Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED CATALY8T8 FOR THE MANQFACTURE OF CARBON
FIBRIhB AND METHODS OF 08E THEREOF
BACKGROUND OF THE INVENTION
Carbon fibrils are vermicular carbon deposits
having diameters less than.500 nanometers. They exist in
a variety of forms, and have been grepared through the
catalytic decomposition of various carbon-containing
gases at metal surfaces.
Tennent, U.S. Patent No. 4,663,230, describes
carbon fibrils that are free of a continuous thermal
carbon overcoat and have multiple graphitic outer layers
that are substantially parallel to the fibril axis. They
generally have diameters no greater than 0.1 micron and
length to diameter ratios of at least 5. Desirably they
are substantially free of a continuous thermal carbon
overcoat, i.e., pyrolytically deposited carbon resulting
from thermal cracking of the gas feed used to prepare
them.
Tubular fibrils having graphitic layers that
are substantially parallel to the microfiber axis and
having diameters broadly between 1.0 and 100 nanometers
have been described in the art.
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Fibrils are useful in a variety of
applications. For example, they can be used as
reinforcements in fiber-reinforced composite structures
or. hybria composite structures (i.e. composites
containing reinforcements such as continuous fibers in
addition to fibrils). The composites may further contain
fillers such as a carbon black and silica,, alone or in
combination with each other. Examples of reinforceable
matrix materials include inorganic and organic polymers,
ceramics (e.g., lead or copper). When the matrix is an
organic polymer, it may be a thermoset resin such as
epoxy, bisamaleimide, polyamide, or polyester resin.; a
thermoplastic resin; or a reaction injection molded
resin. The fibrils can also be used to reinforce
15. continuous fibers. Examples of continuous fibers that
can be reinforced or included in hybrid composites are
aramid, carbon, and glass fibers, alone, or in
combination with each other. The continuous fibers can
be woven, knit, crimped, or straight.
The composites can exist in many forms,
including foams and films, and find application, e.g., as
radiation absorbing materials (e. g., radar or visible
radiation), adhesives, or as friction materials for
clutches or brakes. Particularly preferred are fibril-
reinforced composites in which the matrix is an
elastomer, e.g., styrene-butadiene rubber, cis-1,4-
polybutadiene, or natural rubber.
In addition to reinforcements, fibrils may be
combined with a matrix to create composites having
e~anced thermal, and/or electrical conductivity, and/or
optical properties. They can be used to increase the
surface area of a double layer capacitor plate or
electrode. They can also be formed into a mat (e.g., a
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paper or bonded non woven fabric) and used as a filter,
insulation (e. g., for absorbing heat or sound),
reinforcement, or adhered to the surface of carbon black
to form "fuzzy" carbon black. Moreover, the fibrils can
be used as an adsorbent, e.g., for chromatographic
separations.
Fibrils are advantageously prepared by
contacting a carbon-containing gas with a metal catalyst
in a reactor at temperature and other conditions
.sufficient to produce them with the above-described
morphology. Reaction temperatures are 400-850C
more
,
preferably 600-700C. Fibrils are preferably prepared
continuously by bringing the reactor to the reaction
temperature, adding metal catalyst particles, and then
continuously contacting the catalyst with the carbon-
containing gas.
Examples of suitable feed gases include
aliphatic hydrocarbons, e.g., ethylene, propylene,
propane, and methane; carbon monoxide; aromatic
hydrocarbons, e.g., benzene, naphthalene, and toluene;
and oxygenated hydrocarbons.
Preferred catalysts contain iron and,
preferably, at least one element chosen from Group V
(e.g., vanadium), Group VI (e.g. molybdenum, tungsten,
or
chromium), Group VII (e. g., manganese), Group VIII (e.
g.
cobalt) or the lanthanides (e. g., cerium). The catalyst,
which is preferably in the form of metal particles, may
be deposited on a support, e.g., alumina and magnesia.
The carbon fibrils produced by these catalysts
have a length-to-diameter ratio of at least 5, and more
preferably at least 100. Even more preferred are fibrils
whose length-to-diameter ratio is at least 1000. The
wall thickness of the fibrils is about 0.1 to 0.4 times
the fibril external diameter.
.
The external diameter of the
fibrils is broadly
between 1.0 and 100 nanometers and preferably is between
3.5 and 75 nanometers. Preferably a large proportion
W0 95131281 ~ 2 PCT/US95105956
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have diameters falling within this range. In
applications where high strength fibrils are needed
(e.g., where the fibrils are used as reinforcements), the
"
external fibril diameter is preferably constant over its
length.
Fibrils may be prepared as aggregates having
various macroscopic morphologies (as determined by
scanning electron microscopy) in which they are randomly
entangled with each other to form entangled balls of
fibrils; or as aggregates consisting of bundles of
straight to slightly bent or kinked carbon fibrils having
substantially the same relative orientation in which the
longitudinal axis of each fibril (despite individual
bends or kinks) extends in the same direction as that of
-the surrounding fibrils in the bundles; or, as aggregates
consisting of straight to slightly bent or kinked fibrils
which are loosely entangled with each other to form a
more open structure. In the open structures the degree
of fibril entanglement is greater than observed in the
parallel bundle aggregates (in which the individual
fibrils have substantially the same relative orientation)
but less than that of random entangled aggregates. All
of the aggregates are more dispersable in other media,
making them useful in composite fabrication where uniform
properties throughout the structure are desired. In the
parallel bundle aggregates the substantial linearity of
the individual fibril strands, which are also
electrically conductive, makes the aggregates useful in
EMI shielding and electrical applications.
The macroscopic morphology of the aggregate is
influenced by the choice of catalyst support. Spherical
supports grow fibrils in all directions leading to the "
formation of random, entangled aggregates. Parallel
bundle aggregates and aggregates having more open
structures are prepared using supports having one or more
readily cleavable planar surfaces, e.g., an iron or iron-
containing metal catalyst particle deposited on a support
W095131281 ~~ PCT/US95/05956
material having one or more readily cleavable surfaces
and a surface area of at least 1 square meters per gram.
Preferred support materials include the various
aluminas (stoichiometries corresponding to A1203.H20,or
5 AlO.OH), or gamma-alumina (A1203) or magnesia (Mg0).
Additionally, hydrous aluminas (stoichiometries
corresponding to A1(OH3) or A1203.3H20), calcined lightly
at temperatures below about S00C yield activated
aluminas (A1203.Ha0) which retain the platelet morphology
of the initial hydrous alumina. These result in highly
preferred supports. Such materials are commercially
available, e.g., from ALCOA (hydrous and activated
aluminas) and Martin Marietta (magnesia). The activated
alumina supports yield primarily parallel bundle
aggregates, while the magnesia supports yield primarily
the more open aggregates. Spherical gamma alumina
particles, which yield random entangled aggregates, are
available from Degussa.
It is believed that deposition of fibril growth
catalysts on supports having planar surfaces allow the
fibrils to orient themselves with each other as they
grow, creating a "neighbor effect". This leads then to a
parallel bundle fibril aggregate in which the areas of
all of the individual fibrils have the same relative
orientation. The magnesia supports, although having
readily cleavable planar surfaces, yield primarily
lightly entangled, open net fibril aggregates because
they break apart more readily into smaller particles than
the activated alumina support during fibril growth,
resulting in aggregates that are less ordered than the
parallel bundle aggregates but more ordered than the
' tightly entangled fibril balls. The more readily the
oxide and support can form a mixed oxide at the interface
' between them, the more likely the support is to break
apart.
Further details regarding the formation of
carbon fibril aggregates may be found in the disclosure
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of PCT Publication No. WO 89/07163, and PCT Publication
No. WO 91/05089.
Fibrils are increasingly important in a variety
of industrial uses. While known methods of manufacture
permit production of small quantities of fibrils, it is
important to improve these methods, and in particular the
catalysts used in those methods, to increase the yield of
fibrils, to~improve their quality and to lower their cost
of production. It is also desirable to produce carbon
fibrils of improved purity.
Furthermore, it is desirable to produce fibrils
with enhanced dispersability and electrical conductivity
properties. It is important to improve the ability of
fibrils to disperse in media. In particular, it is
15 desirable to increase the ability of fibrils to disperse
in thermoplastics or engineering plastics. Dispersion of
fibrils into media also imparts enhanced electrical
conductivity properties to said media.
OBJECTS OF THE INVENTION
It is thus a primary object of the invention to
provide improved catalysts for the production of fibrils.
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SUMMARY OF THE INVENTION
Methods have now been found which yield
catalysts that produce substantially superior carbon
fibrils and carbon fibril aggregates. These catalysts
can be obtained by contacting a fibril-forming catalyst
or precursors of a fibril-forming catalyst with an
effective amount of a surfactant and/or polyol. The -
method is preferably carried out by precipitating a
fibril-producing metal oxide or compound from an aqueous
to solution onto slurried particles of a support material in
the presence of surfactant and/or polyol.
This invention further provides a catalyst for
the production of carbon fibril aggregates produced by
the method of contacting a fibril-forming catalyst or
precursors of a fibril-forming catalyst with an effective
amount of a surfactant and/or polyol. Preferably, the
catalyst is formed by precipitating a fibril-producing
metal oxide or compound from an aqueous solution onto
slurried particles of a support material in the presence
of a surfactant and/or polyol.
Also provided by this invention is a volume of
carbon fibrils comprising a multiplicity of fibrils that
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are free of a continuous thermal carbon overcoat, have
graphitic layers that are substantially parallel to the
fibril axis, and possess a substantially constant
diameter. In a preferred embodiment the diameter of the
fibrils is from about 4.0 to about 20 nanometers.
The improved methods of making fibril-forming
catalysts and the improved catalysts themselves produce
superior carbon fibrils and carbon fibril aggregates
possessing enhanced dispersion and electroconductivity
qualities. The resultant carbon fibrils exhibit improved
characteristics that enable fibrils or fibril aggregates
to disperse better in a media. Additionally, the carbon
fibrils produced by the improved catalysts provided by
this invention impart increased electroconductivity to
the media in which they are dispersed.
DETAILED DE8GRIPTION OF THE INVENTION
The term "fibril-forming catalyst" is used to
refer collectively to catalysts for forming discrete
carbon fibrils, carbon fibril aggregates or both.
The term "carbon fibrils" when referring to
products is used to refer collectively to both discrete
carbon fibrils and carbon fibril aggregates, unless the
context indicates a different meaning.
This invention provides a method for the
manufacture of a catalyst for the production of carbon
fibrils comprising contacting a fibril-forming catalyst
or precursors of a fibril-forming catalyst with an
effective amount of a surfactant and/or polyol. The
method for the manufacture of a catalyst for the
production of carbon fibrils preferably comprises the
steps of forming an aqueous solution of a Period Four
transition metal iron compound or a Period Four
transition metal and molybdenum compound, forming a
slurry of catalyst support particles comprising alumina '
and/or magnesia particles, precipitating an iron compound
or iron and molybdenum compounds onto the alumina and/or
magnesia particles in the presence of a surfactant and/or
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polyol, and then processing the slurry to produce a
fibril-forming catalyst.
. Preferably, the surfactant is stable at pH
levels from about 3 to about 9 and does not itself cause
precipitation of ferric oxide or compounds. Members from
the usual classes of anionic, cationic or non-ionic
surfactants are effective. In one embodiment of the
invention the surfactant is non-ionic. The preferred
non-ionic surfactants include ethoxylated alkyl phenols,
other ethoxylated and/or propoxylated derivatives, and
functionalized organosiloxanes.
In another embodiment of this invention, the
surfactant is an anti-foaming agent. Examples of anti-
foaming agents include substituted nonylphenols, organo-
modified polysiloxanes, and emulsified silicone
formulations.
In other preferred embodiments of the invention
the surfactant can be ethylene oxide-propylene oxide
copolymers, substituted alkyl phenols, alkali metal salts
of polymeric carboxylic acids, derivatized
polyalkylsiloxanes, ethoxylated amines, quaternary amine
salts and derivatized nitrogen compounds (such as
imidazoles and pyrimidines).
Examples of preferred polyols used in certain
embodiments of this invention include glycerine, sucrose
and polyethylene glycol.
A preferred method of manufacturing a catalyst
for the production of carbon fibrils comprises forming
an
iron or iron and molybdenum salt solution, forming a
slurry of catalyst support particles comprising alumina
particles, precipitating iron or iron and molybdenum
oxide onto said alumina particles in the presence of a
surfactant, anti-foam agent or polyol at a pH of about
6,
' then filtering and washing the slurry followed by drying
at about 140C to about 200C yield a fibril-forming
catalyst.
WO 95131281 , 2 i 9 0 0 0 2. PCT~S95105956
Embodiments of the invention include, but are
not limited to, adding soluble surfactant and/or anti-
foam and/or polyol to the iron or iron and molybdenum .
aqueous solution; adding surfactant and/or anti-foam
5 and/or polyol to the alumina or magnesia slurry; and ,
adding surfactant and/or anti-foam and/or polyol to both
the iron or iron/molybdenum aqueous solution and the
slurry of alumina or magnesia.
This invention also provides a catalyst for the
10 production of carbon fibrils that are produced by
contacting a fibril-forming catalyst or precursors of a
fibril-forming catalyst with an effective amount of a
surfactant and/or polyol.
Further provided by this invention is a volume
of carbon fibrils comprising a multiplicity of fibrils
having a morphology consisting of tubes that are free of
a continuous thermal carbon overcoat, graphitic layers
that are substantially parallel to the fibril axis, and a
substantially constant diameter. Preferably, the
diameter of the fibrils is from about 4.0 to about 20
manometers.
The immediate improvement in the catalysts of
this invention are seen in the fibrils which they
produce. They make more uniform fibrils of smaller
diameter (from about 4.0 to about 20 manometers most
preferably 7-10 manometers) thereby increasing the
surface area of fibrils. In addition, the aggregates,
which resemble parallel bundle aggregates, are much
smaller (approximately 0.1-1 micron, and some as small as
about 0.1 micron). This results in fibril aggregates
which are much easier to disperse and thereby impart
higher electrical conductivity to the dispersed medium.
The smaller aggregates also allow for dispersions of
fibrils to nearly the individualized state (absence of
bundles or other fibril aggregates) leading to open,
three-dimensional network mats.
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While not wishing to be bound by any theory, it
is believed that the improved properties of the fibrils
(i.e., improved dispersibilities in thermoplastics and/or
polymers, and improved electrical conductivities in these
formulations, and the ability to make open, three-
dimensional network mats from superior dispersions)
results from better dispersion of iron or iron/molybdenum
oxide particles which are deposited on the surface of the
support in the presence of surfactant, anti-foam agent or
polyol. The surfactant, anti-foam or polyol interacts
with the surface of the precipitated iron or
iron/molybdenum oxide to decrease particle-particle
interaction, stabilizing the small aggregate particles by
retarding the growth or sintering into larger aggregates.
The smaller iron or iron/molybdenum particles also lead
to fibrils with smaller average diameters.
One class of surfactants used (although not
limited to) are non-ionic, particularly alkylated
phenols, ethoxylated alkyl phenols, alkoxylated
derivatives and functionalized organosiloxanes. Examples
of commercial surfactants which may be classified more
narrowly as "dispersants" or "anti-foam agents" are
Triton X-100 (ethoxylated nonylphenol, Rohm & Haas) or
Anti-Foam A*(Organomodified polysiloxane, Sigma).
Again, while not wishing to be bound by any
particular theory, it is believed that a second pathway
by which these catalysts yield improved fibril aggregates
is by facilitating the breaking apart of the support
(activated alumina or magnesia) particles. The preferred
support for these catalysts are flat, planar hydrous
alumina (A1(OH)3) platelets which have been lightly
calcined from about 225 to about 800 °C to a composition
approaching activated alumina, AI203.H20, without any
substantial change in the platelet structure. The weight
loss on calcination is 27-33 wt% H20.
The aggregate particles of the support are made
up of submicron, flat platelets which are loosely held
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together into aggregates by binding through surface
hydroxyl ions. Iron, or iron/molybdenum oxide particles
are deposited on the surface of and the crevices between
platelets. These platelets then separate and break apart
into smaller platelets from the heat of reaction and the
force of the fibrils. The planar structure of the
support then orients the individual growing fibrils into
a CY macromorphology.
The use of surfactants ox polyols are believed
to decrease the inter-platelet or inter-particle
attractions by exchanging, neutralizing or binding
surface hydroxy groups which then allows the plates to be
cleaved more easily yielding smaller plates and thereby
smaller fibril bundles (sub-micron in size). These
smaller bundles (0.1-1 micron) are then easier to
disperse than larger bundles (0.5-2 micron) obtained with
conventional catalysts.
Again, while not wishing to be bound by any
particular theory, it is believed that a second pathway
by which these catalysts give improved performance is by
facilitating the breaking apart of alumina particles.
The preferred slurry support for catalysts are hydrous
aluminas (A1(OH)3) which have been lightly calcined to
greater than about 27% weight loss.
The aggregate particles of the support are made
up of submicron, flat plates which are held together by
binding through surface hydroxy ions. Iron oxide
particles are deposited on the open surfaces and in the
crevices between platelets. As fibrils undergo growth
the planar surfaces orient the individual fibrils in the
parallel bundle morphology.
The resulting bundles are easier to disperse
than conventional larger bundles because the sub-micron
dimensions of the plates produce very small bundles
(diameters as small as about 0.1 micron). Additionally,
the use of surfactants to decrease the inter-particle
attractions by exchanging, neutralizing or binding
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surface hydroxy groups, allows the plates to be cleaved
more readily, yielding smaller plates and smaller
bundles.
Examples of surfactants, which may also be more
narrowly defined as Dispersants or Anti-Foams are Triton
X-100 or Tamol-731 (Rohm & Haas), EPO-61 (ethylene oxide-
propylene oxide co-polymer from Harcros), HL-36~or Anto-
Foam~204 (non-silicone Anti-Foams available from Harcros
and Sigma, respectively).
Other preparations combine a surfactant, anti-
foam agent, or polyol added through the iron/molybdenum
solution and a surfactant added to the slurry of alumina
support. The precipitation is carried out as described
below. These preparations use other types of surfactants
besides antifoams. Other surfactants were fonaulations
of ethylene oxide-propylene oxide co-polymers,
substituted alkylphenols, or alkali metal salts of
polymeric carboxylic acids. Other, surfactant
formulations also include derivatized polyalkylsiloxanes,
ethoxylated amines, quaternary amine salts, derivatized
nitrogen compounds (e.g. imidazoles, pyrimidines) or any
of the class of surfactants (cationic, anionic or non-
ionic) which are stable at pH levels from about 3 to
about 9 and by themselves do not cause precipitation of
ferric ions.
Met od
All the catalysts were prepared by
precipitation of iron and molybdenum oxides at a
controlled pH. The surfactant or polyol could be added
to the Fe/Mo salt solution from which the oxides were
precipitated, to the alumina slurry, or both. The
support for all catalyst examples was a hydrous alumina
(A1(OH)3 or A1203.3H2o) available from Alcoa, designated
H-705, which had been lightly calcined between 280-600°C
to give about 27-33 percent weight loss to give an
activated alumina with composition A1203.H20).
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This invention is illustrated in the examples
which follow. The examples are set forth to aid in
understanding the invention but are not intended to and
should not be construed to in any way, limit the scope of
the claims.
Example I
A catalyst was made by precipitating
iron/molybdenum oxides onto Alcoa H-705 (a hydrous
alumina) which had been lightly calcined to about 27
percent weight loss. Precipitation of the oxides was
done at a pH of about 6.0 by concurrent addition of
ammonium carbonate at relative rates to maintain the pH
at about 6Ø
The catalyst slurry was filtered and washed,
dried at 140°C and calcined at 400°C. The yield of
fibrils was 24.7 times the weight of catalyst.
Example II: Comparative Example: Catalyst Without
Surfactant
In, an indented multi-neck, 2 l.r.b. flask, 41.4
g activated alumina made from Alcoa H-705 (calcined to
33% weight loss) was slurried with 39.5 g ammonium
acetate solution (65% weight in water) and 1000 cc DI
water. The slurry was well-stirred for 30 minutes using
an overhead stirrer.
Ammonium paramolybdate ((NH4)6M0~024.4H20), 2.60
g was dissolved in 50 cc DI water and then added with
stirring to 86.1 g of ferric nitrate solution (37.5%
weight, 8.65% Fe content in DI water) to form a clear,
dark red-brown solution (A).
With a pH meter probe immersed in the alumina
slurry and with rapid stirring, solution A was added
dropwise concurrently with a 20% weight solution of
ammonium carbonate at relative rates of each sufficient
to maintain the bulk pH at 6.0 ~ 0.2. The mixed oxides
of Fe(III) and Mo(VI) were precipitated immediately and
adsorbed onto the surface of the alumina particles.
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After addition of the reagents, the slurry was stirred
for 30 minutes.
The slurry was vacuum filtered and the filter
cake was Washed with a total of 1.5 1~DI water either on
5 the filter or by twice res-lurrying and refiltering. The
washed filter cake was a homogeneous, brown solid with no
indication of striated layers or inhomogeneity.
The solids were dried in a forced air oven at
180°C overnight. Recovery of dried catalyst was 54.7 g.
10 The catalyst was ground by hand and sieved through a 100
mesh screen.
The catalyst was tested. The result is
summarized in Table 1.
Exam~~le III
15 The procedure -used was identical to Ex. 2
except for the Fe/Mo solution, which contained 4.0 g.
silicone Anti-Foam*A emulsion (~Sigmaj. The solution,
with emulsion, was mixed in a blaring blender at low speed
for 1 min. prior to addition to the alumina slurry. The
resulting emulsion was stable for several hours with no
indication of separation. Recovered catalyst was 53.1 g.
Example IV
The procedure used was identical to Ex. 2
except that the Fe/Mo solution contained 4Øg. glycerin.
The resulting solution was clear with no. precipitation.
Recovered catalyst was 51.1 g.
Example V
The procedure used was identical to Ex. 2
except that the Fe/Mo solution contained 4.0 g. sucrose.
The resulting solution was clear with ro precipitation.
Recovered catalyst was 48.2 g.
Example VI
The procedure was identical to Ex. 2 except
that the Fe/Mo solution contained 4.0 g Triton X-100
(alkylated nonyl phenol available from Rohm & Haasj. The
resulting solution was clear with no sign of
precipitation. Recovered catalyst was
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WO 95131281 PCT/US95105956
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51.2 g.
Exlmi~le VII
40 g activated alumina made by lightly .
calcining ALCOA H-705 (33% weight loss) was slurried with
30 g ammonium acetate solution (65% weight) and 1 liter
DI water. Slurry was rapidly stirred for 30 min.
81 g of 37.5% ferric nitrate solution was mixed
in a blaring blender with a mix containing 1.0 g
Polysiloxane 200, 0.65 cp (Aldrich), 0.12 g. Triton X-100
(Rohm-Haas) and 100 cc DI water. The resulting emulsion
was stable for several hours without separation.
Precipitation and subsequent work-up was
carried out as in Ex. 2. Recovered catalyst was 49.8 g.
EXample VIII
The procedure was similar to Ex. 2. 80 g
activated alumina made by lightly calcining ALCOA H-705
(33% weight loss) was slurried with 76.3 g ammonium
acetate (65% weight solution) and 1 liter DI water.
Slurry was rapidly stirred by an overhead stirrer for 30
2o min.
The Fe/Mo solution (166.4 g 37.5% ferric
nitrate solution plus 5.0 g ammonium paramolybdate
dissolved in 100 cc DI water) also contained 7.0 g
glycerol and 6.0 g silicone Anti-Foam A emulsion. The
formulation was mixed in a blaring blender for 1 min;
resulting emulsion was stable for several hours without
separation. Precipitation and subsequent work-up was
similar to Ex. 2. A total of 3 1. DI water was used to
wash the filter cake. Recovered catalyst was 106.4 g.
Examples 10-15 describe the preparation of
catalysts by addition of surfactant or polyol to the
alumina dispersion. The results of catalyst tests are
listed in Table 2.
Example IX '
The procedure used was identical to Ex. 2
except that the alumina slurry (Alcoa H-705, lightly
calcined to 27% weight loss) also contained 16.0 g Sigma
WO 95131281 PCT/IT595105956
17
Anti-Foam 204 (organic, non-silicone). The slurry was
well-mixed with an overhead stirrer for 1 hr prior to
precipitation of Fe/Mo oxides. The precipitation,
filtration, washing, drying, grinding and sieving
procedure was identical to Ex. 2. Recovered catalyst was
52.89 g.
F~atamnls X
The procedure similar to Ex. 10 was used, with
the exception that the alumina slurry contained 8.0 g
Sigma Anti-Foam 289 (non-silicone) instead of Anti-Foam
204. The remainder of the procedure was identical.
Recovered catalyst was 53.36 g.
Example XI
The procedure similar to Ex. to was used, with
the exception that the alumina slurry contained 4.0 g
Tamol 731 (Rohm & Haas, Na salt of polymeric carboxylic
acids) instead of Sigma Anti-Foam 204. The remainder of
the procedure was identical. Recovered catalyst was
51.00 g.
Example XII
The procedure similar to Ex. 10 was used, with
the exception that the alumina slurry contained 16.0 g
Anti-Foam HL-36 (Harcros) instead of Sigma Anti-Foam 204.
The remainder of the procedure was identical. Recovered
catalyst was 51.37 g.
Example XIII
The procedure similar to Ex. 10 was used, with
the exception that the alumina slurry contained 16.0 g
EPO-61 (ethylene oxide-propylene co-polymer, Harcros)
instead of Sigma Anti-Foam 204. The remainder of the
procedure was identical. Recovered catalyst was 48.89 g.
Example XIV
' The procedure similar to Ex. 10 was used, with
the exception that the alumina slurry contained 8.0 g
Polyethylene Glycol 400 (Aldrich) instead of Sigma Anti-
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Foam~204. The remainder of the procedure was identical.
Recovered catalyst was 51.02 g:
Examples 16-20 describe the preparation of
catalysts using surfactants or polyols or both by
addition~to both the ferric nitrate/ammonium molybdate
solution and the alumina dispersion. Test results for'
these catalysts are summarized in Table 2.
~xamnle XV
In a procedure similar to Ex. 2, a catalyst on
activated alumina made from Alcos*H-705 by lightly
calcining to 27% weight loss was prepared. In this
example, the Fe/Mo solution also contained 4.0 g Sigma
Anti-Foam A emulsion. The alumina slurry also contained
16.0 g. Sigma Anti-foam 204. The remainder of the
procedure was identical. Recovered catalyst was 52.05 g.
~xamnle XVI
2 kg alumina made from Alcoa H-705, lightly
calcined to 33% weight loss was slurried with 1.5 kg of
ammonium acetate solution (65% weight), 50 g Sigma Anti-.
Foam 204 and 12 gal DI water in a 30 gal reactor also
equipped with a Lightnin~4000 top stirrer and an Omega pH
probe and controller which delivered a 20% weight
solution of ammonium carbonate. The controller was set
to maintain the bulk pH of the slurry at 6.0 ~ 0.2. The
pH of the slurry was adjusted to 6:0.
In a 5 1 flask, 4.2 kg ferric nitrate solution
(37.5% weight, 8.65% weight Fe) was mixed with a solution
of 133 g ammonium paramolybdate dissolved in 1 1 DI water
and 25 g Sigma Anti-Foam A emulsion. The mixture Was
diluted to 6.0 1 and stirred with an overhead stirrer for
30 min. A stable emulsion was obtained. The emulsion
was loaded into a 6 gal feed tank.
The Fe/Mo emulsion was fed into the reactor at
the rate of 5.min/1 with rapid stirring. The pH was kept
at 6.0 ~ 0.2 by addition of the 20% weight ammonium
carbonate which was controlled by the omega pH
probe/controller.
*Trade-mark
WO 95131281 PCT/US95/0595G
19
After the addition of reagents, the slurry was
stirred for 1 hr. The solids were collected and washed
in a plate and frame filter press. The filter cake Was
washed until the conductivity of the effluent wash water
was less than 1.0 mS.
_
The filter cake was dried at 275C in a forced
air oven overnight. Recovered catalyst was 2515 g. The
dried catalyst was ground in a hammer mill and sieved to
-100 mesh.
F.~camt~le XVII
In a procedure similar to Ex. 16, 80.0 g
activated alumina made from Alcoa H-705, lightly calcined
to 33% weight loss, was slurried with 76.0 g ammonium
acetate solution (65% weight), 10.7 g Harcros EPO-61
surfactant and 1 1 DI H20 in a 3-neck flask. The slurry
was well-stirred for 0.5 hr.
In a separate vessel, 170.0 g ferric nitrate
solution (37.5% weight, 8.65% weight Fe) was mixed with
a
solution of 5.3 g ammonium molybdate in 100 cc DI water
and 4.0 g Sigma Anti-Foam A emulsion. The mixture was
stirred vigorously to yield a stable emulsion.
The remainder of the procedure was identical.
Recovered catalyst was 105.8 g.
~'xamDi a xyrTT
In a procedure similar to Ex. 16, 50.0 g
activated alumina made from Alcoa H-705, lightly calcined
to 33% weight loss, was slurried with 48.0 g ammonium
acetate solution (65% weight), 10.0 g Harcros Anti-Foam
HL-36 and 1.5 1 DI water. The mixture was stirred
vigorously for 30 min.
Separately, 106.0 g ferric nitrate solution
(37.5% weight) was mixed with a solution containing 3.3
g
ammonium molybdate in 50 cc DI water, and 3.0 g Sigma
' Anti-foam A emulsion. The mixture was stirred vigorously
to give a stable emulsion.
W0 95131281 , PCTIU595105956
The precipitation of Fe/Mo oxides and
subsequent work-up were identical to Ex 16. Recovered
catalyst was 63.39 g.
Exammle 7CIX
5 The procedure was identical to Ex. 16, except
that the Fe/Mo solution contained 4.0 g glycerin instead
of Sigma Anti-Foam A emulsion. The remainder of the
preparation was the same as Ex. 16. Recovered catalyst
was 52.11 g.
Tests were conducted to measure the
conductivities of the fibrils.
There were two parts to the procedure: 1j,
sample preparation; and 2), sample measurement. A time
gap between the two parts allowed for equilibration the
sample temperature; this time gap was as long as was
convenient.
The mamp measurement can be done using any
conventional electrode assembly at a voltage gradient of
15 v/cm. The actual electrodes were 5 sq-cm and were
placed 1 cm apart.
50 g of steel balls were placed in a bottle
containing fibrils and were shaken on the Red Devil for 1
min. 0.200 g of fibrils were placed in a plastic beaker
(Falcon). 200 g CVS mineral oil were added to a blender
cup. The fibrils were then added to the blender and
blended for 5 min at speed 7. Contents of the blender
were transfered back into the plastic cup; the cup was
then covered and placed into a water bath (already set to
25 °C) .
Samples were left for 1 hr to equilibrate the
temperature.
While samples were still in the water bath at
-25°C, the voltage on the power supply to the cell was
set at 15 v. The temperature of the sample was adjusted
to 25.0 °C by adding hot or cold water to the bath; the
sample was then placed in the Red Devil shaker. The
WO 95/31281 PCT/US95105956
2190002
21
sample was shaken for exactly 30 sec. The sample was
immediately taken to the conductivity bench; 30 seconds
later the electrodes were placed into the cup; a reading
(ma current) was taken after 1.0 min. Conductivity was
calculated as follows:
conductivity (kohm-cm)= 75/current (in ma)
RxAMPi$ XXT
The productivities of the catalyst for
producing carbon fibrils was determined in a 1 inch
quartz tube reactor using the following procedure: a 1
inch quartz tube was fitted with a 1/4 inch thermocouple
tube inserted through the bottom. At the tip of the
thermocouple tube a plug of quartz wool that had been
previously weighed was placed which permitted passage of
gas, but not particles of catalyst or fibrils growing on
the catalyst. The top of the quartz tube was fitted with
a gas line which allowed for a downflow addition of one
or more gases, and a modified ball valve which allowed
addition of a given charge of powdered catalyst. One
opening of the ball was closed off so that it became a
cup or sealed cylinder. Catalyst could then be loaded
into the cup and the valve assembly sealed. The contents
of the cup could then be added to the gas stream without
air contamination by turning the valve.
A thermocouple was inserted upward into the
thermocouple tube to monitor the reactor temperature.
The tube reactor was heated to 680 C in an Argon stream
to purge the reactor after which the gas stream was
switched to a mixture of hydrogen and ethylene at a flow
rate of 400 and 200 cc/min under standard conditions. A
weighed charge of catalyst (about 0.02-.05 g) was dropped
into the downflow gas onto the quartz plug. The reactor
was maintained at temperature for about 20 minutes, after
' which the reactor was cooled in argon and emptied. The
weight of carbon fibrils produced was calculated from the
total recovered weight and the known weights of the
quartz wool plug and the catalyst fed. The yield of
WO 95131281 - - PCTIUS95/05956
22
carbon fibril, or productivity, was calculated as the
weight of carbon produced per weight of catalyst or per
weight of iron in the catalyst.
W0 95131281 PCTlUS951D5956
23
TABLE 1. COMPARATIVE ESAMPLE: CATALYST WITHOUT
EXAMP LE #' pE SURFACTANT
SCRIPTION
RESISTIV ITY
w No
2 surfactant 660
TABLE 2. MODIFIED CATALYSTS
E7~EMpL E ~ pESCRIPTION HE SISTIVITY
3 33%, Anti-Foam A(A-A) 40
4 27%, Glycerine 60
5 27$, Sucrose gp
6 27%, Triton X-100 100
7 33%, Trit X/Silicone 114
8 33%, A-A + Glycerine 45
9 27%, Anti-Foam 204 100
10 27%, Anti-Foam 289 400
11 27%, Tamol 731 g0
12 27%, Anti-Foam HL-36 75
13 27%.EP061 7p
14 27%, Polyethylene Gly 170
ao
15 27%, A-A + A-204 3g
16 33$, A-A + A-204 75
17 33%, A-A + EP061 215
18 33%, A-A + HL-36 7p
19 33%, Glycerin + A-204 80
