KR100221165B1 - Improved process for the calcination/activation of v/p/o catalyst - Google Patents

Abstract

Mixed oxides of vanadium and phosphorus (V / P / O) comprising adding spray dried catalyst precursor to the flow-containing oxygen at a controlled rate such that the temperature is maintained in the range of 370 to 410 ° C. (preferably 390 ± 5 ° C.) Improved method for calcination and activation of catalysts containing In addition to rapid temperature rises, catalyst precursors are dehydrated at elevated temperatures in flow for an average residence time range of about 4 hours or less at 3.5 atm or more and 20 hours or less at 1 atm while simultaneously and continuously maintaining an average Vox of 4.55 or less. / Calculate. This method is useful for preparing V / P / O catalysts with improved activity for oxidizing n-butane to maleic anhydride. The new method provides an improved method for the operation of commercial scale recycle solid reactors.

Description

Improved Process for Calcination / Activation of Vanadium / Phosphorus Mixed Oxide Catalysts {Improved Process for the Calcination / Activation of V / P / O Catalyst}

The present invention relates to an improved process for calcination and activation of catalysts containing mixed oxides of vanadium and phosphorus (V / P / O) useful for preparing maleic anhydride from n-butane. More specifically, the present invention does not limit the scope of the present invention, but more specifically, the present invention provides a method for calcination of V / P / O catalysts that leads to very rapid temperature rises in oxidative flow and a novel process for carrying it out in a commercial bed commercial scale installation. It is about.

Vapor phase oxidation of n-butane to maleic anhydride on V / P / O catalysts is generally known in the art. A prior art review document describing this method is US Pat. No. 4,668,802. In the improved process described in US Pat. No. 4,668,802 and US Pat. No. 5,021,588, the reaction is carried out in a recycle solid reactor with two flow reaction zones. The conversion of n-butane to maleic anhydride first takes place in one reaction zone, and the catalyst is essentially recirculated (ie regenerated before returning to the reaction zone) where the gas stream is removed and transferred to another reaction zone.

Mixed oxide V / P / O compositions used as catalysts in this process are known in the art. A review document describing V / P / O compositions and their preparation is described in US Pat. No. 4,371,702. The catalyst precursor composition is a process in which a conventional vanadium compound, such as V ₂ O ₅ or NH ₄ VO ₃ , in which vanadium is present in the +5 oxidation state, is reacted in either an aqueous or organic liquid medium to partially reduce it to the +4 oxidation state. Manufactured by The catalyst precursor is then formed by adding any suitable phosphorus compound, for example H ₃ PO ₄ , refluxing to cause the reaction, and recovering the catalyst precursor, usually hydrated vanadium phosphate, by filtration and drying or spray drying. . The prior art describes the preferred range of atomic ratios of phosphorus to vanadium and also the incorporation of catalyst promoters. It is preferred that the V / P / O catalyst has good wear resistance, especially when used in a fluidized bed or recycle bed reactor. Prior art related to wear resistant catalysts and methods for their preparation is reviewed in US Pat. No. 4,677,084. The preparation of V / P / O catalysts useful for preparing maleic anhydride from n-butane requires controlled calcination and activation of the catalyst precursor. This is accomplished by heating the precursors under suitable temperature, time and air conditions to dehydrate, while maintaining the average vanadium oxidation state (Vox) between certain limits. For example, US Pat. No. 3,915,892 converts precursor dihydrate to monohydrate by releasing one molecule of hydrated water at 370 to 394 ° C. while maintaining the range of Vox at 4.1 to 4.5. Subsequently, the remaining water is removed by heating at 395 to 425 ° C., and then the bulk crystal phase transition is promoted at a temperature of 450 ° C. or higher in a carrier gas consisting of a controlled amount of oxygen and hydrocarbons together with air or an inert gas, thereby at least 1% by volume An effluent stream containing oxygen or 1% by volume of oxygen and hydrocarbons is provided while maintaining the range of Vox back to 4.1 to 4.5.

In terms of preparing maleic anhydride from n-butane when preparing a V / P / O catalyst at the scale necessary to provide a catalyst for commercial operation using the calcination / activation process described in the prior art literature, It has been found that the catalyst is inferior to the catalyst prepared on a small batch basis. As a result, more stringent controlled production conditions are needed to produce the advanced catalysts on the scale required for commercial plant operation. For example, US Pat. No. 5,573,992, issued Nov. 12, 1996, discloses a relatively low pressure calcining and activation process for catalysts containing mixed oxides of vanadium and phosphorus, which are performed under limited specific operating conditions. This method adjusts the amount of oxygen simultaneously and continuously to adjust the range of Vox to 3.825 to 4.175, while hydrated V / P / O or V / P / O-SiO ₂ catalyst precursors range from 375 to 400 ° C. After dehydration by calcination for a sufficient time at the temperature of and under the gas atmosphere containing n-butane at a partial pressure not exceeding 0.020 atm while adjusting the range of Vox to 3.95 to 4.15 by controlling the amount of oxygen simultaneously and continuously. And further heating the dehydrated catalyst precursor of the previous step in the range of 340 to 500 ° C. The present invention is seen to further refine this method.

An object of the present invention is to prepare a V / P / O catalyst precursor during its preparation to prepare a highly active and selectable V / P / O catalyst capable of oxidizing n-butane to produce maleic anhydride in high yield. It is to provide an improved method for calcination and activation.

The present invention is directed to calcining and activating a V / P / O catalyst precursor at elevated temperatures and pressures during the production of highly active and selectable V / P / O catalysts capable of oxidizing n-butane to produce maleic anhydride in high yield. It is about an improved method. For the purposes of the present invention, catalytic activity is defined in terms of n-butane oxidation, the selectivity relates to the production of maleic anhydride, and the yield is a function of activity and selectivity. The present invention also relates to a method for operating a commercial scale fluid transport bed facility utilizing an improved method of elevated temperature, elevated pressure calcination and activation of the V / P / O catalyst precursor itself. The process of the present invention is particularly suitable for the large-scale preparation of catalysts for use in recycle bed reactors suitable for the production of maleic anhydride on a commercial scale, typically providing substantial operating time while simultaneously producing catalysts with significantly higher activity. To decrease.

Therefore, the present invention

(a) forming a gas stream in a fluidized bed reactor using air or an oxygen containing gas in the temperature range of 370 ° C. to 420 ° C.,

(b) hydrating V / P / O or V / P / O-SiO ₂ catalyst precursor at a rate such that the catalyst precursor experiences a rapid temperature rise in the fluidized bed state in the temperature range of 370 ° C to 420 ° C. To a fluid bed reactor,

(c) maintaining an average Vox of at least 4.05 and at most 4.55, while maintaining the catalyst precursor in step (b) for a sufficient time and at a sufficient pressure and in the above temperature range to remove entrained organics and dehydrate the catalyst precursor,

(d) recovering and storing the calcined V / P / O catalyst prepared from the non-oxidizing gas in step (c),

Provided are methods for calcining a V / P / O catalyst.

An improved method of operating a commercial scale carrier bed plant is a reaction zone where n-butane is converted to maleic anhydride and reduced vanadium / phosphorus oxide using a vanadium / phosphorus oxide (V / P / O) catalyst in oxidized form. Using a recycle solid reactor consisting of a catalyst regeneration zone where the catalyst is regenerated in contact with oxygen, wherein (i) adding the catalyst precursor to the regeneration zone where the temperature is maintained between 380 ° C. and 400 ° C. and (ii) in the regeneration zone. The catalyst precursor is kept in a fluid state for a sufficient time using air or an oxygen-containing gas to remove entrained organics and dehydrate the catalyst precursor, and (iii) the average of the catalyst precursor in the regeneration zone to have an average Vox of 4.55 or less. While maintaining the residence time, convey the calcined catalyst precursor from the regeneration zone to the reaction zone and (iv) until the catalyst cycle begins It relates to a process for selective vapor phase oxidation of n-butane to maleic anhydride with a particular improvement consisting of maintaining a calcined catalyst precursor in a fluid state within the reaction zone using substantially non-oxidizing gases. .

In one embodiment of commercial scale operation according to the present invention, the calcined catalyst precursor is transferred from the regeneration zone to the reaction zone such that the rate of addition of the catalyst precursor is sufficient to maintain the temperature in the regeneration zone until the total input of catalyst is calcined. Adjusted at the same time as carrying. In a related embodiment, the dosage of the calcined catalyst precursor is activated by itself under operating conditions involving the recycling of the catalyst between the reaction zone and the regeneration zone and the supply of n-butane to the reaction zone. Preferably the catalyst precursor is maintained at a temperature of 390 ± 5 ° C. In a commercial operating aspect, the catalyst precursor is in a flow state in a regeneration zone with a pressure of about 3.5 atm, and the average residence time of the catalyst precursor in the regeneration zone is about 4 hours or less at air pressure of 3.5 atm or higher and 20 hours at 1 atm air pressure. Is maintained below. Optionally, direct flame heating with n-butane is used to achieve a temperature range of 380-400 ° C. such that the water vapor content in the air or oxygen containing gas is about 3 mol% or less.

It is an object of the present invention to provide a simple and rapid method for calcining and activating particulate V / P / O catalyst precursors on a commercial scale. A related objective is to significantly reduce the time required to operate a modern conveying fluidized bed commercial scale plant using this V / P / O catalyst. It is a further object of the present invention to provide a method for calcination of a V / P / O catalyst precursor that improves activity and surface area without sacrificing the selectivity of the catalyst.

The present invention relates to a process for preparing a high activity and selectivity V / P / O catalyst capable of oxidizing n-butane to produce maleic anhydride in high yield. The vanadium pyrophosphate catalyst required for this reaction needs to be converted from the precursor to the active crystalline phase by the calcination / activation process. In addition, the elevated temperature and elevated calcining / activation methods of the present invention can be used to prepare V / P / O catalysts on any scale, but are particularly suitable for operation of large scale manufacturing equipment using recycle solid reactors. Prior to the refinement process associated with the present invention, the operating process for commercial recycle solid reactors designed to selectively oxidize n-butane to maleic anhydride was planned in batch, requiring several weeks to complete. The improved method according to the invention is conceptually a method of operation at the same site where the calcination / activation process can be completed in a few days. Desirably calcination is carried out continuously or semi-continuously in a catalyst regeneration vessel of a commercial plant in approximately the time required to load the catalyst in air of 2.5 to about 3.5 atm and heat to 390 ° C. During this time the riser vessel of the recycle solid reactor is maintained at approximately the same temperature in a substantially inert atmosphere. The calcined catalyst produced in the regeneration zone is such that the maximum residence time is typically maintained at about 3.5 atm of air at about 390 ° C. so that the average residence time in the regenerator is maintained below the critical maximum residence time as a function of the regenerator's operating pressure and temperature. 4 hours and a maximum residence time of less than 20 hours at about 1 atm), is transported to the reactor vessel (ie to the riser of the plant) periodically or continuously.

To better understand and understand the adjustments, advantages, and advantages of this operating process in the calcination / activation of V / P / O catalysts in commercial scale recycled solid reactors, certain practical plant design and engineering typical of commercial scale operation is required. It is probably best to consider not only the constraints but also specific experimental data related to catalyst parameters such as temperature, time, pressure, including partial pressures of oxygen and water, combustion of retained organics in the catalyst precursor and average vanadium oxidation state (ie, Vox).

Temperature :

According to the improved calcination method of the catalyst precursor of the present invention, V / P spray-dried into a hot fluidized bed reactor or into a hot fluidized bed which calcinates the precursor in the fluidized bed reactor while maintaining the fluidized gas, fluidized bed reactor and / or fluidized bed at operating temperature / O catalyst precursor and the like are supplied from the beginning. That is, the V / P / O catalyst precursor to be calcined is initially fed into the fluidized bed reactor under calcination conditions to essentially resist instantaneous thermal shock. The actual temperature during calcination is influenced by several considerations. For example, if the calcination temperature is too low, it will not provide enough energy to induce the phase transition of vanadium pyrophosphate from the precursor. In addition, temperatures that are too high or lower than 390 ° C. tend to increase the oxidation rate of the catalyst, resulting in an excessively high oxidation state of the catalyst (ie, too high average Vox). 300 g of catalyst precursor sample calcined 300 g of catalyst precursor sample in a 35 psig air fluidized bed reactor containing 3 mol% of vapor at 360 ° C. exhibited higher catalytic oxidation rates and higher catalyst use when compared to similar experiments conducted at 390 ° C. Lower maleic yield was shown. Similar higher catalyst oxidation rates and lower maleic yields were obtained at catalyst calcination temperatures of 370 ° C. and 420 ° C. compared to 390 ° C. This difference is also evident in the type of X-ray diffraction of each sample. Precursor samples calcined at 360 ° C. are oxidized when converted directly to semi-amorphous VOPO ₄ phase through an amorphous intermediate. In contrast, the precursor calcined at temperatures above 390 ° C. is first converted to the desired pyrophosphate phase, but immediately to a more highly oxidized VOPO ₄ phase. The data indicating that higher temperatures will be required for proper calcination is consistent with thermal gravimetric analysis (TGA) measurements in that significant events are observed near 370 ° C. Thus, temperatures above 370 ° C. are necessary to achieve the desired phase transition. The lower limit of the calcination temperature is also believed to affect the required oxidative removal of the companion hydrocarbons typically present in the V / P / O catalyst precursor. That is, calcination carried out at 370 ° C. or higher results in the desired phase transition to the pyrophosphoric acid phase to achieve an effective oxidation rate and removal of the companion organics. The lower practical temperature limit for phase transition when performed in a commercial scale recycle bed reactor will be closer to 380 ° C. for calcination of 3.5 atm. Preferably a calcination temperature of 390 ± 5 ° C should be used.

The upper limit of the calcination temperature is also influenced by several considerations. For example, it is clear that higher calcination temperatures tend to favor higher average Vox, and Vox above 4.6 will lead to lower catalytic performance. Thus, if Vox was maintained at a value below 4.55 during calcination, previous experiments conducted at 420 ° C., 35 psig produced a calcined catalyst that could improve maleic acid yield. However, similar experiments conducted at 460 ° C. did not provide an improved V / P / O catalyst, demonstrating that the calcining temperature affects maleic acid yield regardless of the oxidation state. In other words, the preferred calcination temperature is considered to be 390 ° C., because both too high or too low temperatures increase the production of excessively oxidized catalyst and decrease the maleic acid yield when tested in fixed bed and riser reactors.

Rapid temperature rise of the catalyst precursor in the oxygen containing gas ensures rapid burning and removal of the accompanying organics in the catalyst precursor. At the same time, the rapid temperature rise associated with feeding the catalyst precursor into the hot flow gas stream already rapidly loses hydrated water to calcinate the catalyst. It is presently believed that a combination of rapid companion organic removal and water loss of typically about 10% by weight will contribute to the observed increase in the resulting catalyst surface area (typically on the order of 30 to 35 m ² / g). This relative surface area increase can also contribute to the observed increase (typically 20-25% or more) in the ultimate catalytic activity. This rapid rise in temperature and the rapid removal of the accompanying organics and hydrated water, resulting from immersion of the catalyst precursor in the hot fluidized bed already under oxidizing conditions at a controlled addition rate, at which the high temperature is maintained, results in the calcination of the V / P / O catalyst according to the invention. And improved methods of activation from the prior art. Perhaps the broadest, but in the simplest sense, the improved process of the present invention places the V / P / O catalyst precursor in a fluid state at a temperature of 390 ± 5 ° C. for a sufficient time to remove the accompanying organics and hydrated water to It can be seen as a method of calcination of the V / P / O catalyst precursor which maintains an average Vox of 4.05 or more and 4.55 or less.

Such calcined V / P / O catalyst precursors can be stored at essentially certain temperatures for the next sustained period of time, essentially in a non-oxidizing environment (ie, in a dry gas phase, typically with an oxygen partial pressure of 0.035 atm or less), and then Significantly increased catalytic activity compared to the vapor phase oxidation of maleic anhydride in n-butane when the reaction is activated, including in its intact conditions simply under the operating conditions, regardless of whether the reaction occurs in a fixed bed, fluidized bed or transport fluidized bed reactor. To produce a continuously visible V / P / O catalyst.

pressure :

The calcination pressure has a significant effect on both the maleic acid yield and the oxidation rate of the resulting V / P / 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. Catalyst performance was measured in an automated fixed bed reactor after calcining the V / P / O catalyst precursor in a compressed fluidized bed reactor. Automated fixed bed reactor evaluation of the resulting catalyst indicates that in both cases ultimately results in a catalyst with significantly improved activity, even if 1 atm and 3.5 atm calcination are activated differently. However, catalysts calcined at high pressures (6 atm) are not suitable. Typically, when evaluated in an automated fixed bed reactor, the catalyst calcined to the final Vox close to 4.55 at each of the three pressures was calcined at 3.5 atm and inferior maleic yield as a function of time for the high pressure (eg 6 atm air pressure) catalyst. It will show consistently good maleic acid yields as a function of run time for the catalyst. 1 atm catalysts typically show improved initial maleic yields that increase during the first 50 to 100 operating hours, but will ultimately exceed the performance of 3.5 atm catalysts. For the purposes of claiming the present invention, the effect of this pressure should be regarded more precisely as the effect of the oxygen partial pressure rather than the total pressure effect. As such, the relationship to the overall pressure limit will use the expression “atm of air” when it relates to the upper limit of operation.

The calcination pressure also has a significant effect on the oxidation state of vanadium in calcining the V / P / O catalyst. The average vanadium oxidation state as a function of time for calcination with air containing 3 mol% water vapor at 1, 3.5 and 6 atm, 390 ° C. shows that the oxidation rate of the precursor increases with increasing pressure. Thus, lower calcination pressures compared to higher pressures can be used to prolong the calcination time. Since this is believed to be an oxygen partial pressure effect, dilution of the air with an inert gas may extend the permissible calcination time, or may actually shorten the time by enriching the oxygen content. Similarly, calcination in batch flow will provide a different residence time before the precursor is excessively oxidized compared to another method of calcination in a regenerator. The continuous or semicontinuous form associated with calcination in the regenerator of the recycle solid reactor, and the inherent backmixing that occurs during the periodic transport of the calcined catalyst to the riser compartment, provides a better guarantee that the high percentage of calcined catalyst is not excessively oxidized. Short average residence times are required. When using air comprising 3 mol% water at 3.5 atm of a batch operated flow reactor at 390 ° C. typically, the calcining residence time to achieve Vox of 4.6 requires 35 to 40 hours. In contrast, the backmixing combined with a commercial scale operating process in a recycle solid reactor plant, when using air containing 3 mol% water at 390 ° C., has a residence time of typically 4 hours or less at pressures of at least 3.5 atm and a pressure of 1 atm Requires a residence time of about 20 hours or less. In other words, the residence time in the backmixing can be adjusted and / or influenced by diluting or increasing the oxygen content in the air, thereby increasing flexibility in selecting the corresponding residence time and operating pressure.

The partial pressure of water vapor in the oxygen containing gas used to calcinate the catalyst precursor also functions and affects Vox as well as the oxidation rate upon calcining. Preferably calcination should be carried out with dry gas. Complete dry gases tend to interfere with the high oxidation of the catalyst precursor upon calcination, bringing Vox close to 4.5. On the contrary, the presence of water vapor during calcination tends to extend the calcination time above the above limit in a humid oxidizing environment to promote excessive oxidation. As a practical design consideration, the design using direct flame heating of air using hydrocarbon fuels such as n-butane and the like, in particular compared to large commercial plants, will inherently allow steam / water vapor to be present on calcination. Similarly, any companion organics oxidized to calcination gas will represent a source of water. However, as described above, the water vapor concentration typical for direct flame heating of the gas phase can be tolerated in the process of the present invention.

V / P / O catalyst compositions that are converted to active catalysts by the process of the present invention can be prepared using processes generally known and practiced in the art. Preferably the V / P / O precursor can be prepared using the process described in US Pat. No. 4,371,702, the teachings of which are incorporated herein by reference. The method of the present invention is also applicable to the wear resistant V / P / O-SiO ₂ precursor compositions described in US Pat. No. 4,677,084, the teachings of which are incorporated herein by reference.

The following examples are provided to more fully demonstrate and further illustrate various individual aspects and features of the present invention, and the comparative examples and examples further illustrate the differences and advantages of the present invention. Since these examples are non-limiting, they are intended to illustrate the present invention, but are not intended to be unreasonably limiting in any way, especially with regard to the ultimate properties of the improved catalyst and the utility of the claimed improved process.

Commercial scale fluid transport bed equipment for direct oxidation of n-butane to maleic anhydride, which requires a riser reactor for n-butane oxidation and a separate fluidized bed reactor for regeneration of the catalyst, is spray dried V / P / The O catalyst precursor was operated by continuously adding to the regeneration zone at a normal rate of about 10,000 pounds per hour. Upon addition of the catalyst, the calcined fluidized bed of catalyst precursor in the regeneration reactor was maintained at 390 ° C. and 2.7 atm using hot air containing about 19% oxygen after direct flame heating using n-butane as fuel. The calcined catalyst precursor was periodically removed from the regenerator reactor and conveyed to the riser reactor of the plant at a rate such that the residence time in the regenerator was 3.25 to 3.5 hours under oxidative calcination conditions. The calcined catalyst precursor transferred to the riser reactor was recycled and maintained at operating temperature up to 50 ° C. below the calcination temperature until the total input of catalyst was added and calcined. As soon as the flow catalyst input was circulated and n-butane was fed to the riser reactor, the catalyst rapidly reached maleic production rate, which was 25% higher than the conventional V / P / O catalyst.

The advantages and advantages of the process according to the invention are considered important and numerous. First of all, an improved method of operating a recycle solid reactor when applied on a commercial scale, while maintaining the fluidized bed temperature, is sprayed at a rate such that it periodically discharges the same amount of calcined catalyst from the reactor's regenerator to the riser. Represents a simplified and streamlined calcination process intact, with continuous addition of a dry catalyst precursor to the regenerator. As a result, the operating process allows for the control and optimization of temperature rises, accompanying organic combustion and the average residence time of catalyst precursors, and this combination ultimately results in an activated catalyst with improved activity and surface area without significant loss in selectivity. do. For large commercial recycle bed reactor type installations, this significantly reduces the operating time, measured in weeks, and alleviates the need to adjust the average Vox within a narrow range of about 4.0. In all types of applications, this leads to V / P / O catalysts up to 25% greater activity or higher.

While the invention has been described and illustrated in some detail, it is to be understood that the following claims are not limited thereto, and that equivalents and equivalents to the terms of each component of the claims are provided.

The V / P / O catalyst precursor calcination process of the present invention controls and optimizes the temperature rise, the accompanying organic combustion and the average residence time of the catalyst precursor to ultimately obtain an activated catalyst with improved activity and surface area without significant loss in selectivity. do. Also for large commercial recycle bed reactor type installations, this significantly reduces the operating time, measured in weeks, and alleviates the need to adjust the average Vox within a narrow range of about 4.0. In all types of applications, this leads to V / P / O catalysts up to 25% greater activity or higher activity.

Claims (8)

A vanadium / phosphorus oxide (V / P / O) catalyst is used in oxidized form to a reaction zone where n-butane is converted to maleic anhydride and a catalyst regeneration zone where the reduced vanadium / phosphorus oxide catalyst is contacted with oxygen and regenerated In a process for selective vapor phase oxidation of n-butane to maleic anhydride comprising using a recycle solid reactor consisting of: (i) adding a catalyst precursor to a regeneration zone where the temperature is maintained between 380 ° C. and 400 ° C., ( ii) maintaining the catalyst precursor in fluid state at sufficient pressure for a sufficient time using air or oxygen containing gas in the regeneration zone to remove accompanying organics and dehydrate the catalyst precursor, and (iii) an average Vox of 4.55 or less. Conveying the calcined catalyst precursor from the regeneration zone to the reaction zone while maintaining the average residence time of the catalyst precursor in the regeneration zone, and (iv) Ring substantially by way of the selective steam with maleic anhydride in, n- butane, characterized in that for holding the catalyst precursor is calcined in flowing state in the reaction zone close to the operating temperature of the oxidation using a non-Mars gas until it is started. The method of claim 1, wherein the rate of addition of catalyst precursor is matched with calcined catalyst precursor from the regeneration zone to the reaction zone to maintain the temperature in the regeneration zone until the total catalyst input is calcined. The process of claim 1 wherein the input of the calcined catalyst precursor is activated in situ under operating conditions including the supply of n-butane to the reaction zone and catalyst recycling between the reaction zone and the regeneration zone. The catalyst precursor of claim 1, wherein the catalyst precursor present in flow in the regeneration zone is maintained at a temperature of 390 ± 5 ° C. at a pressure of about 3.5 atm or less and the average residence time of the catalyst precursor is maintained at about 4 hours or less. Way. The method of claim 1, wherein said average range of residence times for catalyst precursors in the regeneration zone is about 4 hours or less at air pressure of at least 3.5 atm and 20 hours or less at air pressure of 1 atm. The process of claim 1, wherein the temperature range of 380 ° C. to 400 ° C. is directly flame-fired with n-butane to bring the water vapor content in the air or oxygen-containing gas to about 3 mol% or less. (a) forming a gas stream in a fluidized bed reactor using air or an oxygen containing gas in the temperature range of 370 ° C. to 420 ° C., (b) hydrating V / P / O or V / P / O-SiO ₂ catalyst precursor at a rate such that the catalyst precursor experiences a rapid temperature rise in the fluidized bed state in the temperature range of 370 ° C to 420 ° C. To a fluid bed reactor, (c) maintaining an average Vox of at least 4.05 and at most 4.55, while maintaining the catalyst precursor in step (b) for a sufficient time and at a sufficient pressure and in the above temperature range to remove entrained organics and dehydrate the catalyst precursor, (d) recovering and storing the calcined V / P / O catalyst prepared from the non-oxidizing gas in step (c), Calcination Method of V / P / O Catalyst. 8. The method of claim 7, wherein the catalyst precursor is added to a fluidized bed maintained at a temperature of 390 ± 5 ° C.