The disclosed systems and methods relate to generating energy and/or chemical compounds. More particularly, the disclosed systems and methods relate to generating energy and/or chemical compounds while consuming carbon dioxide.
Carbon dioxide (CO2) is used by certain species of microorganisms, which generate byproducts (direct or indirect) that may be used for alternative fuels or other chemicals. Other than cell uptake for energy and cell synthesis (as in photosynthetic and chemoautotrophic microorganisms), some microorganisms reduce CO2 to organic compounds such as methane (via methanogens), acetate (via acetogens), or potentially other organic compounds (via known and unknown metabolic pathways).
The application of photosynthetic microbial transformation of CO2 to organic compounds (e.g., in algal CO2 conversion to biomass and biofuel) has been attempted for decreasing carbon emission from the industry (e.g., coal-fired power production); however, the process is limited by light availability, and longer retention time and stringency in preventing selective cultures from being contaminated. To be effective, the reaction vessel would require an extremely large area (which would be difficult to control) or other methods to substantially increase microbial CO2 conversion rates.
There are some attempts in using pure strain of bacterium to reductively convert CO2 into methane gas; however, the impossibility of maintaining a single strain condition in a large-scale application of such system prevents its wide-spread implementation. Additionally, the product of methane is such case is a more potent gas than CO2.
In some embodiments, a bioelectrochemical system includes a housing defining an internal chamber. A barrier is disposed within the housing and at least partially separates the internal chamber into first and second compartments. The first compartment includes at least one of autotrophic or heterotrophic microorganisms disposed therein. A cathode is disposed within the first compartment and is coupled to a power supply, and an anode is disposed within the second compartment and is coupled to the power supply. Carbon dioxide received within the first chamber is transformed into an organic compound.
In some embodiments, a method includes receiving carbon dioxide within a first compartment disposed within an internal chamber defined by a housing, receiving an electrical potential across a cathode disposed within the first compartment and an anode disposed within a second compartment within the internal chamber, and extracting organic compounds from the first chamber that are derived from the carbon dioxide. The first and second compartments are at least partially separated by a barrier. At least one of autotrophic or heterotrophic microorganisms are disposed within the first compartment.
In some embodiments, a system includes a first bioelectrochemical system disposed within a first well formed in a subsurface formation. The first bioelectrochemical system includes a housing defining an internal chamber. A barrier is disposed within the housing and at least partially separates the internal chamber into first and second compartments. The first compartment includes methanogenic microorganisms disposed therein. A cathode is disposed within the first compartment and is coupled to a first power supply, and an anode is disposed within the second compartment and is coupled to the first power supply. Carbon dioxide received within the first compartment of the first bioelectrochemical system is transformed into an organic compound.
This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description.
The disclosed systems and methods include a variety of aspects, which may be selected in different combinations based upon the particular application or needs to be addressed. In some embodiments, bioelectrochemical (BEC) systems are provided to enhance microbial conversion of CO2, carbonic acid (H2CO3), bicarbonate (HCO3−), and carbonate (CO32−) to organic compounds including, but not limited to, carboxylic acids, hydrocarbons, and alcohols. In some embodiments, the use of specific chemical inhibitors of methanogenesis or manipulations of operational conditions, such as pH, redox potential, and retention time are used to enhance microbial conversion of CO2, H2CO3, HCO3−, and CO32− to organic compounds in BEC systems.
The use of separators comprising a variety of carrier materials that can support physical, chemical, or biological consumption of O2 produced at anodes in BEC systems. In some embodiments, BEC systems of lower voltage/current are used for CO2 removal from gas in above ground engineering configurations and in the subsurface such as coal seams, petroleum reservoirs, deep saline aquifers, and the like, where CO2-containing gas is injected.
In some embodiments, a BEC system stimulates microbial activity, such as in biodegradation, nitrate reduction, and hydrogen production. BEC systems include microbial fuel cells, microbial electrolysis cells, and their hybrids and modifications. In BEC systems where low voltage/current is applied, an external direct current (DC) or alternating current (AC) voltage from external power sources or other BEC reactors is connected to at least two electrodes (i.e., an anode and a cathode). The application of the electric field in BEC systems has been demonstrated to enhance the production of organic acids from carbonaceous feedstocks. BEC systems can be applied to enhance microbial conversion of CO2 to methane. In such systems, separators such as proton exchange membranes (PEMs), cation exchange membranes (CEMs), anion exchange membranes (AESMs), bipolar membranes, and/or glass fibers are used to separate the anode and cathode of a BEC system to prevent exposure to oxygen (O2) that may evolve from the electrolysis of water.
Anaerobic consortia involved in low redox pathways include mixed strains of methanogenic microorganisms that produce methane from CO2. Other microorganisms in the consortium can produce other organic compounds, which are subsequently consumed for production of methane if not regulated. Inhibition of methanogenesis can shift the microbial metabolic pathways and cause the accumulation of other organic compounds such as acetate. The addition of specific inhibitors of methanogenesis such as 2-bromoethanesulfonic acid (2-BESA) can improve BEC system performance to yield higher volumes of hydrogen.
The disclosed systems and methods utilize BEC systems to reduce CO2 and transform it into organic compounds, such as organic acids, and therefore transform CO2 into value-added products. This is achieved by controlling operational conditions, such as pH retention time, temperature, or using inhibitor(s) to block methanogenesis and accumulate pre-methanogenic compounds. The BEC systems utilize separators made from carbon mesh, fiber glass, plastic etc., which function as a biofilm carrier, to consume O2 produced at the anode. The BEC systems can be used in an aboveground or a subsurface process, in both in situ and ex situ layouts. The disclosed BEC systems operate with low electrical potential and current (e.g., less than or equal to 30 V/m and/or less than or equal to 500 mA, and more preferably less than or equal to 20 V/m and less than or equal to 200 mA), and electrical stability and consistency are not required. Therefore, advantageously, renewable energy technologies such as wind or solar power can be readily utilized to provide electricity to BEC systems without adding any carbon foot prints, and achieve a sustainable CO2 reduction and conversion. In some embodiments, a BEC system includes one or more of microbial fuel cells, microbial electrolysis cells, and electrolysis cells, and combinations thereof
First compartment 110 of container 102 includes a first inlet 120 for receiving CO2 from a CO2 source 122. First compartment 110 also includes an outlet 124 configured to expel organic compounds from first section 110. A second inlet 126 may be coupled to the conduit 128 coupled to outlet 124 to provide a return path for CO2 that is expelled through outlet 124. In some embodiments, CO2 produced in anode compartment 112 is received within cathode compartment 110.
Housing or container 102 may be any device having an internal chamber configured to hold a gas or liquid. In some embodiments, water and aqueous solutions are disposed within the interior 108 of container 102 on either side of barrier 106. One of ordinary skill in the art will understand that other liquids or fluids may be used. Container 102 may be fabricated from stainless steel or other suitable material.
The anaerobic microbial consortia, i.e., microbes 104, may include mixed or single strains and be sourced from multiple environments that may include, but are not limited to, anaerobic digesters from municipal or industrial wastewater treatment plants, wetland or marine sediments, landfills, surface waters, groundwater, coal seam and other subsurface formation waters, and custom cultures. The anaerobic microbial consortia 104 may already exist (i.e., indigenous to) in the location of the BEC system in situ. In some embodiments, microbes 104 disposed on the cathode side 110 of container 102 are methanogenic microorganisms that consume CO2 and break it down into other chemicals.
Inhibitors may be added to the cathode side 110 of housing 102 to enhance the conversion of CO2, H2CO3, HCO3−, and CO32− to organic compounds. These methogenic inhibitors may be categorized as structural analogs of coenzyme M, hydroxymethylglutaryl-SCoA (HMG-CoA) reductase inhibitors, nitrocompounds, inorganic salts, and halogenated compounds. In some embodiments, the inhibitors may include, but are not limited to, 2-bromoethane sulfonic acid (2-BESA), lumazine, 2-chloroethanesulfonate, 2 mercaptoethanesulfonate, other coenzyme M structural analogs, propynoic acid, ethyl 2 butynoate, other HMG-CoA reductase inhibitors, methyl chloride, chloroform, methyl fluoride, fluoroacetate, ethylene, acetylene, nitrate, nitrite, nitroethane, 2-nitropropanol, phosphate, medium and long chain fatty acids, mevastatin, fluvastatin, and lovastatin. The inhibitors may be added at different amounts and combinations based on the specific application, requirements, and desired products of the BEC system. In some embodiments, the concentration of inhibitors is between 100 μg/L to 500 mg/L.
Additionally, pH buffers may also be added to the cathode compartment 110. The pH buffers may be added in sufficient amounts to maintain the pH in the cathode compartment 110 between 5.0 and 9.0. Examples of the pH buffers include, but are not limited to, acids and bases such as HCl, NAOH, KOH, MgOH, H2SO3, acetic acid, phosphoric acid, monobasic phosphate salts, dibasic phosphate salts, carbonate salts, bicarbonates salts, Tris buffer, HEPEs, MESs, and MOPs. Concentrations of the pH buffers may be added such that the pH of the system is within the range of 5.0-9.0.[
Barrier 106 disposed between the anode 116 and cathode 114 may be fabricated from carbon mesh, carbon cloth, carbon fiber, glass fiber, polyester, nylon fiber, cellulose, PTFE, plastics, and ion exchange membranes. The material itself may consume or block O2 produced at anode 116 from electrolysis of water, or it may support biofilms composed of microorganisms that consume O2. Barrier 106 may be shaped and configured in different combinations to fit the specific needs of the BEC system that has been designed for a specific application. In some embodiments, barrier 106 completely divides interior 108 into separate compartments 110, 112, and in other embodiments barrier 106 partially divides interior 108 into separate compartments 110, 112.
The electrodes, i.e., cathode 114 and anode 116, may be fabricated from carbon, carbon fiber, stainless steel, galvanized steel, copper, and other conductive materials or nonconductive materials with conductive coatings. The electrodes 114, 116 may be shaped and configured in different combinations to fit the specific needs of the BEC system that has been designed for a specific application. The wires connecting the electrodes to the electrical power source 118 may include stainless steel, copper, aluminum, or titanium, to name a few possible materials. Wire may be connected to the electrodes at single or multiple points through physical joints and configurations that are sealed and insulated to avoid water intrusion. Segments inside water or at close proximity to water may be insulated.
Electrical power source 118 may provide DC and/or AC power to electrodes 114, 116. A battery may be used to provide DC voltage to the BEC system either by direct application or indirectly through recharging batteries. Other electrical sources 118 may include, but are not limited to, fuel driven generators (gasoline, diesel fuel, natural gas, biofuels, hydrogen, etc.), solar power systems, wind power systems, microbial fuel cells, and other renewable energy sources. If a load is used, the resistance of the load may range from 0.001-10,000 ohms. The electrical potentials, currents, and resistances can be increased or decreased depending on the specific needs of the BEC system as will be understood by one of ordinary skill in the art.
Carbon dioxide source 122 may be a flue gas of an industrial power plant, such as a coal-fired plant. One of ordinary skill in the art will understand that CO2 source 122 may be any other source of CO2. For example, stack emission from cement plants, steel plants, landfill incinerators, oil refineries, natural gas power plants, chemical plants, plastic production plants, pulp and paper mills, wastewater treatment plants, and other plants combusting fossil fuels and giving off CO2. In some embodiments, the CO2 is produced by microbial reactions at anode 116.
The organic compounds produced by BEC system 100 from CO2, H2CO3, HCO3−, and CO32− may be produced with or without the addition of chemical inhibitors of methanogenesis. Examples of the organic compounds include, but are not limited to, organic acids, organic salts, hydrocarbons, alcohols, amines, esters, ethers, amides, lactams, and other categories of organic compounds.
These BEC systems 100, 200 described above can be operated as static or continuous flow systems with varying hydraulic retention times and gas injection flows. The organic compounds that are produced can be separated and recovered from the effluent (product) stream and may be utilized based on the typical uses for the type organic compounds that were produced.
BEC systems 100, 200 may be implemented in subsurface formations to enhance the conversion of CO2, H2CO3, HCO3−, and CO32− to organic compounds. For example,
A plurality of wells 304-1, 304-2, 304-3, 304-4, and 304-5 extend from surface 302 into subsurface formation 300. Carbon dioxide and inhibitors may be injected into the subsurface formation 300 via well 300-1. As described above, the CO2 source 122 (not shown in
Power supply 118 may be disposed above surface 302 and connected to BEC systems 100-1, 100-2, and 100-3 via wires as will be understood by one of ordinary skill in the art. As described above, power supply 118 may be from a power grid or from a renewable energy system such as, for example, a solar power system, a hydrogen generator, fuel cell, and/or a wind power system.
Organic compounds may or may not be recovered down gradient from the BEC systems 100, 200 from a recovery or producing well 304. Methane may be a byproduct of the process and can be utilized for energy to power the BEC systems 100, 200 or be transferred to a natural gas pipeline. The organic compounds may be separated and utilized based on the typical uses for the type organic compounds that were produced. The organic compounds may also remain in subsurface formations 300 (coal has been found to be a good subsurface formation for long-term storage) to sequester carbon in a non-hazardous form. The BEC systems 100, 200 may be installed in single or multiple wells 304 as illustrated in
At block 404, additives, e.g., inhibitors and/or pH buffers, are received within cathode chamber 110. Examples of methogenic inhibitors include, but are not limited to, 2-BESA, lumazine, 2-chloroethanesulfonate, 2 mercaptoethanesulfonate, other coenzyme M structural analogs, propynoic acid, ethyl 2 butynoate, other HMG-CoA reductase inhibitors, methyl chloride, chloroform, methyl fluoride, fluoroacetate, ethylene, acetylene, nitrate, nitrite, nitroethane, 2-nitropropanol, phosphate, medium and long chain fatty acids, mevastatin, fluvastatin, and lovastatin. The inhibitors may be added at different amounts and combinations as will be understood by an ordinarily skilled person in the art.
The pH buffers may be from organic or inorganic sources. Examples of such organic or inorganic source of pH buffers include, but are not limited to, phosphates, carbon, Tris buffer, HEPEs, MESs, and MOPs, to name a few possibilities.
At block 406, an electrical potential is established across electrodes 114, 116. The electrical potential may be a DC or AC potential generated by power supply 118. Power supply may be a battery, a fuel driven generators (gasoline, diesel fuel, natural gas, biofuels, hydrogen, etc.), solar power systems, wind power systems, microbial fuel cells, and other renewable energy sources. If a load is used, the resistance of the load may range from 0.001-10,000 ohms. The electrical potentials, currents, and resistances can be increased or decreased depending on the specific needs of the BEC system with as will be understood by those of ordinary skill in the art.
At block 408, organic compounds are removed from BEC system 100, 200. In some embodiments, the organic compounds may be emitted from BEC systems 100, 200, but remain in subsurface formations 300 to sequester carbon in a non-hazardous form. Examples of the organic compounds include, but are not limited to, organic acids, organic salts, hydrocarbons, alcohols, amines, esters, ethers, amides, and other categories of organic compounds. In addition to organic compounds, methane may be a byproduct of the process and can be utilized for energy to power the BEC systems 100, 200 or be transferred to a natural gas pipeline.
A laboratory bench-scale BEC system was tested for transforming CO2 to an organic compound. Two carbon electrodes were installed in a 3.8-L batch reactor and carbon mesh was inserted in between the electrodes. The reactor was filled with 3 L of common mineral medium composed of constituents such as ammonium, phosphates, potassium, magnesium, calcium, sulfate, cobalt, nickel, and other trace metals. The reactor (headspace and the medium) was purged with compressed pure CO2. The reactor was sealed by inserting a connection to a modified manometer and a methanogenic inhibitor, 2-BESA, was added to the solution in the reactor. The BEC reactor was then inoculated with 300 mL of granulated sludge from an anaerobic digester. The electrodes were connected to an AC-DC converter, which was set to 1.5 V. The headspace gas composition and organic compounds in the reactor solution were determined and quantified during operation.
The results shown in
A BEC system 200 in accordance with the embodiment illustrated in
The disclosed systems and methods advantageously utilize BEC systems to transform CO2 into organic compounds. The BEC systems may be implemented in combination with CO2 producing systems, such as coal-burning or other industrial plants, to reduce the amount of CO2 released into the atmosphere. Not only do the BEC systems reduce the amount of CO2 released into the atmosphere, but the improved BEC systems advantageously transform CO2 into value-added products such as organic compounds and methane.
The table illustrated in
A separate test was conducted with different applied electrical potentials of 0.2, 0.29, 0.4, and 0.6 V. As shown in
Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.
This application claims priority to U.S. Patent Application No. 61/440,672, which was filed Feb. 8, 2011 and is herein incorporated by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
61440672 | Feb 2011 | US |