Note: Descriptions are shown in the official language in which they were submitted.
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io SPECIFICATION
IMPROVED METHOD FOR THE MANUFACTURE
OF ACRYLIC ACID
BACKGROUND OF THE INVENTION
The present invention is directed to an improved process for the
manufacture of acrylic acid. Presently, acrylic acid is produced by a two-step
process. Propylene is first oxidized to acrolein over a mixed metal oxide
catalyst
comprising iron, bismuth and molybdenum promoted with suitable elements,
and the acrolein is further oxidized to acrylic acid over a second catalyst in
a
separate reactor. Typically, catalysts containing oxides of iron, bismuth and
molybdenum promoted with suitable elements are readily available for the
selective oxidation of the propylene to acrolein (i.e. this first step in the
two-step
process in the manufacture of acrylic acid). Examples of suitable types of
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catalysts for this first step can be found in U.S. Patent 4,162,234 and
4,280,929
assigned to the assignee of the present application.
In the second step of the two-step process acrolein is oxidized over the
second catalyst to acrylic acid. It is always the case that the selectivity of
the
acrolein to acrylic acid is below 100%. However, the acrylic acid that is
formed
in the first step of the two-step process passes through the second reactor
with no
decomposition. Therefore, it is advantageous to use catalysts that produce
substantially larger amounts of acrylic acid during the oxidation of the
propylene
to acrolein in the first reactor, thereby getting higher yields of acrylic
acid in the
two-step process.
In related patent application U.S. Serial No. 08/923,878 filed
September 2, 1997, and assigned to the assignee of the present invention,
there
is a disclosure of a novel catalyst useful in the manufacture of acrylonitrile
and
hydrogen cyanide. The catalyst was specifically disclosed as containing a
mixed
metal oxide of iron, molybdenum and bismuth promoted with various metals and
useful in the manufacture of acrylonitrile with substantially higher yields of
co-
product hydrogen cyanide. It is the discovery of the instant application that
the
catalyst of co-pending application 08/923,878 can not only be used in the
first
step of the two-step process for the manufacture of acrylic acid, but results
in
unexpected high yield of acrylic acid during the first step of the process.
This
high yield of acrylic acid in the first step leads to a higher yield of
acrylic acid
overall being achieved in the two-step process.
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SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a novel process
for the production of acrylic acid and selected oxidation of propylene to
acrolein.
Additional objects and advantages of the invention will be set forth in
part in the description which follows and in part will be obvious from the
description, or may be learned by the practice of the invention. The objects
and
1o advantages of the invention may be realized and attained by means of the
instrumentalities and combinations particularly pointed out in the appended
claims.
To achieve the foregoing objects and in accordance with the purpose of
the present invention as embodied and described herein, the process of the
present invention comprises reacting propylene and oxygen (preferably in the
form of an oxygen-containing gas such as air) in a reaction zone having a
catalyst characterized by the following formula:
AaBnGCaaFeeBirMo12OX
where A = one or more of Li, Na, K, Rb and Cs
B = one or more of Mg, Sr, Mn, Ni, Co and Zn
C = one or more of Ce, Cr, Al, Sb, P, Ge, Sn, Cu, V and W
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and a = 0.01 to 1.0; b and e = 1.0 - 10
c = 0 to 5.0, preferably 0.05 to 5.0, especially preferred being
0.05 to 4.0
d and f= 0.05 to 5.Orand x is a number determined by the
valence requirements of the other elements present;
at an elevated temperature (e.g. 200 to 600 C) to produce acrylic acid and
acrolein.
In the preferred embodiment of the present invention, A is selected to be
one or more of lithium, sodium, potassium and cesium, especially preferred
being
io cesium and potassium.
In another preferred embodiment, B is selected from the group
consisting of magnesium, manganese, nickel and cobalt, or mixtures thereof.
In still another preferred embodiment, C is selected from the group
comprising cerium, chromium, antimony, phosphorus, germanium, tungsten, or
mixtures thereof, especially preferred being cerium, chromium, phosphorus, and
germanium.
In still another preferred embodiment of the present invention, a may
range from about .05 to .9, especially preferred being above 0.1 to 0.7.
In a further preferred embodiment of the present invention, b and e
may range from about 1 to 10. In still a further preferred embodiment of the
present invention, c, d and f may range from about 0.05 to 4, especially
preferred being 0.1 to 3.
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A further preferred embodiment of the present invention comprises
recovering the acrylic acid and acrolein from the first reaction zone,
introducing
at least acrolein and oxygen into a second reaction zone having a second
catalyst
to react the acrolein and oxygen at an elevated temperature to produce acrylic
acid, and recovering the acrylic acid from the second reaction zone. Any
suitable
acrolein to acrylic acid catalyst may be used in this second step. For
example,
typical second stage catalysts (e.g., 62% SbsSnsVsW1,21VIoi2Ox = 38% Si02) as
described in U.S. Patent 3,840,595, are
In another preferred embodiment of the present invention, the first
reaction from propylene to acrylic acid and acrolein takes place in a fluid
bed
reactor and the second reaction from acrolein to acrylic acid takes place in a
fixed
bed reactor.
The catalyst of the present invention can be used either supported or
unsupported. Preferably the catalyst is supported on silica, alumina or
zirconium or mixtures thereof, especially preferred being silica.
Detailed Descrintion of the Invention
The catalysts of the present invention may be prepared by any of the
numerous methods of catalyst preparation which are known to those of skill in
the art. For example, the catalyst may be manufactured by co-precipitating the
various ingredients. The co-precipitating mass may then be dried and ground to
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an appropriate size. Alternatively, the co-precipitated material may be
slurried
and spray dried in accordance with conventional techniques. The catalyst may
be extruded as pellets or foimed into spears in oil as is well known in the
art.
Alteriiatively, the catalyst components may be mixed with a support in the
form
of the slurry followed by drying or they may be impregnated on silica or other
supports. For particular procedures for manufacturing the catalyst, see U.S.
Patents 5,093,299; 4,863,891 and 4,766,232 assigned to the assignee of the
present invention.
Typically, the A component of the catalyst may be introduced into the
1o catalyst as an oxide or as a salt which upon calcination will yield the
oxide.
Preferably, salts such as nitrates which are readily available and easily
soluble
are used as the-means of incorporating the A element into the catalyst.
Bismuth may be introduced into the catalyst as an oxide or as a salt
which upon calcination wil.l yield the oxide. The water soluble salts which
are
easily dispersed but form stable oxides upon heat treating are preferred. An
especially preferred source for introducing bismuth is bismuth nitrate which
has
been dissolved in a solution of nitric acid.
To introduce the iron component into the catalyst, one may use any
compound of iron which, upon calcination will result in the oxides. As with
the
other elements, water soluble salts are preferred for the ease with which they
may be uniformly dispersed within the catalyst. Most preferred is ferric
nitrate.
Cobalt, nickel and magnesium may also be introduced into the catalyst
using nitrate salts. However, magnesium may also be introduced into the
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catalyst as an insoluble carbonate or hydroxide which upon heat treating
results
in an oxide.
The molybdenum component of the catalyst may be introduced from any
molybdenum oxide such as dioxide, trioxide, pentoxide or heptaoxide. However,
it is preferred that a hydrolizable or decomposable molybdenum salt be
utilized
as the source of the molybdenum. The most preferred starting material is
ammonium heptamolybdate.
Phosphorus may be introduced in the catalyst as an alkaline metal salt
or alkaline earth metal salt or the ammonium salt but is preferably introduced
1o as phosphoric acid. Calcium which is an essential ingredient in the
catalyst of
the present invention can be added via pre-formation of calcium molybdate or
by
impregnation or by other means known in the art. (Usually added as
Ca-nitrate, along with the other nitrates.)
The present invention is directed to a process for the production of
acrylic acid during the oxidation of propylene to acrolein comprising reacting
oxygen and propylene in a reaction zone in contact with a catalyst
characterized
by the following empirical formula:
AaBbCPCadFeeBifMo12Ok
where A= one or more of Li, Na, K, Rb and Cs
B= one or more of Mg, Sr, Mn, Ni, Co and Zn
C= one or more of Ce, Cr, Al, Sb, P, Ge, Sn, Cu, V and W
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and a= 0.01 to 1.0; b and e= 1.0 - 10
c = 0 to 5.0, preferably 0.05 to 5.0, especially preferred being
0.05 to 4.0
d and f= 0.05 to 5.0, and x is a number determined by the
valence requirements of the other elements present;
to produce acrylic acid and acrolein. Preferably, the reaction takes place
between a temperature of 200 to 500 C, preferably 300 to 400 C.
The catalysts of the present invention may be prepared by mixing an
aqueous solution of ammonium heptamolybdate with a silica sol, adding a slurry
l0 containing the compounds of the other elements to the aqueous solution,
drying
the solution, denitrifying and calcining. The catalyst may be spray-dried at a
temperature of between 110 C to 350 C. The denitrification temperature may
range from 100 C to 450 C. Finally, calcination takes place at a temperature
of
between 400 C to 700 C.
A further preferred embodiment of the present invention comprising
recovering the acrylic acid and acrolein produced in the first reaction zone,
introducing at least the acrolein and oxygen (preferably, air is the source
for the
oxygen) into a second reaction zone at an elevated temperature containing a
second catalyst suitable for the conversion of acrolein to acrylic acid to
convert
20 the acrolein to acrylic acid and recovering the acrylic acid from the
second
reaction zone. Suitable catalysts for use in the conversion of acrolein to
acrylic
acid are described in previously cited U.S. Patent 3,840,595.
Specific examples of catalysts useful in the second reaction zone
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include MOgV2W1Cu1Sn0.40x; M010W1V3Sb2Cu1Nb2Ox; M012V3W1.2Cu2T10.50x;
M09V2W1Cu1.5Sno.4P10.; Mo12V3W1.2Cu2Sn0.5Ox and SbgSn3V3W1.2M0120,;. These
catalysts are supported on an inert support such as alumina, zirconia or
silica,
preferably silica. Typically, the supported catalyst comprises 70 to 75 wt%
active
phase and 25 to 30 wt% inert support.
The following examples of the present invention are set forth below for
illustrative purposes only.
In each of the following examples, the process was performed in a 40 cc
fluid bed reactor at 0.05-0.10 wwh with a feed mixture of 1C3 / 1.702 /9.3N2 /
3H20 at a temperature of 360 C and 15 psig.
Table I
Ex. %C3 Acrl+
No. Catalyst Composition Conv %Acrl %AA AA
Comparative Example:
1 Cso.1Ko.1Ni6.2Mg2.5Fe4Bio.5Ceo.5Mo14.sOX 93.4 67.6 14.4 82.0
Examples:
2 Cso.1Ko.1Ni6.2Mg2.5Fe4B1o.5Ceo.5Ca0.75Mo15.6OX 97.1 67.3 17.6 84.9
3 Cso.1Ko.1Co6.2Mg2.5Fe4Bio.5Ceo.5Cao.75Mo15.60X 97.3 74.4 14.1 88.5
4 Cso.1Ko.1Co3.1Mg2.25N13.1Fe4B1o.5Ce0.5Ca1.OM015.6OX 98.0 67.7 18.6 86.3
5 Cso.1Ko.1Ni6.2Mg2.5Fe2.oBio.5Cao.75Mo12.sOX 98.1 65.3 20.8 86.1
9
