Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
Ref.No 20060124-003
Cross Reference to Related Applications
[001] This application claims priority to U.S. Patent Application 60/684,462 filed on May 25,
2005, and is a continuation in part of PCT Patent Application Serial Number PCT/US02/15310 filed on
May 15, 2002, currently pending, and of U.S. Patent Application 10/343,935 filed on February 3,2003,
currently pending, these applications being incorporated herein in their entirety by reference.
Background
[002] The present invention is for a method for producing a high surface area iron material
starting with a low surface area iron metal. The iron material of the present invention has a surface area
of at least about 200 m2/g, and is prepared via a method which comprises reacting a low surface area iron
metal with oxygen and an organic acid. The high surface area iron material formed via this method is
essentially free of contaminants.
[003] Iron-based catalysts are known in the art for use in a variety of chemical reactions. For
example, in water gas shift reactions it is common practice to employ chromium-promoted iron catalysts,
in a high temperature first stage (referred to as a high temperature shift or HTS reaction) to effect carbon
monoxide conversion at temperatures above about 350°C and to reduce the CO content to about 3% - 4%
(see, for example, D.S. Newsom, Catal. Rev., 21, p. 275 (1980)). A typical composition of high
temperature shift (HTS) catalyst comprises from about 60 wt% to about 95 wt% Fe^, from about 0 wt%
to about 20 wt% Cr2O3 from about 0 wt% to about 10 wt% of CuO and from about 0 wt% to about 10
wt% other active components such as ZrO2, TiO2, CO3O4, Al2O3, SiO2 and/or CeO2.
[004] Since the 1950's iron-based Fischer-Tropsch catalysts have been successfully used in
fixed-bed, fluidized-bed and slurry phase reactors, and there have been several methods used for the
preparation of iron-based Fischer-Tropsch catalysts. The earliest catalysts, prepared by Fischer, were iron
turnings treated with alkali. At high pressure, the liquid product was rich in oxygenated compounds, and
at lower pressures hydrocarbons were produced. However, the iron-based catalysts prepared by this
method deactivated rapidly.
Page 1

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
Ref.No 20060124-003
[005] The most common method of preparation of iron-based Fischer-Tropsch catalysts is
precipitation. Typically a solution of an iron salt, such as ferric nitrate, is treated with a base, such as
aqueous ammonia or sodium carbonate. The resulting iron oxyhydroxide precipitate is washed and
filtered repeatedly to remove salts - ammonium nitrate or sodium nitrate - formed during the
precipitation process. The washed filter cake is then dried and calcined. Promotion of the precipitated
iron catalyst with copper and a Group I metal can be done at any time, before or after the drying and
calcination steps. The final catalyst precursor is usually composed of high surface area corundum phase
iron oxide (-Fe2O3 or hematite).
[006] Other types of iron based catalysts include, fused iron, supported iron and sintered iron.
Fused iron catalysts are prepared by melting iron ore and one or more promoter such as SiO2, A12O3, CaO,
MgO and K2O. The resulting catalyst precursor is usually composed predominantly of magnetite (Fe3O4)
and has very low surface area. Active fused iron catalysts can only be achieved by reduction of the oxide
to metallic iron with hydrogen. The reduced catalyst can have surface area up to about 10 to 15 m2/g.
Fused iron catalysts are characterized by high structural integrity and as such are well suited for fluid bed
operations; however, the relatively low surface area results in a Fischer-Tropsch catalyst with inferior
activity as compared to typical precipitated iron catalysts. Supported iron catalysts are usually prepared
by impregnating a solution of an iron salt onto a refractory metal oxide such as Al2O3, SiO2, TiO2 or ZrO2.
The impregnation can be carried out by incipient wetness techniques or by excess wetting followed by
vacuum drying. Supported iron catalysts can have Fischer-Tropsch activity similar to precipitated iron
catalysts on an iron mass basis; however, they are typically inferior on a catalyst volume basis. Supported
iron catalysts inevitably suffer from the acidity of the metal oxide supports which increases the selectivity
of undesirable methane.
[007] Precipitated iron catalysts are generally regarded as superior Fischer-Tropsch catalysts to
the other types of iron catalysts described herein. The major disadvantages of the manufacture of
precipitated iron catalysts include high cost, the method is labor intensive, and the by-products are
deleterious to the environment. Iron nitrate is the preferred iron source of precipitated iron catalysts
Page 2

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
Ref.No 20060124-003
because chloride and sulfur contamination from iron chloride or iron sulfate would have a deleterious
affect on the activity of the resulting F-T catalyst Iron nitrate is manufactured by the digestion of iron
metal in nitric acid which produces nitrogen oxides that must be recovered by a scrubbing process. This
necessary scrubbing step adds additional cost to the process.
[008] A process to produce iron-based Fischer-Tropsch catalysts that reduces or eliminates the
washing and filtration steps and has minimal emissions to the environment would be favorable. A logical
process from a commercial viewpoint would be to promote, form, dry and calcine a commercially
available iron oxide that has high purity and high surface area. Commercial iron oxides are readily
available; however, they are usually prepared by treatment of steel with hydrochloric acid or sulfuric acid.
These iron oxides contain significant amounts of impurities including chloride and sulfur which makes
them unusable as raw materials for Fischer-Tropsch catalysts. As is known in the art, the impurities of
the commercial iron oxides (red or yellow iron oxides) can be reduced to a very low level by the pickling
process under very high temperatures. However, because of the extreme conditions of the pickling
process, the surface area of the iron oxide is generally less than 10 m2/g making the iron oxide unsuitable
for some catalyst applications, for example, low temperature Fischer-Tropsch reaction.
[009] Alternatively, a low contaminant iron oxide material may be used, such as the iron oxide
taught in US. Patent 6,790,274 (issued to Conca et al. on Sept 14, 2004, and assigned to Sud-Chemie
MT), U.S Patent Application 20040009871 (inventors Hu et al., published on January 15,2004) and U.S.
Patent Application 20040202606 (inventors Conca et al, published on October 14, 2004), all three
documents being incorporated in their entirety by reference. However, the iron oxides produced by the
process taught in the '274 patent, the '871 application and the '606 application have surface areas of less
than about 150 m2/g.
Page 3

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
Ref.No 20060124-003
Summary of the Present Invention
[0010] A high surface area iron material is prepared from a low surface area iron metal. The
iron material of the present invention has a surface area of at least about 200 m2/g, and is essentially free
of contaminants. The method for preparation of the iron material comprises reacting iron metal with a
mild organic acid and oxygen. In a preferred embodiment, the reaction temperature is maintained at from
about 0°C to about 40°C in the reaction tank with a condenser temperature of from about 0°C to about
5°C. The reaction solution is well-agitated, and optionally, a defoaming agent may be added. The
resulting iron oxide slurry is then filtered, re-slurried and refiltered. The resultant filter cake is dried to
form the high surface area iron material. Because the process uses iron metal, (he level of potential
contaminants, such as sulfur and chlorine, can be kept to a minimum by starting with clean metal.
Further, by starting with iron metal, there are no residual materials which need to be removed by washing
the iron oxide filtrate.
Detailed Description of the Preferred Embodiments
[0011] The high surface area iron material of the present invention is intended for use in any
iron-based catalyst requiring a high surface area. The iron material differs from the iron oxides of the
prior art by having a surface area of at least about 200 m2/g. Further, the process by which the iron
material is prepared is novel and produces an iron material that is essentially free of contaminants, and
which has a relatively narrow particle size distribution range, and a high surface area, and which can be
produced more efficiently than iron oxide materials of the prior art.
[0012] Broadly presented, the process for preparing a preferred embodiment of the iron material
of the present invention includes directly treating iron metal with a mild organic acid and oxygen while
vigorously agitating the mixture to form a shiny consisting of iron oxyhydroxide, iron hydroxide, iron
oxide hydrate, or the other amorphous or poorly ordered iron phases, then filtering the slurry to produce a
filter cake, then reshirrying the filter cake and refiltering the slurry, and then drying the filter cake. More
Page 4

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
Ref.No 200(50124-003
specifically, to prepare the iron material of the present invention, water is added to a temperature-
controlled reaction vessel fitted with a condenser and chiller, and having a means for mixing or similarly
agitating the contents of the vessel. The reaction vessel is held at a temperature of from about 0°C to
about 40°C and is fitted with a condenser held at from about 0°C to about 5 °C. Iron metal is added to the
reaction vessel and the vessel is purged with an inert gas. As the iron and water are agitated and while
maintaining the inert atmosphere, an organic acid is added to the vessel. After the acid / iron combination
is mixed for a predetermined period of time under the inert atmosphere, oxygen is added to the reaction
vessel with vigorous agitation. Optionally, a defoaming agent may further be added to the vessel as
needed either at the beginning of the oxidation step or during the oxidation step. After a predetermined
amount of oxygen has been added to the reaction vessel, the resultant slurry is filtered. The slurry filter
cake is then added to water, reslurried and the slurry is filtered. The filter cake is men dried to produce
the nigh surface area iron material.
[0013] The iron metal may be a powder, granule, sphere, chip, shard, needle or oiher form of
iron metal, and has a surface area of less man about 25 m2/g, and is essentially free of contaminants. As
described herein, the iron metal has an average diameter of from about I to about 500µ. (As used
herein, the term micron (µ) means a metric distance equal to one millionth of a meter and is used
interchangeably with micrometer.) However, iron metal with a larger average diameter may be used, but
the reaction time may need to be altered (increased) to ensure that the iron metal has adequate time to
react. In one embodiment, the iron metal is in micro-spheroidal form with an average diameter of from
about 40µ. to about 150µ. Further, the iron metal should be essentially contaminant-free, although traces
of carbon, manganese, nickel, copper, silicon and combinations thereof, may be present (As used herein,
"traces" is defined as less than about 1.5 wt% for all the elements combined)
[0014] The organic acid is preferably a carboxylic acid having at least one carboxylic acid group
with a pK, at ambient temperature of from about 0.5 to about 6. (As used herein, the term "ambient"
refers to average room temperature or to a temperature of from about 18°C to about 22°C.) For example,
Page 5

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
~Ref.No 20060124-003
formic acid, acetic acid, glycolic acid, oxalic acid, pyruvic acid, malonic acid and propionic acid may be
used in the reaction. In a preferred embodiment, the organic acid is glacial acetic acid. The acid to iron
ratio may vary. In the present invention, the acid to iron mole ratio is preferably between about 0.1 acid
per 1 iron to about 2.5 acid per 1 iron.
[0015] The inert gas can be any non-reactive material known in the art, such as nitrogen gas or
argon gas. Normally, nitrogen gas is used commercially because of its relatively low cost
[0016] The defoaming agent can be any organic or silicone based defoaming agents, such as oils,
oily alcohols, alcohols, esters, ethers, glycols, polysiloxanes, dimethylpolysiloxane, C8 to C12 alcohols and
a combination thereof. In a preferred embodiment, a long chain oxygenated hydrocarbon, such as
octanol, decanol and polyethylene glycols and a combination thereof can be used.
[0017] The oxidizing agent is preferably oxygen which is forced through the solution via the
hollow shaft of the mixer such that the oxygen flows through the shaft and is discharged underneath the
impeller, or via a stainless steel sparger mounted within a mix tank, however, a variety of other means as
are known in the art may be used to bubble oxygen through the acid / iron combination. The oxygen must
be well dispersed throughout the entire volume of the solution in order to produce the desired high surface
area iron material. In a preferred embodiment, the mixer is equipped with multiple impellers for gas
dispersion and solid mixing, including a radial flow gas dispersion impeller and an axial flow solid
mixing impeller. The oxygen flow is continued and the reaction temperature is held at less than about
40oC until essentially all the free iron is consumed and an iron material slurry is formed. The slurry is
believed to comprise iron oxide hydrate, iron oxide, iron hydroxide, iron oxyhydroxide, amorphous or
poorly ordered phases in a general formula of FexOy(OH)z and a combination thereof. Total iron
consumption time can range from about 18 hours to about 24 hours, or longer depending on the iron
source. During the course of the reaction, the slurry color changes from gray to brown. Typically, the
color change will be evident from about 45 minutes to about 6 hours after the oxygen flow is started.
Unreacted iron can be detected by X-ray diffraction patterns.
Page 6

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
Ref.No 20060124-003
[0018] The following example illustrates and explains the present invention, but is not to be
taken as limiting the present invention in any regard.
[0019] Example 1: A sample of high surface area iron material is prepared by the inventive
method presented herein as follows: A stainless steel air sparger is fitted into the bottom of a 3 liter
jacketed vessel and the temperature is adjusted to hold at about 30°C. About 700 mL of deionized water
is added to the vessel and agitation is started at a mix rate of about 600 RPM. About 93.3g of iron
powder (commercially available from Hoeganaes and designated by product code ATW-432, and having
an iron metal surface area of about 02 m2/g) is added to the water with mixing. The iron powder is added
slowly enough to maintain a reaction temperature of less than about 30°C. A nitrogen purge is started at a
rate of about 35 liters per hour. About 50.4g of glacial acetic acid (commercially available from Fisher
Chemicals) is added to the iron and water mixture with a continuing nitrogen purge. After about a four
hour nitrogen purge, the nitrogen is replaced by a pure oxygen gas flow at a rate of about 50 liters per
hour and is maintained for about 20 hours. As needed during the oxygen addition, 0.7g 1-octanol
(commercially available through Sigma Chemicals) and / or 0.75g 1-octanol plus 0.35g 1-decanol
(commercially available through Sigma Chemicals) is added to the vessel to reduce foaming. The iron
material slurry is then filtered over no. 42 filter paper. The filter cake is then resluiried with about 3000
mL of deionized water and the mixture is filtered a second time. The filter cake is then dried for about 16
hours at about 120°C. The single point surface area (out-gassed at 150°C for about 1.5 hours) is about
200m2/g.
[0020] Example 2: A sample of high surface area iron material is prepared by the inventive
method presented herein as follows: A 0.9 liter jacketed vessel, equipped with a hollow shaft stirrer and
three vertical stainless steel buffles, about 113 mm long, about 16 mm wide and about 2 mm thick is used.
The temperature is adjusted to hold at about 30°C, about 300 mL of deionized water is added to the vessel
and agitation is started at a mix rate of about 450 RPM. About 40g of iron powder (commercially
available from POMETON and designated by product FERCHM RI 63/3.2, and having an iron metal
Page 7

Title: High Surface Area Iron Material Prepared From a Low Surface Area Iron Metal Precursor
Inventors: Petrini, et al.
-Ref:No 20060124-003
surface area of about 0.1 m2/g) is added to the water with mixing. The iron powder is added slowly
enough to maintain a reaction temperature of less than about 30°C. A nitrogen purge is started at a rate of
about 25 liters per hour. About 11.7g of glacial acetic acid (commercially available from Riedel de Haen-
Germany) is added to the iron and water mixture with a continuing nitrogen purge. After about a four
hour nitrogen purge, the nitrogen is replaced by a pure oxygen gas flow at a rate of about 25 liters per
hour and is maintained for about 20 hours. The gas flow was supplied on the top of the reactor. The iron
material slurry is then filtered over no. 42 filter paper. The filter cake is then reslurried with about 300
mL of deionized water and the mixture is filtered a second time. The filter cake is then dried for about 16
hours at about 140°C. The single point surface area (out-gassed at 110°C for about 1.5 hours) is about
290 m2/Vg.
[0021] The iron material of the present invention is intended for use in any catalyst requiring a
high surface area iron. The process by which the material is prepared produces a finished product
essentially free from contaminants, and having a relatively small particle size distribution range, and a
high surface area. It is understood that the specific processing conditions may be varied without
exceeding the scope of this development
Page 8

12/19/2006 12:38 PM FROM: 602-2. 413 J L Simunic, Baq TO; 011-41-22-338-82-70 PAGE. ,8 OF 009
REPLACEMENT SHEET
We therefore claim:
11. A method of making an iron material, said method comprising:
a) adding water to a temperature-controlled reaction vessel fitted with a condenser and
chiller, and having a means for agitating the contents of the vessel;
b) adding iron metal to said vessel with agitation;
c) purging said vessel with an inert gas while maintaining agitation;
d) forming an organic acid / iron combination by adding an aqueous organic acid to said
vessel with continued agitation and while maintaining the inert atmosphere;
e) agitating said organic acid / iron combination for a predetermined period of time
under the inert atmosphere;
f) stopping said inert gas purge and forcing an oxidizing agent through said acid
solution until said iron metal is consumed and an iron material slurry is formed;
g) filtering said iron material slurry and retaining a first filter cake;
h) adding said first filter cake to water to form a second iron material slurry,
i) filtering said second iron material slurry and retaining a second filter cake; and
j) air drying said second filter cake to produce an iron material having a surface area of
at least 200 m2/g.
12. The method of Claim 11 wherein the vessel is held at a temperature of less than 40°C fitted
with a condenser held at 5°C.
13. The method of Claim 11 wherein said iron metal is selected from a powder, granule, sphere,
chip, shard or needle.
14. The method of Claim 13 wherein said iron metal has an average diameter of from lu to 500u.
15. The method of Claim 11 wherein said oxidizing agent is delivered to said acid solution via a
hollow shaft mixer in which oxygen flows through the shaft and is discharged underneath the
impeller.
16. The method of Claim 11 wherein said means for agitating the contents of the vessel are
multiple impellers for gas dispersion and solid mixing.
Page 9

12/19/2006 12:38 PM FROM: 602-2. 413 J L Simunic, Baq TO; 011-41-22-338-82-70 PAGE. ,8 OF 009
REPLACEMENT SHEET
17. The method of Claim 11 wherein said multiple impellers consists of a radial flow impeller
and an axial flow impeller.
18. The method of Claim 11 wherein said inert gas is nitrogen.
19. The method of Claim 11 wherein said organic acid is a carboxylic acid having at least one
carboxylic acid group with a pK, at ambient temperature of from 0.5 to 6.
20. The method of Claim 11 wherein said organic acid is selected from the group consisting of
formic acid, acetic acid, glycolic acid, oxalic acid, pyruvic acid, malonic acid and propionic
acid, and a combination thereof.
21. The method of Claim 11 wherein said organic acid is glacial acetic acid.
22. The method of Claim 11 wherein the mole ratio of acid to iron ranges from 0.1 acid : 1 iron to
2.5 acid : 1 iron.
23. The method of Claim 11 wherein said oxidizing agent is oxygen.
24. The method of Claim 11 further including the addition of a defoaming agent concurrent with
the addition of said oxidizing agent.
25. The method of Claim 24 wherein said defoaming agent is selected from the group consisting
of an organic defoaming agent, a silicone based defoaming agent, an oil, an oily alcohol, an
alcohol, an ester, an ether, a glycol, a polysiloxane, a dimethylpolysiloxane, a C« to C12
alcohol, and a combination thereof.
26. The method of Claim 25 wherein said defoaming agent is polyethylene glycol, octanol,
decanol or a combination thereof.
Page 10

A method for producing a high surface area iron material starting with a low surface area iron
metal is disclosed. The iron material of the present invention has a surface area of at least about 200
m2/g, and is prepared via a method which comprises reacting a low surface area iron metal with oxygen
and an organic acid. The high surface area iron material formed via this method is essentially free of
contaminants.