JP2001039966A - Production of maleic anhydride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a safe method for producing maleic anhydride excellent in economical efficiency. SOLUTION: The safety coefficient F satisfies formula I: F=FL-FR>0 FL is represented by formula II: FL=C/CT/C0; FR indicates a numerical value calculated by formula III: FR=2.319×10-5×T2-1.688×102×T+3.288+(P-0.15)×0.3 [T denotes the temperature ( deg.C) of the reaction product gas; P denotes the reaction pressure (MPaG); C denotes the combustible gas concentration (vol.%) in the reaction product gas; C0 denotes the oxygen gas concentration (vol.%) in the residual gas; and CT denotes the stoichiometric combustible gas concentration (vol.%)]} when the function of the reaction product gas composition is FL and the function of the temperature and pressure of the reaction product gas is FR in a method for producing maleic anhydride by a vapor-phase oxidizing reaction of a >=4C aliphatic hydrocarbon in the presence of a catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing maleic anhydride, and more particularly, to a method for producing maleic anhydride by a gas phase oxidation reaction in the presence of a catalyst using an aliphatic hydrocarbon having 4 or more carbon atoms as a raw material. The present invention relates to a method for efficiently producing maleic anhydride, wherein safety is ensured.

[0002]

2. Description of the Related Art In a method of producing maleic anhydride by a gas-phase oxidation reaction using a hydrocarbon as a raw material in the presence of a catalyst using a fluidized bed reactor, a gaseous raw material hydrocarbon is previously converted to oxygen such as air. The catalytic reaction is carried out by mixing with the contained gas and introducing the mixed gas into the catalyst fluidized bed, or by introducing a gaseous raw material hydrocarbon into the fluidized catalyst fluidized bed with an oxygen-containing gas such as air. At this time, the catalyst is transported above the fluidized bed accompanying the reaction product gas, so that in the fluidized bed reactor, a dense fluidized bed in which most of the catalyst exists and a catalyst having a low catalyst density A thin fluidized bed is formed. In a method of producing maleic anhydride by a gas phase oxidation reaction using an aliphatic hydrocarbon having 4 or more carbon atoms as a raw material in the presence of a catalyst using a fluidized bed reactor, a fixed bed is used for the purpose of improving productivity. The hydrocarbon concentration is higher than that in the reaction using the reactor, that is, the raw material hydrocarbon concentration in the total gas supplied to the reactor is set to 3.7% by volume or more and 7.0% by volume or less, and hydrocarbons and air are supplied as raw materials. The method is general. In this case, the combustible substance concentration (total concentration of hydrocarbon concentration, maleic anhydride concentration and carbon monoxide concentration) in the reaction product gas is
Since the concentration exceeds the so-called lower explosive limit concentration, the reaction product gas may further react by a non-catalytic oxidation reaction.

In a reaction using a fluidized bed reactor, the presence of catalyst particles can suppress this non-catalytic oxidation reaction. However, since the catalyst density is low in the region of a thin fluidized bed, the product maleic anhydride is used. There is a high risk that the non-catalytic oxidation reaction of hydrocarbons and raw materials proceeds. That is,
Under an oxygen-containing gas atmosphere such as high-temperature air, unreacted raw material hydrocarbons contained in maleic anhydride and reaction product gas at a substantial concentration are susceptible to non-catalytic oxidation, and are products due to non-catalytic oxidation. Not only does the yield of maleic anhydride decrease, but also in some cases, there is a risk of runaway reaction due to abnormal heat generation or explosion in severe cases.

[0004] When the concentration of combustibles in the reaction product gas exceeds the lower explosive limit concentration, as a method for preventing the non-catalytic oxidation reaction in the lean fluidized bed region, there are methods to keep the oxygen concentration lower than the limit oxygen concentration. Alternatively, there is a method of keeping the concentration of combustibles higher than the upper limit of explosion.

In order to suppress this non-catalytic oxidation, for example, Japanese Patent Publication No. 9606/1996 discloses that an indirect heat exchanger is installed in a dilute fluidized bed and the reaction product gas is heated to 330 to 450 ° C., preferably 350 to 400 ° C. Although a method of cooling to ℃ has been proposed, excessive cooling rather increases the risk of stopping the reaction and deteriorating the catalyst, and according to studies by the present inventors, in this method, stable safe operation is not necessarily achieved. It turned out not to be enough.

In the method of reducing the oxygen concentration at the outlet of the reactor from the combustible having the lowest critical oxygen concentration among the combustibles contained in the reaction product gas, for example, carbon monoxide or the like, the reaction is carried out at a lower limit. Excessive reduction of the oxygen concentration in the product gas leads to an undesired result of lowering the yield of maleic anhydride as a product, and at the same time, the catalyst is deteriorated by excessive reduction due to the low oxygen concentration atmosphere. There was a problem.

On the other hand, a method for estimating the upper limit of the explosion limit of the reaction product gas with high accuracy has not yet been known. Therefore, a method of keeping the concentration of the combustible material higher than the upper limit of the explosion in a region where the oxygen concentration is relatively high is known. I couldn't take it.
On the other hand, in the case of a reaction using a fixed-bed reactor, the above-described problem does not occur because the concentration of combustibles in the reaction product gas is usually lower than the lower explosive limit. However, in recent years, in order to improve productivity, methods for increasing the raw material concentration and methods for recycling unreacted hydrocarbons have been proposed. A non-catalytic oxidation reaction of the produced gas may occur.

[0008]

DISCLOSURE OF THE INVENTION In view of the above-mentioned prior art, the present invention relates to a method for producing maleic anhydride by a gas phase oxidation reaction of an aliphatic hydrocarbon having 4 or more carbon atoms in the presence of a catalyst. Prevent loss of unreacted hydrocarbons and product maleic anhydride by non-catalytic oxidation of product gas,
The objective is to provide a safe and economical method for producing maleic anhydride by keeping the yield of maleic anhydride as high as possible and at the same time preventing the catalyst from deteriorating due to reduction. It was done as. That is, by providing a means for confirming that the reaction product gas is always in a combustible substance concentration region higher than the upper limit of explosion, it is possible to ensure economical operation while ensuring safety. .

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that the temperature of the reaction product gas,
If the reaction pressure and the gas composition in the reaction product gas satisfy a certain relational expression, the oxidation reaction does not occur even in the absence of a catalyst, so that maleic anhydride can be produced safely and efficiently. And completed the present invention. That is, according to the present invention, in a method for producing maleic anhydride by a gas phase oxidation reaction of an aliphatic hydrocarbon having 4 or more carbon atoms in the presence of a catalyst, a function of a reaction product gas composition is set to _FL, and the function of the temperature and pressure of the gas when the F _R, the safety factor F is a compound represented by the following formula _{(1): F = F L} -F R> 0 (1) [ in the formula (1), F _L is represented by the following formula _{(2): F L = C} / C T / C O indicates value calculated by (2), F _R is the following formula _{(3): F R = 2.319} × 10 -5 × T 2 -1. 688 × 10 ⁻² × T + 3.288 + (P−0.15) × 0.3 (3) Here, a numerical value calculated by the equation (2) and (3) is shown.
In the equation, T indicates the temperature (° C.) of the reaction product gas, P indicates the reaction pressure (MPaG), C indicates the combustible gas concentration (% by volume) in the reaction product gas, and C _O indicates the oxygen in the residual gas. shows the gas concentration (volume%), C _T is the manufacturing method of maleic anhydride, characterized in that satisfies the showing the Ryoron combustible gas concentration (volume%) is provided.

According to another aspect of the present invention, there is provided a method for producing maleic anhydride by a gas phase oxidation reaction of an aliphatic hydrocarbon having 4 or more carbon atoms in the presence of a catalyst using a fluidized bed reactor. When the function of the reaction product gas composition is F _L and the function of the reaction product gas temperature and pressure is F _R , the safety factor F is given by the following equation (1): F = F _L −F _R > 0 ( 1) wherein (1), F _L is represented by the following formula _{(2): F L = C} / C T / C O ( indicating the numeric value calculated at 2), F _R is the following formula (3): F _R = 2.319 × 10 ⁻⁵ × T ² −1.688 × 10 ⁻² × T + 3.288 + (P−0.15) × 0.3 (3) 2) and (3)
In the equation, T indicates the temperature (° C.) of the reaction product gas, P indicates the reaction pressure (MPaG), C indicates the concentration (% by volume) of the combustible gas in the reaction product gas, and C _O indicates the concentration in the residual gas. an oxygen gas concentration (volume%), C _T is Ryoron combustible gas concentration oxygen containing gas supply amount so as to satisfy showing a (volume%), the hydrocarbon supply amount, reaction temperature, the temperature of the reaction product gas, A method for producing maleic anhydride is provided, wherein the reaction pressure or the amount of catalyst is adjusted.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, a raw material hydrocarbon and an oxygen-containing gas are brought into contact in a reactor containing an oxidation catalyst, and maleic anhydride is produced by a gas phase oxidation reaction.

In the present invention, the oxidation catalyst is not particularly limited as long as it is a catalyst effective for the production of maleic anhydride, but a catalyst containing a vanadium-phosphorus complex oxide as a main component can be particularly preferably used. . Examples of the catalyst containing a vanadium-phosphorus-based composite oxide as a main component include an oxidation catalyst containing a composite oxide containing vanadium and phosphorus as main components as active components. For example, US Pat.
No. 25,471, No. 4,317,778, No. 4,
No. 511,670, 4,520,127, 5,530,144, and 5,498,731, and the like. Can be used.

In the present invention, the properties of the catalyst used in the fluidized-bed reactor can be used as long as it is the property of a catalyst used in an ordinary fluidized-bed reactor. Preferably, the weight average particle size is 30 to 100 μm, preferably 40 to 80 μm
m and a fine powder having a particle diameter of 44 μm or less
８０80% by weight, preferably 20-70% by weight, and the particle density is 5,000 kg / m ³ or less, preferably 400 kg / m ³ or less.
A (Geld) of Geldert's particle classification map of 0 kg / m ³ or less
ert D., Powder Technology, 7, 285 (1973)).

When the weight average particle diameter is smaller than 30 μm or when fine particles having a particle diameter of 44 μm or less are present in an amount of more than 80% by weight, the amount of catalyst scattered from the fluidized bed reactor increases, so that it is not economical. Absent. When the weight average particle diameter is larger than 100 μm, when the fine powder having a particle diameter of 44 μm or less is less than 10% by weight, or when the particle density is higher than 5000 kg / m ³ , the particles are too heavy. However, it is not preferable for use in a fluidized bed reactor in which particles are fluidized to perform gas-solid contact.

As the raw material hydrocarbon, an aliphatic hydrocarbon having 4 or more carbon atoms is used. Among them, butanes such as n-butane, butenes such as 1-butene and 2-butene, and 1,2-butadiene are used. C4 aliphatic hydrocarbons such as butadiene such as 1,3-butadiene and the like are preferable, and n-butane is particularly preferable.

Air is usually used as the oxygen-containing gas, but air diluted with an inert gas or air enriched with oxygen can also be used.

The raw material hydrocarbon concentration and oxygen concentration in the feed gas of the reactor are not particularly limited, but in a usual high conversion reaction, the hydrocarbon concentration is not less than 3.7% by volume and not more than 7.0% by volume. % Or less, preferably 4.0% by volume or more.
0 volume% or less is desirable, and the oxygen concentration is 18 volume% or more and 3
The reaction is preferably performed at 5% by volume or less, preferably 19% by volume or more and 30% by volume or less. When the hydrocarbons not reacted in the reactor are recovered and returned to the reactor for reuse, the oxygen concentration should be 20% by volume or more and 50% by volume or less, preferably 25% by volume or more and 40% by volume or less. The concentration (% by volume) is preferably adjusted so that the ratio of the oxygen concentration (% by volume) to the oxygen concentration / hydrocarbon concentration is 1 or more and 5 or less.

In the present invention, when a fluidized bed reactor is used, a gas dispersion plate defining the lower end of the catalyst fluidized bed, an oxygen-containing gas supply pipe, a raw hydrocarbon supply pipe, and the like are provided at the bottom of the reactor. It is preferable to provide a reaction gas extraction tube at the top of the vessel. Further, the hydrocarbon supply port is preferably opened at a position away from the gas dispersion plate, and a cyclone or a catalyst filter for separating a reaction product gas and a catalyst accompanying the reaction gas is preferably used. The particulate recovery device may be installed inside or outside the reactor.
Further, the catalyst recovered by the fine particle recovery device is preferably returned to the lower region of the dense fluidized bed. These devices installed in the fluidized bed reactor and their positions may be those known per se and commonly used. Further, it is preferable to provide an indirect heat exchange device for removing heat of the reaction product gas at a position where the rich fluidized bed and the lean fluidized bed are to be formed, for example, a device having a heat removal coil.

The oxidation catalyst on the gas distribution plate in the fluidized bed reactor is fluidized by the gas blown from the supply port below the bottom gas distribution plate to form a dense fluidized bed above the gas distribution plate. I do. Then, in the dense fluidized bed, maleic anhydride is generated by a gas phase oxidation reaction of the raw material hydrocarbon. After that, the reaction product gas containing various concentrations of unreacted raw material hydrocarbons and oxygen, as well as by-product carbon dioxide, carbon monoxide and water, in addition to the product maleic anhydride, accompanies a small amount of catalyst. While flowing out from the upper surface of the dense fluidized bed, and a thin fluidized bed is formed above the fluidized bed. The reaction product gas is then introduced into a particulate recovery device such as a cyclone installed at the top (inside or outside) of the reactor, separated from the associated catalyst, and extracted from the reactor,
Maleic anhydride is recovered from the extracted reaction product gas.

The maleic anhydride can be separated and recovered by a commonly used method known per se, for example, a method of condensing maleic anhydride by cooling the reaction gas, or a method of contacting the reaction gas with water to convert maleic anhydride to maleic anhydride. A method of trapping in water as an acid, the reaction gas is contacted with an organic solvent such as a dialkyl phthalate ester or an alkyl ester of a hydrogenated phthalic acid such as tetrahydrophthalic acid or hexahydrophthalic acid to be trapped in the organic solvent. A method or the like can be used.

Further, as described in JP-A-8-325256, for example, maleic anhydride was not separated from the reaction product gas flowing out of the reactor and recovered from the remaining gas, and no reaction was caused in the reactor. Recover raw hydrocarbons,
The recovered hydrocarbon gas may be returned to the reactor and reused. In this case, the reactor is supplied with an oxygen-containing gas and a hydrocarbon so as to maintain the oxygen concentration and the hydrocarbon concentration in the entire supply gas to the reactor at predetermined values.

Here, the temperature of the gas phase oxidation reaction in the dense fluidized bed is usually 330 to 500 ° C., preferably 380 to 5 ° C.
The temperature is in the range of 00 ° C, more preferably 400 to 460 ° C. Further, the pressure P is usually 0.5 MPaG from normal pressure,
Preferably it is in the range of 0.05 to 0.3 MPaG.

In the process of the present invention, the function of reaction product gas composition and F _L, when the function of temperature and pressure was F _R, the safety factor F is a compound represented by the following formula _{(1): F = F L} - F _R> 0 (1) [in the formula (1), F _L is represented by the following formula _{(2): F L = C} / C T / C O indicates value calculated by (2), F _R is the following formula ( 3): F _R = 2.319 × 10 ⁻⁵ × T ² −1.688 × 10 ⁻² × T + 3.288 + (P−0.15) × 0.3 (3) Here, equations (2) and (3)
In the equation, T indicates the temperature (° C.) of the reaction product gas, P indicates the reaction pressure (MPaG), C indicates the concentration (% by volume) of the combustible gas in the reaction product gas, and C _O indicates the concentration in the residual gas. an oxygen gas concentration (volume%), C _T is an essential requirement that they are satisfied indicating the Ryoron combustible gas concentration (volume%).

The meaning of these equations means that the condition that the concentration of combustibles in the reaction product gas is higher than the upper explosive limit concentration is satisfied. Left side F of the above equation (1)
Can be said to be a concept representing how much the combustible substance concentration in the reaction product gas has a margin with respect to the explosive limit concentration. The above equations (1) to (3) are empirical equations obtained by the present inventors through various explosion experiments, and do not show a theoretical relationship. However, what is important in the present invention is that if the composition, temperature and pressure of the reaction product gas satisfy the above formulas (1) to (3), the combustible substance concentration of the reaction product gas becomes higher than the explosive upper limit concentration. It has been found that the reaction is maintained, and therefore no non-catalytic reaction occurs and safety is ensured.

[0025] In the above formula (1), the function F _L of the reaction product gas composition is the following formula (2): is calculated from _{F L = C / C T /} C O (2).

Here, in the equation (2), C is a combustible gas concentration (% by volume) in the reaction product gas, and each combustible gas in the reaction product gas is 1, 2, 3,. ..., n
Each combustible gas concentration (% by volume) is represented by C1, C2, C3,.
.., Cn, the following equation (4):

[0027]

(Equation 1)

Can be calculated. Practically, most of the combustible gas in the reaction product gas is maleic anhydride, unreacted hydrocarbon, and carbon monoxide. From these three components, the concentration of combustible gas in the reaction product gas is C (% by volume). You can ask for
Usually, no other components need to be taken into account.

Oxygen gas concentration C _O (volume%) in residual gas
The oxygen gas concentration in the gas, excluding the combustible gas from the total gas (residual gas), i.e., means an oxygen gas concentration of inert gas and oxygen, the following formula (5): C _O = {reaction product gas The oxygen concentration (volume%) / (100−C)｝ × 100 (5) can be calculated. In this case, the inert gas is CO ₂ , H ₂
O, Ar, N _{2 and the} like correspond. The concept of the oxygen gas concentration C _O in the residual gas is a concept that is often used when considering the flammable range of the gas.

The stoichiometric combustible gas concentration C _T (% by volume) means a combustible substance concentration at which a combustible gas having a composition in the reaction gas can be completely burned by oxygen contained in the reaction product gas. The ratio of the stoichiometric oxygen to the combustible gas required to completely combust the combustible gas is represented by R1, R2, R3,.
, Ri, ..., Rn, the following equation (6):

[0031]

(Equation 2)

Can be calculated.

However, substantially, the stoichiometric combustible gas concentration C _T
Similar to the combustible gas concentration C, it may be calculated in consideration of the three components of maleic anhydride, unreacted hydrocarbon and carbon monoxide in the reaction product gas. For example, when the mole fractions of maleic anhydride, butane, and carbon monoxide in the total flammable gas in the reaction product are a, b, and c, respectively, it is necessary for complete combustion of 1 mole of each flammable gas. Since the number of moles of a suitable oxygen gas is 3 moles, 6.5 moles, and 0.5 moles, the following formula (7): C _T = 100 / [1 + {(3a + 6.5b + 0.5c) / Co} × 100 ] (7).

[0034] F _L calculated from equation (2) becomes the oxygen concentration approaches zero as possible infinite, combustibles concentration 0
, Becomes 0, and the numerical range is not particularly limited.

In the above equation (1), the function F _R of temperature and pressure is given by the following equation (3): F _R = 2.319 × 10 ⁻⁵ × T ² −1.688 × 10 ⁻² × T + 3.288 + (P−0.15) × 0.3 (3)

In the equation (3), T indicates the temperature (° C.) of the reaction product gas, and P indicates the reaction pressure (MPaG). As the temperature T and the pressure P, the respective values of the locations that need to be monitored in the above manufacturing process may be used. In general, the pressure of the dilute fluidized bed of the fluidized bed reactor is almost the same regardless of the location, and therefore, the pressure of any part may be used. For temperature,
It depends on each location of the reactor for producing maleic anhydride, and the safety of each location can be shown by the above formulas (1) to (3). In the above-mentioned reactor, the lower the temperature, the safer, and the higher the temperature, as long as the catalyst is sufficiently present, the higher the safety. That is, a place where there is almost no catalyst and where the temperature is high has the highest risk of a non-catalytic reaction. Therefore, if it is confirmed that the most dangerous place in the reaction process is safe by the above formula (1), the safety of the whole reaction process is guaranteed.

By providing the above formula of the present invention, it is possible to easily confirm the safety based on the temperature and the composition of the reaction gas at the most dangerous place during the reaction step, and to obtain a safe and efficient maleic anhydride. Manufacturing becomes possible. In general, where the catalyst and the gas are separated in a particulate recovery device such as a cyclone is the most dangerous place, the inlet temperature or the like of the particulate recovery device may be adopted as the temperature of the reaction product gas of the above formula.

In the formula (3), F _R is a function of temperature and pressure, and the numerical value range is determined by the reaction temperature range and the pressure range in the above-described maleic anhydride production process.
In addition, due to the experimental range from which the equation (3) is derived and the nature of the equation, the numerical range of the temperature T of the reaction product gas is 365 ° C.
If it is at least 460 ° C, it can be used effectively. The numerical range of the pressure is not particularly limited.

The composition of the reaction product gas can be determined by directly analyzing the gas at the site to be monitored, such as the outlet of the reactor, by gas chromatography or the like. Further, the gas after separating the maleic anhydride (gas at the outlet of the absorption tower, etc.) is analyzed, and the gas composition at the outlet of the reactor can be calculated from the result and the composition of the feed gas to the reactor.

[0040] In the above formula (1), calculated up to 4 decimal places for each of the functions F _R of the function F _L and the temperature and pressure of reaction product gas composition, small and rounded to the fourth digit Calculate the numerical value up to three digits below the point and calculate the safety factor F
Is preferably obtained.

[0041] In the case of F _L -F _R = 0 is indicative of the boundaries of the explosion and not explosive, the smaller conditions than or F _L equals F _R, not a safety is ensured operated . Usually, F _L is larger than F _R, that is, it is possible to safely manufacture of maleic anhydride as long as the safety factor F is greater than 0, the range of the safety factor F, 15.0 exceed 0 And more preferably more than 0 and 2.0 or less. Particularly when the raw material hydrocarbon conversion is 70% or more, the range of the safety factor F is preferably from more than 0 to 2.0 or less, particularly preferably from 0.1 to 1.0. If the safety coefficient is 0 or less, the risk of non-catalytic oxidation reaction of the reaction product gas may increase. In addition, considering the error of the analysis value of the reaction product gas and the measurement value of the temperature and the pressure, the safety factor is set to 0.1. It is desirable to secure the above.
On the other hand, if the safety coefficient is set too high, there is a possibility that the yield of maleic anhydride may be reduced, or the catalyst may be reduced and deteriorated due to a reduced oxygen concentration.

Separation of maleic anhydride from the reaction product gas
When the raw material hydrocarbons that have not reacted in the reactor are recovered from the remaining gas after recovery, and the recovered hydrocarbon gas is returned to the reactor and reused, the raw material hydrocarbon conversion rate (Z%)
Indicates that the raw material hydrocarbon concentration is X (volume%) and the oxygen concentration is Y
(Volume%), 20 (Y-10) / X ≧ Z ≧ 25
It is preferably within the range indicated by Y / X. Under these manufacturing conditions, the range of the safety factor F is preferably more than 0 and not more than 15.0, more preferably 0.1 to 10.0.

In the operation of the reactor according to the invention,
Calculate the parameters of the above formulas (2) to (7) from the measured values of the temperature and pressure at the site to be monitored, for example, the cyclone inlet in the diluted fluidized bed in the case of a fluidized bed reactor, and the composition of the reaction product gas. Then, the safety factor F of the equation (1) is calculated. At this time, it is easy to always measure the temperature and pressure, and it is desirable to always use the latest values. On the other hand, regarding the gas composition at the outlet of the reactor, it is usually difficult to always measure the concentrations of all the components. For example, the composition of the reaction product gas is directly analyzed by gas chromatography or the like, or the gas composition at the outlet of the absorption tower is analyzed by gas chromatography. And the like, and the composition of the reaction product gas is calculated from the flow rate of each fluid fed to the reactor. At this time, until the analytical values are updated, the safety factor F can be considered to be constant, but it is assumed that the reaction results (hydrocarbon conversion and maleic anhydride yield, etc.) are constant. Alternatively, a method of constantly calculating the safety coefficient F by making an assumption that the reaction gas composition is constant is more preferable. And the oxygen-containing gas supply amount such that the safety coefficient F always satisfies the above range of the present invention,
The reactor is operated by adjusting the amount of hydrocarbon supplied, the reaction temperature, the temperature of the reaction product gas, the reaction pressure or the amount of catalyst.

When the safety factor F obtained as a result of the above calculation is too small, a specific method of operating the reactor so as to satisfy the formula (1) is to increase _FL in the formula (1). It is effective to change the operating conditions as follows, or to change the operating conditions so as to reduce F _R in equation (1). As a method for increasing the F _L, reduce the oxygen-containing gas supply amount supplied to the reactor, to increase the hydrocarbon feed rate increasing the conversion of hydrocarbon feedstock by increasing the increasing the reaction temperature or amount of catalyst Is effective. On the other hand, as a method of reducing F _R , the temperature of the reaction product gas is lowered by means such as lowering the temperature of the lean fluidized bed region by means of heat removal, or by lowering the reaction temperature by increasing the amount of catalyst. A method and a method of reducing the reaction pressure are effective. These operating conditions may be adjusted individually or a plurality of conditions may be adjusted simultaneously. Thus, maleic anhydride can be produced safely and efficiently.

The description so far has focused on the case where a fluidized-bed reactor is used. However, even in a reaction using a fixed-bed reactor, the concentration of combustibles in the reaction product gas exceeds the lower explosion limit. In the operation under such reaction conditions, it is possible to safely produce maleic anhydride by keeping the concentration of combustibles in the reaction product gas higher than the upper limit of explosion using the method of the present invention.

[0046]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

Examples 1 to 7 and Comparative Examples 1 to 11 Assuming that maleic anhydride was produced using a butane-air system mixed gas as a raw material, and that the feed composition and reaction results at that time were variously changed, The gas composition at the outlet of the reactor was calculated, a make-up gas having the composition was prepared, and the explosion / non-explosion of the make-up gas was experimentally obtained as follows.

In a well-evacuated 1 liter pressurized explosion vessel, maleic anhydride, n-butane, carbon monoxide, air, nitrogen, and water were adjusted to the gas compositions and pressures shown in Tables 1 and 2. Was introduced. Nichrome wire coil (5 rolls of Nichrome wire, 11V × 12A)
(× 1 second = 130 J) to apply red heat, ignite the mixed gas, and measure the change in internal pressure to determine the presence or absence of an explosion.

The results are shown in Tables 1 and 2. In the table,
The “reaction result” is an assumed value, and the “gas composition” is a makeup gas composition of the gas composition at the reactor outlet calculated from the reaction result.

[0050]

[Table 1]

[0051]

[Table 2]

[0052]

According to the present invention, the number of carbon atoms in the presence of a catalyst is 4
In the above-mentioned method for producing maleic anhydride by a gas phase oxidation reaction of an aliphatic hydrocarbon, while preventing the loss of unreacted hydrocarbons and the product maleic anhydride by a non-catalytic oxidation reaction, the reaction is carried out stably. It is possible to maintain the maximum yield of maleic anhydride while ensuring safety,
An efficient method for producing maleic anhydride can be provided.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuyuki Yamauchi 1000 Kamoshita, Aoba-ku, Yokohama-shi, Kanagawa Pref. Chemical Mizushima Plant (72) Inventor Itaru Sawaki 3-10 Utsudori Kurashiki City, Okayama Prefecture Mitsubishi Chemical Mizushima Plant

Claims (7)

[Claims] The presence of 1. A catalyst, a process for preparing maleic anhydride by gas phase oxidation of 4 or more aliphatic hydrocarbons carbon, the function of reaction product gas composition and F _L, the temperature of the reaction product gas When the function of pressure and pressure is F _R , the safety coefficient F is expressed by the following equation (1): F = F _L −F _R > 0 (1) [where F _L is the following equation (2): F _L = C / C _T / C _O (2) where F _R is the following equation (3): F _R = 2.319 × 10 ⁻⁵ × T ² −1.688 × 10 ⁻² × T + 3.288 + (P−0.15) × 0.3 (3) where T represents the temperature of the reaction product gas (° C.) and P represents the reaction pressure (MPaG). ,
C indicates the combustible gas concentration (% by volume) in the reaction product gas,
C _O indicates the oxygen gas concentration (volume%) in the residual gas, and C _T
Represents a stoichiometric combustible gas concentration (% by volume)]. 2. The method according to claim 1, wherein the safety factor F is in the range of more than 0 and not more than 15.0. 3. The method according to claim 1, wherein the safety factor F is in the range of more than 0 and not more than 2.0. 4. The method according to claim 1, wherein the catalyst is a vanadium-phosphorus composite oxide catalyst. 5. The method according to claim 1, wherein the gas phase oxidation reaction is performed using a fluidized bed reactor. 6. The method according to claim 1, wherein the aliphatic hydrocarbon is n-butane. 7. A method for producing maleic anhydride by a gas phase oxidation reaction of an aliphatic hydrocarbon having 4 or more carbon atoms in the presence of a catalyst using a fluidized bed reactor, wherein the function of the reaction product gas composition is _FL and then, the function of the temperature and pressure of the reaction product gas is taken as F _R, the safety factor F is a compound represented by the following formula _{(1): F = F L} -F R> 0 (1) [ wherein, F _L is represented by the following equation _{(2): F L = C} / C T / C O indicates value calculated by (2), F _R is the following formula _{(3): F R = 2.319} × 10 -5 × T 2 -1 .688 × 10 ⁻² × T + 3.288 + (P−0.15) × 0.3 (3) where T is the temperature (° C.) of the reaction product gas, and P is The reaction pressure (MPaG)
C indicates the combustible gas concentration (% by volume) in the reaction product gas,
C _O indicates the oxygen gas concentration (volume%) in the residual gas, and C _T
Indicates the stoichiometric combustible gas concentration (% by volume)] by adjusting the oxygen-containing gas supply amount, hydrocarbon supply amount, reaction temperature, reaction product gas temperature, reaction pressure or catalyst amount. For producing maleic anhydride.