JPH10139773A - Selective vapor-phase oxidation of normal butane into maleic anhydride and calcining of v/p/o catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for selective vapor-phase oxidation of n-butane useful in preparation of a V/P/O catalyst having enhanced activities in oxidizing the n-butane into maleic anhydride and a method for calcining the V/P/O catalyst. SOLUTION: This improved method for calcining and activating a catalyst containing a mixed oxide of vanadium and phosphorus (V/P/O) comprises adding a spray-dried catalyst precursor to a fluidized oxygen containing gas at a rate controlled so as to maintain the temperature within the range of 370-410 deg.C (preferably 39±5 deg.C). The dehydrating/calcining treatments of the catalyst precursor are carried out at an elevated temperature in addition to a sudden increase in temperature in a fluidized state in air under >=3.5atm pressure in about <4hr average residence time or up to 20hr at the maximum in air under 1atm pressure while being simultaneously and continuously maintaining the average Vox at <=4.55.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the present invention on September 2, 1996.
US Patent Application No. 60 / 027,2, filed provisionally on the 7th
There are 71 priority claim applications.

The present invention relates to an improved method for calcining and activating a catalyst comprising an oxidized mixture of vanadium and phosphorus (V / P / O) useful for the synthesis of maleic anhydride from n-butane. More specifically, but not by way of limitation, the present invention relates to a method of calcining a V / P / O catalyst by inducing a very rapid rise in temperature while in an oxidizing fluid state and a moving bed of practical scale. Facility (transfer bed
a new method of accomplishing this within a commercial scale plant.

[0003]

BACKGROUND OF THE INVENTION The gas phase oxidation of n-butane to maleic anhydride over a V / P / O catalyst is well known in the art.
An overview of the prior art describing this method is given in U.S. Pat. No. 4,668,802. No. 4,668,802 and US Pat. No. 5,021,
In the improved method described in US Pat.
It is performed in a recycle solids reactor with two fluidized reaction zones. n
The conversion of butane to maleic anhydride occurs mainly in one reaction zone. Then, the catalyst from which the gas species has been essentially removed is sent to another reaction zone, where it is oxidized again. That is, the catalyst is regenerated before returning to the reaction zone.

[0004] The V / P / O oxide mixed compositions used as catalysts in these processes are well known to those skilled in the art. A review of the prior art describing V / P / O compositions and their preparation is provided in US Pat. No. 4,371,702. The catalyst precursor composition is partially reacted with a conventional vanadium compound, such as V ₂ O ₅ or NH ₄ VO ₃ , in which the vanadium is in the +5 oxidation state, in either a water-soluble or organic liquid medium. Reduce, +
It is usually prepared by the step of bringing it into the oxidation state of 4. Next, the catalyst precursor is formed by adding any suitable phosphorus compound, reacts at reflux, and is typically recovered as a vanadium phosphate hydrate by filtration and drying or spray drying. . The prior art describes a desirable range of atomic ratios of phosphorus to vanadium and the incorporation of catalyst promoters. The V / P / O catalyst desirably has good abrasion resistance, especially in parts used in fluidized bed or recycle bed reactors. Prior art relating to antiwear catalysts and their preparation is discussed in U.S. Pat. No. 4,677,084. The production of V / P / O catalysts useful for the preparation of maleic anhydride from n-butane requires controlled calcination and activation of the catalyst precursor. This is achieved by heating the precursor at a suitable temperature, time, and atmosphere to achieve dehydration while maintaining the average vanadium oxidation state (Vox) within a predetermined range. For example, in U.S. Pat. No. 3,915,892, Vox is set between 4.1 and 4.1.
The precursor dehydrate is converted to the monohydrate by generating monohydrate water at 370 ° C. to 394 ° C. while keeping in the range of 5. Then, after heating at 395 ° C. to 425 ° C., again containing Vox within the range of 4.1 to 4.5, contain at least 1% by volume of oxygen or 1% by volume of oxygen and hydrocarbons each. By promoting a large amount of crystalline phase transition at a temperature above 450 ° C. in a carrier gas consisting of air or an inert gas with a controlled amount of oxygen and hydrocarbons to provide an eluate stream, Remove equilibrium.

[0005] The calcination / activation methods described in the prior art require V.sub.V on the scale required to provide the catalyst in service.
When used in the preparation of / P / O catalysts, the resulting catalyst is of inferior quality to catalysts produced in small batches from the standpoint of producing maleic anhydride from n-butane. It has been found. Therefore, tightly controlled processes are required to produce high quality catalysts on a scale required for operation in a utility facility. For example, US Pat. No. 5,573,992 (199)
Published November 12, 6) discloses a relatively low pressure process for calcination and activation of a catalyst comprising an oxidized mixture of vanadium and phosphorus under limited specific operating conditions. This method reduces Vox from 3.825 to 4.175.
Hydrated V / P / at a temperature range from 375 ° C. to 400 ° C. for a time sufficient to dehydrate the catalyst precursor while simultaneously and continuously controlling the oxygen concentration to maintain within the range of and calcining the O or V / P / O-SiO ₂ catalyst precursor, to maintain the range of the Vox from 3.95 4.15, while controlling simultaneously and continuously the oxygen concentration, Activating the dehydrated catalyst precursor by further heating at a partial pressure not exceeding 0.20 atm and in a temperature range of 340 ° C. to 500 ° C. in the presence of a gas atmosphere containing n-butane; Contains.
The present invention is considered an improvement on this method.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved method for calcining and activating a conventional V / P / O catalyst.

It is an object of the present invention to provide a simplified and rapid method for calcining and activating particulate V / P / O catalyst precursors on a practical scale. A related problem is to significantly reduce the time required to set up a modern transfer fluidized bed commercial scale facility using such a V / P / O catalyst. Yet another object of the present invention is to provide a method for calcining a V / P / O catalyst which results in enhanced activity and increased surface area of the catalyst without sacrificing selectivity.

[0008]

The present invention relates to a process for preparing a highly active and highly selective V / P / O catalyst capable of producing maleic anhydride in high yield by oxidation of n-butane. , V / P / O at elevated temperature and pressure
An improved method for calcining and activating a catalyst precursor. For the purposes of this invention, catalytic activity is defined in relation to n-butane oxidation, selectivity is related to the production of maleic anhydride, and yield is a function of activity and selectivity. The present invention is further directed to a fluidized bed facility on a commercial scale that takes advantage of the improved calcination and activation of the V / P / O catalyst precursor under in-situ elevated temperature and pressure.
nsfer bed plant). The process of the present invention generally recycles bed reactions associated with the production of maleic anhydride on a commercial scale which typically results in significantly reduced start-up times while simultaneously producing a catalyst having significantly higher activity. Particularly suitable for large-scale production of catalysts used in vessels.

The present invention provides a method for calcining a V / P / O catalyst, comprising: (a) using a gas containing air or oxygen at a temperature in the range of 370 ° C. to 420 ° C. Creating a gas stream in the fluidized bed reactor;
(B) The hydrated V / P / O or V / P / O—SiO ₂ is added to the fluidized bed reactor of step (a) in a temperature range from 370 ° C. to 420 ° C. in a fluidized bed state of the catalyst precursor. Adding at a rate such that it is subject to a sharp temperature rise; and (c)
While maintaining the catalyst precursor of step (b) in a fluidized state within the above-mentioned temperature range for a time and pressure sufficient to remove contaminant organic substances and to dehydrate the catalyst precursor, at the same time, the average Vox is increased. A step of exceeding 4.05 but not exceeding 4.55; and (d) the calcined V / obtained in step (c).
Recovering and storing the P / O catalyst in a non-oxidizing gas.

An improved method of setting up a commercial scale transfer bed facility involves a process for the selective gas phase oxidation of n-butane to maleic anhydride. The process employs a recycle solids reactor having a reaction zone and a catalyst regeneration zone in which a recycle solids reactor is provided by use of an oxidized form of a vanadium / phosphorus oxide (V / P / O) catalyst. The reduced vanadium / phosphorus oxide catalyst is regenerated by converting n-butane to maleic anhydride in the reaction zone of and contacting with oxygen in the regeneration zone of the recycle solids reactor. The unique improvement method of the present invention comprises: (i) adding a catalyst precursor to a regeneration zone maintained at a temperature of 380 ° C. to 400 ° C .; (ii) removing contaminating organic matter; With enough time and pressure to dehydrate,
Maintaining the catalyst precursor in a fluidized state in the regeneration zone using a gas containing air or oxygen; (iii)
Transferring the calcined catalyst precursor from the regeneration zone to the reaction zone while maintaining the average residence time for the catalyst precursor in the regeneration zone to maintain an average Vox of 4.5 or less;
(Iv) maintaining the calcined precursor in a fluid state within the reaction zone at about operating temperature using substantially non-oxidizing gas until catalyst circulation is commenced.

In one embodiment of a commercial scale start-up according to the invention, the rate at which the catalyst precursor is added is such that said temperature is maintained in the regeneration zone until the entire charged catalyst has been calcined. Then, the transfer of the calcination catalyst precursor from the regeneration zone to the reaction zone is simultaneously synchronized. In a related embodiment, the charge of the calcined catalyst precursor is reduced in situ under operating conditions involving introduction of n-butane into the reaction zone and catalyst recycle between the reaction and regeneration zones. Activated by. Preferably, the catalyst precursor is kept at a temperature of 390 ± 5 ° C. In a commercial start-up embodiment, the catalyst precursor is about 3.5a
By tm the pressure is maintained in a fluidized state in the regeneration zone, and the average residence time of the catalyst precursor in said regeneration zone is 3.
Less than about 4 hours with air of 5 atm or more, 1 atm
For up to 20 hours. Optionally, the temperature range from 380 ° C. to 400 ° C. is achieved by direct fire heating with n-butane to bring the water vapor content in the air or oxygen containing gas up to about 3 mol%.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for preparing a highly active and highly selective V / P / O catalyst capable of producing maleic anhydride in a high yield by oxidation of n-butane. The vanadium pyrophosphate catalyst required for this reaction needs to be converted from the precursor to the active crystalline phase by a calcination / activation process. Similarly, the calcination / activation process of the present invention at elevated temperature and pressure can be used for the preparation of V / P / O catalysts on any scale, but in particular recycle solids reactors Suitable for starting up a large-scale production facility used. Prior to the improved process associated with the present invention, a process for starting up a practical recycle solids reactor that would attempt to selectively oxidize n-butane to maleic anhydride would require several weeks to complete. It involved calcination / activation of the precursor envisaged as a method of batch production. The improved method according to the invention is conceptually an in-situ start-up method, in which the calcination / activation can be completed in a few days. Preferably, the desired calcination is from 2.5 to about 3.5
The operation is carried out continuously or semi-continuously in the vessel of the catalyst regenerator of the utility facility for the approximate time required to charge the catalyst in air atm and heat it to 350 ° C. During this time, the riser vessel of the recirculating solid reactor is
Approximately the same temperature is maintained in a substantially inert gas.
The calcined catalyst product formed in the regeneration zone may be periodically or continuously controlled to maintain the average residence time in the regenerator below a critical maximum duration that is a function of the operating pressure and operating temperature of the regenerator. Transfer to the reactor vessel (ie, the riser side of the facility) (e.g., typically from about 3.5 atm for a maximum residence time of 4 hours to about 390 ° C., about 1 atm of air for 2 hours).
Up to a maximum residence time of 0 hours).

[0013] V / P /
In order to more fully recognize and understand the justification, benefits and advantages of this mode of operation for calcining / activating the O catalyst, the temperature, the time, the pressure, including the partial pressure of oxygen and water, the catalyst precursor Not only take into account certain experimental data related to the combustion of residual organic matter and catalytic variables such as average vanadium oxidation state (ie, Vox), but also certain practical It may be best to also consider facility design and engineering.

Temperature According to an improved method for calcining the catalyst precursor of the present invention, the spray-dried V / P / O catalyst precursor or similar compound is first treated in a hot fluidized bed reactor or fluidized bed reactor. The fluidized gas, fluidized bed reactor and / or fluidized bed are maintained at operating temperature while being introduced into either one of the calcined precursor thermal fluidized beds in the reactor. Stated another way, the V / P / O catalyst precursor to be calcined is first introduced into the fluidized bed reactor under calcination conditions, and thus experiences essentially instantaneous thermal shock. The actual temperature used during calcination is affected by several conditions. For example,
It is believed that too low a calcination temperature may not provide enough energy to cause a phase transition from the precursor to vanadium pyrophosphate. If the temperature is too high or too low as compared to 390 ° C., the oxidation rate of the catalyst increases, and the catalyst tends to be given an excessively high oxidation state (ie, the average Vox).
Is too high). 35 psi with 3 mole% steam
g of air and a 300 gram sample of the catalyst precursor calcined in a fluidized bed reactor at a temperature of 360 ° C. show a higher rate of catalytic oxidation during use as compared to a similar experimental run at 390 ° C. In addition, a low maleic acid yield was shown. Similarly, 39
At catalyst calcination temperatures of 370 and 420 ° C for 0 ° C,
High catalytic oxidation rates and low maleic acid yields are obtained. Such differences are also evident in the X-ray diffraction of each sample. The precursor sample calcined at 360 ° C. oxidizes enough to be transformed directly into a semi-amorphous VOPO ₄ phase via an amorphous intermediate. In contrast, precursors calcined at temperatures higher than 390 ° C. transform to the more highly oxidized VOPO ₄ phase quickly, although they initially change to the desired pyrophosphate phase. Data indicating that elevated temperatures are necessary for proper calcination are consistent with thermal gravimetric analysis (TGA) measurements, in which a significant phenomenon is observed around 370 ° C. ing. Therefore, a temperature of at least 370 ° C. is required to achieve the desired phase transition. The lower limit of calcination also appears to have a significant impact in terms of desirably oxidizing and removing contaminating hydrocarbons typically present in the V / P / O precursor. Stated another way, calcination at a temperature of 370 ° C. or higher results in the desired phase transition to the pyrophosphate phase, leading to effective oxidation rates and removal of contaminating organics.
The practical lower limit of phase transition when operating in a commercial scale recirculating bed reactor is more than 3 in calcining at 3.5 atm.
It approaches 80 ° C. Preferably, a calcination temperature of 390 ± 5 ° C. should be used.

[0015] The upper limit of the calcination temperature also depends on several conditions. For example, a higher calcination temperature will result in a higher average V
This is advantageous for ox, and when Vox is 4.6 or more, the catalytic performance is completely inferior. Therefore, 420 ° C and 35p
Prior experimental production at sig produced calcining catalysts capable of improving the yield of maleic acid, and Vox was maintained at a value of 4.55 or less during calcination. However, 460 ° C
In a similar experimental production at, no improved V / P / O catalyst could be obtained, which affected the yield of maleic acid regardless of the oxidation state It seems like it seems. Furthermore, the preferred calcination temperature appears to be 390 ° C., with higher and lower temperatures both increasing the formation of overoxidized catalyst and increasing the fixed bed and riser reactor ( The maleic acid yield was reduced when tested in a fixed bed and riser reactor).

The rapid rise in the temperature of the catalyst precursor in the oxygen-containing gas ensures rapid combustion and removal of contaminant organics contained in the catalyst precursor. At the same time, the sharp rise in temperature associated with the introduction of the catalyst precursor into the already heat-fluidized gas stream causes a sudden loss of the compounded water and thus the calcination of the catalyst. At present, the combination of fast removal of contaminating organics, typically with a loss of about 10% by weight of water, provides a discernable increase in catalyst surface area (typically 30-35 m ^2).
/ G is as high as possible). This relative increase in surface area is also due to the increase observed with maximum catalytic activity (typically 20-25% more).
Can also contribute. This rapid temperature increase and the combined water produced by immersing the catalyst precursor in an already hot fluidized bed under oxidizing conditions at a controlled rate of contaminant organics and addition maintained at an elevated temperature. The abrupt removal appears to make a significant difference between the improved method of calcining and activating the V / P / O catalyst according to the invention and the prior art method. Perhaps,
In the broadest, but most simplified sense,
The improved method of the present invention can be used to reduce contaminant organics and average Vo.
Exposing the precursor to a temperature of 390 ± 5 ° C. in a fluid state for a time sufficient to remove contaminating organics and compounded water such that the value of x is greater than 4.05 but less than 4.55 This can be regarded as a method of calcining the V / P / O catalyst precursor. Such calcined V / P /
The O catalyst precursor is then stored at essentially any temperature, in an essentially non-oxidizing environment (ie, a dry gas phase with an oxygen partial pressure typically less than 0.035 atm) for a sustained period of time. And then simply place
Simultaneous with activation, including use in situ, proportional to the gas phase oxidation of n-butane to maleic anhydride, whether the reaction is performed in a fixed-bed, fluidized-bed, or transfer fluidized-bed reactor Thus, V / P / O catalysts are produced which consistently exhibit significantly increased catalytic activity.

Pressure The calcination pressure depends on the yield of maleic acid and the resulting V / P /
It has a significant effect on both the oxidation rate of the O catalyst. Several calcination experiments were performed at pressures of 1, 3.5, and 6 atm, respectively. All experiments were performed at 390 ° C. using an air feed gas containing 3 mol% water vapor.
I went in. The catalyst performance was measured in a pressurized fluidized bed reactor at V / P /
After calcination of the O catalyst precursor, evaluation was performed in an automated fixed reactor. Evaluation of the resulting catalyst with an automated fixed bed reactor shows that although calcination at 1 atm and 3.5 atm works differently, both ultimately produce catalysts with significantly improved activity. .

However, high pressure (6 atm) catalysts are of low quality. Typically, the catalyst calcined at each of the three pressures for a final Vox of approximately 4.55 when evaluated in an automated fixed bed reactor has a time at high pressure (ie, 6 atm air) catalyst. Shows a low maleic acid yield as a function of and a sustained high maleic acid yield as a function of the operating time of the 3.5 atm calcination catalyst. At 1 atm, the catalyst has an improved initial maleic acid yield in the first 50
To 100 hours, and will eventually exceed the performance of the catalyst at 3.5 atm. It should be appreciated that the effect of this pressure for the purposes of claiming the present invention should be seen more accurately as an oxygen partial pressure effect rather than a total pressure effect. As such, references to total pressure limitations use the expression “atm of air” when referenced to the upper limit of operation.

The calcining pressure has a significant effect on the oxidation state of vanadium in the calcined V / P / O catalyst. 3 mol%
Using air containing water vapor at 390 ° C. and 1,3.
At 5 and 6 atm, the average vanadium oxidation state as a function of the time of calcination indicates that the oxidation rate of the precursor increases with increasing pressure. Thus, lower calcination pressures can be used to extend the allowable calcination time compared to higher pressures. Since this seems to be an oxygen partial pressure effect, an acceptable calcination time extension can be achieved by diluting the air with an inert gas, or shortening the time by actually increasing the oxygen content Could be. Similarly, performing the calcination in the fluidized state in a batch mode provides a different residence time before the precursor is overoxidized compared to the calcination options in the regenerator. Continuous or semi-continuous mode is related to calcination in the regenerator of the recycle reactor, and the inherent back-mixing that occurs during the periodic transfer of the calcination catalyst to the riser Require a short average residence time to ensure that the proportion of calcined catalyst that is not overoxidized is high. Typically 390
Using air containing 3 mol% water at 3.5 atm in batch mode at 3.5 ° C., the calcining residence time to achieve a Vox value of 4.6 would require 35 to 40 hours. . In contrast, the reverse mixing mode associated with a start-up method on a commercial scale in a recirculating solid reactor facility typically involves a residence time of less than 4 hours at 390 ° C. with air containing 3.5 atm and 3 mol% water. With time,
It also has a residence time of up to about 20 hours at 1 atm of air. Furthermore, the residence time in the back-mixing mode can be controlled and / or influenced by diluting or concentrating the amount of oxygen in the air, so that the corresponding residence time and the degree of freedom in the choice of the operating pressure. Becomes even larger.

The water vapor partial pressure in the oxygen-containing gas phase used to calcine the catalyst precursor also plays an important role and can affect Vox as well as the oxidation rate during calcination. . Preferably, calcination should be performed with a dry gas. Completely dry gas during calcination tends to prevent over-oxidation of the catalyst precursor, resulting in a Vox of approximately 4.5. In contrast, the presence of water vapor during calcination tends to promote over-oxidation as the calcination time in a wet oxidizing environment is extended beyond the aforementioned limits. Considering the design in practical terms, the concept of using direct-fired heating of air using hydrocarbon fuels such as n-butane or similar compounds, compared to large-scale practical facilities, is inherently / Water vapor is present during calcination. Similarly, when exposed to oxidizing calcining gases, any contaminating organic matter will represent a water source. However, as noted above, typical steam concentrations when directly heating a gas phase can be tolerated in the process of the present invention.

V / P / O precursor compositions which are converted to active catalysts by the process of the present invention are well known to those skilled in the art,
And can be obtained using the procedure being performed.
Preferably, the V / P / O precursor is a US Pat.
No. 71,702, the disclosure of which is incorporated herein by reference to this U.S. patent number. The method of the present invention, in U.S. Pat wear V / P / O-SiO ₂ precursor composition described in No. 4,677,084 Publication applicable, referring to numbers of US patent The disclosure of which is incorporated herein by reference.

The following examples are intended to more fully demonstrate, and further exemplify, the various independent aspects and features of the present invention and to ascertain the advantages of the present invention. As such, the examples do not limit the invention in any way, and are intended to illustrate the invention. However, no limitation is intended, in any respect, particularly with regard to the superior properties of the improved catalyst and the utility of the claimed improved process.

[0023]

EXAMPLE A commercial scale fluidized transfer bed facility for the direct oxidation of n-butane to maleic anhydride, equipped with a riser reactor for the oxidation of n-butane and a separate fluidized-bed reactor for the regeneration of the catalyst, was developed. At a nominal speed of about 10,000 pounds per hour
Start up by adding the spray-dried V / P / O catalyst precursor continuously. During the catalyst addition, the calcined fluidized bed of the catalyst precursor in the regeneration reactor was heated at 390 ° C. by using heated air containing about 19% oxygen after open flame heating using n-butane as fuel. , And 2.7atm
Kept. Removing the calcined catalyst precursor periodically from the regeneration reactor at a rate such that the average residence time in the regeneration reactor under oxidative calcination conditions is 3.25 to 3.5 hours; Transferred to the rising reactor at the above facility. Until the entire charged catalyst has been added and calcined, the calcined precursor transferred to the riser reactor at an operating temperature no greater than 500 ° C. below the calcining temperature by use of recycle nitrogen is used. Held. By initiating the circulation of the fluidized catalyst charge and the introduction of n-butane into the riser reactor, the catalyst is 25% larger than previously experienced with such V / P / O catalysts. Maleic acid production rate was reached quickly.

The benefits and advantages of the method of the present invention are significant and appear to be numerous. First and foremost, the improved method of setting up a recycle solids reactor when applied on a commercial scale is a simplified and streamlined in-situ calcination method. In this method, a spray-dried catalyst precursor is continuously added to a regenerator. In this case, the addition rate is a rate at which the temperature of the fluidized bed is maintained, and at the same time, there is enough time to periodically discharge the equivalent of the calcined catalyst from the regenerator to the rising side of the reactor. Thus, this start-up method has room to control and optimize the temperature rise, average the combustion time of the contaminant organics, and the residence time of the catalyst precursor, and ultimately the catalyst activated by these combinations Has improved activity and improved surface area without significant loss of selectivity. In large practical recirculating bed reactor type facilities, the present invention provides a significant reduction in start-up time measured on a weekly basis and an average Vox during calcination of around a value of 4.0. Alleviates the need to control within a narrow range. For all kinds of applications,
The present invention provides V / P / O catalysts with up to 25% higher activity or even higher.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Harold Saul Horowitz United States 19803 Wilmington Stable Court, Delaware 22 (72) Inventor Gregory Scott Peaceans United States 19809 Wilmington Woodsdale Road, Delaware 705 (72) Inventor John Donal Sullivan United States 19803 Wilmington Brookline Road, Delaware 2214

Claims (8)

[Claims] 1. Using a recycle solids reactor having a reaction zone and a catalyst regeneration zone, n-butane is converted to vanadium / phosphorus oxide (V / P / O) in the reaction zone of the recycle solids reactor. )
The use of a catalyst converts the reduced vanadium / phosphorus oxide catalyst to maleic anhydride and regenerates it by contacting oxygen with oxygen in the regeneration zone of the recycle solids reactor to produce n In the method for selective gas phase oxidation of butane, (i) adding a catalyst precursor to the regeneration zone maintained at a temperature of 380 ° C. to 400 ° C .; and (ii) adding the catalyst precursor in the regeneration zone. Using a gas containing air or oxygen to remove mixed organic matter and maintain the fluidized state for a time and pressure sufficient to at least partially dehydrate the catalyst precursor, and (iii) in the regeneration zone Transferring the calcined catalyst precursor from the regeneration zone to the reaction zone while maintaining the average residence time for the catalyst precursor to be less than or equal to 4.5, and (iv) the calcining. Touch Maintaining the precursor in a fluidized state in the reaction zone, near the operating temperature, using a substantially non-oxidizing gas until the catalyst circulation is started, comprising the steps of: N-butane selective gas phase oxidation method. 2. The regeneration zone of the calcined catalyst precursor such that the rate of addition of the catalyst precursor is maintained in the regeneration zone until the entire charged catalyst is calcined. 2. The process for selective gas-phase oxidation of n-butane to maleic anhydride according to claim 1, wherein the process is simultaneously linked with the transfer from the to the reaction zone. 3. The charge of the calcined catalyst precursor allows for in situ introduction of n-butane into the reaction zone and catalyst recycle between the reaction zone and the regeneration zone. The process for selective gas-phase oxidation of n-butane to maleic anhydride according to claim 1, characterized in that it is activated under the accompanying operating conditions. 4. The catalyst precursor in a fluid state in the regeneration zone is maintained at a temperature of 390 ± 5 ° C. and a pressure of up to about 3.5 atm, and the average residence time of the catalyst precursor in the regeneration zone The process of claim 1 wherein n is maintained for less than about 4 hours. 5. An average residence time of said catalyst precursor in said regeneration zone is less than about 4 hours for air of 3.5 atm or more and up to 20 hours for air of 1 atm. 4. The method for selective gas-phase oxidation of n-butane to maleic anhydride according to item 1. 6. The temperature range from 380 ° C. to 400 ° C. is achieved by direct flame heating using n-butane so that the water vapor content in air or oxygen is up to about 3 mol%. The method for selective gas-phase oxidation of n-butane to maleic anhydride according to claim 1. 7. A method comprising: (a) generating a gas flow in a fluidized bed reactor using air or an oxygen-containing gas at a temperature in the range of 370 ° C. to 420 ° C .; Hydrated V / P /
O or V / P / O-SiO ₂ catalyst precursor, at a rate such that the catalyst precursor is exposed to rapid temperature rise in the temperature range up to 420 ° C. from 370 ° C. in a fluidized bed state, and adding (C) the catalyst precursor of step (b) has an average Vox greater than 4.05 but greater than 4.5 for a time and pressure sufficient to remove contaminating organics and to dehydrate the catalyst precursor;
5) maintaining the fluidized bed state within the temperature range while simultaneously achieving 5 or less; (d) recovering the calcined V / P / O catalyst obtained in step (c) in a non-oxidizing gas; A method for calcining a V / P / O catalyst, comprising the steps of: 8. The method of claim 7, wherein the catalyst precursor is added to a fluidized bed maintained at 390 ± 5 ° C.