Note: Descriptions are shown in the official language in which they were submitted.
DOUBLE PEROXIDE TREATMENT OF OXIDATIVE DEHYDROGENATION
CATALYST
FIELD OF THE INVENTION
The present invention relates to an improved method for making a catalyst
for the oxidative dehydrogenation of lower alkanes to lower alkenes.
Multicomponent metal oxide catalysts for the oxidative dehydrogenation of
alkanes
are known. Such catalysts are typically made by mixing solutions of metals and
then precipitating the metal oxide "mixture" from the solution and calcining
it. As a
result the catalysts are heterogeneous mixtures of various metal oxides and
phases
and may include some highly active species but also some species which have a
significantly lower activity. Applicants have found that by treating the
precipitated
metal oxides with a controlled amount of hydrogen peroxide prior and
subsequent
to calcining, both the consistency and activity of the catalyst is improved.
BACKGROUND OF THE INVENTION
United States Patent 2,895,920 issued July 21, 1959 to Janoski, assigned to
Sun Oil Company teaches a process to prepare a catalyst for the conversion of
hydrocarbons such as dehydrogenation. The catalysts comprise oxides of cobalt,
iron, nickel, molybdenum, manganese, chromium, vanadium, tin, and tungsten.
The catalysts do not incorporate any niobium. In the process to make the
catalysts
a hydrogel is prepared of metal oxide(s) which are difficult to reduce and
metal
oxides which are capable of existing in several oxidation states. A hydrogel
of the
metals is prepared and aged in the presence of hydrogen peroxide. The aged
hydrogel is treated with a compound to precipitate the metals which are then
filtered, dried and calcined. The sequence of treatments is different than
that in the
present invention.
CA 3017900 2018-09-20 1
United States Patent 3,474,042 issued Oct. 21, 1969 to Fattore etal.,
assigned to Montecatini Edison S.p.A. teaches a metal oxide catalyst
comprising
molybdenum or tungsten. The catalysts are prepared by forming peroxy -
compounds of tungsten and molybdenum, by reacting the metal oxide with
hydrogen peroxide or compounds which form hydrogen peroxide. The molar ratio
of peroxide to metal oxide may range from 0.25 to 10, typically from 1 to 3.
The
solution may be spray-dried or impregnated into a carrier.
United States Patent 4,709,070 issued Nov. 24, 1987 to Sasaki et al.,
assigned to Nitto Chemical industry Co., Ltd. teaches a method to regenerate
the
activity of a complex metal oxide catalyst used for oxidation, ammoxidation
and
oxidative dehydrogenation of alkanes. The catalysts prior to reactivation are
quite
different from those herein. They contain a number of elements not present in
the
catalysts of the present invention such as Fe, Sb, Cu, and Co. The
"deactivated"
catalyst is treated with a Te compound, a Mo compound or a mixture thereof.
The
Te and Mo compounds may be oxides. In some instances the Te and Mo
compounds may be prepared by contacting them with H202 in the presence of the
oxide, oxyacid, salts of oxyacids, heteropoly acids or salts thereof of
molybdenum
(Col. 9 lines 38-42). The patent teaches away from treating the entire
catalyst
precursor and resulting catalyst with H202.
The supporting data for "Aiding the Self-Assembly of Supramolecular
Polyoxometalates Under Hydrothermal Conditions to Give Precursors of Complex
Functional Oxides", Angewandte Chemie 201200746, Maricruz Sanchez Sanchez,
Frank Girgsdies, Mateusz Jastak, Pierre Kube, Robert Schlogo and Annette
Trunschke (copyright Wiley ¨ VCH 2012) teaches a hydrothermal process for
making complexes similar to oxidative dehydrogenation catalysts. The
components
2
CA 3017900 2018-09-20
are added step wise to the autoclave apparently without reducing pressure. The
addition of components is monitored by Raman spectroscopy to provide a product
having a high amount of M1 phase without peroxide treatment. The reference
does
not suggest treating the intermediate or the final catalyst with hydrogen
peroxide.
Complexes produced by the process had the formula Mo1V0.2Teo.2Nbo.20d. The
reference does not teach the process or the catalysts of the present
invention.
United States Patent 8,105,972 issued Jan. 31, 2012 to Gaffney et al. from
an application filed April 2, 2009, assigned to Lummus Technology Inc. teaches
a
catalyst for the oxidative dehydrogenation of alkanes. The catalyst is formed
in a
conventional manner by hydrothermal treatment of metal oxide components. The
resulting catalyst is recovered, dried and calcined. Then the calcined
catalyst is
treated with an acid. This process teaches away from the subject matter of the
present invention as it teaches a post calcining treatment. Further the patent
fails
to teach treatment with H202.
The present invention seeks to provide an improved catalyst for oxidative
dehydrogenation by treating the catalyst precursor with H202, prior to
calcining and
the resulting calcined catalyst with H202.
SUMMARY OF THE INVENTION
In one embodiment of the invention an oxidative dehydrogenation catalyst is
prepared by the hydrothermal reaction of compounds of Mo, V, Te, and Nb and,
prior and subsequent to calcining, treating the precursor and calcined
catalyst with
H202.
In one embodiment the present invention provides an oxidative
dehydrogenation catalyst of the empirical formula (measured by PIXE).
MotoVo.25-0.38Teo.io-o.16Nbo.15-o.190d
CA 3017900 2018-09-20 3
where d is a number to satisfy the valence of the oxide.
In one embodiment the present invention involves treating a oxidative
dehydrogenation catalyst precursor, prior to calcining, with H202 in an amount
equivalent to 0.30 ¨ 2.8 mL H202 of a 30% solution per gram of catalyst
precursor
and treating the calcined oxidative dehydrogenation catalyst with H202 in an
amount equivalent to 0.30 ¨ 2.8 mL H202 of a 30% solution per gram of
catalyst.
In a further embodiment the catalyst is prepared by:
i) forming an aqueous solution of ammonium heptamolybdate
(tetrahydrate) and telluric acid at a temperature from 30 C to 85 C and
adjusting
.. the pH of the solution to from 6.5 to 8.5, preferably from 7 to 8, most
preferably
from 7.3 to 7.7 with a nitrogen-containing base to form soluble salts of the
metals;
ii) preparing an aqueous solution of vanadyl sulphate at a temperature
from room temperature to 80 C (preferably 50 C to 70 C, most preferably 55 C
to
65 C);
iii) mixing the solutions from steps i) and ii) together;
iv) slowly (dropwise) adding a solution of niobium monoxide oxalate
(NbO(C204H)3) to the solution of step iii) to form a slurry;
v) heating the resulting slurry in an autoclave under an inert atmosphere
at a temperature from 150 C to 190 C for not less than 10 hours (hydrothermal
treatment);
vi) treating either:
a) the resulting slurry with the equivalent of from 0.3 ¨
2.8 mL of a
30% w/w solution of H202 per gram of catalyst precursor for a time from 5
minutes to 10 hours at a temperature from 20 to 80 C and filtering and
drying the resulting solid; or
CA 3017900 2018-09-20 4
b)
filtering and washing with deionized water, and drying the
washed solid from step v) for a time from 4 to 10 hours at a temperature
from 70 to 100 C treating the dried isolated precursor, with the equivalent of
from 0.3 ¨ 2.8 mL of a 30% w/w solution of H202 per gram of catalyst
precursor for a time from 5 minutes to 10 hours at a temperature from 20 to
80 C;
vii) calcining the resulting precursor in an inert atmosphere at a
temperature from 200 C to 600 C for a time from 1 to 20 hours;
viii) recovering the calcined catalyst from step vii) and treating it with
the
equivalent of 0.3 ¨ 2.8 mL of a 30% w/w solution of H202 per gram of calcined
catalyst for a time from 5 minutes to 10 hours at a temperature from 20 to 80
C;
and
ix) recovering the treated calcined catalyst.
In a further embodiment in the catalyst the molar ratio of Mo:V is from 1:
0.26
to 1:0.38.
In a further embodiment in the catalyst the molar ratio of Mo:Te is greater
than 1:0.11 and less than 1:0.15.
In a further embodiment in the catalyst the molar ratio of Mo:Te is from
1:0.11 to 1: 0.13.
In a further embodiment in the catalyst the molar ratio of Mo:Nb is from
1:0.11 to 1: 0.16.
In a further embodiment the catalyst has a bulk density from 1.20 to 1.53
g/cc.
CA 3017900 2018-09-20 5
In a further embodiment in the crystalline phase of the catalyst the amount of
the phase having the formula (Te0)0.39(Mo3.52V1.06N1b0.42)014 is above 75 wt%
of the
measured crystalline phase as determined by XRD.
In a further embodiment, the active phase of the catalyst after double
hydrogen peroxide treatment has an XRD peak at 21.81 ( 0.4) which is apparent
and not hidden in the reference reflection at 22.29 ( 0.4).
A further embodiment, the active phase of the double H202 treated catalyst
has an XRD height at 21.81 ( 0.4) which is 1-6% relative peak height of the
reference reflection at 22.29 ( 0.4).
A further embodiment of the invention provides a method for the oxidative
dehydrogenation of a mixed feed of ethane and oxygen in a volume ratio from
70:30 to 95:5 at a temperature less than 425 C, preferably less than 400 C
preferably less than 390 C at a gas hourly space velocity of not less than 500
hrl
and a pressure from 0.8 to 1.2 atmospheres comprising passing said mixture
over
the above catalyst.
In a further embodiment a conversion to ethylene is not less than 90%.
In a further embodiment the gas hourly space velocity is not less than
1000 hrl.
In a further embodiment the calcined catalyst forms a fixed bed in the
reactor.
In a further embodiment the catalyst has the empirical formula (measured by
PIXE):
MotoVo.25-o38Teo.io-o.16Nbo.15-o.190d
where d is a number to satisfy the valence of the oxide.
CA 3017900 2018-09-20 6
In a further embodiment the hydrothermal reactor is seeded with the above
double peroxide treated catalyst.
In a further embodiment the internal surface of the hydrothermal reactor is
selected from the group consisting of stainless steel, silica, alumina coating
and
polytetrafluoroethylene.
In a further embodiment the hydrothermal reactor contains particulates
(irregular such as flakes, granules, globules, filaments, etc. or regular such
as
spheres, elliptical, rods, rectangular prisms (both right and non-right),
pentagonal
prisms, pyramids, etc.) of stainless steel, silica, glass (e.g. PYREX ¨
borosilicate
glass) alumina and polytetrafluoroethylene seeded with the above double
peroxide
treated catalyst.
In a further embodiment there is provided a fully fluorinated ethylene
propylene polymer reactor coating seeded with the above double peroxide
treated
catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic drawing of the reactor used for testing the ODH
catalysts.
Figure 2 is plot of the conversion of ethylene as a function of temperature
for
a catalyst prepared without H202 treatment.
Figure 3 is a plot of selectivity for ethylene against temperature for a
catalyst
prepared without H202 treatment.
Figure 4 is a plot of the conversion of ethylene as a function of temperature
for a catalyst prepared only treating the precursor with H202.
Figure 5 is a plot of the selectivity for ethylene against temperature for a
catalyst in which only the precursor was treated with H202.
CA 3017900 2018-09-20 7
Figure 6 is a plot of the conversion of ethylene as a function of temperature
for a catalyst prepared according to the present invention.
Figures 7 is a plot of the selectivity for ethylene against temperature for
the
catalyst of the present invention.
Figure 8 is an XRD diffraction pattern (collected with CuKa source) of the
catalyst prepared according to comparative example 1.
Figure 9 is an XRD diffraction pattern (collected with CuKa source) of the
catalyst prepared according to example 4.
Figure 10 is a blow up of the XRD diffraction pattern (CuKa source) of the
.. catalyst prepared according to comparative example 1, between 21 and 23
two(I).
Figure 11 is a blow up of the XRD (CuKa source) diffraction pattern of the
catalyst prepared according to example 4, between 21 and 23 two(1).
DETAILED DESCRIPTION
Numbers Ranges
Other than in the operating examples or where otherwise indicated, all
numbers or expressions referring to quantities of ingredients, reaction
conditions,
etc. used in the specification and claims are to be understood as modified in
all
instances by the term "about". Accordingly, unless indicated to the contrary,
the
numerical parameters set forth in the following specification and attached
claims
are approximations that can vary depending upon the properties that the
present
invention desires to obtain. At the very least, and not as an attempt to limit
the
application of the doctrine of equivalents to the scope of the claims, each
numerical
parameter should at least be construed in light of the number of reported
significant
digits and by applying ordinary rounding techniques.
CA 3017900 2018-09-20 8
Notwithstanding that the numerical ranges and parameters setting forth the
broad scope of the invention are approximations, the numerical values set
forth in
the specific examples are reported as precisely as possible. Any numerical
values,
however, inherently contain certain errors necessarily resulting from the
standard
deviation found in their respective testing measurements.
Also, it should be understood that any numerical range recited herein is
intended to include all sub-ranges subsumed therein. For example, a range of
"1 to
10" is intended to include all sub-ranges between and including the recited
minimum value of 1 and the recited maximum value of 10; that is, having a
minimum value equal to or greater than 1 and a maximum value of equal to or
less
than 10. Because the disclosed numerical ranges are continuous, they include
every value between the minimum and maximum values. Unless expressly
indicated otherwise, the various numerical ranges specified in this
application are
approximations.
All compositional ranges expressed herein are limited in total to and do not
exceed 100 percent (volume percent or weight percent) in practice. Where
multiple
components can be present in a composition, the sum of the maximum amounts of
each component can exceed 100 percent, with the understanding that, and as
those skilled in the art readily understand, the amounts of the components
actually
used will conform to the maximum of 100 percent.
In the specification the phrase the temperature at which there is 25%
conversion of ethane to ethylene is determined by determining conversion at a
number of temperatures typically with data points below and above 25%
conversion. Then a plot of the data is prepared or the data is fit to an
equation and
CA 3017900 2018-09-20 9
the temperature at which there is a 25% conversion of ethane to ethylene is
determined.
In the specification the phrase selectivity at 25% conversion is determined by
determining the selectivity at a number of temperatures below and above the
temperature for 25% conversion. The data may then be plotted or fit to an
equation. Then having calculated the temperature at which 25% conversion
occurs
one can determine either from the graph or from the equation the selectivity
at that
temperature.
The calcined catalysts of the present invention typically have the formula (as
determined by PIXE):
MotoVo.25-0.38Teo.io-o.i6Nbo.15-0.190d
where d is a number to satisfy the valence of the oxide. In some embodiments
the
molar ratio of Mo:V in the calcined catalyst is from 1: 0.25 to 1:0.35, in
other
embodiments the molar ratio of Mo:V in the calcined catalyst is from 1: 0.27
to
1:0.32, in some embodiments from 1:0.28 to 1:0.30. In other embodiments the
molar ratio of Mo:Te in the calcined catalyst is greater than 1:0.10 and less
than
1:0.16, in further embodiments the molar ratio of Mo:Te in the calcined
catalyst is
from 1:0.11 to 1:0.15.
The catalyst is typically prepared by mixing solutions or slurries
(suspensions) of oxides or salts of the metallic components.
In some embodiments the catalyst may be prepared by a process
comprising the following steps:
i) forming an aqueous solution of ammonium heptamolybdate
(tetrahydrate) and telluric acid at a temperature from 30 C to 85 C and
adjusting
CA 3017900 2018-09-20 10
the pH of the solution to 6.5 to 8.5, preferably from 7 to 8, most preferably
from 7.3
to 7.7 preferably with a nitrogen-containing base to form soluble salts of the
metals;
ii) preparing a aqueous solution of vanadyl sulphate at a temperature
from room temperature to 80 C (preferably 50 C to 70 C, most preferably 55 C
to
65 C);
iii) mixing the solutions from steps i) and ii) together;
iv) slowly (dropwise) adding a solution of niobium monoxide oxalate
(NbO(C204H)3) to the solution of step iii) to form a slurry;
v) heating the resulting slurry in an autoclave under an inert atmosphere
at a temperature from 150 C to 190 C for not less than 10 hours (hydrothermal
treatment);
vi) filtering and washing the slurry from step v) with deionized water and
drying the resulting solid for a time from 4 to 10 hours at a temperature from
70 to
100 C;
vii) treating the dried precursor from step vi with the equivalent of from
0.3 ¨ 2.8 mL of a 30% w/w solution of H202 per gram of catalyst precursor for
a
time from 5 minutes to 10 hours at a temperature from 20 to 80 C;
viii) calcining the resulting catalyst precursor in an inert
atmosphere at a
temperature from 200 C to 600 C for a time from 1 to 20 hours;
ix) recovering the calcined catalyst from step viii) and treating it with
the
equivalent of from 0.3 ¨ 2.8 mL of a 30% w/w solution of H202 per gram of
calcined
catalyst for a time from 5 minutes to 10 hours at a temperature from 20 to 80
C;
and
x) recovering the treated calcined catalyst.
CA 3017900 2018-09-20 11
Following step i) one or more of the following steps may be incorporated in
the process:
a) evaporating the aqueous solvent to obtain a solid;
b) drying the solid at a temperature from 80 C to 100 C; and
c) redissolving the solid in water at a temperature from 40 C to 80 C
(preferably 50 C to 70 C, most preferably 55 C to 65 C).
Following step ii) the solutions may be cooled to a temperature from 20 C to
30 C.
As a part of step vi) the solution may be cooled to a temperature from 20 C
to 30 C.
In a further embodiment the precursor may be made by a process
comprising:
i) forming an aqueous solution of ammonium heptamolybdate
(tetrahydrate) and telluric acid at a temperature from 30 C to 85 C and
adjusting
.. the pH of the solution to 7.3 to 7.7 (preferably 7.4 to 7.5) with a
nitrogen-containing
base to form soluble salts of the metals;
ii) evaporating the aqueous solvent to obtain a solid;
iii) drying the solid at a temperature from 80 C to 100 C;
iv) redissolving the solid in water at a temperature from 40 C to 80 C
(preferably 50 C to 70 C, most preferably 55 C to 65 C);
v) preparing a aqueous solution of vanadyl sulphate at a temperature
from room temperature to 80 C (preferably 50 C to 70 C, most preferably 55 C
to
65 C);
vi) cooling the solutions from steps iv) and v) to a temperature from 20 to
30 C;
CA 3017900 2018-09-20 12
vii) mixing the cooled solutions from step vi together;
viii) slowly (dropwise) adding a solution of niobium monoxide oxalate
(NbO(C204F1)3) to the solution of step vii) to form a (brown) slurry;
ix) heating the resulting slurry in an autoclave under an atmosphere free
of oxygen at a temperature from 150 C to 190 C for not less than 10 hours;
x) cooling the autoclave to room temperature and filtering and washing
with deionized water the resulting solid; and
xi) drying the washed solid for a time from 4 to 10 hours at a temperature
from 70 to 100 C.
In some embodiments the (hydrothermal) reactor may be lined with a coating
selected from the group consisting of stainless steel, silica, alumina coating
and
polytetrafluoroethylene, preferably polytetrafluoroethylene (TEFLON ) seeded
with
catalyst having a 25% conversion to ethylene at 420 C or less and a
selectivity to
ethylene of not less than 90%.
The seed catalyst may be a catalyst having the empirical formula (measured
by PIXE):
MotoVo.25-0.38Teo.io-o.i6Nbo.15-0.190d
where d is a number to satisfy the valence of the oxide and having not less
than 75
wt% of a crystalline component of the formula (Te0)0.39(Mo3.52Wo6Nbo.42)014 as
determined by XRD.
The (hydrothermal) reactor may be lined with a coating of a fully fluorinated
ethylene propylene polymer (FEP) seeded with a catalyst having a 25%
conversion
to ethylene at 380 C or less and a selectivity to ethylene of not less than
90% at a
gas hourly space velocity of not less than 500 hrl. The seed catalyst may have
the
empirical formula (measured by PIXE) Mo1.oVo.25-o38Teo.io-o.16Nbo.15-o.190d
where d is
CA 3017900 2018-09-20 13
a number to satisfy the valence of the oxide. Typically not less than 75 wt%
of a
crystalline component of the seed catalyst has the formula
(Te0)0.39(Mo3.52V1.o6Nb0.42)014 as determined by XRD.
The seed catalyst loadings may range from 1 to 15 wt% of the surface of the
hydrothermal reactor (e.g. steel, TEFLON or FEP).
In some instances the (hydrothermal) reactor contains particulates of
stainless steel, silica, alumina and polytetrafluoroethylene seeded with a
catalyst
having a 25% conversion to ethylene at 420 C or less and a selectivity to
ethylene
of not less than 90% such as that described above.
The particulates may be (irregular such as flakes, granules, globules,
filaments, etc. or regular such as spheres, elliptical, rods (stirring bars),
rectangular
prisms (both right and non-right), pentagonal prisms, pyramids, etc.)
In some circumstances it may be easier to replace particulates on which the
seed catalyst has, for whatever reason, been depleted with new seed particles
having an appropriate loading of seed particles than to replenish the seed
coating
on the interior surface of the catalyst reactor.
A catalyst produced from a hydrothermal reactor seeded with catalyst having
a 25% conversion to ethylene at 380 C or less and a selectivity to ethylene of
not
less than 90% generally has the empirical formula as determined by PIXE
Mo1Vo.25-0.35Teo.io-o.16Nbo.15-0.190d where d is a number to satisfy the
valence of the
oxide.
The peroxide treatments may take place at atmospheric pressure and room
temperature (e.g. from 15 C to 30 C) to about 80 C, in some instances from 35
C
to 75 C in other instances from 40 C to 65 C. The peroxide has a concentration
from 10 to 30 wt%, in some instances from 15 to 25 wt%. The treatment time may
CA 3017900 2018-09-20 14
range from Ito 10 hours, in some cases from 2 to 8 hours, in other cases from
4 to
6 hours.
The catalyst precursor is treated with the equivalent of from 0.3 ¨ 2.8, in
some embodiments from 0.3-2.5 mL of a 30 wt% solution of aqueous H202 per
gram of precursor. The treatment should be in a slurry (e.g. the precursor is
at
least partially suspended) to provide an even distribution of H202 and to
control the
temperature rise. In some cases the peroxide may be added directly to the
slurry
obtained from the hydro thermal reactor while in other cases the product from
the
hydrothermal reactor may be recovered, (filtered) washed, dried and re-
slurried and
then treated with the peroxide.
The process of the present invention is an instantaneous reaction (i.e. there
is no delay before the reaction starts) which is more controlled and safer.
The treated catalyst precursor is then subject to calcining to produce the
active oxidative dehydrogenation catalyst. The treated precursor may be
calcined
in an inert atmosphere at a temperature from 200 C to 600 C for a time from 1
to
hours. The purge gases used for calcining are inert gases, including one or
more of nitrogen, helium, argon, CO2 (preferably high purity > 90%), said
gases or
mixture containing less than 1 vol.- /0 hydrogen or air, at 200-600 C,
preferably at
300-500 C. The calcining step may take from 1 to 20, in some instances from 5
to
20 15 in other instances from about 8 to 12 hours, generally about 10
hours. The
resulting mixed oxide catalyst is a friable solid typically insoluble in
water. Typically
the calcined product has a bulk density from 1.20 to 1.53 g/cc. This bulk
density is
based on how much 1.5 ml of pressed and crushed catalyst weighs.
The calcined catalyst is then redistributed in water and treated with the
equivalent of from 0.3 ¨ 2.8, in some embodiments from 0.3-2.5 mL of a 30 wt%
CA 3017900 2018-09-20 15
solution of aqueous H202 per gram of catalyst. The treatment is in a slurry or
precipitate (e.g. the precursor is at least partially suspended) to provide an
even
distribution of H202 and to control the temperature rise. This may be achieved
by
stirring the mixture. The time of treatment may be from about 1 to about 10
hours,
typically form 2 to 8 hours in some embodiment from 3 to 7 hours.
The resulting twice treated oxidative dehydrogenation catalyst is then
recovered, typically by filtration and optionally washed with deionized water
and
dried in an oven, at low temperatures, typically from about 30 C to 90 C. The
catalyst is then cooled to room temperature. The resulting catalyst may
optionally
be and ground to a particle size from about 200 pm to 500 pm, typically from
about
200 pm to about 300 pm.
The resulting oxidative dehydrogenation catalyst is heterogeneous. It has
an amorphous component and a crystalline component. The elemental analysis of
the catalyst may be determined by any suitable technique. One useful technique
is
Particle Induced X-Ray Emission analysis (PIXE).
The catalyst has one or more crystalline components and an amorphous
component. The crystalline component may be analyzed using X-Ray diffraction
(XRD). There are a number of suppliers of X-Ray diffractometers including
Rigaku
Shimadzu, Olympus and Bruker. A powder sample is irradiated with X-Rays. The
X-Rays given off from the sample pass through a diffraction grid and are
collected
in a goniometer (recorder). The results are typically analyzed using a
computer
program (typically provided by the instrument supplier) and compared to a data
base (International Center for Diffraction Data ICDD) using a computer to
determine
the composition of the crystalline phase(s).
CA 3017900 2018-09-20 16
The crystalline phase of the catalyst is also heterogeneous. The X-Ray
diffraction results may be analyzed by computer programs to identify various
likely
crystalline species and their relative amounts compared to the structures in a
data
base (e.g. deconvoluted).
The crystalline phase typically includes the following crystalline species:
(Mo0.6Nb0.22Vo.18)5014;
Te0o.71(Moo.73Vo.2Nbo.07)309;
(Te0)0.39(Mo3.52V1.o6Nbo.42)014;
WiMoo.905; Mo4V6025; and
VOMo04
X-Ray diffraction analysis of the precursor and the calcined catalyst shows
treatment results in a change in the composition of the crystalline phase. The
treatment in accordance with the present invention increases the phase of the
crystalline component having the empirical formula
(Te0)0.39(Mo3.52V1.06Nb0.42) to
not less than 75 wt%, in some instances not less than 85 wt%.
In some embodiments the phase of the crystalline component having the
empirical formula Te00.71(Mo0.73V0.2Nbo.07)309 is present in an amount of from
about
2.4 to 12 wt%, in some embodiments the phase is present in amounts less than
about 8 wt%, in further embodiments less than 3.5 wt%.
The ODH catalyst twice treated with hydrogen peroxide has an XRD pattern
where the reflection at 21.81 ( 0.4 ) 29 is 1-6% in some embodiments from 2
to
6% relative peak height of the reference reflection at 22.29 ( 0.4 ) 29.
In a further embodiment, ODH catalyst twice treated with hydrogen peroxide
has an XRD pattern where the reflection at 22.29 ( 0.4 ) 20 has a full width
at half
maximum (FWHM) less than 0.185 29.
CA 3017900 2018-09-20 17
Generally, the ODH catalyst twice treated with hydrogen peroxide has a
crystallite size (r) greater than 750 A up to 1100 A, in some case up to 900
to 1000
calculated using the Scherrer equation, where K (dimensionless shape factor)
is
assumed to be 1, A is the X-ray wavelength from Copper source and is 1.5406 A,
is the Bragg angle of 22.29 , and 13 is the line broadening at half the
maximum
intensity (FWHM) as determined for the XRD data.
The calcined catalyst product is a dry friable product typically insoluble in
water. If required the catalyst may be subject to a sizing step, such as
grinding, to
produce a desired particle size. Depending on how the catalyst is to be used
the
particle size may be different. For example for spray drying with a support
the
particle size may range from about 5 to 75 pm, in some cases from 10 to 60 pm.
For use in a bed in unsupported form the particles may have a size from about
0.1
to 0.5 mm in some instances from 0.2 to 0.4 mm.
In the present invention the feed to the oxidative dehydrogenation reactor
includes oxygen in an amount below the upper explosive/flammability limit. For
example for ethane oxidative dehydrogenation, typically the oxygen will be
present
in an amount of not less than about 16 mole % preferably about 18 mole %, for
example from about 22 to 27 mole %, or 23 to 26 mole %. It is desirable not to
have too great an excess of oxygen as this may reduce selectivity arising from
combustion of feed or final products. Additionally, too high an excess of
oxygen in
the feed stream may require additional separation steps at the downstream end
of
the reaction.
To maintain a viable fluidized or moving bed, the mass gas flow rate through
the bed must be above the minimum flow required for fluidization (Umf), and
preferably from about 1.5 to about 10 times Umf and more preferably from about
2
CA 3017900 2018-09-20 18
to about 6 times Umf. Umf is used in the accepted form as the abbreviation for
the
minimum mass gas flow required to achieve fluidization, C. Y. Wen and Y. H.
Yu,
"Mechanics of Fluidization", Chemical Engineering Progress Symposium Series,
Vol. 62, p. 100-111 (1966). Typically the superficial gas velocity required
ranges
from 0.3 to 5 m/s.
The reactor may also be a fixed bed reactor.
The oxidative dehydrogenation process comprises passing a mixed feed of
ethane and oxygen, as described above, at a temperature up to 425 C in some
instances less than 400 C, in some instances less than 390 C, in some
instances
less than 380 C, in some instances as low as 375 C, in some embodiments above
365 C at a gas hourly space velocity of not less than 500 hrl, typically not
less than
1000 hrl, desirably not less than 2800 hrl preferably at least 3000 hrl
through one
or more beds and a pressure from 0.8 to 1.2 atmospheres comprising passing
said
mixture over the oxidative dehydrogenation catalyst. In some embodiments the
oxidative dehydrogenation reactor operates at temperatures below 400 C
typically
from 375 C to 400 C.
If the composition of the reactants is below the lower flammability limit
higher
temperatures could be used up to about 425 C.
The outlet pressure from the reactor may be from 105 kPag (15 psig) to
172.3 kPag (25 psig) and the inlet pressure is higher by the pressure drop
across
the bed which depends on a number of factors including reactor configuration,
particle size in the bed and the space velocity. Generally the pressure drop
may be
below 689 kPag (100 psig) preferably less than 206.7 kPag (30 psig).
The residence time of one or more alkanes in the oxidative dehydrogenation
reactor is from 0.002 to 20 seconds.
CA 3017900 2018-09-20 19
The Support / Binder
If required there are several ways the oxidative dehydrogenation catalyst
may be supported or bound.
Preferred components for forming ceramic supports and for binders include
oxides of titanium, zirconium, aluminum, magnesium, silicon, phosphates, boron
phosphate, zirconium phosphate and mixtures thereof, for both fluidized and
fixed
bed reactors. In the fluidized bed typically catalyst is generally spray dried
with the
binder, typically forming spherical particles ranging in size (effective
diameter) from
40-100 pm. However, one needs to be careful to insure that particles area is
sufficiently robust to minimize the attrition in the fluidized bed.
The support for the catalyst for the fixed bed may further be a ceramic
precursor formed from oxides, dioxides, nitrides, carbides selected from the
group
consisting of silicon dioxide, fused silicon dioxide, aluminum oxide, titanium
dioxide,
zirconium dioxide, thorium dioxide, lanthanum oxide, magnesium oxide, calcium
oxide, barium oxide, tin oxide, cerium dioxide, zinc oxide, boron oxide, boron
nitride, boron carbide, yttrium oxide, aluminum silicate, silicon nitride,
silicon
carbide and mixtures thereof.
In one embodiment the support for the fixed bed may have a low surface
area less than 20 m2/g, alternatively, less than 15 m2/g, in some instances,
less
than 3.0 m2/g for the oxidative dehydrogenation catalyst. Such support may be
prepared by compression molding. At higher pressures the interstices within
the
ceramic precursor being compressed collapse. Depending on the pressure exerted
on the support precursor the surface area of the support may be from about 20
to
10 m2/g.
CA 3017900 2018-09-20 20
The low surface area support could be of any conventional shape such as
spheres, rings, saddles, etc.
It is important that the support be dried prior to use (i.e. before adding
catalyst). Generally, the support may be heated at a temperature of at least
200 C
for up to 24 hours, typically at a temperature from 500 C to 800 C for about 2
to 20
hours, preferably 4 to 10 hours. The resulting support will be free of
adsorbed
water and should have a surface hydroxyl content from about 0.1 to 5 mmol/g of
support, preferably from 0.5 to 3 mmol/g.
The amount of the hydroxyl groups on silica may be determined according to
the method disclosed by J. B. Pen i and A. L. Hensley, Jr., in J. Phys. Chem.,
72 (8),
2926, 1968, the entire contents of which are incorporated herein by reference.
The dried support for a fixed bed catalyst may be compressed into the
required shape by compression molding. Depending on the particle size of the
support, it may be combined with an inert binder to hold the shape of the
compressed part.
Loadings
Typically the catalyst loading on the support for a fixed bed catalyst
provides
from 1 to 30 weight % typically from 5 to 20 weight %, preferably from 8 to 15
weight % of said catalyst and from 99 to 70 weight %, typically from 80 to 95
weight
%, preferably from 85 to 92 weight A, respectively, of said support.
The catalyst may be added to the support in any number of ways. For
example the catalyst could be deposited from an aqueous slurry onto one of the
surfaces of the low surface area support by impregnation, wash-coating,
brushing
or spraying. The catalyst could also be co-precipitated from a slurry with the
ceramic precursor (e.g. alumina) to form the low surface area supported
catalyst.
CA 3017900 2018-09-20 21
The catalyst loading for the fluidized bed may be chosen based on a number
of factors including the volume of bed, the flow rate of alkane through the
bed,
energy balance in the bed, binder type, etc. For the fluidized bed catalyst
loading
may cover a wide range of values ranging from 10 wt% up to 90 wt%, typically
above 20 wt% desirably above 35 wt%.
The process should be operated to have a conversion of ethane to ethylene
of at least 90%, in some instances 95%, desirably greater than 98% and a
selectivity to ethylene of not less than 95%, in some instances greater than
97%."
The Oxidative Dehydrogenation Processes
The catalyst of the present invention may be used with a fluidized bed or a
fixed bed exothermic reaction. The fixed bed reactor is a tubular reactor and
in
further embodiment the fixed bed reactor comprises multiple tubes inside a
shell
(e.g. a shell and tube heat exchanger type construction). In a further
embodiment
the fixed bed reactor may comprise a number of shells in series and/or
parallel.
The reactions may involve one or more dehydrogenation steps including
oxidative
dehydrogenation, and hydrogen transfer steps including oxidative coupling of a
hydrocarbon.
Typically these reactions are conducted at temperatures from about 375 C
up to about 410 C, at pressures from about 100 to 21,000 kPag (15 to 3,000
psig),
preferably at an outlet pressure from rom 105 kPag (15 psig) to 172.3 kPag (25
psig), in the presence of an oxidative dehydrogenation catalyst. The
hydrocarbon
stream may contain a range of compounds including C2-4 aliphatic hydrocarbons.
In some embodiments the reactions include the oxidative coupling of
aliphatic hydrocarbons, typically C1-4 aliphatic hydrocarbons particularly
methane
(e.g. when the ethane stream contains some methane) and the oxidative
CA 3017900 2018-09-20 22
dehydrogenation of C2-4 aliphatic hydrocarbons. Such reactions may be
conducted
using a mixed feed of hydrocarbons, in some embodiments methane or ethane or
both and oxygen in a volume ratio from 70:30 to 95:5 at a temperature less
than
420 C, preferably less than 400 C at a gas hourly space velocity of not less
than
280 hrl, in some embodiments not less than 500 hrl, typically not less than
1000 hrl , desirably not less than 2800 hrl, preferably at least 3000 hrl, and
a
pressure from 0.8 to 1.2 atmospheres. Typically the process may have an
overall
conversion of from about 50 to about a 100%, typically from about 75 to 98%
and a
selectivity to ethylene of not less than 90%, in some instances not less than
95%, in
further embodiments not less than 98%. In some cases the temperature upper
control limit is less than about 400 C, in some embodiments less than 385 C.
The resulting product stream is treated to separate ethylene from the rest of
the product stream which may also contain co-products such as acetic acid, and
un-reacted feed which is recycled back to the reactor.
Separation
The product stream from the reactor should have a relatively low content of
ethane less, than 20 wt%, in some cases less than 15 wt% in some cases less
than
10 wt%. Additionally, the product stream should have a low content of by
products
such as water, carbon dioxide, and carbon monoxide, generally cumulatively in
a
.. range of less than 5, preferably less than 3 wt%.
The feed and by products may need to be separated from the product
stream. Some processes may use so called dilute ethylene streams. For example
if the product stream does not contain too much ethane, for example less than
about 15 vol. % the stream may be used directly without further purification
in a
polymerization reactor such as a gas phase, slurry or solution process.
CA 3017900 2018-09-20 23
The most common technique would be to use a cryogenic C2 splitter.
Other known ethylene/ethane separation techniques could also be used including
adsorption (oil, ionic liquids and zeolite).
The present invention will now be illustrated by the following non limiting
examples.
In the examples the fixed bed reactor unit used for the oxidative
dehydrogenation reaction is schematically shown in figure 1. The reactor was a
fixed bed stainless steel tube reactor having a 2 mm (3/4") outer diameter and
a
length of 117 cm (46 inches). The reactor is in an electrical furnace sealed
with
ceramic insulating material. There are 7 thermocouples in the reactor
indicated at
numbers 1 through 7. Thermocouples are used to monitor the temperature in that
zone of the reactor. Thermocouples 3 and 4 are also used to control the
heating of
the reactor bed. The feed flows from the top to the bottom of the reactor. At
the
inlet there is a ceramic cup 8 to prevent air drafts in the reactor. Below the
ceramic
cup is a layer of quartz wool 9. Below the layer of quartz wool is a layer of
catalytically inert quartz powder. Below the quarts powder is the fixed bed 10
comprising catalyst. Below the fixed bed is a layer of quartz powder 11, a
layer of
quartz wool 12 and a ceramic cup 13. At the exit of the bed was a gas analyzer
to
determine the composition of the product stream. The GHSV was 2685 hrl and
the pressure was ambient.
For the examples the bed temperature was taken as an average of the
temperatures from thermocouples 2, 3 and 4. The feed stream was assumed to
have the same temperature as the bed.
CA 3017900 2018-09-20 24
Comparative Example 1 - Base Line (no peroxide treatment)
Preparation of Baseline: 100 g reaction in glass lined PARR autoclave
Procedure:
= 96.00 g of (NH4)6Mo6Te02x7H20 (s) was dissolved in 300 mL of de-
ionized water in a 1 L three neck round bottom flask (RBF), with a stir rate
of 750
rpm with the addition of a warm water bath
= 70.22 g of VOSO4x3.41H20 (s) was dissolved in 100 mL of de-ionized
water, with the addition of a warm water bath
= 194.35 g of H3[NbO(C204)3] (soln.) was weighed into a 250 mL beaker and
held for later use
= VOSO4x3.41H20 (aq) solution was added to the (NH4)6Mo6Te02x7H20
(aq) solution in the 1 L RBF
= Solution turned black
= Solution was left to stir for 30 minutes, after which the solution turned
a
purple color
= All manipulations were performed in air
= 194.35 g of H3[NbO(C204)3] (soln.) was added to a 250 mL addition funnel,
affixed to the 3 neck RBF
= Solution was added dropwise to the agitating purple slurry (15 minutes
for
addition time)
= Solution remained as a dark purple slurry
= Solution was transferred to a 1 L glass liner inside a 1 L PARR autoclave
= Autoclave set up was sealed and purged 10 times with repeating N2 (g)
evacuation sequences
= Autoclave was connected to the condenser set up
CA 3017900 2018-09-20 25
= Reaction was left to stir overnight in the autoclave set up at room
ternperature
= The following day the PARR autoclave was heated to 175 C, the autoclave
reached a temperature of 172 C after 7.5 hours
= Reaction mixture was left to heat in the autoclave set up overnight at
175 C
with the condenser set up
= The following day the temperature was set back to room temperature
= Reaction set up was not cooled by the end of the day and was left to cool
over the weekend
= After the reaction was cooled it was depressurized and filtered through 4
X
WHATMANN #4 filter paper media
= The filter cake was rinsed with approximately 0.5 L of deionized water
until
the filtrate ran clear
= Filtration time was approximately 2 hours
= Filter dried catalyst was dried in the oven at 90 C overnight
= Dried catalyst was ground and sieved
= Yield: 111 g
= 7 g of the 111 g was calcined under N2 (g)
Activity Testing:
7 grams of calcined catalyst were loaded into the reactor shown in figure 1.
Ethane and oxygen were passed through the reactor at a rate of 140 sccm per
minute at various temperatures and the conversion and selectivity to ethylene
at
various temperatures were recorded. A plot was made of the conversion and
activity of the catalyst at various temperatures. These are shown in figures 2
and 3
respectively.
CA 3017900 2018-09-20 26
From the plots the temperature at which 25% conversion of ethane was
obtained was 368.5 C. At this temperature the conversions to ethylene was
97.7%.
Comparative Example 2 - Catalyst Treated Once with H202
Procedure:
= To a 1L 2 neck round bottom flask was charged 10.2544 g of uncalcined
base catalyst from experiment 1.
= To this black/purple catalyst mixture was charged 35 mL of distilled
deionized water
= Catalyst/water mixture began to bubble and fizz upon the addition of
water
= The catalyst/ water mixture was agitated at 400 rpm to produce a thin
slurry
= 7.14 mL of 30% H202 was charged to the 1L 2 neck round bottom flask
= The catalyst, H202 mixture was agitated at 400 rpm
= The reaction began to bubble and the purple/ black slurry turned into a
dark
brown slurry
= Mixture was left to stir until bubbling subsided and reaction flask
cooled to
touch (approximately 2 hours)
= Mixture was filtered through a Buchner funnel with 3 x WHATMANN # 4
filter
paper
= Catalyst/ H202 solid was dried in a vacuum oven at 90 C under ambient
pressure for 12 hours
= Catalyst was cooled to touch, ground, sieved and calcined
Repeat:
The above procedure was repeated using 5.29 g of uncalcined base
material.
CA 3017900 2018-09-20 27
Samples of the calcined catalysts were tested as above. A plot was made of
the conversion and activity of the catalyst at various temperatures. These are
shown in figures 4 and 5 respectively.
From the plots the temperature at which 25% conversion of ethane was
obtained was 386.0 C. At this temperature the conversions to ethylene was
96.8%
Example 3 - The Invention
Procedure:
= To a 2 L 3 neck round bottom flask was charged 5.2934 g of ODH catalyst
of example 2 (H202 treatment before calcining)
= 20 mL of distilled, deionized water was then charged into the 2L 3 neck
RBF
= The black catalyst bubbled during the addition of the distilled,
deionized
water addition
= 3.78 mL of 30% H202 was charged into the 3 neck round bottom flask
= The slurry mixture bubbled and fizzed during the addition of the 30% H202
= The slurry mixture was agitated at room temperature at 350 rpm for 3
hours
= Mixture was stopped from stirring and filtered using a Buchner funnel
with 3
x WHATMANN #4 filter papers
= The dark purple/ black solid was dried in a vacuum oven at 90 C ambient
pressure
= The solids were cooled to room temperature, ground, sieved
= About a 2 g ( 0.5) sample of the twice treated catalyst was tested in
the
reactor as in example 1. The plots are shown in figures 6 and 7.
From the plots the temperature at which 25% conversion of ethane was
obtained was 363.0 C. At this temperature the conversions to ethylene was
97.2%.
CA 3017900 2018-09-20 28
XRD diffraction patterns were taken for the catalyst made according to
comparative example 1 and example 4. These are figures 8 and 9. A blow up of
the portions of XRD patterns between 21 and 23, 21) are shown as figures 10
and
11 respectively.
The present invention has shown that when a MoVNbTe0x catalyst with
already high performance is treated both before and after calcination, the
resulting
catalyst has high activity which is improved relative to the non-treated
baseline,
whereas with the single treatment method (before calcination) the catalyst
activity
has decreased reactivity relative to the non-treated baseline. Additionally,
washing
with hydrogen peroxide twice increases the intensity of a reflection at 21.7
2Theta
in the X-ray powder diffraction (XRD) relative the baseline catalyst
A chart of XRD diffraction pattern data for the experiments and prior art data
was prepared.
Mitsubishi Claimed Nieto Claimed
Comparative Inventive
Example 1 Example 2 Example 3
(Baseline) (1x H202 (2x H202 ES 2428442
treatment) treatment) JP 3484729 (B2) US 2014011410
WO 2014062046
Relative Relative Relative
Relative
Relative
Intensities Intensities Intensities
i i ties
Intensities
Intenstes
20CuKa (%) to
(%) to 22.29 20 (deg) 20 (deg)
(deg) 22.29* 22.29 22.1* 22.1*
(+0.4 ) 20 (deg) 20
(+0.4 ) 20 ( 0.4 ) 20 ( 0.4 ) 20
)
(deg) (deg) (deg) (deg)
6.77 ( 0.4) 2 5 4
7.97 ( 0.4) 9 18 16 7.7 ( 0.4) 10
to 40
9.13( 0.4) 6 11 10 8.9( 0.4) 10
to 40
10.81 ( 0.4) 2 3 3
13.13 ( 0.4) 3 5 3 ,
14.05 ( 0.4) 2 4 3
14.73 ( 0.4) 7 0 0
21.81 ( 0.4) 4 4 4
22.29* ( 0.4) 100 100 100 22.1* ( 0.4) 100 22.1*
( 0.4) 100
23.65 ( 0.4) 4 6 7
25.13 ( 0.4) 19 2 2
26.29 ( 0.4) 10 13 12 26.1 ( 0.4) 10
to 90
CA 3017900 2018-09-20 29
26.73 ( 0.4) 17 17 18 26.9 ( 0.4)
20 to 80
27.05 ( 0.4) 19 26 23
27.29 ( 0.4) 24 33 33 27.1 ( 0.4) 20 to 120"
28.21 ( 0.4) 20 17 16 28.2 ( 0.4) 400-3 28.1
( 0.4) 20 to 120*
29.29 ( 0.4) 9 13 12
29.57 ( 0.4) 10 2 2
29.85 ( 0.4) 6 8 9
30.53 ( 0.4) 6 11 11
31.37 ( 0.4) 7 10 12 31.2 ( 0.4)
10 to 90
31.85 ( 0.4) 2 4 4
32.81 ( 0.4) 10 2 2
33.65 ( 0.4) 9 1 1
35.45 ( 0.4) 6 9 9 35 ( 0.4) 10
to 90
36.33 ( 0.4) 13 3 2 36.2 ( 0.4) 80-3
37.01 ( 0.4) 4 3 4
44.89 ( 0.4) 5 1 1
45.33 ( 0.4) 10 10 11 45.1 ( 0.4) 40-3 45.06
10 to 60
47.81 ( 0.4) 5 3 4
51.21 ( 0.4) 5 7 8 50 50-3
51.73 ( 0.4) 4 5 6
52.45 ( 0.4) 5 4 5
CA 3017900 2018-09-20 30
