JP5614062B2 - Start-up method for gas phase catalytic oxidation reaction and method for producing (meth) acrylic acid using the same - Google Patents

Description

  The present invention relates to a start-up method for gas phase catalytic oxidation reaction and a method for producing (meth) acrylic acid using the same.

  For example, when acrolein or acrylic acid is produced from propylene or methacrolein or methacrylic acid is produced from isobutylene, it is usually a gas phase catalytic oxidation reaction (hereinafter sometimes simply referred to as “oxidation reaction”). Is used. When the oxidation reaction is carried out industrially, the reaction heat generated during the oxidation reaction is large, so a huge multi-tube heat exchanger type reactor (hereinafter simply referred to as “reactor”) having a plurality of reaction tubes. Is sometimes used.).

  In particular, from the viewpoint of separation of the catalyst from reaction raw materials such as propylene and isobutylene and a raw material gas containing molecular oxygen, an oxidation reaction catalyst is filled into a plurality of reaction tubes to form a catalyst layer, and the raw material gas is supplied to the reaction layers. In many cases, an oxidation reaction proceeds by introducing a heat medium into the barrel of the reactor while passing it through and heating or removing heat from the outside of the reaction tube. This makes it possible to control the reaction amount safely, avoid rapid deterioration of the catalyst, and suppress excessive oxidation reaction to easily maintain a high yield.

  By the way, in a commonly used reactor, like a normal heat exchanger, a flow path of a heat medium called a baffle plate is defined so that the heat medium uniformly passes around the reaction tube in the reactor, A plate for changing the flow direction is installed. This baffle plate can suppress the short circuit flow of the heat medium and maintain the heat removal capability around the reaction tube.

  However, the temperature of the heat medium introduced into the reactor barrel is likely to rise due to the heat generated in the oxidation reaction and the heat necessary for preheating the raw material gas before flowing through the barrel and being discharged. Therefore, the temperature distribution of the heat medium was likely to occur in the reactor. As a result, the reaction state differs between the reaction tube located in the region where the temperature of the heat medium is high and the reaction tube located in the region where the temperature of the heat medium is low. In particular, in a reaction tube located in a region where the temperature of the heat medium is high, an excessive oxidation reaction is induced more easily than in the surrounding reaction tube, which tends to cause a decrease in yield or local deterioration of the catalyst. Furthermore, when the heat generation rate by the oxidation reaction is higher than the heat removal capability, the oxidation reaction may run away. When a situation where an oxidation reaction runaway is likely to occur, it is necessary to suppress the supply of the raw material gas or, in some cases, to stop it urgently, and the production plan cannot be achieved, resulting in a great deal of damage.

On the other hand, the catalyst used for the oxidation reaction may have unstable activity at the initial stage of the reaction. Therefore, as a method for suppressing an excessive oxidation reaction at the start of the reaction, a method is generally used in which an amount smaller than the supply amount of the reaction raw material in the steady operation is supplied, and the supply amount is gradually increased to shift to the steady operation.
However, in the operation of starting the supply of the reaction raw material and gradually increasing the supply amount of the reaction raw material to shift to the steady operation (hereinafter referred to as “startup”), before reaching the target supply amount, When a local high temperature zone called a hot spot is generated even in a part, the supply amount is stopped increasing and it is necessary to wait for the temperature of the catalyst layer in the portion where the hot spot is generated to decrease. Therefore, a lot of time is spent on startup, and the target production volume cannot be obtained, resulting in a great loss.

In order to solve the above problems, usually, an operation for setting a lower temperature at the start of the supply of the reaction raw materials or an operation for waiting for the temperature of the catalyst layer to decrease and stabilize in the middle of the start-up are performed. By such an operation, when the supply amount of the reaction raw material is small, the generation of hot spots can be suppressed. However, when the supply amount gradually increases and approaches steady operation, the temperature of a part of the catalyst layer rises excessively and a hot spot may occur.
In particular, when the oxidation reaction is performed using a huge reactor, the temperature distribution of the heat medium is likely to occur in the reactor, and the reaction conditions are likely to be different for each reaction tube. For this reason, it is not easy to control the temperature of the catalyst layer throughout the reactor, suppress the occurrence of hot spots and the temperature rise of the hot spots, start up smoothly, and shift to steady operation.

  As a method for suppressing the temperature rise of the hot spot during start-up, for example, Patent Document 1 discloses that the supply amount per unit time of the raw material to the reactor is the maximum allowable supply per unit time of the raw material during the start-up of the oxidation reaction. A method is disclosed in which the supply amount per unit time is maintained at 30% or more and less than 80% of the allowable maximum supply amount for 20 hours or more after reaching 30% or more of the amount.

JP 2005-336085 A

  However, in the method described in Patent Document 1, it is not easy to sufficiently suppress the occurrence of hot spots due to the occurrence of the temperature distribution of the heat medium in the reactor, and it may take a long time for startup. there were.

  The present invention was made in view of the above circumstances, and when performing a gas phase catalytic oxidation reaction in a multitubular heat exchanger type reactor, the temperature distribution of the heat medium in the reactor is suppressed to a minimum, An object of the present invention is to provide a start-up method capable of suppressing the occurrence of hot spots and performing start-up in a short time, and a method for producing (meth) acrylic acid using the start-up method.

  As a result of diligent investigations, the present inventors set conditions under which the temperature of the catalyst layer is not low in the reactor, thereby minimizing the temperature distribution of the heat medium and preventing the generation of hot spots. It was found that the system can be started up in a short time, and the present invention has been completed.

That is, the start-up method of the present invention is formed between 10000 to 35000 reaction tubes filled with a catalyst in a cylinder of a multi-tube heat exchanger type reactor, and a heat medium is formed between the reaction tubes. Using a multi-tubular heat exchanger reactor equipped with a circulating space and 1 to 5 baffle plates for changing the flow direction of the heat medium in the space, while introducing the heat medium into the space In the start-up method when supplying a raw material gas containing (meth) acrolein as a reaction raw material to the reaction tube and obtaining (meth) acrylic acid as a reaction product gas by a gas phase catalytic oxidation reaction , The supply amount of the reaction raw material is increased so that the maximum value of the difference (ΔT) between the temperature and the temperature of the heat medium in the space does not exceed 50 ° C., and the supply amount of the reaction raw material is the reaction raw material during steady operation Reached 30% of supply 80% to reach the time required to have five or more and less than 20 hours, and the heat medium introduced into the space during the transition into steady-state operation from the start of supply of the raw material gas temperature (T _h) The temperature (T _s ) of the heat medium introduced into the space during steady operation satisfies the following formula (1).
−5 <(T _h −T _s ) <2 (1)
Moreover, it is preferable that the said catalyst is a catalyst which has a composition represented by following formula (II).
_{Mo j P k V l Cu m} X 2 n Y 2 o Z 2 p O q ··· (II)
(In the formula (II), Mo, P, V, Cu and O represent molybdenum, phosphorus, vanadium, copper and oxygen, respectively, and X ² represents antimony, bismuth, arsenic, germanium, zirconium, tellurium, selenium, silicon and tungsten. Represents at least one element selected from the group consisting of boron and silver, and Y ² is at least one selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum Z ² represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, j, k, l, m, n, o, p and q are atoms of each element Represents the ratio, and when j = 12, k = 0.5-3, l = 0.01-3, m = 0-2, n = 0-3, o = To 3, a p = 0.01 to 3, q is an oxygen atom ratio required for satisfying the valency of each component.)

  In addition, the method for producing (meth) acrylic acid according to the present invention is characterized in that the start-up method is used, and a raw material gas containing (meth) acrolein as a reaction raw material is supplied to a reaction tube to perform gas phase catalytic oxidation.

  According to the present invention, when performing a gas phase catalytic oxidation reaction in a multitubular heat exchanger type reactor, the temperature distribution of the heat medium in the reactor is suppressed to a minimum, the occurrence of hot spots is suppressed, A start-up method capable of performing start-up in a short time and a method for producing (meth) acrylic acid using the start-up method can be provided.

It is a schematic diagram which shows an example of the multitubular heat exchanger type | mold reactor used for this invention. It is the elements on larger scale of the multitubular heat exchanger type reactor shown in FIG.

In the present invention, the gas phase catalytic oxidation reaction is carried out using a multitubular heat exchanger type reactor.
As the multitubular heat exchanger type reactor, a multitubular heat exchanger which is one of chemical machines widely used in the chemical industry can be used. A multi-tube heat exchanger is generally a plurality of heat transfer tubes (reaction tubes) in which at least one tube plate is built in each end of a tubular body, and the outer periphery of each end is fixed between the tube plates. It is what has.

  Here, an example of the multi-tube heat exchanger reactor used in the present invention will be described with reference to FIG. The reactor 10 in this example is formed between a plurality of reaction tubes 12 in which a catalyst layer is formed by filling a catalyst 11 inside a cylinder 11 of the reactor 10, and a heat medium flows therethrough. Space 11a, one or more baffle plates 13 for changing the flow direction of the heat medium into the space 11a, a raw material gas inlet 14 provided at the lower part of the reactor, and a reaction product gas outlet 15 provided at the upper part of the reactor. A heat medium inlet 16 for introducing a heat medium for heating or removing the reaction tube 12 into the space 11a of the reactor 10, a heat medium outlet 17 for discharging the heat medium from the space 11a of the reactor 10, and heat And a pump 18 for circulating the medium in the space 11a of the reactor 10.

  The number of reaction tubes 12 may be a plurality, for example, 10,000 to 35,000. Further, the outer diameter, thickness, and length of the reaction tube 12 are not particularly limited.

The number of baffle plates 13 is not particularly limited, and may be one or two or more. In consideration of the mounting strength of the reaction tube 12, the capacity of the heat medium circulation facility, the pressure loss due to the heat medium circulation, the pressure resistance of the tube plate, and the like, it may be designed to suit the economy as appropriate.
Further, as the form of the baffle plate 13, various types such as a segmental type, a double segmental type, a disk-doughnut type, and a rod type are exemplified. The present invention is particularly effective in a segmented segmental baffle that is susceptible to the flow history of the heat medium, but the type of the baffle plate 13 is not particularly limited.

  In a gas phase catalytic oxidation reaction (hereinafter simply referred to as “oxidation reaction”) using such a reactor 10, a heat medium is introduced into the space 11 a of the reactor 10 from the heat medium inlet 16, and contains a reaction raw material. A source gas is supplied from the source gas inlet 14 to the reactor 10, and the source gas is circulated through each reaction tube 12 heated by the heat medium. Then, when the raw material gas flows through the catalyst layer formed in the reaction tube 12 from the bottom to the top, the reaction raw material is oxidized by the gas phase catalytic oxidation reaction to generate a reaction product gas. At that time, the oxidation reaction heat is transferred from the heat medium through the tube wall of the reaction tube 12, and the oxidation reaction in the reactor 10 can be controlled. The produced reaction product gas is discharged from the reaction product gas outlet 15 and collected. On the other hand, the heat medium is discharged from the heat medium outlet 17.

In the present invention, conditions for starting up in the above-described oxidation reaction are defined.
In the present invention, the “steady operation” is a state in which the reaction raw material reaches a permissible maximum supply amount or a target supply amount in the vicinity thereof and is operating at a constant level. The “allowable maximum supply amount” is a maximum value that may be supplied to the reactor of the reaction raw material. This value correlates with the production capacity of the reactor and is determined at the reactor design stage.

In the present invention, the time (t _L ) required to reach 80% after the supply amount of the reaction raw material reaches 30% of the supply amount of the reaction raw material in the steady operation is set to 5 hours or more and less than 20 hours.
Further, the present invention provides the temperature (T _h ) of the heat medium introduced into the space of the reactor during the transition from the start of the supply of the raw material gas to the steady state (that is, during the start-up), and during the steady operation. The temperature (T _s ) of the heat medium introduced into the reactor space was defined so as to satisfy the following formula (1). The “temperature of the heat medium introduced into the space of the reactor” refers to the temperature of the heat medium immediately before passing through the heat medium inlet of the reactor.
−5 <(T _h −T _s ) <2 (1)

  As a result of intensive studies, the inventors have determined that the temperature distribution of the heat medium is minimized, the occurrence of hot spots is suppressed, and the start-up is completed in a short time without generating a region where the temperature of the catalyst layer is low during startup. I found it important. The reason is as follows.

  In the initial stage of start-up, where the amount of reactant feed is low, the heat medium introduced into the reactor space advances the oxidation reaction until it reaches the back side of the reactor (region away from the heat medium inlet). Therefore, heat is taken away, and the temperature of the heat medium itself tends to decrease. Therefore, the temperature of the heat medium tends to be lower toward the back of the reactor. Therefore, the catalyst layer of the reaction tube installed on the back side of the reactor has a lower temperature than the catalyst layer of the reaction tube installed on the front side of the reactor (near the heat medium inlet), and the reaction amount decreases. Cheap. Therefore, in order to ensure a certain reaction amount as a whole reactor, the reaction tube which is installed outside the back side of the reactor (region where the temperature of the catalyst layer is low) is made to react excessively than usual and the reaction is insufficient. It is necessary to supplement the amount. Therefore, even if an attempt is made to secure a certain reaction amount by increasing the temperature of the heat medium, once a region where the temperature of the catalyst layer is low occurs, the temperature increase in the region is higher than the temperature increase in other regions. Therefore, the temperature difference of the catalyst layer in each reaction tube increases. As a result, the temperature of the catalyst layer further rises in a region where the temperature of the catalyst layer is high, so that the temperature of the heat medium cannot be further increased, and it becomes difficult to ensure a certain reaction amount. Alternatively, it is necessary to wait for the catalyst in the region where the temperature of the catalyst layer is high to be deactivated, or to reduce the supply amount of the reaction raw material, and to start up again, thereby extending the startup time.

  According to the present invention, by defining the start-up conditions as described above, in the initial stage of start-up where the supply amount of the raw material gas including the reaction raw material is small, the temperature of the heat medium is easily reduced (heat The oxidation reaction in the catalyst layer in a region away from the medium inlet can be sufficiently advanced. Therefore, the startup can be completed while maintaining a high temperature without generating a region where the temperature of the catalyst layer is low during startup.

Under the conditions described above, if the time (t _L ) is less than 5 hours, a large amount of reaction raw material is supplied to the reaction tube at an early stage where the activity of the catalyst is high. The reaction proceeds, resulting in a large exotherm. Furthermore, since the supply amount of the reaction raw material increases in this state, further heat generation occurs and a hot spot is generated.
On the other hand, when the time (t _L ) is 20 hours or more, the temperature of the heat medium around the reaction tube installed in the region away from the heat medium inlet becomes low, and the temperature of the catalyst layer of the reaction tube in the region gradually increases. It will decline.
The lower limit of time (t _L ) is preferably 10 hours or longer, and the upper limit is preferably 19 hours or shorter.

  There is no particular limitation on the time required for the supply of the reaction raw material to reach 80% of the supply amount of the reaction raw material during the steady operation until the shift to the steady operation. For example, by increasing the supply amount of the reaction raw material by 1%, maintaining the state for 1 hour, increasing the supply amount by 1% again, and maintaining the state for 1 hour, the temperature of the catalyst layer and the reaction rate It is sufficient to increase the supply amount of the reaction raw material step by step while managing

In addition, when (T _h −T _s ) is −5 ° C. or lower under the above-described conditions, the temperature of the heat medium becomes low before the shift to the steady operation, and thus the catalyst in a region away from the heat medium inlet. It becomes difficult to sufficiently advance the oxidation reaction in the layer and maintain it at a high temperature.
On the other hand, if (T _h −T _s ) is 2 ° C. or higher, the temperature of the heat medium introduced during start-up is too high, so that an excessive oxidation reaction is likely to be induced and hot spots are likely to occur.
The lower limit of (T _h -T _s ) is preferably −4.5 ° C. or higher, more preferably −4.0 ° C. or higher. On the other hand, the upper limit value of (T _h −T _s ) is preferably 1.5 ° C. or less, and more preferably 1.0 ° C. or less.

Note that the temperature of the heat medium introduced during start-up changes freely as long as the temperature satisfies the above formula (1), that is, exceeds (T _s −5) ° C. and is less than (T _s +2) ° C. Can be made.

The temperature of the heat medium introduced into the space of the reactor is not particularly limited as long as it satisfies the above formula (1), and the temperature may be increased according to the supply amount of the reaction raw material, and is always constant. It may be a value. Further, the temperature of the heat medium introduced into the space of the reactor may be raised or lowered depending on the reaction state such as the temperature distribution and reaction rate of the catalyst layer, the temperature distribution of the heat medium in the reactor, and the like. .
On the other hand, the temperature of the heat medium introduced into the space during steady operation is preferably set in advance by actual values, experimental values in experimental facilities, simulations, and the like.

As described above, the present invention performs start-up under conditions that do not generate a low temperature region in the catalyst layer, but in order to grasp the temperature of the catalyst layer, a temperature measurement such as a thermocouple is provided in the catalyst layer in the reaction tube 12. It is preferable to install an instrument. In particular, as shown in FIG. 2, the measurement point A is provided between the end portion 19 on the source gas inlet 14 side of the reaction tube 12 and the first baffle plate 13 a counted from the end portion 19. preferable.
In addition, the x mark (a-1 to a-6) surrounded by the broken line a is a temperature measurement installed in the catalyst layer in each reaction tube 12 when cut from the measurement point A and viewed from above. A part of the position of the instrument is shown. Further, the crosses (b-1 to b-6) surrounded by the broken line b are provided between the second baffle plate 13b and the first baffle plate 13a as counted from the end 19. A part of the position of the temperature measuring instrument installed in the catalyst layer in each reaction tube 12 when cut from the measurement point B and viewed from above is shown.

The more the number of temperature measuring instruments installed, the more accurately the internal state of the reactor can be grasped, but on the other hand, the complexity of installation costs and data processing increases, so the location where the flow direction of the heat medium changes, In view of the reaction characteristics of the catalyst, it is preferable to appropriately select representative points such as a place where heat is likely to be generated, and to minimize the number of installed points. Due to the reaction characteristics of the catalyst, the place where heat is likely to be generated may be set by measuring the temperature of the catalyst layer when an oxidation reaction is performed with one reaction equipment such as a bench reactor, You may obtain | require by calculation using reaction rate analysis or simulation.
Further, without selecting a representative point, the reactor may be virtually divided into a practical number of divisions, and temperature measuring instruments may be uniformly installed in the divided areas.

The temperature measuring instrument may be installed directly in the catalyst layer, or a protective tube may be inserted into the reaction tube 12 and the temperature measuring instrument may be installed in the protective tube. It is assumed that the catalyst is not filled in the protective tube.
In addition, the temperature measuring device may be movable as necessary, and the temperature of many places may be measured with one temperature measuring device.

The source gas used in the present invention contains a reaction source and oxygen. Moreover, it may contain water vapor.
The reaction raw material is not particularly limited as long as it is a raw material that can be used in the gas phase catalytic oxidation reaction, but the present invention generates (meth) acrolein from isobutylene and propylene, or (meth) acrylic acid from (meth) acrolein. It is suitable for an oxidation reaction having a remarkably large heat of oxidation reaction such as a reaction to be generated. Therefore, the present invention is particularly suitable when isobutylene, propylene, tertiary butyl alcohol, (meth) acrolein or the like is used as a reaction raw material, and is particularly suitable when (meth) acrolein is used.
In the present invention, “(meth) acrolein” indicates both methacrolein and acrolein, and “(meth) acrylic acid” indicates both methacrylic acid and acrylic acid.

  The concentration of the raw material gas supplied during start-up, the flow rate of the raw material gas, the reaction pressure, and the temperature are not particularly limited, but are preferably changed stepwise. For example, the time required for start-up may be planned, and the change per unit time may be determined to be constant, or the increase may be gradually decreased within a range in which the amount of reaction raw material supplied is large.

On the other hand, the concentration of the raw material gas supplied during steady operation includes, for example, (meth) acrolein as the reaction raw material, the concentration of the reaction raw material is 3 to 9% by volume, the concentration of oxygen is 5 to 15% by volume, and the concentration of water vapor Is preferably 5 to 50% by volume.
In addition, the source gas may contain a small amount of impurities such as lower saturated aldehydes and ketones that do not substantially affect this reaction, and the source gas is diluted by adding an inert gas such as carbon dioxide. May be.
In addition, it is economically advantageous to use air as the oxygen source of the source gas.

The flow rate of the raw material gas supplied at the time of steady operation is not particularly limited, but a flow rate such that the space velocity per reaction tube and 1 g of catalyst is 0.5 to 2.0 NL / hr / line / g is preferable. .
The reaction pressure can be from normal pressure to several atmospheres.
Moreover, it does not specifically limit as temperature of source gas, However 100-300 degreeC is preferable.
In addition, the supply amount of the reaction raw material is not particularly limited, but the present invention is a value obtained by dividing the supply amount of the reaction raw material by the number of reaction tubes, that is, the reaction raw material supply amount per reaction tube. A particularly excellent effect can be exhibited when the supply amount is 5 mol / hr or more.

  The method of supplying the raw material gas to the reactor during start-up or during steady operation may be selected as appropriate depending on the form of the reaction raw material. For example, when the reaction raw material is a liquid, the raw material may be volatilized and supplied using a kettle-type reboiler or a stripper. Further, when the reaction raw material is a gas, it may be supplied to the reactor as it is using a pressure difference, or may be supplied to the reactor by performing an operation of pushing with a compressor. Furthermore, the raw material gas may be preheated before the raw material gas is supplied to the reactor. However, when the raw material gas is preheated using an external heat exchanger or the like, problems such as an increase in the cost of the heat exchanger and an increase in pressure loss occur.

  Examples of the heat medium introduced into the space of the reactor include salt melts such as potassium nitrate and sodium nitrite, but are not particularly limited, and a suitable one may be selected according to the set temperature and pressure environment. .

  As the heat medium circulation facility, a heat medium tank for storing the heat medium may be provided and circulated in the reactor space via a pump, or a plurality of pumps may be provided to control the circulation flow rate. Also good. Furthermore, as shown in FIG. 1, the pump 18 may be directly connected to the reactor 10 to omit the heat medium tank. One series of heat medium circulation facilities may be provided, or two or more series may be provided.

As a method for introducing the heat medium, a method of uniformly introducing from the circumference of the reactor, a method of introducing from a plurality of nozzles, or a method of introducing from a single nozzle may be used. It may be used.
When a nozzle is used, it is preferable that the inlet (heat medium inlet) to the reactor has an angle and is introduced as uniformly as possible.

  The flow direction of the source gas and the flow direction of the heat medium can be appropriately selected from a co-flow type, a counter flow type, a cross flow type, and the like. However, in general, the reaction rate on the side to which the raw material gas is supplied is large, and the reaction rate on the side on which the reaction product gas is discharged is easily influenced by the reaction history in the middle. It is preferable to use a mold.

As the catalyst used in the present invention, for example, an oxidation reaction using isobutylene as a reaction raw material to generate methacrolein, an oxidation reaction using propylene as a reaction raw material to generate acrolein, and the like are represented by the following formula (I). A solid catalyst having a composition as described above is suitable, but is not particularly limited as long as it is suitable for the intended reaction.
_{Mo a Bi b Fe c M d} X 1 e Y 1 f Z 1 g Si h O i ··· (I)

In formula (I), Mo, Bi, Fe, Si and O each represent molybdenum, bismuth, iron, silicon and oxygen, M represents at least one element selected from the group consisting of cobalt and nickel, and X ¹ Represents at least one element selected from the group consisting of chromium, lead, manganese, calcium, magnesium, niobium, silver, barium, tin, tantalum and zinc, and Y ¹ represents phosphorus, boron, sulfur, selenium, tellurium, cerium. And at least one element selected from the group consisting of tungsten, antimony and titanium, and Z ¹ represents at least one element selected from the group consisting of lithium, sodium, potassium, rubidium, cesium and thallium.
a, b, c, d, e, f, g, h, and i represent the atomic ratio of each element. When a = 12, b = 0.01-3, c = 0.01-5, d = 1 -12, e = 0 to 8, f = 0 to 5, g = 0.001 to 2, h = 0 to 20, and i is an oxygen atomic ratio necessary to satisfy the valence of each component. is there.

In addition, a solid catalyst having a composition represented by the following formula (II) is suitable for an oxidation reaction that uses (meth) acrolein as a reaction raw material and generates (meth) acrylic acid. If it is suitable for, it will not be specifically limited.
_{Mo j P k V l Cu m} X 2 n Y 2 o Z 2 p O q ··· (II)

In the formula (II), Mo, P, V, Cu and O represent molybdenum, phosphorus, vanadium, copper and oxygen, respectively, and X ² represents antimony, bismuth, arsenic, germanium, zirconium, tellurium, selenium, silicon, tungsten, Represents at least one element selected from the group consisting of boron and silver, and Y ² represents at least one element selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum Z ² represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium.
j, k, l, m, n, o, p, and q represent the atomic ratio of each element. When j = 12, k = 0.5 to 3, l = 0.01 to 3, m = 0 to 2 , N = 0-3, o = 0-3, p = 0.01-3, and q is the oxygen atomic ratio necessary to satisfy the valence of each component.

There are no particular restrictions on the shape and size of the catalyst, and it is possible to use a spherical, cylindrical, ring-shaped, star-shaped, or the like molded with a normal tableting machine, extrusion machine, granulator or the like. it can. Further, a supported catalyst in which a catalytically active substance is supported on a support having the above-described shape may be used.
When two or more catalyst groups are used, the shape of the catalyst included in each catalyst group may be different for each catalyst group, but the same shape is preferable because the manufacture of the catalyst is simplified.

  When the catalyst is filled into the reaction tube and the catalyst layer is formed, the catalyst is diluted with an inert carrier such as silica, alumina, silica-alumina, silicon carbide, titania, magnesia, ceramic balls, and stainless steel. Can also be used.

Further, an inert material layer may be provided between the end of the reaction tube on the source gas inlet side and the catalyst layer for the purpose of supporting the catalyst, preheating the source gas, and the like.
The inert material layer is made of only an inert material. The inert substance may be any substance that does not contribute to the target oxidation reaction, such as silica, alumina, silica-alumina, silicon carbide, titania, magnesia, ceramic balls, and stainless steel. In particular, in the case where the catalyst concentration is diluted with an inert carrier in order to adjust the average activity of the catalyst layer, if the same inert substance as the inert carrier is used, extraction after the completion of the reaction, The sieving operation is convenient and convenient.

  As described above, according to the start-up method of the present invention, the time required for the reaction raw material supply amount to reach 80% after reaching 30% of the reaction raw material supply amount in steady operation is 5 hours or more, The temperature of the heat medium that is specified to be less than 20 hours and that is introduced into the space of the reactor during start-up and the temperature of the heat medium that is introduced into the space during steady operation is expressed by the above equation (1). By defining so as to satisfy, it is possible to suppress the generation of a low temperature region in the catalyst layer in the reactor. As a result, the temperature distribution of the heat medium can be suppressed to a minimum, the occurrence of hot spots can be suppressed, and startup can be performed in a short time.

  Further, the present invention is suitable for an oxidation reaction having a remarkably large heat of oxidation reaction, such as a reaction of generating (meth) acrolein from isobutylene or propylene, or generating (meth) acrylic acid from (meth) acrolein. It is particularly suitable for an oxidation reaction for producing (meth) acrylic acid from (meth) acrolein.

Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these.
“T _hmin ”, “T _hmax ”, “T _s ”, “t _L ”, “ΔT”, “ΔT maximum value”, and “ΔT distribution” in Examples and Comparative Examples are defined as follows. The

The "T _hmin" refers to a minimum temperature of the heat medium introduced into the reactor space while performing the startup, the "T _hmax", introduced into the reactor space while performing startup Is the maximum temperature of the heat medium to be used.
“T _s ” is the temperature of the heat medium introduced into the reactor space during steady operation.
“T _L ” is the time required for the reaction raw material supply amount to reach 80% after reaching 30% of the reaction raw material supply amount in steady operation.

The temperature of the catalyst layer is measured by a thermocouple inserted in a protective tube installed at the center of the cross section perpendicular to the tube axis direction of the reaction tube. The protective tube is isolated from the reaction system, and the temperature measurement position can be changed by adjusting the length of the thermocouple to be inserted. “ΔT” is the difference between the temperature of the catalyst layer and the temperature of the heat medium bath measured at this time (ΔT = temperature of the catalyst layer−temperature of the heat medium bath).
The “temperature of the heat medium bath” is the temperature of the heat medium in the space of the reactor. The heat medium in the space of the reactor may have a slightly uneven distribution in temperature depending on the form of the reactor, reaction conditions, and the flow state of the heat medium. When the degree of this non-uniform distribution is small, the average temperature of the heat medium in the space of the reactor may be adopted as the “heat medium bath temperature”. However, when the degree of non-uniform distribution is large, the temperature of the heat medium in the vicinity of the catalyst layer is measured according to the position of the catalyst layer, and this is used as “temperature of the heat medium bath” to obtain ΔT.

The “ΔT maximum value” is a value obtained by subtracting the temperature of the heat medium introduced into the reactor from the maximum temperature among the measured temperature of the catalyst layer.
The “ΔT distribution” is a value obtained by subtracting the minimum value from the maximum value among the temperatures of the plurality of catalyst layers at the same distance from the inflow direction of the raw material gas. In addition, it can be judged that the larger the value of the ΔT distribution, the larger the temperature distribution of the heat medium in the reactor, and the formation of the low temperature region and the high temperature region proceeds.

[Example 1]
The reactor 10 shown in FIG. 1 was used for the gas phase catalytic oxidation reaction.
As the catalyst, a catalyst for synthesizing methacrylic acid by gas phase catalytic oxidation of methacrolein having a composition represented by the above formula (II) and having a cylindrical shape with a diameter of 5 mm and a height of 5 mm was used. In addition, atomic ratios other than oxygen of the catalyst are as follows.
_{Mo 12 P 1.5 V 0.5 Cu 0.3} Te 0.1 Fe 0.4 Cs 1.0

3500 g of each catalyst tube was charged into the reactor 10 having 5 segmental baffle plates 13 having 20000 reaction tubes 12 having an inner diameter of 25.4 mm and a length of 6 m to form a catalyst layer. . Note that alumina spheres having a diameter of 6 mm were filled in the cavity of the reaction tube (between the end on the raw material gas inlet side and the catalyst layer).
Further, a thermocouple was inserted into the catalyst layer of the reaction tube 12, and the temperature of the catalyst layer was measured. As shown in FIG. 2, the measurement point was set at a position (measurement points A and B) separated from each baffle plate by 100 mm downward.

In the space 11a of the reactor 10, a salt melt composed of 50% by mass of potassium nitrate and 50% by mass of sodium nitrite was introduced as a heat medium and circulated in the space 11a.
As a reaction raw material, methacrolein was used. The flow rate of the raw material gas per reaction tube and the raw material when the supply amount of the reaction raw material reaches 30%, 80% and 100% of the supply amount of the reaction raw material during steady operation (that is, during steady operation) Table 1 shows the concentration of the reaction raw material (methacrolein) and oxygen in the gas.

Under the conditions shown in Table 2 (“T _hmin ”, “T _hmax ”, “T _s ”, and “t _L ”), start-up of the gas phase catalytic oxidation reaction of methacrolein was performed as follows.
During startup, if the ΔT maximum value becomes high, the catalyst may cause a runaway reaction. If the ΔT maximum value exceeds 50 ° C, the supply amount of the reaction raw material is not increased, and the ΔT maximum value is reduced to 50 ° C or less. After confirming the decrease, the supply amount of the reaction raw material was increased. Further, the control upper limit value of the ΔT maximum value was set to 60 ° C., and when the upper limit value was exceeded, the supply of the reaction raw material was immediately stopped and the reaction was stopped.
The supply amount of the reaction raw material was increased stepwise by 10% from 0% to the supply amount in steady operation. The supply amount of the reaction raw material was increased after the ΔT maximum value became constant. Here, “the ΔT maximum value becomes constant” means a state in which the temperature change of the ΔT maximum value is within a range of ± 1.0 ° C. over 30 minutes.
The steady operation was performed after the supply amount of the reaction raw material reached the supply amount in the steady operation and the ΔT maximum value became constant.

  A ΔT maximum value and a ΔT distribution were obtained when the supply amount of the reaction raw material reached 80% of the supply amount in the steady operation. The results are shown in Table 2. Moreover, the time (start-up time) required from the start of supply of the raw material gas to the transition to steady operation was 60 hours.

[Examples 2 and 3]
Start-up of gas phase catalytic oxidation reaction of methacrolein in the same manner as in Example 1 except that the conditions shown in Table 2 (“T _hmin ”, “T _hmax ”, “T _s ”, and “t _L ”) were changed. Went.
ΔT maximum value and ΔT distribution at the time when the supply amount of the reaction raw material reaches 80% of the supply amount in the steady operation, and the time (startup time) required from the start of the supply of the raw material gas to the transition to the steady operation It shows in Table 2.

[Comparative Examples 1-4]
Start-up of gas phase catalytic oxidation reaction of methacrolein in the same manner as in Example 1 except that the conditions shown in Table 2 (“T _hmin ”, “T _hmax ”, “T _s ”, and “t _L ”) were changed. Went.
ΔT maximum value and ΔT distribution at the time when the supply amount of the reaction raw material reaches 80% of the supply amount in the steady operation, and the time (startup time) required from the start of the supply of the raw material gas to the transition to the steady operation It shows in Table 2.

As is clear from Table 2, in the case of Example 1, the ΔT maximum value was 21.2 ° C., and the ΔT distribution was 8.2 ° C. And it shifted to the steady operation in 60 hours from the start of the supply of the raw material gas without causing any problems until the steady operation.
In Example 2, the ΔT maximum value was 20.9 ° C., and the ΔT distribution was 8.2 ° C. And it shifted to steady operation in 62 hours from the start of supply of the raw material gas without causing any problems until steady operation.
In the case of Example 3, the ΔT maximum value was 24.8 ° C., and the ΔT distribution was 10.9 ° C. And it shifted to steady operation in 45 hours from the start of supply of raw material gas, without causing a problem until steady operation.
Thus, in each Example, the temperature distribution of the heat medium in the reactor could be suppressed to the minimum, and the generation of hot spots could be suppressed. And it was possible to start up in a short time without any problems until steady operation.

On the other hand, in the case of Comparative Example 1, the ΔT maximum value is 33.6 ° C., the ΔT distribution is 7.0 ° C., and the supply amount of the reaction raw material is increased until the ΔT maximum value decreases (hereinafter referred to as “load-up”). ) Was interrupted. As a result, it took 140 hours from the start of the supply of the raw material gas to the transition to the steady operation.
In the case of Comparative Example 2, the ΔT maximum value was 34.7 ° C., the ΔT distribution was 14.0 ° C., and the load-up was interrupted until the ΔT maximum value decreased. As a result, it took 200 hours from the start of supply of the raw material gas to the transition to steady operation.
In the case of Comparative Example 3, the ΔT maximum value was 25.6 ° C., and the ΔT distribution was 15.4 ° C. In Comparative Example 3, after the supply amount of the reaction raw material reaches 80% of the supply amount in the steady operation, the temperature of the heat medium must be increased to maintain the reaction amount until the transition to the steady operation. There wasn't. As a result, a hot spot was generated, and the load up was interrupted until the ΔT maximum value decreased. Therefore, it took 172 hours from the start of the supply of the raw material gas to the transition to the steady operation.
In the case of Comparative Example 4, the ΔT maximum value was 20.0 ° C., and the ΔT distribution was 11.5 ° C. In Comparative Example 4, after the supply amount of the reaction raw material reaches 80% of the supply amount in the steady operation, there is no problem until the transition to the steady operation, and the steady state is reached in 56 hours from the start of the supply of the raw material gas. Moved to driving. However, a hot spot was generated immediately after the transition to steady operation, and the supply amount of the raw material gas had to be reduced immediately. It took 200 hours to load up again and shift to steady operation. That is, in the case of Comparative Example 4, the total startup time was 256 hours.

  10: multi-tube heat exchanger type reactor, 11: barrel, 11a: space, 12: reaction tube, 13: baffle plate, 14: raw material gas inlet, 15: reaction product gas outlet, 16: heat medium inlet, 17 : Heat medium outlet, 18: Pump.

Claims (3)

In the cylinder of the multitubular heat exchanger type reactor, there are 10,000 to 35,000 reaction tubes filled with a catalyst inside, a space formed between the reaction tubes and through which the heat medium flows, and in the space Using a multi-tube heat exchanger type reactor equipped with 1 to 5 baffle plates that change the flow direction of the heat medium, while introducing the heat medium into the space, In a startup method when supplying a raw material gas containing (meth) acrolein and obtaining (meth) acrylic acid as a reaction product gas by a gas phase catalytic oxidation reaction,
Increasing the supply amount of the reaction raw material so that the maximum value of the difference (ΔT) between the temperature of the catalyst layer of the reaction tube and the temperature of the heat medium in the space does not exceed 50 ° C.,
The time required for the supply amount of the reaction raw material to reach 80% after reaching 30% of the supply amount of the reaction raw material in steady operation is 5 hours or more and less than 20 hours,
In addition, the temperature (T _h ) of the heat medium introduced into the space during the transition from the start of supply of the raw material gas to the steady operation, and the temperature (T _s ) of the heat medium introduced into the space during the steady operation. Satisfies the following formula (1).
−5 <(T _h −T _s ) <2 (1) The start-up method according to claim 1, wherein the catalyst is a catalyst having a composition represented by the following formula (II).
_{Mo j P k V l Cu m} X 2 n Y 2 o Z 2 p O q ··· (II)
(In the formula (II), Mo, P, V, Cu and O represent molybdenum, phosphorus, vanadium, copper and oxygen, respectively, and X ² represents antimony, bismuth, arsenic, germanium, zirconium, tellurium, selenium, silicon and tungsten. Represents at least one element selected from the group consisting of boron and silver, and Y ² is at least one selected from the group consisting of iron, zinc, chromium, magnesium, tantalum, manganese, cobalt, barium, gallium, cerium and lanthanum Z ² represents at least one element selected from the group consisting of potassium, rubidium, cesium and thallium, j, k, l, m, n, o, p and q are atoms of each element Represents the ratio, and when j = 12, k = 0.5-3, l = 0.01-3, m = 0-2, n = 0-3, o = To 3, a p = 0.01 to 3, q is an oxygen atom ratio required for satisfying the valency of each component.) A method for producing (meth) acrylic acid, comprising using the start-up method according to claim 1 or 2 and supplying a raw material gas containing (meth) acrolein as a reaction raw material to a reaction tube to perform gas phase catalytic oxidation.

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