JP5107084B2 - Method for producing methacrylic acid - Google Patents

Description

  The present invention relates to a method for producing methacrylic acid in which methacrolein is vapor-phase catalytically oxidized with molecular oxygen in the presence of a catalyst using a shell-tube reactor.

  Numerous proposals have been made regarding catalysts used in the production of methacrylic acid by gas phase catalytic oxidation of methacrolein. These proposals mainly relate to the elements constituting the catalyst and their proportions.

Since the gas phase catalytic oxidation is an exothermic reaction, heat storage occurs in the catalyst layer. The local abnormally high temperature zone resulting from the heat storage is called a hot spot, and if the temperature of this part is too high, an excessive oxidation reaction occurs and the yield of the target product is lowered.
Further, if the hot spot temperature becomes too high, the catalytic reaction is further promoted by the heat storage, and the heat generation proceeds and the catalyst may burn and deactivate.

  For this reason, in the industrial implementation of the oxidation reaction, temperature control of the hot spot is a serious problem, and particularly when the concentration of methacrolein in the raw material gas is increased in order to increase productivity, the temperature of the hot spot increases. Due to the tendency, the current situation is that there are significant restrictions on the reaction conditions.

  Therefore, it is very important to suppress the temperature of the hot spot part in industrially producing methacrylic acid with a high yield. In particular, when a general molybdenum-containing solid oxidation catalyst is used, it is important to suppress the occurrence of hot spots because the molybdenum component easily sublimates.

  On the other hand, a catalyst used for gas phase catalytic oxidation of methacrolein needs to be heat-treated for activation before use. As a method of heat-treating a catalyst so far, for example, in Patent Document 1, when producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein, a catalyst is filled into a reaction tube and air is supplied from one end. A method is disclosed in which a raw material gas containing methacrolein and molecular oxygen is supplied from the other end of the reaction tube after firing at 300 to 500 ° C.

  By this method, active sites effective for the reaction can be sufficiently expressed, and a highly active catalyst can be obtained. However, as higher-activity catalysts are developed, the above-described problem that the temperature of the hot spot becomes higher has occurred, and more countermeasures are required than ever.

  Several proposals have been made so far for suppressing the temperature rise in the hot spot. For example, in Patent Document 2, a plurality of catalysts having different activities prepared by varying the catalyst composition are packed so that the activity becomes higher from the raw material gas inlet side to the outlet side, and methacrolein and A method of circulating a source gas containing oxygen is disclosed. Patent Document 3 discloses that when acrolein is vapor-phase oxidized to acrylic acid using a multi-tubular fixed bed reactor equipped with a heating medium bath, the temperature of the heating medium bath is set at the inlet and outlet of the reactor. A method of controlling the flow of the heating medium so as to increase by 2 to 10 ° C. is disclosed.

  In these methods, the reaction rate per unit volume on the raw material gas inlet side in the catalyst layer in the reactor is lowered, thereby suppressing the reaction heat generation amount per unit volume, and as a result, trying to lower the temperature of the hot spot part. It is a method to do.

  However, these methods have a problem that the temperature control of the hot spot part is not sufficient and the reaction must be performed with a low load so that an excessive oxidation reaction does not occur, so that the yield of methacrylic acid is lowered.

JP 58-67643 A JP-A-4-210937 JP-A-8-92154

  In the method of producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen in the presence of a catalyst in a shell-tube reactor, the temperature of the hot spot is sufficiently suppressed, and startup It is an object of the present invention to provide a method for producing methacrylic acid that can efficiently carry out the oxidation reaction and perform an oxidation reaction under a high load.

A method for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen in the presence of a catalyst using a shell-tube reactor, comprising the following steps (1) to (5): In the step (2), at the time of preheating, at least one catalyst temperature in the reaction tube including a point within a radius of 1 m from the inlet for introducing the heated gas into the shell portion of the shell-tube reactor. Among these, the maximum temperature is controlled to be 150 ° C. or higher and 195 ° C. or lower, and a method for producing methacrylic acid is characterized.
(1) Step of filling catalyst in the reaction tube of shell-tube reactor (2) While supplying oxygen-containing gas from one end of the reaction tube, the shell portion of the shell-tube reactor was heated. Step of introducing gas and preheating the shell portion (3) Stopping introduction of the heated gas and introducing a heating medium into the shell portion (4) Circulating the heating medium to the shell portion to (5) A step of supplying a raw material gas containing methacrolein and oxygen to the reaction tube.

  According to the present invention, when a methacrylic acid is produced by vapor phase catalytic oxidation of methacrolein with molecular oxygen in the presence of a catalyst using a shell-tube reactor, the time required for heat treatment of the catalyst before the reaction is greatly increased. Shorten and start up efficiently. Moreover, since the oxidation reaction under a high load can be performed, the yield of methacrylic acid can be improved.

  The method for producing methacrylic acid of the present invention is carried out by subjecting methacrolein to gas phase catalytic oxidation with molecular oxygen in the presence of a catalyst using a shell-tube reactor, and the following steps (1) to ( 5).

(1) Step of filling catalyst in the reaction tube of shell-tube reactor (2) While supplying oxygen-containing gas from one end of the reaction tube, the shell portion of the shell-tube reactor was heated. Step of introducing gas and preheating the shell portion (3) Stopping introduction of the heated gas and introducing a heating medium into the shell portion (4) Circulating the heating medium to the shell portion to (5) A step of supplying a raw material gas containing methacrolein and oxygen to the reaction tube.

  In the production of methacrylic acid, the catalyst precursor is filled in a reaction tube, heated to a temperature necessary for the reaction, and heat treatment of the catalyst precursor is performed as a stage before starting up by introducing a raw material gas. Thus, it is suitably used when the catalyst precursor is fired to start production of methacrylic acid.

  In the present invention, the reaction for synthesizing methacrylic acid is carried out using a shell-tube reactor. As a shell-tube type reactor, a reaction tube (tube portion) and a shell portion that encloses the reaction tube remove the heat generated in the reaction tube, that is, a reaction tube outer fluid, that is, a heat medium inlet and outlet. Any known reactor may be used as long as it has a structure including: In particular, a multi-tube reactor having a plurality of reaction tubes is preferable because of high reaction efficiency per volume of the reactor.

  The general structure of a multi-tubular reactor that can be used in the present invention will be described below with reference to FIG. The multitubular reactor 1 has a plurality of reaction tubes 2, and both ends of the reaction tube 2 are fixed by tube plates 3a and 3b. The reaction tube 2 communicates with the introduction port 4a and the outlet port 4b, and can introduce a catalyst into the reaction tube 2 or circulate the raw material. The space surrounded by the tube plates 3a and 3b and the reactor 1 (shell part 5) communicates with the inlet 6a and outlet 6b, and introduces a gas or heat medium capable of controlling the temperature of the reaction tube 2, It can be distributed. The shell part 5 may have a blocking plate for partitioning the inside of the shell part 5 into a plurality of chambers in order to control the flow of gas and heat medium.

  Details of the steps (1) to (5) will be described below.

[Step (1)]
First, the catalyst is filled in the reaction tube of the shell-tube reactor.

  The catalyst used in the production of methacrylic acid in the present invention is not particularly limited as long as it is a known solid oxidation catalyst for methacrylic acid production, and conventionally known composite oxides containing molybdenum can be used. The composite oxide represented by the formula (1) is preferable because the effect of carrying out the present invention is higher.

Mo _a P _b Cu _c V _d X _e Y _f O _g (1)
(In the formula, Mo, P, Cu, V and O represent molybdenum, phosphorus, copper, vanadium and oxygen, respectively. X represents iron, cobalt, nickel, zinc, magnesium, calcium, strontium, barium, titanium, chromium, tungsten. Represents at least one element selected from the group consisting of manganese, silver, boron, silicon, tin, lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium, indium, sulfur, selenium, tellurium, lanthanum and cerium Y represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, a to g represent an atomic composition ratio, and when a is 12, b is 0.1 ≦ b ≦ 3, c is 0.01 ≦ C ≦ 3, d is 0.01 ≦ d ≦ 3, e is 0 ≦ e ≦ 10, f is 0.01 ≦ f ≦ 3, and g is all atoms. An oxygen atom ratio required for satisfying the valency.)

  The method for preparing the catalyst used in the present invention is not particularly limited, and various conventionally known methods can be used as long as there is no significant uneven distribution of components.

  The raw materials used for the preparation of the catalyst are not particularly limited, and nitrates, carbonates, acetates, ammonium salts, oxides, halides and the like of each element can be used in combination. For example, ammonium paramolybdate, molybdenum trioxide, molybdic acid, molybdenum chloride, etc. can be used as the molybdenum raw material.

  The catalyst used in the present invention may be carrier-free, but a supported catalyst supported on an inert carrier such as silica, alumina, silica-alumina, silicon carbide, or a catalyst diluted with these may also be used.

  The catalyst can be filled into the reaction tube from one or both ends of the reaction tube. The length of the catalyst layer after filling is not particularly limited, but can be appropriately selected from the viewpoints of reactivity, selectivity and the like.

[Step 2]
Next, a heated gas is introduced into the shell while supplying oxygen-containing gas from one end of the reaction tube, and the shell is preheated. The catalyst filled in the reaction tube in the step (1) is used after being activated by a final heat treatment at 300 to 500 ° C. while supplying an oxygen-containing gas to the reaction tube. The reaction tube is heated with a medium.

  As the heat medium introduced into the shell, one having a freezing point of 50 to 250 ° C. is generally used, and one having a freezing point of 130 to 180 ° C. is preferably used. A typical example of the heat medium is a nighter. Nighter is a so-called molten salt, and is preferable in that it has excellent thermal stability among heat media used for temperature control of chemical reactions and has excellent stability in heat exchange at a high temperature of 350 to 550 ° C. Nighters have various compositions and have different freezing points. In the present invention, any type of nighter can be suitably used as a heating medium as long as it has the above freezing point. Examples of the compound used in the nighter include sodium nitrate, sodium nitrite, and potassium nitrate, and these can be used alone or in admixture of two or more.

  In order to introduce the heat medium into the shell part, the shell part needs to be equal to or higher than the melting temperature of the heat medium. Therefore, the shell part is heated to a temperature at which the heat medium dissolves using a preheated gas. Operation is required. This heating operation is called preheating.

  In the present invention, the preheating of the shell portion is performed by at least one catalyst in a reaction tube including a point within a radius of 1 m from an inlet for introducing a heated gas into the shell portion of the shell-tube reactor. Among the temperatures, it is necessary to control the maximum temperature to be 150 ° C. or higher and 195 ° C. or lower.

  Usually, when the inside of a shell part is preheated with the heated gas, the temperature in a shell part becomes the maximum in the vicinity of the inlet which introduces the heated gas into a shell part. Therefore, the catalyst temperature in the reaction tube installed in the vicinity of the inlet becomes locally high and activation is promoted, so that a hot spot is generated when performing the gas phase catalytic oxidation reaction of methacrolein.

  In the present invention, in order not to generate hot spots during the reaction, the catalyst temperature is measured at a plurality of locations including at least the temperature of the catalyst existing within a radius of 1 m from the gas inlet of the shell during preheating of the shell. Then, preheating is performed by controlling the maximum temperature to be 150 ° C. or higher and 195 ° C. or lower, and then a heating medium is put into the shell portion.

  When the maximum temperature is lower than 150 ° C., preheating is insufficient, and the heat medium introduced into the shell after preheating cannot be completely dissolved. When the temperature exceeds 195 ° C., the activation of the catalyst at the location where the maximum temperature is reached is locally promoted and becomes a hot spot during the reaction. As a result, it is unavoidable to react with a low load so that excessive oxidation reaction does not occur while paying attention to the temperature of the hot spot part, and it takes time to start up, resulting in a decrease in yield of the target product. A more preferable temperature range is 170 ° C. or higher and 190 ° C. or lower.

  Further, the average rate of temperature rise from the introduction of the heated gas to the shell portion until the catalyst temperature is raised to the target heating medium charging temperature is in the range of 5 ° C./hr or more and 12 ° C./hr or less. Is preferred.

  When the rate of temperature increase is lower than 5 ° C./hr, the time required for the heat treatment becomes longer and the yield of the target product is remarkably lowered, which is not preferable. Further, when the rate of temperature rise is faster than 12 ° C./hr, a thermal history is received in a state where the temperature difference applied to the catalyst layer between the vicinity of the gas inlet and the other portion is larger, and during the subsequent heat treatment of the catalyst In this case, since the activation is promoted more locally, the temperature of the hot spot becomes higher, which is not preferable.

  The gas used for preheating the shell is not particularly limited, but inexpensive air is suitable. An inert gas such as nitrogen or argon can also be used.

  In addition, as the oxygen-containing gas flowing in the reaction tube during preheating, air or oxygen diluted with an inert gas such as nitrogen or helium can be used. In order to perform an appropriate heat treatment, the oxygen concentration of the oxygen-containing gas is preferably 0.1% by volume or more and 10% by volume or less, and more preferably 1% by volume or more and 7% by volume or less.

  As a structure for introducing the heated gas and the heating medium into the shell portion, a line for supplying the heated gas to the shell portion and a line for supplying the heating medium can be arbitrarily switched, and a line for supplying the heated gas. On the side, a blower or the like for sending gas and a heater for heating the gas are used. The heater preferably has a structure capable of controlling the output as needed by feeding back the temperature of a thermocouple capable of measuring the temperature in the reaction tube installed in the shell portion. Further, on the line side for supplying the heat medium, a tank provided with a tank for storing the heat medium and a pump for sending the heat medium from the tank to the shell portion is used.

  The gas and heat medium sent to the shell part are introduced from the introduction port arranged at the upper part of the shell part, and are spread so that there are no spots on the entire shell part by a blocking plate provided inside the shell part. The structure is such that it is discharged from the outlet arranged at the top of the shell.

  The gas discharged from the shell part may have a structure that opens to the atmosphere as it is, or a structure that circulates again to a gas blower or the like. It is preferable that the heat medium is structured so as to return to the tank and circulate again after being discharged from the shell portion.

  As a method for measuring the catalyst temperature, in one or more reaction tubes including at least the inside of the reaction tube in the vicinity of the introduction port so that the catalyst temperature in the vicinity of the introduction port into which the gas or the heat medium is introduced into the shell portion can be measured. Perform by installing a thermocouple. The vicinity of the introduction port is within the range of a shell portion having a radius of 1 m centering on the introduction port.

  Moreover, it is preferable to disperse and arrange a plurality of thermocouples in the cross-sectional direction and the vertical direction of the reactor so that the catalyst temperature in the reaction tubes of each part of the reactor can be measured evenly. Moreover, it is preferable to install each thermocouple so that it may be located in the center in the cross section of a reaction tube. The thermocouple is inserted into a hollow protective tube that is inserted in advance before the catalyst is filled into the reaction tube. The protective tube is inserted at a predetermined length so that the position of the protective tube is at the center in the cross section of the reaction tube and the position where the catalyst layer temperature is to be measured is the tip. The tip is sealed, and the thermocouple inserted into the protective tube is isolated from the catalyst layer.

[Step 3, Step 4]
Next, after stopping the introduction of the heated gas, a heat medium is introduced into the shell portion and circulated in the shell portion, and the catalyst is heat-treated at 300 ° C. or more and 500 ° C. or less.

  The heat medium is heated in a tank that stores the heat medium in advance. The temperature of the heat medium introduced into the shell is preferably 150 ° C. or higher and 220 ° C. or lower from the viewpoint of preventing the catalyst adjacent to the heat medium inlet from being rapidly activated. The heat medium introduced into the shell part is heated by a heater installed in the shell part so as to satisfy predetermined heat treatment conditions.

  The heat treatment conditions for activating the catalyst are not particularly limited, but are preferably 300 to 500 ° C. under an oxygen-containing gas flow with an oxygen concentration of 0.1 to 10% by volume, preferably 1 to 7% by volume. Methacrylic acid can be advantageously produced by performing a heat treatment at a temperature of 360 to 390 ° C. for at least 0.5 hours. In this case, an oxygen concentration of less than 0.1% by volume is not preferable because the activated catalyst is not sufficiently activated. On the other hand, if the oxygen concentration exceeds 10% by volume, the selectivity of methacrylic acid is reduced, and methacrylic acid cannot be produced advantageously, which is not preferable. When the heat treatment temperature is less than 300 ° C., the activated catalyst is not sufficiently activated, which is not preferable. On the other hand, when the heat treatment temperature exceeds 500 ° C., the catalyst structure collapses and methacrylic acid cannot be produced advantageously, which is not preferable. The temperature at the time of heat treatment is a temperature measured at a point within a radius of 1 m from the introduction port for introducing the heat medium.

  The average rate of temperature increase from the introduction of the heat medium into the shell portion until the temperature is raised to the target heat treatment temperature is not particularly limited, but 3 ° C./hr from the viewpoint of preventing the catalyst from being activated rapidly. As mentioned above, 50 degrees C / hr or less is preferable.

  In addition, the time for performing the heat treatment is preferably 5 hours or more and 50 hours or less from the viewpoint of controlling the productivity and the activity of the catalyst to be easily handled.

[Step 5]
After heat-treating the catalyst, a raw material gas containing methacrolein and molecular oxygen is supplied to the reaction tube to perform a gas phase catalytic oxidation reaction of methacrolein.

  The reaction for producing methacrylic acid by vapor-phase catalytic oxidation of methacrolein with molecular oxygen in the presence of a solid oxidation catalyst using a shell-tube reactor is usually carried out at a reaction temperature in the range of 250 to 350 ° C. Is done.

  In the practice of the present invention, the concentration of methacrolein in the raw material gas is not particularly limited, but is usually 1 to 20% by volume, preferably 3 to 10% by volume. In addition, at the start-up of the reaction, the concentration of methacrolein in the raw material gas can be increased stepwise to increase the reaction load stepwise.

  The raw material methacrolein may contain a small amount of impurities such as water and lower saturated aldehyde, and these impurities do not substantially affect the reaction.

  It is economical to use air as the oxygen source, but if necessary, air enriched with pure oxygen can also be used. The oxygen concentration in the raw material gas is defined by a molar ratio to methacrolein, and this value is preferably 0.3 to 4, particularly 0.4 to 2.5. The source gas may be diluted by adding an inert gas such as nitrogen, water vapor or carbon dioxide.

  The reaction pressure is preferably from normal pressure to several atmospheres. The reaction temperature can be selected in the range of 230 to 450 ° C, and 250 to 400 ° C is particularly preferable. The reaction can be carried out in a fixed bed or a fluidized bed.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these. In addition, "part" in an Example and a comparative example means a mass part.

  The catalyst composition was determined from the raw material charge of the catalyst component. As a heat medium for the reactor, a salt melt composed of 50% by mass of potassium nitrate and 50% by mass of sodium nitrite was used. The hot spot was detected by ΔT of the catalyst layer (temperature of the catalyst layer−temperature in the shell portion).

  As the shell-tube reactor filled with the catalyst, one having a structure in which 13,000 steel reaction tubes having an inner diameter of 25.4 mm and a length of 4500 mm were supported by an upper tube plate and a lower tube plate was used. In the shell part, the heat medium was extracted and filled with the catalyst at room temperature in an empty state.

  In order to be able to uniformly measure the catalyst layer temperature in the reaction tube of each part inside the shell-tube reactor, thermocouples were distributed and arranged at 36 locations in the cross-sectional direction and the vertical direction of the reactor, and the temperature of each part was measured. . One of the thermocouples was installed in a reaction tube arranged within a radius of 1 m from the heated gas inlet to the shell. The protective tube is isolated from the reaction system. The temperature in the catalyst layer was measured by installing a thermocouple so as to be located at the center in the cross section of the reaction tube.

  The analysis of the raw material gas and the reaction product gas was performed by gas chromatography. The temperature of the heat medium in the shell is controlled by feeding back the temperature of the heat medium in the shell and controlling the output of the heater installed in the shell. The thing which can control automatically was used.

[Example 1]
<Preparation of catalyst>
100 parts of ammonium paramolybdate, 2.8 parts of ammonium metavanadate and 9.2 parts of cesium nitrate were dissolved in 300 parts of pure water. While stirring this, a solution prepared by dissolving 8.2 parts of 85 mass% phosphoric acid in 10 parts of pure water and a solution of 1.1 parts of telluric acid in 10 parts of pure water were added, and the temperature was raised to 95 ° C. while stirring. Warm up. Next, a solution prepared by dissolving 3.4 parts of copper nitrate, 7.6 parts of ferric nitrate, 1.4 parts of zinc nitrate and 1.8 parts of magnesium nitrate in 80 parts of pure water was added. Furthermore, this liquid mixture was stirred at 100 degreeC for 15 minutes, and the obtained slurry was dried using the spray dryer.

2 parts of graphite was added to and mixed with 100 parts of the resulting dried product, and formed into a ring shape having an outer diameter of 5 mm, an inner diameter of 2 mm, and a length of 3 mm by a tableting machine to obtain a catalyst. The composition of the catalyst was Mo ₁₂ P _1.5 Cu _0.3 V _0.5 Fe _0.4 Te _0.1 Mg _0.15 Zn _0.1 Cs ₁ in terms of atomic ratio excluding oxygen.

<Heat treatment>
A mixture of 620 mL of catalyst and 130 mL of alumina spheres having an outer diameter of 5 mm was charged on the inlet side of the raw material gas of the shell-tube reactor, and 750 mL of catalyst was charged on the outlet side. At this time, the length of the catalyst layer was 3005 mm. At this time, introduction of room temperature air at 1 L / hr into the tube portion of the shell-tube reactor filled with the catalyst was started. At this time, the heat medium is extracted from the shell portion of the shell-tube reactor, and the temperature is also room temperature.

After the catalyst filling into the reaction tube was completed, introduction of air heated in advance to 190 ° C. with a heater at a flow rate of 20 km ³ / hr from the inlet to the shell portion was started. After 14 hours from the start of the introduction of the heated air, it was confirmed that the measured temperature of the thermocouple installed in the reaction tube disposed within a radius of 1 m from the inlet was 190 ° C. Thereafter, the introduction of air heated for about 2 hours was further closed, the route was switched to the introduction route of the heating medium, and the heating medium previously heated to 200 ° C. was introduced. The average rate of temperature increase from the start of air introduction into the shell until the measurement temperature of the thermocouple installed in the reaction tube disposed within a radius of 1 m from the inlet reaches 190 ° C. is 11. It was 8 ° C./hr.

  Thereafter, the heating medium was heated with a heater installed in the shell portion, and the temperature at a point within a radius of 1 m from the introduction port for introducing the heating medium was increased from 5 ° C / hr to 200 ° C to 275 ° C. . Thereafter, the temperature was raised in the range from 275 ° C. to 385 ° C. at 10 ° C./hr, and when the temperature reached 385 ° C., the temperature rise was stopped and held at 385 ° C. for 14 hours.

  After maintaining at 385 ° C. for 14 hours, the heat treatment temperature was lowered to 250 ° C. at a rate of temperature decrease of 25 ° C./hr.

<Gas-phase catalytic oxidation of methacrolein>
Thereafter, the air flowing in the reaction tube of the reactor was temporarily stopped, and a raw material mixed gas comprising 4.0% methacrolein, 9.0% oxygen, 30.0% water vapor and 57.0% nitrogen was added to the reaction tube. Was passed at a reaction temperature of 290 ° C. and a contact time of 4.5 seconds to initiate the reaction. Thereafter, the temperature of the heat medium in the shell portion was changed until the methacrolein conversion rate became 75%. The temperature at this time is defined as the reaction temperature.

  After the reaction temperature was stabilized, the methacrolein concentration of the raw material gas was changed in accordance with the raw material composition table shown in Table 1, and the reaction load level was gradually increased from 1 to 4. At this time, after waiting for the reaction temperature to stabilize at each load level, ΔT at each position at that time is measured, and the raw material gas conditions at the next load level are gradually increased so that the value does not exceed 35 ° C. changed. As a result, the time taken to increase the load level to 4 was 40 hr. The results are shown in Table 2.

[Example 2]
After charging the catalyst into the reaction tube, 14 hours after starting the introduction of the heated air from the inlet of the shell part, a thermocouple installed in the reaction tube arranged within a radius of 1 m from the inlet The oxidation reaction was carried out in the same manner as in Example 1 except that the measurement temperature was 170 ° C. The average rate of temperature increase from the start of air introduction into the shell portion until the measured temperature of the thermocouple installed in the reaction tube disposed within a radius of 1 m from the inlet becomes 170 ° C. is 10. It was 6 ° C./hr.

  As a result, the time taken to increase the load level to 4 was 60 hours. The results are shown in Table 2.

[Comparative Example 1]
After charging the catalyst into the reaction tube, 14 hours after starting the introduction of the heated air from the inlet of the shell part, a thermocouple installed in the reaction tube arranged within a radius of 1 m from the inlet The oxidation reaction was performed in the same manner as in Example 1 except that the measurement temperature was 200 ° C. The average rate of temperature rise from the start of air introduction into the shell until the measurement temperature of the thermocouple installed in the reaction tube disposed within a radius of 1 m from the inlet reaches 200 ° C. is 12. It was 5 ° C./hr.

  As a result, ΔT is likely to exceed 35 ° C. when the load level is 2. Therefore, the reaction temperature is temporarily lowered to wait for ΔT to drop, and then the load level is increased to 4, resulting in a load level of 4 The time taken to rise to 105 hours was 105 hours. The results are shown in Table 2.

[Comparative Example 2]
Measurement of a thermocouple installed in a reaction tube disposed within a radius of 1 m from the introduction port after 14 hours from the start of introduction of heated air from the shell portion introduction port after filling the catalyst into the reaction tube The oxidation reaction was carried out in the same manner as in Example 1 except that the temperature was 210 ° C. The average rate of temperature rise from the start of air introduction into the shell until the measured temperature of the thermocouple installed in the reaction tube disposed within a radius of 1 m from the inlet becomes 210 ° C. is 13.1. It was ° C./hr.

  As a result, ΔT is likely to exceed 35 ° C. when the load level is 2. As a result, the reaction temperature is temporarily lowered to wait for ΔT to drop, and then the load level is increased to 4, resulting in a load level of 4 The time taken to rise to 370 hours was 370 hours. The results are shown in Table 2.

It is sectional drawing of the shell-tube type reactor used for this invention.

Explanation of symbols

1 Multi-tube reactor 2 Reaction tube (tube section)
3a Tube sheet (upper part)
3b Tube sheet (lower part)
4a Inlet 4b Outlet 5 Shell part 6a Inlet 6b Outlet

Claims (2)

A method for producing methacrylic acid, wherein a methacrolein is vapor-phase catalytically oxidized with molecular oxygen in the presence of a catalyst using a shell-tube reactor,
Including the following steps (1) to (5),
In the step (2), at the time of preheating, at least one catalyst temperature in the reaction tube including a point within a radius of 1 m from the inlet for introducing the heated gas into the shell portion of the shell-tube reactor. Is controlled such that the maximum temperature is 150 ° C. or higher and 195 ° C. or lower.
(1) Step of filling catalyst in the reaction tube of shell-tube reactor (2) While supplying oxygen-containing gas from one end of the reaction tube, the shell portion of the shell-tube reactor was heated. Step of introducing gas and preheating the shell portion (3) Stopping introduction of the heated gas and introducing a heating medium into the shell portion (4) Circulating the heating medium to the shell portion to (5) A step of supplying a source gas containing methacrolein and oxygen to the reaction tube. The method for producing methacrylic acid according to claim 1, wherein the catalyst is a composite oxide represented by the following formula (1).
Mo _a P _b Cu _c V _d X _e Y _f O _g (1)
(In the formula, Mo, P, Cu, V and O represent molybdenum, phosphorus, copper, vanadium and oxygen, respectively. X represents iron, cobalt, nickel, zinc, magnesium, calcium, strontium, barium, titanium, chromium, tungsten. Represents at least one element selected from the group consisting of manganese, silver, boron, silicon, tin, lead, arsenic, antimony, bismuth, niobium, tantalum, zirconium, indium, sulfur, selenium, tellurium, lanthanum and cerium Y represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, a to g represent an atomic composition ratio, and when a is 12, b is 0.1 ≦ b ≦ 3, c is 0.01 ≦ c ≦ 3, d is 0.01 ≦ d ≦ 3, e is 0 ≦ e ≦ 10, f is 0.01 ≦ f ≦ 3, and g is all atoms. An oxygen atom ratio required for satisfying the valency.)

Images