Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
  • C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
  • C07C51/215—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of saturated hydrocarbyl groups
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/24—Chromium, molybdenum or tungsten
  • B01J23/28—Molybdenum
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
  • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
  • B01J27/057—Selenium or tellurium; Compounds thereof
  • B01J27/0576—Tellurium; Compounds thereof
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/42—Separation; Purification; Stabilisation; Use of additives
  • C07C51/50—Use of additives, e.g. for stabilisation
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C57/00—Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms
  • C07C57/02—Unsaturated compounds having carboxyl groups bound to acyclic carbon atoms with only carbon-to-carbon double bonds as unsaturation
  • C07C57/03—Monocarboxylic acids
  • C07C57/04—Acrylic acid; Methacrylic acid
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts

Definitions

• the present invention relates to the production of acrylic acid from propane in the presence 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.
• 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 describes the oxidation of propane using a catalyst of formula M ⁇ No ) 33 Nbo, nTeo ) 22 O n 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 about 1 / 3.2 / 12.1 / 14.3.
• a propane / oxygen / molar ratio helium / water vapor of about 1 / 3.2 / 12.1 / 14.3.
• the object of the invention is to propose a process for producing acrylic acid from propane, in the presence of molecular oxygen, which makes it possible to obtain a higher conversion of propane while retaining a high selectivity in acrylic acid.
• this object can be achieved by passing a gaseous mixture of propane, oxygen and water vapor, and where appropriate, an inert gas, over a particular catalyst, under conditions such as oxygen from the gas mixture is in sub-stoichiometric proportion relative to the propane introduced, which presumably allows the catalyst to act as a redox system and to supply the missing oxygen so that the reaction proceeds satisfactorily.
• a is between 0.006 and 1, limits included;
• - b is between 0.006 and 1, limits included;
• - x is the quantity of oxygen linked to the other elements and depends on their oxidation states, to oxidize propane to acrylic acid, this process being characterized in that the propane / molecular oxygen molar ratio in the starting gas mixture is greater than or equal to 0.5.
• Such a process makes it possible to simultaneously obtain a selectivity for acrylic acid of nearly 60%> and a high conversion of propane.
• 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.
• the method according to the invention comprises the following stages: 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 catalyst gas; c) the catalyst is sent to a regenerator; d) the gases are introduced into a second reactor with a transported catalyst bed; e) 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) the catalyst is returned to the regenerator; and g) reintroduced regenerated catalyst from the regenerator into the first and second reactors.
• the reactor or reactors are further provided with a cocatalyst. The above steps can be carried out analogously using a catalyst and a co-catalyst.
• 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:
• the cycle comprises an additional step which precedes or follows step 1) and during which a gas mixture is injected corresponding to that of step 1) but without the molecular oxygen, the molar ratio of propane / molecular oxygen then being calculated overall for step 1) and this additional step.
• the additional step precedes step 1) in the cycle.
• the conversion of propane to acrylic acid by means of the catalyst is carried out by oxidation, probably according to the reactions competitors (1) and (2) below:
• the propane / water volume ratio in the starting gas mixture is not critical and can vary within wide limits.
• 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.
• reactions (1) and (2) are carried out at a temperature of 200 to 500 ° C, preferably 250 to 450 ° C, more preferably still, 350 to 400 ° C.
• the pressure in the reactor (s) is generally from 1.01.1O 4 to 1.01.10 6 Pa (0.1 to 10 atmospheres), preferably from 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 formula (I):
• - x is the quantity of oxygen linked to the other elements and depends on their oxidation states.
• - a is between 0.09 and 0.8, limits included
• - b is between 0.04 and 0.6, 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; as other raw materials, there may be mentioned:
• molybdenum in the case of molybdenum, ammonium molybdate, ammonium paramolybdate, ammonium hepta-molybdate, molybdic acid, halides or oxyhalides of molybdenum such as MoCl 5 , organometallic compounds of molybdenum molybdenum alkoxides such as Mo (OC 2 H 5 ), acetylacetone molybdenyl; in the case of vanadium, ammonium metavanadate, vanadium halides or oxyhalides such as VCl 4j VC1 5 or VOCl 3 , organometallic compounds of vanadium such as vanadium alkoxides such as VO (OC 2 H 5 ); - in the case of tellurium, tellurium, telluric acid, TeO 2 ;
• Nb (On-Bu) 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.
• the catalyst of formula (I) can be prepared by mixing, with stirring, aqueous solutions of niobic acid, ammonium heptamolybdate, ammonium metavanadate, telluric acid, by adding preferably colloidal silica, then precalcining in air between 280 and 340 ° C, preferably at about 320 ° C, and calcining under nitrogen at about 600 ° C.
• a is between 0.09 and 0.8, limits included;
• - b is between 0.04 and 0.6, limits included;
• the catalyst of formula (I) can be prepared by implementing a process in which:
• a niobium solution is prepared by mixing oxalic acid and niobic acid, then optionally separation in order to recover the solute; 2) a solution of molybdenum, vanadium and tellurium is prepared;
• step 1) can be carried out by centrifugation, decantation or filtration.
• step 4) can be carried out in an oven in a thin layer, by atomization, by lyophilization, by zeodratation, by microwave, etc.
• the precalcination can be carried out under air flow at 270-300 ° C or under static air at 320 ° C, in a fluidized bed, in a rotating tube, in a so-called aerated fixed 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 below 600 ° C., for example in a rotary kiln, in a fixed bed, 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 particularly preferred embodiment, the precalcination is carried out
• the precalcination is carried out at approximately 320 ° C. under a zero air flow.
• reaction (3) 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 (3):
• 1 / 1-10 / 0-10 Preferably, they are 1 / 1-5 / 0-5.
• 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 the regeneration, which can be carried out under conditions of temperature and pressure identical to, or different from those of reactions (1) and (2), the catalyst regains initial activity and can be reintroduced into the reactors.
• Reactions (1) and (2) and regeneration (3) can be carried out in a conventional reactor, such as a fixed bed reactor, a fluidized bed reactor or a transported bed reactor.
• the reactions (1) and (2) and the regeneration (3) 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.
• 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).
• 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.
• the catalyst is sent to a regenerator.
• the gases are introduced into a second reactor (Riser 2) also containing a transportable catalyst bed.
• 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 single regenerator can be replaced by two or more regenerators.
• 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.
• 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).
• the gas mixture also passes over a cocatalyst.
• the reactor or, if there are several, at least one of the reactors, comprises a cocatalyst having the following formula (II):
• - I is between 0 and 1, limits included; - k 'is between 0 and 1, limits included; l is between 0 and 1, limits included; m 'is between 0 and 1, limits included; and n '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.
• 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.
• - 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;
• - I is between 0 and 0.4, limits included;
• - k ' 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.
• 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 ⁇ m 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.
• 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
• the conversion ratio is the mass of catalyst (in kg) necessary to convert 1 kg of propane.
• Formula catalyst preparation a Preparation of a niobium solution 640 g of distilled water are introduced into a 5 l beaker, followed by 51.2 g of niobic acid (ie 0.304 moles of niobium). 103.2 g (0.816 mole) of oxalic acid dihydrate are then added.
• the oxalic acid / niobium molar ratio is therefore 2.69.
• the solution obtained above is heated at 60 ° C for 2 hours, covering to avoid evaporation and stirring. A white suspension is thus obtained which is allowed to cool with stirring to 30 ° C, which lasts for about 2 hours.
• the solution obtained above is heated at 60 ° C for 1 hour and 20 minutes, covering to avoid evaporation and stirring. We thus obtain a clear red solution which is allowed to cool with stirring to 30 ° C, which lasts for about 2 hours.
• Ludox AS40 silica containing 40% by weight of silica, supplied by the company Dupont
• the latter retains its clarity and red coloration.
• the niobium solution prepared above is then added. A fluorescent orange gel is thus obtained after a few minutes of stirring. This solution is then spray dried.
• the atomizer used is a laboratory atomizer (ATSELAB from the company Sodeva). The atomization takes place under a nitrogen atmosphere.
• the operating parameters are globally:
• the recovered product (355.2 g), which has a particle size less than 40 microns, is then placed in the oven at 130 ° C. overnight, in a teflon-coated tray. 331 g of dry product are thus obtained.
• the precalcinations and calcinations were carried out under air and nitrogen flow in steel capacities. These capacities are directly installed in muffle furnaces and the air supply is through the chimney. An internal thermowell allows proper temperature control. The cover is useful to avoid a return of air to the catalyst.
• the 331 g of the precursor obtained previously is precalcined for 4 hours at 300 ° C. under an air flow of 47.9 ml / min / g of precursor.
• the solid obtained is then calcined for 2 hours at 600 ° C. under a nitrogen flow of 12.8 ml / min / g of solid.
• the desired catalyst is thus obtained.
• laboratory simulations were carried out in a laboratory fixed bed reactor, generating propane pulses and oxygen pulses.
• the bottom is loaded up into a vertical reactor of cylindrical shape and in pyrex:
• the reactor is then heated to 250 ° C and the evaporator to 200 ° C.
• the electric priming of the water pump is activated.
• the water pump is activated and the temperature of the reactor is raised to the desired test temperature, that is to say 400 ° C.
• the reactor hot spot is then allowed to stabilize for 30 minutes.
• 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 therm ' ocouple placed in the catalytic bed, we can see the temperature fluctuations as a function of the pulses).
• the pressure at the inlet of the reactor was approximately 1.1 to 1.8 bar (absolute) and the pressure drop across the reactor was approximately 0.1 to 0.8 bar (relative).
• the production of acrylic acid was measured using a redox balance.
• a redox assessment is made up of 40 redox cycles.
• a redox cycle represents:
• 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.
• the gases are analyzed during the balance on a micro-GC Chrompack chromatograph.
• An acidity test is carried out on each bottle during handling, to determine the exact number of moles of acid produced and to validate the chromatographic analyzes.
• the procedure was as in test A, except that the redox balance was composed of the following 40 redox cycles: • 10 cycles of: - 30 seconds of propane + 5 seconds of oxygen (the oxygen being injected at the start of the propane pulse), with Propane / O / He-Kr / HO proportions of 30/30/45/45, with a helium-krypton flux of 4.292 Nl / h;
• a catalyst was prepared in the following manner. 5.35 g of ammonium paramolybdate and 0.80 g of tellurium dioxide (TeO 2 ) are successively added to 20 ml of water, 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. The two solutions are then mixed slowly and 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 72 hours.
• the autoclave is cooled by water under the tap for 10 minutes.
• the black 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 pre-calcined in air at 280 ° C for 2 hours.
• the solid obtained is calcined under a stream of nitrogen (25 ml / h / g) at 600 C for 2 hours. Catalyst 3 is thus obtained.
• catalyst 3 500 mg are vigorously ground and poured into a Pyrex® reactor.
• the propane selective oxidation reaction is carried out at atmospheric pressure, in a conventional flow reactor.
• the mixture Propane / Oxygen / Nitrogen / Water vapor reaction gas (6.5% / 10%> / 38> / 45%) is introduced into the reactor while maintaining a contact time of 2.1 s.
• the catalyst is tested at 320 and 360 ° C. The results are collated in Tables 2 and 3.
• Example 4 A catalyst was prepared as follows.
• a catalyst was prepared in the following manner. 5.35 g of ammonium paramolybdate and 1.16 g of telluric acid are added successively, with stirring, to 20 ml of water heated to 80 ° C. 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 3.6 mmol of niobium is prepared simultaneously by dissolving, with stirring, 2.33 g of hydrated niobium oxalate in 10 ml of distilled water heated to 80 ° C. The second solution is added to the first and the mixture is stirred for 5 minutes.
• a catalyst was prepared in the following manner.
• the autoclave is then placed at 175 ° C for 24 hours.
• 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 ml / h / g) to
• tellurium could be introduced into this preparation.
• Example no Composition of the solution Preparation method (without oxygen)
• 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.
• 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 4 below.
• Example 7 In an example, the catalyst prepared in Example 1 was again tested.
• This catalyst has a particle size less than 40 ⁇ m.
• a reactor was then loaded as indicated in example 2 a) and operated according to the procedure indicated in example 2 b).
• 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.
• propane is also oxidized at 400 ° C.
• the solution is milky. As the heating and stirring progresses, the solution becomes less and less cloudy. Allow to cool to about 30 ° C in ambient air while maintaining agitation. To improve clarity, the solution is centrifuged at 6200 rpm for 12 minutes. A white deposit of niobic acid is then observed.
• the orange gel is poured into a teflon-coated plate and then placed in an oven at 130 ° C overnight. We then obtain a coarse powder of brown / black color which does not adhere to the tray.
• the mass of precursor obtained is 122.6 g. According to the quantities initially introduced, the precursor has the formula MoNo ) 33 Te 0; 22 Nb 0; ⁇ If 0 , 95 (Oxalate) o, 33 (NH 4 ) ⁇ > ⁇ 9 O x .
• Table 7 presents the quantities of reagents introduced for the preparation of the other 3 precursors P2, P3 and P4. The same manipulations as above were carried out and the same changes in color and appearance were observed for all these experiments.
• This experiment aims to determine the quantity of niobic acid which did not dissolve during the preparation of the niobium oxalate solution.
• the white deposit formed during centrifugation was removed. This deposit has a mass of 0.5 g. It is placed in a ceramic crucible. After evaporation in ambient air, the deposit weighs 0.4 g. The deposit is then subjected to a temperature rise of 3 ° C / min, from 20 to 600 ° C and left at 600 ° C for one hour.
• a precalcination of the precursors is then carried out in air.
• the purpose of this step is, inter alia, to remove the ammonia provided by ammonium heptamolybdate and ammonium metavanadate.
• 30 g of precursor are placed inside steel buckets and between two pads of silica wool.
• Table 8 presents a summary of the precalcination and calcination conditions carried out on the various precursors.
• the bottom is loaded up into a vertical reactor of cylindrical shape and in pyrex:
• Procedure The reactor is heated to 250 ° C and the vaporizer to 200 ° C. The electric priming of the water pump is activated. The He-Kr flow rate is set to its nominal value of 4.25 Nl / h.
• the water pump is activated. As soon as water is present at the outlet of the reactor, the propane and oxygen flowmeters are activated. The temperature of the reactor is raised to the desired temperature and it is waited 30 minutes for the hot spot to be stabilized.
• thermocouple is placed in the catalytic bed, we can read the temperature of the hot spot.
• Liquid effluents are analyzed on an HP 6890 chromatograph, after performing a specific calibration.
• the gases are analyzed online during the balance on a micro-chromatograph
• Catalysts A1 to A4, B1 to B4, Cl to C4 and Dl to D4 were tested at 3 different temperatures: 380, 390 and 400 ° C.
• Table 10 groups the carbon selectivities.
• the conversion into propane is greater than 15%> for the precalcined catalysts at 273 ° C at flow rates of 10, 30 and 50 ml / min / g of catalyst, at 300 ° C and 320 ° C at low flow rates and at 350 ° C under zero flow. It is also for these values that the highest acrylic acid yields (greater than 10%) and the highest selectivities and the highest acidities (greater than 3000 ppm) are obtained.
• TTG TGT 2
• the reaction temperature can be increased to improve the conversion to oxygen. However, it is preferable to avoid the oxygen conversion exceeding 80%.
• a catalyst E was prepared of formula: MoNo , 33 Teo , 23 Nbo, ⁇ Si ⁇ O x having as precursor: MoNo > 33 Teo ) 23 Nbo, 1 ⁇ Si 1 (Oxalate) o, 33 (NH 4 ) ⁇ ; ⁇ 9 O x in the manner indicated in Example 8 by carrying out a precalcination 319 ° C, under static air. The drying preceding the precalcination, however, was not carried out in an oven but under a flow of microwaves.

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