U.S. patent application number 14/944632 was filed with the patent office on 2016-05-26 for method and system for low voltage electrochemical gas to liquids production.
This patent application is currently assigned to Gas Technology Institute. The applicant listed for this patent is Qinbai FAN, Renxuan LIU, Ronald Justin STANIS. Invention is credited to Qinbai FAN, Renxuan LIU, Ronald Justin STANIS.
Application Number | 20160145750 14/944632 |
Document ID | / |
Family ID | 56009607 |
Filed Date | 2016-05-26 |
United States Patent
Application |
20160145750 |
Kind Code |
A1 |
STANIS; Ronald Justin ; et
al. |
May 26, 2016 |
METHOD AND SYSTEM FOR LOW VOLTAGE ELECTROCHEMICAL GAS TO LIQUIDS
PRODUCTION
Abstract
A method for producing methanol from methane in which methane is
provided to an anode electrode having a metal oxide catalyst
disposed on an anode side of an electrolyte membrane, thereby
producing methanol and electrons on the anode side. The electrons
are conducted to a cathode electrode such as having an oxygen
reduction catalyst disposed on a cathode side of the electrolyte
membrane, thereby transforming oxygen and water provided to the
cathode side to hydroxide ions.
Inventors: |
STANIS; Ronald Justin; (Des
Plaines, IL) ; FAN; Qinbai; (Chicago, IL) ;
LIU; Renxuan; (Chicago, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
STANIS; Ronald Justin
FAN; Qinbai
LIU; Renxuan |
Des Plaines
Chicago
Chicago |
IL
IL
IL |
US
US
US |
|
|
Assignee: |
Gas Technology Institute
Des Plaines
IL
|
Family ID: |
56009607 |
Appl. No.: |
14/944632 |
Filed: |
November 18, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62082751 |
Nov 21, 2014 |
|
|
|
Current U.S.
Class: |
205/452 ;
204/265 |
Current CPC
Class: |
C25B 9/00 20130101; C25B
13/02 20130101; C25B 1/00 20130101; C25B 3/02 20130101 |
International
Class: |
C25B 3/02 20060101
C25B003/02; C25B 9/00 20060101 C25B009/00; C25B 13/02 20060101
C25B013/02; C25B 1/00 20060101 C25B001/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] This invention was made with government support under grant
DE-AR0000307 awarded by the U.S. Department of Energy (DOE). The
government has certain rights in the invention.
Claims
1. A method for converting methane to methanol, the method
comprising: providing a reactor including an anode, a cathode, and
a membrane between the anode and the cathode; feeding methane to
the anode, and converting the methane to form methanol and
electrons; passing the electrons to the cathode and feeding water
and oxygen to the cathode, reducing the oxygen and producing
hydroxide ions; transporting the hydroxide ions through the
membrane to the anode; and recovering the methanol from the
reactor.
2. The method of claim 1 wherein reaction at the cathode is an
oxygen reduction reaction via an oxygen reduction catalyst.
3. The method of claim 2 wherein said oxygen reduction catalyst is
selected from the group consisting of cobalt polypyrrole, silver on
carbon, Pt, and MnO.sub.2.
4. The method of claim 1 wherein said feeding of water and oxygen
to the cathode comprises at least one of bubbling an
oxygen-containing gas through water to the cathode and feeding a
humidified oxygen-containing gas to the cathode.
5. The method of claim 4 wherein said feeding of water and oxygen
to the cathode comprises bubbling an oxygen-containing gas through
water to the cathode.
6. The method of claim 5 wherein the oxygen-containing gas
comprises air.
7. The method of claim 5 wherein the oxygen-containing gas
comprises O.sub.2.
8. The method of claim 4 wherein said feeding of water and oxygen
to the cathode comprises feeding a humidified oxygen-containing gas
to the cathode.
9. The method of claim 8 wherein the oxygen-containing gas
comprises air.
10. The method of claim 8 wherein the oxygen-containing gas
comprises O.sub.2.
11. The method of claim 1 comprising performing the following net
chemical reaction at the cathode:
1/2O.sub.2+H.sub.2O+2e.sup.-.fwdarw.2OH.sup.-.
12. The method of claim 1 comprising performing the following
overall reactor reaction: 2CH.sub.4+O.sub.2.fwdarw.2CH.sub.3OH.
13. A system for converting methane to methanol said system
comprising: a reactor having an anode, a cathode, and a membrane
between the anode and the cathode; the membrane being at least one
being porous or having ionic conducting sites, the membrane
allowing transport of hydroxide ions from the cathode to the anode;
a source of methane interconnected to the anode to permit the feed
of methane to the anode; and a source of oxygen and a source of
water interconnected to the cathode to permit the feed of water and
oxygen to the cathode.
14. The system of claim 13 wherein the cathode includes an oxygen
reduction catalyst.
15. The system of claim 14 wherein the oxygen reduction catalyst is
selected from the group consisting of cobalt polypyrrole, silver on
carbon, Pt, and MnO.sub.2.
16. The system of claim 13 wherein the source of oxygen and the
source of water interconnected to the cathode comprises one of
bubbling air through water to the cathode and feeding humidified
air to the cathode.
17. The system of claim 16 wherein the source of oxygen and the
source of water interconnected to the cathode comprises bubbling
air to the cathode.
18. The system of claim 16 wherein the source of oxygen and the
source of water interconnected to the cathode comprises feeding
humidified air to the cathode.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit of U.S. Provisional
Patent Application, Ser. No. 62/082,751, filed on 21 Nov. 2014. The
co-pending Provisional Application is hereby incorporated by
reference herein in its entirety and is made a part hereof,
including but not limited to those portions which specifically
appear hereinafter.
[0002] The subject matter of this application is also related to
prior U.S. patent application Ser. No. 13/670,501, filed on 7 Nov.
2012 (now U.S. Pat. No. 9,163,316, issued 20 Oct. 2015), Ser. No.
13/719,267, filed on 19 Dec. 2012, and Ser. No. 14/076,445, filed
on 11 Nov. 2013. The disclosures of these related patent
applications are hereby incorporated by reference herein and made a
part hereof, including but not limited to those portions which
specifically appear hereinafter.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention relates generally to gas to liquids
processing and, more particularly, to electrochemical processing of
gas to liquids. In one aspect, this invention relates to a method
for producing liquid organic fuels from hydrocarbons. In one
aspect, this invention relates to an electrochemical method for
producing liquid organic fuels from hydrocarbons. In one aspect,
this invention relates to a system for the electrochemical
production of liquid organic fuels from hydrocarbons.
[0006] 2. Discussion of Related Art
[0007] Methane is an abundant hydrocarbon material especially with
the development and production of shale gas. To date, however,
methane has been generally underutilized as a precursor for
chemicals and liquid fuels due to the difficulty of efficiently
transporting methane (e.g., gas), particularly from remote or
scattered sites. Methanol is one of the 25 top chemicals produced
worldwide; it is the main feedstock for the chemical industry; and
it is a source of dimethyl ether (DME), which could be used as a
vehicular fuel.
[0008] There is presently no commercially available process or
system for the economical, scalable, and portable conversion of
methane to methanol or other gaseous alkanes to alcohols. In the
past, Fischer-Tropsch processing has been applied to produce
methanol via a Fischer-Tropsch reaction involving the high
temperature steam reforming of methane followed by high pressure
reaction of the reformate hydrogen and CO. The efficiency of such
processing, however, is generally only about 50-65% depending on
the waste heat recovery.
[0009] Thus, more efficient and cost effective conversion of
methane to methanol is very much desired. Moreover, while
Fischer-Tropsch processing can perform the ultimate conversion,
such processing is generally only economical on very large scales
and is not readily portable. It is generally not possible to
economically perform Fischer-Tropsch conversion of methane to
methanol or other alkanes to alcohols directly at natural gas wells
or other scattered or smaller scale sites, including wastewater
treatment plants and landfill gas sites, for example.
[0010] More specifically, there is a need and a demand for
processing methods and systems applicable to or for the conversion
of hydrocarbons, such as alkanes, for example, and particularly
lower hydrocarbons, such as lower alkanes such as methane, for
example, to more easily transportable and/or higher valued
hydrocarbon materials such as alcohols, e.g., methanol.
[0011] As disclosed in above-identified and herein incorporated,
U.S. patent application Ser. No. 13/670,501, filed on 7 Nov. 2012,
one current electrochemical gas to liquids approach is based on the
following reactions:
[0012] Anode:
Ni(OH).sub.2+OH.sup.-.fwdarw.NiO.sup.+OH.sup.-+H.sub.2O+1e.sup.-(-0.52V)
1)
Losing Electrons, Oxidation
[0013]
NiO.sup.+OH.sup.-+CH.sub.4.fwdarw.CH.sub.3OH+OH.sup.-+Ni.sup.+
2)
Ni.sup.++2OH.sup.-.fwdarw.Ni(OH).sub.2+1e.sup.- 3)
[0014] Cathode:
2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-(-0.8277 V) 4)
Gaining Electrons, Reduction
[0015] The net reaction is:
CH.sub.4+H.sub.2O.fwdarw.CH.sub.3OH+H.sub.2
[0016] This reaction is based on the water activation of
methane.
[0017] Total Cell Voltage: -1.3477V
[0018] A membrane is used to separate the anode and cathode
electrodes. The membrane can be porous or have ionic conducting
sites. The membrane is not electronically conductive. The membrane
allows for OH.sup.- ions to transport from the cathode to the
anode.
[0019] The portion of the voltage required to split water at the
cathode and generate hydrogen is (-0.8277 V/-1.3477 V)=61.4%.
Though hydrogen can be valuable, it is here ultimately an
undesirable byproduct as the generally sought objective is to
convert gaseous methane to liquid methanol. Thus, generating
gaseous hydrogen is somewhat contrary to the desired goal, and
requires 61.4% of the voltage.
SUMMARY OF THE INVENTION
[0020] This invention relates generally to gas to liquids
processing and, more particularly, to electrochemical processing of
gas to liquids.
[0021] In accordance with one aspect, the invention improves upon
presently used electrochemical gas to liquid reactions by replacing
a cathode water splitting/hydrogen evolution reaction with an
oxygen reduction reaction.
[0022] As described in greater detail, practice of the invention
can significantly lower system voltage and power requirements.
[0023] In accordance with one aspect of the invention, there is
provided a new method for converting methane to methanol. In one
embodiment, such a method involves providing a reactor including an
anode, a cathode, and a membrane between the anode and the cathode.
Methane is fed to the anode and converted to form methanol and
electrons. The electrons are passed to the cathode and water and
oxygen are fed to the cathode, reducing the oxygen and producing
hydroxide ions. The hydroxide ions are transported through the
membrane to the anode and methanol is recovered from the
reactor.
[0024] Thus, the reaction at the cathode is desirably an oxygen
reduction reaction such as catalyzed via an oxygen reduction
catalyst such as cobalt polypyrrole, silver on carbon, Pt, and/or
MnO.sub.2.
[0025] The feeding of water and oxygen to the cathode may desirably
involve at least one of bubbling an oxygen-containing gas through
water to the cathode and feeding a humidified oxygen-containing gas
to the cathode.
[0026] In accordance with another aspect of the invention there is
proved a system for converting methane to methanol. In accordance
with one embodiment, such a system may desirably include:
[0027] a reactor having an anode, a cathode, and a membrane between
the anode and the cathode; the membrane being at least one being
porous or having ionic conducting sites, the membrane allowing
transport of hydroxide ions from the cathode to the anode;
[0028] a source of methane interconnected to the anode to permit
the feed of methane to the anode; and
[0029] a source of oxygen and a source of water interconnected to
the cathode to permit the feed of water and oxygen to the
cathode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] These and other objects and features of this invention will
be better understood from the following detailed description taken
in conjunction with the drawings, wherein:
[0031] FIG. 1 is a diagrammatic representation of the technology
for conversion of methane to methanol at low temperatures in
accordance with one embodiment of the invention;
[0032] FIG. 2 is a diagrammatic representation of a membrane for
use in one embodiment of a method of this invention and the
reactions associated therewith;
[0033] FIG. 3 is a diagram showing a methane to methanol reactor
for carrying out the method in accordance with one embodiment of
this invention;
[0034] FIG. 4 is a graphical presentation of methanol concentration
and applied voltage, respectively, versus time realized with a test
system for converting methane to methanol in accordance with one
embodiment of the invention.
DETAILED DESCRIPTION
[0035] As described in greater detail below, the invention
generally relates to improved methods and systems for low voltage
electrochemical gas to liquids production.
[0036] In accordance with one aspect of the invention, we have
discovered that significantly improved desired performance can be
realized by changing the cathode reaction from reaction #4 set
forth above (i.e., 2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-)
to:
1/2O.sub.2+H.sub.2O+2e.sup.-.fwdarw.2OH.sup.-(+0.401V) 5)
Gaining Electrons, Reduction
[0037] For example, with such change, the system voltage
requirements can be significantly reduced.
[0038] Reaction #5 is a relatively well-known and established
reaction sometimes commonly referred to as the "oxygen reduction
reaction" (ORR). For example, the ORR is a common cathode reaction
for alkaline fuel cells and alkaline metal air batteries. A
significant benefit of the ORR in an alkaline environment is that
precious metal catalysts such as platinum are not required. Prior
experience with reaction #5 in or for the cathode of alkaline fuel
cells, has included using cobalt polypyrrole, silver on carbon, Pt,
MnO.sub.2, or other possible cathode catalysts, for example.
[0039] Since the voltage for reaction #5 is positive, the total
cell voltage combined with reaction 1 is now:
(-0.52 V)+(+0.401 V)=(-0.119 V)
[0040] The required voltage of -0.119V is only 8.83% of the
required voltage for reactions #1-4, representing a voltage savings
of 91%. The required current is the same for both sets of
reactions, i.e., reactions #1-4 and the subject reactions #1-3 and
#5. However, since power=voltage.times.current, the required power
savings realizable through the practice of the invention will be as
high as 91%.
[0041] With the use of reaction #5 in place of reaction #4, the
whole overall reaction is based on the oxygen activation of methane
and becomes:
2CH.sub.4+O.sub.2.fwdarw.2CH.sub.3OH
[0042] The primary changes to the system necessitated by the use of
reaction #5 in place of reaction #4 include:
[0043] 1) change of the cathode catalyst to a catalyst which can
perform the ORR, e.g., cobalt polypyrrole or silver on carbon,
and
[0044] 2) provide oxygen to the cathode such as by bubbling air to
the cathode of the gas to liquids reactor or feeding humidified air
to the cathode, for example.
[0045] Many other catalyst materials can be used including, for
example, conventional Pt or Pt on carbon catalyst.
[0046] As noted above, a system in accordance with one aspect of
the invention can operate at a significantly lower voltage of
around -0.119V per cell. An additional benefit is that the amount
of water consumed by the cathode is equal to the amount of water
generated on the anode. As may be desired, the generated water can
be appropriately separated from the methanol product and recycled
back to the cathode. Thus, theoretically in one preferred practice
of the invention, no external water input is necessary if all water
was recovered from methanol/water separation.
[0047] Previous electrochemical gas to liquids processing via above
reactions #1-4 produces hydrogen and methanol. Both are valuable
products and system economics can work out favorably provided a
source of electricity is readily available and there is a need for
the generated hydrogen. Our models, however, show that when such a
system is scaled to a large size for field use in converting
natural gas at a well head at a flow rate of 1,000,000 standard
cubic feet per day, the power requirement is quite large around
3600 kW. Typically gas wells are found in remote locations where
grid power is not readily available. Additionally the hydrogen gas
formed by such a system may be of little to no use in such remote
locations. Moreover, the need to generate the required power at the
remote site can and typically will involve a significant initial
capital cost. By replacing the water splitting/hydrogen generating
reaction on the cathode with an oxygen reduction reaction, such as
through a preferred practice of one aspect of the invention, the
voltage requirement applied to the cell can be significantly
decreased or reduced. For example, in one embodiment, the voltage
requirement applied to the cell can be decreased from 1.35V to
0.12V. Therefore the power requirement is approximately 1/10.sup.th
of that required before, or about 360 kW which is significantly
much more manageable and greatly improves the operating
profitability such as due to reduced electricity costs.
[0048] A major advantage of processing and systems such as herein
described include increased portability, high scalability and
facilitation of operation at low temperature (e.g., operation at
temperature of less than 200.degree. C.). Moreover, compared to the
existing electrochemical gas to liquids processing, preferred
practice of the invention desirably significantly reduces
electrical consumption, minimizes or avoids formation or production
of hydrogen, and has theoretically zero net water consumption.
[0049] The method of this invention can desirably utilize inorganic
metal oxide cation intermediates as catalysts to oxidize methane to
methanol at temperatures less than 200.degree. C. and, in some
embodiments at a temperature less than or equal to about
160.degree. C., preferably, at room temperature. The metal oxide
cation intermediates, which, upon reaction, are transformed to a
noncatalytic form, are regenerated electrochemically at the anode
in a battery-type reactor with hydrogen production at the cathode.
Thus, this method produces methanol from methane and water at room
temperature with high efficiency and high selectivity without using
a high temperature Fischer-Tropsch process. As used herein, the
term "high efficiency" refers to efficiencies greater than about
80%, and the term "high selectivity" refers to selectivities
greater than about 90%.
[0050] Accordingly, the methane to methanol process of this
invention applies an electrochemical process to continuously
maintain the catalytic property of the metal oxide anode. In this
process, methane is fed to the anode, producing methanol, water and
electrons. The electrons are conducted to the cathode where they
transform oxygen and water provided to the cathode to hydroxide
ions. The hydroxide ions are transferred through the membrane
separator disposed between the anode and cathode electrodes to the
anode for regeneration of the oxidation metal oxide cation
catalyst. The process is continuous as long as sufficient
electrical current is applied. Although regeneration of an anode
oxidation catalyst is a known technology practiced in batteries,
such technology as practiced is unsuitable for methane to methanol
conversion because the anode compositional and structural
engineering and design are unsuitable for this purpose.
[0051] FIG. 1 is a schematic diagram showing the methane to
methanol process in accordance with one embodiment of this
invention in an exemplary electrochemical cell comprising an
electrolyte membrane 10 disposed between an anode and cathode, a
metal oxide catalyst 11 disposed on the anode side of the
electrolyte membrane and a suitable oxygen reduction catalyst 12,
such as described above, disposed on the cathode side of the
electrolyte membrane.
[0052] The system may be in an alkaline environment or an acidic
environment. In an alkaline system in accordance with one
embodiment of this invention, the electrolyte membrane comprises an
alkaline electrolyte. In accordance with one embodiment, the
electrolyte membrane is a porous polymer layer containing an
alkaline electrolyte. An alkaline electrolyte is preferred because,
in an alkaline solution, the oxygen overpotential is much lower
than that in an acidic solution. In an acidic solution, a proton
exchange membrane may be used.
[0053] As shown in FIG. 2, the product at the cathode is hydroxide
ion, which is transported through the membrane to the anode where
it reacts with nickel cations to form nickel oxide hydroxide,
water, and electrons.
[0054] FIG. 3 shows a gas-to-liquid reactor for use in accordance
with one embodiment of the method of this invention. The reactor as
shown comprises two cells. Each cell comprises a membrane separator
20 disposed between gas diffusion electrodes 21. In accordance with
one preferred embodiment of this invention, the membrane separator
has a thickness in a range of about 20-50 .mu.m and the gas
diffusion electrodes have a thickness in a range of about 200-300
.mu.m. The cathode electrode comprises an oxygen reduction catalyst
layer 22 and the anode electrode comprises a NiOOH catalyst layer
23. A bipolar plate 24 separates the individual cells from one
another and is configured to provide flow channels 26. The
apparatus further comprises a current collector 25 disposed between
the bipolar plate 24 and the end plate 27. A power supply 30
provides an electrical current to the cells. This setup is a
combination of fuel cell technology and nickel metal hydride
battery technology for which all of the materials are commercially
available.
[0055] The present invention is described in further detail in
connection with the following examples which illustrate or simulate
various aspects involved in the practice of the invention. It is to
be understood that all changes that come within the spirit of the
invention are desired to be protected and thus the invention is not
to be construed as limited by these examples.
Examples
[0056] In this example, a system for converting methane to methanol
in accordance with one embodiment of the invention and operated in
the manner detailed below, produced or generated the results shown
in FIG. 4.
System:
[0057] Anode: Ni(OH).sub.2, Vulcan XC72, 16 mg/cm.sup.2, 10% PTFE,
2% Nafion, carbon paper
[0058] Membrane: Microporous polyethylene
[0059] Cathode: 5 mg/cm.sup.2 Ag/C on carbon cloth and 6M Liquid
potassium hydroxide
Operation:
[0060] Heated to 80.degree. C., Anode fed pure Methane, and Cathode
fed Air.
[0061] Methane was fed to the anode at 2 ml/min and the anode
exhaust was monitored using gas chromatography. Air was bubbled
through a cathode containing 6M potassium hydroxide. With cell
voltage of 0.2V the methanol concentration in the exhaust was about
50 ppm. When the voltage was increased to 0.35V the methanol
concentration in the exhaust increased to over 100 ppm. After 45
hours the anode was rinsed with DI water and dried with nitrogen.
Upon restarting the experiment at 0.35V applied potential, the
methanol concentration spiked to 4466 ppm before decreasing to 1250
ppm then gradually decreasing to 50 ppm.
[0062] From this experiment it is concluded that the system
produces methanol from methane under an applied voltage. It is
preferred that the anode catalyst remain dry so the transport of
methane to the catalyst surface is not inhibited.
[0063] The invention illustratively disclosed herein suitably may
be practiced in the absence of any element, part, step, component,
or ingredient which is not specifically disclosed herein.
[0064] While in the foregoing detailed description this invention
has been described in relation to certain preferred embodiments
thereof, and many details have been set forth for purposes of
illustration, it will be apparent to those skilled in the art that
the invention is susceptible to additional embodiments and that
certain of the details described herein can be varied considerably
without departing from the basic principles of the invention.
* * * * *