USE OF MOLYBDENUM AND VANADIUM MIXED OXIDES AS CATALYSTS FOR THE OXIDATION OF UNSATURATED ALCOHOLS INTO UNSATURATED CARBOXYLIC ACIDS

Abstract

The present invention relates to the use of molybdenum and vanadium mixed oxides, optionally iron doped, as catalysts for the oxidation of unsaturated alcohols, in particular allyl alcohol, and also to a process for the production of unsaturated carboxylic acids, in particular acrylic acid, in the gas phase, in the presence of such a catalyst.

Claims

1. A molybdenum and vanadium mixed oxide catalyst represented by the following formula (I):
Mo.sub.aVFe.sub.bO.sub.c(I) wherein: a, b, and c denotes the atomic ratio of Mo, Fe and O respectively; a varies from 3 to 4 inclusive, b varies from 0 to 1 inclusive, c varies from 10 to 15 inclusive, said compound of formula (I) being in an orthorhombic or trigonal crystalline phase, wherein said catalyst is for catalysing the oxidation reaction of an alcohol of following formula (II) CH.sub.2C(R.sup.1)CH.sub.2OH (II), in which R.sup.1 represents a hydrogen atom or a methyl radical, to give a unsatured carboxylic acid of following formula (III) CH.sub.2C(R.sup.1)COOH (III), in which R.sup.1 has the same meaning as in the above formula (II), said reaction being carried out in the gas phase, said gas phase comprising at least oxygen.

2. Catalyst according to claim 1, wherein the oxides of formula (I) are chosen among compounds in which a=3, and b=0 to 0.5 inclusive.

3. Catalyst according to claim 1, wherein the oxides of formula (I) are chosen among trigonal Mo.sub.3VO.sub.c, orthorhombic Mo.sub.3VO.sub.c and trigonal Mo.sub.3VFe.sub.0.2O.sub.c in which c has the same signification than in formula (I).

4. Process for the production of an unsatured carboxylic acid from an alcohol in the presence of a catalyst, said process comprising only one step of oxidation of an alcohol of following formula (II):
CH.sub.2C(R.sup.1)CH.sub.2OH(II) in which R.sup.1 represents a hydrogen atom or a methyl radical, to result in an unsaturated carboxylic acid of following formula (III):
CH.sub.2C(R.sup.1)COOH(III) in which R.sup.1 has the same meaning as in the above formula (II), said reaction being carried out in the gas phase, the said gas phase comprising at least oxygen, and in the presence of a solid catalyst chosen from the compounds of following formula (I):
Mo.sub.aVFe.sub.bO.sub.c(I) wherein: a, b and c denotes the atomic ratio of Mo, Fe and O respectively; a varies from 3 to 4 inclusive, b varies from 0 to 1 inclusive, c varies from 10 to 15 inclusive, said compound of formula (I) being in an orthorhombic or trigonal crystalline phase.

5. Process according to claim 4, wherein R.sup.1 represents a hydrogen atom and said process comprises a step of oxidation of allyl alcohol to give acrylic acid.

6. Process according to claim 4, wherein the solid catalyst is chosen among compounds of formula (I) in which a=3 and b=0 to 0.5 inclusive.

7. Process according to claim 4, wherein the solid catalyst is chosen among trigonal Mo.sub.3VO.sub.c, orthorhombic Mo.sub.3VO.sub.c and trigonal Mo.sub.3VFe.sub.0.2O.sub.c, in which c as the same meaning as in the formula (I).

8. Process according to claim 4, wherein the oxidation reaction is carried out at a temperature varying inclusively from 330 to 370 C.

9. Process according to claim 4, wherein the oxidation reaction is carried out at a temperature of 350 C.

10. Process according to claim 4, wherein the oxidation reaction is carried out at a pressure ranging from 1 to 1.10.sup.6 Pa.

11. Process according to claim 4, wherein within the gas phase, the alcohol of formula (II)/oxygen molar ratio varies from 0.1 to 2.

12. Process according to claim 4, wherein the oxidation reaction is carried out using a gas phase comprising nitrogen as carrier gas and in which the alcohol of formula (II)/oxygen/nitrogen molar ratio is 1/2.2/11.8.

13. Process according to claim 4, wherein the oxidation reaction is carried out using a gas phase comprising a mixture of nitrogen and helium as carrier gas and in which the alcohol of formula (II)/oxygen/nitrogen+helium ratio molar ration is 0.7/1.5/8.

14. Process according to claim 4, wherein the catalyst of formula (I) is supported by a porous solid support.

Description

EXAMPLES

[0047] In the examples which follow, the following starting materials were used:

[0048] 99% Allyl alcohol (Sigma Aldrich),

[0049] Oxygen (Air Liquide),

[0050] Helium (Air Liquide),

[0051] All these materials have been used as received from the suppliers, i.e., without additional purification.

[0052] The different catalysts used in the examples are listed hereafter:

[0053] Trigonal Mo.sub.3VO.sub.c, denoted Tr-MoVO,

[0054] Orthorhombic Mo.sub.3VO.sub.c, denoted OrMoVO,

[0055] Tetragonal Mo.sub.3VO.sub.c, denoted TeMoVO,

[0056] Amorphous Mo.sub.3VO.sub.c, denoted AmMoVO,

[0057] Trigonal Mo.sub.3VFe.sub.0.2O.sub.c, denoted Tr-MoVFeO,

[0058] Trigonal Mo.sub.3VCu.sub.0.14O.sub.c, denoted Tr-MoVCuO,

[0059] Trigonal Mo.sub.3VNb.sub.0.13O.sub.c, denoted Tr-MoVNbO,

[0060] Trigonal Mo.sub.3VTe.sub.0.23O.sub.c, denoted Tr-MoVTeO,

[0061] Trigonal Mo.sub.3VTa.sub.0.38O.sub.x, denoted Tr-MoVTaO,

[0062] Trigonal Mo.sub.3VW.sub.0.24O.sub.x, denoted Tr-MoVWO,

[0063] Trigonal Mo.sub.3VW.sub.0.27Cu.sub.0.14O.sub.x, denoted Tr-MoVWCuO.

[0064] The above-mentioned catalysts were prepared as follows:

Preparation of Orthorhombic Mo.sub.3VO.sub.c Mixed Oxide

[0065] As already mentioned, orthorhombic Mo.sub.3VO.sub.c materials were synthesized by a hydrothermal method according to the process described by T. Konya, et al., Catal. Sci. Technol., 2013, 3, 380-387.

[0066] (NH.sub.4).sub.6Mo.sub.7O.sub.24.4H.sub.2O (Mo: 50 mmol, Wako) was dissolved in 120 mL of distilled water. Separately, an aqueous solution of VOSO.sub.4 (Mitsuwa Chemicals) was prepared by dissolving 12.5 mmol of hydrated VOSO.sub.4 in 120 mL distilled water. These two solutions were mixed at 20 C. and stirred for 10 min before being introduced into an autoclave (300 mL Teflon inner tube). After 10 min of nitrogen bubbling to replace the residual air, hydrothermal treatment was carried out at 175 C. for 48 hours. The as-obtained gray solids were washed with distilled water and dried at 80 C. overnight. These solids were purified by treatment with oxalic acid; dry solids were added to an aqueous solution of oxalic acid (0.4 M; 25 mL/1 g solid) and this mixture was stirred at 60 C. for 30 min. Solids were isolated from the suspension by filtration, washed with distilled water, and dried at 80 C. overnight.

Preparation of Trigonal Mo.sub.3VO.sub.c Mixed Oxide

[0067] The same procedure as the one described for the synthesis of orthorhombic Mo.sub.3VO.sub.c just above was used for the synthesis of trigonal Mo.sub.3VO.sub.c except for pH condition and duration of hydrothermal synthesis. The pH value of the mixed solution was adjusted to 2.2 by adding sulphuric acid (2 mol L.sup.1). The hydrothermal synthesis time was 20 h.

Preparation of Amorphous Mo.sub.3VO.sub.c Mixed Oxide

[0068] Mo.sub.3VO.sub.c material well-crystallized in the c-direction but disordered in the other direction was obtained by increasing the concentration of the mixed aqueous solution two-fold higher. Other preparatory conditions were the same as those described above for orthorhombic Mo.sub.3VO.sub.c.

Preparation of Tetragonal Mo.sub.3VO.sub.c Mixed Oxide

[0069] Tetragonal Mo.sub.3VO.sub.c was synthesized by phase transformation from orthorhombic Mo.sub.3VO.sub.c by heat treatment. Dried orthorhombic Mo.sub.3VO.sub.c was heated in air with a heating ramp of 10 C. min.sup.1 to 400 C. and kept at that temperature for 2 h before cooling to ambient temperature. The heat-treated sample was again heated in a nitrogen stream (50 mL min.sup.1) with a heating ramp of 10 C. min.sup.1 to 575 C. and kept at that temperature for 2 h.

Preparation of Trigonal MoVMO (M=Fe, Cu, Nb, Te, Ta, W, Cu and W)

[0070] 1) Preparation of Ethylammonium Isopolymolybdate

[0071] 22.594 g of MoO.sub.3 (0.150 mol, Kanto) were dissolved in 40 wt. % ethylamine aqueous solution (ethylamine: 0.300 mol, Wako). After complete dissolution of the solid, the solution was evaporated under vacuum at about 70 C. and then a solid powder consisting of ethylammonium trimolybdate was obtained and dried in air at about 80 C. overnight.

[0072] 2) Preparation of Trigonal MoVMO

[0073] Prepared ethylammonium trimolybdate (Mo: 50 mmol) was dissolved in 120 mL of distilled water. Separately, an aqueous solution of VOSO.sub.4 (Mitsuwa Chemicals) was prepared by dissolving 12.5 mmol of hydrated VOSO.sub.4 in 120 mL of distilled water. These two solutions and the additional precursor for M were mixed at about 20 C. and stirred for 10 min before being introduced into an autoclave (300 mL Teflon inner tube). The different precursors and their amount were as follows: [0074] Tr-MoVFeO: Fe(NH.sub.4)(SO.sub.4).sub.2.12H.sub.2O (0.63 mmol (Fe)), [0075] Tr-MoVCuO: Cu(NH.sub.4).sub.2Cl.sub.4.2H.sub.2O (0.13 mmol (Cu)), [0076] Tr-MoVNbO: Nb.sub.2O.sub.5.nH.sub.2O (0.63 mmol (Nb)), [0077] Tr-MoVTeO: TeO.sub.3 nH.sub.2O (0.36 mmol (Te)), [0078] Tr-MoVTaO: Ta.sub.2O.sub.5.nH.sub.2O (0.31 mmol (Ta)), and [0079] Tr-MoVWCuO: Cu(NH.sub.4).sub.2Cl.sub.4.2H.sub.2O (0.13 mmol (Cu)) and (NH.sub.4).sub.6[H.sub.2W.sub.12O.sub.40].nH.sub.2O (0.63 mmol (W)).

[0080] After 10 min of nitrogen bubbling to replace the residual air, hydrothermal reaction was carried out at about 175 C. for 48 h. Obtained gray solids were washed with distilled water and dried at about 80 C. overnight. These solids were purified by treatment with oxalic acid; dry solids were added to an aqueous solution of oxalic acid (0.4 M; 25 mL/1 g solids), and this mixture was stirred at about 60 C. for 30 min. Solids were isolated from the suspension by filtration, washed with distilled water, and dried at about 80 C. overnight.

[0081] These catalysts have been activated by calcination at 400 C. in static air during 2 hours before their use in the catalytic tests.

[0082] The synthesis of acrylic acid was carried out in the gas phase in a tubular fixed bed reactor with a inner diameter of 2.6 mm (outer diameter 3 mm) and a length of 300 mm. Injection of allyl alcohol has been performed with a high pressure liquid chromatography (HPLC) pump sold under the denomination PU-2080 by the firm Jasco. The temperature of the reactor was precisely regulated and controlled by a thermocouple.

Example 1

Synthesis of Acrylic Acid with Trigonal or Orthorhombic Molybdenum and Vanadium Mixed Oxides According to the InventionComparison with Catalysts not Forming Part of the Present Invention

[0083] In this example, acrylic acid has been synthetised in gas phase (using nitrogen as carrier gas) starting from allyl alcohol, using trigonal Mo.sub.3VO.sub.c (Tr-MoVO) or orthorhombic Mo.sub.3VO.sub.c (OrMoVO). Comparatively, the synthesis of acrylic acid has also been carried using catalysts not forming part of the present invention, namely tetragonal Mo.sub.3VO.sub.c (TeMoVO) and amorphous Mo.sub.3VO.sub.c (AmMoVO).

[0084] For each synthesis, 50 mg of catalyst have been placed between 2 layers of silicium carbide having a mean granulometry of 210 m. The reactor was heated until the required temperature (300 or 350 C.) under an air flow of 10 mL/min and then fed with reactants (allyl alcohol/O.sub.2/H.sub.2O/N.sub.2) at a pressure of 2.10.sup.5 Pa. The flow rate was adjusted to 40 mL/min. The contact time of the reactants with the catalyst was of the order of 0.00125 g-cat (mL.Math.min.sup.1).sup.1 and the total reaction time was 140 min. The allyl alcohol/O.sub.2/H.sub.2O/N.sub.2 molar ratio was set at 1/2.2/42.1/11.8 for all the experiments.

[0085] The liquid and gaseous products resulting from the reaction were analysed after trapping at the reactor outlet in a bubbler maintained at a temperature of about 10 C. The liquid obtained was subsequently analysed on a gas chromatograph equipped with a flame ionization detector.

[0086] The temperature conditions and corresponding results are summarized in Table I below:

TABLE-US-00001 TABLE 1 Allyl Selectivity alcohol Temperature conversion Acrylic Propionic Acetic Catalyst ( C.) (%) acid acid acid Acrolein Propanal CO.sub.x Tr-MoVO 300 100 55.4 34.2 3.1 0.1 0.2 6.6 Tr-MoVO 350 100 61.0 2.5 12.7 0.9 0.0 23.7 Or-MoVO 300 98.9 46.4 39.6 2.3 3.5 3.1 4.6 Or-MoVO 350 100 66.3 10.0 9.0 0.0 0.0 14.4 Te-MoVO (*) 300 34.8 0.9 0.0 0.0 79.3 9.9 3.7 Te-MoVO (*) 350 74.7 10.2 2.0 0.8 64.1 14.8 4.7 Am-MoVO (*) 300 56.6 6.9 7.5 0.0 58.9 22.2 4.0 Am-MoVO (*) 350 99.9 59.0 9.2 5.1 14.4 1.6 10.4 (*) Comparative Example not forming part of the present invention

[0087] In the above table: [0088] Allyl alcohol conversion (in %)=[(moles of allyl alcohol injected)(moles of allyl alcohol analyzed at the outlet of the reactor)/(moles of allyl alcohol injected)]100 [0089] Selectivity in acrylic acid (in %)=[(moles of acrylic acid analyzed at the outlet of the reactor)/(moles of allyl alcohol injected)(moles of allyl alcohol analyzed at the outlet of the reactor)]100.

[0090] These results show that the total conversion of allyl alcohol ranges from 34.8 to 100% for the different tested catalysts, and the acrylic acid selectivity varies from 0.9 to 66.3. The best conversion of allyl alcohol (66.3%) is obtained with OrMoVO used at 350 C. The main coproducts of the reaction are propionic acid, acetic acid, acrolein and carbon oxides (CO.sub.x). This demonstrates that the crystalline structure has a very important impact on catalytic properties of molybdenum and vanadium mixed oxides for the oxidation of allyl alcohol to acrylic acid. These results also demonstrate that a better selectivity in acrylic acid is observed when the oxidation reaction is carried out at a temperature of 350 C.

Example 2

Synthesis of Acrylic Acid with Optionally Iron Doped Trigonal Molybdenum and Vanadium Mixed Oxides According to the InventionComparison with Doped Catalysts not Forming Part of the Present Invention

[0091] In this example, acrylic acid has been synthetised in gas phase (using nitrogen and helium as carrier gas) starting from allyl alcohol, using Tr-MoVO or Tr-MoVFeO. Comparatively, the synthesis of acrylic acid has also been carried using doped molybdenum and vanadium catalysts not forming part of the present invention, namely Tr-MoVCuO, Tr-MoVNbO, Tr-MoVTeO, Tr-MoVTaO, Tr-MoVWO and Tr-MoVWCuO.

[0092] For each synthesis, 25 mg of catalyst have been placed between 2 layers of silicium carbide having a mean granulometry of 210 m. The reactor was heated until the required temperature (350 C.) under an air flow of 10 mL/min and then fed with reactants (allyl alcohol/O.sub.2/H.sub.2O/N.sub.2/He) at a pressure of 2.10.sup.5 Pa. The flow rate was adjusted to 80 mL/min. The contact time of the reactants with the catalyst was of the order of 0.00031 g-cat (mL.Math.min.sup.1).sup.1 and the total reaction time was 140 min. The allyl alcohol/O.sub.2/H.sub.2O/N.sub.2+He molar ratio was set at 0.7/1.5/29.8/8 for all the experiments.

[0093] In the mixture N.sub.2+He, the flow of N.sub.2 was set at 6 mL/min, and the flow of He at 2 mL/min.

[0094] The results are given in the following Table 2:

TABLE-US-00002 TABLE 2 Allyl alcohol Selectivity conversion Acrylic Propionic Acetic Catalyst (%) acid acid acid Acrolein Propanal CO.sub.x Tr-MoVO 100 71.9 5.9 8.3 0.3 0.1 13.5 Tr-MoVFeO 100 78.8 1.1 8.8 0.7 0.0 10.2 Tr-MoVCuO (*) 100 68.1 2.6 11.4 0.0 0.0 17.7 Tr-MoVNbO (*) 100 67.2 2.9 10.5 1.0 0.0 18.3 Tr-MoVTeO (*) 20.2 14.5 9.1 0.0 58.7 14.1 3.1 Tr-MoVTaO (*) 100 55.2 4.9 15.4 0.0 0.0 24.3 Tr-MoVWO (*) 100 65.2 2.9 16.2 0.0 0.0 15.7 Tr-MoVWCuO (*) 100 68.1 2.6 11.4 0.0 0.0 17.7 (*) Comparative Example not forming part of the present invention

[0095] These results show that the use of trigonal iron doped molybdenum and vanadium mixed oxide leads to a better yield in acrylic acid compared with Tr-MoVO (78.8% versus 71.9%). The use of other metals such as Cu, Te, Ta or W do not have the same enhancement effect on the oxidation of allyl alcohol into acrylic acid.