JP2001064274A - Production of phthalic anhydride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for safely and stably producing phthalic anhydride continuously in a high yield even in case of feeding a feedstock gas in high concentrations with slight catalyst deterioration with time. SOLUTION: This method for producing phthalic anhydride comprises catalytic vapor phase oxidation of o-xylene and/or naphthalene with an oxygen- contg. gas using at least one fixed bed reactor, wherein the catalyst bed where the catalytic vapor phase reaction is conducted is divided into three or more; and the conversion of the o-xylene and/or naphthalene is 30-70% at the exit of the 1st catalyst bed, while that at the exit of the 2nd catalyst bed is >=70%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing phthalic anhydride using a fixed-bed reactor, and more particularly, to a method for preparing orthoxylene and / or naphthalene using molecular oxygen or molecular oxygen using a fixed-bed reactor. The present invention relates to a method for producing phthalic anhydride in a high yield by catalytic gas phase oxidation with a gas.

[0002]

BACKGROUND OF THE INVENTION Ortho-xylene and / or naphthalene are brought into contact with a catalyst layer by molecular oxygen or a molecular oxygen-containing gas (hereinafter collectively referred to as "oxygen-containing gas"). In a method for producing phthalic anhydride by gas phase oxidation, it is widely known to use a catalyst in which a catalytically active substance mainly composed of vanadium oxide and titanium oxide is supported on an inert carrier. For example, JP-B-47-15323, JP-B-49-410
No. 36, JP-B-52-4538, JP-A-47-566
No. 1, JP-A-49-89694, JP-A-57-105
241 is described in each gazette. These catalysts
Each has its own characteristics, and some have been used industrially and have achieved good results.

[0003] However, there is still room for improvement in catalyst performance. For example, by increasing the selectivity of the catalyst,
The yield of phthalic anhydride can be increased. Due to the scale of the manufacturing apparatus, even if the yield is improved by 1%, the economic effect is large. In addition, the improvement of the selectivity facilitates the heat treatment and the distillation operation until the product is obtained. Therefore, it is expected that the improvement of the selectivity can produce a high-quality product at low cost.

[0004] In addition, it is also important to improve productivity and secure stable production by maintaining catalyst activity. One of the methods for improving the productivity is to carry out an oxidation reaction under high load conditions, for example, by increasing the concentration of a raw material gas (ortho-xylene and / or naphthalene) with respect to a feed gas supplied to a reactor having a catalyst layer formed thereon. Things. However, the reaction of obtaining phthalic anhydride from ortho-xylene and / or naphthalene involves a remarkable heat generation, so that under high concentration conditions, the temperature in the hot spot is sharply increased, and an excessive oxidation reaction occurs, resulting in marked deterioration of the catalyst. Is accelerated, resulting in a decrease in the yield of phthalic anhydride. Further, if the temperature rise in the hot spot part becomes too severe, it becomes difficult to remove heat from the reaction tube, and a runaway reaction occurs.

A catalyst having excellent heat resistance and capable of withstanding use under such a high load condition has been proposed in, for example, Japanese Patent Publication No. 59-1378. However, even if such a catalyst is used, if the excessive temperature rise in the hot spot cannot be suppressed, the yield of phthalic anhydride and the deterioration of the catalyst are inevitable, and the hot spot in the hot spot is also inevitable. There is no fundamental solution to the suppression of the runaway reaction.

[0006] Under such circumstances, in order to carry out operation under high concentration conditions, in recent years, catalyst layers having different catalytic activities have been used.
Attempts have been made to suppress excessive temperature rise at the hot spot portion by dividing into layers or more. However, if the conversion of the raw materials in each catalyst layer is not well balanced, the temperature in the hot spot becomes too high and an excessive oxidation reaction occurs. As a result, the yield of phthalic anhydride is reduced, and the deterioration of the catalyst is promoted. Problem cannot be solved. In severe cases, a runaway reaction may occur at the hot spot.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to obtain a high phthalic acid yield even when a high-concentration raw material gas is supplied, and to obtain a long-term catalyst. It is an object of the present invention to provide a method for producing phthalic anhydride, which requires less deterioration and is capable of stably and safely producing phthalic anhydride.

[0008]

That is, the method for producing phthalic anhydride of the present invention comprises subjecting orthoxylene and / or naphthalene to catalytic gas phase oxidation with an oxygen-containing gas using a fixed-bed reactor to produce phthalic anhydride. In the method for producing an acid, the catalyst layer in which the catalytic gas phase oxidation step is performed is divided into three or more layers, and the conversion of orthoxylene and / or naphthalene in each catalyst layer is set in a specified range. Achieved.

The method for producing phthalic anhydride according to the present invention comprises producing one or more fixed bed reactors by subjecting orthoxylene and / or naphthalene to catalytic gas phase oxidation with an oxygen-containing gas to produce phthalic anhydride. Wherein the catalyst layer in which the gas phase contact reaction is performed is divided into three or more,
The conversion of orthoxylene and / or naphthalene at the outlet of the catalyst layer is 30 to 70%, and the conversion of orthoxylene and / or naphthalene at the outlet of the second catalyst layer is 7%.
0% or more.

The hot spot temperature (° C.) of each catalyst layer is denoted by HS, the holding temperature (° C.) of each catalyst layer is denoted by M, and the total mass (g) of ortho-xylene and naphthalene per 1 m ³ of oxygen-containing gas under standard conditions ) Is W,
ΔT defined by the following equation is 0.35 to
0.85 ° C./(g/Nm ³ ), and preferably 0.45 to 1.20 ° C./(g/Nm ³ ) in the second catalyst layer. ΔT = (HS−M) / W

Further, in the method for producing phthalic anhydride of the present invention, the catalyst layer is divided into three parts, and the conversion of orthoxylene and / or naphthalene at the outlet of the first catalyst layer is 30 to 70%. Wherein the conversion of ortho-xylene and / or naphthalene at the outlet of the second catalyst layer following the first catalyst layer is 70 to 95%, and that of the ortho-xylene at the outlet of the third catalyst layer following the second catalyst layer. And / or the conversion of naphthalene is preferably 99% or more.
In this case, the hot spot temperature (° C) in each catalyst layer
Is HS, the holding temperature (° C.) of each catalyst layer is M, and the total mass (g) of ortho-xylene and naphthalene with respect to the oxygen-containing gas per 1 m ³ in a standard state is W, and ΔT defined by the following formula is , 0.35 to 0.85 for the first catalyst layer
° C / (g / Nm ³ ), 0.45 to 1.2 for the second catalyst layer
0 ° C./(g/Nm ³ ), 0.25-0.
It is preferably 70 ° C./(g/Nm ³ ). ΔT = (HS−M) / W

Further, the length of the first catalyst layer relative to the total height of the first catalyst layer, the second catalyst layer and the third catalyst layer is 25 to
Preferably, the length of the second catalyst layer is 54 to 54%, and the length of the third catalyst layer is 14 to 46%.

In the method for producing phthalic anhydride of the present invention, each catalyst used in each of the catalyst layers preferably contains vanadium oxide and titanium oxide, and further contains niobium, phosphorus, antimony, It preferably contains at least one selected from the group consisting of sodium, potassium, rubidium, cesium, and thallium.

In order to achieve the above conversion, (1) the catalyst filled in each of the catalyst layers is supported on an inert carrier, and the catalysts are successively arranged from the first catalyst layer to the subsequent catalyst layer. A method in which the catalyst layer is filled so as to reduce the porosity; (2) a mixture of each catalyst and an inactive substance is used in each of the catalyst layers, and a mixture of the inactive substance in the mixture is used. A method in which the content decreases in order from the first catalyst layer to the subsequent catalyst layer; (3) the catalyst filled in each catalyst layer of the catalyst is supported on an inert carrier; (4) the phosphorus content of the catalyst used in each catalyst layer from the first catalyst layer to the subsequent catalyst layer, in which the rate increases in order from the first catalyst layer to the subsequent catalyst layer; (5) sodium in each of the catalysts Potassium, cesium, a method comprising the total amount of rubidium and thallium, which is sequentially decreased in accordance with the catalyst layer followed by subsequent from the first catalyst layer;
(6) It is preferable to use a method in which the holding temperature of the catalyst layer increases in order from the first catalyst layer to the subsequent catalyst layer.

In the method for producing phthalic anhydride of the present invention, one reactor may be used, and the respective catalyst layers may be formed by lamination in the reactor, or a plurality of reactors may be used. And
The catalyst layer formed in the reactor may be connected so as to have the conversion.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors divide a catalyst layer for performing a catalytic oxidation step into three or more layers, regulate the conversion rate in each catalyst layer, and balance the reaction amount in each catalyst layer in a well-balanced manner. By doing so, it has been found that an excessive rise in the temperature of the hot spot portion in each catalyst layer can be suppressed, and the present invention has been achieved.

That is, the method for producing phthalic acid of the present invention is a method for producing phthalic anhydride by subjecting orthoxylene and / or naphthalene to catalytic gas-phase oxidation with an oxygen-containing gas using a fixed-bed reactor. Wherein the conversion rate of orthoxylene and / or naphthalene at the outlet of the first catalyst layer is 30 to 70%, and the second catalyst layer The conversion of orthoxylene and / or naphthalene at the outlet of is 70% or more.

Preferably, the catalyst layer is divided into three, wherein the conversion of orthoxylene and / or naphthalene at the outlet of the first catalyst layer is 30 to 70%, and the conversion at the outlet of the second catalyst layer is 30%. And the conversion of ortho-xylene and / or naphthalene at the outlet of the third catalyst layer is at least 99%.

The above conversion can be achieved by increasing the activity of the catalyst forming each catalyst layer in the order of the first catalyst layer, the second catalyst layer, and the third catalyst layer.

Here, the conversion refers to a conversion ratio of ortho-xylene and / or naphthalene, which is a raw material of phthalic anhydride. The compound produced by the conversion is not only phthalic anhydride as a final product but also phthalic anhydride. And phthalic anhydride, intermediates and phthalic anhydride, and further oxidized maleic anhydride, benzoic acid, carbon monoxide, carbon dioxide and the like.

In the present invention, the conversion is measured as follows.

[0022] From the first catalyst layer to the catalyst layer to be measured, a portion corresponding to the catalyst layer in the subsequent steps is filled with an inert substance. For example, when measuring the conversion rate of the first catalyst layer, the measurement is performed in a state in which a portion corresponding to the catalyst layer other than the first catalyst layer is filled with an inert substance having no catalytic activity, and the second catalyst layer is measured. When measuring the conversion rate of the first catalyst layer, the first catalyst layer is formed, then the second catalyst layer is formed, and portions corresponding to the third and subsequent catalyst layers are filled with an inert substance.
In such a state, the raw material gas (ortho-xylene and / or naphthalene) and the oxygen-containing gas are introduced under actual operating conditions, and the gas at the outlet of the reaction tube is collected. The collected outlet gas is dissolved in acetone, and the acetone solution is analyzed by gas chromatography to determine the amount of unreacted raw material gas. The conversion is determined by the following equation. Conversion rate (%) = [1− (u / i)] × 100 where u is the amount (g) of the raw material gas contained in the collected outlet gas, and i is the amount of the collected outlet gas. The corresponding amount of introduced source gas (g) is shown.

The conversion at the outlet of the first catalyst layer is 30%
The reason for this is that if it is less than 30%, a gas containing a large amount of raw material will be introduced into the second catalyst layer.
This is because the load on the catalyst layer increases and the hot spot temperature on the second catalyst layer becomes too high, and the yield of phthalic anhydride decreases.

On the other hand, the reason why the conversion at the outlet of the first catalyst layer is set to less than 70% is that if the conversion exceeds 70%, the heat generated in the first catalyst layer is extremely large, so that the hot spot temperature becomes high, This is because the reaction in one catalyst layer becomes very unstable. In such a case, the hot spot cannot be controlled, and a runaway reaction occurs. Even when the runaway reaction does not occur, the catalyst is thermally degraded at the hot spot, and the phthalic anhydride yield is reduced over time.

The reason for setting the conversion rate in the second catalyst layer to 70% or more is that if the conversion rate is less than 70%, the load after the third catalyst layer increases, and the hot spot temperature in the catalyst layers after the third catalyst layer increases. This is because the yield of phthalic anhydride decreases. In addition, in such a case, the reaction cannot be completed in the catalyst layers from the third catalyst layer to the final catalyst layer, and it becomes difficult to maintain the quality of the generated phthalic anhydride.

Each of the divided catalyst layers is specifically formed as follows. An example in which the catalyst layer is divided into three will be described with reference to FIGS.

The first embodiment is a case where, as shown in FIG. 1, a first catalyst layer, a second catalyst layer, and a third catalyst layer are sequentially stacked in a single reactor from the gas introduction side. Yes (catalyst layer continuous type). The reactor used here is a multitubular fixed-bed reactor provided with a plurality of reaction tubes. For each reaction tube, a first catalyst layer, a second catalyst layer, and a third catalyst layer are sequentially laminated. Have been. FIG. 1 shows an embodiment in which a raw material gas and an oxygen-containing gas are supplied from above the reactor and phthalic anhydride is discharged from below, but the present invention is not limited to this. And phthalic anhydride may be discharged from above.

In the second embodiment, as shown in FIG. 2, a plurality of reactors each having one catalyst layer are connected in series (catalyst layer discontinuous type). In this case, as a first reactor, a second reactor, and a third reactor in order from the gas supply side,
Each of the first catalyst layer, the second catalyst layer, and the third catalyst layer is sequentially formed. In FIG. 2, each of the reactors supplies gas from above the reactor, but is not limited to this.
The arrangement may be such that the arrangement of the catalyst layers is reversed so that gas is supplied from below. Although each reactor had only one reaction tube, in order to increase the yield in industrial production, a multi-tube reactor having a plurality of reaction tubes like the reactor used in FIG. 1 was used. A fixed bed reactor may be used.

The third mode is a case where the catalyst layer continuous type and the catalyst layer discontinuous type are combined. FIG. 3 shows that a first catalyst layer and a second catalyst layer are laminated on a reactor (first reactor) installed on the inlet side, and a third catalyst layer is formed on the reactor (second reactor) installed on the outlet side. A catalyst layer is formed. FIG.
A first catalyst layer is formed in a first reactor provided on the inlet side, and a second catalyst layer and a third catalyst layer are formed in a lamination on a second reactor provided on the outlet side.

In each of the reactors used in the present invention, the temperature of the catalyst layer is kept constant by circulating a heating medium kept at a constant temperature around the reaction tube filled with the catalyst. Therefore, in the embodiment shown in FIG. 2, the holding temperature can be set for each catalyst layer by changing the temperature of the heat medium used in each reactor. Further, even in the case of the continuous catalyst layer type, for example, as in the second reactor shown in FIG. 4, the inside of the reactor is divided by a heat insulating plate, and heat mediums having different temperatures are provided around the respective catalyst layers. By circulating,
The holding temperature can be changed.

Each of the catalyst layers is a portion for performing an oxidation step showing an independent hot spot temperature. In other words, even if the composition of the catalyst used is the same, when different hot spot temperatures are shown (for example, when the catalytic activity is changed by changing the temperature of the heating medium of each reactor in the configuration of FIG. 2), it is independent. It is assumed that the catalyst layer is continuous. Conversely, even if the catalyst layer has a two-layer structure in which two types of catalysts are stacked, if it shows only a single hot spot temperature,
This two-layer catalyst layer is regarded as a single catalyst layer.

Here, the hot spot temperature refers to the highest temperature in the catalyst layer, specifically, the highest temperature obtained when measuring the temperature at various positions of the catalyst layer during the reaction. Therefore, when the catalyst layer is divided into three layers, the temperature of the catalyst layer in the production of phthalic anhydride of the present invention is measured, as shown in FIG. In FIG. 5, each catalyst layer is
Each shows a different peak temperature. That is, the hot spot temperature in the first catalyst layer is indicated by HS ₁ , the hot spot temperature in the second catalyst layer is indicated by HS ₂ , and the hot spot temperature in the third catalyst layer is indicated by HS ₃ .

According to the present invention, ΔT defined by the following equation:
However, in the first catalyst layer, 0.35 to 0.85 ° C./(g/Nm
³ ), 0.45 to 1.20 ° C / (g / N
m ³ ), and when the catalyst layer is divided into three layers, ΔT of the third catalyst layer is further 0.25 to 0.7.
It is preferably 0 ° C./(g/Nm ³ ). ΔT = (HS−M) / W where HS is a hot spot temperature (° C.) in each catalyst layer, M is a heating medium temperature (° C.) for heating each catalyst layer, and W is 1 m in a standard state. ^{It is} the amount of the source gas relative to the oxygen-containing gas per ³ (total mass (g) of ortho-xylene and naphthalene).

If ΔT exceeds the upper limit of the above range in each catalyst layer, it means that the heat generation in the catalyst layer has become too large, and it is difficult to achieve the conversion specified in the present invention. On the other hand, when ΔT is less than the lower limit of the above range, it means that the reaction amount in the catalyst layer has become too small, the load on the other catalyst layers increases, and the balance of the reaction is lost. Causes a decrease in yield,
In severe cases, the heat generated in the other catalyst layers becomes too large, making it difficult to achieve the conversion specified in the present invention.

The temperature of the catalyst layer is usually measured with a multipoint thermometer inserted at the center of the cross section of the reaction tube along the gas flow direction of the catalyst layer. In this case, in order to obtain the same catalyst layer temperature as when no thermometer is inserted, the temperature of the catalyst layer is measured using a reaction tube having a thickness that takes into account the thickness of the thermometer.

In the method of the present invention, in order to adjust the conversion in each catalyst layer within the specified range, the catalyst activity in each catalyst layer is increased in order of the first catalyst layer and the second catalyst layer. Need to be

As a method for sequentially increasing the catalytic activity, the following method is specifically mentioned. As a catalyst used in each catalyst layer, a catalyst containing phosphorus is used, and the activity in the catalyst layer is sequentially increased by sequentially increasing the phosphorus content of the catalyst in order from the first catalyst layer to the subsequent catalyst layer. Each catalyst loaded in each of the catalyst layers is supported on an inert carrier, and the supporting rate is increased in the catalyst layers from the first catalyst layer to the subsequent catalyst layers. A method of sequentially increasing the activity, each catalyst filled in each catalyst layer contains at least one element selected from sodium, potassium, cesium, rubidium and thallium, and in each of the catalysts, The catalytic activity is increased in order by decreasing the total content of sodium, potassium, cesium, rubidium and thallium from the first catalyst layer to the subsequent catalyst layer. The method, wherein each catalyst filled in each of the catalyst layers is carried on an inert carrier, and the porosity of the catalyst layers is reduced according to the catalyst layers that follow from the first catalyst layer, Each catalyst layer is filled with a mixture of each catalyst and an inert substance, and the content of the inert substance in the mixture is reduced from the first catalyst layer to the subsequent catalyst layer to thereby increase the catalytic activity. In the order from the first catalyst layer to the catalyst layer following the first catalyst layer,
A method in which the activity in the catalyst layer is increased in order by increasing the holding temperature of the catalyst layer.

The above methods may be used alone or in combination. In particular, the combination with is preferable because the catalyst activity can be widely changed.

The porosity of the catalyst layer refers to the proportion of the catalyst layer not filled with the catalyst, that is, the space occupied by the catalyst. For example, by changing the size of the catalyst supported on an inert carrier, And the porosity can be changed as a result.

The above method can be employed not only when the catalysts used in the respective catalyst layers are different but also when they are the same. In order to maintain each catalyst layer at a different temperature, as shown in FIG. 2, a device in which a plurality of independent reaction tubes are connected in series is used, and the temperature of the heat medium circulated through each reactor is changed. Alternatively, even in the case of the continuous catalyst layer type, a single reactor is divided corresponding to the catalyst layer, and a heat medium having a predetermined holding temperature in a portion corresponding to each catalyst layer. Should be circulated.

The catalyst used for each catalyst layer is preferably a catalyst containing vanadium oxide and titanium oxide.
Further, the catalyst preferably contains niobium, phosphorus and antimony, and more preferably further contains at least one selected from the group consisting of sodium, potassium, rubidium, cesium and thallium. More preferably, the titanium oxide has a specific surface area of 10 to 6
It is preferable to use 0 m ² / g of anatase type titanium oxide. More preferably, vanadium oxide, anatase type titanium oxide having a specific surface area of 10 to 60 m ² / g,
At least one selected from the group consisting of niobium, phosphorus, antimony, sodium, potassium, cesium, rubidium, and thallium, and 5
It is a catalyst obtained by calcining at 00 to 600 ° C for 2 to 10 hours under flowing air. Such catalysts can be prepared by changing the loading or by changing the content of sodium, potassium, cesium, rubidium, or thallium.
Alternatively, the catalytic activity can be easily changed by changing the phosphorus content.

The inert carrier used in the present invention includes
Calcination temperature of the medium and catalyst temperature in producing phthalic anhydride
Stable for a long time at a temperature sufficiently higher than
It is necessary not to react with the substance. Such inertness
Carriers include silicon carbide (SiC), steer
Tight, cordierite, alumina, zirconium oxide,
Titanium oxide or the like can be used. Of these
However, alumina (Al _TwoO_Three) Content is less than 20% by mass,
It is preferably 5% by mass or less and the apparent porosity is 1%.
0% or more, preferably 15 to 45% silicon carbide
A carrier is preferably used. More preferred
Self-fires silicon carbide powder with a purity of 98% or more
List the silicon carbide carrier obtained by sintering
Can be. Shape of the heat-resistant inorganic inert carrier
Is not particularly limited, and its average particle size is about 2 to 15 mm.
Degree, especially what is 3-12mm
Is also good. Typical examples are spherical, pellet,
And a ring shape.

The method of supporting the catalytically active component on the inert carrier is not particularly limited, but a certain amount of the inert carrier is put in a rotating drum which can be heated from the outside, and the catalyst contains the catalytically active substance while maintaining the temperature at 200 to 300 ° C. The simplest method is to spray a liquid material (slurry) to carry the active substance. The amount of the active substance carried on the inert carrier varies depending on the size and shape of the inert carrier to be used.However, when a spherical or cylindrical inert carrier is used, the amount of the active substance carried on the 100 ml of the inert carrier is: It is preferably 3 to 30 g, and more preferably 5 to 20 g.

The inert carrier can be used as an inert substance for changing the catalytic activity in each catalyst layer. In this case, by decreasing the content of the inert substance in the mixture used in the catalyst layer in order from the first catalyst layer, the catalyst activity can be increased in order.

According to the production method of the present invention, a raw material gas and an oxygen-containing gas are introduced into a fixed bed reactor having a catalyst layer formed thereon,
A method for producing phthalic anhydride by gas phase catalytic oxidation, wherein the catalyst layer is divided into three or more layers so that the conversion of the raw material in the oxidation step performed in each catalyst layer falls within a predetermined range. The catalyst activity may be increased in order from the gas introduction side by the above method.

As the source gas, orthoxylene, naphthalene or a mixture thereof can be used.
As the oxygen-containing gas, only oxygen gas may be used, or air may be used.

When the catalyst layer is divided into three layers, preferred specific production conditions of the present invention are as follows.

That is, the inner diameter is 15 to 40 mm, preferably
Used a reaction tube of 15 to 27 mm, in which the first catalyst
Layer, the second catalyst layer, the total height of the third catalyst layer is 1.5 to 4 m,
Fill the catalyst to a height of preferably 2 to 3.5 m
I do. The height (or length) of the first catalyst layer relative to the total catalyst layer height
25) to 54%, and the height (or length) of the second catalyst layer
21 to 54%, the height (or length) of the third catalyst layer is 14 to
Preferably, it is 46%. Also, the catalyst layer holding temperature
Is 300 to 400 ° C, preferably 330 to 380 ° C.
Preferably. The source gas has an oxygen content of 10 to 2
1% by volume oxygen-containing gas, eg air, into the reactor
Preferably introduced, 1m in standard condition ^ThreeOxygen content of
The raw material gas concentration is set to 70 g (hereinafter referred to as 70 g
g / Nm^Three) Or more. In particular
When using orthoxylene as a raw material, 90 g /
Nm^ThreeAs described above, when naphthalene is used, 75 g / Nm^ThreeLess than
Above, gas space velocity 1000-6000h in standard condition
r^-1, Preferably 1500 to 4000 hr^-1To do
Is preferred.

The production method of the present invention is not limited to the above conditions. The catalyst layer for performing the step of oxidizing ortho-xylene and / or naphthalene is divided into three or more layers, and the conversion rate of the raw material gas in each catalyst layer is within a specified range. If it is within the range, the mode of the apparatus, the holding temperature of each catalyst layer, the introduction speed of the raw material gas, and the like may be appropriately selected.

According to the production method of the present invention, even if a high-concentration raw material gas is introduced, the temperature rise at the hot spot portion in each catalyst layer is suppressed, and the deterioration with time of the catalyst is reduced.
Phthalic anhydride can be produced stably with high yield.

[0051]

EXAMPLES [Method of Measuring Conversion] Conversion in case of continuous catalyst layer type The conversion of the first catalyst layer was measured as follows.

At the outlet of an iron reaction tube having an inner diameter of 25 mm and a length of 3.5 m, a spherical SiC self-sintering carrier having a diameter of 6 mm (apparent porosity 35%, purity 98.5% by mass) was added to the third catalyst layer. And a portion corresponding to the second catalyst layer, that is, a height of 1.8 m. On the SiC self-sintering carrier layer, the first catalyst was filled to a height of 0.9 m to form a first catalyst layer.

Using a reactor in which such a reaction tube is immersed in a molten salt bath, a mixed gas of raw material gas and air is introduced from the inlet of the reactor under the conditions according to the following production method, and Of raw material gas contained in the gas collected at (u)
Was measured, and the conversion rate of the raw material was measured from the raw material gas amount (i) corresponding to the collected gas amount at the outlet according to the following equation (1). Raw material conversion rate = [1- (u / i)] × 100 (1)

When measuring the conversion of the second catalyst layer, the outlet of the iron reaction tube was filled with a SiC self-sintering support at a height of 0.9 m corresponding to the third catalyst layer. SiC
On the self-sintering carrier layer, the second catalyst is filled at a height of 0.9 m to form a second catalyst layer, and further thereon, the first catalyst is filled at a height of 0.9 m. A first catalyst layer was formed.

Using a reactor in which such a reaction tube is immersed in a molten salt bath, under the conditions according to the following production method, the conversion in the case where a mixed gas of raw material gas and air is introduced from the inlet of the reactor. The rate was measured.

B. Conversion rate in case of discontinuous catalyst layer type Of the three connected reactors, the first catalyst layer is formed in the first reactor installed on the gas inlet side, and the first catalyst layer is formed under the conditions according to the following production method. A mixed gas of the raw material gas and air was introduced into the first reactor, and the conversion of the raw material gas at the outlet gas of the first reactor was measured as the conversion of the first catalyst layer.

When measuring the conversion of the second catalyst layer,
A first catalyst layer and a second catalyst layer are formed in a first reactor installed on the gas inlet side and a second reactor connected to the first reactor, respectively, and are formed from the inlet of the first reactor under the conditions according to the following manufacturing method. A mixed gas of the raw material gas and air was introduced, and the conversion rate of the raw material gas at the outlet gas of the second reactor was measured as the conversion rate of the second catalyst layer.

[Method of Measuring Hot Spot Temperature] Hot spot temperature in the case of continuous catalyst layer type An iron reaction tube with an inner diameter of 30 mm and a length of 3.5 m was added with a thickness of 10 mm.
mm multi-point thermometer (12 measurement points) is inserted, the thermometer is positioned at the center of the reaction tube, and the outlet of the reaction tube is filled with a third catalyst to a height of 0.9 m. To form a third catalyst layer, and then fill the second catalyst to a height of 0.9 m to form a second catalyst layer.
A catalyst layer was formed, and the first catalyst was filled thereon to a height of 0.9 m to form a first catalyst layer. The temperature of the catalyst layer measured by filling in this manner is substantially equal to the temperature of the catalyst layer filled in the following production example.

The temperature of the molten salt bath in which the reaction tube is immersed is maintained at 350 ° C., and a mixed gas of a raw material gas and air is introduced under the conditions shown in the following production example to cause an oxidation reaction. Three months after the beginning of the reaction, the temperature of the catalyst layer was measured. The highest temperature measured at the first catalyst layer is the hot spot temperature (HS ₁ ) at the first catalyst layer, and the highest temperature measured at the second catalyst layer is the hot spot temperature (HS ₁ ) at the second catalyst layer.
₂ ), and the highest temperature measured in the third catalyst layer is the hot spot temperature (HS ₃ ) in the third catalyst layer.

B. Hot spot temperature in the case of a discontinuous catalyst layer type Three iron reaction tubes having an inner diameter of 30 mm and a length of 1.5 m are connected in series, and a 10 mm-thick multipoint thermometer (12 measurement points) is connected to each reaction tube. ) Was inserted so that the thermometer was positioned at the center of the reaction tube, and a catalyst layer having a height of 0.9 m was formed in each reaction tube. The temperature of the molten salt bath in which each reaction tube is immersed is set in accordance with the following production method, and a mixed gas of a raw material gas and air is introduced under the conditions shown in the following production example, and each of the catalysts during the oxidation reaction is performed. The temperature of the layer was measured. The maximum temperature measured in the first reaction tube is the hot spot temperature (HS ₁₎ of the first catalyst layer, the maximum temperature measured by the second reaction tube is hot spot temperature in the second catalyst layer (HS ₂ ), And the highest temperature measured in the third reaction tube is the hot spot temperature (HS ₃ ) in the third catalyst layer.

[Calculation of ΔT] ΔT in each catalyst layer was determined by the following equation. ΔT = (HS−M) / W HS is the hot spot temperature (° C.) measured in each catalyst layer
And M is a set temperature (° C.) of a molten salt bath as a heating medium in which the reaction tube is immersed, and W is a mass (g) of a raw material (ortho-xylene or naphthalene) per m ³ of air under standard conditions. is there.

[Preparation of Titanium Oxide] Titanium oxide used as a catalytically active component was prepared as follows.

Mix ilmenite with 80% concentrated sulfuric acid,
After sufficient reaction, the reaction mixture was diluted with water to obtain an aqueous solution of titanium sulfate. To this, iron pieces were added as a reducing agent to reduce the iron content in the ilmenite to ferrous ions, and then cooled to precipitate and separate as ferrous sulfate. Steam heated to 150 ° C. was blown into the aqueous titanium sulfate solution thus obtained to precipitate hydrous titanium oxide. The precipitate of hydrous titanium oxide was washed with water, then with acid, and further washed with secondary water.
It was calcined at 00 ° C. for 4 hours under flowing air. The calcined product was subjected to jet stream pulverization to obtain anatase-type titanium oxide having an average particle size of 0.5 μm and a specific surface area of 22 m ² / g.

[Preparation of Catalyst] A slurry liquid to be a raw material of the catalysts A to U was prepared.

This slurry liquid is obtained by changing the ammonium monophosphate or cesium sulfate as shown in Table 2 in the catalyst slurry liquid 1 or 2 having the composition shown in Table 1. The slurry was prepared by first preparing an aqueous solution of oxalic acid, adding predetermined amounts of ammonium metavanadate, monobasic ammonium phosphate, niobium chloride, cesium sulfate, potassium sulfate, and antimony trioxide, followed by stirring. , Titanium oxide and stirring by an emulsifier.

On the other hand, in a stainless steel rotary furnace having a diameter of 35 cm and a length of 80 cm, 2000 ml of the SiC self-sintering support was placed and heated at 200 to 250 ° C. The slurry liquid prepared above was sprayed onto the pre-heated support while rotating the furnace to support the catalytically active substance. Thereafter, the mixture was calcined at 570 ° C. for 6 hours while flowing air to prepare Catalysts A to U.

The supports used in catalysts A to U had diameters as shown in Table 2 and had an apparent porosity of 35% and a purity of 98.5.
% Of SiC. The loading ratio of each catalyst is as shown in Table 2.

[0068]

[Table 1]

[0069]

[Table 2]

[Production of phthalic anhydride by orthoxylene oxidation] 1: a third catalyst (catalyst C) having a height of 0.9 m from an outlet to an iron reaction tube having an inner diameter of 25 mm and a length of 3.5 m.
Then, the second catalyst (catalyst B) is filled to a height of 0.9 m, and the first catalyst (catalyst A) is further filled with a height of 0.9 m.
9 m was filled.

While the reaction tube was immersed in a molten salt bath at 350 ° C., ortho-xylene was mixed with air at a ratio of 100 g / Nm ³ (ortho-xylene 100 m / m ^{3 of} standard air).
The mixed gas obtained in g) was introduced at a speed of 4.0 Nm ³ / hr (space velocity in a standard state of 3000 Hr ⁻¹ ).

At the beginning of the reaction, three months after the beginning of the reaction, the yield of phthalic anhydride and the amount of phthalide as an unreacted by-product were measured. In addition, for each of the initial reaction and after 3 months,
Conversion rate of the first catalyst layer and the second catalyst layer under the above-mentioned production conditions,
In addition, the hot spot temperatures in the first, second, and third catalyst layers were measured according to the above-described method of measuring the catalyst layer continuous type. Table 3 shows the results of the initial reaction, and Table 4 shows the measurement results after 3 months.
Shown in

The conversion of ortho-xylene was almost 100.
%, And the yield of phthalic anhydride can be regarded as the selectivity of phthalic acid.

Production Example No. 2 to 4; the first to third catalysts were changed to the catalysts shown in Tables 3 and 4, and the molten salt bath temperature (M)
Production Example 1 except that was changed to the temperatures shown in Tables 3 and 4.
In the same manner as in the above, phthalic anhydride was produced.

The conversion rate and the hot spot temperature of the first catalyst layer and the second catalyst layer at the beginning of the reaction and three months after the beginning of the reaction were measured in accordance with the above-described method of measuring the continuous catalyst layer type.
Further, the yield of phthalic anhydride and the amount of phthalide were measured. The measurement results are shown in Table 3 (early stage of reaction) and Table 4 (after three months).

Production Example No. 5: Each catalyst layer was formed of a mixture of the catalyst J and a spherical SiC self-sintering support having a diameter of 6 mm (porosity 35%, purity 98.5%). The content of the catalyst J in the mixture was 35% by mass in the first catalyst layer, 60% by mass in the second catalyst layer, and 1% in the third catalyst layer.
It was set to 00% by mass.

The conversion rate and the hot spot temperature of the first catalyst layer and the second catalyst layer at the beginning of the reaction and three months after the beginning of the reaction were measured according to the above-mentioned method of measuring the continuous catalyst layer type.
Further, the yield of phthalic anhydride and the amount of phthalide were measured. The measurement results are shown in Table 3 (early stage of reaction) and Table 4 (after three months).

Production Example No. 6; inner diameter 25 mm, length 1.
Three 5 m iron reaction tubes were connected in series. By filling each reaction tube with catalyst B at a height of 0.9 m, a first catalyst layer, a second catalyst layer, and a third catalyst layer were formed from the gas introduction side.

The temperature (M ₁ ) of the molten salt bath immersing the reaction tube (first reaction tube) on the gas inlet side on which the first catalyst layer was formed was maintained at 335 ° C., and the second catalyst layer was formed. Temperature (M) of the molten salt bath immersed in the reaction tube (second reaction tube)
₂ ) was maintained at 350 ° C., and the temperature (M ₃ ) of the molten salt bath in which the reaction tube (third reaction tube) on the gas outlet side on which the third catalyst layer was formed was maintained at 370 ° C.

In such a state, a mixed gas of the raw material gas and air was introduced into the inlet of the reaction tube filled with the first catalyst layer under the same conditions as in Production Example 1 to perform an oxidation reaction. Was. And the first stage of the reaction and three months after the beginning of the reaction
The conversion and the hot spot temperature of the catalyst layer and the second catalyst layer were measured in accordance with the above-mentioned measurement method of the catalyst layer discontinuous type. Further, the yield of phthalic anhydride and the amount of phthalide were measured. The measurement results are shown in Table 3 (early stage of reaction) and Table 4 (after three months).

[0081]

[Table 3]

[0082]

[Table 4]

Of the above production examples, No. Nos. 1 to 6 correspond to the examples of the present invention. 7 to 9 correspond to comparative examples.

As shown in Tables 3 and 4, when the conversion in the first catalyst layer was low (No. 7), the yield of phthalic anhydride was inferior to the others. When the conversion in the first catalyst layer was too high (No. 8), runaway occurred six days after the start of the reaction. In addition, even if the conversion rate in the first catalyst layer is appropriate, when the conversion rate in the second catalyst layer is low (No. 9), the yield of phthalic anhydride is still lower than that in the example of the present invention ( N
o. 1) to 6), and the yield of phthalide as a by-product was high.

On the other hand, Production Example N corresponding to the embodiment of the present invention
o. In all of the samples Nos. 1 to 6, even after three months from the beginning of the reaction, the conversion ratio and the hot spot temperature in each catalyst layer were almost the same as those in the initial stage of the reaction, indicating that a stable reaction had occurred. Also, the yield of phthalic anhydride is high.

[Production of phthalic acid by naphthalene oxidation] 10: A catalyst M having a height of 0. 3 as a third catalyst was placed in an iron reaction tube having an inner diameter of 25 mm and a length of 3.5 m from the outlet.
The third catalyst layer was formed by filling 9 m, and then the catalyst L was added to 0.1.
The second catalyst layer was formed by filling to a height of 9 m, and the first catalyst layer was formed thereon by further filling the catalyst K to a height of 0.9 m.

While the reaction tube was immersed in a molten salt bath at 365 ° C., a mixed gas of 90 g / Nm ³ of naphthalene and air was supplied at a speed of 4.0 Nm ³ / hr (space velocity of 2 at the standard state).
900 Hr ^-1 ).

At the beginning of the reaction, three months after the beginning of the reaction, the yield of phthalic anhydride and the amount of unreacted by-product naphthoquinone were measured. Table 5 shows the measurement results. The conversion of naphthalene is almost 100%, and the yield of phthalic anhydride can be regarded as the selectivity of phthalic acid.

The conversion rates of the first catalyst layer and the second catalyst layer at the beginning of the reaction and three months after the beginning of the reaction, and the hot spot temperature of each step were measured based on the above-described method of measuring the continuous catalyst layer type. Table 5 shows the measurement results.

Production Example No. Production Examples No. 11 to 14: Except that the catalyst of each catalyst layer and the molten salt bath temperature (M) were changed as shown in Table 5, In the same manner as in Example 10, naphthalene was oxidized to produce phthalic acid. The yield of phthalic anhydride and the amount of naphthoquinone were measured at the beginning of the reaction and three months after the beginning of the reaction. In addition, the conversion rates of the first catalyst layer and the second catalyst layer, and the hot spot temperature of each catalyst layer were measured according to the above-described method of the catalyst layer continuous type. Table 5 shows the results.

[0091]

[Table 5]

Manufacturing Example No. corresponding to the embodiment of the present invention. 1
In Nos. 0 and 11, the values of naphthalene conversion and hot spot temperature were stable from the beginning of the reaction to March, and a high phthalic anhydride yield was maintained not only at the beginning of the reaction but also after March.

On the other hand, in Production Example No. having a low conversion rate in the first catalyst layer. In No. 12, the hot spot temperature in the second catalyst layer was too high, and the yield of phthalic anhydride was inferior from the beginning of the reaction. Conversely, in the case of Production Example No. In No. 13, the hot spot temperature in the first catalyst layer was too high, and the phthalic anhydride yield decreased by 3% by mass three months after the initial stage of the reaction. Also, even if the conversion in the first catalyst layer is within the range of the present invention, if the conversion in the second catalyst layer is too low, the hot spot temperature in the third catalyst layer will increase, and eventually the yield of phthalic anhydride will increase. The rate was poor, and naphthoquinone by-product increased.

[0094]

According to the production method of the present invention, since the catalyst layers are divided and the conversion of each catalyst layer is adjusted, even if a high-concentration raw material gas is introduced, hot spots in each catalyst layer can be obtained. Phthalic anhydride can be produced stably without a runaway reaction and with a high yield.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a first embodiment of a manufacturing apparatus that performs a manufacturing method of the present invention.

FIG. 2 is a diagram illustrating a configuration of a second embodiment of a manufacturing apparatus that performs the manufacturing method of the present invention.

FIG. 3 is a diagram illustrating a configuration of a third embodiment of a manufacturing apparatus that performs the manufacturing method of the present invention.

FIG. 4 is a diagram illustrating a configuration of a fourth embodiment of a manufacturing apparatus that performs the manufacturing method of the present invention.

FIG. 5 is a graph showing a temperature change in a catalyst layer in the production method of the present invention.

Claims (15)

[Claims] 1. Using one or more fixed bed reactors,
A method for producing phthalic anhydride by catalytic vapor-phase oxidation of ortho-xylene and / or naphthalene with an oxygen-containing gas, wherein a catalyst layer in which the gas-phase catalytic reaction is performed is divided into three or more, Anhydrous wherein the conversion of orthoxylene and / or naphthalene at the outlet of the first catalyst layer is 30 to 70%, and the conversion of orthoxylene and / or naphthalene at the outlet of the second catalyst layer is 70% or more. A method for producing phthalic acid. 2. The hot spot temperature (° C.) of each catalyst layer is defined as HS, the holding temperature (° C.) of each catalyst layer is defined as M, and the total mass of orthoxylene and naphthalene per 1 m ³ of oxygen-containing gas under standard conditions (G) is W,
ΔT defined by the following equation is 0.35 to
2. The temperature is 0.85 ° C./(g/Nm ³ ) and 0.45 to 1.20 ° C./(g/Nm ³ ) in the second catalyst layer.
3. The method for producing phthalic anhydride according to 1.). ΔT = (HS−M) / W 3. The catalyst layer is divided into three parts.
The conversion of orthoxylene and / or naphthalene at the outlet of the catalyst layer is 30 to 70%, and the conversion of orthoxylene and / or naphthalene at the outlet of the second catalyst layer following the first catalyst layer is 70 to 95%. The method for producing phthalic anhydride according to claim 1, wherein the conversion of orthoxylene and / or naphthalene at the outlet of the third catalyst layer following the second catalyst layer is 99% or more. 4. The hot spot temperature (° C.) of each catalyst layer is HS, the holding temperature (° C.) of each catalyst layer is M, and the total mass of orthoxylene and naphthalene per 1 m ³ of oxygen-containing gas under standard conditions (G) is W,
ΔT defined by the following equation is 0.35 to
0.85 ° C./(g/Nm ³ ), 0.45 in the second catalyst layer
１．２1.20 ° C./(g/Nm ³ ), and 0.2 g for the third catalyst layer.
^{5~0.70 ℃ / (g / Nm 3} ) a method for producing phthalic anhydride according to claim 3. ΔT = (HS−M) / W 5. The length of the first catalyst layer is 25% to 54% of the total height of the first catalyst layer, the second catalyst layer, and the third catalyst layer, and the length of the second catalyst layer is 21% to 54%. 5. The method for producing phthalic anhydride according to claim 3, wherein the third catalyst layer has a length of 14 to 46%. 6. Each of the catalysts used in each of the catalyst layers contains vanadium oxide and titanium oxide.
5. The method for producing phthalic anhydride according to any one of 5. 7. The anhydrous catalyst according to claim 6, wherein the catalyst further comprises niobium, phosphorus, antimony, and at least one selected from the group consisting of sodium, potassium, rubidium, cesium, and thallium. A method for producing phthalic acid. 8. The catalyst filled in each of the catalyst layers,
The anhydrous phthalate according to any one of claims 1 to 7, wherein the phthalic anhydride is supported on an inert carrier and is packed so that the porosity of the catalyst layer decreases in order from the first catalyst layer to the catalyst layer that follows. Method for producing acid. 9. A mixture of each catalyst and an inert substance is used for each of the catalyst layers, and the content of the inert substance in the mixture is such that the content of the inert substance in the mixture continues from the first catalyst layer to the subsequent catalyst layer. The method for producing phthalic anhydride according to any one of claims 1 to 7, wherein the amount of the phthalic anhydride decreases in order. 10. The catalyst filled in each catalyst layer of the catalyst is supported on an inert carrier, and the supporting rate increases in order from the first catalyst layer to the subsequent catalyst layer. Item 8. The method for producing phthalic anhydride according to any one of Items 1 to 7. 11. The phthalic anhydride according to claim 7, wherein the phosphorus content of the catalyst used in each of the catalyst layers increases in order from the first catalyst layer to the subsequent catalyst layer. Manufacturing method. 12. The catalyst according to claim 7, wherein the total content of sodium, potassium, cesium, rubidium and thallium in each of the catalysts decreases in order from the first catalyst layer to the subsequent catalyst layer. For producing phthalic anhydride. 13. The method for producing phthalic anhydride according to claim 1, wherein the holding temperature of the catalyst layer increases in order from the first catalyst layer to the subsequent catalyst layer. 14. The method for producing phthalic anhydride according to claim 1, wherein a single reactor is used, and each of said catalyst layers is formed by laminating in said reactor. 15. The phthalic anhydride according to claim 1, wherein a plurality of reactors are used, and a catalyst layer formed in the reactors is connected to have the conversion. Production method.