NL8202791A - METHOD FOR PREPARING METHACRYLIC ACID. - Google Patents

Description

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Reg.No. 117658 / ThU / HB

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Process for preparing methacrylic acid. ·

It is known that unsaturated acids, such as acrylic acid and methacrylic acid, can be prepared by oxidizing the corresponding saturated aldehydes with molecular weight vapor in the presence of a -1. 5. suitable oxidation catalyst. A number of different catalyst preparations have been proposed for this purpose. Many; 1 such preparations include the oxides of molybdenum and phosphorus in combination with the oxides of various other ♦ j elements, both metallic and non-metallic. Of particular interest with regard to the present invention are the catalysts described in the following literature locations.

US patent applications 973,354, | filed December 26, 1978 and 047,860, filed June 12, 1979 and U.S. Patents 4,252,682, 4,252,681, 4,252,683, 4,240,930, 4,261,858, 4,261,859, 4,261,860, and 4,271,040.

It has been found that catalysts for oxidation of methacrolein to methacrylic acid have the characteristic i.

They have the property of being stable for a period of time and then rapidly decreasing in activity. The compositions of such catalysts have been adjusted to extend their useful life and to achieve greater methacrylic acid production with a given amount of catalyst. It has now been found that the composition of the reaction. feed gas and in particular the carbon dioxide content! "! > affects service life and productivity of the catalysts; The prior art gives little information about the effect of the composition of the reaction gases. U.S. Pat. No. 3,171,859 shows that recirculation of by-product gases has a high concentration of carbon.

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\ \ - 2 - i! oxides in the reaction feed gas, when oxygen is supplied as pure oxygen. The reaction described is; the oxidation of propene to acrolein rather than the oxidation of methacrolein to methacrylic acid. No effect of the gas composition on the life of the catalyst is effected. wrote.

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The oxidation of olefins including isobutylene is discussed in U.S. Pat. No. 3,883,588. It is stated that diluents are desired to better control the exothermic reaction. In this connection, carbon dioxide produced in the reaction is mentioned as well as nitrogen from the air. Nothing is said about the effect of using such diluents on the cabinet. talizer operation said.

The oxidation of acrolein to acrylic acid is discussed in U.S. Pat. No. 3,985,800, which states that the use of a feed gas containing a large fraction of carbon oxides (example 2) gave similar results as when nitrogen was the diluent j. 20 (example t). Although the catalyst has been attributed a good service life, no effect of the use of carbon oxides is noted and the gas composition is outside the scope of the present invention.

The harmful influence of the inclusion of! . 25 carbon oxides. in the reaction feed gas, in connection with the oxidation of propylene to acrylic acid taught in Araerican Patent 4,147,885.

! As will be seen hereinafter, it has been found that the incorporation of a large amount of carbon dioxide into the reaction feed gas during the oxidation of methacrolein to methacrylic acid in the vapor phase over suitable catalysts has a beneficial effect on life and productivity. of the catalyst.

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It has been discovered that the productivity of molybdenum-based catalysts in the oxidation of methane 8202791

Vv ....... '* c j - 3 - i' - vapor phase croleine can be significantly improved by; increasing the molar ratio of carbon dioxide to carbon monoxide over the molar ratio produced in the oxidation reaction. thing. This can be accomplished by adding carbon dioxide 5 from an external source, selective removal of carbon monoxide or oxidation of carbon monoxide to carbon dioxide.

. The present invention roughly relates to catalysts, which are characterized as molybdenum-based heteropoly acids, such as phosphomolybdates.

Preferably, the oxidation reaction is carried out on a suitable catalyst comprising oxides of molybdenum, copper, phosphorus, antimony and cesium and / or calcium and preferably one or more of the elements Ni, Zn, Ru, Rh, Pd , Pt, As, K, Rb,

Sr, Ba, Cr, V, Nb, W, Mn, Re and rare earth including 15 includes La. The reaction feed gas contains 5-20 volZ methacrolein, 3-15 volZ 2 oxygen and up to 50 volZ steam.

The ratio of carbon dioxide to carbon monoxide in the feed gas is greater than the ratio produced in the oxidation of methacrolein.

In a preferred embodiment, fresh oxygen is fed to the reaction as substantially pure molecular oxygen, and unreacted methacroline and oxygen are recycled until equilibrium | located. The carbon dioxide content of the recycled is left; gases while the carbon monoxide is selectively oxidized over a suitable catalyst in the presence of methacrolein rise to its equilibrium value such that the reactor feed gas has a ratio of carbon dioxide to carbon monoxide. greater than that produced by the oxidation of methacrolein, typically contains a CO 2 / GO molar ratio of <greater than about 1.

The preferred catalyst composition used in the process of the invention can be defined by the following general formula: 35 MoO Cu P, Sb AB O, where A represents cesium and / or calcium in the form of 8202791 V. I ^ <'-4-.

and B represents one or more members of the group consisting of Ni, Zn, Ru, Rh, Pd, Pt, As, K, Rb, Sr, Ba, Cr, V, Nb, W, Mn,

Re and rare earth metals including La and wherein a-e and x indicate the atomic ratio of each component relative to Mo ^ and where a 0.05-3, b 0.1-5, c 0.01-1,

d is 0.1-3 and e is 0-3 and x has a value which is determined J

by the valence and amounts of the other elements in the catalyst. Preferably, b is 0.5-3, more preferably 1-2, and most preferably 1.2-1.8, while c is preferably 0.01-1.

The only figure shows a method according to a preferred embodiment of the invention.

The invention can be broadly viewed as a method of oxidizing methacrolein to methacrylic acid, wherein the ratio of carbon dioxide to carbon monoxide is greater than the ratio produced in the oxidation reaction. In practice, this means that the COCO ratio is changed by either adding carbon dioxide or removing carbon monoxide or; convert carbon monoxide to carbon dioxide.

The selected method is influenced by the form in which oxygen is lysed. There are two main ways of supplying the oxygen required for the oxidation of methacrolein, namely as substantially pure oxygen or as air. A combination of the two ways is less likely, but the invention can also be adapted to such a process.

Since the conversion of methacrolein i is generally less than 100%, it is likely,

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that each technical installation will provide for a separation of unreacted methacrolein and its return to the oxidation reactor. Such a choice is, of course, essentially of an economic nature, balancing the full exploitation of the valuable methacrolein against the cost of return. Although probably for a | 35 return of a methacrolein-containing gas will be j 8202791 m »" - · ·· ** · ..................

If it is selected, it is possible that a reactor with one pass is taken for the oxidation. In such a case, the feed will contain little or no carbon monoxide and thus carbon dioxide must be added to the feed gas either alone or in combination with other gases in order to increase the life and productivity of the catalyst.

Oxygen can be supplied as molecular oxygen to a single pass reactor, but more likely in the form of air. Any amount of carbon dioxide can be successfully added from an external source. For example, when using pure oxygen, up to about 60 vol.% Of the feed gas can be carbon dioxide, with the remainder about 20 vol.% Steam, 7 vol.% Methacrolein and 13 vol.%. oxygen.

When oxygen is supplied as air, carbon dioxide can also be added in any amount, but it also dilutes the feed gas, since a significant amount of nitrogen is present in combination with the required oxygen. In particular, the nitrogen can be replaced with such a part of the carbon dioxide that a feed gas, for example, 5 vol 2 methacrolein, 9.30; volZ oxygen, 14.3 volZ steam, 42.9 volZ nitrogen and 28.5 I, volZ carbon dioxide. Since such a composition is lower in methacrolein, the operation of the oxidation reactor probably needs to be changed compared to the composition in which no nitrogen

i is present. In the above discussion it is assumed that J

In principle, no carbon monoxide is present, since there is In a single pass reactor, no effluent gas recycle is used.

In the measurement typical situation, unreacted having methacrolein is recovered from the methacrylic acid product and returned to the reactor along with other gases. When oxygen is supplied as air, a quantity of nitrogen equivalent to the 8202791 has to be purged; The amount supplied and the nitrogen concentration reaches a relatively high level, for example about 60% by volume. of the returned current in equilibrium. The combustion of any methacrolein or other organics present in the oxidation reactor produces carbon oxides which collect in the recycle stream until the amount of nitrogen sparged equals the amount of carbon oxides produced. The total amount of carbon oxide in such a case can be relatively small, for example 4-6 vol. 2 of the recycled gas. In order to achieve the benefits of the addition of carbon dioxide, it may be preferable to add the carbon dioxide from an external source. since the absolute amount of carbon dioxide would be too small, even if the carbon monoxide were to be oxidized to carbon dioxide as will be discussed further. In addition, such an amount of carbon dioxide must be added that a foodstuff. stream is supplied of a composition similar to that of the stream described above, with a reaction.

. With a single pass, the oxygen is used when air is supplied, i. -

Any other and preferred embodiment! . ...

| form involves the use of nearly pure oxygen in | place of air and the return of unconverted methacroline, as this means that little gas purging is required. In such a situation, the carbon oxides accumulate and equilibrate with the recycled gas at relatively high concentrations, for example about 60 vol.

, Although the present data show that such a 30. high concentration of carbon oxides provides better catalyst life and productivity over use. of nitrogen in feed gas, the present invention contemplates the oxidation of methacrolein at a higher than naturally occurring ratio of carbon dioxide to carbon monoxide from 35. to feed. In practice, this can be done by raising i

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8202791 ..... "" ..... "" ...... ........ - ".......- * \ · '.

- 7 - j of the ratio of carbon dioxide to carbon monoxide in the j recycled gas or the feed stream. Although the ratio varies according to the particular operating conditions in the reactor, the natural ratio is normally found to be approximately! 5 to be from 0.7: 1 to 1.5: 1. According to the present invention, it can be adjusted in at least three main ways.

First, carbon dioxide can be introduced from an external source or facility to increase the CO / CO ratio.

to increase. Second, carbon monoxide can be selectively removed, for example, by washing with a carbon monoxide absorbent. Third, the carbon monoxide can be selectively oxidized to carbon dioxide, which is doubly beneficial. Such an oxidation can be carried out by contacting the recycled gas at a temperature of 200-350 ° C with a suitable catalyst, for example a platinum-containing material. the molecular sieve, which oxidizes the oxidation substantially without oxidation of the methacrolein or other hydrocarbons present; can perform. Ideally, all the carbon monoxide in Ί "; carbon dioxide, but small amounts may be oxidized. In a recirculation system, to avoid a carbon monoxide build-up, an amount of carbon monoxide must be oxidized at least equal to the amount produced by the reactor in each pass.

The process of the invention is believed to be of wide application to molybdenum-based heteropolyacid catalysts of the type known in the art, and in particular to phosphomolybdates. The effect of. Carbon dioxide has proven valuable in methods of oxidizing methacrolein to methacrylic acid over catalysts, which are described in the aforementioned references. ven.

These catalysts contain oxides or oxygen-containing compounds of molybdenum, copper, phosphorus, antimony and cesium and / or calcium and may optionally contain one or more elements from the group marked "B" below.

8202791

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4 - 8 - .. »

These catalysts can be represented by the general formula Mo <0Cu P, Sb AB 0, where A represents cesium and / or calcium, 12 abcdex and B represents Ni, Zn, Ru, Rh, Pd, Pt, As, K, Rb, Sr , Ba,

Cr, V, Nb, W, Mn, Re and rare earth metals including La and where a-e and x indicate the atomic ratio of each component to Mo 2 and wherein! a is 0.05-3, b0.1-5, c 0.01-3, d 0.1-3 and e is 0-3, preferably 0.01-3 and x is a value determined by the valency and amounts of the other elements in the catalyst. Preferably b is 0.5-3, more preferably 1-2 and most preferably 1.2-1.8, while c is 0.01-1. Particular preference is given to the catalysts in which component B is tungsten or rhenium. Other elements may be present in minor amounts in the catalyst composition to promote catalytic activity or selectivity, provided that the benefits of the base composition are retained.

The catalyst preparation can be considered as a mixture of oxides of the said elements or as oxygen compounds of the elements or both. As prepared and / or under reaction conditions, the catalyst may contain either or both forms and both are considered to be included within the term "mixture of oxides."

The catalyst preparation is preferably used in a form without a support, for example, in the form of pellets or other similarly compressed shapes of different sizes, although instead they are used. could use the common carriers. The preparation can be formed in the usual ways. For example, compounds of molybdenum, copper, phosphorus, antimony, cesium and rhenium can be dissolved in a small amount of water or other solvent and the solutions can then be combined and evaporated to dryness, for example in a rotary dryer. The different components can be solved! in the form of various salts or other compounds! 35 of handy types, with no specific shape for the kat 8202791 9 Γ (.

y, - 9 - j lysator precursors is needed. The use of ammonium salts,! halides, for example chlorides, nitrates or acid forms of the elements, for example phosphoric acid, are however particularly suitable. Preferably, however, solutions of water and water-soluble forms of the elements are used. j

In some cases, acids and / or bases may have been added to the solutions to make the catalyst precursors dissolve more easily. For example, if desired, acids such as hydrochloric or nitric acid or bases such as ammonium hydroxide can be used. The powder resulting after evaporation is then thoroughly dried and preferably sieved to remove large particles which make it difficult to produce uniformly compressed shapes, such as pellets.

; Typically, the powder is passed through a 0.84 mm mesh sieve. The powder is then mixed with an organic binder, which may be of any known type, for example polyvinyl alcohol, and the mixture is thoroughly dried and sieved again, in particular to obtain a particulate | size from 0.25 - 0.84 mm. The dried mixture is then added. after preferably. combined with a lubricant, again of any known type, such as stearic acid or graphite, and pressed to the desired shape, for example into pellets, the press shapes being in particular heights and diameters of 3, 2 to 9 , 6 mm. Finally, the catalyst preparation thus produced is activated for a long time at high temperature in the usual manner. This way the press pieces are added For example, placed in an oven or a tube through which high temperature air (e.g., 300-500 ° C, preferably 325-450 ° C) is passed for at least 10 hours. In a particularly preferred activation mode, j. The temperature is raised at a rate of 20 ° C per hour; . to a maximum of 420 ° C, preferably 320-400eC and this temperature is maintained for 8 hours.

The oxidation conditions used are the same as those generally associated with the oxidation of methane. 8202791 - 10 - ί ί erolein are associated, but differ in the intended use of large amounts of carbon dioxide in the dietary | gas. It is preferred that the molar ratio of oxygen to methacrolein is maintained at a high value near the flammable range. Steam is used to improve;

; the selectivity for the desired product is obtained. I

Methacrolein can be present in concentrations of more than 5 to about 20% by volume of the total food! ; y thing, with preference being given to more than 5 to 15 volZ.j 10 In general, at least 6 vol% of | it uses aldehyde. The corresponding ranges for oxygen are 3 to 15 volZ, preferably 5 to 12 volZ, and for steam up to 50 volZ, preferably 5 to 35 volZ. The mole ratio; The amount of carbon dioxide to carbon monoxide exceeds the value of 0.7 / 1-1.5 / 1, which in the case of methacrolein oxidation.

it is common when a recycled process according to the invention is used. When a single pass process is used, carbon dioxide can be added to the feed gas in any desired amount. The remainder - 20 consists of different gases, such as inert gases or | traces of by-products of the oxidation reaction.

The reaction temperature should be 270-450 ° C, preferably 280-400 ° C, most preferably 290-325 ° C, for best results. Since the reaction is exothermic, means are normally used to dissipate the heat from the reactor to avoid a rise in temperature, which favors the destruction of methacrolein by complete oxidation to carbon oxides and water. The reactor temperature can be 1 i! controlled in usual ways, for example by; 30 surrounding tubes containing catalyst with a molten salt bath II. Any other suitable reactor types may be used.

The reaction can be carried out at atmospheric, superatmospheric or subatmospheric pressure. Preferably, however, pressures ranging from atmospheric 8202791 '- 11 - ** to about 8 kg / cm2 absolute, preferably up to about 6.3 kg / cm2 absolute and most preferably up to about 4.5 kg / cm2 absolute are used. -lute.

The unsaturated product can be recovered in a number of known ways. For example, the acid can be condensed or washed with water or other suitable solvents, followed by separation of the unsaturated salt product from the washing liquid.

The gases remaining after the acid removal can be recycled to the reaction to complete the methacrolein oxidation, although the beneficial effect of the invention can also be achieved in a single pass reaction.

The following examples illustrate the invention.

Example I Catalyst preparation.

Dissolve 636 g (NH 4 gMo 2) in 750 ml water.

on. Then 21.7 g CuCNOg ^ ^ I ^ O are dissolved in 100 ml water, 58.4 g CsNO ^ in 150 ml water, 20.5 g SbCl ^ in a mixture of 30 ml water, and 10 ml concentrated HCI 5 gr.,

Re 20 ^ in 100 ml water and 34.5 g H ^ PO ^ in a mixture of 100 ml water and 50 ml 58Z NH ^ OH solution. These solutions are mixed with 400 ml of 58% NH4 OH and the whole is introduced! 25 to a rotary dryer of 4000 ml capacity and the mixture evaporates to dryness at a temperature which reaches a maximum of 140-200 ° C. The resulting powder is taken out of the dryer! taken and dried in an oven at 200 ° C for 4 hours. The dried powder is sieved with a sieve of 0.84 mm mesh size | and a 4% polyvinyl alcohol solution in water is added in an amount sufficient to obtain a moist mixture and this mixture is dried at 75-80 ° C until the moisture content drops to 2-4% by weight. The dried mixture is then sieved into 0.25-0.84 mm particles and thoroughly mixed with 2-6% Stearic acid powder. The resulting mixture. 8202791 <4 ^ 4> * '- 12 - "Ί • is then processed into 3.2 mm high and diameter pellets, in which the catalyst components molybdenum, copper, phosphorus, antimony, cesium and rhenium are present (according to calculation) in the atomic ratios of 12, 5, 0.3, 1, 0.1, Ten 0.07, respectively. The pellets are then activated in an oven by heating them at 100 ° C for 1 hour and then slowly at a rate of 20 ° C to 370 ° G per hour and maintain this temperature for 8 hours.

The catalyst is tested according to the procedure of example! 10 II. j • j

Example II. I

Catalyst test.

57 g of the catalyst preparation of Example 1 are introduced into a reactor, which is determined by a 225 x 1.25 cm stainless steel pipe, the reactor pipe being filled in the usual manner with 100 ml of inert filler above the catalyst bed in order to obtain a evenly tem-:! i ensure contact with the catalytic converter. Feed gas mixtures containing methacrolein, oxygen and steam are fed to the reactor at a pressure of 1.74 kg / cm 2; (absolute) and a spatial flow rate of about 3800 hours. The term "spatial flow rate" has the usual meaning here of liters of gas! (at • standard temperature and pressure) per liter of catalyst per.

i! 25 hours. The nutritional composition, calculated on volume, is originally 6-7% methacrolein, 11-12% oxygen and 20% steam, the remainder being different combinations of nitrogen, carbon dioxide and carbon monoxide, with the determination of moist | i ... 1 basis has been made. The reaction is allowed to continue continuously and! . 30 analyzes the exhaust gas at intervals of several hours. ; ! Analyzes are performed by gas chromatography and infrared spectrography in the usual ways. The average amount of methacrylic acid produced is determined periodically and the reactor temperature is adjusted to the desired yield, if necessary, that is, the product of conversion. 8202791 • selectivity and selectivity, which for the comparisons to be made amounts to about 0.42 g of methacryl acid per hour per gram of catalyst. The catalyst is used until it is no longer possible to produce the desired amount of methacrylic acid, thereby determining the life of the catalyst under these severe conditions. It is to be noted that this test is not intended to reflect conditions for true corameric use of such catalysts, with an economic balance determining the severity of the selected operating conditions.

Example III! 'I ....... I · »" "> 1

The results of a series of tests with the catalyst of Example according to. the procedure of example II are given in the following table.

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TABLE A

Partial feed gas composition (except O2, Productivity,

Test MCHO, BL2O) g MMA / g Cataly. % CO2% CO2% N2 sator_; 1 - 60 71.6 • 1 y 2 - 60 - 240 3 6 54 - 197.9; 4. 30 30 - 92.6 {25 i

It can be clearly seen that the carbon dioxide has a favorable effect on the catalyst productivity compared to operation with only nitrogen present.

Test 4 represents a ratio of C 3 / CO close to that which results in particular in the recycling of unreacted methacrolein and its accompanying gases when pure oxygen is used (i.e. nitrogen is not introduced). This condition j appears to be more favorable for the life of the catalyst than to perform the single pass reaction m 8202791-14-4.

with air, as in Test 1. In order to obtain the advantage of the present invention, the feed gas must contain more CO 2 than, of course, results from the oxidation reaction, and preferably the amount of carbon monoxide 5 should be as low as possible.

Example IV.

In a preferred embodiment of the invention, the oxidation reaction is carried out by returning the unreacted methacrolein and under selective oxidation of the carbon monoxide present to 1 carbon dioxide as shown in the figure. j. i

The oxidation reaction is carried out in reactor 10, which may be of the tubular type, the catalyst being pelleted and charged in vertical tubes surrounded by an I '. . .

j heat transfer fluid, such as the molten salts and special liquids, which are well known. Optionally, other reactor types can be used, provided that the released reaction heat is only sufficiently removed. In this example, the oxygen is considered to be substantially pure and virtually no inert gas purge is reported. A small purging of inert gases is natural. -]. You probably need it in a commercial version; but this is not shown in the simplified figure. Fresh methacrolein is supplied to reactor 10 via line 12 and supplemental oxygen via line 14. These gases add to the recycled stream 16i and are mixed before entering reactor 10. The | recycled stream 16 consists essentially of carbon monoxide, carbon dioxide, unreacted methacrolein, unreacted oxygen and steam plus minor amounts of inert gases and light reaction by-products. The composition of the recycled stream 16 is about 67. i vol% carbon dioxide, 13 vol% carbon monoxide, 4 volZ methacrolein, 8 volZ oxygen and 7 volZ steam plus 1Z impurities. | 8202791 © '.

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; The amount of steam can be adjusted by controlling quench column 20! and if additional steam is required it is added via line 18.

The combined feed gases to oxyda-5 tier reactor 10 have the following composition: 7 vol% • - j.

methacrolein, 12 vol% oxygen, 20 vol% steam, 50 vol% j; carbon dioxide and 10 vol% carbon monoxide plus 1% impurities.

The temperature at the reactor input is about 280 ° C.

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The generated heat is naturally removed by circulating a heat transfer fluid (not shown) along the jacket of reactor 10 as is well known. The operating pressure is approximately 1.8 kg / cm2 absolute. ί

The effluent gases pass through heat exchange for preliminary cooling and then enter quench 20, where they are cooled and condensed by contacting in reverse with a recirculating stream consisting essentially of aqueous methacrylic acid. The condensation heat is removed by circulation of the liquid through blowdown 22 through heat exchanger 24 and return of the liquid to quench tower 20. Part of the flow; dust is removed as stream 26, which is sent to other facilities (not shown) to recover metha. i -. ". J crylic acid. The non-condensed gases are sent to carbon monoxide oxidation reactor 32 at a temperature of about 40 ° C through compressor 29 and line 28. Depending on the catalyst used, a heat exchanger can be used; 30 (optional) heat is applied in order to bring the gas temperature to the desired level. In this example, a fixed bed of 0.02 wt% platinum deposited in the pores of a molecular sieve (described below) is used in reactor 32, which at about 300 ° C is about 10 ° C. % carbon monoxide in the non-condensed gases exiting quench tower 20 into carbon dioxide. In a continuous equilibrium reaction system 35, the gases in line 28 contain about 13 vol% carbon monoxide; 18202791 - 16 - and after the oxidation, the gases in line 16 contain approximately: 11% by volume of carbon monoxide.

The amount of carbon monoxide converted to carbon dioxide can be controlled with the type used and the amount of catalyst and the operating conditions. In order to prevent loss of methacrolein by oxidation the catalyst should be able to oxidize carbon monoxide to carbon dioxide substantially without oxidation of methacrolein. One such catalyst is a noble metal oxidation catalyst, such as platinum, which is deposited in the. pores of a molecular sieve with pores of about 4-5 A0 diameter.

The pores of such sieves are too small for the easy admission and oxidation of methacrolein, but the carbon monoxide molecules can be oxidized to carbon dioxide.

! 15 When working at a sufficiently low temperature, the »· ·. * desired selective oxidation of carbon monoxide possible. The reaction conditions in reactor 32 can, of course, be adjusted to the conversion of an amount of carbon monoxide which provides optimum operation of reactor 20 according to the results. 20 yields invention. This can only be so much carbon monoxide; if the reactor has produced or can be used for each run more, if desired, the ratio of carbon dioxide. oxide to carbon monoxide.

| Another method of increasing the amount in the feed gas to the methacrolein reactor is selective removal of CO from the recycled gas. Since the. The molar ratio of CO / CO 2 under the conditions described is of course about 0.7 / 1 to 1.5 / 1 (especially about 1/1), when pure oxygen is supplied, the concentrations in the recycled gas up to about 30% of each carbon oxide. If CO can be selectively removed, the CO concentration can be allowed to rise to a significant level. CO removal methods are known in combination with other methods and may be used in accordance with the invention. 8202791-17-.

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; adjusted. Examples of methods to be considered are cryogenic methods which are used to recover. synthesis gas carbon monoxide and the extraction of carbon monoxide with cuprous aluminum chloride-toluene liquid or other copper-based heating liquid used to wash out gas streams. «! [-! 10; -. I:

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Claims (11)

1. Process for the gas-phase oxidation of methacrolein to methacrylic acid with molecular oxygen in the presence of a catalyst containing molybdenum, phosphorus, copper, antimony, cesium and / or calcium and optionally one or more of the elements Ni, Zn, Ru , Rh, Pd, Pt ,. As, K, Rb, Sr, Ba, Cr, V, Nb, W, Mn, Re and includes rare earth metals including La, characterized in that this oxidation is carried out in the presence of a higher molar ratio of CO 2 fCO dart • is produced during the oxidation of methacrolein. 2. Process according to claim 1, characterized in that the carbon dioxide is fed from an external source to the oxidation reaction. 1 3. Process according to claim 1, characterized in that the unreacted gases are recycled from the oxidation and carbon monoxide is removed from the recycled gases. ί 4. Process according to claim 3, characterized in that the carbon monoxide in the recycled gases is selectively oxidized to carbon dioxide in the presence of methacrolein. 5. Process according to claim 4, characterized in that the selective oxidation is carried out in the presence of a catalyst. . 6. Process according to claim 5, characterized in that the catalyst is a sieve on a molecular sieve. dropped off. precious metal. I » The method of claim 6, j; characterized in that the catalyst is platinum deposited on a molecular sieve with 4-5 pore diameter pores. j A method according to claim 1; characterized in that the catalyst comprises molybdenum, phosphorus, copper, antimony, cesium and / or rhenium. J. 8202791 ~ 19 - Λ 9. Process according to claim 1, characterized in that a molar ratio of C0n / C0 of ΙΓΙ ΙΓΙ “L more than 1 is used. The method of claim 1. 5 characterized in that the catalyst is defined by the formula Mo._Cu P, Sb AB 0 in which A represents cesium and / or calcium 12 abcdex and B one or more of the elements Ni, Zn, Ru, Rh, Pd, Pt , As, K, Rb, Sr, Ba, Cr, V, Nb, W, Mn, Re and rare; earths including La and where ae and 10. indicate the atomic ratio of each component with respect to where a “0.05 * 3” b = 0.1-5, c β 0.01-1, d = 0, 1-3, you = 0-3. and x has a value determined by the valence and quantities of the other elements. 11. Method, products or device as described in the description and / or examples. i ί · | j t j -: '! i ί · i. i 1 l j 'i! i * i * -} <• i ·! ! • 1 8202791 I P - 0- Improvement of errata in the specification associated with patent application No. 8202791 Ned. proposed by applicant dated July 20, 1982 Biz. 13, line 19: "MMA" should be "methacrylic acid". [ThU / HB / 8202791> s