U.S. patent application number 15/272205 was filed with the patent office on 2017-04-20 for separation methods and systems for oxidative coupling of methane.
The applicant listed for this patent is Siluria Technologies, Inc.. Invention is credited to Andrew Aronson, Joel Cizeron, Suchia Duggal, Divya Jonnavittula, Jarod McCormick, Guido Radaelli.
Application Number | 20170107162 15/272205 |
Document ID | / |
Family ID | 58518505 |
Filed Date | 2017-04-20 |
United States Patent
Application |
20170107162 |
Kind Code |
A1 |
Duggal; Suchia ; et
al. |
April 20, 2017 |
SEPARATION METHODS AND SYSTEMS FOR OXIDATIVE COUPLING OF
METHANE
Abstract
The present disclosure provides a method for generating higher
hydrocarbon(s) from a stream comprising compounds with two or more
carbon atoms (C.sub.2+), comprising introducing methane and an
oxidant (e.g., O.sub.2) into an oxidative coupling of methane (OCM)
reactor. The OCM reactor reacts the methane with the oxidant to
generate a first product stream comprising the C.sub.2+ compounds.
The first product stream can then be directed to a separations unit
that recovers at least a portion of the C.sub.2+ compounds from the
first product stream to yield a second product stream comprising
the at least the portion of the C.sub.2+ compounds.
Inventors: |
Duggal; Suchia; (San Rafael,
CA) ; Radaelli; Guido; (Pleasant Hill, CA) ;
McCormick; Jarod; (San Carlos, CA) ; Aronson;
Andrew; (San Bruno, CA) ; Cizeron; Joel;
(Redwood City, CA) ; Jonnavittula; Divya; (San
Francisco, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Siluria Technologies, Inc. |
San Francisco |
CA |
US |
|
|
Family ID: |
58518505 |
Appl. No.: |
15/272205 |
Filed: |
September 21, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62304877 |
Mar 7, 2016 |
|
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62242777 |
Oct 16, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2253/116 20130101;
C07C 7/005 20130101; B01D 2253/104 20130101; B01D 53/1493 20130101;
C07C 5/32 20130101; B01D 2251/302 20130101; B01D 2252/10 20130101;
C07C 7/11 20130101; B01D 2257/102 20130101; Y02C 20/40 20200801;
B01D 2253/204 20130101; Y02P 30/40 20151101; B01D 2253/106
20130101; B01D 2253/108 20130101; B01D 2253/1122 20130101; B01D
2257/702 20130101; Y02P 20/50 20151101; C07C 1/12 20130101; C07C
2/84 20130101; B01D 53/228 20130101; B01D 2257/502 20130101; Y02P
20/151 20151101; B01D 2253/25 20130101; B01D 2255/104 20130101;
B01D 53/047 20130101; B01D 2257/504 20130101; B01D 2253/1124
20130101; B01D 2255/20761 20130101; B01D 61/246 20130101; B01D
2256/24 20130101; C07C 7/144 20130101; B01D 2251/60 20130101; B01D
2257/108 20130101; B01D 53/1487 20130101; B01D 2253/102 20130101;
B01D 53/229 20130101; C07C 2/84 20130101; C07C 11/04 20130101; C07C
2/84 20130101; C07C 9/06 20130101; C07C 5/32 20130101; C07C 11/04
20130101; C07C 7/005 20130101; C07C 11/04 20130101; C07C 7/144
20130101; C07C 11/04 20130101; C07C 7/11 20130101; C07C 11/04
20130101 |
International
Class: |
C07C 2/84 20060101
C07C002/84; C07C 1/12 20060101 C07C001/12 |
Goverment Interests
STATEMENT OF GOVERNMENT SUPPORT
[0002] This invention was made with government support under grant
numbers DE-EE0005769 awarded by the United States Department of
Energy (DOE). The government has certain rights in the invention.
Claims
1. A method for generating compounds with two or more carbon atoms
(C.sub.2+ compounds), comprising: (a) directing oxygen (O.sub.2)
and methane (CH.sub.4) into an oxidative coupling of methane (OCM)
reactor that reacts said O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) carbon dioxide (CO.sub.2); and
(b) directing said product stream from said OCM reactor into a
separations unit that employs a CO.sub.2 separation unit to
separate said CO.sub.2 from said product stream and enrich said
C.sub.2+ compounds in said product stream, which CO.sub.2
separation unit employs (i) sorbent or solvent separation of
CO.sub.2, (ii) membrane separation of CO.sub.2, (iii) cryogenic or
low temperature separation of CO.sub.2 having an operating
temperature greater than a boiling point of methane and less than a
boiling point of CO.sub.2, (iv) metal-organic framework-based
separation, or (v) antisublimation separation of CO.sub.2.
2. (canceled)
3. The method of claim 1, wherein said sorbent or solvent
separation of CO.sub.2 employs an amine based absorption unit.
4.-19. (canceled)
20. The method of claim 1, further comprising directing said
CO.sub.2 from said product stream to a methanation reactor that
reacts said CO.sub.2 to yield a methanation product stream
comprising methane.
21. (canceled)
22. The method of claim 1, further comprising separating said
product stream into (i) an ethylene product stream comprising
ethylene and (ii) a C.sub.3+ product stream comprising compounds
with three or more carbon atoms (C.sub.3+ compounds).
23.-56. (canceled)
57. A method for generating compounds with two or more carbon atoms
(C.sub.2+ compounds), comprising: (a) directing oxygen (O.sub.2)
and methane (CH.sub.4) into an oxidative coupling of methane (OCM)
reactor that reacts said O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) C.sub.1 compounds including
un-reacted CH.sub.4; and (b) directing said product stream into a
separations unit containing a metal organic framework (MOF) that
produces (i) a bottoms stream comprising said C.sub.2+ compounds
and (ii) an overhead stream comprising said C.sub.1 compounds.
58. The method of claim 57, further comprising: (c) directing said
overhead stream to a methanation unit for converting carbon dioxide
(CO.sub.2) and/or carbon monoxide (CO) into methane (CH.sub.4); and
(d) directing said CH.sub.4 into said OCM reactor.
59. The method of claim 57, further comprising: (e) directing said
bottoms stream to a second separations unit containing a metal
organic framework (MOF) that separates olefins from paraffins.
60. The method of claim 57, wherein the separations unit comprises
a pressure swing absorber (PSA) that contains the MOF.
61. The method of claim 57, wherein the separations unit comprises
a temperature swing absorber (TSA) that contains the MOF.
62. The method of claim 57, wherein the C.sub.1 compounds include
hydrogen (H.sub.2).
63. A method for generating compounds with two or more carbon atoms
(C.sub.2+ compounds), comprising: (a) directing oxygen (O.sub.2)
and methane (CH.sub.4) into an oxidative coupling of methane (OCM)
reactor having a catalytic section and a cracking section to
produce an OCM product stream, which catalytic section reacts said
O.sub.2 and CH.sub.4 to yield ethylene (C.sub.2H.sub.4), ethane
(C.sub.2H.sub.6) and heat, which cracking section uses said heat to
convert C.sub.2H.sub.6 into C.sub.2H.sub.4, and which product
stream comprises (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and ethane (C.sub.2H.sub.6) and (ii) C.sub.1
compounds including un-reacted CH.sub.4; (b) directing said product
stream into a separations unit containing a metal organic framework
(MOF) that produces (i) a first stream comprising said
C.sub.2H.sub.4, (ii) a second stream comprising said C.sub.2H.sub.6
and (iii) a third stream comprising said C.sub.1 compounds; (c)
directing said second stream into said cracking section; and (d)
directing said third stream into said catalytic section.
64. The method of claim 63, wherein said third stream is directed
to a methanation unit prior to directing to said catalytic section,
which methanation unit converts carbon dioxide (CO.sub.2) and/or
carbon monoxide (CO) into methane (CH.sub.4).
65. The method of claim 63, wherein the separations unit comprises
a pressure swing absorber (PSA) that contains the MOF.
66. The method of claim 63, wherein the separations unit comprises
a temperature swing absorber (TSA) that contains the MOF.
67. The method of claim 63, wherein the C.sub.1 compounds include
hydrogen (H.sub.2).
68.-129. (canceled)
130. A system for generating compounds with two or more carbon
atoms (C.sub.2+ compounds), comprising: an oxidative coupling of
methane (OCM) reactor configured to receive oxygen (O.sub.2) and
methane (CH.sub.4) and react said O.sub.2 and CH.sub.4 to produce
an OCM product stream, said OCM reactor having a catalytic section
and a cracking section, which catalytic section reacts said O.sub.2
and CH.sub.4 to yield ethylene (C.sub.2H.sub.4), ethane
(C.sub.2H.sub.6) and heat, which cracking section uses said heat to
convert C.sub.2H.sub.6 into C.sub.2H.sub.4, and which product
stream comprises (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and ethane (C.sub.2H.sub.6) and (ii) C.sub.1
compounds including un-reacted CH.sub.4; and a separations unit
fluidically coupled to said OCM reactor and configured to receive
said product stream from said OCM reactor, wherein said separations
unit contains a metal organic framework (MOF) that produces (i) a
first stream comprising said C.sub.2H.sub.4, (ii) a second stream
comprising said C.sub.2H.sub.6 and (iii) a third stream comprising
said C.sub.1 compounds, and wherein said second stream and said
third stream are directed into said cracking section and said
catalytic section respectively.
131. The system of claim 130, wherein said third stream is directed
to a methanation unit prior to directing to said catalytic section,
which methanation unit converts carbon dioxide (CO.sub.2) and/or
carbon monoxide (CO) into methane (CH.sub.4).
132. The system of claim 130, wherein the separations unit
comprises a pressure swing absorber (PSA) that contains the
MOF.
133. The system of claim 130, wherein the separations unit
comprises a temperature swing absorber (TSA) that contains the
MOF.
134. The system of claim 130, wherein the C.sub.1 compounds include
hydrogen (H.sub.2).
Description
CROSS-REFERENCE
[0001] This application claims priority to U.S. Provisional Patent
Application Ser. No. 62/242,777, filed Oct. 16, 2015, and U.S.
Provisional Patent Application Ser. No. 62/304,877, filed Mar. 7,
2016, each of which is entirely incorporated herein by reference
for all purposes.
BACKGROUND
[0003] The modern refining and petrochemical industry may make
extensive use of fractionation technology to produce and separate
various desirable compounds from crude oil. The conventional
fractionation technology may be energy intensive and costly to
install and operate. Cryogenic distillation has been used to
separate and recover hydrocarbon products in various refining and
petrochemical industries.
SUMMARY
[0004] Recognized herein is a need for non-cryogenic separation
methods and systems, such as for oxidative coupling of methane
(OCM) processes.
[0005] Aspects of the present disclosure provide processes for
recovering olefins from a stream containing mix of hydrocarbons by
utilizing techniques based the use of adsorbents. In some
embodiments, systems and methods enable the separation,
pre-separation, purification and/or recovery of hydrocarbons,
including, but not limited to, olefins, ethylene, propylene,
methane, and ethane, and CO.sub.2, from a multicomponent
hydrocarbon stream such as an effluent stream from an oxidative
coupling of methane (OCM) reactor or an ethylene-to-liquids (ETL)
reactor. The hydrocarbon stream can also be the feed to the OCM or
ETL reactor in certain cases. In certain cases, the feed to the ETL
reactor is the effluent from OCM reactor. In some cases, a
separation process utilizing adsorbents can be used to purify and
pre-treat existing hydrocarbon streams (such as refinery off-gases,
cracker off-gas, streams from NGL plants, and others), followed by
use of the resulting olefin rich stream (e.g., pressure swing
adsorption tail gas) as the ETL feed.
[0006] The present disclosure provides various improvements in OCM
and ETL processes, such as, without limitation, a separation and
pre-separation process to recover desired or predetermined
components from an OCM reactor effluent, CO.sub.2 recovery and
capture techniques, enhanced heat recovery methods to utilize the
OCM reaction heat more efficiently, and techniques and technologies
to further reduce the carbon footprint of the OCM process.
[0007] An aspect of the present disclosure provides a method for
generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor that
reacts the O.sub.2 and CH.sub.4 in an OCM process to yield a
product stream comprising (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and (ii) carbon dioxide (CO.sub.2); and (b)
directing the product stream from the OCM reactor into a
separations unit that employs a CO.sub.2 separation unit to
separate the CO.sub.2 from the product stream and enrich the
C.sub.2+ compounds in the product stream, which CO.sub.2 separation
unit employs (i) sorbent or solvent separation of CO.sub.2, (ii)
membrane separation of CO.sub.2, (iii) cryogenic or low temperature
separation of CO.sub.2 having an operating temperature greater than
a boiling point of methane and less than a boiling point of
CO.sub.2, (iv) metal-organic framework-based separation, or (v)
antisublimation separation of CO.sub.2.
[0008] In some embodiments of aspects provided herein, the product
stream is directed into the separations unit through one or more
additional units. In some embodiments of aspects provided herein,
the sorbent or solvent separation of CO.sub.2 employs an amine
based absorption unit. In some embodiments of aspects provided
herein, the sorbent or solvent separation of CO.sub.2 employs a
Benfield process. In some embodiments of aspects provided herein,
the sorbent or solvent separation of CO.sub.2 employs
diethanolamine. In some embodiments of aspects provided herein, the
sorbent or solvent separation of CO.sub.2 employs glycol
dimethylether. In some embodiments of aspects provided herein, the
sorbent or solvent separation of CO.sub.2 employs propylene
carbonate. In some embodiments of aspects provided herein, the
sorbent or solvent separation of CO.sub.2 employs Sulfinol. In some
embodiments of aspects provided herein, the sorbent or solvent
separation of CO.sub.2 employs a zeolite. In some embodiments of
aspects provided herein, the sorbent or solvent separation of
CO.sub.2 employs active carbon. In some embodiments of aspects
provided herein, the CO.sub.2 separation unit comprises a membrane
CO.sub.2 separation unit. In some embodiments of aspects provided
herein, the membrane separation of CO.sub.2 employs a polymeric
membrane. In some embodiments of aspects provided herein, the
membrane separation of CO.sub.2 employs a metallic membrane. In
some embodiments of aspects provided herein, the membrane
separation of CO.sub.2 employs a ceramic membrane. In some
embodiments of aspects provided herein, the membrane separation of
CO.sub.2 employs a hybrid membrane comprising a membrane supporting
a solvent or sorbent. In some embodiments of aspects provided
herein, the membrane separation of CO.sub.2 employs a poly ionic
liquid membrane. In some embodiments of aspects provided herein,
the membrane separation of CO.sub.2 employs a supported ionic
liquid membrane. In some embodiments of aspects provided herein,
the membrane separation of CO.sub.2 employs a polyetherimide
membrane. In some embodiments of aspects provided herein, the
membrane separation of CO.sub.2 employs an amorphous fluoropolymer
based membrane. In some embodiments of aspects provided herein, the
method further comprises directing the CO.sub.2 from the product
stream to a methanation reactor that reacts the CO.sub.2 to yield a
methanation product stream comprising methane. In some embodiments
of aspects provided herein, the method further comprises directing
the methane in the methanation product stream to the OCM reactor.
In some embodiments of aspects provided herein, the method further
comprises separating the product stream into (i) an ethylene
product stream comprising ethylene and (ii) a C.sub.3+ product
stream comprising compounds with three or more carbon atoms
(C.sub.3+ compounds). In some embodiments of aspects provided
herein, the method further comprises directing ethane from the
product stream to the OCM reactor. In some embodiments of aspects
provided herein, the method further comprises, prior to directing
the product stream into the separations unit, compressing the
product stream. In some embodiments of aspects provided herein, the
CO.sub.2 separation unit employs the sorbent or solvent separation
of CO.sub.2. In some embodiments of aspects provided herein, the
CO.sub.2 separation unit employs the membrane separation of
CO.sub.2. In some embodiments of aspects provided herein, the
CO.sub.2 separation unit employs the cryogenic or low temperature
separation of CO.sub.2 having an operating temperature greater than
a boiling point of methane and less than a boiling point of
CO.sub.2. In some embodiments of aspects provided herein, the
CO.sub.2 separation unit employs the metal-organic framework-based
separation. In some embodiments of aspects provided herein, the
CO.sub.2 separation unit employs the antisublimation separation of
CO.sub.2.
[0009] Another aspect of the present disclosure provides a method
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor that
reacts the O.sub.2 and CH.sub.4 in an OCM process to yield a
product stream comprising (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and (ii) carbon dioxide (CO.sub.2); (b) directing
the product stream from the OCM reactor into a first CO.sub.2
separation unit that separates at least some of the CO.sub.2 from
the product stream to produce an enriched stream comprising (i) the
C.sub.2+ compounds and (ii) at least some of the CO.sub.2; (c)
directing the enriched stream to a cryogenic separations unit that
separates the C.sub.2H.sub.4 from the C.sub.2+ compounds to produce
an ethylene stream comprising (i) the C.sub.2H.sub.4 and (ii) the
CO.sub.2; and (d) directing the ethylene stream to a second
CO.sub.2 separation unit that separates the CO.sub.2 from the
ethylene stream to produce an ethylene product stream.
[0010] In some embodiments of aspects provided herein, the enriched
stream contains at most about 2.0 mol % CO.sub.2. In some
embodiments of aspects provided herein, the enriched stream
contains at most about 1.0 mol % CO.sub.2. In some embodiments of
aspects provided herein, the enriched stream contains at most about
0.5 mol % CO.sub.2. In some embodiments of aspects provided herein,
the first CO.sub.2 separation unit comprises a membrane, a pressure
swing absorption (PSA) unit, an amine unit, or any combination
thereof. In some embodiments of aspects provided herein, the second
CO.sub.2 separation unit comprises a membrane, a pressure swing
absorption (PSA) unit, an amine unit, or any combination thereof.
In some embodiments of aspects provided herein, the cryogenic
separations unit comprises a de-methanizer.
[0011] Another aspect of the present disclosure provides a method
for generating compounds with two or more Carbon atoms (C2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor that
reacts the O.sub.2 and CH.sub.4 in an OCM process to yield a
product stream comprising (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and (ii) carbon monoxide (CO) and/or carbon
dioxide (CO.sub.2); and (b) directing the product stream from the
OCM reactor into a separations unit that selectively separates
olefins from the paraffins.
[0012] In some embodiments of aspects provided herein, the
separations unit selectively separates ethylene from paraffins. In
some embodiments of aspects provided herein, the separations unit
comprises an absorber stripper unit employing pi-complexation. In
some embodiments of aspects provided herein, the separations unit
comprises a membrane unit including a membrane contactor employing
pi-complexation. In some embodiments of aspects provided herein,
the separations unit comprises a pressure swing adsorption (PSA)
unit comprising a sorbent having dispersed metal ions that are
capable of complexing with the olefins. In some embodiments of
aspects provided herein, the PSA unit comprises a sorbent selected
from a zeolite, a molecular sieve sorbent, a carbon molecular
sieve, an activated carbon, a carbon nanotube, and a polymeric
resin. In some embodiments of aspects provided herein, the method
further comprises using an oxidizing agent to regenerate stabilize
the pi-complex. In some embodiments of aspects provided herein, the
oxidizing agent comprises HNO.sub.3 or KMnO.sub.4. In some
embodiments of aspects provided herein, the separations unit
comprises (i) a pressure swing adsorption (PSA) unit, (ii) a
temperature swing adsorption (TSA) unit, or (iii) a membrane unit
employing a metal-organic framework (MOF), and the olefins
separated in (b) comprise ethylene.
[0013] Another aspect of the present disclosure provides a method
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor that
reacts the O.sub.2 and CH.sub.4 in an OCM process to yield a
product stream comprising (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and (ii) C.sub.1 compounds including un-reacted
CH.sub.4; and (b) directing the product stream into a separations
unit that separates the C.sub.2+ compounds from the C.sub.1
compounds, which separations unit does not contain a
de-methanizer.
[0014] In some embodiments of aspects provided herein, the
separations unit contains a distillation column and an oil
absorber. In some embodiments of aspects provided herein, the
distillation column does not condense methane.
[0015] Another aspect of the present disclosure provides a method
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor that
reacts the O.sub.2 and CH.sub.4 in an OCM process to yield a
product stream comprising (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and (ii) C.sub.1 compounds including un-reacted
CH.sub.4; (b) directing the product stream into a pre-separations
unit that produces (i) a bottoms stream comprising the C.sub.2+
compounds and (ii) an overhead stream comprising the C.sub.1
compounds and at least some of the C.sub.2+ compounds; and (c)
directing the overhead stream into an oil absorber that removes the
at least some of the C.sub.2+ compounds to produce a C.sub.1
stream.
[0016] In some embodiments of aspects provided herein, the OCM
process is integrated with a methanol to olefins (MTO) unit, a
steam cracker, or a metathesis process. In some embodiments of
aspects provided herein, the pre-separation unit does not include a
de-methanizer. In some embodiments of aspects provided herein, the
pre-separation unit does not condense methane. In some embodiments
of aspects provided herein, the overhead stream comprises at least
about 10% C.sub.2+ compounds. In some embodiments of aspects
provided herein, the overhead stream comprises at least about 5%
C.sub.2+ compounds. In some embodiments of aspects provided herein,
the overhead stream comprises at least about 1% C.sub.2+ compounds.
In some embodiments of aspects provided herein, the overhead stream
comprises at least about 0.1% C.sub.2+ compounds.
[0017] Another aspect of the present disclosure provides a method
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor that
reacts the O.sub.2 and CH.sub.4 in an OCM process to yield a
product stream comprising (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and (ii) C.sub.1 compounds including un-reacted
CH.sub.4; and (b) directing the product stream into a separations
unit containing a metal organic framework (MOF) that produces (i) a
bottoms stream comprising the C.sub.2+ compounds and (ii) an
overhead stream comprising the C.sub.1 compounds.
[0018] In some embodiments of aspects provided herein, the method
further comprises (c) directing the overhead stream to a
methanation unit for converting carbon dioxide (CO.sub.2) and/or
carbon monoxide (CO) into methane (CH.sub.4); and (d) directing the
CH.sub.4 into the OCM reactor. In some embodiments of aspects
provided herein, the method further comprises (e) directing the
bottoms stream to a second separations unit containing a metal
organic framework (MOF) that separates olefins from paraffins. In
some embodiments of aspects provided herein, the separations unit
comprises a pressure swing absorber (PSA) that contains the MOF. In
some embodiments of aspects provided herein, the separations unit
comprises a temperature swing absorber (TSA) that contains the MOF.
In some embodiments of aspects provided herein, the C.sub.1
compounds include hydrogen (H.sub.2).
[0019] Another aspect of the present disclosure provides a method
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) directing oxygen (O.sub.2) and methane
(CH.sub.4) into an oxidative coupling of methane (OCM) reactor
having a catalytic section and a cracking section to produce an OCM
product stream, which catalytic section reacts the O.sub.2 and
CH.sub.4 to yield ethylene (C.sub.2H.sub.4), ethane
(C.sub.2H.sub.6) and heat, which cracking section uses the heat to
convert C.sub.2H.sub.6 into C.sub.2H.sub.4, and which product
stream comprises (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and ethane (C.sub.2H.sub.6) and (ii) C.sub.1
compounds including un-reacted CH.sub.4; (b) directing the product
stream into a separations unit containing a metal organic framework
(MOF) that produces (i) a first stream comprising the
C.sub.2H.sub.4, (ii) a second stream comprising the C.sub.2H.sub.6
and (iii) a third stream comprising the C.sub.1 compounds; (c)
directing the second stream into the cracking section; and (d)
directing the third stream into the catalytic section.
[0020] In some embodiments of aspects provided herein, the third
stream is directed to a methanation unit prior to directing to the
catalytic section, which methanation unit converts carbon dioxide
(CO.sub.2) and/or carbon monoxide (CO) into methane (CH.sub.4). In
some embodiments of aspects provided herein, the separations unit
comprises a pressure swing absorber (PSA) that contains the MOF. In
some embodiments of aspects provided herein, the separations unit
comprises a temperature swing absorber (TSA) that contains the MOF.
In some embodiments of aspects provided herein, the C.sub.1
compounds include hydrogen (H.sub.2).
[0021] Another aspect of the present disclosure provides a system
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: (a) an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) carbon dioxide (CO.sub.2); and
(b) a separations unit fluidically coupled to the OCM reactor and
configured to receive the product stream from the OCM reactor,
wherein the separations unit comprises a CO.sub.2 separation unit
to separate the CO.sub.2 from the product stream, and to enrich the
C.sub.2+ compounds in the product stream, which CO.sub.2 separation
unit employs (i) sorbent or solvent separation of CO.sub.2, (ii)
membrane separation of CO.sub.2, (iii) cryogenic or low temperature
separation of CO.sub.2 having an operating temperature greater than
a boiling point of methane and less than a boiling point of
CO.sub.2, (iv) metal-organic framework-based separation, or (v)
antisublimation separation of CO.sub.2.
[0022] In some embodiments of aspects provided herein, the
separations unit comprises one or more additional units, and the
product stream is directed into the separations unit through the
one or more additional units. In some embodiments of aspects
provided herein, the sorbent or solvent separation of CO.sub.2
employs an amine based absorption unit. In some embodiments of
aspects provided herein, the sorbent or solvent separation of
CO.sub.2 employs a Benfield process. In some embodiments of aspects
provided herein, the sorbent or solvent separation of CO.sub.2
employs diethanolamine. In some embodiments of aspects provided
herein, the sorbent or solvent separation of CO.sub.2 employs
glycol dimethylether. In some embodiments of aspects provided
herein, the sorbent or solvent separation of CO.sub.2 employs
propylene carbonate. In some embodiments of aspects provided
herein, the sorbent or solvent separation of CO.sub.2 employs
Sulfinol. In some embodiments of aspects provided herein, the
sorbent or solvent separation of CO.sub.2 employs a zeolite. In
some embodiments of aspects provided herein, the sorbent or solvent
separation of CO.sub.2 employs active carbon. In some embodiments
of aspects provided herein, the CO.sub.2 separation unit comprises
a membrane CO.sub.2 separation unit. In some embodiments of aspects
provided herein, the membrane separation of CO.sub.2 employs a
polymeric membrane. In some embodiments of aspects provided herein,
the membrane separation of CO.sub.2 employs a metallic membrane. In
some embodiments of aspects provided herein, the membrane
separation of CO.sub.2 employs a ceramic membrane. In some
embodiments of aspects provided herein, the membrane separation of
CO.sub.2 employs a hybrid membrane comprising a membrane supporting
a solvent or sorbent. In some embodiments of aspects provided
herein, the membrane separation of CO.sub.2 employs a poly ionic
liquid membrane. In some embodiments of aspects provided herein,
the membrane separation of CO.sub.2 employs a supported ionic
liquid membrane. In some embodiments of aspects provided herein,
the membrane separation of CO.sub.2 employs a polyetherimide
membrane. In some embodiments of aspects provided herein, the
membrane separation of CO.sub.2 employs an amorphous fluoropolymer
based membrane. In some embodiments of aspects provided herein, the
system further comprises a methanation reactor that is configured
to receive the CO.sub.2 from the product stream and react the
CO.sub.2 to yield a methanation product stream comprising methane.
In some embodiments of aspects provided herein, the methane in the
methanation product stream is directed to the OCM reactor. In some
embodiments of aspects provided herein, the product stream is
further separated into (i) an ethylene product stream comprising
ethylene and (ii) a C.sub.3+ product stream comprising compounds
with three or more carbon atoms (C.sub.3+ compounds). In some
embodiments of aspects provided herein, ethane is directed from the
product stream to the OCM reactor. In some embodiments of aspects
provided herein, the product stream is compressed, prior to being
directed into the separations unit. In some embodiments of aspects
provided herein, the CO.sub.2 separation unit employs the sorbent
or solvent separation of CO.sub.2. In some embodiments of aspects
provided herein, the CO.sub.2 separation unit employs the membrane
separation of CO.sub.2. In some embodiments of aspects provided
herein, the CO.sub.2 separation unit employs the cryogenic or low
temperature separation of CO.sub.2 having an operating temperature
greater than a boiling point of methane and less than a boiling
point of CO.sub.2. In some embodiments of aspects provided herein,
the CO.sub.2 separation unit employs the metal-organic
framework-based separation. In some embodiments of aspects provided
herein, the CO.sub.2 separation unit employs the antisublimation
separation of CO.sub.2.
[0023] Another aspect of the present disclosure provides a system
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) carbon dioxide (CO.sub.2); a
first CO.sub.2 separation unit fluidically coupled to the OCM
reactor and configured to receive the product steam from the OCM
reactor, wherein the first CO.sub.2 separation unit separates at
least some of the CO.sub.2 from the product stream to produce an
enriched stream comprising (i) the C.sub.2+ compounds and (ii) at
least some of the CO.sub.2; a cryogenic separations unit
fluidically coupled to the first CO.sub.2 separation unit and
configured to receive the enriched stream from the first CO.sub.2
separation unit, wherein the cryogenic separations unit separates
the C.sub.2H.sub.4 from the C.sub.2+ compounds to produce an
ethylene stream comprising (i) the C.sub.2H.sub.4 and (ii) the
CO.sub.2; and a second CO.sub.2 separation unit fluidically coupled
to the cryogenic separations unit and configured to receive the
ethylene stream from the cryogenic separations unit, wherein the
second CO.sub.2 separation unit separates the CO.sub.2 from the
ethylene stream to produce an ethylene product stream.
[0024] In some embodiments of aspects provided herein, the enriched
stream contains at most about 2.0 mol % CO.sub.2. In some
embodiments of aspects provided herein, the enriched stream
contains at most about 1.0 mol % CO.sub.2. In some embodiments of
aspects provided herein, the enriched stream contains at most about
0.5 mol % CO.sub.2. In some embodiments of aspects provided herein,
the first CO.sub.2 separation unit comprises a membrane, a pressure
swing absorption (PSA) unit, an amine unit, or any combination
thereof. In some embodiments of aspects provided herein, the second
CO.sub.2 separation unit comprises a membrane, a pressure swing
absorption (PSA) unit, an amine unit, or any combination thereof.
In some embodiments of aspects provided herein, the cryogenic
separations unit comprises a de-methanizer.
[0025] Another aspect of the present disclosure provides a system
for generating compounds with two or more Carbon atoms (C2+
compounds), comprising: an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) carbon monoxide (CO) and/or
carbon dioxide (CO.sub.2); and a separations unit fluidically
coupled to the OCM reactor and configured to receive the product
stream from the OCM reactor, wherein the separations unit
selectively separates olefins from the paraffins.
[0026] In some embodiments of aspects provided herein, the
separations unit selectively separates ethylene from paraffins. In
some embodiments of aspects provided herein, the separations unit
comprises an absorber unit employing pi-complexation. In some
embodiments of aspects provided herein, the separations unit
comprises a membrane unit including a membrane contactor employing
pi-complexation. In some embodiments of aspects provided herein,
the separations unit comprises a pressure swing adsorption (PSA)
unit comprising a sorbent having dispersed metal ions that are
capable of complexing with the olefins. In some embodiments of
aspects provided herein, the PSA unit comprises a sorbent selected
from a zeolite, a molecular sieve sorbent, a carbon molecular
sieve, an activated carbon, a carbon nanotube, and a polymeric
resin. In some embodiments of aspects provided herein, the system
further comprises an oxidizing agent used to regenerate and/or
stabilize the pi-complex. In some embodiments of aspects provided
herein, the oxidizing agent comprises HNO.sub.3 or KMnO.sub.4. In
some embodiments of aspects provided herein, the separations unit
comprises (i) a pressure swing adsorption (PSA) unit, (ii) a
temperature swing adsorption (TSA) unit, or (iii) a membrane system
employing a metal-organic framework (MOF), and the olefins
separated comprise ethylene.
[0027] Another aspect of the present disclosure provides a system
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) C.sub.1 compounds including
un-reacted CH.sub.4; and a separations unit fluidically coupled to
the OCM reactor and configured to receive the product stream from
the OCM reactor, wherein the separations unit separates the
C.sub.2+ compounds from the C.sub.1 compounds, and wherein the
separations unit does not contain a de-methanizer.
[0028] In some embodiments of aspects provided herein, the
separations unit contains a distillation column and an oil
absorber. In some embodiments of aspects provided herein, the
distillation column does not condense methane.
[0029] Another aspect of the present disclosure provides a system
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) C.sub.1 compounds including
un-reacted CH.sub.4; a pre-separations unit fluidically coupled to
the OCM reactor and configured to receive the product stream from
the OCM reactor, wherein the pre-separations unit produces (i) a
bottoms stream comprising the C.sub.2+ compounds and (ii) an
overhead stream comprising the C.sub.1 compounds and at least some
of the C.sub.2+ compounds; and an oil absorber fluidically coupled
to the pre-separations unit and configured to receive the overhead
stream from the pre-separations unit, wherein the oil absorber
removes the at least some of the C.sub.2+ compounds to produce a
C.sub.1 stream.
[0030] In some embodiments of aspects provided herein, the OCM
process is integrated with a methanol to olefins (MTO) unit, a
steam cracker, or a metathesis process. In some embodiments of
aspects provided herein, the pre-separation unit does not include a
de-methanizer. In some embodiments of aspects provided herein, the
pre-separation unit does not condense methane. In some embodiments
of aspects provided herein, the overhead stream comprises at least
about 10% C.sub.2+ compounds. In some embodiments of aspects
provided herein, the overhead stream comprises at least about 5%
C.sub.2+ compounds. In some embodiments of aspects provided herein,
the overhead stream comprises at least about 1% C.sub.2+ compounds.
In some embodiments of aspects provided herein, the overhead stream
comprises at least about 0.1% C.sub.2+ compounds.
[0031] Another aspect of the present disclosure provides a system
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 in an OCM process to
yield a product stream comprising (i) C.sub.2+ compounds including
ethylene (C.sub.2H.sub.4) and (ii) C.sub.1 compounds including
un-reacted CH.sub.4; and a separations unit fluidically coupled to
the OCM reactor and configured to receive the product stream from
the OCM reactor, wherein the separations unit contains a metal
organic framework (MOF) that produces (i) a bottoms stream
comprising the C.sub.2+ compounds and (ii) an overhead stream
comprising the C.sub.1 compounds.
[0032] In some embodiments of aspects provided herein, the system
further comprises a methanation unit fluidically coupled to the
separations unit and configured receive the overhead stream from
the separations unit, wherein the methanation unit converts carbon
dioxide (CO.sub.2) and/or carbon monoxide (CO) into methane
(CH.sub.4), and wherein the CH.sub.4 is directed into the OCM
reactor. In some embodiments of aspects provided herein, the system
further comprises a second separations unit fluidically coupled to
the separations unit and configured receive the bottoms stream from
the separations unit, wherein the second separations unit contains
a metal organic framework (MOF) that separates olefins from
paraffins. In some embodiments of aspects provided herein, the
separations unit comprises a pressure swing absorber (PSA) that
contains the MOF. In some embodiments of aspects provided herein,
the separations unit comprises a temperature swing absorber (TSA)
that contains the MOF. In some embodiments of aspects provided
herein, the C.sub.1 compounds include hydrogen (H.sub.2).
[0033] Another aspect of the present disclosure provides a system
for generating compounds with two or more carbon atoms (C.sub.2+
compounds), comprising: an oxidative coupling of methane (OCM)
reactor configured to receive oxygen (O.sub.2) and methane
(CH.sub.4) and react the O.sub.2 and CH.sub.4 to produce an OCM
product stream, the OCM reactor having a catalytic section and a
cracking section, which catalytic section reacts the O.sub.2 and
CH.sub.4 to yield ethylene (C.sub.2H.sub.4), ethane
(C.sub.2H.sub.6) and heat, which cracking section uses the heat to
convert C.sub.2H.sub.6 into C.sub.2H.sub.4, and which product
stream comprises (i) C.sub.2+ compounds including ethylene
(C.sub.2H.sub.4) and ethane (C.sub.2H.sub.6) and (ii) C.sub.1
compounds including un-reacted CH.sub.4; and a separations unit
fluidically coupled to the OCM reactor and configured to receive
the product stream from the OCM reactor, wherein the separations
unit contains a metal organic framework (MOF) that produces (i) a
first stream comprising the C.sub.2H.sub.4, (ii) a second stream
comprising the C.sub.2H.sub.6 and (iii) a third stream comprising
the C.sub.1 compounds, and wherein the second stream and the third
stream are directed into the cracking section and the catalytic
section respectively.
[0034] In some embodiments of aspects provided herein, the third
stream is directed to a methanation unit prior to directing to the
catalytic section, which methanation unit converts carbon dioxide
(CO.sub.2) and/or carbon monoxide (CO) into methane (CH.sub.4). In
some embodiments of aspects provided herein, the separations unit
comprises a pressure swing absorber (PSA) that contains the MOF. In
some embodiments of aspects provided herein, the separations unit
comprises a temperature swing absorber (TSA) that contains the MOF.
In some embodiments of aspects provided herein, the C.sub.1
compounds include hydrogen (H.sub.2).
[0035] Another aspect of the present disclosure provides a
non-transitory computer-readable medium comprising
machine-executable code that, upon execution by one or more
computer processors, implements any of the methods above or
elsewhere herein.
[0036] Another aspect of the present disclosure provides a system
comprising one or more computer processors and a non-transitory
computer-readable medium coupled thereto. The non-transitory
computer-readable medium comprises machine-executable code that,
upon execution by the one or more computer processors, implements
any of the methods above or elsewhere herein.
[0037] Additional aspects and advantages of the present disclosure
will become readily apparent to those skilled in this art from the
following detailed description, wherein only illustrative
embodiments of the present disclosure are shown and described. As
will be realized, the present disclosure is capable of other and
different embodiments, and its several details are capable of
modifications in various obvious respects, all without departing
from the disclosure. Accordingly, the drawings and description are
to be regarded as illustrative in nature, and not as
restrictive.
INCORPORATION BY REFERENCE
[0038] All publications, patents, and patent applications mentioned
in this specification are herein incorporated by reference to the
same extent as if each individual publication, patent, or patent
application was specifically and individually indicated to be
incorporated by reference.
BRIEF DESCRIPTION OF THE FIGURES
[0039] The novel features of the invention are set forth with
particularity in the appended claims. A better understanding of the
features and advantages of the present invention will be obtained
by reference to the following detailed description that sets forth
illustrative embodiments, in which the principles of the invention
are utilized, and the accompanying drawings or figures (also "FIG."
and "FIGs." herein), of which:
[0040] FIG. 1 shows an example oxidative coupling of methane (OCM)
system with advanced separation;
[0041] FIG. 2 shows an example OCM system with auto refrigeration
(e.g., methane refrigeration);
[0042] FIG. 3A shows an exemplary OCM system with a silver
complexation ethylene recovery subsystem;
[0043] FIG. 3B shows an example of an OCM process with an
integrated membrane contactor subsystem;
[0044] FIG. 3C shows an example of a membrane contactor;
[0045] FIG. 4 shows an exemplary pressure swing adsorption (PSA)
system;
[0046] FIG. 5A shows a schematic of CO.sub.2 separation
methods;
[0047] FIG. 5B shows a schematic of CO.sub.2 separation
methods;
[0048] FIG. 5C shows a schematic of CO.sub.2 separation
methods;
[0049] FIG. 5D shows a schematic of CO.sub.2 separation
methods;
[0050] FIG. 6 shows an example CO.sub.2 distillation system;
[0051] FIG. 7 shows an example water electrolysis sub system;
[0052] FIG. 8 shows an example OCM system with CO.sub.2 as a quench
medium;
[0053] FIG. 9 shows an example organic Rankine cycle (ORC)
subsystem;
[0054] FIG. 10 shows an exemplary typical OCM system;
[0055] FIG. 11 shows an exemplary OCM system with a single stage
PSA unit;
[0056] FIG. 12 shows an exemplary OCM system with a multi stage PSA
unit;
[0057] FIG. 13 shows an exemplary retrofit of OCM to a cracker,
with a single stage PSA unit;
[0058] FIG. 14 shows an exemplary retrofit of OCM to a cracker,
with a multi stage PSA unit;
[0059] FIG. 15 shows exemplary configurations of ethylene to
liquids (ETL) systems without PSA;
[0060] FIG. 16 shows exemplary configurations of ETL systems with
PSA;
[0061] FIG. 17 shows an exemplary PSA unit integrated with an
OCM-ETL system for a midstream application;
[0062] FIG. 18 shows an exemplary PSA unit integrated with an
OCM-ETL system in a natural gas liquids (NGL) application;
[0063] FIG. 19 shows an exemplary PSA unit integrated with an
OCM-ETL system for a refining application;
[0064] FIG. 20 shows an exemplary alternate scheme for a PSA unit
integrated with an OCM-ETL system for a refining application;
[0065] FIG. 21 shows an exemplary OCM process scheme employing
metal-organic framework (MOF) separations;
[0066] FIG. 22 shows an exemplary OCM process scheme employing MOF
separations;
[0067] FIG. 23 shows an exemplary OCM process scheme employing MOF
separations;
[0068] FIG. 24 shows an exemplary OCM process scheme employing MOF
separations;
[0069] FIG. 25 shows an exemplary OCM process scheme employing MOF
separations;
[0070] FIG. 26 shows an exemplary OCM process scheme employing MOF
separations;
[0071] FIG. 27A shows an example of OCM separations using an oil
absorption tower; and
[0072] FIG. 27B shows an example of a pre-cut and absorption
system.
DETAILED DESCRIPTION
[0073] While various embodiments of the invention have been shown
and described herein, it will be obvious to those skilled in the
art that such embodiments are provided by way of example only.
Numerous variations, changes, and substitutions may occur to those
skilled in the art without departing from the invention. It should
be understood that various alternatives to the embodiments of the
invention described herein may be employed.
[0074] The term "higher hydrocarbon," as used herein, generally
refers to a higher molecular weight and/or higher chain
hydrocarbon. A higher hydrocarbon can have a higher molecular
weight and/or carbon content that is higher or larger relative to
starting material in a given process (e.g., OCM or ETL). A higher
hydrocarbon can be a higher molecular weight and/or chain
hydrocarbon product that is generated in an OCM or ETL process. For
example, ethylene is a higher hydrocarbon product relative to
methane in an OCM process. As another example, a C.sub.3+
hydrocarbon is a higher hydrocarbon relative to ethylene in an ETL
process. As another example, a C.sub.5+ hydrocarbon is a higher
hydrocarbon relative to ethylene in an ETL process. In some cases,
a higher hydrocarbon is a higher molecular weight hydrocarbon.
[0075] The term "OCM process," as used herein, generally refers to
a process that employs or substantially employs an oxidative
coupling of methane (OCM) reaction. An OCM reaction can include the
oxidation of methane to a higher hydrocarbon and water, and
involves an exothermic reaction. In an OCM reaction, methane can be
partially oxidized and coupled to form one or more C.sub.2+
compounds, such as ethylene. In an example, an OCM reaction is
2CH.sub.4+O.sub.2.fwdarw.C.sub.2H.sub.4+2H.sub.2O. An OCM reaction
can yield C.sub.2+ compounds. An OCM reaction can be facilitated by
a catalyst, such as a heterogeneous catalyst. Additional
by-products of OCM reactions can include CO, CO.sub.2, H.sub.2, as
well as hydrocarbons, such as, for example, ethane, propane,
propene, butane, butene, and the like.
[0076] The term "non-OCM process," as used herein, generally refers
to a process that does not employ or substantially employ an
oxidative coupling of methane reaction. Examples of processes that
may be non-OCM processes include non-OCM hydrocarbon processes,
such as, for example, non-OCM processes employed in hydrocarbon
processing in oil refineries, a natural gas liquids separations
processes, steam cracking of ethane, steam cracking or naphtha,
Fischer-Tropsch processes, and the like.
[0077] The terms "C.sub.2+" and "C.sub.2+ compound," as used
herein, generally refer to a compound comprising two or more carbon
atoms. For example, C.sub.2+ compounds include, without limitation,
alkanes, alkenes, alkynes and aromatics containing two or more
carbon atoms. C.sub.2+ compounds can include aldehydes, ketones,
esters and carboxylic acids. Examples of C.sub.2+ compounds include
ethane, ethene, acetylene, propane, propene, butane, and
butene.
[0078] The term "non-C.sub.2+ impurities," as used herein,
generally refers to material that does not include C.sub.2+
compounds. Examples of non-C.sub.2+ impurities, which may be found
in certain OCM reaction product streams, include nitrogen
(N.sub.2), oxygen (O.sub.2), water (H.sub.2O), argon (Ar), hydrogen
(H.sub.2) carbon monoxide (CO), carbon dioxide (CO.sub.2) and
methane (CH.sub.4).
[0079] The term "small scale," as used herein, generally refers to
a system that generates less than or equal to about 250 kilotons
per annum (KTA) of a given product, such as an olefin (e.g.,
ethylene).
[0080] The term "world scale," as used herein, generally refers to
a system that generates greater than about 250 KTA of a given
product, such as an olefin (e.g., ethylene). In some examples, a
world scale olefin system generates at least about 1000, 1100,
1200, 1300, 1400, 1500, or 1600 KTA of an olefin.
[0081] The term "item of value," as used herein, generally refers
to money, credit, a good or commodity (e.g., hydrocarbon). An item
of value can be traded for another item of value.
[0082] The term "carbon efficiency," as used herein, generally
refers to the ratio of the number of moles of carbon present in all
process input streams (in some cases including all hydrocarbon
feedstocks, such as, e.g., natural gas and ethane and fuel streams)
to the number of moles of carbon present in all commercially (or
industrially) usable or marketable products of the process. Such
products can include hydrocarbons that can be employed for various
downstream uses, such as petrochemical or for use as commodity
chemicals. Such products can exclude CO and CO.sub.2. The products
of the process can be marketable products, such as C.sub.2+
hydrocarbon products containing at least about 99% C.sub.2+
hydrocarbons and all sales gas or pipeline gas products containing
at least about 90% methane. Process input streams can include input
streams providing power for the operation of the process. In some
cases, power for the operation of the process can be provided by
heat liberated by an OCM reaction. In some cases, the systems or
methods of the present disclosure have a carbon efficiency of at
least about 50%, at least about 55%, at least about 60%, at least
about 65%, at least about 70%, at least about 75%, at least about
80%, at least about 85%, or at least about 90%. In some cases, the
systems or methods of the present disclosure have a carbon
efficiency of between about 50% and about 85%, between about 55%
and about 80%, between about 60% and about 80%, between about 65%
and about 85%, between about 65% and about 80%, or between about
70% and about 80%.
[0083] The term "C.sub.2+ selectivity," as used herein, generally
refers to the percentage of the moles of methane that are converted
into C.sub.2+ compounds.
[0084] The term "specific oxygen consumption," as used herein,
generally refers to the mass (or weight) of oxygen consumed by a
process divided by the mass of C.sub.2+ compounds produced by the
process.
[0085] The term "specific CO.sub.2 emission," as used herein,
generally refers to the mass of CO.sub.2 emitted from the process
divided by the mass of C.sub.2+ compounds produced by the
process.
[0086] The term "unit," as used herein, generally refers to a unit
operation. A unit operation may be one or more basic steps in a
process. A unit may have one or more sub-units (or sub-systems).
Unit operations may involve a physical change or chemical
transformation, such as separation, crystallization, evaporation,
filtration, polymerization, isomerization, and other reactions. A
unit may include one or more individual components. For example, a
separations unit may include one or more separations columns or an
amine unit may include one or more amine columns.
Separations
[0087] Various non-cryogenic separation techniques have been
increasingly employed for gas separations, purifications and
recovery of hydrocarbons. Membrane based processes and adsorbents
have been intensively studied for large scale applications for
olefins recovery. Since the development of synthetic adsorbents and
pressure swing adsorption (PSA) cycles, adsorption has been playing
an increasingly important role in gas separation and
purification.
[0088] PSA technology can be used in a large variety of
applications: hydrogen purification, air separation, CO.sub.2
removal, noble gases purification, methane upgrading, n-iso
paraffin separation and so forth. While new applications for gas
separations by adsorption are continually being developed, the most
important applications have been air separation (for production of
O.sub.2 and N.sub.2) and hydrogen separation (from fuel gas).
Approximately 20% of O.sub.2 and N.sub.2 are currently produced by
PSA. The increasing industrial applications for adsorption have
stimulated a growing interest in research and new applications.
[0089] Processes of the present disclosure can employ a variety of
different separations techniques, alone or in combination. For
example, OCM processes can employ amine and caustic systems for
CO.sub.2 removal, molecular sieve guard beds for water removal, and
cryogenic distillation or other separation techniques for recovery
and purification of hydrocarbon components. Cryogenic separation
can refer to separations using temperature levels below 120 K or
about -153.degree. C. Other techniques include Selexol.TM. and
Rectisol.TM. processes for CO.sub.2 removal.
[0090] OCM product effluent can comprise a mixture of hydrocarbons
including but not limited to methane, ethane, ethylene, propane,
propylene, butanes, butenes, and higher hydrocarbons. OCM product
effluent can also comprise varying amounts of other components such
as H.sub.2, N.sub.2, CO, CO.sub.2 and H.sub.2O. The product of an
OCM reaction can include ethylene. The ethylene product can be
polymer grade, refinery grade or chemical grade. Depending on the
purity level required, different separation and/or purification
techniques can be employed with the OCM process. To recover high
purity ethylene, separation methods such as those discussed herein
can be used to remove a wide range of components.
[0091] Advantages of the advanced OCM processes described herein
can include reducing the cost, reducing the number of unit
operations ("units") used, and hence improving the overall process
for producing high purity polymer grade ethylene. Overall
conversion and carbon efficiency can also be improved. The
separation methods disclosed herein can also improve the overall
conversion and carbon efficiency.
[0092] The different separation and purification techniques
discussed herein can be used to separate the OCM product effluent
(e.g., process gas) into a plurality of streams, including but not
limited to a first stream comprising methane, hydrogen, carbon
monoxide and other lighter inerts and a second stream comprising
ethane, ethylene, propylene, and higher hydrocarbons. Separation
systems or subsystems employed can include those discussed herein,
such as a cryogenic demethanizer, a membrane separation system, or
a PSA based system.
[0093] The separation techniques discussed herein can be employed
to remove CO.sub.2, such as from an OCM product effluent stream.
One or more separations techniques can be used to remove CO.sub.2
including but not limited to absorption, adsorption, CO.sub.2
distillation, and membrane separation. The separation technique can
be non-cryogenic.
[0094] FIG. 1 shows a block flow diagram for an exemplary OCM
process. Oxygen 110 and methane 121 can be fed into an OCM reactor
101 for conversion into higher hydrocarbon compounds including
ethylene. The OCM product stream 111 can be directed to a
compressor 102, and the compressed product stream 112 can be fed
into a separations system 103. The separations system can include
pretreatment units 104, such as impurity and CO.sub.2 removal
units, as well as separations units 105, such as cryogenic,
non-cryogenic, complexation, membrane, and other separations units.
The separations system can be a combination of more than one
separation techniques, such as those discussed in this application.
The separation system can replace CO.sub.2 removal, moisture
removal, and cryogenic separation systems of existing OCM process
systems. The compressor system may not be required for some types
of separation processes. From the separations system, CO.sub.2 can
be vented 113, ethane 114 can be recovered, for example for
recycling to the OCM reactor, ethylene product 115 can be
recovered, and C.sub.3+ products 116 can be recovered.
Additionally, CO.sub.2 117 and methane 118 can be directed from the
separations system into a methanation unit 106. The methanation
unit can produce methane from the CO.sub.2, for recycling 119 back
to the OCM reactor. Additional methane 120 can be added to the OCM
reactor supply stream 121.
Auto Refrigeration
[0095] OCM process systems can use refrigeration subsystems to
condense overhead vapors, for example from a demethanizer, a
deethanizer, and/or a C.sub.2 splitter. The temperatures employed
can be in the range from about 12.degree. C. to about -100.degree.
C. These low temperatures can be achieved through the use of
multiple refrigeration systems, such as ethylene refrigeration and
propylene refrigeration systems, to provide different levels of
refrigeration. These can be similar to those employed in existing
steam crackers.
[0096] Alternatively, an open loop methane refrigeration system can
be employed to provide refrigeration for a demethanizer. OCM
product effluent can comprise methane as the major component, for
example at a concentration of at least about 50 mol %, 60 mol %, 70
mol %, 80 mol %, 90 mol %, or more. The demethanizer can have the
lowest temperature requirements in the entire separations unit. Use
of methane refrigeration (e.g., auto-refrigeration) can provide
benefits such as elimination of the need for an additional
refrigeration system (e.g., new) for any added capacity. For
grassroots or greenfield OCM applications, this can considerably
reduce refrigeration compressor sizes needed. In some cases, an
entire refrigeration system can be eliminated. FIG. 2 shows a block
flow diagram for an exemplary open loop methane refrigeration
system, such as can be used in gas processing plants and steam
crackers to produce chilling for condensing overhead vapors from a
demethanizer. Most elements of FIG. 2 correspond to the description
in FIG. 1; the separations unit 205 can include an open loop
methane refrigeration system to provide cooling for the
separations. The system can be combined with a single or multiple
stage (e.g., two-stage) expansion system (e.g., Joule Thompson) to
chill the incoming feed. In certain cases, multiple separate
lighter products are recovered, such as a light H.sub.2-rich
stream, a low pressure methane rich stream, and a high pressure
methane rich stream.
Mixed Refrigeration
[0097] Another alternative to ethylene and propylene refrigeration
subsystems is the use of a mixed refrigeration system. The mixed
refrigerant can be, for example, a mix of methane, ethylene and
propylene. The mixed refrigerant can be a mix of ethane and
propane. A wide range of possible mixed refrigerants can be
employed, and can be selected based on, for example, the
availability of certain components and the degree of refrigeration
required. A mixed refrigerant system can provide advantages for use
with an OCM reactor system, including the use of only one
refrigeration sub system. Rather than two refrigeration systems
each comprising multiple stages of refrigerant compressor,
associated vessels, exchangers, and other components, the process
can use a single refrigeration system. This can substantially
reduce capital cost. This can also reduce equipment count, which
can be a benefit especially for OCM retrofits at places where plot
space may be a concern.
Pi Complexation
[0098] Pi complexation techniques can be used to separate alkenes
from alkanes. Some metal ions complex selectively with unsaturated
organic compounds. Some of these complexes are reversible while
others are irreversible. For example, aqueous silver salt in
solution forms reversible complexes with olefins, and forms
irreversible complexes with acetylenes. This property can be
employed in an OCM process to recover ethylene and propylene from
OCM reactor effluent.
[0099] As shown in FIG. 3A, separation of ethylene and/or propylene
by metal complexation can be divided into three major sections:
absorption, purification or venting of impurities, and desorption.
An exemplary process is provided for separation of ethylene and/or
propylene from a purified multi-component gas stream from the OCM
reactor. FIG. 3A shows a process for purifying a stream containing
ethylene using an aqueous silver nitrate solution. Metal
complexation (e.g., silver or cuprous ion complexation) can be used
to separate ethylene and/or propylene from a purified
multi-component gas stream produced via OCM comprising C.sub.2
compounds, C.sub.3 compounds, and lighter components such as
hydrogen and nitrogen. First, the multi-component gas stream 310
can be introduced into an absorber 301 with aqueous silver salt
solution, such that the ethylene and/or propylene undergo
absorption or complexing with the silver metal ions, and such that
trace acetylenes react with the silver metal ions. Vent gas 311 can
be removed from the absorber. Then, the silver salt solution stream
312 can be vented 313 in a vent column 302 at reduced pressure to
remove any dissolved low molecular weight components. Then, the
resulting silver salt solution stream can be treated in a stripper
303 to separate the absorbed or complexed ethylene and/or propylene
from the silver salt solution, and further treated in a treatment
unit 304 to release the trace acetylenes. Purified ethylene 316 can
be recovered, and some product can be recycled 317. The aqueous
silver salt stream 318 can then be recycled to the first step, in
some cases after regeneration in a regeneration unit 305 with
AgMnO.sub.4 320. MnO.sub.2 321 can be removed from the regeneration
unit. H.sub.2O.sub.2 319 can be added to the solvent stream being
returned to the absorber.
[0100] Useful adsorbents include but are not limited to metal
compounds, such as silver or copper, supported on high surface area
carriers with a plurality of pores. These adsorbents can be used in
pressure swing adsorption or temperature swing adsorption
processes. When operating pressure and/or temperature is changed,
the silver or copper compound can release the alkene-rich component
from the adsorbent. These adsorbents can be very effective for
selective adsorption of alkenes such as ethylene, propylene, and
mixtures of these from gaseous mixtures.
[0101] When a gaseous component solubilizes in a liquid and
complexes with its ions, the loading of the gas can be affected by
its partial pressure and the temperature and the concentration of
the complexing ions in the solution. Therefore, by changing the
physical conditions separately or collectively, the active gaseous
component can either be formed into or out of the solution.
Adjusting or swinging one or more physical parameters can be used
to carry out an ethylene or propylene separation using an aqueous
silver nitrate solution. Purification or venting of impurities can
result in a product stream that is free or substantially free of
impurities including but not limited to CO.sub.2, sulfur compounds,
acetylenes, and hydrogen. Acetylene and hydrogen can cause
operational problems and so the process gas can be treated to bring
the concentration of such impurities to within an acceptable
limit.
[0102] Metal complexation can be used in combination with other
processes, such as membrane-based processes, or a PSA system with
metal ions dispersed on the sorbent. For good adsorption, the
cations can be spread (e.g., with high dispersion) on solid
substrates with a high surface area. There are at least three types
of metal complexation sorbents that can be used in the methods and
systems described herein (i.e., monolayer or near monolayer salts
supported on porous substrates, ion-exchange zeolites, and
ion-exchange resins). For bulk separation, the monolayer salts on
porous substrates and ion-exchange resins can be more suitable in
some cases. Ion-exchange zeolites are usually more suitable for
olefin recovery or purification. Substrates for supporting salts
may include Y-Alumina (porous), silica gel, activated carbon,
TiO.sub.2, and a number of zeolites. The metal ion can be Ag.sup.+
or Cu.sup.+ ion.
[0103] Membrane contactors using a silver nitrate solution or a
copper salt solution can be used to separate the olefins from the
OCM effluent stream. The contactor can include the salt solution in
a membrane module or unit. Many such modules or units can be put
together in a contactor system where the salt solution is
circulated. Such membrane contactors can result in substantial
olefin recovery from a feed containing a mixture of olefins and
paraffins (e.g., propane and/or propylene). The process described
herein can be used to separate ethylene from the OCM effluent
containing methane and ethane, resulting in elimination of whole,
or part of the cryogenic recovery system in a typical OCM
system.
[0104] As described herein, OCM process can be integrated with a
Permylene membrane system to recover or separate the bulk of
ethylene. In some cases, Permylene membranes can be used to
separate olefins from paraffins. The Permylene process can use a
flat sheet composite structure based on chitosan material and
silver cations as facilitating agents. Chitosan can be produced by
the deacetylation of chitin, which is the structural element in the
exoskeleton of crustaceans. Chitosan can act as the active layer of
the Permylene membrane. In contact with an aqueous solution
containing silver ions, a hydrogel can be formed and the silver
ions can form metal complexes with the olefins. The olefin
molecules can be transported across the membrane under the
influence of the olefin partial pressure differential between the
feed and permeate sides of the membrane and can be released on the
low pressure permeate side. Gases without a carbon-carbon double
bond are rejected.
[0105] In some instances, an oxidizing agent can be used to either
stabilize or improve the formation of the desired metal complex
with olefin, and/or to regenerate or destabilize the undesired
complexes formed. For example, in a copper based system, adding
nitric acid can improve the stability of formation of the
metal-olefin complex.
[0106] FIG. 3B shows an example of a membrane contactor module (or
unit) with an OCM system. The membrane contactor module separates
the incoming feed into an olefin rich product stream and a lighter
reject stream. The lighter stream can contain predominantly
methane, CO, CO.sub.2 and some ethane, and is recycled to the OCM
loop (e.g., to methanation and back to OCM reactor). The
pretreatment comprises acetylene and diene removal, since those are
more active in forming metal-complexes than olefins. The lean
(olefin depleted) solution can be recycled back to the membrane
contactor, as shown in FIG. 3C. The metal complex can be subjected
to a low pressure and/or a high temperature in order to break the
olefin-metal complex and recover the olefin and metal solution.
[0107] FIG. 3B shows an example of an OCM process with an
integrated membrane contactor module. The OCM feedstock 322 (e.g.,
comprising methane) and oxygen feed 324 (e.g., air) can be mixed
and reacted in an OCM module 326. The OCM product can be
pre-treated 328 and sent to a membrane contactor module 330. The
membrane contactor module can provide an olefin-rich stream 332 and
send some of the remaining material back to a methanation module
334. Some of the material can be purged 336. The methanation module
334 can produce methane and recycled to the OCM module 326.
[0108] FIG. 3C shows an example of a membrane contactor module. The
feed 338 (e.g., from a pre-treatment unit 328) can go into a
membrane unit 340. The olefin rich stream 342 can be sent to a
first flash vessel 344, which produces an olefin product 346. The
lean solution 348 (e.g., depleted in olefin) can be recycled to the
membrane unit 340. In some cases, the membrane contactor module
contains a second stage, in this example a second flash vessel 350
can produce a C.sub.1 recycle stream 352.
Membranes
[0109] Membranes can be used to perform a variety of separations,
such as separations of olefins and paraffins, or separations of
CO.sub.2. A membrane can be essentially a barrier that separates
two phases and restricts transport of various chemicals in a
selective manner. Polymer membranes can be used to separate
mixtures such as propylene/propane mixtures and ethylene/butene
mixtures. Separations in polymeric membranes are dependent on the
solubility and diffusion of the species through the membrane. While
zeolite-based separations are predominantly depended on molecular
size differences, the differing permeation of olefins through a
polymeric membrane can be largely attributed to differences in
solubility, which can depend on the critical temperature and the
kinetic diameter. Membrane separations can be employed even when
there are small molecular size differences.
[0110] The OCM process can utilize a membrane based separation
process to further enhance the efficiency and energy consumption of
the process. Cryogenic distillation can be used for the separation
of alkenes, but is highly energy intensive. Membrane based
separations can be used for a variety of purposes in the context of
an OCM process, such as to separate and purify ethylene product
from OCM reactor effluent, to separate a stream rich in CO.sub.2,
to separate a stream containing lighter hydrocarbons and inerts, or
to separate C.sub.2 compounds from C.sub.1 and lighter
compounds.
[0111] Membranes can include but are not limited to isotropic
membranes, anisotropic membranes, and electrically charged
membranes. A membrane can be a ceramic membrane, a metal membrane,
or a liquid membrane. An isotropic membrane can be a microporous
membrane or a non-porous dense membrane. Membranes can be used for
separations including but not limited to CO.sub.2 separation,
paraffin-olefin separation, or selective recovery of pure ethylene
from the OCM reactor effluent. Polymer derived carbon molecular
sieve membranes can be used to separate paraffins from olefins.
These membranes can be used, for example, to separate ethylene from
a mix of methane and ethane.
[0112] Membrane separations can be used in combination with other
types of separation and purification subsystems to remove other
impurities such as acid gases, hydrogen, and nitrogen.
[0113] Transport through a membrane can take place when a driving
force is applied to the components in the feed. A driving force can
be a pressure differential or a concentration (activity) gradient
across the membrane. Membrane based separation techniques can be
used in an OCM process by applying either of the above mentioned
driving forces. A membrane based separation can also be a component
of a hybrid separation set-up, such as a membrane and an absorption
system (e.g., a membrane contactor) or a membrane in a pressure
swing adsorption (PSA) or a temperature swing adsorption (TSA)
system.
[0114] An OCM reactor can employ membranes as a part of the reactor
system to effectively separate the ethylene product within the
reactor system itself. A section of the reactor can include
membranes that aid in recovering the ethylene product, with a
methane rich stream being recycled to a methanation system and
eventually to the OCM reactor. Such a system can also use advanced
heat recovery or quench methods so as to facilitate the use of
membranes.
Pressure Swing Adsorption (PSA) and Adsorption Technology
[0115] Cryogenic separation (e.g., distillation) can be used for
the recovery of ethylene, propylene, and other components from
olefin plants, refinery gas streams, and other sources. These
separations can be difficult to accomplish because of the close
relative volatilities, and can have significant temperature and
pressure requirements for operation. The ethane/ethylene
distillation can be performed at about -25.degree. C. and 320
pounds per square inch gauge (psig) in a column containing over 100
trays. Distillation of propane and propylene can be performed at
about -30.degree. C. and 30 psig. These can be some of the most
energy intensive distillations in the chemical and petrochemical
industry. In general, the use of distillation towers to separate
recover and purify components is an energy intensive process.
[0116] The present disclosure provides the use of adsorbents that
can achieve separation and purification of olefin rich streams. In
particular, the present disclosure applies the use of PSA-based
adsorbent systems to separate, purify, and recover olefins like
ethylene and propylene from streams containing one or more
impurities such as methane, hydrogen, carbon monoxide, carbon
dioxide, ethane, or others. The streams, or parts of the streams,
can be generated via an OCM process, an ETL process, or
combinations thereof. The streams can be final product streams
where PSA is used to recover and purify the final product. The
streams can be intermediate streams which are purified prior to use
as a feed in a subsequent process, such as an ETL process, an
ethylene cracker (steam cracker), a refining unit, a fuel gas
system, a natural gas recovery plant or any other product
fractionation or product treatment unit.
Pressure Swing Adsorption (PSA)
[0117] A pressure swing adsorption (PSA) process cycle is one in
which desorption takes place at a different (e.g., lower) pressure
than the adsorption pressure. Reduction of pressure can be used to
shift the adsorption equilibrium and affect regeneration of the
adsorbent. Low pressure may not be as effective as temperature
elevation in totally reversing adsorption, unless very high feed to
purge pressure ratios are applied. Therefore, most PSA cycles are
characterized by high residual loadings and thus low operating
loadings. These low capacities at high concentration require that
cycle times be short for reasonably sized beds (e.g., seconds to
minutes). These short cycle times are attainable because particles
of adsorbent respond quickly to changes in pressure. Major uses for
PSA processes include purification as well as applications where
contaminants are present at high concentrations.
[0118] As shown in FIG. 4, the PSA system can comprise two fixed
bed adsorbers 401 and 402 undergoing a cyclic operation of four
steps--adsorption, blowdown, purge, and pressurization. The PSA
system can receive a feed 410 and produce a product stream 411,
with a PSA off gas stream 412. For improving the performance of the
basic Skarstrom.TM. cycle (FIG. 4), additional operation steps can
be employed such as pressure equalization, product pressurization,
and co-current depressurization. Besides these steps, the number of
beds can be modified to achieve the optimal operation and multi-bed
processes can be used in commercial applications like hydrogen
recovery. Similarly, a TSA system can be used where a swing in
temperature causes the sorption and desorption.
[0119] PSA cycles are used primarily for purification of wet gases
and of hydrogen. High pressure hydrogen employed in processes such
as hydrogenation, hydrocracking, and ammonia and methanol
production can be produced by PSA beds compounded of activated
carbon, zeolites and carbon molecular sieves. Other exemplary
applications include: air separation, methane enrichment,
iso/normal separations, and recovery of CO and CO.sub.2.
Adsorbents
[0120] Adsorbents can be natural or synthetic materials, such as
those having amorphous or microcrystalline structure. Exemplary
adsorbents useful for large scale operation include but are not
limited to activated carbon, molecular sieves, silica gels, and
activated alumina. Other useful adsorbents include pi complexation
sorbents, silver and copper complexation adsorbents, zeolites,
synthetic zeolites, mesoporous materials, activated carbons, high
surface area coordination polymers, molecular sieves, carbon
molecular sieves (CMS), silica gels, MCM, activated alumina, carbon
nanotubes, pillared clays, and polymeric resins.
[0121] For systems where the incoming stream is a multi-component
mixture of gases and the number of compounds to be separated cannot
be removed by a single adsorbent, different layers of adsorbents
can be used. For example, hydrogen purification from a methane
stream in a reforming operation, where H.sub.2 is contaminated with
H.sub.2O, CO.sub.2, CO, and unconverted CH.sub.4, can employ
activated carbon to remove H.sub.2O and CO.sub.2 in combination
with additional layers of different adsorbents used to increase the
loading of CO.
[0122] Zeolites, molecular sieves, and carbon molecular sieves
(CMS) can be used for most industrial separations employing PSA.
Inorganic materials, like special kinds of titanosilicates, can be
used for kinetic separations.
[0123] For systems specifically configured to separate
ethane/ethylene and propane/propylene, exemplary types of
adsorbents include zeolites/molecular sieves and pi complexation
sorbents. Zeolites/molecular sieves can be used for kinetic
separation, such as separation based on higher diffusivity of
olefins over that of paraffins. The use of 4A zeolite is one such
example. For example, a three-bed system can be used to recover
olefins from a stream containing 80-85% olefins and 10-15%
paraffins, using a 4A type zeolite at elevated temperatures (e.g.,
the Petrofin process). Pi complexation sorbents, such as
AgNO.sub.3/SiO.sub.2, can give excellent results as compared to 4A
zeolite. PSA units as discussed herein can employ a range of
different sorbents, including but not limited to a
zeolite/molecular sieve sorbent, a pi complexation based sorbent, a
carbon molecular sieve sorbent or any other form of activated
carbon, carbon nanotubes, polymeric resin based sorbents, or other
sorbents.
[0124] Adsorbents can be selected based on a number of different
criteria. Adsorbent selection criteria can include capacity for the
target components (e.g., affinity for the desired components to be
separated from the multi-component feed stream), selectivity
between components competing for same adsorption sites,
regenerability of the adsorbent, (e.g., the ability of the
adsorbent to release the adsorbed target components at a reasonable
pressure rate of gas diffusion into the adsorbent--this can also
affect the size of the bead that is chosen and consequently the
pressure drop across the bed; an insufficient diffusion rate can
require smaller diameter beads that can result in higher pressure
drop and hence increased operating costs), and chemical
compatibility (e.g., selecting an adsorbent resistant to chemical
attack that may poison or destroy the adsorbent, such as liquid
hydrocarbons causing physical breakdown of the adsorbent resulting
in loss of efficiency and back pressure).
[0125] Separations, such as of ethylene and propylene, can be
conducted using an amorphous fluoropolymer based membrane.
Facilitated transport using silver ions can selectively transport
ethylene and/or propylene. The membrane can be a part of a membrane
contactor system. The feed to the system can be of a low to
moderate olefin concentration. The feed to the system can contain
other hydrocarbons, including, but not limited to, methane, ethane,
propane, butane, butenes, C.sub.5 components and higher
hydrocarbons. The feed can also contain CO.sub.2, CO, H.sub.2, and
inert components, such as nitrogen.
CO.sub.2 Separation
[0126] There are many technologies available for CO.sub.2 capture,
such as from flue gases, natural gas, or from any process gas rich
in CO.sub.2. Various processes for post-combustion or
pre-combustion capture can be used reduce CO.sub.2 emissions. FIG.
5A, FIG. 5B, FIG. 5C, and FIG. 5D show exemplary schematics of
different separation methods available to separate CO.sub.2 from a
process gas or a flue gas.
[0127] OCM processes can utilize an amine based absorption system
for CO.sub.2 removal, which can be followed by use of a caustic
scrubber to obtain high degree of separation. The amine system is
prone to corrosion, solvent degradation, and above all, has high
energy requirements. Separations with sorbents and/or solvents can
involve placing the CO.sub.2 containing gas in intimate contact
with a liquid absorbent or a solid sorbent that is capable of
capturing the CO.sub.2. As shown in FIG. 5A, a stream with CO.sub.2
510 can be directed into a capture vessel 501, where it contacts
sorbent which captures CO.sub.2 from the stream. The stream, with
reduced or removed CO.sub.2, can then exit 511 the vessel. Sorbent
512 loaded with captured CO.sub.2 can be transferred to a sorbent
regeneration vessel 502 where it releases the CO.sub.2 after being
heated (e.g., with the use of energy 513), after a pressure
decrease, or after any other change in the conditions around the
sorbent, thereby regenerating the sorbent. Spent sorbent 515 and
CO.sub.2 516 can be removed from the vessel, and make up sorbent
514 can be added. After the regeneration step the sorbent can be
sent back to capture more CO.sub.2 in a cyclic process. The sorbent
can be a solid. Solid sorbent can remain in a single vessel rather
than being cycled between vessels; sorption and regeneration can be
achieved by cyclic changes (e.g., in pressure or temperature) in
the vessel where the sorbent is contained. A make-up flow of fresh
sorbent can be used to compensate for natural loss of activity
and/or sorbent losses.
[0128] Amine scrubbing technology can be used to remove acid gases
from process gases. Primary amines (e.g., MEA, DGA), secondary
amines (e.g., DEA, DIPA), tertiary (e.g., MDEA, TEA), sterically
hindered amines, chilled ammonia, potassium carbonate, and other
compounds can be used to remove CO.sub.2 from process gases.
Traditional amine based systems can be characterized by high energy
requirements and solvent degradation. Improved solvents, which can
require less energy for regeneration of the solution, include the
Benfield process and two stage diethanolamine. Combination with an
OCM process can reduce the energy consumption of amine scrubbing
processes. Improved solvents can reduce the energy requirements by
as much as 40% compared to the traditional MEA solvents. This has
the potential of reducing the energy, and hence steam, consumption
of the OCM process, thereby increasing the amount of steam
available for export from the OCM, or making alternative waste heat
recovery methods feasible.
[0129] Physical absorption solvents used can include but are not
limited to glycol dimethylethers (e.g., Selexol) and propylene
carbonate (e.g., IPTS/EC). Regeneration of the solution can be
performed by vacuum flashing and air stripping; this approach can
consume significantly less energy than in chemical absorption. In
using physical solvents CO.sub.2 can be released mainly by
depressurization, thereby avoiding the high heat of consumption of
amine scrubbing processes.
[0130] Mixed or hybrid solvents can include but are not limited to
Sulfinol (sulfolane, water, and amine), such as Sulfinol-M and
Sulfinol-X.
[0131] Solid adsorbents, such as zeolites and activated carbon, can
be used to separate CO.sub.2 from gas mixtures. In pressure swing
adsorption (PSA), a gas mixture can flow through a packed bed of
adsorbent at elevated pressure until the concentration of the
desired gas approaches equilibrium. The bed can be regenerated by
reducing the pressure. In temperature swing adsorption (TSA), the
adsorbent can be regenerated by raising its temperature. In general
usage, adsorption is not yet considered attractive for large scale
separation of CO.sub.2 because the capacity and CO.sub.2
selectivity of available adsorbents are low. However, when the OCM
process is a recycle process, an adsorbent based separation method
can be used to separate bulk CO.sub.2 followed by consuming the
remaining CO.sub.2 in a methanation reactor system, or by using a
caustic scrubber to treat the remaining CO.sub.2.
[0132] Many different types of membrane materials (e.g., polymeric,
metallic, ceramic) can be used for CO.sub.2 capture to
preferentially separate CO.sub.2 from a range of process streams.
FIG. 5B shows an exemplary schematic of separation of CO.sub.2 from
a gas stream 530 in a separation vessel 520 using a membrane 521.
CO.sub.2 can be removed from the stream via the membrane, and
CO.sub.2 and other gases can exit the vessel in separate streams
531 and 532. The main limitation of currently existing membranes is
the occurrence of severe plasticization of the membrane in the
presence of high pressure CO.sub.2. Due to excessive swelling of
the polymer membrane upon exposure to CO.sub.2, the performance
(e.g., selectivity) can decrease significantly, thus reducing the
purity of the CO.sub.2 and consequently reducing the possibilities
for reuse of the gas. Energy requirements can be significantly
lower for membrane based technologies; for example, membrane
technology can use 70-75 kWh per ton of recovered CO.sub.2 compared
to significantly higher values for pressure swing adsorption (e.g.,
160-180 kWh), cryogenic distillation (e.g., 600-800 kWh), or amine
absorption (e.g., 330-340 kWh), making membrane technology an
attractive option for integration with OCM for CO.sub.2
separation.
[0133] Membrane and amine technologies can be combined to form a
hybrid process to capture CO.sub.2. Micro-porous hollow fiber
membranes can be used for CO.sub.2 separation using amine-based
chemical absorption processes. Micro-porous membranes can be used
in a gas-liquid unit where the amine solution is contacted with
CO.sub.2 containing gas. Using the membrane can lead to a reduction
in the physical size and weight of the gas-liquid contacting unit.
The separation is based on reversible chemical reaction, and mass
transfer occurs by diffusion of the gas through the gas/liquid
interface as in traditional contacting columns. Such a hybrid
membrane contactor can provide a high contact area between gas and
liquid, reduce or essentially eliminate foaming and flooding
problems, and give better operational flexibility while reducing
solvent degradation problems.
[0134] A membrane contactor can combine the advantages of membrane
technology and solvent absorption for CO.sub.2 separation. A
membrane contactor is a combination of advanced membrane techniques
with an effective absorption process. A membrane contactor is a
hybrid mass exchanger where a porous membrane separates two phases.
The selective sorbent performs the separation while the membrane
facilitates the mass exchange process by expanding the phase
contact surface area. The modified surface properties can improve
the selectivity of the process by selectively inhibiting the
transport of one of the mixture constituents. Compared to a
conventional column device, membranes can allow for up to five
times increase in yield per unit volume. Since the sorptive liquid
flows within capillaries and both phases are not directly
contacting each other, membrane absorbers can operate in any
spatial configuration (horizontal or vertical) and at any flux
rations between both phases. Also, there is no flooding or uneven
packing moisturization. Since the system operates with unchanging
yields, independent of the diameter and height; scaling up is
fairly simple. Membranes used can be micromembranes or
ultrafiltration membranes made a variety of different polymer and
ceramic materials. Polypropylene fiber membranes can be used to
separate CO.sub.2 from CH.sub.4, for example by using amines like
MEA as absorption liquid. Hollow fiber membranes, such as porous
polypropylene, perfluoroalkoxy (PFS), and asymmetric poly(phenylene
oxide) hollow fiber membranes with a dense ultrathin skin at the
outside of the membrane can also be used. Besides amines as
absorption liquid, other absorption liquids may be used, such as
aqueous sarcosine salt solutions, for example in a gas-liquid
membrane contactor system. A membrane contactor can be used to
separate the CO.sub.2 from the OCM effluent in which CH.sub.4 is
the major component. Membrane contactors can also be used for
separation of olefins and paraffins, and the separation of CO.sub.2
from light gases.
[0135] An activator, such as piperazine, diethanolamine, and
arsenic trioxide, can be used to further enhance the effectiveness
of CO.sub.2 capture. DGA and tertiary amines may provide more
improvement than primary or secondary amines.
[0136] Gas selective poly ionic liquid membranes, which are
polymerized room temperature ionic liquids (RTIL), can be used to
be highly selectively separate CO.sub.2. RTILs can be synthesized
as a monomer and subsequently polymerized to obtain gas selective
membranes. The ionic nature of the polymers can result in tight
arrangements between the oppositely charged ionic domains in the
poly RTIL, which can eventually prevent the membrane from excessive
swelling and deterioration of its performance at increased pressure
and/or temperature. This intrinsic property of poly RTIL can be
used to increase the resistance against plasticization and to
restrict strong swelling of the polymer membrane to maintain its
permeation properties in the presence of a strong plasticizing
agent such as CO.sub.2 at higher pressures. For example, an
imidazolium-based poly RTIL can be used as base material and the
length of the alkyl chain can serves to strengthen or weaken the
ionic interactions within the poly RTIL. High pressure mixed
CO.sub.2/CH.sub.4 gas separation measurements at different
temperatures.
[0137] Gas components like CO.sub.2, from N.sub.2 or CH.sub.4 can
be separated with supported ionic liquid membranes. Ionic liquids
are molten salts with a very low melting point (many are liquids at
room temperature). Many ionic liquids show a high solubility for
carbon dioxide and hence can be highly suitable for use with an OCM
process. For example, ionic liquids can include but are not limited
to imidazolium, pyrollidinium, pyridinium, cuanidinium,
phosphonium, morpholinium, piperidinium, sulfonium, ammonium,
hexafluorophosphate, tetraflouroborate, alkylsulphate, triflate,
dicyanamide, bis(trifluoromethylsulfonyl)imide, and combinations
thereof. Specific advantages of ionic liquids include very low to
negligible vapor pressure, good dissolution characteristics for
many substances, and lack of flammability or toxicity. Ionic
liquids can have good thermal, mechanical and chemical stability as
well as favorable densities and viscosities. The required
specifications can be adjusted easily by the large number of
possible combinations of anions and cations when formulating an
ionic liquid. Ionic liquids can be used as chemical solvents,
catalysts, electrolytes in fuel cells as well as for gas-separation
and storage by absorption. Ionic liquid membrane systems can
comprise an adequate porous support material, e.g. a polymer film,
coated by ionic liquids. The system can separate CO.sub.2 and
sulfur compounds from different gas mixtures. Competitive
selectivity and permeability are obtained for the separations.
[0138] Novel membrane materials, such as polyetherimides, can be
used as membrane material with improved plasticization resistance
for CO.sub.2 removal, for example with an OCM process. Other
membrane materials that can be used include, but are not limited
to, polymeric membranes based on or comprising polyamides,
polysemicarbazides, polycarbonates, polyarylates, polyaniline,
poly(phenylen oxide), polysulfones, polypyrrolones, or combinations
thereof. In some cases, the polymeric membrane is solvent resistant
and can reduce the plasticization effects of hydrocarbons in the
feed stream, e.g., polyketone, polyether ketone, polyarylene ether
ketone, polyimide, polyetherimide, and/or polyphenylene sulphide,
which have intrinsic solvent inertness and can therefore withstand
organic rich operation conditions.
[0139] An adequate porous support material, e.g. a polymer film,
coated by ionic liquids can be used in continuous separation of
CO.sub.2 and sulfur compounds from different gas mixtures,
including a methane rich stream. This separation can improve the
efficiency of OCM processes. The OCM reactor effluent can enter the
supported ionic liquid separation subsystem, and CO.sub.2 and other
contaminants can be removed from the process gas. Other
contaminants can include but are not limited to traces of sulfur
compounds, inerts, CO, SO.sub.2, H.sub.2S, and tetrahydrothiophene
(THT).
[0140] CO.sub.2 can be separated from other gases by cooling and
condensation, for example as shown in FIG. 5C. A stream containing
CO.sub.2 550 can be compressed in a compressor 540, and the
compressed stream 551 can be directed to a distillation column 541.
Some components can be recovered from the overhead stream 552, with
heat recovered in a heat exchanger 542. Other components can be
recovered from the bottoms 555. Cryogenic separation is widely used
commercially for streams that already have a high concentration of
CO.sub.2 (typically greater than 90%). Cryogenic separation of
CO.sub.2 has the advantage that it enables direct production of
high purity liquid CO.sub.2 that can be used as a feedstock to
convert the carbon to higher value hydrocarbons, or otherwise be
captured. The amount of energy required can be high, and water may
need to be removed before the feed gas is cooled.
[0141] Low temperature distillation can give better results when
there is a high concentration of CO.sub.2 in the feed gas. For the
OCM process gas, the CO.sub.2 concentration can be increased by,
for example, having a recycle stream, or by using a modified OCM
reactor where excess CO.sub.2 is used as a quench medium for the
reaction heat. Low temperature separation can refer to separations
using temperature levels above -90.degree. C.
[0142] As shown in FIG. 5D, another method of the present
disclosure for removing CO.sub.2 from the OCM system involves a
two-step CO.sub.2 removal. The first step can be a bulk CO.sub.2
removal, followed by the recovery section (e.g., cryogenic
fractionation system), and then a second polishing step to remove
the CO.sub.2 from the purified ethylene product to meet the polymer
grade ethylene specifications.
[0143] As shown in FIG. 5D, oxygen 560 can be fed with methane 562
into an OCM reactor 564. The effluent can be compressed 566. The
first (bulk) CO.sub.2 removal 568 can be carried out before the
cryogenic section. The first CO.sub.2 removal lowers the CO.sub.2
content to a level tolerable in the cryogenic de-methanizer 570.
The demethanizer is operated at conditions that ensure that no
CO.sub.2 freezes and all of the residual CO.sub.2 that is not
removed in the bulk separation 568 is separated with the heavy
C.sub.2+ stream at the bottom and sent to the de-ethanizer 572. An
acetylene hydrogenation system 574 and a C.sub.2 splitter 576 can
follow the de-ethanizer 572 to produce high purity ethylene 578.
The high purity ethylene can contain the residual CO.sub.2 that is
not removed by the first CO.sub.2 removal unit 568. This residual
CO.sub.2 can be removed by a second CO.sub.2 removal step 580 to
produce polymer grade ethylene 582. In some cases, a depropanizer
584 can be used to produce a C.sub.3+ product 586, ethane 588 can
be recycled to (the cracking section of) the OCM reactor 564, and
C.sub.1 compounds 590 can be methanated 592 and returned to the OCM
reactor 564 or purged 594. In some cases CO.sub.2 from the first
568 or second 580 CO.sub.2 removal units can be send to the
methanation reactor 592 (not shown).
[0144] The first (bulk) CO.sub.2 separations system can be a
membrane or a PSA system, an amine removal system, or any other
solvent based CO.sub.2 removal system as described herein. The
final CO.sub.2 removal step can be a caustic tower, a membrane
based system, a PSA based system, or any other CO.sub.2 removal
system as described herein. The ethylene product CO.sub.2 removal
system 580 can be followed by further drying and/or purification
steps.
[0145] One advantage of the two step process described herein can
be energy saving that arise from decreasing the gas volumes being
processed for the final CO.sub.2 removal step. If CO.sub.2 removal
is done entirely upstream of the demethanizer, the energy
consumption is much greater than described in FIG. 5D because the
entire methane rich recycle stream dilutes the CO.sub.2. When final
CO.sub.2 removal is performed at the back-end, the ethylene product
has a far lower flow rate and hence the final CO.sub.2 removal step
is more energy efficient.
[0146] The concentration of CO.sub.2 going into the de-methanizer
(following the first CO.sub.2 removal unit) can be any suitable
amount (i.e., such that CO.sub.2 doesn't freeze in the
de-methanizer). In some embodiments, the concentration of CO.sub.2
going into the de-methanizer is about 0.1 mol %, about 0.2 mol %,
about 0.3 mol %, about 0.4 mol %, about 0.5 mol %, about 0.6 mol %,
about 0.7 mol %, about 0.8 mol %, about 0.9 mol %, about 1.0 mol %,
about 1.2 mol %, about 1.4 mol %, about 1.6 mol %, about 1.8 mol %,
about 2.0 mol %, about 2.2 mol %, about 2.4 mol %, about 2.6 mol %,
about 2.8 mol %, about 3.0 mol %, about 3.5 mol %, about 4.0 mol %,
or about 5.0 mol %. In some cases, the concentration of CO.sub.2
going into the de-methanizer is at least about 0.1 mol %, at least
about 0.2 mol %, at least about 0.3 mol %, at least about 0.4 mol
%, at least about 0.5 mol %, at least about 0.6 mol %, at least
about 0.7 mol %, at least about 0.8 mol %, at least about 0.9 mol
%, at least about 1.0 mol %, at least about 1.2 mol %, at least
about 1.4 mol %, at least about 1.6 mol %, at least about 1.8 mol
%, at least about 2.0 mol %, at least about 2.2 mol %, at least
about 2.4 mol %, at least about 2.6 mol %, at least about 2.8 mol
%, at least about 3.0 mol %, at least about 3.5 mol %, at least
about 4.0 mol %, or at least about 5.0 mol %. In some cases, the
concentration of CO.sub.2 going into the de-methanizer is at most
about 0.1 mol %, at most about 0.2 mol %, at most about 0.3 mol %,
at most about 0.4 mol %, at most about 0.5 mol %, at most about 0.6
mol %, at most about 0.7 mol %, at most about 0.8 mol %, at most
about 0.9 mol %, at most about 1.0 mol %, at most about 1.2 mol %,
at most about 1.4 mol %, at most about 1.6 mol %, at most about 1.8
mol %, at most about 2.0 mol %, at most about 2.2 mol %, at most
about 2.4 mol %, at most about 2.6 mol %, at most about 2.8 mol %,
at most about 3.0 mol %, at most about 3.5 mol %, at most about 4.0
mol %, or at most about 5.0 mol %. In some cases, the concentration
of CO.sub.2 going into the de-methanizer is between any of the two
values described above, for example, between about 0.5 mol % and
about 2.0 mol %.
[0147] FIG. 6 shows a schematic of CO.sub.2 separation using
distillation. OCM reactor effluent 606 can be fed to a treatment
unit 601, such as a molecular sieve dryer, a sulfur removal bed, or
an acetylene removal bed. The treated gas is fed to the first
distillation column 602 that separates the bulk of the methane from
the CO.sub.2 and other heavier hydrocarbons. Depending on the
CO.sub.2 concentration in the stream 606, the bottom stream 608 may
contain at least about 50%, 60%, 70%, 80%, 90%, or more (or any
value in between) of the incoming CO.sub.2. The overhead from 607
contains majority of the methane and other light gases and is fed
to the column 603. Column 603 further recovers methane rich gas
611, which can be the feed to a methanation system. The bottoms
product 616 may be recycled or sent as a purge to the fuel gas
system. The CO.sub.2 rich gas 608 is distilled in the CO.sub.2
column 604 to recover pure CO.sub.2 609 in the overhead. The
bottoms product 610 can contain some methane along with ethane,
ethylene, and other heavier hydrocarbons, and can be sent to
recover the ethylene product in a separator 605. The CO.sub.2
product can be sent to methanation unit, and a part of the CO.sub.2
can be recycled to achieve the desired concentration of CO.sub.2 in
the feed stream 606. Such a CO.sub.2 distillation sub system can
offer many benefits, including but not limited to reducing the loop
size of the OCM process considerably, as the function of the
existing cryogenic demethanizer can be reduced by a large extent.
Additionally, amine and caustic systems can be replaced by
cryogenic or low temperature distillation systems.
[0148] Alkaline salt-based processes can be used for carbon dioxide
removal. These processes can utilize the alkali salts of various
weak acids, such as sodium carbonate and potassium carbonate. These
processes can provide advantages such as low cost and minimal
solvent degradation. Processes that can be used for H.sub.2S and
CO.sub.2 absorption include those using aqueous solutions of sodium
or potassium compounds. For example, potassium carbonate can absorb
CO.sub.2 at high temperatures, an advantage over amine-based
solvents.
[0149] Hot potassium carbonate (K.sub.2CO.sub.3) solutions can be
used for the removal of CO.sub.2 from high-pressure gas streams,
among other applications. Potassium carbonate has a low rate of
reaction. To improve CO.sub.2 absorption, mass transfer promoters
such as piperazine, diethanolamine, and arsenic trioxide can be
used. Less toxic promoters such as borate can also be used, for
example with flue gas streams (see, e.g., Ghosh et al., "Absorption
of carbon dioxide into aqueous potassium carbonate promoted by
boric acid", Energy Procedia, pages 1075-1081, February 2009, which
is hereby incorporated by reference in its entirety). To limit
corrosion, inhibitors can be added. These systems can be known as
activated hot potassium carbonate systems. Licensed hot activated
potassium carbonate systems include the Benfield and the Catacarb
process. The processes can be used for bulk CO.sub.2 removal from
high-pressure streams, but can also produce high-purity
CO.sub.2.
[0150] Flue gas impurities such as SOx and NOx can reduce the
operational efficiency of the potassium carbonate as a solvent.
SO.sub.2 and NO.sub.2 may not able to be released from the solvent
under industrial conditions. Selective precipitation of the
impurity salts formed by SOx and NOx can be used to remove such
compounds (see, e.g., Smith et al., "Recent developments in solvent
absorption technologies at the CO2CRC in Australia" Energy
Procedia, pages 1549-1555, February 2009, which is hereby
incorporated by reference in its entirety).
[0151] A variety of materials can be used as CO.sub.2 sorbents
through chemical reactions and physical absorptions, including but
not limited to soda-lime, active carbon, zeolites, molecular
sieves, alkali metal oxides, silver oxide, lithium oxide, lithium
silicate, carbonates, silica gel, alumina, amine solid sorbents,
metal organic frameworks and others.
[0152] Physical impregnation of CO.sub.2-reactive polymers, such as
tetraethylene pentamine or polyethyleneimine, inside a porous
support, such as alumina, pumice, clay or activated carbon, can be
used for CO.sub.2 removal. Amine based sorbents can be easily
regenerated. Alternatively, a mixture of an amine compound with a
polyol compound can be impregnated in a porous support. The polyol
compound can be used to increase the CO.sub.2 desorption rate of
the amine. The supported amine-polyol sorbent can comprise at least
about 1 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %,
35 wt %, or more amine and/or polyol. In some cases, the supported
amine-polyol sorbent can comprise from about 1 wt % to about 25 wt
% amine and from about 1 wt % to about 25 wt % polyol, with the
balance being the support. Solid sorbent can adsorb and desorb
CO.sub.2 a relatively high rates at ambient temperatures. Enhanced
CO.sub.2 cyclic removal capacities in either dry or humid air flows
can further be achieved by using a solid sorbent at an increased
amine concentration of amines from about 35 wt % to about 75 wt
%.
[0153] Solid sorbents that can selectively remove multiple gases
can be used to remove CO.sub.2, H.sub.2O, nitrogen oxides, and
hydrocarbons. This can be achieved by using composite adsorbents,
for example by using a mixed adsorbent of alumina and zeolite to
remove CO.sub.2 and H.sub.2O simultaneously.
[0154] CO.sub.2 can be separated from flue gas using an ion pump
method instead of relying on large temperature and pressure changes
to remove CO.sub.2 from a solvent. Ion pump methods can
dramatically increase the overlying vapor pressure of CO.sub.2. As
a result, the CO.sub.2 can be removed from the downstream side of
the ion pump as a pure gas. The ion pumping can be obtained from
techniques including but not limited to reverse osmosis, electro
dialysis, thermal desalination methods, or an ion pump system
having an oscillation flow in synchronization with an induced
electric field.
[0155] By making use of energy such as renewable or nuclear energy,
carbon dioxide and water can be recycled into sustainable
hydrocarbon fuels in a non-biological process. Various pathways can
enable such a conversion, for example by H.sub.2O and CO.sub.2
dissociation followed by fuel synthesis. The methods of
dissociation can include heat, electricity, and solar driven
methods such as thermolysis, thermochemical loops, electrolysis,
and photoelectrolysis. High temperature electrolysis can make
efficient use of electricity and heat, provide high reaction rates,
and integrate well with fuel synthesis.
[0156] Synthetic analogues of enzymes as a polymer thin film
supported on micro-porous substrates can be used to separate
CO.sub.2 from gas mixtures. For example, a polymer thin film
containing carbonic anhydrase mimicking sites can supported on a
porous substrate and can separate CO.sub.2 from a stream containing
O.sub.2 and N.sub.2. The system can be, for example, about 30%
lower in cost compared to amine-based systems.
CO.sub.2 Anti-Sublimation
[0157] Carbon capture (e.g., CO.sub.2 capture) can be used to
reduce greenhouse gas (GHG) emissions. For example, carbon can be
captured from stationary fired sources (e.g., flue gas emissions
from fired equipment in power plants and industry). CO.sub.2
capture technologies may be cost prohibitive. The cost of disposing
CO.sub.2 can be divided into: separation (for example, the cost
range for CO.sub.2 separation from flue gas using amine absorption
is $30-$50 per ton of CO.sub.2); compression (for example, CO.sub.2
is compressed typically to 2000 psi for pipeline delivery and
compression costs can range from $8-$10 per ton of CO.sub.2);
pipelines (for example, CO.sub.2 pipelining costs can range from
$0.7 to $4 per ton CO.sub.2 per 100 km); and injection (for
example, compressed CO.sub.2 injection to geological reservoirs on
land can cost from $2-$8 per ton CO.sub.2.
[0158] The separation of process CO.sub.2 from the OCM process can
be simpler and less expensive than a CO.sub.2 capture from a flue
gas system. Flue gas CO.sub.2 capture may have inherent challenges,
which are absent from the OCM system CO.sub.2: low pressure (for
example, the typical flue gas pressures are at or about atmospheric
pressure, and therefore involve high volumes that can need to be
compressed and treated, resulting in bigger and hence more
expensive equipment); high temperature (for example, flue gases can
exit a furnace or heater at a high temperature); oxygen content
(for example, oxygen can cause corrosion problems); NOx and fly ash
content (for example, this can cause degradation in certain
systems); and CO.sub.2 concentration (for example, in flue gases
CO.sub.2 concentration can range from 10%-15%; in OCM CO.sub.2
concentrations can be 95% and higher post amine system or 4-6% at
OCM outlet).
[0159] To integrate well with OCM, a CO.sub.2 separation process
can be: less energy and capital intensive than current designs
(e.g., amine system); scalable downwards and upwards; capable of
reliable and continuous operation; able to take advantage of high
CO.sub.2 concentrations and convert to high purity CO.sub.2, which
can be used as a feedstock for other operations.
[0160] CO.sub.2 anti-sublimation can be used to remove CO.sub.2
(e.g., from flue gas). CO.sub.2 anti-sublimation can use an
SO.sub.2 removal unit followed by a water cooling step. The water
can be eventually removed, for example first as liquid then below
the triple point as ice. Dry flue gas can be further cooled until
CO.sub.2 precipitates. The process can employ anti-sublimating
CO.sub.2 on a low temperature surface, thus transforming the carbon
dioxide from its gaseous phase to a solid phase frosted on a cold
surface. Anti-sublimation can allow CO.sub.2 capture at a pressure
slightly higher than atmospheric. CO.sub.2 anti-sublimation can be
used with a flue gas system (flue gas composition, e.g., in mol %:
CO.sub.2 15%, H.sub.2O 13%, N.sub.2 70% and O.sub.2 3%) at various
temperatures (e.g., about 51.degree. C.).
[0161] The triple point of CO.sub.2 is -56.4.degree. C. and 5.11
atm. For 100% pure CO.sub.2 at a pressure P' (where P' is less than
5.11 atm) the frosting temperature can be given by
T'=(P'-15.6)*(22.1/4.11). Accordingly, for a pressure of 4.5 atm,
T=-59.6.degree. C.
[0162] The sublimation temperature of a substance within a gas
mixture can depend on its partial pressure (its corresponding
concentration within the mixture). Table 1 shows frosting
temperatures at different exemplary CO.sub.2 concentrations.
TABLE-US-00001 TABLE 1 Frosting temperature versus concentration.
Concentration (% v/v) 100 10 1 0.1 Frosting temperature (.degree.
C.) -78.5 -103.1 -121.9 -136.7
[0163] For use in an OCM process, a CO.sub.2 anti-sublimation unit
may encounter higher pressure of OCM effluent (e.g., feed to
CO.sub.2 capture system), lower CO.sub.2 concentration, and higher
hydrocarbon content (e.g., methane, ethane, ethylene). Lower
CO.sub.2 concentration can be addressed by a recycle.
Process Configurations
Electrolysis to Generate Oxygen and Hydrogen for OCM Process
[0164] Electrolysis can be used to produce industrial hydrogen. OCM
processes can have a lot of synergistic benefit from deploying a
water electrolysis subsystem with the OCM process. The water
electrolysis unit can replace an air separation unit (ASU) to
supply the oxygen required for the OCM process. The products from
the electrolytic unit can be consumed within the OCM process:
oxygen can be consumed within the OCM reactor and hydrogen can be
used in a methanation reactor. Availability of more hydrogen in the
methanation unit has the potential to increase the carbon
efficiency to about 100%, by converting the CO.sub.2 produced in
the OCM reaction to methane, which can be recycled back to the OCM
reactor. The OCM unit can be a net exporter of high purity excess
hydrogen, after consuming the entirety of the CO.sub.2 produced in
the OCM Process.
[0165] The water electrolysis subsystem can be an electrolytic cell
employing alkaline water electrolysis, a proton exchange membrane
electrolysis system, or a steam electrolysis system. The
electricity source to the electrolytic sub system can be renewable,
such as photo voltaic/solar power, which can make the entire system
100% carbon efficient with a zero carbon footprint. A storage
system for oxygen, or a backup power supply, may be used to ensure
the continuous supply of oxygen and hydrogen.
[0166] With steam electrolysis, a substantial part of the energy
needed for the electrolysis process can be added as heat, which can
be much cheaper than electric energy, and which the OCM reactor can
produce in abundance. Therefore, integration of steam electrolysis
can take advantage of the extra heat from the OCM reactor to
provide energy for the steam electrolysis. This can be of
particular benefit to OCM deployments where no additional steam or
power is required.
[0167] FIG. 7 depicts an exemplary electrolysis subsystem combined
with an OCM system. The electrolysis subsystem 701 can take water
710 and electric power 711 as inputs and generate pure oxygen 712
and hydrogen 713 as products. The oxygen can be fed into an OCM
reactor 702 with a methane feed 714, for conversion to higher
hydrocarbon products including ethylene. The OCM product stream can
be compressed in a compressor 704 and separated in a separations
unit 705. Higher hydrocarbon products 716 can be recovered from the
separations unit, and other compounds such as methane and CO.sub.2
can be recycled 717 and/or purged 718. The recycle stream can be
directed to a methanation unit 703, which can generate methane 715
using the hydrogen from the electrolysis subsystem. The extra
hydrogen that is now available to the methanation unit can enable
the conversion of most or all of the CO.sub.2 produced in the OCM
process to methane, which can drive the process to a higher
efficiency. The process can also be almost 100% emission free. The
CO.sub.2 produced in the process that may be discarded as waste may
be converted to methane and hence to ethylene in the OCM
reactor.
Different Quench Media for the OCM Reaction
[0168] The OCM reaction is highly exothermic. Various quenching
media can be used to extract the OCM reaction heat. For example,
CO.sub.2 can be injected to extract the heat, which results in the
OCM effluent containing excess CO.sub.2, such effluent can be
suitable for the advanced CO.sub.2 recovery methods described
herein. FIG. 8 shows an exemplary system where CO.sub.2 814 is
removed from an OCM product stream 812 (generated in an OCM unit
801 from an oxygen stream 810 and a methane stream 811) in a
CO.sub.2 separation unit 802 and recycled from back to the OCM
reactor 801. A waste gas or purge stream 815 can also be removed
from the CO.sub.2 separation unit. The OCM product stream 813 can
then be separated in a separations unit 803 into a product stream
816 comprising ethylene and a purge and/or recycle stream 817.
Separation methods can include low temperature separation, membrane
separation, or other separation methods discussed herein. The OCM
loop can be decreased to just a CO.sub.2 recycle stream. The system
can also comprise a methanation unit (not shown).
[0169] Such an approach can provide advantages including a smaller
recycle loop and more efficient CO.sub.2 removal methods, resulting
in lower capital expenditure (CAPEX). This can also result in the
feasibility of small distributed scale OCM units, since after the
removal of excess CO.sub.2, the relatively richer ethylene stream
needs fewer treatment and recovery steps.
Heat Recovery
[0170] Waste heat from the OCM process can be used to generate
superheated high pressure steam that can be used in the process,
exported to other users on site, or can be used to generate power.
Excess process heat can also be used to preheat the feed streams.
Other uses for excess heat can be less capital intensive, and offer
a greater operational flexibility and low maintenance.
Thermoelectric energy conversion can be used to convert waste heat
to power. Example uses for waste heat include single fluid rankine
cycles (e.g., steam cycle, hydrocarbons, and ammonia), binary/mixed
fluid cycles (e.g., ammonia/water or mixed hydrocarbon cycle).
Organic Rankine Cycle
[0171] The organic Rankine cycle (ORC) can be used to generate
power from heat. In ORC, an organic component is used instead of
water. The organic compound can be a refrigerant, a hydrocarbon
(e.g., butane, pentane, hexane), silicon oil, or a perfluorocarbon.
The boiling point of the organic fluid can be lower than that of
water, which can allow recovering heat at a lower temperature than
in the traditional steam Rankine cycle.
[0172] Owing to the exothermicity of the OCM reaction, the ORC
system can be deployed as a waste heat recovery method for use with
OCM. Waste heat at relatively low temperature can be recovered by
an intermediate heat transfer loop and used to evaporate the
working fluid of the ORC.
[0173] FIG. 9 shows an exemplary OCM system with an ORC subsystem.
The working fluid can be chosen which can be condensed with cooling
water or air at normal atmospheric pressure. FIG. 9 shows the heat
source as the OCM reaction heat from an OCM unit 901. Heat can be
recovered from the OCM product stream 910 in an evaporator 902, and
the product stream 911 can then be directed for downstream
processing from the OCM unit. The heat recovered in the evaporator
can be used to evaporate a working fluid stream 912, which can then
be directed to a turbine 903 to generate power in a generator 904.
From the turbine, the working fluid 913 can be directed to a
condenser 905 and cooled using a cooling medium 914. The cooled
working fluid 915 can then be pumped by a pump 906 in a stream 916
back to the evaporator.
Thermoelectric Power Generation
[0174] The OCM process can make use of a heat exchanger with
thermoelectric (TE) generators for heat recovery. A Thermoelectric
Power Generator (TPG) can have four basic components: Heat source,
P and N type semiconductor stack (or a TE module), heat sink (cold
side), and an electrical load (output voltage). The TE module can
include two or more of P-type and N-type semiconductor pellets
connected in series or parallel depending on the served load.
[0175] The TE devices can be solid state engines that do not
require any working fluid. Thermoelectric materials can provide
efficiencies of up to 15% or greater. Thermoelectric generators
coupled with heat exchangers can produce electricity even at
temperatures as low as 350 K with low maintenance. TE modules can
be used with OCM including large bulk TE modules and thin film or
micro TE modules.
[0176] For high temperatures, micro TE modules can be used. Micro
TE modules can also have low equipment weights. TE devices can be
very reliable, scalable, and modular. Some TE modules can give best
results at small scales. The OCM process can generate medium level
waste heat that is highly suitable for a TE device to generate
power.
OCM and ETL Systems with Advanced Separations Sub-Systems
[0177] PSA technology can be applied to processes including those
involving a hydrocarbon stream containing a mix of the following
hydrogen, carbon dioxide, carbon monoxide, methane, ethane,
ethylene, propane, propylene, butanes, butenes and/or other higher
hydrocarbons needing to be purified or separated into desirable
products (e.g., ethylene, methane, hydrogen, or propylene).
[0178] Hydrocarbon streams can be produced via traditional refining
and petrochemical processes. Hydrocarbon streams can be produced
from OCM or ETL reactor systems.
[0179] The present disclosure provides the use of PSA in processes
and systems for oxidative coupling of methane (OCM) and
ethylene-to-liquids (ETL) operations, and the application of
adsorbent based processes used in conjunction with OCM and ETL
processes to generate significant process improvements and enhance
the economic value of the processes. OCM systems are described in,
for example, U.S. Patent Publication No. US 2015/0210610, which is
entirely incorporated herein by reference. ETL systems are
described in, for example, U.S. Patent Publication No.
2015/0232395, which is entirely incorporated herein by
reference.
[0180] An OCM system, such as that shown in FIG. 10, can include an
OCM or OCM-post-bed-cracking (PBC) reactor 1002, a process gas
compression system 1003, a process gas treatment system 1004, a
cryogenic separations system, and a methanation system 1001. The
feed to the OCM system can be an oxygen feed 1012 and a methane
source feed 1011 (such as a natural gas feed stream or other
methane source). In some cases, additional ethane feed can be
supplied to the PBC section of the OCM reactor, where paraffins
such as ethane in the OCM product stream and/or additional ethane
can be cracked to olefins such as ethylene. The separations
sub-system can comprise a series of fractionation towers, like a
demethanizer 1005, deethanizer 1006, C.sub.2 splitter 1007,
depropanizer 1008, debutanizer, and others. Overhead 1013 from the
demethanizer can be directed into the methanation system along with
hydrogen or natural gas 1010 to produce additional methane. The
bottoms stream 1014 from the demethanizer can be directed to the
deethanizer. The overhead stream 1015 from the deethanizer can be
directed to the C.sub.2 splitter, and there split into ethylene
1016 and ethane 1017 streams. The bottoms stream 1018 from the
deethanizer can be directed to the depropanizer, and there split
into a C.sub.3 product stream 1019 and a C.sub.4+ product stream
1020. The cryogenic separations system can comprise additional
ethylene and propylene refrigeration sub-systems to provide for the
chilling requirements of the system.
OCM Process Standalone with Advanced Separations Systems
[0181] In certain cases, the separations section of the OCM system
can be eliminated, or partially eliminated, by utilizing an
advanced separations method as discussed in this application. The
advanced separation method can be a PSA unit or a membrane based
method, or a cryogenic system. FIG. 11 shows an exemplary schematic
of OCM with a PSA unit. The PSA unit can separate methane,
CO.sub.2, CO, and/or H.sub.2 from ethane, ethylene, propane,
propylene, and/or higher hydrocarbons. Methane 1111 and oxygen 1112
can be directed into an OCM reactor 1102 and reacted to produce
higher hydrocarbon products including ethylene. The OCM product can
be compressed in a process gas compression system 1103, treated in
a process gas treatment system 1104, and separated in the PSA 1105
into a product stream 1113 and a recycle stream 1114. The recycle
stream can be directed to a methanation unit 1101, which can also
receive a natural gas stream 1110 and produce methane for the OCM
reactor. The extent of separation and degree of recovery can depend
on the type of adsorbent(s), pressure differential, and number of
PSA stages employed. The feed to the PSA unit can have one or more
of the following components: H.sub.2, N.sub.2, O.sub.2, CO,
CO.sub.2, CH.sub.4, ethane, ethylene, acetylene, propane,
propylene, butanes, butenes, butadiene, water, and higher
paraffinic and olefinic components. The PSA product gas can
comprise components including but not limited to: H.sub.2, N.sub.2,
CO, CO.sub.2, CH.sub.4, O.sub.2, ethane, ethylene and acetylene.
PSA product gas can comprise components from about 0% to about
99.99% recovery. The PSA tail gas can comprise less than or equal
to about 99.99%, 90%, 80%, 70%, 60%, 50% or less ethylene. The PSA
tail gas can comprise at least or equal to about 50%, 60%, 70%,
80%, 90%, 99.99% or more ethylene. The PSA tail gas can comprise
about less than or equal to about 99%, 90%, 80%, 70%, 60%, 50%,
40%, 30%, 20%, 10%, 1% or less ethane. The PSA tail gas can
comprise at least about 0.1%, 1%, 10%, 20%, 30%, 40%, 50%, 60%,
70%, 80%, 90%, 99% or more ethane. The PSA tail gas can comprise
about less than or equal to about 60%, 50%, 40%, 30%, 20%, 10%, 1%
or less methane, hydrogen, acetylene, N.sub.2, O.sub.2, H.sub.2O
and/or CO.sub.2. The PSA tail gas can comprise at least about 0.1%,
1%, 10%, 20%, 30%, 40%, 50%, 60% methane, hydrogen, acetylene,
N.sub.2, O.sub.2, H.sub.2O and/or CO.sub.2. Based on the process
configuration, including the type of adsorbents employed, pressure
differential and the operation, various different recoveries are
possible.
[0182] As discussed above, the PSA unit can comprise one or more
adsorbent materials that can be suitable to achieve the component
recoveries. The sorbent can be a zeolite/molecular sieve based
material, a carbon based sorbent, or a .pi.-complexation sorbent.
In some cases the sorbent material can be a polymeric resin, carbon
nanotubes, and carbon fibers. The PSA unit can be configured to
have layers of different sorbents so as to result in high
recoveries from the multi-component feed streams to the desired
products.
[0183] In certain cases the PSA can be a multi stage unit (see,
e.g., FIG. 12). In such a unit, an OCM reactor 1202 can receive a
methane stream 1211 and an oxygen stream 1212, and react the
methane and oxygen to produce higher hydrocarbon products including
ethylene in an OCM product stream. The OCM product stream can be
compressed in a first compressor 1203 and directed to a first PSA
separation 1204. The tail gas 1214 from the first PSA can be
compressed in a second compressor 1205 and fed to a second PSA
separation 1206, the tail gas 1216 from which can be compressed in
a third compressor 1207 and separated in a third PSA separation
1208. The tail gas from the third PSA can be the final purified
stream 1217 containing ethylene up to 99.9% purity. PSA product
streams 1213, 1215, and 1218 can be directed to recycle, such as
via a methanation unit 1201 along with a natural gas stream 1210.
Each PSA stage can be a dual-bed PSA or a multi-bed PSA system.
[0184] In certain cases, the process requirements can dictate that
only a limited amount of recovery is required in the PSA unit and
subsequent recovery and purification is performed in a
fractionation column or the gas is a feed for a downstream process
unit. The downstream process unit can be an ETL system, an ethylene
steam cracker system, a gas processing plant, NGL extraction plant,
a refinery off-gas separations system, or other process unit.
Retrofits for OCM
[0185] OCM can be employed to convert a feedstock comprising
methane to ethylene and other olefins. Historically, ethylene has
been produced via steam cracking of gaseous or liquid hydrocarbon
feedstocks like ethane, propane, LPG, or naphtha. As in most of the
refining and petrochemical operations, a steam cracking operation
can involve a cryogenic fractionation or a separations section that
consists of a series of fractionation columns to successively
recover various components at high product purity.
[0186] The present disclosure includes the application of PSA
processes to an OCM retrofit of an existing ethylene cracker (e.g.,
steam cracker).
[0187] An example application for OCM combined with a PSA unit
involves an existing petrochemical plant such as a steam cracker is
considering low cost ways to add ethylene capacity. A typical
revamp to add capacity may include addition of, or debottlenecking
of, the existing fractionation towers for the entire flow addition
for the revamp. However, as shown in FIG. 13, the use of a PSA unit
as disclosed herein can provide a low cost alternative to
traditional revamps. An OCM unit with a PSA unit retrofitted to an
existing steam cracker can be an effective way of adding ethylene
capacity at a low marginal cost. The advantages of adding a PSA
unit include that no additional cryogenic separation is required
for the added capacity. For ethylene revamps, one of the key areas
during debottlenecking may be the refrigeration systems and/or the
fractionation columns, but utilizing the PSA to separate or
pre-separate the additional product stream can result in a simpler
and easier debottlenecking. As in shown in FIG. 13, for example,
the tail gas from the PSA can be sent to the cracker system where
the ethylene is recovered.
[0188] FIG. 13 shows an example of an OCM process integrated with
an existing ethylene cracker using a PSA system for separations.
The OCM reactor 1301 takes in methane 1310 and oxygen 1311 and
produces an OCM effluent 1312 having CO.sub.2, CH.sub.4 and
C.sub.2H.sub.4, in some cases amongst other components, such as
H.sub.2 and CO. The OCM reaction can be exothermic and can produce
steam 1313. The OCM effluent can be compressed in a compressor 1302
and optionally treated in an acid gas removal system 1303, and fed
into a pressure swing adsorption (PSA) unit 1304. In some cases the
acid gas removal system may have an additional knock out drum to
condense and separate any condensates and water. It also can
include a drier to remove water. The PSA unit can produce a product
stream that can include H.sub.2, CH.sub.4, ethane, CO.sub.2 and CO.
The overhead stream 1315 can be fed into a methanation subsystem
1305 (e.g., methanation reactor) to provide methane for the OCM
reactor, and some of the overhead stream can be purged 1316 to a
fuel gas system, for example. Additional methane can be provided by
way of a natural gas stream or other methane stream. The PSA tail
gas 1317 can comprise most of the ethylene, the content of which
may range from about 50% to about 99.9% depending on the process
configuration and operation of the PSA system. The PSA tail gas can
also comprise H.sub.2, CO, CO.sub.2, CH.sub.4, ethane, propane,
propylene, butanes, butenes, and other components. The process of
FIG. 13 can further include an existing ethylene cracker 1306. The
PSA tail gas can be fractionated using existing separations
capacity in the ethylene cracker. The heavy components can be
processed in the fractionation towers of the ethylene cracker,
optionally first being compressed in the existing process gas
compressor of the ethylene cracker. In some cases, the heavy
components stream can be routed to the CO.sub.2 removal unit of the
existing ethylene cracker subsystem to meet the CO.sub.2
specification. The OCM reactor can receive a C.sub.2 recycle stream
1319 from the cracker complex.
[0189] The combination of a new OCM unit and an existing ethylene
cracker can provide synergistic benefits. It can provide for a low
cost alternative to add ethylene capacity to the existing cracker.
In some cases, prior to retrofit of an ethylene cracker with OCM,
the entire overhead from the existing demethanizer is used as fuel
gas, and can now be available as one of the feeds to the
methanation unit. In some cases, the demethanizer overhead off-gas
comprises up to 95% methane, which can be converted to ethylene in
the OCM reactor, hence increasing the total ethylene capacity. In
some cases, the hydrogen content in the existing demethanizer
overhead is substantial, and may be enough to meet the hydrogen
requirement of the methanation unit.
[0190] In some cases, retrofitting an ethylene cracker with OCM
reduces (or allows for reduction of) the severity of cracking in
the existing cracker, enabling value addition by increasing the
production of pyrolysis gasoline components in the cracker
effluent, as the OCM reactor produces the ethylene that may be
needed to achieve the total system capacity. The cracker can then
be operated on high propylene mode to produce more propylene and at
the same time meeting the ethylene production rate by the new OCM
unit. This retrofit can result in greater flexibility for the
ethylene producer with respect to the existing cracker
operation.
[0191] In some instances, the overall carbon efficiency can be
increased as the methane and hydrogen from the existing
demethanizer off-gases can be utilized to convert the carbon
dioxide and carbon monoxide to methane, which is fed to the OCM
reactor.
[0192] In some instances, ethane and/or propane recycle streams
from the existing cracker can be routed to the OCM unit (e.g.,
instead of the cracking furnaces). These recycle streams are
typically routed to the cracking furnaces where they are cracked to
extinction. This can provide an advantage over routing the recycle
streams to OCM over the cracking furnace, such as higher
selectivity to ethylene in the OCM process.
[0193] In certain cases, more than one stages or PSA columns may be
employed to achieve higher recovery and higher product purity. As
in shown FIG. 14, for example, up to 99.9% recovery is possible
using the multi stage PSA units. An OCM reactor 1402 can receive a
methane stream 1410 and an oxygen stream 1411, and react the
methane and oxygen to produce higher hydrocarbon products including
ethylene in an OCM product stream. The OCM product stream can be
compressed in a first compressor 1403 and directed to a first PSA
separation 1404. The tail gas 1412 from the first PSA can be
compressed in a second compressor 1405 and fed to a second PSA
separation 1406, the tail gas 1414 from which can be compressed in
a third compressor 1407 and separated in a third PSA separation
1408. The tail gas from the third PSA can be the final purified
stream 1417 can be directed to a cracker unit, such as an existing
cracker unit, where it can be processed and separated into an
ethylene product stream 1418, a propylene product stream 1419, and
an additional product stream 1420. PSA product streams 1413, 1415,
and 1416 can be directed to recycle, such as via a methanation unit
1401, along with a demethanizer off gas stream 1421 from the
cracker unit. Each PSA stage can be a dual-bed PSA or a multi-bed
PSA system.
[0194] The application of a PSA unit to OCM systems, standalone or
retrofits to existing facilities exhibits immense potential in
terms of cost savings and ease of integration and retrofit to
existing facilities.
ETL Systems
[0195] FIG. 15 shows various exemplary configurations for an
OCM-ETL process. In the upper left, FIG. 15 shows a standalone
skimmer configuration, where a methane stream 1505 can be directed
into an OCM reactor 1501 with an oxygen feed 1506 and optionally an
ethane feed 1507. The OCM reactor product stream can be directed
into a compressor 1502 and then into an ETL reactor 1503. The ETL
product stream can be directed into a gas separations unit 1504,
where it can be separated into a C.sub.2+ product stream 1508, a
C.sub.5+ product stream 1509, and an overhead stream 1510
comprising methane which can be returned to a pipeline, sold to a
consumer, or otherwise used. In the upper right, FIG. 15 shows a
standalone recycle configuration, where a methane feed stream 1518
(e.g., from a natural gas pipeline) is directed into a treatment
unit 1511 and then into a separations system (e.g., cryogenic)
1512. A methane feed stream 1519 can be directed to an OCM reactor
1513, while another methane stream 1520 can be purged or used for
power generation. A C.sub.2+ stream 1521 can also be recovered from
the separations system. An oxygen feed stream 1522 and optionally
an ethane stream 1523 can also be directed into the OCM reactor,
and the reactor can produce an OCM product stream. The OCM product
stream can be directed into a compressor 1514 and then into an ETL
reactor 1515. The ETL product stream can be processed in a knockout
drum 1516 or other separator to remove a C.sub.5+ product stream
1524. The remaining ETL product stream can be directed to a
compressor 1517 and recycled to the treatment unit. In the lower
left, FIG. 15 shows a hosted skimmer configuration, where a methane
stream 1532 can be directed from a separations system 1526 (e.g.,
cryogenic) into an OCM reactor 1527 with an oxygen feed 1533 and
optionally an ethane feed 1534. The OCM reactor product stream can
be directed into a compressor 1528 and then into an ETL reactor
1529. The ETL product stream can be directed into a gas separations
unit 1530, where it can be separated into a C.sub.2+ product stream
1535, a C.sub.5+ product stream 1536, and an overhead stream 1537
comprising methane which can be returned to a recompressor 1531. In
the lower right, FIG. 15 shows a hosted recycle configuration,
where a methane stream is directed into a treatment unit 1538 and
then into a separations system (e.g., cryogenic) 1539. A methane
feed stream 1546 can be directed to an OCM reactor 1541, while
another methane stream can be directed to a recompressor 1540. A
C.sub.2+ stream 1551 can also be recovered from the separations
system. An oxygen feed stream 1547 and optionally an ethane stream
1548 can also be directed into the OCM reactor, and the reactor can
produce an OCM product stream. The OCM product stream can be
directed into a compressor 1542 and then into an ETL reactor 1543.
The ETL product stream can be processed in a knockout drum 1544 or
other separator to remove a C.sub.5+ product stream 1549. The
remaining ETL product stream can be directed to a compressor 1545
and recycled 1550 to the treatment unit.
[0196] FIG. 16 shows similar configurations as FIG. 15, with an
added pressure swing adsorption (PSA) unit to pre-separate the OCM
effluent to remove most of the methane, hydrogen, CO and CO.sub.2
from the olefinic stream, which is then fed to the ETL reactor.
This can result in a feed to the ETL reactor that is concentrated
in olefins. Though the process remains similar, the entire ETL and
separations train becomes considerably smaller; that is, larger
capacities can be achieved in the same set-up or same footprint. In
some cases this can improve the ETL reaction operation. In the
upper left, FIG. 16 shows a standalone skimmer configuration, where
a methane stream 1606 can be directed into an OCM reactor 1601 with
an oxygen feed 1607 and optionally an ethane feed 1608. The OCM
reactor product stream can be directed into a compressor 1602 and
then into a PSA unit 1603. A light stream 1609 comprising methane,
hydrogen, CO and CO.sub.2 can be directed from the PSA back to a
pipeline, sold to a consumer, or otherwise used. An olefinic stream
can be directed from the PSA to an ETL reactor 1604. The ETL
product stream can be directed into a gas separations unit 1605,
where it can be separated into a C.sub.2+ product stream 1610, a
C.sub.5+ product stream 1611, and an overhead stream 1612
comprising methane which can be returned to a pipeline, sold to a
consumer, or otherwise used. In the upper right, FIG. 16 shows a
standalone recycle configuration, where a methane feed stream 1628
(e.g., from a natural gas pipeline) is directed into a treatment
unit 1620 and then into a separations system (e.g., cryogenic)
1621. A methane feed stream 1629 can be directed to an OCM reactor
1622, while another methane stream 1630 can be purged or used for
power generation. A C.sub.2+ stream 1631 can also be recovered from
the separations system. An oxygen feed stream 1632 and optionally
an ethane stream 1633 can also be directed into the OCM reactor,
and the reactor can produce an OCM product stream. The OCM product
stream can be directed into a compressor 1623, and at least a
portion 1634 of the OCM product stream can be directed from the
compressor into a PSA unit 1624. A light stream 1635 comprising
methane, hydrogen, CO and CO.sub.2 can be directed from the PSA
back to the treatment unit. An olefinic stream 1636 can be directed
from the PSA to an ETL reactor 1625. The ETL product stream can be
processed in a knockout drum 1626 or other separator to remove a
C.sub.5+ product stream 1637. The remaining ETL product stream can
be directed to a compressor 1627 and recycled to the treatment
unit. In the lower left, FIG. 16 shows a hosted skimmer
configuration, where a methane stream 1647 can be directed from a
separations system 1640 (e.g., cryogenic) into an OCM reactor 1641
with an oxygen feed 1648 and optionally an ethane feed 1649. The
OCM reactor product stream can be directed into a compressor 1642
and then into and then into a PSA unit 1643. A light stream 1650
comprising methane, hydrogen, CO and CO.sub.2 can be directed from
the PSA to a recompressor 1646. An olefinic stream can be directed
from the PSA to an ETL reactor 1644. The ETL product stream can be
directed into a gas separations unit 1645, where it can be
separated into a C.sub.2+ product stream 1651, a C.sub.5+ product
stream 1652, and an overhead stream 1653 comprising methane which
can be returned to the recompressor. In the lower right, FIG. 16
shows a hosted recycle configuration, where a methane stream is
directed into a treatment unit 1660 and then into a separations
system (e.g., cryogenic) 1661. A methane feed stream 1669 can be
directed to an OCM reactor 1663, while another methane stream can
be directed to a recompressor 1662. A C.sub.2+ stream 1677 can also
be recovered from the separations system. An oxygen feed stream
1670 and optionally an ethane stream 1671 can also be directed into
the OCM reactor, and the reactor can produce an OCM product stream.
The OCM product stream can be directed into a compressor 1664 and
at least a portion 1672 of the OCM product stream can be directed
from the compressor into a PSA unit 1665. A light stream 1673
comprising methane, hydrogen, CO and CO.sub.2 can be directed from
the PSA back to the treatment unit. An olefinic stream 1674 can be
directed from the PSA to an ETL reactor 1666. The ETL product
stream can be processed in a knockout drum 1667 or other separator
to remove a C.sub.5+ product stream 1675. The remaining ETL product
stream can be directed to a compressor 1668 and recycled 1676 to
the treatment unit.
[0197] The ETL reactor can be a tubular, packed bed, moving bed,
fluidized bed, or other reactor type. An ETL reactor can be an
isothermal or adiabatic reactor. The ETL system can benefit from a
feed concentrated in olefins. The ETL reactor system can use a
recycle stream to control and moderate the temperature increase in
the reactor bed due to the highly exothermic nature of the ETL
reactions. ETL systems are described in, for example, U.S. Patent
Publication No. 2015/0232395, which is entirely incorporated herein
by reference.
[0198] In some cases, one or more of the fractionation towers can
be deemed redundant if using the PSA, as an example, a demethanizer
may not be required and the sales gas or purge gas to fuel can be
sent from the PSA itself.
Retrofit Applications for Midstream and Refining
[0199] Systems, such as those of FIG. 17, can be integrated with an
existing gas processing plant where one or more of the existing
subsystems can be utilized. The utilization may arise from the fact
that the existing subsystems are no longer used, or have an
additional capacity available to allow for the integration.
[0200] FIG. 17 shows an exemplary application of an OCM-ETL system
using a PSA system for pre-separations to an existing gas
processing plant, where one or more existing sub systems may be
utilized. As shown in FIG. 17, the existing separations sub-system
can be integrated with the OCM-ETL system to add value by
converting natural gas to higher value liquid hydrocarbons. The PSA
unit can be used to pre-separate the lighter components like
methane, hydrogen, carbon monoxide, carbon dioxide, ethane, and
other components, and the olefin rich stream can be sent to the ETL
reactor that converts the olefins to higher molecular weight liquid
hydrocarbons. One advantage of using a PSA system is the reduction
in net additional feed to the existing separation system, which can
be de-bottlenecked easily. If the separation system is no longer in
use, addition of a PSA can bring about larger total capacities that
can be achieved by adding larger OCM-ETL systems. A natural gas
stream 1720 can be directed to a treatment unit 1701 and then into
a separations system (e.g., cryogenic) 1702. At least portion of a
methane stream 1724 from the separations unit can be directed to an
OCM reactor 1705, while a portion of the methane stream can be
directed to a compressor 1703 and used as sales gas 1721 or other
purposes. A higher hydrocarbon stream can be directed from the
separations system to a C.sub.2 removal unit 1704, which can
produce a natural gas liquids stream 1722 and a C.sub.2 stream
1723. The C.sub.2 stream can be fed into the OCM reactor with the
methane stream and an oxygen stream 1725, and reacted to form
higher hydrocarbon products including ethylene. The OCM product
stream can be directed into a heat recovery system 1706, which can
generate a high pressure superheated (HPSH) steam stream 1726. The
OCM product stream can then be directed to a knockout drum to
recover a condensate stream 1727. The OCM product stream can then
be directed to a compressor 1708, which can operate using the HPSH
steam stream. From the compressor, the OCM product stream can be
directed to a PSA unit 1709. From the PSA unit, light stream
comprising methane, hydrogen, CO and CO.sub.2 can be directed to a
methanation unit 1710, and an olefinic stream can be directed to an
ETL reactor 1711 and reacted to form higher hydrocarbon products.
The ETL product stream can be directed to a heat recovery unit
1712, where boiler feed water (BFW) 1728 can be heated, at least a
portion of which can be fed 1729 to the heat recovery unit 1706.
The ETL product stream can then be directed to another knockout
drum 1713. The overhead stream from the knockout drum can be
directed to a low temperature separations unit 1714, while the
bottoms stream from the knockout drum can be directed to a C.sub.4
removal unit 1715, which can produce a C.sub.4 stream 1730 and a
C.sub.5+ stream 1731. Overhead from the low temperature separations
unit, as well as product from the methanation reactor, can be
directed back to the compressor 1703.
[0201] OCM-ETL systems of the present disclosure can be integrated
into and combined into conventional NGL extraction and NGL
fractionation sections of a midstream gas plant. Where NGLs in the
gas stream are declining (or gas is dry), the deployment of OCM-ETL
can utilize an existing facility to produce additional liquid
streams. The implementation of OCM-ETL can allow for the generation
of on specification "pipeline gas." The products from the facility
can be suitable for use (or on specification or "spec") as pipeline
gas, gasoline product, hydrocarbon (HC) streams with high aromatic
content, and mixed C.sub.4 products. The PSA systems discussed
above can be employed to separate, pre-separate or purify the
hydrocarbon feed streams in the integrated NGL OCM-ETL system. FIG.
18 shows an exemplary NGL extraction facility integrated with an
OCM-ETL system. As shown in FIG. 18, for example, the feed to the
PSA 1802 can be the net incoming gas from the treatment system
1801, which can treat a methane stream (e.g., natural gas) 1810.
The PSA system can separate the feed to the OCM reactor 1803, which
is mostly methane and lighter components with some ethane to
utilize a PBC section of the OCM reactor, and the feed to the ETL
reactor 1805, which can first be processed in a natural gas liquids
extraction system 1804. The feed to the ETL system can be the PSA
tail gas and OCM effluent comprising ethylene, propylene, ethane,
propane, hydrogen, methane, and other components. In some cases,
the OCM effluent can be directly fed to the ETL reactor. In some
cases the OCM effluent is hydrogenated and fed to the ETL system.
In some cases, as shown for example in FIG. 18, the OCM effluent is
fed back to the PSA unit for separation; additional natural gas
1811 can be added, and a stream can be recovered 1812 (e.g., for
use as pipeline gas). In some examples, the system may have a
methanation unit that takes in the effluent from ETL reactor or OCM
reactor and converts the CO, CO.sub.2 and H.sub.2 to methane,
thereby further increasing the carbon efficiency of the process.
The existing NGL extraction and product fractionation 1806
sub-systems can then be used to fractionate the final products,
including into a mixed C.sub.4 stream 1814 and a C.sub.5+ product
stream 1815.
Refining
[0202] Refinery gas typically contains valuable components like
hydrogen, methane, ethane, ethylene, propane, propylene, and
butane. Most commonly, refinery off-gases (ROG) are exported to the
fuel gas system, thereby losing the value of the components
contained therein. The OCM-ETL process can be used to improve the
value of products as the OCM converts the methane to ethylene and
the ETL converts olefins (e.g., those existing in the ROG and those
generated by OCM) to higher value liquids as C.sub.4 components,
gasoline blends, or aromatic components.
[0203] FIG. 19 shows an exemplary PSA unit integrated to a refinery
process scheme. A refinery gas plant 1901 can receive gas 1910 from
cracking or other units. The PSA unit 1903 (after, for example,
treatment of the gas in a treatment unit 1902) can separate
components in refinery gas plant off gas to methane and a C.sub.2+
cut which contains most or all of the olefinic materials. The
methane can be used as refinery fuel 1911 and/or directed to an OCM
unit 1904 with post-bed cracking. The OCM feed can be supplemented
with additional natural gas 1912. The olefinic materials can be
directed to an ETL reactor 1905. The OCM effluent can also be
routed to the PSA where the olefins produced in the OCM are also
sent to the ETL reactor. In some cases, the OCM effluent can be
routed to the ETL reactor. In some cases, the OCM effluent may be
hydrogenated before being sent to the PSA unit or ETL reactor. Some
techniques may dictate the use of a cryogenic demethanizer in place
of the PSA, but the application of PSA to pre-separate the refinery
off-gas into a product stream and a tail gas stream containing the
heavier hydrocarbons which is the feed to ETL reactor can result in
significant cost savings. The product stream can contain methane,
ethane, CO, CO.sub.2, and other components, with of each component
from 1 to 99%. A C.sub.3+ stream 1913 from the refinery gas plant
can be directed to a product fractionation system 1906, which can
provide a C.sub.2/C.sub.3 stream 1914 (which can be directed to the
OCM reactor), an iC.sub.4 stream 1915, a gasoline blend stream
1916, and/or a kerosene/jet stream 1917.
[0204] As shown in FIG. 20, in some cases the system can have a
methanation unit to further improve the carbon efficiency of the
process. A refinery gas plant 2001 can receive gas 2010 from
cracking or other units. The PSA unit 2003 (after, for example,
treatment of the gas in a treatment unit 2002) can separate
components in refinery gas plant off gas to methane and a C.sub.2+
cut which contains most or all of the olefinic materials. The
methane can be used as refinery fuel 2011 and/or directed to a
methanation unit 2004, and then to an OCM reactor 2005 with
post-bed cracking. The methanation feed can be supplemented with
additional natural gas 2012. The olefinic materials can be directed
to an ETL reactor 2006. The OCM effluent can be routed to the ETL
reactor. In some cases, the OCM effluent can also be routed to the
PSA where the olefins produced in the OCM are also sent to the ETL
reactor. In some cases, the OCM effluent may be hydrogenated before
being sent to the PSA unit or ETL reactor. Some techniques may
dictate the use of a cryogenic demethanizer in place of the PSA,
but the application of PSA to pre-separate the refinery off-gas
into a product stream and a tail gas stream containing the heavier
hydrocarbons which is the feed to ETL reactor can result in
significant cost savings. The product stream can contain methane,
ethane, CO, CO.sub.2, and other components, with of each component
from 1 to 99%. A C.sub.3+ stream 2013 from the refinery gas plant
can be directed to a product fractionation system 2007, which can
provide a C.sub.2/C.sub.3 stream 2014 (which can be directed to the
OCM reactor), an iC.sub.4 stream 2015, a gasoline blend stream
2016, and/or a kerosene/jet stream 2017.
Metal-Organic Frameworks (MOFs) for Hydrocarbon Separation
[0205] The separation section of OCM unit can employ cryogenic
distillation systems. In some cases, the distillation section can
be partially or completely replaced by efficient advanced
separation technologies that operate at higher/room temperatures,
such as membranes or PSA. This can result in energy savings.
[0206] Among the materials used for membranes and adsorption beds,
metal-organic frameworks (MOFs) can be highly beneficial. MOFs can
comprise metal ions and organic linkers. MOFs can be highly porous
sponge-like materials. The choice of metal ion and linker can
define the structure and hence the properties of MOFs. MOFs can
exhibit advantages of both organic and inorganic moieties. They can
be more advantageous than zeolites due to higher surface areas and
higher flexibility in pore sizes (e.g., based on their synthesis).
They can be better than typical membranes for separation since they
can be more robust, more mechanically and thermally stable, and can
avoid issues such as carrier poisoning or reduction of complexing
agents.
[0207] The process effluent from OCM can comprise light gases, such
as methane, hydrogen, carbon dioxide, ethylene, ethane, acetylene,
propane, propene and C.sub.4+ compounds. MOFs can be used to
separate C.sub.2+ compound streams from the bulk CH.sub.4 and
H.sub.2 in effluent. MOFs can also be used to recover ethylene from
a mixed stream of C.sub.2 compounds, C.sub.3 compounds and C.sub.4+
compounds, remove CO.sub.2, and recover hydrogen for further
processing.
[0208] Different combinations of MOFs can be synthesized to provide
different separation properties. MOFs can be useful in hydrocarbon
separation due to their capability of separating component gases by
mechanisms such as molecular sieving, characteristic gate opening
pressures for different penetrant molecules or other changes in the
structure of the MOFs due to adsorbent/adsorbate interactions.
Without being limited by theory, adsorption selectivity can arise
from interactions using .pi.-complexation between the double bond
in ethylene molecules and partial positive charges of
co-ordinatively unsaturated metal ions (e.g., Cu(II)). MOFs such as
HKUST-1 can be used to separate ethylene from ethane. Other MOFs
capable of separating ethylene over ethane include Ag.sup.+ based
MOFs, Co.sub.2(2,5-dihydroxyterephthalate, or "dhtp"), and
Mg.sub.2(dhtp). MOFs such as ZIF-7, ZIF-8, and ZIF-4 can be used
for selective adsorption of paraffins (e.g., ethane) over ethylene
due to the gate-opening effect or the breathing behavior of the
MOF. ZIF-8 can adsorb alkanes (e.g., methane) over alkenes (e.g.,
ethylene). The selectivity of this separation can be controlled by
adjusting the hydration level of the MOF. MOFs such as ZIF-67,
SBMOF-1, SBMOF-2, Cu-TDPAT, USTA-33a, ZJU-61, USTA-33, USTA-10a can
be used for selective separation of methane from other hydrocarbons
such as C.sub.2 compounds. The MOF M.sub.2(dobdc) can be used to
effectively separate acetylene, ethylene, ethane, and methane
collectively or individually from their mixtures. The
M.sub.2(dobdc) can be in the meta form M.sub.2(m-dobdc) or the para
form M.sub.2(p-dobdc). The metal can be any suitable metal such as
iron (Fe), nickel (Ni) or cobalt (Co). Further information on these
MOFs can be found in PCT Publication No. WO 2015/066693A1, which is
incorporated herein by reference in its entirety. IRMOFs, such as
MOF-5, can be used for separation of hydrogen from hydrogen/methane
and hydrogen/C.sub.2 mixtures. RPM3-Zn can be used to separate
C.sub.1-C.sub.4 paraffins. MOFs such as UTSA-100, SIF SIX, ZJU-5
can be utilized for acetylene removal from the olefins stream where
back-end acetylene removal is used rather than acetylene
hydrogenation. MOFs such as M-(dobdc) can be modified with amines
to selectively remove CO.sub.2. Several MOFs such as ZIF-68-70, 78,
79, 81 82, MOF-11, MOF-508b, PCN-60, 61, MIL-100, MIL-101, ZIF-8,
SNU-9, MIL-102(Cr), MIL-53(Cr) have been studied for removal of
CO.sub.2 from methane and nitrogen and can be utilized for, e.g., a
front end CO.sub.2 removal system. MOFs such as M.sub.2(dobpdc) can
be used to remove CO.sub.2 from other gases and can be used for
CO.sub.2 removal front or back of the OCM process described herein.
MOFs such as Fe-BTTri can be used for CO removal from various
components such as CO.sub.2, N.sub.2, CH.sub.4 and can be used for
back end CO removal in the OCM unit.
[0209] MOFs can be used in the adsorbent beds of PSA/TSA system or
as a part of membrane based applications. As part of membrane
systems, they can be incorporated in thin film membranes or mixed
matrix membranes (MMMs). With MMMs, MOFs have shown improved gas
separation qualities, with increased permeability and selectivity
using MMMs. Mixed matrix membranes can combine the advantages of
easy and cheap fabrication of polymer membranes with the improved
gas separation properties of different MOFs.
[0210] For an OCM process, MOFs can be utilized for separation of
various light hydrocarbons. In FIG. 21, for example, oxygen 2101
and methane 2102 feed the OCM reactor 2103. The process effluent
2104 comprising mainly hydrogen, CO, CO.sub.2, CH.sub.4,
C.sub.2H.sub.4, C.sub.2H.sub.6 and C.sub.3+ hydrocarbons is first
sent to a pretreatment unit 2105. Any potential contaminants to the
downstream recovery systems (e.g., contaminants to membranes,
adsorbent beds containing zeolites, polymers or MOF membranes or
adsorbents) can be removed in this unit. This unit can include a
CO.sub.2 removal system, acetylene removal bed for diene sensitive
beds, sulfur removal bed, or molecular sieve dryer. Hydrogen can
also be recovered from this stream, for example by utilizing an MOF
bed selective to hydrogen over other light hydrocarbons such as
methane. Hydrogen removal can be important for separation systems
using adsorbents/membranes that are sensitive to hydrogen in the
operations that follow. The hydrogen, CO.sub.2 and CO streams can
be sent to the methanation unit 2106 for further conversion to
methane. The outlet 2107 from the pretreatment unit can then be
sent to a C.sub.1/C.sub.2+ bulk separation unit 2108 capable of
separating methane from C.sub.2 and higher hydrocarbons. This
separation unit can be a PSA, membranes made of zeolites such as
CaX, NaX zeolite, microporous titanosilicates such as ETS-4,
ETS-10, or selective MOF adsorbents/membrane systems that can
perform the same function (for example, MOFs such as SBMOF-1,
SBMOF-2, Zn-SIFSIX-Pyrazine, PCN-250, Cu-TDPAT, ZIF-67, ZJU-61,
USTA-33, and USTA-10 can be used). These materials can be used for
separating the light components including N.sub.2 and H.sub.2 along
with methane and hence may not require any pre-treatment beds prior
to a C1/C2+ bulk separation unit. A methane gas stream 2109
separated can be recycled back to the OCM reactor. Alternatively,
the outlet from the C.sub.1/C.sub.2 separation containing methane
can be recycled back to the methanation unit 2106, for example if
the stream contains portions of CO, CO.sub.2 or H.sub.2. The
C.sub.2+ stream 2110 can then be sent into an olefin/paraffin
separation unit 2111, for example made of MOFs, zeolites, or
polymeric membranes in a PSA or membrane unit. MOFs that can be
useful for this operation include HKUST-1, CO.sub.2 (dhtp),
Mg.sub.2 (dhtp), M (dobdc) (M can be Mg, Mn, Fe, Co, Ni, Zn),
ZIF-7, ZIF-8, ZIF-4, and other Ag ion based MOFs such as
Ag-MIL-101, Silver-Organic Frameworks Constructed with
1,1'-Biphenyl-2,2',6,6'-tetracarboxylic Acid or Silver
m-phosphonobenzoate
Ag.sub.6(m-O.sub.3PC.sub.6H.sub.4CO.sub.2).sub.2, Ag(I)
coordination polymer with 2,5-dimethylpyrazine ligand. Polymeric
adsorbents capable of silver complexation such as Ag+ exchanged
Amberlyst resin can also be used for such applications. The olefins
stream can then be sent into a separator 2112 such as a flash unit
operation or distillation column or any other separation system
(e.g., PSA/TSA/membranes) that can separate pure ethylene 2113 from
the C.sub.3+ olefins 2114. A combination of the separation
techniques can also be used to recover polymer grade ethylene. The
paraffin stream can also be sent into a separator 2115 such as
flash operation, distillation section, PSA, TSA unit, or membrane
system to separate ethane from C.sub.3+ paraffins. Ethane can be
recycled 2116 back to the OCM reactor. Alternatively, the entire
paraffin stream 2117 can also be recycled back into the OCM reactor
to take advantage of the post bed cracking section of the reactor
to convert into further ethylene. Separation of paraffins can also
be performed using MOF adsorbent beds of RPM3-Zn.
[0211] In FIG. 22, a similar process scheme as FIG. 21 is proposed,
except for the acetylene removal unit 2118 location, separating
acetylene 2119 from ethylene 2120. Here the acetylene removal unit
is downstream of the ethylene/propylene+ separation unit. This
scheme can be utilized when acetylene is not a contaminant/poison
to the olefin/paraffin separation beds or any of the separation
systems prior to olefin separation unit (MOF/PSA/membrane systems).
This scheme can be utilized if olefin/paraffin separation system is
based on non-Ag.sup.+ adsorbent beds/membranes such as Fe-MOF-74.
In such a system, acetylene removal can be performed on the final
product stream using MOF adsorbent beds/membranes selective to
acetylene removal, for example, USTA-67a.
[0212] In FIG. 23, the OCM effluent, after pre-treatment and
hydrogen recovery (where necessary), is sent to adsorbent beds in a
PSA system or to a membrane system containing MOFs such as
M.sub.2(dobdc) (meta or para form, M can be Mg, Mn, Fe, Co, Ni)
2108, 2121 that are by themselves capable of separating all the
lighter hydrocarbons into individual components (CH.sub.4,
C.sub.2H.sub.4, C.sub.2H.sub.6, C.sub.2H.sub.2). In such a system,
the effluent from pre-treatment section can be first sent into an
initial methane removal unit (PSA with multiple beds for
simultaneous adsorption/desorption to run the process
continuously). The desorbed mixture of C.sub.2+ streams can then be
separated into ethylene 2122, ethane 2116 and acetylene 2123 based
at least in part on their different elution rates from the
adsorbent bed (permeation times if membranes were to be used).
Multiple beds operating simultaneously for this unit can help with
continuous separation of the C.sub.2 streams. Such a scheme can use
a C.sub.3+ removal system (PSA/membrane based on MOFs) for removing
the C.sub.3+ components prior to the methane removal unit.
[0213] FIG. 24 represents a similar system utilizing MOFs such as
M.sub.2(dobdc) (meta or para form, M can be Mg, Mn, Fe, Co, Ni)
capable of separating individual light hydrocarbons, but each
running in a different mode. A system utilizing 4 different
adsorption systems (e.g., PSA) 2124, 2125, 2126, and 2127, with
each bed operating in different mode is represented. Each bed is
either in CH.sub.4 removal mode 2124, C.sub.2H.sub.2 removal mode
2127, C.sub.2H.sub.4 recovery mode 2126 or C.sub.2H.sub.6 removal
mode 2125. Using different valve-sequencing for the process gas
(feed and outlet) between beds, the feed gas can be directed
appropriately and effectively separated continuously into
individual components thus recovering ethylene without lag times
that may be generated in the adsorbent beds.
[0214] FIG. 25 shows another example of an OCM system. In this
case, oxygen 2500 and methane 2502 can be fed into an OCM reactor
2504 to produce an OCM effluent. The OCM effluent can be sent
through a pre-treatment unit 2506 (e.g., for water, sulfur removal)
followed by a (bulk) separation unit 2508 such as PSA or membranes
that utilize adsorbent materials capable of separation C.sub.1
compounds from C.sub.2+ compounds. These materials can be
adsorbents that aid in separation using molecular size differences
(e.g., CaX Zeolite, ETS-4). This PSA/membrane can separate the
quenched OCM reactor effluent into two streams. The methane rich
stream with hydrogen 2510 can be recycled back to OCM via
methanation 2512. The C.sub.2+ compounds 2514 can be fed into an
optional acetylene hydrogenation unit 2516 that selectively
hydrogenates acetylene to ethylene and ethane. This stream can then
be fed to the an olefin/paraffin separation module 2518 containing,
for example adsorbents or membranes with pi-complexation materials
such as silver ion MOFs, resins such as Ag+ exchanged Amberlyst 15
resin or M.sub.2(dobdc) (meta or para form, M can be Mg, Mn, Fe,
Co, Ni) MOFs, or any material which can selectively separate olefin
from paraffins. A post-CO.sub.2 removal unit 2520 can follow. A
post CO.sub.2 removal unit can reduce the cost since the operation
can be performed on a stream with much lower flow rate. The
CO.sub.2 removal unit may use liquid absorption or CO.sub.2 removal
adsorbents in a PSA or TSA or a membrane system. The CO.sub.2
stream 2522 can then be recycled into the methanation reactor for
further conversion into methane. The CO.sub.2-free stream can then
be sent into an acetylene removal unit (if acetylene is not
hydrogenated prior to olefin/paraffin separation) utilizing
materials and adsorbents capable of removing acetylene from
ethylene such as UTSA-100, SIFSIX, or ZJU-5 (not shown). Once free
from acetylenes, the product stream can go through a final
separation unit 2524 to separate ethylene 2526 and propylene 2528.
In some cases, some CO.sub.2 can be vented 2530 and/or the C.sub.2+
paraffin stream 2532 can be recycled to (the cracking section of)
the OCM reactor 2504.
[0215] FIG. 26 shows another example of an OCM system. In this
case, oxygen 2600 and methane 2602 can be fed into an OCM reactor
2604 to produce an OCM effluent. The OCM effluent can, after
pre-treatment where necessary (not shown), can be sent to an olefin
recovery module 2606. The olefin recovery module can contain
adsorbent beds in a PSA or TSA system and/or can be a membrane
system containing MOFs such as M.sub.2(dobdc) (meta or para
version, M can be Mg, Mn, Fe, Co, Ni for example) that are by
themselves capable of separating the lighter hydrocarbons into
individual components or groups thereof (e.g., CH.sub.4,
C.sub.2H.sub.4, C.sub.2H.sub.6, C.sub.2H.sub.2). In such a system,
the effluent from pre-treatment section can be sent into an initial
bulk lights removal unit (e.g., PSA with multiple beds for
simultaneous adsorption/desorption to run the process continuously
and remove methane and lighter components). The desorbed mixture of
C.sub.2+ streams (with lower amounts of C.sub.1 and lighter
components) can then be separated into ethylene, ethane and
acetylene based at least in part on their different elution rates
from the adsorbent bed (permeation times if membranes were to be
used). Such a configuration can use a C.sub.3+ removal system
(e.g., PSA/membrane based on MOFs) for removing the C.sub.3+
components prior to the methane removal unit. The separations
module can send a stream of C.sub.1 molecules and hydrogen 2608 to
a methanation unit 2610 and/or can send C.sub.2+ paraffins 2612 to
(the cracking section of) the OCM reactor 2604. A back-end CO.sub.2
and acetylene removal unit 2614 can then be utilized to purify
olefins stream from CO.sub.2 and acetylenes. The CO.sub.2 removal
unit can include typical CO.sub.2 removal liquid absorption columns
or PSA/TSA/membranes systems that incorporate CO.sub.2 removal
adsorbents. Acetylene removal may be performed by adding additional
acetylene selective MOF beds such as UTSA-100, SIF SIX, ZJU-5. A
back-end purification system can greatly reduce the operating and
capital cost of removal units. The CO.sub.2 removal unit can send
CO.sub.2 to methanation 2610 and/or to vent 2616. An olefin
separation module 2618 can produce an ethylene stream 2620 and a
propylene stream 2622.
[0216] In summary, different MOFs can be utilized for their
specific selectivities and adsorption capabilities, for example in
MMMs or adsorbent beds as PSA systems for hydrocarbon separation of
the OCM effluent. MOFs can be very advantageous for their
on-purpose synthesis and high surface areas (highest surface
area/gram compared to any other material). MOFs in combination with
other separation systems (such as polymeric membranes, zeolites,
and cryogenic distillation) can be used in novel process schemes to
produce OCM product (e.g., ethylene).
Separations Systems Using an Oil Absorption Tower
[0217] Another aspect of the present disclosure provides a method
and system for separating the OCM reactor product mixture using an
oil absorption system along with distillation. The oil absorption
system may include (a) an oil absorption and stripper system and/or
(b) an oil absorption system preceded by a pre-separation column to
do a bulk separation between C.sub.1 and C.sub.2 compounds. This
system can eliminate the need of a demethanizer, thereby reducing
the overall energy consumption and capex by eliminating the need
for C.sub.2 or C.sub.1 refrigeration.
[0218] As shown in FIG. 27A, oxygen 2700 and methane 2702 can be
fed to an OCM reactor 2704 and reacted to produce an OCM effluent
2706. The OCM effluent can be compressed 2708, and the compressed
stream can be sent to a treatment unit 2710. The treatment unit can
include a CO.sub.2 removal system, drying and/or removal of
oxygenates. The treatment unit can be followed by a heavies removal
system 2712. The heavies removal system can remove C.sub.4+
compounds 2714. The overhead from the heavies removal system can be
fed to a pre-separation and absorption system 2716. The overhead
2718 from the pre-separation and oil absorption system can consist
mainly of the C.sub.1 and lighter components. The majority of the
methane rich overhead product can be recycled to the OCM reactor
via a methanation reactor system 2720. A small fraction can be
purged 2722 to remove any inerts building up in the system,
alternately, the C.sub.1 fraction can be sent to the fuel gas. The
C.sub.2+ components (e.g., propane, propylene, ethane, ethylene,
methane, and lights such as H.sub.2) can be sent to a de-ethanizer
2724 followed by acetylene hydrogenation 2726 and a C.sub.2
splitter 2728 to produce high purity polymer grade ethylene 2730.
Ethane 2732 can be recycled to OCM (not shown). A C.sub.3 splitter
2734 can be used to produce a propylene product 2736.
[0219] FIG. 27B shows an example of the pre-separation and
absorption system 2716 comprising a pre-separation column 2740 and
an oil absorption unit 2742. The pre-separation column can be a
distillation column which performs a bulk separation between
C.sub.1 and lighter components and C.sub.2 and heavier components.
In this instance, bulk separation implies that the distillation
doesn't necessarily achieve high purity streams (non-sharp
distillation). The overhead from the pre-separation column, which
consists of C.sub.1 and lighter components can be sent to an oil
absorber where the circulating lean oil absorbs C.sub.2 and heavier
components to complete separation of C.sub.1 from C.sub.2+
components. The heavy oil can be regenerated in the first
pre-separation column. Alternatively, the oil can be regenerated in
a separate system 2744. One advantage of using a pre-separation
column and an oil absorption system is the reduction in the energy
consumption that is incurred in a conventional cryogenic
demethanizer.
[0220] In some cases, the feed to the separation system can be the
product from either an OCM reactor as discussed above, an OCM
process integrated with a Methanol to Olefins (MTO) unit, an OCM
process integrated with a steam cracker, or an OCM process
integrated with a dimerization and metathesis unit for example.
[0221] Methods and systems of the present disclosure can be
combined with or modified by other methods and systems, such as
those described in U.S. patent application Ser. No. 14/591,850,
filed Jan. 7, 2015, now published as U.S. Patent Pub. No
2015/0232395; U.S. patent application Ser. No. 13/936,783, filed
Jul. 8, 2013, now published as U.S. Patent Pub. No. 2014/0012053;
U.S. patent application Ser. No. 13/936,870, filed Jul. 8, 2013,
now published as U.S. Patent Pub. No. 2014/0018589; U.S. patent
application Ser. No. 13/900,898, filed May 23, 2013, now published
as U.S. Patent Pub. No 2014/0107385; U.S. patent application Ser.
No. 14/553,795, filed Nov. 25, 2014, now published as U.S. Patent
Pub. No. 2015/0152025; U.S. patent application Ser. No. 14/592,668,
filed Jan. 8, 2015, now published as U.S. Patent Pub. No.
2015/0210610; and U.S. patent application Ser. No. 14/789,953,
filed Jul. 1, 2015, now U.S. Pat. No. 9,334,204, each of which is
entirely incorporated herein by reference.
[0222] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. It is not intended that the invention be limited by
the specific examples provided within the specification. While the
invention has been described with reference to the aforementioned
specification, the descriptions and illustrations of the
embodiments herein are not meant to be construed in a limiting
sense. Numerous variations, changes, and substitutions will now
occur to those skilled in the art without departing from the
invention. Furthermore, it shall be understood that all aspects of
the invention are not limited to the specific depictions,
configurations or relative proportions set forth herein which
depend upon a variety of conditions and variables. It should be
understood that various alternatives to the embodiments of the
invention described herein may be employed in practicing the
invention. It is therefore contemplated that the invention shall
also cover any such alternatives, modifications, variations or
equivalents. It is intended that the following claims define the
scope of the invention and that methods and structures within the
scope of these claims and their equivalents be covered thereby.
* * * * *