CA1059532A - Process for the preparation of unsaturated acids from unsaturated aldehydes - Google Patents

Abstract

PROCESS FOR THE PREPARATION OF UNSATURATED
ACIDS FROM UNSATURATED ALDEHYDES

ABSTRACT OF THE DISCLOSURE

Methacrylic acid or acrylic acid are produced by the oxidation of methacrolein or acrolein respectively, with molecular oxygen in the vapor phase in the presence of a catalytic oxide of molybdenum, phosphorus, and promoted with chromium or at least one element selected from the group consisting of thallium, rubidium, cesium, potassium, titanium and arsenic, or a mixture thereof, wherein at least part of the molybdenum employed in the preparation of the catalyst is supplied in the form of molybdenum trioxide. The oxidation of methacrolein in the presence of a catalyst wherein all the molybdenum employed in the preparation of the catalyst has been supplied by molybdenum trioxide gives especially desirable high yields and selectivities to methacrylic acid.

Description

BACKGROUND OF THE INVENTION

U. S. Patent No. 3,882,o47 and Japane~e Patent No. 4,733,082 dl~close catalysts that are userul ln the oxidatlon of unsaturatcd aldehyde~ to unsaturated aclds, 20 wherein the catalysts are p~epared ln an ~queou~ ~olutlon '-¢ o~ phosphomolybdlc acld. U. S. 3,882,047 dlscloses catalysts of molybdenumJ phosphorus, at least one element such as thalllum, rubldlum3 ceslum and potasslum, ~nd at ,...
lea~t one element such as chromium, slllconJ alumlnum, C
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lron and tltanlu~. Japane~ Patent No. 4,733,082 dlsclo~es cRtaly~ts Or molybdsnum, phosphorus, and at l~st one elem~nt euch aa ar~enlc, boronJ slllcon, c~dmlum, l~a~, tung~ten, thQlllum, indlum, germ~nlum and tln. The pre~ent ln~ntion is the result o~ a seQrch ~or moro ef~lcient catalysts ror use ln the oxldation Or acroleln or mothacroleln to produce acryllc ~cld or methQcryl1c acld re~psctlvely.

~ SUMMARY OF THE INV~N~ION

:` It hae now been dl~cov~red according to the pre~ent; 10 ln~ention in the procc~s ~or the pieparatlon o~ acrylic acid.~ or methacryllc acid by the oxidatlon o~ acroleln or m~thacroloin respectiYely, with mol~cular oxygen in the vapor phase at a reaction temperature Or about 200C to about 500C in the ~: pre~ence o~ an oxide cat~ly~t, ~nd optlonally ln the presonce Or steam, the lmprovement comprislng u~ing as a c~aly~t a cataly~t dcscrlbed by the emplrical formula . Aa Crb Mo3 P O*
wherein A 1~ at least one of the element~, selected from the group consl~ting o~ rubi~ium, ~hallium, cesium, ar~enlc, titanlum and pota881um;
and wherb~n a 18 a po~ltlve number le3s than about 3;
b 1~ zero to about 3;
c i~ a posltive number less than about 2;
x 1~ the number of oxygen~ requlred by the valence states of the ether element~
pres~nt; .
and whereln at least part o~ the molybdenum employed in the preparatlon of the cQtalyst i8 ~upplled ln the ~orm of molyb~enum ~ trioxide.

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Unexpected improvements are achieved in yields of acrylic acid and methacrylic acid by the use of the catalysts of the present invention wherein molybdenum trioxide is incorporated into the preparation of the catalysts as compared to results obtained with the art catalysts prepared from phosphomolybdic acid.
The most important aspect of the present invention is the preparation of the catalyst employed. The incorporation of molybdenum trioxide into the catalyst preparations is critical to the present invention. The central feature is the fact that the stability, activity and selectivity of the catalyst is significantly enhanced when at least part of the molybdenum employed in the catalyst preparations is supplied in the form of molybdenum trioxide.
By the preferred procedure of the invention, molybdenum trioxide must supply at least 25% of the molybdenum employed in the preparation of the catalysts. More preferred ; catalysts of the invention are described wherein at least 50% of the molybdenum employed in the preparation of the catalysts is supplied in the form of molybdenum trioxide.
However, the catalysts of greatest interest in the invention, whereby optimal results are obtained, are described wherein all the molybdenum employed in the preparation of the catalysts is supplied by molybdenum trioxide.
In the preparation of the catalysts of this invention, the methods of incorporating molybdenum trioxide ~05~53'~
may vary widel~. A number o~ different techniques are known to those skilled in the art. The incorporation of molybdenum trioxide into the preparation of the catalysts may be before or after the addition of the remaining catalytic components.
The most preferred procedure of this invention involves the preparation of the catalysts in a refluxed aqueous slurry of molybdenum trioxide.
As noted, the catalysts employed in the present invention may be any catalyst delineated by the above formula. The catalysts can be prepared by a number of different techniques known to those skilled in the art, such as coprecipitation of soluble salts, evaporative drying, or oxide mixing, followed by calcining the resulting catalysts. In the broad concept of the invention, the particular method of preparing the catalysts is not critical.
The preferred procedure of the preæent invention involves the refluxing of an aqueous slurry of molybdenum trioxide for 1.5 to 3 hours, followed by the addition of compounds containing phosphorus and the remaining catalytic components; boiling the aqueous mixture to a thick paste;
drying at 110C to 120C in air; crushing and screening the resulting catalysts for testing. Soluble salts of the catalytic components other than molybdenum are preferred, however, insoluble salts or oxides may be used. Suitable phosphorus compounds that may be employed in the preparation of the catalysts include orthophosphoric acid, metaphosphoric acid, triphosphoric acid, phosphorus pentabromide, phosphorus ~ 4 -~OS9S3'~
pentachloride, and the like. The remaining catalytic components may be added as oxide, acetate, formate, sulfate, nitrate, carbonate, and the like.
Preferred catalysts of the invention are de-scribed wherein the preparation of the catalyst is accomplished by adding compounds containing phosphorus, chromium, and at least one element containing A to a refluxed aqueous slurry of molybdenum trioxide. More preferred catalysts are described wherein the preparation of the catalyst is accomplished by adding compounds containing phosphorus and at least one compound containing A to a refluxed aqueous slurry of molybdenum trioxide. However, the most preferred catalysts are described wherein the preparation of the catalyst is accomplished by adding compounds of phosphorus and at least one element selected ; from the group consisting of rubidium, cesium, and thallium.The reactants of the reaction of the invention are acrolein or methacrolein and molecular oxygen. Molecular oxygen is normally supplied to the reaction in the form of air, but oxygen gas could also be employed. About 0.5 to about 10 moles of oxygen are normally added per mole of acrolein or methacrolein.
Optionally added to the reactants is steam or ; an inert diluent. Preferred reactions are conducted in ' 25 the presence of substantial quantities of steam in the range of about 2 to about 20 moles of steam per mole of acrolein or methacrolein.
The reaction temperature may vary as different catalysts are employed. Normally, temperatures of about ..

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200C to about 500C are employed with tempera~ur~s Or about 250C to about 400C belng pre~erred.
The reactlon may be convenlently conducted ln sither a fixed-bed or fluid-bed reactor. m e contact time 5 ~ay be as low as a fractlon of ~ ~econd or a~ hlgh ~a 20 seconds or more, the preferred contact tlme i8 4 to 5 se¢onds. me reactlon may be conducted at atmohpheric, superatmo~pherlc or subatmospheric pressure, wlth ab~olute pres~ures Or about 0.5 to Qbout 4 atmosphere~ being pre~erred.
; When used in the reactor, the cat~lyst may be ln a supported or unsupported rorm. Sultable 8uppo~t m~tcrlals lnclude ~illc~, alumlna, boron, phosphate, zirconla~ titanium flnd the like, but the mo~t preferred i8 zirconla.
The example~ below are representative of the catalyst preparati~ns that are sultable for the proce~
o~ thi~ ln~entlon~ howe~er, the ~cope o~ the lnvention i8 not limlted to the~e example~. me preferred reaction o~ the lnventlon i5 the oxidation Or methacrolein to metha¢ryllc actd. or course, acrolein c~n be con~erted to acryllc ~cid using the catalyst~ and technique# of the prc~ent inventlon.

SPECIFIC EMBODIMENTS
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Exam~le 1 Com~aratl~e Exam~les A, ~, and C -.~
Production o~ methQeryl~c acid u~lng ~ catalyst~ Rb ~bo ~Mo~P 220x, prepared ~rom molybdenum trloxlde comp~rea i~h u~lng thl~ cat~ly~t prepared from dif~erent sources o~ molybd~num.

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Preparation and use of this catalyst are as follows:
Example 1 - Preparation from molybdenum trioxide.
An aqueous slurry was prepared by adding 55.3 g.
of molybdenum trioxide to one liter of boiling distilled water with stirring; the slurry was boiled ~or about 2 hours.
To this aqueous slurry, 4.9 g. of 85% phosphoric acid was added; the color of the slurry changed to yellow. About 200 ml. of distilled water was added to maintain an approximately 800 mls. solution level. About 1-1/2 hours after the addition of 85% phosphoric acid, the color of the slurry changed to a pronounced yellow-green; then 100 mls.
of distilled water was added to maintain solution level.
To this aqueous mixture, 7.5 g. of rubidium carbonate were added; the color of the slurry became bright yellow;
after about 30 minutes 25 mls. of distilled water were added. The catalyst was heated with stirring; boiled to ~ ;
dryness; and dried in air at about 110C.
Comparative Example A - Preparation from phosphomolybdic acid.
An aqueous solution was prepared by dissolving 118.3 g. of phosphomolybdic acid in about 1400 mls. of distilled water. To this solution, 1.92 g. of 85%
phosphoric acid was added. The pale yellow solution was boiled for about eight hours; stirred without heating for 12 hours. Heating was resumed, 11.6 g. of rubidium carbonate was added and the color of the solution changed rapidly to bright yellow. The aqueous mixture was boiled to dryness;
dried in air at 110C overnight.

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Com~arative Example B - Preparation from ammonium heptamolybdate.
A slurry consisting of 105.9 g. of ammonium heptamolybdate, (NH4)6Mo7O24-4H2o~ g acid and 1400 mls. of distilled water was boiled with stirring. The color of the slurry changed slowly from pale yellow to white. After boiling, the slurry was stirred without heating for 12 hours. Heating was resumed, and 11.6 g. of rubidium car~onate was added; the color of the aqueous mixture remained white. The aqueous mixture was boiled to dryness; dried in air at 110C overnight.
Comparative_Example C - Preparation from molybdic acid.
Preparation of this catalyst was in the same manner as Comparative Example B, except 7.7 g. of 85~
phosphoric acid were employed, and the ammonium heptamolybdate was replaced by 101.6 g. of molybdic acid.
The catalysts prepared in Example 1, Comparative Examples A, B and C were ground and screened to recover these particles of 20 to 30 mesh size. A portion of these catalyst particles were charged to a 20 cc. fixed-bed reactor consisting of a 1.3 cm. stainless steel tubing equipped with a 0.3 cm. axial thermowell. The reactor was heated to a reaction temperature of 343C under a flow of air and a feed of methacrolein/air/steam of -1/6.2/5.2 and was fed over the catalyst at an apparent contact time of 4.6 seconds.
In Comparative Examples B and C the catalysts were calcined at 430C for 1 hour, and then the temperature , 8 ., .

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was reduced to 343C. The reactor was run under the reaction conditions for 1.6 hours and then the product was collected by scrubbing the reactor off gases in two series water scrubbers. The scrubber contents were combined and diluted to 100 cc. for analysis and titration for acid content. The scrubbed fixed gases were dried and ;
analyzed on a conventional Houdry split column system.
The results of these experiments are shown in Table I
below. The following definitions are used measuring the carbon atoms in the feed and the products.
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% Single Pass Yield = Methacrylic Acid recovered 100 Methacrolein feed x - % ~onversion = Methacrolein reacted 1 0 Methacrolein feed x 0 % Selectivity = Methacrylic Acid recovered x 100 Methacrolein reacted ! Examples 2-5 - Effect of on stream time on catalytic activity using the catalyst Rbo 5Mo3P 33x The catalyst prepared in accordance with Example 1 and reacted with methacrolein was left on stream for further determination of methacrolein conversion to methacrylic acid. The results of this experiment are shown in Table II.

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Examples 6-10 - Preparation and use of various catalysts of the invention.
Various catalysts of the present invention were prepared. These catalysts have the general formula Ao sMO3P 33x The catalysts were prepared according to the procedure of Example 1, except 86.2 g. of MoO3, and 7.7 g. of 85% H3PO4 were employedO The element, A, was added following the addition of the phosphoric acid.
To prepare the catalysts, the following compounds and amounts were used:
Element Compound Amount Tl thallous acetate 26.3 Ti titanium trioxide 7.19 Cs cesium acetate 19.2 K potassium acetate 9.81 As arsenic trioxide 9.9 Following the addition of the element, A, the catalysts were boiled and dried according to Example 1. The catalysts were ground, screened and tested as shown in the examples above. The results of using these catalysts in the oxidation of methacrolein are given in Table III.

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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In the process for the preparation of acrylic acid or methacrylic acid by the oxidation of acrolein or methacrolein respectively, with molecular oxygen in the vapor phase at a reaction temperature of about 200°C to about 500°C in the presence of an oxide catalyst, and optionally in the presence of steam, the improvement comprising using as a catalyst a catalyst described by the empirical formula AaCrbMo3PcOx wherein A is at least one of the elements selected from the group consisting of rubidium, thallium, cesium, arsenic, titanium and potassium;
and wherein a is a positive number less than about 3;
b is zero to about 3;
c is a positive number less than about 2;
x is the number of oxygens required by the valence states of the other elements present;
and wherein at least part of the molybdenum employed in the preparation of the catalyst is supplied in the form of molybdenum trioxide.

2. The process of Claim 1 wherein at least fifty percent of the molybdenum employed in the catalyst preparation is supplied in the form of molybdenum trioxide.

3. The process of Claim 1 wherein all the molybdenum employed in the catalyst preparation is supplied in the form of molybdenum trioxide.

4. The process of Claim 1 wherein an aqueous slurry of molybdenum trioxide is employed in the preparation of the catalyst.

5. The process of Claim 1 wherein A is the element arsenic and b is zero.

6. The process of Claim 1 wherein A is at least one element selected from the group consisting of rubidium, cesium and thallium, and b is zero.

7. The process of Claim 1 wherein the preparation of the catalyst is accomplished by adding compounds containing phosphorus, chromium, and at least one compound containing A to a refluxed aqueous slurry of molybdenum trioxide.

8. The process of Claim 1 wherein the preparation of the catalyst is accomplished by adding compounds containing phosphorus and at least one compound containing A to a refluxed aqueous slurry of molybdenum trioxide.

9. The process of Claim 1 wherein the catalyst prepared is RbO.5Mo3P0.33O.

- 15.