EP1539669A1

EP1539669A1 - Method for producing acrylic acid from propane

Info

Publication number: EP1539669A1
Application number: EP03769594A
Authority: EP
Inventors: Jean-Luc Dubois; Fabienne Desdevises; Stéphanie SERREAU; Damien Vitry; Wataru Ueda
Original assignee: Arkema SA
Current assignee: Arkema France SA
Priority date: 2002-09-10
Filing date: 2003-09-09
Publication date: 2005-06-15
Also published as: WO2004024665A1; JP2005538172A; US7332625B2; KR20050053643A; AU2003278285A1; US20060183941A1

Abstract

The invention concerns a method for producing acrylic acid from propane, which consists in passing a gas mixture including propane, water vapour, and optionally an inert gas and/or molecular oxygen, on a catalyst of formula (I): Mo1VaSbbNbcSidOx, wherein: a ranges between 0.006 and 1, inclusively; b ranges between 0.006 and 1, inclusively; c ranges between 0.006 and 1, inclusively; d ranges between 0 and 3.5, inclusively; and x is the amount of oxygen bound to the other elements and depends on their state of oxidation, for oxidizing propane into acrylic acid, and which is carried out in the presence of molecular oxygen, the propane/molecular oxygen mol ratio in the initial gas mixture is not less than 0.5.

Description

PROCESS FOR THE MANUFACTURE OF ACRYLIC ACID FROM PROPANE

The present invention relates to the production of acrylic acid from propane in the presence or absence of molecular oxygen. It is known from European patent application No. EP-A-608838 to prepare an unsaturated carboxylic acid from an alkane according to a catalytic oxidation reaction in the vapor phase in the presence of a catalyst containing a metal oxide mixed comprising essential components, Mo, V, Te, O, as well as at least one element chosen from the group consisting of niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium and cerium, these elements being present in very precise proportions. The reaction can be carried out starting from a gas mixture composed of the alkane, oxygen, an inert gas and water vapor corresponding to the following molar proportions: alkane / oxygen / inert gas / vapor d water = 1 / 0.1-10 / 0-20 / 0.2-70 and preferably 1 / 1- 5 / 0-10 / 5-40.

Furthermore, European patent application No. EP-A-895809 describes catalysts based on oxides comprising molybdenum, vanadium, niobium, oxygen, tellurium and / or antimony, as well as '' at least one other element such as iron or aluminum. These catalysts can be used for the conversion of propane to acrylic acid, in the presence of molecular oxygen, as illustrated in Examples 9 and 10. Example 9, in particular, describes the oxidation of propane using a catalyst of formula Mo ₁ No _{! 33} Nb _0jll Te _0j22 O _rι from a gas stream composed of propane, oxygen and helium and a stream of water vapor, according to a propane / oxygen molar ratio / helium / water vapor of approximately 1 / 3.2 / 12.1 / 14.3. In such a gas stream, the reactive gas flow is very little concentrated in propane. It follows that the recycling of unconverted propane is much more difficult because this unconverted propane is too diluted in the reaction flow. The object of the invention is to propose a process for the production of acrylic acid from propane, in the presence or absence of molecular oxygen, which makes it possible to obtain a high propane conversion while retaining good selectivity for acrylic acid. .

The inventors have discovered that this object can be achieved by passing a gaseous mixture comprising propane, steam, and possibly an inert gas and / or molecular oxygen, over a particular catalyst. When operating in the presence of molecular oxygen oxidation takes place under conditions such that the oxygen of the gas mixture is in sub-stoichiometric proportion relative to the propane introduced, which probably allows the catalyst to act as a redox system and to supply the missing oxygen so that the reaction is performed satisfactorily. The advantages of this new way of proceeding are therefore the following: the limitation of the overoxidation of the products formed which takes place in the presence of too large a quantity of molecular oxygen; according to the present invention, because one operates in sub-stoichiometry, the formation of COχ (carbon monoxide and carbon dioxide), degradation products, is reduced, which makes it possible to increase the selectivity for acrylic acid; the selectivity for acrylic acid remains at a good level; the conversion is increased without loss of selectivity; the catalyst undergoes only a small reduction and therefore a small loss of its activity; it can be easily regenerated by heating in the presence of oxygen or an oxygen-containing gas after a certain period of use; after regeneration, the catalyst regains its maximum activity and can be used in a new reaction cycle; - In addition, it is possible to provide for the separation of the stages of reduction of the catalyst and of regeneration of the latter, which makes it possible to increase the partial pressure of propane, such a partial pressure of propane supply being little limited by the existence of an explosive zone created by the propane + oxygen mixture, since the latter is present in molecular form in sub-stoichiometric proportions; moreover, this process makes it possible to reduce the formation of products resulting from hydration, in particular, propionic acid, acetone and acetic acid.

The present invention therefore relates to a process for the manufacture of acrylic acid from propane, in which a gaseous mixture comprising propane, steam, optionally an inert gas and / or molecular oxygen, on a catalyst of formula (I):

MotN _a SbbNbcSi _d Ox (I) in which: - a is between 0.006 and 1, limits included; - b is between 0.006 and 1, limits included; c is between 0.006 and 1, limits included; - d is between 0 and 3.5, limits included; and

- x is the quantity of oxygen linked to the other elements and depends on their oxidation states, to oxidize propane to acrylic acid, and when operating in the presence of molecular oxygen, the propane / molecular oxygen molar ratio in the starting gas mixture is greater than 0.5.

Such a process makes it possible to simultaneously obtain a selectivity for acrylic acid of almost 60% and a high propane conversion. In addition, it can be easily implemented in a fluidized bed or in a transported bed and the injection of the reagents can be carried out at different points of the reactor, so that one is outside the flammability zone while having a high propane concentration and, consequently, a high catalyst productivity.

According to a particularly advantageous embodiment, the method according to the invention comprises the following steps: 1 / In the absence of molecular oxygen

When the starting gas mixture is devoid of molecular oxygen, the propane is oxidized according to the following redox reaction (A):

SOLID _oxidized + PROPANE - "SOLID _reduced + ACRYLIC ACID (A)

11 / In the presence of molecular oxygen a) the starting gas mixture is introduced into a first reactor with a transported catalyst bed, b) at the outlet of the first reactor, the gases are separated from the catalyst; c) the catalyst is sent to a regenerator; d) optionally the gases are introduced into a second reactor with a transported catalyst bed; e) where appropriate, at the outlet of the second reactor, the gases are separated from the catalyst and the acrylic acid contained in the separated gases is recovered; f) if necessary, the catalyst is returned to the regenerator; and g) reintroduced regenerated catalyst from the regenerator into the first reactor and, where appropriate, into the second reactor.

According to another advantageous embodiment of the invention, the reactor or reactors are further provided with a cocatalyst.

According to another advantageous embodiment of the invention, the process comprises repeating, in a reactor provided with the catalyst of formula (I) and, where appropriate, a co-catalyst, the cycle comprising the following successive steps: 1) a step of injecting the gas mixture as defined above; 2) a step of injecting steam and, if necessary, inert gas;

3) a step of injecting a mixture of molecular oxygen, water vapor and, if necessary, inert gas; and

4) a step of injecting steam and, if necessary, inert gas. According to an improvement of the advantageous embodiment which has just been described, the cycle comprises an additional stage which precedes or follows stage 1) and during which a gaseous mixture corresponding to that of stage 1 is injected but without molecular oxygen, the propane / molecular oxygen molar ratio then being calculated globally for step 1) and this additional step. According to an advantageous embodiment of the improvement which has just been presented, the additional step precedes step 1) in the cycle.

Other characteristics and advantages of the invention will now be described in detail in the description which follows and which is given with reference to the single appended figure which schematically represents an apparatus suitable for implementing an embodiment. advantageous of the process according to the invention.

Detailed description of the invention

According to the invention, in the alternatives where molecular oxygen is introduced, since the propane / molecular oxygen molar ratio in the starting gas mixture is greater than or equal to 0.5, the conversion of propane to acid acrylic by means of the catalyst is carried out by oxidation, presumably according to the following common reactions (A) and (B):

- the classic catalytic reaction (B):

CH ₃ -CH ₂ -CH ₃ + 2O ₂ -> CH ₂ = CH-COOH + 2H ₂ O (B)

- and the redox reaction (A) mentioned above: SOLID _oxidized + CH ₃ -CH ₂ -CH ₃ -_ "SOLID _eds uit + CH ₂ = CH-COOH (A)

The propane / water volume ratio in the starting gas mixture is not critical and can vary within wide limits.

Similarly, the proportion of inert gas, which can be helium, krypton, a mixture of these two gases, or nitrogen, carbon dioxide, etc., is also not critical and may also vary within wide limits.

The proportions of the constituents of the starting gas mixture are generally as follows (in molar ratios): propane / oxygen / inert (He-Kr) / Η ₂ O (vapor) = 1 / 0.05-2 / 1-10 / 1 -10 Preferably, they are 1 / 0.1-1 / 1-5 / 1-5. / 024665

Even more preferably, they are 1 / 0.167-0.667 / 2-5 / 2-5. The following particularly interesting proportions can also be mentioned:

1 / 0.2-0.4 / 4-5 / 4-5.

Generally, reactions (A) and (B) are carried out at a temperature of 200 to 500 ° C, preferably from 250 to 450 ° C, more preferably still, from 350 to

400 ° C. The pressure in the reactor (s) is generally from 1.01.10 ⁴ to 1.01.10 ⁶

Pa (0.1 to 10 atmospheres), preferably 5.05.10 ⁴ to 5.05.10 ⁵ Pa (0.5-5 atmospheres).

The residence time in the reactor, or if there are several, in each reactor, is generally from 0.01 to 90 seconds, preferably from 0.1 to 30 seconds.

The catalyst corresponds to the following formula (I):

MotNaSbbNbcSi _d Ox (I) in which: - a is between 0.006 and 1, limits included;

- b is between 0.006 and 1, limits included; c is between 0.006 and 1, limits included; d is between 0 and 3.5, limits included; and

- x is the quantity of oxygen linked to the other elements and depends on their oxidation states.

Advantageously: a is between 0.09 and 0.8, limits included;

- b is between 0.04 and 0.6, limits included; c is between 0.01 and 0.4, limits included; and - d is between 0.4 and 1.6, limits included.

The oxides of the different metals used in the composition of the catalyst of formula (I) can be used as raw materials in the preparation of this catalyst, but the raw materials are not limited to oxides; among the raw materials which can be used, there may be mentioned, without limitation: - in the case of molybdenum, ammonium molybdate, ammonium paramolybdate, ammonium hepta-molybdate, molybdic acid, molybdenum halides or oxyhalides such as MOCI ₅ , organometallic compounds of molybdenum such as molybdenum alkoxides such as Mo (OC H ₅ ) 5, acetylacetone molybdenyl; - in the case of vanadium, ammonium metavanadate, halides or oxyhalides of vanadium such as VCl, VC1 ₅ or VOCl ₃ , organometallic vanadium compounds such as vanadium alkoxides such as NO (OC ₂ H ₅ ) ₃ ;

- in the case of antimony, for example antimony oxide (antimony trioxide), in particular the Senarmontite variety, antimony sulfate (Sb ₂ (SO) ₃ ) or an antimony chloride (trichloride antimony, antimony pentachloride);

- in the case of niobium, niobic acid, niobium tartrate, niobium hydrogen oxalate, oxotrioxalato-ammonium niobiate {(ΝH ₄ ) 3 [ΝbO (C ₂ O ₄ ) ₃ ] ^# l , 5H ₂ O}, niobium and ammonium oxalate, niobium and tartrate oxalate, niobium halides or oxyhalides such as NbCl ₃ , NbCl ₅ and organometallic compounds of niobium such as niobium alkoxides such that Nb (OC ₂ E- ₅ ) ₅ , Nb (On-

Bu) ₅ ; and, in general, all the compounds capable of forming an oxide by calcination, namely, the metal salts of organic acids, the metal salts of mineral acids, complex metal compounds, etc.

The source of silicon generally consists of colloidal silica and / or polysilicic acid.

In accordance with particular embodiments, the catalyst of formula (I) can be prepared by mixing, with stirring, aqueous solutions of niobic acid, oxalic acid, ammonium heptamolybdate, ammonium metavanadate, antimony oxide, adding if necessary colloidal silica, then preferably by pre-calcining in air at a temperature between 280 and 340 ° C, preferably at about 300-320 ° C, and calcining under nitrogen at about 600 ° C.

Preferably, in the catalyst of formula (I) thus prepared: a is between 0.09 and 0.8, limits included;

- b is between 0.04 and 0.6, limits included;

- c is between 0.01 and 0.4, limits included; and - d is between 0.4 and 1.6, limits included.

More particularly, the process for preparing the catalyst of formula (I) is implemented by preparing a solution of niobic acid, oxalic acid, preparing a solution of molybdenum, vanadium, antimony and optionally silica, mixing the 2 solutions giving rise to the formation of a gel, drying the gel obtained giving rise to the formation of a precursor of formula (F) below, precalcination then calcination.

More specifically, according to a particularly preferred process, the catalyst can be prepared by implementing the following steps: 4/024665

1) dissolving in water a source of vanadium, for example, ammonium metavanadate, with stirring and possibly heating;

2) addition to the solution obtained previously of a source of antimony, for example, antimony oxide, in particular the variety Sénarmontite; 3) addition of a molybdenum source, for example, ammonium heptamolybdate;

4) reaction of the solution obtained, under reflux;

5) addition of an oxidant such as hydrogen peroxide;

6) if necessary, addition of silica; 7) addition of a solution prepared by mixing, under heating, a source of niobium, for example, niobic acid, with oxalic acid; 8) reaction of the reaction mixture under reflux and preferably under an inert atmosphere, until a gel is obtained; drying the gel obtained leading to a precursor; 9) precalcination of the precursor; and

10) calcination of the precalcined gel to obtain the catalyst. Alternatively, instead of having three successive steps 1), 2) and 3), these steps are merged by introducing the sources of vanadium, antimony and molybdenum in cold water and stirring to obtain a solution . Preferably, in step 5), hydrogen peroxide is added until a clear orange-colored solution is obtained.

In the above process alternatives: the drying (for example of step 9)) can be carried out in a thin layer oven, by atomization, by lyophilization, by zeodratation, by microwave, etc .; the precalcination can be carried out under air flow at 280-300 ° C or under static air at 320 ° C, in a fluidized bed, in an oven rotating in a fixed so-called aerated bed, so that the catalyst grains are separated each other to prevent them from fusing during precalcination or possibly during calcination; the calcination is preferably carried out under very pure nitrogen and at a temperature in the region of 600 ° C., for example in a rotary kiln or in a fluidized bed and for a period which may be 2 hours.

The catalyst obtained at the end of the calcination can be ground to give smaller particles. If the grinding is carried out until a powder consisting of particles of the size of a micron is obtained, the powder can subsequently be reshaped using a binder such as for example silica in the form of polysilicic acid, the suspension then being dried again, for example by atomization. According to a more particularly preferred embodiment of the invention, the precalcination is carried out: either at a temperature below 300 ° C under an air flow of at least 10 ml / min g of catalyst; - Either at a temperature ranging from 300 to 350 ° C under an air flow of less than 10 ml / min / g of catalyst.

According to a particularly preferred embodiment, the precalcination is carried out: at approximately 320 ° C. under an air flow rate of less than 10 ml / min / g; or - at around 290 ° C, under an air flow of around 50 ml / min / g.

Catalyst regeneration

During the redox reaction (B), the catalyst undergoes a reduction and a progressive loss of its activity. This is why, once the catalyst has at least partially gone to the reduced state, its regeneration is carried out according to reaction (C):

SOLLOE _reduced it + O ₂ - »SOLID _oxidized (C) by heating in the presence of oxygen or an oxygen-containing gas at a temperature of 250 to 500 ° C, for the time necessary for the reoxidation of the catalyst . The proportions of the constituents of the regeneration gas mixture are generally as follows (in molar ratios): oxygen / inert (He-Kr) / HO (vapor) =

1 / 1-10 / 0-10

Preferably, they are 1 / 1-5 / 0-5. Instead of using oxygen alone, dry air (21% O ₂ ) can be used.

Instead of or in addition to water vapor, humid air can then be used.

The regeneration temperature is generally 250 to 500 ° C.

The process is generally carried out until the reduction rate of the catalyst is between 0.1 and 10 g of oxygen per kg of catalyst.

This reduction rate can be monitored during the reaction by the quantity of products obtained. The equivalent amount of oxygen is then calculated. It can also be followed by the exothermicity of the reaction. We can also follow the reduction rate by the amount of oxygen consumed in the regenerator. After regeneration, which can be carried out under conditions of temperature and pressure identical to, or different from those of reactions (A) and (B), the catalyst regains initial activity and can be reintroduced into the reactors.

Reactions (A) and (B) and regeneration (C) can be carried out in a conventional reactor, such as a fixed bed reactor, a fluidized bed reactor or a transported bed reactor.

It is therefore possible to carry out reactions (A) and (B) and the regeneration (C) in a two-stage device, namely a reactor and a regenerator which operate simultaneously and in which two catalyst charges alternate periodically.

Reactions (A) and (B) and regeneration (C) can also be carried out in the same reactor by alternating the reaction and regeneration periods.

Preferably, the reactions (A) and (B) and the regeneration (C) are carried out in a reactor with a transported catalyst bed, in particular in a vertical reactor, the catalyst then preferably moving from the bottom to the top.

It is possible to use an operating mode with a single gas passage or with gas recycling.

According to a preferred embodiment, the propylene produced and / or the unreacted propane are recycled (or returned) at the inlet of the reactor, that is to say that they are reintroduced at the inlet of the reactor, in mixture or in parallel with the starting mixture of propane, water vapor and, where appropriate, inert gas (ies). Use of equipment with two reactors and a regenerator

According to an advantageous embodiment of the invention, the method according to the invention is implemented in an apparatus such as that shown in the appended figure.

The starting gas mixture comprising propane, molecular oxygen, water vapor, as well as, if necessary, an inert gas, is introduced into a first reactor (Riser 1) containing the transportable catalyst bed.

Then, at the outlet of the first reactor, the effluents are separated into gases and the catalyst transported.

The catalyst is sent to a regenerator. The gases are introduced into a second reactor (Riser 2) also containing a transportable catalyst bed.

At the outlet of the second reactor, the effluents are separated into gases and the catalyst transported.

The catalyst is sent to a regenerator. The gases are treated in a known manner, generally by absorption and purification, with a view to recovering the acrylic acid produced. The regenerated catalyst is reintroduced into the first reactor as well as into the second reactor.

The process thus works continuously, the circulation of the catalyst between the reactors and the regenerator takes place regularly and generally continuously.

Of course, the single regenerator can be replaced by two or more regenerators.

In addition, it is possible to add following the second reactor other reactors also having a catalyst circulating between each of these reactors and the regenerator or other regenerators.

Preferably, the first and second reactors are vertical and the catalyst is transported upward by the flow of gases.

A mode of operation with a single gas passage or with recycling of the products leaving the second reactor can be used. According to a preferred embodiment of the invention, after treatment of the gases from the second reactor, the propylene produced and / or the unreacted propane are recycled (or returned) at the inlet of the first reactor, this is that is to say, they are reintroduced at the inlet of the first reactor, as a mixture or in parallel with the starting mixture of propane, oxygen, water vapor and, where appropriate, inert gas (ies).

Use of a co-catalyst

According to another advantageous embodiment of the invention, the gas mixture also passes over a cocatalyst.

This has the advantage of reducing the production of propionic acid, which is generally a by-product of the conversion reaction and which poses problems in certain applications of acrylic acid when it is present in too large a quantity.

Thus, the propionic acid / acrylic acid ratio is greatly reduced at the outlet of the reactor. In addition, the formation of acetone, which is also a by-product of the manufacture of acrylic acid from propane, is reduced.

To this end, the reactor, or, if there are several, at least one of the reactors, comprises a cocatalyst having the following formula (II):

MoιBi _a .Feb> Co _v. Nest>Ke'SbfTig.Sih'Ca _i .Nbj'Te _k .Pbι. _π) > Cu _n '(II) in which: a' is between 0.006 and 1, limits included; b 'is between 0 and 3.5, limits included; - it is between 0 and 3.5, limits included;

- d is between 0 and 3.5, limits included;

- e 'is between 0 and 1, limits included;

- f is between 0 and 1, limits included; - g 'is between 0 and 1, limits included;

- h 'is between 0 and 3.5, limits included;

- i 'is between 0 and 1, limits included;

- I is between 0 and 1, limits included;

- k 'is between 0 and 1, limits included; - F is between 0 and 1, limits included;

- m 'is between 0 and 1, limits included; and

- is between 0 and 1, limits included.

Such a co-catalyst can be prepared in the same way as the catalyst of formula (I). The oxides of the various metals used in the composition of the cocatalyst of formula (II) can be used as raw materials in the preparation of this cocatalyst, but the raw materials are not limited to oxides; as other raw materials, mention may be made in the case of nickel, cobalt, bismuth, iron or potassium, the corresponding nitrates. In general, the co-catalyst is present in the form of a transportable bed and preferably, it is regenerated and if necessary circulates in the same way as the catalyst.

Preferably, in the co-catalyst of formula (II):

- a 'is between 0.01 and 0.4, limits included; - b 'is between 0.2 and 1.6, limits included;

- It is between 0.3 and 1.6, limits included; d is between 0.1 and 0.6, limits included; e 'is between 0.006 and 0.01, limits included.

- f is between 0 and 0.4, limits included; - g 'is between 0 and 0.4, limits included;

- h 'is between 0.01 and 1.6, limits included;

- i 'is between 0 and 0.4, limits included;

- I is between 0 and 0.4, limits included;

- k 'is between 0 and 0.4, limits included; - F is between 0 and 0.4, limits included;

- m 'is between 0 and 0.4, limits included; and

- is between 0 and 0.4, limits included. The mass ratio of the catalyst to the co-catalyst is generally greater than 0.5 and preferably at least 1.

Advantageously, the cocatalyst is present in the two reactors.

The catalyst and the cocatalyst are in the form of solid catalytic compositions.

They can each be in the form of grains generally from 20 to 300 μm in diameter, the grains of catalyst and of cocatalyst being generally mixed before the implementation of the method according to the invention.

The catalyst and the cocatalyst can also be in the form of a solid catalytic composition composed of grains, each of which comprises both the catalyst and the cocatalyst.

Examples

The following examples illustrate the present invention without, however, limiting its scope. In the formulas indicated in Example 1, x is the quantity of oxygen bound to the other elements and depends on their oxidation states.

Conversions, selectivities and yields are defined as follows:

Number of moles of propane reacted Conversion (%) = x 100 of propane Number of moles of propane introduced

Number of moles of acrylic acid formed

Selectivity (%) = - x 100 in acrylic acid Number of moles of propane reacted

Number of moles of acrylic acid formed Yield (%) = x 100 of acrylic acid Number of moles of propane introduced

The selectivities and yields relative to the other compounds are calculated in a similar manner.

The conversion ratio is the mass of catalyst (in kg) necessary to convert 1 kg of propane.

Example 1 (comparative)

A catalyst was prepared in the following manner. In 30 ml of water heated to 80 ° C., 5.35 g of ammonium paramolybdate and 1.33 g of antimony sulphate (Sb ₂ (SO) ₃ ) are added successively, with stirring. Stirring is continued for 15 minutes. Separately, a solution containing 10 mmol of vanadium is prepared by dissolving 2.63 g of hydrated vanadyl sulphate in 10 ml of distilled water heated to 80 ° C. The second solution is added to the first and the mixture is stirred for 15 minutes before being introduced into a 70 ml autoclave coated with Teflon®. Nitrogen is then bubbled for 5 minutes so that it replaces the air present in the autoclave, before closing it. The autoclave is then placed at 175 ° C for 24 hours. After this time, the autoclave is cooled by water under the tap for 10 minutes. The black-purple solid obtained in the autoclave is separated from the solution by filtration, washed thoroughly with distilled water and dried for 12 hours at 80 ° C. The precursor thus obtained is then precalcined in air at 280 ° C for 2 hours, then calcined under nitrogen flow (25 ml / h / g) at 600 ° C for 2 hours. Catalyst 1 is thus obtained. This catalyst is tested. The results are collated in Tables 2 and 3.

Example 2 (comparative) A catalyst was prepared as follows.

In 20 ml of water heated to 80 ° C., 5.35 g of ammonium paramolybdate and 0.55 g of a 3% hydrogen peroxide solution are added successively with stirring, and 0 , 74 g of antimony trioxide. Stirring is continued for 60 minutes until the antimony oxide dissolves. Separately, a solution containing 12 mmol of vanadium is prepared by dissolving 3.16 g of hydrated vanadyl sulphate in 10 ml of distilled water heated to 80 ° C. The second solution is added to the first and 1.89 g of powdered oxalic acid is added to the solution. The mixture is stirred for 10 minutes before being introduced into a 70 ml autoclave coated with Teflon®. Nitrogen is then bubbled for 5 minutes so that it replaces the air present in the autoclave, before closing the latter. The autoclave is then placed at 175 ° C for 48 hours.

After this time, the autoclave is cooled by water under the tap for 10 minutes. The black-purple solid obtained in the autoclave is separated from the solution by filtration, washed thoroughly with distilled water and dried for 12 hours at 80 C. The precursor thus obtained is then calcined under a stream of nitrogen (25 ml / h / g) at 600 C for 2 hours. Catalyst 2 is thus obtained. This catalyst is tested. The results are collated in Tables 2 and 3.

Example 3

A catalyst was prepared in the following manner. In 20 ml of water heated to 80 ° C., 5.35 g of ammonium paramolybdate and 0.55 g of a 31% o hydrogen peroxide solution are added successively, with stirring. , 74 g of antimony trioxide. Stirring is continued for 60 minutes until the antimony oxide dissolves. Separately, a solution containing 9 mmol of vanadium is prepared by dissolving 2.37 g of hydrated vanadyl sulphate in 10 ml of distilled water heated to 80 ° C. A third solution containing 3 mmol of niobium is prepared simultaneously by dissolving, with stirring, 1.94 g of hydrated niobium oxalate in 10 ml of distilled water heated to 80 ° C. The second solution is added to the first and stirring is continued for 5 minutes. Finally, the solution containing niobium is added. The mixture is stirred for 10 minutes before introducing it into a 70 ml autoclave coated with Teflon®. Nitrogen is then bubbled for 5 minutes so that it replaces the air present in the autoclave, before closing the latter. The autoclave is then placed at 175 ° C for 48 hours.

After this time, the autoclave is cooled by water under the tap for 10 minutes. The black-purple solid obtained in the autoclave is separated from the solution by filtration, washed thoroughly with distilled water and dried for 12 hours at 80 ° C. The precursor thus obtained is then calcined under a stream of nitrogen (25 ml / h / g) at 600 ° C for 2 hours. Catalyst 3 is thus obtained. This catalyst is tested under the same conditions as the other catalysts. The results are collated in Tables 2 and 3.

Example 4 A catalyst was prepared as follows.

In 20 ml of water heated to 80 ° C., 5.35 g of ammonium paramolybdate and 0.55 g of a 31% hydrogen peroxide solution are added successively, with stirring, and 0, 74 g of antimony trioxide. Stirring is continued for 60 minutes until the antimony oxide dissolves. Separately, a solution containing 12 mmol of vanadium is prepared by dissolving 3.16 g of hydrated vanadyl sulphate in 10 ml of distilled water heated to 80 ° C. A third solution containing 1.5 mmol of niobium is prepared simultaneously by dissolving, with stirring, 0.97 g of hydrated niobium oxalate in 10 ml of distilled water heated to 80 ° C. The second solution is added to the first and stirring is continued for 5 minutes. Finally, the solution containing niobium is added. The mixture is stirred for 10 minutes before introducing it into a 70 ml autoclave coated with Teflon®. Nitrogen is then bubbled for 5 minutes so that it replaces the air present in the autoclave, before closing the latter. The autoclave is then placed at 175 ° C for 48 hours. After this time, the autoclave is cooled by water under the tap for 10 minutes. The black-purple solid obtained in the autoclave is separated from the solution by filtration, washed thoroughly with distilled water and dried for 12 hours at 80 ° C. The precursor thus obtained is then calcined under a stream of nitrogen (25 ml / h / g) at 600 ° C for 2 hours. Catalyst 4 is thus obtained. This catalyst is tested under the same conditions as catalyst 3. The results are collated in Tables 2 and 3. Example 5 (comparative)

A catalyst was prepared in the following manner. In 45 ml of water, 2,0008 g of ammonium metavanadate are dissolved hot (90 ° C). Then, 1.2149 g of antimony trioxide (senarmontite phase) and 10.0142 g of ammonium heptamolybdate are added. The whole is refluxed under argon, the temperature is fixed at 70 ° C. and the solution is left under stirring for 14 hours. The resulting mixture is opaque blue-black. 2 ml of 30% hydrogen peroxide are added using a syringe, and the solution is allowed to stir. The color gradually evolves towards orange through green-khaki hues. There is then a slight precipitate in a dark orange solution. At the same time, 1.7254 g of oxalic acid had been dissolved in 20 ml of water and this solution was added to the first, which remained at 70 ° C., without any change in color or appearance being noted. The pH of the solution is then 3 to 4. The mixture is left to mature for another 30 minutes, then it is put to dry in an oven for 12 hours at 110 ° C. The amorphous precursor is then pre-calcined in air (15 mFmin / g) at 300 ° C, for 4 hours, then calcined under nitrogen flow (15 mFmin / g) for 2 hours at 600 ° C. Catalyst 5 is thus obtained. This catalyst is tested under the same conditions as the other catalysts. The results are collated in Table 4.

Example 6 Catalyst 6 is prepared like catalyst 5, except that 0.75 g of niobic acid is dissolved in the oxalic acid solution, by heating it at 70 ° C. for 2 hours. This solution is centrifuged before being mixed with the solution containing the other elements. The results are collated in Table 4.

Example 7 A catalyst was prepared as follows.

In 20 ml of water heated to 80 ° C., 5.35 g of ammonium paramolybdate are added with stirring. Separately, a solution containing 15 mmol of vanadium is prepared by dissolving 3.94 g of hydrated vanadyl sulphate in 20 ml of distilled water heated to 80 ° C. The second solution is added to the first and the mixture is then stirred for 10 minutes before being introduced into a 70 ml autoclave coated with Teflon®. Nitrogen is then bubbled for 5 minutes so that it replaces the air present in the autoclave, before closing the latter. The autoclave is then placed at 175 ° C for 24 hours.

After this time, the autoclave is cooled by water under the tap for 10 minutes. The black-blue solid obtained in the autoclave is separated from the solution by filtration, washed thoroughly with distilled water and dried for 12 hours at 80 ° C. The precursor thus obtained is then calcined under a stream of nitrogen (25 mFh / g) at 500 ° C for 2 hours. Catalyst 7 is thus obtained. This catalyst is tested under the same conditions as the other catalysts.

In the case of Examples 1 and 3, the test effluents are collected for 4 hours in an ice trap. 2 analyzes by chromatography coupled to a mass spectrometer are carried out per sample.

5 main products are detected per sample: acetone, water, acetic acid, propionic acid and acrylic acid.

The propionic acid / acrylic acid molar ratios are thus calculated for each sample, for reaction temperatures of 320 ° C. and 360 ° C. The average of the two analyzes carried out per sample is reported in Table 5 below.

It is noted that the molar ratio decreases with an increase in temperature and the presence of niobium in the composition of the catalyst.

Example 8

Preparation of a catalyst A of formula: Mo ₁ No. ₃ oSb ₀ . ₁₅ Nbo.ιoSi _{0. 3} O _x and its precursor.

Synthesis of the Precursor

This synthesis makes it possible to prepare approximately 100 g of dry precursor.

Step 1: Dissolution-precipitation

Solution A 12.3 g (0.1052 mol V) of ammonium metavanadate (MNA) are dissolved in 260 ml of demineralized water, in a 1 liter SNL® glass reactor, with stirring, in a bath oil temperature controlled at 128 ° C. A yellow solution is obtained.

7.7 g (0.0528 mol Sb) of Sb ₂ O ₃ are added to the clear solution (slight addition of water to rinse the funnel), then 61.8 g of ammonium heptamolybdate (HMA, 0 , 3501 mole of Mo) are added. After the addition of HMA, the reactor is put under nitrogen sweeping, the reaction is maintained under stirring, at reflux, for 4 hours.

Gradually a blue - black solution is obtained.

Solution B

6 g (0.0530 mol) of an aqueous solution of H O ₂ at 30% by weight, dissolved in 100 g of water, are then added slowly (approximately 30 minutes). In order to obtain a clear orange solution, two drops of pure hydrogen peroxide are added.

Solution C

Then 49.1 g of Ludox® AS40 silica (nsi = 0.327 mole) are added all at once, and the solution becomes slightly cloudy. The solution formed is called solution C. Solution D

A solution D is prepared simultaneously with the solution A. In a 500 ml beaker, 100 g of distilled water are introduced, 5.9 g of niobic acid marketed by the Brazilian company CB is n _Ν b = 0.035 mole, and 13.2 g Prolabo oxalic acid or no _xa i _ates - 0.105 mole. The mixture is heated to 60 ° C with stirring for 2 hours, then brought back to 30 ° C. The solution is then centrifuged at 6200 rpm for 12 minutes to obtain a clear solution.

Solution D is added to solution C, all at once. An orange then yellow fluid gel is obtained. Stirring is maintained for 30 minutes under a flow of nitrogen, under reflux. Step 2: Drying

The gel is then dried in a ventilated oven, on trays covered with Teflon®, overnight, at 130 ° C. 86.3 g of dry precursor are recovered. The precursor is in the form of leaves, black above and a thin green film below. A precursor is thus obtained.

Step 3: Heat treatment

30 g of precursor previously obtained are precalcined at 305 ° C with an air flow rate of 18.7 ml / min / g.

After calcination, at 601 ° C. under a nitrogen flow rate of 49.8 ml / min / g, a mass of calcined solid is obtained of 24.6 g. This catalyst is called CATALYST A.

Example 9

Preparation of a catalyst B of formula: Mo ₁ V _{0 0} Sbo. ₁₅ Nbo.ioSio. ₇₆ O _x and its precursor.

Synthesis of the precursor The procedure is as in Example 8, but with:

- 30.75 g (0.2630 mole V) of ammonium metavanadate (MVA);

- 19.25 g (0.1321 mole of Sb) of Sb ₂ O ₃ ;

- 154.5 g (0.8753 mol of Mo) of ammonium heptamolybdate (HMA); 15.25 g (0.1346 mol) of an aqueous solution of H O at 30% by weight; - 100 g of silica Ludox® AS 40 (n _si = 0.6667 mole);

14.75 g of niobic acid CBMM, ie n _Nb = 0.088 mole; and

- 33.0 g of Prolabo® oxalic acid or noxaiate- = 0.262 mole.

259 g of dry precursor are recovered. The precursor is in the form of black leaves above and thin yellow-green films below. 25 g of this precursor are precalcined at 321 ° C under static air for 4 hours, then calcined at 598 ° C under a nitrogen flow of 51.85 ml / min / g for 2 hours. A mass of calcined solid is obtained of 20.30 g. This catalyst is called catalyst B.

Example 10 Preparation of a catalyst C of formula: Mo ₁ V _{0 0} Sbo. ₁₅ Nbo _.10 Sio _. g ₃ O _x and its precursor. Synthesis of the precursor

A 10 liter jacketed reactor is used. The diagram of the installation is given in FIG. 2. The installation comprises the jacketed reactor 1, provided with a withdrawal orifice 2 and an oil bath 3 thermostatically controlled at 140 ° C (so as to the temperature inside the reactor is around 99 ° C), an agitator 4 designed to operate at 125 rpm, an inlet 5 for the reagents, an inlet 6 for the nitrogen, from a refrigerant 7 connected to a vent 8. Cold, with stirring and under a flow of nitrogen, 2600 g of water, 123 g of ammonium metavanadate (1.052 mole), 77 g of oxide are introduced. antimony (0.528 mole), and 618 g of ammonium heptamolybdate (3.501 mole). After heating, the mixture quickly evolves towards green, then towards blue-black. After stabilization of the internal temperature of the reactor (T = 99 ° C), 4 hours of stirring of the solution allow it to be perfectly homogeneous. 60 g of hydrogen peroxide diluted in 500 g of water are added so as to obtain a clear orange solution (oxidation of all the cations present).

30 minutes later, 491 g (3.27 mole) of colloidal silica are introduced as well as a solution of niobic acid (59 g, 0.5 mole) and oxalic acid (132 g, 1.05 mole) beforehand heated for two hours and centrifuged (12 minutes at 6200 rpm). Another 30 minutes later, the heating is stopped but the stirring is maintained overnight in order to keep a homogeneous solution. The mixture took on a yellow color and the consistency of a gel.

Formatting

A laboratory atomizer (ATSELAB® from the company Sodeva) is used. The atomization takes place in an air atmosphere. The operating parameters are globally:

• nitrogen flow of around 40 m ³ / h;

• slip flow of the order of 2600 g / h;

• gas inlet temperature: 290 ° C; • gas outlet temperature: 134 ° C.

The increase in the dry matter content in the slip is carried out on a rotary evaporator up to 30.8% by weight.

A fraction of between 40 and 160 μm is recovered in the chamber which corresponds to the precursor. Heat treatment

26.6 g of the fraction obtained previously, that is to say the precursor, are precalcined for 4 hours at 316 ° C. under static air to give a precalcined solid. The precalcined solid is then calcined for 2 hours at 598 ° C. under a nitrogen flow rate of 49.83 ml / g / min and thus gives 21 g of catalyst called CATALYST C.

Example 11

Catalyst tests a) Apparatus

In order to simulate the method according to the invention, laboratory simulations were carried out in a laboratory fixed bed reactor, generating propane pulses and oxygen pulses.

One loads, from bottom to top, into a vertical reactor of cylindrical shape and in pyrex: a first height of 2 ml of silicon carbide in the form of particles of 0.125 mm in diameter,

- a second height of 5.00 g of catalyst in the form of particles of 0.02 to 1 mm diluted with 10 ml of silicon carbide in the form of particles of 0.125 mm in diameter,

a third height of 2 ml of silicon carbide in the form of particles of 0.125 mm in diameter, and

a fourth height of silicon carbide in the form of particles 1.19 mm in diameter, so as to fill the entire reactor. b) Catalyst A tests

1) Procedure

The reactor is heated to 250 ° C and the vaporizer to 200 ° C. The electric priming of the water pump is activated.

Once the reactor and the vaporizer have reached the temperatures indicated above, the water pump is activated and the temperature of the reactor is raised to 400 ° C and waiting 30 minutes for the hot spot to stabilize.

Then, oxygen is introduced in 10 pulses of 23 seconds each to oxidize the catalyst well. The catalyst is considered to be completely oxidized when the temperature of the hot spot has stabilized, that is to say when there is no longer any exotherm due to the reaction (by following the temperature of the catalyst measured by means of 'a thermocouple placed in the catalytic bed, we can see the temperature fluctuations as a function of the pulses).

We can then proceed to the measurements concerning the production of acrylic acid proper. During each balance, liquid withdrawals are made. Gas samples are also taken using gas bags, each sample representing a certain number of cycles.

Each small washing bottle (25 ml of capacity and filled with 20 ml of water) is equipped with a gas pocket, and when the bottle is connected to the outlet of the reactor (as soon as the liquid bubbles) , the pocket is opened and the stopwatch is started.

To check the oxidation state of the catalyst, a new series of 10 pulses of 23 seconds of oxygen is carried out. It shows that the solid state of oxidation was maintained during the balance.

Liquid effluents are analyzed on an HP 6890 chromatograph, after performing a specific calibration.

The gases are analyzed during the balance on a micro-GC Chrompack chromatograph. An acidity assay is performed on each bottle to determine the exact number of moles of acid produced during each micro-balance and to validate the chromatographic analyzes. i) TA1 test

This is a propane oxidation test carried out in the absence of molecular oxygen. This test was carried out with partial pressures of propane and oxygen corresponding to the following ratios:

For oxidation: Propane / He-Kr / H ₂ O: 10/45/45

For regeneration: O ₂ / He-Kr / H ₂ O: 20/45/45, with a flow of He-Kr of 4.262 Nl / h (NFh = normal liters per hour), i.e. liters / h at 0 ° C and at atmospheric pressure) and at a temperature of 400 ° C.

In this test, a redox balance is made up of 60 cycles. A redox cycle represents:

12.2 seconds of propane in a continuous stream of helium-krypton / water, - 45 seconds of continuous stream of helium-krypton / water, - 20 seconds of oxygen in a continuous stream of helium-krypton / water,

45 seconds of continuous helium-krypton / water flow. During each assessment, 4 liquid samples are taken, each representing 15 cycles and 4 gas samples using gas bags, each sample representing 15 cycles. ii) TA2 test It is also a propane oxidation test carried out in the absence of molecular oxygen.

In this test, the duration of the propane pulse (as well as that of the oxygen) is modified during the assessment, thus making it possible to observe the behavior of the catalyst in the face of a more or less rich redox mixture.

The duration of the oxygen pulse is always twice as long as that of propane, and with a double flow, to keep the catalyst oxidized.

The partial pressures of propane and oxygen remain the same as in the previous test TA 1: For oxidation: Propane / He-Kr / H ₂ O: 10/45/45

For regeneration: O ₂ / He-Kr / H ₂ O: 20/45/45, with a flow of He-Kr of 4.262 Nl / h at a temperature of 400 ° C.

The balance sheet is in this example of 60 cycles divided into six micro-balance sheets in the following manner: 2 first micro-balance sheets of 7 and 8 cycles:

10 seconds of propane in a He-Kr / H O flow,

45 seconds under He-Kr,

20 seconds of O ₂ in a flow of He-Kr,

45 seconds under He-Kr. ^3rd micro-balance 15 cycles:

5 seconds of propane in a flow of He-Kr / H ₂ O,

50 seconds under He-Kr,

10 seconds of O ₂ in a flow of He-Kr,

55 seconds under He-Kr. ^4th micro-balance 8 cycles:

2 seconds of propane in a flow of He-Kr / H ₂ O,

50 seconds under He-Kr,

4 seconds of O in a He-Kr stream,

55 seconds under He-Kr. ^5th micro-balance 8 cycles:

20 seconds of propane in a flow of He-Kr / H ₂ O,

45 seconds under He-Kr,

40 seconds of O ₂ in a flow of He-Kr,

45 seconds under He-Kr. 6 ^th micro-assessment of 7 cycles:

30 seconds of propane in a He-Kr / H2O flow, 45 seconds under He-Kr,

60 seconds of O ₂ in a flow of He-Kr,

45 seconds under He-Kr.

The durations of the pulses which have just been indicated are theoretical durations. iii TA3 test

In this test, propane is oxidized in the presence of molecular oxygen at 400 ° C.

The duration of oxygen injection in the propane pulse is varied by keeping the propane and oxygen pressures constant. The balance of 40 cycles is broken down as follows:

10 cycles of 30 s of propane + 5 s of O ₂ (oxygen being injected from the start of the injection of propane), with Propane / O ₂ / He-Kr / H ₂ O proportions of 30/30 / 45/45, with a helium-krypton flux of 4.262 Nl / h.

Then there is an intermediate pulse composed only of the flow of carrier gas He-Kr / H ₂ O of 60 s, then an oxygen pulse with the proportions O ₂ / He-Kr / H ₂ O of 20/45/45, for 60 s and again an intermediate pulse of He-Kr / H ₂ O of 60 s.

Then we have a new series of 10 cycles of 30 s of propane + 10 s of oxygen, with Propane / O ₂ / He-Kr / HO proportions of 30/30/45/45, with a flow of helium- 4.262 Nl / h krypton. We then have an intermediate pulse composed only of the flow of carrier gas He-Kr / HO of 60s, then an oxygen pulse with the proportions O ₂ / He-Kr / H ₂ O = 20/45/45, for 60 s and again an intermediate implusion of He-Kr / H ₂ O of 60 s.

Then, we have a new series of 10 cycles of 30 s of propane + 15 s of O, with Propane / O ₂ / He-Kr / H ₂ O proportions of 30/30/45/45, with a flow of helium-krypton of 4.262 Nl / h. We then have an intermediate pulse composed only of the flow of carrier gas He-Kr / H ₂ O of 60 s, then an oxygen pulse with the proportions O / He-Kr / H ₂ O = 20/45/45, during 60 s and again an intermediate pulse of He-Kr / H ₂ O of 60 s. Then, we have a new series of 10 cycles of 30 s of propane + 20 s of O ₂ , with Propane / O ₂ / Ηe-Kr / H ₂ O proportions of 30/30/45/45, with a flow 4.262 Nl / hr helium-krypton. There is then an intermediate pulse composed only of the carrier gas flow He-Kr / H ₂ O of 60 s, then an oxygen pulse with the proportions O ₂ / He-Kr / H ₂ O of 20/45/45, for 60 s and again an intermediate pulse of He-Kr / H ₂ O of 60 s.

As in the TA2 test, the durations of the pulses which have just been indicated are theoretical durations. 2) Results

The results of the TAl, TA2 and TA3 tests are grouped in the tables below.

In these tables, the theoretical durations of the pulses were no longer indicated as before, but the corresponding real durations which were calculated using a specific calibration.

In the TA3 test, where one operates in the presence of molecular oxygen, it is noted that the yields of acrylic acid increase much faster, as a function of the addition of oxygen in the propane pulse, than the yields of CO _x and acetic acid. This results in a substantial gain in selectivity for acrylic acid. There is also a decrease in the selectivity of hydration products (acetone, propionic acid).

The addition of oxygen also leads to a gain in conversion ratio which thus goes from 1107 to 803 kg / kg. c) Catalyst B tests 1) Procedure

The apparatus used is that described in Example 11 a). i) TB1 and TB2 tests

Catalyst B is tested under the same conditions and in the same manner as for the TAl test. ii) TB3 test

Catalyst B is tested under the same conditions and in the same manner as for the TA3 test (presence of molecular oxygen). iii) TB4 to TB6 tests

In the case of the TB4 test, the catalyst B is tested under the same conditions and in the same manner as for the TA2 test, at 420 ° C.

In the case of tests TB5 and TB6, the content of propane is simply modified during oxidation and of oxygen during regeneration. iv) TB7 tests

In this test, propane is oxidized in the presence of molecular oxygen, at 420 ° C.

The duration of oxygen injection in the propane pulse is varied by maintaining constant propane and oxygen pressures.

Oxygen is injected at the end of the propane pulse to see if there is an influence on the catalytic performance compared to an injection at the start of the pulse.

The balance of 40 cycles is broken down as follows: 10 cycles of 30 s of propane + 20 s of O ₂ (oxygen being injected at the end of the propane pulse), with Propane / O ₂ / He proportions -Kr / HO of 30/30/45/45, with a flux of helium-krypton of 4.27 Nl / h. We then have an intermediate pulse composed only of the carrier gas flow He-Kr / HO of 60 s, then an O pulse with the proportions O ₂ / He-Kr / H ₂ O = 20/45/45, for 60 s and again a carrier gas pulse of 60 s. Then, we have a new series of 10 cycles of 30 s of propane + 15 s of oxygen, with propane / O / He-Kr / H ₂ O proportions of 30/30/45/45, with a flow of 4.27 NFh helium-krypton. We then have an intermediate pulse composed only of the flow of carrier gas He-Kr / H ₂ O of 60 s, then an oxygen pulse with the proportions O / He-Kr / HO = 20/45/45, for 60 s and again an intermediate pulse of carrier gas of 60 s. Then, we have a new series of 10 cycles of 30 s of propane + 10 s of O ₂ , with Propane / O ₂ / He-Kr / H ₂ O proportions of 30/30/45/45, with a flow of helium-krypton of 4.27 Nl / h. We then have an intermediate pulse composed only of the carrier gas flow He-Kr / HO of 60 s, then an O ₂ pulse with the proportions O ₂ / He-Kr / H ₂ O = 20/45/45, during 60 s and again an intermediate carrier gas pulse of 60 s.

Then, we have a new series of 10 cycles of 30 s of propane + 5 s of O ₂ , with Propane / O ₂ / He-Kr / H ₂ O proportions of 30/30/45/45, with a flow 4.27 Nl / h helium-krypton. We then have an intermediate pulse composed only of the carrier gas flow He-Kr / H ₂ O of 60 s, then an O ₂ pulse with the proportions O / He-Kr / HO = 20/45/45, for 60 s and again an intermediate pulse of carrier gas of 60 s. v) TB8 tests

In this test, propane is also oxidized in the presence of molecular oxygen. The effect of the injection of oxygen at the end and at the start of the propane pulse is compared by maintaining constant propane and oxygen pressures but also a constant oxygen injection duration in the propane pulse.

The balance of 40 cycles is broken down as follows: 10 cycles of 30 s of propane + 20 s of O ₂ (oxygen being injected at the end of the propane pulse), with Propane / O ₂ / He proportions -Kr / HO of 30/30/45/45, with a flux of helium-krypton of 4.27 Nl / h. Then there is an intermediate pulse composed only of the carrier gas flow He-Kr / H ₂ O of 60 s, then an intermediate pulse of O with the proportions O ₂ / He-Kr / HO = 20/45/45, during 60 s and again an intermediate carrier gas pulse of 60 s. Then, we have a new series of 10 cycles of 30 s of propane + 20 s of oxygen (O ₂ being injected at the end of the propane pulse), with Propane / O ₂ / He-Kr / H proportions ₂ O of 30/30/45/45, with a flow of helium-krypton 4.27 Nl / h. We then have an intermediate pulse composed only of the flow of carrier gas He-Kr / H ₂ O of 60 s, then an intermediate pulse of oxygen with the proportions O / He-Kr / Η ₂ O = 20/45/45, for 60 s and again an intermediate pulse of carrier gas of 60 s. 10 cycles of 30 s of propane + 20 s of O ₂ (oxygen being injected at the start of the propane pulse), with Propane / O ₂ / He-Kr / H ₂ O proportions of 30/30/45 / 45, with a helium-krypton flux of 4.27 Nl / h. We then have an intermediate pulse composed only of the carrier gas flow He-Kr H ₂ O of 60 s, then an intermediate pulse of O ₂ with the proportions O ₂ / He-Kr / H ₂ O = 20/45/45 , for 60 s and again an intermediate pulse of carrier gas of 60 s.

Then, we have a new series of 10 cycles of 30 s of propane + 20 s of O ₂ (oxygen being injected at the start of the propane pulse), with Propane / O ₂ / He-Kr / proportions proportions ₂ O of 30/30/45/45, with a helium-krypton flux of 4.27 N h. We then have an intermediate pulse composed only of the flow of carrier gas He-Kr / H ₂ O of 60 s, then an intermediate pulse of O ₂ with the proportions O ₂ / He-Kr / H ₂ O = 20/45 / 45, for 60 s and again an intermediate pulse of carrier gas of 60 s.

2) Test results a) TBl and TB2 tests

A better conversion is observed at 420 ° C than at 400 ° C. The selectivity for acrylic acid goes from 57.4% to 52.2% when the temperature is changed. There is a marked decrease (halving) in the selectivities of acetone and propionic acid.

Increasing the temperature increases the conversion and decreases the formation of hydration products as well as the conversion ratio. The conversion ratio goes from 3300 to 2900 kg / kg from 400 to 420 ° C. b TB4 to TB6 tests

The results are shown in the two tables below. It is noted that the increase in the partial propane pressure and / or the duration of the propane injection leads to a reduction in the yield of acrylic acid, but to a maintenance of the yield of hydration products. The selectivities of hydration products therefore increase with the reduction of the catalyst. The selectivities for acrolein and propylene also increase with the reduction of the catalyst. The reduced catalyst becomes less active.

c) TB3 tests. TB7 and TB8

The results are shown in the three tables below.

It is noted that the addition of molecular oxygen allows a clear reduction in the conversion ratio while maintaining good selectivity. We go from 2904 kg of catalyst / Kg of propane converted for a standard test to 1019 kg of catalyst / Kg of propane converted for a test in pulse duration variation (30 s of propane with propane or oxygen / He-Kr H ₂ O: 30 or 30/45/45). With the addition of oxygen, it is 460 to 500 kg of catalyst / kg of propane converted.

It is advantageous to add oxygen which not only makes it possible to further reduce the conversion ratio, but also to raise the selectivities for acrylic acid. It is noted that the catalyst, even reduced, can remain dehydrogenating.

An analysis problem was detected on bottle 2, for this reason the results obtained are not indicated.

d) Catalyst C tests

1) Procedure

The apparatus used is that described in Example 11 a). i) TC1 test Catalyst C is tested in the same way as for the TAl test. The conditions are identical except for the He-Kr flow rate which is 4.27 Nl / h and the test temperature which is 420 ° C. ii) TC2 to TC4 tests

In the case of the TC2 test, the catalyst C is tested under the same conditions and in the same manner as for the TA2 test.

In the case of the TC3 and TC4 tests, the propane content is simply modified during the oxidation and the oxygen during the regeneration.

These three tests were carried out at 420 ° C and with a He-Kr flow rate of 4.27 Nl / h. ni) Test TC5 Catalyst C is tested in the same way as for the TA3 test (presence of molecular oxygen). The conditions are also identical except for the flow of He-Kr which is now 4.27 M / h. The temperature is 420 ° C. iv TC6 test

Catalyst C is tested in the same way as for test TB7. The conditions are identical. v) TC7 test

Catalyst C is tested in the same way as for the TB8 test. The conditions are identical except for the He-Kr flow rate which is 4.27 Nl / h and the test temperature which is 420 ° C. 2) Results a) TCl to TC4 tests

The results are grouped in the following two tables.

It is found, as for catalyst B, that the selectivity for propionic acid and for acetone increases with the partial pressure of propane, that is to say that the more the catalyst is reduced the less it is selective.

The kinetics of initial oxygen consumption is very fast, then seems to change over time.

b) Tests TC5 to TC7

The results are grouped in the following three tables.

It is noted that the addition of oxygen at the start of the propane pulse, rather than at the end of the pulse, leads to a slight gain in selectivity for acrylic acid, which seems to come from a lower selectivity for CO _x .

Example 12

Preparation of the precursor of a catalyst of formula:

1) Stage 1: dissolution - precipitation Solution A The assembly illustrated in FIG. 2 is used which comprises a reactor of the SVL type of 1 liter provided with an agitator connected to a motor and with a water cooler containing raschig rings. A nitrogen supply is installed on the reactor and a bubbler is placed at the outlet of the refrigerant. Heating is provided by a thermostatically controlled oil bath. 12.3 g of ammonium metavanade (MVA) (ie 0.1052 mol of vanadium) are dissolved in 260 ml of demineralized water, in the reactor, with stirring. A yellow solution is obtained. 7.7 g of Sb ₂ O ₃ (i.e. 0.0528 mole of antimony) are added to the clear solution, then 61.8 g of ammonium heptamolybdate (HMA) (i.e. 0.3501 mole of molybdenum) are added. After the addition of HMA, the reactor is placed under a flow of nitrogen, the reaction is maintained under stirring, at reflux, for 4 hours. Gradually, a black solution is obtained; the reaction is considered to be complete after 1 hour. The solution obtained is called solution A.

Solution B

6.1 g (0.0532 mole) of an aqueous solution of H O ₂ at 30% by weight are dissolved in 98 g of water, are then added in 2 to 3 minutes to solution A. The solution becomes clear orange in 4-5 minutes. Then 40 g of ludox silica (0.2663 mole of Si) are added all at once and the solution becomes cloudy. The solution formed is called solution B.

Solution C

Solution C is prepared simultaneously with solution A: 13.2 g (0.1047 mole) of oxalic acid and 5.9 g of niobic acid (i.e. 0.0351 mole of Nb) are dissolved with stirring at 80 ° C, in 100 g of water, for 2 hours. This solution is then centrifuged at 6200 rpm for 12 minutes, to obtain a clear solution C.

Then, Solution C is added to solution B, all at once. An orange then yellow fluid gel is obtained. Stirring is maintained for 30 minutes under a flow of nitrogen, under reflux.

2) Step 2: drying The gel obtained above is dried in a ventilated oven, on teflon-coated trays, overnight, at 130 ° C. 104.2 g of dry precursor are recovered. This precursor, hereinafter called PI, is in the form of leaves, black above, with a green film below.

Example 13

Preparation of the precursors P2 to PI 5 The procedure is as indicated in Example 12, with the exception of the conditions indicated in Table 14 below, in which also appear the aspects of the precursors obtained. TABLE 14 Summary of precursor syntheses

TABLE 14 (continued)

Example 14

Precalcination and calcination of PI to PIS precursors

The precalcinations and calcinations are carried out in nacelles respectively under air and nitrogen flow, in steel capacities. These capacities are directly installed in muffle furnaces and the air or nitrogen supply is through the chimney. An internal thermowell allows proper temperature control. The cover prevents the return of air to the catalyst, (see figure 3)

The precursors PI to PI 5 obtained in Examples 12 and 13 are precalcined at 300 ° C, for 4 hours, under air flow, then calcined at 600 ° C, for 2 hours under nitrogen flow of 50 ml / min / g in a muffle oven. Calcinations

The following conditions for thermal treatment of the precursors are studied: calcination furnace; precalcination air flow in ml / min / g; - calcination temperature variation slope in ° C / min.

These conditions are grouped in Table 15 below.

TABLE 15 Heat treatment of precursors (for masses from 25 to 30 g)

Example 15

Tests of the catalysts obtained at Apparatus

In order to simulate the process according to the invention, simulations were carried out in the laboratory in a laboratory fixed bed reactor. We therefore load, from bottom to top, into a vertical reactor of cylindrical shape and in pyrex:

- a first height of 1 ml of silicon carbide in the form of particles of 0.125 mm in diameter, - a second height of 5 g of catalyst in the form of particles of 0.02 to 1 mm diluted with 10 ml of silicon carbide in form of particles of 0.125 mm in diameter,

- a third height of 1 ml of silicon carbide in the form of particles of 0.125 mm in diameter, and - a fourth height of silicon carbide in the form of particles of

1.19 mm in diameter, so as to fill the entire reactor. b) Test conditions

The catalyst is supplied with propane and oxygen simultaneously. Helium acts as a diluent gas and water is vaporized in the gas stream. The catalysts are tested at 380 ° C, 390 ° C and 400 ° C with a propane / O ₂ / He- ratio

Kr / H ₂ O from 10/10/45/45. The total flow rate of the gas flow is 8.65 Nl / h.

The reactor is placed in an isothermal oven. It is supplied with propane, oxygen and helium by mass flow meters. An HPLC pump and a vaporizer ensure the production of steam. Thermocouples are placed in the furnace to allow regulation, and in the reactor for the measurement of the "hot spot", that is to say the highest temperature in the catalyst bed. c) Test results

Only the results of tests carried out at 400 ° C are given. It is at this temperature that it has been found that the best results are generally obtained.

The results of the tests are recorded in the following Tables 16 and 17 in which the yields are only calculated on the basis of the routine chromatographic analyzes. The selectivities are calculated as the yield of a given product over the sum of the yields of products. Carbon balances are used to ensure the homogeneity of the data. They are considered acceptable for values between 95 and 105%. The yield calculations are based on the krypton content of the gas. The measurement of the dry gas flow rate at the outlet of the reactor makes it possible to make calculations based on this gas flow rate. The yield calculations can thus be validated. The yields and selectivities in each of the dosed products are given, as well as the acid yield, obtained by dosing with 0.1N sodium hydroxide. It is a pseudo yield obtained by supposing that all the acids formed have 3 carbon atoms.

TABLE 17 Summary table of catalyst selectivities

Example 16

P16 precursors of the catalyst of formula are prepared according to the procedure indicated in Example 12

From these PI 6 precursors, a series of catalysts is prepared which are tested.

The precalcination and calcination conditions for the precursor PI 6 are grouped in Tables 18 and 19 below.

1) Stage 1: dissolution - precipitation Solution A The assembly illustrated in FIG. 2 is used which comprises a reactor of the SVL type of 1 liter provided with an agitator connected to a motor and with a water cooler containing raschig rings. A nitrogen supply is installed on the reactor and a bubbler is placed at the outlet of the refrigerant. Heating is provided by a thermostatically controlled oil bath. 30.75 g of ammonium metavanade (MVA) (ie 0.2629 mole of vanadium) are dissolved in 650 ml of demineralized water, in the reactor, with stirring. A yellow solution is obtained. 19.25 g of Sb ₂ O ₃ (or 0.1321 mole of antimony) are added, with 154.5 g of ammonium heptamolybdate (HMA) (or 0.8753 mole of molybdenum) are added. After the addition, the reactor is placed under a flow of nitrogen, the reaction is maintained under stirring, at reflux, for 4 hours. Gradually, a black solution is obtained; the reaction is considered to be complete after 1 hour.

The solution obtained is called solution A. Solution B 15.25 g (0.1346 mole) of an aqueous solution of H ₂ O at 30% by weight are dissolved in 90 g of water, are then added in 5 minutes to solution A. The solution turns clear orange in 4-5 minutes. Then 100 g of ludox AS 40® silica (0.6667 mole of Si) are added all at once and the solution becomes slightly cloudy. The solution formed is called solution B. Solution C

A solution C is prepared simultaneously with solution A: 33.0 g (0.2618 mole) of oxalic acid and 14.75 g of niobic acid (i.e. 0.0877 mole of Nb) are dissolved with stirring at 66 ° C, in 250 g of water, for 2 hours. This solution is then centrifuged at 6200 rpm for 12 minutes, to obtain a clear solution C.

Then, Solution C is added to solution B, all at once. We get a gel orange then yellow fluid. Stirring is maintained for 30 minutes under a flow of nitrogen, under reflux.

2) Step 2: drying

The gel obtained above is dried in a ventilated oven, on teflon-coated trays, overnight, at 130 ° C. 259 g of dry precursor are recovered. This precursor is in the form of leaves, black above, with a green film below. The precursor hereinafter called PI 6 is thus obtained.

Table 18 shows the carbon yields (TTUc), with TTGc = Σ TTUc and TTG ₀₂ = Σ TTUo, the acidities measured by dosing with sodium hydroxide, the carbon and oxygen balances.

Table 19 shows the carbon selectivities.

TABLE 18 Product yields obtained during catalyst tests

TABLE 19 Selectivities of products obtained during catalyst tests

It is therefore found that the best results are obtained with precalcination at 320 ° C. and under a zero air flow rate, followed by calcination at 600 ° C. for 2 hours under a nitrogen flow rate of 50 ml / min / g.

Claims

1. A method of manufacturing acrylic acid from propane, characterized in that a gaseous mixture comprising propane, steam, and possibly an inert gas and / or molecular oxygen, on a catalyst of formula (I):

MotV _a Sb _b Nb _o Si _d Ox (I) in which: a is between 0.006 and 1, limits included; - b is between 0.006 and 1, limits included;

- c is between 0.006 and 1, limits included;

- d is between 0 and 3.5, limits included; and

- x is the quantity of oxygen linked to the other elements and depends on their oxidation states, to oxidize propane to acrylic acid, and when operating in the presence of molecular oxygen, the propane / molecular oxygen molar ratio in the starting gas mixture is greater than or equal to 0.5.

2. Method according to claim 1, in which the molar proportions of the constituents of the starting gas mixture are as follows: propane / O ₂ / inert gas / H ₂ O (vapor) = 1 / 0.05-2 / 1-10 / 1-10; and preferably 1 / 0.1-1 / 1-5 / 1-5.

3. Method according to claim 1 or claim 2, in which, in the catalyst of formula (I): a is between 0.09 and 0.8, limits included; - b is between 0.04 and 0.6, limits included;

- c is between 0.01 and 0.4, limits included; and

- d is between 0.4 and 1.6, limits included.

4. Method according to one of claims 1 to 3, characterized in that the oxidation reactions are carried out at a temperature of 200 to 500 ° C.

5. Method according to claim 4, characterized in that the oxidation reaction is carried out at a temperature of 250 to 450 ° C.

6. Method according to one of claims 1 to 5, characterized in that one ccoonndduuiitt lleess rrééaaccttiiions of oxidation under a pressure of 1.01.10 ⁴ to 1.01.10 ⁶ Pa (0.1 10 atmospheres).

7. Method according to claim 6, characterized in that the oxidation reactions are carried out under a pressure of 5.05.10 ⁴ to 5.05.10 ⁵ Pa (0.5-5 atmospheres).

8. Method according to one of claims 1 to 7, characterized in that it is used up to a reduction rate of the catalyst comprised 0.1 and 10 g of oxygen per kg of catalyst.

9. Method according to one of claims 1 to 8, characterized in that once the catalyst has at least partially gone to the reduced state, its regeneration is carried out according to reaction (C):

SOLIDreduced + O ₂ - »SOLID _oxidized (C) by heating in the presence of oxygen or an oxygen-containing gas at a temperature of 250 to 500 ° C, for the time necessary for the reoxidation of the catalyst.

10. The method of claim 9, characterized in that one conducts the oxidation reactions and the regeneration (C) in a two-stage device, namely a reactor and a regenerator which operate simultaneously and in which periodically alternate two catalyst charges.

11. Method according to claim 9, characterized in that the oxidation and regeneration reactions (C) are carried out in the same reactor by alternating the reaction and regeneration periods.

12. Method according to claim 9, characterized in that the oxidation reactions and the regeneration (C) are carried out in a transported bed reactor.

13. Method according to one of claims 1 to 7, in which: a) the starting gas mixture is introduced into a first reactor with a transported catalyst bed, b) at the outlet of the first reactor, the gases are separated from the catalyst ; c) the catalyst is sent to a regenerator; d) optionally the gases are introduced into a second reactor with a transported catalyst bed; e) where appropriate, at the outlet of the second reactor, the gases are separated from the catalyst and the acrylic acid contained in the separated gases is recovered; f) if necessary, the catalyst is returned to the regenerator; and g) reintroduced regenerated catalyst from the regenerator into the first reactor and, where appropriate, into the second reactor.

14. The method of claim 13, wherein the first and second reactors are vertical and the catalyst is transported upward by the flow of gases.

15. Method according to one of claims 1 to 14, characterized in that the oxidation reactions are carried out with a residence time of 0.01 to 90 seconds in each reactor.

16. Method according to claim 15, characterized in that the oxidation reactions are carried out with a residence time of 0.1 to 30 seconds.

17. Method according to one of claims 1 to 16, characterized in that the propylene produced and / or the unreacted propane are recycled at the inlet of the reactor, or if there are several reactors, to the entrance to the first reactor.

18. Method according to one of claims 1 to 17, in which the reactor, or when there are several reactors, at least one of the reactors further comprises a cocatalyst corresponding to the following formula (II) :

Mo ₁ Bi _a .Fe _b .Co _{C '} Ni _d .K _e' Sb _f Tig _' Si _h' Ca _i 'Nb _j' Te _k .Pbι.W _{m '} Cu _n' (II) in which:

- a 'is between 0.006 and 1, limits included;

- b 'is between 0 and 3.5, limits included;

- it is between 0 and 3.5, limits included;

- d is between 0 and 3.5, limits included; - e 'is between 0 and 1, limits included;

- f is between 0 and 1, limits included;

- g 'is between 0 and 1, limits included;

- h 'is between 0 and 3.5, limits included;

- i 'is between 0 and 1, limits included; - I is between 0 and 1, limits included;

- k 'is between 0 and 1, limits included;

- F is between 0 and 1, limits included;

- m 'is between 0 and 1, limits included; and

- is between 0 and 1, limits included.

19. The method of claim 18, wherein the co-catalyst is regenerated and circulates, if necessary, in the same manner as the catalyst.

20. The method of claim 18 or claim 19, wherein, in the co-catalyst of formula (II): - a 'is between 0.01 and 0.4, limits included;

- b 'is between 0.2 and 1.6, limits included; it is between 0.3 and 1.6, limits included;

- d is between 0.1 and 0.6, limits included; e 'is between 0.006 and 0.01, limits included; - f is between 0 and 0.4, limits included; g 'is between 0 and 0.4, limits included; h 'is between 0.01 and 1.6, limits included; i 'is between 0 and 0.4, limits included;

- I is between 0 and 0.4, limits included; - k 'is between 0 and 0.4, limits included;

- F is between 0 and 0.4, limits included;

- m 'is between 0 and 0.4, limits included; and n 'is between 0 and 0.4, limits included.

21. Method according to one of claims 18 to 20, in which a mass ratio of the catalyst to the co-catalyst is used greater than 0.5 and preferably at least 1.

22. Method according to one of claims 18 to 21, wherein the catalyst and the cocatalyst are mixed.

23. Method according to one of claims 18 to 21, wherein the catalyst and the cocatalyst are in the form of grains, each grain comprising both the catalyst and the cocatalyst.

24. Method according to one of claims 1 to 23, comprising repeating, in a reactor provided with the catalyst of formula (I) defined in claim 1, and if necessary, the co-catalyst of formula (II) defined in claim 18, of the cycle comprising the following successive steps:

1) a step of injecting the gas mixture as defined in claims 1 to 3;

2) a step of injecting steam and, if necessary, inert gas; 3) a step of injecting a mixture of molecular oxygen, water vapor and, if necessary, inert gas; and

4) a step of injecting steam and, if necessary, inert gas.

25. The method of claim 24, characterized in that the cycle comprises an additional step which precedes or follows step 1) and during which a gaseous mixture is injected corresponding to that of step 1) but without the molecular oxygen, the propane / molecular oxygen molar ratio then being calculated overall for step 1) and this additional step.

26. The method of claim 25, characterized in that the additional step precedes step 1) in the cycle.

27. Method according to one of claims 24 to 26, characterized in that the reactor is a transported bed reactor.