Note: Descriptions are shown in the official language in which they were submitted.
CA 02859192 2014-08-13
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CATALYST AND METHOD FOR THE DIRECT SYNTHESIS OF DIMETHYL
ETHER FROM SYNTHESIS GAS
TECHNICAL FIELD
[0001] The invention relates to catalysts, methods for preparing
catalysts and
methods using the catalyst to produce dimethyl ether from synthesis gas.
BACKGROUND
[0002] Fossil fuels are known to have the disadvantages of being a finite
resource
and a cause of global warming. As such, there has been much research on
alternative
fuels due to these ecological and economical considerations. Among the
alternative fuels,
dimethyl ether (DME) is a clean fuel, and can be synthesized from synthesis
gas, also
known as syngas. Synthesis gas is a mixture of mainly hydrogen, carbon
monoxide and
carbon dioxide that can be generated from a variety of different primary
sources. These
primary sources can include natural gas, coal, heavy oil, and also from
biomass. The
syngas is passed over a catalyst to produce methanol according to the
following chemical
equation:
[0003] CO +2 H2 -> CH3OH
[0004] Methanol can then be converted into DME by dehydration over an
acidic
catalyst according to the following chemical equation:
[0005] 2 CH3OH --> CH3OCH3 + H20
[0006] In the direct DME production there are mainly two overall
reactions that
occur from synthesis gas. These reactions, reaction (I) and reaction (2), are
listed below.
[0007] 3 CO + 3 H2 -) CH3OCH3 I CO2 (1)
[0008] 2 CO + 4 1-12 CH3OCH3 +1-120 (2)
[0009] Reaction (I) is a combination of three reactions, which are methanol
synthesis reaction, methanol dehydration reaction, and water gas shift
reaction:
[00101 2 CO + 41-12 -> 2 CH3OH (methanol synthesis reaction)
10011] 2CH3OH CH3OCH3 +1-120 (methanol dehydration reaction)
- [0012] CO + 1120 -3 CO2 + H2 (water gas shift
reaction)
100131 The reaction (1) has a stoichiornetric ratio 1-12/C0 of 1:1 and has
some
advantages over reaction (2). For example reaction (1) generally allows higher
single
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CA 02859192 2014-08-13
pass conversions and less energy-consuming in comparison to the removal of
water from
the system in reaction (2)
[0014] Recently, attention has been directed towards the direct synthesis
of
dimethyl ether from synthesis gas using a catalytic system that combines a
methanol
synthesis catalyst and a catalyst for dehydration of said alcohol. Depending
on the
synthesis gas used, the catalyst might additionally show water gas shill.
activity.
However, the processes for the preparation of dimethyl ether according to the
prior art
have the drawbacks that additional steps have to be taken to get an efficient
DIVIE,
production. Additionally, the catalyst used in the methods known in the prior
art do not
achieve the thermodynamic possibilities. Therefore it is still desirable to
increase the
yield of DME in the synthesis gas conversion, and do so in one step.
SUMMARY
[0015] A first aspect of the invention relates to a catalyst composition
for the
synthesis of dimethyl ether. The catalyst composition comprises about 10 to
about 75
weight % Cu0; about 5 to about 50 weight % Zn0; about 1 to about 30 weight %
Zr02;
=
about 1 to about 40 weight % of one or more of boron oxide, niobium oxide,
tantalum
oxide, phosphorus oxide, and combinations thereof; and about 5 to about 80
weight %
alumina, wherein at least a portion of alumina comprises 7-alumina. In one or
more
embodiments, the catalyst composition further comprises ceria. In some
embodiments,
the catalyst composition comprises about I to about 30 weight 'A of ceria.
[0016] In one or more embodiments, the catalyst comprises about 0.1 to
about 20
weight % of one or more of boron oxide, tantalum oxide, phosphorus oxide,
niobium
oxide and combinations thereof In some embodiments, the alumina comprises one
or
more of dispersible alumina, 7-alumina, malumina, x-alumina, other
transitional
aluminas, boehmite, pseudoboehmite, gibbsite, bayerite, and mixtures thereof.
In one or
more embodiments, the alumina consists essentially of 7-alumina. In some
embodiments,
the alumina consists essentially of dispersible alumina and 7-alumina.
[0017] In one or more embodiments, the alumina comprises
dispersible alumina
that has a dispersibility of at least about 70% or greater. In some
embodiments, at least a
portion of the dispersible alumina is replaced with a 7-alumina. In one or
more
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CA 02859192 2014-08-13
embodiments, at least a portion of the dispersible alumina is replaced with a
7-alumina.
In_some emboditnents,Jhe_catalyst coinp_osition_comprises_boron o_xid_e, and
the alumina
comprises gamma alumina. In one or more embodiments, the catalyst composition
comprises niobium oxide, and the alumina comprises gamma alumina.
[0018] In some embodiments, at least a portion of the alumina comprises
alumina
prepared by peptizing dispersible alumina with a dispersibility of at least
about 50% or
greater and reacting the alumina with precursors of CuO, ZnO, and Zr02. In one
or more
embodiments, a portion of the alumina comprises alumina prepared by peptizing
dispersible alumina with a dispersibility of at least about 50% or greater. In
some
embodiments, the alumina comprises y-alumina. In one or more embodiments, the
alumina consists essentially of y-alurnina. In one or more embodiments, the
catalyst
composition has a high copper dispersion.
[0019] Another aspect of the invention pertains to a method of making
dimethyl
ether. The method comprises contacting a stream of synthesis gas comprising
carbon
monoxide and hydrogen with any variations of the catalyst described above. In
one or
more embodiments, the synthesis gas has a ratio of carbon monoxide to hydrogen
is
about 1. In some embodiments, the synthesis gas has a ratio of carbon monoxide
to
hydrogen is less than about 1 . In one or more embodiments, the synthesis gas
has a ratio
of carbon monoxide to hydrogen is greater than about I. In some embodiments,
the
synthesis gas further comprises carbon dioxide.
[0020] Yet another aspect of the invention relates to methods of producing
one or
more of the described catalyst compositions. In one or more embodiments, the
method
comprisespreparing a first powder, preparation of the first powder comprising
(i) forming
a first slurry by peptizing a dispersible alumina in an acid at a pH between 2
and 5 and a
temperature of about 20 C to 30 C; (ii) forming a second slurry of zirconyl
nitrate and
water at a pH of less than about 1.5 and a temperature in the range of about
20 C to 30
C; and (iii) calcining the first and second slurries to provide a first
powder; preparing a
second powder, preparation of the second powder comprising calcinng a salt
comprising
niobium, tantalum, phosphorus or boron with a mixture of -y-alumina; and
mixing the first
and second powder. In one or more embodiments, the ratio of the first powder
makes up
about 70 to about 90 % by weight of the total catalyst.
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,
DETAILED DESCRIPTION
-[00211 Before- describing-severaLexemplaienibodimentsof-
theinvention,iListo
be understood that the invention is not limited to the details of construction
or process
steps set forth in the following description. The invention is capable of
other
embodiments and of being practiced or being carried out in various ways.
[0022] As used herein, the term ''synthesis gas" is used
synonymously with
"syngas," and refers to a gas mixture comprising carbon monoxide (CO) and
hydrogen
(H2). The gas may also comprise carbon dioxide (CO2). The relative amounts of
the
various components may differ.
[0023] As used herein, the term "calcination" refers to a thermal
treatment
process applied to ores and other solid materials to bring about a thermal
decomposition,
phase transition, or removal of a volatile fraction. The calcination process
normally takes
place at temperatures below the melting point of the product materials, and is
done under
an oxygen-containing atmosphere. In some cases, the calcination can be
performed under
an inert atmosphere (e.g. nitrogen).
[0024] A first aspect of the present invention pertains to a
dimethyl ether catalyst
comprising CuO, ZnO, 7,r0, A1203 and one or more of niobium oxide, tantalum
oxide,
boron oxide, phosphorus oxide and combinations thereof. In a particular
embodiment, the
amount of CuO has a range of about 10 to about 75 weight percent of the
catalyst. In an
even more particular embodiment, the catalyst composition has a high copper
dispersion.
In another embodiment, the. amount of ZnO has a range of about 5 to about 50
weight
percent. In other embodiments, the catalyst composition comprises from about 1
to about
30 weight percent Zr02. In yet another embodiment, the about of alumina ranges
from
about 5 to about SO weight percent alumina. In some embodiments, the amount of
boron
oxide, tantalum oxide, niobium oxide, phosphorus oxide or combinations
thereof, has a
range of about 0.1 to about 40 weight percent. In other specific embodiments,
the
amount of boron oxide, tantalum oxide, niobium oxide, phosphorus oxide or
combinations thereof, has arrange of about 0.1 to about 20 weight percent. In
one or more
embodiments, the catalyst composition further comprises ceria. In a more
specific
embodiment, the catalyst composition comprises about 1 to about 30% of ceria.
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CA 02859192 2014-08-13
. .
100251- As used herein, percents given in terms of weight are
relative to the weight
of the final catalyst composition, unless otherwise stated,
10026] The catalyst composite comprises alumina, which can come in
various
forms. For example, one or more embodiments may comprise one or more of
dispersible
alumina, 7-alumina, n-alumina, x-altimina, other transitional aluminas,
boehmite,
pseudoboehmite, gibbsite, bayerite, and mixtures thereof.
[0027] In certain embodiments where the alumina comprises
dispersible alumina,
it has a dispersibility of at least about 70% or greater. As used herein, the
term
"dispersible alumina" refers to the amount of alumina that becomes colloidal
at a certain
pH, which is typically in the acid range, a process that is referred to as
acid peptizing.
Acid peptizing results in the formation of particles that are less than 1
micron (um).
Examples of dispersible alumina include alumina having 40% or greater
dispersibility in
water after peptizing at a pH of 2 to 5. Other examples of alumina having 50%
or greater
dispersibility, 60% or greater dispersibility, 70% or greater dispersibility,
80% or greater
dispersibility, or 90% or greater dispersibility in water after peptizing at a
pH of 2 to 5 are
included in this definition of dispersible alumina. As used herein, the
percent
dispersibility of alumina refers to the percentage of alumina that is less
than 1 micron in
size in the acidic solution after peptizing at a pH from about 2 to about 5.
Non-limiting
examples of aluminas that arc dispersible include boehmite or pseudo-boehmite
aluminas. In some embodiments, the alumina utilized in the catalysts described
herein is
characterized as peptized until the desired dispersibility or a "dispersible
alumina," as
defined above, is achieved. According to one or more specific embodiments, the
use of a
highly dispersible alumina allows more of the surface area of the Cu to be
exposed for
reaction and thus may provide a higher catalytic activity. In one or more
embodiments,
the peptized alumina has a particle size of 1 um or less. In one more
embodiments, the
alumina has 40% or greater dispersibility in water after peptizing at a pH of
2 to 5. That
is; the percentage of alumina having a particle size of 1 pm or less in water
after
peptizing at a pH of 2 to 5 is at least 40%. In one more embodiments, the
alumina has
50% or greater dispersibility in water after peptizing at a pH of 2 to 5. In a
more specific
embodiment, the alumina has 80% or greater dispersibility in water after
peptizing at a
pH of 2 to 5. Other suitable alumina may have 90% or greater dispersibility in
water after
CA 02859192 2014-08-13
peptizing at a pH of 2 to 5. In one or more alternative embodiments, non-
dispersible
_altimina.may be usedin_combirtati_on_with dispersible alumina. In such
embodiments, the
non-dispersible alumina is milled into a fine powder before use.
[0028J The catalyst may, in certain embodiments, include alumina which
may be
formed or derived from boehinite, pseudoboehmite and combinations thereof.
Suitable
boehmite and pseudoboehmites have 70% or greater dispersibility in water after
peptizing
at a pH of 2 to 5. For example, suitable alum inas are available from Sasol
North America
Inc. of Houston, Texas, under the trademarks Catapal , Pural , Dispersal , and
Dispal .
Examples of aluminas that may be utilized in the Catalysts described herein
include
aluminas available under the trade names Catapal A, B, Cl, and D and Pura!
SB. A
specific example of a suitable alumina is available under the trade name
CATAPAL D
and has a particle size (150 of about 40 um. The alumina available under the
trade name
CATAPALO D also has a BET surface area of 220 m2/g and a pore volume of about
0.55
mug after activation at 550 C for 3 hours.
[0029] Accordingly,- in certain specific embodiments, the alumina
comprises
dispersible alumina selected from one or more of boehmite, pseudoboehmite, and
mixtures thereof In alternative embodiments wherein the catalyst composite
comprises
dispersible alumina, at least a portion of the dispersible alumina is replaced
with a
nondispersible alumina. In a specific embodiment, at least a portion of the
dispersible
alumina is replaced with a y-alumina. In another specific embodiment wherein
the
catalyst composition comprises boron oxide, the alumina comprises gamma
alumina.
[0030] In other embodiments, at !cast a portion of the alumina comprises
alumina
prepared by peptizing dispersible alumina with a dispersibility of at least
about 50% or
greater and reacting the alumina with precursors of CuO, ZnO, and Zr02. In a
specific
embodiment, a portion of the alumina comprises alumina prepared by peptizing
dispersible alumina with a dispersibility of at least about 50% or greater.
[0031] As will be understood, other sources of alumina can be used and
include
such diverse materials as aluminum nitrate. Some dispersible alumina sources
are thought
to be unsuitable for industrial scale applications because of their tendency
to gel or
become solid under normal operating conditions in an industrial or large-scale
setting.
Accordingly, many known catalysts and methods of making and using such
catalysts
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CA 02859192 2014-08-13
utilized aluminum nitrate as an alumina source. Specifically, as stated above,
the Cu of
._one_or_more_catalysts_ciescribed_hereinis_highly_disp.ersed b_y the reaction
of an alumina
derived by peptizing of boehtnite or pseudoboefunite and precursors of ZnO,
CuO, Zr02
and/or Ce02.
[0032] Preparation
[0033] A second aspect of the present invention pertains to a method of
preparing
a catalyst composition as described herein. In one or more embodiments, the
catalyst
composition is formed by preparing two powders, followed by mixing and/or
pelleting
the two powders. In one or more embodiments, the first powder is a methanol-
active
component, and the second powder is an acidic component. In one or
more
embodiments, the first powder will make up about 70 to about 90% by weight of
the total
catalyst, and the second powder will constitute about 10 to 30% by weight of
the total
catalyst composite, and about 0-10% by weight of the catalyst composite may
comprise
an additive.
[0034] In one or more embodiments, the first powder includes ZnO, Zr02
and
CuO, and in some embodiments Ce02, which are formed from various precursors.
For
example salts of copper, zinc or aluminum are dissolved in a solvent, in
particular water.
At least two salts of either copper, zinc, or aluminum can be dissolved in a
solvent,
heated and a basic solution can be prepared and added. Both solutions can be
added in
parallel to the template, until the salt-solution is consumed. After this the
suspension is
filtered, dried, and calcined under air or inert gas flow. Non-limiting
examples of anions
in the salts for copper, zinc, or aluminum are selected from the group
consisting of,
nitrate, acetate, carbonate, halide, nitrite, sulfate, sulfite, sulfide,
phosphate ion or silicate.
Specifically, salts of copper, zinc or aluminum formed with the above
mentioned anions
can be converted into oxides of copper, zinc or aluminum applying a
calcination step.
[0035] A suitable Zr02 precursor includes zirconyl nitrate, though other
known
precursors may be utilized. When zirconyl nitrate is used as the zirconia
precursor, the
Zr02 precursor is provided by forming a slurry of zirconyl nitrate and water.
In such
embodiments, it is desirable to maintain the reaction mixture or the zirconyl
nitrate and
water slurry at a pH of less than about 2, and in specific embodiments at a pH
of less than
about 1.5 or 1. In one or more specific embodiments, the reaction mixture or
the zirconyl
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CA 02859192 2014-08-13
nitrate slurry is maintained at a pH of about I. In one or more embodiments,
the reaction
_mixture_isinaintained_or_has_a_temperature_in_the.rangefrom_about.20
Cio_about 30 C.
In one or more embodiments, the temperature of the zirconyl nitrate slurry may
be
maintained at a temperature of about 25 C.
[0036] A suitable CuO precursor includes copper nitrate. A suitable ZnO
precursor includes zinc nitrate. In one or more embodiments, the catalyst is
formed by
first reacting a Zr02 precursor with the peptized alumina to provide a first
reaction
product, a mixed slurry or a new slurry. A second reaction is then performed
in which the
CuO and ZnO precursors are reacted in a separate vessel to form or provide a
second
reaction product. The first reaction product and second reaction product are
then
subsequently mixed together.
[00371 In certain embodiments, the method includes peptizing a highly
dispersible alumina to form a peptized alumina and reacting the peptized
alumina with
precursors of ZnO, Zr02 and CuO, and in some embodiments Ce02, as described
above.
A highly dispersible alumina, as otherwise described herein, is prepared by
adding the
alumina to water to provide approximately 5 wt% to 35 wt% solids. The alumina
and
water mixture is mixed at high shear for approximately one hour to form a
slurry. In one
or more embodiments, the alumina and water mixture is maintained at a pH in
the .range
from about 2 to about 5 during the mixing process at a temperature in the
range from
about 20 C to about 30 C. In a specific embodiment, the alumina and water is
maintained at a pH of about 3 during the mixing process. In an even more
specific
embodiment, the temperature of the alumina and water is maintained at about 25
C. The
pH of the alumina and water mixture is maintained by adding an amount of acid
to the
mixture. Examples of suitable acids include nitric acid, formic acid, other
known acids
and combinations thereof. As described herein, in one or more embodiments the
dispersible alumina may be replaced with nondispersible alumina. For example,
up to
99% of the dispersible alumina may be replaced with nondispersible alumina
that may
include y-alumina, n-alumina, x-alumina, other transitional aluminas,
boehmite,
pseudobochmite, gibbsite, bayerite, and mixtures thereof. In one or more
embodiments,
the alumina consists essentially of 'y-alumina. In other embodiments, the
alumina
consists essentially of dispersible alumina. In yet other embodiments, the
alumina
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CA 02859192 2014-08-13
comprises both y-alumina and dispersible alumina. In further embodiments, the
ratio of
--y-alumina_to_dispersible alumina rangesfrom
about_10:90_to_90:10,.20:80_to_80:20,10:70_
to 70:30, 40:60 to 60:40 or 50:50. In one or more embodiments, the ratio of y-
alumina to
dispersible alumina is about 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30,
80:20, or
90:10.
[0038] A first reaction product containing the Zr02 precursor may be
prepared as
a slurry in a separate vessel from the highly dispersible alumina. The process
includes
maintaining the Zr02 precursor at a low pH and a controlled temperature. In
one or more
embodiments, the Zr02 precursor is maintained at a pH of less than 2 or less
than about
1.5. In one or more specific embodiments, the Zr02 precursor is maintained at
a pH in
the range from about 1.0 to about 2Ø In a more specific embodiment, the Zr02
precursor
is maintained at a pH of about 1Ø The temperature of the Zr02 precursor of
one or more
embodiments is maintained at a temperature in the range from about 20 C to
about 30
'C. In one or more specific embodiments, the Zr02 precursor is maintained at a
temperature in the range from about 22 C to about 28 C, or, more
specifically, in the
range from about 24 C to about 26 C. In one variant, the Zr02 precursor is
maintained
at a temperature of about 25 C. In one or more embodiments, a cerium oxide
precursor is
added to the zirconium oxide precursor during the preparation of the first
reaction
product.
[0039] In one or more embodiments, the C110 and ZnO precursors are
prepared
separately for reaction with the first reaction product, new slurry or mixed
slurry. In a
separate vessel, a solution of the CuO precursor and ZnO precursor is prepared
to form a
second reaction product. In one or more specific embodiments, the second
reaction
product is provided by forming a solution of copper nitrate and zinc nitrate
in a separate
vessel. The temperature of second reaction product is maintained at a
temperature in the
range from about 30 C to about 50 C. In one or more specific embodiments the
temperature of the second reaction product is maintained at about 40 C. In
one variant,
the pH of the second reaction product is maintained at a pH of less than about
1.5 or, in a
more specific variant, at about 1. In one or more specific embodiments, the
second
reaction product is maintained at this pH by the addition of soda ash, or
other suitable
sodium source, for example, sodium hydroxide, sodium carbonate or sodium
bicarbonate.
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CA 02859192 2014-08-13
[0040] The second reaction product is then added to the first reaction
product or
¨m ixed_slu my_to_create_a _third _reaction_product. TheSi rst, reaction
_product .and _the second_
reaction product are well mixed for a duration from about 30 minutes to about
60
minutes. The temperature and/or pH may be adjusted or controlled to create an
acidic
slurry. The acidic slurry may contain copper nitrate, zinc nitrate, zirconyl
nitrate, and
cerium nitrate.
[0041] In one or more embodiments, the third reaction product is
maintained at a
pH of less than about 1.5, or in a more specific embodiment, at about 1 or as
close to
about 1 as possible. The temperature may also be controlled. For example, in
one variant,
the temperature of the third reaction product is raised and maintained at a
temperature in
the range from about 30 C to about 50 C. In one or more specific embodiments,
the
temperature of the third reaction product is raised and maintained at a
temperature of
about 40 C.
[0042] The dispersed alumina and water slurry is added to and is well
mixed for a
duration from about 30 minutes to about 60 minutes to form a fourth reaction
product,
new slurry or mixed slurry. While the alumina slurry and the third reaction
product are
mixed, the pH is maintained at less than about 1.5. In one or more
embodiments, the
process includes maintaining the pH at about I or as close to 1 as possible.
The
temperature is also maintained at a range from about 20 C and about 30 C or,
more
specifically, at 25 C.
[0043] The fourth reaction product is then combined with a precipitation
solution
and a heel of water to form a precipitate slurry. The precipitation solution
may include a
basic solution of one or more of sodium carbonate and sodium bicarbonate and
is formed
separately from the heel of water. The precipitation solution may he formed at
a
temperature and/or have a temperature in the range from about 30 C to about
70 C or,
in one or more specific embodiments, a temperature of about 40 C. In one or
more
embodiments, the slurry is formed by adding the acidic slurry and the
precipitate solution
simultaneously and slowly to a separate vessel containing a heel of water to
form a
precipitate slurry. The heel of water may have a temperature in the range from
about 30
C to about 70 C or, in one or more specific embodiments, a temperature of
about 40 C.
CA 02859192 2014-08-13
This simultaneous addition of the acidic slurry and the precipitation solution
improves the
sistency-in-the_precipitation-ofthe_carbonates.
[0044] In one or more embodiments, precipitation reaction is performed or
carried out at a pH that is controlled, for example, by adjusting the flow of
the fourth
reaction product and/or the flow of the precipitation solution. In one or more
embodiments, the pH is controlled to an amount in the range from about 6 to
about 7 or,
more specifically, in the range from about 6.4 to about 6.7. In one or more
specific
embodiments, the pH is controlled at about 6.5. The temperature of the
precipitation may
be carried out at a temperature in the range from about 30 C to about 70 C,
or more
specifically, a temperature of about 40 C.
100451 In one or more embodiments, the precipitate slurry is digested or
aged for
a duration of about 15 minutes to about 15 hours. In a specific embodiment,
the
precipitate slurry is digested or aged for a duration of about I hour to about
3 hours. In
an even more specific embodiment, the precipitate slurry is digested or aged
for a
duration of about 2 hours. The temperature of the precipitate slurry is
increased to a
temperature in the range from about 30 C to about 70 'V during aging or, more
specifically, to a temperature of about 60 'C. In one variant, the pH of the
precipitate
slurry during digestion or aging is not controlled. In such embodiments, the
pH of the
precipitate slurry undergoes some changes by increasing and decreasing, though
the
amount of increase and decrease may not be uniform. During the digestion or
aging
process, the color of the slurry changes from blue to green. In one variant,
the method
includes filtering and washing the slurry to form a filter cake. The method
may also
include drying the filter cake to form a dry filter cake or dried powder. The
dry filter cake
or dried powder may then be calcined to decompose any carbonates to oxides. In
one or
more embodiments, the dry filter cake or dried powder may be calcined for a
duration of
about 2 hours at a temperature range of about 300 C to 'about 500 C to form
the first
powder. In one or more embodiments, the dry filter cake or dried powder may be
calcined for a duration of about 2 hours at a temperature of about 350 C to
form the first
powder.
[0046] In a specific embodiment of the method, at least a part of the first
powder
is prepared by a precipitation reaction and/or calcination. In one or more
embodiments,
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CA 02859192 2014-08-13
precursors of the first powder comprise a salt in a solution and can be heated
and adjusted
-to-a-defined-pH-value. -After_this, _a calcination _step_ may be carried_out.
In_another_
specific embodiment of the method, at least one component of the first powder
is
precipitated and at least one part of the first powder, (which is not
subjected to the first
precipitation) is added to the precipitate. In an even more specific
embodiment, it is
added by spray drying or precipitation.
[00471 In certain embodiments, the first powder has a particle size
distribution
characterized by a D10 value of 5-140 jun, a D50 value of 40-300 pm, and a D90
value of
180-800 pm. This particle size distribution can be determined via state of the
art analysis
techniques, e.g. via analysis apparatus like Mastersizer 2000 or 3000 by
Malvern
Instruments GmbH. The particle size distribution in the sense of the invention
is
characterized by the D10, D50, and 1390 value. As used herein, "D10" refers to
the
equivalent diameter where 10 mass % of the particles of the sample has a
smaller
diameter and hence the remaining 90% is coarser. The definition of D50 and D90
can be
derived similarly. In specific embodiments, the first powder has a particle
size
distribution characterized by a D10 value of 5-80 pm, a D50 value of 40-270
pm, and a D90
value of 250-800 jun. In particular embodiments, the first powder has a
particle size
distribution characterized by a Di0 value of 5-50 pm, a 1)50 value of 40-220
pm, and a D,0
value of 350-800 pm.
[0048] The final composition of the first powder may be varied. In one or
more
embodiments, the amount of copper oxide ranges from about 50% to about 55%
weight
of the total weight of the first powder. In some embodiments, the amount of
zinc ranges
from about 16% to about 20% of the total weight of the first powder. In one or
more
embodiments, the amount of zirconium ranges from about 14% to about 15% by
weight
of the total weight of the first powder. In some embodiments, the amount of
cerium
ranges from about 14% to about 15% by weight of the total weight of the first
powder. In
one or more embodiments, the amount of alumina ranges from about 20% to about
30%
by weight of the total weight of the first powder.
[0049] In one or more embodiments, the second powder comprises one or more
of aluminum hydroxide, aluminum oxide hydroxide and/or y-aluminum oxide with
one or
more of niobium, tantalum, phosphorus or boron, or mixtures thereof. The
second
12
CA 02859192 2014-08-13
powder may be generally made by the calcination of a salt comprising niobium,
tantalum,
¨phosphorus or-boron with a
mixture_ofalutninum_hydroxide,_aluminum_oxide_hydroxide_
and/or y-aluminum oxide. In one embodiment, the salt further comprises one Or
more of
oxalate, acetate and acetylacetonate. In some embodiments, the second
powder
comprises at least some y-alutnina, which can provide acid sites. In such
embodiments,
the resulting catalyst composition will contain at least some fly-alumina even
if the first
powder does not contain '-alumina. In one or more embodiments, the amount of
alumina
ranges from about 80 to about 90% by weight of the total weight of the second
powder.
[0050] In some embodiments, the niobium, tantalum, phosphorus and/or
boron
oxide are present in amount as low as about 0.1 or 1 percent by weight, and as
high as
about 20, 30 or 40 percent by weight of the catalytic material. In a specific
embodiment,
the second powder comprises one or more of aluminum hydroxide, aluminum oxide
hydroxide and y-aluminum oxide with about 1-25, 5-20, 10-15 or 1-10 % by
weight of
one or more of niobium, with about 1-25, 5-20, 10-15 or 1-10 % by weight of
tantalum,
with about 1-25, 5-20, 10-15 or 1-10 % by weight of phosphorus or with about 1-
25, 5-
20, 10-15 or 1-10% by weight of boron.
[0051] In one or more embodiments of the catalyst composition, the
resulting
material from the second powder has a surface area from about 40, 50, 60, 70,
100 or 130
to about 170, 200, 240, 250 or 270 m2/g, with a pore volume in the range of
from about
0.35-0.1.45 ml/g, and specifically a surface area from about 55, 85, 100 or
125 to about
140, 160, 180 200 or 220 m2/g with a pore volume in the range of from about
0.35-1.35
ml/g, and even more specifically a surface area from about 110-200 m2/g with a
pore
volume in the range of from about 0.51-1.14 ml/g.
100521 In a specific embodiment of the catalyst composition, the
resulting
material from the second powder comprises boehmite, and more specifically a
boehmite-
containing mineral. Boehmite occurs in tropical laterites and bauxites
developed on
alumino-silicate bedrock. It also occurs as a hydrothermal alteration product
of corundum
and nepheline. It occurs with kaolinite, gibbsite and diaspore in bauxite
deposits and with
nepheline, gibbsite, diaspore, natrolite and analcime in nepheline pegmatites.
[0053] The second powder that is used can vary as described above. In
certain
embodiments, the second powder has a size distribution characterized by a D10
value of
13
CA 02859192 2014-08-13
5-140 Rm, a D50 value of 40-300 pm, and a D90 value of 180-800 tun. The
particle sizes
-of-the-two-powders -may-be_the-same or-d fferent_In_preferred_ embod
ments,_the_second
powder has a particle size distribution characterized by a Dio value of 5-80
j.un, a D50
value of 40-270 pm, and a D-go value of 250-800 run. In particular
embodiments, the
second powder has a particle size distribution characterized by a Dic, value
of 5-50 pm, a
D50 value of 40-220 pm, and a Dgo value of 350-800 pm.
[0054] Additives
[0055] In one or more embodiments, additives may be included in the
catalyst
composition. For example, an additive can be a structure-promoter, which can
help to
build up pores or channels. Examples of a structure-promoter include, but are
not limited
to, thermally decomposable compounds like polymers, wood dust, flour,
graphite, film
material, straw, stearic acid, palm itic acid, celluloses or combinations
thereof
[0056] Mixing and/or Pelleting of the Two Powders
[0057] In one or more embodiments, the two dried powders are mixed
together,
meaning that they are brought into contact without further chemical
modification. In one
variant, the catalyst composition comprises about 70-90% by weight of the
first powder,
about 10-90% by weight of the second powder, and about 0-10% by weight of one
or
more additives (these three components total 100%).
[0058] In several embodiments, the catalyst composition can be in any form
known in the art that contains pores or channels or other features for
enlargement of
surface, which will help to bring the educts in contact such that they can
react with the
syngas to form the desired product. In one or more embodiments, the catalyst
composition can be understood as a physical mixture, whereby the powders
contact each
other and exhibit channels and/or pores between their contact surfaces. In a
specific
embodiment, the powders are not melted or sintered at their contact surfaces.
[0059] In one or more embodiments, the catalyst composition is a pellet
with a
size in the range from 1 x 1 mm to 10 x 10 mm, specifically in the range from
2 x 2 mm
to 7 x 7 rum. The pellet is obtained by pressing the mixture of the two
powders (along
with any other promoters or components) into a pellet. In various embodiments,
the pellet
can be ring-shaped, star-shaped or spherical-shaped, hollow strings, trilobes,
multihole
pellets, extrudates and alike.
14
CA 02859192 2014-08-13
100601 In particular, the powders and any other components can be
compacted in
-a-presser,a-squeezer,-a-crusher-or-a-
squeezing_machine._1n_one_or_rnore_embodiments,
compacting means that particles of a defined particle size distribution are
pressed
together, which have a diameter in the range of 1 to 10 mm and a height of 1
to 10 mm.
hi specific embodiments, the particle size distribution is left intact after
the compaction.
[0061j In a specific embodiment of the method, a pellet is formed with a
size in
the range of from about 1 x 1 mm to 10 x 10 mm, and specifically in the range
from 2 x 2
mm to 7 x 7 mm.
[00621 In one embodiment of the method, the two powders are independently
pressed through at least one sieve, wherein the sieve exhibits a mesh size
from about
0.005 to about 5 mm in order to obtain a particle size distribution
characterized by a Dio
value of about 5-140 gm, a D50 value of about 40-300 pm, and a D90 value of
about 180-
800 pm. Specifically, the sieve exhibits a mesh size from about 0.005 to about
1.5 mm,
and even more specifically a mesh size from about 0.005 to about 0.9 mm. In
another
embodiment, the particles can also exhibit particle size distribution
characterized by a
D50, and Dgo value of about 5-140 pm, about 40-300 pm, and about 180-800 pm,
respectively.
[0063] In a specific embodiment of the preparation of a catalyst
composition
described herein, at least three different sieves arc used, wherein the two
powders are
pressed through the sieves starting from the sieve with the largest mesh size
and
progressing in mesh size order to the sieve with the smallest mesh size.
Specifically, in
one or more variants, the particle size distribution of the first and/or
second powder may
be characterized by a D10 value of about 5-140 nm, a D50 value of about 40-300
ttm, and
a Dgo value of about 180-800 pm. These particles can also be broken during the
sieving,
so that smaller particles are obtained that can be passed on through to the
smaller sized
sieve. Therefore, a first fraction with a particle size distribution can be
obtained before
the second sieve. This fraction can also be used as a catalyst composition.
Additionally,
in embodiments with three sieves, the particles which go through the second
sieve with a
mesh size smaller than the first sieve, but bigger than the third sieve, can
be obtained
behind the second sieve and before the smallest sieve with the smallest mesh
size. Again,
the particles obtained after the second (middle) sieve can be used as a
catalyst
CA 02859192 2014-08-13
--
composition. In addition to this; the particles obtained after the sieve with
the biggest
¨mesh-size-could- be- pressed- throu gh_the .second.sieve_in.
order_to_reduce_the_particle_size. _
[0064] In a specific embodiment, the preparation method further comprises
adding a mixture of hydrogen and nitrogen. The mixture of hydrogen and
nitrogen may
be added to the first and/or second powder. In a very specific embodiment,
content of the
volume of the hydrogen is less than 5% of the mixture.
[00651 In one or more embodiments, the resulting catalyst, containing
both
powders and before reduction of the copper oxide to form copper metal,
includes cupric
oxide in an amount in the range from about 10% by weight to about 75%, or
about 15%
to about 50% by weight of the total catalyst. It is noted that the amounts of
the various
components will depend on the ratio of the two powders utilized. In one
variant, ZnO is
present in the resulting catalyst, before reduction, in an amount in the range
from about
5% by weight to about 70%, about 5% to about 50%, or about 5% to about 25% by
weight. In one or more embodiments, the catalyst includes Zr02 in an amount in
the
range frdm about 1% by weight to about 50%, or about I% to about 25% by
weight,
before reduction. In one or more embodiments, the catalyst includes cerium
oxide in an
amount in the range or from about 5% by weight to about 70%, about 5% to about
50%,
or about 5% to about 25%, before reduction. In one or more embodiments, the
catalyst
includes niobium oxide, tantalum oxide, phosphorus oxide and/or boron oxide in
an
amount in the range from about 1% by weight to about 50%, or about 1`)/0 to
about 40%
by weight, before reduction. In one or more embodiments, the catalyst includes
alumina
in an amount in the range from about 5% by weight to about 80%, or about 10%
to about
60% by weight, before reduction. This alumina amount is the total alumina from
both
powders,
[0066] In one or embodiments, the prepared catalyst composition is further
reduced. A variant of the reducing step utilizes a hydrogen-containing gas.
Specifically,
such methods may include heating the catalyst to a temperature in the range
from about
150 C to about 200 C while flowing nitrogen gas at atmospheric pressure over
the
catalyst in a reactor. In one or more specific embodiments, the catalyst is
heated to a
temperature in the range from about 165 C to about 185 C in flowing N2. In a
more
specific embodiment, the catalyst is heated to a temperature of about 170 C
in flowing
16
CA 02859192 2014-08-13
N2. The nitrogen is replaced incrementally by hydrogen. In one or more
embodiments,
the-tem peratu re -may-be -s low ly- and-incremental ly-increased-to _ max
imum-of about-250
C.
[00671 The resulting catalyst composition includes copper metal, formed
form the
reduction of the CuO precursor. The catalyst also includes ZnO, Zr02, niobium
oxide
which function as promoters or active materials, while the alumina functions
as a
structural component. In some embodiments, the catalyst composition also
comprises
ceria. In one or more embodiments, at least the ZnO, Zr02, and/or cerium oxide
are
closely associated .with the copper metal.
[0068] DME Synthesis
[00691 In one or more embodiments, the catalyst composition exhibits the
ability
to directly convert synthesis gas to dimethyl ether. The catalyst compositions
described
herein are able to convert carbon monoxide at levels close to the
thermodynamic limits,
as compared to commercially available catalyst compositions at similar testing
conditions
(e.g., 84% conversion versus about 55% conversion at 250 C, 50bar, GHSV 2400
hi,
F12/C0=1). This is highly advantageous, as normally two steps are required in
the
synthesis of dimethyl ether: conversion of synthesis gas to methanol, and then
conversion
of methanol to the dimethyl ether end product.
[0070) Thus, another aspect of the present invention pertains to a method
of
making dimethyl ether. The method comprises contacting a stream of synthesis
gas
comprising carbon monoxide and hydrogen with a catalyst comprising about 10 to
about
75 weight % Cu0; about 5 to about 50 weight % ZnO; about I to about 30 weight
%
Zr02; about 1 to about 40 weight % of one or more of boron oxide, tantalum
oxide,
niobium oxide, phosphorus oxide and combinations thereof; and¨about 5 to about
80
weight % alumina.. In one embodiment, the synthesis gas has a ratio of carbon
monoxide
to hydrogen is about I. In an alternate variant, the synthesis gas has a ratio
of carbon
monoxide to hydrogen is less than 1. In yet another variant, the synthesis gas
has a ratio
of carbon monoxide to hydrogen is greater than I. In one or more embodiments,
the
synthesis gas further comprises carbon dioxide. Thus, in yet another
embodiment, the
catalyst composition is contacted with a synthesis gas comprising carbon
dioxide.
17
CA 02859192 2014-08-13
[0071] In other embodiments, the method of making DME further comprises
-red ucing-the-catalyst-co mposi tion,wherein_ the _stream _of_synthesis
_gas_is_contacted _with _
the reduced catalyst composition. In variants of this embodiment, the catalyst
composition is reduced at a temperature having a range of about 140 C to about
240 C,
and may have one or more of nitrogen, hydrogen, and a mixture thereof. In some
embodiments, a reactor may be filled with the catalyst composition. In some
specific
embodiments, a reactor is filled with pelletized version of the catalyst
composition.
[0072] One or more of the embodiments of this method relates to a high
turnover
of carbon monoxide. The reaction conditions are selected to achieve suitable
DME
synthesis. In some embodiments, the temperature is about 180 C to 300 C, or
200 C to
300 C, or 200 C to 250 C. Suitable pressures for the synthesis of DME include,
but are
not limited to, about 20 to 80 bar, and in particular from 30 to 50 bar.
[0073] Without intending to limit the invention in any manner,
embodiments of
the present invention will be more fully described by the following examples.
EXAMPLES:
[0074] Example Syntheses of three different Methanol-active components
(0075] Synthesis of A
[0076] Two solutions are prepared for the precipitation of the components:
(0077] Solution 1: A solution of 1.92 kg copper nitrate, 0.58 kg zinc
nitrate, 0.51
kg zirconia nitrate and 0.66 kg pseudoboehmite alumina dispersion arc
dissolved/mixed
in 2.84 L water.
[0078] Solution 2: 1.147 kg sodium carbonate is dissolved in 3.841 1.
water.
[0079] Both solutions are separately heated to 40 C. A mix pot containing
2.13 L
water is heated to 40 C. Solution 1 and Solution 2 are simultaneously added to
the mix
pot with agitation while maintaining a pH=6.5 +/- 0.20 for 90 minutes. The
precipitation
ends once Solution 1 is consumed. The temperature is raised to 60 C for 2
hours while
maintaining agitation. The precipitate is filtered and washed with 60 C
deionized water
until sodium oxide content is <0.10% and free of nitrates. The filter cake is
dried at
18
CA 02859192 2014-08-13
120 C overnight and calcined for 4 hours at 350 C in air. The metal oxide
content of the
--catalyst-in-wG%-is-asfollows-Cu0-48.0;-Zn0-1,7.0:_A1203,23.0:_Zr02_12Ø
[0080] Synthesis of B
[0081] Two solutions are prepared for the precipitation of the
components:
[0082] Solution 1: A solution of 1.92 kg copper nitrate, 0.58 kg zinc
nitrate, 0.51
kg zirconia nitrate and 0.66 kg Catapa149D alumina are dissolved/mixed in 2.84
I; water.
[0083) Solution 2: 1.147 kg sodium carbonate is dissolved in 3.841 L
water
[0084] Both solutions are separately heated to 40 C. A mix pot containing
2.13 L
water is heated to 40 C. Solution 1 and Solution 2 are simultaneously added to
the mix
pot with agitation while maintaining a pfl--6.5 -1-1- 0.20 for 90 minutes. The
precipitation
ends once Solution 1 is consumed. The temperature is raised to 60 C for 2
hours while
maintaining agitation. The precipitate is filtered and washed with 60 C
deionized water
until sodium oxide content is <0.10% and free of nitrates. The filter cake is
dried at
120 C overnight and calcined for 4 hours at 350 C in air. The metal oxide
content of the
catalyst in wt.% is as follows CuO 50.7: ZnO 15.4: A1203 20.2: Zr02 13.7.
[0085] Synthesis of C
[0086] Two solutions are prepared for the precipitation of the
components:
100871 Solution 1: A solution of 1.75 kg copper nitrate, 0.55 kg zinc
nitrate, 0.46
kg zirconia nitrate, 0.74 kg gamma alumina suspension and 73.7g cerium nitrate
are
dissolved/mixed in 2.84 I, water.
[0088] Solution 2: 1.147 kg sodium carbonate is dissolved in 3.841 L
water.
[0089] Both solutions are separately heated to 40 C. A mix pot containing
2.13 L
water is heated to 40 C. Solution 1 and Solution 2 are simultaneously added to
the mix
pot with agitation while maintaining a p1-1-6.5 +/- 0.20 for 90 minutes. The
precipitation
ends when Solution 1 is consumed. The temperature is raised to 60 C for 2
hours while
maintaining agitation. The precipitate is filtered and washed with 60 C
deionized water
until sodium oxide content is <0.10% and free of nitrates. The filter cake is
dried at
120 C overnight and is calcined for 4 hours at 350 C in air. The metal oxide
content of
the catalyst in wt.% is as follows CtiO 50.5: ZnO 16.5: A1203 20.5: Zr02 9.5:
Ce02 3Ø
19
CA 02859192 2014-08-13
-100901_ _Example _2: _Syntheses of the_acidic_components_
100911 Synthesis of X
[00921 A solution is prepared that consists of 4 grams ammonium
niobate(V)
oxalate and 27.4 ml demineralized water. This solution is applied onto a 40 g
A1203/A100H-mixture (crushed extrudates consisting of 60 % gamma- A1203 and
40%
boehmite) by spray-watering. This material is then dried for 12 II at 90 C in
a drying
oven. After drying, the material is calcined in a rotating tube for 3 hours at
450 C under a
nitrogen atmosphere (30n1/h). The heating rate is 5 C/min. After cooling to
room
temperature, the material is ready for use.
10093] Synthesis of Y
[0094] A solution is prepared that consists of 4 grams boronic acid and
27.4 ml
demineralized water. This solution is applied onto a 40 g A1203/A1001-4-
mixture (crushed
extrudates consisting of 60 % gamma- A1203 and 40% boehmite) by spray-
watering. This
material is then dried for 12 h at 90 C in a drying oven. After drying, the
material is
calcined in a rotating tube for 3 hours at 450 C under a nitrogen atmosphere
(30n1/h).
The heating rate is 5 C/nnin. After cooling to room temperature, the material
is ready for
use.
[0095] Synthesis of 7.
100961 An solution is prepared that consists of 4 grams phosphoric acid
arid 27.4
ml demineralized water. This solution is applied Onto a 40 g A1203/A1001-1-
mixture
(crushed extrudates consisting of 60 A gamma- A1203 and 40% boehmite) by
spray-
watering. This material is then dried for 12 h at 90 C in a drying oven.
After drying, the
material is calcined in a rotating tube for 3 hours at 450 C under a nitrogen
atmosphere
(30n1/h). The heating rate is 5 C/min. After cooling to room temperature, the
material is
ready for use.
100971 - __ Example 3: Preparation of the final catalyst composition:
CA 02859192 2014-08-13
=
100981 The methanol-active compound and the acid compound are compacted
--separately-
in_a_tablet_press_and/or_pelletizing_machine_The_molding_obtained_(diameter =
ca, 25mm, height ¨ ca, 2min) is squeezed through sieves with an appropriate
mesh size,
so that the desired split fraction is obtained. From both fractions the proper
quantity is
weight in (9/1, 8/2, or 7/3 methanol-active/acidic compound) and mixed in a
mixing
machine (Heidolph. Reax 2 or Reax 20/12). Any promoters or additional
components are
added in advance of pellet ization.
[0099] Example 4: Testing conditions for non-pelletized mixtures:
(00100i The catalyst composition (5 cm3 by volume) is incorporated into a
tubular
reactor (inner diameter 0.4 cm, bedded in a metal heating body) on a catalyst
bed support
consisting of alumina powder as a layer of inert material, and is then
pressure-less
reduced with a mixture of 1 Vol.-% H2 and 99 Vol.-% N2. The temperature is
increased
in intervals of 8 hours from 150 C to 170 C, 170 C to 190 C and finally to 230
C. At a
temperature of 230 C the synthesis gas is introduced and heated within 2 hours
up to
250 C. The synthesis gas consists of 45% 1-12 and 45% CO and 10% inert gas
(argon).
. The catalyst composition is run at an input temperature of 250 C, GHSV of
240011' and a
pressure of 50 bar.
[00101] Example 5: Testing conditions for pelletized mixtures:
[00102] Tests for pelletized materials are conducted in a similar test rick
compared
to the setup described above for non-pelletized materials using the same
routine. The only
difference is that the tubular reactor does not have an inner diameter of 0.4
cm, hut
instead an inner diameter of 3 cm. The tests for the pelletized materials are
carried out
with a catalyst volume of 100 cm3.
[00103] Example 6: Results
[00104] Table 1 shows the results of various catalyst compositions. In
comparison
to the state of the art (see also PhD thesis "Dimethylether-Direktsynthese aus
kohlenmonoxidreichem Synthesegas" --- Miriam Stiefel, University of
Heidelberg, 03.
21
CA 02859192 2014-08-13
December 2010) the catalyst performances shown in table 1. Experiments 1-5
reveal that
significant_higher C_O conversions_are_achieveci.Turthermore the catalysts
show Very low
S(Others) values.
[00105] Inventive experiment 6 was done using 3x3 mm pellets that were
formed
of a physical mixture of A and Z that were mixed in a ratio by weight of 4/1.
It can be
seen that the superior performance is maintained within this catalyst
composition
compared to Experiment 5.
Table 1: Results
Exp. Me0H- acidic CO S(Me0H) S(1)ME) S(CO2) S(Others)
No. active component conversion
component X, Y, or Z 14)/01
A, 13, or C
1 A X 76.22 11.13 48.31 40.4 0.16
2 B X 63.17 13.18 47.68 39.06 0.08
3 C X 76.39 6.43 48.95 44.35 0.27
4 A Y 78.63 5.18 45.94 48.69 0.19
A Z 81.72 2.43 47.50 49.98 0.09
6 3 x 3 inm pellet of A & Z 79,54 11.94 48.97 I 49.07
0.02
[001061 All mixtures comprise Me0H-active and acidic components in a weight
ratio of 4/1.
1001071 All gaseous streams were analyzed via online-CC. Argon was used as
internal standard to correlate in and oil gas streams.
1001081 CO conversion is given as follows: (CO,õ-(CO,õt * Argonõ, /
Argonou())
* 100%
1001091 S(Me0H) - Volume (Me0H) in product stream / Volume
(MeOHI-DNIE-(CO2I-Others without hydrogen and CO) in product stream * 100%
[00110] S(DME) = Volume (DME) in product stream / Volume
(Me0H+DME+CO2I-Others without hydrogen and CO) in product stream * 100%
[00111] S(CO2) = Volume (CO2) in product stream / Volume
(Me0H+DME-I-0O2+0thers without hydrogen and CO) in product stream * 100%
22
CA 02859192 2014-08-13
[00112] S(Others) =
Volume (Others) in product stream / Volume
(Me0H+DME.+CO2+0thers,without hydrogen and CO) in product stream * 100%
[00113] "Others" are
compounds that are formed out of I-12 and CO that are not
Me0H, DME, or CO2.
[00114] Reference
throughout this specification to "one embodiment," "certain
embodiments," "one or more embodiments" or "an embodiment" means that a
particular
feature, structure, material, or characteristic described in connection with
the embodiment
is included in at least one embodiment of the invention. Thus, the appearances
of the
phrases such as "in one or more embodiments," "in certain embodiments," "in
one
embodiment" or "in an embodiment" in various places throughout this
specification are
not necessarily referring to the same embodiment of the invention.
Furthermore, the
particular features structures, materials, or characteristics may be combined
in any
suitable manner in one or more embodiments.
[00115] Although the
invention herein has been described with reference to
particular embodiments, it is to be understood that these embodiments are
merely
illustrative of the principles and applications of the present invention. It
will be apparent
to those skilled in the art that various modifications and variations can be
made to the
method and apparatus of the present invention without departing from the
spirit and
- scope of the invention. Thus, it is
intended that the present invention include
modifications and variations that are within the scope of the appended claims
and their
equivalents.
23
