JPS615043A - Production of methacrylic acid - Google Patents

Abstract

PURPOSE:To produce methacrylic acid in high yield, stably for a long period, by the vapor-phase catalytic oxidation of methacrolein with molecular O2 in the presence of a specific heteropolyacid catalyst obtained by adding a Ce source such as cerium oxide, etc. and other component to an Mo-V-P catalyst. CONSTITUTION:Methacrylic acid is produced by the vapor-phase catalytic oxidation of methacrolein with molecular O2 or a gas containing molecular O2 at 200-350 deg.C under atmospheric pressure at a space velocity of the raw material gas of 100-5,000hr<-1> (STP) in the presence of a catalyst composition containing the molybdovanadophosphoric acid of formula (Mo, V, P, Ce and O are molybdenum, vanadium, phosphorus, cerium and oxygen, respectively; X is K, Rb, Cs or Tl; Y is Cu, As Sb, Co, Zr, Bi, Ni, Cr or Mn; a-g are atomic ratios of the elements; b, c, d, e and f are <=3 and >0 when a=12, and g is a value determined by the atomic valences and atomic ratios of other elements).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing methacrylic acid. Specifically, the present invention uses a heteropolyacid catalyst containing molybdenum, vanadium, phosphorus, etc. to catalytically oxidize methacrolein with molecular oxygen or a molecular oxygen-containing gas in a high yield and over a long period of time. The present invention relates to a method for producing methacrylic acid with stable performance.

More specifically, the present invention contains a heteropolyacid mainly composed of molybdenum, vanadium, and phosphorus, which contains at least one member from the group consisting of potassium, rubidium, cesium, and thallium, copper, arsenic, antimony, cobalt, and zirconium. An object of the present invention is to provide a method for producing methacrylic acid from methacrolein using an oxide catalyst coexisting with at least one member from the group consisting of bismuth, nickel, chromium, manganese, and zinc and cerium. .

Many catalysts for the catalytic gas phase oxidation of methacrolein have been proposed, and some of them have begun to be used in the production of methacrylic acid on an industrial scale. The proposed catalyst is
Most of them are mainly composed of molybdenum and phosphorus, and as far as their preparation methods are concerned, their structure consists of phosphomolybdic acid or its salts, such as ammonium salts, alkali metal salts, heteropolyacids, and heteropolyacid salts. It is believed that a mixed composition having this structure is more effective.

However, it has been pointed out that such a catalyst system still has defects not only in terms of the yield of methacrylic acid but also in terms of the life span that it should have as an industrial catalyst. That is, if the reaction is continued for a long period of time, in this catalyst system, the heteropolyacid structure is more markedly decomposed than the heteropolyacid structure, and becomes unusable.

This is because both the salts of heteropolyacids and their salts act effectively in terms of catalytic activity.

Therefore, it is required to stabilize heteropolyacids with good durability and maintain their catalytic activity over a long period of time.
Various studies have been made. For example, as catalyst systems containing molybdenum, vanadium, phosphorus, alkali metals or thallium and cerium,
-36619, 52-12231, 54-14
No. 4311, No. 55-2619, No. 55-10564
No. 1, No. 55-122734, No. 55-124734
There are inventions such as No. 56-91846, No. 57-56043, No. 57-171934, and No. 57-204230. However, looking at the technical details of such catalyst systems, they are still not satisfactory in terms of the high yield and long life that industrial catalysts must have. In particular, even in inventions aimed at the stabilizing effect of heteropolyacids, although there is a disclosure that the addition effect can be found at reaction temperatures of 300°C or higher, the yield is not completely satisfactory, and furthermore, the reaction temperature is 300°C or higher. This is because it is impossible to maintain the durability of this type of heteropolyacid catalyst by setting it beyond this range.

By the way, many examples of descriptions and countermeasures regarding the thermal stability of heteropolyacid catalysts have been disclosed. - For example, in the specification of Japanese Patent Publication No. 40-27526, it is stated that the physical deterioration of phosphomolybdic acid is due to a change in its crystal structure, and separate particles of phosphomolybdic acid recrystallize at high temperatures in the presence of water vapor. It is described that it has a tendency to clump and agglomerate into solid lumps. As a countermeasure against this, a method is disclosed in which it is supported on silicon carbide. Separately, in the specification of JP-A-55-79341, it is stated that the salt structure of alkali gold heteropolyacid salts tends to decompose, and as a preventive measure, the structure is stabilized by adding other components.

Furthermore, in the example of JP-A-55-122734, the catalyst is stabilized by the coexistence of an activity-enhancing component and a small amount of alkali metal salt. However, both have high reaction temperatures of 300° C. or higher, and problems remain as industrial catalysts.

The present inventors found that salts of heteropolyacids containing molybdenum and phosphorus, such as potassium, rubidium, cesium, and thallium salts, are relatively stable thermally and in redox atmospheres, but free salts containing molybdenum and phosphorus are heteropolyacid [
For example, 2θ in X-ray diffraction (Anticathode Cu-Ka)
= 8.0°, 8.9', 9.3', etc.] was extremely unstable during long-term reactions. From instrumental analysis such as line diffraction, we obtained the following findings and estimated the cause.

In other words, the present inventors carried out an accelerated deterioration test under severe reaction conditions of high space velocity, high concentration of methacrolein and low concentration of oxygen-containing raw material gas, and the highest possible reaction temperature. Using a heteropolyacid catalyst containing a metal salt (however, the heteropolyacid is not completely replaced with its alkali metal salt), a catalytic gas phase oxidation reaction is performed on the catalyst to reduce the catalytic activity in an extremely short period of time. I forced it. When the catalyst was extracted and analyzed after such a test, the formation of molybdenum trioxide was observed, clearly indicating that the heteropolyacid or its salt had decomposed. In particular, it was found that tertiary and quaternary aggregation occurs during the free heteropolyacid fertilization reaction, which tends to cause decomposition, resulting in a significant deterioration of catalyst performance.

In order to suppress this phenomenon, we added potassium, rubidium, cesium, and thallium as the X component to the free heteropolyacid, and copper, arsenic, antimony, cobalt, zirconium, bismuth, nickel, chromium, and manganese as the Y component. The inventors discovered a catalyst composition that can suppress the tertiary and quaternary agglomeration of free acids to an extremely low level by blending zinc and cerium to stabilize the free acids, thereby completing the present invention. It is.

That is, the present invention is specified as follows.

il+ When producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen or molecular oxygen-containing gas, the general formula % formula % [In the formula, MO, v, p, Ce, and o are molybdenum and vanadium, respectively. , phosphorus, cerium and oxygen;
X represents at least one element selected from the group consisting of potassium, rubidium, cesium, and thallium, and Y
Indicates at least one element selected from the group consisting of copper, arsenic, antimony, cobalt, zirconium, bismuth, nickel, chromium, manganese, and zinc. Also, the subscripts JL, b, es dz esf and g represent the atomic ratio of each element, and when a = 12, bNc%d%
e and f each have a value of 3 or less and do not include 0 (zero), and take values determined by the valence and atomic ratio of gti and other elements. ] A method for producing methacrylic acid, which comprises using a catalyst composition represented by the following formula and containing molybdovanadric acid.

121 The method described in (1) above, characterized in that cerium oxide is used as the cerium source.

(3) The method described in 11) or 121 above, characterized in that each oxide is used as a starting material for the Y component.

The present invention is based on the above, but the gist of the invention lies in how to stabilize free heteropolyacid in a catalyst and improve its performance. In the present invention, cerium oxide and thallium, potassium, rubidium, and cesium components are added to stabilize the existing free heteropolyacid. Furthermore, it has been discovered that Y components such as copper and cobalt are added to reduce catalyst performance deterioration, and that good results can be obtained by including these Y components in the catalyst to prevent them from forming salts with heteropolyacids. be.

Thus, the feature of the present invention lies in the effect of adding the cerium component, the form of the cerium component in the catalyst, and the specification of the timing of addition of the Y component.

Regarding the cerium component, the form in the catalyst is cerium oxide. Cerium oxide is generally said to be an oxide that exhibits basicity, although it is not as strongly basic as alkaline earths.

If the basicity is too strong, side reactions such as decomposition of methacrylic acid occur, which is undesirable. On the other hand, if the basicity is too weak, the acid-base reactivity with heteropolyacids, for example, will be poor, and the stability of the free acid cannot be expected to contribute much.

This promising result will be shown in Examples and Comparative Examples, and when looking at the changes in the catalyst during the accelerated deterioration test, the aggregation of free acid was suppressed, and as a result, the formation of molybdenum trioxide was suppressed. It is also believed that the basicity of cerium oxide contributes to controlling the acid-base content of the entire catalyst, resulting in an improvement in yield.

Regarding other effects of cerium oxide, it has a high affinity for gas-phase oxygen, and has the effect of extremely smoothing the redox cycle of the catalyst during the methacrolein-catalyzed gas-phase oxidation reaction on the catalyst. This was confirmed from the fact that the dependence on gas phase oxygen was closer to zero order in terms of reaction kinetics. Yet another advantage is that
Heteropolyacid catalysts (including salts) containing molybdenum and phosphorus are generally said to have strong oxidizing power, but despite this, the oxygen to methacrolein ratio is low, for example, in the case of acrylic acid produced by acrolein oxidation, which has been industrialized for many years. It is said that a higher ratio is usually required compared to the reaction conditions in synthesis. However, despite this drawback, it was found that the presence of cerium oxide made it possible to carry out the reaction for a long period of time even under conditions where the ratio of oxygen to methacrolein was low.

Another advantage of the catalyst of the present invention is that it can sufficiently exhibit its performance even in reactions at high space velocities. Furthermore, addition of cerium oxide can provide sufficiently high reaction activity even at a reaction temperature of 300° C. or lower.

As mentioned above, we have talked about the effect of adding cerium component,
It is preferable to add such cerium oxide before adding the Y component so that it can react with the free heteropolyacid as selectively as possible.

Next, the Y component, which is a feature of the present invention, will be described.

The effect of adding the Y component is its contribution to improving the activity. Here Y
Most of the component oxides are weakly acidic or at most amphoteric oxides when used alone. In the present invention, when adding the Y component, it is present in the catalyst in the form of an oxide consisting of at least one Y component, thereby contributing to the stabilization of the free heteropolyacid and improving the performance. was recognized as doing so. Many of the Y components, for example, tend to preferentially form heteropolyacid salts when a water-soluble salt is used as a starting material; It is easily unstable. Therefore, a feature of the present invention is that the free heteropolyacid is stabilized in advance by an acid-base reaction using an oxide of cerium, and the free heteropolyacid and salt are also stabilized when adding the Y component. By preparing to prevent the formation of free heteropolyacids, it is possible to further stabilize the free heteropolyacid and improve the performance of the catalyst. Therefore, when adding the Y component, the starting material does not necessarily have to be an oxide, but as long as it can be prepared as a raw material that can ultimately exist in the catalyst as an oxide (not in the form of a heteropolyacid salt). That's good. For example, in one example of catalyst preparation, molybdenum, phosphorus, vanadium, and alkali metal components are reacted in an aqueous solution, and cerium oxide is added thereto. After drying the slurry or aqueous solution prepared in this manner at around 100° C., the Y component is added and the mixture is formed into tablets or extruded with the addition of water. After molding using a conventional molding method, the catalyst is calcined.

In this way, the life of the catalyst is greatly extended due to the combination of cerium oxide and free heteropolyacid, as well as the coexistence of potassium and cesium salts of heteropolyacid, or the synergistic effect with components such as vanadium, copper, and cobalt. improved yield of methacrylic acid. Analysis of the catalyst prepared according to the present invention during an accelerated test shows that aggregation of free heteropolyacids is suppressed to a minimum, and that changes in catalyst surface area, pore distribution, and pore volume are slight; It was also confirmed that the production of molybdenum trioxide was suppressed to the utmost.

When using the catalyst according to the present invention, the catalyst composition may be extruded or tablet-molded into a pellet, spherical, cylindrical, ring, etc. shape.
α-alumina, silica alumina, silicon carbide,
It may be impregnated or adhered to a pre-formed carrier such as titanium oxide, magnesium oxide, or aluminum sponge, or it may be formed by adding powder of silicon carbide, diatomaceous earth, alumina, etc. Good too. Moreover, various materials can be used as catalyst raw materials. For example, molybdenum compounds include ammonium paramolybdate, molybdic acid, molybdenum trioxide, phosphomolybdic acid, lymphanatomolybdic acid, etc.
Ammonium metavanadate as a vanadium compound,
Vanadium pentoxide, vanadyl 6ate, vanadyl *acid, etc. are used as phosphorus compounds such as phosphoric acid, primary ammonium phosphate,
Secondary ammonium phosphate and the like are used as the X and Y components, hydroxides, sulfates, carbonates, oxides, etc. of these component elements are used, and cerium oxide is used as the cerium compound.

The catalyst according to the present invention is used for the gas phase catalytic oxidation reaction of methacrolein (methacrolein as a raw material).
It may be a methacrolein-containing gas leaked from a gas phase catalytic oxidation reaction using butanol as a raw material, or a gaseous methacrolein obtained from methacrolein synthesized by a liquid phase method, and is not particularly limited. Raw Materials Gas Co., Ltd. Molecular oxygen is mixed with any of these and used. Air is industrially advantageous as the oxygen source. Inert gases such as nitrogen gas, carbon dioxide, helium, argon, -
Carbon oxide, water vapor, etc. can be used.

The methacrolein concentration in the oxidation reaction is 0.5 to 15 volumes, preferably 1 to 10 volumes.

The volume ratio of oxygen to methacrolein is in the range of 0.5 to 10, preferably in the range of ul to 5. The space velocity of the raw material gas is suitably in the range of 100 to 5ooohr-1 (STP), preferably 1d300 to 3000hr-1 (STP).Reaction temperature #' is in the range of 1200 to 350°C, preferably 240 to 300°C. The reaction pressure is usually operated near normal pressure, but it is also possible to operate under increased pressure or reduced pressure.

When using the catalyst according to the invention, the reactor is generally of a fixed bed type, but either a fluidized bed or a moving bed type can be used.

The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

In addition, the conversion rate, selectivity,
Depends on the definition of single flow yield.

Selectivity of the number of moles of methacrylic acid produced (a) = Number of moles of consumed methane rhein 8”0
0 Example l Molybdenum trioxide 288. Of, vanadium pentoxide 15
．． 29.3 f of 29 and 85% orthophosphoric acid in 1 t of water
and heated under reflux for 24 hours. Thereto, 14.3 F of powdered cerium oxide and 25.3 F of potassium nitrate were added to the heated solution, and the solution was heated and concentrated while stirring. The obtained clay-like substance was dried at about 100℃ for 4 hours, then crushed, 2.72 kg of powdered copper oxide was added thereto, mixed well, 20% of water was added, kneaded well, and further dried at 200℃ for 4 hours. The powder was then crushed to a particle size of about 5 gourds, and then heated at 430 °C in a nitrogen stream.
C. for 3 hours, followed by firing at 400.degree. C. for 4 hours in a stream of air. The composition of the catalyst thus obtained was Mo1. V.

P1. s K +, s Cu 6.2 Ce 6.6
(atomic ratio excluding oxygen).

20 ml of this catalyst was filled into a stainless steel U-shaped tube with an inner diameter of 13 mm, and the tube was immersed in a molten salt bath at 270°C. In this reaction tube, 5 mol% of methacrolein, 10 mol of oxygen, and 3 mol% of water vapor were added.
A mixed gas with a composition of 0 molar width and 55 mol% nitrogen is introduced, and its space velocity is set to 1500 hr-1 (STP
), the oxidation reaction of methacrolein was carried out and a catalyst performance test was conducted, resulting in a methacrolein conversion rate of 91.6% and a selectivity to methacrylic acid of 81.2%.

Next, we conducted long-term reaction tests using this catalyst to observe changes in performance over time. The reaction conditions were as follows: A reactor for producing methacrolein was installed before the methacrolein oxidation long-term reaction test equipment, and the reactor was filled with a molybten-cobalt-containing multi-component catalyst. A long-term reaction test was conducted by introducing isobutylene, oxygen, water vapor, and nitrogen to contain 5 mol of methacrolein, 10 mol of oxygen, and 30 mol % of water vapor, and supplying the resulting gas to the catalyst. Ta. The space velocity for the long-term reaction test was 1500 hr-1 (STP), and the reaction temperature was 270°C.
It was set to As a result, the yield after 3000 hours was 92.0% methacrolein conversion, and the selectivity to methacrylic acid was 8.
It was 1.51. After 6000 hours, the methacrolein conversion rate was 91.3%, and the selectivity line for methacrylic acid was 81.
4%, after 12,000 hours, by simply increasing the reaction temperature by 4°C from 6,000 hours, the methacrolein conversion rate remained at a constant level of #1, and the selectivity to methacrylic acid remained at a level of 81. did.

After 12,000 hours of reaction, the catalyst was taken out and the state of molybdenum trioxide formed was examined by X-ray diffraction of the catalyst at the exothermic peak position, and it was found that the amount of molybdenum trioxide was very small, but could be observed.

Example 2 Using the catalyst obtained in Example 1 and using the same reaction apparatus as in Example 1, the following accelerated catalyst deterioration test method was adopted to perform a life test. That is, after conducting a catalyst performance test, the molten salt bath temperature was raised to 380°C, and the supply gas composition was changed to methacrolein:oxygen:nitrogen:steam=2 in a volume ratio.
:6:32:10, and the space velocity was changed to 2000 hr-1 (STP), and after each time period, the salt bath temperature, feed gas composition, and space velocity were adjusted to the catalyst performance test conditions. A long-term reaction test was carried out by repeating the process of returning the sample to the performance test and then returning the reaction condition to the accelerated deterioration test condition. As a result, under the catalyst performance test conditions at the beginning of the reaction, the conversion rate of methacrolein was 91.2% and the selectivity to methacrylic acid was 81.4%. The conversion rate of methacrolein after 300 hours of accelerated deterioration test was 88.6%, and the selectivity to methacrylic acid was 81.7.
%, methacrolein conversion after 500 hours 86.0%, selectivity to methacrylic acid 81.0%, methacrolein conversion after 1000 hours 80.1%, methacrylic acid selectivity 7
It was 8.2%. After the 1000 hour reaction test, the catalyst was taken out and the state of molybdenum trioxide formation was examined by X-ray diffraction, and the presence of a peak was slight but noticeable.

Comparative Examples 1 to 6 A catalyst in which orthophosphoric acid, potassium nitrate, cerium oxide, and oxidized steel are not added in the catalyst preparation method of Example 1 (Comparative Example 1), a catalyst in which potassium nitrate, cerium oxide, and oxidized steel are not added (Comparative Example 2), A catalyst to which vanadium pentoxide and copper oxide were not added (Comparative Example 3), a catalyst to which orthophosphoric acid and copper oxide were not added (Comparative Example 4), and a catalyst to which potassium nitrate and copper oxide were not added (Comparative Example 5) were prepared and used in Examples. A catalyst performance test was conducted under the same reaction conditions as in Example 1. Further, a catalyst deterioration acceleration test and a catalyst performance test were conducted under the same reaction conditions as in Example 2 using a catalyst prepared according to the method of Example 1 without adding cerium oxide (Comparative Example 6). The results are shown in Table-1.

Comparative Example 7 Molybdenum trioxide 288. Of, vanadium pentoxide l
5.2 t and 29.3 f of 85 thiorthophosphoric acid were added to water Xt and heated under reflux for 24 hours. Copper nitrate 8.1 there
f, potassium nitrate 25.39 and cerium oxide 14.
39 was added, and the mixture was heated and concentrated while stirring.

The resulting clay-like material was dried at about 100°C for 4 hours, crushed, added with 20% water, kneaded well, and further crushed with 20% water.
After drying at 0° C. for 4 hours, it was pulverized to a size of about 5 m, and this was calcined at 430° C. in a nitrogen stream for 3 hours, and then at 400° C. in an air stream for 4 hours. Composition of the catalyst thus obtained/d M
o l* Vt P t, s Ki, s Cuo, xC
eo, 5 (atomic ratio excluding oxygen).

Example 1: Catalytic performance test and accelerated deterioration test of this catalyst
It was carried out according to method 2. The results are shown in Table 2.

As is clear from Table 2, when the catalyst is prepared by changing the timing of addition of the Y component and adding it in the form of copper nitrate to form a copper salt of heteropolyacid after catalyst calcination, the activity decreases significantly. I understand that.

Examples 3 to 21 Each catalyst shown in Table 3 was prepared according to the method of Example 1, but the amount of orthophosphoric acid, vanadium pentoxide, potassium nitrate, steel oxide, and cerium oxide were changed. . All other procedures were carried out in accordance with Example 1, including the catalytic performance test using the oxidation reaction of methacrolein. The results obtained are shown in Table 3.

Examples 22 to 24 Each catalyst shown in Table 4 was prepared according to the method of Example 1 except that rubidium nitrate, cesium nitrate, and thallium nitrate were used instead of potassium nitrate, and the performance test for methacrolein oxidation reaction was also carried out. It was carried out according to Example 1. The results obtained are shown in Table 4.

Example 25 353 ammonium molybdate in 1.2 t of heated water
．． 29, 19.52 t of ammonium metavanadate, and 29.3 t of 85% orthophosphoric acid were dissolved and stirred. 25.3 F of potassium nitrate dissolved in 50 g of water was added thereto, an aqueous nitric acid solution was added to adjust the pH to around 1, and then 14.39 g of powdered cerium oxide was added, followed by heating and concentration with stirring. The resulting clay-like substance is heated to approximately 100℃.
After drying, crush the powder and 20m7! After kneading well with an aqueous solution of cobal nitrate (14.62) dissolved in water, the mixture was dried at 200°C for 4 hours and then ground to a particle size of about 500ml. 4th year middle school
It was baked at 00°C for 4 hours. The composition of the catalyst thus obtained was Mo 12 VIP +, s Kl, 5 Co o,
s Ce o,s (atomic ratio excluding oxygen).

The reaction was carried out in the same manner as in Example 1 using this catalyst. The results are shown in Table-5.

Examples 26 to 33 Nickel nitrate substituted for cobalt nitrate in Example 25,
Chromium oxide, manganese oxide, bismuth nitrate, zinc oxide,
A catalyst was prepared according to the method of Example 25 using arsenite, antimony oxide, and zirconium oxide. The catalyst performance test followed the method of Example 1. The results are shown in Table-5.

Claims (3)

[Claims] (1) When producing methacrylic acid by vapor phase catalytic oxidation of methacrolein with molecular oxygen or molecular oxygen-containing gas, the general formula Mo_aV_bP_cX_dY_eCe_fO_g [wherein Mo, V, P, Ce, and O are molybdenum and vanadium, respectively] , phosphorus, cerium, and oxygen; , represents at least one element selected from the group consisting of manganese and zinc. Also, the subscripts a, b, c, d, e, f and g represent the atomic ratio of each element, and when a=12, b, c, d, e, f are respectively 3 excluding 0 (zero). The following values are taken, and g takes a value determined by the valence and atomic ratio values of other elements. ] A method for producing methacrylic acid, which comprises using a catalyst composition represented by the following formula and containing molybdovanadric acid. (2) The method according to claim (1), characterized in that cerium oxide is used as the cerium source. (3) Claim (1) or (2) characterized in that each oxide is used as the starting material for the Y component.
Method described.