Method for producing (meth) acrolein or (meth) acrylic acid

Abstract

Provided is a method for producing (meth) acrolein or (meth) acrylic acid with which it is possible to perform an oxidation reaction in a stable state while reducing the concern of catalyst deterioration or uncontrolled oxidation reaction at the time of restart after shutdown. A method for producing (meth) acrolein or (meth) acrylic acid using a fixed bed reactor provided with a heat medium and a catalyst layer, the method comprising (i) operating and supplying a raw material gas to the fixed bed reactor with the temperature of the heat medium being Ta [DEG C] and the supply rate of the raw material gas being maximum A [Nm3 / hr], (ii) shutting down, and (ii) supplying the raw material gas to the fixed bed reactor with the temperature of the heat medium being Ta [DEG C] and the supply rate of the raw material gas being maximum A [Nm3 / hr]. (iii) stopping the supply of the raw material gas to the fixed bed reactor, and (ii-1) restarting the operation, restarting the supply of the raw material gas to the fixed bed reactor, and increasing the supply speed of the raw material gas to a stable operation state; the maximum temperature of the temperature Tb [DEG C] of the heat medium in the restart operation (ii-1) is higher than Ta [DEG C].

Description

Technical Field

[0001] This invention relates to methods for manufacturing (meth)acrylaldehyde or (meth)acrylic acid. Furthermore, this invention relates to methods for manufacturing (meth)acrylic acid using (meth)acrylaldehyde and methods for manufacturing (meth)acrylates using (meth)acrylic acid. Background Technology

[0002] Traditionally, acrylic acid has been produced by using a fixed-bed reactor (hereinafter also referred to as a "reactor") filled with a gas-phase oxidation catalyst and by a two-step gas-phase catalytic oxidation reaction of propylene, or by using a two-step gas-phase catalytic oxidation reaction of isobutylene. In the gas-phase catalytic oxidation reaction using these reactors, the feed gas is circulated relative to the catalyst bed formed in the reaction tube of the reactor and heated by a heat medium.

[0003] These gas-phase catalytic oxidation reactions using reactors are typically carried out continuously. Temporary shutdowns (stopping the gas-phase catalytic oxidation reaction) are sometimes necessary for troubleshooting during startup or stable operation (steady-state operation), reactor maintenance, or air treatment of the gas-phase oxidation catalyst. Furthermore, while the gas-phase catalytic oxidation reaction is restarted after a shutdown, it is not preferable to use the same restart temperature conditions as the initial startup. That is, the catalyst has already been activated at the restart temperature compared to the initial startup. Therefore, if the temperature of the heat transfer medium is the same as the initial startup temperature, the maximum temperature of the catalyst bed (hot spot temperature) becomes higher than the desired temperature range, raising concerns about catalyst degradation or runaway oxidation reaction.

[0004] Patent Document 1 describes a method for producing corresponding reactants by catalytic gas-phase oxidation of reactant gases using a fixed-bed reactor equipped with a catalyst. The reactor is started to produce the reactants for a period of time, then shut down and restarted. In a similar method described in Patent Document 1, stable operation is achieved by controlling the partial pressure of water vapor to maintain the temperature of the heat medium after shutdown at 2°C or 3°C higher than the temperature before shutdown (see Example 1). While the sublimation of the catalyst components is suppressed according to the method described in Patent Document 1, the aforementioned problems are not fully resolved.

[0005] Patent Document 2 discloses a method for manufacturing oxidation products, characterized by using a fixed-bed reactor equipped with a catalyst, wherein the temperature of the heat medium at maximum load during restart after shutdown is lower than the temperature of the heat medium at maximum load during initial startup. However, using the method described in Patent Document 2, the maximum temperature of the catalyst layer may actually increase depending on the location of the hot spots in the catalyst layer, thus failing to solve the aforementioned problem.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2009-263352

[0009] Patent Document 2: Japanese Patent Application Publication No. 2017-178817 Summary of the Invention

[0010] The present invention was made in view of the above-mentioned problems, and its object is to provide a method for producing at least one oxidation product selected from (meth)acrolein and (meth)acrylic acid, which can reduce concerns about the deterioration of the gas-phase oxidation catalyst or the runaway of the oxidation reaction during restart after shutdown and carry out the oxidation reaction in a stable state. Furthermore, the present invention provides a method for producing (meth)acrylic acid or (meth)acrylate using (meth)acrolein or (meth)acrylic acid obtained by such a method.

[0011] The present invention comprises the following components:

[0012] [Composition 1]

[0013] A method for producing (meth)acrylaldehyde or (meth)acrylic acid using a fixed-bed reactor equipped with a heat transfer medium and a catalyst bed, comprising the following (i) to (iii-1):

[0014] (i) Operation: Set the temperature of the above-mentioned heat medium to Ta [°C], and set the supply rate of the raw material gas to the maximum A [Nm]. 3 / hr], supplying the above-mentioned raw material gas to the above-mentioned fixed-bed reactor,

[0015] (ii) Shutdown, ceasing the supply of the aforementioned feed gas to the fixed-bed reactor, and

[0016] (iii-1) Restart the operation, resume the supply of the raw material gas to the fixed bed reactor, and increase the supply rate of the raw material gas to a stable operating state.

[0017] The highest temperature Tbmax of the heat medium in the above restart operation (iii-1) is higher than that of Ta [°C].

[0018] [Composition 2]

[0019] According to the method for manufacturing (meth)acrylonitrile or (meth)acrylic acid as described in composition 1, after the above-mentioned restart operation (iii-1), the following (iii-2) is performed:

[0020] (iii-2) Re-stabilize the operation, set the temperature of the above-mentioned heat medium to Tc [°C], and set the supply rate of the above-mentioned raw material gas to the maximum C [Nm]. 3 [ / hr], supplying the above-mentioned raw material gas to the fixed-bed reactor.

[0021] [Composition 3]

[0022] According to the manufacturing method of (meth)acrylaldehyde or (meth)acrylic acid described in configuration 2, in the above-mentioned re-stabilization operation (iii-2), when the length of the long side of the catalyst layer is set as L1 and the distance from the end of the raw material gas inlet side of the catalyst layer to the position where the temperature difference between the catalyst layer and the heat medium reaches its maximum (ΔTmax) is set as L2, L2 / L1 is 0.50 or less.

[0023] [Composition 4]

[0024] According to the manufacturing method of (meth)acrylonitrile or (meth)acrylic acid as described in any one of 1 to 3, in the above-mentioned restart operation (iii-1), the supply rate of the raw material gas when the temperature of the heat medium reaches the above-mentioned Tbmax [°C] is set to B [Nm]. 3 When [ / hr], A×0.50≤B≤A×0.80 is satisfied.

[0025] [Component 5]

[0026] According to the method for manufacturing (meth)acrylonitrile or (meth)acrylic acid as described in any one of 1 to 4, the difference between the above-mentioned Tbmax [°C] and the above-mentioned Ta [°C] (Tbmax - Ta [°C]) is in the range of 2°C to 7°C.

[0027] [Composition 6]

[0028] According to the method for manufacturing (meth)acrylonitrile or (meth)acrylic acid as described in any one of 2 to 5, the difference between the above-mentioned Tc [°C] and the above-mentioned Ta [°C] (Tc-Ta [°C]) is in the range of 0°C to 3°C.

[0029] [Composition 7]

[0030] According to the method for manufacturing (meth)acrylonitrile or (meth)acrylic acid as described in any one of 2 to 6, wherein the maximum supply rate A [Nm] of the raw material gas in the above-mentioned operation (i) is... 3 / hr] and the maximum supply rate C [Nm] of the above-mentioned raw material gas in the above-mentioned re-stabilization operation (iii-2). 3 [ / hr] satisfies A×0.80<C<A×1.2.

[0031] [Composition 8]

[0032] According to the method for manufacturing (meth)acrylaldehyde or (meth)acrylic acid as described in any one of 1 to 7, the supply of the raw material gas in the restart operation (iii-1) is restarted within 9,000 hours from the start of the supply of the raw material gas for the above-mentioned operation (i).

[0033] [Composition 9]

[0034] According to the method for manufacturing (meth)acrylaldehyde or (meth)acrylic acid as described in any one of 1 to 8, the fixed-bed reactor comprises a reaction tube having the catalyst layer inside and a heat medium outside the reaction tube.

[0035] [Composition 10]

[0036] A method for manufacturing (meth)acrylic acid includes a step of oxidizing (meth)acrylaldehyde manufactured by any one of the methods described in 1 to 9.

[0037] [Composition 11]

[0038] A method for manufacturing a (meth)acrylate includes a step of esterifying (meth)acrylate manufactured by any one of the methods described in 1 to 10.

[0039] According to the present invention, a method for producing at least one oxidation product selected from (meth)acrolein and (meth)acrylic acid can be provided, which can reduce concerns about degradation of the gas-phase oxidation catalyst or runaway oxidation reaction during restart after shutdown and allow the oxidation reaction to proceed in a stable state. Furthermore, according to the present invention, (meth)acrylic acid or (meth)acrylates can be produced using (meth)acrolein or (meth)acrylic acid obtained by such a method. Attached Figure Description

[0040] Figure 1 This is a schematic diagram illustrating the configuration of a fixed-bed reactor according to one embodiment of the present invention.

[0041] Figure 2 This is a conceptual diagram used to illustrate the ΔT distribution in diluted and undiluted layers.

[0042] Figure 3 This is a conceptual diagram used to illustrate the ΔT distribution in the diluted and undiluted layers of the invention in (A) the present invention and (B) the comparative example.

[0043] Figure 4 This is a conceptual diagram used to illustrate the various components of the manufacturing method of the present invention. Detailed Implementation

[0044] <Methods for manufacturing (meth)acrylaldehyde or (meth)acrylic acid>

[0045] This invention relates to a method for producing (meth)acrylaldehyde or (meth)acrylic acid by using a fixed-bed reactor equipped with a heat medium and a catalyst layer to carry out a gas-phase catalytic oxidation reaction of propylene and / or isobutylene, etc. For example... Figure 4 As shown, the manufacturing method of the present invention includes at least the following (i) to (iii-1):

[0046] (i) Operation: Set the temperature of the heat medium to Ta [°C] and the supply rate of the raw material gas to the maximum A [Nm]. 3 / hr], supplying feed gas to the fixed-bed reactor,

[0047] (ii) Shutdown, stopping the supply of feed gas to the fixed-bed reactor, and

[0048] (iii-1) Restart the operation, resume the supply of raw material gas to the fixed bed reactor, and increase the supply rate of raw material gas to a stable operating state.

[0049] It should be noted that in this invention, "(meth)acrylaldehyde" refers to both methacrolein and acrolein, and "(meth)acrylic acid" refers to both methacrylic acid and acrylic acid. Therefore, the method for producing (meth)acrylaldehyde or (meth)acrylic acid of this invention is a method for producing at least one oxidation product selected from methacrolein, acrolein, methacrylic acid, and acrylic acid by a gas-phase catalytic oxidation reaction of propylene and / or isobutylene, etc. The invention will now be described in detail.

[0050] [Fixed-bed reactor]

[0051] The fixed-bed reactor used in this invention is not particularly limited, and conventional reactors used in the manufacture of acrylic acid and the like can be used. Figure 1 This is a schematic diagram illustrating the configuration of a fixed-bed reactor according to one embodiment of the present invention. Figure 1As shown, reactor 1 includes at least a reaction tube 3 with a catalyst layer 2 inside, and a heat medium bath 4 on the outside of the reaction tube 3 through which a heat medium is introduced and circulated. In a gas-phase catalytic oxidation reaction using such a reactor 1, a mixed gas containing a feed gas, oxygen, and inactive gases (nitrogen, carbon dioxide, etc.) is introduced into the reaction tube 3 through the feed gas inlet 5. Then, the reaction tube 3 is heated by the heat medium present on the outside of the reaction tube 3, causing the feed gas to undergo a gas-phase catalytic oxidation reaction, thereby obtaining oxidation products. It should be noted that since the gas-phase catalytic oxidation reaction in this invention is an exothermic reaction, the catalyst layer inside the reaction tube is heated by the heat medium from the start of the reaction until the reaction proceeds to a certain extent. On the other hand, if the oxidation reaction proceeds to a certain extent, the temperature of the catalyst layer becomes higher than the temperature of the heat medium. In this case, it is more accurate to say that the catalyst layer is slowly heated or temperature-controlled by the heat medium rather than being heated by the heat medium. That is, in this invention, "heating the reaction tube by the heat medium" strictly includes the meaning of the catalyst layer inside the reaction tube being slowly heated or temperature-controlled by the heat medium.

[0052] In this invention, the gas-phase catalytic oxidation reaction can be a so-called single-flow method, that is, the generated oxidation products are recovered, and the by-product gas (hereinafter also referred to as "waste gas"), which is mainly composed of other components, i.e., inactive gases and contains oxygen and unreacted raw material gases, is treated harmlessly by a prescribed method and discharged outside the system. Alternatively, the gas-phase catalytic oxidation reaction of this invention can also be a so-called waste gas recycling method, in which part or all of the aforementioned waste gas is reused as a mixed gas introduced into the reactor. Furthermore, the reactor structure is not particularly limited; for example, it can be a single-stage reactor, a series multi-stage reactor consisting of an independent first-stage reactor and a second-stage reactor connected by piping, or an integrated multi-stage reactor consisting of an integrated first-stage reactor and a second-stage reactor.

[0053] The reactor used in the manufacturing method of the present invention for forming the catalyst layer is not particularly limited, and can be a multi-tube reactor comprising multiple reaction tubes filled with catalyst as a catalyst layer and in which a heat medium flows between the multiple reaction tubes. Alternatively, it can be a plate reactor, etc., comprising a pair of heat-conducting plates in which the catalyst is filled in the form of a catalyst layer between them and in which a heat medium flows outside the heat-conducting plates. It should be noted that, in this embodiment, for ease of explanation, [the following is used:] Figure 1 The reactor 1 shown has one reaction tube and is used for gas-phase catalytic oxidation reaction.

[0054] [catalyst]

[0055] The gas-phase oxidation catalyst used as the catalyst layer can be any general catalyst without particular limitation. For example, conventionally known catalysts such as composite oxides containing molybdenum and bismuth can be used, and composite oxides represented by the following formula (I) are preferred.

[0056] Mo a Bi b Fe c A d X e Y f Z g O h …(I)

[0057] In formula (I), Mo, Bi, Fe, and O represent molybdenum, bismuth, iron, and oxygen, respectively; A represents at least one element selected from nickel and cobalt; X represents at least one element selected from magnesium, zinc, chromium, manganese, tin, and lead; Y represents at least one element selected from phosphorus, boron, sulfur, tellurium, silicon, germanium, cerium, niobium, titanium, zirconium, tungsten, and antimony; and Z represents at least one element selected from potassium, sodium, rubidium, cesium, and thallium. Furthermore, a, b, c, d, e, f, g, and h represent the atomic ratios of each element. When a = 12, 0.1 ≤ b ≤ 5, 0.1 ≤ c ≤ 5, 1 ≤ d ≤ 12, 0 ≤ e ≤ 10, 0 ≤ f ≤ 10, and 0.01 ≤ g ≤ 3. h represents the atomic ratio of oxygen required to satisfy the valence requirements of the above elements. When a = 12, the preferred atomic ratios of each element are 0.2 ≤ b ≤ 3, 0.5 ≤ c ≤ 4, 2 ≤ d ≤ 10, 0 ≤ e ≤ 8, 0 ≤ f ≤ 8 and 0.1 ≤ g ≤ 2.

[0058] There are no particular limitations on the preparation method of the catalyst; any conventionally known method can be used as long as there is no significant inhomogeneity in the composition. Furthermore, there are no particular limitations on the raw materials used in the preparation of the catalyst; nitrates, carbonates, acetates, ammonium salts, oxides, and halides of the elements constituting the catalyst can be used in combination. For example, examples of raw material compounds for molybdenum include ammonium paramolybdate, molybdenum trioxide, molybdic acid, and molybdenum chloride. Examples of raw material compounds for bismuth include bismuth nitrate, bismuth oxide, bismuth acetate, and bismuth hydroxide. The raw material compounds for the catalyst can use one element alone or in combination of two or more elements constituting the catalyst.

[0059] The catalyst used in this invention can be unsupported, or it can be a supported catalyst supported on an inactive support such as silica, alumina, silica-alumina or silicon carbide, or a catalyst diluted with these inactive supports.

[0060] The catalyst prepared as described above is filled into the interior of the reaction tube of the reactor, forming a catalyst layer inside the reaction tube. It should be noted that, in this invention, "catalyst layer" refers to a region within the reaction tube that contains at least the catalyst. That is, as... Figure 1 As shown, not only the region filled with catalyst (undiluted layer 2B) is catalyst layer 2, but also the region where the catalyst is diluted by an inactive support or the like (dilution layer 2A) is catalyst layer 2. However, the empty spaces at both ends of the reaction tube, and the regions filled only with inactive supports or the like, do not actually contain catalyst and are therefore not included in the catalyst layer.

[0061] In the catalyst layer, from the viewpoint of suppressing excessive reaction with the feed gas, it is particularly preferable that the portion formed on the side of the reaction tube near the feed gas inlet is diluted by the aforementioned inactive support. More specifically, such as Figure 1 As shown, preferably, a dilution layer 2A containing catalyst and inactive support is formed on the side of the catalyst layer 2 near the feed gas inlet 5 of the reaction tube, and the remaining portion is an undiluted layer 2B consisting only of catalyst. Alternatively, inactive support layers 6 filled only with inactive support can be formed at both ends of the reaction tube.

[0062] The formation range of the dilution layer, which dilutes the catalyst from the inactive support, is not limited. For example, the length L1 relative to the long side direction (the tube axis direction of the reaction tube) of catalyst layer 2 is not limited. Figure 1 The portion of the catalyst layer shown (from end X to Y) extending 0.1 × L1 to 0.8 × L1 from the end X of the catalyst layer located on the side of the reaction tube where the catalyst layer is formed, near the feed gas inlet, is designated as a dilution layer 2A diluted by an inactive carrier. Furthermore, the portion of the catalyst layer outside this range can be designated as an undiluted layer 2B. From the viewpoint of controlling hotspot locations, the formation range of the dilution layer 2A is preferably 0.2 × L1 to 0.7 × L1 from the end X of the catalyst layer.

[0063] The temperature of the catalyst bed can be determined, for example, by placing a protective tube inside the reaction tube before filling it with catalyst, inserting a thermocouple inside the protective tube, and measuring the temperature of the catalyst bed at various locations during the oxidation reaction. In this method, the protective tube is preferably positioned near the center of a cross-section perpendicular to the axis of the reaction tube. Furthermore, the length of the protective tube needs to exceed the length of the catalyst bed. This method allows for easy measurement of the temperature at all locations within the catalyst bed. It should be noted that when using industrially employed multi-tube reactors, it is practically difficult to measure the temperature of the catalyst bed in all reaction tubes. Therefore, it is sufficient to select multiple reaction tubes that substantially represent the entire reactor and measure the temperature of the catalyst bed within each selected reaction tube.

[0064] [Heat medium]

[0065] The heat medium introduced into the heat medium bath is not particularly limited as long as it can maintain the internal temperature of the reactor at a specified temperature. As a heat medium, molten salts, especially molten mixtures of potassium nitrate and sodium nitrite, are preferred due to their wide usable temperature range, large heat capacity, and low viscosity. The temperature of the heat medium can sometimes exhibit some non-uniformity depending on the reactor shape, reaction conditions, and the flow state of the heat medium. When the degree of non-uniformity is small, the average temperature of the heat medium bath containing the heat medium is defined as the "temperature of the heat medium." On the other hand, when the degree of non-uniformity is large, the temperature obtained by measuring the temperature of the heat medium bath near each catalyst layer based on the position of the catalyst layer is defined as the "temperature of the heat medium."

[0066] [Gas-phase catalytic oxidation reaction]

[0067] In this invention, a mixed gas comprising a feed gas containing reactants, oxygen, and an inert gas (nitrogen, carbon dioxide, etc.) is supplied to a reaction tube, and (meth)acrylic acid or (meth)acrylic acid is produced by a gas-phase catalytic oxidation reaction between the feed gas and the oxygen-containing gas. At least one reactant selected from propylene, isobutylene, tert-butanol (TBA), and methyl tert-butyl ether (MTBE) is used. It should be noted that TBA and MTBE rapidly dehydrate and convert to isobutylene upon being supplied to the reaction tube. Therefore, when using TBA or MTBE as reactants, the same results are expected as when using isobutylene.

[0068] The composition of the mixed gas is not particularly limited, and can be the same as that used in general gas-phase catalytic oxidation reactions. The mixed gas may contain water vapor. Specifically, the composition of the mixed gas used to produce methacrolein by gas-phase catalytic oxidation of a feed gas containing isobutylene may be 1-12% by volume, preferably 4-10% by volume, 3-20% by volume, preferably 4-18% by volume, molecular oxygen, 0-60% by volume, preferably 5-50% by volume, and 20-80% by volume, preferably 30-78% by volume, of inactive gases (nitrogen, carbon dioxide, etc.).

[0069] The composition of the mixed gas used to generate acrolein by gas-phase catalytic oxidation of a raw material gas containing propylene can be 1-12% by volume of propylene, preferably 4-10% by volume of propylene, 3-20% by volume of molecular oxygen, preferably 4-18% by volume of propylene, 0-60% by volume of water vapor, preferably 5-50% by volume of water vapor, and 20-80% by volume of inactive gases (nitrogen, carbon dioxide, etc.), preferably 30-78% by volume of propylene.

[0070] The reaction temperature for the gas-phase catalytic oxidation reaction can be 250℃ to 450℃, preferably 280℃ to 330℃. The reaction pressure for the gas-phase catalytic oxidation reaction can be 20 kPa to 100 kPa, preferably 25 kPa to 90 kPa. The supply rate of the mixed gas containing the feed gas can be, for example, 1.5 Nm. 3 / hr~3.5Nm 3 / hr. It should be noted that, as described below, in this invention, the gas-phase catalytic oxidation reaction can be a multi-step reaction comprising multiple reactions satisfying the various conditions described above.

[0071] The following describes the various operations included in the manufacturing method of the present invention.

[0072] (i) Start-up and stable operation)

[0073] (i) is to set the temperature of the heat medium to Ta [°C] and the supply rate of the raw material gas to the maximum A [Nm]. 3 [ / hr] refers to the operation of supplying feed gas (a mixture of feed gas and feed gas) to the fixed-bed reactor. That is, Ta is the temperature of the heat medium when the feed gas supply rate reaches its maximum A during operation (i). It should be noted that, unless otherwise specified in this specification, "supplying feed gas" means "supplying a mixture of feed gas and feed gas" and "feed rate of feed gas" means "feed rate of the mixture of feed gas and feed gas".

[0074] More specifically, operation (i) includes start-up operation and subsequent stable operation. That is, the catalyst used in gas-phase catalytic oxidation reactions is sometimes unstable in activity at the beginning of the reaction. Therefore, in order to suppress over-oxidation reactions that accompany the abnormal exothermic reaction of the catalyst at the start of the reaction, the following operation is typically performed at the start of the reaction (start-up): a smaller amount of feed gas is supplied compared to the amount supplied during stable operation, and the supply is slowly (in stages) increased to transition to stable operation. Therefore, as Figure 4 As shown, operation (i) includes: start-up operation, which involves gradually increasing the feed gas supply rate to a stable operating state (maximum), and stable operation, which operates at the maximum feed gas supply rate. It should be noted that in... Figure 4 During startup, although the supply rate of raw material gas increases linearly, Figure 4 This is only a conceptual diagram; in reality, the supply rate of the preferred feedstock gas increases in stages. Additionally, Figure 4 The temperatures of the various operating heat transfer media shown are just examples; in this invention, the temperature of the heat transfer media is not limited to... Figure 4 The temperature shown.

[0075] The start-up operation in operation (i) does not necessarily refer to the start-up operation that begins with the initial (first) oxidation reaction. For example, the start-up operation in operation (i) could be the third start-up operation, in which case the fourth start-up operation after shutdown is equivalent to the restart operation (iii-1) described later.

[0076] Operation (i) requires at least setting the temperature of the heat medium to Ta [°C] and the supply rate of the raw material gas to the maximum A [Nm]. 3 The operation of supplying feed gas to the fixed-bed reactor can be carried out by [ / hr]. As a preferred method of operation (i), for example, maintaining the feed gas supply rate at a maximum A [Nm] during stable operation can be cited. 3 The temperature of the heat medium is also maintained at Ta [℃] during [hr].

[0077] Operation (i) may, for example, include a startup operation comprising multiple reactions:

[0078] In the first reaction, the feed gas supply rate is set to A×0.50~A×0.80, preferably A×0.55~A×0.75, for example, A×0.67 [Nm]. 3 / hr] and undergo oxidation reaction;

[0079] In the second reaction, the feed gas supply rate is set to A×0.70~A×0.90, preferably greater than A×0.75 and less than A×0.90, for example, A×0.87 [Nm]. 3 / hr] and carry out oxidation reaction; and

[0080] In the third reaction, the supply rate of the raw material gas is set to A [Nm]. 3 / hr] and undergoes an oxidation reaction.

[0081] Furthermore, in the third reaction described above, the supply rate of the raw material gas reaches the supply rate under stable operating conditions (supply amount 100%, the maximum supply rate A of the raw material gas in operation (i)), and then shifts to stable operation. It should be noted that the above illustrates an example of phased start-up operation; the start-up operation in operation (i) may include two or more reaction steps. Additionally, the supply rate of the raw material gas in each reaction can be set appropriately and is not limited to the supply rates described above.

[0082] (ii) Shutdown

[0083] (ii) is the process of temporarily halting the oxidation reaction described in (i) above, which involves stopping the supply of feed gas to the fixed-bed reactor and moving it to stable operation. It should be noted that during shutdown, it is preferable to stop the supply of feed gas and switch to air at, for example, 0.5 Nm³. 3A supply rate of / hr circulates in the catalyst bed. Additionally, during shutdown, the heat medium can be maintained at, for example, the temperature of the heat medium during operation (i) before shutdown.

[0084] (iii-1) Restart operation)

[0085] (iii-1) is a restart operation that restarts the feed gas supply to the fixed-bed reactor, which was stopped in (ii) above, by increasing the feed gas supply rate to a stable operating state while simultaneously restarting the oxidation reaction. The restart operation (iii-1) is the same as the start-up operation in (i) above. That is, initially, a smaller amount of feed gas is supplied for the oxidation reaction compared to the amount supplied during stable operation, and the feed gas supply is gradually increased. Furthermore, it is preferable to eventually operate at the same feed gas supply rate as the stable operating state (the maximum feed gas supply rate in the start-up operation (iii-1)) and then proceed to the re-stabilization operation described later. In addition, in the restart operation (iii-1), the feed gas supply rate at which the temperature Tb of the heat medium reaches the maximum temperature Tbmax [°C] is set as B [Nm]. 3 When the feed gas supply rate is [A×0.50 / hr], it is preferable to satisfy A×0.50≤B≤A×0.80. That is, after restarting operation, the preferred feed gas supply rate is A×0.50 [Nm]. 3 / hr]~A×0.80[Nm 3 The temperature of the thermal medium at [ / hr] (e.g., the first reaction mentioned above) is Tbmax [°C].

[0086] The restart after shutdown is preferably carried out within 9000 hours from the start of the initial oxidation reaction (start-up) according to the method described in this specification. That is, in the manufacturing method of the present invention, it is preferable to restart the supply of raw material gas in operation (iii-1) within 9000 hours (cumulative time) from the start of the supply of raw material gas for operation (i). Here, "from the start of the supply of raw material gas for operation (i)" means "from the start of the supply of raw material gas for the first (initial) operation (i)". Within 9000 hours from the start of the initial reaction is due to the particularly high activity of the catalyst and the high suppression effect of runaway reactions, etc., of the present invention. It should be noted that the shutdown time in (ii) is not included in the above-mentioned cumulative time.

[0087] (iii-2) Re-stabilize operation

[0088] The manufacturing method of the present invention preferably involves the following restart operation: after restarting operation (iii-1), the temperature of the heat medium is set to Tc [°C], and the supply rate of the raw material gas is set to the maximum C [Nm]. 3 / hr], feed gas is supplied to the fixed-bed reactor. Typically, from the restart (iii-1) to the stabilization (iii-2), the feed gas supply rate becomes the original maximum supply rate, i.e., it becomes the maximum feed gas supply rate A[Nm] during operation (i). 3 The feed gas supply rate is increased at the same rate as [ / hr]. Therefore, the maximum feed gas supply rate C [Nm] during the re-stabilization operation (iii-2) is... 3 [ / hr] Preferably, A×0.80<C<A×1.2, where C can be the same as A. It should be noted that the maximum supply rate C of the raw material gas in the re-stabilized operation (iii-2) is also the maximum supply rate of the raw material gas in the restart operation (iii-1), where the temperature of the heat medium is Tc.

[0089] (Requirement 1)

[0090] The manufacturing method of the present invention is characterized in that the highest temperature Tbmax [°C] of the heat medium in the restart operation (iii-1) is higher than Ta [°C] (hereinafter also referred to as "Requirement 1"). More specifically, Requirement 1 refers to the highest temperature Tbmax [°C] of the heat medium in the restart operation (iii-1) being higher than the maximum supply rate of the raw material gas in operation (i) (A [Nm³]). 3 The temperature of the heat medium, Ta [°C], during stable operation (or, for example, the third reaction mentioned above) at [hr].

[0091] In such Figure 1 In the gas-phase catalytic oxidation reaction shown in the fixed-bed reactor with a catalyst layer consisting of a dilution layer 2A and an undilution layer 2B, the oxidation reaction begins when a feed gas (a mixture containing the feed gas) is supplied. At this time, the catalyst is first diluted by an inactive support in the dilution layer 2A, which serves as the inlet side of the feed gas. Therefore, during a certain stage of the oxidation reaction, the exothermic reaction of the catalyst layer is temporarily suppressed. Then, when the feed gas reaches the undilution layer 2B, the deheating of the oxidation reaction deteriorates, and the catalyst layer exotherms again. That is, in the above-described gas-phase catalytic oxidation reaction, typically, as... Figure 2 As shown, the distribution of ΔT (°C), representing the temperature difference between the catalyst bed and the thermal medium (equivalent to the degree of exothermic reaction of the catalyst), relative to the distance (mm) from the end X of the catalyst bed on the feed gas inlet side, shows peaks P1 and P2 observed on the dilution layer side and the non-dilution layer side, respectively. It should be noted that... Figure 2 This is a conceptual diagram used to illustrate the case where the distribution of ΔT (°C) has two peaks, and does not represent the actual distribution of ΔT (°C) at a distance (mm) from X.

[0092] In this invention, as shown in element 1, by initiating restart operation (iii-1), the temperature of the heat medium in the stage of re-stabilizing operation (iii-2) is made higher than the temperature of the heat medium during stable operation before shutdown (ii), thereby further promoting the oxidation reaction on the dilution layer side near the feed gas inlet during restart operation (iii-1). This allows for a smoothing of the ΔT across the entire catalyst layer and reduces the difference between peak P1 on the dilution layer side and peak P2 on the non-dilution layer side (the absolute value of the ΔT difference). As a result, the overall reaction amount is consistent, and the extent of localized reactions is reduced. That is, according to this invention, the risk of catalyst degradation or runaway oxidation reaction during restart after shutdown can be reduced, allowing the oxidation reaction to proceed in a stable state.

[0093] In this invention, Tbmax [°C] is higher than Ta [°C], and the difference between Tbmax [°C] and Ta [°C] (Tbmax - Ta [°C]) is preferably in the range of 2°C to 7°C. Furthermore, the difference between Tc [°C] and Ta [°C] (Tc - Ta [°C]) is preferably in the range of 0°C to 3°C.

[0094] (Requirement 2)

[0095] In the preferred embodiment of the manufacturing method of the present invention, during the re-stabilization operation (iii-2), when the length of the catalyst layer formed in the reactor along its long side is defined as L1 [mm], and the distance from the end X of the catalyst layer at the feed gas inlet side to the position where the temperature difference between the catalyst layer and the heat medium (temperature of the catalyst layer - temperature of the heat medium) reaches its maximum (ΔTmax) is defined as L2 [mm], L2 / L1 is 0.50 or less (hereinafter also referred to as "Requirement 2"). It should be noted that L2 / L1 is a value greater than 0. That is, as... Figure 3 As shown in (A), in this invention, it is preferable to set the temperature of the heat medium during restart higher and control the hot spots so that the ΔT (ΔTmax) at peak P1 on the dilution layer 2A side is greater than the ΔT at peak P2 on the non-dilution layer 2B side, and to reduce the difference in ΔT between peak P1 and peak P2. This smooths out the temperature difference between the entire catalyst layer and the heat medium, further suppressing localized heat release at the hot spots during restart.

[0096] On the other hand, in the inventions of the comparative examples described later, such as Figure 3 As shown in (B), the ΔT (ΔTmax) at peak P2 on the undiluted layer 2B side is larger than the ΔT at peak P1 on the dilution layer 2A side. Furthermore, the difference in ΔT between peak P1 and peak P2 is greater than that of the present invention. It should be noted that... Figure 3 The ΔT distributions shown in (A) and (B) are conceptual diagrams used to illustrate the difference between L2 / L1 in the invention and the comparative example, and do not represent the actual distribution of ΔT (°C) at a distance (mm) from X.

[0097] The L2 / L1 ratio is preferably 0.10 or higher. More preferably, it is 0.45 or lower, and even more preferably 0.40 or lower. There are no particular limitations on the method for adjusting the location of the hot spot (ΔTmax). For example, methods such as diluting the catalyst packed on the feed gas inlet side with an inactive support, as described above, or filling multiple sections with catalysts of different activities, can be used.

[0098] <Method for manufacturing (meth)acrylic acid>

[0099] The method for producing (meth)acrylic acid of the present invention includes a step of oxidizing (meth)acrylaldehyde produced by the above-described method of producing (meth)acrylic acid of the present invention. The oxidation of (meth)acrylaldehyde can be carried out using known methods. For example, a method for producing (meth)acrylic acid by gas-phase catalytic oxidation of (meth)acrylaldehyde with molecular oxygen in the presence of a suitable catalyst can be cited. In this method, (meth)acrylic acid is produced by contacting a feed gas containing (meth)acrylaldehyde and molecular oxygen with a catalyst. A fixed-bed reactor can be used in this reaction. Specifically, the reaction can be carried out by filling a reaction tube of the reactor with a catalyst and supplying the reaction tube with a feed gas. The catalyst layer can be a single layer, or multiple layers of catalysts with different activities can be filled separately. Furthermore, to control the activity, the catalyst can be diluted with an inactive support before filling.

[0100] The concentration of (meth)acrylaldehyde in the feed gas is not particularly limited, but is preferably 1% to 20% by volume, more preferably 3% by volume, and more preferably 10% by volume. The concentration of molecular oxygen in the feed gas relative to 1 mole of (meth)acrylaldehyde is preferably 0.4 to 4 moles, more preferably 0.5 moles by volume, and more preferably 3 moles by volume. It should be noted that, from an economic point of view, air is preferred as the source of molecular oxygen. If necessary, a gas enriched with molecular oxygen by adding pure oxygen to air can be used. The feed gas can be a gas diluted with inert gases such as nitrogen or carbon dioxide. Furthermore, water vapor can also be added to the feed gas. By reacting in the presence of water vapor, (meth)acrylic acid can be obtained in a higher yield. The concentration of water vapor in the feed gas is preferably 0.1% to 50% by volume, more preferably 1% by volume, and more preferably 40% by volume.

[0101] The contact time between the feed gas and the catalyst is preferably 1.5 to 15 seconds. The reaction pressure is preferably 0.1 MPa(G) to 1 MPa(G), where (G) represents gauge pressure. The reaction temperature is preferably 200°C to 450°C, more preferably 250°C (lower limit) and more preferably 400°C (upper limit).

[0102] <Methods for the manufacture of (meth)acrylates>

[0103] The method for producing (meth)acrylates of the present invention includes a step of esterifying (meth)acrylate produced by the method for producing (meth)acrylic acid or (meth)acrylate of the present invention described above. The esterified (meth)acrylate may be (meth)acrylate obtained by the method for producing (meth)acrylate of the present invention described above. Esterification can be carried out by known methods. The alcohol used in the esterification is not particularly limited, and examples include methanol, ethanol, isopropanol, n-butanol, and isobutanol. Examples of the resulting (meth)acrylates include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate. The esterification reaction can be carried out, for example, in the presence of an acidic catalyst such as a sulfonic acid-type cation exchange resin, and the reaction temperature is preferably 50°C to 200°C.

[0104] Example

[0105] The present invention will now be specifically described by way of examples. However, the present invention is not limited to these examples. It should be noted that "parts" in the examples and comparative examples means "parts by mass".

[0106] <Definition of ΔTmax>

[0107] ΔTmax is defined as follows.

[0108] The temperature of the catalyst layer is measured using a thermocouple (trade name: sheathed thermocouple, manufactured by Okazaki Corporation) inserted into a protective tube located at the center of a cross-section perpendicular to the tube axis of the reaction tube. It should be noted that the protective tube is isolated from the reaction system, and the position for measuring the catalyst layer temperature can be adjusted by changing the length of the inserted thermocouple. The temperature of the heat medium is measured using a resistance temperature sensor (trade name: sheathed resistance temperature sensor, manufactured by Okazaki Corporation). Based on the difference between the measured temperature of the catalyst layer and the temperature of the heat medium bath (ΔT = catalyst layer temperature - heat medium bath temperature), hot spots are detected at that time. Then, in the detected ΔT distribution, locally abnormally high-temperature regions are designated as "hot spots," and the highest temperature ΔT is set as ΔTmax (hot spot) at that time. Furthermore, the position of ΔTmax is the distance (L2) from the end X of the catalyst layer on the feed gas inlet side. It should be noted that in the comparative and exemplary cases, ΔTmax was measured during the stable oxidation reaction phase (re-stabilization) after the start of restart operation and the supply rate of the mixed gas (raw material gas) reached its maximum supply rate.

[0109] <Calculation of Isobutylene Conversion Rate>

[0110] The raw material gas and the reaction product gas were analyzed using a gas chromatograph (trade name: GC-2014, manufactured by Shimadzu Corporation). Furthermore, the conversion rate of the reactant (isobutylene) was calculated using the following formula (i).

[0111] Isobutylene conversion rate (%) = (A / B) × 100···(i)

[0112] Here, "A" represents the number of moles of isobutylene reacting, and "B" represents the number of moles of isobutylene supplied.

[0113] <Preparation of Catalysts>

[0114] Add 500 parts of ammonium molybdate, 23.0 parts of cesium nitrate, 34.3 parts of antimony trioxide, and 38.5 parts of bismuth trioxide to 2000 parts of pure water, heat and stir to prepare solution A.

[0115] In addition, 209.8 parts of ferric nitrate, 102.9 parts of nickel nitrate, and 412.1 parts of cobalt nitrate were added sequentially to 1000 parts of pure water to dissolve them and prepare solution B.

[0116] Next, liquid B was added to liquid A to prepare an aqueous slurry. This aqueous slurry was then dried at 180°C using a spray dryer to produce dry spherical particles with an average particle size of 60 μm. The obtained dry spherical particles were then calcined at 300°C for 1 hour, and further calcined at 510°C for 3 hours, thereby producing a catalyst material in the shape of spherical particles.

[0117] To 100 parts of the obtained catalyst material, 5 parts of hydroxypropyl methylcellulose and 2 parts of curdlan gum were added and dry-mixed. 39 parts of pure water were added to the resulting mixture, and the mixture was kneaded using a mixer until it became a clay-like substance. Next, the resulting mixture was extruded using a piston extruder to form rings with an outer diameter of 5 mm, an inner diameter of 2 mm, and a height of 5 mm, thus producing granular solid oxidation catalyst. The elemental composition of the obtained solid oxidation catalyst, excluding oxygen, is as follows. It should be noted that the elemental composition is calculated based on the amount of catalyst raw materials fed:

[0118] Mo 12 Bi 0.7 Fe 2.2 Sb 1.0 Ni 1.5 Co 6.0 Cs 0.5 .

[0119] <Catalyst Filling>

[0120] In gas-phase catalytic oxidation reactions, the following are used: Figure 1 The reactor shown is a fixed-bed tubular reactor with a reaction tube having an inner diameter of 26.5 mm and a length of 6 m, and a heat medium bath on the outside of the reaction tube. As the heat medium, a salt melt consisting of 50% by mass potassium nitrate and 50% by mass sodium nitrite is used, and the temperature of the heat medium bath is set to 180°C.

[0121] A mixture of 500g of previously prepared solid oxidation catalyst and 400g of inert spheres with an outer diameter of 5.5mm, serving as an inactive support, is filled into the feed gas inlet side of the reaction tube. Then, 1000g of solid oxidation catalyst is filled onto this mixture, forming a catalyst layer with a total length of 4095mm (L1) relative to the tube axis. It should be noted that in the formed catalyst layer, the portion from the end X of the feed gas inlet side of the reaction tube to 1798mm is a dilution layer, and the portion from 1798mm to 4095mm is an undiluted layer.

[0122] While sending oxygen-containing gas, consisting of 9% oxygen, 10% water vapor, and 81% nitrogen, at a space velocity of 240 hr... －1 While the catalyst layer flows, the temperature of the heat medium bath is increased to 350°C at a rate of 50°C / hour and maintained for 10 hours. It should be noted that in this embodiment, the temperature of the heat medium bath refers to the temperature measured using a resistive temperature sensor (trade name: sheathed resistive temperature sensor, manufactured by Okazaki Corporation), and the temperature of the heat medium is the temperature of the heat medium bath. The reaction pressure is 90 kPa.

[0123] The following series of reactions, from startup 1 to restart 5 and re-stabilization 5, were carried out continuously, except for a brief shutdown. The catalyst layer formed in the reaction tube at the start of startup 1 was also carried out without alteration during the process.

[0124] (Startup 1: Compare Example 1 (i))

[0125] The temperature of the heat medium is set to 320°C, and a mixed gas containing the raw material gas is supplied to the reaction tube to start the oxidation reaction of isobutylene.

[0126] As the first reaction, a mixed gas consisting of 4.5% isobutylene, 10.0% oxygen, 10.0% water vapor, and 75.5% nitrogen was introduced at a flow rate of 2.0 Nm. 3 The supply speed is 3 hours per hr.

[0127] Next, as a second reaction, a mixed gas consisting of 5.5% isobutylene, 12.0% oxygen, 10.0% water vapor, and 72.5% nitrogen was introduced at 2.6 Nm. 3 The supply speed is 3 hours per hr.

[0128] Next, as a third reaction, a mixed gas consisting of 6.0 capacity % isobutylene, 13.0 capacity % oxygen, 10.0 capacity % water vapor, and 71.0 capacity % nitrogen was introduced at 3.0 Nm. 3 The gas mixture in the third reaction is supplied at a rate of / hr. The reaction continues at the maximum supply rate A. It should be noted that the maximum supply rate A is reached 8 hours after the start of the oxidation reaction. After the maximum supply rate A is reached, a further 3 hours are passed (11 hours after the start of the oxidation reaction in Start-up 1), and the ΔTmax and isobutylene conversion rates during the stable reaction phase are shown in Table 2. It should be noted that the stable reaction phase specifically refers to the phase where the oxidation reaction proceeds stably through stabilization of ΔTmax, etc.

[0129] (Stable operation 1: Compare with Example 1 (i))

[0130] The conditions for the third reaction described above were continued to carry out a continuous reaction. ΔTmax and the conversion rate of isobutylene at a cumulative reaction time of 1430 hours (before shutdown 1) from the start of the first reaction are shown in Table 2.

[0131] (Stop 1: Compare Example 1 (ii))

[0132] The supply of the mixed gas containing the raw material gas was stopped and the unit was shut down after a cumulative reaction time of 1440 hours.

[0133] During shutdown, maintain the temperature of the heat transfer medium at 320℃, and introduce air at a rate of 0.5 Nm. 3 The catalyst bed is supplied at a rate of / hr. The shutdown lasts for 48 hours. It should be noted that cumulative reaction time is not included during the shutdown.

[0134] [Comparative Example 1]

[0135] (Restart 2 and Re-stabilize Operation 2: Comparative Example 1 (iii-1), (iii-2), Example 1 (i))

[0136] Change the temperature of the heat medium to 313°C, and otherwise carry out the first reaction in the same manner as in Startup 1.

[0137] Next, the temperature of the heat medium is changed to 318°C, and the second reaction is carried out in the same manner as in Startup 1.

[0138] Next, the temperature of the heat medium was set to 320°C, and the third reaction was carried out in the same manner as in Startup 1, continuing the reaction under these conditions. ΔTmax and isobutylene conversion at a cumulative reaction time of 1451 hours (11 hours after the start of the oxidation reaction in Restart 2) are shown in Table 2.

[0139] (Stop 2: Example 1 (ii))

[0140] The supply of the mixed gas containing the raw material gas was stopped and the unit was shut down after a cumulative reaction time of 1460 hours.

[0141] During shutdown, the temperature of the heat transfer medium is maintained at 320℃, and air is propelled at a rate of 0.5 Nm. 3 The catalyst bed is supplied at a rate of / hr. The shutdown lasts for 48 hours. It should be noted that cumulative reaction time is not included during the shutdown.

[0142] [Example 1]

[0143] (Restart 3 and Re-stabilize Operation 3: (iii-1) and (iii-2) of Example 1, and (i) of Comparative Example 2)

[0144] Change the temperature of the heat medium to 327°C, and otherwise carry out the first reaction in the same manner as in Startup 1.

[0145] Next, the temperature of the heat medium is changed to 322°C, and the second reaction is carried out in the same manner as in Startup 1.

[0146] Next, the temperature of the heat medium was set to 320°C, and the third reaction was carried out in the same manner as in start-up 1, continuing the reaction under these conditions. ΔTmax and isobutylene conversion at a cumulative reaction time of 1471 hours (11 hours after the start of the oxidation reaction in restart 3) are shown in Table 2.

[0147] (Stop 3: Compare Example 2 (ii))

[0148] When the cumulative reaction time reaches 1480 hours, the supply of the mixed gas containing the raw material gas is stopped, and the unit is shut down.

[0149] During shutdown, the temperature of the heat transfer medium is maintained at 320℃, and air is propelled at a rate of 0.5 Nm. 3 The catalyst bed is supplied at a rate of / hr. The shutdown lasts for 48 hours. It should be noted that the shutdown time is not included in the cumulative reaction time.

[0150] [Comparative Example 2]

[0151] (Restart 4 and Re-stabilize 4: Comparison of (iii-1) and (iii-2) of Example 2 and (i) of Example 2)

[0152] Change the temperature of the heat medium to 319°C, and otherwise carry out the first reaction in the same manner as in Startup 1.

[0153] Next, the temperature of the heat medium is changed to 319°C, and the second reaction is carried out in the same manner as in Startup 1.

[0154] Next, the temperature of the heat medium was set to 320°C, and the third reaction was carried out in the same manner as in start-up 1, continuing the reaction under these conditions. ΔTmax and isobutylene conversion at a cumulative reaction time of 1491 hours (11 hours after the start of the oxidation reaction in restart 4) are shown in Table 2.

[0155] (Stop 4: Example 2 (ii))

[0156] When the cumulative reaction time reaches 1500 hours, the supply of the mixed gas containing the raw material gas is stopped, and the unit is shut down.

[0157] During shutdown, the temperature of the heat transfer medium is maintained at 320℃, and air is propelled at a rate of 0.5 Nm. 3 The catalyst bed is supplied at a rate of / hr. The shutdown lasts for 48 hours. It should be noted that cumulative reaction time is not included during the shutdown.

[0158] [Example 2]

[0159] (Restart 5 and Re-stabilize 5: (iii-1) and (iii-2) of Example 2)

[0160] Change the temperature of the heat medium to 322°C, and otherwise carry out the first reaction in the same manner as in Startup 1.

[0161] Next, the temperature of the heat medium is changed to 321°C, and the second reaction is carried out in the same manner as in Startup 1.

[0162] Next, the temperature of the heat medium was set to 320°C, and the third reaction was carried out in the same manner as in start-up 1, continuing the reaction under these conditions. ΔTmax and isobutylene conversion at a cumulative reaction time of 1511 hours (11 hours after the start of the oxidation reaction in restart 5) are shown in Table 2.

[0163] Table 1 shows the temperatures of the heat medium during operation (i) to (iii-1) in each embodiment and comparative example. It should be noted that Ta [°C] is the temperature of the heat medium during operation (i) when the feed gas supply rate is at its maximum A [Nm]. 3 The temperature of the heat medium at / hr]. Tbmax [°C] is the highest temperature of the heat medium Tb [°C] during restart operation (iii-1). Tc [°C] is the maximum temperature of the feed gas supply rate C [Nm] during the re-stabilization operation (iii-2). 3 The temperature of the heat medium at / hr is the same as the temperature of the heat medium in the third reaction when restarting operation (iii-1).

[0164] [Table 1]

[0165]

[0166] [Table 2]

[0167]

[0168] As shown in Table 2, according to the methods of Examples 1 and 2, the position of ΔTmax can be moved towards the feed gas inlet side of the catalyst layer. This allows the reaction to proceed smoothly throughout the entire catalyst layer, reducing ΔTmax. That is, according to the present invention, upon restarting, the temperature of local reaction hotspots can be reduced, suppressing runaway oxidation reactions. On the other hand, in Comparative Examples 1 and 2, Ta and Tbmax are equal, and ΔTmax is higher compared to the examples. Therefore, in the comparative examples, there is concern about excessive temperature increases at hotspots, leading to catalyst degradation and runaway oxidation reactions.

[0169] The preferred embodiments of the present invention have been described in detail above, but it should be understood that the present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit or scope of the appended claims.

[0170] This application claims priority based on Japanese Patent Application No. 2023-136136, filed on August 24, 2023, the entire contents of which are incorporated herein by reference.

[0171] Symbol Explanation

[0172] 1. Fixed-bed reactor

[0173] 2 Catalyst layer

[0174] 2A dilution layer

[0175] 2B No dilution layer

[0176] 3. Reaction tube

[0177] 4. Heat medium bath

[0178] 5. Raw material gas inlet

[0179] 6. Inactive carrier layer

[0180] The ends of the X and Y catalyst layers

Claims

1. A method for producing (meth)acrylaldehyde or (meth)acrylic acid, comprising a fixed-bed reactor having a heat medium and a catalyst bed, comprising the following (i) to (iii-1): (i) Operation: Set the temperature of the heat medium to Ta, set the feed gas supply rate to the maximum A, and supply the feed gas to the fixed-bed reactor. (ii) Shutdown, ceasing the supply of the feed gas to the fixed-bed reactor, and (iii-1) Restart the operation, resume the supply of the raw material gas to the fixed bed reactor, and increase the supply rate of the raw material gas to a stable operating state; During the restart operation (iii-1), the highest temperature Tbmax of the heat medium Tb is higher than that of Ta. The units for Ta, Tb, and Tbmax are °C, and the unit for A is Nm³. 3 / hr.

2. The method for manufacturing (meth)acrylaldehyde or (meth)acrylic acid according to claim 1, wherein, After restarting operation (iii-1), proceed as follows (iii-2): (iii-2) Re-stabilize the operation, set the temperature of the heat medium to Tc, set the supply rate of the raw material gas to the maximum C, and supply the raw material gas to the fixed bed reactor. The unit of Tc is °C, and the unit of C is Nm³. 3 / hr.

3. The method for manufacturing (meth)acrylaldehyde or (meth)acrylic acid according to claim 2, wherein, In the re-stabilization operation (iii-2), when the length of the long side of the catalyst layer is set as L1 and the distance from the end of the raw material gas inlet side of the catalyst layer to the position ΔTmax where the temperature difference between the catalyst layer and the heat medium reaches its maximum is set as L2, L2 / L1 is less than 0.

50.

4. The method for manufacturing (meth)acrylaldehyde or (meth)acrylic acid according to claim 1, wherein, In the restart operation (iii-1), when the supply rate of the raw material gas is set to B when the temperature of the heat medium reaches Tbmax, the following condition is satisfied: A×0.50≤B≤A×0.80, where Tbmax is in °C and B is in Nm³. 3 / hr.

5. The method for producing (meth)acrylaldehyde or (meth)acrylic acid according to claim 1, wherein, The difference between Tbmax and Ta, i.e., Tbmax-Ta, is within the range of 2℃ to 7℃, and the units of Tbmax and Ta are ℃.

6. The method for producing (meth)acrylaldehyde or (meth)acrylic acid according to claim 2, wherein, The difference between Tc and Ta, i.e., Tc-Ta, is within the range of 0℃ to 3℃, and the units of Tc and Ta are ℃.

7. The method for producing (meth)acrylaldehyde or (meth)acrylic acid according to claim 2, wherein, The maximum supply rate A of the raw material gas in operation (i) and the maximum supply rate C of the raw material gas in the re-stabilization operation (iii-2) satisfy A×0.80<C<A×1.2, where the units of A and C are Nm. 3 / hr.

8. The method for producing (meth)acrylaldehyde or (meth)acrylic acid according to claim 1, wherein, The supply of the raw material gas in the restart operation (iii-1) shall be restarted within 9000 hours from the start of the supply of the raw material gas for the operation (i).

9. The method for producing (meth)acrylaldehyde or (meth)acrylic acid according to claim 1, wherein, The fixed-bed reactor includes a reaction tube having the catalyst layer inside and the heat medium outside the reaction tube.

10. A method for manufacturing (meth)acrylic acid, comprising a step of oxidizing (meth)acrylaldehyde manufactured by any one of claims 1 to 9.

11. A method for manufacturing (meth)acrylate, comprising a step of esterifying (meth)acrylate manufactured by any one of claims 1 to 9.

Images