U.S. patent application number 16/965370 was filed with the patent office on 2021-03-25 for method and reactor for oxidative coupling of methane.
The applicant listed for this patent is SABIC Global Technologies B.V.. Invention is credited to Vemuri Balakotaiah, Tian Gu, Sagar Sarsani, David West.
Application Number | 20210087121 16/965370 |
Document ID | / |
Family ID | 1000005444571 |
Filed Date | 2021-03-25 |
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United States Patent
Application |
20210087121 |
Kind Code |
A1 |
Sarsani; Sagar ; et
al. |
March 25, 2021 |
Method and Reactor for Oxidative Coupling of Methane
Abstract
A method of autothermal oxidative coupling of methane (OCM)
utilizes introducing a methane-containing feedstock and an
oxygen-gas-containing feedstock into a reactor (10) as a flowing
mixture (18) with a space time of 500 ms or less. The reactor (10)
contains a catalyst bed (20) of an OCM catalyst that contacts the
flowing mixture and wherein the catalyst bed (20) has a heat Peclet
number (Pe.sub.h) of from 5 or less, a mass Peclet number
(Pe.sub.m) of from 5 or more, and a transverse Peclet number (P) of
from 1 or less while contacting the flowing mixture. The methane
and oxygen of the feedstocks are allowed to react within the
reactor (10) to form methane oxidative coupling reaction products.
A reactor (10) for carrying out the OCM reaction is also
disclosed.
Inventors: |
Sarsani; Sagar; (Pearland,
TX) ; West; David; (Bellaire, TX) ;
Balakotaiah; Vemuri; (Bellaire, TX) ; Gu; Tian;
(Richmond, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SABIC Global Technologies B.V. |
Bergen op Zoom |
|
NL |
|
|
Family ID: |
1000005444571 |
Appl. No.: |
16/965370 |
Filed: |
May 2, 2019 |
PCT Filed: |
May 2, 2019 |
PCT NO: |
PCT/US2019/030329 |
371 Date: |
July 28, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62665663 |
May 2, 2018 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J 2208/00982
20130101; C07C 2523/04 20130101; B01J 8/085 20130101; C07C 2523/656
20130101; C07C 2/84 20130101; B01J 2208/00938 20130101; C07C
2523/652 20130101; C07C 2521/10 20130101; B01J 35/023 20130101;
B01J 8/082 20130101; C07C 2521/08 20130101; C07C 2523/14
20130101 |
International
Class: |
C07C 2/84 20060101
C07C002/84; B01J 35/02 20060101 B01J035/02; B01J 8/08 20060101
B01J008/08 |
Claims
1. A method of carrying out autothermal oxidative coupling of
methane (OCM) comprising: introducing a methane-containing
feedstock and an oxygen-gas-containing feedstock into a reactor as
a flowing mixture with a space time of 500 ms or less, the reactor
containing a catalyst bed of an OCM catalyst that contacts the
flowing mixture and wherein the catalyst bed has a heat Peclet
number (Pe.sub.h) of from 5 or less, a mass Peclet number
(Pe.sub.m) of from 5 or more, and a transverse Peclet number (P) of
from 1 or less while contacting the flowing mixture; and allowing
the methane and oxygen of the feedstocks to react within the
reactor to form methane oxidative coupling reaction products.
2. The method of claim 1, wherein: the catalyst bed comprises at
least one of the following: a layer of OCM catalyst formed as
catalyst particles having a particle size of from 0.1 mm to 3 mm;
at least one monolithic body of one of a ceramic or metal material
having pores or channels with a pore or channel size from 0.1 to 5
mm, the monolithic body having an OCM catalyst material present on
at least all or a portion of the surface of the monolithic body; at
least one monolithic body of one of a ceramic or metal material
having pores or channels with a pore or channel size from 0.1 to 5
mm, and wherein the pores or channels contain an OCM catalyst
powder.
3. The method of claim 1, wherein: the catalyst bed comprises at
least one monolithic body of one of a ceramic or metal material
having pores or channels with a pore or channel size from 0.1 to 5
mm, and wherein the pores or channels contain an OCM catalyst
powder having a particle size of less than 400 microns.
4. The method of claim 1, wherein: the methane-containing feedstock
is introduced into the reactor at a temperature of from
-100.degree. C. to 300.degree. C.
5. The method of claim 1, wherein: the methane-containing feedstock
is introduced into the reactor at a temperature of from -20.degree.
C. to 150.degree. C.
6. The method of claim 1, wherein: the reactor is operated at a
space time of from 100 ms or less.
7. The method of claim 1, wherein: the catalyst bed temperature is
from 500.degree. C. to 1000.degree. C.
8. The method of claim 1, wherein: the catalyst bed temperature is
from 800.degree. C. to 950.degree. C.
9. The method of claim 1, wherein: the OCM catalyst is comprised of
at least one of La.sub.2CeO.sub.2, SrO/La.sub.2O.sub.3, CeO.sub.2,
La.sub.2O.sub.3--CeO.sub.2, Ca/CeO.sub.2, Mn/Na.sub.2WO.sub.4,
Li.sub.2O, Na.sub.2, Cs.sub.2O, WO.sub.3, Mn.sub.3O.sub.4, CaO,
MgO, SrO, BaO, CaO--MgO, CaO--BaO, Li/MgO, MnO, W.sub.2O.sub.3,
SnO.sub.2, Yb.sub.2O.sub.3, Sm.sub.2O.sub.3, SrO/La.sub.2O.sub.3,
La.sub.2O.sub.3, Ce.sub.2O.sub.3, La/MgO, and combinations
thereof.
10. The method of claim 1, wherein: the heat Peclet number
(Pe.sub.h) is from 1 or less, the mass Peclet number (Pe.sub.m) is
from 10 or more, and the transverse Peclet number (P) is from 0.1
or less.
11. An oxidative coupling reactor comprising: a reactor that
defines a reaction chamber and having at least one inlet for
introducing a flowing methane-containing feedstock and an
oxygen-gas-containing feedstock into the reaction chamber; a
catalyst bed positioned within the reaction chamber that receives
the flowing methane-containing feedstock and an
oxygen-gas-containing feedstock as a flowing mixture with a space
time of 500 ms or less, the catalyst bed containing an OCM
catalyst, the catalyst bed configured to have a heat Peclet number
(Pe.sub.h) of from 5 or less, a mass Peclet number (Pe.sub.m) of
from 5 or more, and a transverse Peclet number (P) of from 1 or
less as gases pass through the catalyst bed; and a reactor outlet
in fluid communication with the reaction chamber for removing
reaction products from the reactor.
12. The reactor of claim 11, wherein: the catalyst bed comprises a
layer of OCM catalyst formed as catalyst particles having a
particle size of from 0.1 mm to 3 mm.
13. The reactor of claim 12, wherein: the layer of OCM catalyst is
from 5 to 20 particles deep.
14. The reactor of claim 11, wherein: the catalyst bed comprises at
least one monolithic body of one of a ceramic and metal material
having pores or channels with a pore or channel size from 0.1 to 5
mm, the monolithic body having an OCM catalyst material present on
at least all or a portion of the surface of the monolithic
body.
15. The reactor of claim 14, wherein: the at least one monolithic
body has a thickness of from 5 mm to 50 mm.
16. The reactor of claim 11, wherein: the catalyst bed comprises at
least one monolithic body of one of a ceramic and metal material
having pores or channels with a pore or channel size from 0.1 to 5
mm, and wherein the pores or channels contain an OCM catalyst
powder.
17. The reactor of claim 16, wherein: the at least one monolithic
body has a thickness of from 5 mm to 100 mm.
18. The reactor of claim 16, wherein: the catalyst powder has a
particle size of less than 400 microns.
19. The reactor of claim 11, wherein: the OCM catalyst is selected
from at least one of La.sub.2CeO.sub.2, SrO/La.sub.2O.sub.3,
CeO.sub.2, La.sub.2O.sub.3--CeO.sub.2, Ca/CeO.sub.2,
Mn/Na.sub.2WO.sub.4, Li.sub.2O, Na.sub.2, Cs.sub.2O, WO.sub.3,
Mn.sub.3O.sub.4, CaO, MgO, SrO, BaO, CaO--MgO, CaO--BaO, Li/MgO,
MnO, W.sub.2O.sub.3, SnO.sub.2, Yb.sub.2O.sub.3, Sm.sub.2O.sub.3,
SrO/La.sub.2O.sub.3, La.sub.2O.sub.3, Ce.sub.2O.sub.3, La/MgO, and
combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national stage application under 35
U.S.C. .sctn. 371 of International PCT Application No.
PCT/US2019/030329, filed May 2, 2019, which claims the benefit of
U.S. Provisional Application No. 62/665,663, filed May 2, 2018,
each of which is incorporated herein by reference in its
entirety.
TECHNICAL FIELD
[0002] The invention relates to the conversion of methane and
oxygen to C.sub.2 and higher hydrocarbons and reactor designs for
such conversion.
BACKGROUND
[0003] Methane can be used to produce ethane and/or ethylene
through the oxidative coupling of methane (OCM) reaction. While
extensive research and development has been devoted to this
reaction, the reaction largely remains inefficient on a commercial
scale. One of the key challenges is the high reaction temperature
(typically greater than 750.degree. C.) required to make the
reaction proceed. The need for such a high temperature is due to
the bond strength (bond dissociation energy) of the tetrahedral
C--H bonds in methane, which is 104 kcal per mol (kcal/mol). This
C--H bond strength makes methane less reactive and difficult to
undergo oxidative conversion to form ethylene.
[0004] The oxidative coupling of methane reaction can be
represented by Equations (1) and (2) below:
2CH.sub.4+O.sub.2.fwdarw.C.sub.2H.sub.4+2H.sub.2O .DELTA.H=-67.4
kcal/mol (1)
2CH.sub.4+1/2O.sub.2.fwdarw.C.sub.2H.sub.6+H.sub.2O .DELTA.H=-84.6
kcal/mol (2)
As shown in Equations (1) and (2), oxidative conversion of methane
to ethylene or ethane is exothermic. Excess heat produced from
these reactions can push conversion of methane to carbon monoxide
and carbon dioxide rather than the desired C.sub.2 hydrocarbon
product, as shown in Equations (3) and (4) below:
CH.sub.4+11/2O.sub.2.fwdarw.CO+2H.sub.2O .DELTA.H=-82.8 kcal/mol
(3)
CH.sub.4+2O.sub.2.fwdarw.CO.sub.2+2H.sub.2O .DELTA.H=-95.9 kcal/mol
(4)
It should be noted that the heats of reaction for Equations (1) to
(4) are given per mole of oxygen consumed. The excess heat from the
reaction in Equations (3) and (4) further exacerbates this
situation, thereby substantially reducing the selectivity of
ethylene production when compared with carbon monoxide and carbon
dioxide production.
[0005] Equations (5) through (8), set forth below, illustrate the
chemical pathway in which the OCM reaction can occur in the
presence of a catalyst:
O.sub.2+2[*].fwdarw.2[O] (5)
CH.sub.4+[O].fwdarw.CH.sub.3+[OH] (6)
2CH.sub.3.fwdarw.C.sub.2H.sub.6.fwdarw.C.sub.2H.sub.4.fwdarw.CO.sub.X
(7)
2[OH].fwdarw.[O]+[*]+H.sub.2O (8)
where * is a vacant catalytic surface site. The coupling of methyl
radicals in Equation (7) occurs in the gas phase while the
formation of C.sub.2H.sub.4 and CO.sub.X may either be catalytic or
in the gas phase. The remaining reactions Equations (5), (6), and
(8) occur on the catalyst.
[0006] There are two practical problems that have prevented the
development of commercially feasible OCM processes. One is the very
large heat of reaction (Equations 1-4); and two is the very high
temperature to initiate the reaction (typically 700-950.degree.
C.). There is no commercially available liquid heat transfer fluid
capable of operating at such high temperatures. Consequently, the
only way to cool a reactor at this range of temperature is with
very inefficient gas phase coolants (e.g., air, steam, ethane,
etc.). In a cooled multi-tubular fixed bed reactor, the methane
conversion must be limited by the oxygen concentration in the feed
to less than about 8% in order to avoid a runaway reaction. A
runaway reaction is one in which the temperature rise within the
catalyst bed is high enough to damage or deactivate the catalyst or
to increase the production of by-products (CO.sub.x).
[0007] The present invention overcomes these disadvantages, with
the methods and reactors described herein being particularly useful
for commercial scale OCM operations.
SUMMARY
[0008] A method of carrying out autothermal oxidative coupling of
methane (OCM) is carried out by introducing a methane-containing
feedstock and an oxygen-gas-containing feedstock into a reactor as
a flowing mixture with a space time of 500 ms or less. The reactor
contains a catalyst bed of an OCM catalyst that contacts the
flowing mixture and wherein the catalyst bed has a heat Peclet
number (Pe.sub.h) of from 5 or less, a mass Peclet number
(Pe.sub.m) of from 5 or more, and a transverse Peclet number (P) of
from 1 or less while contacting the flowing mixture. The methane
and oxygen of the feedstocks are allowed to react within the
reactor to form methane oxidative coupling reaction products.
[0009] In specific embodiments, the catalyst bed may have different
configurations. In one, the catalyst bed is configured as at least
one of a layer of OCM catalyst formed as catalyst particles having
a particle size of from 0.1 mm to 3 mm. In another the catalyst bed
is at least one monolithic body of one of a ceramic or metal
material having pores or channels with a pore or channel size from
0.1 to 5 mm, the monolithic body having an OCM catalyst material
present on at least all or a portion of the surface of the
monolithic body. In another configuration, the catalyst bed is at
least one monolithic body of one of a ceramic or metal material
having pores or channels with a pore or channel size from 0.1 to 5
mm, and wherein the pores or channels contain an OCM catalyst
powder.
[0010] The methane-containing feedstock may be introduced into the
reactor at a temperature of from -100.degree. C. to 300.degree. C.
In certain instances, the methane-containing feedstock is
introduced into the reactor at a temperature of from -20.degree. C.
to 150.degree. C.
[0011] The reactor may be operated at a space time of from 500 ms
or less, and in some instances from 100 ms or less. The catalyst
bed temperature may range from 500.degree. C. to 1000.degree. C. In
some cases, the catalyst bed temperature may range from 800.degree.
C. to 950.degree. C.
[0012] The OCM catalyst may be comprised of at least one of
La.sub.2CeO.sub.2, SrO/La.sub.2O.sub.3, CeO.sub.2,
La.sub.2O.sub.3--CeO.sub.2, Ca/CeO.sub.2, Mn/Na.sub.2WO.sub.4,
Li.sub.2, Na.sub.2, Cs.sub.2O, WO.sub.3, Mn.sub.3O.sub.4, CaO, MgO,
SrO, BaO, CaO--MgO, CaO--BaO, Li/MgO, MnO, W.sub.2O.sub.3,
SnO.sub.2, Yb.sub.2O.sub.3, Sm.sub.2O.sub.3, SrO/La.sub.2O.sub.3,
La.sub.2O.sub.3, Ce.sub.2O.sub.3, La/MgO, and combinations
thereof.
[0013] In certain embodiments, the heat Peclet number (Pe.sub.h) is
from 1 or less, the mass Peclet number (Pe.sub.m) is from 10 or
more, and the transverse Peclet number (P) is from 0.1 or less.
[0014] An oxidative coupling reactor is also provided. The
oxidative coupling reactor comprises a reactor that defines a
reaction chamber and has at least one inlet for introducing a
flowing methane-containing feedstock and an oxygen-gas-containing
feedstock into the reaction chamber. A catalyst bed is positioned
within the reaction chamber that receives the flowing
methane-containing feedstock and an oxygen-gas-containing feedstock
as a flowing mixture with a space time of 500 ms or less. The
catalyst bed contains an OCM catalyst, the catalyst bed configured
to have a heat Peclet number (Pe.sub.h) of from 5 or less, a mass
Peclet number (Pe.sub.m) of from 5 or more, and a transverse Peclet
number (P) of from 1 or less as gases pass through the catalyst
bed. A reactor outlet is in fluid communication with the reaction
chamber for removing reaction products from the reactor.
[0015] In specific embodiments, the catalyst bed comprises a layer
of OCM catalyst formed as catalyst particles having a particle size
of from 0.1 mm to 3 mm. In some cases, the layer of OCM catalyst is
from 5 to 20 particles deep.
[0016] The catalyst bed may comprise at least one monolithic body
of one of a ceramic and metal material having pores or channels
with a pore or channel size from 0.1 to 5 mm, the monolithic body
having an OCM catalyst material present on at least all or a
portion of the surface of the monolithic body, in some embodiments.
In certain cases, the at least one monolithic body may have a
thickness of from 5 mm to 50 mm.
[0017] In other embodiments, the catalyst bed may comprise at least
one monolithic body of one of a ceramic and metal material having
pores or channels with a pore or channel size from 0.1 to 5 mm, and
wherein the pores or channels contain an OCM catalyst powder. In
some cases, the monolithic body may have a thickness of from 5 mm
to 100 mm at least one monolithic body has a thickness of from 5 mm
to 100 mm. The catalyst powder may have a particle size of less
than 400 microns.
[0018] The catalyst used for the reactor may be an OCM catalyst
selected from at least one of La.sub.2CeO.sub.2,
SrO/La.sub.2O.sub.3, CeO.sub.2, La.sub.2O.sub.3--CeO.sub.2,
Ca/CeO.sub.2, Mn/Na.sub.2WO.sub.4, Li.sub.2O, Na.sub.2O, Cs.sub.2O,
WO.sub.3, Mn.sub.3O.sub.4, CaO, MgO, SrO, BaO, CaO--MgO, CaO--BaO,
Li/MgO, MnO, W.sub.2O.sub.3, SnO.sub.2, Yb.sub.2O.sub.3,
Sm.sub.2O.sub.3, SrO/La.sub.2O.sub.3, La.sub.2O.sub.3,
Ce.sub.2O.sub.3, La/MgO, and combinations thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] For a more complete understanding of the embodiments
described herein, and the advantages thereof, reference is now made
to the following descriptions taken in conjunction with the
accompanying figures, in which:
[0020] FIG. 1 is a schematic of an exemplary OCM reactor configured
in accordance with particular embodiments described herein; and
[0021] FIG. 2 is a plot of simulated OCM reactions from Example 2
that were carried out for a packed bed reactor configured in
accordance with particular embodiments described herein and showing
the effect of catalyst bed depth and feed temperatures on oxygen
conversion and the Peclet numbers for the different catalyst bed
depths.
DETAILED DESCRIPTION
[0022] Oxidative coupling of methane has a very large heat of
reaction resulting in large adiabatic temperature rises (typically
>500.degree. C.). In addition, the reaction has very high
temperature sensitivity (i.e., an increase in reaction rate with
increasing temperature) because of the high energy barrier for
activating methane. These two characteristics make it difficult, if
not impossible, to remove the heat of reaction as fast as it is
released, making the reaction uncontrollable.
[0023] It has been discovered that by the use of a unique catalyst
bed and very high space velocities, so that the reaction takes
place under near adiabatic conditions, very high yields and higher
volumetric productivity from OCM can be obtained per unit volume of
catalyst. This also allows the use of low cost adiabatic reactors,
as contrasted with the use of cooled multi-tubular reactors or the
use of complex fluidized bed reactors.
[0024] By the use of the particular configuration of catalyst bed
and operating state, adiabatic or near-adiabatic auto-thermal
oxidative coupling of methane can be achieved. While adiabatic
conditions are desired, in practice only near-adiabatic conditions
can be maintained. This is true even though reference is commonly
made to the use of adiabatic reactors. Those skilled in the art
will recognize that there is some heat transfer in such adiabatic
reactors so they are not perfectly adiabatic. Accordingly, the use
of the term "adiabatic" throughout this disclosure may therefore
refer to such near-adiabatic conditions, which can be defined as
from 10% or 5% or less heat transfer or heat loss from the reactor
(relative to the total heat generated). Furthermore, as used
herein, the expression "auto-thermal" with respect to the OCM
reaction described means that only the heat produced by the
reaction itself is used to carry out the reaction. This means that
once the reaction commences, no heating from other sources is
provided to carry out the oxidative coupling reaction when it
reaches steady state.
[0025] It should be noted in the description, if a numerical value,
concentration or range is presented, each numerical value should be
read once as modified by the term "about" (unless already expressly
so modified), and then read again as not so modified unless
otherwise indicated in context. Also, in the description, it should
be understood that an amount range listed or described as being
useful, suitable, or the like, is intended that any and every value
within the range, including the end points, is to be considered as
having been stated. For example, "a range of from 1 to 10" is to be
read as indicating each and every possible number along the
continuum between about 1 and about 10. Thus, even if specific
points within the range, or even no point within the range, are
explicitly identified or referred to, it is to be understood that
the inventor appreciates and understands that any and all points
within the range are to be considered to have been specified, and
that inventor possesses the entire range and all points within the
range.
[0026] The unique catalyst bed design and its operation provide
several advantages. First, it expands the region of the
auto-thermal operating conditions. This includes broadening the
range of oxygen concentration that can be used, the feed
temperature range, and feed flowrates over which the auto-thermal
operation is possible. Second, it leads to the existence of an
ignited state within the catalyst bed with ambient feed and the
optimum catalyst temperature, which promotes catalyst stability.
Third, it leads to higher yields of the OCM reaction products by
making the temperature almost constant (and within the optimum
temperature range) over the entire catalyst bed. Fourth, it
minimizes dispersion of reactants and thus maximizes the
concentration driving force for the reaction, thus maximizing the
rate of reaction. The catalyst bed is designed so that the mass
flow rate of reactants by convection is about ten times higher than
the rate of dispersion of reactants. The ratio of convection to
dispersion is controlled or determined by the mass Peclet number.
These characteristics make it possible to obtain higher yields of
OCM reaction products (e.g., C.sub.2 hydrocarbons) and higher
volumetric productivity than can be obtained with conventional
adiabatic reactors, as well as cooled tubular and fluidized bed
reactors.
[0027] Referring to FIG. 1, a schematic representation of an
exemplary reactor 10 employing the novel catalyst bed and in which
the OCM reaction may be carried out is shown. The reactor 10
includes a reactor vessel 12 that defines an interior reaction
chamber 14. One or more inlets 16 for introducing a flowing feed
mixture 18 of a methane-containing feedstock and an
oxygen-gas-containing feedstock into the interior of the reactor
vessel 12. The reactor 10 is configured as an adiabatic reactor (or
near-adiabatic) to prevent or reduce heat transfer or loss through
the walls of the reactor vessel 12. Typically, the reactor 10 will
be oriented for vertical flow, with the inlet 16 being located on
the top or bottom of the reactor vessel 12. In the embodiment
shown, the inlet 16 is located at the top of the reactor vessel 12
so that fluid flow is directed downward through the reactor 10.
[0028] A catalyst bed 20 is positioned within the reaction chamber
14 of the reactor vessel 12. The catalyst bed 20 may be supported
on a catalyst bed support 22, such as a perforated ceramic support
plate. As will be described in more detail later on, the catalyst
bed is configured to meet certain requirements related to the
dimensionless Peclet (Pe) numbers. The catalyst bed 20 may be
configured to have a rather large width or diameter but a
relatively shallow depth or thickness. As used herein with
reference to the catalyst bed 20 and its components, the terms
"length," "thickness," "depth," and the like, as it refers to the
catalyst bed refers to the linear distance as measured axially
between the opposite upstream and downstream surfaces of the
catalyst bed 20. The flow through the reactor 10 may be axial and
parallel to a central longitudinal vertical axis (not shown) that
passes through the center of the reactor vessel 12 and through the
catalyst bed 20. In certain embodiments, the catalyst bed thickness
may range from 5 mm to 200 mm.
[0029] The width or diameter of the catalyst bed 20 may be
significantly greater than the catalyst bed depth or thickness so
that the catalyst bed 20 has a generally flat or pancake-shaped
configuration. In certain embodiments, the catalyst bed 20 may have
a width or diameter of several meters (e.g., from 1 to 5 meters).
In some embodiments, the reactor vessel 12 may have a generally
cylindrical configuration along generally its entire length, with
the length of the reactor vessel 12 greatly exceeding its width or
diameter. In the embodiment shown, however, the wall portion 24 of
the reactor vessel 12 that immediately surrounds and houses the
catalyst bed 20 may be generally cylindrical in shape with other
portions of the reactor vessel being conical or frusto-conical. As
is shown in FIG. 1, the reactor vessel 12 may have conical-shaped
or sloped reactor walls that extend from the cylindrical wall
portion 24 surrounding the catalyst bed 20. In the embodiment
shown, a conical or frusto-conical upstream reactor wall 26 joins
the upstream end of the cylindrical wall 24 and tapers radially
inwardly along its longitudinal axis to the inlet 16. A gas flow
distributor 28 may be provided in the upstream section of the
reactor vessel 12 defined by the upstream reactor wall 26 to
facilitate distributing the flowing gas mixture from the inlet 16
across the width of the upstream surface of the catalyst bed 20. In
certain embodiments, the need for a flow distributor may be
eliminated by use of a conical diffuser with walls tapered at angle
of from 3 to 10 degrees.
[0030] As shown in FIG. 1, a radiation shield 30, such as a ceramic
foam, may be provided above the catalyst bed in certain
embodiments.
[0031] A conical or frusto-conical downstream reactor wall 32 may
join the downstream end of the cylindrical wall 24 and taper
radially inward along its longitudinal axis to an intermediate
downstream section of the reactor vessel 12. The intermediate
section 34 may be formed from a generally cylindrical portion of
the reactor vessel 12 that has a width or diameter that is less
than that of the cylindrical wall 24 surrounding the catalyst bed
20.
[0032] An outlet 36 of the reactor vessel 12 receives the products
from the reaction chamber 14 where they are discharged from the
reactor vessel 12 and may be collected and stored or directed to
other processing equipment for further processing. This may include
cracking and/or quenching of the reaction products, which may be
carried out in other vessels or equipment external to the reactor
10 or reactor vessel 12 for such purposes.
[0033] The catalyst used for the catalyst bed 20 may not be limited
to any particular type of catalyst provided it is suitable for the
OCM reaction and facilitates meeting the necessary requirements for
the catalyst bed configuration and operation, as is described in
more detail later on. The OCM catalyst should have a high enough
activity to provide the desired OCM conversion with the high space
velocities or space time used and reaction conditions, as described
herein. One or more different OCM catalysts can be used. These may
be supported catalysts, bulk metal catalysts, and/or unsupported
catalysts, or combinations of these. The support can be active or
inactive. The catalyst support can include MgO, Al.sub.2O.sub.3,
SiO.sub.2, or the like. All the support materials are those
currently available or that can be formed from those processes
known in the art. These may include precipitation/co-precipitation,
sol-gel, templates/surface derivatized metal oxides synthesis,
solid-state synthesis, of mixed metal oxides, microemulsion
techniques, solvothermal, sonochemical, combustion synthesis, etc.
One or more of the catalyst can include one or more metals or metal
compounds thereof. Non-limiting catalytic metals include Li, Na,
Ca, Cs, Mg, La, Ce, W, Mn, Ru, Rh, Ni, and Pt, and combinations and
alloys of these. Non-limiting examples of suitable catalysts
include: (1) La on a MgO support; (2) Na, Mn, and La.sub.2O.sub.3
on an aluminum support; (3) Na and Mn on a silicon dioxide support;
(4) Na.sub.2WO.sub.4 and Mn on a silicon dioxide support, and
combinations of these. Non-limiting examples of some particular
catalysts that can be used include La.sub.2CeO.sub.2,
SrO/La.sub.2O.sub.3, CeO.sub.2, La.sub.2O.sub.3--CeO.sub.2,
Ca/CeO.sub.2, Mn/Na.sub.2WO.sub.4, Li.sub.2O, Na.sub.2O, Cs.sub.2O,
WO.sub.3, Mn.sub.3O.sub.4, CaO, MgO, SrO, BaO, CaO--MgO, CaO--BaO,
Li/MgO, MnO, W.sub.2O.sub.3, SnO.sub.2, Yb.sub.2O.sub.3,
Sm.sub.2O.sub.3, SrO/La.sub.2O.sub.3, La.sub.2O.sub.3,
Ce.sub.2O.sub.3, La/MgO, and combinations thereof.
[0034] The catalyst of the catalyst bed 20 may take several
different forms. In one form, this may include a shallow layer of
catalyst particles having particle sizes of from 0.1 mm to 10 mm,
more particularly from 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, 0.6
mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1 mm to 2 mm, 3 mm, 4 mm, 5 mm, 6
mm, 7 mm, 8 mm, 9 mm, or 10 mm. In certain embodiments the catalyst
particles making up the shallow layer may have particle size
ranging from 0.1 mm to 3 mm, 4 mm, or 5 mm. The catalyst particles
making up the catalyst bed may be of the same or different sizes.
The layer of catalyst particles forming the catalyst bed may be
from 5 mm to 200 mm deep, and in certain embodiments from 5 mm to
25 mm deep. The catalyst particles may rest on the catalyst bed
support 22. Such support 22 may include, but is not limited to a
perforated ceramic support plate, quartz fiber mats, stainless
steel screens, stainless steel coated with fused silica, etc. The
catalyst particles can be of eggshell type or constitute a coating
on a high conductivity non-catalytic particle. The catalyst bed can
be a mix of OCM catalyst and non-catalytic high conductivity
particles.
[0035] In another form, the catalyst bed 20 may be composed of one
or more porous monolithic bodies. The monolithic body may be a
ceramic or metal material having pores or channels with a pore or
channel size (i.e., the transverse width or diameter) of from 0.1
mm to 5 mm, more particularly from 0.5 mm to 2.0 mm. The length or
thickness of the monolithic bodies forming the catalyst bed 20 may
range from 5 mm to 200 mm, more particularly from 5 mm, 10 mm, 20
mm, 30 mm, or 40 mm to 50 mm, 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm
or more. All or a portion of the pore channels of the monolithic
body may be oriented parallel to the central axis or direction of
flow through the reactor 10. In other embodiments, the pores may be
non-parallel to the direction of flow or may be randomly oriented,
such as a ceramic or metal foam material. The pores should be
continuous or contiguous through the thickness of the monolithic
body to allow passage of gases therethrough from the upstream side
to the downstream side of the catalyst bed 20. The cross-sectional
shape of the pores may vary but in particular embodiments may be
circular, oval, square, rectangular, polygonal, etc. In other
embodiments, all or a portion of the cross-sectional shape of the
pores may be irregular or non-uniform in shape.
[0036] The monolithic body or bodies are either formed from or are
provided with an OCM catalyst material present on at least all or a
portion of the surfaces of the monolithic body. In particular, at
least all or a portion of the surfaces of the pore channels are
coated with such OCM catalyst material, such as those OCM catalyst
material described previously. The amount of OCM catalyst material
provided on the monolithic bodies is that sufficient to carry out
the OCM reaction, as described herein.
[0037] In still another form, the catalyst bed 20 may be composed
of one or more porous monolithic bodies similar to those described
above. The pore sizes may be the same as those previously
described, i.e., pore or channel size (i.e., the transverse width
or diameter) of from 0.1 mm to 5 mm, more particularly from 0.5 mm
to 2.0 mm. The length or thickness of the monolithic bodies forming
the catalyst bed may range from 5 mm to 200 mm, more particularly
from 5 mm, 10 mm, 20 mm, 30 mm, or 40 mm to 50 mm, 60 mm, 70 mm, 80
mm, 90 mm, or 100 mm or more. Unlike the monolithic bodies
previously described, the surfaces of the monolithic may not be
coated or provided with an OCM catalytic material, although in
certain instances they may be coated with such an OCM catalytic
material, as well. Instead, all or a portion of the pore channels
of the monolithic body or bodies are filled with OCM catalyst
particles or powder, such as the OCM catalyst particle materials
described previously. The OCM catalyst particles or powder may have
a particle size of from 400 microns, 300 microns, 200 microns, 100
microns or less. All or a portion of the pores of the monolithic
are filled with the OCM catalyst particles or powder to carry out
the OCM reaction.
[0038] The reactor/catalyst bed is configured to give selected
dimensionless Peclet numbers based upon the flow through the
reactor 10. The feed gas mixture is delivered to the reactor to
provide a flowing gas mixture with a high enough velocity to
provide a space time that is from 500 milliseconds (ms) or less. In
particular embodiments, the flowing mixture flow provides a space
time of from 500 ms, 400 ms, 300 ms, 200 ms, 100 ms, 50 ms, 25 ms,
or 10 ms or less.
[0039] Based upon such flow rates to provide the selected space
time during the autothermal reaction, the dimensionless Peclet (Pe)
numbers provide a means for configuring the catalyst bed containing
the OCM catalyst, as previously described. The Pe numbers provide a
means for determining the optimal catalyst bed depth. This can be
achieved by calculating the three dimensionless Peclet numbers,
i.e., the Heat Peclet Number (Pe.sub.h), the Mass Peclet Number
(Pe.sub.m), and the Transverse Peclet Number (P).
[0040] The Heat Peclet Number (Pe.sub.h) is defined in Equation (9)
below:
Pe h = uLC pv k b , eff ( 9 ) ##EQU00001##
where, u is the superficial gas velocity, L is the catalyst bed
depth or thickness, C.sub.pv is the volumetric specific heat of the
reaction mixture, and k.sub.b,eff is the effective bed thermal
conductivity. Pe.sub.h is the ratio of thermal conduction time in
the axial direction to the convection time within the catalyst bed.
In configuring the OCM catalyst bed of the reactor, a catalyst bed
for the selected catalyst bed length or thickness and selected
operating conditions, such as a space time of 500 ms or less, when
subjected to the flowing gas mixture provides a Pe.sub.h of from 5
or less. In certain embodiments, the catalyst bed under the
selected operating conditions when subjected to the flowing gas
mixture provides a Pe.sub.h of from 5, 4, 3, 2, or 1 or less, more
particularly from 2 or 1 or less.
[0041] The Mass Peclet Number (Pe.sub.m) is defined in Equation
(10) below:
Pe m = uL D m , eff ( 10 ) ##EQU00002##
where, D.sub.m,eff is the effective axial mass dispersion
coefficient. Pe.sub.m is the ratio of mass dispersion time in the
axial direction to the convection time. In configuring the OCM
catalyst bed of the reactor, a catalyst bed for the selected
catalyst bed length or thickness and selected operating conditions
when subjected to the flowing mixture provides a Pe.sub.m of from 5
or more. In certain embodiments, the catalyst bed under the
selected operating conditions provides a Pe.sub.m of from 5, 6, 7,
8, 9, or 10 or more, more particularly from 8, 9, or 10 or
more.
[0042] The Transverse Peclet Number (P) is defined in Equation (11)
below:
P = u k c a v L ( 11 ) ##EQU00003##
where, k.sub.c is the local mass transfer coefficient and a.sub.v
is the specific surface area of the catalyst (external catalyst
surface area per unit volume of bed). P is the ratio of external
mass transfer time (from the flow to the catalyst surface) to the
convection time. In configuring the OCM catalyst bed of the
reactor, a catalyst bed for the selected catalyst bed length or
thickness and selected operating conditions when subjected to the
flowing mixture provides a P of from 1 or less. In certain
embodiments, the catalyst bed under the selected operating
conditions provides a P of from 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4,
0.3, 0.2, or 0.1 or less, more particularly from 0.3, 0.2, or 0.1
or less. Reactors with OCM catalyst beds that are operated in the
autothermal state at high gas flow rates to provide a low space
time of from 500 ms or less and that meet the specified Peclet
number parameters presented above can be used in an adiabatic
autothermal operation in which the feed gas mixture can be used as
the coolant and which provides increased yields of OCM reaction
products of C.sub.2+ hydrocarbons and high volumetric productivity
than with conventional OCM reactors.
[0043] The gaseous feedstocks used with the reactor and method
include hydrocarbons and oxygen. The hydrocarbon feedstock may be
methane, natural gas, light-alkane gases (e.g., C.sub.2-C.sub.6),
etc. All or a majority portion of the hydrocarbon feedstock may
comprise methane in certain embodiments. The methane-containing gas
may be a pure methane gas or may be methane gas source containing
other gases. In certain instance, the feed stream may be
predominantly methane (i.e., >50 mol %) or entirely methane. In
particular embodiments, the feed stream may be composed of natural
gas, which may have a methane content of from 85 mol % to 97 mol %
or more, or other hydrocarbon-rich gases. In some cases the
hydrocarbon feedstock may be a pretreated feed that has been
treated to remove undesirable components, such as sulfur-containing
compounds and the like. The oxygen-containing gas may be air,
oxygen-enriched air, or pure oxygen gas. In particular embodiments,
the oxygen-containing gas is pure oxygen. The reactant gas mixture
may contain other gases, provided such gases do not negatively
affect the reaction. These can include nitrogen (N.sub.2), carbon
dioxide (CO.sub.2), hydrogen (H.sub.2), etc.
[0044] The OCM reaction is ignited in a manner that avoids
transient states at which the temperatures would destroy or damage
the OCM catalyst of the catalyst bed. In particular embodiments,
the reaction startup methods described in Applicant's U.S. Patent
Application No. 62/457,119, filed Feb. 7, 2017, which is
incorporated herein by reference in its entirety for all purposes,
may be used. As is described U.S. Patent Application No.
62/457,119, during the reaction startup, the feed gas mixture
having a selected HC/O.sub.2 or CH.sub.4/O.sub.2 molar ratio, which
may range from 3:1 to 40:1, is initially heated to a temperature of
at least 400.degree. C., more particularly from 400.degree. C. to
750.degree. C. The heated feed gas mixture is introduced into the
OCM reactor so that the catalyst bed is also heated and the OCM
reaction commences. The feed gas mixture may be introduced to
provide a space time of from 0.1 ms to 1000 ms. Upon ignition, the
temperature and/or HC/O.sub.2 or CH.sub.4/O.sub.2 molar ratio can
be incrementally reduced over a startup period. Additionally, the
flow rate may be adjusted to provide a shorter space time. Once a
selected operating temperature is achieved, the OCM reaction
remains ignited and the reactor can be maintained in an autothermal
state.
[0045] Once the OCM reaction is in an ignited state, the reaction
is made to operate continuously in an autothermal state by
supplying feed gas for the oxidative coupling reaction to the
reactor at a rate and at a low enough temperature to compensate for
the heat of reaction generated in the reactor. In this way, the
feed gas serves as a coolant as the reactor is heated to a higher
temperature by the heat generated by the oxidative coupling
reaction in the reactor. Once the reactor reaches the autothermal
state, the feed gas mixture to the reactor may comprise a
hydrocarbon gas (HC) or methane-containing gas, which may contain
at least some portion of methane (CH.sub.4), and oxygen gas
(O.sub.2). The HC/O.sub.2 or CH.sub.4/O.sub.2 molar ratio of the
feed gas mixture may range from 2.5:1 to 10:1, more particularly
from 3:1 to 9:1.
[0046] The temperature of the feed gas mixture during the
autothermal state, which is a HC-containing or methane-containing
feedstock along with an oxygen-gas-containing feedstock, is
introduced into the reactor at a temperature of from -100.degree.
C. to 300.degree. C. In particular embodiments the temperature of
the mixed gas feedstock introduced into the reactor ranges from
-20.degree. C. to 150.degree. C., more particularly from
-20.degree. C., -10.degree. C., or 0.degree. C. to 50.degree. C.,
100.degree. C., or 150.degree. C. The cooler feedstock gas mixture
introduced into the reactor and the high space velocity facilitates
maintaining the catalyst bed temperature at the desired temperature
during the autothermal state even while the OCM generates a
significant amount of heat during the reaction.
[0047] The OCM reactor is operated in the ignited or autothermal
state to provide a catalyst bed temperature of from 500.degree. C.
to 1000.degree. C. In particular embodiments, the reactor is
operated to provide a catalyst bed temperature of from 800.degree.
C. to 950.degree. C. in the ignited or autothermal state. The
reactor may be operated at a pressure of from 0.1 MPa to 1 MPa,
more particularly from 0.1 MPa to 0.5 MPa in the autothermal
state.
[0048] The products produced from the OCM reaction include ethane,
ethylene, as well as other C.sub.2+ hydrocarbon products along with
carbon oxides like CO and CO.sub.2.
[0049] The following examples serve to further illustrate various
embodiments and applications.
EXAMPLES
Example 1
[0050] A 41 mm I.D. alumina reactor was used as the near adiabatic
reactor for each run. Different height catalyst beds of the reactor
containing OCM catalyst particles were used in the reactions. The
reactions were started using those startup procedures described in
U.S. Patent Application No. 62/457,119. At steady state, a gaseous
feed mixture that included the reactant gases CH.sub.4 and O.sub.2
at selected CH.sub.4:O.sub.2 molar ratios were introduced into the
reactor. Analysis of a sample stream at the center of the catalyst
bed showed that both the conversion and C2+ selectivity were higher
with the shorter bed when a similar space time was maintained. The
results are presented in Table 1 below:
TABLE-US-00001 TABLE 1 Bed height, mm 25 10 O.sub.2 conversion, %
97.8 98.0 99.6 99.2 99.5 Flow rate, L/min 28.5 28.1 10.0 10.0 11.6
Feed CH.sub.4/O.sub.2 ratio 6.6 5.5 6.6 5.6 5.9 Selectivities, %
C.sub.2+ 56.1 53.0 67.6 63.8 65.2 CO 10.3 11.3 5.3 5.6 5.7 CO.sub.2
33.7 35.7 27.1 30.5 29.1
[0051] Estimated Peclet numbers for the two reactor bed
configurations are summarized in Table 2 below:
TABLE-US-00002 TABLE 2 Bed ID .times. Height 41 mm .times. 25 mm 41
mm .times. 10 mm Pe.sub.h 21 3.2 Pe.sub.m 94 29
Example 2
[0052] FIG. 2 shows the oxygen (O.sub.2) conversion obtained during
computer simulated OCM reactions for a packed bed reactor
containing an OCM catalyst at different catalyst bed depths. The
reactions were those with a mixed gas feed at a CH.sub.4/O.sub.2
molar ratio of 6 at different feed temperatures using a feed
velocity to provide a constant space time. The Peclet numbers for
each catalyst bed depth are provided in Table 3 below:
TABLE-US-00003 TABLE 3 T.sup.in Max T.sub.s at extinction at
extinction Bed Depth Pe.sub.m Pe.sub.h P (.degree. C.) (.degree.
C.) 25 mm 94 25 0.007 341 1016 10 mm 34 4.7 0.009 145 873 3 mm 5.5
0.45 0.011 -100 680 1 mm 0.75 0.05 0.014 -69 662
[0053] While the invention has been shown in some of its forms, it
should be apparent to those skilled in the art that it is not so
limited, but is susceptible to various changes and modifications
without departing from the scope of the invention based on
experimental data or other optimizations considering the overall
economics of the process. Accordingly, it is appropriate that the
appended claims be construed broadly and in a manner consistent
with the scope of the invention.
* * * * *