Note: Descriptions are shown in the official language in which they were submitted.
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HEXAALUMINATE-COMPRISING CATALYST FOR THE REFORMING OF
HYDROCARBONS AND A REFORMING PROCESS
Description
The invention relates to a process for preparing a catalyst for the reforming
of hydrocarbon-
comprising compounds and the use of the catalyst of the invention in
connection with the
reforming of hydrocarbons, preferably CH4, in the presence of CO2. To prepare
the catalyst,
an aluminum source, preferably an aluminum hydroxide, preferably made up of
small primary
particles, preferably having a primary particle size of less than or equal to
500 nm, is brought
into contact with a cobalt-comprising metal salt solution, dried and calcined.
The metal salt
solution comprises at least one element of the group consisting of La, Ba, Sr
in addition to
the cobalt species.
The reforming of methane and carbon dioxide is of great economic interest
since synthesis
gas can be produced by means of this process. Synthesis gas forms a raw
material for the
preparation of basic chemicals. In addition, the use of carbon dioxide as
starting material is
of significant importance in the chemical syntheses in order to bind carbon
dioxide obtained
as waste product in numerous processes by a chemical route and thereby avoid
emission
into the atmosphere.
In accordance with its great economic importance, the reforming of
hydrocarbons in the
presence of carbon dioxide is subject matter of numerous publications. A short
overview of
the substantive focal points of these publications will be given below.
The catalytic properties of nickel-modified hexaaluminates for the reforming
of methane and
carbon dioxide to give synthesis gas are disclosed, for example, in a
publication by Zhalin Xu
et al. (Zhalin Xu, Ming Zhen, Yingli Bi Kaiji Zhen, Applied Catalysis A:
General 198 (2000)
pp. 267 ¨ 273). The nickel-modified hexaaluminates used here have a greater
activity and
display a better stability compared to the conventional nickel-comprising
catalyst in which the
nickel is deposited on the support materials.
A publication by Yokata et al. reports the use of hexaaluminate-comprising
catalysts for
synthesis gas production from the reforming of methane in the presence of CO2
and steam
(O. Yokata, T. Tanaka, Z. Hou, T. Yashima; Stud. Surf. Sci. and Cat. 153
(2004) p. 141 ¨
144. The study relates to nickel- and manganese-comprising hexaaluminates,
with the
manganese-comprising hexaaluminates being able to comprise elements from the
group
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consisting of Ba, La and Sr and also a mixture of Sro8 Lao 2. The catalytic
characterization of
the catalysts is carried out in the presence of CH4/H20/CO2 (in a volume ratio
of 150/100/50)
under atmospheric pressure at a temperature of 700 C. The flow rate is 18 000
hr-1.
J. Wang et al. reports the reforming of methane to give synthesis gas using
catalysts
composed of nickel-comprising magnetoplumbites which are doped with cobalt or
in which
the nickel has been completely replaced by cobalt (J. Wang, Y. Liu, TX. Cheng,
WX. Li,
YL. Bi, KJ. Zhen, Appl. Catalysis A: General 250 (2003) p. 13 ¨ 23). The
catalysts disclosed
by Wang et al. are described by the empirical formula LaNixCoi_xAlii019., and
a cobalt-
lanthanum-comprising hexaaluminate in which x = 0, which is free of nickel,
also disclosed.
The preparation of the catalysts disclosed by Wang et al. is based on the use
of aluminum
nitrate salt which is decomposed together with the other metal nitrate salts
(i.e. La, Ni and Co
or La and Co) in the presence of PEG/isopropyl alcohol. The catalytic
reforming studies are
carried out at temperatures of up to 800 C and a GHSV of 9600 hr-1. The nickel-
free
hexaaluminate catalyst having the composition LaCoAl11019 displays only a very
low activity
in respect of the conversion of methane and CO2 studied. In general, the
results of Wang et
al. show that the catalytic efficiency of the catalysts is disadvantageously
influenced by the
addition of cobalt.
In US 7,442,669 B2, D. Wickham et al. disclose an oxidation catalyst
comprising metal-
exchanged hexaaluminates. The catalyst has a good catalytic activity and
stability at high
temperatures, with the activity also being maintained over a prolonged period
of time. In
general the catalysts are suitable as oxidation catalysts and in particular in
methane
combustion, with, in particular, the use in turbines operated using natural
gas being of
importance. The synthesis of the hexaaluminate-comprising catalysts is based
on the use of
boehmite particles.
The hexaaluminates disclosed in US 7,442,669 B2 comprise up to three different
metal
species selected from the groups M1, M2 and M3. The group Mi comprises
elements from the
group of the rare earths, the group M2 comprises elements from the group of
the alkaline
earth elements and the group M3 comprises elements from the group of the
transition metals,
with mention being made of Mn, Fe, Co, Ni, Cu, Ag, Au, Rh, Ru, Pd, Ir and Pt.
To
characterize the catalysts, these were tested for the methane decomposition
activity, with the
catalysts being exposed to a gas stream comprising 3% by volume of methane.
The studies
were carried out at a pressure of 5 bar and a GHSV of 17 000 hr-1. The
temperature T112
which is required for fifty percent of the methane to react was determined as
a measure of
--
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the efficiency of the catalysts. The catalysts tested were subjected to
different aging regimes
before the catalytic study.
EP 2 119 671 discloses the synthesis of hexaaluminate-comprising catalysts in
the presence
of template materials. The template materials are advantageous for the
formation of
particular pore structures in the hexaaluminates, which are prepared by means
of the
process according to EP 2 119 671.
A large number of publications relate to the use of hexaaluminate-comprising
catalysts for
the oxidation or partial oxidation of hydrocarbons in the presence of oxygen.
When carrying
out partial oxidations, very short contact times are desirable in order to
prevent complete
oxidation of the hydrocarbons. For this purpose, it is necessary to carry out
the reactions at
high flow rates, a low hydrocarbon concentration and in the presence of
oxygen. Examples of
such disclosures are: Kikuchi et al. (R. Kikuchi, Y. lwasa, T. Takeguchi, K.
Eguchi; Applied
Catalysis A: General 281 (2005) p. 61 ¨ 67), G. Groppi (Applied Catalysis A:
General 104
(1993) p. 101 ¨ 108.
In general, various processes for preparing hexaaluminate-comprising catalysts
have been
published in the prior art, but in all of these the respective starting
components are subjected
to a thermal treatment at temperatures of 1200 C and above.
For example, S. Nugroho et al. describe the preparation of phase-pure barium
hexaaluminate which was obtained by heating of barium oxide and aluminum oxide
(i.e. BaO
and A1203) in a solid state reaction at temperatures of 1450 C (see S. Nugroho
et al., Journal
of Alloys and Compounds, 2010, 502, pp. 466-471).
M. Machida et al. (M. Machida et al, Journal of Catalysis, 1987, 103, pp. 385 -
393) disclose
the preparation of phase-pure barium hexaaluminates which are obtained by
hydrolysis of
the corresponding alkoxides, with these being treated at temperatures up to
1300 C. The
resulting hexaaluminate phases have surface areas of 11 m2/g.
Chu et al. describe a preparation of barium hexaaluminates by carbonate
precipitation (see
W. Chu et al., Catalysis Letters, 2001, 74, pp. 139-144). In the thermal
treatment,
temperatures of 1200 C were necessary in order to obtain the materials with a
high phase
purity in respect of the barium hexaaluminate phase. It is reported that the
materials have
surface areas of 17 m2/g.
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Apart from the above, there is also a single disclosure in the prior art by F.
Yin et al. on the
preparation of hexaaluminates by means of combustion of urea (i.e. the urea
combustion
process) which differs from other disclosures in that the thermal treatment of
the starting
materials is carried out at a much lower temperature than in the case of the
other known
processes. F. Yin et al. indicate that the phase-pure hexaaluminate material
was obtained at
as low as 500 C. The material obtained had a surface area of 20 m2/g.
US2007/0111884 A1 (Laiyuan Chen et al and Delphi as applicant) discloses and
claims
catalyst support materials which comprise hexaaluminates and alumina and are
provided
with rhodium as active component. To produce the catalyst material, the
starting materials
are combined with a stoichiometric excess of an aluminum-comprising component,
so that
not only the hexaaluminate-comprising phase but also the alumina secondary
phase is
formed in the synthesis. US2007/0111884 A1 discloses hexaaluminates which can
comprise
various cations, which mention also being made of lanthanum-comprising
hexaaluminates
which can comprise various divalent cations such as Mg, Ca, Ni, Co, Zn and Fe.
Various
processes are disclosed for producing the catalyst support materials and
catalysts, and these
differ from one another in respect of the mixing steps used and the thermal
treatment steps.
The catalysts according to the invention, which according to the disclosure
are all doped with
rhodium as active metal, are used in a process for the partial oxidation of
gasoline in the
presence of oxygen so as to produce a hydrogen-rich gas mixture. In the
partial oxidation
reactions used for reforming fuels, temperatures in the region of 1000 C and
higher can
occur and because of the high temperatures it is necessary to develop
particularly sintering-
resistant catalysts for this purpose.
In his doctoral thesis in 2007, Todd H. Gardner discussed in a very pioneering
way the use of
hexaaluminates as catalysts for the partial oxidation of fuels obtained in the
middle fraction
from the distillation. In particular, lanthanum-comprising, barium-comprising
and strontium-
comprising hexaaluminates which can comprise various transition metal cations
are also
described. The focus of the work is the examination of hexaaluminates
comprising nickel,
cobalt or iron, with the transition metals being present in different ratios
and being combined
with the cations from the group consisting of Sr, La and Ba, which are
likewise present in
various ratios. The work is aimed at examination of pure-phase hexaaluminates.
Gardner
reports that although phase impurities are not ruled out, they would have been
present only
in very low concentrations. To characterize the catalytic properties, the
catalysts were used
for the partial oxidation of n-tetradecane. The partial oxidations were
carried out at a
pressure of about 2 bar, a GHSV of 50 000 h-1 and using an oxygen-to-carbon
ratio (i.e. 0 to
C) of 1.2.
¨
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A publication by J. Kirchnerova (in Catalysis Letters 67 (2000) p. 175-181)
describes the
criteria for the design of new high-temperature catalysts for the catalysis of
combustion
reactions. The publication also relates to the production and testing of
materials having a
5 perovskite structure and to materials having a hexaaluminate structure.
Here,
hexaaluminates comprising Sr, La and Mn (i.e. have the structural formula
Sr0.8
La0.2MnAlii019) are described. It may also be mentioned that the use of
boehmites as
starting material in the synthesis of the materials is disclosed. A conclusion
drawn by
Kirchnerova et al is that those perovskites which have particular transition
metals can display
activity in catalytic combustion. The catalytic experiments to characterize
the catalysts are
based on the oxidation of methane to carbon dioxide in the presence of air,
with the methane
content being indicated to be 2%.
CN 101306361 A discloses hexaaluminates which are used as catalysts for
carrying out
reactions for the oxidation of hydrocarbons. The hexaaluminates have the
cationic species
La, Ba or Ca as stabilizing elements and the hexaaluminates can have Cr, Mn,
Fe, Co, Ni or
Cu as transition metal cations.
It is an object of the invention to provide an improved catalyst, an improved
process for
preparing hexaaluminate-comprising catalysts and an improved process for the
reforming of
hydrocarbons and CO2 to give synthesis gas.
Apart from the above, the preparative process should also be very energy-
efficient and
sparing of resources. At the same time, it is an object to obtain material
with a low proportion
of impurities.
A further object of the invention is to provide a hexaaluminate-comprising
catalyst which
comprises a very small proportion of lanthanum or in which lanthanum can be
replaced by
chemical elements which are available on an industrial production scale and
are not toxic.
The objects mentioned here and further objects are achieved by provision of a
hexaaluminate-comprising catalyst and by a process for preparing a
hexaaluminate-
comprising catalyst. The hexaaluminate-comprising catalyst is used in a
process for the
reforming of hydrocarbons, preferably methane, and 002, which is described in
more detail
below.
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A. The hexaaluminate-comprising catalyst of the invention comprises cobalt and
at least one
further element from the group consisting of Ba, Sr, La, where the Co content
is in the range
2 - 15 mol%, preferably 3 - 10 mol% and more preferably in the range 4 - 8
mol%, the
content of the at least one further element from the group consisting of Ba,
Sr, La is in the
range 2 - 25 mol%, preferably 3 -15 mol%, more preferably 4 - 10 mol%, and the
content of
Al is in the range 70 - 90 mol%.
On the basis of the ranges for the molar proportions indicated here, the
following molar ratios
for the metal ion species can be determined: the molar ratio of Co to Al (i.e.
the nco/nAi ratio)
is in the range 0.03-0.17, preferably 0.043-0.11 and more preferably 0.057-
0.08. The molar
ratio of MBaSrLa to Al (i.e. the nMBaSrLa/nAl ratio) is in the range 0.029-
0.28, preferably 0.043-
0.17 and more preferably in the range 0.057-0.11. The molar ratio of Co to
MBaSrLa (i.e. The
nco/nMBaSrLa ratio) lies in the range 1.0-0.6, preferably 1.0-0.67 and more
preferably 1.0-0.8.
In addition, particular preference is given to the molar ratios of the
elements comprised in the
catalyst to be in the following ranges: the ratio of cobalt to aluminum (i.e.
the nco/nAl ratio) is
in the range from 0.05 to 0.09 and particularly preferably in the range from
0.06 to 0.08. In a
preferred embodiment of the catalyst of the invention, the molar ratio of
MBasrLa to aluminum
(i.e. the the nMBaSrLa/nAl ratio) is in the range from 0.09 to 0.25,
particularly preferably in the
range from 0.092 to 0.20. Furthermore, the molar ratio of Co to MBaSrLa (i.e.
the nco/ nMBaSrLa
ratio) is preferably in the range from 1.0 to 0.3 and particularly preferably
in the range from
0.85 to 0.40.
A material which consists entirely of cobalt hexaaluminate and comprises at
least one
element from the group consisting of Ba, Sr, La can be described by the
empirical formula
comBaSrLaAli 1019. In this case, the metallic species have the following
stoichiometric ratios:
the molar ratio of Co to Al (i.e. the nco/nAi ratio) is 1, the molar ratio of
MBasrLa to Al (i.e. the
rIMBaSrLa/nAl ratio) is 0.091 and the molar ratio of Co to MBasr" (i.e. the
nco/ nMBaSrLa ratio) is 1.
Comparison of the composition of the catalyst of the invention with a material
which consists
entirely of cobalt hexaaluminate phase indicates that the catalyst of the
invention (preferably)
has a lower proportion of cobalt (relative to aluminum) and a higher
proportion of cationic
species from the group consisting of Ba, Sr, La (relative to cobalt) compared
to the pure-
phase cobalt hexaaluminate. Based on the pure-phase cobalt hexaaluminate, this
means
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that the catalyst of the invention has a substoichiometric amount of cobalt
and a
superstoichiometric amount of cationic species from the group consisting of
Ba, Sr, La.
An explanation of the formation of the catalyst of the invention is that the
cobalt-comprising
species added to the synthesis system are virtually completely or completely
incorporated
into the structure of the cobalt hexaaluminate phase and cobalt is no longer
available for the
formation of the secondary phase. The formation of the secondary phase
proceeds from the
aluminum-comprising species and the cationic species from the group consisting
of Ba, Sr,
La used in each case, which leads to aluminates or perovskites (e.g. SrA1204,
LaA103 etc.) or
other phases of the elements La, Sr, Ba, Al known to those skilled in the art
being
predominantly formed as secondary phase. It follows therefrom that the
proportion of free
aluminum oxide and the associated number of Lewis acid sites can be minimized.
However,
the explanation given above is not intended to restrict the invention in any
way.
In a preferred embodiment, the catalyst of the invention comprises secondary
phases or a
secondary phase, where the total proportion of the secondary phases is in the
range 0 - 50%
by weight, preferably in the range 3 - 40% by weight and more preferably in
the range 5 -
30% by weight. The secondary phase preferably comprises oxides, and these are
more
preferably from the group consisting of alpha-aluminum oxide, theta-aluminum
oxide, LaA103,
BaA1204, SrA1204, CoA1204, La-stabilized aluminum oxide and/or La-stabilized
aluminum
oxide hydroxide.
In a preferred embodiment, the catalyst comprises at least one noble metal-
comprising
promoter from the group consisting of Pt, Rh, Pd, Ir, where the proportion of
noble metal-
comprising promoters is in the range 0.1 - 3 mol%.
In a further embodiment, the catalyst also comprises a proportion of further
cations which are
preferably selected from the group consisting of Mg, Ca, Ga, Be, Ni, Fe, Cr,
Mn, with Mg
being particularly preferred.
It is also conceivable that, as alternatives to the at least one element from
the group
consisting of Ba, Sr, La, a further element or plurality of elements from the
group of the
lanthanides can be present in the catalyst of the invention. It is also not to
be ruled out that
the performance properties of the catalyst of the invention can be improved
further by the
incorporation of specific secondary phases or a combination of secondary
phases within the
catalyst.
- -
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B. The hexaaluminate-comprising catalyst can be prepared by means of the
following steps:
(i) producing of an aluminum source, preferably a finely divided aluminum
oxide and/or
hydroxide modification,
(ii) contacting of the finely divided aluminum source with a fusible or
soluble cobalt-
comprising compound and at least one further soluble or fusible metal salt,
(iii) intimate mixing of the aluminum source and the dissolved or molten metal
salts,
(iv) drying of the mixture,
(v) low-temperature calcination of the mixture,
(vi) molding or shaping,
(vii) high-temperature calcination of the mixture.
The at least one further soluble or fusible metal salt comprises a metal salt
which is selected
from the group consisting of barium, strontium and lanthanum.
In a preferred embodiment, the further soluble metal salt comprises at least
two metal salts,
in which at least barium-comprising species are present in combination with
strontium-
comprising species or at least barium-comprising species are present in
combination with
lanthanum-comprising species or strontium-comprising species are present in
combination
with lanthanum-comprising species.
When the metal salts are not present in the form of the melt but in the form
of the dissolved
metal salts during mixing in step (iii), a solvent is also added to the metal
salts if these have
not been used in the dissolved state.
In a particularly preferred embodiment, the aluminum source is selected from
the group
consisting of high reactive aluminum oxides and aluminum hydroxides. The
aluminum source
preferably comprises dispersible primary particles, with a primary particle
size of less than or
equal to 500 nm being preferred.
C. Part of the invention also provides the process for preparing the
hexaaluminate-
comprising catalyst.
Hexaaluminate-comprising catalyst/hexaaluminate phase
For the purposes of the present disclosure, the term hexaaluminate-comprising
catalyst
comprises materials which have a high proportion of hexaaluminate phase. This
means that
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the hexaaluminate-comprising catalyst can, in particular embodiments, also
comprise a
certain proportion of secondary phases. The term hexaaluminate phase comprises
phases
which have a sheet structure similar to or the same as the types of
magnetoplumbite
structure and/or the beta-aluminate structure, e.g. beta'- or beta"-aluminate
structure. If the
catalyst comprises secondary phases, the proportion of secondary phase is in
the range 0 -
50% by weight, preferably in the range 3 - 40% by weight and more preferably
in the range
5 - 30% by weight.
The proportion of hexaaluminate-comprising phase can be determined by
diffractometric
methods, for example the Rietfeld refinement. If particularly finely divided
or nanocrystalline
materials are present, the proportion of hexaaluminate phase is determined by
means of an
optic analysis by the Kubelka-Munk method. Here, a highly sintered reference
sample having
the same stoichiometry as the sample to be measured (in respect of the
proportion of
crystalline phase) is prepared and this is then designated as standard sample.
The samples
to be measured are compared to the standard sample as reference, with the
reference
having been assigned a value of one hundred percent beforehand. The optical
analysis
method is preferred in the case of nanocrystalline material when these have
very small
crystallites having a short coherence length. Short coherence lengths are
present, (in the
case of diffractometric studies using an X-ray wavelength of 0.154 nm),
particularly when the
crystallite sizes are less than 0.5 nm, preferably less than 0.4 nm and more
preferablyless
than 0.3 nm. Such nanocrystalline materials can be provided such that they
appear as X-ray-
amorphous in powder diffraction and as crystalline in the UV analysis.
Aluminum source
As aluminum source, it is in principle possible to use all aluminum-comprising
starting
materials, and a preferred aluminum source is selected from the group
consisting of:
pseudoboehmite, boehmite, gibbsite, bayerites, gamma-aluminum oxide, theta-
aluminum
oxide, hydrotalcites such as magnesium hydrotalcite, colloidal basic aluminum
oxides and
other colloidal aluminum sources known to those skilled in the art and also
mixtures of these.
Included are, in particular, the following products, inter alia, from Sasol:
Disperal and all
Disperal types, Dispal, Pural, Puralox, Catalox, Catapal and also all Pural MG
types.
Without restricting the process of the invention by a theory, it is assumed
that the surface
structure of the highly reactive aluminum oxide or aluminum hydroxide source,
for example
theta-aluminum oxide, gamma-aluminum oxide, pseudoboehmite, boehmite,
gibbsite,
bayerite and mixtures of the abovementioned and other highly reactive aluminum
oxide or
CA 02864063 2014-08-07
aluminum hydroxide sources could have a substantial influence on the formation
of an active
catalyst. The boehmite used preferably comprises dispersible particles, with
the primary
particle size preferably being in the range of less than or equal to 500 nm.
The term
dispersible particles means that the particles dispersed or slurried in water
form a stable
5 dispersion and precipitate only after a long time.
The aluminum source is preferably a nanoparticulate aluminum-comprising
starting material
or colloidal primary particles. As nanoparticulate aluminum-comprising
starting materials, it is
possible to use, for example, peptized aluminum hydroxides, aluminum oxide
hydrates or
10 aluminum oxides. The peptization can be carried out by means of organic
acids, for example
acetic acid, propionic acid, or by means of inorganic acids, for example
nitric acid or
hydrochloric acid. The colloidal particles can be admixed with stabilizers
such as surfactants,
soluble polymers or salts, or such stabilizers can be used in the production
process. The
colloidal primary particles can also comprise partially hydrolyzed alkoxides.
In a specific embodiment, it is also possible to use shaped bodies of the
abovementioned
aluminum oxide sources, which are then brought into contact with the metal
compounds.
Examples of such shaped bodies are, inter alia, pellets, extrudates or
granulated material or
other shaped bodies known to those skilled in the art.
The use of a highly reactive aluminum oxide or aluminum hydroxide source is
particularly
advantageous because it aids the formation of desired phases.
As metal compounds, preference is given to using any compounds which are
soluble in
solvents or can be melted in the temperature range up to 250 C and are
available industrially
at low cost. Preferred solvents include, inter alia, the following: water,
acidic or alkaline
aqueous solutions, alcohols such as methanol, ethanol, propanol, isopropanol,
butanol,
ketones such as acetone or methyl ethyl ketone, aromatic solvents such as
toluene or
xylenes, aliphatic solvents such as cyclohexane or n-hexane, ethers and
polyethers such as
tetrahydrofuran, diethyl ether or diglyme, esters such as methyl acetate or
ethyl acetate.
Furthermore, particular preference is given to using soluble salts, complexes
or metal-
organic compounds as metal compounds. Examples of salts are, inter alia,
nitrates, nitrites,
carbonates, halides, acetates, octanoates. Examples of complexes are, inter
alia, EDTA
complexes, complexes with amino acid or amines, complexes with polyols or
polyacids,
complexes with phosphanes. Examples of metal-organic compounds are, inter
alia,
_
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acetylacetonates, alkoxides, alkyl compounds, compounds with aromatics, e.g.
cyclopentadienyl adducts.
As fusible metal compounds, preference is given to using metal salts which do
not
decompose during melting or in the case of which the decomposition is greatly
kinetically
inhibited. Examples of such metal salts are, inter alia, nitrates, nitrites,
halides, chlorates,
bromates, iodates, sulfates, sulfites. Particular preference is given to
nitrates, nitrites or salt
melts comprising nitrates and nitrites.
Suitable metals of contacting the metal compounds with the aluminum source
are, inter alia,
impregnation methods in which the metal compounds are dissolved in suitable
solvents
which are subsequently removed by drying. Such a drying step can, in the case
of a
pulverulent aluminum source, be carried out, for example, by freeze drying or
spray drying;
as an alternative, spray granulation or pure static drying of the composites
formed can be
carried out. For the purposes of the invention, impregnation is a particularly
preferred
method.
Further suitable methods of contacting are, inter alia, kneading or milling of
the aluminum
source in the presence of the metal compounds with or without addition of
liquids. Kneading
in particular is, for the purposes of the invention, a preferred method since
it allows coupling
with subsequent extrusion and can thus be advantageous for shaping.
For the purposes of the invention, preference is given, in particular, to
metal salts which aid
formation of the hexaaluminate phase in the presence of cobalt.
Such salts are, inter alia, lanthanum, barium and strontium. Lanthanum, barium
and
strontium are incorporated as interlayer cations. According to the invention,
the use of one or
more of these cations is included. This can form both materials which
incorporate various
cations in the interlayer plane (mixed crystal formation, i.e. single
crystallites which
incorporate both strontium and barium in the interlayer planes, for example)
and also those
which in each case form only crystallites having one type of cation species in
the interlayer
plane but are then present as a mixture of crystallites having different types
of cation species
(i.e., for example, a crystal mixture of crystallites having only barium as
interlayer cations
with crystallites having only strontium as interlayer cations). According to
the invention, both
types of mixture (i.e. mixed crystals and crystal mixture) are included.
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Further cations which are preferred for the purposes of the invention are
those which like
cobalt are incorporated in the spinel blocks. Preference is given to, inter
alia, magnesium,
calcium, gallium, beryllium, nickel, iron, chromium, manganese. Particular
preference is
given to magnesium.
It has, completely surprisingly, been found that carrying out the high-
temperature calcination
at relatively low temperatures in the temperature range from 800 C to 1300 C,
preferably in
the temperature range from 850 C to 1200 C, particularly preferably in the
temperature
range from 900 C to 1100 C, also leads to catalysts which have very good
catalytic
performance properties in respect of the process of the invention for
producing synthesis
gas.
We have thus found an advantageous temperature window for the high-temperature
calcination and the preparation of the catalyst of the invention which gives a
synergist effect
between the performance properties of the materials of the invention in
respect of synthesis
gas production and the particularly high energy efficiency in the process for
preparing the
catalyst.
The preparative process for the catalyst or the catalyst precursor material is
particularly
preferably carried out in the presence of seed crystals. Particular preference
is given to using
seed crystals which have the hexaaluminate structure or a composition similar
to the target
phase. The seed crystals very particularly preferably have a high
crystallinity. Particular
preference is given to carrying out the preparative process for the catalyst
or the catalyst
precursor material in the presence of seed crystals.
A possible effect which can be achieved by the addition of seed crystals is
lowering of the
formation temperature of the hexaaluminate phase when carrying out the process
of the
invention or an increase in the yield of hexaaluminate-comprising phase. It is
also not ruled
out that the formation temperature is lowered and at the same time the yield
is increased. A
further advantageous effect associated with the addition of seed crystals is a
possible
shortening of the crystallization time.
As regards the seed crystals, it may be said that these comprise, in a
preferred embodiment
of the process of the invention, a material having a hexaaluminate phase, the
target product,
more preferably phase-pure hexaaluminate. Furthermore, it is also preferred
that the seed
crystals have a small particle size and a high specific surface area, or
comprise
agglomerates having a small crystallite size and a high specific surface area.
CA 02864063 2014-08-07
13
Seed crystals can be produced from an appropriate hexaaluminate material by
subjecting
this to a suitable mechanical and/or chemical treatment, for example milling
in the dry state,
milling in the presence of water or milling in the presence of acids or bases.
In a particularly preferred embodiment, the seed crystals are brought into
contact with the
aluminum source by intensive mixing. This mixing can be effected by milling,
kneading, pan
milling or other methods known to those skilled in the art. Mixing of the
aluminum source with
the seed crystals can be carried out before, during or after contacting with
the cobalt-
comprising compound and the at least one metal compound.
The aluminum oxide source can, firstly, be provided in the form of a solid,
e.g. powder or
granulated material, and secondly in liquid form. If the aluminum oxide source
is present in
liquid form, preference is given to the aluminum-comprising species being
dispersed in the
solvent or being present as colloidal particles in this. The stability of the
colloidal aluminas or
the formation of the colloidal aluminas can be improved by selecting a pH
which is either in
the range from 2 to 4.5 or in the range from 8 to 12.5. Suitable agents for
producing or
stabilizing the colloidal aluminas are acids such as HNO3, acetic acid or
formic acid or bases
such as aqueous NaOH, KOH or ammonia solution.
In a preferred embodiment of the process of the invention, a colloidal alumina
solution which
has peptized alumina particles and a pH in the range from 2 to 4.5 is used.
The aluminum source is brought into contact with at least one metal compound.
In the case
of addition to the aluminum source present as a liquid, particular attention
is paid to ensuring
that no precipitation of the metal compounds or of the colloids is observed.
The addition of
seed crystals can occur before, during or after addition of the metal
compounds. As an
alternative, the seed crystals can also be added after the drying step.
In a further preferred embodiment of the process of the invention, a
dispersible
nanoparticulate aluminum oxide source is used as finely divided powder. The
finely divided
powder comprises primary particles which have a particle size of less than or
equal to
500 nm and are present as agglomerates having a D50 of from 1 to 100 pm.
In this preferred embodiment, the aluminum source is brought into contact with
at least one
metal compound. The metal compound can be added either as solution or as a
solid. In the
case of a solid, a liquid is subsequently added. In the addition of the
solution or the liquid,
particular attention is paid to ensure that a homogeneous, dough-like
composition which is
CA 02864063 2014-08-07
14
kneadable and displays very intimate mixing of the aluminum oxide source and
the metal
compound is formed. The addition of seed crystals can occur before or after
addition of the
metal compounds. An important feature of this preferred embodiment is that
extrusion as
shaping step (i.e. step (vi)) precedes drying (i.e. step (iv)).
In another preferred embodiment of the process of the invention, the finely
divided powder of
the aluminum source is brought into contact with at least one fusible metal
compound. The
intimate mixing of the aluminum oxide source and the fusible metal compound is
carried out
at a temperature in the range from 25 C to 250 C. In selecting the
temperature, particular
attention is paid to ensure that it is above the melting point of the metal
compound. Melting of
the metal compound results in particular homogeneous distribution of the
components in the
mixture. The addition of seed crystals can occur before, during or after
addition of the metal
compounds. As an alternative, the seed crystals can also be added only after
cooling of the
mixture. =
The low-temperature calcination of the dried mixture or of the molded and
dried material
obtained after the abovementioned process steps serves basically to remove the
anions from
the metal compounds used and convert them into the corresponding metal oxides.
The
temperature in the calcination depends on the metal compounds used and is
preferably less
than or equal to 550 C and more preferably in the temperature range from 150 C
to 550 C.
The high-temperature calcination of the molded and dried mixture or of the low-
temperature-
calcined mixture obtained by above-mentioned process steps is an important
process step in
the preparation of the catalyst of the invention. The temperature in the high-
temperature
calcination must be higher than 800 C and is preferably equal to or greater
than 850 C and
more preferably equal to or greater than 900 C.
It is also important to carry out the calcination for a period of time which
is greater than 0.5
hour, more preferably greater than 1 hour and particularly preferably greater
than 12 hours.
In a further preferred embodiment of the process of the invention, the low-
temperature
calcination (v) and high-temperature calcination (vii) steps can be carried
out in a continuous
process step. This is particularly advantageous when the drying step is
preceded by a
shaping step.
If the temperature in the calcination is below the target temperature of 800
C, preparation of
the catalyst of the invention is adversely affected since the formation of
hexaaluminate fails
_ _
CA 02864063 2014-08-07
or an excessively low proportion of hexaaluminate is formed. If a calcination
temperature
above the suitable temperature range is chosen, two phases which have some
catalytic
activity are formed, but these materials have a surface area which is too low.
The upper limit
to the calcination temperature in the calcination is 1500 C, preferably 1450 C
and more
5 preferably 1400 C.
It is conceivable that the invention could be specified in more detail by
setting down of
specific calcination conditions. However, in industrial operation, a very long
calcination time
is uneconomical and undesirable.
For the specific application of the material as catalyst for producing
synthesis gas, a high
surface area is required. For the purposes of the invention, materials having,
in particular,
surface areas of greater than 2 m2/g are preferred, materials having surface
areas greater
than 4 m2/g are particularly preferred, materials having surface areas greater
than 8 m2/g are
very particularly preferred and materials having surface areas greater than 15
m2/g are very
particularly preferred.
A shaping process is important for the preparation of the catalyst so that the
catalyst can be
used in a suitable way in a tube reactor. This is also related to the fact
that boehmite, which
is particularly preferably used as aluminum oxide source, is preferably
particularly finely
divided, with the primary particle size preferably being in the range from 10
to 500 nm. Direct
introduction of such a very finely divided catalyst prepared from a finely
divided powder
would lead, in a tube reactor, to a high pressure drop or to complete blocking
of the reactor,
which would adversely affect the catalytic reforming process.
The material prepared by the process of the invention can be used in reforming
to produce
synthesis gas in the form of loose material, pellets or extrudates. The choice
of the
appropriate catalyst form depends on the prevailing process conditions which
are important
for the production of synthesis gas.
Shaping is usually carried out after the process steps (iii) or (v), but can
also be undertaken
after process step (vii).
The production of a pelletized shaped body is carried out by means of the
steps (x.1)
compacting, (x.2) sieving and (x.3) tableting. Binders and lubricants can be
added to the
catalyst material or precursor material used for compacting and tableting. As
lubricants, it is
possible to use, for example, graphite or stearic acid. Preference is given to
using graphite.
CA 02864063 2014-08-07
16
The amount of lubricant is usually not more than 10% by weight based on the
catalyst
material.
In addition, it is also possible to produce the target fraction by means of a
compacting
machine which carries out a plurality of steps in succession. The loose
material produced by
the compacting machine can possibly have a lower mechanical stability than the
material
produced by the pressing machine.
Furthermore, it is also possible for a shaped body to be produced by means of
an extrusion
step. Such an extrusion can be carried out after step (ii) or step (iii) of
the production
process.
Apart from the above, it is also possible for the suspension to be dried by
means of a spray
drier and subsequently be subjected to a calcination process.
As binder material for compacting and tableting, an oxide or a plurality of
oxides can be
added to the catalyst or particular oxides can be formed during the synthesis
of the material
by means of specific process features or process steps. Such process features
or process
steps can be, inter alia: preferred selection of the stoichiometry of the
starting compounds,
preferred selection of the type of starting compounds and in particular of the
aluminum
source, preferred selection of the thermal treatment steps. A particularly
suitable binder
material has a positive effect on the formation of a high surface area of the
catalyst of the
invention.
Examples of oxides which are formed from the binder material during
calcination and
represent particularly preferred secondary phases are, inter alia: theta-
aluminum oxide,
alpha-aluminum oxide, lanthanum aluminate (LaA103), barium aluminate
(BaA1204), strontium
aluminate (SrA1204) La-stabilized aluminum oxide, La-stabilized aluminum oxide
hydroxide.
In a further embodiment, it is, for example, possible to apply the catalyst or
the catalyst
precursor material to a ceramic support material by means of a coating
process. As support
material, it is possible to use a ceramic honeycomb body or other shaped
bodies.
To produce a particularly effective catalyst, it is necessary for the
stoichiometry of the
elements which form the catalyst material to be in a particular preferred
range.
CA 02864063 2014-08-07
17
=
For the present purposes, the preferred range of the composition is in each
case based on
the metallic elements and reported in mol percent. The numbers add up to one
hundred
parts, with the presence of oxygen not being taken into account.
For the purposes of the invention, preference is given to a hexaaluminate-
comprising
material whose cobalt content is preferably in the range 2 - 15 mol%,
particularly preferably
in the range 3 - 10 mol%, in particular in the range 4 - 8 mol%.
For the purposes of the invention, preference is given to a hexaaluminate-
comprising
material which has at least one metal species which is present in addition to
cobalt and is
selected from the group consisting of barium, strontium and lanthanum, where
the metal
content of this at least one metal species is preferably in the range 2 - 25
mol%, more
preferably in the range 3 - 15 mol% and in particular in the range 4 - 10
mol%.
Further promoters such as magnesium, gallium, nickel are, for the purposes of
the invention,
preferably added in an amount of less than 10 mol% to the material.
Some examples of materials which have a preferred composition are given below:
A particularly preferred material has a composition in which the La content is
in the range 3 -
20 mol%, the Co content is in the range 2 - 10 mol%, the content of noble
metal-comprising
promoter or additional promoter is in the range 0.25 - 3 mol% and the Al
content is in the
range 70 - 90 mol%.
A further example of a material which is preferred according to the invention
has a
composition in which the content of La and/or Ba is in the range 3 - 20 mol%,
the content of
Co is in the range 2 - 10 mol%, the content of noble metal-comprising promoter
is in the
range 0.1 - 3 mol% and the content of aluminum is in the range 70 - 90 mol%.
Very particular preference is given to a material having a composition in
which the content of
La and/or Sr is in the range 3 - 20 mol%, the Co content is in the range 2 -
10 mol%, the
content of noble metal-comprising promoter or additional promoter is in the
range 0.25 -
3 mol% and the Al content is in the range 70 - 90 mol%.
Very particular preference is given to a material having a composition in
which the Ba
content is in the range 3 - 20 mol%, the Co content is in the range 2 - 10
mol%, the content
of noble metal-comprising promoter or additional promoter is in the range 0.25
- 3 mol% and
the Al content is in the range 70 - 90 mol%.
CA 02864063 2014-08-07
18
Very particular preference is given to a material having a composition in
which the Sr content
is in the range 3 - 20 mol%, the Co content is in the range 2 - 10 mol%, the
content of noble
metal-comprising promoter or additional promoter is in the range 0.25 - 3 mol%
and the Al
content is in the range 70 - 90 mol%.
According to the invention, preference is given to those cobalt hexaaluminate-
comprising
catalysts whose molar ratio of cobalt to aluminum (i.e. the nco/nAl ratio) is
in the range from
0.05 to 0.09 and particularly preferably in the range from 0.06 to 0.08. In a
preferred
embodiment of the catalyst of the invention, the molar ratio of MBasrLa to
aluminum (i.e. the
nMBaSrLainAl ratio) is in the range from 0.09 to 0.25, particularly preferably
in the range from
0.092 to 0.20. The molar ratio of Co to MBaSrLa (i.e. the nco/nMBaSrLa ratio)
is preferably in the
range from 1.0 to 0.3 and particularly preferably in the range from 0.85 to
0.40. The
abbreviation MBasrta indicates that at least one element from the group
consisting of Ba, Sr,
La is comprised.
If the preparation of the catalyst is carried out by impregnation using a
metal salt solution:
suitable metal salts are all salts which can be dissolved in a solvent in
order to be able to
produce a very homogeneous distribution of the metal species on the surface of
the
aluminum source, preferably the boehmite.
The metal salts introduced are preferably nitrates or hydrating nitrates.
Water is used as
preferred solvent.
The aluminum source preferably comprises only small amounts of nitrate or is
nitrate-free.
Considering the nitrate content and the total content of all metallic
components in the
synthesis system (i.e. Al together with Co and the further metals), the
nitrate content is
preferably less than 40 mol%, more preferably less than 25 mol% and even more
preferably
less than 18 mol%.
It is conceivable for noble metal-comprising salts which act as promoters and
lead to an
increase in the activity of the catalyst to be added as secondary constituents
to the
impregnation solution. However, it also has to be taken into account that, for
example, the
use of noble metal-comprising promoters can lead to an increase in the cost of
the catalyst.
Preferred noble metals as promoters are, inter alia, platinum, rhodium,
palladium.
CA 02864063 2014-08-07
19
As regards the introduction of the noble metal-comprising promoters, it may be
said that
these can be introduced during the catalyst synthesis or can be deposited on
the finished
catalyst.
Reforming process
The invention also provides a process for the reforming of hydrocarbons,
preferably
methane, in the presence of carbon dioxide, wherein the process comprises the
following
steps:
(a.1) contacting of a reforming gas comprising more than 70% by volume of
hydrocarbons,
preferably methane, and carbon dioxide with a catalyst whose preparation
comprises
the abovementioned process steps (i) to (vii),
(a.2) heating of the reactor or the catalyst present therein at a temperature
greater than
700 C, preferably greater than 800 C and more preferably greater than 900 C,
during
contacting with the reforming gas,
(a.3) operation of the reactor at a process pressure greater than 5 bar,
preferably greater
than 10 bar and more preferably greater than 15 bar, while carrying out the
reaction,
(a.4) passing a reforming gas stream over the catalyst at a GHSV in the range
from 500 to
20 000 hr-1, preferably in the range from 1500 to 10 000 hr-1 and more
preferably in
the range from 2000 to 5000 hr-1.
In a preferred embodiment of the process of the invention, the reforming
process is preceded
by an activation process. The activation process makes it possible to set the
catalyst to the
desired process parameters under controlled conditions.
The activation process comprises the thermal treatment of the catalyst in a
reducing gas
atmosphere at a temperature in the range from 300 C to 900 C. The catalyst is
preferably
heated to the process temperature using a controlled heating process. The
heating rate is
preferably in the range from 1 C/min to 30 C/min, with a range from 5 C/min to
15 C/min
being preferred.
The activation process is preferably coupled with conditioning of the
catalyst, or the
conditioning follows the activation. For the purposes of the present
invention, conditioning is
a procedure in which the catalyst is brought stepwise to the process
parameters of the target
CA 02864063 2014-08-07
reaction. The conditioning step effectively prevents uncontrolled coke
formation of the
catalyst during start-up.
The conditioning of the catalyst comprises, for example, heating the catalyst
to the process
5 temperature in the presence of methane, steam and/or hydrogen. It is also
possible for the
catalyst to be conditioned in the presence of steam.
The reforming gas, which forms the main constituent of the feed fluid, has a
preferred
composition in which the total proportion of hydrocarbon, preferably methane,
and carbon
10 dioxide is greater than 70% by volume.
The methane and the carbon dioxide are preferably present in equimolar or
virtually
equimolar amounts in the feed fluid. A preferred ratio of methane to carbon
dioxide is in the
range from 4 : 1 to 1 : 2, particularly preferably in the range from 3: 1 to 3
: 4, very
15 particularly preferably in the range from 2: 1 to 3 : 4. The most
preferred ratio of methane to
carbon dioxide is, as mentioned above, 1 : 1. If the hydrocarbon-comprising
starting gas is
ethane, carbon dioxide and ethane are present in a ratio of 2 : 1.
Steam is introduced into the feed fluid during the process. The proportion of
steam in the
20 feed fluid is preferably equal to or less than 30% by volume, more
preferably equal to or less
than 20% by volume and even more preferably equal to or less than 15% by
volume. A
preferred reforming gas composition comprises the components CH4/CO2/H20 in a
percentage ratio range of the gas volumes from 35/35/30 to 48/48/4, more
preferably in the
range from 43/43/14 to 45/45/10.
For process engineering reasons, standard gases or auxiliary gases can be
added to the
reforming gas. The standard gas is, for example, a noble gas which is added in
a proportion
of from 1 to 5% by volume. The addition of an internal standard in laboratory
tests serves to
determine the recovery.
In a preferred process variant, a synthesis gas having an H2/C0 ratio in the
range from 0.85
to 1.4 is produced by means of the process of the invention; the H2/C0 ratio
is more
preferably in the range from 0.9 to 1.2 and even more preferably in the range
from 0.95 to
1.1.
CA 02864063 2014-08-07
21
The process of the invention makes it possible to carry out the reforming
process under
severe process conditions without a significant amount of coke being deposited
on the
hexaaluminate-comprising catalyst as a result. Owing to the very high thermal
stability and
pressure resistance of the catalyst, the latter can be used over long process
running times.
In a preferred embodiment, the reforming process of the invention using the
catalyst of the
invention is distinguished by the cobalt species being present in the cobalt
hexaaluminate
phase of the catalyst and remaining predominantly in the hexaaluminate phase
while
carrying out the process. Thus, the catalyst obtained after carrying out this
preferred process
has only a very low content of metallic cobalt species.
Carrying out reforming at high process pressures is advantageous since a
synthesis gas
which is also under a very high pressure is formed. The synthesis gas can be
used for further
processes in which the synthesis gas as starting material has to be present
under high
pressure. The downstream processes can be the synthesis of methanol, a Fischer-
Tropsch
synthesis or other gas-to-liquid syntheses. The synthesis gas is preferably
used for
downstream processes in which it is necessary to have an H2/C0 ratio which can
also be
provided by the process of the invention using the hexaaluminate-comprising
catalysts.
Since the process of the invention is able to provide a synthesis gas which is
under high
pressure, the process of the invention is superior to the processes known from
the prior art.
I. Example of the preparation of a catalyst according to the invention
To prepare the catalyst E3, cobalt nitrate and a lanthanum nitrate present in
a glass beaker
are firstly admixed with 250 ml of distilled water and dissolved completely.
The cobalt nitrate
is 83.1 g of Co(NO3)3x6H20 and the lanthanum nitrate is 284.9 g of
La(NO3)3x6H20. The
metal salt solution is admixed with 250 g of boehmite, whereupon a suspension
is formed.
The boehmite used is Disperal from SASOL.
The suspension is stirred by means of a mechanically driven stirrer for a
period of 15 minutes
at a stirrer speed of 2000 rpm. The suspension is subsequently introduced
dropwise by
means of a pipette into a cold bath composed of liquid nitrogen in order to
freeze out almost
spherical particles having a particle diameter of 5 mm. The frozen suspension
particles are
firstly dried by means of a freeze drying unit and subsequently pressed
through a sieve to
break them up. The mesh opening of the sieve used here is 500 pm.
CA 02864063 2014-08-07
22
After freeze drying and comminution, the material is precalcined at 520 C in a
furnace. The
calcined material is then pressed by means of a punch press to give pellets,
the pellets are
subsequently comminuted and pressed through a sieve having a mesh opening of 1
mm.
The pellets have a diameter of 13 mm and a thickness of 3 mm. The target
fraction has a
particle size of from 500 to 1000 pm.
For the high-temperature calcination, the material obtained after sieving is
heated at 1100 C
in a muffle furnace for 30 hours while passing a stream of air of 6
liters/minute over the
material. The furnace is heated at a heating rate of 5 C to the temperature of
1100 C.
The catalysts according to the invention El and E2 were produced by the
synthesis
procedure described for E3, with the amounts of cobalt nitrate and lanthanum
nitrate being
selected so as to obtain the catalyst samples which have the molar
stoichiometries indicated
in Table 1.
To produce the catalyst E4, which is an example of a catalyst according to the
invention and
comprises strontium cobalt hexaaluminate, 64.7 g of cobalt acetate, 71.2 g of
strontium
acetate and 250 g of boehmite (Disperal) were used. It was produced by a
method
analogous to the synthesis procedure described for E3.
II. Catalysis tests
To illustrate the process of the invention, six different hexaaluminate-
comprising catalyst
samples (B1 to B3 and El to E3) were tested under the process conditions for
the
conversion of reforming gas in a laboratory catalysis apparatus having six
reactors arranged
in parallel. The catalyst samples B1 to 83 were hexaaluminate-comprising
samples produced
from nickel nitrate and lanthanum nitrate salts. The samples El to E3 were
prepared from
cobalt nitrate and lanthanum nitrate salts. The catalyst samples B1 to B3 were
obtained by
the same preparative process as the catalysts of the invention El to E3, which
is described
under point I., using a nickel nitrate salt instead of the cobalt nitrate
salt. An overview of the
composition of the catalysts tested is given in table 1.
To carry out the tests, samples were introduced into the individual reactors,
using a minimum
amount of in each case 20 ml of sample per test. The reforming tests were
carried out at a
temperature of 850 C and at a temperature of 950 C. As process parameters, a
pressure of
20 bar was selected and a GHSV of 3800 hr-1 was selected. The composition of
the product
CA 02864063 2014-08-07
23
fluids obtained in the reactions was determined by means of GC analyses using
an Agilent
GC equipped with two TCDs and one FID.
Test series 1
A summary of the process conditions and the catalysis data achieved in the
reforming tests
is shown in table 2.
As regards the catalyst tests, it may be said that the test conditions during
the test were
changed stepwise in order to increase the severity (the severity level of the
process
conditions) and thus set more severe process conditions. The change related to
the
composition of the feed fluid and the temperature of the tests. To designate
the different test
stages, an ending from the series S1, S2, S3, ... S9 relating to the
conditions of the
respective test stage was in each case added to the sample numbers in table 2.
The testing
of the catalyst samples was stopped when coke formation commenced, which was
detected
by means of a decrease in activity in the conversion of methane.
The tests were carried out in the presence of 5% by volume of argon as
standard gas, which
was added to the feed fluid for analytical reasons in order to monitor the
recovery.
The starting point for each of the tests was the steam reforming conditions of
stage 1 (i.e.
designated by S1 in table 2) in which the samples were subjected to a reaction
temperature
of 850 C and a methane: H20 ratio of 1 : 1.
In the second stage (i.e. stage S2), the catalysts were subjected to
trireforming conditions in
which the feed fluid comprised methane, carbon dioxide and steam.
In stages 3 to 7, the addition of steam was entirely omitted, but hydrogen was
added to the
feed fluid. The proportion of hydrogen was reduced stepwise from 40% by volume
to 10% by
volume from stage 3 through to stage 7, while the proportion of methane and
carbon dioxide
was in each case increased from 27.5% by volume to 42.5% by volume. An
exception is the
transition from stage 4 to stage 5, in which the catalyst temperature was
increased from
850 C to 950 C but the composition of the feed fluid was kept constant.
From step 8 onward, hydrogen was again added to the feed fluid, but compared
to stage 7,
half of the hydrogen (i.e. 5% by volume of H2) was replaced by steam. From
stage 9 onward,
CA 02864063 2014-08-07
24
the addition of hydrogen to the feed fluid was completely omitted, and the
proportion of
steam was increased from 5% by volume to 10% by volume.
The cobalt-comprising hexaaluminates displayed a greater activity than the
nickel-comprising
hexaaluminates at higher process severity (i.e. at increased severity). Thus,
in the case of
samples B1, B2 and B3, coke formation commenced from test stages S5, S7 and
S6, so that
the tests had to be stopped at these test stages. The time until commencement
of coke
formation was here in the range from 260 to 360 hours. The commencement of
coke
formation on the catalyst samples has been denoted by the letters KA in table
2.
The cobalt-comprising hexaaluminate samples El, E2 and E3, on the other hand,
could still
be used under the reaction conditions of process stages S8 and S9. During test
stage S9,
the catalyst samples were tested at a temperature of 950 C, with the feed gas
having a
composition of 42.5% by volume of methane, 42.5% by volume of carbon dioxide
and 10%
by volume of H20.
Table 1 shows the composition of the catalyst samples B1 to B3 and El to E3
(the values
indicated are in mol%), the associated BET surface area (SA - surface area)
and the bulk
density (LBD = loose bulk density).
SA LBD
Sample Ni Co La Al
[m2/g] [g/m1]
B1 6 8 86 6.1 0.953
B2 6 10 84 4.0 1.042
B3 6 14 80 3.1 1.196
El 6 8 86 13.8 0.953
E2 6 10 84 7.1 1.036
E3 6 14 80 8.3 1.008
CA 02864063 2014-08-07
Table 2 shows a summary of the composition of the catalysts tested, the
reaction conditions
and the conversions.
Exam- Temp. CH4 CO2 H20 H2 CH4 002 H2/C0
ple [ C] [vol.%] [vol.%] [vol.%] [vol.%] conv. conv. ratio
Fol r/ol
B1_S1 850 47.5 - 47.5 0 32 4.4
B1_S2 850 27.5 27.5 40 50 24 1.7
B1_S3 850 27.5 27.5 - 40 4 56 1.35
B1 S4 850 32.5 32.5 - 30 36 73 1.2
B1_S5 950 32.5 32.5 - 30 KA
B2_S1 850 47.5 - 47.5 - 40 4.5
B2_S2 850 27.5 27.5 40- 65 30 1.6
B2_S3 850 27.5 27.5 - 40 6 58 1.6
B2_S4 850 32.5 32.5 - 30 4 40 1.45
B2_S5 950 32.5 32.5 - 30 40 75 1.2
B2_S6 950 37.5 37.5 - 20 55 85 1.05
B2_S7 950 42.5 42.5 - 10 KA
5
B3_S1 850 47.5 - 47.5 - 34 4.8
B3_52 850 27.5 27.5 40 52 23 1.7
B3_S3 850 27.5 27.5 - 40 4 56 1.71
B3_S4 850 32.5 32.5 - 30 36 75 1.25
B3_S5 950 32.5 32.5 - 30 58 80 1.4
B3_S6 950 37.5 37.5 - 20 KA
E1_S1 =850 47.5 - 47.5 - 25 6
E1_S2 850 27.5 27.5 40- 35 16 1.7
= E1_S3 850 27.5 27.5 - 40 17 66 1.6
E1_S4 850 32.5 32.5 - 30 18 63 1.08
E1_S5 950 = 32.5 32.5 - 30 60 = 86 1.28
E1_S6 950 37.5 37.5 - 20 62 85 1.05
E1 S7 950 42.5 42.5 - 10 57 79 0.86
E1_S8 950 42.5 42.5 5 5 60 74 0.86
E1_S9 950 42.5 42.5 10 - 82 78 1.1
CA 02864063 2014-08-07
26
E2_S1 850 47.5 - 47.5 - 5 12
E2_S2 850 27.5 27.5 40 - 8 2 2.25
E2 S3 850 27.5 27.5 - 40 25 70 1.6
E2_S4 850 32.5 32.5 - 30 41 75 1.2
E2_S5 950 32.5 32.5 - 30 65 90 1.3
E2_S6 950 37.5 37.5 - 20 68 90 1.09
E2 S7 950 42.5 42.5 - 10 71 89 0.93
E2_S8 950 42.5 42.5 5 5 75 85 0.93
E2_S9 950 42.5 42.5 10- 82 79 1.0
E3 S1 850 47.5 - 47.5 - 6 7.2
E3 S2 850 27.5 27.5 40- 10 5 1.82
E3_S3 850 27.5 27.5 - 40 30 74 1.55
E3 S4 850 32.5 32.5 - 30 38 74 1.2
E3_S5 950 32.5 32.5 - 30 65 90 1.3
E3_S6 950 37.5 37.5 - 20 68 90 1.08
E3_S7 950 42.5 42.5 - 10 70 88 0.92
E3_S8 950 42.5 42.5 5 5 74 85 0.92
E3 S9 950 42.5 42.5 10- 85 75 1.15
Test series 2
Part of the catalyst sample from the experimental example E2 was subjected to
a further
catalytic test under altered test conditions. The composition of the feed and
the test
procedure 2 are shown in table 3. In the test, the sample E2 was supplied with
a feed which
had very low steam partial pressures compared to the tests shown in table 2.
Test procedure
2 is changed from the first test procedure in that hydrogen was added to the
feed gas only in
a few process stages. In those process stages in which hydrogen was introduced
into the
feed gas, the content of hydrogen was low and was 5% by volume or 10% by
volume. In the
first process stages (S01 to SO4), the thermodynamic equilibrium was not
achieved, even
approximately. A conceivable explanation of the failure to achieve a state in
the vicinity of the
thermodynamic equilibrium would be that the catalyst has initially been
reduced only
incompletely at the high steam partial pressures.
=
CA 02864063 2014-08-07
27
An unexpected finding was that the catalyst E2 displayed a very high catalytic
activity over
an extremely long period of time under the high-severity conditions (i.e.
extremely harsh and
demanding process conditions) and this was maintained over a very long period
time of more
than 250 hours. After the end of the test, the catalyst was removed from the
reactor and
displayed no coke deposits. The results thus demonstrate the high resistance
to coke
formation of the catalyst during operation of the catalyst under the process
conditions
indicated in table 3. At the same time, a product stream having an
advantageous ratio of H2
to CO was obtained.
Table 3 shows the test conditions and results for the testing of catalyst
sample E2 using test
procedure 2 with changed process stages (S01 to S05). The catalytic
measurements were
carried out at 850 C.
Example TOS CH4 CO2 H20 H2 CH4 CO2 Hz/CO
[h] [vol.%] [vol.%] [vol.%] [vol.%] conv. conv. ratio
[Vo]
E2 _S01 0- 27.5 27.5 40.0 0 10-33 3-9 1.7-1.9
94
E2 SO2 94¨ 32.5 32.5 30.0 0 37-31 21-19 1.4
141
E2S03 141- 37.5 37.5 20.0 10.0 30 33-31 1.3-1.4
167
E2_SO4 167- 37.5 37.5 25.0 5.0 29-26 28-27 1.2
191
E2_505 191- 37.5 37.5 20.0 0 26-65 23-57 1.1-1.0
453
'15 Test series 3
In a further trial, examples of catalysts according to the invention which had
been prepared
as described in Examples E1, E2 and E4 and a comparative sample which had been
prepared as described in Example B2 were subjected to catalytic reforming in
which a
hydrogen-free feed gas was used. The results of these studies and the
experimental
conditions in respect of the temperature and the feed gas composition are
shown in Table 5.
Samples El and E2 were hexaaluminate-comprising catalysts in which the
hexaaluminate
phase comprised cobalt and lanthanum, sample E4 was a hexaaluminate-comprising
catalyst in which the hexaaluminate phase comprised cobalt and strontium and
sample B2
CA 02864063 2014-08-07
28
was a hexaaluminate-comprising catalyst in which the hexaaluminate phase
comprised
nickel and lanthanum.
Compared to the catalysis experiments which were carried out in test series 1
and 2 and
whose results are shown in Tables 2 and 3, a smaller amount of steam was added
to the
feed gas in test series 3. Overall, the feed gas in test series 3 has a low
steam partial
pressure and does not comprise any hydrogen (see Table 5). The test procedure
used in test
series 3 (i.e. test procedure 3) is divided into various process stages. In
the first process
stage (S001), the catalyst was brought into contact with a feed gas comprising
an equimolar
ratio of methane to water (H20 to CH4 = 1.0). In the second process stage, a
feed gas
comprising an equimolar ratio of 27.5% by volume of methane and 27.5% by
volume of
carbon dioxide and additionally 40% by volume of H20 was used. In the next
three process
stages (S003-S005), the equimolar ratio of methane to carbon dioxide was then
maintained
while the water content was decreased stepwise from 30% by volume (in process
stage
S003) to 15% by volume (in process stage S005). (In process stage S005, the
H20 to CH4
ratio is 0.38.)
The results achieved in test series 3 show that the cobalt hexaaluminate-
comprising catalyst
samples El, E2, E4 make a high catalytic activity and stable operation
possible over long
periods of time and under very severe process conditions (high-severity
conditions) in
particular at high temperatures and very low H20 partial pressures of only 15%
by volume. In
comparison, the nickel hexaaluminate-comprising sample B2 could be operated
only up to
process stage S003 (30% by volume of H20). Making the process conditions more
severe
led to rapid coking of the sample B2, so that the experiment had to be
stopped.
The studies carried out on the samples El, E2 and E4 were in each case stopped
after a
cumulative running time of more than a thousand hours and the samples were
removed from
the reactor tube. None of the samples recovered after the test had coke
deposits. The results
are thus a further finding which demonstrates the extremely high coking
resistance of the
cobalt hexaaluminate-comprising catalysts of the invention under the severe
process
conditions indicated in Table 5. At the same time, as can be seen from Table
5, a product
stream having an advantageous ratio of H2 to CO could be obtained in the
catalysis
experiments.
CA 02864063 2014-08-07
29
Table 4 shows the composition of the catalyst sample E4 (the values are
reported in mol%),
the associated BET surface area ("surface area") and the bulk density ("loose
bulk density").
SA LBD
Sample Co Sr Al
[m2/g] [g/ml]
E4 6 8 86 25.0 1.035
'
Table 5 shows the test conditions and results obtained in the examination of
catalyst
samples El, E2, E4 and B2 in test series 3. Test series 3 was carried out
using a test
procedure (test procedure 3) in which the samples were in each case subjected
to five
process stages (S001 to S005). The catalytic tests were carried out at a
temperature of
850 C and a pressure of 20 bar.
Example Temp. CH4 CO2 H20 CH4 CO2 H2/C0
[ C] [vol.%] [vol.%] [vol.%) cony. cony. ratio
[%] [%]
B2_S001 850 47.5 - 47.5 32- 4.9
B2 S002 850 27.5 27.5 40 43 16 1.7
B2_S003 850 32.5 32.5 30 40 21 1.4
B2_S004 850 37.5 37.5 20 - - KA
B2_S005 850 40.0 40.0 15 - - KA
E1_S001 850 47.5 - 47.5 58 - 3.8
E1_S002 850 27.5 27.5 40 75 24 1.9
E1_5003 850 32.5 32.5 30 62 33 1.6
E1_S004 850 37.5 37.5 20 71 59 1.1
E1_S005 850 40.0 40.0 15 65 65 1.0
E2_S001 850 47.5 - 47.5 52 - 4.0
E2_S002 850 27.5 27.5 40 77 31 1.8
CA 02864063 2014-08-07
E2 S003 850 32.5 32.5 30 57 31 1.6
E2_S004 850 37.5 37.5 20 70 58 1.1
E2_S005 850 40.0 40.0 15 65 65 1.0
E4_S001 850 47.5 - 47.5 41 4.4
E4_S002 850 27.5 27.5 40 60 21 1.8
E4_S003 850 32.5 32.5 30 72 49 1.3
E4_S004 850 37.5 37.5 20 67 60 1.1
E4_3005 850 40.0 40.0 15 64 64 1.0
Fig. 1 shows three diffraction patterns which were recorded on the catalyst
samples El, E2
and E3 according to the invention before the catalysis test (i.e. on the fresh
catalyst samples
E1-f to E3-f). The diffraction patterns of all three samples have reflections
at 32.08, 34.01
5 and 36.10 020 which can be assigned to cobalt hexaaluminate and a
reflection at 33.42 020
which can be assigned to the perovskite phase. Further crystalline phases
cannot be
discerned by means of the present XRD analysis.
Fig. 2 shows two diffraction patterns which were recoded on catalyst samples
E2 before and
10 after the catalysis test and have been designated as E2-f (fresh
catalyst sample) and E2-g
(aged catalyst sample). The diffraction pattern recorded on the sample before
the catalysis
test was carried out displays no difference from the diffraction pattern
recorded on the aged
sample. It can be seen from the studies that the cobalt remains in the
hexaaluminate phase
and is not dissolved out from this. Cobalt in the form of the free metal could
not be detected
15 even in the aged sample.
Fig. 3 shows two diffraction patterns recorded on the catalyst samples B2
before (i.e. sample
B2-f) and after (i.e. sample B2-g) the catalysis test. The diffraction pattern
recorded on the
aged sample (B2-g) displays a reflection at 44.40 020, which can be assigned
to a phase
20 composed of metallic nickel. The metallic nickel phase cannot be
discerned in the diffraction
pattern of the fresh catalyst sample, since a corresponding reflection is not
present.
CA 02864063 2014-08-07
31
Fig. 4 shows the results of the XPS analyses which were in each case measured
on a fresh
catalyst sample E2-f and an aged catalyst sample E2-g. The cobalt species
detected in the
fresh sample E2-f can all be assigned to the cobalt hexaaluminate phase. The
aged catalyst
sample E2-g displays different cobalt species. It is noteworthy that the
majority of the cobalt
species can be assigned to the hexaaluminate phase and the content of metallic
cobalt is
only low.
The samples E2-f (fresh catalyst sample before catalysis testing) and E2-g
(aged catalyst
sample after catalysis testing) were each subjected to XPS analysis (XPS: X-
ray
photoelectron spectroscopy). The results of these XPS analyses are shown in
Table 6. In the
catalyst sample E2-f (i.e. the fresh catalyst), the cobalt is present
exclusively as cobalt
lanthanum hexaaluminate (Co-HA, 781.2 eV).
Table 6 shows the relative proportions of cobalt in the cobalt lanthanum
hexaaluminate
phase (Co-HA), the cobalt(II) oxide phase (Co(II) oxide) and the metallic
cobalt phase (Co
metal). In sample E2-g (i.e. the aged catalyst sample removed from the
reactor), two further
cobalt species, namely a cobalt(II) oxide (CoO, 780.4 eV) and a cobalt metal
(Co metal,
778.4 eV) were detected in addition to the cobalt species present in the
cobalt lanthanum
hexaaluminate (Co-HA, 781.2 eV). Quantification of the XPS data (Table 6)
confirms the
unexpected finding that a significant proportion of nonmetallic cobalt is
present in the aged
sample and that the cobalt remains substantially in the cobalt lanthanum
hexaaluminate
phase. It can be assumed that the unexpected finding represents a critical
characteristic of
the catalyst of the invention and plays an important role in the extraordinary
coking
resistance and activity of the catalyst.
CA 02864063 2014-08-07
32
Table 6 summarizes the XPS data of a fresh sample of catalyst E2-f and an aged
sample of
catalyst E2-g after removal from the test reactor (n.d. = not detected).
Relative proportions of cobalt species (%)
Co-HA Co(II)
oxide
(781.2 Co metal (778.4 eV)
(780.4
eV)
eV)
E2-f
100 n.d. n.d.
(fresh sample)
E2-g
82.6 9.2 8.3
(aged sample)
Physical characterization of all catalyst sample described in the examples was
carried out by
means of XRD analyses, nitrogen sorption measurements and bulk density
measurements.
The XRD analyses were carried out using a D8 Advance Series 2 from Bruker/AXS
using a
CuK alpha source (having a wavelength of 0.154 nm at 40 kV and 40 mA). The
measurements were carried out over the measurement range: 5-80 (2 theta),
0.02 steps
with 4.8 seconds/step.
The XPS analyses were carried out on a PHI 5000 VersaProbe spectrometer using
Al K-a X-
radiation (1486.6 eV, monochromator) and a 180 hemispherical analyzer with a
16-channel
detector. A spot size of 200 p.m (50 watt) was used in the measurements. The
C1s peak
(284.8 eV) was used for calibration of the energy axis of the XPS spectrum.
