Note: Descriptions are shown in the official language in which they were submitted.
1060467 :-
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BACKGROUND
This invention concerns the selective preparation
of two-carbon atom oxygenated hydrocarbons, namely acetic
acid~ ethanol~ and/or acetaldehyde, from synthesis gas.
More particularly, the invention concerns reaction of
synthesis gas in the presence of a heterogeneous catalyst
to produce such products.
The preparation of hydrocarbons and oxygenated
hydrocarbons from synthesis gas (essentially a mixture of
carbon monixide with varying amounts of carbon dioxide and
hydrogen) has received extensive study and has achieved
c~mmercial adoption. Reaction conditions generally involved
temperatures on the order of 150-450C, pressures of from
atmospheric to about 10,000 psig, and hydrogen-to-carbon
monixide ratios in the range of 4:1 to about 1:4, with
an iron group or a noble metal group hydrogenation catalys~.
--1--
--~ D-9406-1
i O ~0 ~ 6'7
One serious disability of most synthesis gas
processes has been the non-selective or non-specific nature
of the product distribution. Catalysts which possess
acceptable activity generally tend to give a wide spectrum
of products--hydrocarbons and oxygenated hydrocarbons--having
a broad distribution of carbon atom contents. This not
only complicates the recovery of desired products, but
results in the wastage of reactants to commercially
uninteresting byproducts.
SUMMARY OF INVENTION
In accordance with the invention, a process is
provided for the reaction of carbon monoxide with hydrogen
to prepare, selectively, oxygenated hydrocarbons of two
carbon atom~ per molecule. Synthesis gas is continuously
contacted with a catalyst essentially comprising rhodium
metal, at a c~mbination of reaction conditions correlated
so as to favor the formation of a substantial proportion
of acetic acid, ethanol, and/or acetaldehyde.
The reaction is conducted at reactive conditions
of temperature, pressure, gas composition and space
velocity correlated so as to collectively produce acetic
acid, ethanol, and/or acetaldehyde in an amount which is
at least about 50 weight percent, preferably at least about
75 weight percent, of the two and more carbon atom compounds
obtained by the reaction, Desirably, the reaction is
conducted at these correlated conditions to achieve product
efficiencies based on carbon consumption in excess of 10%,
--2--
~~~ D-9406-1
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and frequently in excess of 50%. Ethyl esters and acetates
formed are included as ethanol and acetic acid in
determining productivities and selectivities as used in
data presented herein. At optimum reaction conditions,
and particularly at relatively low conversions, there is
little conversion to three carbon atom and higher
hydrocarbons and oxygenated hydrocarbons, and conversion
to methane and methanol may readily be minimized. As will
appear, it is also possible, through variations in catalyst
composition and reaction conditions, to direct the selectivity
toward only one of the three products, e.g. acetic acid or
ethanol.
REL~TION TO PRIOR ART
The literature on synthesis gas conversion i~
extensive. While it is rare to find a metal that has not been
investigated as a catalyst for the reaction, most efforts
to date have focused on the iron group metals, on ruthenium,
and on various metal oxide systems.
Extensive literature surveys have revealed that
five prior workers have investigated the use of rhodium metal
as a synthesis gas conversion ~atalyst. Their publications,
identified in Table I below, report results which are no more
impressive than are obtained with iron group catalysts. In
view of these recults and the relatively high price of
rhodium, it is not surprising to find there has been so
little interest in the use of rhodium as a catalyst for
synthesis gas conversion.
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The relationship between reaction conditions
employed and the results achieved by prior workers are
well summarized in the above Table. None reported or found
more than 3.4 mole percent of two carbon atom oxygenated
compounds in the reaction products. This contrasts with
as much as 80 mole percent two carbon atom oxygenated
compounds in the presently described process. There is
evidently an importance in associating a rhodium metal
catalyst with correlated reaction conditions to favor the
formation of a substantial proportion of acetic acid,
ethanol, and/or acetaldehyde.
A more detailed illustration of the difference
~etween Soufi's results and those obtained by the
practice of the present invention is shown in Table II.
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DETAILED DESCRIPTION
_
In keeping with the invention, a synthesis gas
containing carbon monoxide and hydrogen is contacted with
a rhodium metal catalyst under reactive conditions of
temperature, pressure, gas composition and space velocity
correlated so as to favor as stated previously, the
formation of a substantial proportion of acetic acid,
ethanol, and/or acetaldehyde. The reaction efficiency, or
selectivity, to these two-carbon atom compounds is invariably
at least about 10%, and is usually upwards of about 25%;
under the preferred conditions it exceeds 50% and, under -~-
optimum conditions, has reached 90% or more. Selectivity is
deined herein as the percentage of carbon atoms converted from
carbon monoxide to a speci~ied compound or compounds.
Thus, the independent reaction variables are
correlated so as to favor the formation of a substantial ~ -
proportion of the desired two carbon atom oxygenated
hydrocarbons (acetic acid, ethanol, and/or acetaldehyde).
This proportion, expressed as carbon conversion efficiency,
is usually upwards of 25% and frequently exceeds 50%.
In one aspect of the invention, this correlation
is a combination of conditions which result in maintaining
moderate reaction conditions to thereby limit the conversion
of CO to not more than about one fourth, preferably not
more than about one eighth. As will be discussed in detail
below, this may be achieved primarily by a combination
of high space velocity and low temperature, but other
--7--
~ ~4,~j,7 D- 9406 -1
factors (e.g. H2/CO ratio, catalyst activity, pressure,
bed ge~metry, etc.) also affect the conversion. At high
conversions, it has been noted that higher carbon
ntImber hydrocarbons and oxygenated hydrocarbons are produced
in excess, with a resulting loss in efficiency to two-carbon
atom compounds.
Conditions of temperature, of pressure, and of
gas composition are usually ~ithin the ranges that are
essentially conventional for synthesis gas conversions,
particularly those employed in the production of methanol.
Thus, existing technology and, in some instances, existing
equipment may be used to effect the reaction,
The reaction is highly exothermlc, with both the
thermodynamic equilibrium and the kinetic reaction rates
being governed by the reaction temperature Average
catalyst bed temperatures are usually within the range
of about 150-450C., but for optimum conversions, bed
temperatures are kept within the range of about 200-400C.,
typically about 250-350C.
The reaction temperature is an important process
variable, affecting not only total productivity but
selectivity toward one or more of the desired two carbon
atom products. Over relatively narrow temperature ranges,
as for example 10 or 20C., an increase in temperature
may somewhat increase total synthesis gas conversion, tending
to increase the efficiency of ethanol production but
decreases the efficiency of acetic acid and acetaldehyde
production. At the same time, however, higher temperatures
--8--
- D-9406-1
~ ;0~;()4~i7
favor methane production, and apparently methane production
increases much more rapidly at higher temperatures than do
conversions to the more desirable two carbon atom products.
l~us, for a given catalyst and with all other variables
held constant, the optimum temperature will depend more on
product and process economics than on thermodynamic
or kinetic considerations, with higher temperatures tendin~
to increase the production of oxygenated products but
disproportionately increasing the co-production of methane.
In the discussions above the indicated temperatures
are expressed as average, or mean, reaction bed temperatures.
Because of the highly exothermic nature of the reaction,
~t is desirable that the temperature be controlled so as
not to produ~e a runaway methanation, in which methane
formation i8 increased with higher temperature, and the
resulting exotherm increases the temperature further. To
accomplish this, conventional temperature control techniques
are utilized, as for example the use of fluidized bed
reaction zones, the use of multi-stage fixed bed adiaba~ic
reactors with interstage cooling, or relatively small
(1/16th inch or less) catalyst particles placed in
tube-and-shell type reactors with a coolant fluid
surrounding the catalyst-filled tubes.
The reaction zone pressure is desirably within
the range of about 15 psig to about 10,000 psig, economically
w~thin the range of about 300-5,000 psig. Higher reaction
zone pressures increase the total weight of product
obtained per unit time and likewise improve the selectivity
_g_
~ D-9406-l
~ 0~04~7
toward two carbon atom compounds.
The ratio of hydrogen to carbon monoxide in the
synthesis gas may vary widely, and in large measure is
dictated by the process or processes employed to make the
gas~. Normally the mole ratio of hydrogen to carbon monoxide
is within the range of 20:1 to 1:20, or preferably within
the range of about 5:1 to about 1:5. In most of the
experimental work reported herein the mole ratio of the
hydrogen pressure to the carbon monoxide pressure is
somewhat less than 1:1. Increasing the ratio ~ends to
increase the total rate of reaction, sometimes quite
significantly, and has a small but favorable effect on
production of two carbon atom products, but concurrently
lncrea8e8 sele~tivity to methane. Increasing the hydrogen
to carbon monoxide ratio also favors the formation of
more highly reduced products, that i8, ethanol rather than
acetaldehyde or acetic acid.
Impurities in the synthesis gas may or may not
have an effect on the reaction, depending on their nature
and concentration. Carbon dioxide, normally present in
an amount of up to about 10 mole percent, has essentially
no effect. ~f a recycle operation is conducted, in
which all or part of the reacted gas is recycled to the
catalyst zone, it is desirable to remove oxygenated
hydrocarbons before recycling
To provide empirical orientation, a set of ten
experiments, in the form of a two-level, fractional factorial
-10-
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D-9406-1
~ 0~04~
design plus centerpoints, was conducted. The independent
variables were temperature (275 and 300C.), hydrogen and
carbon monoxide partial pressures (350 and 500 psig), and
gas hourly space velocities (3600 and 4700 volumes of gas
at standard conditions per volume of catalyst per hour).
All variables, with the exception of space velocity,
proved to be significant in their influences on the rates
and efficiencies to the principal products, i.e., acetic
acid, ethanol, acetaldehyde, and methane.(Note, ~owever,
that space velocity was varied over a comparatively narrow
range, and in each instance was quite high.) Qualitatively,
the8e responses are indicated in Table III below. In
each instance, the effect of an increase in the specified
variab~e is represented by either one or more positive
or negative signs to characterize the degree of response
of the rate and/or of the efficiency.
-11-
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The results of Table IIT, above, suggest that the
conditions most favorable to high selectivity toward acetic
acid and acetaldehyde are the lowest practical operating
temperature, low hydrogen partial pressure, and high carbon
monoxide partial pressure. Verification of this prediction
is provided in the following data (here and in Table III
utilizing a 5% rhodium on silica catalyst) presented in
Table IV below.
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One of the features of the present invention is
the recognition that a low conversion--preferably less
than 20% of the CO--favors the formation or production of
a substantial proportion of acetic acid, ethanol and/or
acetaldehyde, generally in excess of 10% as compared with a
maximum of 3 4% in the prior art (Table I). This
conversion is conveniently achieved by employing a high
space velocity correlated with other reaction variables
(e.g. temperature, pressure, gas composition, catalyst,
etc ). Space velocities in excess of about 10 gas
hourly space velocity (volumes of reactant gas, at 0C and
760mm mercury pressure, per volume of catalysts per hour)
are generally employed, although it is preferable that the
space velocity bs within the range of about 104 to about
106 per hour. Excessively high space velocity result in
an uneconomically low conversion, while excessively low
space velocities cause the production of a more diverse
spectrum of reaction products, including higher boiling
hydrocarbons and oxygenated hydrocarbons.
The rhodium catalyst is rhodium metal provided
in the reaction zone by a number of techniques, or a
combination of a number of these techniques. One technique
is to coat the reaction zone (or reactor) walls with
rhodium metal. Another is to coat a porous screen or
screens with a thin coating of the metal. Still another
way involves placing particles of rhodium in the reaction
zone, generally supported by an inert porous packing material.
--~ D-9406-1
~O~ ~ 4 ~7
Another way is to deposit rhodium onto a particulate
support material and place the supported rhodium into the
reaction zone. Any combination of these techniques can
be employed.
However, important advantages within the scope
of the invention are achieved when the rhodium metal
catalyst is in a highly dispersed form on a particulate
support. ~n the basis of experience to date the amount of
catalysts on the support should range from about 0.01
weight percent to about 25 weight percent, based on the
combined weight of the metal catalyst and the support
material. Preferably, the amount of catalyst is within
the range of about 0.1 to about 10 weight percent.
A wide variety of support materials has been
tested. A relatively high surface area particulate support,
e.g. one having a surface area upwards of about 1.0 square
meters per gram (BET low temperature nitrogen adsorption
isotherm method), is preferred, desirably upwards of about
1.5 square meters per gram, although surface area alone
is not the sole determinative variable. Based on research
to date, silica gel is preferred as the catalyst base or
support, with alpha alumina, magnesia, eta alumina, gamma
alumina, and active carbon being progressively less
desirable. Zeolitic molecular sieves, primarily the
higher silica-to-alumina crystalline zeolites, also
have promise.
The rhodium metal may be deposited onto the
base or support by any of the techniques commonly used for
-16-
.
.. . .. ~; . . . .
`` D-9406-1
4~7
catalyst preparation, as for example impregnation
from an organic or inorganic solution, precipitation,
coprecipitation, or cation exchange (on a zeolite).
Numerous specific embodiments of catalysts preparatory
techniques are described in the Examples below; it
suffices for the present to say that an inorganic or
organic rhodium compound is appropriately contacted
with the support material, and the support then dried
and heated, the latter advantageously under reducing
conditions, to form the finely dispersed rhodium metal.
The invention in its various aspects is
illustrated in the different "Series" of experiments
presented below. In each instance it will be appreciated
that the tests are exemplary only, and are not intended
to be wholly definitive or exclusive with respect to
scope or conditions of the invention.
SERIES A
This Series illustrates the preparation and testing
of supported rhodium metal catalysts on a variety of high
surface area supports. It also contrasts supported
rhodium with supported iridium, supported ruthenium,
supported palladium, supported platinum, supported
copper, and supported cobalt.
Preparation of Catalysts
Catalysts tested in this study were all prepared
by essentially the same sequence of steps: An aqueous
solùtion of the desired component was impregnated on the
-17-
~ D-9406-1
1(3~04~7
support; the impregnated support was carefully dried;
the metal salt was reduced slowly in a flowing hydr~gen
atmosphere. When metal components were impregnated as
nltrate salts, a pyrolysis step preceeded the hydrogen
reduction step. In most cases, rhodium was impregnated
as a RhCl3 solution.
The description below illustrates this procedure for
the catalyst used in Tests 1-7(5% rhodium on Davison TM
Grade 59 Silica Gel). Table V summarized preparative
details for the catalysts whose activities are described
in this Series.
Thodium trichloride (22.58 gm, 41.93% Rh) was
dissolved in 240 ml of distilled water at ambient temperature.
Davison TM Grade 59 si~ica gel (200.0 gm, 3-6 mesh) was
placed in a vacuum flask. The top of the flask was sealed
with a rubber septum, and the flask was evacuated through the
side arm. A syringe needle was then used to inject the
rhodium solution onto the evacuated support. When addition
was complete, the impregnated support was allowed to stand
at one atmosphere for ca. 30 minutes. It was then carefully
dried in a nitrogen atmosphere: 80C (l hr); 110C (2 hrs);
150C (2 hrs). The dried, impregnated support was placed
in a quartz tube through which hydrogen was continuously
.,
passed. The temperature was raised to 450C and held at
that value for 2 hours. The reduced catalyst was cooled
to ambient temperature in an atmosphere of flowing
nitrogen.
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De~scr~ of Test Reactor
The reactor used in these studies was a bottom-
agitated "Magnedrive" autoclave of the J. M. Berty design
with a centrally positioned catalyst basket and a side
product effluent line. It is of the type depicted in
Figure 1 of the paper by Berty, Hambrick, Malone and Ullock,
entitled "Reactor for Vapor-Phase Catalytic Studies",
presented as Preprint 42E at the Symposium on Advances in
High-Pressure Technology - Part II, Sixty Four~h National
Meeting of the American Institute of Chemical Engineers
(AlChE), at New Orleans, Louisiana, on March 16-20, 1969
and obtainable from AlChE at 345 East 47 Street, New York,
N.Y. 10017. A variable æpeed, magnetically driven, fan
continuously rccirculated the reaction mixture over the
catalyst bed. The following modifications were found to
facilitate operation and inhibit run-away methanation
reactions.
1. Hydrogen feed gas was introduced c~ntinuously
at the bottom of the autoclave through the well for the
shaft of the Magnedrive agitator.
2. Carbon monoxide feed gas was introduced
continuously through a separate port at the bottom of the
autoclave, in order to avoid a hydrogen-rich zone in the
autoclave. When carbon dioxide was fed, it was added
with the carbon monoxide feed stream
Experimentsl
Rhodium catalysts supported on silica gel,
gamma-A1203, and carbon were tested for synthesis activity
-20-
D-9406-1
~ 0~04~7
in a backmixed autoclave described above. Reaction
conditions and salient features of the product distribution
are described in Table VI below. In all cases, the
feed gases included a quantity of carbon dioxide; the
nominal leve] of carbon dioxide in the feed was 5% by
volume, but the actual feed rates achieved probably
varied widely from this value. There was no indication
that carbon dioxide had any effect on the activity or
selectivity of any of the catalysts studied.
Under the conditions of these studies, rhodium
catalysts supported on silica gel had a selective activity
for production of two-carbon, oxygenated compounds.
Carbon efficiency tata are given for ethanol and acetic
acid. Methyl-, ethyl-, and propyl-acetate esters are
also formed (Other work had shown that acetaldehyde
was also produced by these catalysts. Acetaldehyde
production was very poorly reflected in the results
reported here, because the analytical system did not
distinguish acetaldehyde fr~m methanol.) A number of
relatively minor products were also formed. m ese
included methanol, propanol, and propanal. The major
inefficiency in these syntheses was methane.
Those rhodium catalysts for which the support was
gamma-A1203 or carbon also showed significant selectivities
to ethanol and acetic acid. However, these catalysts were
much less active than silica gel supported catalysts at
closely similar reaction conditions, despite the fact that
the Rh dispersion was much higher.
-21-
D-9406-l
1C~j0 ~ 7
A brief study of the RPM of the fan in the
backmixed autoclave was made in Tests 1-4 to determine
the effect of RPM on productivity. Dropping RPM fr~m
1500 to 750 did not affect the productivity; however,
decreasing RPM to 400 did decrease the productivity, An
RPM of 800 was used in all later work.
-22-
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1CNj04~7 D-9406-1
Table VI also reports data on iridium, ruthenium,
palladium, platinum, copper, and cobalt catalysts supported
on silica gel. Testing of these catalysts was carried
out under substantially the same conditions described above
for the rhodium catalysts. Although two-carbon products
were detected, in no case was the productivity comparable
to that observed with rhodium catalys~s.
The iridium catalyst was very inactive. Under
the conditions used, it produced primarily methane.
The ruthenium catalyst was active, but it
produced large quantities of hydrocarbon oil. This oil
production was not surprising; an extensive literature
has documented the use of ruthenium catalysts for synthesis
of high molecular weight hydrocarbons. The results of
Table VI reflect the analysis of the gaseous and aqueous
layer products only.
The copper catalyst was inactive under these
conditions.
The cobalt catalyst produced methane as the
ma;or product.
The data obtained for the platinum and palladium
catalysts showed only very low activity for two-carbon
products. These data were of low quality,
-25-
- . - . . . .
.
-~~ D-9406-l
1()~i04~7
SERIES B `
This Series illustrates the preparation and
testing of a group of supported rhodium metal catalysts,
employing a variety of rhodium c~mpounds and catalyst
supports In the tests, the reaction was carried out in
a one gallon Berty autoclave.
The procedure described below was used in Tests
1-15 recited-in Table VII below. The carbon monoxide
used contained a few percent carbon dioxide. It and the
hydrogen were fed to the reactor in the desired molar
ratio from 4,500 psig headers The carbon monoxide
stream to the reactor was purified in all but tests 1-4~
inclusive, using 1/8 inch activated carbon pellets which
had bee~ dried at 250C in a nitrogen flow overnight.
~ ne hundred eighty milliliters (ml) of catalyst
were placed in the reactor in a perforated basket having
a capacity of approximately 200 ml. The reactor was
pressurized with hydrogen to 2,000 psig and the flows of
carbon monoxide and hydrogen were adjusted to achieve the
desired composition. During the pressurization of the
reactor, the reactor temperature was adjusted to
approximately 25C below that desired for that particular
run.
The pressure was then raised to 2500 psig and
the temperature raised to the desired reaction temperature.
Approxlmately one hour was allowed for the reactor to
come to a steady state before beginning to measure actual
-26-
.. . ...
~ ................................ .
D-9406-1
~ 7
time of reaction. After one hour of reaction, a sample of
liquid product was collected by cooling the product-containing
gals through a brine condenser and then trapping the liquid
product in a series of four traps having a capacity of
approximately one liter per trap. The traps were maintained
in a low temperature bath containing a mixture of dry-ice
and acetone The liquid products from all the traps and the
condenser were then combined to obtain a single liquid
sample, which was then analyzed and the results reported
in the Table below. The non-condensable gases were
metered through a wet-test meter to determine the volume
of gas, and a gas sample was collected to determine its
composition.
After the desired time of reaction, the reactor was
shut down overnight and the catalyst maintained under a
slight hydrogen flow at 600 psig. When testing was
resumed the following day, the reactor was again brought
to the selected set of reaction conditions in the manner
described previously. m erefore the catalyst of Test 1
was stored overnight in hydrogen and then used the following
day under the reaction conditions of Test 2, then stored
overnight under hydrogen, and used the following day for
Test 3 and the same procedure repeated through Test 4.
The period for the reaction of the examples was one hour
except for Tests 9 and 11 where the reactions in Tests 8
and 10 respectively, were allowed to continue three
additional hours ~efore a second sample was taken.
-27-
-- D-9406-1
10~4~7
The fourth hour sample of Tests 8 and 10 are reported as
Tests 9 and 11 respectively.
The following illustrate the preparation and
compositions of the catalysts used in the Table below.
Catalyst A:
Three grams of rhodium carbonyl acetylacetonate
were dissolved in 66 ml o toluene preheated to about ,0~.
The toluene-catalyst solution was added to 200 grams of an
alpha-alumina support in the form of l/8-inch cylindrical
pellets having a surface area characteristic of about
3.5 square meters/gram (m /gm.) The alpha-alumina
support was prepared by heating CONOC ~ N-alumina, obtained
from Continental Oil Co. of New York, N.Y., to 1,200C.
for about 24 hours. The toluene was evaporated from the
impregnated support by drying in a nitrogen purged oven
at 100C.
After removing the toluene, the impregnated support
was heated to 150C. and the temperature held therefor
1-1/2 hours. The impregnated support was then oxidized by
air at 500C. in a tubular furnace for a sufficient time
to remove any remaining organic residue from the catalyst.
The oxidized catalyst was then reduced in the presence of
hydrogen at 300C. to yield a catalyst having a metal
dispersion characteristic of 3.4 percent. (Although
0.6 percent rhodium is the intended metal composition of
the finished catalyst, the actual metal dispersion may be
somewhat higher and the total metal content proportionately
-28-
~ D-9406-1
O4~7
lower depending ~pon the fraction ~f rhodium lost during
the decomposition step by partial vaporization of the
rhodium carbonyl acetylacetonate. Therefore, the metal
composition of the finished catalyst is very likely
somewhere on the order of 0.5 percent rather than the
intended 0.6 percent.)
Catalyst B:
The equipment and techniques used in this
preparation were the same as those used in the preparation
of Catalyst A, except that the metal salt rhodium chlori~e,
RhC13 3H2O, containing 41.4 weight percent rhodium, was
used in place of the rhodium carbGnyl acetylacetonate
used in making Catalyst A. About 3.1 grams of the rhodium
chloride salt were dissolved in approximately 66 ml of
distilled water at room temperature. Inasmuch as the
rhodium chloride c~mpletely dissolved in the water, there
was no need to preheat the water or the support. Impregnation
of the support was done as previously described in the
making of Catalyst A. The support used was a commercially
available alpha-alumina (AL-3920) from Harshaw Chemical
Company of Cleveland, Ohio of 3/16 inch size and
cylindrical shape, having a surface area of approximately
5 m2/g. The impregnated support was then dried in three
successive stages: 85C. for two hours, 200~. for two
hours. The impregnated support was then heated in air at
500C. for two hours and reduced at 500C. in hydrogen for
1.5 hours. me catalyst showed no loss of rhodium metal,
-29-
D-9406-l
~0~04~7
which is believed due to the use of the inorganic rhodium
salt. The finished catalyst had a rhodium metal concentration
of about 0 6 percent.
Catalyst C:
This involved the use of the rhodium organic salt
of Catalyst A on the Harshaw alpha-alumina support of
Catalyst B. The preparation procedure was the same as
that used in Catalyst A except that the mixture was
reduced, after the oxidation step, at 500C. for two hours
before charging it to the reactor. The finished catalyst
showed a percent dispersion of 7.5 per cent and a rhodium
content of 0 6 percent.
Catal~st D:
12.46 grams of the metal salt rhodium chloride
was dissolved in 120 ml of distilled water at room
temperature. m is solution was then used to impregnate
100 gms. of DavisonTM, grade 59, silica gel, obtained from
Davison Chemical Co. of Baltimore, Maryland. The support
;~ was then dried sequentially, at 80C. for 1-1/2 hours, 110C.
for 1.5 hours, and 150C for 3.0 hours. me dried,
impregnated support was then heated at 400C. for two
hours, cooled in air at 100C., and then heated in
hydrogen up to 300C. for 3.0 hours. me finished catalyst
had a rhodium content of 5 per cent on the DavisonTM,
grade 59, silica gel and a percent dispersion of
15,6 percent.
-30-
~ D-9406-1
CatalYst E: 1CHj0~7
This involved the use of the rhodium organic salt
of Catalyst A on the silica gel support of Catalyst D. The
preparation and procedure used are the same as that used
in Catalyst A except that the catalyst was dried at 105C.
for 2.5 hours and then heated immediately to 150~C. for 3
hours. The dried catalyst was then oxidized at 500C. for
1.5 hours and reduced in the presence of hydrogen at 500C.
for 1.5 hours. The finished catalyst should have a
rhodium content of 0.6 percent on DavisonTM, grade 59,
~ilica gel and a percent metal dispersion of 15.3 percent.
-31-
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-32 -
D-9406-1
1~04~7
Percent metal dispersion, as used herein, is
defined as the percentage of metal atoms exposed on the cata-
lyst surface as ¢ompared to the totalnumb~r of metal atoms
deposited. The per cent metal dispersion was obtained by
determining the chemisorption of carbon monoxide at room
temperature on a clean metal catalyst surface, and then
calculating the number of exposed surface atoms by
assuming that one carbon monoxide molecule is chemisorbed
per surface metal atom. These analytical pr~cedures
can be found in S. J. Gregg and K. S. W. Sing~
Adsorp ion Surface Area And Porosity, where C0 adsorption
is described at pages 263-267 and the dynamic gas
chromatographic technique is described at pages 339-343.
The surface purity of the catalyst was measured by
Auger Spectroscopic Analysis. The analysis of product
and unreacted gases was accomplished by the use of gas
chromatographic analysis of the various liquids and
gases.
Tests 1 through 15 of Table VII were conducted
at an early investigative stage of the present invention
when reproduceability of metal catalyst activity was a
problem. Auger Spectroscopic Analysis of the various
fresh and used catalysts of the examples indicated that the
inability consistently to produce a particular product
distribution could be attributed to the presence of iron
and/or nickel impurities on the surface of the used
catalyst. There is no direct evidence that iron and/or
-33-
D-9406-1
~04~7
nickel impurities preferentially attached themselves tO
the surface of the metal catalyst; however, it appears
to be highly probable that this did occur. For example,
the ùse of argon ion sputtering of an impure catalyst
indicated that as the iron signal decreased several fold
the rhodium signal increased ~omewhat. If the iron did il.
fact attach itself to the surface of the metal catalyst,
it very likely would be in the form of iron metal or iron
oxide as a result of its reaction with water. The presence
of iron on the metal surface woùld explain the low values
of rhodium dispersion measured by carbon monoxide
chemisorption. Inasmuch as iron and nickel are known
methanation catalysts, this could possibly account for the
high amount of methane found in some of the examples.
Installation of activated carbon traps in the carbon
monoxide feed gas stream helped reduce the amount of iron
and nickel present during the reaction.
The effect of increasing reaction temperature,
studied in Tests 1 through 4 of Table VII was to increase
overall productivity, to increase methane formation, and
to increase the ratio of ethanol to methanol obtained
while the ratio of the yield to acetic acid plus
ace~ates remained about constant.
Changing the source ofthe rhodium on the cataly~t
support from carbonyl acetylacetonate to rhodium chloride
did not alter the product spectrum nor did it appear to
affect the level of conversion of products as illustrated
-34-
D-9406-1
~0~()4~7
by Tests S and 6 in Table VII. The lower overail
activity of the catalyst derived from rhodium carbonyl
acetylacetonate can be explained in terms of its lower
dispersion and/or lower rhodium metal content. The
lower yield of acetates in the rhodium chloride preparation
run is primarily due to the lower partial pressure of
carbon monoxide, which tends to favor the production of
ethanol over acetic acid andacetates.
Increasing the rhodium concentration from 0.6
percent to 5 percent on the support increased the reaction
rate and the product yield,
The effect of carbon monoxide and hydrogen partial
pressures and of c~talyst aging are illustrated in Tests 7
through 11. The tests show that a high ratio of carbon
monoxide to hydrogen favors the formation of acetic acid
while a low ratio of carbon monoxide to hydrogen favors the
formation of ethanol. Production of higher alcohols was
minimal in both cases. Increasing the partial pressure of
carbon monoxide from 25% to approximately 75% decreased
methane formation while increasing the yield of total acetic
acid and acetates substantially. Carbon efficiency to
useful liquid products at high carbon monoxide partial
pressures (75%) was about 64% while carbon efficiency at
low carbon monoxids partial pressures (25%) was about 35%
as shown in Tests 7 through 11.
It can be seen fr~m Tests 8, 9 and 12 that the
activities of catalysts containing different levels of rhodium
-35-
D-9406-1
1 0t~ 7
but having similar metal dispersions increase as the
amount of rhodium present increases.
-36-
D-9406-1
1o~i0 4
SERIES C
This Series illustrates the effects of reaction
temperature and catalyst age on product distribution.
The same procedure and equipment used for the
tests in Table VIII were used for all the tests in Table VIII
except for the following conditions which were held constant:
the pressure was 2500 psia; feed gas c~mposition was 77%
volume CO, 20% H2 and 3% CO2; reactant feed rate was 600
liters/hour; and there was a one (1) hour reaction time.
The catalyst used in Tests 16 through 33 of
Table VIII was Catalyst D, above, i.e., rhodium, at a
concentration of 5 percent, on a DavisonTM, grade 59,
silica gel 8upport. In Table VIII, after tests 18 and
21, the catalyst was stored overnight at 250C in a 600
p8ig carbon monoxide atmosphere. After Test 23, the
catalyst was stored for two days at 285C in a 2000 psig
carbon monoxide atmosphere. After Test 26, the catalyst was
stored overnight at 300C in a 600 psig hydrogen atmosphere.
The catalysts used in Tests 16 and 29 are freshly prepared
and were then reduced with hydrogen in the reactor before
the reaction was commenced. The catalyst used in each
test, other than for Tests 16 and 29, was obtained from the
preceeding test.
The results reports in Table VIII indicate a
substantial shift in catalyst performance as time progressed.
The catalyst became more selective to the production of
ethanol and less selective toward methane production
-37-
lC~04~7 D-94~6-]
with age. The molar ratio of acetic aci~ to ethanol
producecl decreased from a high of 63 in Test 16 to less
t:han one (1) in Tests 24 through 28. This change in
catalyst selectivity can perhaps best be explained by
th~ presence of iron found in the recovered catalyst.
Sur~ace lron of 1.2 atomic percent was detected by
Auger atomic analysis on the recovered catalyst of Test 28
while no iron was detected on the unused catalyst. The
atomic percent ratio of rhodium to iron for the used
catalyst of Test 28 was 12.2, The atomic percent ratio
of Rh to Fe for the used catalyst from Test 33 was 40. The
iron contamination probably arises through the generation
of iron carbonyl from the reactor walls and its subsequent
decomposition on the catalyst surface. This suggests that
by purposely contaminating the catalyst with iron one
provides a process which favors ethanol production.
me decrease in methane production in the results
reported in Table VIII as compared with that of Table VII
is perhaps due to the absence of nickel on the surface of
the catalysts of Table VIII.
-38-
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10~04~7 D-9406-1
SERIES D
A series of studies were designed to determine the
effect of space velocity on the product distribution over
rhodium catalysts. These experiments were directed toward
the more inclusive goal of a better definition of the
reasons for the differences between the process of this
invention and descriptions in the prior art.
Modifications to the reactant gas feed system to
the Berty reactor permitted operation in a well-controlled
manner at space velocities of about 400-500 hr 1. Most
previous experlmentations hsd been with space velocities
in the range 800-3000hr 1.
Additionally, it was found possible to operate the
back-mixed Berty reactor (internally goldplated) in a
quasi-static mode. This involved manually closing valves
to stop all flow of reactants into the reactor. Flow of
gas out of the reactor was controlled by a pressure-
actuated valve whose leakage rate proved to be low
(0.5-3.0 STP l/hr). Several experiments were conducted
with the reactor sealed in this manner and maintained at
reaction conditions of pressure and temperature.
Reactant gases were added as needed by manual manipula-
tion in order to maintain the total pressure near the
desired nominal value. Liquid samples were collected by
purging small volumes of gas from the reactor through the
-40-
'~ D-9406-1
~ 4 ~7
condenser in the product gas line.
Three catalysts were studied in both the low space
velocity and the quasi-static operating modes. Many of
these esperiments attempted to study the product distri-
bution obtained at low synthesis temperatures and low
reaction rates. Moreover, the major objective was to
study the product distribution at conditions of high
conversion. The relevant catalysts studied wPre:
(1) 5% rhodium on Davison 59 silica gel; and (2) powder-
ed, bulk rhodium metal prepared by in situ reduction ofrhodium oxyhydrate (prepared by Soufi's method for making
"Catalyst D", pagè 23 of dissertation). The rhodium
oxyhydrate was charged to the reactor in a "jelly-roll"
of glass wool and ~tainless steel screen.
The silica-gel-supported rhodium catalyst was
studied at 2500 psi and temperatures of 200, 250, 300,
~nd 325C. Several (7 out of 34) of the liquid product
samples contained measurable quantities of hydrocarbon
oil. Here too the product distributions were generally
similar to the usual experience with two-carbon products
greatly exceeding longer chain organics. However, in
two cases (out of 34), the yield of heavies exceeded the
yield of two-carbon products, and in several more cases
the yield of heavies was more than 20% of the yield of
two-carbon products (weight basis). In general, these
results provide only weak support for the original hypo-
,
D-9406-1
1 0~ 0 4 ~ ~
thesis that longer c~ain products result from long contact
times and high conversions.
Unsupported rhodium was studied at 2500 psi and
temperatures of 160, 200, 300, and 325C. Quæsi-static
experiments were made at 300 and 325C. The experiments
at 160 and 200C produced only very small qusntities of
products ~nd these products contained m~ch more two-
carbon products thsn heavies. The experiment~ at 300 and
325C were distinctly different. The productivities were
greater, and the quantities of heavies were almost always
~ubstantially (2- to 8-fold) greater than the quantities
of two-carbon products. Fiv~ out of 22 s~mples contained
me~surable quantitie8 of oil. Ihe proportlon of heavles
W~8 very ~ubstantially le88 than that reported by Soufi,
however. It would appe~r that the form in which the
rhodium ig introduced is spparently not the only factor
which dete~mines the product distribution. Comparison of
these results to those reported by Soufi implies that
either reaction condition~ (notably temperature, GHSV, and
extent of conversion) or other unitent~fied factors also
strongly influence the product distributlon.
The Table below summa~izes results in a somewhst
over-simplified form.
-42-
D-9406-l
04~7
Comparison of Product Distributions
Catalyst C3 1 2 (wel~t ~atio)***
5% Rh on D 59 ca. 0.5 to 0.05*
Rh black (UCC) ca. 5.*
~h black (Soufi Thesis) ca. 170.**
* ca. 2H2 per C0 at 2500 psi. Temperature ca. 300C -
** 2H2 per C0 at 7500 psi. Temperature 160C
***The ratio of the sum of the weights of three and higher
number carbon products and the sum of the weights of
acetaldehyde, ethanol and acetic acid.
-43-
- D-9406-1
10~0467
SERIES E
This series illustrates prelLminary tests, utilizing
a silver plated reactor of the type employed in the previous
Series, to study the effect of reaction temperature on
product di~tribution.
Except for the silver plating of the reactor, and
for the following recited conditions, the equipment and
procedure in experiments A through J were the same as
those used in the previous Series above. All of the
experiments A-J were made using a fresh 60 gram sample of
Catalyst D above, i.e., 5 percent rhodium on Davison TM,
grade 59, silica gel, at 2,500 psig, a feed gas composition
of 3 moles of carbon monoxide per mole of hydrogen and
a feed ga~ rate of 450 liters/hour. The C0 feed gas of
experiments A through K contained about 3 to 5 mole
percent C02
In each experiment the reaction was allowed to
proceed for one hour before a sample was taken for analysis
or the reactor was shut down overnight. Experiments A
and B were consecutive one hour runs, i.e., there was no
shut down of the reactor after the first sample but the
reaction was allowed to proceed for one more additional
hour before sample B was taken. A~ter experiment B, the
reactor was shut down and the catalyst was stored overnight
in the reactor at 250C., under a 600 psig H2 atmosphere
and a slight H2 flow through the reactor before being used
in experiment C. Experiments C through F were four
consecutive one hour runs. After experiment F, the
catalyst was removed from the reactor and heated at 350C.
in air for 2.5 hours and then reduced overnight in the
-44-
.
D-9406-1
1()~04f~'7
reactor at 200C. and a H2 pressure of 500 psig. The cata-
lyst from experiment F was then used to make the consecutive ~.~
one hour runs of experiments G and H. A fresh sample -
of Catalyst D above was used on the two consecutive
one hour runs of experiments I and J.
Auger analysis of the used catalyst of experiment
F showed sulfur at levels of 10 to 15 atomic percent of
that surface. rhodium. The reason for the presence of
sulfur is presently unaccounted for. .-
.:
.
.
:
-45-
1()~04~'7
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