CHEMICAL EXTRACTION FROM AN AQUEOUS SOLUTION

A method of chemical extraction from an aqueous solution includes receiving an aqueous solution including dissolved inorganic carbon. The method also includes increasing a pH of a first portion of the aqueous solution to form a basic solution. The basic solution is then combined with a second portion of the aqueous solution to precipitate calcium salts. The calcium salts are then collected.

TECHNICAL FIELD

This disclosure relates generally to chemical extraction.

BACKGROUND INFORMATION

Pure carbon dioxide (CO2) has many industrial uses. The separation of CO2from a mixed-gas source may be accomplished by a capture and regeneration process. More specifically, the process generally includes a selective capture of CO2, by, for example, contacting a mixed-gas source with a solid or liquid adsorber/absorber followed by a generation or desorption of CO2from the adsorber/absorber. One technique describes the use of bipolar membrane electrodialysis for CO2extraction/removal from potassium carbonate and bicarbonate solutions.

For capture/regeneration systems, a volume of gas that is processed is generally inversely related to a concentration of CO2in the mixed-gas source, adding significant challenges to the separation of CO2from dilute sources such as the atmosphere. CO2in the atmosphere, however, establishes equilibrium with the total dissolved inorganic carbon in the oceans, which is largely in the form of bicarbonate ions (HCO3−) at an ocean pH of 8.1-8.3. Therefore, a method for extracting CO2from the dissolved inorganic carbon of the oceans would effectively enable the separation of CO2from atmosphere without the need to process large volumes of air.

DETAILED DESCRIPTION

Throughout the specification and claims, compounds/elements are referred to both by their chemical name (e.g., carbon dioxide) and chemical symbol (e.g., CO2). It is appreciated that both chemical names and symbols may be used interchangeably and have the same meaning.

This disclosure provides for the removal of carbon from water sources containing dissolved inorganic carbon (e.g., bicarbonate ions HCO3−). The world's oceans act as carbon sinks absorbing large quantities of atmospheric carbon. As will be shown, systems and methods in accordance with the teachings of the present disclosure may be used to remove bicarbonate ions from the water and convert the ions into other useful materials. Removing excess carbon from the oceans may be both lucrative and environmentally restorative.

FIG. 1Ais an illustration of a system100A for chemical extraction from an aqueous solution, in accordance with an embodiment of the disclosure. System100A includes: input102(to input an aqueous solution containing dissolved inorganic carbon), treatment unit104, first precipitation unit106, acidification unit108, electrodialysis unit110, pH adjustment unit112, CO2gas collection unit114, CaCl2output116, water output118, and brine output132.

As shown, input102is coupled to a water reservoir containing dissolved inorganic carbon (e.g., bicarbonate ions). The water reservoir may be an ocean, lake, river, manmade reservoir, or brine outflow from a reverse osmosis (“RO”) process. Input102may receive the water through a system of channels, pipes, and/or pumps depending on the specific design of the facility. As shown, water received through input102is diverted into two separate sections of system100A. A first (smaller) portion of the water is diverted to treatment unit104, while a second (larger) portion of the water is diverted to first precipitation unit106. One skilled in the art will appreciate that large aggregate may be removed from the water at any time during the intake process.

In the illustrated embodiment, the first portion of water is diverted into treatment unit104. Treatment unit104outputs a relatively pure stream of aqueous NaCl. In other words, an aqueous solution (possibly including seawater) is input to treatment unit104, and aqueous NaCl is output from treatment unit104. Treatment unit104may be used to remove organic compounds and other minerals (other than NaCl) not needed in, or harmful to, subsequent processing steps. For example, removal of chemicals in the water may mitigate scale buildup in electrodialysis unit110. Treatment unit104may include filtering systems such as: nanofilters, RO units, ion exchange resins, precipitation units, microfilters, screen filters, disk filters, media filters, sand filters, cloth filters, and biological filters (such as algae scrubbers), or the like. Additionally, treatment unit104may include chemical filters to removed dissolved minerals/ions. One skilled in the art will appreciate that any number of screening and/or filtering methods may be used by treatment unit104to remove materials, chemicals, aggregate, biologicals, or the like.

Electrodialysis unit110is coupled to receive aqueous NaCl and electricity, and output aqueous HCl, aqueous NaOH, and brine (to brine output132). Aqueous HCl and aqueous NaOH output from electrodialysis unit110may be used to drive chemical reactions in system100A. The specific design and internal geometry of electrodialysis unit110is discussed in greater detail in connection withFIG. 2(see infraFIG. 2). Brine output from electrodialysis unit110may be used in any applicable portion of system100A. For example, brine may be cycled back into electrodialysis unit110as a source of aqueous NaCl, or may be simply expelled from system100A as wastewater.

In the illustrated embodiment, first precipitation unit106has a first input coupled to receive an aqueous solution including dissolved inorganic carbon (e.g., seawater) from input102. First precipitation unit106also has a second input coupled to electrodialysis unit110to receive aqueous NaOH. In response to receiving the aqueous solution and the aqueous NaOH, first precipitation unit106precipitates calcium salts (for example, but not limited to, CaCO3) and outputs the aqueous solution. However, in other embodiments, other chemical processes may be used to basify the aqueous solution in first precipitation unit106. For example, other bases (not derived from the input aqueous solution) may be added to the aqueous solution to precipitate calcium salts.

In one embodiment, NaOH is added to incoming seawater until the pH is sufficiently high to allow precipitation of calcium salts without significant precipitation of Mg(OH)2. The exact pH when precipitation of CaCO3occurs (without significant precipitation of Mg(OH)2) will depend on the properties of the incoming seawater (alkalinity, temperature, composition, etc.); however, a pH of 9.3 is typical of seawater at a temperature of 25° C. In a different embodiment, the quantity of NaOH added is sufficient to precipitate CaCO3and Mg(OH)2, then the pH is lowered (e.g., by adding HCl from electrodialysis unit110until the pH is <9.3) so that the Mg(OH)2(but not CaCO3) redissolves.

In one embodiment, first precipitation unit106may be a large vat or tank. In other embodiments first precipitation unit106may include a series of ponds/pools. In this embodiment, precipitation of calcium salts may occur via evaporation driven concentration (for example using solar ponds) rather than, or in combination with, adding basic substances. First precipitation unit106may contain internal structures with a high surface area to promote nucleation of CaCO3; these high surface area structures may be removed from the first precipitation unit106to collect nucleated CaCO3. First precipitation unit106may include an interior with CaCO3to increase nucleation kinetics by supplying seed crystals. The bottom of first precipitation unit106may be designed to continually collect and extract precipitate to prevent large quantities of scale buildup.

In another or the same embodiment, heat may be used to aid precipitation. For example solar ponds may be used to heat basified water. In continuously flowing systems, low temperature waste heat solution may be flowed through heat exchange tubes with basified seawater on the outside of the tubes. Alternatively, heating the bottom of first precipitation unit106may be used to speed up precipitation.

After CaCO3is precipitated from the water, CaCO3is transferred to acidification unit108. In the depicted embodiment, acidification unit108is coupled to receive CaCO3from first precipitation unit106and coupled to receive aqueous HCl from electrodialysis unit110. In response to receiving CaCO3and aqueous HCl, acidification unit108produces CO2. In the depicted embodiment, acidification unit108is used to evolve CaCO3into CO2gas and aqueous CaCl2according to the following reaction: CaCO3(s)+2HCl(aq)→CaCl2(aq)+H2O(l)+CO2(g). Reaction kinetics may be increased by agitating/heating the acidified mixture. By adding HCl to CaCO3, CO2is spontaneously released due to the high equilibrium partial pressure of CO2gas. This may eliminate the need for membrane contactors or vacuum systems.

The example system100A further includes gas collection unit114coupled to acidification unit108to collect the CO2. Gas collection unit114may include one or more compressors (and/or gas purifiers) to contain evolved CO2in compressed gas cylinders. It is appreciated that concentrated CO2has many industrial uses including, but not limited to: a chemical precursor (e.g., for creating biofuels—by feeding the CO2to algae; for creating hydrocarbon fuels via hydrogenation of the CO2to methanol—by feeding the CO2along with steam into a solid oxide electrolysis cell to make syngas and subsequently using Fischer Tropsch reactions to make liquid hydrocarbons), as a food additive (e.g., drink carbonation), as an inert gas, etc. CO2extracted by the process disclosed here may be used in any of these applications and others not listed.

Once all CO2has been extracted from acidification unit108, wastewater containing CaCl2is output from system110A via CaCl2output116. In one embodiment, the wastewater is returned to the ocean or other water source after the pH of the wastewater has been adjusted. In other embodiments, the wastewater maybe contained and further processed to remove other minerals.

In the depicted embodiment, the second portion of seawater (that was used as a carbon source in first precipitation unit106) is flowed to a pH and alkalinity adjustment unit112. The pH and alkalinity adjustment unit112is coupled to electrodialysis unit110to receive HCl and NaOH, and adjust a pH and alkalinity of the combined second portion of the aqueous solution and basic solution to a pH of seawater (or other environmentally safe pH value). In one embodiment, the pH and alkalinity of wastewater flowed into pH and alkalinity adjustment unit112is monitored in real time, and HCl or NaOH is flowed into pH and alkalinity adjustment unit112in response to the real time measurements. Adjusting the pH of wastewater flowing from system100A ensures minimal environmental impact of running system100A, while adjusting the alkalinity ensures sufficient reabsorption of atmospheric CO2once the water is returned to the ocean. Further, system100A removes carbon from the oceans, improving ocean heath while producing economically viable raw materials.

FIG. 1Bis an illustration of system100B for chemical extraction from an aqueous solution, in accordance with an embodiment of the disclosure. System100B is similar in many respects to system100A ofFIG. 1A. However, one major difference is system100B does not include acidification unit108, CO2gas collection unit114, and CaCl2output116. Alternatively, system100B produces precipitated calcium salts as a raw material output.

It is appreciated that CaCO3has many industrial uses including (but not limited to): building materials (e.g., limestone aggregate for road building, an ingredient of cement, starting material for the preparation of builder's lime, etc.), dietary supplements (e.g., calcium supplement or gastric antacid), soil neutralizers, and the like. Calcium salts from the process shown inFIG. 1Bmay be used for any of these purposes and others not discussed such as sequestration of carbon by burying the CaCO3.

FIG. 1Cis an illustration of system100C for chemical extraction from an aqueous solution, in accordance with an embodiment of the disclosure. System100C is similar in many respects to systems100A &100B ofFIGS. 1A & 1B. However, one major difference is that system100C includes an additional precipitation step. Further, system100C includes acid and base processing unit198and raw materials output199.

In the depicted embodiment, system100C includes second precipitation unit122with a first input coupled to receive the aqueous solution (e.g., seawater) from first precipitation unit106, and a second input coupled to electrodialysis unit110to receive aqueous NaOH. In response to receiving the aqueous solution and the aqueous NaOH, second precipitation unit122precipitates magnesium salts (for example, but not limited to, Mg(OH)2) and outputs the aqueous solution. In other words, after precipitating the CaCO3, the pH of the second portion of the aqueous solution is adjusted to a second pH threshold where Mg(OH)2precipitates (e.g., a pH of 10.4). Like first precipitation unit106, second precipitation unit122can use any number of structures/techniques to speed up nucleation kinetics of Mg(OH)2. For example, second precipitation unit122may include high surface area inserts, Mg(OH)2seed crystals, or may be heated/cooled to promote nucleation of Mg(OH)2.

The Mg(OH)2may be used in its natural state (e.g., medical applications such as to neutralize stomach acid), or may be converted into pure Mg and/or other compounds, depending on the desired use case.

As depicted, second precipitation unit122is coupled to output the spent aqueous solution to pH and alkalinity adjustment unit112. As stated above in connection with discussion ofFIG. 1A, pH and alkalinity adjustment unit112may be coupled to electrodialysis unit110to receive NaOH or HCl. The pH and alkalinity adjustment unit112may restore the pH and alkalinity of the wastewater to the same pH as the oceans for safe introduction of wastewater back into nature via water output118. The pH and alkalinity adjustment unit112may also restore the alkalinity to a value that enables sufficient absorption of atmospheric CO2 once the water is returned to the ocean.

As illustrated, system100C includes acid and base processing unit198and raw materials output199. Acid and base processing unit198is coupled to receive NaOH and/or HCl from electrodialysis unit110. Acid and base processing unit198may simply output (e.g., bottle and package) excess NaOH or HCl for sale, or may receive other minerals (e.g., silicate rock, Mg(OH)2, magnesium silicates, etc.) through an input port to react with the acid/base and form other useful raw materials/elements. These raw materials and/or elements may be output from an output port and packaged for sale. In one embodiment, acid and base processing unit198may include bottling equipment to bottle the acids and bases for sale. One skilled in the art will recognize that any number of raw materials may be output from raw materials output199; these materials may be sold or used for other purposes.

Although not depicted inFIGS. 1A-1C, in other embodiments, heavy metals may be extracted from the aqueous solution along with CaCO3and Mg(OH)2. Extraction of heavy metals may help remove harmful contaminants from the world's oceans. Furthermore, extracted calcium and magnesium salts may be formed into blocks that can be placed in the ocean to form artificial reefs and breakwaters. In some low-lying islands, blocks of extracted Mg/Ca salts may be used to create land to combat rising sea levels. Ca/Mg salt blocks derived from seawater may be useful on coral-atolls where earth for landfill is already extremely scarce.

Systems100A-100C may be coupled to, and run by, electronic control systems. Regulation and monitoring may be accomplished by a number of sensors throughout the system that either send signals to a controller or are queried by controller. For example, with reference to electrodialysis unit110, monitors may include one or more pH gauges to monitor a pH within the units as well as pressure sensors to monitor a pressure among the compartments in electrodialysis unit110(to avoid inadvertent mechanical damage to electrodialysis unit110). Another monitor may be a pH gauge placed within first precipitation unit106to monitor a pH within the tank. The signals from such pH monitor or monitors allows a controller to control a flow of brine solution (from input102) and a basified solution (from electrodialysis unit110) to maintain a pH value of a combined solution that will result in a precipitation of CaCO3.

Alternatively, systems100A-100C may be controlled manually. For example, a worker may open and close valves to control the various water, acid, and base flows in systems100A-100C. Additionally, a worker may remove precipitated calcium salts from first precipitation unit106. However, one skilled in the relevant art will appreciate that systems100A-100C may be controlled by a combination of manual labor and mechanical automation, in accordance with the teachings of the present disclosure.

FIG. 2is an example electrodialysis unit110(e.g., electrodialysis unit110ofFIG. 1), in accordance with an embodiment of the disclosure. Electrodialysis unit110may be used to convert seawater (or other NaCl-containing aqueous solutions) into NaOH and HCL. As shown, inFIGS. 1A-1C, NaOH and HCl may be used to adjust the pH of the aqueous solution to precipitate calcium and magnesium salts.

In the depicted embodiment, electrodialysis unit110representatively consists of several cells in series, with each cell including a basified solution compartment (compartments210A and210B illustrated); an acidified solution compartment (compartments225A and225B illustrated); and a brine solution compartment (compartments215A and215B).FIG. 2also shows a bipolar membrane (BPM) between a basified solution compartment and an acidified solution compartment (BPM220A and220B illustrated). A suitable BPM is a Neosepta BP-1E, commercially available from Ameridia Corp. Also depicted are anion exchange membranes (AEM), such as Neosepta ACS (commercially available from Ameridia Corp.), disposed between a brine compartment and an acidified solution compartment (AEM230A and230B illustrated). A cation exchange membrane (CEM) such as Neosepta CMX-S (commercially available from Ameridia Corp.), is disposed adjacent to a brine compartment (CEM240A and CEM240B illustrated). Finally,FIG. 2shows end cap membranes245A and245B (such as Nafion® membranes) that separate the membrane stack from electrode solution compartment250A and electrode solution compartment250B, respectively.

Broadly speaking, under an applied voltage provided to electrodialysis unit110, water dissociation inside the BPM (and the ion-selective membranes comprising a BPM) will result in the transport of hydrogen ions (H+) from one side of the BPM, and hydroxyl ions (OH−) from the opposite side. AEMs/CEMs, as their names suggest, allow the transport of negatively/positively charged ions through the membrane. The properties of these membranes such as electrical resistance, burst strength, and thickness are provided by the manufacturer (e.g., Neosepta ACS and CMX-S are monovalent-anion and monovalent-cation permselective membranes, respectively). In one embodiment, electrodialysis unit110includes electrodes260A and260B of, for example, nickel manufactured by De Nora Tech Inc.FIG. 2also shows electrode solution compartment250A and electrode solution compartment250B through which, in one embodiment, a NaOH(aq) solution is flowed. Where electrode260A is a positively-charged electrode, sodium ions (Na+) will be encouraged to move across cap membrane245A and where electrode260B is negatively-charged, sodium ions will be attracted to electrode solution compartment250B. In one embodiment, the solution compartments between adjacent membranes are filled with polyethylene mesh spacers (e.g., 762 μm thick polyethylene mesh spacers), and these compartments are sealed against leaks using axial pressure and 794 mm thick EPDM rubber gaskets.

One skilled in the art will appreciate that using electrodialysis unit110to produce the acids and bases necessary to create Ca/Mg salts is highly advantageous in environments with ample power but limited raw materials. For example, on a coral atoll electrodialysis unit110could be powered by solar panels, allowing people on the atoll to create building materials from nothing but renewable energy and seawater.

FIG. 3is a flow chart illustrating a method300for chemical extraction from aqueous solutions, in accordance with an embodiment of the disclosure. The order in which some or all of process blocks301-307appear in method300should not be deemed limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will understand that some of method300may be executed in a variety of orders not illustrated, or even in parallel. Additionally, method300may include additional blocks or have fewer blocks than shown, in accordance with the teachings of the present disclosure.

Block301illustrates receiving an aqueous solution including dissolved inorganic carbon. In one embodiment, this may include receiving seawater from the ocean or may include receiving water input/output from a power plant, water input/output from a treatment facility, or the like. It is appreciated that many industrial processes use large quantities of water. The process described herein may be coupled to many preexisting industrial systems and use the existing infrastructure to derive additional commercial gains (via valuable mineral/CO2extraction or the like). Accordingly, in practice intermediate steps may be present that relate to other industrial processes.

Block303shows converting a first portion of the aqueous solution into a basic solution. In one example, this may involve using electrodialysis equipment to convert aqueous NaCl into aqueous NaOH. However, in other embodiments, different chemical processes may be used to basify the first portion of the aqueous solution.

Block305discusses combining the basic solution with a second portion of the aqueous solution to precipitate calcium salts. In one embodiment, this occurs in a tank/vat with a high internal surface area to promote nucleation and growth of the calcium salts. For example, the tank/vat may have plate inserts which are used to collect the precipitated calcium salts. During the salt collection processes some of the nucleated calcium salt crystals may be left on the plate inserts to speed up nucleation in subsequent precipitation steps. In another embodiment, heat and evaporative concentration methods may be employed to enhance calcium salt nucleation from the second portion of the aqueous solution.

Block307illustrates collecting the calcium salts from the second portion of the aqueous solution. In one embodiment, collecting calcium salts is a continuous process where sites of nucleation are removed from the precipitation unit as they form. Alternatively, precipitated calcium slats may be collected batchwise. For example, a worker may remove collection plates/vessels from the precipitation unit once a sufficient quantity of calcium salts have nucleated on the plates/vessels.

Again, any portion of method300may be completed with low-tech or high-tech systems. For example, all of method300may be completed with computer controlled equipment and little or no manual intervention. Alternatively, method300may be performed by filling earthen ponds with seawater, and adjusting the pH of the ponds by manually adding acidic or basic solutions.