Method for producing (meth)acrolein and method for producing (meth)acrylic acid

Abstract

To sufficiently cool a reaction product gas and to prevent the pressure loss in reaction tubes over time from increasing in a method for producing (meth)acrolein and (meth)acrylic acid in which a catalytic gas phase oxidation reaction is carried out using a multi-tubular reactor including a plurality of reaction tubes having a reaction part and a cooling part.SOLUTION: There is provided a method for producing (meth)acrolein by a catalytic gas-phase oxidation reaction of propylene or isobutylene in a multi-tubular reactor including a plurality of reaction tubes having a reaction part filled with a catalyst containing molybdenum oxide and a cooling part filled with an inert substance, wherein a temperature of a heat medium flowing outside of the cooling part is lower than a temperature of a heat medium flowing outside the reaction part, and the inert substance includes an inert substance whose long diameter is 1.7 times or more with respect to a long diameter of the catalyst. There is also provided a method for producing (meth)acrylic acid which comprises forming (meth) acrylic acid by the catalytic gas-phase oxidation reaction of a resultant (meth)acrolein.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing (meth)acrolein by catalytic gas-phase oxidation using a multi-tubular reactor having a plurality of reaction tubes each equipped with a reaction section and a cooling section. The present invention also relates to a method for producing (meth)acrylic acid by catalytic gas-phase oxidation of (meth)acrolein produced by the method for producing (meth)acrolein. In this specification, "(meth)acrolein" means "acrolein and / or methacrolein", and "(meth)acrylic acid" means "acrylic acid and / or methacrylic acid". [Background technology]

[0002] As a method for producing (meth)acrolein and (meth)acrylic acid, there is a method in which propylene or isobutylene is subjected to a catalytic gas-phase oxidation reaction with an oxygen-containing gas in the presence of a catalyst to first produce (meth)acrolein, and then the (meth)acrolein is subjected to a catalytic gas-phase oxidation reaction to produce a reaction gas containing (meth)acrylic acid.

[0003] In commercial production facilities for (meth)acrolein or (meth)acrylic acid by such catalytic gas-phase oxidation reaction, a multi-tubular reactor having a plurality of reaction tubes each equipped with a reaction section and a cooling section is usually used. The multi-tubular reactor has the following advantages: the temperature in each reaction tube can be kept at or above the temperature required for the catalytic gas-phase oxidation reaction; a large amount of heat generated by the oxidation reaction can be removed; and a high reaction conversion rate can be obtained by forming a plug flow in each reaction tube.

[0004] (Meth)acrolein produced by the catalytic gas-phase oxidation reaction undergoes an oxidation reaction (hereinafter sometimes referred to as "autoxidation") with oxygen in the gas phase even in the absence of a catalyst. Autoxidation not only reduces the yield of the target product, but also causes a vicious cycle in which the increase in gas temperature due to the reaction heat of autoxidation further accelerates the autoxidation, ultimately leading to a runaway combustion reaction (hereinafter sometimes referred to as "thermal runaway"), which may force the shutdown of the multi-tubular reactor.

[0005] One method to avoid autoxidation is to reduce the concentration or amount of the raw material propylene or isobutylene fed to the multi-tubular reactor, but this method reduces the production volume relative to the scale of the production facility, i.e., the productivity, and is therefore undesirable for commercial production where economic efficiency is important.

[0006] Another method to avoid autoxidation is to reduce the residence time of the reaction product gas in the multi-tubular reactor. The longer the residence time of the gas in the multi-tubular reactor, the more autoxidation and the associated increase in gas temperature progress. Therefore, reducing the residence time can mitigate autoxidation and the associated increase in gas temperature. Patent Document 1 discloses a method for preventing a rapid temperature rise due to the decomposition reaction of (meth)acrolein and the resulting shutdown of the multi-tubular reactor by providing a conical or other rectifier in the reaction product gas outlet section of the multi-tubular reactor to eliminate retention of the reaction product gas in the reaction product gas outlet section.

[0007] Yet another method of avoiding autoxidation is to retard it to a point where it is virtually insignificant by rapidly cooling the reaction product gases discharged from the reactor. Patent Document 2 discloses a method for preventing autoxidation of an acrolein-containing gas obtained by catalytic gas-phase oxidation of propylene by rapidly cooling the gas to 280° C. or less.

[0008] Another problem with catalytic gas phase oxidation reactions using a multi-tubular reactor is the clogging of the reaction tubes. As the clogging of the reaction tubes progresses, it causes a decrease in production. To avoid this, excessive supply pressure is required to supply the required amount of raw material mixed gas to each reaction tube, and if the supply pressure exceeds the equipment capacity, operation is forced to be stopped. The most common cause of clogging of the reaction tubes is the accumulation of carbides (hereinafter sometimes referred to as "coke"). Although the accumulation of carbides (hereinafter sometimes referred to as "coking") can be alleviated by changing the operating conditions, it is difficult to completely prevent coking, and it is necessary to remove the coking by periodically passing an oxygen-containing gas through the reaction tube (hereinafter sometimes referred to as "decokking"). Non-Patent Document 1 discloses a method of decoking by burning charcoal accumulated in a reactor at 350 to 500° C. while gradually increasing the oxygen concentration in the gas being passed. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2005-325043 A [Patent Document 2] Japanese Patent Application Publication No. 56-73041 [Non-patent literature]

[0010] [Non-Patent Document 1] Chemical Engineering / January18, 1988, p.111-114 Summary of the Invention [Problem to be solved by the invention]

[0011] However, these conventional methods for preventing autoxidation, preventing coking, and decoking have sometimes been unable to sufficiently prevent an increase in pressure loss and clogging over time in the multi-tubular reactor.

[0012] As a result of investigating the cause of this, the following became clear. Catalysts used in the catalytic gas-phase oxidation of propylene or isobutylene for the commercial production of (meth)acrolein and (meth)acrylic acid generally contain molybdenum oxide. Although molybdenum oxide has a low vapor pressure, it is prone to form hydrates in the presence of water vapor, and the vapor pressure of the hydrates tends to increase. On the other hand, in the catalytic gas-phase oxidation reaction of propylene or isobutylene, the presence of water vapor is considered to be advantageous. In addition, water is by-produced in the catalytic gas-phase oxidation reaction. Furthermore, water vapor may be used as an inert gas to avoid an explosive composition of the raw material mixed gas introduced into a multi-tubular reactor. For these reasons, the reaction product gas after the catalytic gas-phase oxidation reaction may contain 10 to 50% by volume of water vapor. As a result, the reaction product gas in the multi-tubular reactor contains molybdenum oxide at a concentration of several ppb to several ppm, which has become a hydrate in the presence of water vapor and has an increased vapor pressure. For this reason, as the reaction product gas is rapidly cooled, a part of molybdenum oxide in the reaction product gas precipitates, and the precipitates such as molybdenum oxide cause an increase in pressure loss over time in the multi-tubular reactor, which ultimately leads to clogging.

[0013] The present invention aims to provide a method for producing (meth)acrolein and (meth)acrylic acid by catalytic gas-phase oxidation reaction in the presence of a catalyst containing molybdenum oxide using a multi-tubular reactor having a plurality of reaction tubes each equipped with a reaction section and a cooling section, which method provides sufficient cooling of the reaction product gas and also suppresses an increase in pressure drop over time in the reaction tubes. [Means for solving the problem]

[0014] The present inventors conducted a detailed investigation of the inside of a multi-tubular reactor where an increase in pressure drop occurred in the reaction tube, and found that in the reaction tube where an increase in pressure drop occurred, the precipitation sites of molybdenum oxide-containing precipitates were concentrated in specific locations in the cooling section of the reaction tube. In order to disperse the precipitation sites of the precipitates, the size of the packing used in the cooling section was examined. As a result, it was found that the precipitation sites of molybdenum oxide-containing precipitates precipitated in the cooling section may be significantly affected by the size of the packing. Therefore, the present inventors have invented the method of the present invention, which can mitigate the increase in pressure drop of the reaction tube over time by using packing of a specific size in the cooling section. The present invention has been achieved based on these findings, and has the following gist.

[0015] [1] A method for producing (meth)acrolein by catalytic gas-phase oxidation of propylene or isobutylene in a multi-tubular reactor having a plurality of reaction tubes each equipped with a reaction section packed with a catalyst containing molybdenum oxide and a cooling section packed with an inert substance, wherein the temperature of a heat transfer medium flowing outside the cooling section is lower than the temperature of a heat transfer medium flowing outside the reaction section, and the inert substance contains an inert substance whose major axis is 1.7 times or more the major axis of the catalyst.

[0016] [2] The method for producing (meth)acrolein according to [1], wherein the inactive substance comprises an inactive substance having a thermal conductivity represented by the following formula (1): Thermal conductivity of inert material ≦ Thermal conductivity of molybdenum oxide × 0.1 (1)

[0017] [3] The method for producing (meth)acrolein according to [1] or [2], wherein the inactive substance comprises a ring-shaped inactive substance.

[0018] [4] The method for producing (meth)acrolein according to [3], wherein the inner diameter of the ring-shaped inactive substance is 1.0 times or more the major axis of the catalyst.

[0019] [5] The method for producing (meth)acrolein according to any one of [1] to [4], wherein the inert material comprises a ceramic inert material.

[0020] [6] The method for producing (meth)acrolein according to any one of [1] to [5], wherein the inner diameter of the reaction tube is 1.3 to 2.5 times the major axis of the inert substance.

[0021] [7] The method for producing (meth)acrolein according to any one of [1] to [6], wherein the temperature of the heat medium flowing outside the cooling section and the temperature of the heat medium flowing outside the reaction section satisfy the following formula (2): Temperature of heat transfer medium flowing outside the cooling section (℃) ≦ Temperature of the heat transfer medium flowing outside the reaction section (℃) -50℃ (2)

[0022] [8] A method for producing (meth)acrylic acid, in which (meth)acrolein obtained by the method for producing (meth)acrolein according to any one of [1] to [7] is converted into (meth)acrylic acid by catalytic gas-phase oxidation reaction. Effect of the Invention

[0023] According to the process for producing (meth)acrolein and the process for producing (meth)acrylic acid of the present invention, the reaction product gas can be sufficiently cooled, and the deposition sites of the deposits in the cooling section of the reaction tube can be dispersed over a wide range, so that an increase in pressure drop in the reaction tube over time can be suppressed. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram showing reaction tubes in a multi-tubular reactor and a circulation system of a heat transfer medium around the reaction tubes. [Diagram 2] FIG. 2 is a schematic diagram showing the packing specifications of the catalyst and the inert substance in the reaction tube. [Diagram 3] FIG. 2 is a schematic cross-sectional view of the vicinity of an intermediate tube plate of a multi-tubular reactor. [Figure 4] FIG. 4 is a conceptual diagram showing distortion due to thermal expansion of an intermediate tube sheet. [Diagram 5] 1 is a graph showing the average value of pressure drop in a reaction tube before and after acrolein production operation in Experimental Example 1. [Figure 6] 6 is a graph showing an enlarged view of the outlet part of the reaction section and the cooling section of the reaction tube in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] The method of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the following description in any way, and can be practiced with various modifications within the scope of the gist of the present invention. In the following, the method for producing (meth)acrolein of the present invention will be mainly described. However, the method for producing (meth)acrylic acid of the present invention can also be carried out by further subjecting (meth)acrolein obtained by a catalytic gas-phase oxidation reaction to a catalytic gas-phase oxidation reaction, similarly to the method for producing (meth)acrolein of the present invention.

[0026] FIG. 1 is a schematic diagram showing reaction tubes and a circulation system of a heat transfer medium around the reaction tubes in a multi-tubular reactor (vertical multi-tubular reactor) for carrying out a catalytic gas-phase oxidation reaction of propylene or isobutylene in the (meth)acrolein production method of the present invention.

[0027] A plurality of reaction tubes 2 are arranged vertically in a shell 1 of a multi-tubular reactor. The reaction tubes 2 are fixed to the shell 1 by being installed between an inlet side tube plate 3 and an outlet side tube plate 4, which are arranged at the upper end side and the lower end side of the shell 1, respectively.

[0028] An intermediate tube sheet 5 is provided between the inlet side tube sheet 3 and the outlet side tube sheet 4 and close to the outlet side tube sheet 4 in parallel thereto, and three flow path baffle plates 6 are provided between the intermediate tube sheet 5 and the inlet side tube sheet 3 in parallel thereto. The lowermost flow path baffle plate 6 and the uppermost flow path baffle plate 6 have an opening for the flow of the heat transfer medium in their centers, and a gap for the flow of the heat transfer medium is provided between the outer periphery of the flow path baffle plate 6 provided between them and the shell 1. In order to heat the reaction section of the reaction tube 2 by the intermediate tube plate 5 and the flow path baffle plate 6, the heat medium (hereinafter may be referred to as "heating heat medium") introduced from the heat medium supply passage 7 provided on the outer circumferential surface of the lower part of the shell 1 flows between the intermediate tube plate 5 and the lowest flow path baffle plate 6, rises from the openings of the flow path baffle plate 6 onto the flow path baffle plate 6, flows between the lowest flow path baffle plate 6 and the intermediate flow path baffle plate 6, rises between the shell 1 and the outer periphery of the intermediate flow path baffle plate 6, further flows between the intermediate flow path baffle plate and the uppermost flow path baffle plate 6, rises from the central opening of the uppermost flow path baffle plate 6 onto the flow path baffle plate 6, further flows between the flow path baffle plate 6 and the inlet side tube plate 3, and is discharged from the heat medium discharge passage 8 provided on the upper side circumferential surface of the shell 1. While the heating heat transfer medium flows in this manner, the reaction section of the reaction tubes 2 (the reaction tubes 2 between the inlet side tube plate 3 and the intermediate tube plate 5) is heated.

[0029] On the other hand, in order to cool the cooling portion of the reaction tubes 2, a heat transfer medium (hereinafter, may be referred to as "cooling heat transfer medium") introduced through a heat transfer medium supply passage 9 provided on a lower side peripheral surface of the shell 1 flows between the intermediate tube plate 5 and the outlet side tube plate 4 and is discharged through a heat transfer medium discharge passage 10 provided on the opposite side peripheral surface of the shell 1, during which the cooling portion of the reaction tubes 2 (the reaction tubes 2 between the intermediate tube plate 5 and the outlet side tube plate 4) is cooled.

[0030] As described above, the reaction section and the cooling section are continuously formed in the reaction tube 2 in its longitudinal direction (flow direction of the raw material mixed gas). The reaction section of the reaction tube 2 is filled with a catalyst containing molybdenum oxide (hereinafter, may be referred to as "catalyst"), and the cooling section is filled with an inert material.

[0031] The raw material mixed gas supplied from the reactor inlet 11 undergoes a catalytic gas-phase oxidation reaction by the catalyst packed in the reaction section of the reaction tube 2 to become a reaction product gas containing (meth)acrolein. The reaction product gas is cooled in the cooling section of the reaction tube 2 and discharged from the reactor outlet 12.

[0032] The raw material mixed gas is a mixture of the raw material propylene or isobutylene, an oxygen-containing gas such as air, and an inert gas such as water vapor, and the composition of each gas is appropriately set depending on the reaction conditions, etc.

[0033] FIG. 2 is a schematic diagram showing the packing specifications of the catalyst and inert material in the reaction tube of the multi-tubular reactor of FIG. 1. The packing layers in the reaction tube 2 are composed of a preheating layer 21 for heating the raw material mixed gas, three catalyst layers 22-24 (reaction section) for converting the heated raw material mixed gas into a reaction product gas by a catalytic gas phase oxidation reaction, a quenching layer 25 (cooling section) for cooling the reaction product gas, and a catalyst stopper 26 at the lower end of the reaction tube, in order from the inlet side of the multi-tubular reactor, that is, in the order in which the raw material mixed gas passes through. The preheating layer and the quenching layer (cooling section) are each packed with an inert material, and the catalyst layer (reaction section) is mainly packed with a catalyst. The inert material is a material that does not contribute to the catalytic gas phase oxidation reaction.

[0034] In the present invention, the inert material filled in the quenching layer (cooling section) 25 contains an inert material satisfying the following requirement (1), and preferably further contains an inert material satisfying the following requirements (2) to (6). Note that the inert material containing an inert material satisfying the following requirements is preferably one containing an inert material satisfying the following requirements in an amount of 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95 to 100% by mass, based on the total inert material.

[0035] (1) The major axis of the inert material is 1.7 times or more the major axis of the catalyst. In the present invention, it is an essential requirement that the inert material packed in the quenching layer (cooling section) contains an inert material whose major axis is 1.7 times or more the major axis of the catalyst packed in the catalyst layer (reaction section), i.e., the major axis ratio of the inert material to the catalyst is 1.7 or more. If the ratio of the long axis of the inert material to the long axis of the catalyst is 1.7 or more, the gas cooling area per bed volume is reduced, thereby suppressing the drop in gas temperature and preventing the concentration of deposits. Here, the "long diameter" corresponds to the length of the gap between two parallel plates at the portion where the gap is greatest when the object is sandwiched between the two plates. From the viewpoint of suppressing the gas cooling area, the ratio of the major axis of the inert material to the major axis of the catalyst is preferably 1.8 or more, more preferably 1.9 or more. However, since it is difficult to make the ratio of the major axis of the inert material to the major axis of the catalyst excessively large in terms of designing the multi-tubular reactor, this ratio is usually 3.4 or less, preferably 3.3 or less.

[0036] (2) The thermal conductivity of the inert material is 0.1 times or less than that of molybdenum oxide. The inert material filled in the quenching layer (cooling section) preferably contains an inert material having a thermal conductivity represented by the following formula (1). Thermal conductivity of inert material ≦ Thermal conductivity of molybdenum oxide × 0.1 (1) By filling the quenching layer (cooling part) with an inert material satisfying the above formula (1), it becomes possible to widely disperse the precipitation sites of the precipitates in the quenching part (cooling part) in the reaction tube, and thus it is possible to suppress an increase in pressure drop in the reaction tube over time. When the reaction product gas is cooled in the quenching layer (cooling section), some of the molybdenum oxide contained in the reaction product gas precipitates on the surface of the inert material, but if the thermal conductivity of the inert material satisfies the above formula (1), the overall heat transfer coefficient in the quenching layer (cooling section) remains low unless the amount of molybdenum oxide that precipitates is large. In other words, it is possible to avoid a vicious cycle in which the precipitation of molybdenum oxide in the quenching layer (cooling section) increases the overall heat transfer coefficient in the quenching layer (cooling section), which in turn increases the cooling rate, causing further precipitation of molybdenum oxide. From the above viewpoints, the thermal conductivity of the inactive substance more preferably satisfies the following formula (1A), and further preferably satisfies the following formula (1B). Thermal conductivity of inert material ≦ Thermal conductivity of molybdenum oxide × 0.095 (1A) Thermal conductivity of inert material ≦ Thermal conductivity of molybdenum oxide × 0.090 (1B) However, because it is necessary to cool the gas before it reaches the outlet of the quenching layer in order to prevent the auto-oxidation of acrolein, the thermal conductivity of the inert material usually satisfies the following formula (1C) relative to the thermal conductivity of molybdenum oxide. Thermal conductivity of inert material ≧ Thermal conductivity of molybdenum oxide × 0.01 (1C)

[0037] (3) Ring-shaped inert material The inert material packed in the quenching layer (cooling section) preferably includes a ring-shaped inert material. By providing the inert material in a ring shape, the void ratio in the packed bed can be kept high to allow the reaction product gas to flow smoothly while maintaining appropriate thermal conductivity and the mechanical strength of the inert material can be maintained.

[0038] (4) The inner diameter of the ring-shaped inert material is 1.0 times or more the major axis of the catalyst. It is preferable that the inner diameter of the ring-shaped inactive material is 1.0 times or more the major axis of the catalyst, i.e., the ratio of the inner diameter of the inactive material to the major axis of the catalyst is 1.0 or more, and this ratio is more preferably 1.01 or more, even more preferably 1.02 or more, and is preferably 1.5 or less, more preferably 1.4 or less. By having the ratio of the inner diameter of the inert material to the major axis of the catalyst within the above range, the porosity within the cooling section is kept high to allow the reaction product gas to flow smoothly while maintaining appropriate thermal conductivity, and it is possible to prevent the catalyst from entering the cooling section, thereby enabling efficient cooling of the reaction product gas.

[0039] (5) Inert porcelain materials The inert material filled in the quenching layer (cooling section) preferably contains a ceramic inert material, and more preferably, all of the inert materials are ceramic inert materials. By containing a ceramic inert material, it becomes possible to avoid a negative cycle of an increase in the cooling rate over time and further progression of blockage caused by precipitation of molybdenum oxide and the like in the quenching layer (cooling section).

[0040] (6) The inner diameter of the reaction tube is 1.3 to 2.5 times the major axis of the inert substance. The inner diameter of the reaction tube in the multi-tubular reactor is preferably 1.3 to 2.5 times the major axis of the inert material, i.e., the ratio of the inner diameter of the reaction tube to the major axis of the inert material is 1.3 to 2.5. This ratio is more preferably 1.4 or more, and even more preferably 1.5 or more, and the upper limit is more preferably 2.2 or less, and even more preferably 2.0 or less. By having the inner diameter of the reaction tube / major axis ratio of the inert substance within the above range, a sufficient porosity can be obtained in the cooling part of the reaction tube, and also, it is possible to keep small the difference in packing density when the inert substance is repeatedly filled, discharged, and refilled.

[0041] In the present invention, the temperature of the cooling heat transfer medium flowing outside the cooling part of the reaction tube is lower than the temperature of the heating heat transfer medium flowing outside the reaction part of the reaction tube, and it is preferable that the temperatures of these heat transfer mediums satisfy the following formula (2): Temperature of heat transfer medium flowing outside the cooling section (℃) ≦ Temperature of the heat transfer medium flowing outside the reaction section (℃) -50℃ (2) When the heat transfer medium temperature satisfies the above formula (2), the reaction product gas can be efficiently cooled. More preferably, the temperature of the cooling heat medium is at least 60°C lower than the temperature of the heating heat medium. Specifically, the temperature of the cooling heat medium is preferably 200 to 280°C, and the temperature of the heating heat medium is preferably 300 to 360°C.

[0042] As described above, the catalyst layer (reaction section) is mainly filled with a catalyst, but in order to suppress excessive reaction in the catalyst layer (reaction section) through which the raw material mixed gas passes after the preliminary layer, the catalyst and an inert material may be mixed and filled in the catalyst layer (reaction section) near the preheating layer. In this case, it is preferable to increase the mixture ratio of the inert material to the catalyst. When only the catalyst is filled, it is preferable to fill a catalyst with a relatively low reaction activity.

[0043] The inert material filled in the preheating layer is not limited as long as it can raise the temperature of the raw material mixed gas. The inert material mixed with the catalyst and filled in the reaction section is not limited as long as it is easy to mix with the catalyst and has a size similar to that of the catalyst. The material of the inert material filled in either the preheating layer or the reaction section is not limited to ceramic, but may be silicon carbide, ceramic balls, stainless steel, etc., and various shapes such as spherical, cylindrical, cylindrical, saddle-shaped, and ring-shaped can be applied.

[0044] Fig. 3 is a schematic cross-sectional view of the intermediate tube plate 5 of the multi-tubular reactor. As described above, the temperature of the cooling heat medium flowing outside the cooling section is lower than the temperature of the heating heat medium flowing outside the reaction section, so that the intermediate tube plate 5 is subjected to thermal stress. In Fig. 3, retention baffles 31 are arranged on the upper and lower parts of the intermediate tube plate 5 and fixed with fixing jigs 32 for the purpose of reducing this thermal stress. The thermal conductivity of the heat transfer medium is usually 1 / 100 or less of the thermal conductivity of the intermediate tube plate 5. By disposing the retention baffle 31 on one or both sides of the intermediate tube plate 5, a temperature gradient in the longitudinal direction of the reaction tubes 2 is generated in the heat transfer medium held by the intermediate tube plate 5 or the retention baffle 31, but since the held heat transfer medium is capable of flowing, no excessive effect is generated.

[0045] Since the heat transfer medium between the retention baffles 31 has a temperature difference in the longitudinal direction of the reaction tube 2, the temperature difference in the reaction tube 2 also becomes large near the boundary between the reaction section and the cooling section. Therefore, when precipitates are generated due to rapid cooling of the reaction product gas, it may be possible to prevent the concentration of the precipitation points by increasing the number of retention baffles 31 or widening the interval between the retention baffles 31. However, in this case, it becomes necessary to lengthen the reaction tube 2, which may lead to an increase in the size of the reactor and an increase in the equipment cost.

[0046] FIG. 4 is a conceptual diagram showing distortion due to thermal expansion of the intermediate tube sheet 5. The degree of expansion and contraction due to temperature change varies depending on the type of metal, but for general-purpose steel, it is about 1 / 100,000 / °C. That is, even if there is a temperature difference of 100°C, the degree of expansion and contraction is only about 1 / 1000, which is not a problem for small equipment. However, if the diameter of the shell of the multi-tubular reactor is 5m and the thickness of the intermediate tube sheet 5 is 10cm, both ends of the intermediate tube sheet 5 are calculated to rise by 3cm, and measures are required. As measures, a strong structure that can withstand the thermal stress can be used; or the temperature difference between the front and back of the intermediate tube sheet 5 can be reduced by utilizing a retention baffle plate 31 or the like; etc.

[0047] In the catalytic gas phase oxidation reaction of propylene or isobutylene according to the present invention, (meth)acrolein and (meth)acrylic acid are obtained by catalytic gas phase oxidation reaction of a part of the (meth)acrolein. In addition, (meth)acrylic acid is obtained by catalytic gas phase oxidation reaction of (meth)acrolein.

[0048] To a multi-tubular reactor used for a catalytic gas phase oxidation reaction, a mixed gas of propylene or isobutylene, a molecular oxygen-containing gas, and an inert gas such as water vapor is mainly supplied as a raw material mixed gas. The concentration of propylene or isobutylene in the raw material mixed gas is preferably 6 to 10 mol %, oxygen is 1.5 to 2.5 times by mol relative to propylene or isobutylene, and the inert gas is 0.8 to 5 times by mol. The introduced raw material mixed gas is divided into each reaction tube and passes through the reaction tube to react in the presence of the catalyst packed in the reaction tube.

[0049] The oxygen-containing gas may be, for example, air or an oxygen-containing waste gas generated in other production facilities, with air being preferred. As the inert gas, industrially inexpensive water vapor, nitrogen, carbon dioxide gas, etc. are used, but a mixed gas of these separated and recovered from the catalytic gas phase oxidation reaction gas can also be recycled and used.

[0050] As catalysts, there are those suitable for the pre-stage reaction of producing (meth)acrolein by the catalytic gas-phase oxidation reaction of propylene or isobutylene, and those suitable for the post-stage reaction of producing (meth)acrylic acid by the catalytic gas-phase oxidation reaction of (meth)acrolein. However, in any reaction, a catalyst containing molybdenum oxide is used.

[0051] As the catalyst for the pre-stage reaction, a catalyst represented by the following formula (I) is preferred. Mo a W b Bi c Fe d A e B f C g D h E i O x (I)

[0052] In the above formula (I), A is at least one element selected from nickel and cobalt, B is at least one element selected from sodium, potassium, rubidium, cesium and thallium, C is at least one element selected from alkaline earth metals, D is at least one element selected from phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic, boron and zinc, E is at least one element selected from silicon, aluminum, titanium and zirconium, and O represents oxygen respectively. a, b, c, d, e, f, g, h, i and x represent the atomic ratios of Mo, W, Bi, Fe, A, B, C, D, E and O respectively. When a = 12, 0 ≦ b ≦ 10, 0 < c ≦ 10 (preferably 0.1 ≦ c ≦ 10), 0 < d ≦ 10 (preferably 0.1 ≦ d ≦ 10), 2 ≦ e ≦ 15, 0 < f ≦ 10 (preferably 0.001 ≦ f ≦ 10), 0 ≦ g ≦ 10, 0 ≦ h ≦ 4, 0 ≦ i ≦ 30, and x is a value determined by the oxidation state of each element.

[0053] As the catalyst for the post-stage reaction, a catalyst represented by the following formula (II) is preferred. Mo a V b W c Cu d X e Y f Og (II)

[0054] In the above formula (II), X is at least one element selected from Mg, Ca, Sr, and Ba; Y is at least one element selected from Ti, Zr, Ce, Cr, Mn, Fe, Co, Ni, Zn, Nb, Sn, Sb, Pb, and Bi; and O represents oxygen. a, b, c, d, e, f, and g respectively represent the atomic ratios of Mo, V, W, Cu, X, Y, and O. When a = 12, 2 ≤ b ≤ 14, 0 ≤ c ≤ 12, 0 < d ≤ 6, 0 ≤ e ≤ 3, 0 ≤ f ≤ 3, and g is a numerical value determined by the oxidation state of each element.

[0055] The above catalyst is produced, for example, by the methods disclosed in JP-A-63-54942, JP-B-6-13096, JP-B-6-38918, and the like.

[0056] The catalyst used in the present invention may be a shaped catalyst formed by an extrusion molding method or a tableting molding method, or a supported catalyst in which an oxide composed of catalyst components is supported on an inert carrier such as silicon carbide, alumina, zirconium oxide, or titanium oxide. In the case of the supported catalyst, the composition of the catalyst represented by the above formula is the composition of the catalyst excluding the carrier. Further, the shape of the catalyst used in the present invention is not particularly limited, and it may be any of spherical, cylindrical, tubular, star-shaped, ring-shaped, and amorphous. Usually, the major axis of the catalyst is about 5.0 to 7.0 mm.

Examples

[0057] The present invention will be described more specifically below with reference to experimental examples, examples, and comparative examples.

[0058] [Experimental Example 1] Using the vertical multi-tubular reactor of FIG. 1 in which the number of reaction tubes 2 is 20,000, acrolein was produced using propylene as a raw material. Three retention baffle plates 31 shown in FIG. 3 were laid on the lower side of the intermediate tube sheet 5. The acrolein obtained from the multi-tubular reactor was converted to acrylic acid in the next step. The reaction tube (inner diameter 27 mm) 2 of the multi-tubular reactor was filled with catalyst in three catalyst layers (reaction sections) 22 to 24 as shown in Figure 2. The catalyst was obtained by tableting and had a ring shape (outer diameter 5 mm, inner diameter 2 mm, height 3 mm, major axis 5.8 mm). The catalyst composition was Mo. 12 Bi3Fe 0.5 Ni 2.5 Co 2.5 Na 0.4 K 0.1 B 0.4 S 24 It was. The quenching layer (cooling section) 25 was filled with porcelain Raschig rings having an outer diameter of 6.4 mm, an inner diameter of 3.5 mm, and a height of 6.4 mm (long diameter = 9.1 mm). The thermal conductivity of the porcelain Raschig rings was 1 to 1.5 W / mK, which was 0.04 to 0.06 times the thermal conductivity of molybdenum oxide (24 W / mK). The long diameter of the porcelain Raschig rings was 1.6 times the long diameter of the catalyst. After filling the catalyst and the ceramic Raschig rings, 500 reaction tubes were selected, a certain amount of dry air was passed through them, and the pressure drop before the start of operation (initial stage) was measured. The average pressure drop of the 500 reaction tubes was 5 kPa. The catalyst and the ceramic Raschig ring were removed stepwise from the inlet of the reaction tube where the average pressure drop was 5 kPa, and the pressure drop was measured. The measured pressure drop was (1) Pressure drop from the reactor inlet to the quenching layer outlet (2) The pressure drop from the top of the catalyst bed to the outlet of the quenching bed was measured after the catalyst was removed. (3) Furthermore, the pressure drop from the top of the quenching layer to the outlet of the quenching layer was measured after removing the porcelain Raschig ring. These pressure losses were measured as the pressure at the inlet of the reaction tube when dry air was passed through the inlet of the reaction tube at 1000 NL / H. The temperature of the heating heat medium in the heat medium supply passage was 315 to 325° C., and the temperature of the cooling heat medium in the heat medium supply passage was 235 to 245° C. The gas temperature after passing through the quenching layer was 235 to 245° C., the same as that of the cooling heat medium.

[0059] After 11 consecutive months of acrolein production operation by catalytic gas-phase oxidation of propylene, the operation was stopped for one month to carry out maintenance work. Then, after another 11 consecutive months of acrolein production operation by catalytic gas-phase oxidation of propylene (2 years later), all reaction tubes were decoked by circulating air heated to about 400°C through them. Then, after cooling the reaction tubes, they were introduced into a multi-tubular reactor, and the pressure loss was measured for the 500 reaction tubes for which the pressure loss was measured before the start of operation (initial stage), and the two reaction tubes with the highest pressure loss were selected. Next, the catalyst and the porcelain Raschig rings were removed stepwise from the inlet of the reaction tube for the two reaction tubes, and the pressure loss was measured in the same manner as above.

[0060] FIG. 5 shows the average pressure drop across the entire reaction tube before the start of operation (initial stage) and after acrolein production operation had been carried out (after two years). FIG. 6 shows an enlarged view of the outlet of the reaction section of the reaction tube in FIG. 5 (position 2.9 m from the upper end inlet of the reaction tube) and the cooling section (up to 3.5 m from the upper end inlet side of the reaction tube).

[0061] In addition, a fiberscope was inserted into each of the two selected reaction tubes to observe the inside of the reaction tubes.

[0062] As a result, it was found that the areas where the pressure drop was significantly different before and after the start of operation overlapped with the areas where deposits were occurring. That is, the average value of pressure drop fluctuates greatly at the intermediate tube plate section and the retention baffle section where the heat transfer medium temperature changes suddenly as shown in Fig. 5, especially at the retention baffle section. When the inside of the reaction tube was observed with a fiberscope, it was confirmed that a bright white thin film and needle-like crystals of molybdenum oxide were concentrated on the inner wall surface of the cooling section near the reaction section of the reaction tube, and further, it was confirmed that the needle-like crystals, which were considered to have peeled off, were scattered in the porcelain Raschig ring of the cooling section near the reaction section of the reaction tube.

[0063] From the above observation results, it was estimated that the deposits narrowed the path in the cooling section (hereinafter referred to as "section A") close to the reaction section of the reaction tube, and this narrowed the path, increasing the linear velocity of the reaction product gas passing through section A, and as a result, it was predicted that the deposits would spread downstream of section A over time.

[0064] [Example 1] All the filling materials including the catalyst were removed from five reaction tubes (inner diameter 27 mm) in a vertical multi-tubular reactor that had been decoked prior to regular maintenance. The catalyst was filled into catalyst layers (reaction sections) 22 to 24 of the five reaction tubes. The filled catalyst was obtained by tableting and had a ring shape (outer diameter 5 mm, inner diameter 2 mm, height 3 mm, major axis 5.8 mm). The catalyst composition was Mo. 12 Bi3Fe 0.5 Ni 2.5 Co 2.5 Na 0.4 K 0.1 B 0.4 S 24 It was. The quenching layer (cooling section) 25 was filled with porcelain Raschig rings having an outer diameter of 10.0 mm, an inner diameter of 6.0 mm, and a height of 10.0 mm (long diameter = 14.1 mm). The thermal conductivity of the porcelain Raschig rings was 1 to 1.5 W / mK, which was 0.04 to 0.06 times the thermal conductivity of molybdenum oxide (24 W / mK). The long diameter of the porcelain Raschig rings was 2.4 times the long diameter of the catalyst. Before the acrolein production operation, a certain amount of dry air was circulated through the reaction tubes, and the pressure loss of each reaction tube was measured. The pressure loss before the production operation was the average value of the pressure losses of all the reaction tubes. The temperature of the heat medium for heating was 315 to 325° C. in the heat medium supply passage, and the temperature of the heat medium for cooling was 235 to 245° C. in the heat medium supply passage. The acrolein obtained from the multi-tubular reactor was converted to acrylic acid in the next step.

[0065] Acrolein was produced by catalytic gas-phase oxidation of propylene in the vertical multi-tubular reactor for 11 consecutive months, and acrylic acid was produced in the next step. The reactor was then shut down for one month and maintenance work was performed. Acrolein was then produced by catalytic gas-phase oxidation of propylene for another 11 consecutive months, and acrylic acid was produced in the next step (2 years later). After decoking, the pressure loss of each reaction tube was measured. The pressure loss at this time was the pressure loss from the reaction tube inlet to the quenching layer outlet, and was measured as the pressure at the reaction tube inlet when dry air was circulated from the reaction tube inlet at 1000NL / H. The pressure loss after the production operation was the average value of the pressure losses of all reaction tubes. As a result, the increase in pressure loss in the reaction tube after one year of acrolein production compared to the pressure loss before acrolein production was 1.1 kPa, and the increase in pressure loss after two years was 1.3 kPa. The gas temperature after passing through the quenching layer was 235 to 245°C, the same as that of the heat transfer medium for cooling.

[0066] [Comparative Example 1] Acrolein was produced by catalytic gas phase oxidation of propylene under the same conditions as in Example 1, except that the inert material packed in the quenching layer (cooling section) 25 was changed to a porcelain Raschig ring with an outer diameter of 6.4 mm, an inner diameter of 3.5 mm, and a height of 6.4 mm (long diameter 9.1 mm, long diameter ratio of inert material / long diameter of catalyst 1.6). In the next step, acrylic acid production operation was carried out. As in Example 1, a certain amount of dry air was circulated through the reaction tubes before the acrolein production operation, and the pressure loss of each reaction tube was measured, and the average value was taken as the pressure loss before the production operation. Similarly, the pressure loss after the production operation was taken as the average value of the pressure losses of all reaction tubes. As a result, the increase in pressure loss in the reaction tube after one year of acrolein production compared to the pressure loss before acrolein production was 1.3 kPa, and the increase in pressure loss after two years was 1.9 kPa. The gas temperature after passing through the quenching layer was 235 to 245°C, the same as that of the heat transfer medium for cooling.

[0067] [Example 2] Acrolein was produced by catalytic gas phase oxidation of propylene under the same conditions as in Example 1, except that the inert material packed in the quenching layer (cooling section) 25 was changed to a porcelain Raschig ring with an outer diameter of 12.0 mm, an inner diameter of 8.0 mm, and a height of 12.0 mm (long diameter 17.0 mm, long diameter ratio of inert material to catalyst: 2.9). In the next step, acrylic acid production was carried out. As in Example 1, a certain amount of dry air was circulated through the reaction tubes before the acrolein production operation, and the pressure loss of each reaction tube was measured, and the average value was taken as the pressure loss before the production operation. Similarly, the pressure loss after the production operation was taken as the average value of the pressure losses of all reaction tubes.

[0068] [Comparative Example 2] Acrolein was produced by catalytic gas phase oxidation of propylene under the same conditions as in Example 1, except that the inert material packed in the quenching layer (cooling section) 25 was changed to stainless steel Raschig rings with an outer diameter of 6.35 mm, an inner diameter of 5.35 mm, and a height of 6.5 mm (long diameter 9.1 mm, inert material long diameter / catalyst long diameter ratio 1.6). In the next step, acrylic acid production operation was carried out. The thermal conductivity of the stainless steel Raschig rings was 14 W / mK, which was 0.58 times the thermal conductivity of molybdenum oxide (24 W / mK). As in Example 1, a certain amount of dry air was circulated through the reaction tubes before the acrolein production operation, and the pressure loss of each reaction tube was measured, and the average value was taken as the pressure loss before the production operation. Similarly, the pressure loss after the production operation was taken as the average value of the pressure losses of all the reaction tubes. As a result, the increase in pressure loss in the reaction tube after one year of acrolein production compared to the pressure loss before acrolein production was 0.9 kPa, and after two years the increase in pressure loss was 20.0 kPa. The gas temperature after passing through the quenching layer was 235-245°C, the same as the heat transfer medium used for cooling. It is believed that the high thermal conductivity of the stainless steel Raschig ring used as an inert material caused localized molybdenum oxide precipitation to progress over time, resulting in a significant increase in pressure loss after two years. These results show that the increase in pressure loss over the long term can be significantly improved by filling the quenching layer (cooling section) with an inert material whose major axis is 1.7 times or more larger than the major axis of the catalyst and whose thermal conductivity is 0.1 times or less than that of molybdenum oxide. [Explanation of symbols]

[0069] 1. Shell of the multi-tubular reactor 2 Reaction tube 3 Inlet tube sheet 4 Outlet side tube plate 5 Intermediate tube sheet 6 Flow path baffle plate 7 Heat medium supply path 8 Heat medium extraction path 9 Heat medium supply path 10 Heat medium extraction path 11 Reactor inlet 12 Reactor outlet 21 Preheating layer 22 Catalyst layer 1 23 Catalyst layer 2 24 Catalyst layer 3 25 Quenching layer (cooling section) 26 Catalyst stop 31 Retention baffle 32 Fixture

Claims

1. A method for producing (meth)acrolein by catalytic gas phase oxidation reaction of propylene or isobutylene in a multi-tubular reactor having a plurality of reaction tubes each equipped with a reaction section filled with a catalyst containing molybdenum oxide and a cooling section filled with an inert substance, comprising: the temperature of the heat transfer medium flowing outside the cooling section is lower than the temperature of the heat transfer medium flowing outside the reaction section, The method for producing (meth)acrolein, wherein the inert substance is a ring-shaped inert substance whose major axis is 1.7 times or more the major axis of the catalyst.

2. The method for producing (meth)acrolein according to claim 1 , wherein the inactive substance comprises an inactive substance having a thermal conductivity represented by the following formula (1): Thermal conductivity of inert material ≦ Thermal conductivity of molybdenum oxide × 0.1 (1)

3. 3. The method for producing (meth)acrolein according to claim 1 or 2, wherein the inner diameter of the ring-shaped inactive substance is 1.0 times or more the major axis of the catalyst.

4. The method for producing (meth)acrolein according to any one of claims 1 to 3, wherein the inert material comprises a ceramic inert material.

5. 5. The method for producing (meth)acrolein according to claim 1, wherein the inner diameter of the reaction tube is 1.3 to 2.5 times the major axis of the inert substance.

6. The method for producing (meth)acrolein according to any one of claims 1 to 5, wherein a temperature of the heat medium flowing outside the cooling section and a temperature of the heat medium flowing outside the reaction section satisfy the following formula (2): Temperature of the heat transfer medium flowing outside the cooling section (℃) ≦ Temperature of the heat transfer medium flowing outside the reaction section (℃) - 50℃ (2)

7. A method for producing (meth)acrylic acid, comprising converting (meth)acrolein obtained by the method for producing (meth)acrolein according to any one of claims 1 to 6 into (meth)acrylic acid by catalytic gas-phase oxidation reaction.

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