MXPA01000749A - Method for cyclizing hydrolysis of an aminonitrile compound into lactam - Google Patents

Abstract

The invention concerns a method for cyclizing hydrolysis of an aminonitrile compound into a lactam in the presence of a catalyst. More particularly, it concerns a method for cyclizing hydrolysis of an aminonitrile compound in the presence of a macroporous particulate catalyst resulting from deposit/impregnation of an oxygen-containing compound on a macroporous support such as alumina. The invention is particularly useful for preparing&egr;-caprolactam by cyclizing hydrolysis of aminocapronitrile.

Description

PROCESS FOR THE CYCLIZING HYDROLYSIS OF A COMPOUND OF AMI ONITRILO IN A LACTAMA DESCRIPTION OF THE INVENTION The invention relates to a process for the cyclizing hydrolysis of an aminonitrile compound in a lactam in the presence of a catalyst. The invention relates more particularly to a process for the cyclizing hydrolysis of an aminonitrile compound in the presence of a macroporous particulate catalyst obtained by deposition / impregnation or adsorption of an oxidized compound on a macroporous support. Lactams, such as e-caprolactam, are base compounds for the manufacture of polyamides and in particular PA 6. Among the various known processes for the synthesis of these lactams, one of the processes is the cyclizing hydrolysis of the corresponding aminonitrile, and more particularly of a corresponding aliphatic aminonitrile, in the presence of water and a catalyst.

In this way, the Patent of the States No. 2,357,484 describes a process for the preparation in vapor phase of lactam, with activated alumina, silica in the form of gel or acid borophosphoric acid as a catalyst. U.S. Patent No. 4,628,085 also describes a process for the preparation of lactams by cyclizing hydrolyzing in the vapor phase in the presence of a silica-based catalyst with a specific surface area greater than 250 m2 / g. This reaction is carried out in the presence of hydrogen and ammonia. U.S. Patent Application No. WO98 / 0669 proposes catalysts based on hydrous or non-hydrated metal oxides, the metals being chosen from the group comprising tin, zirconium, hafnium, bismuth, vanadium, niobium and tantalum, or mixtures thereof. thereof. These catalysts are of the bulk type and do not have macroporosity. Its cycle time is very short and incompatible with an industrial exploitation of the lactam manufacturing process, a process for the vaporizing cyclizing hydrolysis of aminonitrile using, as a catalyst, an alumina which has specific surface area domains and volume of determined pore. The lactams produced are generally used for the manufacture of polymer, such as, for example, e-caprolactam for the manufacture of PA 6. The applications of these polymers are many and varied. However, one of the most important applications is the manufacture of yarns, filaments or fibers in particular for the textile indus These varied applications, and in particular that described above, require the use of an outgoing pole which has very specific physicochemical and chemical properties. To obtain such properties, it is necessary to synthesize these polymers from monomers or lactams which also have very strict purity properties. In this way, caprolactam must generally satisfy the following specifications: - perganganate index (according to ISO 8660 standard): < 5 free bases: < 0.1 milliequivalent (meq) / kg CPL volatile bases (according to ISO 8661 standard): < 0.5 meq / kg UV absorbance at 290 nanometers (according to ISO 7059 standard): < 0.05 To obtain these specifications, it is necessary to carry out complete purification processes. Such processes have many economic disadvantages, in particular high energy consumption and large investments of materials. One of the reasons for the need to purify the crude lactam produced by the known processes is the presence of collateral reactions that arise in particular during the cyclizing hydrolysis step of the aminonitrile. In order to avoid these collateral reactions, it is thus necessary for the catalyst to promote the main reaction of lactam formation.

This property of the catalyst can be illustrated by the selectivity of the process towards the raw lactam. The quality of raw lactam can also be evaluated by titrating it with an aqueous solution of potassium permanganate 0.2 N (index of permanganate). Furthermore, in order that the purity of the raw lactams produced be high and continuous, it is necessary that the selectivity level of the catalyst be conserved throughout the time of the catalyst cycle. The aluminas proposed in the patent application W096 / 22974 of the Applicant, represents the beginning of a solution to this problem when proposing A highly active and selective catalyst, which has a long cycle time. However, it seems necessary to further improve the performance levels of the catalysts for the cyclizing hydrolysis of the lactams, in order to improve the initial selectivity of the catalyst, as well as the purity of the raw lactam, while at the same time maintaining This high level throughout the catalyst cycle time. One of the objects of the present invention is to propose a solution to improve the catalysis for the cyclizing hydrolysis of the aminonitriles, and in particular the selectivity of this catalysis to produce a crude lactam with a high degree of purity. In this way, the raw lactam produced can be used for the manufacture of the polymer with high chemical and physicochemical properties, after carrying out a purification process that is simpler and more economical than those currently used. The term "crude lactam" refers to the product from the cyclizing hydrolysis reaction after the removal of the ammonia and any solvents such as water, for example. The term "purified lactam" denotes the lactam obtained by purification of the crude lactam. For this purpose, the invention proposes a process for the cyclizing hydrolysis of an aminonitrile compound in a lactam, by reaction of an aminonitrile of the general formula (I) following: N = CR-NH2 (I) in which: R represents a substituted or unsubstituted aliphatic, cycloaliphatic or arylaliphatic radical comprising from 3 to 12 carbon atoms, with water, in the presence of a solid catalyst, characterized in that the catalyst is a particulate catalyst obtained by the deposition and / or adsorption of at least one oxygenated compound of at least one element selected from the group consisting of the elements belonging to groups 1 to 16 of the universal classification of the elements (new classification), this list also including the rare earth metals, on a particulate support made of simple and mixed inorganic oxide of at least one element chosen from the group consisting of silicon, aluminum, titanium, zirconium, vanadium, niobium, tantalum, tungsten, molybdenum, iron and rare earth metals, or by mixing together / 'at least one of said oxygenated compounds or a precursor of the oxygenated compounds with the inorganic oxide or oxides, forming the support before forming them. According to the invention, the particulate catalyst comprises at least one macroporosity 'characterized by a pore volume, corresponding to pores larger than 500 A in diameter, greater than or equal to 5 ml / 100 g. This macroporosity is advantageously formed during the process for shaping the particles by the techniques described below, or the like, for example, the addition of porogen. The catalyst can be used in various forms, such as spheres, sprays, extruded in the form of hollow or solid cylindrical granules, combs or pellets, the forming being optionally carried out using a binder. These may be, firstly, spheres of inorganic oxides derived from a shaping per drop of oil (or drop coagulation). Spheres of this type can be prepared, for example, by a process similar to that described for the formation of alumina spheres in European patents EP-A-0, 015, 801 or EP-A-0, 097, 539. The control of porosity can be achieved in particular, according to the process described in European patent EP-A-0, 097, 539, by the coagulation of drop of an aqueous suspension or aqueous dispersion of inorganic oxide. The spheres can also be obtained by an aggregation process in a rotating drum or granulator. These can also be extruded from inorganic oxides. These can be obtained by mixing and then extruding a material based on inorganic oxide. The control of the porosity of these extrudates can be achieved by choosing the oxide used and by the conditions for the preparation of this oxide or by the conditions for mixing this oxide before extrusion. The inorganic oxide can thus be mixed with porogens during mixing. By way of example, the extrudates can be prepared by the process described in U.S. Patent No. 3,856,708. Similarly, controlled porosity spheres can be obtained by the addition of porogen and aggregation in a rotary or granulator or by "oil drop" process. These shaping processes can be carried out by using a mixture of the inorganic oxide and an oxidized compound according to the invention, or a precursor of the oxygenated compound, the precursor being converted to the oxidized compound by heat treatment of the catalyst, for example, and advantageously after shaping. According to yet another feature of the invention, the catalyst particles have a surface area greater than 10 m2 / g and a pore volume greater than or equal to 10 ml / 100 g, the pore volume corresponding to pores greater than 500 A. in diameter, which is greater than or equal to 10 ml / 100 g. According to yet another feature of the invention, the catalyst particles have a specific surface area greater than 50 m2 / g. Advantageously, they have a total pore volume greater than or equal to 15 ml / 100 g with a pore volume corresponding to larger pores of 200 A in diameter, greater than or equal to 15 ml / 100 g, preferably greater than or equal to 20 ml / 100 g. According to another feature of the invention, the catalyst has a total pore volume greater than or equal to 20 ml / 100 g with a pore volume corresponding to pores greater than 70 A in diameter, greater than or equal to 20 ml / 100 g In the process comprising a porous support supporting oxygenated compounds of elements, these elements are advantageously chosen from the list comprising silicon, titanium, zirconium, vanadium, niobium, tantalum, tungsten, molybdenum, phosphorus, boron, iron, alkaline earth metals and rare earth metals. The oxygenate is advantageously a simple or mixed oxide of one or more of the aforementioned elements or a mixture of these oxides. In this embodiment, the porous support is preferably a porous alumina. Advantageously, this alumina has the specific surface, the pore volume and the pore distribution properties defined above. This embodiment is particularly advantageous since the specific porosity of this catalyst shows a high cycle time in the catalysis of the reaction for the cyclizing hydrolysis of the aminonitriles, as described in the patent application W096 / 22974. The presence of the aforementioned oxygenated compounds on the surface of the pores makes it possible to have a better catalytic effect than that with the catalyst prepared with the same oxygenated compound but in bulk, unsupported form. When the inorganic oxide forming the support has catalytic activity in the cyclizing hydrolysis reaction, the presence of these oxidized compounds modifies the catalytic activity of the catalyst in particular by improving the selectivity of the reaction, by minimizing side reactions.

According to yet another characteristic of the invention, the efficiency of the catalyst, and more particularly its selectivity, can be improved by the presence, with the oxygenate, of anions chosen from the group comprising / of fluorine, anions of the general formula (Mx0y ) in which M represents an element chosen from the group comprising silicon, arsenic, antimony, nitrogen, sulfur, carbon and phosphorus., where x is an integer between 1 and 4 and is an integer between 1 and 8, or heteropolyaniones (HPA), of the general formula X < n +) T? 204o (6"n)" in which T is tungsten or molybdenum and X is silicon, germanium, phosphorus, arsenic or vanadium.; As examples of anions which are more particularly suitable for the invention, mention may be made in particular of the phosphates, sulfate silicates and the heteropolyanions of dodecamolybdate and dodecatungstate. Consequently, the obtained raw lactam is of better quality. The production of a pure lactam that meets the specifications mentioned above, is made easier. The concentration by weight of the oxygenated compound present in the catalyst is advantageously between 1000 ppm and 30% expressed as the mass of the element in the oxygenated compound, in relation to the total mass of the catalyst. This concentration is more preferably between 0.5% and 15% by weight. The concentration of the anions present in the catalyst is advantageously between 0.5 and 15% by weight. When the porous supports correspond to the aluminas according to the invention, these aluminas are generally obtained by the dehydration of gibbsite, bayerite, nordstrandite or various mixtures thereof. The various processes for the preparation of aluminas are described in the Kirk-Othmer encyclopedia, Volume 2, pages 291-297. The aluminas used in the present process can be prepared by placing a hydrated alumina, in finely divided form, in contact with a hot gas stream at a temperature between 400 ° C and 1000 ° C, followed by the maintenance of contact between the hydrate and the gases for a period ranging from a fraction of 1 second to 10 seconds, and finally the separation of partially dehydrated alumina and hot gases. Reference may be made in particular to the process described in U.S. Patent No. 2,915,365. It is also possible to carry out the autoclaving of the alumina agglomerates obtained above, in an aqueous medium, optionally in the presence of acid, at a temperature above 100 ° C and preferably between 150 ° C and 250 ° C, for a preferably between 1 and 20 hours, followed by drying and calcination thereof. The calcination temperature is adjusted such that the specific surface and the pore volumes within the range of values indicated above are obtained. The catalysts of the invention advantageously have a specific surface greater than 50 m2 / g. In addition, they advantageously have pores larger than 0.1 μm in diameter, the pore volume provided by these pores is greater than or equal to ml / 100 g, advantageously greater than or equal to 10 ml / 100 g. In a preferred embodiment of the invention, these catalysts also comprise pores greater than or equal to 0.5 μm in diameter, the corresponding pore volume being greater than or equal to 5 ml / 100 g, preferably greater than or equal to 10 ml / 100. g. This pore volume generated by pores larger than 500 A in diameter, preferably larger than 0.1 μm and advantageously larger than 0.5 μm, makes it possible to obtain catalysts with a high cycle time as a catalyst for the cyclizing hydrolysis reaction of the aminonitriles in / lactams. In this way, such catalysts can be used in industrial processes for the production of lactams. According to the invention, catalysts comprising oxygenated compounds supported by a porous support are obtained, generally by impregnation of the support, in particular alumina, with a solution of a salt or compounds of the elements mentioned above, and are then dried and calcined at a temperature greater than or equal to 400 ° C, in order to optionally and advantageously convert said compounds or salts into the oxygenated compounds, preferably into the oxides.

Similarly, the addition of the anions can be carried out by placing the porous support in contact, before impregnation with the oxygenates or together with this impregnation, with a solution containing salts / based on these anions, which are advantageously thermally decomposable, such as ammonium salts. This addition can also be made by placing the porous catalyst, which comprises the oxygenate, in contact with a solution containing the anion to be added. Oxides and anions are generally present on the surface of the support pores, by these modalities. In yet another embodiment, already mentioned above, the compounds of the elements can be added to the material constituting the support before forming it or during the forming process. The calcination of the impregnated supports is preferably carried out under an oxidizing atmosphere such as air. Thus, as will be demonstrated below, the cyclizing hydrolysis reaction can be performed with a minimum of collateral reactions, thereby substantially improving the selectivity of the process to the lactam, and therefore the purity of the obtained crude product. The cyclizing hydrolysis reaction requires the presence of water. The molar ratio between the water and the aminonitrile used is usually between 0.5 and 50 and preferably 1 and 20. The higher value of this ratio is not critical to the invention, but larger proportions are of little interest on the economic background. Aminonitrile and water can be used in the form of their mixtures in the form of vapor. In yet another embodiment, the aminonitrile and the aqueous reagents are used in liquid form under pressure, optionally in the presence of a solvent. In the preferred embodiment of the invention, the reactants are maintained in the form of vapor in the reactor charged with a predetermined amount of catalysts. The free volume of the reactor can be occupied by an inert solid such as, for example, quartz, in order to promote the vaporization and dispersion of the reagents.

It is possible, without inconvenience, to use any inert gas as a vector, such as nitrogen, helium or argon. The temperature at which the process of the invention is carried out should be sufficient for 'the reagents are correctly in the vapor form. This is generally between 200 ° C and 450 ° C and preferably between 250 ° C and 400 ° C. The contact time between the aminonitrile. and the catalyst is not critical. This contact time is preferably between 0.5 and 200 seconds and more preferably between 1 and 100 seconds. Pressure is not a critical parameter of the process. In this way, the process can be 'carried out under pressure of 10 ~ 3 bar up to 200 bar.

Preferably, the process will be carried out under a pressure of 0.1 to 20 bar. In the case of a hydrolysis carried out in the vapor phase, this pressure is advantageously between 10"3 bar and 3 bar. It is not excluded to use an inert solvent under the reaction conditions, such as, for example, an alkane, a cycloalkane , an aromatic hydrocarbon or a halogenated form of one of the aforementioned hydrocarbons, and thus have a liquid phase in the reaction flow.Aminonitriles which can be cyclized by the process of the invention are / advantageously? -aliphatic aminonitriles such as? -aminovaleronitrile,? -aminocapronitrile,? -aminooctanitrile,? -aminononatyryl,? -aminodecanitrile,? -aminodecanonitrile,? -aminododecanonitrile or methylaminovaleronitrile.The preferred and most important compound is aminocapronitrile, which gives e-caprolactam. The last compound is the monomer of polyamide 6 used for the manufacture of various articles such as molded components, yarns, fibers, - fi laments, cables or movies. The e-caprolactam produced by the cyclizing hydrolysis reaction is sold by purification by the various known purification processes, such as distillation, crystallization in solvent or molten phase, treatment on resin, treatment with an oxidizing agent and / or hydrogenation. These various steps can be partially or totally combined in different orders and depending on the degree of purity of the e-caprolactam produced.

One of the advantages of the invention lies in the simplification of the purification process, by involving only one or two of these steps. Other objectives, advantages and details will emerge more clearly in the light of the examples given below, purely for indicative purposes.

EXAMPLES 1 TO 3 200 g of catalyst are charged and distributed in a cylindrical reactor 40 mm in diameter and equal to 1 m in height, as follows: in a first section of the reactor, 43.7 g of the catalyst are mixed with 889 g of glass spheres , in a second section of the reactor, 156.3 g of the catalyst are mixed with 169 g of glass spheres. Water and aminocapronitrile are injected at mass flow rates equal to 129 g / hour and 200 g / hour, respectively. The reactor is maintained at a temperature of 300 ° C.

The test stops after an operation time of 500 hours. The reaction mixture is evaluated by gas chromatography, in particular for (determining the concentration of caprolactam) - The degree of conversion (DC) of the aminocapronitrile and the selectivity S towards caprolactam (CPL) in relation to the converted aminocapronitrile are also determined The quality of the raw caprolactam obtained It is measured by titration of a solution of caprolactam sulfuric with aqueous solution of potassium permanganate 0.2 N. This is expressed in my KMn0 solution per kg of caprolactam. / This test is carried out according to the following procedure: 3 g of a solution containing caprolactam whose caprolactam concentration has been determined by liquid chromatography, are added to 60 ml of water. 3 ml of concentrated sulfuric acid solution (98%) are added to the caprolactam solution. The permanganate index, determined after the neutralization of the medium at a pH of 7, is measured by the addition of 0.2 N potassium permanganate solution. The alumina used as a catalyst has the following properties: i - Alumina: surface area ( SS): 139 m2 / g total pore volume: 117 ml / 100 g pore volume corresponding to pores larger than 500 A in diameter: 50 ml / 100 g - pore volume corresponding to pores larger than 200 A in diameter : 70 ml / 100 g pore volume corresponding to pores larger than 70 A in diameter: 116 ml / 100 g. The following table compares the results obtained in: - Example 1, which is representative of the prior art (patent application 096/22974) and was made with the alumina described above; Examples 2 and 3 are representative of the invention; these were made with catalysts made, respectively, by impregnation, drying and calcination of 3% TiO2 and 3% La2O3 deposited on the alumina described above.

Table 1 EXAMPLES 4 TO 11 '166.5 g of catalyst are charged and distributed in a cylindrical reactor of 40 mm in diameter and equal to 1 m in height, in the following manner: - in a first section of the reactor, 36.5 g of the catalyst are mixed with 845 g of glass spheres, in a second section of the reactor, 130 g of the catalyst are mixed with glass spheres.

The water and aminocapronitrile are injected at mass flow rates equal to 128 g / hour and 200 g / hour, respectively. The reactor is maintained at a temperature of 300 ° C. / The test stops after an operation time of 200 hours. The reaction mixture is evaluated by gas chromatography, in particular in order to determine the concentration of caprolactam. The degree of conversion (DC) of the aminocapronitrile and the selectivity S towards the caprolactam (CPL) are determined in relation to the converted aminocapronitrile. The quality of the crude caprolactam contained in the reaction medium is evaluated by measuring the permanganate index, determined by neutralizing the medium at a pH of 7, by adding hydrochloric acid solution and measuring the UV absorbance at a length wavelength of 290 nm. This quality is also characterized by the determination of the polarographic index, known as IPOL, which is representative of the concentration of electorreducible imines in the analyzed medium.

This index is determined according to the following procedure: The electrolyte (a solution at 10% by weight of HMD in water) is introduced into a container / polarographic volume of 10 or 20 ml. After de-aeration with agitation, the electrolyte is subjected to a flow of argon or nitrogen for 5 minutes. A "white" polarogram is produced under a nitrogen or argon atmosphere. 0.1 g of the sample to be analyzed is added to this electrolyte. After de-aeration and passage under an inert atmosphere of nitrogen or argon, a polarogram "white + sample" is established. A standard isobutanal sample containing 500 mg of isobutanal in methanol, the volume of the solution being 50 ml, is added to the electrolyte medium + sample. A polarogram is established under the same conditions as described above. Polarograms are recorded under the following conditions: initial potential = 1.1 V / Ag-AgCl - final potential = -1.9 V / Ag-AgCl sweep speed = 4 mV / s The calculation of the IPOL index is given by the formula: IPOL = 108 x VxU x I2-I1 72.11 M1 I3-I: in which: M1 represents the mass in grams of the sample taken from the medium to be analyzed, Ii represents the reduction current corresponding to the "target" of the electrolyte in nA, measured at -1.7 V / Ag-AgCl, 12 represents the reduction current corresponding to the "target + sample" measured at -1.7 'V / Ag-AgCl, 13 represents the reduction current corresponding to the "target + sample + standard", measured at -1.7 V / Ag-AgCl, - V represents the volume in me of the aggregate standard, U represents the title in g / liter of the isobutanal in the standard solution, IPOL is the polarographic index of the imines, expressed in mmol of isobutanal / ton of sample.

The alumina used as catalyst has the following properties: surface area (SS): 140 m2 / g total pore volume: 112.9 ml / 100 g - pore volume corresponding to pores larger than 10,000 A in diameter: 12 ml / 100 g pore volume corresponding to pores greater than 1000 A in diameter: 34.8 ml / 100 g pore volume corresponding to pores larger than 200 A in diameter: 92 ml / 100 g pore volume corresponding to pores greater than 70 A Diameter: 111 ml / 100 g. Table II below compares the results obtained. - Comparative Example 4 was carried out with the above alumina as a catalyst, free of oxidized compounds and / or anions, Examples 5 to 11 are representative of the invention. These were made with catalysts obtained by impregnation of the aforementioned alumina with a precursor of oxygenated elements, drying and calcination. The composition of the catalysts tested is indicated in Table II below.

This Table II also compares the results obtained regarding the activity of the catalyst in terms of the degree of conversion of the ACN and selectivity to the caprolactam. The results regarding the quality of the obtained caprolactam are compared in Table III. These results clearly show the effects of the presence of these oxygenated elements on the surface of the porous support on the imine content (IPOL index) and on the permanganate index and the UV absorbance. Accordingly, the invention makes it possible to produce a purer caprolactam which can be more easily purified and with fewer basic purification steps to meet the specifications required for its use, in particular for the manufacture of polyamide for textile use.

Table II Table III

Claims (13)

1. A process for the cyclizing hydrolysis of an aminonitrile compound in a lactam, by the reaction of an aminonitrile of the general formula (I): N = C-R-NHz (I) wherein R represents a substituted or unsubstituted aliphatic, cycloaliphatic or arylaliphatic radical comprising from 3 to 12 carbon atoms, with water, in the presence of a solid catalyst, characterized the process because the catalyst is a particulate catalyst obtained by deposition and / or adsorption of at least one oxygenated compound of at least one element chosen from the group consisting of the elements belonging to groups 1 to 16 of the universal classification of the elements (new classification), this list also includes the metals of the rare earths, on a support made of simple or mixed inorganic oxide, or a mixture of oxides of at least one element selected from the group consisting of silicon, aluminum, titanium, zirconium, vanadium, niobium, tantalum, tungsten, molybdenum, iron and metals of the rare earths, and because it comprises at least one macroporosity characterized by a pore volume, corresponding to pores larger than 5. 00 A diameter, greater than or equal to 5 ml / 100 g.

2. The process according to claim 1, characterized in that the particulate catalyst has a surface area greater than 10 m2 / g and a total pore volume greater than or equal to 10 ml / 100 g, the pore volume corresponding to pores greater than 500 A diameter, which is greater than or equal to 10 ml / 100 g.

3. The process according to any of claims 1 and 2, characterized in that the catalyst has a specific surface greater than 50 m2 / g.

4. The process according to any of claims 1 to 3, characterized in that the catalyst has a total pore volume, greater than or equal to 20 ml / 100 g with a pore volume corresponding to pores greater than 70 A in diameter, greater that or equal to 20 ml / 100 g.

5. The process according to any of claims 1 to 3, "Characterized in that the catalyst has a total pore volume greater than or equal to 15 ml / 100 g, with a pore volume corresponding to pores greater than 200 A in diameter, greater than or equal to 15 ml / 100 g.

6. The process according to any of the preceding claims, characterized in that the oxygenated compounds supported on a porous support are oxygenated compounds of the elements chosen from the group comprising silicon, titanium, zirconium, vanadium, niobium, tantalum, tungsten, molybdenum, hafnium , scandium, phosphorus, boron, iron, alkaline earth metals and rare earth metals, or mixtures thereof, or mixed oxides.

7. The process according to any of the preceding claims, characterized in that the catalyst comprises anions chosen from the group comprising fluorine, anions of the general formula (Mx0y) in which M represents an element chosen from the group comprising silicon, arsenic, antimony, nitrogen, sulfur, carbon and phosphorus, where x is an integer between 1 and 4 and that is an integer between 1 and 8, or heteropolyaniones (HPA) of the general formula X (n +) T? 204o (6"n) ~ in which T is tungsten or molybdenum and X is silicon, germanium, phosphorus, arsenic or vanadium.

8. The process according to any of the preceding claims, characterized in that the concentration of the oxygenated compounds, expressed by weight of the element relative to the weight of the catalyst, is between 1000 ppm and 30%.

9. The process according to claim 8, characterized in that the concentration of the oxygenates is between 0.5% and 15% by weight relative to the weight of the catalyst.

10. The process according to claim 7, characterized in that the concentration of the anions is between 0.5 and 15% by weight relative to the weight of the catalyst.

11. The process according to any of the preceding claims, characterized in that the particulate catalyst is in the form of spheres, pieces of grinding, extruded in the form of cylindrical granules or in hollow or solid multi-lobular form, or in the form of honeycombs or pellets .

12. The process according to any of the preceding claims, characterized in that the porous support is alumina.

13. The process according to any of the preceding claims, characterized in that the cyclizing hydrolysis reaction is carried out in the vapor phase.