MXPA97004285A - Obtaining caprolactma through hydrolytic lixiviation of policaprolactamafund - Google Patents

Abstract

The present invention relates to a process for obtaining caprolactam from polymers containing caprolactam in the presence of superheated water, which comprises putting polymers containing the repeating unit - [- N (H) - (CH2) 5-C (O) -] - or mixtures consisting essentially of 40 to 99.99% by weight of a polymer containing the repeating unit - [- N (H) - (CH2) 5-C (O) -], from 0.01 to 50% by weight of additives selected from the group consisting of inorganic fillers, pigments and organic and inorganic dyes, from 0 to 10% by weight of organic or inorganic additives, from 0 to 40% by weight of polymers not containing polyamide, and from 0 to 40% by weight 60% by weight of polyamides, with the exception of polycaprolactam and copolyamides prepared from caprolactam, with water superheated to 280 to 320 ° C and 7.5 to 15 MPa and a weight ratio of water to polymer containing the repeating unit - [-N (H) - (CH2) 5-C (O) -] - from 5: 1 to 13: 1 and in a reaction time of less than 3 h The condition that the reaction mixture consisting essentially of water and the polymer used or the mixture used does not contain a gas phase under the conditions of the hydrolysis.

Description

OBTAINING CAPROLACTMA THROUGH HYDROLYTIC LEACHING FROM FLOWED PO-LICAPROLACTAMA The present invention relates to an improved process for obtaining caprolactam from polymers containing prolactam in the presence of superheated water. The present invention also relates to an apparatus for carrying out the novel process and to the use of the novel process and of the novel apparatus for recycling waste that has polycaprolactam. U.S. Patent 4,605,762 describes a continuous process for the hydrolytic depolymerization of condensation polymers, in which waste material which is obtained during the production of articles from densation polymers is subjected to aqueous hydrolysis at 200 [deg.] C. at 300ºC and at a superatmospheric pressure of at least 15 atmospheres in a special room. In the manifested process, the hydrolysis was carried out using steam under high pressure. However, f drolysis of condensates that may contain fillers, such as glass fibers, or blends is not described. U.S. Patent 3,939,153 discloses a process for the preparation of caprolactam from polycaprola tama, in which a melting of the polymer and superheated vapor continuously bring each other into contact with each other and at 315 [deg.] C. The disadvantage of this process is a low yield of no more than 0%. An object of the present invention is to provide a process for obtaining caprolactam from polymers that contain, as a repeating unit, - / ~ -N (H) - (CH2) 5-C (0) -_ 7-, or of mixtures containing said polymers, whose process provides superior yields of caprolactam in the absence of a -catalyst. It is also intended to provide a process that makes it possible to use wastes containing polyprolactam-which contain inorganic fillers to obtain caprolactam without having to accept reduced yield. It has been found that this object is achieved by a process to obtain caprolactam from polymers containing caprolactam in the presence of superheated water, carrying the polymers containing the repeating unit - / ~ -N (H) - (CH2) 5-C (0) -7- or mixtures consisting essentially of 40 to 99.9% by weight of a polymer containing the repeating unit - / ~ -N (H ) - (CH -) - C (0) - 7-, from 0.01 to 50% by weight of additives selected from the group consisting of inorganic, organic fillers and inorganic pigments and dyes, from 0 to 10% by weight of organic and / or inorganic additives, from 0 to 40% by weight of polymers containing no polyamide, and from 0 to 60% by weight of Doliamides, with the exception of polycaprolactam and copolyamides prepared from caprolactam, in contact with superheated water at 280 to 320 ° C and 7.5 to 15 MPa, in a weight ratio of water to polymer containing - the repetitive unit - / ~ -N (H) - (CH2) 5-C (0) -7- from 5: 1 to 13: 1 and for a reaction time of less than 3 hours, with the proviso that the reaction mixture, consisting essentially of water and the polymer used or the mixture used, does not contain phase -gassing under the conditions of the hydrolysis. We have also found an apparatus to carry out the novel process and the use of the novel process and the apparatus -novety to recite waste containing polyprolactam. According to the invention, the starting materials used are polymers containing the repetitive undiad - / -N (H) - (CH2) 5-C (0) -7- or are mixtures consisting essentially of from 40 to 99.99, preferably from 70 to 90% by weight of a polymer containing the repeating unit - / -N9H) - (CH2) 5-C (0) -7- from 0.01 to 50, preferably from 4 to 10% by weight of additives selected from the group consisting of inorganic fillers, organic and inorganic pigments and dyes, from 0 to 10, preferably from 0.1 to 5% by weight of organic and / or inorganic additives, from 0 to 40 , preferably from 5 to 25% by weight of polymers not containing polyamide, and from 0 to 60, preferably from 10 to 30% by weight of poiiamides, with the exception of poly-caprolactam and co-polyamides prepared from caprolactam. The polymer used is preferably polycaprolactam having a relative viscosity of 1 to 10, preferably 2.0 to 4.0 (measured at a concentration of 1 g of polymer per 100 ml in 96% strength by weight of sulfuric acid at 25 QC) . It is well possible to use polyprolactam containing oligomers in an amount of 0.01 to 10, preferably 1 to 5% by weight, based on the total amount. In principle, the novel process can also be carried out if oligomers of caprolactam are used instead of polyprol acta a. The copolyamides obtained from caprolactam and other polyamide forming monomers, for example salts formed from dicarboxylic acid, such as adipic acid, sebacic acid and terephthalic acid, and a diamine, such as hexamethi lendia i-na and tetrameti lendi amine, preferably salt AH (obtained from adipic acid and hexamethi lend i amine), and lactams, such as laurolac-tama, can also be used. Observations to date have shown that all polycaprolactams can be converted to caprolactam by the novel process, for example, also a polyprolactam which was prepared in the presence of mono- or polycarboxylic acids or amines, which act as regulators. chain, for example acetic acid, propionic acid, benzoic acid, Alcandicarboxylic acids of C »-C1Q, such as adipic acid, pimelic acid, suberic acid, acelaic acid, sj bacic acid, undecanedioic acid, dodecanedioic acid and mixtures of the same, cycloalkanedicarboxylic acids of Cr-Cn, such as - cyclopentan-1,3-dicarboxylic acid, cyclohexane-1,4-dicarboxylic acid and mixtures thereof, benzene and naphthalenedicarboxylic acids which can carry up to two sulfo groups, including the corresponding non-alkali metal salts, and whose carboxyl groups are not adjacent such as terephthalic acid, isophthalic acid, naft acid alen-2, 6-dicarboxy 1 ico, soft 5-sulfoi acid and its lithium sodium salts, and mixtures thereof, and 1,4-piperazindi-C, -Cfi-acaricarboxylic acids, such as 1,4-piperazindiacetic acid, 1,4-piperazindipropionic acid, 1,4-piperazindibutic acid, 1,4-piperazindipentanoic acid, and 1,4-piperazindihexanoic acid. The corresponding copolyamides are known to a person skilled in the art and can be prepared by processes which are described, for example, in WO 93/25736, DE-A 14 95 198 and DE-A 25 58 480. The observations to date have It has been shown that all fillers, such as glass fibers, calcium carbonate and talc, which are usually used in the polyade composition can be used as inorganic fillers. Observations to date have shown that all pigments and dyes, such as titanium dioxide, cadmium sulfide, iron oxides or carbon dioxide, which are usually used to color polyamides, and conventional spinning dyes, such as Complexes of chromium or copper complexes can be used as inorganic and organic pigments and dyes. Conventional stabilizers and antioxidants, heat stabilizers and UV stabilizers, antistatic agents and flameproofing agents can be used as organic and inorganic additives. Antioxidants and heat stabilizers, for example, are sterically hindered phenols, hydroquinones, phosphites and derivatives and substituted members of this group and mixtures of compounds, as well as copper compounds, such as copper (I) iodide and acetate of copper (II). Examples of UV stabilizers are substituted resorcinols, silicilates, benzotriazoles, benzophenones and compounds of the HALS (hindered amine light stabilizer) type, and manganese (II) compounds are also suitable for this purpose. The conventional substances, for example, polyalkylene oxides and derivatives thereof, can be used as antistatic agents. The conventional phosphorus and nitrogen / phosphorus-containing compounds, such as esters of phosphoric acid, or phosphorous acid, and of phosphonic and phosphinic acid and tertiary phosphines and phosphine oxides, such as triphenyl phosphonium oxide, phosphonyl chloride, amides of Phosphoric esters, phosphoramides, phosphine, midas, trisaziridinium lphosphine oxide and trachis chloride (hydroximeti 1) phosphonium, can be used as flame-proofing agents. Conventional thermoplastic engineering polymers, such as polymers based on ethylene, propylene and styrene, and copolymers thereof with butadiene and acrylonitrile (ABS plastics), can be used as polymers that do not contain polyamide. Suitable polyamides with the exception of polycaprolactam and copolyates prepared from caprolactam are, for example, polyamide 66, polyamide 610 and polyamide 46. Preferred starting materials are polyprolactam containing inorganic fillers, in particular fibers of glass, and to be discarded, and wastes obtained in the production of polyacryl actama and in the processing thereof to provide filaments, films and cast or extruded parts, and shaped utility articles, such as films , packaging, fabric, carpet fibers, filaments and extruded parts, which are going to be discarded. According to the invention, the above-prepared polymers or mixtures are contacted with superheated water, which is at 280 to 320 ° C, preferably 295 to 310 ° C, preferably 300 to 30 ° C, and 7.5 ° C. to 15, preferably 10 to 15, particularly preferably 10 to 12 MPa, the weight ratio of water to the polymer containing the repeating unit - / ~ -N (H) - (CH2) 5-C (0 ) 7- being selected on the scale from 5: 1 to 13: 1, preferably from 8: 1 to 13: 1. In addition, in accordance with the invention, the reaction time is selected to be less than 3 hours, preferably 15 to 90, particularly preferably 30 to 60 minutes. By selecting the conditions of the hydrolysis within the stated values so that the reaction mixture, consisting essentially of water and the polymer used or the mixture used, does not contain gas phase is essential for the success of the novel process. Observations to date have shown that gaseous fractions in the reaction mixture lead to lower yields. The reaction mixture obtained after the hydrolysis can be worked in the usual way, for example by removing caprolactam from any solids present, such as glass fibers, fillers, pigments, etc., and feeding it to an additional purification step, preferably a distillation The caprolactam obtained by the novel process, of course, can be converted back into polyprolactam or into corresponding copolymers and mixtures. In a preferred embodiment, the aforementioned polymers or mixtures are melted by heating at 250-350 ° C, preferably 290-300 ° C. The resulting melt is subsequently subsequently compressed, preferably simultaneously, at a pressure of from 7.5 to 30, preferably from 10 to 15 MPa, the pressure being advantageously selected so that it is slightly above the pressure of the superheated water. In this case, the fusion (fusion A) is subsequently brought into contact, in order to prevent the superheated water from flowing back into the melting apparatus 91). In a particularly preferred embodiment, the melting process and the compression are carried out simultaneously in a conventional extruder as the melting apparatus (1). The superheated water and the melt (melt A) compressed in the melting apparatus (1) are then contacted in a hydrolysis area (2). In accordance with the invention, the temperatures and the pressure scale are selected so that no gaseous phase is present, in particular during hydrolysis - in the hydrolysis reactor. Here, temperatures are generally from 280 to 320 ° C, preferably from 290 to 31 ° C, particularly preferably from 300 to 30 ° C, and the pressure, as a rule, is from 7.5 to 15, preferably from 10 to 10 ° C. at 12 MPa. The residence time in the hydrolysis reactor depends essentially on the amount of water added, based on the repeating unit _ N (H) - (CH2) 5-C (0) -7-, and is usually 15 to 90, preferably 30 to 60 minutes. Pressure resistant tubes can be used as a hydrolysis reactor (2), and the reactor may or may not be provided with diverters, such as Sulzer SMX type mixing elements (cf Chem. -Ing, -Tech., 62 (1990)). 650-654). In a preferred embodiment, a tube reactor having an L / D ratio of from 20: 1 to 150: 1, preferably from 50: 1 to 120: 1, is used. In a preferred embodiment, the mixture discharged from the hydrolysis reactor is fed to a downgoing apparatus (3) - which may be a single-stage or two-stage apparatus, essentially forming two phases as a result of the pressure drop at 0.1-1.6, preferably 0.1-0.4 Pa: a gaseous phase B, which - essentially contains water and may contain small amounts of other volatile substances, such as caprolactam and traces of volatile amine compounds, and a non-gaseous phase C which it contains essentially the main quantity of caprolactam 1 i x_ viada and, depending on the mixture used, may contain additives, such as glass fibers, pigments, additives, etc. The gaseous and vapor-containing phase B is usually separated from the non-gaseous phase C in a falling apparatus (3), the water being preferably separated in an appropriate apparatus, for example in a distillation apparatus or a stage. of evaporator, and then mixed with the water that is introduced into the hydrolysis reactor (2) to hydrolyze the polymers or mixtures.

The non-gaseous phase C, which as a rule contains water and may contain additives, organic and inorganic additives, polymers which do not contain polyamide and polyamides, with the exception of polyprolactam and copolyamides prepared from caprolactam, and generally contains 5%. at 20% by weight of caprolactam, is fed, in a preferred embodiment, to a separation apparatus (4), in which any insoluble components present, such as additives, for example glass fibers, pigments, other polymers, etc. , they are eliminated. The separation apparatus (4) used can be a conventional filter apparatus, such as a band filter or a backwash tube fixture, or other conventional apparatus that allows continuous or periodic discharge, preferably a low-capacity filter. or a backwashable tube filter. The solution released from the insoluble components can then be worked up by methods known per se, for example by separating the water from the caprolactam by distillation and adding it to the hydrolysis water, similarly to the work of the gas phase B, and feeding the caprolactam to a step of purification, for example the purification step for crude caprolactam in an existing caprolactam plant. Other possibilities, if desired, for purifying the caprolactam obtained according to the invention are described, for example, in EP-A 568, 882 and 570 843. The purified caprolactam is then generally available for further use, in particular for the PREPARATION OF -PA 6. In accordance with the invention, the novel process is used to recycle polycaprolactam-containing wastes such as used carpets, carpet cuts, polyamide 6 -production wastes and polyamide blends which may contain up to 60% by weight of polyamides that were not prepared from caprolactam. The advantages of the novel process over the processes of the prior art are leaching yields of up to 96%, short residence times and minor amounts of solvents and waste requiring treatment and disposal.

EXAMPLES Example 1 0.3 kg / hour of polycapol actama (Ultramid (R *) 'BS 700, having a relative viscosity of 2.7, measured at a strength of 1% by weight of solution in strength of 96% by weight of sulfuric acid at 235C maintained at 270 QC and under a pressure of 20 MPa and 2.7 kg / hour of water maintained at 290 QC and a pressure of 12 MPa were fed to a 3-liter tube reactor (length / diameter ratio 110: 1) The average residence time was 60 minutes After leaving the reactor, the mixture was cooled to 115 ° C and lowered to 0.1 kPa The reaction mixture obtained was analyzed by gas chromatography. -trans in the box below.

Examples 2 to 11 Example 1 was repeated at different ratios of water to polymer and different temperatures. The results are summarized in the table below.

Example table Weight ratio of temperature Pressure Residejp time CaH20 yield: polycaprolactam (MPa) cia (min.) Prolactam (%) 1 10.2 290 12.0 35 75 2 10.6 292 12.0 51 92.5 3 10.0 296 12.0 54 93.6 4 10.4 296 12.0 60 94 5 8.0 300 12.0 70 92 6 8.3 300 12.0 68 90.1 7 11.0 305 12.0 60 96 8 11, 0 300 12.0 55 95.6 9 13.0 300 12.0 55 96.4 10 11.0 320 13.0 50 85 11 10.0 300 13.0 90 80

Claims (6)

CLAIMS:

1. - A process to obtain caprolactam from caprolactam-containing polymers in the presence of super-slow water, which comprises putting polymers containing the reagent unit - / ~ -N (H) - (CH2) 5-C (0) -7- or mixtures consisting essentially of 40 to 99.99% by weight of a polymer containing the repeating unit - / ~ -N ( H) - (CH2) dC (0) -7-, from 0.01 to 50% by weight of additives selected from the group consisting of inorganic fillers, pigments and organic and inorganic dyes, from 0 to 10% by weight of organic or inorganic additives, from 0 to 40% by weight of polymers not containing polyamide and from 0 to 60% by weight of polyamides, with the exception of polycaprolactam and copolyamides prepared from caprolactam, with superheated water 280 to 320eC already from 7.5 to 15 MPa and - a weight ratio of water to polymer containing the repeating unit - / - N (H) - (CH2) 5-C (0) -_ T- of 5: 1 to 13: 1 and in a reaction time of less than 3 hours, with the proviso that the mixture-ratio, consisting essentially of water and the polymer used or the mixture used, does not contain gas phase under the conditions of the hydrolys is.

2. The process as claimed in claim 1, wherein the following steps are carried out: (a) melting and compression of the polymer or mixture at 250 to 350 g C and at a pressure of 7.5 to 30 MPa to provide a fusion A, (b) mixing of the maintained water at 280 to 3209C and 7.5 to 15 MPa with the A fusion in a hydrolysis reactor, (c) discharge of a non-gaseous phase leaving the hydrolysis reactor, with flash evaporation to provide a gas phase B and a non-gas phase C, (d) separation of any non-liquid fractions in the non-gas phase C to provide a liquid phase D, containing caprolactam, and a solid phase E and (e) if desired, transfer of the liquid phase D obtained in step (d) to a purification step for caproiac-tama. 3.- An apparatus to obtain caprolactam from -polymers containing the repetitive unit - / - N (H) (CH2) 5-C (0) -7- or mixtures consisting essentially of 40 to 99.9% by weight of a polymer containing the repeating unit - / -N (H) - (CH2) 5-C (0) -7- from 0.01 to 50% by weight of additives selected from the group consisting of inorganic fillers, pigments and organic and inorganic dyes, from 0 to 10% by weight of organic or inorganic additives, 0 to 40% by weight of polymers not containing polyamide, and 0 to 60% by weight of polyamides, with the exception of polycaprolactam and copolyamides prepared from prolactam , by means of hydrolysis with superheated water, consisting essentially of a melting apparatus, a hydrolysis reactor connected thereto and intended to mix and carry out the hydrolysis, and a lowering apparatus, connected to the hydrolysis reactor, and a separation apparatus. 4. The use of an apparatus as claimed in claim 3 for recycling waste containing polycapro-1 actama. 5. The use of a process as claimed in claim 1, for recycling waste containing polycaprolactam. 6. A process as claimed in claim 1, wherein the oligomers containing the repetitive undiad ~ L -N (H) - (CH2) 5-C (0) -7- are used in place of polymers that contain the repeating unit - / _ ~ -N (H) - (CH2) 5-C ( 0) -7-.