Title of Invention	OBTAINING CAPROLACTAM BY HYDROLYTIC CLEAVAGE OF MOLTEN POLYCAPROLACTAM
Abstract	(57) Abstract: recovering The present invention relates to a process for — /— caprolactam from caprolactam containing polymer wast which is subjected to hydrolysis with superheated water at 280°C to 320°C with the proviso that the reaction mixture contains no gaseous phase under the reaction conditions. PRICE: THIRTY RUPEES

Full Text

I The present invention relates to an improved- process for recover¬ing caprolactam from caprolactam-containing polymers in the pres¬ence of superheated water. The present invention furthermore relates to an apparatus for carrying out the novel process and to the use of the novel pro¬cess and of the novel apparatus for recycling polycaprolactam containing wastes. . US 4,605,762 describes a continuous process for the hydrolytic depolymerization of condensation polymers, in which waste mate¬rial which is obtained during the production of articles from the condensation polymers is subjected to aqueous hydrolysis at from 200 to SOO'C and at a superatmospheric pressure of at least 15 atmospheres in a special apparatus. In the stated process, the hydrolysis is carried out using steam under high pressure. How¬ever, the hydrolysis of condensates which may contain fillers, such as glass fibers, or of blends is not described. US 3,939,153 describes a process for the preparation of caprolac¬tam from polycaprolactam, in which a melt of the -polymer and superheated steam are brought continuously into contact with one another at not less than 315°C. The disadvantage of this process is a low yield of not more than 20 %. It is an object of the present invention to provide a process for obtaining caprolactam from polymers containing, as a repeating unit, -[-N(H)-{CH2)5-C(0)-]-, or from mixtures containing such polymers, which process gives higher yields of caprolactam in the absence of a catalyst. It is also intended to provide a process which makes it possible to utilize polycaprolactam-containing wastes which contain inorganic fillers to obtain caprolactam without having to accept a reduced yield. We have found that this object is achieved by a process for ob¬taining caprolactam from caprolactam-containing polymers in the presence of superheated water, by bringing polymers which contain the repeating unit -[-N(H)-(CH2)5-C{0)-]-or mixtures consisting essentially of from 40 to 99.9 % by weight of a polymer containing the repeat¬ing unit -[-N(H)-(CH2)5-C(0)-]-, from 0.01 to 50 % by weight of additives selected from the group consisting of inorganic fillers, organic and inorganic pigments and dyes, from 0 to 10 % by weight of organic and/or inorganic addi¬tives, from 0 to 40 % by weight of non-polyamide-containing polymers and from 0 to 60 % by weight of polyamides, with the exception of polycaprolactam and copolyamides prepared from caprolactam, into contact with superheated water at from 280 to 320°C and from 7.5 to 15 MPa, in a weight ratio of water to polymer containing the repeating unit - [-N (H) - (CH2) 5-C (0)-] - of 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 of the, polymer used or of the mixture used, contains no gaseous phase under the conditions of the hydrolysis. We have also found an apparatus for carrying out the novel pro¬cess and the use of the novel process and of the novel apparatus for recycling polycaprolactam-containing waste. According to the invention, the starting materials used are poly-Tiers which contain the repeating unit -[-N(H)-(CH2)5--C(0)-]- Dr are mixtures consisting essentially of from 40 to 99.99, preferably from 70 to 90, % by weight of a polymer containing the repeating unit -[-N(H)-(CH2)5-C(0)-]- Erom 0.01 to 50, preferably from 4 to 10, % by weight of additives selected from the group consist¬ing of inorganic fillers, organic and in¬organic pigments and dyes, from 0 to 10, preferably from 0.1 to 5, % by weight of organic and/o;: inorganic additives. from 0 to 40, preferably from 5 to 25, % by weight of non-polyamide-containing polymers and from 0 to 60, preferably from 10 to 30, % by weight of polyamides, with the exception of polyca¬prolactam and copolyamides prepared from caprolactam. polymer used is preferably polycaprolactam having a relative of from 1 to 10, preferably of from 2.0 to 4.0 (measured at a concentration of 1 g of polymer per 100 ml in 96 % strength by weight sulfuric acid at 25°C). It is also possible to polycaprolactam which contains oligomers in an amount of from 3.01 to 10, preferably from 1 to 5, % by weight, based on the to-:al amount. In principle, the novel process can also be carried 3ut if oligomers of caprolactam are used instead of polycaprolac-:am. 5-C8-cycloalkanedicarboxylic acids, such as cyclopentane-1,3-di-arboxylic acid, cyclohexane-1,4-dicarboxylic acid and mixtures hereof, enzene- and naphthalenedicarboxylic acids which may carry up to wo sulfa groups, including the corresponding alkali metal salts, ad whose carboxyl groups are not adjacent, such as terephthalic cid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, 5-sul-oisophthalic acid and their sodium and lithium salts, and mix-uses thereof, and 1, 4-piperazinedi-Ci-C6-alkanedicarboxylic cuds, such as 1,4-piperazinediacetic acid, L,4-piperazinedipropionic acid, 1, 4-piperazinedibutyrfc acid, L,4-piperazinedipentanoic acid and 1,4-piperazinedihexanoic acid. :corresponding copolyamides are known to a person skilled in the art and can be prepared by processes which are described, for ex-impel, in WO 93/25736, DE-A 14 95 198 and DE-A 25 58 480. )observations to date have shown that all fillers, such as glass 'biers, calcium carbonate and talc, which are usually used in the :impounding of polyamides may be employed as inorganic filers. observations to date have shown that all pigments and dyes, such .s titanium dioxide, cadmium sulfide, iron oxides or carbon lacks, which are usually used for coloring polyamides, and the conventional spinning dyes, such as chromium complexes or copper :complexes, may be employed as inorganic and organic pigments and [yes. he conventional stabilizers and antioxidants, heat stabilizers and UV stabilizers, antistatic agents and flameproofing agents ay be used as organic and inorganic additives. engineering polymers, such as polymers based on ethylene, propylene and styrene, and copolymers thereof with butadiene and acrylonitrile (ABS plastics), maybe used as non-polyamide-containing polymers. Suitable polyamides with the exception of polycaprolactam and co-polyamides prepared from caprolactam are, for example, polyamide 66, polyamide 610 and polyamide 46. Preferred starting materials are polycaprolactam which contains inorganic fillers, in particular glass fibers, and is to be dies¬ posed of, and wastes which are obtained in the production of polycaprolactam and in the processing thereof to give filaments, Elms. and injection-molded or extruded parts, and shaped utility articles, such as films, packaging, fabric, carpet fibers, file¬ mints and extruded parts, which are no be disposed of. to the invention, the abovementioned polymers or mix-:urges are brought into contact with superheated water which is at Erom 280 to 320°C, preferably from 295 to 310°C, particularly pre¬ferably from 300 to 305°C, and at from 7.5 to 15, preferably from LO to 15, particularly preferably from 10 to 12, MPa, the weight ratio of water to the polymer containing the repeating unit - [-N(H)-(CH2) 5-C (0)- - being chosen in the range from 5:1 to L3:l, preferably from 8:1 to 13:1. Furthermore, according to the .invention, the reaction time is chosen to be less than 3 hours, preferably from 15 to 90, particularly preferably from 30 to jO, minutes . Choosing the conditions of the hydrolysis within the stated 'aloes so that the reaction mixture, consisting essentially of fatter and the polymer used or the mixture used, contains no gas-pious phase is essential for the success of the novel process. )bservations to date have shown that gaseous fractions in the reation mixture lead to lower yields. ?he reaction mixture obtained after the hydrolysis can be worked reactor may or may not be provided with baffles, such as Xing elements of the type SMX from Seltzer (cf. Chem.-Inch. £2 (1990) 650-654). In a preferred embodiment, a tube actor having an L/D ratio of from 20:1 to 150:1, preferably ohm 50:1 to 120:1, is used. a preferred embodiment, the mixture discharged from the hydro-sis reactor is fed into a let-down apparatus (3) which may be a angle-stage or two-stage apparatus, essentially two phases being rimed as a result of the pressure drop to 0.1-1.6, preferably 1-0.4, )cPa: a gaseous phase B, which contains essentially water d may contain small amounts of other volatile substances, such caprolactam and traces of volatile amine compounds, and a non-seous phase C which contains essentially the main amount of evade caprolactam and, depending on the mixture used, may con-in additives, such as glass fibers, pigments, additives, etc. e gaseous and steam-containing phase B is usually separated om the nongaseous phase C in a let-down apparatus (3), the war preferably being separated off in a suitable apparatus, for ample in a distillation apparatus or an evaporator stage, and then being mixed with the water which is introduced into the hy¬drolysis reactor (2) for hydrolyzing the polymers or mixtures. The nongaseous phase C, which as a rule contains water and may contain additives, organic and inorganic additives, non-poly-amide-containing polymers and polyamides, with the exception of polycaprolactam and copolyamides prepared from caprolactam, and generally contains from 5 to 20 % by weight of caprolactam, is fed, in a preferred embodiment, into a separation apparatus (4), in which any insoluble components present, such as additives, for example glass fibers, pigments, other polymers, etc., are re¬moved. The separation apparatus (4) used may be a conventional filter apparatus, such as a belt filter or a back-washable tube filter, or another conventional apparatus which permits continuous or periodic discharge, preferably a belt filter or a back-washable tube filter. The solution freed from insoluble consonants can then be worked by methods known per se, for example by separating the water from caprolactam by distillation and adding it to the hydrolysis rafter, similarly to the working up of the gaseous phase B, and Eeeding the caprolactam to a purification stage, for example the 3urification stage for crude caprolactam in an existing caprolac-;am plant. Other possibilities for, if desired, purifying the :aprolactam obtained according to the invention are disclosed, :or example, in EP-A 568,882 and 570,843. The purified caprolac-:am is then in general available for further use, in particular :or the preparation of PA 6. According to the invention, the novel process is used for recycling polycaprolactam-containing wastes, such as used carpets, car-set offcuts, polyamide 6 production wastes and polyamide mixtures which may contain up to 60 % by weight of polyamides which were lot prepared from caprolactam. :he advantages of the novel process over prior art processes are ;he cleavage yields of up to 96 %, short residence times and mailer amounts of solvents and wastes which require treatment disposal. Accordingly, the present invention provides a process for recovering aprolactam from caprolactam containing waste selected from a caprolactam containing oligomer/polymer, containing the repeating unit -[-N(CH)-(CH2)5-C(0)-]- or a mixture consisting essentially of from 40 to 99.9 % by weight of a polymer containing the repeating unit -[- N(CH)-(CH2)5-C(0)-]- from 0.001 to 50% by weight of additives selected from the group consisting of inorganic fillers, organic and inorganic pigments & dyes, from 0 to 10% by weight of organic or inorganic additives from 0 to 40% by weight of polyamide containing polymers and 0 to 60% by weight of polyamides with the exception of polycaprolactam and copolyamides prepared from caprolactam comprises hydrolyzing the same with superheated water at a temperature from 280°C to 320°C and at from 7.5 to 15 MPa and a weight ratio of water to the polymer containing the repeating unit -[-N(CH)- (CH2)5-C(0)-]- of 5:1 to 13:1 for a period of less than three hours with the proviso that the reaction mixture contains no gaseous phase under the conditions of hydrolysis and separating the liquid phase containing caprolactam in a known manner. Examples Example 1 0.3 kg/hour of polycaprolactam (Ultramid® BS 700, having a rela¬tive viskosity of 2.7, measured in a 1 % strength by weight at 270°C and under a pressure of 20 MPa and 2.7 kg/hour of water maintained at 290'c and a pressure of 12 MPa were fed into a 3 1 tube reactor (length/diameter ratio: 110:1). The average resi¬dence time was 60 minutes. After leaving the reactor, the mixtur was cooled to 115°C and let down to 0,1 kPa. The reaction mixtur obtained was analyzed by gas chromatography. The results are shown in the table below. Examples 2 to 11 Example 1 was repeated at different water-to-polymer ratios and different temperatures. The results are summarized in the table below. WE CLAIM: A process for recovering caprotactam from caprolactam containing waste selected from a caprolactam containing oligomer/polymer, containing the repeating unit -[-N(CH)-(CH2)5-C(0)-] or a mixture consisting essentially of from 40 to 99.9 % by weight of a polymer containing the repeating unit -[- N(CH)-(CH2)5-C(0)-]- from 0.001 to 50% by weight of additives selected from the group consisting of inorganic fillers, organic and inorganic pigments & dyes, from 0 to 10% by weight of organic or inorganic additives from 0 to 40% by weight of polyamide containing polymers and 0 to 60% by weight of polyamides with the exception of polycaprolactam and copolyamides prepared from caprolactam comprises hydrolyzing the same with superheated water at a temperature from 280°C to 320°C and at from 7.5 to 15 MPa and a weight ratio of water to the polymer containing the repeating unit -[-N(CH)- (CH2)5-C(0)-]- of 5:1 to 13:1 for a period of less than three hours with the proviso that the reaction mixture contains no gaseous phase under the conditions of hydrolysis and separating the liquid phase containing caprolactam in a known manner. The process as claimed in claim 1, wherein the following steps are carried out: (a) melting and compression of the polymer or of the mixture at from 250°C and to a pressure of from 7.5 to 30 MPa to give a melt A, (b) mixing of water maintained at from 280° to 320°C and from 7.5 to 15 MPa with the melt A in a hydrolysis reactor, (c) discharge of a nongaseous phase leaving the hydrolysis reactor, with flash evaporation (d) separating off any no liquid fractions in the nongaseous phase C to give a liquid phase D, containing caprolactam, and a shod phase E and (e) optionally, transfer of the liquid phase D obtained in stage (d) to a purification stage for caprolactam. The process as claimed in claims 1 and 2 wherein said process is carried out in an apparatus consisting essentially of a melting apparatus (1), a hydrolysis reactor connected thereto intended for mixing and for effecting the hydrolysis, a let-down apparatus (3) connected to said hydrolysis reactor and a separation apparatus connected thereto. A process for recovering caprolactam from caprolactam containing waste selected from a caprolactam containing oligomer/polymer, substantially as herein described with reference to the accompanying drawings.

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1613-mas-95 abstract.pdf

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1613-mas-95 correspondence others.pdf

1613-mas-95 correspondence po.pdf

1613-mas-95 description (complete).pdf

1613-mas-95 drawing.pdf

1613-mas-95 form-1.pdf

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