Note: Descriptions are shown in the official language in which they were submitted.
5~
A Method for the Activation, Maintenance of Activity
and Reactivation of Phosphomolybdic Acid Based CatalYsts
Technical Field
Catalysts comprising phosphomolybdic acid and various
salts thereof have recognized utility in several areas of
petrochemical processing. An area of particular importance and
which relates to the present invention is the use of
phosphomolybdic acid based compounds as catalysts for the
selective direct oxidation of unsaturated aldehydes such as
methacrolein to its corresponding acid, methacrylic acid.
Catalysis with supported or unsupported dehydrated
phosphomolybdic acid in combination with small amounts of
promoters such as antimony, arsenic, bismuth, copper, tellurium
and hydroxides or decomposable salts of alkalis and alkali
earth metals is a process of specific economic interest.
More generally, ehe catalysts which can be activated
according to the method set forth herein are redox type
catalys~s which are utilized in oxidation, a3moxidation and
hydrolytic reactions. Such catalysts are often thermalLy
sensitive but can be satisfactorily activated by the method of
this invention.
It has become well known that phosphomolybdic acid
(PMA) and salts thereof are sensitive to significant struc-
tural change caused by thermal, hydrolytic or reductive stress.
As is to be expected, such physical and chemical changes
caused by these stresses are directly reflected in a reduction
in catalytic activity. Thus, it has not been uncommon for
much of the catalytic activity to be lost after only a rela-
tively short on-stream time.
Deactivation of PMA based catalysts can occur by
processes which cause loss of acid sites via condensation
crosslinking. Contacting an active deammoniated PMA based
catalyst with moisture below about 100C is a certain means
of causing deactivation. In this temperature range water vapor
undergoes capillary and surface condensation within the cata-
lyst particles. Generally, shutdown of the reactor for signi-
ficant periods of time is marked by a significant decrease
in catalytic activity.
Scheduled and unscheduled reactor shutdowns during
catalytic operations inevitably occur. Experience in both
laboratory and pilot plants has shown that the usual procedure
of flusing the reactor with air, nitrogen and/or steam or,
the static system for shutting down and holding PMA based
catalysts at bath temperatures has caused a substantial decline
in catalytic performance when the oxidation reaction is again
resumed.
In addition to the cooling down deactivation, other
processes that c~n cause mass transport and result in
deactivating condensation crosslinking are deep reduction and
thermal excursion. Overheating of the catalyst can also
result in complete decomposition o~ the acld structure to
its components oxides MoO3 and P2O5. While the occurrence
of these deactivations can be minimized by avoiding r~actor
shut-down and otherwise controlling the catalytic process,
nevertheless, deactivation inevitably occurs. In fact, in
36
the conversion of methacrolein to methacrylic acid, signi-
ficant loss of catalytic activity can be noted after only a
few hundred hours of use.
The subject invention relates to methods for the
effective reactivation of PMA based catalysts having been
deactivated in the foregoing conversion of aldehyde to acid.
In order for the catalyst reactivation to be practical from
a consideration of technical as well as economic aspects, it
is necessary that the reactivation scheme be practiced without
necessitating reactor shut-down and catalyst removal or, in
the case of a fluid-bed operation, that reactivation be
capable of execution in a conventional regenerator vessel.
This restriction therefore dictates that the deactivated
catalyst be reactivated in the vapor phase.
Background Art
Catalysts for the oxidation of unsaturated aldehydes
to unsaturated acids are generally well known in the litera-
ture and in various patents. U.S. Pats. No. 2,865,873 and
3,882,047 and Japanese Pat. No. 47-33082 disclose such
catalysts wherein ammonia or an ammonium-containing compound
is incorporated in the preparation of the catalysts.
U.S. Pat. No. 2,865~873 in Column 13, Examples 101
to 104 discloses a process for the preaparation of metha-
crylic acid using catalysts consisting of molybdenum, phos-
phorous, titanium and oxygen, wherein ammonium paramolybdateis employed in the preparation of the catalysts. The highest
yield of methacrylic acid produced is about 39.56~.
U.S. Pat. No. 3,882,047 discloses the preparation
of methacrylic acid using catalysts containing molybdenum,
phosphorous, at least one element such as thallium, rubidium,
cesium and potassium, and at least one element such as
chromium, silicon, aluminum, iron and titanium. This refer-
ence teaches the incorporation of ammonia or ammonium-
containing compounds in the preparation of all catalysts
exemplified in the oxidation of methacrolein or acrolein;
..
phosphomolybdic acid is employed in the preparation of
virtually all catalysts exemplified; and in a few examples,
ammonium molybdate is employed. This patent discloses in
Column 3, lines 30-40 as follows:
"It is preferred that the catalyst be prepared
so that the constituent elements will form complex
compcunds such as heteropolyacids, then acid salts
or ammonium salts."
Japanese Pat. No. 47-33082 discloses a process for
reclaiming an ammonia-modified phosphorous-molybdenum-X-
oxygen catalyst, wherein X is at least one element selected
from the group consisting of antimony, arsenic, bismuth,
cadmium, germanium, indium, iron, lead, silicon, thallium and
tin. Preparation of the catalyst involves treating the
catalyst with ammonia and water by oxidizing the catalyst in
advance or by oxidizing it simultaneously with the treatment
of ammonia and water. This patent discloses that the ammonia
forms a complex compound with the other elements present.
Notwithstanding the various methods of preparation disclosed
in the foregoing patents, none discloses a fast, low tempera-
ture activation of thermally unstable catalysts. We are
furthermore unaware of any reference which discloses the
activation of these catalysts with oxides of nitrogen.
While much has been published or patented on the
subject of PMA based catalysts and their uses as oxidation
catalysts and, reactivation of other catalysts is generally
known, very little prior work directed toward the reactiva-
tion of PMA based catalysts has been reporied. One such
method that is known is disclosed in Japanese patent appli-
cation, No. 77/29,660, filed by Mitsubishi Rayon Co., Ltd.,
which describes the regeneration of a PMA based catalyst by
treatment with ammonium hydroxide, and hydrogen peroxide or
ozone and optionally also with nitric acid or ammonium nitrate.
The inventors reported that the initial oxidation of metha-
crolein with the fresh catalyst gave 88% selectivity to
methacrylic acid with 66% conversion of methacrolein; the
~ . :
.
.,
1~5~
spent catalyst gave only 71.5% selectivity to methacrylic
acid with 30.3% conversion of methacrolein and, that following
regeneration with ammonium nitrate and ammonium hydroxide and
5 parts of 30% hy~rogen peroxide for 30 minutes at ~0C, the
catalyst gave 88.1% selectivity to methacr~lic acid with 65.1%
conversion of methacrolein. This process is undesirable in-
as much as it merely attempts to oxidize the deactivated
catalyst and to do so outside of the reactor, necessitating
shut-down.
Several other Japanese patents exist which disclose
the use of ammonia for regeneration of spent PMA catalysts.
However, none of which we are aware is directed toward
reactivation of PMA based catalysts with nitrogen oxides.
Use of nitric o~ide to reactivate a supported
palladium catalyst containing 1% palladium has been described
in Japan Kokai 75,75,587, wherein full reactivation was
obtained by heating the catalyst with acetic acid in the
presence of a nitrogen containing oxidant followed by treat-
ment with potassium acetate. The latter treatment is indica-
tive of a reconstructive regeneration. German Offenlegungsschrift
2,126,007 sets forth a regeneration scheme for a spent
aluminum oxide/boric oxide rearrangement catalyst by heating
while fluidizing with air containing nitrogen oxide.
In more recent work, conducted in the laboratories
of the Assignee of record herein, PMA based catalysts can be
regenerated in the presence of ammonia and hydrochloric acid.
Such a process is referred to as corrosive reconstruction
wherein a reconstructive transformation occurs generally
involving the breakdown of one crystal lattice and the
reorganization of another. Unless cataly~ed in some manner,
such reconstructive transitions have an appreciable activa-
tion energy compared to displacive transitions wherein only
relati~ely minor shifts of atoms occur. It is believed that
displacive transition would permit a deactivated catalyst to
be reactivated ln situ with a single oxidizing gas.
Thus, the prior art of which we are aware has not
, ~ , . . .
~,
,
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set forth a method by which a deactivated PMA based catalyst
can be reactivated with only a gaseous oxide of nitrogen or
mixtures thereof. ~o be useful, we believe the reactivation
of PMA based catalysts must occur in the vapor phase, and
whether inside or outside of the reactor, without catalyst
removal. It is also necessary to reactivate the catalyst in
a manner that is compatible with a fluid-bed process. It
would be further useful to be able to treat the catalyst
during on-stream use thereby maintaining its activity over
greater periods of time.
Disclosure of the Invention
It is therefore an object of the present invention
to provide a.method for the activation of PMA based catalysts
utilized in the oxidation of unsaturated aldehydes to acids.
It is another object of the present invention to
provide a method for the activation of PMA based catalysts
in shorter times than have been employed heretofore to yield
highly active and selective catalysts.
It is yet another objec-t of the present invention
to provide a method for the preparation of thermally unstable
catalysts such as PMA based catalysts at temperatures well
below normal activation temperatures whereby catalyst life
is prolonged.
It is another object of the present invention to
provide a method for readily reactivating PMA based catalysts
without necessitating removal of the catalyst from the reactor
for treatment followed by the reloading thereof.
It is yet another object of the present invention
to provide a vapor phase method for reactivating PMA based
catalysts.
It is still another object of the present invention
to provide a method for reactivating P-~A based catalysts
that can be employed during on-stream use of the catalystO
- - -
These and other objects, together wlth the advan-
tages thereof over known methods, which shall become
apparent from the specification which follows, are accom-
plished by the invention as hereinafter described and claimed.
In general the method of the present invention
involves the step of feeding an oxide of nitrogen or mix-tures
thereof over the deactivated catalyst at a temperature of
from about 100C to about 400C. When the method is to be
conducted _ situ, the additional steps of terminatiny the
reactant feed, adjusting the reactor temperature to that which
is necessary for the reactivation or maintenance of activity,
and in the case of reactivation, sweeping the reactor with
an inert gas are first conducted. If the reactivation is to
be conducted outside of the reactor, its initial removal to a
suitable regenerating vessel is all that is required prior
to treatment, followed by its return to the reactor.
As will be discussed in greater detail hereinbelow,
the nitrogen oxide preferably employed is nitric oxide which
is passed over the catalyst for a period of at least five
minutes and at a rate to provide a contact time therewith of
at least two seconds. The nitric oxide is preferably fed
to the reactor in admixture with an inert gas such as nitrogen.
Preferred Mode for Carrying Out the Invention
The catalyst commonly employed in the preparation
of methacrylic acid from methacrolein and possibly acrylic
acid from acrolein is a PMA based catalyst which can be pro-
vided with one or more metallic promoters and which has the
general formula MoxPyAaBbCcDdEeOz. Suitable promoters include
the following : where A is ammonium, cesium, potassium,
rubidium and/or thallium; B is copper and/or vanadium; C is
antimony, arsenic, bismuth and/or tellurium; D is palladium;
E is aluminum, barium, calcium, cerium, chromium, cobalt,
iron, magnesium, manganese, nickel, tantalum, titanium,
tungsten, zinc, zirconium, chlorine and/or bromine; and,
wherein x can be 6 to 14 and is preferably 1~, y can be 0.1 to 15 a~d is
'
3~i
preferably 1 to 1.5, a can be 0.1 to 3 and is preferably 1 to 2, can be
0.1 to 3 and is preferably 0.1 to 1, c can be 0 to 2 and is
preferably 0 to 0.7, d can be 0 to 2 and is preferably 0 to
1, e can be 0 to 4 and is preferably 0 to 1, and z is a number
necessary to satisfy the other elements. Suitable catalysts
and the preparation thereof have been described in several
U.S. patents commonly owned by the Assignee of record herein
and include, for instance, U.S. Pats. No. 4,083,805 and
4,138,366. Of these many catalysts, those having a ratio of
molybdenum to phosphorous of from about 3:1 to as high as
15:1 can be employed with 9 to 12:1 being preferred. Two
catalysts which were treated according to the method of the
present invention have the formulae Mol2PAsO 5CuO 25z and
Mol2Psbo.22cuo.25oz
The conversion of aldehyde to acid is accomplished
with molecular oxygen, conducted directly to the reaction
vessel, or supplied as air. The oxygen and aldehyde reactants
are preferably carried by steam with the foregoing reactants
collectively being referred to as the reactant feed. The
steam can optionally be replaced by recycle gases from the
reactor which would normally include nitrogen, oxygen, carbon
oxides and other gases which would also comprise a portion
of the reactant feed. In some oxidation systems, the reactant
feed could also include the effluent from a first stage
reactor wherein isobutylene is principally converted to
methacrolein. When the effluent comprises the reactant Eeed,
it will be understood that other components will also be
present; several that are by products of the first stage
conversion and others such as air which would normally be
added for the conversion of methacrolein.
The conversion reaction can be conducted in either
a fixed-bed or fluid-bed reactor at temperatures of from
about 2~0C to about 400C and pressures of about 0.2 to
about 10 atmospheres. The catalyst may be in a supported
or unsupported form; suitable support materials including
silica, alumina, boron-phosphate~ titania, zirconia and the like and
'.,~
~5~6
preferably Alundum as well as mixtures thereof. The catalyst
can have any of the conventional fixed-bed forms such as
coated, tablet, pellet, extruded, spherical, or fluid-bed
forms such as micro-spherical or other forms known in the
art. Presence of the catalyst increases the rate and percent
of conversion, the selectivity of the reaction, wherein the
aldehyde to acid conversion is favored, and the single pass
yield.
ACTIVATION
Activation of the catalyst can be carried out in
the reactor by charging the catalyst precursor to the reactor
and treating with a nitrogen-containing gas or compound which
can be any of the oxides of nitrogen gas or a nitrogen acid
such as nitric or nitrous including decomposition components
thereof. Nitric oxide has been found to be particularly
suitable for this method. If desired, the reactor can be
initially flushed with an inert gas, such as helium or nitrogen,
although this step is not essential. Similarly, the reactiva-
ting gas can be carried with nitrogen or other inert gas to
the reactor for treatment of the catalyst.
The feed of nitric oxide is generally conducted
over the catalyst precursor for a period of time of from about
one minute to about several hours when a low amount of feed
is employed. The amount of the nitric oxide introduced into
the reactor can vary as desired but generally an amount
volume equal to about 0.5 to about 50 times the volume of the
- catalyst would be satisfactory. The step of treating can be
conducted at a temperature ranging from about 125C to about
400C with about 150C to about 350C being preferred.
Treatment can be conducted at pressures ranging from near
atmospheric to superatmospheric.
In constrast to the known air activation of these
catalysts which is conducted at about 370C, the catalyst
composition can be activated according to the method herein 7
-
~L5~
at temperatures between about 125C to about 400C, with a
range of about 150C to about 350C bein~ preferred. Regarding
pressure, subatmospheric, ambient or slightly elevated, l.e.,
between 0.2 and three or four atmospheres, is suitable. Time
for the treatment with the nitrogen~containing compound can
range from about one minute to about three hours with one hour
being preferred.
In actual operation, it is contemplated th~t a
catalyst precursor, comprising the dried salts of the active
catalyst component in suitable form for loading in a reactor,
would be placed in a reactor and optionally flushed with
nitrogen. Heating of the precursor is then conducted followed
by the step of treating the catalyst precursor with a nitrogen-
containing compound to form the activated catalyst. Following
activation treatment, the reactor is heated to reaction
conditions as may be necessary and the hydrocarbon reactant,
~, methacrolein or reactant feed is passed over the
catalyst for the desired selective chemical reaction to occur.
Three types of promoted catalysts were activated
and subsequently employed for the selective oxidation of
methacrolein (MA) to methacrylic acid (MAA). Table I presents
the activation conditions and results for the arsenic-copper
promoted catalyst precursor Mol2PAsO 5CuO 25z and subsequent
oxidations reactions with the catalyst. Examples 1-5 pre-
sented therein were given an activation temperature of 245Cand time of one hour. Nitric oxide with nitrogen, volume
percent ratio of 49/51 NO/N2, respectively, was selected as
the nitrogen-containing compound for the activation of the
catalyst precursor. Using the nitric o~ide activated catalyst,
a feed of methacrolein/ water/air in the volume ratio of
1:8.7:10.6 respectively was fed thereover at 315C. The
volume of the hydrocarbon feed to that of the catalyst per
hour was approximately 30. Contact time of the hydrocarbon
feed over the catalyst was between two and three seconds.
Example 1 was a control catalyst having only air
10 .
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,., ~ . :
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activation at 245C. Activity was determined at 320C by
measuring the conversion to methacrylic acid after one hour
of use with the hydrocarbon feed. Another charge of the
catalyst precursor was then given an activation treatment with
NO/N2 and tested at successive periods of time on-stream with
the reactant feedr as presented in Examples 2-5.
In order to evaluate the effectiveness of the method
set forth herein, certain yields were calculated by measuring
the percent total conversion, percent per single pass yield
or percent yield (~ Yield) and percent selectivity (% Sel),
which are defined as follows:
Moles of methacrolein reacted
Percent Conversion = x 100
Moles of methacrolein fed
Moles of product recovered
Percent Single Pass Yield = x 100
Moles of methacrolein fed
Moles of methacrylic acid
recovered
20 Percent Selectivity = x 100
Moles of methacrolein reacted
:
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U~ . . Cl~ d'
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As is evident from Table I, activation in air a~
only 245C for one hour was insufficient to bring the catalyst
to its full potential. This is reflected by the extremely
poor yields for Example 1. In order to activate the catalyst
in air, a temperature of approximately 370C and a period of
time of several hours is necessary. By reviewing the signi-
ficantly high yields for Examples 2-5, it can readily be seen
that the method of the present invention permits the activation
of PMA based catalysts to occur at a relatively low tempera-
ture and quickly. Inasmuch as the catalyst is activated ata relatively low temperature it will have a greater activity
for a longer period of time before regeneration is required.
Table II presents the activation conditions of
another catalyst precursor~ Mol2pKl.2Mgo~5Aso.6cuo-2vo-5
and subsequent oxidation reactions with the catalyst. The
catalyst was supported on a 0.3 cm spherical Alundum carrier
at the 33 weight percent level. Nitric oxide was again
employed with nitrogen gas as in Table I.
Example 6 was a control given an air activation for
three hours at 400C followed by one hour of hydrocarbon
feed at 345C. For Example 7, another charge of the catalyst
precursor received the NO/N2 activation for 0.75 hour at 320C
followed by one hour of the hydrocarbon feed, after which
activity tests were conducted for both examples at 320C.
Significant improvements in total conversion, yield and
selectivity were observed following the nitric oxide activation.
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Ta~le III presents the activation conditions of
another catalyst precurSr Ml2Pl.33Kl.5cuo-25 0-25 0-1 Z
and subsequent oxidations with the Gatalyst. The catalyst
was supported on a 0.3 cm spherical Alundum carrier at the
35 weight percent level. Nitric oxide was employed with
nitrogen gas as a carrier for Examples 10, 11, 15 and 16 and
with helium for Examples 17 and 18.
Examples 8 and 9 represented a control that had
received air activation at 370C for one hour and hydrocarbon
feed for one hour at 345C. Two activation tests are reported,
one at 320C, Example 8, and the other at 315C, Example 9.
For Examples 10 and 11, the catalyst received one
hour of air activation at 370C, one hour of hydrocarbon feed
at 345C and 0.25 hour of the NOjN2 treatment at 315C.
Activation tests were conducted at 315C and 305C and have
been reported as Examples 10 and 11, respectively.
For Examples 12 and 13, the catalyst received three
hours of air activation at 370C and one hour of hydrocarbon
feed at 345C. Activation tests were conducted at 320C and
305C and have been reported as Examples 12 and 13, respectively.
For Example 14, the catalyst received three hours
of treatment with nitrogen gas at 370C followed by one hour
of hydrocarbon feed at 345C. An activation test was con-
ducted at 320C and has been reported as Example 14.
For Examples 15 and 16, the catalyst received 0.75
hour of treatment with NO/N2 at 315C. Activation tests
were conducted at 315C and 305C and have been reported as
Examples 15 and 16, respectively.
For Examples 17 and 18, the catalyst received 0.75
hour of treatment with NO/He at 315C following which
activation tests were conducted at 315C and 305C which
have been reported as Examples 17 and 18, respectively.
15.
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Hf~lrl~ . ~ ~ . . . -
Hm ~o~ Ln LD ~ ~ N~r ~ ~ ~ Ln
Ln L~ D ~D W1~ 1` t~ 1` 1-- r-- 1~ 1~
~P O
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E~ Ln o o o o o o
Ln Ln Ln Ln Ln Ln
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O O O O O ~ O ~ O O O ~ r~
O O OO 1~ 1~ 1
Ln o
o rl
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K ~d ~ h ~ h
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. ~ r~S~ Ln h Ln h ~ ~ Ln Ln Ln Ln
a~
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,, ~ Z Z z æ ~
h ~1 ~ S-
rd r~ ~1 0 ~1 0 rl ~ 1 0 0 0 0
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36
As is evident from Table II, air activation of
the catalyst precursor was highly unsatisfactory, in fact,
it was so low that proper activation could not be achieved.
Activation with NO/N2, on the other hand, reported
S in Example 7, was highly satisfactory.
From Table III, it can be seen that the catalyst-
precursor could be activated in air or nitrogen gas at a tem-
perature of 370C for three hours. Treatment with nitric
oxide at 315C for as little as 0.75 hour provided comparable
to slightly better activation.
Based upon the satisfactory yields of methacrylic
acid that have been obtained when a PMA based catalyst has
been activated according to the method set forth herein, it
should be apparent that the objects of the invention have
been met. It is to be understood that the activation disclosed
herein is applicable in general to PMA based catalysts which,
as stated hereinabove, can include one or more promoters~
Presence or absence of these additional elements or compounds
will not affect the method of preparation set forth herein.
And, while these may be employed to improve some aspect of
the ac ivity of the catalyst, the specific catalyst composi-
tion is not deemed to be a portion of the invention claimed
herein.
REACTIVATION
In normal use, the apparent contact time of feed
over catalyst in the reactor can vary from about a fraction
of a second to as many as 20 seconds or more. A charge of
fresh catalyst will remain active for approximately 100-200
hours after which time a marked decrease in conversion single
pass yield and percent total conversion is observed. In order
to improve these, the catalyst can be reactivated according
to the method of the present invention.
Reactivation includes the step of feeding a
nitrogen oxide over the deactivated catalyst. Nitrogen oxides
having utility in the present invention include all
gaseous oxides of nitrogen as well as nitric or nitrous acid,
17.
. .
36
with nitric oxide being preferred. Additionally, it is
believed that other oxidants can be employed; examples of
which would include hydrogen peroxide, chlorine and nitrosyl
chlorine.
The feed of nitrogen oxide is generally conducted
over the deactivated catalyst until CO2 evolution is complete.
The feed of nitric oxide is generally conducted over the
catalyst for a period of time of from about one minute to
about several hours when a low rate of feed is employed.
The amount of the nitric oxide introduced into the reactor
can vary as desired but generally an amount in volume equal
to about 0.5 to about 50 times the volume of the catalyst
would be satisfactory. Treatment can be conducted at pres-
sures ranging from near atmospheric to superatmospheric.
The nitrogen oxide can be separately fed over the deactivated
catalyst or combined with an inert carrier such as helium or
nitrogen in any ratio of NO:N2 of from about 5:95 to 95:5 by
volume percent. Of course, other gasesl ratios of reactivant
to carrier, and pressures can be employed as may be desired.
The temperature at which reactivation can be conducted ranges
from about 100C to about 400C with temperatures of 175C
to 350C being preferred.
When the reactivation is to be conducted in situ,
the reactant feed to the reactor would first be terminated,
following which the reactor should be swept with a gas such
as air, nitrogen or steam. During this time the temperature
could be adjusted from that for the methacrolein conversion
to the desired temperature for reactivation as necessary.
At this point the nitric oxide/nitrogen mixture would be fed
to the reactor, and, following reactivation, the catalyst
will be ready for selective oxidation of the methacrolein.
In this manner, downtime for removal of the catalyst is
avoided.
Alternatively, in fluid-bed systems, a s]ip stream
could be treated with nitric oxide and then returned to the
18~
;
~L~S~, ~3~
reaction zone thereby providiny continuous catalyst reacti-
vation. It is further envisioned in ~ither fluid or fixed-
bed systems that a stream of the nitrogen oxide could be fed
concurrently with the hydrocarbon feed at a rate sufficient
to prevent deactivation.
In the examples which follow, a mixture of nitric
oxide in nitrogen, concentration of the former being approxi-
mately 49 volume percent, was fed to deactivated catalysts
at a flow rate of 190 cc/minute for a contact time of two to
three seconds. Reactivation temperatures ranged between
175C and 315C while the treatment time ranged ~etween one
and two hours. At the end of reactivation treatment, the
reactor temperature was ad~usted to 315C, the nitrogen oxide/
nitrogen flow was terminated and the reactant feed resumed.
Two types of promoted catalysts were reactivated
and subsequently employed for the selective oxidation of
methacrolein (MA) to methacrylic acid (MAA). Table IV presents
the reactivation conditions and results for the arsenic-
copper promoted catalyst PMol2AsO.5CuO.25Oz
component was supported on a 0.3 cm Alundu~) carrier for
Examples 18-28 35 weight percent of the catalyst component
thereon in Examples 19-23 and 30 weight percent of the catalyst
component thereon in Examples 24-28 Contact time of the
reactant feed over the catalyst varied from 1.95 seconds t
2.81 seconds and atmospheric pressure was employed.
Example 19 was a control catalyst having no reactiva-
tion treatment. Conversion measurements were made after the
catalyst had been used for 20 hours. The control was treated
successively to the NO/N2 reactivation feed for periods of
one hour in each of the succeeding examples, 20-23. Following
reactivation, the reactant feed was again resumed and conver-
sion measurements made after various periods of tim~ following
each reactivation as indicated in Table IV under the heading
Run (hrs.).
Example 24 was another charge of the same catalyst
composition which had been run for 143.4 hours and received
no reactivation. The control was reactivated for Example 25
~ 19.
. .
3~i
with one treatment of NO/N2 at 175C and tested at successive
periods of time on-stream with the reactant feed, as pre-
sented in Table IV, Examples 25-28.
20.
.. ~
, ,~
3~i
.,, U~
U~ .. . . . .
S~ o o o ~ o ~ o er a~ 1--
~r
o
~1 U~ ~) ~ ~ ~ ~ t~l 1` ~ N ~1
o
d~ c.
O
N ~I F2~ ~ ~1 ~J a) co O
O ~ (`
u~ ~ a~
. d~
o
U
U~
. ~
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U~
~ ~ ~ 1~ ~ CO O ~ ~ ~ ~ 1--
,~ a~
O ~1 ~ o : o o 1` ~o Lr) Ln ~r
L~ In Lt~
o~o
~~1
HO
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m .,,
~ ~ o
E~ ~ ~1
~ ~ h h h
,~ rl U
~) ~ o o
C) ~ o ~ ,~
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~ U ~ ~ ~
P; C) O O O
S E-~ ~ rl rl rl ~)
~ O I~ ~ O.,1_1 0 ~1 01 (~ I I I
~ .rl~ ) I rl Orl O rl LJ-) I ¦ I ¦
.rl 1~ ~ I~ ~'a U~ ~ U~ ~ II ~ I I I
X 1~
O rl a) ~ 11~
~ ~ r-l r-l ~r ¦ (~r I ~ r-l
.rl U rl
h ~ ~1
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F~ ~ ~ N t~
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.~ o o o o o o o
h ZZ Z Z Z ZZ
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Table V presents the reactivation conditions and
subsequent use of the catalyst composition of Table IV. The
catalyst was supported on a 0.3 cm spherical Alundum carrier
coated at the 30 weight percent level. Contact time varied
from 3.07 seconds to 3.21 seconds; pressure was 6 psig and
atmospheric and the reactivating gas mixture was 50/50, NO/N2
unless otherwise noted.
Example 29 was a control which had been run for
144.6 hours. Reactivation was conducted in Example 30 with
one treatment of NO/N2 at 6 psig. Tests were run at succes-
sive time intervals following reactivation and are reported
for Examples 2g-32.
Example 33 was another charge of the control used
for Example 29 reactivated with one treatment of NO/N2 at
atmospheric pressure and again tested at successive periods
of time on-stream and reported in Examples 33-35.
Example 36 was another charge of the control used
for Example 29 reactivated with one treatment of NO/N2, 6.5/
93.5, at atmospheric pressure and again tested at successive
periods of time on-stream and reported in Examples 36-39.
22.
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L~
. ~D O O ~ O
u~ ~ ~o ~ ~ ~o o
~: h ~r ~1 ~r u~ ~1 ~1
X ~
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o
1~ h
O ~ ~o 1~ 0
E~ ~
o
o~O ~
o
N Ll-) r-- ~ ~ Ln U~ ~--1 ~ 1-- U~ ~S'
O (L) ~ ~ ~ o u~
O o\o
C
. IH
O O
U~
O ~ ~D ~ ~ ~D ~P
O ~ Ln ~ ~ ~ ~ In 1-- ~ ~ I
Ln ~O U~ I` ~ ~ ~D ~D ~D
o`~
o
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m ~ o
.
.~, r~ C~ O O O
U~ L~^)
~ O ~ r~
~;
E~ ~ 0 a
~ ~~ ~ I ' I I ' I I ' I I I
.,1 ~ ~ I Sl I I ~_I I I Sl I I I
O ~ 0
'1 a
O ~ ~
.,1 C) r1
5~ td E~
.,
Z;
Z Z ~; Z Z; Z Z Z Z Z
~ ZZZOZOOzOZO;ZOZOZZ
E~
X O 'J' --' '~ ~ ~ '~ l ~ t` OD cr~
~:1 Z N ~ ~ frl r~) ~ ~ ~ ~ r~) t'')
, .
` ~ ' `` ~'" ;
i
Table VI presents the reactivation conditions and
subsequent use of the antimony-copper promoted catalyst
PMol2SbO 22CuO 25z^ The catalyst component was supported
on a 0.3 cm Alundum carrier coated at the 28 weight percent
level. Contact time varied from 3.05 seconds to 3.16 seconds;
pressure was atmospheric and the reactivating gas mixture was
50/50 NO/N2
Example 40 was a control which had been run for
273.8 hours. It was reactivated in Example 41 with one
treatment of NO/N2 and tested at successive time intervals
as reported for E~ples 41-45. Example 46 was the catalys-t
of Example 45 sub]ected to one additional reactivation.
24.
.~ ,
'
L3
~ r~ In i~ 0 r~ ~
u~
~1 '1 0 N C~ O
~ S~
~) /U ~ N a~ t-- N 1` ~r
O ~>
E~ ~
o
O
~ I~ ~ ~r
r~ ~ ~ r; ~ I`
oN u~ ~ ~ ~ i` i` i` ~ i`
\o
N
O
~ ~H
N O
~ r~ ~
O ,~ f~ r~ o ~ u~ o ~ oo
Q a) ~:C
~n ~ In 0~ Lt~ ~ 0
N ~ ~~r 11
~ d,
. ~ ~
o
O
~ 3 ~ o
~ ~ o ~ o o
.,, o ~ ~ .,i .,.
V
o a) ~ ,i r~
0
o , , , i ,
~; ., ~
~ ~ ~ ~ ~r
x ~ ,~
o ~ ri
e~ ~ E~
h ~
~i
Z ~
~ N ~ N N N N
Z Z Z Z Z Z
~ OOOOOOO
h Z Z Z; ~; Z Z Z
~C ol O r-l N t~ ~ Ul
; :" .
By reviewing the data presented in Tables IV-VI,
it can be seen that in every instance a deactivated catalyst
was reactivated according to the method of the present inven-
tion/ an increase in percent yield and total conversion
occurred. Generally speaking, the more severely deactivated
the catalyst was prior to treatment, the more improved was
its performance following reactivation. Based on the work
reported in Tables IV-VI, it is envisioned that a catalyst
not be permitted to reach a stage of deactivation wherein
the percent yield decreases to less than about 55%. At this
point, the catalyst can be reactivated with relative ease and
restored to substantially its full acitivity.
By observing the dramatic increases in percent yield
of methacrylic acid from methacrolein that have been obtained
when a deactivated catalyst has been reactivated according
to the method set forth herein, it should be apparent that
the objects of the invention have been met. It is to be
understood that the reactivations disclosed herein are
applicable in general to PMA based catalysts which, as stated
hereinabove, can include one or more promoters. Presence or
absence of these additional elements or compounds will not
affect the method of reactivation set forth herein. And~
while these may be employed to improve some aspect of the
activity of the catalyst when fresh or reactivated, the
specific catalyst composition is not deemed to be a portion
of the invention claimed herein.
Thus, it should also be apparent to those skilled
in the art that the subject invention is operable on PMA
based catalysts having certain ratios of molybdenum -to phos-
phorous and it is operable when other oxides of nitrogen,temperatures and pressures axe employed. It is to be under-
stood that while these variables fall within the scope of
the claimed invention, the subject invention is not to be
limited by the examples set forth herein. These have been
provided merely to provide a demonstration of operability and
therefore the selection of other oxides of nitrogen and the
26.
~`'`'1
.
~ ~5~L3~
amounts thereof can be determined without departing from the
spirit of the invention herein disclosed and described.
Moreover, the scope of the invention shall include all modi-
fications and variations that fall within the scope of the
attached claims.
....
t'~ t
.- . .
