Note: Descriptions are shown in the official language in which they were submitted.
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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(4857)
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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.
-- 2 --
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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
..
(4857)
~ 05~ 5 3'~
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
, ~
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.
- 6 -
105~53;~
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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3~3S953'~
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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lUS5~53~
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.
;, :
% 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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