MXPA97003920A - Caprolact preparation - Google Patents

Abstract

The present invention relates to a process for the preparation of caprolactam by unfolding the oligomers or polymers containing essentially the repeating unit - [- N (H) - (CH 2) 5-C (O) -] - in the presence of a catalyst high temperatures, where the splitting is carried out in liquid phase, in the presence of a heterogeneous catalyst and an organic solvent.

Description

PREPARATION OF CAPROLACTAMA The present invention relates to an improved process for the preparation of caprolactam by splitting the oligomers and / or polymers containing essentially the repeating unit -fN (h) - (CH2) 5_ (0) -] - in the presence of a catalyst and at elevated temperatures. The cleavage of polyamide 6 (polycaprolacta a) to caprolactam is generally carried out in the presence of acidic or basic catalysts at elevated temperatures, often in the presence of low pressure steam. In Chem. Ing. Techn. 45 (1973), 1510 describes a technical procedure for a splitting process in the presence of superheated steam, but to function there must be a concentrated solution of caprolactam / water. EP-A 209 021 discloses the unfolding in a bed of fluidized alumina. Often the result is the formation of by-products and the deactivation due to the agglomeration of the catalyst bed. In the process, according to the patent EP 529 470, potassium carbonate is added as a catalyst to unfold the polyamide 6, the reaction is carried out from 250 to 320 ° C with simultaneous removal of caprolactam by distillation under reduced pressure.

The disadvantages of all the processes to date for the splitting of polyamide 6 to give caprolactam are the separation, with energy consumption, of large quantities of water and the removal of the catalysts, such as phosphoric acids or salts thereof, carbonate of potassium or alkali metal oxides. An object of the present invention is to provide an improved process for the preparation of caprolactam starting with caprolactam polymers or polymers, which do not have the disadvantages mentioned. We have found that this goal is achieved by a process for the preparation of caprolactam by unfolding the oligomers or polymers containing essentially the repeating unit - [- N (h) - (CH2) 5_C (0) -] - in the presence of a catalyst at elevated temperatures, where the cleavage is carried out in the liquid phase in the presence of a heterogeneous catalyst and an organic solvent. According to the invention, the oligomers and / or polymers containing the repeating unit ~ [-N (h) - < CH2) s _C (0) -] - are used as starting materials. Preferably, polycaprolactam and oligomers of caprolactam, as well as copolymers of caprolactam are used, for example, those obtained by polymerization of caprolactam in the presence of hexamethylenediamine and terephthalic acid (for example, described in EP-A 299 444). Furthermore, it is possible to use caprolactam oligomers and / or polymers which are available, from the waste obtained from the preparation of caprolactam or polycaprolactam or from their processing, for filaments, films, injection molded parts or parts extruded, shaped articles, such as films, packaging, fabrics, filaments, fibers and extruded parts. Advantageously, the articles to be split are triturated, for example, by grinding before splitting. According to the invention, the reaction is carried out in liquid phase, in general from 140 to 320 ° C, preferably from 160 to 320 ° C. In general, the pressure is chosen from 0.5 to 25, preferably from 5 to 20 MPa, it being necessary to ensure that the reaction mixture is liquid under the conditions that are used. The times of stay are generally chosen from 5 to 300, preferably from 7 to 180 minutes. According to the invention, the unfolding is carried out without the addition of water. In a preferred embodiment, water is preferably used from 0.5 to 20, in particular from 1 to 5 moles of water per mole of the repeating unit - [- In accordance with the invention, the cleavage is carried out in the presence of a solvent organic, oligomers or polymers are advantageously used in the 1-50 form in particular 5-40, particularly preferred 5-25 * by weight of the solution in the organic solvent, a mixture of water and the organic solvent with the aforementioned percentages by weight of the oligomers and / or polymers is particularly preferred for use. Examples of the organic solvents are C Ciu alkanols, such as methanol, ethanol, n-propanol isoprapanol, n-butanol, isobutanol, sec-butanol, n-pentanol, n-hexanol, n-heptanol, n-octanol, n-nonanol, and n-decanol, in particular the C1-C4 alkanols such as methanol, ethanol, n-propanol, isopranol, n-butanol, isobutanol, and sec-butanol, particularly preferred are methanol, ethanol, n-propanol , and n-butanol; polyols such as diethylene glycol and tetraethylene glycol, preferably tetraethylene glycol; hydrocarbons, such as petroleum ether, benzene, toluene, and xylene; lactates as well as pyrrolidone and caprolactam, and N-alquillactam of CpC4, such as N-methylcaprolactam, N-ethylcaprolacta a and N-methylporrilodine. In another embodiment, it is possible to add to the action mixture from 0 to 5, preferably from 0.1 to 2% by weight of ammonia and / or hydrogen and / or nitrogen.

The heterogeneous catalysts that are used can be, for example, oxides, acids, basic or amphoteric of the elements of the second, third and fourth main groups, such as calcium oxide, magnesium oxide, boron oxide, alumina, tin oxide, or silicon such as pyrogenic silicon, silica gel, kieselguhr, quartz or mixtures thereof, and metal oxides from the second to the sixth subgroups of the Periodic Table such as titanium oxide, in amorphous form or as anatase or rutile, zirconium oxide, oxide of zinc, manganese oxide or mixtures of these. For example, oxide of the lanthanides and actinides such as rust, thorium oxide, praseodymium oxide, samarium oxide, neodymium oxide, mixed oxides with rare earths and mixtures of these with the aforementioned oxides can also be used. In addition, the catalysts can be, for example, vanadium oxide, niobium oxide, iron oxide, chromium oxide, molybdenum oxide, tungsten oxide and mixtures thereof., Mixtures of these oxides with those of the second, third and fourth major groups are also possible. Some sulfides, selenides, and tellurides such as zinc teluriide, zinc selenide, molybdenum sulphide, tungsten sulfide, nickel sulfide, zinc, and chromium can also be employed. The aforementioned compounds may be mixed with compounds of major groups 1 and 7 of the Periodic Table or may contain these. In addition, the catalysts are, for example, zelites, phosphates and heteropoly acids and acidic and alkaline ionic interca bers, such as Naphion®. If required, these catalysts can contain up to 50% by weight in each case of copper, tin, zinc, manganese, iron, cobalt, nickel, ruthenium, palladium, platinum, silver or rhodium. Depending on the composition of the catalyst, it can be used as a supported or unsupported catalyst. For example, titanium dioxide can be used as extruded titanium dioxide or as titanium dioxide applied in a thin layer on a support. The observations to date have shown that it is possible to use all the methods described in the literature by applying titanium dioxide on a support such as silicon, alumina or zirconium dioxide. In this way, a thin layer of titanium dioxide can be applied by hydrolysis of titanium organyls, such as titanium isopropylate or titanium butylate, or by hydrolysis of titanium tetrachloride or other inorganic compounds containing titanium. Solutions containing titanium oxide can also be used. The advantage of the novel process is that this method eliminates the separation, consuming a lot of energy, large amounts of water and the elimination of catalysts, such as phosphoric acids and salts of these, potassium carbonate or alkali metal ethoxides, in contrast to the processes of the prior art.

EXAMPLES Example 1 A 10% solution by weight of 6-aminocapronitrile (ACN) in 6.4% by weight of water and 83.6 by weight of ethanol was passed at 200 ° C and 100 bar (10 Pa), in a heated reactor tube with a capacity of 25 ml, diameter of 6 ml and a length of 800 mm and was filled with titanium dioxide (anatase) in the form of 1.5 mm extrudates. The time of stay was 30 minutes. The product stream leaving the reactor was analyzed by gas chromatography and high pressure liquid chromatography. Conversion to caprolactam: 100%, selectivity with respect to caprolactam: 88%. The mixture thus obtained was subjected to distillation (temperature: 110 ° C, pressure: 0. 1 bar (10 Pa) to obtain caprolactam.) As residual product was left a mixture containing 9% by weight of oligomers and polymers, 1% by weight of caprolactam, 6.4% by weight of water and 83.4% by weight of ethanol.

Example 2 (a) ßOml / h The residual product of Example 1 was fed at 100 bar (10 Pa) in a reactor tube heated to 230 ° C, with a capacity of 25ml a diameter of 6 mm and a length of 800 mm and it was filled with titanium oxide (anatase) in the form of 1.5 mm extrudates. The time of stay in the reactor was 15 minutes. The conversion to caprolactam was 53%, based on the amount of oligomers and polymers used, which contained the repeating unit - [- N (h) - (CH2) s_C (0) -J-. Examples 3, 4 and 5 Example 2 was repeated with the difference shown in the following table.

Claims (4)

1. A process for the preparation of caprolactam by unfolding the oligomers or polymers containing essentially the repeating unit - [- N (H) - (CH 2) 5-C (0) -] - in the presence of a catalyst at elevated temperatures, wherein the splitting is carried out in liquid phase in the presence of a heterogeneous catalyst and an organic solvent.

2. The process according to claim 1, wherein the reaction is carried out from 140 to 320 ° C.

3. The process, according to claim 1 or 2, wherein the reaction is carried out in a concentration of the oligomers or polymers from 5 to 50% by weight.

4. The process, according to any of claims 1 to 3, wherein the time of stay is chosen from 5 to 300 minutes. 5, The process according to any of claims 1 to 4, wherein the organic solvent used is a CrC4 alkanol or tetraethylene glycol. 6. The process according to any of claims 1 to 5, wherein the splitting is carried out in the presence of water.