EP4003592A1 - Bismuth molybdate-based catalyst, process for the production thereof and use of this catalyst in the oxidation of propene to acrolein - Google Patents

Abstract

The invention relates to a process for producing a multiphase, mixed-oxide catalyst comprising at least one bismuth molybdate-based active phase and a co-catalyst based on iron molybdate and at least one of the two elements cobalt and nickel, said process comprising the following steps: preparing a mixture of the precursors of said mixed oxides in a solvent, reacting said precursors by microwave-assisted hydrothermal reaction, and isolating the mixed oxides in order to obtain the catalyst. The subject matter of the invention is made up of a catalyst and a catalytic system thus prepared and also the uses of this catalyst and this catalytic system, in particular in the oxidation of propene to acrolein.

Description

DESCRIPTION

BISMUTH MOLYBDATE CATALYST, PROCESS OF

ITS MANUFACTURE AND USE OF THIS CATALYST IN

OXIDIZATION OF PROPEN TO ACROLEIN

The present invention relates to a process for preparing a mixed oxide and multiphase catalyst based on bismuth molybdate, a catalyst and a catalyst system thus obtained and the uses thereof in various oxidation reactions.

The performances of the catalyst or of the catalytic system according to the invention are set out below and demonstrated in the controlled oxidation reaction of propene to acrolein. They are not restricted thereto and are particularly useful in the oxidative dehydrogenation of butene to butadiene, the oxidation of isobutene to methacrolein, the ammoxidation of propene to acrylonitrile and the ammoxidation of isobutene to methacrylonitrile. All these well-known reactions are carried out on an industrial scale because they provide source monomers for the production of numerous polymers and essential precursors in organic synthesis. For this reason, they are continually the subject of research with a view to improving their performance and reducing their ecological impact.

The controlled oxidation of propene shown below leads to acrolein which is an intermediate in the synthesis of methionine and its derivatives, widely used in animal nutrition.

[Chem 1]

It is carried out in the presence of a mixed oxide and multiphase catalyst, composed of at least four metallic elements: molybdenum and bismuth, which form the selective phases of bismuth molybdate, and a combination of metals. in the state of oxidation +2 (generally Ni or Co) and oxidation +3 (generally iron) and molybdenum which form phases which strongly enhance the catalytic activity by promoting the re-oxidation of the catalyst. It thus meets the minimum Mo (Co / Ni) FeBiO formula which is supplemented by various elements present as doping elements and / or in the form of oxides or molybdate, with a view to improving the properties of the catalyst, such as selectivity, thermal stability, mechanical stability ...

Document US2019 / 076829A1 describes such a catalyst and, inter alia, a catalyst corresponding to the following formula:

Moi2Bii-4Co4-ioFei-4Nio-4Ko-20 _x

as well as a process for preparing it comprising the following steps:

an aqueous mixture of the precursors of the elements of the catalyst is prepared in amounts appropriate to achieve the stoichiometry,

after adjusting the pH of the mixture to 5.5-8.5, said precursors are reacted by hydrothermal reaction in an autoclave at a temperature of 100 ° C to 600 ° C, for 5.5 hours to 48.5 hours, then

the catalyst is recovered.

Since such a preparation requires long reaction times, the authors have developed a process for manufacturing a catalyst of the aforementioned type, by replacing the above hydrothermal reaction with a hydrothermal reaction assisted by microwaves. They discovered that while making it possible to considerably reduce the reaction time, the catalyst obtained exhibits unexpected characteristics, giving it better properties, in particular greater reactivity.

Thus, the invention relates to a process for the manufacture of a mixed oxide and multiphasic catalyst comprising at least one active phase based on bismuth molybdate and a cocatalyst based on iron molybdate and at least one of the two elements cobalt and nickel, said process comprising the following steps: a mixture of the precursors of said mixed oxides is prepared in a solvent, said precursors are reacted by a hydrothermal reaction assisted by microwaves, and the mixed oxides are isolated to obtain the catalyst.

By microwaves according to the invention is meant intermediate radiation between the infrared and the broadcasting waves, that is to say the waves whose frequency is between 800 and 3000 MHz. In practice, all wavelengths not being authorized, it will be preferred, without of course that the invention is limited thereto, domestic microwaves and used in industrial applications with a vacuum wavelength of about 12 cm, or with a frequency of about 2450 MHz, as well as the microwaves used in mainly industrial applications, with a no-load wavelength of about 33 cm, or a frequency of about 915 MHz.

The method is described below in more detail, the following characteristics being able to be considered alone or in any combination between them.

According to a particular implementation of the method of the invention, said precursors are reacted by microwave assisted hydrothermal reaction in two stages: namely, a first microwave assisted hydrothermal reaction and a second microwave assisted hydrothermal reaction, between which the pH of the reaction mixture resulting from the first hydrothermal reaction assisted by microwaves is adjusted to 8-8.5.

More precisely, in a first synthesis step, said precursors are added and they are made to react by a first hydrothermal reaction assisted by microwaves, and in a second synthesis step, the pH of the reaction medium is adjusted to a value preferably of 8 -8.5, and a second hydrothermal reaction assisted by microwaves is carried out, then the microwave catalyst is isolated.

The hydrothermal reaction (s) assisted by microwave are preferably carried out at a temperature not exceeding 300 ° C, advantageously from 150 ° C to 240 ° C.

As said before, the reaction time is greatly shortened and if the hydrothermal reaction (s) assisted by microwave can be carried out over a period of 2 minutes to 10 hours, after a few hours, or even only a few minutes, the reaction can be almost complete. The catalyst prepared according to the process of the invention optionally has the following characteristics, which can be considered alone or in any combination thereof:

it further comprises molybdenum oxide;

it is supported; in the process of the invention, the addition of one or more support materials, such as silica, alumina, their mixtures, is advantageously carried out before the hydrothermal reaction or reactions assisted by microwaves; of course, an unsupported catalyst obtained according to the process of the invention may then be supported according to any technique well known to those skilled in the art, the active phase of the catalyst corresponds to the following stoichiometry Bi _x Mo _y O _z with

2> x / y> 0.5 and z is between 6 and 12; more preferably, this stoichiometry is chosen from the following: B12M03O12, B12M02O9 and B ^ MoOe;

the active phase of the catalyst is activated by at least one alkali metal, preferably at least potassium; in an advantageous mode of manufacture, only the active phase of the catalyst is activated by one or more alkali metals, such as potassium;

the cocatalyst responds to the following stoichiometry Fe _x Coi- _x Mo04 where x is a decimal number such that 0 <x <1, preferably such that 0.5 <x <0.9;

the catalyst has the formula Mo _m Co _n Ni _p Fe _q Bi _r M _s where M is an alkali metal, m, n, p, q, r and s are whole or decimal numbers, with m varying from 1 to 5 , n and p vary independently of each other from 0 to 1 with n + p different from 0, 0 <q <1, 0 <r <3 and 0 <q <0.2.

The invention also relates to the catalyst thus obtained.

In a particular implementation of the method of the invention:

a mixture of the precursors of the active phase in a solvent, on the one hand, and a mixture of the precursors of the co-catalyst in the same solvent or another solvent, on the other hand, is prepared;

the precursors of the active phase and the precursors of the cocatalyst are reacted separately by a hydrothermal reaction assisted by microwaves;

the active phase and the cocatalyst are respectively isolated; and the active phase and the cocatalyst are assembled to obtain the catalyst.

Preferably, the mixture (s) of the precursors of the mixed oxides is obtained in one or more solvents chosen from water, organic solvents and any combination of said organic solvents with one another or with water.

According to this implementation, the catalyst can be supported, said process then comprising the addition of one or more support materials, and / or the catalyst can comprise molybdenum oxide, said process also comprising the addition of molybdenum oxide, the addition of said support material (s) and / or molybdenum oxide being carried out during the synthesis or assembly of the active phase and the cocatalyst to obtain the catalyst. Molybdenum oxide makes it possible, on the one hand, to compensate for the loss over time of the molybdenum which vaporizes and thus to keep the active phase and the cocatalyst in an optimal state, and on the other hand, to wet the active phase and remove non-selective sites. Of course, any other phase making it possible to improve the properties of the catalyst can be added.

The active phase and the cocatalyst, which may comprise any other phase mentioned above, are each generally obtained in powder form. Their assembly to obtain the catalyst can be done by any means allowing an amalgam as complete as possible. It can thus be carried out by co-grinding or any other mixing technique. Also at this step any other phase or support material (s) can be added.

As indicated above, this process makes it possible to manufacture a mixed and multiphasic oxide catalyst which proves efficient in numerous catalytic reactions, among which: the oxidation of propene to acrolein, the oxidative dehydrogenation of butene to butadiene, the oxidation of isobutene to methacrolein, the ammoxidation of propene to acrylonitrile and the ammoxidation of isobutene to methacrylonitrile.

The invention also relates to a catalytic system comprising separately at least one active phase based on bismuth molybdate and a cocatalyst based on iron molybdate and at least one of the two elements cobalt and nickel. In view of his use, the separated phases are assembled as indicated above, for example by co-grinding.

This catalytic system which can be obtained according to the method described above, comprises the following advantageous characteristics, considered alone or in any combination:

the active phase responds to the following stoichiometry Bi _x Mo _y Oz with Bi _x Mo _y Oz where 2> x / y> 0.5 and z is between 6 and 12; more preferably, this stoichiometry is chosen from the following: B1 ₂ M0 ₃ O ₁₂ , B1 ₂ M0 ₂ O ₉ and B ^ MoOe;

the active phase is activated by at least one alkali metal, preferably at least potassium; advantageously, only this phase is activated by an alkali metal; the cocatalyst catalyst corresponds to the following stoichiometry IOC-Fe _{x x} Mo0 ₄ where x is a decimal number such that 0 <x <1, preferably such that 0.5 <x <0.9;

the active phase content is less than or equal to 50% by weight relative to the weight of the catalytic system, preferably it ranges from 10% to 45%.

The invention also relates to any use of a catalytic system as defined above, in particular for at least one of the following catalytic reactions: oxidation of propene to acrolein, oxidative dehydrogenation of butene to butadiene, oxidation of isobutene to methacrolein, ammoxidation of propene to acrylonitrile and ammoxidation of isobutene to methacrylonitrile.

Before illustrating the implementations of the various objects of the invention, certain terms / expressions are defined.

By mixing the precursors of mixed oxides in a solvent, there is in particular a solution or a suspension of said precursors in the solvent.

By isolation of the catalyst, or of one of its phases, in particular the active phase or the cocatalyst, is meant all the treatment operations well known to those skilled in the art, such as recovery from the reaction medium. hydrothermal liquid, washing, drying, and any other treatment leading to the separation of the catalyst or one of its phases, with a view to their use in a catalytic reaction. In the examples which follow, the activity of catalysts of the invention and of a catalytic system of the invention is compared with that of a so-called industrial catalyst, that is to say prepared by calcination. The manufacturing process was as follows:

Ammonium heptamolybdate, (NH ₄ ) ₆ Mq ₇ q ₂₄ , was used as the precursor of molybdenum, while all other metals other than cations were added as nitrates. The solubility of the precursors in water being very high, the desired concentration ranges were easily obtained. On the other hand, the bismuth nitrate being immediately hydrolyzed into water-insoluble bismuth oxy-nitrate, BÎ ₅ 0 (0H) g (N0 ₃ ) ₄ , and in order to promote the complete dissolution of the sparingly soluble bismuth in the water. water, a first solution was prepared by dissolving 2 g of tartaric acid in 100 ml of demineralized water which had previously been acidified with 1.5 ml of nitric acid (65%). After the addition of the bismuth nitrate, the solution was heated to 60 ° C and kept stirring for 30 min, until a colorless and clear solution was obtained. The addition of iron, cobalt and potassium as nitrate was performed in this order and each new salt was added only after the previous one had completely dissolved. Finally, solutions 1 and 2 were mixed with stirring and kept at 60 ° C for 3 hours. The resulting suspension was completely evaporated in an oven at 120 ° C. Finally, the obtained product was calcined at 350 ° C for 2 hours to decompose the residual nitrates and then heated to 500 ° C at the rate of 5 ° C / min and kept at this temperature for 2 hours.

Example 1: Synthesis of a catalyst of the invention by hydrothermal reaction assisted by microwaves

The prepared catalyst corresponds to the BiMoFeCoK formula, it was manufactured as follows:

Bismuth acetate (or nitrate), iron nitrate and cobalt (or / and nickel) nitrate were dissolved in 10 ml of H ₂ O to form solution 1. Secondly, a quantity stoichiometrically of ammonium heptamolybdate was dissolved in 10 ml of H ₂ O to form solution 2. Then, solution 1 was slowly added to solution 2 to form a suspension, which was kept stirring for 1 hour. The pH of the mixture was adjusted to 1.8 with the addition of HNO ₃ or NH ₄ OH. The suspension was then warmed to 150 ° C via microwave irradiation and kept at this temperature for 10 minutes in a first step. Once the first step is completed, KOH is added and the mixture is basified to pH 8.5 by adding 32% ammonia. The suspension was then warmed to 200 ° C via microwave irradiation and kept at this temperature for 30 minutes The solid obtained was recovered by centrifugation, washed twice with 10 ml of H2O and once with 10 ml of ethanol. and finally dried for 16 hours at 120 ° C.

The following variations were tested: solvents, pH, reaction time (2 minutes to 96 h), irradiation temperature (150-240 ° C), stoichiometry

Bi _x Fe _y CO _z Ni _c Mo _b K _a with 0 <a, b, c, x, y, z <15.

An implementation of the method is shown in the following Table 1: [Table 1]

Example 2: Synthesis of a catalytic system of the invention by hydrothermal reaction assisted by microwaves

Industrial catalysts currently contain several phases types M0O3, B12M03O12, Fe2 (MoO4) 3, Fe _x Coi- _x Mo04, N 1M0O4, B12M02O9 ... The two most useful phases are Fe _x Coi- _x Mo0 ₄ and BΪ ₂ Mq ₃ 0 _ΐ2 . Since the mixed iron / cobalt molybdenum phase is very difficult to synthesize via the precipitation / calcination method because of the oxidation of Iron II to Iron III, synthesis of this phase on an industrial scale is not possible. Indeed, Fe2 (Mo04) 3 is always formed.

The two phases could be synthesized according to a process of the invention involving a hydrothermal synthesis assisted by microwaves, which makes it possible to be freed from the oxidation of iron. via the following protocol:

B12M03O12

Bismuth nitrate, and nitric acid, were dissolved in 150 ml of bi-distilled water. A second solution was prepared by dissolving the ammonium heptamolybdate in 100 mL of bi-distilled water. The two solutions were then mixed and the resulting mixture was kept under stirring for 10 minutes at 300 rpm, the pH was adjusted to 1 by addition of ammonium hydroxide, It was then transferred to a flask of 1 L Teflon for microwave irradiation.

Microwave assisted hydrothermal synthesis was carried out at 150 ° C for 10 minutes. After the microwave treatment, the collected product was collected by centrifugation at 3000 rpm, then washed twice with deionized water and ethanol. Finally, the sample was dried at 90 ° C for 8 hours.

Fe _x Coi- _x Mo04 with 0.5 <x <0.9

A first solution of sodium molybdate was dissolved in 250 mL of

H ₂ O bi-distilled. Iron II chloride, and cobalt nitrate hexahydrate were then dissolved in 250 ml of triethylene glycol. The two solutions were then mixed and the resulting solution was kept stirred for 10 minutes at 300 rpm. The solution is then transferred to a 1 L Teflon vial for microwave irradiation. Microwave-assisted hydrothermal synthesis was carried out at 150 ° C for 10 min. After the microwave treatment, the collected product was collected by centrifugation at 3000 rpm, then washed twice with water and ethanol. Finally, the sample was dried at 90 ° C for 8 hours. Example 3:

In this example, the catalyst prepared by microwave was tested in the controlled oxidation reaction of propene to acrolein and compared to isomass with the industrial catalyst prepared by calcination. The stoichiometry of the catalyst is:

Moi2Co7, i2Fei, 8Bio, 65K _x .

The test is carried out under a gas flow consisting of C3H6 / O2 / N2: 1/1, 5/8, 6, for a total gas flow of 60 ml / min with 250 mg of catalyst and at 350 ° C. Table 2 below gives the conversion to propene and the selectivity to acrolein after 48 h under gas flow.

[Table 2]

Example 4

In this example, catalysts prepared by microwaves and exhibiting different stoichiometries in Mo were compared with each other in the reaction of controlled oxidation of propene to acrolein.

The test is carried out under a gas flow consisting of C3H6 / O2 / N2: 1/1, 5/8, 6, for a total gas flow of 60 ml / min with 250 mg of catalyst and at 350 ° C. Table 3 below gives the conversion to propene and the selectivity to acrolein after 48 h under gas flow. [Table 3]

Example 5

In this example, catalysts prepared by microwaves and exhibiting different stoichiometries in Bi were compared with one another in the reaction of controlled oxidation of propene to acrolein.

The test is carried out under a gas flow consisting of C3H6 / 02 / N2: 1/1, 5/8, 6, for a total gas flow of 60 ml / min with 250 mg of catalyst and at 350 ° C. Table 4 below gives the conversion to propene and the selectivity to acrolein after 48 hours under a gas stream.

[Table 4]

Example 6

In this example, the catalyst prepared by microwave was tested in the controlled oxidation reaction of propene to acrolein. The stoichiometry of the MW catalyst is: Mol2Co7,12Fel, 8Bi0,65Kx

The test is carried out under a gas flow consisting of C3H6 / O2 / N2: 1/1, 5/8, 6, for a total gas flow of 60 ml / min with 250 mg of catalyst and at 350 ° C. Table 5 below gives the conversion to propene and the selectivity to acrolein after 358h under gas flow [Table 5]

Example 7

In this example, the catalyst prepared by microwave with nickel was tested in the controlled oxidation reaction of propene to acrolein. The stoichiometry of this catalyst is: M0 ₁₂ Co ₄ NÎ _{3, i2} Fei _{, 8} Bio _{, 65} K _x .

The test is carried out under a gas flow consisting of C ₃ H ₆ / O ₂ / N ₂ : 1/1, 5/8, 6, for a total gas flow of 60 ml / min with 250 mg of catalyst and at 350 ° C. Table 6 below gives the conversion to propene and the selectivity to acrolein after 48 h under gas flow.

[Table 6]

Example 8

In this example, the catalyst prepared by microwaves is prepared by mechanical mixing of the useful phases: Fe _x Coi- _x Mo0 ₄ and BΪ ₂ Mq ₃ 0 _ΐ2 . [Table 7]

* IOC-Fe _{x x} Mo0 ₄ with x = 0.67

The test is carried out under a gas flow consisting of C3H6 / 02 / N2: 1/1, 5/8, 6, for a total gas flow of 60 ml / min with 250 mg of catalyst and at 350 ° C. Table 7 below gives the conversion to propene and the selectivity to acrolein after 48 h under gas flow.

Claims

[Claim 1] Process for the manufacture of a mixed oxide and multiphase catalyst comprising at least one active phase based on bismuth molybdate and a cocatalyst based on iron molybdate and at least one of two elements cobalt and nickel, said method being characterized in that it comprises the following steps: a mixture of the precursors of said mixed oxides is prepared in a solvent, said precursors are reacted by a hydrothermal reaction assisted by microwaves, and the mixed oxides are isolated to obtain the catalyst. [Claim 2] A method according to claim 1, characterized in that said precursors are reacted by microwave assisted hydrothermal reaction in two stages, a first microwave assisted hydrothermal reaction and a second microwave assisted hydrothermal reaction, between which the pH of the reaction mixture resulting from the first hydrothermal reaction assisted by microwaves is adjusted to 8-8.5. [Claim 3] A process according to claim 1 or 2, characterized in that the catalyst comprises molybdenum oxide. [Claim 4] A method according to any one of claims 1 to 3, characterized in that the catalyst is supported, said method comprising the addition of one or more support materials, before the hydrothermal reaction (s) assisted by microwave. [Claim 5] A method according to any one of claims 1 to 4, characterized in that the hydrothermal reaction (s) assisted by microwave is carried out at a temperature of 150 ° C to 240 ° C. [Claim 6] A method according to any one of claims 1 to 5, characterized in that the hydrothermal reaction or reactions assisted by microwaves are carried out over a period of 2 minutes to 10 hours. [Claim 7] Process according to any one of claims 1 to 6, characterized in that the active phase of the catalyst corresponds to the following stoichiometry Bi _x Mo _y Oz where 2> x / y> 0.5 and z is between 6 and 12; this stoichiometry is preferably chosen from BΪ2Mq3q _ΐ 2, B12M02O9 and B ^ MoOe. [Claim 8] A method according to any one of claims 1 to 7, characterized in that the active phase of the catalyst is activated by at least one alkali metal, preferably at least potassium. [Claim 9] A process according to any one of claims 1 to 8, characterized in that the cocatalyst corresponds to the following stoichiometry Fe _x Coi- _x Mo04 where x is a decimal number such that 0 <x <1,, preferably such that 0.5 <x <0.9. [Claim 10] The method according to any one of claims 1 to 9, characterized in that the catalyst has the formula Mo _m Co _n NipFeqBi _r M _s where M is an alkali metal, m, n, p, q, r and s are integers or decimals, with m varying from 1 to 5, n and p varying independently of each other from 0 to 1 with n + p different from O, 0 <q <l, 0 <r <3 and 0 <q <0.2. [Claim 11] A method according to any one of claims 1 to 10, characterized in that: a mixture of the precursors of the active phase in a solvent, on the one hand, and a mixture of the precursors of the co-catalyst in the same solvent or another solvent, on the other hand, is prepared; the precursors of the active phase and the precursors of the cocatalyst are reacted separately by a hydrothermal reaction assisted by microwaves; the active phase and the co-catalyst are respectively isolated; and the active phase and the cocatalyst are assembled to obtain the catalyst. [Claim 12] A method according to any one of claims 1 to 11, characterized in that the mixture or mixtures of the precursors of the mixed oxides are obtained in one or more solvents chosen from water, organic solvents and any combination of said organic solvents with each other or with water. [Claim 13] A process according to claim 11 or 12, characterized in that the catalyst is supported, said process comprising the addition of one or more support materials, and / or the catalyst comprises molybdenum oxide, said process comprising the addition of molybdenum oxide, the addition of said support material (s) and / or molybdenum oxide being carried out during the synthesis or assembly of the active phase and the co-catalyst to get the catalyst. [Claim 14] A method according to any one of claims 1 to 13 for the manufacture of a mixed oxide and multiphasic catalyst intended for at least one of the following catalytic reactions: the oxidation of propene to acrolein, oxidative dehydrogenation of butene to butadiene, oxidation of isobutene to methacrolein, ammoxidation of propene to acrylonitrile and ammoxidation of isobutene to methacrylonitrile. [Claim 15] Catalytic system comprising separately at least one active phase based on bismuth molybdate and a co-catalyst based on iron molybdate and at least one of cobalt and nickel. [Claim 16] Catalytic system according to Claim 15, characterized in that the active phase corresponds to the following stoichiometry BixMO _y Oz where 2> x / y> 0.5 and z is between 6 and 12; preferably, this stoichiometry is chosen from BΪ2Mq3q _ΐ 2, B12M02O9 and Bi Mo0 ₆ . [Claim 17] Catalytic system according to claim 15 or 16, characterized in that the active phase is activated by at least one alkali metal, preferably at least potassium. [Claim 18] Catalytic system according to any one of claims 15 to 16, characterized in that the catalyst cocatalyst corresponds to the following stoichiometry Fe _x Coi- _x Mo04 where x is a decimal number such that 0 <x <1 , preferably such that 0.5 <x <0.9. [Claim 19] Catalytic system according to any one of claims 15 to 18, characterized in that the active phase content is less than or equal to 50% by weight relative to the weight of the catalytic system, preferably it varies by 10% at 45%. [Claim 20] Use of a catalytic system according to any one of claims 15 to 19, for at least one of the following catalytic reactions: the oxidation of propene to acrolein, the oxidative dehydrogenation of butene to butadiene, the oxidation of isobutene to methacrolein, ammoxidation of propene to acrylonitrile and ammoxidation of isobutene to methacrylonitrile.