U.S. patent application number 12/152515 was filed with the patent office on 2008-12-25 for process for converting hydrocarbon feedstocks with electrolytic recovery of halogen.
This patent application is currently assigned to GRT, INC.. Invention is credited to Philip Grosso, Eric W. McFarland, Jeffrey H. Sherman.
Application Number | 20080314758 12/152515 |
Document ID | / |
Family ID | 40122241 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080314758 |
Kind Code |
A1 |
Grosso; Philip ; et
al. |
December 25, 2008 |
Process for converting hydrocarbon feedstocks with electrolytic
recovery of halogen
Abstract
An improved continuous process for converting methane, natural
gas, and other hydrocarbon feedstocks into one or more higher
hydrocarbons, methanol, amines, or other products comprises
continuously cycling through hydrocarbon halogenation, product
formation, product separation, and electrolytic regeneration of
halogen, optionally using an improved electrolytic cell equipped
with an oxygen depolarized cathode.
Inventors: |
Grosso; Philip; (Auburn,
CA) ; McFarland; Eric W.; (Santa Barbara, CA)
; Sherman; Jeffrey H.; (Vero Beach, FL) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Assignee: |
GRT, INC.
|
Family ID: |
40122241 |
Appl. No.: |
12/152515 |
Filed: |
May 14, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60930220 |
May 14, 2007 |
|
|
|
Current U.S.
Class: |
205/431 ;
204/277; 205/451; 205/462 |
Current CPC
Class: |
C07C 209/08 20130101;
C07C 1/26 20130101; C25B 1/24 20130101; C10G 29/02 20130101; H01L
2924/014 20130101; C10G 2400/30 20130101; C25B 1/04 20130101; C10B
53/04 20130101; C10G 2300/1011 20130101; Y02E 60/36 20130101; C07C
29/124 20130101; C10G 2300/1025 20130101; C07C 11/02 20130101; Y02P
20/145 20151101; C10B 57/06 20130101; C07C 1/30 20130101; C07C 1/30
20130101; C07C 11/02 20130101; C07C 1/26 20130101; C07C 11/02
20130101; C07C 29/124 20130101; C07C 31/04 20130101; C07C 1/26
20130101; C07C 11/04 20130101; C07C 1/26 20130101; C07C 11/06
20130101; C07C 209/08 20130101; C07C 211/03 20130101 |
Class at
Publication: |
205/431 ;
205/462; 205/451; 204/277 |
International
Class: |
C25B 3/06 20060101
C25B003/06; C25B 3/00 20060101 C25B003/00 |
Claims
1. A continuous process for converting a hydrocarbon feedstock into
higher hydrocarbons, comprising: (a) forming alkyl halides by
reacting molecular halogen with a hydrocarbon feedstock under
process conditions sufficient to form alkyl halides and hydrogen
halide, optionally with substantially complete consumption of the
molecular halogen; (b) forming higher hydrocarbons and hydrogen
halide by contacting the alkyl halides with a first catalyst under
process conditions sufficient to form higher hydrocarbons and
hydrogen halide; (c) separating the higher hydrocarbons from
hydrogen halide; (d) converting the hydrogen halide into hydrogen
and molecular halogen electrolytically, thereby allowing the
halogen to be reused; and (e) repeating steps (a) through (d) a
desired number of times.
2. A continuous process as recited in claim 1, wherein the
hydrocarbon feedstock comprises natural gas.
3. A continuous process as recited in claim 1, wherein the
hydrocarbon feedstock comprises methane.
4. A continuous process as recited in claim 1, wherein electrolysis
is carried out in aqueous media.
5. A continuous process as recited in claim 1, wherein electrolysis
is carried out in the gas phase.
6. A continuous process as recited in claim 1, wherein the higher
hydrocarbons comprise fuel grade hydrocarbons and/or aromatic
hydrocarbons.
7. A continuous process as recited in claim 6, wherein the aromatic
hydrocarbons comprise benzene, toluene, and xylenes.
8. A continuous process for converting a hydrocarbon feedstock into
methanol, comprising: (a) forming alkyl halides by reacting
molecular halogen with a hydrocarbon feedstock under process
conditions sufficient to form alkyl halides and hydrogen halide,
optionally with substantially complete consumption of the molecular
halogen; (b) forming methanol and alkaline halide by contacting the
alkyl halides with aqueous alkali under process conditions
sufficient to form methanol and alkaline halide; (c) separating the
methanol from the alkaline halide; (d) converting the alkaline
halide into hydrogen, molecular halogen, and aqueous alkali
electrolytically, thereby allowing the halogen and the alkali to be
reused; and (e) repeating steps (a) through (d) a desired number of
times.
9. A continuous process as recited in claim 8, wherein the
hydrocarbon feedstock comprises natural gas.
10. A continuous process as recited in claim 8, wherein the
hydrocarbon feedstock comprises methane.
11. A continuous process as recited in claim 8, wherein
electrolysis is carried out in aqueous media.
12. A continuous process as recited in claim 8, wherein
electrolysis is carried out in the gas phase.
13. A continuous process for converting a hydrocarbon feedstock
into an alkyl amine, comprising: (a) forming alkyl halides by
reacting molecular halogen with a hydrocarbon feedstock under
process conditions sufficient to form alkyl halides and hydrogen
halide, optionally with substantially complete consumption of the
molecular halogen; (b) forming alkyl amines and alkaline halide by
contacting the alkyl halides with aqueous alkaline amine under
process conditions sufficient to form alkyl amines and alkaline
halide; (c) separating the alkyl amines from the alkaline halide;
(d) converting the alkaline halide into hydrogen and molecular
halogen electrolytically, thereby allowing the halogen to be
reused; and (e) repeating steps (a) through (d) a desired number of
times.
14. A continuous process as recited in claim 12, wherein, wherein
the alkaline amine comprises NaNH.sub.2.
15. A continuous process as recited in claim 12, wherein the alkyl
halides comprise ethyl bromide, the alkaline amines comprise
NaNH.sub.2, and the alkyl halides comprise ethyl bromide.
16. In a production facility where oil or gas is pumped from a well
and thereby extracted from the earth, and having an electrical
generator or electrical power supply, the improvement comprising:
(a) forming alkyl halides by reacting molecular halogen with oil or
gas pumped from the well, under process conditions sufficient to
form alkyl halides and hydrogen halide, optionally with
substantially complete consumption of the molecular halogen; (b)
forming higher hydrocarbons and hydrogen halide by contacting the
alkyl halides with a first catalyst under process conditions
sufficient to form higher hydrocarbons and hydrogen halide; (c)
separating the higher hydrocarbons from hydrogen halide; and (d)
converting the hydrogen halide into hydrogen and molecular halogen
electrolytically, using electricity provided by the electrical
generator or electrical power supply, thereby allowing the halogen
to be reused.
17. The improvement as recited in claim 16, wherein the oil or gas
production facility is located offshore.
18. In a production facility where oil or gas is pumped from a well
and thereby extracted from the earth, and having an electrical
generator or electrical power supply, the improvement comprising:
(a) forming alkyl halides by reacting molecular halogen with a
hydrocarbon feedstock under process conditions sufficient to form
alkyl halides and hydrogen halide, optionally with substantially
complete consumption of the molecular halogen; (b) forming methanol
and alkaline halide by contacting the alkyl halides with aqueous
alkali under process conditions sufficient to form methanol and
alkaline halide; (c) separating the methanol from the alkaline
halide; (d) converting the alkaline halide into hydrogen, molecular
halogen, and aqueous alkali electrolytically, using electricity
provided by the electrical generator or electrical power supply,
thereby allowing the halogen and the alkali to be reused.
19. The improvement as recited in claim 18, wherein the oil or gas
production facility is located offshore.
20. A continuous process for converting coal into coke and
hydrogen, comprising: (a) forming brominated coal intermediates
coke and hydrogen halide by reacting crushed coal with molecular
halogen under process conditions sufficient to form brominated coal
intermediates and hydrogen halide; (b) forming coke and hydrogen
halide by reacting the brominated coal intermediates over a
catalyst under process conditions sufficient to form coke and
hydrogen halide; (c) separating the coke from the hydrogen halide;
(d) converting the hydrogen halide found in step (a) and/or step
(b) into hydrogen and molecular halogen electrolytically, thereby
allow the halogen to be reused; and (e) repeating steps (a) through
(e) a desired number of times.
21. A continuous process for converting coal or biomass-derived
hydrocarbons into polyols, comprising: (a) forming alkyl halides by
reacting molecular halogen with coal or a biomass-derived
hydrocarbon feedstock under process conditions sufficient to form
alkyl halides and hydrogen halide, optionally with substantially
complete consumption of the molecular halogen; (b) forming polyols
and alkaline halide by contacting the alkyl halides with aqueous
alkali under process conditions sufficient to form polyols and
alkaline halide; (c) separating the polyol(s) from the alkaline
halide; (d) converting the alkaline halide into hydrogen and
molecular halogen electrolytically, thereby allowing the halogen to
be reused; and (e) repeating steps (a) through (d) a desired number
of times.
22. A continuous process for converting a hydrocarbon feedstock
into higher hydrocarbons, comprising: (a) forming alkyl halides by
reacting molecular halogen with a hydrocarbon feedstock under
process conditions sufficient to form alkyl halides and hydrogen
halide, optionally with substantially complete consumption of the
molecular halogen; (b) forming higher hydrocarbons and hydrogen
halide by contacting the alkyl halides with a first catalyst under
process conditions sufficient to form higher hydrocarbons and
hydrogen halide; (c) separating the higher hydrocarbons from
hydrogen halide; (d) converting the hydrogen halide into water and
molecular halogen in an electrolytic cell or cells equipped with an
oxygen depolarized cathode, thereby allowing the halogen to be
reused; and (e) repeating steps (a) through (d) a desired number of
times.
23. A continuous process for converting a hydrocarbon feedstock
into methanol, comprising: (a) forming alkyl halides by reacting
molecular halogen with a hydrocarbon feedstock under process
conditions sufficient to form alkyl halides and hydrogen halide,
optionally with substantially complete consumption of the molecular
halogen; (b) forming methanol and alkaline halide by contacting the
alkyl halides with aqueous alkali under process conditions
sufficient to form methanol and alkaline halide; (c) separating the
methanol from the alkaline halide; (d) converting the alkaline
halide into molecular halogen and aqueous alkali in an electrolytic
cell or cells equipped with an oxygen depolarized cathode, thereby
allowing the halogen and the alkali to be reused; and (e) repeating
steps (a) through (d) a desired number of times.
24. An electrolytic cell for converting a halide into molecular
halogen, comprising: a gas supply manifold through which oxygen
gas, air, or oxygen-enriched air can be introduced; a gas diffusion
cathode, which is permeable to oxygen or an oxygen-containing gas;
a cation exchange membrane; a cathode electrolyte chamber disposed
between the cation exchange membrane and the gas diffusion cathode;
an anode electrolyte chamber; and an anode extending into the anode
electrolyte chamber.
25. A method for converting a halide into molecular halogen,
comprising: providing an electrolytic cell comprising a gas supply
manifold, a gas diffusion cathode that is permeable to oxygen or an
oxygen-containing gas, a cation exchange membrane, a cathode
electrolyte chamber disposed between the cation exchange membrane
and the gas diffusion cathode, an anode electrolyte chamber, and an
anode extending into the anode electrolyte chamber; introducing
water into the cathode electrolyte chamber; introducing oxygen or
an oxygen-containing gas into the gas supply manifold introducing
aqueous alkaline halide into the anode electrolyte chamber;
supplying electrical power to the cell; forming bromine gas by
reducing alkaline bromide at the anode; forming alkaline hydroxide
by reducing oxygen at the cathode; removing aqueous alkaline
hydroxide from the cathode electrolyte chamber; and removing
molecular bromine from the anode electrolyte chamber.
26. A method as recited in claim 25, wherein the alkaline halide
comprises sodium bromide.
27. A method as recited in claim 25, wherein the alkaline hydroxide
comprises sodium hydroxide.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of priority to U.S.
Provisional Application No. 60/930,220, filed May 14, 2007, the
entire contents of which are incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention is directed to a process for
converting natural gas and other hydrocarbon feedstocks into
higher-value products, such as fuel-grade hydrocarbons, methanol,
and aromatic compounds.
BACKGROUND OF THE INVENTION
[0003] U.S. patent application Ser. No. 11/703,358 ("the '358
application."), entitled "Continuous Process for Converting Natural
Gas to Liquid Hydrocarbons", filed Feb. 5, 2007, based on U.S.
Provisional Application No. 60/765,115, filed Feb. 3, 2006,
describes a continuous process for reacting molecular halogen with
a hydrocarbon feedstock to produce higher hydrocarbons. In one
embodiment, the process includes the steps of alkane halogenation,
"reproportionation" of polyhalogenated compounds to increase the
amount of monohalides that are formed, oligomerization (C--C
coupling) of alkyl halides to form higher carbon number products,
separation of products from hydrogen halide, continuous
regeneration of halogen, and recovery of molecular halogen from
water. Hydrohalic acid (e.g., HBr) is separated from liquid
hydrocarbons in a liquid-liquid phase splitter, and then converted
into molecular halogen (e.g., bromine) by reaction with a source of
oxygen in the presence of a metal oxide catalyst. The '358
application is incorporated by reference herein in its
entirety.
[0004] The '358 application represents a significant advance in the
art of C--H bond activation and industrial processes for converting
a hydrocarbon feedstock into higher value products. The present
invention builds on the '358 application by employing electrolysis
to regenerate molecular halogen (e.g., Br.sub.2, Cl.sub.2) from
hydrohalic acid (e.g., HBr, HCl).
[0005] Electrolysis of aqueous solutions to produce hydrogen and
oxygen is a known way of producing hydrogen with electrical energy.
Similarly, halogens have been produced by electrolysis of halide
brines or metal halide vapor. Conventional hydrogen production
relies on reforming of hydrocarbons with water (steam) to produce
carbon monoxide and molecular hydrogen:
CH.sub.4+H.sub.2O.fwdarw.CO+3H.sub.2.DELTA.H=+206 kJ/mol
C.sub.xH.sub.y+xH.sub.2O.fwdarw.xCO+(x+y/2)H2.DELTA.H>>0
kJ/mol
[0006] The energetically unfavorable reforming reaction can be
compared to the exothermic complete oxidation of hydrocarbons in
oxygen to produce the low-energy products water and carbon
dioxide:
CH.sub.4+2O.sub.2.fwdarw.CO.sub.2+2H.sub.2O.DELTA.H=-882 kJ/mol
C.sub.xH.sub.y+(x+y/2)O.sub.2.fwdarw.xCO.sub.2+y/2H.sub.2O.DELTA.H<&l-
t;0 kJ/mol
[0007] Typically, the reforming process is coupled with complete
oxidation to provide energy to drive the otherwise endothermic
reaction. The resulting overall reaction produces both carbon
oxides and hydrogen and can be operated nearly isoergically:
C.sub.nH.sub.m+xO.sub.2+yH.sub.2O.fwdarw.(n-m)CO+mCO.sub.2+(m/2+y)H.sub.-
2
[0008] Alternatively, hydrogen can be produced by dissociation of
water:
H.sub.2O.fwdarw.1/2O.sub.2+H.sub.2.DELTA.H=286 kJ/mol H.sub.2
[0009] Although energetically unfavorable, the reaction can be
driven by electrolysis using 2.times.10.sup.5 Coulombs per
gram-mole H.sub.2. Water is the source of both the hydrogen and the
oxygen, and the high activation energy for oxygen production
requires over potentials of approximately 1.6 Volts and a
stoichiometric current. In practice, the electrical energy required
is approximately 300 kJ/mol H.sub.2.
[0010] In halogen production by electrolysis of halide salts, e.g.
the chloralkali process, halogen (Cl.sub.2) and alkali base (NaOH)
are produced from the haloanion and water in an aqueous solution of
salt (NaCl). Water is again the source of the hydrogen. Similarly,
bromine can be produced from bromine salts (NaBr). In the latter
instance, the production of molecular halogen from the haloanion is
energetically and kinetically advantageous compared to oxygen
production, requiring a lower over potential (1.1 V versus
1.6V):
H.sub.2O+NaBr.fwdarw.Br.sub.2+H.sub.2+NaOH
[0011] With 2.times.10.sup.5 Coulombs per gram-mole H.sub.2 and the
required electrical energy reduced significantly (compared to
H.sub.2O alone) to approximately 200 kJ/g mol H.sub.2.
[0012] Many attempts have been made to develop economically viable
hydrogen production processes. In principle, hydrocarbons can be
directly oxidized electrochemically using oxygen (as in a solid
oxide fuel cell) and/or water to produce hydrogen; however this
typically leads to complex, difficult to separate intermediates and
is not economically useful. Another means of removing hydrogen from
hydrocarbons is by stepwise partial oxidation with a halogen,
(preferably bromine). The major advantage is that complete
oxidation of hydrocarbon to carbon dioxide cannot occur and the
hydrogen is transferred to the less stable HBr
(.DELTA.H.sub.formation=-36 kJ/mol), rather than water
(.DELTA.H.sub.formation=-286 kJ/mol):
C.sub.nH.sub.m+p/2Br.sub.2.fwdarw.C.sub.nH.sub.m-pBr.sub.p+pHBr
C.sub.nH.sub.zBr.sub.z+x/2Br.sub.2.fwdarw.C.sub.nH.sub.zBr.sub.p+xHBr
[0013] Final products after removal of HBr depend on the reaction
conditions and may consist of mixtures of coke and brominated and
perbrominated hydrocarbons:
C.sub.x+C.sub.yH.sub.zBr.sub.t+C.sub.rBr.sub.q. Combustion of these
final products in an oxygen atmosphere containing trace water may
be used to produce heat and carbon oxides and to convert the
residual bromine to HBr:
C.sub.x+C.sub.yH.sub.zBr.sub.t+C.sub.rBr.sub.q+n/2O.sub.2+(t+q)/2H.sub.2-
O.fwdarw.(x+y+r=n)CO.sub.2+(t+q)HBr
[0014] Another process for making hydrogen, based on HBr
electrolysis, reportedly yields energy savings of about 25%
relative to water electrolysis. However, this process requires that
bromine produced in electrolysis be converted back to HBr, and this
conversion step is a major disadvantage of the HBr electrolysis
route to hydrogen. In contrast, the present invention uses the
bromine generated in electrolysis to produce valuable products,
rather than simply converting it back to HBr.
SUMMARY OF THE INVENTION
[0015] The present invention combines the thermal
(non-electrochemical) reactivity of halogens (preferably bromine)
with hydrocarbons to produce hydrogen halide (preferably HBr) and
reactive alkyl halides or other carbon-containing intermediates
that may be converted to subsequent products, more readily than the
original hydrocarbon, with the facile electrolysis of hydrogen
halides or halide salts to create an overall process with
significantly higher efficiency. The use of halogens prevents the
total oxidation of the hydrocarbon to carbon dioxide and allows
subsequent production of partial oxidation products.
[0016] In one aspect of the invention, a continuous process for
converting a hydrocarbon feedstock into one or more higher
hydrocarbons comprises: (a) forming alkyl halides by reacting
molecular halogen with a hydrocarbon feedstock under process
conditions sufficient to form alkyl halides and hydrogen halide,
preferably with substantially complete consumption of the molecular
halogen; (b) forming higher hydrocarbons and hydrogen halide by
contacting the alkyl halides with a first catalyst under process
conditions sufficient to form higher hydrocarbons and hydrogen
halide; (c) separating the higher hydrocarbons from hydrogen
halide; (d) converting the hydrogen halide into hydrogen and
molecular halogen electrolytically, thereby allowing the halogen to
be reused; and (e) repeating steps (a) through (d) a desired number
of times. These steps can be carried out in the order presented or,
alternatively, in a different order. Electrolysis is carried out in
aqueous media, or in the gas phase. Optionally, the alkyl halides
are "reproportionated" by reacting some or all of the alkyl halides
with an alkane feed, whereby the fraction of monohalogenated
hydrocarbons present is increased. Also, in some embodiments,
hydrogen produced in the process is used for power generation.
[0017] In a second aspect of the invention, a continuous process
for converting a hydrocarbon feedstock into methanol comprises: (a)
forming alkyl halides by reacting molecular halogen with a
hydrocarbon feedstock under process conditions sufficient to form
alkyl halides and hydrogen halide, preferably with substantially
complete consumption of the molecular halogen; (b) forming methanol
and alkaline halide by contacting the alkyl halides with aqueous
alkali under process conditions sufficient to form methanol and
alkaline halide; (c) separating the methanol from the alkaline
halide; (d) converting the alkaline halide into hydrogen, or
molecular halogen, and aqueous alkali electrolytically, thereby
allowing the halogen and the alkali to be reused; and (e) repeating
steps (a) through (d) a desired number of times. These steps can be
carried out in the order presented or, alternatively, in a
different order. Optionally, the polyhalogenated hydrocarbons are
"reproportionated" by reacting some or all of the alkyl halides
with an alkane feed, whereby the fraction of monohalogenated
hydrocarbons present is increased.
[0018] The production of methanol by this process requires that the
reaction of alkyl halides with aqueous alkali be carried out under
alkaline conditions. However, the electrolysis process yields
alkali and acid in stoichiometrically equivalent amounts. Hence,
simply recombining all of the alkali with all of the acid would
result in a neutral solution. The process described herein provides
for disproportionation of the acid and base such that more than
sufficient alkali is available to react with the alkyl bromides to
achieve alkaline conditions. The acid removed in the
disproportionation step is later recombined with the excess alkali
after methanol and other products have been formed and
separated.
[0019] In some embodiments it may be necessary to maintain the
anolyte in acidic condition, which may require a small amount of
acid to be added. The separation of a portion of the acid can be
accomplished by a liquid phase process or, alternatively, by the
use of a regenerable solid reactant or adsorbent. Acid can also be
provided from an external source, either from on-site or off-site
generation. Alternatively, an overall excess of acid can be
achieved by removal of a small amount of alkali from the
system.
[0020] In a third aspect of the invention, a continuous process for
converting a hydrocarbon feedstock into an alkyl amine comprises:
(a) forming alkyl halides by reacting molecular halogen with a
hydrocarbon feedstock under process conditions sufficient to form
alkyl halides (e.g., ethyl bromide) and hydrogen halide, preferably
with substantially complete consumption of the molecular halogen;
(b) forming alkyl amines and alkaline halide by contacting the
alkyl halides with ammonia or aqueous ammonia under process
conditions sufficient to form alkyl amines and alkaline halide; (c)
separating the alkyl amines from the alkaline halide; (d)
converting the alkaline halide into hydrogen and molecular halogen
electrolytically, thereby allowing the halogen to be reused; and
(e) repeating steps (a) through (d) a desired number of times.
These steps can be carried out in the order presented or,
alternatively, in a different order. Optionally, the alkyl halides
are "reproportionated" by reacting some or all of the alkyl halides
with an alkane feed, whereby the fraction of monohalogenated
hydrocarbons present is increased.
[0021] In a fourth aspect of the invention, a continuous process
for converting coal into coke and hydrogen is provided and
comprises the steps of (a) forming brominated coal intermediates
and hydrogen halide by reacting crushed coal with molecular halogen
under process conditions sufficient to brominate and dissociate
significant elements of the coal skeleton, thereby forming a
mixture of brominated coal intermediates (e.g., polybrominated
hydrocarbons); (b) forming coke and hydrogen halide by reacting the
brominated coal intermediates over a catalyst under process
conditions sufficient to from coke and hydrogen halide; (c)
separating the coke from the hydrogen halide; (d) converting
hydrogen halide formed in step (a) and/or step (b) into hydrogen
and molecular halogen electrolytically, thereby allowing the
halogen to be reused; and (e) repeating steps (a) through (d) a
desired number of times. These steps can be carried out in the
order presented or, alternatively, in a different order. The coke
that is produced can be used to generate electrical power for the
process (via combustion, steam generation, and production of
electricity), or collected and sold.
[0022] In a fifth aspect of the invention, a continuous process for
converting coal or biomass-derived hydrocarbons into polyols and
hydrogen is provided and comprises: (a) forming alkyl halides by
reacting molecular halogen with coal or a biomass-derived
hydrocarbon feedstock under process conditions sufficient to form
alkyl halides and hydrogen halide, preferably with substantially
complete consumption of the molecular halogen; (b) forming polyols
and alkaline halide by contacting the alkyl halides with aqueous
alkali under process conditions sufficient to form polyols and
alkaline halide; (c) separating the polyols from the alkaline
halide; (d) converting the alkaline halide into hydrogen and
molecular halogen electrolytically, thereby allowing the halogen to
be reused; and (e) repeating steps (a) through (d) a desired number
of times. These steps can be carried out in the order presented or,
alternatively, in a different order. Optionally, the alkyl halides
are "reproportionated" by reacting some or all of the alkyl halides
with an alkane feed, whereby the fraction of monohalogenated
hydrocarbons present is increased.
[0023] In an important variation of the invention, an
oxygen-depolarized electrode is used in the electrolyzer, and
electrolysis of hydrogen halide yields molecular halogen and water,
and electrolysis of alkaline halide yields molecular halogen and
alkaline hydroxide, rather than hydrogen. This variation has the
advantage of greatly reducing the power requirements of the
electrolytic cell(s). An improved electrolytic cell, having an
oxygen-depolarized electrode is also provided as yet another aspect
of the invention.
[0024] A number of elements are common to various aspects of the
invention, including: (1) halogenation of a hydrocarbon feedstock
in the presence of molecular halogen to produce hydrogen halide and
an oxidized carbon-containing product; (2) further reaction of the
oxidized carbon products to produce final products; (3) separation
of carbon-containing products from bromine-containing components;
(4) electrolysis of the remaining halogen-containing components
(e.g., HBr, NaBr) to form halogen and hydrogen in an electrolytic
cell (or, alternatively, use of an oxygen-depolarized electrode to
yield halogen and water, or halogen and alkaline hydroxide, instead
of hydrogen). Hydrogen that is produced can be used to power one or
more process components, or compressed and sold.
[0025] The present conventional commercial process for utilizing
methane, coal, and other hydrocarbons yields syngas (CO+H.sub.2),
which can be converted to higher value products, such as methanol
and linear alkanes. The intermediate syngas is extremely expensive
to form, and the nearly fully oxidized carbon must be reduced to
form useful products. When compared to the conventional syngas
process, the present invention is superior in many respects and has
at least the following advantages: [0026] Use of alkyl halide
intermediates to produce higher value products, including fuels and
higher value chemicals. [0027] Lower operating pressure (e.g.,
.about.1-5 atm vs. .about.80 atm). [0028] Lower peak operating
temperature (e.g., .about.50.degree. C. vs. .about.1,000.degree.
C.). [0029] No need for pure oxygen [0030] No fired reformer, and
thus greater safety when used on offshore platforms. [0031] Simple
reactor design vs. complex syngas-to-methanol converter. [0032] No
catalyst necessary vs. catalysts required for reforming and for
syngas conversion. [0033] Fewer by-products and thus simpler
methanol purification operations. [0034] No steam supply for
reforming is needed. [0035] Hydrogen is produced on a separate
electrode as a relatively pure product. [0036] The reaction is
pushed to completion in the final step by the removal of products
from the reaction vessel.
[0037] According to the invention, molecular halogen used to form
alkyl halides is recovered as hydrogen halide and recycled to the
electrolytic cell, and the alkyl halides are converted to higher
value products. Examples include the conversion of methyl bromide
over a zeolite catalyst to aromatic chemicals and HBr, and
conversion of mono alkyl bromides (e.g. ethyl bromide) over a
catalyst to olefins (e.g. ethylene) and HBr. Alternatively, the
alkyl halides are readily converted to oxygenates, such as
alcohols, ethers, and aldehydes. Examples include the conversion of
methyl bromide in an aqueous solution of NaOH to methanol and NaBr,
and the conversion of dibromomethane in NaOH to ethylene glycol and
NaBr. In still another embodiment, the alkyl halides are readily
converted to amines. Examples include the conversion of
bromobenzene in an aqueous solution of ammonia to phenol and
aniline, and the conversion of ethyl bromide in ammonia to
ethylamine and NaBr.
[0038] The invention finds particular utility when it is used
on-site at an oil or gas production facility, such as an offshore
oil or gas rig, or at a wellhead located on land. The continuous
processes described herein can be utilized in conjunction with the
production of oil and/or gas, using electricity generated on-site
to power the electrolytic cell(s).
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Various features, embodiments, and advantages of the
invention will become better understood when considered in view of
the detailed description, and by referring to the appended
drawings, wherein:
[0040] FIG. 1 is a schematic diagram of a continuous process for
converting a hydrocarbon feedstock into higher hydrocarbons
according to one embodiment of the invention;
[0041] FIG. 2 is a schematic diagram of a continuous process for
converting a hydrocarbon feedstock into higher hydrocarbons
according to another embodiment of the invention;
[0042] FIG. 3 is a schematic diagram of a continuous process for
converting a hydrocarbon feedstock into methanol according to one
embodiment of the invention, in which a membrane-type electrolytic
cell is used to regenerate molecular bromine;
[0043] FIG. 4 is a schematic diagram of a continuous process for
converting a hydrocarbon feedstock into methanol according to
another embodiment of the invention, in which a diaphragm-type
electrolytic cell is used to generate molecular bromine;
[0044] FIG. 5 is a schematic diagram of a continuous process for
converting a hydrocarbon feedstock into higher hydrocarbons in
which an oxygen-depolarized cathode is provided, according to one
embodiment of the invention;
[0045] FIG. 6. is a schematic illustration of an electrolytic cell
according to one embodiment of the invention;
[0046] FIG. 7 is a schematic illustration of a continuous process
for converting coal into coke and hydrogen, according to one
embodiment of the invention;
[0047] FIG. 8 is a schematic illustration of a process for
converting coal or biomass into polyols and hydrogen, according to
one embodiment of the invention;
[0048] FIG. 9 is a chart illustrating product selectivity for
bromination of methane according to one embodiment of the
invention;
[0049] FIG. 10 is a chart illustrating product selectivity for
coupling of methyl bromide according to one embodiment of the
invention; and
[0050] FIG. 11 is a chart illustrating product selectivity for
coupling of methyl bromide according to another embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0051] The present invention provides a chemical process for
converting hydrocarbon feedstocks into higher value products, such
as fuel-grade hydrocarbons, methanol, aromatics, amines, coke, and
polyols, using molecular halogen to activate C--H bonds in the
feedstock and electrolysis to convert hydrohalic acid (hydrogen
halide) or halide salts (e.g., sodium bromide) formed in the
process back into molecular halogen. Nonlimiting examples of
hydrocarbon feedstocks appropriate for use in the present invention
include alkanes, e.g., methane, ethane, propane, and even larger
alkanes; olefins; natural gas and other mixtures of hydrocarbons;
biomass-derived hydrocarbons; and coal. Certain oil refinery
processes yield light hydrocarbon streams (so-called "light-ends"),
typically a mixture of C.sub.1-C.sub.3 hydrocarbons, which can be
used with or without added methane as the hydrocarbon feedstock.
With the exception of coal, in most cases the feedstock will be
primarily aliphatic in nature.
[0052] The hydrocarbon feedstock is converted into higher products
by reaction with molecular halogen, as described below. Bromine
(Br.sub.2) and chlorine (Cl.sub.2) are preferred, with bromine
being most preferred, in part because the over potential required
to convert Br.sup.- to Br.sub.2 is significantly lower than that
required to convert Cl.sup.- to Cl.sub.2 (1.09V for Br.sup.- vs.
1.36V for Cl.sup.-). It is contemplated that fluorine and iodine
can be used, though not necessarily with equivalent results. Some
of the problems associated with fluorine can likely be addressed by
using dilute streams of fluorine (e.g., fluorine gas carried by
helium nitrogen, or other diluent). It is expected, however, that
more vigorous reaction conditions will be required for alkyl
fluorides to couple and form higher hydrocarbons, due to the
strength of the fluorine-carbon bond. Similarly, problems
associated with iodine (such as the endothermic nature of certain
iodine reactions) can likely be addressed by carrying out the
halogenation and/or coupling reactions at higher temperatures
and/or pressures. In general, the use of bromine or chlorine is
preferred, with bromine being most preferred.
[0053] As used herein, the term "higher hydrocarbons" refers to
hydrocarbons having a greater number of carbon atoms than one or
more components of the hydrocarbon feedstock, as well as olefinic
hydrocarbons having the same or a greater number of carbon atoms as
one or more components of the hydrocarbon feedstock. For instance,
if the feedstock is natural gas--typically a mixture of light
hydrocarbons, predominantly methane, with lesser amounts of ethane,
propane and butane, and even smaller amounts of longer chain
hydrocarbon such as pentane, hexane, etc.--the "higher
hydrocarbon(s)" produced according to the invention can include a
C.sub.2 or higher hydrocarbon, such as ethane, propane, butane,
C.sub.5+ hydrocarbons, aromatic hydrocarbons, etc., and optionally
ethylene, propylene and/or longer olefins. The term "light
hydrocarbons" (sometimes abbreviated "LHCs") refers to
C.sub.1-C.sub.4 hydrocarbons, e.g., methane, ethane, propane,
ethylene, propylene, butanes, and butenes, all of which are
normally gasses at room temperature and atmospheric pressure. Fuel
grade hydrocarbons typically have 5 or more carbons and are liquids
at room temperature.
[0054] Both in this written description and in the claims, when
chemical substances are referred to in the plural, singular
referents are also included, and vice versa, unless the context
clearly dictates otherwise. For example, "alkyl halides" includes
one or more alkyl halides, which can be the same (e.g., 100% methyl
bromide) or different (e.g., methyl bromide and dibromomethane);
"higher hydrocarbons" includes one or more higher hydrocarbons,
which can be the same (e.g., 100% octane) or different (e.g.,
hexane, pentane, and octane).
[0055] FIGS. 1-5 are schematic flow diagrams generally depicting
different embodiments of the invention, in which a hydrocarbon
feedstock is allowed to react with molecular halogen (e.g.,
bromine) and converted into one or more higher value products.
Referring to FIG. 1, one embodiment of a process for making higher
hydrocarbons from natural gas, methane, or other light hydrocarbons
is depicted. The feedstock (e.g., natural gas) and molecular
bromine are carried by separate lines 1, 2 into a bromination
reactor 3 and allowed to react. Products (HBr, alkyl bromides,
optionally olefins), and possibly unreacted hydrocarbons, exit the
reactor and are carried by a line 4 into a carbon-carbon coupling
reactor 5. Optionally, the alkyl bromides are first routed to a
separation unit (not shown), where monobrominated hydrocarbons and
HBr are separated from polybrominated hydrocarbons, with the latter
being carried back to the bromination reactor to undergo
"reproportionation" with methane and/or other light hydrocarbons,
as described in the '358 application.
[0056] In the coupling reactor 5, monobromides and possibly other
alkyl bromides and olefins react in the presence of a coupling
catalyst to form higher hydrocarbons. Nonlimiting examples of
coupling catalysts are provided in the '358 application, at 61-65.
The preparation of doped zeolites and their use as carbon-carbon
coupling catalysts is described in Patent Publication No. US
2005/0171393 A1, at pages 4-5, which is incorporated by reference
herein in its entirety.
[0057] HBr, higher hydrocarbons, and (possibly) unreacted
hydrocarbons and alkyl bromides exit the coupling reactor and are
carried by a line 6 to a hydrogen bromide absorption unit 7, where
hydrocarbon products are separated from HBr via absorption,
distillation, and/or some other suitable separation technique.
Hydrocarbon products are carried away by a line 8 to a product
recovery unit 9, which separates the higher hydrocarbon products
from any residual natural gas or other gaseous species, which can
be vented through a line 10 or, in the case of natural gas or lower
alkanes, recycled and carried back to the bromination reactor.
Alternatively, combustible species can be routed to a power
generation unit and used to generate heat and/or electricity for
the system.
[0058] Aqueous sodium hydroxide or other alkali is carried by a
line 11 into the HBr absorption unit, where it neutralizes the HBr,
and forms aqueous sodium bromide. The aqueous sodium bromide and
minor amounts of hydrocarbon products and other organic species are
carried by a line 12 to a separation unit 13, which operates via
distillation, liquid-liquid extraction, flash vaporization, or some
other suitable method to separate the organic components from the
sodium bromide. The organics are either routed away from the system
to a separate product cleanup unit or, in the embodiment shown,
returned to the HBr absorption unit 7 through a line 14 and
ultimately exit the system via line 8.
[0059] Aqueous sodium bromide is carried from the NaBr-organics
separation unit 13 by a line 15 to an electrolytic cell 16, having
an anode 17, and a cathode 18. An inlet line 19 is provided for the
addition of water, additional electrolyte, and/or acid or alkali
for pH control. More preferably, a series of electrolytic cells,
rather than a single cell, is used as an electrolyzer. As an
alternative, several series of cells can be connected in parallel.
Nonlimiting examples of electrolytic cells include diaphragm,
membrane, and mercury cell, which can be mono-polar or di-polar.
The exact material flows with respect to make-up water,
electrolyte, and other process features will vary with the type of
cell used. Aqueous sodium bromide is electrolyzed in the
electrolytic cell(s), with bromide ion being oxidized at the anode
(2Br.sup.-.fwdarw.Br.sub.2+2e.sup.-) and water being reduced at the
cathode (2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-). Aqueous
sodium hydroxide is removed from the electrolyzer and routed to the
HBr absorption unit via line 11.
[0060] Bromine and hydrogen produced in the electrolyzer are
recovered, with bromine being recycled and used again in the
process. Specifically, wet bromine is carried by a line 20 to a
dryer 21, and dry bromine is carried by a line 22 to a heater 23,
and then by line 2 back into the bromination reactor 3. In
instances where the amount of water associated with the bromine is
tolerable in bromination and coupling, the dryer may be eliminated.
Hydrogen produced at the anode of the electrolytic cell can be
off-gassed or, more preferably, collected, compressed, and routed
through a line 24 to a power generation unit, such as a fuel cell
or hydrogen turbine. Alternatively, hydrogen produced can be
recovered for sale or other use. The electrical power that is
generated can be used to power various pieces of equipment employed
in the continuous process, including the electrolytic cells.
[0061] Exemplary and preferred conditions (e.g., catalysts,
pressure, temperature, residence time, etc.) for bromination, C--C
coupling, reproportionation, product separation, HBr clean-up, and
corrosion-resistant materials are provided in the '358 application
at 39-42 (bromination), 43-50 (reproportionation), 61-65 (C--C
coupling), 66-75 (product separation), 82-86 (HBr clean-up and
halogen recovery), and 87-90 (corrosion-resistant materials), which
paragraphs are incorporated herein in their entirety. Anodes,
cathodes, electrolytes, and other features of the electrolytic
cell(s) are selected based on a number of factors understood by the
skilled person, such as throughput, current power levels, and the
chemistry of the electrolysis reaction(s). Nonlimiting examples are
found in U.S. Pat. Nos. 4,110,180 (Nidola et al.) and 6,368,490
(Gestermann); Y. Shimizu, N. Miura, N. Yamazoe, Gas-Phase
Electrolysis of Hydrocarbonic Acid Using PTFE-Bonded Electrode,
Int. J. Hydrogen Energy, Vol. 13, No. 6, 345-349 (1988); D. van
Velzen, H. Langenkamp, A. Moryoussef, P. Millington, HBr
Electrolysis in the Ispara Mark 13A Flue Gas Desulphurization
Process Electrolysis in a DEM Cell, J. Applied Electrochemistry,
Vol. 20, 60-68 (1990); and S. Motupally, D. Mak, F. Freire, J.
Weidner, Recycling Chlorine from Hydrogen Chloride, The
Electrochemical Society Interface, Fall 1998, 32-36, each of which
is incorporated by reference herein in their entirety.
[0062] In one embodiment of the invention, illustrated in FIG. 1,
methane is introduced into a plug flow reactor made of the alloy
ALCOR, at a rate of 1 mole/second, and molecular bromine is
introduced at a rate of 0.50 moles/second with a total residence
time of a 60 seconds at 425.degree. C. The major hydrocarbon
products include methyl bromide (85%) and dibromomethane (14%), and
0.50 moles/s of HBr is produced. The methane conversion is 46%. The
products are carried by a line 4 into a coupling reactor 5, which
is a packed bed reactor containing a transition metal (e.g., Mn)
ion-exchanged alumina-supported ZSM5 zeolite coupling catalyst at
425.degree. C. In the coupling reactor 5, a distribution of higher
hydrocarbons is formed, as determined by the space time of the
reactor. In this example, 10 seconds is preferred to produce
products that are in the gasoline range. HBr, higher hydrocarbons,
and (trace) unreacted alkyl bromides exit the coupling reactor and
are carried by a line 6 to a hydrogen bromide separation unit 7,
where HBr is partially separated by distillation. Aqueous sodium
hydroxide is introduced and allowed to react at 150.degree. C.,
forming sodium bromide and alcohols from the HBr and unreacted
alkyl bromides. The aqueous and organic species are carried by a
line 12 to a separation unit 13, which operates via distillation to
separate the organic components from the sodium bromide. Aqueous
sodium bromide is carried from the NaBr-organics separation unit 13
by line 15 to an electrolytic cell 16, having an anode 17, and a
cathode 18. An inlet line 19 is provided for the addition of water,
additional electrolyte, and the pH adjusted to be less then 2 by
addition of acid. Electrolysis is performed in a membrane cell
type. Aqueous sodium bromide is electrolyzed in the electrolytic
cell, with bromide ion being oxidized at the anode
(2Br.sup.-.fwdarw.Br.sub.2+2e.sup.-) and water being reduced at the
cathode (2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-). Aqueous
sodium hydroxide is removed from the electrolyzer and routed to the
HBr absorption unit via line 11. Bromine and hydrogen are produced
in the electrolyzer.
[0063] Referring to FIG. 2, an alternate embodiment for converting
natural gas, methane, or other hydrocarbon feedstocks into higher
hydrocarbons, such as fuel grade hydrocarbons and aromatic
compounds, is depicted. In this embodiment, electrolysis takes
place in a non-alkaline medium. Products from the coupling reactor
(i.e., higher hydrocarbons and HBr) are carried by a line 6 to an
HBr absorption unit 7, where hydrocarbon products are separated
from HBr. After residual organic components are removed from the
HBr in a separation unit 13, rich aqueous HBr is carried by a line
15 to the electrolytic cell 16. Make-up water, electrolyte, or
acid/base for pH control, if needed, is provided by a line 19. The
aqueous HBr is electrolyzed, forming molecular bromine and
hydrogen. As Br.sub.2 is evolved and removed from the electrolyzer,
the concentration of HBr in the electrolyzer drops. The resulting
lean aqueous HBr, along with some bromine (Br.sub.2) entrained or
dissolved therein, is carried by a line 25 to a bromine stripper
26, which separates bromine (Br.sub.2) from lean aqueous HBr via
distillation or some other suitable separation operation. The lean
aqueous HBr is carried back to the HBr absorption unit by a line
27. Wet bromine is carried by a line 28 to the dryer 21, where it
is dried.
[0064] In another embodiment of this aspect of the invention (not
shown), natural gas, methane, or another hydrocarbon feedstock is
converted into higher hydrocarbons, and halogen (e.g., Br.sub.2) is
recovered by gas phase electrolysis of hydrogen halide (e.g., HBr).
Products from the coupling reactor (i.e., higher hydrocarbons and
HBr) are carried by a line to an HBr absorption unit, where
hydrocarbon products are separated from HBr. After residual organic
components are removed from the HBr in a separation unit, gaseous
HBr is carried by a line to the electrolytic cell. The gaseous HBr
is electrolyzed, forming molecular bromine and hydrogen. Wet
bromine is carried by a line to the dryer, where it is dried.
Optionally, if dry HBr is fed to the electrolysis cells, the dryer
can be eliminated.
[0065] FIG. 3 depicts one embodiment of another aspect of the
invention, in which natural gas, methane, or another hydrocarbon
feedstock is converted into methanol via the intermediate, methyl
bromide. Natural gas and gaseous bromine are carried by separate
lines 201 and 202 into a bromination reactor 203 and allowed to
react. The products (e.g., methyl bromide and HBr), and possibly
unreacted hydrocarbons, are carried by a line 204 through a heat
exchanger 205, which lowers their temperature. If necessary, the
gasses are further cooled by passing through a cooler 206. A
portion of the gasses 206 are carried by a line 207 to an HBr
absorber 208. The remainder by-passes the HBr absorber and are
carried by a line 209 directly to the reactor/absorber 210. The
split proportions are determined by the acid/base
disproportionation needed to achieve the proper pH in the reactor
absorber.
[0066] Water, optionally pre-treated in, e.g., a reverse osmosis
unit 211 to minimize salt content, is provided to the methanol
reactor 210 via line 212. In addition, a separate line 213 carries
water to the HBr absorber 208.
[0067] HBr solution formed in the HBr absorber 208 is sent via a
line 214 to a stripper 215 (where organics are separated by
stripping or other means) and then sent to the reactor/absorber 210
via a line 216. Gasses from the HBr absorber join the by-passed
stream from the cooler 206 and are carried by a line 209 to the
reactor/absorber 210. HBr solution from the stripper 215 is carried
by a line 217 to an HBr holding tank 218.
[0068] Aqueous sodium hydroxide (e.g., 5-30 wt %) is provided to
the methanol reactor 210 by a line 219. A weak NaBr/water solution
is also delivered to the methanol reactor 210 by a line 220.
[0069] In the methanol formation reactor, methyl bromide reacts
with water in the presence of strong base (sodium hydroxide), and
methanol is formed, along with possible byproducts such as
formaldehyde or formic acid. A liquid stream containing methanol,
by-products, aqueous sodium bromide, and aqueous sodium hydroxide
is carried away from the reactor via a line 221, to a stripper 222.
A portion of the bottom liquid from the reactor/absorber 210 is
circulated via a line 223 through a cooler 224 to control
temperature in the reactor/absorber 210.
[0070] The stripper 222 is equipped with a reboiler 225 and,
optionally, a partial reflux. Aqueous sodium bromide and sodium
hydroxide are removed with most of the water as the "bottoms"
stream of the stripper. The vapor exiting the top of the stripper
is carried by a line 226 to another distillation unit 227 equipped
with a reboiler 228 and a condenser 229. In the distillation unit
227, by-products are separated from methanol, and the methanol is
removed from the distillation unit 227 via a line 230, through a
cooler 231, to a storage tank 232. The vapor from the distillation
unit 227 (which contains by-products) is carried via a line 233
through the condenser 229 and then through a line 234 to a
by-product storage tank 235. Optionally, depending on the
particular by-products produced and their boiling points, methanol
may be taken as a distillate while by-products are recovered as
bottoms.
[0071] The effluent stream removed from the distillation unit 222
and reboiler 225 contains water and aqueous sodium bromide and
sodium hydroxide. This is carried away from the distillation unit
via a line 236 and cooled by passing through a cooler 237 before
being delivered to a sodium bromide holding tank 238. It is
desirable to lower the pH of this salt solution. This is
accomplished by metering the delivery of aqueous HBr from the
hydrogen bromide holding tank 218 via a line 239 to a pH control
device 240 coupled to the sodium bromide holding tank 238.
[0072] With the pH of the sodium bromide in the holding tank 238
brought to the desired level (e.g., slightly acidic), aqueous
sodium bromide is removed from the tank and carried via a line 241
through a filter 242, and delivered to an electrolytic cell 243,
having an anode 244 and a cathode 245. The filter is provided to
protect the membranes in the electrolytic cells. Preferably, a
series of electrolytic cells, rather than a single cell, is used as
an electrolyzer.
[0073] Aqueous sodium bromide is electrolyzed in the electrolytic
cell(s), with bromide ion being oxidized at the anode
(2Br.sup.-.fwdarw.Br.sub.2+2e.sup.-) and water being reduced at the
cathode (2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-). This results
in the formation of sodium hydroxide, which is carried away from
the electrolyzer as an aqueous solution via line 246 to a holding
tank 247. The sodium hydroxide solution is then routed to the
methanol reactor 210 via a line 219.
[0074] Molecular bromine is removed from the electrolyzer via a
line 248 to a compressor 249, and then to a dryer 250. The bromine
is returned to the bromination reactor 203 by passing it through a
heat exchanger 205 and, if necessary, a heater 251. Molecular
bromine that is dissolved in the anolyte is also removed from the
electrolytic cell(s) 243 by carrying the anolyte from the cell(s)
via a line 252 to a stripper 253, where bromine is removed by
stripping with natural gas (supplied via a line 254) or by other
means. The molecular bromine is carried by a line 255 to the
compressor 249, dryer 250, etc., before being returned to the
bromination reactor as described above.
[0075] Hydrogen generated in the electrolyzer is removed by a line
256, compressed in a compressor 257 and, optionally, routed to a
power generation unit 258. Residual methane or other inert gasses
can be removed from the methanol formation reactor via a line 259.
The methane or natural gas can be routed to the power generation
unit 258 to augment power generation. Additional natural gas or
methane can be supplied to the unit via a line 260 if needed.
[0076] In a laboratory implementation of elements of the process
depicted in FIG. 3, methane is reacted with gaseous bromine at
450.degree. C. in a glass tube bromination reactor, with a space
time is a 60 seconds. The products are methyl bromide, HBr, and
dibromomethane with a methane conversion of 75%. In the methanol
formation reactor, the methyl bromide, HBr, and dibromomethane,
react with water in the presence of sodium hydroxide to form
methanol and formaldehyde (from the dibromomethane). It is further
demonstrated that the formaldehyde is disproportionated to methanol
and formic acid. Hence, overall, the products are methanol and
formic acid.
[0077] The process shown in FIG. 3 employs membrane-type
electrolytic cells, rather than diaphragm-type cells. In a membrane
cell, sodium ions with only a small amount of water flow to the
cathode compartment. In contrast, in a diaphragm-type cell, both
sodium ions and water proceed into the cathode compartment. In an
alternate embodiment of the invention shown in FIG. 4, diaphragm
cells are used, resulting in continuous depletion of the anolyte
with respect to NaBr. To replenish the NaBr, depleted anolyte is
taken through a line 252 to a bromine stripper 253 where bromine is
removed and carried to a compressor 249 and then a dryer 250. NaBr
solution from the stripper 253 is carried by a line 270 to the NaBr
holding tank 238, where it combines with a richer NaBr solution.
Other features of the process are similar to those in FIG. 3.
[0078] In another aspect of the invention, molecular halogen is
recovered by electrolysis using a non-hydrogen producing cathode,
i.e., an oxygen depolarized cathode, which significantly reduces
the power consumption by producing water instead of hydrogen. FIG.
5 depicts one embodiment of this aspect of the invention, in this
case involving the production of higher hydrocarbons. The flow
diagram is similar to that shown in FIG. 1, with the differences
noted below.
[0079] Bromine and natural gas, methane, or another light
hydrocarbon are caused to react in a bromination reactor 303, and
followed by a coupling reactor 305. The organics and HBr are
separated in an HBr absorption unit 307. Aqueous sodium bromide is
carried via line 315 to an electrolytic cell 316 equipped with an
anode 317, oxygen depolarized cathode 318, and an oxygen inlet
manifold or line 324. Optionally, additional water or electrolyte
or pH control chemicals are carried into the cell via a line
319.
[0080] Molecular bromine is generated at the anode
(2Br.sup.-.fwdarw.Br.sub.2+2e.sup.-), and the wet bromine is
carried via a line 320 to a dryer 321, through a heater 323, and
then routed back to the bromination reactor 303. At the cathode,
oxygen is electrolytically reduced in the presence of water
(1/2O.sub.2+H.sub.2O+2e.sup.-.fwdarw.2OH.sup.-), and hydroxyl ions
are carried away as aqueous sodium hydroxide, via line 311, to the
HBr absorption unit 307.
[0081] The invention also provides an improved electrolytic cell
for converting halides into molecular halogen, one embodiment of
which is shown in FIG. 6. The cell 400 includes a gas supply
manifold 401, through which oxygen gas, air, or oxygen-enriched air
can be introduced; a gas diffusion cathode 402, which is permeable
to oxygen (or an oxygen-containing gas); a cation exchange membrane
403; a cathode electrolyte chamber 404 disposed between the cation
exchange membrane and the gas diffusion cathode; an anode
electrolyte chamber 405; and an anode 406, extending into the anode
electrolyte chamber. When operating under basic (alkaline)
conditions, water is introduced into the cathode electrolyte
chamber through a port 407, and aqueous sodium hydroxide is removed
from the chamber via another port 408. Similarly, aqueous sodium
bromide is introduced into the anode electrolyte chamber through a
port 409, and molecular bromine is carried away from the anode
electrolyte chamber via a line 410. The anode and cathode can be
connected to an electrical power supply (not shown), which may
include equipment for converting AC to DC current (e.g. mechanical
rectifier, motor-generator set, semiconductor rectifier,
synchronous converter, etc.) and other components.
[0082] In operation, water is introduced into the cathode
electrolyte chamber through the water inlet port 407, and aqueous
sodium bromide is introduced into the anode electrolyte chamber 405
through port 409. Oxygen flow through the gas supply manifold 401
is commenced and the power to the cell is turned on. Sodium bromide
is reduced at the anode, bromine gas is evolved and carried away by
line 410, and sodium ions are carried through the cation exchange
membrane into the cathode electrolyte chamber. At the cathode,
oxygen is electrolytically reduced to hydroxyl ion in the presence
of water. Aqueous sodium hydroxide exits the cathode electrolyte
chamber through port 408.
[0083] The electrolytic cell described herein can be used in
conjunction with various processes, including the embodiments
presented above. It is particularly advantageous when power
consumption is an issue, and where it is desirable not to form
hydrogen (for example, where the risk of fire warrants extra
precautions, such as on an offshore drilling rig).
[0084] Although the invention can be used in a variety of
industrial settings, particular value is realized where a
continuous process as described herein for making, e.g., higher
hydrocarbons or methanol, is carried out at an offshore oil rig or
drilling platform, or at a facility located onshore in a remote
location. Part of the utility lies in the conversion of a difficult
to transport material (e.g., natural gas) into a more easily
transported liquid material, such as higher hydrocarbons or
methanol. Another utility resides in the use of the production
facility's existing electrical generation capacity, such as an
electrical generator or other power supply.
[0085] According to one embodiment of this aspect of the invention,
an improved production facility where oil or gas is pumped from a
well and thereby extracted from the earth is provided, the facility
having an electrical generator or other electrical power supply,
the improvement comprising: (a) forming alkyl halides by reacting
molecular halogen with oil or gas pumped from the well, under
process conditions sufficient to form alkyl halides and hydrogen
halide; optionally with substantially complete consumption of the
molecular halogen; (b) forming higher hydrocarbons and hydrogen
halide by contacting the alkyl halides with a first catalyst under
process conditions sufficient to form higher hydrocarbons and
hydrogen halide; (c) separating the higher hydrocarbons from
hydrogen halide; and (d) converting the hydrogen halide into
hydrogen and molecular halogen electrolytically, using electricity
provided by the electrical generator or electrical power supply,
thereby allowing the halogen to be reused.
[0086] In another embodiment, an improved production facility where
oil or gas is pumped from a well and thereby extracted from the
earth is provided, the facility having an electrical generator or
other electrical power supply, the improvement comprising: (a)
forming alkyl halides by reacting molecular halogen with a
hydrocarbon feedstock under process conditions sufficient to form
alkyl halides and hydrogen halide, optionally with substantially
complete consumption of the molecular halogen; (b) forming methanol
and alkaline halide by contacting the alkyl halides with aqueous
alkali under process conditions sufficient to form methanol and
alkaline halide; (c) separating the methanol from the alkaline
halide; (d) converting the alkaline halide into hydrogen, molecular
halogen, and aqueous alkali electrolytically, using electricity
provided by the electrical generator or electrical power supply,
thereby allowing the halogen and the alkali to be reused.
[0087] In another aspect of the invention, the general approach
described above, including the steps of halogenation, product
formation, product separation, and electrolytic regeneration of
halogen is used to make alkyl amines. Thus, in one embodiment,
natural gas, methane, or another aliphatic hydrocarbon feedstock is
converted into alkyl amines via intermediate alkyl bromides. The
feedstock and gaseous bromine are carried by separate lines into a
bromination reactor and allowed to react. The bromination products
(e.g., methyl bromide and HBr), and possibly unreacted
hydrocarbons, are carried by a line through a heat exchanger, which
lowers their temperature. The alkyl bromides are then carried by a
line to an amination reactor. Ammonia or aqueous ammonia is also
provided to the amination reactor by a separate line. The alkyl
bromide and ammonia are allowed to react under process conditions
sufficient to form alkyl amines (e.g., RN.sub.2) and sodium
bromide, which are then separated in a manner analogous to that
described above with respect to the production of methanol. Aqueous
sodium bromide is carried by a line to an electrolytic cell or
cells, where it is converted into hydrogen and molecular bromine
electrolytically, thereby allowing the bromine to be reused in the
next cycle.
[0088] Referring now to FIGS. 7 and 8, two other aspects of the
invention are presented, in which coal is converted to higher value
coke, or coal or biomass is converted into higher value polyols
(poly-alcohols), and the halogen used in the process is regenerated
electrolytically. In the embodiments shown in FIG. 7, crushed coal
is allowed to react with molecular bromine at elevated temperature,
forming coke, HBr, and brominated coal intermediates
("C.sub.xBr.sub.n"). The brominated coal intermediates are
converted into coke by allowing them to contact a catalyst, thereby
forming additional hydrogen bromide. The coke and hydrogen bromide
are then separated, and the hydrogen bromide is then carried by a
line to an electrolytic cell or cells, similar to that described
above, thereby allowing molecular bromine to be regenerated and
reused.
[0089] FIG. 8 depicts a similar process in which coal or
biomass-derived hydrocarbons are brominated, thereby forming alkyl
bromines or alkyl bromides and HBr, which are then processed in a
manner analogous to that described above, e.g., the alkyl bromides
and HBr are at least partially separated and the alkyl bromides are
allowed to react with alkali, (e.g., sodium hydroxide), thereby
forming sodium bromide, water, and poly-alcohols
("C.sub.xH.sub.y-q(OH).sub.q"). The poly-alcohols are separated
from sodium bromide, and the aqueous sodium bromide is carried by a
line to an electrolytic cell or cells, where molecular bromine is
regenerated and subsequently separated and reused.
[0090] The following nonlimiting examples illustrate various
embodiments or features of the invention, including methane
bromination, C--C coupling to form higher hydrocarbons, e.g., light
olefins and aromatics (benzene, toluene, xylenes ("BTX")),
hydrolysis of methyl bromide to methanol, hydrolysis of
dibromomethane to methanol and formaldehyde, and subsequent
disproportionation to formic acid.
EXAMPLE 1
Bromination of Methane
[0091] Methane (11 sccm, 1.0 atm) was combined with nitrogen (15
sccm, 1.0 atm) at room temperature via a mixing tee and passed
through an 18.degree. C. bubbler full of bromine. The
CH.sub.4/N.sub.2/Br.sub.2 mixture was passed into a preheated glass
tube (inside diameter 2.29 cm, length, 30.48 cm, filled with glass
beads) at 500.degree. C., where bromination of methane took place
with a residence time of 60 seconds, producing primarily
bromomethane, dibromomethane and HBr:
CH.sub.4+Br.sub.2.fwdarw.CH.sub.3Br+CH.sub.2Br.sub.2+HBr
[0092] As products left the reactor, they were collected by a
series of traps containing 4M NaOH, which neutralized the HBr and
hexadecane (containing octadecane as an internal standard) to
dissolve as much of the hydrocarbon products as possible. Volatile
components like methane were collected in a gas bag after the
HBr/hydrocarbon traps.
[0093] After the bromination reaction, the coke or carbonaceous
deposits were burned off in a flow of heated air (5 sccm) at
500.degree. C. for 4 hours, and the CO.sub.2 was captured with a
saturated barium hydroxide solution as barium carbonate. All
products were quantified by GC. The amount of coke was determined
based on the CO.sub.2 evolution from decoking. The results are
summarized in FIG. 9.
EXAMPLE 2
CH.sub.3Br Coupling to Light Olefins
[0094] 2.27 g of a 5% Mg-doped ZSM-5 (CBV8014) zeolite was loaded
in a tubular quartz reactor (1.0 cm ID), which was preheated to
400.degree. C. before the reaction. CH.sub.3Br, diluted by N.sub.2,
was pumped into the reactor at a flow rate of 24 .mu.l/min for
CH.sub.3Br, controlled by a micro liquid pump, and 93.3 ml/min for
N.sub.2. The CH.sub.3Br coupling reaction took place over the
catalyst bed with a residence time of 0.5 sec and a CH.sub.3Br
partial pressure of 0.1 based on this flow rate setting.
[0095] After one hour of reaction, the products left the reactor
and were collected by a series of traps containing 4M NaOH, which
neutralized the HBr and hexadecane (containing octadecane as an
internal standard) to dissolve as much of the hydrocarbon products
as possible. Volatile components like methane and light olefins
were collected in a gas bag after the HBr/hydrocarbon traps.
[0096] After the coupling reaction, the coke or carbonaceous
deposits were burned off in a flow of heated air (5 sccm) at
500.degree. C. for 4 hours, and the CO.sub.2 was captured with a
saturated barium hydroxide solution as barium carbonate. All
products were quantified by GC. The amount of coke was determined
based on the CO.sub.2 evolution from decoking. The results are
summarized in FIG. 10.
[0097] Even at such a short residence time, CH.sub.3Br conversion
reached 97.7%. Among the coupling products, C.sub.3H.sub.6 and
C.sub.2H.sub.4 are the major products, and the sum of them
contributed to 50% of carbon recovery. BTX, other hydrocarbons,
bromohydrocarbons and a tiny amount of coke made up the balance of
the converted carbon.
EXAMPLE 3
CH.sub.3Br Coupling to BTX
[0098] Pellets of Mn ion exchanged ZSM-5 zeolite (CBV3024, 6 cm in
length) were loaded in a tubular quartz reactor (ID, 1.0 cm), which
was preheated to 425.degree. C. before the reaction. CH.sub.3Br,
diluted by N.sub.2, was pumped into the reactor at a flow rate of
18 .mu.l/min for CH.sub.3Br, controlled by a micro liquid pump, and
7.8 ml/min for N.sub.2. The CH.sub.3Br coupling reaction took place
over the catalyst bed with a residence time of 5.0 sec and a
CH.sub.3Br partial pressure of 0.5 based on this flow rate
setting.
[0099] After one hour of reaction, the products left the reactor
and were collected by a series of traps containing 4M NaOH, which
neutralized the HBr and hexadecane (containing octadecane as an
internal standard) to dissolve as much of the hydrocarbon products
as possible. Volatile components like methane and light olefins
were collected in a gas bag after the HBr/hydrocarbon traps.
[0100] After the coupling reaction, the coke or carbonaceous
deposits were burned off in a flow of heated air (5 sccm) at
500.degree. C. for 4 hours, and the CO.sub.2 was captured with a
saturated barium hydroxide solution as barium carbonate. All
products were quantified by GC. The amount of coke was determined
based on the CO.sub.2 evolution from decoking. The results are
summarized in FIG. 8.
[0101] With this BTX maximum operation mode, CH.sub.3Br can be
converted completely. BTX yield reached 35.9%. Other hydrocarbons,
aromatics, bromohydrocarbons, and coke contributed to the carbon
recovery of 51.4%, 4.8%, 1.0%, and 6.9% respectively. Propane is a
major components of the "other hydrocarbons," and can be sent back
for reproportionation followed by further coupling to boost the
overall BTX yield even higher.
EXAMPLE 4
Caustic Hydrolysis of Bromomethane to Methanol
[0102] CH.sub.3Br+NaOH CH.sub.3OH+NaBr
[0103] In a 30 ml stainless steel VCR reactor equipped with a stir
bar, 13.2 g 1M sodium hydroxide aqueous solution (13.2 mmol) and
1.3 g bromomethane (12.6 mmol) were added in sequence. The reactor
was gently purged with nitrogen to remove the upper air before
closing the cap. The closed reactor was placed in an aluminum
heating block preheated to 150.degree. C. and the reaction started
simultaneously. The reaction was run for 2 hours at this
temperature with stirring.
[0104] After stopping the reaction, the reactor was placed in an
ice-water bath for a start time to cool the products inside. After
opening the reactor, the reaction liquid was transferred to a
vessel and diluted by cold water. The vessel was connected with a
gas bag used to collect the un-reacted bromomethane, if any. The
reaction liquid was weighed and the product concentrations were
analyzed with a GC-FID, in which an aqueous injection applicable
capillary column was installed.
[0105] The gas product analysis shows that there was no
bromomethane remaining, indicating that bromomethane was converted
completely. Based on the concentration measurements for the liquid
product, the methanol yield including tiny amount of dimethyl
ether, was calculated to be 96%.
EXAMPLE 5
Caustic Hydrolysis of Dibromomethane to Formaldehyde Followed by
Disproportionation to Methanol and Formic Acid
[0106] CH.sub.2Br.sub.2+2NaOH.fwdarw.HCHO+2NaBr+H.sub.2O
HCHO+1/2H.sub.2O.fwdarw.1/2CH.sub.3OH+1/2HCOOH
[0107] Caustic hydrolysis of dibromomethane was carried out
according to the same procedure as in Example 5, with the exception
that a high NaOH/CH.sub.2Br.sub.2 ratio (2.26) was employed. After
collecting the reaction liquid, a sufficient quantity of
concentrated hydrogen chloride solution was added to neutralize the
extra sodium hydroxide and acidify sodium formate. Methanol and
formic acid were observed to be the only products, indicating that
hydrolysis to methanol and formaldehyde was followed by complete
disproportionation of formaldehyde to (additional) methanol and
formic acid. The GC analysis shows that the conversion of
dibromomethane reached 99.9%; while the yields of methanol and
formic acid reached 48.5% and 47.4% respectively.
[0108] Examples 4 and 5 demonstrate that bromomethane can be
completely hydrolyzed to methanol, and dibromomethane can be
completely hydrolyzed to methanol and formic acid, under mild
caustic conditions. The results are summarized in Table 1.
TABLE-US-00001 TABLE 1 Caustic Hydrolysis of CH.sub.3B and
CH.sub.2B.sub.2 and Subsequent Disproportionation of HCHO Starting
from CH.sub.3Br CH.sub.2Br.sub.2 NaOH/CH.sub.3Br or
CH.sub.2Br.sub.2 1.05 2.17 Temperature (.degree. C.) 150 150
Reaction time (hr) 2 2 Conversion (%) 100.0 99.9 CH.sub.3OH yield
(%) 96.0 48.5 HCOOH yield (%) 47.4
[0109] The invention has been described with reference to various
representative and preferred embodiments, but is not limited
thereto. Other modifications and equivalent arrangements, apparent
to a skilled person upon consideration of this disclosure, are also
included within the scope of the invention.
[0110] As one example, molecular bromine can also be removed from
the electrolytic cell(s) using a concurrent extraction technique,
wherein an inert organic solvent, such as chloroform, carbon
tetrachloride, ether, etc. is used. The solvent is introduced on
one side of a cell; bromine partitions between the aqueous and
organic phases; and bromine-laden solvent is withdrawn from another
side of the cell. Bromine can then be separated from the solvent by
distillation or another suitable technique and then returned to the
system for reuse. Partitioning is favored by bromine's
significantly enhanced solubility in solvents such as chloroform
and carbon tetrachloride, as compared to water. Extraction in this
way serves a dual purpose: it separates Br.sub.2 from other forms
of bromine that may be present (e.g., Br.sup.-, OBr.sup.-, which
are insoluble in the organic phase); and it allows bromine to be
concentrated and easily separated from the organic phase (e.g., by
distillation). An optimal pH for extraction (as well as for
separation of bromine by heating bromine-containing aqueous
solutions in a gas flow) is pH 3.5--the pH at which the
concentration of molecular bromine (Br.sub.2) is at its highest, as
compared to other bromine species.
[0111] As another example of modifications to the process disclosed
herein, various pumps, valves, heaters, coolers, heat exchangers,
control units, power supplies, and equipment in addition or in the
alternative to that shown in the figures can be employed to
optimize the processes. In addition, other features and
embodiments, such as described in the '358 application and
elsewhere, can be utilized in the practice of the present
invention. The invention is limited only by the accompanying claims
and their equivalents.
* * * * *