Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROCESS FOR CONVERTING HYDROCARBON FEEDSTOCKS WITH
ELECTROLYTIC RECOVERY OF HALOGEN
FIELD OF THE INVENTION
[0001] 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
[00021 U.S. Patent Application No. 11/703,358 ("the '358 application."),
entitled "Continuous
Process for Converting Natural Gas to Liquid Hydrocarbons", filed February 5,
2007, based on
U.S. Provisional Application No. 60/765,115, filed February 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.
[0003] 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., Br2, C12) from hydrohalic acid (e.g., HBr, HCI).
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[0004] 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 refoiniing of
hydrocarbons with water (steam) to produce carbon monoxide and molecular
hydrogen:
CH4 +.H20 --> CO + 3H2 AH = +206 kJ/mol
CxHy + xH2O -- xCO +(x+y/2)H2 AH >> 0 kJ/ mol
[0005] 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:
CH4 + 202 -+ COZ + 2H20 AH= -882 kJ/ mol
CxHy +(x+y/2)OZ -+ xCO2 + y/2H20 AH 0 kJ/ mol
[0006] 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:
CõHm + x02 + yH2O --> (n-m)CO + mCO2 + (m/2+y)H2
[0007] Alternatively, hydrogen can be produced by dissociation of water:
H20 --+ 1/202 + H2 AH= 286 kJ/ mol H2
[0008] Although energetically unfavorable, the reaction can be driven by
electrolysis using
2x105 Coulombs per gram-mole H2. 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 H2.
[0009] In halogen production by electrolysis of halide salts, e.g. the
chloralkali process,
halogen (C12) and alkali base (NaOH) are produced from the baloanion and water
in an aqueous
solution of salt (NaCI). Water is again the source of the hydrogen. Similarly,
bromine can be
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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):
H20 + NaBr --> Br2 + HZ + NaOH
(0010] With 2x 105 Coulombs per gram-mole H2 and the required electrical
energy reduced
significantly (compared to H20 alone) to approximately 200 kJ/g mol H2.
[0011] 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
(AHfo1,,,.UOõ = -36 kJ/ mol),
rather than water (AHfmti,õ = -286 kJ/ mol):
CõHm +p/2Br2 - CõHm_pBrp +pHBr
CõHZBrZ + x/2Br2 -- CõHZBrP +xHBr
[0012] Final products after removal of HBr depend on the reaction conditions
and may consist
of mixtures of coke and brominated and perbrominated hydrocarbons:
C,,+CyHZBrt+CrBrq.
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, + CyHZBrt + C~Brq + n/202 + (t+q)/2H20 --> (x+y+r=n)CO2 + (t+q)HBr
[0013] Another process for maldng 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
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bromine generated in electrolysis to produce valuable products, rather than
simply converting it
back to HBr.
SUMMARY OF THE INVENTION
[0014] 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.
[0015] 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 bydrogen 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.
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[0016] 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.
[0017] 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.
[0018] 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
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off-site generation. Alternatively, an overall excess of acid can be achieved
by removal of a small
amount of alkali from the system.
[0019) In a third aspect of the invention, a continuous process for converting
a hydrocarbon
feedstock into an alkyl amine comprises: (a) forrning 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.
[0020] 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) fomaing 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
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electrical power for the process (via combustion, steam generation, and
production of electricity),
or collected and sold.
[0021] 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)
fonning 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, altematively, 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.
[0022] 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.
[0023] 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.,
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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.
[00241 The present conventional commercial process for utilizing methane,
coal, and other
hydrocarbons yields syngas (CO + H2), 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:
= Use of alkyl halide intermediates to produce higher value products,
including fuels and
higher value chemicals.
= Lower operating pressure(e.g., -1-5atm vs. -80atm).
= Lower peak operating temperature ( e.g., -50 C vs. -1,000 C).
= No need for pure oxygen
= No fired reformer, and thus greater safety when used on offshore platforms.
= Simple reactor design vs. complex syngas-to-methanol converter.
= No catalyst necessary vs. catalysts required for reforming and for syngas
conversion.
= Fewer by-products and thus simpler methanol purification operations.
= No steam supply for reforming is needed.
= Hydrogen is produced on a separate electrode as a relatively pure product.
= The reaction is pushed to completion in the final step by the removal of
products from the
reaction vessel.
[0025] 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
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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 brorriide) 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.
[0026] 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 withthe production
of oil and/or gas,
using electricity generated on-site to power the electrolytic cell(s).
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] 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:
[0028] 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;
[0029] 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;
[0030] 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;
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[0031] 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;
[0032] 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;
[0033] FIG. 6. is a schematic illustration of an electrolytic cell according
to one embodiment of
the invention;
[0034] FIG. 7 is a schematic illustration of a continuous process for
converting coal into coke
and hydrogen, according to one embodiment of the invention;
[0035] 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;
[0036] FIG. 9 is a chart illustrating product selectivity for bromination of
methane according to
one embodiment of the invention;
[0037] FIG. 10 is a chart illustrating product selectivity for coupling of
methyl bromide
according to one embodiment of the invention; and
[0038] 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
[0039] 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
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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 C1-C3 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.
[0040] The hydrocarbon feedstock is converted into higher products by reaction
with molecular
halogen, as described below. Bromine (Br2) and chlorine (C12) are preferred,
with bromine being
most preferred, in part because the over potential required to convert Br to
Br2 is significantly
lower than that required to convert Cl- to ClZ (1.09V for Br vs. 1.36V for
Cl'. 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.
[0041] 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
C2 or higher
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hydrocarbon,.such as ethane, propane, butane, C5+ hydrocarbons, aromatic
hydrocarbons, etc., and
optionally ethylene, propylene and/or longer olefins. The term "light
hydrocarbons" (sometimes
abbreviated "LHCs") refers to Ci-C4 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.
[0042] Both in this written description and in the claims, when chemical
substances are refen:ed
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).
[0043] 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. Refen-ing 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 olefms), 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.
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[0044) 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 Al, at pages 4-5, which is incorporated by reference herein in
its entirety.
[00451 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.
[0046] 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.
[0047) 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,
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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 - Br2 + 2e ) and water being
reduced at the cathode
(2H20 + 2e -+ H2 + 20H'. Aqueous sodium hydroxide is removed from the
electrolyzer and
routed to the HBr absorption unit via line 11.
[0048] 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.
Altematively; 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.
[0049] 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
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found in U.S. Patent 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.
[0050] 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 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 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 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
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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 --), Br2 + 2e-) and water being reduced at the cathode (2H20 +
2e -+ H2 + 20H7.
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.
[0051] Refening 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 Br2 is evolved and removed from the electrolyzer, the
concentration of
HBr in the electrolyzer drops. The resulting lean aqueous HBr, along with some
bromine (Br2)
entrained or dissolved therein, is carried by a line 25 to a bromine stripper
26, which separates
bromine (Br2) 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.
[0052] In another embodiment of this aspect of the invention (not shown),
natural gas,
methane, or another hydrocarboin feedstock is converted into higher
hydrocarbons, and halogen
(e.g., Br2) 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.
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The gaseous HBr is electrolyzed, forming molecular broniine 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.
[0053] 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.
[0054] 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.
[0055] 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.
[0056] 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.
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100571 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.
[0058] 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.
100591 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.
[0060] 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
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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.
[0061] Aqueous sodium bromide is electrolyzed in the electrolytic. cell(s),
with bromide ion
being oxidized at the anode (2Br -- Br2 + 2e7 and water being reduced at the
cathode (2H20 +
2e- --). H2 + 20H-). 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.
[0062] 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 canying
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 retumed to the bromination
reactor as described
above.
[0063] 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.
[0064] In a laboratory implementation of elements of the process depicted in
FIG. 3, methane is
reacted with gaseous bromine at 450 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
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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.
[0065] 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 catried 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.
[0066] 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.
[0067] 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.
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[0068] Molecular bromine is generated at the anode (2Br --- Br2 + 2e7), 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 ('/z02 +
H20 + 2e - 20H-), and hydroxyl ions are carried away as aqueous sodium
hydroxide, via line
311, to the HBr absorption unit 307.
(0069] 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.
[0070] 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 tumed 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
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in the presence of water. Aqueous sodium hydroxide exits the cathode
electrolyte chamber through
port 408.
[0071] 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).
[0072] 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.
[0073] 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 fonn 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.
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100741 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.
[0075] 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.,
RN2) 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.
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[0076] 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,,Br,;').
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.
[00771 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
("CXHy_q(OH)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.
[0078] 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.
[0079] Example 1 Bromination of Methane
Methane (11 sccm, 1.Oatm) was combined with nitrogen (15 sccm, 1.Oatm) at room
temperature via a mixing tee and passed through an 18 C bubbler full of
bromine. The CH4/N2/Br2
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mixture was passed into a preheated glass tube (inside diameter 2.29 cm,
length, 30.48 cm, filled
with glass beads) at 500 C, where bromination of methane took place with a
residence time of 60
seconds, producing primarily bromomethane, dibromomethane and HBr:
CH4 + Br2 -- CH3Br + CH2Br2 + HBr
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.
After the bromination reaction, the coke or carbonaceous deposits were burned
off in a flow of
heated air (5sccm) at 500 C for 4 hours, and the CO2 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 CO2 evolution from decoking. The results are
summarized in FIG. 9.
Example 2 CH3Br Coupling to Light Olefins
2.27g of a 5% Mg-doped ZSM-5 (CBV8014) zeolite was loaded in a tubular quartz
reactor (1.0cm
ID), which was preheated to 400 C before the reaction. CH3Br, diluted by N2,
was pumped into the
reactor at a flow rate of 24 l/min for CH3Br, controlled by a micro liquid
pump, and 93.3m1/min
for N2. The CH3Br coupling reaction took place over the catalyst bed with a
residence time of
0.5sec and a CH3Br partial pressure of 0.1 based on this flow rate setting.
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.
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After the coupling reaction, the coke or carbonaceous deposits were burned off
in a flow of heated
air (5sccm) at 500 C for 4hours, and the CO2 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 CO2 evolution from decoking. The results are
summarized in FIG. 10.
Even at such a short residence time, CH3Br conversion reached 97.7%. Among the
coupling
products, C3H6 and C2H4 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 CH3Br Coupling to BTX
Pellets of Mn ion exchanged ZSM-5 zeolite (CBV3024, 6 cm in length) were
loaded in a tubular
quartz reactor (ID, 1.0cm), which was preheated to 425 C before the reaction.
CH3Br, diluted by
N2, was pumped into the reactor at a flow rate of 181il/min for CH3Br,
controlled by a micro liquid
pump, and 7.8ml/min for N2. The CH3Br coupling reaction took place over the
catalyst bed with a
residence time of 5.0 sec and a CH3Br partial pressure of 0.5 based on this
flow rate setting.
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.
After the coupling reaction , the coke or carbonaceous deposits were burned
off in a flow of heated
air (5sccm) at 500 C for 4hours, and the, COZ 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 CO2 evolution from decoking. The results are
summarized in FIG. 8.
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With this BTX maximum operation mode, CH3Br 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
CH3Br + NaOH -> CH3OH + NaBr
In a 30m1 stainless steel VCR reactor equipped with a stir bar, 13.2g IM
sodium hydroxide
aqueous solution (13.2mmo1) and 1.3g bromomethane (12.6mmol) 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 C and the
reaction started
simultaneously. The reaction was run for 2 hours at this temperature with
stirring.
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.
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
CH2Br2 + 2NaOH --~ HCHO + 2NaBr + H20
HCHO + 1/2H20 -> 1/2CH3OH + 1/2HCOOH
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Caustic hydrolysis of dibromomethane was carried out according to the same
procedure as in
Example 5, with the exception that a high NaOH/CH2Br2 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.
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.
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Table I
Caustic Hydrolysis of CH3B and CH2B2 and
Subsequent Disproportionation of HCHO
Starting from
CH3Br CH2Br2
NaOH/CH3Br or CH2Br2 1.05 2.17
Temperature ( C) 150 150
Reaction time (hr) 2 2
Conversion (%) 100.0 99.9
CH3OH yield (%) 96.0 48.5
HCOOH yield (%) 47.4
[0080] 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.
[0081] 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
tetrachioride, as
compared to water. Extraction in this way serves a dual purpose: it separates
Br2 from other forms
of bromine that may be present (e.g., Br , OBr , which are insoluble in the
organic phase); and it
allows bromine to be concentrated and easily separated from the organic phase
(e.g., by
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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 (Br2) is at its highest, as compared to other bromine
species.
100821 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 altemative 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.
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