JPH0343258B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing acrylic acid or methacrylic acid by catalytic gas phase oxidation of propylene, isobutylene or tertiary-butanol with molecular oxygen. Specifically, the present invention relates to a method for producing acrylic acid or methacrylic acid safely and in a high space-time yield by carrying out the above-mentioned catalytic gas phase oxidation reaction in multiple stages. The object of the present invention is to provide an industrial method for producing acrylic acid or methacrylic acid by preventing "post-reaction" of the intermediate gases contained therein. Acrylic acid or methacrylic acid [hereinafter referred to as (meth) In general, the method for producing acrylic acid is carried out by filling a catalyst (so-called "pre-stage catalyst") that mainly produces acrolein or methacrolein (hereinafter referred to as (meth)acrolein) from propylene, isobutylene or tertiary-butanol. The first reactor and (meth)acrolein (meth)
Using a second reactor filled with a catalyst (so-called "post-catalyst") for oxidizing acrylic acid, the gas at the outlet of the first reactor is directly or indirectly quenched, and then the gas is directly or supplemented with an oxygen-containing gas. A method has been adopted in which a conventional fixed bed reactor has a hemispherical shape between the outlet tube plate of the reactor and the shell lid. Therefore, a large volume of space exists, and the residence time of the generated gas increases in this space, resulting in (meta)
This is because "post-reactions" including autoxidation reactions of acrolein occur, and it is necessary to suppress these. Therefore, as a measure to prevent such "after-reaction", in addition to the above-mentioned quenching operation, there is a method of continuously charging the first stage catalyst and the second stage catalyst into a single reactor (for example, British Patent No. 1256595 discloses reference)
In order to rapidly cool the outlet gas from the front reactor, a multi-tubular heat exchanger is installed directly connected to the reactor outlet, or the tube side of this heat exchanger is filled with an inert material. Methods for more effective cooling (for example, JP-A No. 49-132007, JP-A No. 40
-28340) have been proposed. However, in order to efficiently perform two types of reactions in the first and second stages in the same reactor, it is difficult to find a first stage catalyst and a second stage catalyst that are compatible with the same reaction temperature, and the concentration of propylene, isobutylene, and tertiary-butanol is difficult. It has disadvantages that cannot be mentioned. If these concentrations are increased, the oxygen concentration must be increased in order to improve the reactivity, which may result in entering the flammable range, which is extremely dangerous in terms of operation. In addition, the above-mentioned heat exchanger method for rapidly cooling the produced gas requires the reactor to be large in size, which is not a good idea in terms of cost. It has the disadvantage that when adhesion of polymers, etc. occurs, the pressure loss rapidly increases, and its effectiveness cannot be maintained sufficiently. As an alternative method, JP-A-49-
According to Publication No. 54317, when producing methacrolein, a method is proposed in which water is sprayed onto the produced gas at the outlet of the reactor, but in this case as well, the final product, methacrylic acid, is captured as an aqueous solution. This is accompanied by the disrepute of lowering its concentration in the collection. Generally, the post-reaction (mainly autoxidation or polymerization reaction) of (meth)acrolein-containing gas obtained by gas phase catalytic oxidation reaction of propylene, isobutylene or tertiary-butanol depends on the concentration of (meth)acrolein and oxygen. It also depends greatly on the residence time in the space, the gas temperature, and the pressure within the system. Normally, it is difficult to suppress the after-reaction by removing such factors all at once. For example, if the raw material concentration is lowered in an attempt to suppress the (meth)chlorein concentration, the productivity of (meth)acrylic acid will deteriorate, and if the oxygen concentration is lowered, catalyst reduction will proceed and shorten the catalyst life. Become. On the other hand, as mentioned above, many methods have been proposed for shortening the residence time and lowering the gas temperature, but all of them have drawbacks. The present inventors have studied ways to overcome these drawbacks and have completed the present invention. That is, the present invention is specified as follows. (1) In the process of producing acrylic acid or methacrylic acid by oxidizing propylene, isobutylene or tertiary-butanol in a multi-stage catalytic manner in the gas phase in the presence of molecular oxygen, propylene,
A first catalyst layer provided in contact with a catalyst layer for mainly producing acrolein or methacrolein from isobutylene or tertiary-butanol and for producing mainly acrylic acid or methacrylic acid through gas phase oxidation of acrolein or methacrolein. A reactor and a second reactor provided with a catalyst layer for gas-phase oxidation of acrolein or methacrolein to produce acrylic acid or methacrylic acid, in which one of the acrolein or methacrolein is oxidized in the first reactor. % of acrolein or methacrolein in the gas exiting the first reactor is converted to a molar ratio of 2.0 or less to acrylic acid or methacrylic acid, and further added to the reaction product gas exiting the first reactor. Introducing molecular oxygen into
A method for producing acrylic acid or methacrylic acid, which comprises supplying this to a second reactor. The present invention will be explained in more detail below. Propylene, isobutylene or tert-butanol is mixed with a molecular oxygen-containing gas, e.g. air, in the presence or absence of water vapor,
It is known that acrolein or methacrolein can be oxidized in a catalytic gas phase using a multi-element catalyst containing molybdenum oxide. When the target is acrylic acid or methacrylic acid, it is known to further carry out catalytic gas phase oxidation using an oxidation catalyst containing molybdenum or vanadium. The process of the invention is carried out using these catalysts. The first reactor filled with the first stage catalyst and second stage catalyst as described above has a composition of 1 to 15 volume % of the starting materials propylene, isobutylene or tert-butanol, 1 to 20 volume % of molecular oxygen, and water vapor. The raw material gas containing 1 to 30% by volume and inert gases such as nitrogen and carbon gas is heated at a reaction temperature (reactor heating medium temperature) of 200 to 450℃ and a space velocity of 300℃.
~10000 hr ^-1 (STP) to react more than 90%, especially 95-100% of the starting materials, converting them mainly into (meth)acrolein and (meth)acrylic acid. The content of (meth)acrolein in the latter stage catalyst layer of the first reactor is 35% or more, preferably
It is necessary to convert more than 45% to (meth)acrylic acid. This is because (meth)acrylic acid is partially produced in the front catalyst layer, but (meth)acrolein is further oxidized and becomes (meth)acrylic acid, which must exit the first reactor. That is, the molar ratio of (meth)acrolein in the first reactor outlet gas to (meth)acrylic acid is 2.0.
Hereinafter, the object of the present invention is achieved by converting it to preferably 1.5 or less in the latter catalyst layer of the first reactor. In the first reactor, the first stage catalyst packed part and the second stage catalyst packed part can be maintained at almost the same temperature by the same heat medium circulation and subjected to the reaction, or depending on the structure of the reactor, It is also possible to carry out the reaction by separately circulating the heating medium with a temperature difference of about 0.degree. In the latter case, preferably JP-A-54-
Reactors such as those shown in Publications No. 19479 and No. 54-19480 are used. In this sense, the second-stage catalyst to be filled in the first reactor is selected to have activity under reaction conditions as close as possible to the reaction conditions of the first-stage catalyst. Thus, the reaction product gas leaving the first reactor contains (meth)acrolein and (meth)acrylic acid as the main reaction products, and this gas is temperature-controlled to suit the reaction conditions of the second reactor. The required amount of oxygen is further mixed with a molecular oxygen-containing gas, and water vapor is also added if necessary, and the mixture is supplied to the second reactor. The reaction conditions for the second reactor are such that the raw material gas contains molecular oxygen capable of converting the supplied (meth)acrolein into the corresponding (meth)acrylic acid; The sum of the molecular oxygen in the feed gas to the reactor, relative to the supplied propylene, isobutylene or t-butanol.
A ratio of 1.5 to 5.0 moles, preferably 1.8 to 4.0 moles, is preferably maintained. Reaction temperature (heating medium temperature) is 200 to 400℃, space velocity 200 to 10000ht ^-1
(STP) was adopted. The second reactor only needs to be filled with a sufficient amount of post-catalyst to convert the supplied (meth)acrolein into (meth)acrylic acid, and the load is equal to the post-catalyst in the first reactor. Because of its small size, the reactor will be small. Further, in this case, the downstream catalyst of the second reactor does not necessarily have to have the same composition as the downstream catalyst of the first reactor. It is clear that there is no problem even if (meth)acrolein or (meth)acrylic acid coexists in the additional oxygen-containing gas to the second reactor. By employing the method according to the present invention, the concentration of (meth)acrolein and oxygen decreases at the outlet of the catalyst layer of the first reactor, making it difficult for post-reactions such as autooxidation to occur in the large volume space. ,
In the past, it was considered dangerous to increase the raw material gas concentration due to fear of abnormal reactions at the outlet gas of the first reactor, but now it is possible to increase the concentration freely, and production in the first reactor is now possible. This gave the advantage of being able to increase the performance (load of raw materials per unit catalyst), and enabled industrial production to be carried out safely and at high yields. Example 1 As the first reactor, a reactor having a structure as disclosed in JP-A-54-19479 was used. In other words, this is a vertical multitubular reactor that has 24 stainless steel reaction tubes with a length of 6 meters, an inner diameter of 25.0 mm, and an outer diameter of 29.0 mm, with a shield plate installed horizontally at approximately the center height. , has a structure in which the distance between the reaction tube wall penetrating the shield plate and the shield plate is adjusted to approximately 0.6 millimeters, and molten salt (a mixture of potassium nitrate and sodium nitrite) is flowed to the shell side as a heating medium. The two partitioned sections are circulated by pumps to maintain a constant temperature in each section. As the first-stage catalyst, one prepared according to the method of Example 15 disclosed in Japanese Patent Publication No. 47-42241 was used. This catalyst composition has an atomic ratio of elements other than oxygen expressed as Co ₄ Fe ₁ Bi ₁ W ₃ Mo ₉ Na _0.1 Si _1.35 . The second-stage catalyst used was one prepared according to the method of Example 1 disclosed in Japanese Patent Publication No. 57-297. This catalyst composition has an atomic ratio of elements other than oxygen expressed as Cu _0.3 K _1.0 P _2.0 V ₁ Mo ₁₂ . First, the latter stage catalyst was filled in the lower stage of the reaction tube at a rate of 1230 c.c. per reaction tube, and the bed height was set to 2500 mm.
A spherical Alundum 250 c.c. with a diameter of 5 mm was filled on top of it so that its upper end was exactly on the same plane as the shielding plate. Furthermore, 1,400 c.c. of pre-stage catalyst was packed on top of it, and the height of the wedge-packed bed was set to 2,860 mm. The second reactor had a structure in which no shielding plate was provided in the first reactor, and 1230 c.c. of the latter stage catalyst was wedged into each reaction tube so that the height of the packed bed was 2500 mm. A molecular oxygen supply port was provided at the inlet of the second reactor to ensure uniform mixing via a dispersion plate. As for the reaction conditions, the heating medium temperature was 340°C in the first stage catalyst packed part of the first reactor and 295°C in the second stage catalyst packed part.
℃, and the second reactor was adjusted to 300℃, where the gas composition was 5.0% by volume of isobutylene, 13.5% by volume of oxygen, 66.0% by volume of nitrogen, 15.0% by volume of water vapor, and the others were isobutylene, n-butane, propane, The space velocity of the raw material gas consisting of inert gas such as carbon dioxide at the front stage catalyst of the first reactor is
It was introduced at 1000 Hr ^-1 (STP) and subjected to reaction. Second
The molecular oxygen-containing gas newly introduced from the reactor inlet was added using air so that the molar ratio of molecular oxygen to the starting isobutylene was 2.92 (oxygen/isobutylene). The gas composition at the inlet of the second reactor and the single flow yield of methacrylic acid at the outlet of the second reactor 10 days after the start of the reaction are shown in Table 1, and the amount of carbon monoxide in the gas composition at the inlet of the second reactor. Because of the low level of ``post-reaction'' that can be seen as an autoxidation reaction, almost no phenomenon was observed. Comparative Example 1 Two reactors having the same structure as the second reactor used in Example 1 were used, and the same pre-catalyst as used in Example 1 was used in the first reactor per reaction tube.
The second reactor was filled with 2460 c.c. of the same post-stage catalyst as used in Example 1, and one reaction tube was filled with 2460 c.c. The reaction temperature was adjusted to 340° C. for the heat medium in the first reactor and 300° C. for the heat medium in the second reactor, and a raw material gas having the same composition as used in Example 1 was supplied. Note that air was mixed and supplied in the same amount as in Example 1 from the inlet of the second reactor. Table 1 shows the gas composition at the inlet of the second reactor (after air is supplied and mixed) and the single flow yield of methacrylic acid (relative to isobutylene, mol%) at the outlet of the second reactor 10 days after starting the reaction. show. Since the oxygen concentration and methacrolein concentration in the first reactor outlet gas were high, the carbon monoxide concentration in the second reactor inlet gas was high, and it was clearly observed that a post-reaction was occurring.

[Table] Example 2 Acrylic acid was produced from propylene using the same first reactor and second reactor as used in Example 1. The first stage catalyst for producing mainly acrolein from propylene was prepared according to the method of Example 1 disclosed in Japanese Patent Publication No. 47-42813. This catalyst composition has an atomic ratio of elements other than oxygen expressed as Co ₄ Fe ₁ Bi ₁ W ₂ Mo ₁₀ K _0.06 Si _1.35 . The latter stage catalyst mainly produces acrylic acid from acrolein.
A product prepared according to the method of Example 1 disclosed in Japanese Patent Publication No. 49-11371 was used. This catalyst composition has an atomic ratio of elements other than oxygen expressed as Mo ₁₂ V _4.6 Cu _2.2 Cr _0.6 W _2.4 . First, in the first reactor, the latter stage catalyst was packed in the lower stage of the reaction tube at a rate of 735 c.c. per reaction tube, and the bed height was adjusted.
1,500 mm, and 740 c.c. of spherical alundum with a diameter of 5 mm was filled on top of it so that its upper end was flush with the shielding plate. Then, 1470 c.c. of pre-stage catalyst was filled on top of it, and the bed height was set to 3000 mm. Next, the second reactor was filled with the second stage catalyst at a rate of 735 c.c. per reaction tube so that the bed height was 1500 mm. In addition, a new inlet for molecular oxygen (air) was provided at the inlet of the second reactor to ensure uniform mixing using a dispersion plate. As a reaction condition, the heating medium temperature was set at the first stage catalyst packed part of the first reactor.
310℃, 240℃ in the latter stage catalyst filling section, and 2nd reactor.
Adjust the temperature to 240℃ and add the gas composition here.
A raw material gas consisting of 10% by volume of propylene, 15% by volume of oxygen, 64.5% by volume of nitrogen, 10% by volume of water vapor, and other inert gases such as propane and carbon dioxide is fed to the first reactor at a space velocity of 1500Hr ^-1 (STP). )
was introduced and subjected to the reaction. Fresh air introduced from the second reactor inlet added molecular oxygen to the starting propylene at a molar ratio of 1.80 (oxygen/propylene). Table 2 shows the gas composition at the inlet of the second reactor (after air supply) and the single flow yield of acrylic acid (relative to propylene, mol %) at the outlet of the second reactor 10 days after the start of the reaction. Judging from the carbon monoxide concentration in the gas at the inlet of the second reactor in the same table, almost no "post-reaction" that is considered to be an autoxidation reaction is observed. Comparative Example 2 Two reactors having the same structure as the second reactor used in Example 2 were used, and the same pre-catalyst as used in Example 2 was used in the first reactor per reaction tube.
1470 c.c. was used in the second reactor, and the same latter-stage catalyst as used in Example 2 was used in a reaction tube filled with 1470 c.c. per reaction tube. The reaction temperature was adjusted to 310°C for the heat medium in the first reactor and 255°C for the heat medium in the second reactor, and a raw material gas having the same composition as used in Example 2 was supplied. Note that air was mixed and supplied in the same amount as in Example 2 from the second reactor inlet. Table 2 shows the gas composition at the inlet of the second reactor (after supplying and mixing air) and the single flow yield of acrylic acid (relative to propylene, mol%) at the outlet of the second reactor 10 days after starting the reaction. show. Since the oxygen concentration and acrolein concentration in the first reactor outlet gas were high, the carbon monoxide concentration in the second reactor inlet gas was high, and it was observed that post-reactions were clearly occurring.

[Table] Example 3 In Example 1, the isobutylene concentration was 7% by volume,
Oxygen concentration 16.0% by volume, water vapor concentration 15% by volume, nitrogen
It was set as 61.5% by volume. Furthermore, the same reaction as in Example 1 was carried out except that the temperature was set at 350° C. in the first stage catalyst-filled part of the first reactor, 300°C in the second stage catalyst-filled part, and 300°C in the second stage catalyst-filled part. Table 3 shows the gas composition at the inlet of the second reactor (after air was supplied and mixed) and the single flow yield of methacrylic acid (relative to isobutylene, mol %) at the outlet of the second reactor 10 days after starting the reaction. . As is clear from the table, even when the isobutylene concentration increased, almost no abnormal increase in the carbon monoxide concentration due to autoxidation at the inlet of the second reactor was observed. Comparative Example 3 The reaction format was the same as in Comparative Example 1, the reaction gas composition at the inlet of the first reactor was the same as in Example 3, and the first
The reaction temperature of the reactor was 350°C, and the reaction temperature of the second reactor was 300°C. Further, the additional air at the inlet of the second reactor was adjusted so that the molar ratio of oxygen to isobutylene at the inlet of the first reactor was 2.92, which was also the same as in Example 3. Table 3 shows the gas composition at the inlet of the second reactor (after air supply and mixing) and the single flow yield of methacrylic acid (relative to isobutylene, mol%) at the outlet of the second reactor 10 days after the start of the reaction. Indicated. Since the concentration of oxygen and methacrolein in the gas at the outlet of the first reactor was high, the concentration of carbon monoxide at the inlet of the second reactor was high, and it was clearly observed that a post-reaction was occurring.

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Claims (1)

[Claims] 1 In the process of producing acrylic acid or methacrylic acid by oxidizing propylene, isobutylene or tertiary-butanol in a multi-stage catalytic gas phase in the presence of molecular oxygen, acrolein or methacrolein is mainly produced from propylene, isobutylene or tertiary-butanol. A first reactor provided with a catalyst layer for producing mainly acrylic acid or methacrylic acid by oxidizing acrolein or methacrolein in a vapor phase in contact with a catalyst layer for producing acrylic acid or methacrylic acid; a second catalyst layer provided with a catalyst layer for producing acrylic acid or methacrylic acid;
At this time, a part of acrolein or methacrolein is added in the first reactor so that the molar ratio of acrolein or methacrolein in the gas exiting the first reactor to acrylic acid or methacrylic acid is 2.0 or less. A method for producing acrylic acid or methacrylic acid, which comprises converting the acrylic acid or methacrylic acid until the reaction product gas leaves the first reactor, and then newly introducing molecular oxygen into the reaction product gas leaving the first reactor, and supplying this to the second reactor.