|Title of Invention||
"A PROCESS FOR THE TREATMENT OF A LIQUID MEDIUM COMPRISING A LACTAM"
|Abstract||Process for the treatment of a liquid medium comprising at least one lactam of the kind described herein which consists in subjecting the said medium to a hydrogenation in the presence of a hydrogenation catalyst of the kind described herein, characterized in that the medium comprises dissolved ammonia.|
|Full Text||The present invention relates to a process for the treatment of a liquid medium.
It relates more particularly to a process which makes it possible to modify the chemical nature of the impurities present in a medium comprising lactams, either in order to convert them into harmless compounds or into compounds which can be extracted in subsequent purification operations.
Lactams and in particular e-caprolactam, a monomer in the preparation of polycaproamide (PAS), are prepared according to several synthetic processes.
The most widely used process industrially employs a Beckmann rearrangement reaction of cyclohexanone oxime with sulphuric acid or oleum, followed by the neutralization of the medium with ammonia and then by the separation and purification of the lactam.
Another process proposed for the synthesis of the lactam consists in carrying out a cyclizing hydrolysis of an aminoalkylnitrile, such as 6-aminocapronitrile in the preparation of ε-caprolactam. This reaction can be carried out in the presence or in the absence of a catalyst and in the liquid or vapour phase. This reaction releases ammonia.
The latter process is disclosed in numerous patents. Mention may be made, by way of example, of Patents US 2,357,484, US 2,301,964 and FR 2,029,540.
The process for the preparation of lactams by the vapour-phase cyclizing hydrolysis of aminonitriles is also disclosed in Patent Applications EP 0,659,741 and WO 96/22974.
The conversion of aminocapronitrile to e-caprolactam in the presence of water is exemplified in Patents US 2,245,129 and EP 0,150,295.
Generally, in the latter processes,
aminocapronitrile is obtained by hemihydrogenation of adiponitrile by known processes disclosed in particular in Patents DE.836,938, DE 848,654 or US 5,151,543.
As the main use of the lactams produced is the manufacture of polymers or copolymers and more particularly of polyamides or copolyamides intended to be shaped for the production of yarns, fibres, moulded items or films, the purity of the lactams must comply with specific and strict specifications.
Thus, one of the major specifications is the UV absorbance of an aqueous caprolactam solution represented by a UV number. This number is determined by measurement of the absorbance of an aqueous caprolactam solution (50% by weight) at a wavelength of 290 [lacuna] in a cell with a width of 1 cm.
In order to obtain a low UV number, it is known in particular to subject the lactam to a hydrogenation in the presence of a catalyst.
Thus, German Patent 1,253,716 discloses the hydrogenation of caprolactam obtained by the Beckmann rearrangement process in the presence of a suspended hydrogenation catalyst.
Likewise, Patent DE 1,004,616 and East German Patent 75 083 discloses a process for the hydrogenation of caprolactam after treatment with active charcoal and ion-exchange resins.
Patent US 5,496,941 discloses a process for the purification of the lactam obtained by cyclizing hydrolysis of an aminonitrile. This process comprises a stage of hydrogenation of the lactam in the presence of a hydrogenation catalyst. A solvent, such as water or an alcohol, is preferably present.
The hydrogenation stage is carried out on the isolated lactam separated from the cyclizing hydrolysis reaction mixture. This is because this process requires the separation from the cyclizing hydrolysis medium of the compounds which are more volatile and less volatile than caprolactam. This separation therefore requires the removal of the ammonia produced and the distillation of the caprolactam.
These various processes give satisfactory results in the production of a lactam with a low UV
number. However, this purification stage has a disadvantageous effect-on the general economics of the process. This is because the efficiency of the catalyst decreases very quickly. This short cycle time of the catalyst requires frequent replacement of the latter and results in the risk of a lactam of unsatisfactory purity being obtained at the end of the catalyst cycle. This process is even more disadvantageous when the catalyst cannot be regenerated by a simple and economic process.
One of the aims of the present invention is in particular to overcome these disadvantages by providing conditions for implementing the hydrogenation stage which make it possible to greatly increase at least the cycle time of the hydrogenation catalysts and thus the general economics of the process for the manufacture of lactams of high purity.
According to the present invention there is provided a Process for the treatment of a liquid mediumcomprising at least one lactam of the kind described herein which consists in subjecting the said medium to a hydrogenation in the presence of a hydrogenation catalyst of the kind described herein, characterized in that the medium comprises dissolved ammonia.
The presence of ammonia makes it possible to significantly increase the cycle time of the hydrogenation catalyst.
To prevent or limit the condensation reaction of the lactam, the temperature for implementation of the hydrogenation will be carried out at a temperature which makes it possible to have hydrogenation kinetics compatible with an industrial use but which is as low as possible. This temperature is preferably less than 150°C, in particular when the lactam is e-caprolactam. The temperature is advantageously)between 50°C and 150°C, preferably between 70°C and 130°C.
The concentration of ammonia in the medium can vary within wide proportions but is advantageously greater than 10 g/1, preferably between 50 g/1 and 200 g/1.
The medium comprising the lactam comprises, according to one characteristic of the invention, a solvent chosen, for example, from alcohols comprising from 1 to 3 carbon atoms. However, the preferred solvents of the invention are water and water/alcohol mixtures. In addition, it is possible to carry out the hydrogenation of a molten lactam without a solvent other than ammonia.
The treatment process of the invention is carried out in the presence of a hydrogenation catalyst. This catalyst can be suspended in the medium
or present in the form of a fixed bed or fluidized bed deposited in a tubular reactor. The catalyst can be a bulk or supported catalyst.
The preferred catalysts of the invention are those derived from one or more metals chosen from the group consisting of iron, nickel, cobalt, ruthenium, rhodium, palladium, osmium, iridium and platinum.
Use may be made, as catalyst support, of, for example, active charcoal, aluminas, silicas, titanium oxides, rare earth metal oxides, such as lanthanum or cerium oxides, or zirconium or zinc oxides. Use may also be made of a mixture of these oxides or mixed oxides. Use may also be made, as catalyst support, of magnesium, aluminium or boron silicates or phosphates.
In the case of a supported catalyst, the concentration of catalytic element, expressed as weight of metal, is advantageously between 0.01 and 80% of the total weight of the catalyst, preferably from 0.1 to 50% by weight.
Furthermore, the catalysts can comprise additives which improve the catalytic effect, such as, for example, zirconium, manganese, copper, chromium, titanium, molybdenum, tungsten, iron or zinc.
These doping elements usually represent from 0 to 15% and preferably from 0.1 to 10% by weight with respect to the catalytically active metal.
The manufacture of these supported or nonsupported catalysts is described in numerous documents, such as Ullmann's Encyclopaedia of Industrial Chemistry, Volume A5, pages 348-350, 5th edition.
The hydrogenation treatment is carried out either at atmospheric pressure or at a pressure of between 1 and 100 bar.
As is disclosed in the cited documents, this treatment with hydrogen makes it possible to decrease in particular the UV number of caprolactam. However, the presence of dissolved ammonia makes it possible to obtain a low UV number even after a lengthy continuous operating time for the process, that is to say to treat a large amount of lactam without having to replace or regenerate the catalyst present in the reactor or by minimizing the consumption of catalyst consumed per kilogram of lactam treated.
The invention applies to the treatment of lactams of various origins, such as those obtained by the Beckmann rearrangement reaction, lactams obtained by depolymerization of polyamide or lactams obtained by cyclizing hydrolysis of an aminonitile, for example.
However, the invention applies more
particularly to the treatment of the lactam solutions obtained by hydrolysis of an aminonitrile, either in the vapour phase or in the liquid phase.
Thus, the process of the invention applies more particularly in the hydrogenation stages disclosed in the processes for the purification of caprolactam obtained by cyclizing hydrolysis of an aminonitrile, in the vapour phase or in the liquid phase, disclosed in Patent US 5,496,941 and Patent Application WO 98/05636.
Another subject-matter of the invention is a process for the purification of a lactam obtained by cyclizing hydrolysis of an aminonitrile in the vapour phase and more particularly a process for the purification of £-caprolactam obtained by cyclizing hydrolysis in the vapour phase of 6-aminocapronitrile.
This process consists:
- in cooling the hydrolysis reaction mixture to a
temperature of less than 150°C,
- in subjecting the cooled reaction mixture, at least
partially comprising the ammonia formed, to a
hydrogenation in the presence of a hydrogenation
- after hydrogenation, in optionally separating the
ammonia from the reaction mixture,
- and in subjecting the reaction mixture to one or more
purification processes, in order to obtain a lactam
which satisfies the desired purity specifications.
The hydrogenation treatment, carried out directly on the reaction mixture resulting from the cyclizing hydrolysis, makes it possible to use the
ammonia produced in order to carry out this hydrogenation under satisfactory economic conditions, in particular with a cycle time of the catalyst which is compatible with an economic industrial use. If necessary, it is possible to adjust the concentration of ammonia, either by addition of ammonia or partial evaporation of the ammonia produced by the hydrolysis reaction.
In addition, it also has the effect of reducing the deterioration in the UV number which is observed during the separation of the light fractions from the reaction mixture, in particular during the distillation of the ammonia and optionally of the water or of the solvent present in the mixture.
According to the invention, the lactam recovered after the hydrogenation treatment and optionally the separation of the ammonia can be subjected to various known purification stages described in numerous patents, such as, for example Patent US 5,496,941, WO 98/05636, and the like.
The possible treatments are oxidation,
distillation in acidic or basic medium, liquid/liquid extraction, treatment over ion-exchange resins, or crystallization, for example.
All these treatments are given solely by way of example, it is possible for all of them to be carried out or just some of them, in any order.
Other advantages and details of the invention will become more clearly apparent in the light of the examples given below solely by way of indication, without any limiting effect on the invention.
Comparative Example 1
An aqueous solution composed of 60% of caprolactam resulting from a cyclizing hydrolysis of 6-aminocapronitrile, the conditions of which are disclosed in French Patent Application 2,714,379, is continuously introduced into a hydrogenation reactor at 80°C under 25 bar charged with 5% of Raney nickel as hydrogenation catalyst.
This caprolactam solution no longer comprises ammonia, the latter having been distilled off on leaving the cyclizing hydrolysis stage.
The UV number of this measured solution is 24 at 290 nm.
The UV number of the solution exiting from the hydrogenation stage is periodically monitored in order to determine the efficiency of the hydrogenation and thus the activity of the catalyst.
The results are shown in the table hereinbelow.
The results show that the catalyst has lost its activity from the 2nd day of operating.
Example 1 is repeated but using as solution of caprolactam in water to which has been added ammonia, in order to obtain a solution comprising 90 g/1 of ammonia and 61% of caprolactam.
The caprolactam solution, before treatment, exhibits a UV number, measured at 290 nm, of 1.6.
The results are shown in the following table.
These results clearly show the effect of the presence of ammonia on the preservation of the activity of the catalyst. Thus, after operating for eight days, the UV number of the resulting solution is identical to that obtained at the beginning of the operation. The hydrogenation treatment retains its efficiency.
The caprolactam solution treated by
hydrogenation according to the conditions of Example 1 is the reaction mixture resulting from the reaction of 6-aminocapronitrile with water. This mixture was subjected to rapid cooling to a temperature of 80°C at the reactor outlet, in order to prevent polycondensation of the caprolactam. The mixture comprises 90 g/1 of ammonia produced by the reaction. This mixture exhibits a UV number at 290 nm of 1.8. The mixture is subjected directly to a hydrogenation according to the conditions of Example 1. The results obtained are given in the table hereinbelow.
Furthermore, the aminocapronitrile which has not been converted to caprolactam 'is completely hydrogenated to hexamethylenediamine, even after the hydrogenation catalyst has been operating for 192 hours.
1. Process for the treatment of a liquid medium comprising at least
one lactam of the kind described herein which consists in subjecting the
said medium to a hydrogenation in the presence of a hydrogenation
catalyst of the kind described herein, characterized in that the medium
comprises dissolved ammonia.
2. Process as claimed in claim 1, wherein the medium comprises a
solvent chosen from the group consisting of alcohols having from 1 to 3
carbon atoms, water and water/alcohol mixtures.
3. Process as claimed in claim 1 or 2, wherein the hydrogenation
treatment is carried out at a temperature of less than 150°C
4. Process as claimed in claim 3, wherein the hydrogenation
treatment is carried out at a temperature of between 50 and 150°C,
preferably between 70°C and 130°C.
5. Process as claimed in one of the preceding claims, wherein the
concentration of dissolved ammonia is greater than 10 g/1.
6. Process as claimed in one of the preceding claims, wherein the
hydrogenation catalyst is chosen from the group consisting of iron,
nickel, cobalt, ruthenium, rhodium, palladium, osmium, iridium and
platinum, taken alone or in combination.
7. Process as claimed in claim 6, wherein the catalyst is a bulk
catalyst or a supported catalyst.
8. Process as claimed in either of claims 6 and 7, wherein the catalyst
comprises at least one additive chosen from the group consisting of
zirconium, manganese, copper, chromium, titanium, molybdenum,
tungsten, iron and zinc.
9. Process as claimed in either of claims 7 and 8, wherein the support
of the catalyst is chosen from the group consisting of active charcoals,
aluminas, silicas, titanium oxides, rare earth metal oxides, zirconium
oxides, zinc oxides, magnesium and/or aluminium silicates or
phosphates, and boron phosphates.
10. Process as claimed in one of claims 7 to 9, wherein the
concentration of catalytic element in the supported catalysts is between
0.01% and 80% by weight, expressed as metal element, with respect to
the weight of catalyst.
11. Process as claimed in one of the preceding claims, wherein the
lactam is ε-caprolactam.
12. Process for the treatment of a liquid medium substantially as
herein described with reference to the foregoing examples.
|Indian Patent Application Number||IN/PCT/2001/00512/DEL|
|PG Journal Number||41/2009|
|Date of Filing||14-Jun-2001|
|Name of Patentee||RHODIA POLYAMIDE INTERMEDIATES,|
|Applicant Address||AVENUE RAMBOZ, F-69190 SAINT-FONS, FRANCE.|
|PCT International Classification Number||C07D 201/16|
|PCT International Application Number||PCT/FR99/02823|
|PCT International Filing date||1999-11-18|