U.S. patent application number 14/730413 was filed with the patent office on 2015-12-17 for conversion of carboxylic acids to alpha-olefins.
The applicant listed for this patent is CERAMATEC, INC.. Invention is credited to Patrick McGuire, James M. Mosby.
Application Number | 20150361565 14/730413 |
Document ID | / |
Family ID | 54834122 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150361565 |
Kind Code |
A1 |
Mosby; James M. ; et
al. |
December 17, 2015 |
Conversion of Carboxylic Acids to Alpha-Olefins
Abstract
An electrolytic method of producing olefins from alkali metal
salts of carboxylic acids is disclosed. The carboxylic acid may be
from a variety of sources including fermented biomass that is
subsequently neutralized using an alkali metal base. The method
enables the efficient production of olefins including alpha-olefins
as well as useful olefin products such as synthetic oils.
Inventors: |
Mosby; James M.; (Salt Lake
City, UT) ; McGuire; Patrick; (Salt Lake City,
UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CERAMATEC, INC. |
Salt Lake City |
UT |
US |
|
|
Family ID: |
54834122 |
Appl. No.: |
14/730413 |
Filed: |
June 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62012053 |
Jun 13, 2014 |
|
|
|
Current U.S.
Class: |
205/413 ;
204/252 |
Current CPC
Class: |
Y02E 60/36 20130101;
C25B 9/08 20130101; C25B 3/02 20130101; C25B 3/00 20130101; C25B
1/04 20130101; Y02E 60/366 20130101 |
International
Class: |
C25B 9/08 20060101
C25B009/08; C25B 3/00 20060101 C25B003/00 |
Goverment Interests
U.S. GOVERNMENT INTEREST
[0002] This invention was made with government support under
Contract No. 2012-10008-20263 awarded by the U.S. Department of
Agriculture, National Institute of Food and Agriculture. The
government has certain rights in the invention.
Claims
1. A electrochemical method of preparing olefins from an alkali
metal salt of a carboxylic acid, comprising: providing an
electrochemical cell comprising: an anolyte compartment comprising
an electrochemically active anode selected to perform a
two-electron decarboxylation reaction of an alkali metal salt of a
carboxylic acid, wherein the anode comprises a carbonaceous
surface; a catholyte compartment comprising an electrochemically
active cathode where reduction reactions occur; an alkali ion
conductive membrane separating the anolyte compartment from the
catholyte compartment that permits selective transport of alkali
ions between the anolyte compartment and the catholyte compartment;
providing a solution of an alkali metal salt of the carboxylic acid
to the anolyte compartment, wherein the solution has a pH in the
range from about 8 to 14; and applying an electrical potential to
the anode and cathode to electrochemically decarboxylate the
carboxylic acid salt into one or more olefins.
2. The method of claim 1, wherein the cell has a voltage between 2
and 20 volts.
3. The method of claim 1, wherein a current density of between 5
and 100 mA/cm.sup.2 is applied to the anode.
4. The method of claim 1, wherein the solution has a pH in the
range of about 10 to 12.
5. The method of claim 1, further comprising mixing the alkali
metal salt of the carboxylic acid with an organic solvent.
6. The method of claims 5, wherein the organic solvent comprises
one or more organic alcohols and mixtures thereof.
7. The method of claim 6, wherein the one or more organic alcohols
are selected from the group consisting of: methanol, ethanol,
propanol, isopropanol, butanol, and mixtures of the same.
8. The method of claim 5, wherein the organic solvent is selected
form the group consisting of: acetonitrile, dimethylformamide,
sulfolane, pyridine, 2,6-pyridine, and mixtures thereof.
9. The method of claim 1, further comprising adjusting the pH of
the alkali metal salt of the carboxylic acid with a base.
10. The method of claim 9, wherein the base is an alkali metal
hydroxide.
11. The method of claim 1, further comprising mixing the alkali
metal salt of the carboxylic acid with an electrolyte selected from
the group consisting of: a metal halide, a metal nitrate, a metal
sulfate, a metal perchlorate, and a metal tetrafluoroborate.
12. The method of claim 1, wherein the alkali ion conducting
membrane is a NaSICON membrane.
13. The method of claim 1, further comprising fermenting biomass to
produce the carboxylic acid and neutralizing the carboxylic acid
with an alkali metal hydroxide to form the alkali metal salt of the
carboxylic acid.
14. The method of claim 1, wherein the alkali metal salt of the
carboxylic acid has an even number of carbon atoms.
15. The method of claim 1, wherein the alkali metal salt of the
carboxylic acid is derived from a carboxylic acid selected from the
group consisting of: octanoic acid, decanoic acid, dodecanoic acid,
tetradecanoic acid, hexadecanoic acid, and octadecanoic acid.
16. The method of claim 1, wherein the one or more olefins
comprises an alpha-olefin.
17. The method of claim 1, wherein the olefin comprises
1-undecene.
18. The method of claim 1, further comprising oligomerizing the one
or more olefins to make a synthetic lubricant.
19. An electrochemical reactor comprising: an anolyte compartment
comprising: an alkali metal salt of a carboxylic acid having a pH
in the range from about 9 to 12; and an electrochemically active
anode selected to perform a two-electron decarboxylation reaction
of the alkali metal salt of carboxylic acid, wherein the anode
comprises a carbonaceous surface; a catholyte compartment housing
an electrochemically active cathode where reduction reactions
occur; an alkali ion conductive membrane separating the anolyte
compartment from the catholyte compartment that permits selective
transport of alkali ions between the anolyte compartment and the
catholyte compartment; and a source of electric potential connected
to the anode and to the cathode.
20. The electrochemical reactor of claim 19, wherein the alkali
metal ion is sodium and the alkali ion conducting membrane is a
NaSICON membrane.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 62/012,053 entitled "CONVERSION OF
BIOMASS TO ALPHA-OLEFINS," filed Jun. 13, 2014, which application
is incorporated by reference.
TECHNICAL FIELD
[0003] The present application relates to methods of preparing
olefins from carboxylic acids, particularly using electrolytic
techniques.
BACKGROUND
[0004] For over a decade, government agencies like the U.S.
Department of Energy have investigated biomass conversion into
biofuels, bioproducts and biopower leading to advances in the
research, development and deployment of different bioenergy
technologies. The majority of this effort has focused on producing
biofuels for the transportation markets, with successes in the
renewable gasoline, biodiesel and bio-jet markets. Yet, the current
large supply of natural gas and liquid petroleum from fracking
technologies has made it difficult for biofuels to compete
economically in these high-volume, low-margin markets.
[0005] The development of biofuels and other bioproducts has also
resulted in the development of technologies for converting and
upgrading those fuels and other bioproducts for specialty chemicals
such as synthetic lubricants. High quality synthetic based oil is
mainly composed of poly-alpha-olefins (PAOs), for which market
demand outweighs available supply. The disparity between the supply
and demand for PAOs arises because the necessary starting material
is made using fractions of petroleum that are used in the
production of kerosene and diesel. In most crude oil refineries,
the later products take priority over the PAOs, and thus limited
amounts of these fractions are diverted to make PAOs. To produce
PAOs, not only is the volume of diesel and kerosene reduced, but
the refinery must invest additional money and energy into
converting the hydrocarbons from these fractions to alpha-olefins.
This process produces a range of alpha-olefins, of which only a few
have significant commercial value. One of the more valuable
alpha-olefins, 1-dodecene (C12 alpha-olefin), is selectively used
to make the PAOs for synthetic lubricants.
[0006] Another route currently used for the production of olefins
requires steam cracking hydrocarbons to produce ultra-high-purity
ethylene, followed by ethylene oligomerization that produces
1-decene (C10 alpha-olefin) and 1-dodecene. Because of the high
production cost, the supply of C12 alpha-olefins available to make
the PAOs synthetic oil is limited even though there is a large
commercial market for this high performance oil. The higher market
demand for PAO synthetic oil arises from their improved lubricating
properties such as: higher viscosity index, lower temperature
fluidity, lower volatility, better oxidative stability, greater
thermal stability, and lower traction force.
[0007] Thus, there remains a need for alternative techniques for
preparing alpha-olefins using hydrocarbon feedstock derived from
biomass.
SUMMARY OF THE INVENTION
[0008] In one aspect, an electrochemical method of preparing
olefins from an alkali metal salt of a carboxylic acid is
disclosed. The method includes providing an electrochemical cell
having an anolyte compartment, a catholyte compartment, and an
alkali ion conductive membrane separating the anolyte compartment
from the catholyte compartment. The method further includes
providing an anolyte solution of an alkali metal salt of the
carboxylic acid to the anolyte compartment. The anolyte solution
may have a pH in the range from about 8 to 14. An electrical
potential is applied to the anode and cathode to electrochemically
decarboxylate the alkali metal salt of the carboxylic acid into one
or more olefins.
[0009] The anolyte compartment comprises an electrochemically
active anode selected to perform a two-electron decarboxylation
reaction of the alkali metal salt of the carboxylic acid, wherein
the anode comprises a carbonaceous surface. The catholyte
compartment comprises an electrochemically active cathode where
reduction reactions occur. The alkali ion conductive membrane
permits selective transport of alkali ions between the anolyte
compartment and the catholyte compartment under influence of the
electric potential.
[0010] In some embodiments, the current has a voltage between 2 and
20 volts. In other embodiments, the voltage is between 4 and 12
volts. In some embodiments, the current has a current density of
between 5 and 100 mA/cm.sup.2. In other embodiments, the current
density is between 5 and 50 mA/cm.sup.2. In some embodiments, the
carboxylic acid is neutralized to have a pH between about 8 and 14.
In other embodiments, the pH is between 9 and 13. In still other
embodiments, the pH is between 10 and 12.
[0011] In some non-limiting embodiments, the method also includes
mixing the alkali metal salt of the carboxylic acid with an organic
solvent. In some embodiments the organic solvent comprises one or
more organic alcohols and mixtures thereof. In some embodiments,
the one or more organic alcohols are selected from the group
consisting of: methanol, ethanol, propanol, isopropanol, butanol,
and mixtures thereof. In other embodiments, the organic solvent is
selected form the group consisting of: acetonitrile,
dimethylformamide, sulfolane, pyridine, 2,6-pyridine, and mixtures
of the same.
[0012] In some non-limiting embodiments, the method also includes
adjusting the pH of the alkali metal salt of the carboxylic acid
with a base. In some embodiments, the base is an alkali metal
hydroxide. In some embodiments, the base is sodium hydroxide.
[0013] In some non-limiting embodiments, the method also includes
mixing the alkali metal salt of the carboxylic acid with an
electrolyte selected from the group consisting of: a metal halide,
a metal nitrate, a metal sulfate, a metal perchlorate, and a metal
tetrafluoroborate.
[0014] In some non-limiting embodiments, the alkali ion conducting
membrane is a NaSICON membrane.
[0015] In some non-limiting embodiments, the method also includes
fermenting biomass to produce the carboxylic acid and neutralizing
the carboxylic acid with an alkali metal hydroxide to form the
alkali metal salt of the carboxylic acid. The carboxylic acid may
have an even number of carbon atoms. In some embodiments, the
carboxylic acid is selected from the group consisting of: octanoic
acid, decanoic acid, dodecanoic acid, tetradecanoic acid,
hexadecanoic acid, and octadecanoic acid. In some embodiments, the
carboxylic acid is dodecanoic acid.
[0016] In some embodiments, the one or more olefins is an
alpha-olefin. In some embodiments, the one or more olefins is
1-undecene. In another aspect, a method further comprises
oligomerizing the one or more olefins to make a synthetic
lubricant.
[0017] In another aspect, an electrochemical cell or reactor for
producing olefins is disclosed. The reactor includes an anolyte
compartment, a catholyte compartment, an alkali ion conductive
membrane, and a source of electric potential to operate the
electrochemical reactor.
[0018] The anolyte compartment includes a solution of an alkali
metal salt of a carboxylic acid. The solution has a pH in the range
from about 8 to 14, and preferably a pH in the range from 9 to 13,
and more preferably a pH in the range from about 10 to 12. The
anolyte compartment includes an electrochemically active anode
selected to perform a two-electron decarboxylation reaction of the
alkali metal salt of carboxylic acid. In one embodiment, the anode
comprises a carbonaceous surface.
[0019] The catholyte compartment houses an electrochemically active
cathode where reduction reactions occur.
[0020] The alkali ion conductive membrane separates the anolyte
compartment from the catholyte compartment and permits selective
transport of alkali ions between the anolyte compartment and the
catholyte compartment.
[0021] The source of electric potential is electrically connected
to the anode and to the cathode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Embodiments of the innovations described herein will be best
understood by reference to the enclosed drawings. It will be
readily understood that the components of the present invention, as
generally described, could be arranged and designed in a wide
variety of different configurations. Thus, the following more
detailed description of the embodiments of the methods and cells of
the present innovations is not intended to limit the scope of the
invention, as claimed, but is merely representative of embodiments
described herein.
[0023] FIG. 1 is a schematic representation of a possible
electrochemical reactor that may be used in the disclosed method of
preparing olefins from carboxylic acids.
[0024] FIG. 2A is a graph showing voltage and current density
verses time for comparative one electron decarboxylation of sodium
octanoate to a hydrocarbon dimer coupling product.
[0025] FIG. 2B is a gas chromatograph showing the resulting
products from applying voltage and current densities for the
decarboxylation process from FIG. 2A.
[0026] FIG. 3A is a graph showing voltage and current density
verses time for a two electron decarboxylation of sodium
dodecanoate to olefins.
[0027] FIG. 3B is a chromatograph showing the resulting products
from applying voltage and current densities for the decarboxylation
process from FIG. 3A.
DETAILED DESCRIPTION
[0028] Reference throughout this specification to "one embodiment,"
"an embodiment," or similar language means that a particular
feature, structure, or characteristic described in connection with
the embodiment is included in at least one embodiment of the
innovation described herein. Thus, appearances of the phrases "in
one embodiment," "in an embodiment," and similar language
throughout this specification may, but do not necessarily, all
refer to the same embodiment. Additionally, while the following
description refers to several embodiments and examples of the
various components and aspects of the described innovation, all of
the described embodiments and examples are to be considered, in all
respects, as illustrative only and not as being limiting in any
manner.
[0029] Furthermore, the described features, structures, or
characteristics of the innovation may be combined in any suitable
manner in one or more embodiments. In the following description,
numerous specific details are disclosed to provide a thorough
understanding of embodiments of the innovation. One having ordinary
skill in the relevant art will recognize, however, that the
innovation may be practiced without one or more of the specific
details, or with other methods, components, materials, and so
forth. In other instances, well-known structures, materials, or
operations are not shown or described in detail to avoid obscuring
aspects of the innovation.
[0030] To address the aforementioned need for alternative
techniques to efficiently produce olefins, the present disclosure
describes an economically viable and novel upgrading process to
produce olefins from carboxylic acids, including biomass, without
using hydrogen gas or expensive catalysis. In one embodiment, the
present technique is used for the production of alpha-olefins. The
olefins produced can be a direct replacement of the olefins
synthesized from crude oil for a variety of applications, including
but not limiting to co-monomers, PAO synthetic lubricants, drilling
lubricants, and surfactants. Unlike the routes to producing olefins
from petroleum, the method disclosed can selectively produce
specific olefins with yields above 50% at moderate temperatures and
pressures and without the use of a catalyst. Also, hydrogen gas can
be concurrently produced in an electrochemical reactor such as with
a two-compartment cell. This hydrogen can be recovered and used for
other processes that require hydrogen input. Thus, the innovation
can produce bio-derived olefins that are just an alternative to
petroleum based olefins, but at an economical advantage.
[0031] Another benefit of the innovation is the resulting reduction
in green-house gas (GHG) emissions relative to conventional
production techniques of olefins. Such reductions arise from three
aspects of the disclosed process: (1) the proposed electrochemical
reactor produces olefins without the need for hydrogen gas for
chemical reduction; (2) the source of feedstock of the olefins is
renewable; and (3) and the reduced cost in producing
poly-alpha-olefins will enable the greater availability and use of
synthetic oil in the transportation market increasing fuel economy
and reducing GHG emissions from combustion engines.
[0032] In one embodiment, the process uses an electrochemical
reactor that converts an alkali metal salt of lauric acid (a
twelve-carbon (C12) carboxylic acid), optionally produced from the
fermentation of lignocellulose sugar, into a corresponding
alpha-olefin, for example 1-undecene (also known as
undec-1-ene).
##STR00001##
[0033] The oxidation is carried out in a simple electrochemical
reactor that can be used on a distributed scale, following the two
electron oxidation reaction represented as:
C.sub.11H.sub.23CO.sub.2M.fwdarw.C.sub.11H.sub.22+CO.sub.2+2e.sup.-+M.su-
p.++H.sup.+
and for example where the metal (M) is sodium as:
C.sub.11H.sub.23CO.sub.2Na.fwdarw.C.sub.11H.sub.22+CO.sub.2+2e.sup.-+Na.-
sup.++H.sup.+
[0034] The process described herein is a two electron
decarboxylation. In contrast, a one electron decarboxylation
process is known as Kolbe electrolysis that results in radical
coupling products that are undesirable according to the presently
disclosed invention. Thus, two electron decarboxylation to produce
olefins is desired according to the present invention, whereas one
electron decarboxylation to produce radical coupling products is
not desired.
[0035] Upon diffusing through an optional membrane, the alkali
metal ions, for example sodium-ions, react with hydroxide anions
produced by the corresponding reduction of water in the reaction
shown below.
2Na.sup.++2H.sub.2O+2e.sup.-.fwdarw.2NaOH+H.sub.2
[0036] Thus, hydrogen and alkali hydroxide are produced at the
cathode. The alkali hydroxide may optionally be used to saponify
the feedstock carboxylic acid to form the alkali metal salt of the
carboxylic acid as follows:
R--COOH+NaOH.fwdarw.R--COONa+H.sub.2O
[0037] Advantageously, the alkali hydroxide may be regenerated in
the catholyte compartment as described above.
[0038] FIG. 1 schematically shows one possible electrochemical cell
or reactor 100 that may be used in the electrochemical process of
producing olefins within the scope of the present invention. The
electrolytic cell 100 includes an anolyte compartment 110, a
catholyte compartment 112, and an alkali ion conductive membrane
114 separating the anolyte compartment 110 from the catholyte
compartment 112.
[0039] The anolyte compartment 110 comprises an electrochemically
active anode 116 selected to perform a two-electron decarboxylation
reaction of an alkali metal salt of a carboxylic acid. The anode
116 preferably comprises a carbonaceous surface. The catholyte
compartment 112 comprises an electrochemically active cathode 118
where reduction reactions occur. The alkali ion conductive membrane
114 permits selective transport of alkali ions (M.sup.+) 120
between the anolyte compartment 110 and the catholyte compartment
112 under influence of an electric potential 122 while preventing
solvent or anion transfer between the anolyte and catholyte
compartments. Alkali ions 120 include, but are not limited to,
sodium ions, lithium ions, potassium ions and mixtures of the
same.
[0040] The alkali ion conductive membrane 114 can be virtually any
suitable alkali ion conductive membrane that selectively conducts
alkali ions and prevents the passage of water, hydroxide ions, or
other reaction products. The alkali ion conducting membrane 114 may
include a ceramic, a polymer, or combinations thereof. In one
embodiment, the alkali ion conducting membrane is an alkali ion
super ion conducting (MSICON) membrane. Some non-limiting examples
of such membranes include, but are not limited to, a NaSICON
(sodium super ionic conductor membrane) and a NaSICON-type
membrane. The alkali ion conductive membrane may be any of a number
of sodium super ion conducting materials, including, without
limitation, those disclosed in United States Patent Application
Publications Nos. 2010/0331170 and 2008/0245671 and in U.S. Pat.
No. 5,580,430. The foregoing applications and patent are hereby
incorporated by reference. In some embodiments, a sodium selective
ceramic membrane NaSelect.RTM. (Ceramatec, Salt Lake City, Utah
USA) may be used.
[0041] Where other non-sodium alkali metals are used, it is to be
understood that similar alkali ion conductive membranes such as a
LiSICON membrane, a LiSICON-type membrane, a KSICON membrane, a
KSICON-type membrane may be used. In some embodiments, an alkali
ion conducting ion-exchange polymeric membrane may be used. In some
embodiments, the alkali ion conducting membrane may comprise an
alkali ion conductive glass or beta alumina.
[0042] The electrochemical cell 100 may be a parallel plate
configuration where flat plate electrodes and membranes are used.
The anode 116 can be any suitable anode material that allows
two-electron oxidation (decarboxylation) reaction in the anolyte
compartment 110 when electrical potential 122 passes between the
anode 116 and the cathode 118. Some non-limiting examples of
suitable anode materials include carbonaceous electrodes or
electrodes with carbonaceous surfaces such as natural or artificial
graphite, graphite nanopowder, acetylene black, Super P.RTM.
(available from Westlake Chemical, Westlake, Ohio), MesoCarbon,
high surface active carbon, glassy carbon, carbon nanotubes, and
graphene.
[0043] The cathode 118 may be any suitable cathode that allows the
cell to reduce water, methanol, or other suitable electrolyte
containing-solvent in the catholyte compartment 112 to produce
hydroxide ions, methoxide ions, or other corresponding organic
oxide ions and hydrogen gas. Some non-limiting examples of suitable
cathode materials include, without limitation, nickel, stainless
steel, graphite, and any other suitable cathode material that is
known or novel.
[0044] In one embodiment, the electrolytic cell 100 is operated by
feeding or otherwise providing an anolyte solution 124 into the
anolyte compartment 110. The anolyte solution 124 includes a
solvent and a carboxylic acid or an alkali metal salt of carboxylic
acid. The alkali metal salt of the carboxylic acid can be obtained
by reacting the carboxylic acid with alkali metal hydroxide, for
example sodium hydroxide (NaOH), lithium hydroxide (LiOH), and
potassium hydroxide (KOH).
[0045] The carboxylic acid can be obtained from a variety of
sources, including biomass. Some non-limiting examples of suitable
carboxylic acids are fatty acids listed in Table 1. In some
embodiments, the carboxylic acid has from 6-20 carbon atoms. In
some embodiments, the carboxylic acid has from 6-12 carbon atoms.
In some embodiments, the carboxylic acid has from 16-18 carbon
atoms. In some embodiments, the carboxylic acid has from 12-18
carbon atoms.
TABLE-US-00001 TABLE 1 Number of carbon atoms Common name IUPAC
name 6 Caproic acid Hexanoic acid 7 Enanthic acid Heptanoic acid 8
Caprylic acid Octanoic acid 9 Pelargonic acid Nonanoic acid 10
Capric acid Decanoic acid 11 Undecylic acid Undecanoic acid 12
Lauric acid Dodecanoic acid 13 Tridecylic acid Tridecanoic acid 14
Myristic acid Tetradecanoic acid 15 Pentadecanoic acid 16 Palmitic
acid Hexadecanoic acid 17 Margaric acid Heptadecanoic acid 18
Stearic acid Octadecanoic acid 19 Nonadecanoic acid 20 Arachidic
acid Icosanoic acid
[0046] As can be appreciated by one of skill in the art, a
decarboxylation using the techniques disclosed herein would result
in the loss of one carbon atom from any of the fatty acids
identified in Table 1. Thus, in some embodiments, the resulting
olefins have from 5-19 carbon atoms. In some embodiments, the
olefins have from 5-11 carbon atoms. In some embodiments, the
olefins have from 15-17 carbon atoms. In some embodiments, the
olefins have from 11-17 carbon atoms.
[0047] The anolyte solution 124 may include one or more solvents.
In some embodiments, the solvent may be an organic lower alkanol
such as methanol, ethanol, propanol, isopropanol, butanol, or
mixtures of the same. In some embodiments, the solvent may be
acetonitrile, dimethylformamide, sulfolane, pyridine, 2,6-pyridine,
and mixtures of the same. In some embodiments the solvent may be
comprised of an ionic liquid. In other embodiments that solvent may
be comprised of a molten salt. It should be clear to those familiar
with the art that the choice of solvent for the anolyte will be
determined in part by the carboxylic acid or alkali carboxylate
solubility, the electrochemical stability of the solvent, the lack
of nucleophilic nature, and other properties that improve the 2
electron oxidation and subsequent E1 elimination reaction.
[0048] The anolyte solution 124 may optionally contain a supporting
electrolyte that is soluble in the solvent and which provides high
electrolyte conductivity in the anolyte solution. One non-limiting
example of a supporting electrolyte includes an alkali metal
tetrafluoroborate. Another example may include tetramethylammonium
hexafluorophosphate. Other ionic solids may also be used such as
metal halides, nitrates, sulfates, perchlorates, and mixtures of
the same. In one embodiment, supporting electrolytes that act as a
Bronsted base are used. In such a case, the supporting electrolyte
not only increases the conductivity of the anolyte solution, it
also increases the rate of the olefin formation by promoting an E1
elimination reaction.
[0049] An electrical potential 122 is applied to the anode 116 and
cathode 118 to electrochemically decarboxylate the alkali metal
salt of the carboxylic acid into one or more olefins 126 and carbon
dioxide (CO.sub.2) 128. The olefins produced include alpha olefins
and internal linear olefins. The carbon number of the olefin
produced depends on the carboxylic acid or alkali carboxylate salts
used in the decarboxylation. In one embodiment the decarboxylation
of laurate (C12) produces the C11 alpha-olefin, 1-undecene, and
also the internal linear olefins such as 2-undecene, 3-undecene,
4-undecene, and 5-undecene, and mixtures of the same.
[0050] The electric potential 122 may be applied at a voltage of
between 2 and 30 V. In some embodiments, the voltage applied is
between 4 and 18 V. In some embodiments, the voltage applied is
between 4 and 12 V. The electric potential may be applied with a
current density of between 5 and 100 mA/cm.sup.2. In some
embodiments, the current density is between 5 and 50 mA/cm.sup.2.
In some embodiments, the anolyte solution 110 has a pH in the range
from about 8 to 14. In other embodiments, the anolyte solution 110
has a pH in the range from about 9 to 13. In still other
embodiments, the anolyte solution 110 has a pH in the range from
about 10 to 12. It should be understood by those of ordinary skill
that the electrical potential, current density, and pH can be
controlled to modify the ratio of olefins produced by the
electrochemical decarboxylation.
[0051] In some non-limiting embodiments, the anolyte compartment
may have an operating temperature in the range from 20.degree. C.
to 150.degree. C. In other embodiments, the anolyte compartment may
have an operating temperature in the range from 50.degree. C. to
150.degree. C. It is believed that a temperature greater than
ambient temperature (>20.degree. C.) may facilitate the
decarboxylation reaction to produce olefins.
[0052] In some embodiments, a catholyte solution 130 is provided
into the catholyte compartment 112. The catholyte solution 130 may
comprise a solvent that is the same or different than the anolyte
solvent. The anolyte and catholyte solvents may be different
because the alkali conductive membrane 114 isolates the
compartments and from each other. The catholyte solvent may
comprise a mixture of solvents with or without water. In the
embodiment shown in FIG. 1, the catholyte solution comprises water.
At least initially, the catholyte solution includes alkali ions,
which may be in the form of an unsaturated alkali hydroxide
solution. The concentration of alkali hydroxide can be between
about 0.1% by weight and about 50% by weight of the solution. In
one embodiment, the catholyte solution includes a dilute solution
of alkali hydroxide. During operation, the source of alkali ions
may be provided by alkali ions transporting across the alkali ion
conductive membrane from the anolyte compartment to the catholyte
compartment. While alkali hydroxide is used in the following
discussion and shown in FIG. 1, persons skilled in the art will
appreciate that methanol may substitute alkali hydroxide in the
apparatus for preparing alkali methylate instead. Thus, the
catholyte solution may include methanol.
[0053] At the cathode 118, reduction of water to form hydrogen gas
132 and hydroxide ions takes place (Reaction 1). The hydroxide ions
react with available alkali ions (M.sup.+) 120 transported from
anode compartment 110 via the alkali conductive membrane 114 to
form alkali hydroxide as shown in Reaction 2. The alkali hydroxide
134 may be recovered from the catholyte compartment 112.
2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+20H.sup.- (1)
M.sup.++2H.sub.2O+2e.sup.-.fwdarw.2MOH+H.sub.2 (2)
[0054] In the case of catholyte solution 130 having methanol,
methoxide ions will react with available alkali ions to form alkali
methoxide as shown in Reaction 3. The alkali methoxide may be
recovered from the catholyte compartment 112.
2M.sup.++2CH.sub.3OH+2e.sup.-.fwdarw.MOCH.sub.3+H.sub.2 (3)
[0055] It will be appreciated that the catholyte solution comprises
a base which may be used to neutralize the carboxylic acid to
produce the alkali metal salt of the carboxylic acid. Thus, the
base consumed in the acid neutralization step may be produced in
the catholyte compartment, recovered, and re-used in acid
neutralization reactions or other chemical processes.
[0056] In one embodiment, the electrolytic cell may be operated in
a continuous mode. In a continuous mode, the cell is initially
filled with anolyte solution and catholyte solution and then,
during operation, additional solutions are fed into the cell and
products, by-products, and/or diluted solutions are removed from
the cell without ceasing operation of the cell. The feeding of the
anolyte solution and catholyte solution may be done continuously or
it may be done intermittently, meaning that the flow of a given
solution is initiated or stopped according to the need for the
solution and or to maintain desired concentrations of solutions in
the cell compartments, without emptying any one individual
compartment or any combination of the two compartments. Similarly,
the removal of solutions from the anolyte compartment and the
catholyte compartment may also be continuous or intermittent.
Control of the addition and or removal of solutions from the cell
may be done by any suitable means. Such means include manual
operation, such as by one or more human operators, and automated
operation, such as by using sensors, electronic valves, laboratory
robots, etc. operating under computer or analog control. In
automated operation, a valve or stopcock may be opened or closed
according to a signal received from a computer or electronic
controller on the basis of a timer, the output of a sensor, or
other means. Examples of automated systems are well known in the
art. Some combination of manual and automated operation may also be
used. Alternatively, the amount of each solution that is to be
added or removed per unit time to maintain a steady state may be
experimentally determined for a given cell, and the flow of
solutions into and out of the system set accordingly to achieve the
steady state flow conditions.
[0057] In another embodiment, the electrolytic cell is operated in
batch mode. In batch mode, the anolyte solution and catholyte
solution are fed initially into the cell and then the cell is
operated until the desired concentration of product is produced in
the anolyte and catholyte. The cell is then emptied, the products
collected, and the cell refilled to start the process again.
Alternatively, combinations of continuous mode and batch mode
production may be used. Also, in either mode, the feeding of
solutions may be done using a pre-prepared solution or using
components that form the solution in situ.
[0058] It should be noted that both continuous and batch mode have
dynamic flow of solutions. In one embodiment of continuous mode
operation, the anolyte solution is added to the anolyte compartment
so that the sodium concentration is maintained at a certain
concentration or concentration range during operation of the
electrolytic cell. In one embodiment of batch mode operation, a
certain quantity of alkali ions are transferred through the alkali
ion conductive membrane to the catholyte compartment and are not
replenished, with the cell operation is stopped when the alkali ion
concentration in the anolyte compartment reduces to a certain
amount or when the appropriate product concentration is reached in
the catholyte compartment.
[0059] In some embodiments, the resulting alpha-olefins may be
oligomerized to poly-alpha olefins (PAOs) by conventional
techniques to synthetic oils. In one embodiment, the C11 olefins
are oligomerized to produce poly-internal-olefins (PIOs) by
conventional techniques and thereby produce synthetic oil.
[0060] In some embodiments, the entire process is
hydrogen-independent. In some embodiments, the process requires
small amounts of electricity. In some embodiments, the
electrochemical reactor can be commercialized for distributed
manufacturing of the olefins. In some embodiments, the sodium salt
of lauric acid obtained from fermentation from biomass can be
directly fed into the membrane reactor, thereby obviating the need
for any separation or purification. In some embodiments, the
electrochemical reactor uses inexpensive electrode materials with
low power consumption. In some embodiments, the resulting
alpha-olefins are oligomerized to produce a synthetic
bio-lubricant.
EXAMPLES
[0061] Several examples will be given to demonstrate the technical
feasibility of producing olefins via the decarboxylation of
carboxylic acids or alkali carboxylates. The examples demonstrate
the decarboxylation of sodium salts of carboxylic acids using
electrolytic cells equipped with a NaSelect.RTM. NaSICON membrane
manufactured by Ceramatec, Inc., Salt Lake City, Utah.
[0062] The examples disclosed herein, used an experimental setup
which consisted of a micro flow cell, allowing both the anolyte and
catholyte to be pumped through the cell while minimizing the
distance between the electrodes and the membrane. The membranes
used in the examples consisted of 2.54 cm diameter NaSICON disks of
about 1 mm thickness that were housed on scaffolds in the center of
the cells. As the scaffold and membrane physically separate the
anode and cathode compartments, there was a separate reservoir and
temperature controlled hotplate for the anolyte and catholyte. This
allowed the chemistry and conditions of each electrolyte to be
optimized for the respective electrode reactions. A multiple-head
peristaltic pump was used to pump both electrolyte solutions into
the electrolysis cell. The tubing between the cell, pump, and
reservoir was insulated for temperature sensitive electrolytes.
[0063] The anolyte solution that contains the sodium salt of the
carboxylic acid, was made by dissolving at least 10% of the salt
into a solvent system consisting of different mixtures that contain
water, methanol, ethanol, and butanol. The sodium salts were
prepared in separate solutions following conventional
saponification reactions followed by dissolution of the prepared
salt into an electrolyte solution. For this method, a general
saponification product was used during which the sodium carboxylate
forms as the carboxylic acid is neutralized. The details of the
electrolyte preparation will be given in the different examples.
The catholyte was made from aqueous sodium hydroxide solutions. To
obtain low solution resistance the temperature of the electrolyte
were increased to 50.degree. C. to improve both the solubility and
conductivity.
[0064] Once the reservoirs reached the desired temperature, a power
supply was connected and a current density between 10 and 100
mA/cm.sup.2 was applied. During electrolysis, the voltage and
current were monitored using a Data Acquisition Unit (Agilent
3490A) controlled by LabVIEW software. The applied current density
caused oxidation to occur at the anode (smooth platinum or
graphite) and reduction to occur at the cathode (nickel), with each
electrode having a surface area of 11 cm.sup.2. As the power supply
transport electrons from the anode to the cathode, a charge balance
must be maintained across the cell by the diffusion or positively
charge ions. Given the high selectivity of the NaSICON membrane for
Na-ions, sodium ions are the only species that can provide this
balance. Thus a high concentration of the sodium salts was desired
and used.
[0065] To separate the olefins from the electrolyte, hexane was
used to perform liquid-liquid extraction. After the extraction, the
olefins were analyzed in the hexane using, IR (Bruker, Tensor 37),
GC (Bruker, SICON 465), and GC-MS (Bruker, SCION465 GC-SQ). The
olefins could be isolated and purified by removing the hexane using
a slight vacuum and low heat affording the recovered olefins at a
98% purity level.
Comparative Example 1
[0066] To show the conventional product selectivity of the one
electron Kolbe electrolysis, a reaction was performed using 10%
sodium octanoate dissolved in a water methanol solution as the
anolyte having a pH of 8. 10% aqueous sodium hydroxide was used as
the catholyte. The catholyte was heated to 50.degree. C. and the
anolyte was maintained at room temperature. The electrolysis was
conducted in batch mode, during which the anolyte and catholyte
were cycled through the corresponding anode and cathode
compartments of the cell. The cell was operated until enough charge
passed to theoretically convert 80% of the sodium octanoate. As
shown in FIG. 2A the electrolysis was conducted at a constant
current density of 65 mA/cm.sup.2, which produced a cell potential
of 8 V.
[0067] The reactions that occurred during the electrolysis in the
anode and cathode compartment are shown below.
C.sub.7H.sub.115CO.sub.2Na.fwdarw.C.sub.7H'.sub.15+CO.sub.2+Na.sup.++e.s-
up.-
H.sub.2O+e.sup.-.fwdarw.H.sub.2+OH.sup.-
[0068] The conditions used in this example promoted the
radical-radical coupling and produced tetradecane according to the
reaction below.
2C.sub.7H'.sub.15.fwdarw.C.sub.14H.sub.30
[0069] After the electrolysis was complete the product was
extracted/removed from the electrolyte using liquid-liquid
extraction with hexane. The product of the electrolysis was then
analyzed using GC-MS, producing the GC shown in FIG. 2B. From this
it was determined that the product distribution was 80%
tetradecane, 5% heptanol, 10% esters, and 5% heptenes.
EXAMPLE 2
[0070] The electrolysis conditions from Example 1 were changed to
show the selective production of olefins instead of paraffins using
the techniques disclosed herein. One difference between the two
examples that caused the change in product selectivity was the use
of a graphite electrode in this example while a platinum electrode
was used in Example 1. For this example, 10% sodium laurate was
dissolved in an electrolyte containing a mixture of methanol,
butanol, and water having a pH of 10.5. The catholyte consisted of
10% aqueous sodium hydroxide. The catholyte and anolyte were heated
to 50.degree. C. Electrolysis was conducted in batch mode during
which the anolyte and catholyte were cycled through the
corresponding anode and cathode compartments of the cell. The cell
was operated until enough charge passed to theoretically convert
80% of the sodium laurate. As shown in FIG. 3A, electrolysis was
conducted at a constant cell potential of 4 V and a current density
of 20 mA/cm.sup.2.
[0071] The reactions that occurred during the electrolysis in the
anode and cathode compartment are shown below.
C.sub.11H.sub.23CO.sub.2Na.fwdarw.C.sub.11H.sup.+.sub.23CO.sub.2+Na.sup.-
++2e.sup.-+H.sup.+
H.sub.2O+e.sup.-.fwdarw.H.sub.2+OH.sup.-
[0072] The conditions used in this example promoted the two
electron oxidation, after which the carbocation could undergo
either S.sub.N1 substitution reactions forming alcohols, or E1
elimination reactions forming olefins as shown in the reactions
below.
C.sub.11H.sup.+.sub.23+H.sub.2O.fwdarw.C.sub.11H.sub.23OH+H.sup.+
C.sub.11H.sup.+.sub.23+OH.sup.=.fwdarw.C.sub.11H.sub.22+H.sub.2O
[0073] After the electrolysis was complete the product was
extracted/removed from the electrolyte using liquid-liquid
extraction with hexane. The product of the electrolysis was then
analyzed using GC-MS, producing the gas chromatogram shown in FIG.
3B. From this it was determined that the product distribution was
<5% docosane, 40% undecanol, <5% esters, and over 50%
undecenes. Of the undecenes, 50% corresponded to the alpha-olefin,
1-undecene.
[0074] It will be appreciated that the disclosed invention provides
an electrochemical method of preparing olefins from alkali metal
salts of carboxylic acids. Low-cost, renewable biomass may provide
a source of alkali metal salts of carboxylic acids.
* * * * *