Note: Descriptions are shown in the official language in which they were submitted.
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~ACKGROUND OF TH~ INVEWTION
Field of the Invention
This invention relates to a process for the con
version by oxydehydrogenation o~ isobutyric acid to
methacrylic acid. The process applies as well to
functional equivalents of isobutyric acid such as pro-
pionic acid and methylisobutyrate.
Description of the Prior Art
There is considerable prior art directed to the
oxydehydrogenation of the lower saturated mono-carboxylic
acids to prepare the correspondiny a, ~ unsaturated
acids. The initial work reported in this area was that
of thermally effecting the indicated oxydehydrogenation
by the vapor phase reaction of the acid substrate with
iodine and oxygen. This approach has not attracted
much aktention as a potentially viable way for com~
mercially implementing the underlying reaction~ This
is understandably so inasmuch as iodine is costly,
exhibits extreme corrosive properties and poses con-
siderable problems in realizing complete recovery ofthe comparatively large amounts thereof required in
the process.
As the subsequent prior art picture amply points
~7~
up, the heterogeneous catalytic method for effecting
the oxydehydrogenation reaction is viewed as being
much more attractive from the standpoint of potential
commercial applicability. In the main, the more recent
relevant prior art activities have centered on the use
of two types of catalyst compositions for this purpose.
One type includes generally the heteropoly-acids,
typically representative of which is 12-molybdophosphoric
acid optionally including vanadium and/or tungsten
elements in a like structural arrangement. The other
type catalyst includes those systems having in common
a calcined iron phosphate matrix.
Iron phosphates sub~ected to calcination exist
in a plurality of crystalline phases or species. While
it is believed that the oxidation/reduction couple in-
volved in the underlying reaction is attributable to
the iron phosphate, which species is or are catalytically
active has not been identified. There is, however,
evidence that the presence of an additional metal com-
ponent in the preparation serves to facilitate theormation of the catalytically active species~ For
example, U.S. Patent 3,~48,959 nota~ly teaches that an
alkali or alkaline earth metal as the additional metal
component is effective for this purpose. The present
invention accordingly represents a furtherance of this
particulax aspect of the current state of the art.
SUMMA:RY_OF THE IN~TENTION
In accordance with this invention, a catalytic
process is provided for effecting the oxidative de-
hydrogenation of isobutyric acid to form methacrylicacid~ The process of this invention compris~s con-
tacting a heterogeneous catalyst at a temperature from
300-550C. with a co-feed of said isobutyric acid
~8t7g~
substrate and diluted oxygen gas, characterized in
that said catalyst is calcined iron phosphate containing
the additional metal alumin~ as the modifier or dopant
component. Other Group IIIa elements; ~oron, gallium
and indium may serve as the modifier or dopant component.
In the broadest aspect of the invention the contemplated
catalyst is defined by the gram-atom empirical formula
FeM0 01 lPl 2x in which M represents aluminum,
boron, gallium or indium and x represents the number of
oxygen atoms bound to the other metals in their res-
pective states of oxidation in the catalyst. It has
been found that the aluminum modi~ied iron phosphate
catalyst is active over long periods of time. Unlike
the iron phosphate catalyst which loses activity over
time, the aluminum modifi~d catalyst has been shown to
retain activity in studies of 100 hour duration.
DESCRIPTION OF THE PREFERRED EMBODI~lENTS
There are a number of techniques applica~le ~or
preparing the catalyst useful in the practice of this
invention. Of these, the more facile methods involve
preparing the integral composition prior to calcination.
This can be readily accomplished by employing the
so-called slurry method or the precipitation method.
In the latter me-thod an aqueous solution of salts of
the contemplated metals and phosphoric acid is first
prepared and thereupon neutralized with an appropriate
base in order to precipitate the mixed metal phosphates.
The precipitate is desirably carefully washed to remove
all traces of water solubles and then dried prior to
calcining. In the alternative, one can add ammonium
phosphate to the solution of metal salts in order to
precipitate directly the metal phosphates. As indicated,
any water-soluble salt of iron or aluminum can be used.
~37~
However, because of the solubility characteristics of
the nitrate salts, among other reasons ! such salts
are preferred.
The so-called slurry method is even more convenient
to carry out and ~or this reason represents the pre-
ferred method herein~ In accordance with this pro
cedure, the aqueous solution of the iron and aluminum
salts together with the phosphoric acid is obtained~
The solution is heated continuously until the mass
can be no longer stirred~ The residue is then frag-
mented and again heated at a moderately elevated tem
perature in the order of a~out 120C. until completely
dried. Thereupon the dried composite is sized and
calcined. Su~table calcination temperatures broadly
range from 400-1000C. or more preferably from 400 to
850C.
In the manner of either of these techniques~ a
supported catalyst can be prepared~ For example, in
the slurry method colloidal silica or colloidal alumina
or any other form thereof can be added prior to removing
the water content. When colloidal alumina is used it
may serve ~s well as an add~tional source o$ the
aluminum cations which pro~ide the impro~ed activity
and long catalyst life observed in the aluminum modified
iron phosphate catalyst o~ the present ~nvention.
Supports such as alumina! Silica~ titania~ etc. !
can be added prior to removin~ the water content.
The support may also be soaked ~n a solution o~ the
metal phosphate and allowed to dry. The soaking and dry-
ing steps may be repeated until the desired number o~layers of dried metal phosphate are obtained~ Simil~rly,
in the alternate method described, the precipitat-`on
of the metal phosphates can be accomplished in the presence
of suspended particulates of the intended support, In a
typical commercial catalyst preparation a spray drying
~ 3'7~
technique is used in which the slurry i5 fed to a spray
drier and the solid product is then tableted or extruded
and then calcined.
The catalyst compositions of this invention can be
employed in a fluidized bed reactor, stirred tank reactor,
or fixed-bed type reactor Because of the convenience
associated with the use of a fixed~bed reactor in a small
scale operation, such a reactor will be exemplified
herein. In the preferred mode of operation the feed to
the reactor comprises a pre-heated gaseous mixture of
the substrate, molecular oxygen, steam and inert diluent
gas, A pre-heat temperature in the range of about 300
to 350C. is customarily observed. A broad range of
applicable reaction temperatures is from 250-550C.
but more generally a temperature of from 350 to 450C.
provides for optimum processing.
The mole ratio of molecular oxygen to substrate is
~rom 0.2 to 1.5 and more preferably 0.5 to 1.0, While
steam is not necessary for the purpose of effecting the
reaction, the presence thereof in the feed improves the
y~eld of the desired product~ An applicable mole ratio
of water to the substrate in the feed IS from about
1 to 75. The optimum ratio is more in the order of about
10 ~o 30.
Another important parameter re$ides in the concen~
tration of the substrate in the feed. Expressed in terms
of mole percents, the concentration of the contemplated
su~strates ran~es broadly from 0.1-20. As is common in
reactions of this type~ y~eld of the desired product
3Q is an inverse function of the concentration. From the
standpoint of achieving a reasonable through~put combined
with an acceptable yield, the concentration of the sub-
strate in -the feed is from about 3-6 mole percent~ Con-
centration is controlled by the amount of water and inert
gas present in the feed stream. The preferred diluent
~7~g8
~6--
g~s is nitrogen although other gases such as carbon
diox~de, helium, argon, and the like are suitable, Of
coùrse if the desired concentration of substrate permits,
air represents a suitable diluted oxidant.
Another applicable parameter is that of contact time.
Contact time is deined as the catalyst volume d~vided
by the volume o gas feed per second at reaction tem-
perature. The catalyst volume is the bulk volume occupied
~y the catalyst in the reactor. The term catalyst in
this sense not only includes the modified iron phosphate
itself but also the solid diluent or support if present.
Accordin~ly~ applicable contact times range fxom 0.05~50
seconds and more yenerally in the order o~ from 0.1~20
seconds. The reaction is carried out at atmospheric
pressure.
~EX~MP-~E~l
The purpose of this example is to ~llustrate the
hereinabove described slurry method ~ox preparlng a cata-
lyst useful in the pract~ce of this in~ention. Iron
nitrate nona-hydrate in the amount of 122 gS alon~
with 11.33 g. of aluminu~ nitrate nona hydrate were
dlssolved in 250 ml. of water~ Concentrated phosphoric
ac~d in the amount of 42~4 g, was added with stirring
to the solution of metal salts. The solution was then
stirred and heated until the bulk of the water was
evaporated~ The result~nt paste was further dried at
125C. until in condition to be fragmented whereupon
the solid was broken into half-inch and smaller pieces
and calcined for 16 hours in flowing air at 450C. The
calcined material was crushed and screened to 12/20
mesh size before use. The gram~atom empirical formula
of the calcined mixed phosphates of iron and aluminum
follows: FeA1o,llPl.1x'
~8~
7~
~EXAMPLE 2
This example illùstrates the preparation of an
aluminum modified iron phosphate catalyst having a higher
ratio of phosphorus to aluminum than the catalyst of
Example 1. Iron nitrate nona-hydrate in the amount of
610.0 grams along with 62.6 g. aluminum nitrate nona-
hydra~e were dissolved in 1,2 liters of distilled watex,
Concentrated phosphoric acid in the amount of 250 g.
was added~ The remaining procedure was followed as
given in Example 1. The gram atom empirical formula
of the calcined mixed phosphates of iron and aluminum
follows; Fe~lo,l1P1~4 ~
EXAMPLE 3
This example illustrates the preparation of an alu~
minum modified iron phosphate catalyst of the gram atom
empirical formula o FeAl~,05Pl.05Ox
nona-hydrate in the amount of 128,6 g, along with
5.86 g. aluminum nitrate nona-hydrate were dissolved in
250 ml. distilled water, Concentrated phosphoric acid
in the amount of 50.0 g. was added, The remaining pro-
cedure as given in Example 1 was followed.
EX~MPLE` 4
This example illustrates the preparation of an
aluminum modified iron phosphate catalyst of the gram
atom empirical formula of FeAl0,llPl 1x
has the same gram atom empirical formula as the catalyst
of Example 1. This catalyst differs, however, from the
catalyst of Example 1 in that the preparation avoids
the use of additional water. The catalyst of Example 4
was prepared by mixing 610 g. of iron nitrate nona-
hydrate and 56.65 g. aluminum nitrate nona-hydrate. This
mixture was heated ~mtil melted and 212 grams of 85%
phosphorîc acid was then added with stirring. The
remaining procedure as given in Example l ~as followed.
EXAMPLE 5
This example il]ustrates the preparation of a gallium
modified iron phosphate catalyst having the gram atom
empirical formula of Fe~aO llPl 1x~ Iron nitrate nona-
hydrate in the amount of 71,0 g. along with 5.0 g.
gallium nitrate nona-hydrate was dissolved in lO0 ml.
water. Concentrated phosphoric acid in the amount of
24.8 g. was then added. The remaining procedure as
giv~n in Example l was followed.
EXAMPLE 6
This example illustrates the preparation of a gallium
modified iron phosphate catalyst having the gram atom
empirical f~rmula of FeGaO llPl 44x~ Iron nitrate
nona-hydrate in the amount of 71.0 g. along with 5.0 g
gallium nitrate nona-hydra-te was dissolved in lO~ ml.
water and 29.3 g. concentrated phosphoric acid was then
added. The remaining procedure as given in Example l
was followed.
EXAMP~E 7
This example illustrates the preparation of an iron
phosphate catalyst which is not modified ~y the addition
of another metal. Iron nitrate nona-hydrate in the
amount of 101 g. was dissolved in 200 ml. water, Con-
centrated phosphoric acid in the amount of 29.1 g. was
then added. The remaining procedure a~ given in Example l
was followed. The gram atom empirical formula of the
calcined iron phosphate ~ollows; FePOx.
- ~L87~98
.
g
EXAMPLE 8
This exam~le illustrates the use o,~ the catalyst
composition of the foregoing examples in effecting the
oxidative dehydrogenation of isobutyric acid ~IBA~.
The reactor and -the general manner of conduct~ng the
reaction was the same for each o~ the enumerated runs,
The catalyst was diluted ~itn quartz chips (1 part by
volume catalyst to 4 parts by volume quartz chips) and
loaded into a conventional down flow tuhular reactor.
Tests were conducted at 400 to 425C. The procedure
consisted of feeding a pre-heated mixture of iso~utyric
acid, oxygen, nitrogen and steam through a stainless
steel tube of 1~2" OD (3/8" ID) and approximately 18"
in length containing the test catalyst as a 15 cc ? packed
bed maintained at the reaction temperature utilized in
the particular run. The ratio of water to isobutyric
acid in the feed was 20 to 1, the ratio of oxygen to
isobutyric acid in the feed was 1 to 1 and contact time
was on the order of 0.4 to 0,5 seconds. These ratios
result in a feed mixture containing 4 mole % isobutyric
acid, 78 mole % water, 4 mole % oxygen and 14 mole % of
diluent nitrogen.
The pre-heater consisted o~ a length of stainless
steel tube similar to the reactor but packed with glass
beads~ The condensed organic product was collected and
analyzed by gas chromatography. Gaseous products were
analyzed separately by gas chromat~graphy.
Pertinent results observed for the individual runs
are set forth in Table I presented hereinbelow. The
results obtained in texms of selectivity and conversion
axe likewise given in said table. Conversion represents
the mole ratio of substrate consumed to that charged to
the reactor. Selectivity to methacrylic acid (~
represents the mole ratio of methacrylic acid found in
the effluent to that of IBA consumed in the reaction,
.
:
--10--
The catalyst prepared as described in Example 1 and used
as described in Example 8 to effec~ the oxydehydro~enation
of isobutyric acid has ~een on-stream for 100 hour~
without showing signs of deactivation.
TABLE I
Temp. Hours IBA MAA
Catalyst O~ _ On Stream Conv. ~ Sel. %
Example 1 401 10 96 70
Example 1 406 30 98 69
10 Example 1 402 70 97 69
Example 1 399 100 37 68
F.xample 2 420 25 95 67
Example 2 420 45 97 70
Example 3 421 12 95 73
Example 3 399 30 94 75
Example 4 408 20 97 69
Example 4 409 40 98 70
Example 5 409 3 93 67
Example 5 416 24 8~ 69
20 Example 6 397 ~ 69 72
Example 7 413 4 99 60
Example 7 412 22 85 67
Example 7 411 42 62 53
