METHOD OF PRODUCING COUPLED RADICAL PRODUCTS
A method that produces coupled radical products from biomass. The method involves obtaining a lipid or carboxylic acid material from the biomass. This material may be a carboxylic acid, an ester of a carboxylic acid, a triglyceride of a carboxylic acid, or a metal salt of a carboxylic acid, or any other fatty acid derivative. This lipid material or carboxylic acid material is converted into an alkali metal salt. The alkali metal salt is then used in an anolyte as part of an electrolytic cell. The electrolytic cell may include an alkali ion conducting membrane (such as a NaSICON membrane). When the cell is operated, the alkali metal salt of the carboxylic acid decarboxylates and forms radicals. Such radicals are then bonded to other radicals, thereby producing a coupled radical product such as a hydrocarbon. The produced hydrocarbon may be, for example, saturated, unsaturated, branched, or unbranched, depending upon the starting material.
This application is a divisional of U.S. patent application Ser. No. 12/840,508 filed Jul. 21, 2010 (the '508 application). The '508 application claimed the benefit of U.S. Provisional Patent Application No. 61/228,078, filed on Jul. 23, 2009 (the '078 application), U.S. Provisional Patent Application No. 61/258,557, filed on Nov. 5, 2009 (the '557 application), and U.S. Provisional Patent Application No. 61/260,961, filed on Nov. 13, 2009. The '508 application also claimed the benefit of, and was a continuation application of, U.S. patent application Ser. No. 12/840,401 filed on Jul. 21, 2010, which claimed the benefit of the '078 and '557 applications. These provisional and non-provisional patent applications are expressly incorporated herein by reference.
BACKGROUND OF THE INVENTIONHydrocarbon fuels are currently used throughout the world. One specific example of a hydrocarbon fuel is gasoline (which includes octane). Another common hydrocarbon fuel is diesel fuel, which is used in diesel engines. Waxes, oils, and fuels are also desirable hydrocarbon products. Hydrocarbons are used in cosmetic and medical applications.
Biomass is a renewable feedstock. Biomass may comprise lipids (such as fats or oils) that are available from plant, algal, or animal origin. These fats or oils may include fatty acids. Obviously, given its abundance in nature, it is desirable to find a way to use this biomass as a starting material to form a useable product, such as a hydrocarbon fuel.
Current methods to convert biomass to a hydrocarbon fuel involve the process known as “hydroreacting” in which hydrogen gas is added to the biomass (in the presence of a catalyst) to convert the biomass to hydrocarbons. Unfortunately, hydroreacting is generally expensive because hydrogen gas is an expensive reactant. Also, a catalyst is involved in this process, and such catalysts are often intolerant with Ca, Cl, V, N, As, Hg, Si, P, Cr or other materials that may be found in the biomass. Other impurities include soluble vitamins, steroids, terpenes, alkaloids, etc. Another process to convert biomass to hydrocarbons is decarboxylation, wherein the carboxylic acid functionality of a fatty acid is “decarboxylated,” thereby leaving a hydrocarbon. (In some situations, this decarboxylation step may be preceded by a fermentation step and/or a hydrolysis step, depending upon the starting material.) Employing the decarboxylation process to produce the hydrocarbon is generally expensive.
Accordingly, there is a need for a new process by which biomass (such as carboxylic acids, oils, etc.) may be converted into a hydrocarbon. It would be desirable for this process to be inexpensive to use and capable of producing a variety of different hydrocarbons. Such a process is disclosed herein.
SUMMARY OF THE INVENTIONBiomass may be obtained from plant, animal, or algal materials and may be comprised of a carbohydrates, lipids, lignins and the like. Biomass may be converted into carboxylic acid, which may be a fatty acid material (or other lipid material). Nonlimiting examples of carboxylic acids may include high-carbon carboxylic acids such as fatty acids (a Carbon content of C12 or higher) or low-carbon carboxylic acids (a Carbon content of C12 or lower). (“Low-carbon carboxylic acids” are also referred to herein as a “carboxylic acid with a small number of carbon atoms.”) The carboxylic acids may be aliphatic carboxylic acids or aromatic carboxylic acids. The carboxylic acids may be monocarboxylic acids, dicarboxylic acids, or polycarboxylic acids, depending upon the number of COOH groups contained therein. As used herein throughout, the use of “carboxylic acids” may mean any of the foregoing examples. Similarly, the use of any one of the foregoing examples may be substituted if appropriate for any one of the other foregoing examples. Other embodiments may be designed in which the biomass is obtained through one or more processing steps, before being converted into a carboxylic acid. Such steps may include isolating lipid materials or a carbohydrate material, or lignin material. Obtaining the biomass may also include extracting or converting biomass into lipid materials or a carbohydrate material, or lignin material. It will be appreciated by those of skill in the art that the biomass may already be in the form of a lipid, a carbohydrate, or lignin, fatty acids, or other forms and may need to be extracted, converted, isolated, and the like from the biomass. Thus, the word “obtaining” as used herein throughout may or may not include the steps of extracting, converting, isolating, and the like. Examples of a lipid material include fatty acids, esters of fatty acids, triglycerides of fatty acids, fatty acid derivatives, and/or metal salts of fatty acids. Examples of lignin material may include resins. Examples of carbohydrate material may include cellulose, glucose, among many other examples.
Once this biomass material is obtained (from any source), this material is converted to at least one alkali metal salt of a carboxylic acid. (Typically, this alkali metal salt is a sodium salt, however, other alkali metal salts may also be used.) In some embodiments, conversion of the biomass or biomass material (collectively “biomass”) into the alkali metal salt of carboxylic acid involves an intermediate step of conversion into the carboxylic acid itself. Then, depending upon the source of biomass, another conversion reaction may be needed to convert the biomass into an alkali metal salt of carboxylic acid. The terms “alkali salt” and “alkali metal salt” are used interchangeably throughout. For example, if the biomass is a lipid, the lipid may first be hydrolyzed into a carboxylic acid, which in this case may be a fatty acid, and then a “saponification” reaction using a base (such as sodium methoxide or NaOH) is reacted with the carboxylic acid to form the alkali metal salt of carboxylic acid. Examples of saponification reactions are shown below:
R—COOX+CH3ONa→R—COONa+CH3OH
R—COOX+NaOH→R—COONa+H2O
In the above reactions, “X” is the remaining section of an ester, the remaining section of a triglyceride, hydrogen, or a metal other than an alkali metal. The “R” represents the (carboxylic acid) chain of the lipid material. In embodiments where the biomass is a carbohydrate or a lignin, or some other type of biomass, one or more different intermediate steps may be needed to convert the biomass into an alkali metal salt of carboxylic acid. For example, it may be that the biomass is fermented into the alkali metal salt of carboxylic acid. In other embodiments, the biomass may be fermented into the carboxylic acid and then saponified as described above to from the alkali metal salt of carboxylic acid. It will be appreciated by those of skill in the art that after the conversion steps, if the starting biomass was a lipid, the resulting alkali metal salt of a carboxylic acid may be in the form of an alkali metal salt of a fatty acid. Similarly, where the starting biomass is a carbohydrate, the resulting alkali metal salt of a carboxylic acid may be in the form of an alkali metal salt of a low-carbon carboxylic acid. Likewise, where the starting biomass is a lignin, the resulting alkali metal salt of a carboxylic acid may be in the form of an aromatic carboxylic acid alkali metal salt.
In some embodiments, one more of the intermediate steps are omitted and the biomass is converted directly into at least one alkali metal salt of a carboxylic acid by reacting a base with a quantity of the biomass itself to produce the at least one alkali metal salt of the carboxylic acid. There are many ways to convert biomass into a alkali metal salt of a carboxylic acid.
Continuing with the example where the biomass is a lipid and the intermediate conversion step of saponification has been used (see paragraph 7 above), the next step is to separate the R—COONa and incorporate this chemical into an anolyte for use in an electrolytic cell. This anolyte may also include a solvent (such as methanol) and optionally a supporting electrolyte (in addition to the R—COONa) such as sodium acetate.
The anolyte is fed into an electrolytic cell that uses a sodium ion conductive ceramic membrane that divides the cell into two compartments: an anolyte compartment and a catholyte compartment. A typical membrane is a NaSICON membrane. NaSICON typically has a relatively high ionic conductivity for sodium ions at room temperature. Alternatively, if the alkali metal is lithium, then a particularly well suited material that may be used to construct an embodiment of the membrane is LiSICON. Alternatively, if the alkali metal is potassium, then a particularly well suited material that may be used to construct an embodiment of the membrane is KSICON. Other examples of such solid electrolyte membranes include those based on NaSICON structure, sodium conducting glasses, beta alumina and solid polymeric sodium ion conductors. Such materials are commercially available. Moreover, such membranes are tolerant of impurities that may be in the anolyte and will not allow the impurities to mix with the catholyte. Thus, the impurities (which were derived from the biomass) do not necessarily have to be removed prior to placing the anolyte in the cell.
The electrolytic cell may use standard parallel plate electrodes, where flat plate electrodes and/or flat membranes are used. In other embodiments, the electrolytic cell may be a tubular type cell, where tubular electrodes and/or tubular membranes are used.
An electrochemically active first anode may be found in the cell and may be housed in the first anolyte compartment. The anode may be made of smooth platinum, stainless steel, or may be a carbon based electrode. Examples of carbon based electrodes include boron doped diamond, glassy carbon, synthetic carbon, Dimensionally Stable Anodes (DSA), and lead dioxide. Other materials may also be used for the electrode. The first anode allows the desired reaction to take place. In this anolyte compartment of the cell, the oxidation (decarboxylation) reaction and subsequent radical-radical coupling takes place. In one embodiment, the anodic decarboxylation/oxidative coupling of carboxylic acids occurs via a reaction known as the “Kolbe reaction.” The standard Kolbe reaction is a free radical reaction and is shown below:
This Kolbe reaction is typically conducted in non-aqueous methanolic solutions, with partially neutralized acid (in the form of alkali salt) used with a parallel plate type electrochemical cell. The anolyte used in the cell may have a high density.
As can be seen from the Kolbe reaction, the “R” groups of two carboxylic acid molecules are coupled together, thereby resulting in a coupled radical product. In one embodiment, the Kolbe reaction is a free radical reaction in which two “R radicals” (R.) are formed and are subsequently combined together to form a carbon-carbon bond. It will be appreciated by those of skill in the art, that depending upon the starting material used, the coupled radical product may be a hydrocarbon or some other carboxylic acid chain. The coupled radical product may be a dimer, or a mixed product comprising one or more high- or low-carboxylic acids. The radical in the coupled radical product may include an alkyl-based radical, a hydrogen-based radical, an oxygen-based radical, a nitrogen-based radical, other hydrocarbon radicals, and combinations thereof. Thus, although hydrocarbons may be used in the examples below as the coupled radical product, hydrocarbon may be freely substituted for some other appropriate coupled radical product.
As noted above, however, the present embodiments may use a sodium salt (or alkali metal salt) of the carboxylic acid in the anolyte rather than the carboxylic acid itself. Thus, rather than using the standard Kolbe reaction (which uses a carboxylic acid in the form of a fatty acid), the present embodiments may involve conducting the following reaction at the anode:
Again, this embodiment results in two “R” groups being coupled together to form a coupled radical product such as a hydrocarbon. There are distinct advantages of using the sodium salt of the carboxylic acid instead of the carboxylic acid itself:
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- R—COONa is more polar than R—COOH and so it is more likely to decarboxylate (react) at lower voltages;
- The electrolyte conductivity may be higher for sodium salts of carboxylic acids than carboxylic acids themselves; and
- The anolyte and catholyte may be completely different allowing different reactions to take place at either electrode.
As noted above, the cell contains a membrane that comprises a sodium ion conductive membrane. This membrane selectively transfers sodium ions (Na+) from the anolyte compartment to the first catholyte compartment under the influence of an electrical potential, while at the same time preventing the anolyte and catholyte from mixing.
The catholyte may be aqueous NaOH or a non aqueous methanol/sodium methoxide solution. (The anolyte may also be aqueous or non-aqueous). An electrochemically active cathode is housed in the catholyte compartment, where reduction reactions take place. These reduction reactions may be written as:
2Na++2H2O+2e−→2NaOH+H2
2Na++2CH3OH+2e−→2NaOCH3+H2
Hydrogen gas is the product of the reduction reaction at the cathode. NaOH (sodium hydroxide) or NaOCH3 (sodium methoxide) is also produced. This NaOH or NaOCH3 is the base that was used above in the saponification reaction. Thus, this reaction may actually regenerate (in the catholyte compartment) one of the reactants needed in the overall process. This NaOH or NaOCH3 may be recovered and re-used in further reactions. The ability to regenerate and re-use the NaOH or NaOCH3 is advantageous and may significantly reduce the overall costs of the process.
In an alternative embodiment, a sodium salt of carboxylic acid with a small number of carbon atoms (such as CH3COONa (sodium acetate)) may be added to the anolyte in addition to the R—COONa. The addition of sodium acetate may be advantageous in some embodiments because:
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- Sodium acetate may act as a suitable supporting electrolyte as it is highly soluble in methanol solvent (up to 26 wt. %), thereby providing high electrolyte conductivity in the anolyte;
- Sodium acetate will itself decarboxylate (in the electrolytic process) and produce CH3. (methyl radicals) by the following reaction:
-
- In turn, the methyl radical may react with a hydrocarbon group of the carboxylic acid to form hydrocarbons with additional CH3— functional group:
Therefore, in one embodiment, by using sodium acetate as part of the anolyte, this embodiment may couple two hydrocarbon radicals from the carboxylic acid together (R—R) or couple the radical of the carboxylic acid with a methyl radical from the acetate (R—CH3), thereby producing mixed hydrocarbon products. This mixture of products may be separated and used as desired. Of course, this embodiment is shown using sodium acetate as the additional reactant. In the alternative, other sodium salts of a carboxylic acid with a small number of carbon atoms may also be used to couple a carbon radical to the radical of the carboxylic acid.
It will be appreciated that a variety of different hydrocarbons or coupled radical products may be formed using the present embodiments. For example, the particular “R” group that is selected may be chosen and/or tailored to produce a hydrocarbon that may be used for diesel, gasoline, waxes, JP8 (“jet propellant 8”), etc. The particular application of the hydrocarbon may depend upon the starting material chosen.
In order that the manner in which the above-recited and other features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:
A method for producing a coupled radical product from biomass is disclosed. This method comprises obtaining a quantity of biomass and then converting the biomass into an at least one alkali metal salt of a carboxylic acid. In some embodiments, the alkali metal may comprise sodium such that the alkali metal salt of the carboxylic acid comprises a sodium salt of the carboxylic acid. An anolyte may comprise a quantity of the alkali metal salt of the carboxylic acid. In one embodiment, the alkali metal salt of the carboxylic acid is decarboxylated. The decarboxylation converts the alkali metal salt of the carboxylic acid into an alkyl radical that reacts to form the coupled radical product. In one embodiment, the coupled radical product is a hydrocarbon. A mixture of hydrocarbons may also be produced. The alkyl radical may couple to another alkyl radical or to a hydrogen radical. The hydrogen radicals may be formed in addition to the alkyl radicals. The hydrogen radicals may also be formed from an alkali metal formate or from a photolysis process of hydrogen gas within the anolyte compartment. It will be appreciated by those of skill in the art that any irradiation process may be used instead of photolysis. The decarboxylation of the alkali metal salt of the carboxylic acid may also be performed via photolysis. At least one alkali metal salt of the carboxylic acid may further comprise a quantity of an alkali metal acetate and/or a quantity of an alkali metal formate.
The biomass may be converted into at least one alkali metal salt of a carboxylic acid in a variety of different ways. For example, embodiments may be constructed in which converting the biomass comprises saponification, wherein a base is reacted with a quantity of the carboxylic acid to produce the alkali metal salt of the carboxylic acid. In other embodiments, a lipid is extracted from the biomass, and, if necessary, the lipid may be hydrolyzed to form carboxylic acid. This carboxylic acid may then be saponified to produce at least one alkali metal salt of carboxylic acid. In other embodiments, the biomass is fermented to produce a carboxylic acid. The carboxylic acid may then be saponified to produce at least one alkali metal salt of carboxylic acid. In other embodiments, the biomass is fermented to directly produce at least one alkali metal salt of carboxylic acid. Further embodiments are designed in which a carbohydrate is hydrolyzed to produce a carboxylic acid (which may then be saponified). The saponification may occur in the same electrolytic cell where decarboxylation occurs. In other embodiments, a base is reacted directly with a quantity of biomass to produce the at least one alkali metal salt of the carboxylic acid. Accordingly, the alkali metal salt may be derived from carbohydrates, lipids, such as oils, including tall oil, fatty acids, esters of fatty acids, triglycerides of fatty acids, phospholipids, fatty acid derivatives, and/or metal salts of fatty acids, lignins, such as resins, and mixtures of the foregoing. The alkali metal salt of the carboxylic acid may be derived from the forgoing in the form of wood chips, forestry residue, energy crops (switch grass, miscanthus, sorghum, energy cane and other genetically modified plants), algae, cyanobacteria, jatropha, soy bean, corn, palm, coconut, canola, rapeseed, Chinese tallow, animal fats and products of genetically modified organisms, whether natural, synthetic, man-made, or even genetically altered.
The electrolytic cell used to decarboxylate alkali metal salt of the carboxylic acid may comprise an anolyte compartment and a catholyte compartment. The anolyte compartment houses the anolyte and the catholyte compartment houses a catholyte. The anolyte compartment and the catholyte compartment are separated by an alkali ion conducting membrane. In some embodiments, the alkali ion conducting membrane is a NaSICON membrane. During this reaction, the catholyte in the catholyte compartment produces hydrogen gas and a base. This base may or may not be the same base used in the saponification reaction that produces the alkali metal salt of the carboxylic acid. The anolyte and catholyte may both comprise a solvent. The anolyte may comprise a first solvent or a first mixture of solvents, and the catholyte may comprise a second solvent or second mixture of solvents, wherein the first solvent or the first mixture of solvents included in the anolyte do not have to be the same as the second solvent or the second mixture of solvents included in the catholyte. The first solvent may comprise a two-phase solvent system, wherein one phase is capable of dissolving ionic materials and the other phase is capable of dissolving non-ionic materials. The anolyte may be reacted at a higher temperature and/or pressure than the catholyte (or vice versa).
A method for producing a coupled radical product is also disclosed. The method comprises preparing an anolyte for use in an electrolytic cell, the cell comprising an alkali ion conducting membrane, wherein the anolyte comprises a first solvent and a quantity of an alkali metal salt of a carboxylic acid. The method also comprises decarboxylating at least one alkali metal salt of the carboxylic acid within the cell, wherein the decarboxylation converts at least one alkali metal salt of the carboxylic acid into an alkyl radical that reacts to form a coupled radical product. In one embodiment, the coupled radical product is a hydrocarbon.
Another method of producing a coupled radical product is also disclosed. The method may comprise obtaining a alkali metal salt of a carboxylic acid, the alkali metal salt being derived from, for example, carbohydrates, fatty acids, dicarboxylic fatty acids, polycarboxylic fatty acids, esters of fatty acids, triglycerides of fatty acids, lipids, phospholipids, fatty acid derivatives, and/or metal salts of carboxylic acids. The method may also comprise preparing an anolyte for use in an electrolytic cell, the electrolytic cell comprising an anolyte compartment, a catholyte compartment, and a NaSICON membrane that separates the anolyte compartment from the catholyte compartment, wherein anolyte is housed within the anolyte compartment and catholyte is housed within the catholyte compartment. The anolyte comprises a solvent and a quantity of the sodium salt of the carboxylic acid. The anolyte is electrolyzed within the cell, wherein the electrolyzing decarboxylates the sodium salt of the carboxylic acid and converts the sodium salt of the carboxylic acid into an alkyl radical that reacts to form a coupled radical product, which in one embodiment, may be a hydrocarbon.
The embodiments of the present invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the present embodiments, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of embodiments of the invention.
As shown in
This lipid material 112 may be subjected to a hydrolysis process 115 that converts the lipid 112 into a fatty acid 120 (such as carboxylic acid 120). In turn, this fatty acid 120 may undergo a saponification reaction 121 to produce the alkali salt of the fatty acid 108. As shown in
The saponification reaction uses the base 150 to produce an alkali metal salt of a fatty acid. Examples of this reaction are shown below using sodium methoxide or NaOH as the base:
R—COOX+CH3ONa→R—COONa+CH3OH
R—COOX+NaOH→R—COONa+H2O
The “R” in this embodiment represents the hydrocarbon tail or hydrocarbon moiety of the molecule. The “X” represents the remaining section of an ester, the remaining section of a triglyceride, a hydrogen or a metal other than sodium. As shown by this reaction, R—COONa is produced, which is the sodium salt of the fatty acid.
As shown in
In other embodiments, the fermentation reaction 131 may convert the biomass 104 into a lipid material 112, as shown by dashed line 131a. This is especially useful for biomass from tall oils, pulp produced from paper mills, etc. Such lipid materials 112 may then be processed in the manner outlined above.
In other embodiments, the biomass 104 may be a carbohydrate 140. This carbohydrate material 140 may undergo a hydrolysis reaction 143 that converts the carbohydrate into acetic acid 134 and/or into another fatty acid 120. The particular carbohydrate material used will determine whether the resulting acid is branched or unbranched, saturated or unsaturated. Examples of carbohydrates could be starch, cellulose, hemi-cellulose, glucose, pentoses, and sucrose. Once the acetic acid 134 or fatty acid 120 has been obtained, this acid may be subjected to saponification 121 to produce the alkali salt of the fatty acid 108. Other types of conversion reactions that convert the carbohydrate into the alkali salt of the fatty acid 108 may also be used.
In other embodiments, the biomass 104 comprises tall oil, resins, and/or lignins 190. Such materials may be converted 192 into carboxylic acids 120 (and then processed as outlined herein). In one embodiment, the lignin 190 is first subjected to a conversion reaction 192 whereby the lignin is hydrolyzed into carboxylic acid and then saponified into the alkali metal salt of carboxylic acid. In other embodiments, the materials 190 may be directly converted 191 to the alkali metal salts of carboxylic acids.
It should be noted that the various processes described and shown in
Once the alkali salt of the fatty acid 108 has been obtained, the salt of the fatty acid 108 will be added to an electrochemical cell that includes a sodium conducting membrane (or other alkali conducting membrane). An example of a typical embodiment of a cell is shown in
The hydrocarbon 170 produced in the process 100 (and more specifically in the advanced Kolbe reaction 167) may be of significant value. Hydrocarbons have significant value for use in fuels, diesel fuels, gasoline, medical applications, waxes, perfumes, oils, and other applications and products. With the process of the present invention, different types of hydrocarbons may be used. Hydrocarbons are often classified by the number of carbons in their chain. In addition, hydrocarbons may often be classified into the following “fractions”:
Note that these classifications are not exact and may change according to the particular embodiment. For example, the “gasoline fraction” could have a portion of C11, the JP8 fraction could have some C14, etc.
By forming the coupled radical products according to the present embodiments, various hydrocarbons could be made in some or all of these fractions. For example, embodiments may be constructed in which a C8 hydrocarbon (octane) is formed, which is a principal ingredient in commercial gasoline. Likewise, a C12 hydrocarbon may be formed, which may be used in making JP8. Of course, the exact product that is obtained depends upon the particular starting material(s) and/or the reaction conditions used. Thus, the present embodiments allow biomass to be converted into synthetic lubricants, gasoline, JP8, diesel fuels, or other hydrocarbons.
In order to form the hydrocarbon, an advanced Kolbe reaction 167 occurs within an electrochemical cell. This reaction, along with an example of a typical cell, will now be described in greater detail in conjunction with
The particulars of each cell 200 will depend upon the specific embodiment. For example, the cell 200 may be a standard parallel plate cell, where flat plate electrodes and/or flat plate membranes are used. In other embodiments, the cell 200 may be a tubular type cell, where tubular electrodes and/or tubular membranes are used. An electrochemically active first anode 218 is housed, at least partially or wholly, within the anolyte compartment 208. More than one anode 218 may also be used. The anode 218 may comprise, for example, a smooth platinum electrode, a stainless steel electrode, or a carbon based electrode. Examples of a typical carbon based electrode include boron doped diamond, glassy carbon, synthetic carbon, Dimensionally Stable Anodes (DSA) and relatives, and/or lead dioxide. Other electrodes may comprise metals and/or alloys of metals, including S.S, Kovar, Inconel/monel. Other electrodes may comprise RuO2—TiO2/Ti, PtOx—PtO2/Ti, IrOx, CO3O4, MnO2, Ta2O5 and other valve metal oxides. In addition, other materials may be used to construct the electrode such as SnO2, Bi2Ru2O7 (BRO), BiSn2O7, noble metals such as platinum, titanium, palladium, and platinum clad titanium, carbon materials such as glassy carbon, BDD, or Hard carbons. Additional embodiments may have RuO2—TiO2, hard vitrems carbon, and/or PbO2. Again, the foregoing serve only as examples of the type of electrodes that may be employed. The cathode compartment 204 includes at least one cathode 214. The cathode 214 is partially or wholly housed within the cathode compartment 204. The material used to construct the cathode 214 may be the same as the material used to construct the anode 218. Other embodiments may be designed in which a different material is used to construct the anode 218 and the cathode 214.
The anolyte compartment 208 is designed to house a quantity of anolyte 228. The catholyte compartment 204 is designed to house a quantity of catholyte 224. In the embodiment of
The anode compartment 208 and the cathode compartment 204 are separated by an alkali metal ion conductive membrane 212. The membrane utilizes a selective alkali metal transport membrane. For example, in the case of sodium, the membrane is a sodium ion conductive membrane 212. The sodium ion conductive solid electrolyte membrane 212 selectively transfers sodium ions (Na+) from the anolyte compartment 208 to the catholyte compartment 204 under the influence of an electrical potential, while preventing the anolyte 228 and the catholyte 224 from mixing. Examples of such solid electrolyte membranes include those based on NaSICON structure, sodium conducting glasses, beta alumina and solid polymeric sodium ion conductors. NaSICON typically has a relatively high ionic conductivity at room temperature. Alternatively, if the alkali metal is lithium, then a particularly well suited material that may be used to construct an embodiment of the membrane is LiSICON. Alternatively, if the alkali metal is potassium, then a particularly well suited material that may be used to construct an embodiment of the membrane is KSICON.
As noted above, the saponification reaction 121 and/or the other reactions of
The anolyte compartment 208 may include one or more inlets 240 through which the anolyte 228 may be added. Alternatively, the components that make up the anolyte 228 may be separately added to the anolyte compartment 208 via the inlets 240 and allowed to mix in the cell. The anolyte includes a quantity of the alkali metal salt of a fatty acid 108. In the specific embodiment shown in
The catholyte compartment 204 may include one or more inlets 242 through which the catholyte 224 may be added. The catholyte 224 includes a second solvent 160b. The second solvent 160b may be an alcohol or water (or a mixture of alcohol and water). Significantly, the solvent 160b in the catholyte 224 is not necessarily the same as the first solvent 160a in the anolyte 228. In some embodiments, the solvents 160a, 160b may be the same. The reason for this is that the membrane 212 isolates the compartments 208, 204 from each other. Thus, the solvents 160a, 160b may be each separately selected for the reactions in each particular compartment (and/or to adjust the solubility of the chemicals in each particular compartment). Thus, the designer of the cell 200 may tailor the solvents 160a, 160b for the reaction occurring in the specific compartment, without having to worry about the solvents mixing and/or the reactions occurring in the other compartment. This may be a significant advantage in designing the cell 200. A typical Kolbe reaction only allows for one solvent used in both the anolyte and the catholyte. Accordingly, the use of two separate solvents may be advantageous. In other embodiments, either the first solvent 160a, the second solvent 160b, and/or the first and second solvents 160a, 160b may comprise a mixture of solvents.
The catholyte 224 may also include a base 150. In the embodiment of
The reactions that occur at the anode 218 and cathode 214 will now be described. As with all electrochemical cells, such reactions may occur when voltage source 290 applies a voltage to the cell 200.
At the cathode 214, a reduction reaction takes place. This reaction uses the sodium ions and the solvent to form hydrogen gas 270 as well as an additional quantity of base 150/150a. Using the chemicals of
2Na++2H2O+2e−→2NaOH+H2
2Na++2CH3OH+2e−→2NaOCH3+H2
The hydrogen gas 270 and/or the base 150/150a may be extracted through outlets 244. The hydrogen gas 270 may be gathered for further processing for use in other reactions, and/or disposed of or sold. The production of the base 150/150a may be a significant advantage because the base 150 that was consumed in the saponification reaction 121 of
The reactions that occur at the anode 218 may involve decarboxylation. These reactions may involve an advanced Kolbe reaction (which is a free radical reaction) to form a quantity of a hydrocarbon 170 and carbon dioxide 172. Using the chemicals of
The carbon dioxide 172 may be vented off (via outlets 248). This is a safe, naturally-occurring chemical that may be collected, disposed of, or re-used. The coupled radical product 170 may also be collected via an outlet 248. For example, a quantity of the solvent 160/160a may be extracted via an outlet 248 and recycled, if desired, back to the inlet 240 for future use.
The advanced Kolbe reaction may comprise a free radical reaction. As such, the reaction produces (as an intermediate) a hydrocarbon radical designated as R.. Accordingly, when two of these R. radicals are formed, these radicals may react together to form a carbon-carbon bond:
As shown in
As shown in
The methyl radicals may then be reacted with hydrocarbon group of the fatty acid to form hydrocarbons with additional CH3— functional group:
CH3.+R.→CH3—R
Alternatively or additionally, the methyl radical may react with another methyl radical to form ethane:
CH3.+CH3.→CH3—CH3
Ethane (CH3—CH3) is a hydrocarbon that may form a portion of the hydrocarbon product 170. This ethane is designated as 170c. The CH3—R formed in the reaction may also be part of the hydrocarbon product 170 and is designated as 170b. Thus, a mixture of hydrocarbons may be obtained. If desired, the various hydrocarbons 170a, 170b, 170c may be separated from each other and/or purified, such as via gas chromatography or other known methods. The present embodiments may couple two hydrocarbon radicals or couple methyl radicals with hydrocarbon radicals. The amount of the CH3—R or R—R in the product may depend upon the particular reaction conditions, quantities of reactants used in the anolyte, etc.
The foregoing example involved the use of sodium acetate in addition to the fatty acid salt to produce reactive methyl radicals, thereby producing CH3—R in addition to the R—R product. However, rather than acetate, other salts that have a small number of carbons may be used in place of or in addition to acetate. These salts having a small number of carbons may produce, for example, ethyl radicals, propyl radicals, isopropyl radicals, and butyl radicals during decarboxylation. Thus, by changing the optional component, additional hydrocarbons may be formed in the cell 200. The user may thus tailor the specific product formed by using a different reactant. Thus, it is possible to create a mixture of products as different alkyl radicals react together or even react with a methyl radical, a hydrogen radical, etc. The different alkyl radicals may be added by adding acetate, formate, etc. into the anolyte through, for example, an additional port in the anolyte compartment. Such a different mixture of products may be, in some embodiments, similar to what would occur in a disproportionation reaction.
In a similar manner, instead of and/or in addition to using sodium acetate, an alkali metal formate (such as sodium formate) may be used as part of the anolyte. Sodium formate has the formula H—COONa. During the electrochemical reaction, the formate, like the acetate, will undergo decarboxylation to form a hydrogen radical:
In turn, this hydrogen radical will react to form:
H.+R.→H—R
AND/OR
H.+H.→H2
The use of sodium formate as an optional reactant may result in the R—R product being formed as well as a quantity of an R—H product (and even a quantity of hydrogen gas (H2)). (The hydrogen gas may be re-used if desired). The use of formate may prevent the unnecessary formation of ethane and/or may be used to tailor the specific hydrocarbon (R—H) product.
The particular R group that is shown in these reactions may be any “R” obtained from biomass, whether the R includes saturated, unsaturated, branched, or unbranched chains. When the R—R product is formed, this is essentially a “dimer” of the R group. For example, if the R group is CH3 (such as is the case with sodium acetate), two methyl radicals react (2CH3.) and “dimerize” into ethane (CH3—CH3). If the R group is a C18H34 hydrocarbon, then a C36H78 product may be formed. By using these simple principles, as well as using the formate or the small chain carbon salt, any desired hydrocarbon may be obtained. For example, by using a C4 sodium salt, a C8 R—R hydrocarbon may be formed, which may be useable as part of a gasoline. Likewise, if a C6 sodium salt is used, a C12 R—R hydrocarbon may be formed, which may be useable as JP8. Synthetic lubricants, waxes, and/or other hydrocarbons may be formed in the same or a similar manner.
An alternate embodiment to that of
R—COONa+H2 and Pd→Pd—Hx→Pd+H—R+CO2+e−+Na+
By using one or more of the noble metals with hydrogen gas in the anolyte compartment, the particular product (R—H) may be selected. In the embodiment of
Referring now to
This photolysis process may be combined with the electrolysis process of the cell described above:
The hydrogen radicals and the hydrocarbon radicals may then combine to form a mixture of products:
2H.+2R→H—R+R—R+H2
Alternatively, the photolysis device may be used to conduct decarboxylation and to generate hydrocarbon radicals:
Thus, a combination of photolysis and electrolysis may be used to form the hydrocarbon radicals and/or hydrogen radicals in the anolyte compartment 208:
This combination of electrolysis and photolysis may speed up the rate of the decarboxylation reaction.
Yet additional embodiments may be designed using such photolysis techniques. For example, the following reactions may occur:
This combination of reactions (using photolysis and electrolysis) forms carbocations and H− anions that may combine to form the hydrocarbon. Thus, photolysis may be used as a further mechanism for forming hydrocarbons. As has been discussed above, although hydrocarbons are being used in these examples, the coupled radical product need not be a hydrocarbon. In certain embodiments, the method and apparatus of the present invention may be used to create nonhydrocarbon radicals which may couple together to form useful coupled radical products.
Referring now to
-
- two separate environments for different reaction conditions—for example, the anolyte may be non-aqueous, while the catholyte is aqueous (and vice versa);
- anolyte may be at a higher temperature than the catholyte (and vice versa);
- anolyte may be pressurized and catholyte not (and vice versa);
- anolyte may be irradiated and catholyte not (and vice versa);
- anolyte and/or anode may be designed to conduct specific reactions that are not dependent upon the catholyte and/or cathode reactions (and vice versa);
- the different chambers may have different flow conditions, solvents, solubilities, product retrieval/separation mechanisms, polarities, etc.
The ability to have separate reaction conditions in the anolyte compartment and catholyte compartment may allow the reactions in each compartment to be tailored to achieve optimal results.
Likewise, a membrane, comprising, for example, NaSICON, has a high temperature tolerance and thus the anolyte may be heated to a higher temperature without substantially affecting the temperature of the catholyte (or vice versa). (NaSICON can be heated and still function effectively at higher temperatures). This means that polar solvents (or non-polar solvents) that dissolve fatty acids and sodium salts at high temperatures may be used in the anolyte. For example, palmitic acid may be heated to form a liquid and this liquid is an excellent solvent for sodium palmitate. At the same time, the catholyte is unaffected by temperature. In fact, a different solvent system could simultaneously be used in the catholyte. Alternatively, other molten salts or acids may be used to dissolve ionic sodium carboxylic acids and salts in the anolyte. Long chain hydrocarbons, ethers, triglycerides, esters, alcohols, or other solvents may dissolve carboxylic acids and sodium salts. Such compounds could be used as the anolyte solvent without affecting the catholyte. Ionic liquids could be used as the anolyte solvent. These materials not only would dissolve large quantities of fatty acid sodium salts, but also, may operate to facilitate the decarboxylation reaction at higher temperatures. Ionic liquids are a class of chemicals with very low vapor pressure and excellent dissolving abilities/dissolving properties. A variety of different ionic liquids may be used.
Referring now to
As explained above, one of the advantages of the present cell is that it produces a base 150 in the catholyte compartment 204. As noted above, this base 150 may then be used as part of the saponification reaction 121 that produces the sodium salt of the fatty acid. In the context of
2H2O+2e−+2Na+→2NaOH+H2
2CH3OH+2e−+2Na+→2NaOCH3+H2
The Na+ ions for this reaction come from the anolyte 228. Specifically, the sodium ions migrate through the membrane 212 as shown by
Alternatively, embodiments may be made in which the fatty acids may be saponified directly in the catholyte compartment 208. In other words, the saponification reaction 121 occurs within the cell itself to produce the fatty acid sodium salt, and this sodium salt is then taken from the catholyte compartment 204 to the anolyte compartment 208 (such as via conduit 510). Fatty acid is added to the catholyte 224 and may react (saponified) as follows:
R—COOH+2e−+2Na+→R—COONa+H2
This R—COONa is the sodium salt of the fatty acid 108, which is then introduced into the anolyte compartment 208 either through a conduit 510 (or perhaps through an inlet 240). This sodium salt would then be reacted (decarboxylated), forming coupled radical products such as hydrocarbons. This process thus allows the fatty acid to be saponified in situ (e.g., within the cell). This process would be a one step process (e.g., simply running the cell) rather than a two step process (saponification and decarboxylation within the cell).
Triglycerides may also be saponified as used in the present processes. Such saponification may occur within the cell 500 or exterior of the cell. Such saponification of triglycerides may occur, for example, as follows:
If sodium methoxide (or another organic base) is used rather than sodium hydroxide, the reaction with a triglyceride may be as follows:
Referring now to
Using this type of “two-phase” system, the hydrocarbon, when formed, will readily dissolve in the organic phase, and will be repelled by the aqueous/ionic phase. This means that the formed hydrocarbon(s) will readily separate from the aqueous/ionic phase. The reaction may be summarized as follows:
Similar separation may be obtained by using two solvents of different polarities as well. Another example of this principle involves glutaric acid. Sodium glutarate is not soluble in methanol, but is soluble in water. Accordingly, if water is used as one of the solvents in a two-phase system, it will dissolve the sodium glutarate. Another non-polar and/or organic solvent is used with water. When the hydrocarbon is formed, this hydrocarbon is not soluble in water. Rather, the hydrocarbon will dissolve into the non-polar/organic solvent. The reactions associated with this example are provided below:
This hydrocarbon H—(CH2)3—CH2)3—CH2)3—H is non-polar and will migrate to the non-polar/organic solvent. Also, the non-polar nature of the solvent may also operate to terminate the reaction so that a product with nine carbon atoms forms, rather than allowing a larger polymer to form (by repeated addition of the —(CH2)3— monomer unit). Thus, by selecting the particular solvent, the reaction conditions for a di-, tri-, or polycarboxylic acid may be tailored to produce a specific product. This use of organic or inorganic solvents may also be applied to the catholyte in a similar manner.
In one embodiment, the anolyte comprises G-type solvents, H-Type solvents, and/or mixtures thereof. G-type solvents are di-hydroxyl compounds. In one embodiment the G-type compound comprises two hydroxyl groups in contiguous position. H-type solvents are hydrocarbon compounds or solvent which can dissolve hydrocarbons. For example, H-type solvents include, hydrocarbons, chlorinated hydrocarbons, alcohols, ketones, mono alcohols, and petroleum fractions such as hexane, gasoline, kerosene, dodecane, tetrolene, and the like. The H-type solvent can also be a product of the decarboxylation process recycled as a fraction of the hydrocarbon product. This will obviate the need of procuring additional solvents and hence improve overall economics of the process.
By way of further description, G-type of solvents solvate a —COONa group of a alkali metal salt of carboxylic acid by hydrogen bonding with two different oxygen atoms, whereas the hydrocarbon end of the alkali metal salt of carboxylic acid is solvated by an H-type of solvent. For a given G-type solvent, the solvency increases with increase of hydrocarbons in the H-type solvent.
The table below shows some non-limiting examples of G-type and H-type solvents:
The solubility of various sodium salts of carboxylic acids were tested at room temperature in a magnetically stirred glass beaker using G-type solvents, H-type solvents, and combinations of G- and H-type solvents. The following tables show solubility test results for various salts.
It should be noted that although there are specific advantages of using a divided cell, embodiments may be constructed in which the cell is undivided. This cell may be summarized as follows:
Pt∥R—COONa+CH3ONa+CH3OH∥Pt
The Pt electrodes may be replaced by other electrodes, as outline herein. Also, the sodium methoxide base (CH3ONa) may be replaced by other bases (such as hydroxide, sodium methylate, or other bases), as desired. Likewise, the solvent, methanol (CH3OH), may be replaced by other solvents, as desired. In this embodiment, the anode reaction is a decarboxylation reaction to form carbon dioxide and R—R. The cathode reaction is a reduction to form hydrogen gas (the H being provided by the methanol). In other embodiments, acetate (or other carboxylic acid anions) may optionally be used. Similarly, the acidic form of the sodium salt may be used, provided that there is also base to convert it to a sodium salt.
Although many of the examples provided herein involve the use of monocarboxylic acids, dicarboxylic acids or polycarboxylic acids may also be used. However, when using dicarboxylic acids or polycarboxylic acids, steps (in some embodiments) may be taken to avoid or reduce polymerization. This polymerization reaction is summarized below by a dicarboxylic acid, but a similar reaction is possible for a polycarboxylic acid:
Since these hydrocarbon radicals have reactive sites at each end, these .R—R. radicals could then line up to polymerize:
. . . R—R.+.R—R. .R—R.+.R—R. . . .In some embodiments, such polymerization may be desired. In other embodiments, polymerization is not desired. Accordingly, techniques may be employed to reduce the likelihood of polymerization (e.g., “cut off” the polymerization). This may involve, for example, forming methyl radicals (CH3.) via acetate, forming H. radicals to truncate the R group. Likewise, the techniques associated with using a mixed solvent system may also reduce such polymerization. For example, by using a nonpolar solvent in combination with a polar solvent in the anolyte, the formed hydrocarbon will be pulled into the non-polar solvent quickly, thereby preventing it from polymerizing.
Various examples of the techniques described herein may be used and performed readily. Some of these examples include:
A number of different methods may be employed to form coupled radical products within the scope of the present disclosure. For example,
After placing the anolyte in the cell, the alkali metal salt of the carboxylic acid is decarboxylated 624. This decarboxylation may involve electrolysis and/or photolysis. Such decarboxylation forms one or more radicals that react to form a coupled radical product such as hydrocarbon or a mixture of hydrocarbons. These hydrocarbons may then be collected, purified (as needed) and/or used in industry.
An electrolytic cell will also be obtained 708. An anolyte is also prepared 712. The anolyte may be of the type described herein. The anolyte comprises a quantity of the alkali metal salt of the fatty acid. A quantity of an alkali metal acetate, a quantity of hydrogen gas, and/or a quantity of an alkali metal formate may optionally be added 716 to the anolyte. The anolyte may be placed 720 in the electrolytic cell.
The anolyte is electrolyzed 724 within the cell. This electrolyzing operates to decarboxylate the alkali metal salt of the fatty acid to form alkyl radicals. These alkyl radicals react to form a hydrocarbon or a mixture of hydrocarbons. These hydrocarbons may then be collected, purified (as needed) and/or used in industry.
Further embodiments may be employed in which the anolyte includes a mixture of a fatty acid (R—COOH) and an alkali metal salt of a fatty acid (R—COO—AlMet). As described above, this anolyte (including the mixture of the fatty acid and the alkali metal salt of the fatty acid) is fed into a compartment (such as the anolyte compartment 208) in which decarboxylation will occur.
When this mixture is decarboxylated, embodiments may be designed in which only the alkali metal salt of the fatty acid will decarboxylate and not the fatty acid. The alkali metal salt of the fatty acid (R—COONa) is more polar than the fatty acid (R—COOH) and thus, the alkali metal salt of the fatty acid is more likely to decarboxylate at lower voltages. Thus, by selecting a lower applied voltage, embodiments may be constructed in which only the alkali metal salt of the fatty acid decarboxylates and not the fatty acid.
When the alkali metal salt of the fatty acid (R—COONa) decarboxylates, it creates an alkyl radical:
In turn, this alkyl radical (R.) can extract a hydrogen radical (H.) from the fatty acid in the anolyte:
As can be seen from this reaction, a R—H hydrocarbon is obtained. This reaction may not create a dimer hydrocarbon product (R—R). At the same time, the formed fatty acid radical (R—COO.) can also decarboxylate under the applied electric potential:
This formed alkyl radical (R.) will itself react, either by reacting with another alkyl radical (R.) to form the (dimer) hydrocarbon R—R, or by extracting a hydrogen radical from the fatty acid to create another fatty acid radical (RCOO.). These two reactions are summarized below:
As can be seen from these reactions, the reaction continues to product fatty acid radicals (RCOO.) as it is being consumated and these R—COO. radicals may continue to react in the manner described herein. This reaction is therefore characterized as a free radical “chain reaction.” This chain reaction will continue to react until the fatty acid supply in the anolyte is exhausted, at which point the alkyl radical (R.) will react with another alkyl radical (R.) to create the R—R hydrocarbon. Alternatively, the reaction may be quenched using other techniques.
By using a free radical chain reaction, the reaction will be naturally driven on its own once started. An electric potential (or electric current or perhaps irradiation) is needed to start (initiate) the reaction. However, once started, the voltage/current (potential or perhaps the radiation) needed to continue the reaction become smaller (or perhaps even zero). This decrease in the required current/voltage/radiation needed to run the reaction decreases the costs associated with conducting the reaction.
An additional application for the present embodiments may be in the field of bio-diesel synthesis. During some currently used bio-diesel synthesis processes, vegetable oil is reacted with methanol in the presence of a sodium methylate catalyst in order to form the bio-diesel product. This bio-diesel product is a methyl ester. During this synthesis process, there are two phases produced, namely an upper phase and a lower phase. The “upper” phase is the non-polar phase and contains the methyl ester (bio-diesel product). The “lower” phase is the polar phase and includes methanol, glycerol, and the products of the vegetable oil, namely, fatty acids (or sodium salts of fatty acids), and/or other sodium salts (such as sodium chloride or sodium sulfate, etc.). This lower phase can contain, in some embodiments, nearly 20% fatty acid (by weight). In some bio-diesel synthesis processes, there is a large amount of this lower phase produced, and thus this “lower phase” material is readily available. Accordingly, if the lower phase is obtained, it could be directly fed into a cell of the type that is described herein. Alternatively, the lower phase may be pre-processed through additional reactions (such as saponification or other reactions to increase the content of the sodium salt of the fatty acid). This lower phase could be decarboxylated in a cell having a NaSICON membrane, thereby producing a hydrocarbon (and more particularly a methyl ester) that is non-polar. This produced hydrocarbon/methyl ester product could be used as a new “upper phase” for further processing and/or may be the desired bio-diesel fuel product itself. Thus in a NaSICON cell, it may be possible to recover and/or re-use the fatty acid in the bio-diesel process, thereby making the process more cost-efficient and environmentally-friendly. This process may also remove the sodium salts from the lower phase.
Non-Exclusive ExamplesBelow is listed some examples of embodiments described herein. These embodiments are not to be construed as being limiting but are exemplary.
Preparation:Due to the changing composition of commercially available mixtures of fatty acids, surrogates (mixtures of fatty acids) were used as starting materials for some of the reactions. Accordingly, the following surrogates were prepared and/or purchased:
1) sodium oleate
2) sodium oleate & sodium linoleate, and
3) sodium oleate, sodium linoleate, sodium palmitate & sodium stearate.
In some situations, the sodium salts of the fatty acid were directly purchased and mixed to make the surrogates. In other situations, the fatty acids were purchased and converted into the corresponding sodium salts by a saponification reaction using 12-15% sodium methylate/methanol.
The appropriate solvent(s) available for the reactions was first investigated to determine a solvent that may effectively solubilize the fatty acids and is also highly conductive. Solvents were considered based upon their ability to form highly concentrated anolyte solutions with the selected acid starting materials. Both single phase and multi phase solvent mixtures were considered. The following solvents were considered based on one or more of the following factors: (1) high solubility at low temperatures, (2) liquids at room or low temperatures, (3) low viscosity, (4) cost, and (5) ease of product separation. Based on the above criteria, the following solvents were identified for Sodium Oleate & Linoleate: (1) Methanol, and (2) Isopropanol+Ethylene glycol. For a mixture of Sodium Oleate, Linoleate, Palmitate and Stearate, appropriate solvent systems were: (1) Butanol+Ethylene glycol, (2) Methanol+Ethanol+Isopropanol+Ethylene glycol. Once these solvents had been determined, anolytes were prepared by dissolving sodium fatty acids in minimal amount of selected solvent system.
The sodium salt solutions that were prepared had low conductivity, because of the limited number of sodium ions (when compared to a conductive solution such as brine or NaOH). Therefore, a supporting electrolyte that is electrochemically inert to the anolyte was added for solution conductivity purposes and to achieve a low operational voltage. Tetraethylammonium tetrafluoroborate was chosen as the supporting electrolyte based on its cost, high solubility in the solvent systems, and its large electrochemical stability window.
A two compartment micro-reactor with a small gap between the ion-conducting membrane and the anode was fabricated and used in the decarboxylation process. The small (minimal) gap was chosen to create optimum mass transfer conditions in the anolyte compartment. A smooth platinum anode was used where decarboxylation occurs. A 1″ diameter and 1 mm thick NaSelect ion-conducting membrane (available from Ceramatec, Inc., of Utah) was used between the anode and cathode compartment. A nickel cathode was used in the cathode compartment. A 1 liter glass flask sealed with 3-holed rubber stoppers was used. The appropriate anolyte and catholyte reservoirs were prepared and connected to the sealed flask. Each reservoir was placed on a hot plate and thermocouples were placed in each of the reservoirs. About 300 mL of anolyte and catholyte (15 wt. % NaOH) were used. The temperature was controlled by a temperature controller to maintain the temperature of feed solutions to the anolyte, and catholyte at 40 to 60° C. Peristaltic pumps were used to circulate the solutions at flow rate of 60 to 100 mL per minute (depending on the viscosity). Lab view data acquisition was used to measure the voltage and current. The carbon dioxide evolved from the anolyte was fed into a CO2 IR sensor (Detcon) where the wt. % of CO2 was qualitatively determined.
The electrolysis reactor was operated in batch mode. Batch mode means that the anolyte and catholyte were re-circulated until majority of the sodium salts were converted to hydrocarbons in the anolyte and the majority of the sodium ions were transferred to the catholyte compartment via the membrane formed sodium hydroxide in the catholyte (where aqueous sodium hydroxide is concentrated). Alternatively, the electrolysis reactor was also operated in semi-continuous mode, i.e., the anolyte and catholyte were re-circulated until a pre-determined amount of sodium salts starting material (e.g., 10%) was converted to hydrocarbons in the anolyte. The reactors were operated at constant current densities≧50 mA/cm2 to 200 mA/cm2 of membrane area. A continuous process may be preferred for large-scale processing in which the starting salt concentration is always maintained and the hydrocarbon product is continuously removed.
The hydrocarbon product from the anolyte was at times recovered using a solvent immiscible with the starting solvent mixture. Hexane and Dodecane were the choices for hydrocarbon product recovery. The hexane or dodecane phase was analyzed by GC (gas chromatography) or GC-MS (gas chromatography-mass spectrometry) analysis for the estimation of product. In some cases for quantification purpose, the starting anolyte and final anolyte were submitted without extraction with hexane or dodecane.
Test #1Decarboxylation of sodium oleate. Sodium oleate was dissolved in a methanol solvent. The purpose of this test was to determine the product conversion efficiency in a semi-continuous mode of operation. The test was conducted at a constant current density of 200 mA/cm2 until about 50% of starting material was theoretically converted.
The GC profile for the reacted anolyte is shown in Table 1. Table 1 shows the major peaks, name of the chemical identified, retention time in minutes, height in microvolts, area under the curve in (μV·Min) and % area under curve. The peaks at retention time at 18.65 and 27.36 are tentatively identified as sodium oleate (C18) and C34 hydrocarbon dimer. The area under the curve for C18 peak before and after the test was compared to determine the conversion efficiency. The product conversion efficiency based on this analysis was nearly 80%.
ICP (inductively coupled plasma) analysis of the reacted liquid sample showed that 51% of the sodium was removed from the anolyte. The sodium transport current efficiency was determined to be 99%.
Test #2Decarboxylation of a mixture of sodium oleate and sodium linoleate. Sodium oleate and sodium linoleate was dissolved in a methanol solvent. The purpose of the test was to determine the reactor power consumption and to determine a current-voltage profile when the reactor was operated in batch mode. The test was conducted at a constant current density of 50 mA/cm2 until a preset voltage limit of 12 volts was reached.
Decarboxylation of a mixture of sodium oleate, sodium linoleate, sodium palmitate and sodium sterate. Sodium oleate, sodium linoleate, sodium palmitate and sodium sterate were dissolved in a four solvent mixture of Methanol/Ethanol/Isopropanol/Ethylene Glycol. The purpose of the test was to determine the current-voltage profile when the reactor is operated in batch mode. The test was conducted at a constant current density of 50 mA/cm2 for about 18 hours.
This test used an anolyte with the same composition as in Test #2 (sodium oleate and sodium linoleate dissolved in a methanol containing 10% water). The purpose of this test was to determine the product conversion efficiency in a continuous mode of operation while eliminating the formation of fatty acid esters during decarboxylation process. The test was conducted at a constant current density of 200 mA/cm2 (4 times higher than test #2 but equal to the current density of test #1) for a short period. The Gas Chromatogram (GC) profile for the reacted anolyte showed that only hydrocarbons as the products. Thus it appears that operation at high current density may be employed, for some embodiments, to produce the hydrocarbons.
It has also been determined that the production of hydrocarbons, could in some embodiments, be economically feasible. For example it has been estimated that using a continuous mode processing, 1 gallon of hydrocarbon could be made for between $0.798 to $0.232.
Accordingly, the foregoing examples indicate the following:
-
- Conversion of sodium salts of fatty acids to >C30 hydrocarbons was achieved;
- Mixtures of sodium salts of fatty acids were converted to hydrocarbons;
- Additives were used to assist in lowering the decarboxylation reactor voltage at high operational current densities;
- Nearly 80% product conversion efficiency was achieved for a sodium oleate conversion;
- Greater than 90% product conversion efficiency was achieved for conversion of a sodium oleate/sodium linoleate mixture (during continuous mode operation);
- An NaSelect ion-conducting membrane (available from Ceramatec, Inc. of Utah) operated at near 100% sodium ion transfer efficiency;
- Approximately 90% of sodium ions was transferred to the catholyte compartment to form sodium hydroxide at a low operational voltage;
- The power consumption was observed to be 0.95 kWh/kg of hydrocarbon processed;
- The selectivity for forming hydrocarbons may be improved by operating the reactor at high current density; and
- The presence of water may help the selectivity towards hydrocarbon formation.
The present invention may be embodied in other specific forms without departing from its structures, methods, or other essential characteristics as broadly described herein and claimed hereinafter. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Claims
1. A method for producing a coupled radical product comprising:
- preparing an anolyte for use in an electrolytic cell, the electrolytic cell comprising an alkali ion conducting membrane, wherein the anolyte comprises a first solvent or mixture of solvents, a quantity of an alkali metal salt of a carboxylic acid, and a quantity of a supporting electrolyte comprising an alkali metal salt of a lower alkyl carboxylic acid; and
- electrochemical decarboxylating the alkali metal salt of the carboxylic acid within the electrolytic cell, wherein the electrochemical decarboxylating converts the alkali metal salt of the carboxylic acid into alkyl radicals and converts the supporting electrolyte into a lower alkyl radical or to a hydrogen radical, wherein the alkyl radicals and the lower alkyl radical or hydrogen radical react to form a coupled radical product, wherein the alkali metal salt of the carboxylic acid is formed via a saponification reaction that occurs within the electrolytic cell.
2. A method as in claim 1, wherein the coupled radical product comprises a mixture of different hydrocarbons.
3. A method as in claim 1, wherein the electrochemical decarboxylating the alkali metal salt of the carboxylic acid occurs by electrolyzing the anolyte.
4. A method as in claim 1, wherein the alkali metal comprises sodium such that the alkali metal salt of the carboxylic acid comprises a sodium salt of the carboxylic acid and wherein the alkali ion conducting membrane comprises a NaSICON membrane, wherein the membrane divides the cell into an anolyte compartment and a catholyte compartment, the anolyte being housed within the anolyte compartment and a catholyte being housed within the catholyte compartment.
5. A method as in claim 1, wherein hydrogen radicals are formed by electrochemical decarboxylating an alkali metal formate during the electrochemical decarboxylating of the alkali salt of the carboxylic acid, and/or photolysis of hydrogen gas.
6. A method as in claim 1, wherein the first solvent comprises a two-phase solvent system, wherein one phase is capable of dissolving ionic materials and the other phase is capable of dissolving non-ionic materials.
7. A method as in claim 1, wherein the first solvent or first mixture of solvents comprises methanol.
8. A method as in claim 4, wherein the catholyte comprises a second solvent or mixture of solvents, wherein the second solvent or mixture of solvents included in the catholyte and the first solvent or mixture of solvents included in the anolyte are different.
9. A method as in claim 4, wherein an electrochemical reaction of the catholyte produces a base.
10. A method as in claim 1, wherein the supporting electrolyte is an alkali metal salt of a lower alkyl carboxylic acid having from one to five carbon atoms.
Type: Application
Filed: Jun 28, 2013
Publication Date: Oct 31, 2013
Inventors: Sai Bhavaraju (West Jordan, UT), Ashok V. Joshi (Salt Lake City, UT), Mukund Karanjikar (West Valley City, UT), David Joel Hunt (Monticello, IL), Pallavi Chitta (West Valley City, UT)
Application Number: 13/930,211
International Classification: C25B 3/10 (20060101);
