Note: Descriptions are shown in the official language in which they were submitted.
HYDROCARBON OXIDATION VIA CARBON MONOXI~E REDUCED CATALYST
Abstract of the Invention
The present invention provides a supported catalyst for use
in a vapor phase reaction for the high yield conversion of lower aliphatic
hydrocarbons such as butane to corresponding monocarboxylic acids such as
acetic acid. The catalyst is prepared by the carbon monoxide reduction of
a vanadium pentoxide-impregnated, inert porous carrier.
Background of the Invention
Processes for producing lower aliphatic monocarboxylic acids
such as acetic acid by the vapor phase oxidation of lower aliphatic hydro-
carbons are known. For example, acetic acid is prepared by the vapor phase
oxidation of butane according to the following equation:
C4Hlo + 5/2 2 -~ 2CH3COOH + H20
However, processes for the oxidation of hydrocarbons in the vapor
phase by means of oxygen-containing gases have not proven entirely satis-
factory primarily due to the excessive formation of undesirable carbon
oxides, and to the difficulty in maintaining control of the highly exo-
thermic oxidation reaction. U. S. Patent 3,395,159 provides an improved
process wherein the oxidation of hydrocarbons is performed in a reactor
system having fused vanadium oxide catalyst coated on the inner surface of
the reactor, which system has the advantage of better temperature control
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and isothermal operation. The use of early catalysts such as vanadium pent-
oxide, either supported or unsupported, for the vapor phase oxidation of
; . l~wer aliphatic hydrocarbons generally results in y elds and process effi-
- ciencies which fall substantially short of theoretical potential. Also, the
resulting products are often impure due to a lack of selectivity when such
catalysts are employed.
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Neat (i.e., unsupported) reduced vanadium oxides such as vanadium
tetroxide bave been suggested as a remedy for the above disadvantages but
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heretofore the use of the catalysts in the vapor phase oxidation of lower
aliphatic hydrocarbons has resulted in inefficient processes which lack a
high degree of selectivity. Furthermore, reduced vanadium oxides in neat
form (pellets) lose crush strength during use. This is extremely critical
for if the loss of crush strength is excessive such that extensive cata-
lyst fines are developed, the pressure drop over the reactor will become
too great to operate the unit thus requiring the catalyst to be removed
and recharged. This, of course, is an expensive and time-consuming opera-
tion that may result in the whole process being too uneconomical to be
commercially feasible.
One way to eliminate this crush strength loss is to support the
reduced vanadium oxide on an inert and rigid carrier.
Typical of the elaborate steps taken to obviate the crush strength
loss via a carrier is the procedure disclosed in U. S. Patent 3,962,137
wherein an abrasion resistant catalyst is produced for the oxidation of
lower aliphatic hydrocarbons by intimately mixing an aqueous suspension of
colloidal non-porous silica particles with a water soluble metal salt which
is decomposable by heat to a metal oxide, calcining the mixture, adding a
further amount of the aqueous suspension of colloidal non-porous silica
particles, and drying this catalyst composition. The essence of this
patented invention is the formation of an outer porous net of non-porous
colloidal silica particles over the calcined mixture of metal oxide and
non-porous colloidal silica.
Ob;ects and Summary of the Invention
Accordingly, a general object of the present invention is to
avoid or substantially alleviate the above problems of the prior art in
a simple and straightforward manner.
A more specific object is the provision of a process for
the production of acetic acid by the vapor phase oxidation of
lower aliphatic hydrocarbons.
Another object is ~o provide a highly efficient process
for the production of acetic acid by the vapor phase oxidation
of lower aliphatic hydrocarbons using a catalyst which has
significantly improved physical strength.
Since selectivity in the vapor phase oxidation of lower
aliphatic hydrocarbons to acetic acid is almost proportional to
the amount of reduced vanadium oxide present, yet another object
is to provide a method of achieving increased vanadium oxide
loadings on an inert carrier.
These and other objects are achieved by a process for
preparing acetic acid by the vapor phase oxidation of allower
aliphatic hydrocarbon such as butane, which process comprises
reacting the lower aliphatic hydrocarbon feed stream comprising
alkanes with an oxygen-containing gas in the vapor phase pre-
ferably in the presence of steam and a catalytic amount of a
reduced vanadium oxide supported on an inert porous carrier,
said catalyst having been activated by the carbon monoxide
reduction of vanadium pentoxide-impregnated inert porous carrier,
said catalyst having an excess of 50 weight percent of vanadium
pentoxide prior to said reduction.
The invention also provides a catalyst prepared by the
steps of: impregnating an inert porous carrier with V205;
reducing the V205 in a carbon monoxide atmosphere.
The essence of the invention lies in the discovery that
CO reduction of an inert porous support which has been impregnat-
ed with V2O5 to give V2O5 loadings in excess of 50 weight percent
yields an extremely crush-resistant catalyst which, when utilized
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in a vapor phase oxidation of a lower aliphatic hydrocarbon such
as butane, realizes high efficiency to acetic acid; low efficiency
to butenes and rapid conversion of recycled butenes to acetic
acid which avoids butene buildup within the reactor. Furthermore,
since the temperatures and pressures needed for the CO reduction
step are well within the operating capability of commercial
vapor-phase oxidation reactors, the supported vanadium oxide
catalyst can be reduced or regenerated ln situ without having to
remove the catalyst from the reactor tubes.
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Other objects and advantages of the present invention will be-
come apparent from the following description of the preferred embodiments.
Description of the Preferred Embodiments
The first step in the preparation of the catalyst of the instant
invention is to impregnate a highly porous, predominantly inert support
with vanadium pentoxide (V20s). Techniques to accomplish this with high
loadings are well known in the art. For example, the inert supports can
be impregnated with aqueous solutions of soluble vanadium salts such as
vanadyl oxalate, ammonium meta-vanadate or decavanadate; dried, and then
calcined in an oxygen-containing gas such as air to produce the vanadium
pentoxide impregnated starting support. A preferred method for generating
this V~05 impregnated support is to physically mix V20s powder with high
surface area silica catalyst supports such as Houdry's macroporous
silica beads or a silicon carbide and increase the temperature until the
V20s is molten. The amount of V20s present should be such as to avoid
agglomeration of the impregnated beads. When all of the V20s has been
absorbed by the support, the catalyst precursor is cooled to room tempera-
ture. The V20s impregnated support is then subjected to a carbon monoxide
atmosphere at temperatures high enough to effect reasonable reduction rates
yet below about 600C to avoid remelting the V20s. This process is con-
tinued until all of the V205 is in a reduced state as can be determined
by carbon dioxide (C02) measurements in the vent gases. Of course, if the
CO reduction is accomplished under elevated pressures such as for example
from about 150 to about 250 psig, the reduction times are significantly
reduced.
In the process of the present invention a lower aliphatic hydro-
carbon is reacted with an oxygen-containing gas in the presence of a
catalytically effectiveamount of the above-described reduced vanadium oxide
supported catalyst to produce acetic acid.
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By "lower aliphatic hydrocarbon" is meant any saturated or un-
saturated aliphatic hydrocarbon containing from 2 to 10 carbon atoms. These
r' lower aliphatic hydrocarbons include alkanes, alkenes and al~ynes such as ethylene,
propylene, butene, propane, butane, pentene, octane, and their isomers. ~articu-
larly preferred aliphatic hydrocarbons are the alkanes and alkenes including pro-
; pane, butane, butene, isobutane, isobutene and mixtures thereof.
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The production of acetic acid from butane can give particularly
advantageous results.
; By the term "reduced vanadium oxide or reduced vanadium pentoxide" is
meant a vanadium oxide in which the average vanadium ion valency is less
than 5. A lower oxidation state of vanadium ions is an essential feature
of the present invention catalysts. This is based on the observation that
vanadium pentoxide (i.e., a catalyst containing vanadium ions with a valence
of 5) is not an active catalyst under the process conditions to be described,
and it i8, therefore, advantageous to exclude vanadium pentoxide from the
catalyst compositions to the greatest extent possible.
The reduced vanadium oxides employed in the catalysts of the
,~ present invention are all intermediate in average oxidation states, i.e.,
between V20s and V203. Although the initial charge can contain V20s and V203,
X-ray diffraction studies confirm that vanadium oxide catalysts operable in
the process are effectively expressed empirically as V305~ V407~ V50g~ V6ll-
V7013, V204 and/or V6013. The average valence of the vanadium ions in these
oxidés generally ranges from 3 to about 4.5.
The oxygen necessary as a reactant in the present process may be
from practically any molecular oxygen-containing gas such as molecular oxygen
or air. Also, the molecular oxygen-containing gas may be one wherein mole-
cular oxygen is mixed in varying amounts with an inert diluent gas surh as
nitrogen, argon, or a carbon oxide. The lower aliphatic hydrocarbon and
oxygen-containing gas can be reacted within a wide range of molar ratios.
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However, it is an essential feature of the invention process that the quantity
of oxygen gas in the feed stream be the least required to convert efficiently
the hydrocarbon stream to acetic acid consistent with necessary temperature
control and retention of catalyst activity. It is important that the
vanadium oxide catalyst is not oxidized to vanadium pentoxide. Even the
presence of a small amount of vanadium pentoxide is effective in reducing
the yield of acetic acid. The quantity of oxygen gas in the feed stream
usually is maintained in the range between about 0.05 and 1 moles per mole
of lower aliphatic hydrocarbon. At elevated pressures, the preferred range
is from about 0.05 to about 0.30.
In a preferred embodiment of the invention process, water is in-
cluded in the feed stream in a quantity between about 0.1 and 2.0 moles
per mole of lower aliphatic hydrocarbon. The presence of water vapor in
the oxidation reaction system can increase the yield of acetic acid by as
much as 10 percent in the case where the hydrocarbon feed st~eam is normal
butane.
The present process is carried out at a temperature generally
between about 180 and about 400C, typically between about 200 and about
350C, and preferably between about 220 and about 300C.
The present process can be carried out at subatmospheric, atmos-
pheric, or super atmospheric pressures, generally from about 0.1 to about
50 atmospheres, typically from about 0.5 to about 30 atmospheres, and
preferably from about 1 to about 20 atmospheres.
The contact time of the reactants with the catalyst is generally
between about 0.1 and 100 seconds, typically between about 0.25 and 50
seconds. By contact time as used herein, is meant the contact time adjusted
to 25C and 1 atmospheric pressure (i.e., standard temperature and pressure,
denoted STP). Thus, the contact time is calculated by dividing the volume
of the catalyst bed (including voids) by the volume per unit time flow rate
of the reactants at STP.
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The process of the present invention may be carried out con-
tinuously and the catalyst may be present in various forms such as in
one or more fixed beds or as a fluidized system.
Portions of the reactants which do not undergo reaction may be recycled
if necessary. Selected intermediate products, such as butenes and acetaldehydes,
are preferably recycled also. The desired acetic acid product ~ay be
separated from any impurities by condensation followed by fractionation and
aqueous or non-aqueous extraction of the product from the unreacted lower
aliphatic hydrocarbon.
In this specification, the terms conversion and efficiency are
defined as follows:
moles lower aliphatic hydrocarbon
conversion, ~ = or oxygen converted X lO0
moles lower aliphatic hydrocarbon
or oxygen fed
% carbon effi- moles component i formed X carbon atoms
ciency to com-= per mole of component i X 100
ponent i total moles of carbon in all products
analyzed
Acetic acid is generally produced by the present process with a
conversion (based on oxygen) generally of at least 90 percent, often at
least about 95 percent, a conversion based on lower aliphatic hydrocarbon
(which, as noted above, is present in substantial excess) generally of at
least about 1 percent, typically from about 3 to about 5 percent, and a
carbon efficiency of generally at least about 50 percent, typically at
least about 55 percent, often at least about 60 percent with recycled intermediates.
As indicated hereinabove, the present process is useful for pre-
paring acetic acid with improved yield and process efficiency with a cata-
lyst of superior crush strength. The recovery of the product stream and
the separation of the acetic acid from the acetaldehyde, maleic acid and
other by-products can be accomplished by conventional procedures. U. S.
Patent 3,624,148 describes a method for the separation of acetic acid from
maleic acid.
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The present invention is further illustrated by the following
examples. All parts and percentages in the examples as well as in the
specification and claims are by weight unless otherwise specified. The
reactants and other specific ingredients are presented as being typical,
and various modifications can be devised in view of the foregoing dis-
closure within the scope of the invention.
Catalyst Preparation
The following two examples illustrate the preferred method for
making the catalysts of the instant invention.
Example I
600 grams of V205 powder is physically mixed with 261 grams of
silica beads, placed in a quartz calcining dish, and heated to 816C. The
mixture is held at that temperature for about 16 hours and then allowed to
cool to room temperature. Nearly all of the V205 is absorbed into the
silica beads ~bout 1/8'l to 1/4" in diamete~.
The supported V20s on silica is placed in the center of a two
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inch diameter quartz tube, flushed with carbon monoxide, and heated to 200 C.
The temperature is increased from 200 to 500C over a period of 5 hours,
kept at 500C for about 116 hours, and then cooled rapidly to room tempera-
ture - still under a steady stream of carbon monoxide.
Example II
310 grams of V205 is poured over 151 grams of silica beads in two
large quartz dishes heated to 816C and held at that temperature for about 16 hours
The dishes are removed from the oven and cooled rapidly to room temperature. The
V205 is melted and absorbed by the beads(about 1/8" to 1/4" in diameter)to yield
free flowing yellow beads. Six batches of the above are prepared and comhined.
1500 grams from the above V205 impregnated silica beads are
placed in a one inch diameter pyrex tube and thoroughly flushed with carbon
monoxide. The material is heated to 500 C over a 3 hour period; held at
that temperature for 136 hours; and then cooled to room temperature still
under one atmosphere of carbon monoxide.
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Example III
300 grams of the V20s impregnated silica beads are also activated
by subjecting the beads to a temperature of 275C while under a carbon
monoxide blanket at pressure of from about 150 to 190 psig. The V20s is
completely reduced, i.e., activated in about 16 hours.
Example IV
This example illustrates the use of the preferred catalyst in the
vapor phase oxidation of lower aliphatic hydrocarbons to acetic acid.
A 3/4" schedule 40 steel pipe is employed to hold the catalyst
charge.- The pipe is about 10 feet long with an inside diameter of about 0.82
inches. The usual catalyst charge is about 500 cc of spherical or pelleted
catalyst. Silicon carbide spheres or pellets are used in front of the cata-
lyst to serve as a preheat zone for the reactant gases. The reactor is heated
to the desired temperature using pressurized steam. Flow rates of the lower
aliphatic hydrocarbons and air (or oxygen) are determined by mass fiowmeters.
Steam is introduced as water at a known flow rate and flashed to steam with
the flow rate of steam calculated by application of the ideal gas law. After
the flow rates are stabilized, the temperature of the reactor (initially about
240C) is then slowly raised until the desired oxygen conversion rate is achieved.
Material balances are then obtained at this temperature.
Reactions can be conducted at or near atmospheric pressure but it
is preferréd to operate the reactor under pressures so that cooling waterncan
be used to condense the butane recycle stream.
Analysis of the vent gas stream entails passing the reaction products
' plus unreacted lower aliphatic hydrocarbon and steam through a water-cooled
condenser after leaving the heated reaction zone to remove the liquid products
and water from the vent stream. The vent stream, leaving the condenser, now
containing primarily lower aliphatic hydrocarbons, carbon oxides, and nitrogen
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is analyzed by standard gas chromatographic techniques. Components analyzed
include butane, butenes, acetaldehyde, oxygen, nitrogen, carbon monoxide, and
carbon dioxide. The liquid sample is collected after the end of the run and
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~ analyzed by standard gas chromatographic techniques. Components analyzed
include: acetic acid, acetaldehyde, acetone, maleic acid, acrylic acid,
propionic acid, butyric acid, formaldehyde, formic acid, methyl ethyl ketone,
and butanol.
The following represents typical results realized when the cata-
lyst of Example I is utilized on the above-described process.
Reactor Pressure (psig? 180
Reactor Temperature (C) 275
Feed Stream (Mol Ratio)
C4 : 2 : H20 9.0 : 1.0 : 9.5
Total Feed Rate
l/m~n (STP) 26.95
Butane Conversion (%) 3.8
Oxygen Conversion (%) 96
Carbon Efficiency (%)
Butenes 24
Acetic Acid 42
Acetaldehyde 3.8
Carbon Oxides 23
Example V
The following represents typical results when the catalyst of
; Example II is utilized in the process of Example IV. The test is conducted
: in an 18 foot plpe (0;78 inch inside diameter~ using about 1700 cc of catalyst.
- Reactor Pressure (psig) 180
Reactor Temperature (C) 275
Feed Stream (Mol Ratio)
C4 : 2 : H20 7.8 : 1 : 3.7
Total Feed Rate
l/min (STP) 172.4
Butane Conversion (%) 3.15
2 Conversion (%) 98
Carbon Efficiency (%)
Butenes 13
Acetic Acid 46
Acetaldehyde 6.2
Carbon Oxides 28
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Example VI
The following shows the superior crush strength of the instant
catalysts. After the run of Example V is completed~(1000 hours) the cata-
lyst is tested at various bed depth levels.
Percent Fines Av. Crush Strength,
- Distance into Bed (%) in Sample (wt. %) lbs. (Range)
6.7 - 13.9 0.03 23.8
13.9 - 20.6 0.01 25.0
- 31.1 - 35.6 0.02 22.4
46.1 - 51.1 0.02 23.9
61.1 - 66.1 0.04 17.9
76.1 - 80.6 0.04 17.7
84.4 - 88.3 0.07 20.4
- 92.8 - 96.7 0.09 20.2
96.7 - 100 0.10 22.3
For comparison purposes, the average crush strength of an unused
portion of this catalyst is 21.6 lbs.
Typical crush strength measurements for bulk unsupported reduced
vanadium oxide catalyst (prepared by the thermal decomposition of vanadyl
oxalate) are as follows:
Unused: 10 - 15 lbs.
Used (300 + hrs): 2 - 3 lbs.
Examples VII and VIII
Samples of V20s impregnated on porous silica beads are prepared
as in Examples I and II. One half of these samples are activa~ed by sub-
jecting the beads to a hydrogen flush while heating the material to 500C
over a 3 hour period. The material is held at that temperature for 136
hours and then cooled to room temperature while still under a blanket of
; an atmosphere of hydrogen (Example VII).
The other half of the V20s impregnated silica beads are activated
, by subjecting the beads to an ethanol saturated nitrogen purge while heating
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the material to 500C over a 3 hour period. The material is held at that
temperature for 136 hours and then cooled to room temperature while still
under a blanket of one atmosphere of ethanol saturated nitrogen (Example
VIII).
Examples IX to XV
The following illustrates the unexpectedly improved results
realized when using the catalysts of the instant invention (Examples I -
III) i.e. the CO reduced V20s impregnated beads, as compared to V205 im-
pregnated beads which had been reduced with hydrogen (Example VII) or
ethanol (Example VIII) in the process of Example IV.
Furthermore, acetic acid efficiency figures are provided to
illustrate the increased carbon efficiency realized when the butenes are
recycled into the feed stream. Of course, acetaldehyde recycle into the
feed stream, in addition to the butenes, would increase acetic acid
efficiencies even more.
Catalyst Activating or Reactor ConversionAcetic Acid
Identification Reducing Agent Temp. (oC) 2 ButaneEfficiency
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59 wt ~ V~05 on
: )~ Houdry SiO2 CO 275 952.9 41
;~ ~ 6~L wt % V20s
jr9 Houdry SiO2 ~ CO 267 97~} ~h~
~rwt % V25
Houdry SiO2 C0 242 100 1.7 45
~wt % on 3~
Houdry SiO2 C2H50H 270 91~k~ 35
60 wt % on
Girdler SiO2 H2 273 901.9 26
wt % on
Houdry SiO2 H2 242 100 2.0 34
% Carbon Efficiency
Acetic Acid
: Acetaldehyde C0 + C02 Butenes Efficiency on Butene Recycle
5.0 31 25 54
5.7 31 31 54
3.0 31 27 62
7.5 36 27 48
8.7 38 45 47
3.3 38 39 55
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Thus, as can be seen from the above, with similar overall con-
- versions, catalysts reduced with CO give significantly improved selectivity
to acetic acid and at the same time give significantly less butane to
butene conversion with its attendant carbon by-product formation.
While all of the above runs are conducted with a fixed bed
reactor, it is quite obvious that the superior crush strength of the in-
stant catalyst makes it ideally suited for fluid bed operations.
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