U.S. patent application number 10/217522 was filed with the patent office on 2002-12-26 for two stage process for the production of unsaturated carboxylic acids by oxidation of lower unsaturated hydrocarbons.
This patent application is currently assigned to Saudi Basic Industries Corporation, Saudi Arabia. Invention is credited to Bhat, Yajnavalkya Subrai, Karim, Khalid, Khan, Asad Ahmad, Nafisa, Abdullah Bin, Zaheer, Syed Irshad.
Application Number | 20020198406 10/217522 |
Document ID | / |
Family ID | 24412792 |
Filed Date | 2002-12-26 |
United States Patent
Application |
20020198406 |
Kind Code |
A1 |
Karim, Khalid ; et
al. |
December 26, 2002 |
Two stage process for the production of unsaturated carboxylic
acids by oxidation of lower unsaturated hydrocarbons
Abstract
A process for the production of alpha-beta unsaturated
carboxylic acid with high yield at low temperature and atmospheric
pressure, includes two stages for catalytic vapor-phase oxidation
of olefins with molecular oxygen. In a first stage, olefins are
oxidized using catalyst A having a composition according to the
formula
Mo.sub.aPd.sub.bBi.sub.cFe.sub.dX.sup.1.sub.eX.sup.2.sub.fX.sup.3.sub.gO.s-
ub.z, wherein X.sup.1=one or more of Co, Ni, V, Pt, Rh; X.sup.2=one
or more of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si, W; X.sup.3=at least
one or more of K, Mg, Rb, Ca, Sr, Ba, Na; and O=oxygen; to produce
a first stage product containing alpha-beta unsaturated aldehydes
In a second stage, alpha-beta unsaturated aldehydes in the first
stage product are oxidized using catalyst B having a composition
according to the formula
Mo.sub.aV.sub.bAl.sub.cX.sub.dY.sub.eO.sub.z wherein X=W or Mn or
both; Y=at least one or more of Pd, Sb, Ca, P, Ga, Ge, Si, Mg, Nb,
K; and O is oxygen which satisfies the valences of the other
elements; to produce mainly alpha-beta unsaturated carboxylic acid.
A portion of the oxygen is introduced into the reaction stream
between the first and second stages or in multistages. More
particularly, the invention relates to a two stage process for
catalytic oxidation of propylene or iso-butylene to yield acrylic
acid or methacrylic acid.
Inventors: |
Karim, Khalid; (Burnage,
GB) ; Bhat, Yajnavalkya Subrai; (Riyadh, SA) ;
Khan, Asad Ahmad; (Riyadh, SA) ; Zaheer, Syed
Irshad; (Riyadh, SA) ; Nafisa, Abdullah Bin;
(Riyadh, SA) |
Correspondence
Address: |
William J. Spatz, Esq.
Kramer Levin Naftalis & Frankel LLP
919 Third Avenue
New York
NY
10022
US
|
Assignee: |
Saudi Basic Industries Corporation,
Saudi Arabia
|
Family ID: |
24412792 |
Appl. No.: |
10/217522 |
Filed: |
August 12, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10217522 |
Aug 12, 2002 |
|
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|
09602784 |
Jun 23, 2000 |
|
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6441227 |
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Current U.S.
Class: |
562/546 |
Current CPC
Class: |
C07C 51/252 20130101;
C07C 51/252 20130101; C07C 57/04 20130101 |
Class at
Publication: |
562/546 |
International
Class: |
C07C 051/16 |
Claims
What is claimed is:
1. A process for production of carboxylic acid using a two-stage
catalytic vapor-phase oxidation of olefins comprises introducing
into a first stage reactor, a feedstream comprising olefins,
oxygen, steam and inert gas; contacting the feedstream in the first
stage reactor with a catalyst composition comprising a catalyst
having the formulaMo.sub.aPd.sub.bBi.su-
b.cFe.sub.dX.sup.1.sub.eX.sup.2.sub.fX.sup.3.sub.gO.sub.z wherein
X.sup.1=at least one or more of Co, Ni, V, Pt, Rh X.sup.2=at least
one or more of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si, W X.sup.3=at
least one or more of K, Mg, Rb, Ca, Sr, Ba, Na O=oxygen a is 1, b
is 0< to 0.3, c is 0< to 0.9, d is 0< to 0.9, e is 0<
to 0.9, f is 0< to 0.9, g is 0< to 0.3, z is a number which
satisfies the valences of the other elements in the formula, said
contacting in the first stage reactor under reaction conditions
sufficient to produce a first stage product comprising aldehyde;
introducing the first stage product into a second stage reactor;
contacting the first stage product in the second stage reactor with
a catalyst composition comprising a catalyst having the
formulaMo.sub.aV.sub.bAl.sub.cX.sub.dY.sub.eO.sub.z wherein X=W or
Mn or both Y=at least one or more of Pd, Sb, Ca, P, Ga, Ge, Si, Mg,
Nb, K O is the valence oxygen, and a is 1, b is 0.01 to 0.9, c is
0< to 0.2, d is 0< to 0.5, e is 0< to 0.5, z is a number
which satisfies the valences of the other elements in the formula;
said contacting in the second stage reactor under conditions
sufficient to produce a second stage product comprising carboxylic
acid.
2. The process of claim 1 further comprising introducing oxygen
into the product stream intermediate between the first and second
stages or at multistages.
3. The process according to claim 1, wherein the olefins are
propylene or isobutylene and carboxylic acids are acrylic acid or
methacrylic acid.
4. The process according to claim 1, wherein the feedstream
comprises olefins in an amount of about 2% to about 50% by volume,
oxygen in an amount of about 3% to about 40% by volume, steam in an
amount of about 3% to about 50% by volume, and inert gas in an
amount of about 3% to about 80% by volume.
5. The process according to claim 4 wherein the feedstream
comprises olefins in an amount of about 5% to about 30% by volume,
oxygen in an amount of about 5% to about 30% by volume, steam in an
amount of about 5% to about 40% by volume, and inert gas in an
amount of about 5% to about 75% by volume.
6. The process according to claim 4 wherein the inert gas comprises
nitrogen, propane, argon, carbon dioxide or mixtures thereof.
7. The process according to claim 1, wherein the conditions in the
first stage comprise a temperature in the range of about
250.degree. C. to about 450.degree. C. and a pressure of 1 atm to
30 atm, and the conditions in the second stage comprise a
temperature in the range of about 180.degree. C. to about
350.degree. C. and a pressure of 1 atm to 30 atm.
8. The process according to claim 1, wherein the oxygen is in the
form of molecular oxygen, air or mixture thereof.
9. The process according to claim 1, wherein part of the amount of
oxygen is introduced between the first and second stages or at
multistages.
10. The process according to claim 9 wherein the part of the amount
of oxygen is about 2% to 15% by volume.
11. The process according to claim 1, wherein conversion of olefins
in the first-stage reaction is at least 90% and conversion of
aldehydes in second-stage reaction is at least 95%.
12. The process according to claim 1, wherein the olefin comprises
propylene, the carboxylic acid product comprises acrylic acid, and
conversion of propylene in a once through process produces at least
88% acrylic acid product yield.
13. The process according to claim 1, wherein oxygen is supplied as
a molecular oxygen-containing gas having purity of at least 90% by
volume.
14. The process according to claim 1, wherein the olefins comprise
ethylene, propylene, iso-butylene, or n-butylene; the aldehydes
comprise acetaldehyde, acrolein or methacrolein; and carboxylic
acids corresponding to the aldehydes are produced in the
process.
15. The process according to claim 1, wherein the second stage
product further comprises off-gas, and the process further
comprises separating the off-gas from the carboxylic acid product
of the second stage, and recycling the off-gas to the
first-stage.
16. The process according to claim 15, wherein the separated
off-gas contains steam which is recycled to the first stage.
17. A catalyst for oxidation of unsaturated hydrocarbons, said
catalyst having the
formulaMo.sub.aPd.sub.bBi.sub.cFe.sub.dX.sup.1.sub.eX.sup.2.su-
b.fX.sup.3.sub.gO.sub.zwherein X.sup.1=at least one or more of Co,
Ni, V, Pt, Rh X.sup.2=at least one or more of Al, Ga, Ge, Mn, Nb,
Zn, Ag, P, Si, W X.sup.3=at least one or more of K, Mg, Rb,Ca, Sr,
Ba, Na O=oxygen a is 1, b is 0< to 0.3, c is 0< to 0.9, d is
0< to 0.9, e is 0< to 0.9, f is 0< to 0.9, g is 0< to
0.3, z is a number which satisfies the valences of the other
elements in the formula.
18. The catalyst of claim 17 further comprising a support.
19. The catalyst of claim 18 wherein said support is selected from
the group consisting of alumina, silica, titania, zirconia,
zeolites, heteropoly acids, silicon carbide, molecular sieves,
microporous or nonporous materials, and mixtures thereof.
20. The catalyst of claim 19 wherein said supported catalyst is in
fluidizable form or another physical shape.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a two-stage process for the
production of alpha-beta carboxylic acids through catalytic
vapor-phase oxidation of olefins by molecular oxygen using mixed
metal oxide catalysts having the formulas A)
Mo.sub.aPd.sub.bBi.sub.cFe.sub.dX.sup.1.sub.eX.sup.2.sub.fX.s-
up.3.sub.gO.sub.z (X.sup.1=Co, Ni, V, Pt and/or Rh; X.sub.2=Al, Ga,
Ge, Mn, Nb, Zn, Ag, P and/or Si; X.sup.3=K, Mg, Rb, Ca, Sr, Ba
and/or Na); and B) Mo.sub.aV.sub.bAl.sub.cX.sub.dY.sub.eO.sub.z
(X=W or Mn or both; Y=Pd, Sb, Ca, P, Ga, Ge, Si, Mg, Nb and/or K).
The exothermic nature (exothermicity) or .DELTA.T of the oxidation
reaction can be controlled by addition of oxygen at an intermediate
stage of the process while achieving same high output yield and
catalyst life of the overall reaction.
[0003] 2. Description of the Related Art
[0004] A two stage vapor phase oxidation process for the production
of acrylic acid from propylene is well known in the art. Attempts
have been made to improve the productivity of a process for
production of acrylic acid by using different types of catalysts
and process parameters, described, e.g., in JP1165543; JP59013746;
EP911313; U.S. Pat. No. 5,602,280 (EP0630879); EP145469; U.S. Pat.
No. 5,218,146 (EP293224); U.S. Pat. No. 4,365,087 (DE3002829); and
U.S. Pat. No. 5,077,434. For example, U.S. Pat. No. 5,218,146
describes a process for the production of acrylic acid by a
two-stage catalytic vapor-phase oxidation of propylene with
molecular oxygen: the first stage oxidizes propylene to produce
mainly acrolein and the second stage oxidizes acrolein to produce
mainly acrylic acid. In this process there is supplied to the first
stage reaction, a raw gas containing a saturated aliphatic
hydrocarbon having 1 to 5 carbon atoms in an amount in the range of
5-70% by volune, carbon dioxide in an amount in the range 3-50% by
volume, aliphatic hydrocarbon and carbon dioxides in a total amount
in the range of 20 to 80% by volume and the gas also contains steam
in an amount in the range of 0.5 to 8 mol per mol of propylene.
[0005] Further process improvements are needed to deal with
problems in the removal of heat of the reaction, in space velocity,
in limitations on the life of the catalyst due to ineffective heat
removal and in limitations in catalyst activity related to its
composition.
[0006] It is an object of the present invention to provide a
substantially safe process for the production of acrylic acid by
the catalytic vapor phase oxidation of propylene with a high
productivity.
[0007] It is a further object of the invention to provide a process
for the production of an acrylic acid or methacrylic acid from
propylene or isobutylene in which .DELTA.T of reaction is lower
because of the specific composition of catalysts. A lower .DELTA.T
enhances the life of the catalyst.
[0008] It is another object of the invention to provide a process
which exhibits long-term operation or stability in term of catalyst
performance by intermediate addition of oxygen in between the two
stages of the process, or at multistages in the process.
SUMMARY OF THE INVENTION
[0009] The invention relates to a process for the production of
carboxylic acids using a two-stage catalytic vapor-phase oxidation
of olefins. The invention also includes a new catalyst for the
first stage of the process.
[0010] The process comprises:
[0011] introducing into a first stage reactor, a feedstream
comprising olefins, oxygen, steam and inert gas,
[0012] subjecting the feedstream to oxidizing conditions in the
first stage to produce an intermediate product stream comprising
aldehydes;
[0013] introducing the intermediate product stream into a second
stage reactor under aldehyde oxidizing conditions to produce a
second stage product comprising carboxylic acid.
[0014] Besides introduction of oxygen into the first stage, oxygen
can also be introduced into the product stream intermediate between
the first and second stages or at multistages within the same
reaction zone or reactor.
[0015] Moreover, the second stage product is a mixed reaction gas
which contains off-gas and carboxylic acid product. Off-gas
obtained by separating carboxylic acid from the second stage mixed
reaction gas product can be recycled to the first stage. In
addition, steam can also be present in the second stage mixed
reaction gas product. Steam obtained by separating the carboxylic
acid product from the mixed reaction gas product can be supplied to
the first stage.
[0016] The olefins are, for example, ethylene, propylene, or iso-
or n-butylenes; and the aldehydes are, for example, acetaldehyde,
acrolein and methacrolein, producing corresponding carboxylic
acids.
[0017] In a first stage, olefins are oxidized to produce an
intermediate product stream containing alpha-beta unsaturated
aldehydes using catalyst A having a composition according to the
formula
Mo.sub.aPd.sub.bBi.sub.cFe.sub.dX.sup.1.sub.eX.sup.2.sub.fX.sup.3.sub.gO.s-
ub.z,
[0018] wherein
[0019] X.sup.1=one or more of Co, Ni, V, Pt, Rh;
[0020] X.sup.2=one or more of Al, Ga, Ge, Mn, Nb, Zn, Ag, P, Si,
W;
[0021] X.sup.3=at least one or more of K, Mg, Rb, Ca, Sr, Ba, Na;
and
[0022] O=oxygen (which satisfies the valences of the other
elements);
[0023] and wherein
[0024] a, b, c, d, e, f, g, and z are as defined below.
[0025] In a second stage, alpha-beta unsaturated aldehydes in the
intermediate product stream are oxidized to produce mainly
alpha-beta unsaturated carboxylic acid using catalyst B having a
composition according to the formula
MO.sub.aV.sub.bAl.sub.cX.sub.dY.sub.eO.sub.z
[0026] wherein
[0027] X=W or Mn or both;
[0028] Y=at least one or more of Pd, Sb, Ca, P, Ga, Ge, Si, Mg, Nb,
K; and
[0029] O is oxygen which satisfies the valences of the other
elements;
[0030] and wherein
[0031] a, b, c, d, e, and z are as defined below.
[0032] In a preferred embodiment, the invention relates to a
process for the production of alpha-beta carboxylic acids, such as
acrylic acid or methacrylic acid, by the catalytic vapor-phase
oxidation of olefins, such as propylene or isobutylene. More
particularly, the invention relates to a process for highly
efficient production of acrylic acid or methacrylic acid through
the use of a feed gas having a particular composition. In the
production of acrylic acid by a two-stage catalytic vapor-phase
oxidation of propylene with molecular oxygen, a first stage
oxidizes propylene to produce mainly acrolein and the second stage
oxidizes acrolein to produce mainly acrylic acid.
[0033] In preferred embodiments, a gas mixture is supplied to the
first stage. The gas mixture preferably contains unsaturated
aliphatic hydrocarbon of about C1 to C5, most preferably propylene
or isobutylene, in an amount from about 3% to about 90%; oxygen in
an amount from about 2% to about 50%; steam in an amount from about
5% to about 50% by volume; and 5 % to 80% inert gas or gas with
high specific heat such as nitrogen, argon, propane, carbon
dioxide.
[0034] Additional oxygen in an amount from about 2% to 50% can be
added at an intermediate stage of the process or at multiple stages
in the reaction zone, in order to control the total oxidation
reaction and to achieve a long catalyst life and high productivity
of the acrylic acid. The part of the amount of oxygen added at an
intermediate stage or multistage is preferably from about 2% to
about 15% by volume.
[0035] A catalytic process according to the present invention shows
improvement in the catalyst performance and/or good catalyst
stability. While it is not intended to be bound by theory, it is
believed that these improvements can be attributed to low .DELTA.T
of the reaction and introduction of oxygen at multi- or
intermediate stages of the reaction zones to control the extent of
exotherm and keep the reaction mixture out of explosive regimes or
explosive ranges. Moreover, catalysts provided to carry out the
reactions are relatively active at lower temperature than
temperatures described in the prior art.
BRIEF DESCRIPTION OF THE DRAWING
[0036] FIG. 1 is a schematic diagram illustrating the process of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0037] In a preferred reaction gas composition, a content of
olefin, e.g., propylene or isobutylene, is in the range of 1% to
50% by volume, preferably 3% to 30% by volume; a content of oxygen
(air, molecular oxygen, or mixture thereof) is in the range of 5%
to 40% by volume, preferably 8% to 30% by volume; a content of
carbon dioxide is in the range of 3% to 50% by volume, preferably
5% to 40% by volume, with a total content of hydrocarbon and carbon
dioxide in the range of 20% to 80% by volume, preferably 30% to 70%
by volume; and a content of steam is in the range of 3% to 50% by
volume, preferably 5% to 40% by volume.
[0038] Preferably, the molecular oxygen is supplied as a molecular
oxygen-containing gas having purity of at least 95% by volume.
[0039] Preferably, recycle gas obtained by separating carboxylic
acid, e.g., acrylic acid, from the mixed reaction gas produced by
the second-stage reaction can be fed to the first-stage reaction,
which can have a large thermal effect as well in controlling the
.DELTA.T of the reaction. Conveniently, the steam to be supplied to
the first-stage reaction is the steam contained in the recycle gas
obtained by separating acrylic acid from the mixed reaction gas
produced by the second-stage reaction. Build up gases may be
purged.
[0040] Preferably the reaction in the first-stage is carried out in
the presence of an oxide catalyst A (CAT-A), as more fully
described in U.S. patent application Ser. No. 09/560989, and the
reaction in the second-stage is carried out in the presence of an
oxide catalyst B (CAT-B), as more fully described in U.S. patent
application Ser. No. 09/560988.
[0041] CAT-A is mixed metal oxide catalyst in a composition having
a formula
Mo.sub.aPd.sub.bBi.sub.cFe.sub.dX.sup.1.sub.eX.sup.2.sub.fX.sup.3.sub.gO.s-
ub.z
[0042] wherein
[0043] X.sup.1=at least one or more of Co, Ni, V, Pt, Rh
[0044] X.sup.2=at least one or more of Al, Ga, Ge, Mn, Nb, Zn, Ag,
P, Si, W
[0045] X.sup.3=at least one or more of K, Mg, Rb, Ca, Sr, Ba, Na,
In
[0046] O=oxygen, and
[0047] a is 1
[0048] b is 0< to 0.3
[0049] c is 0< to 0.9
[0050] d is 0< to 0.9
[0051] e is 0< to 0.9
[0052] f is 0< to 0.9
[0053] g is 0< to 0.3.
[0054] z is a number which satisfies the valences of the other
elements in the formula.
[0055] CAT- B is mixed metal oxides in a composition having the
formula
Mo.sub.aV.sub.bAl.sub.cX.sub.dY.sub.eO.sub.z
[0056] wherein
[0057] X=W or Mn or both,
[0058] Y=at least one or more of Pd, Sb, Ca, P, Ga, Ge, Si, Mg, Nb,
K
[0059] O is oxygen, and
[0060] a is 1,
[0061] b is 0.01 to 0.9,
[0062] c is 0< to 0.2,
[0063] d is 0< to 0.5,
[0064] e is 0< to 0.5,
[0065] z is a number which satisfies the valences of the other
elements in the formula.
[0066] Catalysts A and B can used over supports in the form of
shapes, or in fluidizable form. Suitable supports for the catalyst
include alumina, silica, titania, zirconia, zeolites, silicon
carbide, Mo carbide, molecular sieves and other microporous or
nonporous materials, and mixtures thereof. Support material can be
pretreated with acids such as HCl, HNO.sub.3, H.sub.2SO.sub.4,
peracids or heteropoly acids and alkali base materials. When used
on a support, the supported catalyst usually comprises from about
5% to 90% by weight of the catalyst composition, with the remainder
being the support material.
[0067] Heat of the reaction for oxidation process is related to the
concentration of the oxygen or extent of oxidation reaction, which
ultimately affects reaction product selectivity. For a two stage
oxidation process, addition of oxygen at intermediate level,
maintains the yield, while having a positive impact on the amount
of heat generated and removed out of the reaction zone. This
results in an optimum rate of partial oxygenation or total
oxidation, depending on the type of the catalyst. In addition,
propane, carbon dioxide and other gases with higher specific heat
capacity can also be used to remove heat of the reaction in order
to eliminate the possibility of explosion. Steam in an adequate
amount as a co-feed is used to promote the de-sorption of the main
products of the catalytic vapor-phase oxidation of propylene, i.e.,
acrolein and acrylic acid. The presence of the steam with recycle
gases such as carbon dioxide also increases the rate of
oxygenation.
[0068] The first stage of the reaction is performed preferably in
the range of 250.degree. C. to 450.degree. C., more preferably
270.degree. C. to 390.degree. C., at a contact time between the
reaction mixture and the catalyst preferably from about 0.01 second
to 100 seconds, more preferably from 0.1 second to 10 seconds; and
a space hourly velocity preferably from about 50 to about 50,000
h.sup.-1, more preferably from about 100 to 10,000 h.sup.-1.
Reaction product shows a conversion of olefins in the range of
preferably not less than 90 mol %, more preferably not less than 97
mol %. In preferred conditions for the second-stage oxidation, the
reaction temperature is preferably in the range of 180.degree. C.
to 370.degree. C., more preferably 200.degree. C. to 350.degree.
C., and the contact time is preferably in the range of 1.0 to 10
seconds, more preferably 1 to 6.0 seconds. The two-stage operation
shows a per pass reaction product yield of preferably not less than
85 mol %, more preferably not less than 88 mol %.
[0069] The terms "conversion," and "per pass yield," as used herein
are defined as follows: 1 Conversion ( % ) of olefin = Mols of
olefin converted Mols of olefin supplied .times. 100 Per pass yield
( % ) of carboxylic acid = Mols of carboxylic acid produced Mols of
olefin supplied .times. 100
[0070] FIG. 1 is a schematic representation of the two-stage
process for the production of carboxylic acid according to an
embodiment of the invention. As non-limiting examples, POR can
represent a Propylene Oxidation Reactor, AOR can represent an
Acrolein Oxidation Reactor, ACE can represent Acrolein, ACA can
represent Acrylic Acid. A feed comprising olefin 1 (e.g.,
propylene) (also steam and inert diluent, e.g., N.sub.2, CO.sub.2)
and oxygen 2 is fed into oxidation reactor 3 (POR) which contains a
first stage catalyst 4 (CAT-A) that converts olefin-containing
(e.g., propylene) feedstock with oxygen into aldehyde, (e.g.,
acrolein), water and carbon dioxide. The effluent 5 of POR reactor
1 comprising aldehyde (e.g., ACA), (also unoxidized olefin, e.g.,
C.sub.3H.sub.6; CO.sub.2, N.sub.2 and H.sub.2O), is fed via
optional heat exchanger 8 to second stage (AOR) reactor 6
containing catalyst 7 (CAT-B). Heat exchanger 8 allows adjustment
of the temperature of the feed to second stage reactor 6.
Optionally, the two catalysts CAT-A and CAT-B can be in one reactor
in the form of a physical mixture or in alternating layer form (not
shown). An appropriate amount of oxygen in line 9 is added to
second stage reactor 6, depending upon the process conditions, for
the oxidation of aldehyde to carboxylic acid (e.g., acrolein to
acrylic acid). Also, by using an appropriate reactor configuration,
oxygen can be added via a multi injection system reactor, e.g.,
where one of the reactants (oxidant) is introduced and controlled
through microporous or mesoporous materials or through a
configuration of holes placed at regular or random intervals in the
reactor (not shown). The effluent 10 from the second stage (AOR)
reactor 6 comprising carboxylic acid (e.g., acrylic acid (ACC),
also H.sub.2O and CO.sub.2), is fed to gas/liquid separation unit
11, where gases including CO.sub.2 and nitrogen (inert) are
separated from liquid carboxylic acid and water. The inert gas
streams 12 comprising CO.sub.2 and N.sub.2 from gas/liquid
separation unit 11 are cycled through carbon dioxide removal unit
13 and the stream 14 from the carbon dioxide removal unit 13 is
recycled through lines 20 and 22 to the feedstream 1 to the first
stage reactor 3. Optionally, the gas streams 12 can also be
recycled to first stage reactor 3 without the carbon dioxide
absorption (not shown), as the catalyst 4 (CAT-A) in reactor 3 is
not affected by the presence of carbon dioxide. Co-feed of carbon
dioxide can also help in controlling the extent of exothermic heat
of the reaction. Liquid stream 15 from separator unit 11 is fed to
distillation unit 16 where carboxylic acid (e.g., acrylic acid) 17
is separated from water 18, and water 18 can be recycled back to
first stage reactor unit 3 via lines 19, 20 and 22. Gases and water
in streams 14 and 19 can be combined into stream 20 and partially
purged in purge unit 21 to control the build-up of gases before
being conveyed to first stage reactor unit 3.
[0071] The following examples illustrate the invention, but the
invention is not limited to these working examples.
EXAMPLE
[0072] First Stage Catalyst (Cat A) Preparation:
Mo.sub.1Pd.sub.01.57e-4Bi.sub.0.09Co.sub.0.8Fe.sub.0.2Al.sub.0.123V.sub.4.-
69e-3K.sub.5.33e-3
[0073] Ammonium metavanadate (Aldrich Chemicals, Assay=99.0%) in
the amount of 0.11 grams was added in distilled water and heated to
90.degree. C. with stirring. A yellow color solution with pH
between 4 and 7 was obtained (Solution A). 8.75 grams of bismuth
nitrate, 16.2 grams of ferric nitrate and 46.68 grams of cobaltous
nitrate were added with water to solution A with continuous
stirring, followed by slow addition of the required amount of
palladium, potassium and aluminum salts solution to the mixture.
Ammonium paramolybdate tetra hydrated (Aldrich Chemicals
A.C.S-12054-85-2) in the amount of 35.4 grams was added to the
solution and the mixture was then dried. The resulting solid was
dried in an oven at 100.degree. C.-120.degree. C. The dried
material was cooled to room temperature and calcined in range of
300.degree. C. to 600.degree. C.
[0074] Second Stage Catalyst (Cat B) Preparation:
Mo.sub.1V.sub.0.396Al.sub.2.04.e-1Mn.sub.8.96e-2Sb.sub.2.51e-2Ca.sub.6.89e-
-3
[0075] Ammonium metavanadate (Aldrich Chemicals, Assay=99.0%) in
the amount of 5.7 grams was added in distilled water and heated to
90.degree. C. with stirring. A yellow color solution with pH
between 4 and 7 was obtained (Solution A). 0.45 grams of antimony
trioxide and 11 grams of oxalic acid were added with water to the
solution with continuous stirring followed by slow addition to the
mixture of the required amount of calcium, aluminum, and manganese
salts solution. Ammonium paramolybdate tetra hydrated (Aldrich
Chemicals A.C.S-12054-85-2) in the amount of 21.7 grams was added
to the solution. The resulting solid was dried in an oven at
100.degree. C.-120.degree. C. The dried material was cooled to room
temperature and calcined in range of 300.degree. C. to 600.degree.
C.
[0076] 4 cc of 40-60 mesh size of catalyst A was packed into
stainless steel tubular reactor (first (I) stage). The reactor was
placed in a bubbling sand bath and was heated to 330.degree. C. 4
cc of 40-60 mesh size catalyst B was packed in another tubular
reactor (second (II) stage), placed in a similar-type sand bath,
and heated to 235.degree. C. The two reactors were interconnected
in such a manner that the first stage reactor outlet was introduced
into the second reactor containing the second-stage catalyst. A
mixed gas containing propylene, oxygen, steam and nitrogen was
introduced with a flow of 8 liters/hour to the first (I) stage
reactor. An additional amount of oxygen gas was introduced at an
intermediate stage between reactor I and reactor II. Outlet gas of
the second (II) stage reactor was conveyed to a condenser where
acrylic acid was collected in the form of aqueous solution using
water containing polymerization inhibitor, hydroquinone. The
product showed almost complete conversion of propylene with a 90%
yield to acrylic acid. Overall .+-.4 .DELTA.T of the reaction was
observed. Reaction was continued over a period of 8000 hours
without any sign of deactivation of catalysts.
* * * * *