EP0662944A1

EP0662944A1 - Process for isomerization of lactones into pentenoic acids by acid or basic catalysis

Info

Publication number: EP0662944A1
Application number: EP93920924A
Authority: EP
Inventors: Philippe Denis; Laurent Gilbert; Jean-Michel Grosselin; François Metz
Original assignee: Rhone Poulenc Fiber and Resin Intermediates SA; Rhone Poulenc Chimie SA
Current assignee: Rhodia Fiber and Resin Intermediates SAS
Priority date: 1992-10-02
Filing date: 1993-09-23
Publication date: 1995-07-19
Also published as: CZ79795A3; SG45321A1; SK41895A3; JPH08500608A; CA2146153A1; CN1089933A; PL308208A1; WO1994007835A1; MX9306070A; BR9307159A; KR950703508A

Abstract

The present invention relates to a process for isomerization of lactones, more particularly various valerolactones and isomers thereof into pentenoic acids. It relates more particularly to a process for isomerization into a pentenoic acid of at least one lactone having 5 carbon atoms, caracterized in that said lactone is brought in contact in vapour phase with a solid acid catalyst selected amongst molecular acid sieves, clays, bridged clays (or pillar clays), massic oxides and acid phosphates or with a solid basic catalyst selected amongst metal basic phosphates, metal basic oxides, metal carbonates and molecular basic sieves.

Description

PROCESS FOR THE ISOMERIZATION OF LACTONES TO PENTENOIC ACIDS BY ACID OR BASIC CATALYSIS

The present invention relates to a process for the isomerization of lactones, more particularly of the various valerolactones and their isomers, into pentenoic acids.

The hydroxycarbonylation of pentene-3-oic acid to prepare adipic acid always leads to the formation of gamma-valerolactone as a by-product. The recovery of gamma-valerolactone (or 4-methylbutyrolactone) therefore represents an important problem to be solved, within the framework of a possible industrial process for the preparation of adipic acid by hydroxycarbonylation of pentene-3-oic acid.

One of the possible modes of recovery consists in trying to carbonylate gamma-valerolactone. Thus, patent EP-A-0 395 038 describes this carbonylation, at a temperature greater than or equal to 190 ° C. and in the presence of rhodium / H I or rhodium / H Br.

This process is relatively selective in adipic acid, with however also the formation of valeric acid; but the productivity of adipic acid is low, despite a high concentration of rhodium. The problem of increasing the yield of a hydroxycarbonylation process of pentene-3-oic acid, by the transformation of gamma-valerolactone into valorisam compounds therefore did not find a satisfactory solution.

The present invention aims precisely to solve this problem by allowing the isomerization of ia gamma-valerolactone or its isomers into pentenoic acids, which can again be hydroxycarbonylated to adipic acid. It consists of a process for isomerizing pentenoic acid from at least one lactone having 5 carbon atoms, characterized in that said lactone is brought into contact in vapor phase with a solid acid or basic catalyst. In the present text, the expression “solid acid catalysts” means solid compounds, most often metal oxides or metal salts, which cause the dehydration of methylbutynol to methylbutenyne (“methylbutynol” test) according to the reaction:

OH H +

I CH 3 _, - C _| -C = CH → CH 2 = C | -CsCH + H 20

CH ₃ CH ₃ The term solid basic catalysts will mean solid compounds, most often metal oxides or metal salts, which cause the downgrading of methylbutynol to acetylene and acetone ("methylbutynol" test) according to the reaction:

One can refer for more details on this test to the article of "Applied

Catalysis, 78 (1991), pages 213 to 225.

The lactones which can be used in the process of the invention are more particularly gamma-valerolactone (or 4-methyl butyrolactone), delta-valerolactone, 2-methyl butyrolactone, 3-ethyl propiolactone, ethyl -2 propiolactone, 2,3-dimethyl propiolactone.

Among these lactones, gamma-valerolactone is the most interesting because of its formation in the hydroxycarbonylation processes of pentene-3 oic acid to adipic acid.

Among the acid solid catalysts, there may be mentioned acid molecular sieves, acid clays, bridged clays (or pillar clays), mass oxides and acid phosphates.

The acid molecular sieves are more particularly the zeolites of pentasil structure, such as for example ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-48, of ferrierite structure, of mordenite structure and zeolites with a faujasite structure, such as, for example, zeolite X or zeolite Y.

The zeolites of pentasil or mordenite structure are more particularly the zeolites of type ZSM-5, ZSM-11, ZSM-22, ZSM-23 and ZS -48 and mordenite having the general formula (I) expressed in terms of oxide ratios :

M _{2 / n} O, X ₂ O ₃ , mSiO ₂ , pH ₂ O (I)

in which : . M represents an element chosen from hydrogen, NH ₄ and the metals mono-, di-, tri-, and tetravalents,. X represents a trivalent element chosen from Al, Ga, Fe and B,. n represents a number from 1 to 4,. m represents a number equal to or greater than 10,. p represents a number from 0 to 40.

Zeolites of the faujasite type of structure are more particularly those having the general formula (II) expressed in terms of oxide ratios:

M _{2 / n} O, Z ₂ O ₃ , dSiO ₂ , xH ₂ O (II)

in which :

. M represents an element chosen from hydrogen,

NH ₄ and the metals mono-, di-, tri-, and tetravalent, M being at least partly a hydrogen atom,. Z represents a trivalent element chosen from Al, Ga, Fe and B,. n represents a number from 1 to 4,

. d represents a number equal to or greater than 2,. x represents a number from 5 to 100.

The acid zeolites used in the context of the invention are in particular those in the formula of which the oxide associated with the silica is that of a trivalent metal. Zeolites are generally preferred in formula (I) or (II) in which M is chosen from hydrogen, NH ₄ , alkali metals such as, for example Na, K, Li, Rb or Cs, alkaline earth metals teis as for example Be, Mg, Ca, Sr or Ba, rare earth metals such as for example La or Ce, transition metals such as for example Fe.

For a more detailed description of acid clays, reference may be made to patent FR-A-2 622 575 which is incorporated into the present text by reference.

It is preferred in the process of the invention to use smectites such as for example montmorillonites, beidellites, nontronites, hectorites, stevensites and saponites. Bridged clays, which can be used as catalysts in the present process, are clays between the sheets of which bridges or pillars have been introduced which maintain a basic spacing. The basal spacing is the sum of the thickness of a sheet of clay and the interfoiial spacing. The preparation of these bridged clays has been described in particular in patent FR-A-2,563,446 as well as in patent FR-A-2,618,143.

As starting clay, we will generally prefer beidellites.

The bridging of clays can be carried out in particular using hydroxides of aluminum, vanadium, molybdenum, zirconium, iron, nobium, tantalum, chromium, lanthanum, cerium, titanium, gallium or mixed hydroxides of several of these metals.

These bridged clays can be modified, in particular by the action of a dihalogen, an ammonium halide or an acid such as sulfuric acid or hydrohalic acids. The halogen thus optionally introduced is preferably chlorine or fluorine.

Preferably, clays, particularly beidellites, bridged with aluminum hydroxide are used in the process of the invention.

The mass oxides are metal oxides, mixtures of metal oxides or modified metal oxides, in particular by the action of a dihalogen, an ammonium halide or an acid such as sulfuric acid or hydrohalic acids. The halogen thus optionally introduced is preferably chlorine or fluorine.

By way of nonlimiting examples, mention may be made of mixtures SiO ₂ / ALO ₃ , SiO ₂ / Ga ₂ O ₃ , SiO ₂ / Fe ₂ O ₃ , SiO ₂ / B ₂ O ₃ , halogenated aluminas such as in particular the chlorinated aluminas and fluorinated aluminas, sulfated zirconia, niobium oxide or tungsten oxide.

The acid phosphates which can be used in the process of the invention are in particular by way of examples the boron phosphates, alone or as a mixture with alumina or with silica, corresponding to different molar ratios H. _j BO .JHgPO. introduced during synthesis, lanthanum phosphate, aluminum phosphates corresponding to different molar ratios introduced during the synthesis, phosphorus pentoxide / silica mixtures (usually called UOP catalysts), aluminophosphates with zeolitic structure (AIPO) and silico-aluminophosphates with zeolitic structure (SAPO). The basic solid catalysts which can be used in the process of the invention are in particular basic metal phosphates. Basic metal oxides, metal carbonates and basic molecular sieves.

The basic metal phosphates are in particular the phosphates, the hydrogenophosphates and the dihydrogenophosphates of general formula (III):

(PO ₄ A _y ), (imp) _z (III)

in which :

- A represents a metal atom, a group of metal atoms or in part a hydrogen atom;

- y represents a whole or fractional number from 3/4 to 3 depending on the valence of the elements A;

- Imp corresponds to a basic impregnation compound consisting of metal chosen from alkaline earth metals, alkali metals and their mixtures associated with a counter anion to ensure electrical neutrality;

- the coefficient z represents the weight ratio between the impregnating agent and the impregnating agent (PO. A) and it is between 0% and 20% and preferably between 2% and 10%.

Preferably the basic phosphates used in the process of the invention are compounds of general formula (III) in which:

- A more particularly represents calcium, zirconium, lanthanum, cerium, samarium, aluminum, boron, iron and partly hydrogen; - y represents a whole or fractional number from 3/4 to 3 depending on the valence of the elements A;

- Imp consists of an alkali metal or a mixture of alkali metals and a basic counter anion;

- the coefficient z is between 2% and 10%. By way of nonlimiting examples of basic phosphates, mention may be made of lanthanum phosphate associated with a cesium, rubidium or potassium compound, cerium phosphate associated with a cesium, rubidium or potassium compound, phosphate samarium associated with a cesium, rubidium or potassium compound, calcium phosphate associated with a cesium, rubidium or potassium compound, calcium hydrogen phosphate associated with a cesium, rubidium or potassium compound, zirconium hydrogen phosphate associated with a compound of cesium, rubidium or potassium.

The basic phosphates of formula (III) can be prepared by impregnation of a compound of formula (IV) PO ₄ A ', in which A' has the same meaning as A, with a solution or a suspension of Imp in a solvent volatile, such as water preferably.

The results are even better than Imp is more soluble and as compound PO ₄ A 'is freshly made _there. Thus an advantageous process for the preparation of phosphates of formula (III) consists in: a) carrying out the synthesis of the compound PO ₄ A '; then preferably without separating PO ₄ A 'from the reaction medium; b) introducing the impregnating agent Imp into the reaction medium; c) separating any residual liquid from the reaction solid; d) dry and possibly calcine.

If we refer to the general techniques for the preparation of phosphates (as described in particular in "PASCAL P. New treaty of mineral chemistry" volume X (1956), pages 821-823 and in "GMELINS Handbuch der anorganischen

Chemie ^"(8th Edition) volume 16 (C), pages 202-206 (1965), there are two main routes to phosphates. On the one hand, the precipitation of a soluble metal salt (chloride, nitrate) with ammonium hydrogen phosphate and finishing treatment with ammonia, then possibly additional neutralization. On the other hand, the reaction of the metal oxide with hot phosphoric acid and a possible finishing treatment with alkaline hydroxide.

The basic metal oxides used in the process of the invention are the basic oxides or those which are made basic by treatment with a base such as an alkali metal or alkaline earth metal hydroxide. As basic metal oxides, non-limiting mention may be made of the oxides of alkali metals, alkaline earth metals, metals of group IIIa of the periodic table of elements, transition elements or rare earths treated or not with a hydroxide of alkali metal. By way of examples, there may be mentioned more particularly alumina treated with sodium hydroxide, zinc oxide, calcium oxide.

The basic molecular sieves used in the process of the invention are more particularly zeolites of pentasil structure such as for example ZSM-5, ZSM-11, ZSM-22, ZSM-23 or ZSM-48, of mordenite structure, ferrierite structure or faujasite structure such as zeolite X or zeolite Y, of general formula (V) expressed in terms of oxides:

E _{2 / a} O, T ₂ O ₃ , bSiO ₂ , rH ₂ O (V)

in which :

- E represents an alkali or alkaline earth metal, in whole or with a small proportion of hydrogen, - T represents a trivalent metal chosen from Al, Ga, Fe and

B.

- a represents a number from 1 to 2,

- b represents a number equal to or greater than 2,

- r represents a number from 0 to 100.

In the general formula (V) the expression "low proportion of hydrogen" for the meaning of the symbol E means that the possible presence of protons in the molecular sieve must not be such that it has an acid reaction to the test indicated previously.

Preferably, among the basic molecular sieves of formula (V), those for which E represents an alkali metal will be used.

As nonlimiting examples of basic molecular sieves, mention may be made of the NaZSM-5 zeolite, the NaMOR zeolite, the 13XCs zeolite, the NaY zeolite, the KY zeolite and the CsY zeolite. The process is carried out continuously.

The catalyst used can be placed in a fixed bed or be used in a fluidized bed. It can be used in mixture with inert solids, in order to increase the contact surface. - The isomerization process is generally carried out at a temperature of 200 ° C to 500 ° C and preferably from 250 ° C to 400 ° C.

The contact time, defined as the ratio between the volume of the catalyst and the total gas flow (lactone + carrier gas if applicable) at the chosen temperature, usually varies from 0.1 seconds to 50 seconds and most often from 1 second at 10 seconds.

The pressure is not critical. It generally ranges from atmospheric pressure to 10 MPa (100 bar) and preferably from atmospheric pressure to 1.5 MPa (15 bar).

The lactone can be introduced alone into the reactor containing the catalyst.

It can also be introduced together with an inert gaseous vector; this joint introduction can be carried out in the form of a mixture or in the form of separate simultaneous introductions.

The inert gaseous vector can consist of a gas or a mixture of gases inert under the reaction conditions, such as, for example, nitrogen, argon, air, water vapor, gaseous carboxylic acids at the temperature at which the reaction takes place.

The lactone represents from 10% to 100% by weight relative to the total weight of the gases introduced into the reaction and preferably from 40% to 100%. The process of the invention leads to the formation of a mixture of pentenoic acids, pentene-2-oic acid, pentene-3-oic acid and pentene-4-oic acid.

Pentene-3-oic and pentene-4-oic acids can be hydroxycarbonylated by reaction with carbon monoxide and water to adipic acid.

The pentene-2-oic acid can itself be isomerized into pentene-3-oic and pentene-4-oic acids which are directly valorized as indicated above.

The isomerization reaction according to the invention being a thermodynamically difficult reaction, the rate of transformation of the lactone will be limited in practice generally to less than 80% and most often to less than 60%, the unprocessed lactone can then be easily recycled. The following examples illustrate the invention.

The following procedure will be used (unless otherwise stated) in the examples.

In a vertically arranged reactor (quartz tube of length = 15

3 cm and diameter = 2 cm), we successively load 2 cm of quartz, a mixture

3 3 3 intimate with 2 cm of catalyst and 10 cm of quartz, then 5 cm of quartz. Then filling the reactor with glass beads (diameter: 2 to 3 mm).

The catalyst is conditioned to the temperature chosen for the reaction (300 ° C. unless otherwise indicated), by passing for two hours a stream of nitrogen (2 liters / hour under normal pressure and temperature conditions).

The lactone is then injected via a syringe pump.

The lactone injection rates will be specified for each example: 3 they are expressed in cm (ml) of lactone in the liquid state.

After a warm-up of approximately 15 minutes, the test generally lasts 1 hour. The products leaving the reactor are trapped in a receiver containing 10 3 cm of acetonitrile.

The analysis of the reaction products and of the unprocessed lactone is carried out by gas chromatography (GC).

We calculate for each test:

- hourly weight productivity (PPH): weight of hired lactone

1 relative to the weight of the catalyst and per hour (expressed in h ");

- the transformation rate (TT) of the lactone:% of the transformed lactone compared to the engaged lactone;

- the yields (RR) of the various pentenoic acids: mole% of each pentenoic acid formed relative to the engaged lactone.

EXAMPLES 1 TO 7 (substrate: gamma-valerolactone)

Tests of different zeolites of the ZSM-5 type of general formula (I) having different molar ratios Si / Ai and more or less acidified:

- zeolite 1: Si / Ai = 30 75% of the elements M in formula (I) are H, - zeolite 2: Si / Ai = 52

75% of the elements M in formula (I) are H,

- zeolite 3: Si / Ai = 120 75% of the elements M in formula (I) are H,

- zeolite 4: Si / Ai = 30

M in formula (I) mainly represents NH ₄ and minority H,

- zeolite 5: Si / Ai = 50

- zeolite 6: Si / Ai = 120

M in formula (I) mainly represents NH ₄ and minority H,

- zeolite 7: Si / Ai = 50

M in formula (I) represents H in full.

The operating conditions are those given in the general operating mode described above.

The contact time (te) is approximately 1.4 seconds for each of the examples.

Table 1 below collates the results obtained. The abbreviations P2, P3 and P4 used have the following meanings:

P2 = pentene-2-oic acid P3 = pentene-3-oic acid P4 = pentene-4-oic acid

TABLE 1

EXAMPLES 8 TO 15 (substrate: gamma-valerolactone)

Tests of various acid catalysts

- SiO ₂ / AL0 ₃ (marketed by DEGUSSA) comprising 16% by weight of Si0 ₂ ,

- Y zeolite having an SiO ₂ / ALO ₃ ratio of 5 (marketed by TOYO SODA),

- PO ₄ B (ratio B / P = 1),

- P0 ₄ .

- Montmorillonite Volclay clay (MONTMO),

- ZSM-5 type zeolite of formula (I) with X representing Fe and with an SiO ₂ / Fe ₂ O ₃ ratio = 120 (ZSM-5 / Fe)

- chlorinated AL0 ₃ ,

- niobium oxide.

The operating conditions are those described above. The reaction time is 1 hour except -; __ 3 Example 14 with chlorinated alumina where this time is 0.5 h, the temperature can be different from 300 ° C, the nitrogen flow can be different from 2 liters / hour and the rate of introduction of gamma-valerolactone can be different from 3.2 ml / h of liquid / hour.

15

20

25

30

35

TABLE 2

EXAMPLE 16 (substrate: delta-valerolactone)

Tests on the zeolite Y exchanged Fe (SiO ₂ / ALO ₃ ratio = 5 and M = Fe).

The operating conditions are those which have been described previously in the general operating mode, with the following differences:

- reaction temperature: 370 ° C

3

- catalyst volume: 1.5 cm - N ₂ flow rate: 3 l / h

- lactone flow rate: 3.2 ml / h.

The following results are obtained:

Tests of different basic solid catalysts:

- Ce phosphate doped with 3% Cs hydrogen phosphate

- Ca hydrogen phosphate (hydroxyapatite)

- 13XCs zeolite

- alumina treated with soda (10% soda by weight per weight)

3 3 (value 4 cm instead of 2 cm).

Table 3 below collates the results obtained as well as the values of the parameters which have been changed with respect to the general operating mode.

TABLE 3

EXAMPLES 21 TO 24 (substrate: gamma-valerolactone)

La phosphate tests associated with different impregnants (the percentage of impregnator relative to La phosphate is expressed by weight by weight).

Table 4 below collates the results obtained as well as the values of the reaction temperature and of the injection rate of the lactone.

TABLE 4

Claims

1 - Process for isomerization into pentenoic acid of at least one lactone having 5 carbon atoms, characterized in that said lactone is brought into contact in vapor phase with a solid acid or basic catalyst.

2 - Process according to claim 1, characterized in that the lactone is chosen from gamma-valerolactone (or 4-methyl butyrolactone), delta-valerolactone, 2-methyl butyrolactone, 3-ethyl propiolactone, 2-ethyl propiolactone, 2,3-dimethyl propiolactone.

3 - Method according to one of claims 1 or 2, characterized in that the catalyst is an acidic solid catalyst chosen from acid molecular sieves, acid clays, bridged clays (or pillar clays), mass oxides and acid phosphates.

4 - Process according to claim 3, characterized in that the acid molecular sieves are zeolites of pentasil structure, such as ZSM-5, ZSM-11, ZSM-22, ZSM-23, ZSM-48, ferrierite, mordenites and zeolites of faujasite structure, such as zeolite X or zeolite Y.

5 - Method according to one of claims 3 or 4, characterized in that the acid zeolites of pentasil or mordenite structure are zeolites of type ZSM-5, ZSM-11, ZSM-22, ZSM-3 and ZSM-48 or mordenite having the general formula (I) expressed in terms of oxide ratios:

^M 2 / n ⁰ ' ^X 2 ° 3' ^mSi0 2 ' ^pH 2 ° ^(l)

in which :

. M represents an element chosen from hydrogen, NH ₄ and the metals mono-, di-, tri-, and tetravalents,. X represents a trivalent element chosen from Al, Ga, Fe and B,. n represents a number from 1 to 4,

. m represents a number equal to or greater than 10,. p represents a number from 0 to 40. 6 • Process according to claim 3, characterized in that the acid molecular sieves are zeolites of faujasite structure of zeolite X or zeolite Y type having the general formula (II) expressed in terms of oxide ratios:

^M 2 / n ^{0, Z} 2 ° 3 ' ^dSi0 2' ^xH 2 ° ^(ll)

in which :

. M represents an element chosen from hydrogen, NH ₄ and the metals mono-, di-, tri-, and tetravalents,

M being at least partly a hydrogen atom,. Z represents a trivalent element chosen from Al, Ga, Fe and B,

. n represents a number from 1 to 4,. d represents a number equal to or greater than 2,

. x represents a number from 5 to 100.

7 - Method according to one of claims 3 to 6, characterized in that the acid molecular sieves are the acid zeolites in the formula of which the oxide associated with the silica is that of a trivalent metal.

8 - Process according to claim 3, characterized in that the clays used are smectites such as montmorillonites, beidellites, nontronites, hectorites, stevensites and saponites.

9 - Process according to claim 3, characterized in that the bridged clays used are clays between the sheets of which have been introduced bridges or pillars which maintain a basic spacing, by bridging with the aid of aluminum hydroxides, vanadium , molybdenum, zirconium, iron, nobium, tantalum, chromium, lanthanum, cerium, titanium, gallium or mixed hydroxides of several of these metals and are preferably beidellites, bridged with using aluminum hydroxide.

10 - Method according to one of claims 3 or 9, characterized in that the bridged clays used are modified, by the action of a dihalogen, an ammonium halide or an acid such as sulfuric acid or hydrohalic acids, the halogen thus optionally introduced preferably being chlorine or fluorine. 11 - Process according to claim 3, characterized in that the mass oxides used are metal oxides, mixtures of metal oxides or metal oxides modified by the action of a dihalogen, an ammonium halide or a acid such as sulfuric acid or hydrohalic acids, the halogen thus optionally introduced being preferably chlorine or fluorine.

12 - Method according to one of claims 3 or 11, characterized in that the mass oxides used are chosen from mixtures SiO ₂ / ALO ₃ , SiO ₂ / Ga ₂ O ₃ , SiO ₂ / Fe ₂ O ₃ , SiO ₂ / B ₂ O _3> halogenated aluminas such as chlorinated aluminas and fluorinated aluminas, sulphated zirconia, niobium oxide or tungsten oxide.

13 - Process according to claim 3, characterized in that the acid phosphates are chosen from boron phosphates, alone or as a mixture with alumina or with silica, corresponding to different molar ratios

H ₃ BO ₃ / H ₃ PO ₄ introduced during synthesis, lanthanum phosphate, aluminum phosphates corresponding to different molar ratios AO ₃ / H ₃ PO ₄ introduced during synthesis, phosphorus pentoxide / silica mixtures (usually called UOP catalysts), aluminophosphates with zeolitic structure (AIPO) and silico-aluminophosphates with zeolitic structure (SAPO).

14 - Method according to one of claims 1 or 2, characterized in that the catalyst is a basic solid catalyst chosen from basic metal phosphates, basic metal oxides, metal carbonates and basic molecular sieves.

15 - Process according to claim 14, characterized in that the basic metal phosphates are more particularly the phosphates of general formula (III):

(P0 ₄ A _y ), (lmp) _z (III)

in which:

- A represents a metal atom, a group of metal atoms or in part a hydrogen atom; - y represents a whole or fractional number from 3/4 to 3 depending on the valence of the elements A;

- the coefficient z represents the weight ratio between the impregnating agent and the impregnating agent (PO ₄ A) and it is between 0% and 20% and preferably between 2% and 10%.

16 - Method according to one of claims 14 and 15, characterized in that the basic metal phosphates are more particularly the phosphates of general formula (III):

(PO ₄ A _y ), (lmp) _z (III)

in which :

- A more particularly represents calcium, zirconium, lanthanum, cerium, samarium, aluminum, boron, iron and partly hydrogen;

- y represents a whole or fractional number from 3/4 to 3 depending on the valence of the elements A; - Imp consists of an alkali metal or a mixture of metals a. alins and a basic counter anion;

- the coefficient z is between 2% and 10%.

17 - Method according to one of claims 14 to 16, characterized in that the basic metal phosphates are more particularly lanthanum phosphate associated with a compound of cesium, rubidium or potassium, cerium phosphate associated with a compound of cesium, rubidium or potassium, samarium phosphate associated with a compound of cesium, rubidium or potassium, calcium phosphate associated with a compound of cesium, rubidium or potassium, calcium hydrogen phosphate associated with a composed of cesium, rubidium or potassium, zirconium hydrogen phosphate associated with a compound of cesium, rubidium or potassium. 18 - Method according to one of claims 14 to 17, characterized in that the basic metal phosphates are prepared by impregnation of a compound of formula (IV) PO ₄ A ', in which A' has the same meanings as A, with a solution or suspension of Imp in a volatile solvent, such as water preferably.

19 - Process according to one of claims 14 to 18, characterized in that the basic metal phosphates are prepared according to a process which consists: a) in carrying out the synthesis of the compound PO ₄ A '; then preferably without separating PO ₄ A 'from the reaction medium; b) introducing the impregnating agent Imp into the reaction medium; c) separating any residual liquid from the reaction solid; d) dry and possibly calcine.

20 - Process according to claim 14, characterized in that the basic metal oxides are more particularly the oxides of basic character or those which are made basic by a treatment using a base such as an alkali metal hydroxide or of alkaline earth metal.

21 - Method according to one of claims 14 and 20, characterized in that the basic metal oxides are chosen from es oxides of alkali metals, alkaline earth metals, metals of group IIIa of the periodic table of elements, elements transition or rare earth or not treated with an alkali metal hydroxide.

22 - Process according to claim 14, characterized in that the basic molecular sieves are more particularly zeolites of pentasil structure such as ZSM-5, ZSM-11, ZSM-22, ZSM-23 or ZSM-48, of mordenite structure , of ferrierite structure or of faujasite structure such as zeolite X or zeolite Y, of general formula (V) expressed in terms of oxides:

E _{2 / a} O, T ₂ O ₃ , bSiO ₂ , rH ₂ O (V)

in which: - E represents an alkali or alkaline-earth metal, in whole or with a small proportion of hydrogen, - T represents a trivalent metal chosen from Al, Ga, Fe and B, - a represents a number from 1 to 2,

- b represents a number equal to or greater than 2,

- r represents a number from 0 to 100.

23 - Process according to claim 14, characterized in that the basic molecular sieves are more particularly the zeolites ZSM-5, ZSM-11, ZSM-22, ZSM-23 and ZSM-48, the mordenites, the ferrierites and the faujasites zeolite X and zeolite Y.

24 - Method according to one of claims 1 to 23, characterized in that it is implemented at a temperature of 200 ° C to 500 ° C and preferably from 250 ° C to 400 ° C.

25 - Method according to one of claims 1 to 24, characterized in that the lactone is introduced alone into the reactor containing the catalyst.

26 - Method according to one of claims 1 to 24, characterized in that the lactone is introduced together with an inert gaseous vector which is constituted by a gas or a mixture of inert gases under the reaction conditions, such as nitrogen, l argon, air, water vapor, gaseous carboxylic acids at the temperature at which the reaction takes place.

27 - Method according to one of claims 25 or 26, characterized in that the lactone represents from 10% to 100% by weight relative to the total weight of the gases introduced into the reaction and preferably from 40% to 100%.