ñ PTRACT OF WASTE CONTAINING NYLQN BACKGROUND OF THE INVENTION 1. Field of the invention The invention and the invention relates to a process for the recovery of caprolactane from wastes containing nylon that have been converted into depollution products. After de-polishing, the caprolactane is extracted from the de-pollinated products using alkyl phenolic solvents. 2. - Description of the Related Art Wastes containing nylon, specifically waste carpets, simultaneously represent not only an environmental problem but also a source of potential value if useful materials can be recovered from them. For example, many scrap carpets contain significant amounts of nylon, and in particular, nylon 6 or polycaprolactane. Procedures have been developed for the de-polishing of waste nylon 6 to its valuable raw material, caprolactam. However improvements are still needed in these procedures. The de-polishing of nylon 6 is normally carried out in the presence of water. Although caprolactane is formed by despolpaneption, the depolipnection reaction is an equilibrium reaction and at least a part, and often significant amounts, of cyclical and linear caprolactane oligorneros are also formed. However, pure caprolac is ultimately desirable, but the purification procedures for separating the oligorneros from the mononer can be complicated and expensive. Once separated from the monornero, the caprolactane oligonuclears can be recited for further depopulation. Therefore, in spite of the usefulness of the depolarization of the known nylon 6 and caprolactane screening methods, improved methods are still needed to make said procedures economically attractive. Ideally, complete removal of one or more purification steps is desirable. The extraction is a method to separate the caprolactane from complex mixtures that result from the de-polishing of the nylon waste. 6. For the extraction to be effective, the solubilities of the different components must be carefully considered. The patent of E.U.fl. No. 5,359,062 discloses that nylon 6 can be depolymerized in the presence of water and alkali metal hydroxide to produce aqueous solutions containing caprolactane and oligomer. After despolirnepzación, the caprolactarna can be separated by distillation or extraction. In order to have an economically attractive procedure, it is essential to separate the oligoinero from La caprolactama rnonornenca and recycle the oli gomeros. However, the distillation route suffers from the disadvantage that the distillation residue may not be easily recyclable due to the formation of tar. Other circumstances that prevent recycling or waste include the repolirnection and solidification of oligomers. The extraction route suffers from, among other things, the need for large quantities of an extra-race agent Lon. For example, more than twice the amount of the extraction agent compared to the amount of the aqueous solution containing caprolactane, may be necessary. Moreover, although this patent description mentions the formation and separation of the oligomer, it does not describe or suggest solutions for the particular problem of removing cyclical or linear oligorneros from caprolactena. The extraction agents described in the U.S. patent. No. 5,359.06? they include benzene, toluene and xylene, all of which are relatively low boiling solvents compared to caprolactone. During the extraction, these solvents extract not only non-cyclic caprolact olymphores, but also non-cyclic caprolact. After extraction, these solvents can be removed from the caprolactane by distillation. Nevertheless, then an additional distillation step is needed to separate the caprolact from the cyclic olí gomeros. Therefore, following the caprolactan extraction step, two distillations are still required to obtain the caprolactam pur. The patent of E.U.A. No. 4,013,640 describes an amide purification process that includes the purification of caprolactide. However, this patent does not even refer to the problem of removing olí gomeros and, in particular, cyclical oligomers of the caprol ctarna. Even this patent publication does not describe caprolactarine purification procedures that follow the depolarization of the product. nylon 6. Instead, it describes the extraction of caprol ctarna from unspecified industrial wastewater. The impurities described in these wastes are not impurities of a similar chemical nature as the amide that will be dissolved. The extraction is carried out using alkyl phenol type solvents which have higher boiling points than caprolactene. The extraction step is followed by vacuum distillation of the extract to obtain caprolactam. This distillation can be hindered by the presence of oligoiners. However, the patent of E.U.A. Mo. 4,013,640 neither suggests nor discloses that alkyl phenol extraction agents would be useful for separating caprolactane oligomers from caprolactena.

BRIEF DESCRIPTION OF THE INVENTION The objects of the present invention include improving the efficiency of the caprolactane purification process by following the despollution of nylon, and in particular of nylon 6. An additional object is to improve the ability to separate oligoes from La caprol ct rna. An additional object is to improve the economy in the recycling of waste carpets. These and other objects are achieved by a process comprising the combination of the steps of: a) treating a first mixture comprising nylon 6 with water at a temperature between about 200 ° C and about 400 ° C to produce a second mixture comprising nylon 6 components, filled, where the second mixture contains caprolactone at a concentration between about 5% by weight and about 35%; • b) optionally separate moluble materials from the second rne c1 a; c) extracting the second mixture with an extraction agent to produce a third mixture of aqueous refined material and a fourth organic phase mixture comprising caprolactane and the extraction agent, in which the extraction agent is an alkyl phenol having an boiling point higher than that of caprolactam; d) recovering caprolactane from the fourth organic tase mixture by distillation; e) recycling the third mixture of aqueous refined material to step (a).

The advantages of the present invention include improved efficiency in the caprolactin purification processes, particularly in the separation of the caprol-like oligomers.

DESCRIPTION OF THE INVENTION The present invention is effective for treating waste mixtures comprising nylon 6. In addition to nylon 6, other types of polymers, nylons and polyamides that may be present in the waste mixture include polypropylene, polyethylene terephthalate, jute, SBR, wool, cotton and nylon h & The composition of the waste mixture is not strictly limited, as long as the advantages of the present invention can be achieved. The waste mixture, for example, can be relatively homogeneous or heterogeneous. In particular, the present invention can be used to process industrial and post-consumer carpet wastes. The carpet is preferably mechanically ground first by, for example, milling, chopping, tearing or cutting with knives and / or cutters. The largest part of the non-polyamide components of the carpet may contain, for example, L tex not filled, latex filled with CaCO3, jute and polypropylene. Such non-licking components can be separated from the polyarynide or nylon 6 component of the carpet in one or more separation steps before the depolymerization treatment at elevated temperatures.

Alternatively, the fob parts can also be supplied directly to the reactor for de-polimerization. The inventions produce good results with about 5% by weight and about 50% by weight of polyamide in the reactor, apart from other components (such as those mentioned above). The waste mixture that has nylon 6 is treated with water at elevated temperature and, if desired, at elevated pressure to carry out the depolymerization of nylon 6. In general, de-polishing is carried out with a quantity of water. so that, after depopulation, an aqueous solution containing at least about 5% by weight to about 35% by weight, and preferably less than about 25% by weight of caprolactane relative to the amount of water is obtained. The temperature at which the depolymerization process can be carried out is not particularly limited, but is generally between about 200 ° C and about 400 ° C, and preferably it is about 250 ° C and approximately 350 ° C. The depopulation pressure is also not particularly limited, but it can be, generally less than about 200 bars, and preferably less than about 130 bars. For example, pressures of approximately 100 bars or 10 MPas at approximately 300 ° C are contemplated When the depolymerization is carried out for about 1 hour under these conditions, a virtual equilibrium is reached and the caprolactane ratio: ol i gomero is generally about 4: 1 by weight, however, the invention also contemplates amounts of oligorier of up to 35% by weight with respect to caprolactane.The amounts of oligornero formation make recycling essential for economic reasons. preferably, without a catalyst or accelerator, however, to control the rate and selectivity of the reaction, catalysts or despoling accelerators can also be used if desired. Suitable catalysts include the Le? Is, such as, for example, AI2O3, S1O2; and Brensted acids, such as, for example, H3 O4, paratoluensulfon acid, for-imco acid, H3DO3 or salts thereof, for example, ammonium salts. Base catalysts such as, for example, NaOH, KOH or a2C? 3 can also be used. These compounds are optionally present in an amount of about 0.1 wt% to about 20 wt%, and preferably between about 0.1 wt% to about 5 wt% relative to the pol lide. After de-polishing, a mixture comprising caprolactane and other despolbed products such as linear and cyclic olí gomers is formed. The mixture will normally contain insoluble material, although as an alternative, substantial amounts of more soluble material will not be present in some cases if the insolub materials are removed before depopulation. The most soluble materials include jute, CaC 3 and polypropylene. Prior to the extraction step, measurements are preferably taken so that virtually no solid or undissolved waste is present in the aqueous solution. This can be achieved by methods known to those skilled in the art including filtration or centrifugation. Alternatively, the separation can be carried out by separating the aqueous solution with caprolactaine as an aerosol. This means that the debris imbalance step (a) and the separation step (b) can be separate or simulated steps. The caprolactarine extraction step is carried out with a phenol type extraction agent. The amount of alkyl phenol is not particularly limited, as long as the advantages of the present invention can be achieved. For example, it is believed that the upper limit is not critical, but it depends on the economy of the procedure. In general, the amount of alkyl phenol will be less than about one and one-half times the volume amount of the aqueous solution. Preferably, about 5 to about 100 volume% of alkyl phenol is used in relation to the amount of aqueous solution. Very good results are obtained if approximately 30 to approx. 80% by volume alkyl phenol is used in relation to the amount of aqueous solution a. The extraction agent may be an alkyl phenol having a boiling point which is higher than the boiling point of caprolactane, which is from? 72 ° C to 1 bar. The alkyl phenols have a high boiling point at atmospheric pressure. Therefore, the boiling points are advantageously compared at reduced pressures of, for example, L.3 kPa (10 mrn Hg). Caprolactan has a boiling point of 140 ° C to 10 mm Hg, while dodecyl phenol, for example, has a boiling point of 190 ° C at that pressure. It is preferred that the boiling point of the alkyl phenol be more than about 5 ° C and in particular, about 15 ° C higher than the boiling point of the capolactam at 1.3 kPa (10 nm Hg). The upper limit for the boiling point of alkyl phenol is about 4n ° C. The alkyl phenol is preferably non-azeotropic with caprolactane. Alkyl phenol mixtures can be used. The alkyl component of the alkyl phenol may, for example, be an alkyl component of C 6 -C 2 S, and preferably an alkyl component of C -C 15. Alternatively, the alkyl component may consist of one or more alkyl groups which together contain 6 or more carbon atoms. The alkyl component consists preferably of an aliphatic hydrocarbon or IL aromatic, and in particular, aliphatic hydrocarbon. Examples of specific alkyl phenol compounds include dodedl phenoL, octyl phenol, nonyl phenol, n-hexyl phenol, 2,4-d-butyl butyl phenol, 2-methyl-4, b-d? -ter-but? l phenol, 3-et 11-4, 6-di-t-butyl-11-phenol, 2,4-b-tri-tert-butyl phenol, and mixtures of any of these. The Patent of E.U.A. No. 4, 013,640 discloses additional alkyl phenols, the full disclosure thereof is incorporated herein by reference. The extraction step is carried out by - Generally at a temperature which is higher - than the melting point of the alkyl phenol. The extraction temperature may be generally between about 50 ° C and about 220 ° C, and preferably, about about 0 ° C and about. L70 ° C. In general, the extraction temperature is selected so that the maximum amount of solid non-nylon products can be cut separately. If, for example, polypropylene is present in the mixture to be extracted, the temperature is preferably lower than the melting point of the waste polypropylene. Therefore, in this case, the extraction temperature is preferably lower-about 130 ° C. The pressure during the extraction step is generally not critical and may be, for example, between about 1 barium and about 20 baths, and preferably, about 1 barium and about 5 bars.

The extraction step produces an orgamca phase containing caprolactam which, in general, contains up to 50% by weight of caprolact and between about 0 and approximately 15% by weight of water. The amount of cyclic oligomers in the organic phase extract is generally less than about 10% by weight, and preferably less than about 5% by weight, and the number of linear oligorneros is generally less than about 1% by weight. weight, and preferably less than about 0.1% by weight. After extraction and removal of the extraction agent, a mixture of aqueous raster remains. However, even after having extracted the largest amount of caprolactane, the aqueous solution still contains some caprolactane. In general, the remaining caprolactane concentration is less than about 2% by weight, and preferably less than about 1% by weight. After extraction, the aqueous solution also still contains caprolactan oligomers, including mainly linear oligomers, soluble polymers, or mixtures thereof. The oligomers and polymers of caprolactam can be precipitated partially during the extraction of caprolactane, resulting in a suspension formation. If desired, additional water can be added to the suspension to form a solution once more. The aqueous solution or suspension is recirculated to the depollution step (a). If the rafmate still contains solid, waste that is not nylon, said scrap < It would preferably be separated in advance by means of filing. After extraction, caprolactam and rosidual water can be distilled from the organic phase. After this distillation, the cyclic OILgomeros containing alkyl phenol can be used once in other extraction operations, if required after the purification of the extraction agent. In this distillation step, the required purification of caprolactam is partially achieved directly since all the heavy components remain behind in the alkyl phenol. The liquid caprolactane, after distillation outside the alkyl phenol, which contains between about 5 to about 50% by weight of water, is subsequently purified and / or concentrated. This results in a caprolactam of a quality that is comparable to that of caprolactena virgin. In a preferred embodiment, the purification of the extracted and distilled caprolactam comprises the following steps: 1) ion exchange 2) hydrogenation 3) distillation of water and other light components 4) distillation of caprolactam. The order of the ion exchange step (1) and step L4 of hydrogenation (2) can be inverted if desired. This purification procedure results in a caprolactam of very good quality. In a second preferred embodiment, the purification of the distilled caprolactam is achieved by crystallization in a concentration process. The crystallized caprolactam resulting from the concentration is usually purely thin to be used directly. After crystallization, it may be necessary to purify the mother liquor, for example by recirculating it to the aqueous solution before extraction with the alkyl phenol. The mother liquor can be purified, for example, by distillation. The inventions will now be elucidated by the following non-restrictive examples.

EXAMPLES EXAMPLE 1 46.4 Vq of water phase were added to L6.8 Lg of carpet pieces having a size of approximately 1-5 crn2 (38% by weight of nylon 6) to give a heterogeneous mixture. The water phase was obtained from the extraction (the raffinate mixture) and had approximately 3.4% by weight of nylon 6 linear oligorneros. The depolymerization of nylon 6 was carried out in a depolymerization reactor at a temperature of 300 ° C. and at a pressure of 100 bar-ios during one hour to give a mixture of suspension. The resulting suspension was cooled and no longer subjected to pressure, so that part of the water evaporated (100 ° C, 1 barium). After this, the solid particles were removed from the suspension by filtration at a temperature of 100 ° C to give a filtered mixture. This mixture had approximately 31 kg of water, 6.3 kg of caprolactam and L.6 kg of caprol ctarna oligomeres. The oligorneros were linear oligorneros of 1.44 kg and cyclical olí gomeros of 0.16 kg. This mixture was extracted with 25 kg of dodecyl phenol at 100 ° C, so that almost all of the cyclical and caprolactam olygotes and 1.3 kg of water were present in the resulting organic phase mixture. The resulting raffinate mixture was fed back to the reactor hydrolysis-depopulation section. This raffinate contained the linear oligoes that were present in the water phase after de-polimerization and extraction. The caprolactane and water were distilled from the dodecyl phenol which resulted in a caprolactane flow containing 18% by weight of water. This flow (1 barium, 55 ° C) was treated with an exchange of ions and then subjected to hydrogenation. The water and light components were distilled at 0.2 barium and 56 ° C, after which the pure caprolactarine was recovered through distillation at 5 bar and 116 ° C. Although the present invention has been illustrated by means of several preferred embodiments, one skilled in the art will realize that changes, modifications and improvements can be made at the same time remaining within the scope and spirit of the present invention. All references disclosed herein are incorporated herein by reference.

Claims (1)

NOVEDfiD OF THE INVENTION CLAIMS 1. - Procedure for the roeuperación of caprolactarna from waste containing nylon 6 a) by treating a first mixture that compresses water comprising nylon 6 with water at a temperature between 200 ° C and 400 ° C to give a second mixture which comprises nylon 6 components depolymerized, b) optionally, separating the second mixture from any more soluble waste (carpet) that is present, c) subjecting said second mixture to an extraction with an organic extraction agent to produce a third mixture aqueous raffinate and a fourth organic phase mixture comprising caprolactane and said extraction agent, d) recovering the caprolactam of said fourth organic phase mixture by distillation, e) recirculating the third aqueous raffinate mixture to step (a), further characterized in that the concentration of caprolactam in the second mixture is 5-35% by weight and that the extractant used in an alkyl phenol having a melting point which is greater than that of caprolactena. 2. Method according to claim 2, further characterized in that step (a) is carried out at such a pressure that the system is in the liquid phase. 3. - Process according to one of claims 1, 2, further characterized in that the caprolactin is extracted with 5-100% by volume of alkyl phenol relative to the amount of said second mixture. 4. Method according to one of claims 1-3, further characterized in that the extraction step (c) is carried out at a temperature of 5u-220 ° C and at a temperature of 1-20 bar. 5. Process according to any of claims 1-4, further characterized in that the melting point of the alkyl phenol is more than 15 ° C higher than the melting point of capr olactarna at 1.3 kPa (10 mm Hg). &- Method according to any of claims 1-5, further characterized in that the alkyl component of the alkyl phenol contains 6-25 carbon atoms. 7. Method according to claim 6, further characterized in that the alkyl component of the alkyl phenol contains 9-15 carbon atoms. 8. Method according to claim 6 or 7, further characterized in that the alkyl phenol used is dodecyl phenol, octyl phenol, phenol name, n-hexyl phenol, 2,4-d-sobutyl phenol, 2-methyl. ? l-, -d? -ter-but? 1 phenol, 3-et? I-4,6-d? -ter ~ but? L phenol, 2, 4, 6-tp-ter-but? L phenol, and mixtures of any of these. 9.- Procedure of conformity with any of

1. 9 Claims L ~ 8, further characterized in that the distillation in said recovery step (d) is a distillation of caprolactam, water and light components of the organic phase to produce a fifth mixture comprising caprolactans, said fifth mixture being subjected to ( i) exchange of ions and hydrogen, or hydrogenation and ion exchange and subsequently (11) distilling the light components and (m) finally recovering caprolactane by distillation. 10. Process according to any of claims 1-8, further characterized in that the distillation in said recovery step (d) is a distillation of caprolactane, water and light components of said organic phase to produce a fifth mixture that it comprises caprol ctama, said fifth mixture being concentrated to realize crystallization of caprolactane and finally separating the caprolactene cri talizada.