U.S. patent application number 12/297920 was filed with the patent office on 2010-03-11 for electrochemical oxidation of organic matter.
This patent application is currently assigned to AIC NEVADA, INC.. Invention is credited to Robert Lewis Clarke, John Kerr, Vinoid Nair.
Application Number | 20100059388 12/297920 |
Document ID | / |
Family ID | 38668379 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100059388 |
Kind Code |
A1 |
Clarke; Robert Lewis ; et
al. |
March 11, 2010 |
Electrochemical Oxidation of Organic Matter
Abstract
Carbonaceous feedstock is at least partially oxidized using a
concentrated metal ion solution that is regenerated in an
electrochemical hydrogen gas producing process. The at least
partially oxidized feedstock and/or hydrogen are then
advantageously used as an energy carrier in a downstream
process.
Inventors: |
Clarke; Robert Lewis;
(Orinda, CA) ; Kerr; John; (Alameda, CA) ;
Nair; Vinoid; (Concord, CA) |
Correspondence
Address: |
FISH & ASSOCIATES, PC;ROBERT D. FISH
2603 Main Street, Suite 1000
Irvine
CA
92614-6232
US
|
Assignee: |
AIC NEVADA, INC.
Alameda
CA
|
Family ID: |
38668379 |
Appl. No.: |
12/297920 |
Filed: |
May 4, 2007 |
PCT Filed: |
May 4, 2007 |
PCT NO: |
PCT/US07/10976 |
371 Date: |
April 14, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60797873 |
May 5, 2006 |
|
|
|
60909677 |
Apr 2, 2007 |
|
|
|
Current U.S.
Class: |
205/343 ;
205/560; 205/573; 205/586; 205/587 |
Current CPC
Class: |
C10J 2300/092 20130101;
C25B 1/02 20130101; C10J 2300/0943 20130101; C10J 2300/0983
20130101; C10J 2300/1659 20130101; C10J 2300/0989 20130101; C10J
2300/093 20130101; H01M 8/0612 20130101; Y02E 60/50 20130101 |
Class at
Publication: |
205/343 ;
205/560; 205/587; 205/586; 205/573 |
International
Class: |
C25B 1/02 20060101
C25B001/02; C25C 1/00 20060101 C25C001/00; C25C 1/06 20060101
C25C001/06; C25C 1/12 20060101 C25C001/12; C25C 1/10 20060101
C25C001/10 |
Claims
1. A method of oxidizing a carbonaceous feedstock, comprising:
combining a metal and a solubility-enhancing compound to form a
metal-containing solution; wherein the solubility-enhancing
compound is present at a concentration and has a composition
effective to increase solubility of the metal over solubility of
the same metal in sulfuric acid in an amount of at least 10%;
wherein the solubility-enhancing compound has a composition
effective to resist oxidation under conditions at which the metal
is electrochemically oxidized from a reduced form; combining the
carbonaceous feedstock with the metal-containing solution to
thereby at least partially oxidize the feedstock and form the
reduced form of the metal; optionally electrochemically
regenerating the metal from the reduced form of the metal, wherein
the step of regenerating is carried out under conditions effective
to produce hydrogen; and using at least one of the hydrogen and the
at least partially oxidized feedstock as an energy carrier in a
subsequent reaction.
2. The method of claim 1 wherein the carbonaceous feedstock
comprises a material selected from the group consisting of a
cellulosic material, lignocellulosic material, paper, cotton, plant
materials, coal, tar, and coke.
3. The method of claim 1 wherein the metal is a transition metal
ion.
4. The method of claim 3 wherein the transition metal ion is a
period 4 transition metal ion.
5. The method of claim 3 wherein the transition metal ion is
selected from the group consisting of an iron ion, a copper ion,
and a manganese ion.
6. The method of claim 1 wherein the solubility-enhancing compound
comprises an organic acid that comprises a sulfur atom, and wherein
the solubility-enhancing compound is not sulfuric acid.
7. The method of claim 1 wherein the solubility-enhancing compound
is an optionally substituted alkyl sulfonic acid or an optionally
substituted alkyl sulfamic acid.
8. The method of claim 1 wherein the solubility-enhancing compound
is present at a concentration effective to increase solubility of
the metal over solubility of the same metal in sulfuric acid in an
amount of at least 50%.
9. The method of claim 1 wherein the solubility-enhancing compound
is present at a concentration effective to increase solubility of
the metal over solubility of the same metal in sulfuric acid in an
amount of at least 100%.
10. The method of claim 1 wherein the metal-containing solution has
an acid pH of between pH 2.0 and pH 6.0.
11. The method of claim 1 wherein the step of at least partially
oxidizing the feedstock is performed at a temperature between
20.degree. C. and 50.degree. C.
12. The method of claim 1 wherein the step of at least partially
oxidizing the feedstock is performed at a temperature between
50.degree. C. and 300.degree. C.
13. The method of claim 1 wherein the metal is electrochemically
regenerated.
14. The method of claim 1 wherein the metal is electrochemically
regenerated in a divided cell under conditions such that the
hydrogen is produced in only one side of the cell without oxygen
production in another side of the cell.
15. The method of claim 1 wherein the hydrogen is used in a fuel
cell to generate energy.
16. The method of claim 1 wherein the at least partially oxidized
feedstock is used as a feed component in a fermentation.
17. A liquid intermediate in the oxidation of a carbonaceous
feedstock comprising (1) an organic acid other than sulfuric acid,
(2) a transition metal ion, and (3) a carbonaceous feedstock
selected from the group consisting of an oligosaccharide, a
polysaccharide, coal, tar, and coke.
18. The intermediate of claim 17 wherein the organic acid comprises
an optionally substituted alkyl sulfonic acid or an optionally
substituted alkyl sulfamic acid, optionally further comprising a
complexing agent.
19. The intermediate of claim 17 wherein the transition metal ion
is selected from the group consisting of an iron ion, a copper ion,
and a manganese ion.
20. The intermediate of claim 17 wherein the intermediate is an
aqueous intermediate having a pH between 2.0 and 6.0.
Description
[0001] This application claims priority to our copending U.S.
provisional patent applications with the Ser. No. 60/797,873, filed
May 5, 2006, and Ser. No. 60/909,677, filed Apr. 2, 2007, both of
which are incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The field of the invention is oxidation of carbonaceous
feedstocks, especially as it relates to chemical oxidation of
cellulosic materials to prepare yeast fermentable materials for
ethanol production.
BACKGROUND OF THE INVENTION
[0003] Electrochemical oxidation of various organic materials, and
particularly coal was studied by numerous groups to generate
hydrogen and useful organic products in aqueous medium. The
exemplary reaction for aqueous combustion of coal below illustrates
such process:
C+2 H.sub.2O-4e.sup.-=CO.sub.2+4 H.sup.+ at the anode
4 H.sup.++4e.sup.-=2 H.sub.2 at the cathode
[0004] Remarkably, it was found that presence of iron ions in coal
significantly accelerated this reaction, and in most cases even
acted as a redox reagent in which ferric iron (i.e., Fe.sup.+3)
lowered the required voltage by about 0.7 V. While such
acceleration provides at least some cost reduction of
electrochemically produced hydrogen, the benefits of the catalyzed
reaction in heretofore known systems are limited by the rather poor
solubility of the iron ions in the (commonly sulfuric acid)
electrolyte. For example, ferric sulfate has a solubility maximum
of about 0.5M in aqueous systems, which negatively impacts the
current density of the electrochemical process and/or the low
temperature rate of oxidation required to make useful quantities of
desired products. Thus, electrochemical generation of hydrogen from
carbon in aqueous systems is under most circumstances impractical
and economically not attractive.
[0005] Further related electrochemical processes are described, for
example, in R. W. Coughlin and M. Farooque, Nature 249, 301 (1979),
R. L. Clarke, P. C. Foller, R. J. Vaughan Paper 587, 163 Meeting of
Electrochemical Society. San Francisco (1983), P. M. Dooge, S. M.
Park, J. Electrochem. Soc 130,1029 (1983), and S. Lavani, M. Pata,
R. Coughlin; Fuel 62,427 (1983) 14. Electrochemical hydrogen
production configurations and methods are described in U.S. Pat.
Nos. 4,279,710 and 4,268,363, and iron-assisted electrochemical
hydrogen production is described in U.S. Pat. Nos. 4,592,814,
4,608,136, 4,412,893, and 4,608,137.
[0006] Electrochemical oxidation processes using iron ions as redox
carrier can also be used to generate a variety of organic products.
For example coal and/or petroleum coke can be partially oxidized to
humic acid at temperatures of 150.degree. C., or completely
oxidized to carbon dioxide at temperatures in excess of 300.degree.
C. (e.g., Electrochemical Hydrogen Technologies, Clarke and Foller
p. 345-371; Elsevier 1990). Thus, it should be recognized that
oxidation of carbonaceous fuels using an iron redox carrier is
impacted by both the temperature of the electrolyte and the
concentration of the ferric ions. Unfortunately, while the
temperature can be raised, solubility problems will remain even at
high temperatures. Furthermore, especially where partially oxidized
byproducts are desired, higher temperatures often thermally destroy
such products.
[0007] Therefore, while numerous configurations and methods of
electrochemical oxidation of organic matter are known in the art,
all or almost all of them suffer from one or more disadvantages.
Thus, there is still a need to provide improved configurations and
methods for efficient electrochemical oxidation of organic
matter.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to compositions and
methods of oxidizing various organic materials, and especially
carbonaceous feedstock using highly concentrated metal ion
solutions. Most preferably, the metal ion is a transition metal
ion, and high concentrations of the metal are achieved by an
additive that is stable under conditions at which the metal ion is
regenerated after oxidation of the feedstock.
[0009] In one aspect of the inventive subject matter, a method of
oxidizing a carbonaceous feedstock includes a step of combining a
metal and a solubility-enhancing compound to form a
metal-containing solution. Most preferably, the
solubility-enhancing compound is present at a concentration and has
a composition effective to increase solubility of the metal over
solubility of the same metal in sulfuric acid in an amount of at
least 10%, and wherein the solubility-enhancing compound has a
composition effective to resist oxidation under conditions at which
the metal is electrochemically oxidized from a reduced form. In
another step, the carbonaceous feedstock is combined with the
metal-containing solution to thereby at least partially oxidize the
feedstock and form the reduced form of the metal, and optionally,
the metal is electrochemically regenerated from the reduced form of
the metal, wherein the step of regenerating is carried out under
conditions effective to produce hydrogen. In a still further step,
the hydrogen and/or the oxidized feedstock are then used as an
energy carrier in a subsequent reaction.
[0010] Most preferably, the carbonaceous feedstock is a cellulosic
material, lignocellulosic material, paper, cotton, plant materials,
coal, tar, and/or coke, and the metal is a transition metal ion
(preferably a period 4 transition metal ion, and particularly an
iron ion, a copper ion, and/or a manganese ion). With respect to
the solubility-enhancing compound it is generally preferred that
the compound is an acid, and especially an organic acid comprising
a sulfur atom (but not sulfuric acid). Most preferably, the
solubility-enhancing compound is an optionally substituted alkyl
sulfonic acid or an optionally substituted alkyl sulfamic acid, and
present at a concentration effective to increase solubility of the
metal over solubility of the same metal in sulfuric acid in an
amount of at least 50%, and more typically at least 100%. While
contemplated reactions can be carried out at various temperatures,
it is preferred that the step of at least partially oxidizing the
feedstock is performed at a temperature between 20.degree. C. and
50.degree. C., and more typically between 50.degree. C. and
300.degree. C. Regeneration of the metal is preferably carried out
via electrochemical oxidation of the reduced metal, preferably
under conditions such that hydrogen is produced in only one side of
the cell without or at reduced oxygen production (e.g., at least
10%, more typically at least 30%, and most typically at least 50%
less as compared to same setup but without metal in electrolyte) in
another side of the cell.
[0011] Therefore, in another aspect of the inventive subject
matter, a liquid intermediate in the oxidation of a carbonaceous
feedstock comprises an organic acid other than sulfuric acid, a
transition metal ion, and a carbonaceous feedstock selected from
the group consisting of an oligosaccharide, a polysaccharide, coal,
tar, and coke. Most typically, the organic acid includes an
optionally substituted alkyl sulfonic acid or an optionally
substituted alkyl sulfamic acid, optionally further comprising a
complexing agent, and/or the transition metal ion is selected from
the group consisting of an iron ion, a copper ion, and a manganese
ion.
[0012] Various objects, features, aspects and advantages of the
present invention will become more apparent from the following
detailed description of preferred embodiments of the invention.
DETAILED DESCRIPTION
[0013] The inventors have discovered that electrochemical oxidation
of organic matter in aqueous media using ionic species of metals,
and especially iron ions as redox agents can be dramatically
improved by using in the electrolyte an acid or corresponding salt
of the acid that increases solubility of the metal ion.
Additionally, or alternatively, a complexing agent may be added
that increases solubility of the metal ion. In especially preferred
aspects, the metal ion is an iron ion (e.g., ferric iron
[Fe.sup.+3] and/or ferrous iron [Fe.sup.+2]).
[0014] In one preferred exemplary aspect of the inventive subject
matter, the metal ion is a ferric and/or ferrous iron, and the
electrolyte is a 1.5M aqueous ferrous methane sulfonate solution
that is electrochemically oxidized in a standard divided cell
(e.g., with NAFION.TM. [sulfonated tetrafluorethylene copolymer]
separator) on a platinum coated titanium electrode to generate a
ferric methane sulfonate solution.
[0015] Carbonaceous feedstock is then combined with the ferric
methane sulfonate solution and reacted at a desired temperature for
a time appropriate to generate the desired product or to exhaust
the ferric iron. While the nature of the feedstock is generally not
limiting to the inventive subject matter, it is typically preferred
that where hydrogen and/or carbon dioxide is the desired product,
coal, coke, tar, and/or other high-carbon content materials are
used as a feedstock, while in applications where fermentable
carbohydrates are the desired products, suitable feedstocks include
various processed (e.g., cotton, paper, pulp, etc.) or unprocessed
(e.g., plant fibers, leafs, etc.) cellulosic materials. High-carbon
content materials typically include those in which at least 25 wt
%, and more typically at least 30 wt % of the materials are carbon
(in elemental form and/or bonded to other atoms). For example,
suitable high-carbon content materials include oligo- and
polysaccharides, which may be linear, branched, and/or chemically
modified, lignin and lignaceous materials, combustion and/or
pyrolysis products, coke, tar, coal, hydrocarbons, etc.
[0016] Depending on the particular nature of the feedstock, desired
reaction endpoint, and molar ratio between the ferric iron and
oxidizable atoms or groups, the reaction temperature may be
elevated (e.g., between 30-300.degree. C., more typically between
50-150.degree. C., and most typically between 60-90.degree. C.) for
at least part of the reaction time. Furthermore, preferred reaction
times will typically be chosen such that the ferric iron
concentration will remain above 0.2-0.3M, more preferably above
0.3-0.5M, and most preferably above 0.5-0.7M. On the other hand,
and especially in batch operations, the processing time may be less
critical and the reaction can be driven to exhaustion of the ferric
iron and/or the oxidizable material. Thus, the ratio of the ferric
iron to oxidizable material may vary considerably. For example,
where relatively fast reaction is desired, the ferric iron may be
in molar excess over the oxidizable material (e.g., up to 2-fold
molar excess, more typically up to 5-fold molar excess, even more
typically up to 10-fold molar excess, and in some instances up to
20-fold molar excess and even higher). Similarly, where complete
oxidation of the oxidizable material is less critical (or even
undesirable), the oxidizable material may be in molar excess over
the ferric iron (e.g., up to 2-fold molar excess, more typically up
to 5-fold molar excess, even more typically up to 10-fold molar
excess, and in some instances up to 20-fold molar excess and even
higher).
[0017] It should be further recognized that numerous compounds
other than methane sulfonic acid (and its corresponding salts) are
also suitable as compounds to increase the solubility of the metal
ion. For example, suitable compounds include various alkylsulfonic
acids (e.g., ethane sulfonic acid) and/or an alkylsulfamic acids
(e.g., methylsulfamic acid), which may entirely replace sulfuric
acid of previously known systems. However, where needed (e.g., to
adjust the pH of the aqueous solution) sulfuric acid and/or other
organic or inorganic acids (e.g., hydrochloric acid, phosphoric
acid, nitric acid, etc.) may be added. More generally, it should be
recognized suitable compounds increase solubility of the metal ions
over solubility of the same metal ions in sulfuric acid in an
amount of at least 10%, more typically at least 25%, even more
typically at least 50%, and most typically at least 100% absolute.
Thus, appropriate compounds can be easily identified by their
solubilizing properties using various protocols well known in the
art. Most preferably, contemplated compounds will be include
(typically substituted) organic or inorganic acids, but may also
include polymeric materials (soluble or insoluble) with cationic
and/or anionic groups (which may be part of the polymer backbone or
be pendant groups). Alternatively, in less preferred aspects of the
inventive subject matter, suitable compounds also include bases and
neutral compositions.
[0018] Similarly, with respect to oxidation resistance of suitable
compounds, the person of ordinary skill in the art is well equipped
to recognize appropriate alternative acids. It is generally
preferred that the compounds will resist oxidation under conditions
at which the metal ion is electrochemically (or chemically)
oxidized from the reduced form. Thus, in most preferred aspects, at
least 85 mol %, more typically at least 95 mol %, and most
typically at least 98 mol % of contemplated compounds will remain
chemically unchanged in the electrolyte after 10 cycles of
re-oxidation. Furthermore, suitable compounds will be heat stable
at temperatures of between 10-150.degree. C. (and even higher),
more typically between 20-100.degree. C., and most typically
between 30-90.degree. C. Therefore, and among other choices,
suitable compounds may also be fluorinated (e.g., fluorinated
methylsulfonic and/or fluorinated methylsulfamic acid).
[0019] It is still further preferred that contemplated compounds
(or mixture thereof) are present in the aqueous electrolyte at a
concentration of at least 5-10 wt %, more typically at least 20 wt
%, even more typically at least 40 wt %, and most typically at
saturation. Depending on the particular compound, the compound will
be present in concentrations between about 0.1 M to 0.5 M, more
typically 0.5 M to 1.0 M, even more typically between 1.0 M and 1.5
M, and most typically above 1.5-2.0 M. Therefore, the solubility of
the metal ion (e.g., ferrous and ferric iron) in the electrolyte at
25.degree. C. may be between 0.2 M and 0.5 M, more preferably
between 0.5 M and 1.0 M, even more preferably between 1.0 M and 2.0
M, and most preferably above 2.0 M. Consequently, it should be
recognized that the electrolyte will have an acid pH of between pH
0 and pH 6.7, and more typically between pH 2.0 and pH 6.0.
[0020] With respect to metal- and especially iron complexing
agents, it is contemplated that all compounds suitable for
complexing iron ions are suitable for use in conjunction with the
teachings presented herein. Thus, suitable complexing agents
include various oligodentate compounds, crown ethers, exchange
resins, etc. For example, especially preferred compounds that
complex iron ions include desferrioxamine and desferrioxamine
analogs, bacterial or synthetic siderophores, humates (including in
situ electrochemically generated humates), EDTA
(ethylenediaminetetraacetic acid), EDMA (ethylenediiminobis
(2-hydroxy-4-methyl-phenyl)acetic acid), and DTPA
(diethylenetriamine-pentaacetic acid). Depending on the particular
reaction conditions, temperature, pH, and other parameters, the
complexing agents may be present at a concentration of between
about 0.1 M to 1.0 M, and more preferably between 1.0 M to 2.0 M
(and higher). Most preferably, one or more complexing agents are
combined with contemplated compounds (e.g., with methane sulfonic
acid), but they may also be used separately.
[0021] It is particularly preferred that the metal ion is an iron
ion, and especially ferric iron in the oxidized state and ferrous
iron in the reduced state. However, it should be recognized that
various alternative metals and/or oxidation states are also deemed
suitable, and especially contemplated metals and metal ions include
transition metals, lanthanides (and particularly cerium), and
metals of the fourth (e.g., titanium, chromium, copper, etc.) and
fifth (e.g., molybdenum, indium, tin, etc.) period. Depending on
the particular metal, it should be recognized that the ionic charge
may therefore be between +1 and +7, and more typically between +1
and +4 (or the metal may be elemental in one state). Where the
metal is in a complex (e.g., with an organic ligand or inorganic
component), ionic charges may also be between -1 and typically -4.
Still further, it should be recognized that mixtures of various
metals may also be appropriate.
[0022] In a typical exemplary process in which coal and/or coke
were oxidized to CO2, the inventors discovered that the
concentration of ferrous ions created by the reaction between
ferric ions and the organic matter (here: coal and coke) was a
critical parameter. In presently contemplated electrochemical cells
(see below), the ferrous ion was oxidized at the anode. Remarkably,
in such systems, oxygen evolution was not favored, and the current
increased with increasing concentration of ferrous ions before the
voltage increased. In stark contrast, heretofore known devices
needed to flow the electrolyte as quickly as possible to overcome
mass transfer limitations of low iron solubility in sulfuric
electrolytes. Moreover, it should be noted that in configurations
and methods according to the inventive subject matter presented
herein the reaction rate between the ferric ions and the carbon
fuel increased with higher temperatures, which is particularly
advantageous as iron sulfates reach their maximum solubility at
80.degree. C. Still further, it should be appreciated that methane
sulfonic acid not only considerably increased solubility of ferrous
and ferric iron, but also enhanced the reaction by the
compatibility of methane sulfonic acid with the carbon and carbon
oxidized surface, possibly via a detergent-like effect.
[0023] Depending on the particular metal, feedstock, electrolyte
composition (aqueous or non-aqueous, type of compound, etc.) and
other factors, it should be appreciated that the (preferably
metal-mediated) oxidation can be carried out in a reactor that is
separate from the electrochemical cell in which the electrolyte is
regenerated, or that the oxidation of the feedstock and the
regeneration can be carried out in the same reactor. Similarly,
under certain conditions, (preferably metal-mediated) oxidation of
the feedstock and regeneration of the electrolyte may be carried
out at the same time.
[0024] Remarkably, the configurations and methods according to the
inventive subject matter were substantially inert to sulfur in the
coal and did not impact the purity of carbon dioxide that issued
from the reactor as sulfur compounds were oxidized to sulfuric acid
that remained in the electrolyte. Similarly, the carbon dioxide was
also free of oxides of nitrogen as all nitrogen compounds were
oxidized to nitrates. Furthermore, hydrogen produced in such
electrolytic cells was free of oxygen as the catholyte was
separated from the anolyte by an ion exchange membrane. Thus,
heretofore know problems with gas separation can be entirely
avoided and substantially pure hydrogen is created as the hydrogen
is produced in only one side of the cell without oxygen production
(i.e., less than 10) in another side of the cell. It was also
observed that heavy metals were separated from the gaseous stream
and collected on the cathode or in the oxidized coke product.
[0025] Consequently, it should be appreciated that contemplated
systems and methods will not only generate partially oxidized
feedstock but also produce hydrogen. Such products can be used
(alone or in combination) as an energy carrier in downstream
reactions. For example, the at least partially oxidized feedstock
can be employed in a fermentation reaction as nutrient for the
fermenting microorganism. In another example, hydrogen may be
employed as a direct fuel in a hydrogen fuel cell for energy
production, or as an indirect fuel in which hydrogen is a component
for fuel production (e.g., via Fischer-Tropsch reaction of CO and
H2 produced in such systems [CO can be produced from CO2 in a
reverse shift reaction]), wherein that fuel then provides energy.
Thus, the term "energy carrier" as used herein refers to compounds
that are either used as a fuel in combustion or feed component in a
fermentation and/or used as precursor(s) in the synthesis of a
hydrocarbon fuel (and especially methane). Consequently, subsequent
reactions may be catalyzed or uncatalyzed in a reactor, or
performed in an in vitro or in vivo enzyme-containing system.
[0026] In heretofore known studies it was shown that wood flour,
corn husk, and sewage sludge (mainly cellulose) could be completely
solubilized at temperatures below 100.degree. C. It was assumed
that some of the organic material had been oxidized to carbon
dioxide but some remained as organic materials like sugars.
Therefore, it is now contemplated that with more concentrated iron
redox carriers it is now possible at temperatures lower that
100.degree. C. to consider (preferably selective) oxidation of
cellulose like materials to products that are more easily converted
to benign or useful products. For example, cellulose can be
converted to sugars that are then biologically converted to
alcohol. The first part of such process is the breaking of the
cellulose polymer into smaller molecules and then to individual
sugars by hydrolysis with strong acids. In another example, ferric
ions are used to convert aniline to polyaniline for example, one
very toxic the other relatively benign. Of course, it should be
recognized that all of the contemplated processes herein can be
applied with or without the electrochemical recycling of the metal
redox carriers and/or attempts to electrochemically produce
hydrogen. Therefore, suitable temperatures for oxidation reactions
will be between 20.degree. C. and 50.degree. C., more typically
between 50.degree. C. and 80.degree. C., even more typically
between 80.degree. C. and 100.degree. C., and in some cases between
50.degree. C. and 300.degree. C.
[0027] It should further be recognized that by changing the
temperature and/or the feed stock (e.g., wood, husk, fiber, stalks,
etc.) various products will be formed in various ratios. Thus, the
organic materials can be broken down to smaller molecules (e.g.,
cellulose and lignins present in plant materials into
polysaccharides and sugars) that may be converted to biofuels by
subsequent biological processes, and especially fermentation (see
below). As it will be much easier to control the breakdown process
without use of aggressive mineral acids, it is expected that the
overall processing costs will significantly drop. Furthermore, the
impact on the cost of generating hydrogen electrochemically at high
current density is easily forecast from extrapolation from the
results of Clarke and Foller.
[0028] In a further especially contemplated aspect, it should be
recognized that pure H2 and CO2 (essentially free from NO.sub.X and
SO.sub.X) can be prepared at a substantially lower price than in
conventional electrolysis processes. Moreover, these products can
be combined to make carbon monoxide and hydrogen (syngas), which is
an ideally suitable feedstock for Fischer-Tropsch synthesis as the
so produced gas mixture is free of interfering sulfur compounds
and/or nitrogen oxides.
Examples
[0029] The following examples and calculations are provided as
exemplary guidance for a person of ordinary skill in the art to
illustrate various advantages and benefits of the inventive concept
presented herein.
Energy Balance in Typical Iron-Mediated Reaction for Ethanol
Production
[0030] A typical reaction is started with 50 kg of lignocellulosic
material to obtain water soluble materials of about 40 kg. The
typical fermentable sugar content is in the range of 70%, which
translates to about 30 kg fermentable sugar. According to the below
net equation for the fermentation process, 180 g of sugar will give
46 g of ethanol.
C.sub.6H.sub.12O.sub.6(s).fwdarw.2CO.sub.2(g)+2C.sub.2H.sub.5OH(1)
[0031] With an approximate 30% fermentation efficiency, about 2.5
kg of ethanol are being produced. Theoretical Energy density of
ethanol is 26.8 MJ/Kg, which will produce 65 MJ total energy from
ethanol. Assuming about 90% purity of the ethanol, total energy
available from ethanol is about 60 MJ.
(a) Energy Consumption During Electrolysis
[0032] 2Fe.sup.2+MSA.fwdarw.2Fe.sup.3+MSA+2e.sup.-
2H.sup.++2e.sup.-.fwdarw.H.sub.2
[0033] A typical electrolysis of 100 A for 10 hrs at 2 V for a 2
electron reaction needs,
100.times.10.times.3600.times.2=720,000 Coulombs
[0034] That will give an energy consumption for the electrolysis
about 15 MJ. Assuming 50% current efficiency for the process this
will need an energy of 30 MJ.
(b) By-Product Credit: Hydrogen Energy Produced
[0035] 720,000 Coulombs will produce 37 moles of H.sub.2. Energy
density of H.sub.2 is 120 MJ/kg. 37 moles of H2=74 g of
H.sub.2which gives an energy of 8.8 MJ assuming 50% efficiency for
electrolysis the net energy from hydrogen is 4 MJ.
(c) Energy Consumed For Heating
[0036] The reaction is carried out at 80.degree. C. Energy required
to keep water at that temperature for the electrolysis time is
(assuming only the heat capacity of water and if all the energy
supplied is used to heat the water) specific heat capacity of water
is 4180 J kg-1 K-1. The energy needed to heat 5 kg of water at
80.degree. C. for 100 hrs is 2 MJ.
(d) Energy Equation
[0037] Total energy produced=60 MJ+4 MJ=64 MJ; Total energy
consumed=30 MJ+2 MJ=32 MJ. Energy needed to produce ethanol=12.8
MJ/kg=35000 BTU/gal (1 BTU=1054 J)
[0038] If one uses state of the art technology, the net energy
ratio for the ethanol production will be better than 2:1. That is,
if 100 BTU's of energy is used for the overall process, 200
[0039] BTU's of energy is available in the fuel ethanol. This is a
very rough estimate of the energy content in the process and we are
confident that as processing technologies improve ethanol
production will become lass and less energy intensive. It should be
noted that the Fe-MSA used in the above process is not consumed and
is 100% recyclable. The process has further advantages associated
with of electrochemical processes, including lack of thermal energy
loss, and simplicity of operation. With the anticipated development
of new fermentation processes, the overall yield of the process
should further significantly increase.
Comparison Corn Ethanol Versus Cellulosic Ethanol
[0040] Currently, corn is the primary raw material for ethanol
production, accounting for about 92% of the total feedstock in the
ethanol industry. Most ethanol in the United States is produced by
either a wet milling or a dry milling process and utilizes shelled
corn as the principal feedstock. According to most generally
accepted energy calculations, about 70 percent more energy is
required to produce corn-based ethanol than the energy that is
actually available in ethanol. The corn based ethanol has a net
energy value of about .about.5000 BTUs. As the production of
ethanol from corn is a relatively mature technology, it is not
likely that significant reductions in production costs will be
achieved using conventional technology. Another major drawback of
the corn-based ethanol technology is the potential environmental
damage during the process. The environmental system in which corn
is being produced is being rapidly degraded. The use of croplands
to grow corn for ethanol production will also eventually affect the
food industry. It is at this point that alternative ethanol
production from widely available materials gains significant
interest. Clearly, what is needed is configurations and methods to
produce ethanol in an energetically and economically favorable
manner, which has been achieved by the inventors by combining
electrochemistry, organic chemistry, and biotechnology.
[0041] Cellulosic ethanol is an alternative fuel made from a wide
variety of nonfood plant materials (or feedstocks), including
agricultural wastes such as corn stover and cereal straws,
industrial plant waste like saw dust and paper pulp, and energy
crops grown specifically for fuel production like switch grass. By
using a variety of regional feed stocks for refining cellulosic
ethanol, the fuel can be produced in nearly every city of the
country. With the current status of corn price as the dominant cost
factor, the development of low-cost feedstock is the key to further
reduce the cost.
[0042] Still further, lignocellulosic biomass is the earth's most
attractive alternative among fuel sources and most sustainable
energy resource and is reproduced by the bioconversion of carbon
dioxide. Lignocellulosic biomass is the most abundant biodegradable
substance with an annual net yield of 1.8.times.10.sup.15 kg which
can give about 10.sup.14 Kg of cellulose and 10.sup.13 Kg of
ethanol using current technologies, which is sufficient to meet
current gasoline consumption in America (200 Billion
Gallons=10.sup.12 Kg). The low cost of lignocellulosic materials
makes them a promising feedstock for ethanol production. Although
lignocellulosic materials often require a more complex refining
process, cellulosic ethanol contains more net energy and results in
lower greenhouse emissions than traditional corn-based ethanol.
E85, an ethanol fuel blend that is 85% ethanol, is already
available in more than 1,000 fueling stations nationwide and can
power millions of flexible fuel vehicles already on the roads. The
high cost of cellulose enzymes is the key barrier to economic
production of cellulosic ethanol.
Exemplary Ethanol Process with Ferric Iron
[0043] In contrast to currently known systems and methods, the
unique aspect of the ethanol processes contemplated herein is the
use of a redox system that can act in a manner similar to a surface
active reagent and as an electron source at the same time. While
not limiting to the inventive subject matter, it is thought that
the hydrophobic part of the methane sulfonic acid facilitates the
solubilizing of the rigid cellulose molecules while the Fe.sup.3+
provides the energy to break down the organic material to
fermentable sugars. Thus, use of costly and unstable enzymes is
reduced, or even entirely avoided, and contemplated processes can
be integrated in a simple manner into known yeast fermentation
processes. Remarkably, the methods and processes contemplated
herein also produce two desirable side products, lignin and
hydrogen. The following table exemplarily illustrates some of the
advantages of contemplated methods and configurations:
TABLE-US-00001 Contemplated Cellulosic Ethanol Corn Ethanol
Gasoline Ethanol process Current Price $0.74/Kg $ 0.60/Kg 1.07 $/Kg
$0.5 $/Kg Density 0.8 g/ml 0.8 g/ml 0.74 g/ml 0.8 g/ml Energy
Content 25443 BTU/Kg 25443 BTU/Kg 44642 BTU/Kg 25443 BTU/Kg Energy
Cost 34382 BTU/$ 34382 BTU/$ 41721 50886 BTU/$ BTU/$ Cost matching
$0.61/kg to match the price of gasoline Octane Number 129 129 95
129 CO.sub.2 Emission 10 75 100 10 Energy Balance 60,000 Btu per
gallon 25,000 Btu per gallon Capital Cost 0.85 $/Kg 0.6$/Kg 0.3
$/Kg Capital Charge@ $0.085/kg 0.06$/Kg 0.03 $/Kg 10% Feed Cost
$0.05/Kg $0.3/Kg $0.01/Kg Production cost $0.5/Kg $0.4/Kg $0.35/Kg
$0.1/kg (total)
[0044] Thus, it should be appreciated that the methods and
configurations presented herein are the first reported ethanol
producing process in which hydrogen is being produced as a side
product. The lignin produced can be used to enhance the net energy
value or as source for producing biodiesel and other valuable
organic chemicals.
[0045] The exemplary ethanol process contemplated herein includes
five different stages: (1) Optional digestion of the biomass to
separate lignin and cellulose form raw materials such as wood and
straw to make it amenable to hydrolysis. (2) An optional
pretreatment with dilute sulfuric acid at 80.degree. C. to make the
material more porous. (3) Electrochemically controlled acid
hydrolysis of the cellulosic material (preferably in a flow reactor
at about 80.degree. C.) to produce a fermentable carbohydrate
solution. (4) Yeast fermentation of the carbohydrate solution to
produce ethanol. (5) Optional purification (e.g., passing through
molecular sieves) to produce 99.5% pure alcohol.
[0046] It should also be recognized that metal-mediated
electrochemical oxidation is also a promising technology for the
destruction of other organic waste material, and/or for the
remediation of mixed wastes containing transuranic components. The
combination of a powerful oxidant and an organic sulfonic acid
solution allows the conversion of nearly all organics, whether
present in hazardous or in mixed waste. Moreover, insoluble
transuranics are dissolved in this process and may be recovered by
separation and precipitation. The oxidant, or metal mediator, is
preferably a multivalent transition metal ion, which is cleanly
recycled in a number of charge transfer steps in an electrochemical
cell. It should be noted that the mediated electrochemical
oxidation technique offers several advantages: First, the
oxidation/dissolution processes are accomplished at near ambient
pressures and temperatures (30-90.degree. C.). Second, all waste
stream components and oxidation products (with the exception of
evolved gases) are contained in an aqueous environment. The
electrolyte therefore acts as an accumulator for inorganics, which
were present in the original waste stream, and the large volume of
electrolyte provides a thermal buffer for the energy released
during oxidation of the organics. Third, the generation of
secondary waste is minimal, as the process needs no additional
reagents. Finally, the entire process can be shut down by simply
turning off the power, affording a level of control unavailable in
many other techniques.
Experiments
[0047] (a) Iron powder is dissolved in commercially available 70%
methane sulfonic acid. The ferrous ion solution is diluted with
water to produce 1.5 molar ferrous methane sulfonate in excess
methane sulfonic acid. The solution is treated in a divided
electrochemical cell fitted with an iridium oxide or platinum
coated titanium electrode. Current is applied until the ferrous
iron is converted to ferric ion. Wood flour is added to form a
suspension. The mixture is heated to 80.degree. C. and stirred for
one hour or until all the iron is converted to the ferrous state.
The mixture is filtered to remove any unreacted wood flour. The
solution is then treated by liquid/liquid extraction to remove
organic materials formed, and regenerated in the electrochemical
cell to form ferric ion for treatment with more wood flour.
[0048] (b) In a second example, powdered coal (100 mesh) is treated
in a reactor with ferric methane sulfonic acid in excess methane
sulfonic acid at 180.degree. C. The solution after reaction is fed
to the anode compartment of an electrochemical cell. The cell has
an ion exchange membrane made from NAFION.TM.. The cathode is made
from stainless titanium, the anode is iridium oxide coated
titanium. The product from the cathode is hydrogen and the anodic
products are oxidized coal, carbon dioxide, and a small amount of
sulfuric acid. Oxidized coal can be further oxidized by repeated
cycling of the process, or the solution is mixed with further
quantities of coal to top up the available fuel. At even higher
temperatures (e.g., 300.degree. C. and higher) complete oxidation
of the coal to carbon dioxide is possible.
[0049] (c) In a third example, a solution of Fe.sup.+3 was made up
in methane sulfonic acid at a concentration of 100 gm/l Fe.sup.+3
to which was added cotton muslin that had been previously soaked in
sulfuric acid 80.degree. C. for 2 hours, then washed and dried. The
color of the ferric MSA solution changed immediately to a color
characteristic of a ferrous MSA solution, indicating that
significant oxidation had taken place. The resultant reaction
products (cellulose, starch, and possibly other oxidized
carbohydrate species) were washed and appeared as a white powder
similar to starch. Most preferably, the acid treatment and
oxidation is carried out under conditions that will only partially
hydrolyze the feedstock. The best degree of partial oxidation can
be readily determined by a person of ordinary skill in the art
based on energy consumption and ethanol yield. This starch-like
material was added to a small quantity of water, brewers yeast was
added, and the mixture left over two days, during and after which
the mixture vigorously evolved CO2 and had a clear odor of ethanol.
Thus, it should be recognized that contemplated compositions and
processes allow for efficient conversion of materials otherwise not
amenable to yeast fermentation.
[0050] Of course, it should noted that numerous other cellulosic
materials may be employed as a feedstock for the oxidation process
provided herein, and exemplary alternative feedstocks include
switchgrass, lignocellulosic materials, paper products, cotton
products, agricultural waste products, and other plant-derived
polysaccharides that are ordinarily not fermentable by
microorganisms. Suitable feedstocks are described in EP 0091221 and
WO 02/12529, which are incorporated by reference herein.
Furthermore, it should be noted that additional and/or alternative
oxidating species may be employed, and particularly suitable
alternative oxidizing species include aluminum ions and manganese
ions in various oxidation states.
[0051] Still further, it should be appreciated that the hydrogen
evolved in such systems can be used as fuel component to regenerate
the oxidizing species (e.g., using electrochemical regeneration of
Fe.sup.+3 from Fe.sup.+2 in a hydrogen powered fuel cell).
Therefore, it should be particularly noted that the partial
oxidation of the feedstock will not only provide fermentable
materials for ethanol production, but also reduce overall energy
consumption by energetic coupling of the hydrogen byproduct with
the regeneration of the oxidant. Moreover, as the MSA significantly
increases solubility of the oxidant and, reaction time and
temperature can be further reduced. Additional configurations,
contemplations and details suitable for use herein are described in
U.S. Pat. No. 3,939,286, which is incorporated by reference
herein.
[0052] Thus, specific embodiments and applications of
electrochemical oxidation of organic matter have been disclosed. It
should be apparent, however, to those skilled in the art that many
more modifications besides those already described are possible
without departing from the inventive concepts herein. The inventive
subject matter, therefore, is not to be restricted except in the
spirit of the appended claims. Moreover, in interpreting both the
specification and the claims, all terms should be interpreted in
the broadest possible manner consistent with the context. In
particular, the terms "comprises" and "comprising" should be
interpreted as referring to elements, components, or steps in a
non-exclusive manner, indicating that the referenced elements,
components, or steps may be present, or utilized, or combined with
other elements, components, or steps that are not expressly
referenced. Furthermore, where a definition or use of a term in a
reference, which is incorporated by reference herein is
inconsistent or contrary to the definition of that term provided
herein, the definition of that term provided herein applies and the
definition of that term in the reference does not apply.
* * * * *