Patent Application
20100224503
In many chemical processes a solution of hydroxide ions (OH−) is required to achieve or modulate a chemical reaction. One way to obtain OH− in a solution is to dissolve an alkali hydroxide such as sodium hydroxide or magnesium hydroxide in the solution. However, conventional processes for producing hydroxides are very energy intensive, e.g., the chlor-alkali process, and they emit significant amounts of carbon dioxide and other greenhouse gases into the environment.
In various embodiments the present invention pertains to a low energy electrochemical system and method of producing OH− utilizing an ion exchange membrane in an electrochemical cell. The system in one embodiment comprises an anionic or cationic exchange membrane positioned between a first electrolyte and a second electrolyte, the first electrolyte contacting an anode and the second electrolyte contacting a cathode. Suitable electrolytes comprise a saltwater including sodium chloride, seawater, brackish water or freshwater. On applying a low voltage across the anode and cathode, OH− forms at the cathode and protons form at the anode without a gas, e.g., chlorine or oxygen, forming at the anode. Depending on the electrolytes used, a hydroxide solution, e.g., sodium hydroxide, forms in the second electrolyte in contact with the cathode and an acid, e.g., hydrochloric acid forms in the first electrolyte in contact with the anode. In various embodiments, OH− forms when a volt of less than 0.1 V is applied across the electrodes.
In another embodiment the system comprises an electrochemical cell in which an anion exchange membrane separates a first electrolyte from a third electrolyte; a cation exchange membrane separates the third electrolyte from a first electrolyte; an anode is in contact with the first electrolyte; and a cathode is in contact with the second electrolyte. On applying a low voltage across the anode and cathode, OH− forms at the cathode without a gas, e.g., chlorine or oxygen forming at the anode. Depending on the electrolyte used, a hydroxide solution, e.g., sodium hydroxide, forms in the second electrolyte in contact with the cathode, and an acid, e.g., hydrochloric acid forms in the first electrolyte in contact with the anode. In various embodiments, OH− forms when a volt of less than 0.1 V is applied across the electrodes.
In one embodiment the method comprises migrating ions across an ion exchange membrane that is situated between a first electrolyte and a second electrolyte, the first electrolyte contacting an anode and the second electrolyte contacting a cathode, by applying a voltage across the anode and cathode to form hydroxide ions at the cathode without forming a gas, e.g., chlorine or oxygen at the anode. Depending on the electrolyte used, a hydroxide solution, e.g., sodium hydroxide forms in the second electrolyte in contact with the cathode and an acid, e.g., hydrochloric acid forms in the first electrolyte in contact with the anode. In various embodiments, OH− forms when a volt of less than 0.1 V is applied across the electrodes.
In another embodiment the method comprises applying a voltage across an anode and cathode, wherein (i) the anode is in contact with a first electrolyte that is also in contact with an anion exchange membrane; (ii) the cathode is in contact with a second electrolyte that is also in contact with a cation exchange membrane; and (iii) a third electrolyte is situated between the anion exchange membrane and the cation exchange membrane to form hydroxide ions at the cathode without forming a gas e.g., chlorine or oxygen at the anode. By the method OH− forms at the cathode in contact the second electrolyte without a gas e.g., chlorine or oxygen at the anode. Depending on the electrolyte used, a hydroxide solution, e.g. sodium hydroxide, forms in the second electrolyte in contact with the cathode, and an acid, e.g., hydrochloric acid forms in the first electrolyte in contact with the anode. In various embodiments, OH− forms when a volt of less than 0.1 V is applied across the electrodes.
In various configurations, the system and method are adapted for batch, semi-batch or continuous flows. Depending on the electrolytes used, the system is adaptable to form OH− in solution, e.g., sodium hydroxide at the cathode, or an acidic solution, e.g., hydrochloric acid at the anode without forming a gas e.g., chlorine or oxygen at the anode. In various embodiments, the solution comprising OH− can be used to sequester CO2 by contacting the solution with CO2 and precipitating alkaline earth metal carbonates, e.g., calcium and magnesium carbonates and bicarbonates from a solution comprising alkaline earth metal ions as described U.S. Provisional Patent Application Ser. No. 60/931,657 filed on May 24, 2007; U.S. Provisional Patent Application Ser. No. 60/937,786 filed on Jun. 28, 2007; U.S. Provisional Patent Application 61/017,419, filed on Dec. 28, 2007; U.S. Provisional Patent Application Ser. No. 61/017,371, filed on Dec. 28, 2007; and U.S. Provisional Patent Application Ser. No. 61/081,299, filed on Jul. 16, 2008, herein incorporated by reference. The precipitated carbonates, in various embodiments, are useable as building products, e.g., cements, as described in United States patent applications herein incorporated by reference. Similarly, the system and method are adaptable for desalinating water as described in United States patent applications herein incorporated by reference.
The following drawings illustrate the present system and method by way of examples and not limitations. The methods and systems may be better understood by reference to one or more of these drawings in combination with the description herein:
Before the present methods and systems are described in detail, it is to be understood that this invention is not limited to particular embodiments described and illustrated herein, and as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Where a range of values is provided, it is to be understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.
Ranges are presented herein at times with numerical values being preceded by the term “about.” The term “about” is used herein to provide literal support for the exact number that it precedes, as well as a number that is near to or approximately the number that the term precedes. In determining whether a number is near to or approximately a specifically recited number, the near or approximating unrecited number may be a number that, in the context in which it is presented, provides the substantial equivalent of the specifically recited number.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods, systems and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods, systems and materials are herein described.
All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates that may need to be independently confirmed.
As used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Also, the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Additionally, the term “reservoir” as used herein refers to an enclosure for holding a liquid such as a vessel, tank, chamber or bag.
As will be apparent to those of skill in the art, each of the embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any possible logical order.
In the description herein, the invention will be described for convenience in terms of production of hydroxide. It will be appreciated that in some embodiments hydroxide may not be produced, e.g., in embodiments where the pH of the electrolyte solution in contact with the cathode, as described herein, is kept constant or even decreases, there is no net production of hydroxide ions and can even be a decrease in hydroxide ion production. This can occur, e.g., in embodiments in which CO2 is introduced into the second electrolyte solution, as described further herein.
The present invention in various embodiments is directed to a low voltage electrochemical system and method for forming OH+ in a solution, e.g., a saltwater solution, utilizing ion exchange membranes. On applying a voltage across a cathode and an anode, OH+ forms in solution in the electrolyte contacted with the cathode, protons form in the solution contacted with the anode, and a gas e.g., chlorine or oxygen is not formed at the anode. Hydroxide ions are formed where the voltage applied across the anode and cathode is less than 2.8, 2.7, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 V.
In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 2.5 V without the formation of gas at the anode. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 2.2V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 2.0V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 1.5 V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 1.0V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.8 V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.7V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.6V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.5V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.4V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.3V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.2V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.1V. In certain embodiments hydroxide ions are formed where the voltage applied across the anode and cathode is less than 0.05V. In various embodiments an acidic solution, e.g., hydrochloric acid is formed in the electrolyte in contact with the anode.
With reference to
In the embodiment illustrated in
In various embodiments, anion exchange membrane (102) and/or cation exchange membrane (124) are any ion exchange membranes suitable for use in an acidic and/or basic electrolytic solution temperatures in the range from about 0° C. to about 100° C., such as conventional ion exchange membranes well-known in the art, or any suitable ion exchange membrane. Suitable anion exchange membranes are available from PCA GmbH of Germany, e.g., an anion exchange membrane identified as PCSA-250-250 can be used; similarly, a cation exchange membrane identified as PCSK 250-250 available from PCA GmbH can be used. As will be appreciated, in the system the ion exchange membranes are positioned to prevent mixing of the first and second electrolytes.
With reference to
As illustrated in
With reference to
As can be appreciated by one ordinarily skilled in the art, and with reference to
With reference to
As can be appreciated by one ordinarily skilled in the art, and with reference to
With reference to
Exemplary results achieved with the present system are summarized in Table 1.
With reference to Table 1, using saltwater as the first electrolyte and a sodium chloride as the second electrolyte, a process and method in accordance with the present invention as illustrated in
The system used included two 250 mL compartments separated by an anion exchange membrane in one embodiment, and a cation membrane in another embodiment. In both compartments a 0.5M NaCl 18MΩ aqueous solutions (28 g/L of NaCl was solvated with de-ionized water) was used. Both the anode and cathode comprised a 10 cm by 5 cm 45 mesh Pt gauze. In the anode compartment H2 gas was sparged under the Pt electrode, and the two electrodes were held at a voltage bias as indicated in Table 1 e.g., 0.4, 0.6 V and 1.0 V, for 30 minutes. The pH of the electrolyte in contact with the anode before applying the voltage was 6.624. The cathode compartment where the hydroxide formation occurred was stirred at 600 rpm. As set forth in Table 1, significant changes in the pH in the cathode and anode compartment were achieved.
In these examples, and in various embodiments of the invention, a pH difference of more than 0.5, 1, 1, 5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, or 12.0 pH units may be produced in a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membrane, when a voltage of 1.0V or less, or 0.9V or less, or 0.8V or less, or 0.7 or less, or 0.6V or less, or 0.5V or less, or 0.4V or less, or 0.3V or less, or 0.2V or less, or 0.1V or less, or 0.05V or less, is applied across the anode and cathode.
For example, in particular embodiments the invention provides a system that is capable of producing a pH difference of more than 0.5 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 0.05V or less is applied across the anode and cathode. In some embodiments the invention provides a system that is capable of producing a pH difference of more than 1.0 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 0.1V or less is applied across the anode and cathode. In some embodiments the invention provides a system that is capable of producing a pH difference of more than 2.0 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 0.2V or less is applied across the anode and cathode.
In some embodiments the invention provides a system that is capable of producing a pH difference of more than 4.0 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 0.4V or less is applied across the anode and cathode. In some embodiments the invention provides a system that is capable of producing a pH difference of more than 6 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 0.6V or less is applied across the anode and cathode. In some embodiments the invention provides a system that is capable of producing a pH difference of more than 8 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more exchange membranes, when a voltage of 0.8V or less is applied across the anode and cathode. in particular embodiments the invention provides a system that is capable of producing a pH difference of more than 8 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 1.0 V or less is applied across the anode and cathode. In some embodiments the invention provides a system that is capable of producing a pH difference of more than 10 pH units between a first electrolyte solution and a second electrolyte solution where the first electrolyte solution contacts an anode and the second electrolyte solution contacts a cathode, and the two electrolyte solutions are separated, e.g., by one or more ion exchange membranes, when a voltage of 1.2V or less is applied across the anode and cathode.
It will be appreciated that the voltage need not be kept constant and that the voltage applied across the anode and the cathode may be very low, e.g., 0.05V or less, when the two electrolytes are the same pH or close in pH, and that the voltage may be increased as needed as the pH difference increases. In this way, the desired pH difference or production of hydroxide ions may be achieved with the minimum average voltage. Thus in some embodiments described in the previous paragraph, the average voltage may be less than 80%, 70%, 60%, or less than 50% of the voltages given in the previous paragraph for particular embodiments.
In various embodiments and with reference to
In some embodiments, one or more of the electrolyte solutions is depleted in divalent cations, e.g., in magnesium or calcium, during parts of the process where the electrolyte is in contact with the ion exchange membrane (or membranes, see embodiments described below in which more than one membrane is used). This is done to prevent scaling of the membrane, if necessary for that particular membrane. Thus, in some embodiments the total concentration of divalent cations in the electrolyte solutions when they are in contact with the ion exchange membrane or membranes for any appreciable time is less than 0.06 mol/kg solution, or less than 0.06 mol/kg solution, or less than 0.04 mol/kg solution, or less than 0.02 mol/kg solution, or less than 0.01 mol/kg solution, or less than 0.005 mol/kg solution, or less than 0.001 mol/kg solution, or less than 0.0005 mol/kg solution, or less than 0.0001 mol/kg solution, or less than 0.00005 mol/kg solution.
In another embodiment as illustrated in
In system illustrated in
In various embodiments, anion exchange membrane (102) and cation exchange membrane (124) of
With reference to
With reference to
As can be appreciated by one ordinarily skilled in the art, and with reference to
As will be appreciated and with reference to
As with the embodiments of
With reference to
With reference to
In one embodiment, when a volt of about 0.6 volt or less is applied across the anode and cathode, the pH of the second electrolyte solution increased; in another embodiment, when a volt of about 0.1 to 0.6 volt or less is applied across the anode and cathode the pH of the second electrolyte increased; in yet another embodiment, when a voltage of about 0.1 to 1 volt or less is applied across the anode and cathode the pH of the second electrolyte solution increased. Other exemplary results achieved in accordance with the present system are summarized in Table 1.
With reference to
(iii) a third electrolyte (130) is situated between the anion exchange membrane and the cation exchange membrane to form hydroxide ions at the cathode without forming a gas at the anode. As described with reference to the system of
In all embodiments described herein, optionally, CO2 is dissolved into the second electrolyte solution; as protons are removed from the second electrolyte solution more CO2 may be dissolved in the form of bicarbonate and/or carbonate ions; depending on the pH of the second electrolyte the balance is shifted toward bicarbonate or toward carbonate, as is well understood in the art. In these embodiments the pH of the second electrolyte solution may decrease, remain the same, or increase, depending on the rate of removal of protons compared to rate of introduction of CO2. It will be appreciated that no hydroxide need form in these embodiments, or that hydroxide may not form during one period but form during another period. Optionally, another electrochemical system as described herein may be used to produce concentrated hydroxide, which, when added to the second electrolyte containing the dissolved CO2, causes the formation of a precipitate of carbonate and/or bicarbonate compounds such as calcium carbonate or magnesium carbonate and/or their bicarbonates. In some embodiments, divalent cations such as magnesium and/or calcium are present in certain solutions used in the process, and/or are added. The precipitated carbonate compound can be used as cements and building material as described in United States patent applications incorporated herein by reference.
In an optional step, the acidified first electrolyte solution 104 is utilized to dissolve a calcium and/or magnesium rich mineral, such as mafic mineral including serpentine or olivine, for precipitating carbonates and bicarbonates as described above. For example, the acidified stream can be employed to dissolve calcium and/or magnesium rich minerals such as serpentine and olivine to create the electrolyte solution that can be charged with bicarbonate ions and then made sufficiently basic to precipitate carbonate compounds. Such precipitation reactions and the use of the precipitates in cements are described in the United States patent applications incorporated by herein by reference.
In alternative embodiments, rather than precipitating carbonates, the carbonate and bicarbonate solution is disposed of in a location where it will be stable for extended periods of time. For example, the carbonate/bicarbonate electrolyte solution can be pumped to an ocean depth where the temperature and pressure are sufficient to keep the solution stable over at least the time periods set forth above.
Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.
Accordingly, the preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements, which, although not explicitly described or shown herein, embody the principles of the invention, and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary embodiments shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12375632 | Mar 2009 | US |
| Child | 12697926 | US |
