JPS5865240A - Gas phase oxidation of methacrolein to methacrylic acid - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION As is well known, unsaturated acids such as acrylic acid and methacrylic acid are prepared by gas phase oxidation of the corresponding unsaturated aldehydes with molecular oxygen in the presence of a suitable oxidation catalyst. can do.

Various catalyst compositions have been proposed for this purpose. Many such catalysts consist of molybdenum oxides and phosphorus oxides and oxides of various other metal and non-metal elements. Of particular interest with respect to the present invention are known and pending patent specifications, such as U.S. Patent Application No. 973.354 (December 6, 1978) and U.S. Patent Application No. 047.860. Specification(
June 12, 1979), U.S. Patent No. 4,252,68
No. 2, No. 4,252,681, No. 4,252,683
No. 4,240,930, No. 4,261,858, No. 4,261,859, No. 4,261,860, and No. 4,271.040. .

Methacrolein to methacrylic acid 11? Chemical catalysts have the characteristic property of being stable for a certain period of time and then rapidly decreasing in activity. Formulation of such a catalyst F! The effectiveness is adjusted to extend life and increase the production of methacrylic acid for a given amount of catalyst. It is shown herein that the composition of the reaction feed gas, particularly the carbon dioxide content, affects the useful life and productivity of the catalyst.

The prior art shows little about the influence of the composition of the reactant gas. No. 3,171,859 shows that when oxygen is supplied as pure oxygen, recycling of by-product gas increases the carbon oxide concentration of the reaction feed gas. The reaction disclosed is the oxidation of propylene to acrolein rather than the oxidation of methacrolein to methacrylic acid. No mention is made of the effect of gas composition on catalyst life.

The oxidation of olefins such as isobutylene is described in U.S. Pat. No. 3,883,588. According to that specification, the use of diluents is desirable to facilitate control of this exothermic reaction. The carbon dioxide produced in the reaction is shown along with nitrogen from the air as a diluent.

The oxidation of acrolein to acrylic acid is described in U.S. Pat. No. 3,985,800, which does not discuss the effect of such dilute use on catalyst performance.

The specification states that the use of a feed gas containing a large amount of carbon oxide (Example 2) gives similar results to the use of nitrogen as a diluent (Example 1).

It states that the catalyst has an excellent lifespan, but does not mention the effect of carbon dioxide use on this lifespan.
Gas composition is also included in the operational data, but this is outside the scope of the disclosed invention.

The adverse effects of carbon oxides in the reaction feed gas are discussed in U.S. Pat. No. 4,147,885 for the oxidation of propylene to acrylic acid. contains carbon dioxide as a large portion of the reaction feed gas, then 1 ft/a
It has been found that when used in the gas phase oxidation of methacrolein to methacrylic acid with a catalyst, there is a beneficial effect on the lifetime and productivity of the catalyst.

It has been found that the productivity of molybdenum-based catalysts in the gas-phase oxidation of methacrolein is considerably improved by increasing the molar ratio of carbon dioxide to carbon monoxide to that produced in the oxidation reaction. . This can be carried out by adding carbon dioxide from an external source, - selectively removing carbon oxides, or - selectively oxidizing carbon oxides to carbon dioxide.

Generally speaking, the invention applies to molybdenum-based heteropolyacid catalysts, such as those characterized as phosphomolybdates. Preference is given to carrying out the oxidation reaction using suitable catalysts containing one or more of the following elements: molybdenum, copper, phosphorous, antimony and cesium and/or calci and rare earth metals such as La. The reaction feed may contain 5-20% by volume methacrolein, 3-15% by volume oxygen, and up to 50% by volume water vapor. The ratio of carbon dioxide to carbon monoxide in the feed gas can be greater than the ratio resulting from oxidation of methacrolein.

In a preferred embodiment, fresh oxygen is supplied to the reaction as substantially pure molecular oxygen and unreacted methacrolein and unreacted oxygen are recycled to achieve an equilibrium condition. The carbon dioxide content of the recycle gas may be increased to its equilibrium value, while carbon monofluoride is selectively oxidized by a suitable catalyst in the presence of methacrolein, so that the reactor feed gas is It has a molar ratio greater than the molar ratio of carbon dioxide and carbon monoxide produced by the oxidation of rhein, which is larger than the normal molar ratio of 1.

A preferred catalyst composition for use in the process of the invention is 't
General formula MO12CuaPbSbcAaBeOx [
J: Two c can be defined. Here, one is cesium and/or calcium, BkeNiS'Z
・nXRu, R,) (Pd, Pt, A-s, Rb,
Sr, Ba, Cr, V, Nb, W, Mn, Re
and rare earth metals such as La, and 3% bs Cs dse and X indicate the ratio of the number of atoms of each component to MO12, and a is 0.05 to 3 b i 0.1~5, CU
O.

01-1, d is 0.1-3, e is 0-3-r, and X has a value determined by the valence number and ratio of other elements in the catalyst. Preferably, %b is 0.5 to 6, more preferably 1 to 2, most preferably about 1.2 to 1.8, and preferably C is 0.01 to 1. Generally, it can be said that this is a method in which the oxidation of methacrolein to methacrylic acid is carried out at a ratio greater than the ratio of carbon dioxide and carbon monoxide produced by the oxidation reaction. What this means in practice is that the ratio C02
/CO by either the addition of carbon dioxide, the removal of carbon oxide or the conversion of carbon monoxide to carbon dioxide.

The method to be selected depends on the method of oxygen supply. There are two basic methods for supplying the oxygen necessary for the oxidation of methacrolein. That is, it is either supplied as substantially pure oxygen or supplied as air. Although the combination of these two methods is not often used, the present invention can also be adapted to such cases.

Since the conversion of methacrolein is generally less than 100%, industrial scale plants often separate unreacted methacrolein and recycle it to the oxidation reactor. As will be clear to those skilled in the art, the choice to recycle is an essentially economic question of whether the full use of valuable methacrolein provides benefits that justify the cost of recycling. That's a problem. Therefore, although the methacrolein-containing gas is usually recycled, a recirculation reactor may also be used for this oxidation. In such cases, the feed gas is believed to be largely, if not entirely, free of carbon monoxide, and therefore carbon dioxide is added to the feed gas either alone or in combination with other gases; Catalyst useful life and productivity are increased. Although oxygen can be supplied to the single-pass reactor as molecular oxygen, it is often supplied in the form of air. Any amount of carbon dioxide can be added to effect from an external source.

For example, if pure oxygen is used, up to about 60% by volume of the feed gas can be carbon dioxide. If the carbon dioxide is about 60% by volume, the remainder can be about 20% by volume water vapor, about 7% by volume methacrolein, and about 13% by volume oxygen.

If the oxygen is supplied as air, any amount of carbon dioxide can also be added, but the large amount of nitrogen present with the required amount of oxygen dilutes both the carbon dioxide and the feed gas. Typically, the nitrogen excludes some of the carbon dioxide, so the feed gases are 1, e.g. 5% by volume methacrolein, 9.30% by volume oxygen, 14.3% by volume water vapor, 42.9% by volume. of nitrogen and 28.5% by volume of carbon dioxide. In such a composition,
Because methacrolein is somewhat dilute, the oxidation reactor operates somewhat differently than if nitrogen were not present.

Since single-pass reactors do not provide recirculation of the effluent gas, the foregoing discussion assumes that substantially no carbon monoxide is present.

More commonly, unreacted methacrolein is recovered from the produced methacrylic acid and recycled to the reactor along with other gases. When oxygen is supplied as air, it is necessary to purge with an equal amount of nitrogen to the amount supplied;
The nitrogen concentration therefore equilibrates at a fairly high level, for example about 60% by volume of the recycle stream. Carbon oxides are produced by the combustion of some amount of methacrolein and other organic matter present in the oxidation reactor and accumulate within the recirculating stream until the needle, which is purged with nitrogen, equals the amount of carbon oxides produced. be done. In such cases, the total amount of carbon oxide is relatively small, for example 4-6% by volume of the recycle gas. Since the absolute amount of carbon dioxide is small, it is preferable to add carbon dioxide from an external source in order to obtain a higher effectiveness of carbon dioxide.

As will be explained below, this is the case even when carbon oxide is oxidized to carbon dioxide. Carbon dioxide can be added to result in a feed stream having a composition similar to that when the reactor is operated in one pass and the oxygen is supplied as air, as described above.

A more preferred alternative method of operation is to use substantially pure oxygen in place of air and recirculate unconverted methacrolein so that less gas purging is required. In such cases, carbon oxides will accumulate and equilibrate to fairly high concentrations, eg, up to about 60% by volume of the recycle gas. Such higher concentrations of carbon oxide have been found to increase catalyst life and productivity compared to when nitrogen is used in the feedstock. It is an object of the present invention to carry out the oxidation of methacrolein using a ratio of carbon dioxide to carbon monoxide that is greater than the naturally occurring ratio. In practice, this can be done by increasing the ratio of carbon dioxide to carbon monoxide in the recycle gas or feed stream. This ratio will vary depending on the specific operating conditions of the reactor, but a typical natural ratio is approximately 0.1 = 1 to 1.5:1.
It is.

This ratio can be adjusted according to the invention in at least three basic ways. First, carbon dioxide can be introduced from an external source to increase the CO2/CO ratio. Second, -carbon oxides can be selectively removed, for example by scrubbing with -carbon oxide absorbers. Thirdly, -carbon oxide can be selectively oxidized to become highly refined carbon. This has a double effect. Such oxidation reduces the recycle gas to 200 to 650
It can be carried out by contacting a suitable catalyst, such as a platinum-containing molecular sieve, in the temperature range of .degree. This platinum-containing molecular sheep is such that the above-mentioned oxidation can be carried out without significantly oxidizing methacrolein or other hydrocarbons present.

Ideally, all of the carbon oxide should be converted to carbon dioxide, but in reality less can be oxidized.

In the recirculation system, an amount of carbon monoxide must be oxidized at least equal to the amount produced in each pass through the reactor to prevent carbon monoxide accumulation.

The process of the present invention is believed to be broadly applicable to molybdenum-based heteropolyacid catalysts, particularly phosphomolybdates, which are well known to those skilled in the art. Carbon dioxide has been found to be effective in the oxidation process of methacrolein to methacrylic acid using the catalysts described in the aforementioned patents.

These catalysts contain molybdenum, copper, phosphorus, antimony and cesium and/or calcium oxidation-containing compounds and also contain the element λ(01,CuaPb
8b (can be expressed as AdBeOx, where:
A is cesium and/or calcium, B is N ts
Z n s It, u, Thh, Pd, P t
, As, K, Rb, Sr, Ba, Cr.

V, Nb, wSMn, Re and rare metals, for example La, are the elements selected. The atomic ratio of each component to aSb, c, dSe and X to M012 is shown.
01 to Otsu, d to 0.1 to 6, e to D to 3, preferably 0.
01 to 3, and is a value determined by the valence numbers and ratios of other components in the X-catalyst. Preferably bke 0.5 to 3,
More preferably 1 to 2, more preferably about 1.2 to 1
．． 8, and C is preferably 0.01 to 1. Particularly preferred catalysts include those in which component B is tungsten or rhenium. If the characteristics of the basic formula are maintained, trace amounts of other elements can be added to the catalyst in order to increase the activity or selectivity of the catalyst. The catalyst can be considered as a mixture of oxides of the aforementioned elements or as a mixture of oxygen-containing compounds of said elements or as a mixture of both.

In its as-prepared state and/or under the reaction conditions, the catalyst may contain the above-mentioned oxide mixtures, oxygen-containing compound mixtures, or both;
We will use the word ``mixture of oxides.''

The catalyst is conveniently used in unsupported form, for example in the form of pellets of various sizes, or in other compacted forms, although conventional supports may be used. This catalyst can be manufactured using conventional methods well known to those skilled in the art. For example, compounds of molybdenum to copper, phosphorus, antimony, cesium and rhenium are each dissolved in a small amount of water or other solvent, and the solutions are mixed and evaporated to dryness, for example in a rotary dryer. Some of the components can be introduced into the solution in the form of various salts or other compounds of convenient type, and no special form is required as the catalyst precursor. However, ammonium salts, halides such as chlorides, nitrates, and also the acid forms of self-containing elements such as phosphoric acid are particularly suitable. However, preferably
Use aqueous solutions and use water-soluble forms of elements. Optionally, the aqueous solution includes an acid and/or! to promote dissolution of the catalyst precursor. f. A base may be added.

For example, an acid such as hydrochloric acid or nitric acid, or a base such as ammonium hydroxide can be used if desired. The powder produced by evaporation is completely dried and then preferably sieved to remove large particles which would interfere with the production of compacted articles of the same size, for example pellets. Typically, this powder passes through a 20 mesh sieve. This powder is then mixed with a binder. The binder may be of any conventional type, such as polyvinyl alcohol. After this mixture is thoroughly dried, it is sieved again. Usually 20~
It will be large enough to pass through a 60 mesh sieve. A lubricant is then preferably mixed into the dry mixture. This may also be of any conventional type, for example stearic acid or graphite.

Next, it is compression molded, for example, pelletized, into the desired shape.

The compression molded shapes typically have heights and diameters from 1.6 mW (in.) to 95 mW (in.) inches. Finally, the catalyst composition thus produced is activated by a prolonged treatment at elevated temperatures by methods well known to those skilled in the art. For example, put pellets in an oven or kiln,
Or put it in a tube through which air can pass and put it at a high temperature (e.g. 300-5"
00°C (preferably 325-450°C) for at least 10 hours.

A particularly preferred activation method involves increasing the temperature up to 42°C (lli°C
Preferably, the temperature is increased to 320-400°C at a rate of 20°C/hour and maintained at this temperature for 8 hours.

The oxidation conditions used are the same as those commonly used in the oxidation of methacrolein, with the exception of the intentional use of a large proportion of carbon dioxide in the feed gas. The molar ratio of oxygen to methacrolein is preferably maintained at a high value close to the flammable range. Steam is used to increase selectivity to the desired product.

The concentration of methacrolein ranges from 5 to about 20 of the total feed gas.
The volume N% can preferably be from 5 to about 15% by volume. Generally, the aldehyde is used at least 6% by volume of the feedstock. Usage range of oxygen: 5 to 15% by volume
, preferably from 5 to 12% by volume, up to 50% by volume within the range of steam usage, preferably from 5 to 35% by volume. The molar ratio of carbon dioxide to carbon monoxide is between 0.7/1 and 1.5 A, which is normally found in the oxidation of methacrolein when the recycling method is used according to the invention.
Make it bigger than. - When using a recirculation process, carbon dioxide can be added to the feed gas in any required amount. The remainder is various gases such as inert gases and trace by-products of the oxidation reaction.

For best results, the temperature of this oxidation reaction should be approximately 2
It should be 70 to 450'C, preferably 280 to 400C, more preferably 290 to 625C.

Since this reaction is exothermic, means to remove heat from the reactor are usually used to prevent temperature rise. By preventing temperature rise, methacrolein is less likely to be destroyed by complete oxidation to carbon oxide and water. The temperature of the reactor can be controlled in known manner, for example by surrounding the tubes containing the catalyst with a bath of molten salt. Other types of conventional reactions may also be used.

This reaction can be carried out at atmospheric pressure, superatmospheric pressure or under reduced pressure. However, it is preferable to use a pressure of about 8 (absolute pressure) from atmospheric pressure, more preferably about 6.3 yen (absolute pressure) from atmospheric pressure, and even more preferably about 4.5 yen (absolute pressure) from atmospheric pressure. i (absolute pressure).

This unsaturated acid product can be obtained by several methods well known to those skilled in the art. For example, the acid can be condensed or scrubbed with water or other suitable solvent to separate the unsaturated acid product from the scrubbing liquid. The gas remaining after the acid extraction step can be recycled to the reaction to complete the oxidation of methacrolein. However, the effects of the present invention can be similarly obtained even in a simultaneous reaction.

The invention will be more fully understood by the following examples. However, it should be understood that these examples are intended to be illustrative only and should not be construed as limiting the invention.

Example 1 Preparation of catalyst 636 g of (NH4)sMoF024.4H20 was
Dissolved in 50cc of water. Then, 21.71 Cu
(NO3)z ・3 H2Ot 100 ccfJ water K
fft KaL, 5a49 CsNO3 was dissolved in 150 cc of water, 20.59 of 5bCt3 was dissolved in a mixture of 300 cc of water and 10 cc of concentrated hydrochloric acid, 5 g of Re,
Dissolve O, in 100 cc of water, 34.59 H, PO
4 was dissolved in a mixture of 100 CC of water and 50 CC of 58% NH4OH solution. These bath solutions were mixed with 400 cc of 58% NH,OH, placed in a rotary dryer with a capacity of 4000 cc, and evaporated to dryness at a maximum temperature of 140-200°C.

Take out the generated powder from the dryer and dry it in the open for 20 minutes.
It was dried at 0°C for 4 hours. Sift this dry powder through a 20-mesh sieve, then add 4% polyvinyl alcohol.
The aqueous solution is added in sufficient quantity to form a wet mixture and the mixture is heated at 75-80°C to a moisture content of 2-4% by weight.
dried until it decreased to . Then, from this dry mixture, particles with a size of 20 to 60 mesh are sieved,
Thoroughly mixed with about 2-6% stearic acid powder. This product mixture was then made into pellets with a height and diameter of 3.2 mm (% inches). In this pellet, the catalyst components molybdenum, copper, phosphorus, antimony, cesium, and rhenium each have an atomic ratio of 12.0.3.
．． 1.0.6.1 and 0.07 (calculated value). The pellets were then activated by heating at 100°C for 1 hour in an open, then gradually increasing the temperature to 370°C at a rate of 20°C/hour and holding at this temperature for 8 hours. This catalyst was tested according to the method of Example 2.

Example 2 Catalyst Testing 57 g of the catalyst composition of Example 1 was reacted in a 12.7 x 2286 (% inch x 90 inch) stainless steel tube =
=% entered. The reactor steel tube was conventionally packed with 100 cc of inert packing above the catalyst bed to ensure uniform temperature contact with the catalyst.

A feed gas mixture containing methacrolein, oxygen and water vapor was heated to a pressure of 1.74 υ (absolute) and a space velocity of about 3
800 hr-1 was fed to the reactor. The term "space velocity" has the conventional meaning, i.e. catalyst 1.
It is used to mean the number of liters of gas (at standard temperature and pressure) per ton and per hour. The approximate composition of the feed gas is 6-7% by volume methacrolein, 11-12% by volume oxygen and 20% by volume water vapor, with the remainder being various combinations of nitrogen, carbon dioxide and carbon monoxide.

Quantification was performed on a wet basis. The reaction was carried out continuously and the effluent gas was analyzed at intervals of several hours. Analysis was performed by gas chromatography and infrared spectroscopy using well known techniques. The average production of methacrylic acid was measured at regular time intervals and the reactor temperature was adjusted as necessary to obtain the required yield. That is, the conversion products and selectivities were adjusted for comparison purposes so that the amount of methacrylic acid produced per catalyst per hour was approximately 0.42 g. The catalyst was used until it could no longer produce the required amount of methacrylic acid.1 The useful life of the catalyst was determined under these severe conditions.

It should be noted that this test is not intended to be representative of conditions typical of industrial use of the catalyst, where economic considerations determine the severity of the selected operating conditions. be.

Example 3 Table 1 shows the results of a series of tests carried out using the catalyst of Example 1 and according to the method of Example 2.

As is clear from the results in Table 1 --60 71.6 2 -□ 6'o -240 3654-197,9 43030-92, the presence of carbon dioxide Catalyst productivity is increasing. Test 4 is a representative example of CO! obtained by recycling unreacted methacrolein and associated gas when pure oxygen is used (i.e., no nitrogen is introduced). It shows a value close to the ZCO ratio. It can be seen that these conditions give better results in terms of catalyst life than when the reaction is carried out in one pass with air, similar to test 1. To further enhance this effect, the feedstock gas must contain the CO2 naturally produced in this oxidation reaction.
It should contain more C02 than -
Preferably, the amount of carbon oxide is as small as possible.

Example 4 A preferred method of practicing the invention is to carry out the oxidation reaction by recycling unreacted methacrolein and converting any carbon monoxide present to carbon dioxide by selective oxidation. This implementation is illustrated in the accompanying drawings.

The methacrolein oxidation reaction can be carried out within reactor 10. This reactor is a 10-vertical type.

The catalyst is pelletized and loaded inside a vertical tube.

This vertical tube is surrounded by heat transport liquids such as molten salts and special liquids commonly used by those skilled in the art. Alternatively, other types of reactors may be used, provided that the heat generated by the reaction can be successfully removed. Substantially pure oxygen is used in this example.

Thorough purging with inert gas is not necessary. As is well known, industrial-scale equipment designs often include some level of purging with inert gas;
Nothing related to this is shown to simplify the diagram.

Fresh methacrolein is sent to reactor 10 via line 12 and oxygen is sent via line 14. These gases mix together with recycle stream 16 before entering reactor 10. The recycle stream 16 I/'i is substantially free of carbon dioxide, -carbon oxides, unreacted methacrolein, unreacted oxygen, water vapor, small amounts of inert gases and light reaction by-products.

The composition of recycle stream 16 is approximately 67% by volume carbon dioxide, 1
3% by volume carbon monoxide, 4% by volume methacrolein, 8
% oxygen by volume and 7% water vapor by volume, and 1% by volume
It is an impurity. The amount of water vapor can be adjusted by operating the quench bath 20, and if additional water vapor is required, it is added by the limer 18.

Oxidation reactor 10vc fresh methacrolein, oxygen and recycle stream 16 combined feed gas composition is 7% by volume methacrolein, 12% by volume oxygen, 2% by volume.
0 volume % water vapor, 50 volume % carbon dioxide, 10 volume f
fi% carbon monoxide and 1% by volume impurities. The temperature upon entry into the reactor is approximately 28[1"C"'C.

As is well known to those skilled in the art, the released heat is removed by circulating a heat transport liquid (not shown) through the shell of reactor 10. The working pressure is approximately 1.8 mm (absolute pressure).

The effluent gas passes through heat exchanger 19 for precooling before entering quench bath 20 where it is cooled and condensed by countercurrent contact with the recirculating liquid stream.

This recycled liquid stream is essentially an aqueous solution of methacrylic acid. Heat of condensation is removed by circulating the liquid through purge cock 22 to heat exchanger 24 and returning the liquid to quench bath 20. A portion of the liquid is removed as liquid stream 26 and sent to other equipment (not shown) for methacrylic acid extraction. The gas that does not condense at a temperature of about 40° C. is sent via compressor 29 and line 28 to carbon monoxide oxidation reactor 62. Depending on the catalyst used, heat can be added to heat exchanger 30 (optional) to raise the gas temperature to the required height. In this example, a fixed bed of platinum weighing 0.02 wt.
Use within. Reactor 32 is capable of converting approximately 10% of the carbon monoxide in the uncondensed gas coming from quench bath 20 to carbon dioxide at a temperature of approximately 600°C. In a continuous equilibrium reaction system, the gas in line 28 contains approximately 13% carbon monoxide by volume, and after oxidation the gas in line 16 is iI! J11
Contains % carbon monoxide by volume.

The amount of carbon monoxide converted to carbon dioxide can be controlled by the type and amount of catalyst used and the operating conditions.

In order to avoid oxidative losses of methacrolein, the catalyst used must be capable of selectively oxidizing carbon monoxide to carbon dioxide without substantial oxidation of methacrolein. Such a catalyst uses a metal group oxidation catalyst, such as platinum, which is incorporated into the pores of a molecular sheep having pores of about 4 to 5 amps in diameter. The pores of such sieves are too small for methacrolein to easily enter and therefore not easily oxidized, but smaller carbon monoxide molecules can be oxidized to carbon dioxide. By operating at sufficiently low temperatures, monoxide 1
The necessary selective oxidation of carbon can be carried out. It will be appreciated that, in accordance with the principles of the present invention, the reaction conditions within reactor 32 may be adjusted to provide the effect of converting an amount of carbon monoxide to optimize the performance of reactor 10. .

The amount of conversion can be simply equal to the amount of carbon monoxide produced during each pass through reactor 10, or more if the ratio of carbon dioxide to carbon monoxide needs to be adjusted. Much carbon monoxide can also be converted.

Another method of increasing the amount of CO in the methacrolein reactor feed gas is to selectively remove CO from the recycle gas. 001760 molar ratio naturally occurs under the reactor operating conditions described above.
5/L (typically 1/1), so when pure oxygen is used as the feedstock, the concentration of each carbon oxide in the recycle gas increases to about 60%. If CO can be selectively removed, CO2 concentrations can be raised to considerable levels. Methods of CO removal are well known for other processes and can be adapted for use in the present invention. Examples of possible methods include cryogenic methods used to extract monomer carbon from synthesis gas, and cuprous chloride-aluminum chloride-toluene solvents or copper-based methods used for flue gas scrubbing. There is extraction of carbon monoxide by other similar compounds as agents.

[Brief explanation of drawings]

FIG. 1 shows an example of an apparatus for carrying out the method of the invention. In the figure, 10 is a methacrolein oxidation reactor and a 32 carbon monoxide oxidation reactor. Agent Patent attorney Masamitsu Akizawa and 1 other person (February 1942) - Q Patent Office Head 1, Indication of the case σto Gansho Ta Z - 1 α 2, DA 3, amendment Relation to case No. 11 of Hirotaka Mata Residence: Chushi-ku, Tokyo] 12-1 Taiyo Building, Honkyo Kabuto-cho Correction Order 1 (shipped) 1985/Ta month 28 Patent Office, Palace 1, Indication of the case Patent application 1987-124'?64-No. 2, issue eB name MEC n rain, Metaktal mk ki A publication hook Compromised b'V-
3. 3. Person who makes corrections” 1. Relationship with Shiruto Idushio 0 people

Claims (1)

[Claims] (1) Contains molybdenum, phosphorus, copper, antimony, and cesium and/or calcium, and contains N1, Zn,
Ru, Rh, Pd, PL, As, wind Rb,
Sr, Ba, Cr. Gas-phase oxidation of methacrolein to methacrylic acid with molecular oxygen in the presence of a catalyst containing one or more elements arbitrarily selected from the group consisting of A method characterized in that the oxidation is carried out under a CO/Co molar ratio greater than that generated by methacrolein. (2) The method according to claim 1, wherein carbon dioxide is supplied from a source other than an oxidation reaction. 3. The method of claim 1, wherein unreacted gases in the oxidation are recycled and carbon monoxide is removed from the recycled gas. 4. The method of claim 3, wherein the carbon oxide in the recycle gas is selectively oxidized to carbon dioxide in the presence of methacrolein. (5) The method according to claim 4, wherein the selective oxidation is carried out in the presence of a catalyst. (6) The method according to claim 5, wherein the catalyst is a noble metal supported on a molecular sieve. (8) The method of claim 6, wherein the catalyst is platinum supported on a molecular sheet having pores of about 4-5 A' in diameter. (8) The catalyst is molybdenum, phosphorous, copper, antimony,
A method according to claim 1, comprising cesium and rhenium. (9) The method of claim 1, wherein the CO,/Co molar ratio is greater than about 1. (10 The catalyst has the formula MO12CuaPbSbcAdBe
Ox is defined as cesium and/or calcium, B is Ni, Zn, Ru, Rtt, P
d, Pt, As, K, Rh, Sr. Ba, Cr1VSNb, W, Mn, TLe k
J: U persimmon earth metal m An example is one or more elements of the element group consisting of La, where a, b, c, d, e and X are λ
The ratio of the number of atoms of each component to 4012 is shown, a = 0.05 ~ 6, b = C1, 'l ~ 5, C20
．． 01-1, d=o, 1-3, e=0-6, and X has a value determined by the valences and proportions of the other elements.