JPH0427224B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for the oxidative dehydrogenation of isobutyric acid to methacrylic acid using a catalytic catalyst. The synthesis of methacrylic acid and its esters for use in polymer production is of great economic importance. In addition to the common industrial method of saponifying acetone cyanohydrin to produce methyl methacrylate, which is the most important monomer in the methacrylate system, using acetone as a starting material, recently, isobutyraldehyde or olefin, e.g. Synthetic methods using isobutylene, ethylene or propylene are also of technical interest. DE 2517148 describes a process for the preparation of methacrylic acid starting from methacrolein, obtained for example from isobutylene or isobutyraldehyde, by catalytic gas phase oxidation using oxygen. The catalyst used in this _reaction has _{the formula} : _{Mo 12} P _a
or represents thallium, a and b have a value of 0.1 to 10, c has a value of 0..1 to 8, d has a value of 0 to 10, and the value of e is another atom. Depending on the valence of , the sum of a + b + c has a value from 0.3 to 20]
corresponds to Many catalysts have been proposed for the oxidative dehydrogenation of isobutyric acid to methacrylic acid. JP-A-50-4017 discloses molybdenum, phosphorus,
Catalysts containing thallium and oxygen have been proposed. JP-A-50-4014 also discloses the use of molybdo or molybdovanadium phosphoric acid treated with nickel, cobalt or alkali metal sulfates as a catalyst for the oxidative dehydrogenation of isobutyric acid in the gas phase. This is described. Furthermore, using calcined iron phosphate/lead phosphate as a dehydrogenation catalyst, alkanecarboxylic acids and -esters were
A method of oxidative dehydrogenation to β-unsaturated aliphatic acids and esters has also been proposed (German Published Patent Application No. 2450878). The dehydrogenation of compounds of this type with oxygen using calcined precipitated phosphates containing bismuth, iron and optionally lead is described in German Patent Application No.
No. 2118904. However, the known methods were not completely satisfactory. Recent observations suggest that in addition to mere equipment costs,
The balance between power and raw material consumption against space-time yield and reaction selectivity has become of decisive importance. That is, for example, in a reaction using an iron-phosphate base as a catalyst, the conversion rate of isobutyric acid is relatively low. In other words, unreacted isobutyric acid must be refluxed during the reaction process. Because the physical properties of isobutyric acid and methacrylic acid are very similar, separation of both compounds on an industrial scale is problematic and in any case expensive. According to West German Patent Publication No. 2550979, solid catalysts consisting of molybdenum and/or tungsten or their oxides are generally used in amounts of 300 to 500%.
It is described to be used at a temperature of °C. From DE 2722375 A1 a hydrothermal process is known for the preparation of catalysts based on heteromultiacids from molybdenum, vanadium, phosphorus and optionally tungsten oxides or oxyacids, which Suitable for oxidative dehydrogenation of isobutyric acid or its methyl ester and methacrolein. However, in tests using heteromultiacid catalysts, relatively high conversion rates with good selectivity were achieved.
A relatively narrow range of temperatures above 330℃ (approximately 330-350
It was shown that this can only be achieved when working at Below this temperature range, the reaction is significantly reduced, and above 350° C. the catalyst is apparently irreversibly damaged and the reaction rate and therefore the selectivity of the reaction are also significantly reduced. Maintaining such a narrow temperature range at relatively high temperature levels under conditions of heterogeneous catalysis is technically difficult to achieve without significant expense. In other words, in practice such catalyst systems are only slightly durable under the reaction conditions mentioned above. By the way, it is based on molybdenum oxide and also contains P and V as essential elements, as well as Na, alkaline earth metals, Zn, Ag, Al, Ti, Mn, Fe,
It consists of one, two, or several elements M selected from the group of Co, Ni, or Sn, and the composition of the catalyst is the formula: M _a Mo _b V _c P _d O _e [where a is 0.4 to 2.5] b has a value of approximately 12, c has a value of 1 to 2, and d has a value of 0.5 to 3
isobutyric acid to methacrylic acid by using a substantially sulfate-free metal oxide catalyst represented by It has been found that the oxidative dehydrogenation process can be carried out with very good yields and high selectivities. Preferred metals M are magnesium, calcium and aluminum. Particularly advantageous is that in the above formula b has a value of approximately 6a, d has a value approximately similar to a, and c approximately
This is a group of catalysts with a value of 0.75a. Molybdenum compounds such as molybdenum oxide or molybdate H ₂ MoO ₄ or salts such as ammonium salts, 5
Compounds of valent phosphorus such as phosphoric acid or polyphosphoric acid or salts thereof, phosphorus pentoxide, salts of panadium such as nitrates, carbonates, sulfates or halides or salts of organic acids or oxides of panadium and salts of the metals M mentioned above. or hydroxides such as metal halides, -
Carbonates, -nitrates, -sulphates or salts of organic acids can be used. If one of the metals mentioned above is added to the catalyst production mixture in the form of a sulfate, care must be taken that the sulfate salt is almost completely separated off during catalyst preparation. Preferably no forming components in the form of sulfates are used. Known methods for producing metal oxide catalysts with complex compositions can be applied to the production of the catalyst. The catalyst system is obtained, for example, by mixing the components dissolved or suspended in a liquid reaction medium, such as water. At this time, care should be taken to ensure that the distribution is as uniform as possible. Advantageously, especially when ammonium compounds are used, alkanolamines such as monoethanolamine can also be added to the aqueous solution. The liquid reaction medium can subsequently be removed by evaporation, preferably under heating. If water is used as the reaction medium, the water removal can be carried out at 100-150°C, in particular at approximately 120°C. Subsequently, the catalyst system is preferably calcined, for example at a temperature of 200 DEG to 400 DEG C. This can take about 1-2 hours. Particular preference is given to the embodiment in which a solid support is used for the catalyst system according to the invention. aluminum,
Preference is given to supports based on oxygen compounds of titanium and especially silicon or mixtures of various oxygen compounds thereof. Particularly advantageous are support systems based on silicon dioxide and "activated silicon dioxide" (Unger, Angew.
Chemie (1972, Vol. 84, p. 331), especially those based on diatomaceous earth and Aerosil. Preferred mixing ratios of silicon dioxide (eg diatomaceous earth) and activated silicon dioxide (eg Aerosil) are from 14:2 to 9:2, especially 5:1. The ratio of catalyst to support can then be varied within certain limits. Generally from 5 to 80% by weight of catalyst, preferably from 20 to 70% by weight, based on the total weight (catalyst+support). The same products can be prepared in any suitable manner for use as catalyst systems, such as by micronization, granulation, tabletting, etc. Granulation or micronization and tabletting can be followed by another heat treatment, for example at between 300 and 500°C, which can take for example from about 1 to about 24 hours. The catalytic system can be used on its own or advantageously mixed with inert substances such as quartz or zirconium dioxide.
The latter method has economic and technical advantages, such as improved temperature distribution, stabilization of reactor conditions, etc. The catalyst system according to the invention can be applied to the oxidative dehydrogenation process of isobutyric acid within a relatively wide temperature range without loss of activity or deactivation. Advantageously, the process according to the invention is carried out at temperatures between 300 and 450°C, especially between 340 and 370°C.
It is carried out at ℃. In that case the residence time is generally 0.1
~5 seconds. Thus, if temperatures above the optimum temperature range occur during the contacting operation, this generally does not result in irreversible deactivation of the catalyst system. The catalyst system according to the invention is distinguished by very good space-time yields and high selectivities. The oxidative dehydrogenation process according to the invention uses oxygen as oxidizing agent, for example in the form of air. The reaction is preferably carried out as a gas phase reaction, using isobutyric acid and oxygen in the gas phase, preferably using a gas mixture of isobutyric acid, water, oxygen and nitrogen. The ratio between each component in the above order is advantageously within the following limits: (1-2.5): (0-3): (1-
2):(4-20) mol, a particularly advantageous ratio is 1:
2:1.7:20 mol. In the process of the invention, the presence of water has an advantageous effect on the reaction process. The process according to the invention can be carried out in conventional reactors, for example under pressure. The relevant pressures are between 0.5 and 5 bar, preferably between 0.8 and 2.0 bar. If the proportion of oxygen increases during the reaction, the temperature may increase considerably, but this does not usually lead to deactivation of the catalyst due to the unexpectedly high stability of the catalyst system. In the process according to the invention, the catalyst can be used either as a fixed bed or as a fluidized bed. The following examples illustrate the invention in detail. Percentage values are by weight unless otherwise stated. The stated reaction rate or selectivity is defined as follows: Reaction rate of isobutyric acid (%) = Amount of isobutyric acid reacted (mol) / Amount of isobutyric acid used (mol) ・100 Selection of methacrylic acid production Rate (%) = Amount of methacrylic acid produced (mol) / Amount of reacted isobutyric acid (mol)・100 A) Catalyst production 1 (NH ₄ ) ₆ Mo ₇ O ₂₄・4H 2 in 300 ml of 10% ammonia _solution A solution of 106 g of O, 100 g of water
11.52 g of 85% orthophosphoric acid dissolved in 200 ml of water are added and the whole is stirred into 8.5 g of sodium nitrate dissolved in 200 ml of water. And 10
8.8 g of NH ₄ VO ₃ dissolved in 140 ml of % hydrous monoethanolamine are added. The solution thus obtained contains ±40.8 g of purified and heat-treated diatomaceous earth as a catalyst carrier and Aerosil.
8.18 g of 200 are added under stirring and then evaporated. The solid catalyst body is dried at 120° C. for 7 hours and then calcined at 300° C. for 3 hours.
70% Na ₂ Mo ₁₂ V _1.5 P ₂ O _45.8 on diatomaceous earth/Aerosil 200 so obtained - _the catalyst is a very hard material and then for the reactor filling a particle size of about 3
Produce catalyst particles of mm. 2. To produce the catalysts in the examples listed in the table below, the metals listed in the table are used in equivalent amounts in the form of salts in place of the Na salt, and the process is otherwise carried out in the same manner as in 1. B Examples of oxidative dehydrogenation of isobutyric acid 1 to 10 The table below shows the oxidative dehydrogenation of isobutyric acid to methacrylic acid using yet another catalyst with the general formula: M _a Mo _b V _c P _d O _e . We summarize the results obtained. In this case, a mixture of isobutyric acid, water and oxygen (as air) in a molar ratio of 1:2:1.7 was passed over the catalyst in a temperature range of 340 DEG to 370 DEG C. with a residence time of 0.3 to 0.4 seconds.

[Table] Examples 11 to 17 A) Four types of catalysts A to D having the following compositions are prepared using the same working method as described in 2: A) MnMo ₁₂ V _1.5 P ₂ O _45.8 B) Fe _0.67 Mo ₁₂ V _1.5 P ₂ O _45.8 C) CoMo ₁₂ V _1.5 P ₂ O _45.8 D) NiMo ₁₂ V _1.5 P ₂ O _45.8 Molar ratio of isobutyric acid, water and air oxygen on catalysts A to D in the temperature range from 320 to 350 °C 1:
A 2:1.7 mixture was introduced with a convection time of 0.3 seconds. The table below lists the values obtained for the reaction rate of isobutyric acid and the selectivity for the production of methacrylic acid.

[Table] Example 18 Catalysts of composition C according to Examples 11 to 17 (on diatomaceous earth support)
At a temperature of 360 °C and a residence time of 0.5 seconds on 13 ml,
Molar ratio of isobutyric acid, water, oxygen and nitrogen: 1:
A gas mixture of 2:1.5:20 was introduced. Methacrylic acid was obtained with a selectivity of 74.1% at a reaction rate of isobutyric acid of 99.8%.

Claims (1)

[Claims] 1. Metal oxide based on molybdenum oxide
In the oxidative dehydrogenation of isobutyric acid to methacrylic acid using a catalyst, the substantially sulfate-free metal oxide catalyst contains elements P and V in addition to molybdenum;
Furthermore, Na, alkaline earth metals, Zn, Ag, Al, Ti,
1 selected from the group of Mn, Fe, Co, Ni or Sn
The composition of the catalyst is represented by the formula: M _a Mo _b V _c P _d O _e [where a has a value of 0.4 to 2.5 and b has a value of approximately 12]. , c has a value of 1 to 2, and d has a value of 0.5 to 3
, and e has a value determined from the valence and content of other elements. 2. Process according to claim 1, in which a metal oxide catalyst is used together with a solid support based on silicon dioxide/activated silicon dioxide. 3. The method according to claim 2, wherein the ratio of silicon dioxide/activated silicon dioxide in the carrier is from 14:2 to 9:2. 4. Any one of claims 1 to 3 in which the metal oxide-catalyst occupies 5 to 80% by weight based on the total weight (support + metal oxide-catalyst)
The method described in section. 5. The method according to any one of claims 1 to 4, wherein the catalyst is calcined at a temperature of 200 to 400°C. 6. The method according to any one of claims 1 to 5, which is carried out as a gas phase reaction. 7. Process according to claim 6, working with a gas mixture consisting of isobutyric acid, water, oxygen and nitrogen. 8 The molar ratio of isobutyric acid to water to oxygen to nitrogen is (1-
2.5):(0-3):(1-2):(4-20) The method according to claim 6 or 7. 9 Claim 1 in which the reaction is carried out at 300 to 450°C
The method described in any one of paragraphs to paragraphs 8 to 8. 10 The gas mixture is introduced at a space velocity of about 100 to 15,000 gas/catalyst/h.
The method described in section. 11. The method according to any one of claims 7 to 10, operating at a pressure of 0.5 to 5 bar. 12. The method according to claim 1, wherein the metal oxide-catalyst contains one metal selected from the group of magnesium, calcium, and aluminum.