U.S. patent number RE43,859 [Application Number 11/363,148] was granted by the patent office on 2012-12-11 for method for producing vinyl acetate monomer from ethane or ethylene oxidation.
This patent grant is currently assigned to Saudi Basic Industries Corporation. Invention is credited to Alaa E. M. Adris, Khalid Karim.
United States Patent |
RE43,859 |
Karim , et al. |
December 11, 2012 |
Method for producing vinyl acetate monomer from ethane or ethylene
oxidation
Abstract
Methods for the catalytic production of vinyl acetate monomer
from ethane, ethylene or an ethane/ethylene mixture using a first
catalyst containing MoVNbPd, MoVLaPdNbX (where X is Al, Ga, Ge or
Si) or MoVNbX (where X is P, B, Hf, Te, As or mixtures thereof) in
the first step of oxidation and using a conventional VAM catalyst
for the second step. The method produces high yields to acetic acid
and vinyl acetate without the coproduction of carbon monoxide.
Further-more, the ethylene and acetic acid produced in the first
step may be utilized in the second step for VAM production
Inventors: |
Karim; Khalid (Riyadh,
SA), Adris; Alaa E. M. (Cairo, EG) |
Assignee: |
Saudi Basic Industries
Corporation (Riyadh, SA)
|
Family
ID: |
23212532 |
Appl.
No.: |
11/363,148 |
Filed: |
February 8, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09312683 |
May 14, 1999 |
6143921 |
Nov 7, 2000 |
|
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Current U.S.
Class: |
560/245; 562/549;
560/261; 562/607 |
Current CPC
Class: |
C07C
67/055 (20130101); C07C 67/05 (20130101); C07C
67/05 (20130101); C07C 69/01 (20130101); C07C
67/055 (20130101); C07C 69/01 (20130101); C07C
67/055 (20130101); C07C 69/15 (20130101); C07C
67/05 (20130101); C07C 69/15 (20130101); Y02P
20/582 (20151101) |
Current International
Class: |
C07C
67/05 (20060101); C07C 51/16 (20060101); C07C
67/02 (20060101); C07C 53/08 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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19630832 |
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Feb 1998 |
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DE |
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98/05620 |
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Feb 1998 |
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WO |
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WO98/05620 |
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Feb 1998 |
|
WO |
|
9847851 |
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Oct 1998 |
|
WO |
|
9913980 |
|
Mar 1999 |
|
WO |
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20592 |
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Apr 1999 |
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WO |
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WO99/20592 |
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Apr 1999 |
|
WO |
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0000284 |
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Jan 2000 |
|
WO |
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0069802 |
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Nov 2000 |
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WO |
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Other References
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Cordonna et al.; "Gas Turbine Emission Control: Platinum and
Platinum-Palladium Catalysts for Carbon Monoxide and Hydrocarbon
Oxidation"; Platinum Metals Rev.; vol. 33, Issue 2; 1989; pp.
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Decision to Revoke; Opposition Against European Patent No. 1180092
(B1); Mailed Mar. 29, 2010; 7 Pages. cited by other .
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Industries Corporation (SABIC); Opposition Against European Patent
No. 1180092 (B1); Submitted to the European Patent Office Feb. 27,
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(B1); Submitted to the European Patent Office on Mar. 16, 2011; 23
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Written Submissions; Submitted by Saudi Basic Industries
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(B1); Submitted to the European Patent Office Dec. 18, 2009; 14
Pages. cited by other.
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Primary Examiner: Zucker; Paul A
Attorney, Agent or Firm: Cantor Colburn LLP
Claims
What is claimed is:
.[.1. A process for the production of vinyl acetate monomer
comprising the steps of: (1) contacting a gaseous feed mixture of
ethane or ethylene or ethane/ethylene, steam and a molecular oxygen
containing gas in the presence of a first catalyst active for
oxidation of ethane, ethylene or ethane/ethylene to produce a
selective stream of acetic acid, ethylene, carbon dioxide and water
and (2) converting a second feed mixture comprising ethylene,
acetic acid and oxygen to vinyl acetate monomer in the presence of
a second catalyst active for the production of vinyl acetate,
wherein said process does not include an intermediate separation
step to remove the CO between the two reaction steps..].
2. The process of claim .[.1.]. .Iadd.3.Iaddend., wherein said
process produces no carbon monoxide.
3. .[.The process of claim 2,.]. .Iadd.A process for the production
of vinyl acetate monomer comprising the steps of: (1) contacting a
gaseous feed mixture of ethane or ethylene or ethane/ethylene,
steam and a molecular oxygen containing gas in the presence of a
first catalyst active for oxidation of ethane, ethylene or
ethane/ethylene to produce a selective stream of acetic acid,
ethylene, carbon dioxide and water, .Iaddend.wherein the first
.[.oxidation.]. catalyst is selected from the following catalyst
compositions: a) a catalyst composition .[.comprising.].
.Iadd.consisting of .Iaddend.the elements Mo, V, Nb, and Pd, in the
form of oxides, in the ratio Mo.sub.aV.sub.bNb.sub.cPd.sub.d
wherein: a is 1 to 5; b is 0 to 0.5; c is 0.01 to 0.5; and d is
>0 to 0.2; b) a catalyst composition .[.comprising.].
.Iadd.consisting of .Iaddend.the elements Mo, V, Pd, Nb, La and X,
in the form of oxides, wherein X is Al, Ga, Si or Ge, in the ratio
Mo.sub.aV.sub.bLa.sub.cPd.sub.dNb.sub.eX.sub.f wherein: a is 1; b
is 0.01 to 0.9; c is >0 to 0.2; d is >0 to 0.2; e is >0 to
0.2; and f is >0 to 0.3; and c) a catalyst composition
.[.comprising.]. .Iadd.consisting of .Iaddend.the elements Mo, V,
Nb and X which is selected from P, B, Hf, Te, As or mixtures
thereof in the form of an oxide, in the following ratio
Mo.sub.aV.sub.bNb.sub.cX.sub.d wherein: a is 1 to .[.S.].
.Iadd.5.Iaddend.; b is >0 to 0.1; c is 0.01 to 0.5; d is >0
to 0.1.Iadd.; and (2) converting a second feed mixture comprising
ethylene, acetic acid, and oxygen to vinyl acetate monomer in the
presence of a second catalyst active for the production of vinyl
acetate, wherein said process does not include an intermediate
separation step to remove CO between the production of the
selective stream and the converting of the second feed mixture,
wherein at least a portion of the ethylene, acetic acid, and oxygen
in the second feed mixture are from the selective
stream.Iaddend..
.[.4. The process of claim 3, wherein said first catalyst consists
essentially of catalyst composition (a), catalyst composition (b),
catalyst composition (c) or mixtures thereof..].
5. The process of claim 2, wherein said first catalyst and second
catalyst are in the form of a fixed or fluidized bed or a solid
moving bed reactor.
6. The process of claim 2, wherein said feed mixture is fed into a
second reaction zone.
7. The process of claim 6, wherein the second feed mixture for the
second step comprises ethylene, acetic acid, CO.sub.2 and
oxygen.
8. The process of claim 2, wherein said feed mixture comprises
molecular oxygen ranging from 0.1 to 25% by volume of the feed
mixture.
9. The process of claim 2, wherein said feed mixture is diluted
with N.sub.2 in an amount ranging from 5 to 90% by volume.
10. The process of claim 2, wherein said feed mixture is diluted
with steam in an amount ranging from 0 to 40% by volume.
11. The process of claim 2, wherein said feed mixture comprises
from 1% to 95% by volume of ethane, ethylene or mixtures
thereof.
12. The process of claim 2, wherein first step oxidation is
achieved at a temperature of from 150 to 450.degree. C., under a
pressure of from 15 to 600 psi, and with a contact time between
reaction mixture and the catalyst of from 0.1 to 60 seconds.
13. The process of claim 2, wherein said contacting comprises
reacting ethane or ethane/ethylene with steam and oxygen or a
compound capable of providing oxygen in the presence of said first
catalyst in a first reaction zone to form a first product mixture
comprising ethylene, oxygen, steam and acetic acid and the said
first product mixture is fed into a second reaction zone wherein
the ethylene and acetic acid react to form vinyl acetate in the
presence of said second .[.reaction.]. catalyst.
14. The process of claim 13, wherein said first product mixture is
fed directly into said second reaction zone without adding
additional components.
15. The process of claim 13, wherein said first product mixture is
fed into said second reaction zone with addition/adjustment of
ethylene, acetic acid, oxygen or combinations thereof.
16. The process of claim 13, wherein said first product mixture is
subjected to temperature and/or pressure adjustments prior to being
fed into said second reaction zone.
17. A process of producing vinyl acetate monomer comprising the
step of catalytically oxidizing ethane to form vinyl acetate in a
single reaction zone containing a first catalyst having activity
for oxidation of ethane to ethylene and acetic acid and a second
catalyst having activity for oxidation of ethylene with acetic acid
to vinyl acetate, wherein said first catalyst is at least one
catalyst selected from the following catalyst compositions: a) a
catalyst composition .[.comprising.]. .Iadd.consisting of
.Iaddend.the elements Mo, V, Nb, and Pd in the form of oxides, in
the ratio Mo.sub.aV.sub.bNb.sub.cPd.sub.d wherein: a is 1 to 5; b
is 0 to 0.5; c is 0.01 to 0.5; and d is >0 to 0.2; b) a catalyst
composition .[.comprising.]. .Iadd.consisting of .Iaddend.the
elements Mo, V, Pd, Nb, La and X, in the form of oxides, wherein X
is Ga, Si, Al or Ge, in the ratio
Mo.sub.aV.sub.bLa.sub.cPd.sub.dNb.sub.eX.sub.f wherein: a is 1; b
is 0.01 to 0.9; c is >0 to 0.2; d is >0 to 0.2; e is >0 to
0.2; and f is >0 to 0.3; and c) a catalyst composition
.[.comprising.]. .Iadd.consisting of .Iaddend.the elements Mo, V,
Nb and X which is selected from P, B, Hf, Te, As or mixtures
thereof in the form of an oxide, in the following ratio
Mo.sub.aV.sub.bNb.sub.cX.sub.d wherein: a is 1 to 5; b is >0 to
0.1; c is 0.01 to 0.5; and d is >0 to 0.1.
18. The process of claim 17, wherein said single reaction zone
comprises a mixture of said first catalyst and said second
catalyst.
19. The process of claim 17, wherein said single reaction zone
comprises layers of said first .[.reaction.]. catalyst and said
second catalyst.
20. The process of claim 2, wherein said process produces ethylene,
acetic acid, VAM or combinations thereof.
.Iadd.21. A process for the production of vinyl acetate monomer
comprising the steps of: (1) contacting a gaseous feed mixture of
ethane or ethylene or ethane/ethylene, steam and a molecular oxygen
containing gas in the presence of a first catalyst active for
oxidation of ethane, ethylene or ethane/ethylene to produce a
selective stream of acetic acid, ethylene, carbon dioxide and
water, wherein the first catalyst is selected from the following
catalyst compositions: a) a catalyst composition consisting of the
elements Mo, V, Nb, and Pd, in the form of oxides, in the ratio
Mo.sub.aV.sub.bNb.sub.c,Pd.sub.d wherein: a is 1 to 5; b is 0 to
0.5; c is 0.01 to 0.5; and d is >0 to 0.2; b) a catalyst
composition consisting of the elements Mo, V, Pd, Nb, La and X, in
the form of oxides, wherein X is Al, Ga, Si or Ge, in the ratio
Mo.sub.aV.sub.bLa.sub.cPd.sub.dNb.sub.eX.sub.f wherein: a is 1; b
is 0.01 to 0.9; c is >0 to 0.2; d is >0 to 0.2; e is >0 to
0.2; and f is >0 to 0.3; and c) a catalyst composition
consisting of the elements Mo, V, Nb and X which is selected from
P, B, Hf, Te, As or mixtures thereof in the form of an oxide, in
the following ratio Mo.sub.aV.sub.bNb.sub.cX.sub.d wherein: a is 1
to 5; b is >0 to 0.1; c is 0.01 to 0.5; d is >0 to 0.1; and
(2) optionally adjusting the selective stream; and converting a
second feed mixture comprising ethylene, acetic acid, and oxygen to
vinyl acetate monomer in the presence of a second catalyst active
for the production of vinyl acetate, wherein at least a portion of
the ethylene, acetic acid, and oxygen in the second feed mixture
are from the selective stream; wherein no detectable or measurable
levels of CO is produced when contacting said gaseous feed mixture
in the presence of said first catalyst, and wherein said process
does not include an intermediate separation step to remove CO
between the production of the selective stream and the converting
of the second feed mixture..Iaddend.
.Iadd.22. The process of claim 21, wherein said process produces no
carbon monoxide..Iaddend.
.Iadd.23. The process of claim 22, wherein said first catalyst and
second catalyst are in the form of a fixed or fluidized bed or a
solid moving bed reactor..Iaddend.
.Iadd.24. The process of claim 22, wherein said gaseous feed
mixture is fed into a second reaction zone..Iaddend.
.Iadd.25. The process of claim 24, wherein the second feed mixture
for the second step comprises ethylene, acetic acid, CO.sub.2 and
oxygen..Iaddend.
.Iadd.26. The process of claim 22, wherein said gaseous feed
mixture comprises molecular oxygen ranging from 0.1 to 25% by
volume of the feed mixture..Iaddend.
.Iadd.27. The process of claim 22, wherein said gaseous feed
mixture is diluted with N.sub.2 in an amount ranging from 5 to 90%
by volume..Iaddend.
.Iadd.28. The process of claim 22, wherein said gaseous feed
mixture is diluted with steam in an amount ranging from 0 to 40% by
volume..Iaddend.
.Iadd.29. The process of claim 22, wherein said gaseous feed
mixture comprises firm 1% to 95% by volume of ethane, ethylene or
mixtures thereof..Iaddend.
.Iadd.30. The process of claim 22, wherein first step oxidation is
achieved at a temperature of from 150 to 450.degree. C., under a
pressure of from 15 to 600 psi, and with a contact time between
reaction mixture and the catalyst of from 0.1 to 60
seconds..Iaddend.
.Iadd.31. The process of claim 22, wherein said contacting
comprises reacting ethane or ethane/ethylene with steam and oxygen
or a compound capable of providing oxygen in the presence of said
first catalyst in a first reaction zone to form a first product
mixture comprising ethylene, oxygen, steam and acetic acid and the
said first product mixture is fed into a second reaction zone
wherein the ethylene and acetic acid react to form vinyl acetate in
the presence of said second catalyst..Iaddend.
.Iadd.32. The process of claim 31, wherein said first product
mixture is fed directly into said second reaction zone without
adding additional components..Iaddend.
.Iadd.33. The process of claim 31, wherein said first product
mixture is fed into said second reaction zone with
addition/adjustment of ethylene, acetic acid, oxygen or
combinations thereof..Iaddend.
.Iadd.34. The process of claim 31, wherein said first product
mixture is subjected to temperature and/or pressure adjustments
prior to being fed into said second reaction zone..Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to improved integrated methods of making
vinyl acetate monomers from ethane or ethylene using metal oxide
catalysts.
2. Description of the Related Art
Several publications are referenced in this application. These
references describe the state of the art to which this invention
pertains and are hereby incorporated by reference.
The utilization of lower alkanes (C.sub.1-C.sub.4) as feed stock to
produce value added petrochemicals is an industrially desired
process. Lower alkanes are low cost and environmentally acceptable
because of their low chemical reactivity. There are only a few
commercially available chemical catalytic processes, which utilize
lower alkanes as a feed, such as butane to maleic anhydride.
Vinyl acetate monomer (VAM) is a well-known industrial chemical.
The production of VAM from ethylene, oxygen and acetic acid using
conventional VAM catalysts is known in the art. VAM is typically
used as a raw material for vinyl resins such as polyvinyl acetate.
VAM was previously primarily manufactured from the vapor phase
reaction of ethylene, acetic acid and oxygen with a zinc acetate
catalyst.
More recently, VAM has been produced from the vapor-phase reaction
of ethylene, acetic acid and oxygen, with a palladium catalyst. For
example, VAM may be made from ethylene wherein the first step
involves reacting the ethylene to form acetic acid, followed by a
second step of reacting a mixture of the acetic acid and ethylene
to form vinyl acetate.
Numerous methods are known for the catalytic oxidation of ethylene
to acetic acid. See, for example, U.S. Pat. Nos. 3,792,087 and
3,970,697. Similarly, numerous methods are known for the catalytic
production of vinyl acetate by reacting ethylene with acetic acid
and oxygen in the gaseous phase. See, U.S. Pat. Nos. 3,190,912;
3,637,819; 3,650,896; 4,370,492; 5,185,308; and 4,902,823.
PCT Patent Publication WO 98/05620 describes the production of
acetic acid and/or vinyl acetate from ethylene (or ethane) using a
first catalyst active for the oxidation of ethylene to acetic acid
and/or active for the oxidation of ethane to acetic acid, ethylene
and carbon monoxide, and a second catalyst active for the
production of vinyl acetate. The patent also describes an
additional necessary step for conversion of carbon monoxide to
carbon dioxide. This is because carbon monoxide is poisonous to the
VAM catalyst.
U.S. Pat. No. 4,188,490 relates to a catalytic oxidation process
for the production of mixtures of acetic acid and vinyl acetate
comprising the step of contacting a feed mixture containing
ethylene, oxygen and water (as steam) with a catalyst composition
to provide a mixture of acetic acid and vinyl acetate. The catalyst
system comprises a palladium metal on a zinc oxide support treated
in the presence of a sulfur modifier. The method requires the
subsequent step of fractional distillation to separate the acetic
acid from the vinyl acetate. Alternatively, the acetic acid
contained in the product mixture is converted in situ to an alkali
metal salt such as sodium acetate. The method also requires the
step of treating the catalyst with the sulfur modifier by, for
example, flowing moist air containing SO.sub.2 over the catalyst at
200.degree. C. for about one hour.
Several methods for producing vinyl acetate from ethylene result in
the production of carbon monoxide. The production of carbon
monoxide is disadvantageous because it is poisonous to the second
stage catalyst. Moreover, carbon monoxide is also a less desirable
by-product due to environmental law constraints. In order to avoid
this problem, it is necessary to introduce another catalytic
reactor for the total oxidation of CO to CO.sub.2. This can add
significant costs to the catalytic process.
Accordingly, it would be desirable to provide an improved method
for the selective production of vinyl acetate monomer from ethane
without the production of carbon monoxide.
OBJECTS OF THE INVENTION
It is an object of the invention to overcome the above-identified
deficiencies.
It is another object of the invention to provide an improved
catalytic method for the production of vinyl acetate.
It is a further object of the invention to provide an improved
catalytic method for the oxidation of ethylene to produce vinyl
acetate.
It is a further object of the invention to provide an improved
catalytic method for the oxidation of ethane to produce vinyl
acetate.
It is a still further object of the invention to provide an
improved catalytic method for the oxidation of ethane, ethylene or
a mixture of ethane and ethylene to produce vinyl acetate without
the production of carbon monoxide as a by-product.
It is yet another object of the invention to provide an improved
catalytic method for the single stage oxidation of ethane or
ethylene or mixtures thereof to vinyl acetate.
The foregoing and other objects and advantages of the invention
will be set forth in or be apparent from the following
description.
SUMMARY OF THE INVENTION
According to the present invention, vinyl acetate is produced
catalytically from ethane feed stocks. Another aspect of the
invention relates to the production of vinyl acetate from ethylene.
The catalysts suitable for use in the methods of the invention are
active and selective to the desired end product, vinyl acetate. The
catalytic process for the production of VAM from ethane involves
two steps. In the first step, a catalyst (the "first catalyst") is
used to provide the function of activation of ethane to ethylene
and acetic acid. In the second step, ethylene and acetic acid are
further oxidized to VAM in the presence of a conventional VAM
catalyst (the "second catalyst"). Another preferred embodiment
relates to a method of forming a stoichiometric mixture of ethylene
and acetic acid using the first catalyst, which mixture can be
directly fed into a vinyl acetate reactor containing the VAM
catalyst without adjustments. Yet another preferred embodiment
relates to a catalytic method wherein ethylene or ethane is
converted to vinyl acetate in a single stage reactor.
Advantageously, the preferred catalytic methods of the invention do
not produce carbon monoxide. This is advantageous because carbon
monoxide is not environmentally friendly and can have a significant
impact on down stream separation costs, as well as on the poisoning
of the VAM catalyst.
Other objects as well as aspects, features and advantages of the
present invention will become apparent from a study of the present
specification, including the claims, figures and specific
examples.
DESCRIPTION OF THE FIGURES
FIG. 1 is a schematical representation of a ethane to VAM reaction
scheme according to one embodiment of the invention.
FIG. 2 is a schematical representation of a ethane to VAM reaction
scheme according to another embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention relates to novel methods of producing vinyl acetate.
In the first step, the first catalyst is used which provides the
dual functions of (a) activation of ethane (or ethane/ethylene) to
acetic acid and ethylene and (b) ethylene to acetic acid. In the
second step, vinyl acetate is formed through further oxidation of
ethylene with acetic acid in the presence of a second catalyst, the
VAM catalyst. According to one preferred embodiment, the catalysts
of the invention can also be used to provide an optimal feed to a
vinyl acetate reactor. That is, catalytically oxidizing ethane (or
ethylene/ethane) to form a mixture containing the optimal
stoichiometric mixture of ethylene and acetic acid for use as a
feed to a vinyl acetate reactor containing the conventional VAM
catalyst, such as a Pd/Al catalyst.
The catalyst system suitable for the first step of the present
invention (the first catalyst) can be formed from compositions
including a catalyst (a) of the formula
Mo.sub.aV.sub.bNb.sub.cPd.sub.d, wherein: a is 1 to 5; b is 0 to
0.5; c is 0.01 to 0.5; and d is 0 to 0.2.
The numerical values of a, b, c and d represent the relative
gram-atom ratios of the elements Mo, V, Nb and Pd, respectively, in
the catalyst. The elements are preferably present in combination
with oxygen in the form of various oxides.
Another catalyst system, catalyst (b), has a composition comprising
the elements Mo, V, Pd, Nb, La, and X where X is Al, Ga, Si, or Ge)
in the form of oxides in the ratio
Mo.sub.aV.sub.bLa.sub.cPd.sub.dNb.sub.eX.sub.f wherein: a is 1; b
is 0.01 to 0.9; c is >0 to 0.2; d is >0 to 0.2. e is >0 to
0.2; and f is >0 to 0.3.
The numerical values of a, b, c, d, e and f represent the relative
gram-atom ratios of the elements Mo, V, Pd, La, Nb and X,
respectively, in the catalyst. The elements are preferably present
in combination with oxygen in the form of various oxides.
Another catalyst system, catalyst (c), suitable for the invention
is formed from a calcined composition of
Mo.sub.aV.sub.bNb.sub.cX.sub.d, wherein: X is at least one promoter
element selected from the group consisting of: P, B, Hf, Te, and
As; a is about 1 to 5; b is 1; c is about 0.01 to 0.5; and d is
about 0 to 0.1.
The numerical values of a, b, c and d represent the relative
gram-atom ratios of the elements Mo, V, Nb and X, respectively, in
the catalyst. The elements are preferably present in combination
with oxygen in the form of various oxides.
The first catalyst (catalysts (a) or (b) or (c) or mixtures
thereof) and methods of making the first catalyst are set forth in
copending U.S. application Ser. No. 08/932,075, filed Sep. 17,
1997, entitled "Catalysts for the Oxidation of Ethane to Acetic
Acid, Processes of Making the Same and Processes of Using the
Same"; U.S. patent application Ser. No. 08/997,913, filed Dec. 24,
1997, entitled "Catalyst for Producing Acetic Acid from Ethane
Oxidation, Processes of Making the Same and Methods of Using the
Same" and U.S. Ser. No. 09/219,702, filed Dec. 23, 1998, entitled
"Catalysts for the Oxidation of Ethane to Acetic Acid, Methods of
Making and Using the Same", each of which is herein incorporated by
reference.
One broad aspect of the invention relates to the production of
vinyl acetate from ethane, ethylene or mixtures of ethane and
ethylene. The method utilizes a first catalyst ((a) or (b) or (c)
or mixtures thereof) providing the functions of activation of
ethane to acetic acid and ethylene and further oxidation of
ethylene with acetic acid to vinyl acetate using a conventional VAM
catalyst such as a Pd/Al catalyst. Overall, the recycled yield for
vinyl acetate can be greater than 95%.
Advantageously, the methods of the invention produce vinyl acetate
with zero (or nondetectable) or insignificant production of carbon
monoxide. Preferably, less than 0.1 wt % carbon monoxide is
produced as an end product using the invention, more preferably
less than 0.01% and most preferred no detectable carbon monoxide is
produced. Accordingly, one preferred aspect of the invention
relates to a method which employs a catalyst designed in such way
that it does not produce any CO, which saves the treatment step of
converting CO to CO.sub.2.
One embodiment of the invention comprises reacting ethane with
oxygen and water (e.g. steam) in the presence of a first catalyst
((a) or (b) or (c) or mixtures thereof) to form a mixture
containing ethylene and acetic acid which is then reacted to form
vinyl acetate.
The raw material used as the source for the ethane or
ethylene/ethane can be a gas stream, which preferably contains at
least five volume percent of ethane/ethylene. The gas can also
contain minor amounts of the C.sub.3-C.sub.4 alkanes and alkenes,
preferably less than five volume percent of each. The gas stream
can also contain major amounts, preferably more than five volume
percent, of nitrogen, carbon dioxide, and water in the form of
steam.
The reaction mixture useful in carrying out the process is
generally from 5 to 50 moles % of ethane, 5 to 50 moles % of
molecular oxygen either as pure oxygen or in the form of air, and
optionally 2 to 50 moles % of water in the form of steam. The
amount of oxygen present may be a stoichiometric amount, or lower,
of the hydrocarbons in the feed. Other gases may be used as
reaction diluents or heat moderators such as helium, nitrogen, and
carbon dioxide.
The gaseous components of the reaction mixture are preferably
uniformly admixed prior to being introduced into the reaction zone.
The components may be preheated, individually or after being mixed,
prior to being introduced into the reaction zone.
The first reaction zone, containing the first catalyst ((a) or (b)
or (c) or mixtures thereof), generally has a pressure of from 15 to
500 psi, preferably from 150 to 350 psi; a temperature of from
about 100.degree. C. to about 450.degree. C., preferably from
200.degree. C. to 350.degree. C., more preferably from 250.degree.
C. to 300.degree. C.; a contact time between the reaction mixture
and the catalyst of from about 2 seconds to about 100 seconds,
preferably from 5 seconds to 30 seconds; and a space hourly
velocity of from about 50 to about 50,000 h.sup.-1, preferably from
100 to 10,000 h.sup.-1 and most preferably from 200 to 3,000
h.sup.-1.
According to one preferred embodiment, the process occurs in two
stages. In the first stage, a mixture comprising ethane or
ethylene, oxygen or a compound capable of providing oxygen and
water (e.g., steam) is reacted to form a mixture containing
ethylene, acetic acid, oxygen and water (e.g., steam). The product
mixture of the first stage is then fed into the second stage and
reacted to produce vinyl acetate.
The feed from the first stage may be adjusted prior to being
introduced into the second stage. For example, the oxygen, ethylene
and acetic acid concentration may be adjusted to optimize the
catalytic reaction. Preferably, the first stage of the process
produces a stoichiometric composition of acetic acid and ethylene
as a feed for the second stage. According to one particularly
preferred embodiment, adjustments of the feed for the second
reactor are not required as the mixture produced in the first stage
can be directly fed into the second stage. Thus, a dual-function
catalyst can be used in the first stage to provide the feed stock
for the second stage, which may contain a conventional Pd/Al VAM
catalyst or any catalyst suitable for converting the feed stock of
acetic acid and ethylene to VAM.
Therefore, using the present invention, VAM can also be directly
produced from only ethane, oxygen and water without additional
components since the outlet of the first reactor may be optimized
to contain a stoichiometric mixture of acetic acid, ethylene and
oxygen which is the feed mixture for the second reactor.
Preferably, the temperature and pressure of the feed from the first
stage are also not adjusted prior to the second stage.
According to one embodiment, the output from either the first or
second stage is recycled into the same or an earlier stage. For
example, the output from stage 1 may be recycled into stage 1 or
the output from stage 2 may be recycled into stage 1 and/or stage
2.
According to another embodiment, the reaction zone comprises
multiple stages of bilayered catalyst consisting of layers of a
first catalyst ((a) or (b) or (c) or mixtures thereof) according to
the invention and a second conventional vinyl acetate catalyst. In
this manner, the first catalyst converts ethane to a mixture of
acetic acid and ethylene, preferably to an optimal mixture, and the
second catalyst converts the ethylene/acetic acid to vinyl acetate
in a single reaction zone.
Accordingly, one preferred embodiment relates to a process carried
out in a single stage with all the reactants being supplied as a
single feed with unreacted initial reactants being recycled.
However, multiple stage addition of oxygen to the reactor with an
intermediate hydrocarbon feed can also be used. This may improve
productivity to vinyl acetate and avoid potentially hazardous
conditions.
Two possible integrated schemes using the first catalyst and the
second VAM catalyst for direct production of VAM from ethane or
ethane/ethylene mixtures without producing carbon monoxide are
shown in FIGS. 1 and 2.
FIG. 1 is schematical representation of one reaction scheme A
according to one embodiment of the invention. The partial oxidation
reactor 1 containing the first catalyst (CAT-A) converts fresh and
recycled ethane or ethane/ethylene with oxygen into ethylene,
acetic acid and carbon dioxide. An optimum amount of water from
distillation reactor 3 is also introduced to partial oxidation
reactor 1 in order to increase the acetic acid selectivity. The
effluent from partial oxidation reactor 1 enters a gas/liquid
separation unit 2. The gas stream from gas/liquid separation unit 2
is recycled to partial oxidation reactor 1 or goes to carbon
dioxide absorption unit 4, where CO.sub.2 is removed. The liquid
stream from gas/liquid separation unit 2 goes to distillation unit
3, where acetic acid is separated from water or the liquid stream
from gas/liquid separation unit 2 can directly go to VAM reactor 5
containing a conventional VAM catalyst (CAT-B). The treated gases
consisting of ethane, ethylene and oxygen and the liquid stream
consisting of acetic acid or acetic acid and water are fed to VAM
reactor 5 to produce VAM, CO.sub.2 and unreacted ethane, ethylene
and acetic acid. The effluent of VAM reactor 5 is then fed to gas
liquid separation unit 6 where gases including ethane, ethylene and
CO.sub.2 are separated, partially purged to control the build up of
non reacting species in purge unit 8 and recycled back to partial
oxidation reactor 1. The liquids are sent to distillation unit 7
for recovery of VAM. Acetic acid or unreacted acetic acid is
recycled back to VAM reactor 5.
FIG. 2 is a schematical representation of reaction scheme B
according to another embodiment of the invention. The partial
oxidation reactor 21 containing the first catalyst (CAT-A) converts
fresh and recycled ethane or ethane/ethylene with oxygen into
ethylene, acetic acid and carbon dioxide. The effluent of reactor
21 is fed to VAM reactor 23 containing the VAM catalyst (CAT-B) via
optional heat exchanger 22, which allows adjustment of the
temperature of the feed to VAM reactor 23. 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. Additional amounts
of gases to VAM reactor 23, such as ethylene, acetic acid, and
oxygen may be added depending upon the process conditions. The
effluent from VAM reactor 23 is fed to gas/liquid separation unit
24, where gases including CO.sub.2, C.sub.2H.sub.4, and
C.sub.2H.sub.6 are separated from liquid VAM, acetic acid and
water. The gas streams from gas/liquid separation unit 24 are
recycled via carbon dioxide removal unit 25 to reactor 21.
Optionally, the gas streams can also be recycled to reactor 21
without the absorption unit 25, as the catalyst CAT-A in the
reactor 21 is not affected by the presence of carbon dioxide.
Further, a specific amount of carbon dioxide also enhances the
performance of the catalyst CAT-A. Gases are partially purged to
control the build up of non reacting species in purge unit 27.
Liquid stream from separator unit 24 is fed to distillation unit 26
where acetic acid is separated from VAM and water and is optionally
recycled to reactor 23 for make up or can be recovered. VAM goes to
a recovery unit and H.sub.2O is recycled to reactor unit 21 for
enhancement of acetic acid and selectivity.
EXAMPLES
The following examples are illustrative of some of the products and
methods of making and using the same falling within the scope of
the present invention. They are, of course, not to be considered in
any way limitative of the invention. Numerous changes and
modifications can be made with respect to the invention.
Catalytic oxidation processes using a first catalyst ((a) or (b) or
(c) or mixtures thereof) were carried out in a tubular reactor
under the following conditions. All experiments were run at the
temperatures set forth below ranging from 260.degree. C. to
286.degree. C., at a pressure of about 200 psig.
Reaction products were analyzed on-line by gas chromatography.
Oxygen, nitrogen and carbon monoxide were analyzed using a 3 mm by
3 mm column of 13X molecular sieve. Carbon dioxide, ethane,
ethylene and water were analyzed using a 1.8 m by 3 mm column
packed with material sold under the name HAYASEP.TM.Q. Acetic acid
was analyzed using a 0.5 m by 3 mm column packed with material sold
under the name PORAPACK.TM. N.
In all cases, the conversion and selectivity calculations were
based on the stoichiometry.
Data for the stage I reaction mentioned in the examples is
experimental and the production of vinyl acetate (VAM) data in the
stage II is calculated based on 92% yield to VAM from ethylene
(Chem. System 91-10, October 1992, herein incorporated by
reference).
Example 1
The Production of VAM from Ethylene
The first catalyst (catalyst (a)):
MoV.sub.0.396Nb.sub.0.128Pd.sub.xO.sub.y (where x=1.90e-04 and y is
based on the co-ordination valence)
Process conditions for stage I reactor: 286.degree. C./200 psi
Process conditions for stage II reactor as described in reference
Chem. System 91-10, October 1992.
Results data:
TABLE-US-00001 Compound Stage I Stage II (g.mol.min.) Feed Product
Feed Product Ethylene 5.65E-4 2.07E-4 2.07E-4 Oxygen 6.73E-4
1.23E-4 1.23E-4 Nitrogen 2.53E-3 2.47E-4 Water 2.23E-5 2.13E-4
Acetic Acid 2.80E-4 2.80E-4 CO.sub.2 1.56E-4 VAM 1.90E-4
The nitrogen, CO.sub.2 and water are diluents in the stage II
reaction.
Example 2
The Production of VAM from Ethane
First catalyst (catalyst (a)):
MoV.sub.0.396Nb.sub.0.128Pd.sub.xO.sub.y (where x is 1.90e-04 and y
is based on the co-ordination valence)
Process conditions for stage I reactor: 286.degree. C./200 psi.
Process conditions for stage II reactor as described in Chem System
91-10, October 1992.
Results data:
TABLE-US-00002 Compound Stage I Stage II (g.mol.min.) Feed Product
Feed Product Ethane 4.43E-04 2.40E-4 Oxygen 5.10E-04 5.07E-05
5.07E-05 Nitrogen 1.92E-03 1.98E-03 Water 3.18E-04 Ethylene
8.86E-05 8.86E-05 Acetic Acid 9.28E-05 9.28E-05 CO.sub.2 1.77E-04
VAM 9.00E-5
The nitrogen, CO.sub.2 and water act as diluents in stage II.
Example 3
The Production of VAM from Ethane
First catalyst (catalyst (a)):
Mo.sub.2.5V.sub.1.0Nb.sub.0.32Pd.sub.0.03O.sub.y (where y is based
on the coordination valence)
Process conditions for stage I reactor: 260.degree. C./200 psi.
Process conditions for stage II reactor as described in Chem.
System 91-10, October 1992.
Results Data:
TABLE-US-00003 Compound Stage I Stage II (g.mol.min.) Feed Product
Feed Product Ethane 1.91E-04 7.87E-05 Oxygen 2.25E-04 1.30E-05
5.07E-5 Nitrogen 8.45E-04 8.40E-04 Water 1.87E-04 Ethylene 3.41E-05
3.41E-05 Acetic Acid 4.08E-05 4.08E-05 CO.sub.2 3.53E-05 CO
4.68E-05 VAM 3.13E-5
The nitrogen, CO.sub.2 and water act as diluents in stage II.
Based on the above-described catalytic data, the following general
characteristics can be concluded for the methods of the invention:
1. The catalytic methods used show high selectivity to vinyl
acetate by oxidizing mixtures of ethane and ethylene. 2. The
catalytic methods used also show high selectivity to vinyl acetate
by oxidizing ethane. 3. The catalytic method systems used produce
vinyl acetate without the production of by-products such as carbon
monoxide. This advantage reduces the step of CO conversion to
CO.sub.2 in the conventional VAM process.
The above description of the invention is intended to be
illustrative and not limiting. Various changes or modifications in
the embodiments described may occur to those skilled in the art.
These can be made without departing from the spirit or scope of the
invention.
* * * * *