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Carbon Dioxide Capture by Electrochemical Mineralization
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Carbon Dioxide Capture by Electrochemical Mineralization Heping Xie,1,* Bin Liang,1,2 Hairong Yue,2 and Yufei Wang1,* Recently in ChemSusChem, Lamb et al. reported a novel electrochemical cell comprising a dual-component graphite and earth-crust-abundant-metal anode, a hydrogen-producing cathode, and an aqueous sodium chloride electrolyte for sustainable carbon dioxide mineralization and hydrogen production. The natural global carbon cycle cannot counteract the ever-increasing levels of anthropological carbon dioxide (CO2), which brings about great challenges in reducing CO2 emissions for sustainable development in both energy and the environment. CO2 capture and utilization is an ideal way to convert CO2 to highvalue chemical products to tackle the environmental concerns of increasing global CO2 levels, particularly in the transition from a fossil-fuel-based economy to a renewable-energy-based economy. The chemical utilization of CO2 has remarkably increased over the past decade, and mineralization is one of the most efficient methodologies given that it is thermodynamically favorable and could reduce CO2 emissions with a relatively low overall cost and energy expenditure. CO2 mineralization is the chemical carbonation of CO2 with metal ions, such as calcium and/or magnesium, for the formation of stable carbonates.1 It is a permanent and safe way to store CO2 and does not garner potential concerns over long-term monitoring and liability issues, such as geological storage.2 In recent years, natural minerals (serpentine, olivine, and K-feldspar) and industrial wastes (phosphogypsum, steel slag, and fly ash) have been extensively investigated as candidates for fixing CO2 through mineralization. Because of the low reactivity of natural minerals, CO2 mineralization by natural
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weathering is too slow to match the increasing atmospheric CO2 level. Therefore, the pretreatment of natural ores, such as acid dissolution and thermal activation, is necessary for accelerating the mineralization process, contributing to mineralization’s high energy consumption and high cost. Using industrial wastes that are normally chemically active makes CO2 mineralization practical; on the other hand, it is an alternative way to cut waste discharge. Recently in ChemSusChem, Lamb et al. reported a capacitance-assisted electrochemical process for sustainable CO2 mineralization.3 Electrochemical mineralization has already been proposed to intensify the carbonation of CO2 with earth-abundant silicates,4 soluble magnesium and/or calcium salts,5 and industrial alkaline wastes6 and has the advantage of directly mineralizing CO2 from flue gas and generating valuable products. In the present study, electrochemical mineralization based on two hydrogen electrodes was highly efficient at CO2 mineralization. It generated hydroxide to remove CO2 from flue gas by hydrogen evolution at the cathode as follows: 2CO2 + 2H2O + 2e = 2HCO3 + H2, E0 = 0.463 V. The formed hydrogen carbonate was precipitated by metal ions. Simultaneously, hydrogen produced by the cathode was electro-oxidized to pro-
Chem 4, 16–26, January 11, 2018 ª 2017 Published by Elsevier Inc.
2e = tons by giving electrons (H2 2H+, E0 = 0 V) at the anode. The proton was exploited for producing acid or dissolving ores to provide calcium and magnesium ions for the mineralization of CO2. Compared with traditional electrolysis used in the chlor-alkali industry, this process can reduce the energy consumption of CO2 mineralization by over 50% by displacing the chloride ion oxidation reaction with a hydrogen oxidation reaction at the anode, which changed the standard redox potential of the anode from 1.36 to 0 V. The energy requirement for electrochemical CO2 mineralization highly depends on the alkalinity and reactivity of the feedstock. Figure 1 summarizes the theoretical and actual energy consumption of electrochemical CO2 mineralization with different feedstocks. It should be noted that electricity can be harvested by electrochemical CO2 mineralization when the feedstock is alkali and reactive enough, such as portlandite in industrial alkaline wastes. In contrast to such approaches, Lamb et al. reported a fundamentally distinct electrochemical CO2 mineralization process that uses scrap aluminum or steel as the feedstock in place of natural minerals or industrial alkaline wastes. In this process, the authors constructed an electrochemical cell comprising a graphite-lined aluminum anode and a hydrogen-evolving cathode with sodium chloride as the electrolyte. The graphite acted as a supercapacitive
1Institute
of New Energy and Low-Carbon Technology, Sichuan University, Chengdu 610207, China
2School
of Chemical Engineering, Sichuan University, Chengdu 610065, China *Correspondence: [email protected] (H.X.), [email protected] (Y.W.) https://doi.org/10.1016/j.chempr.2017.12.024
Figure 1. Theoretical and Actual Energy Requirement for Electrochemical CO2 Mineralization with Different Feedstocks
reagent concentrator by pumping CO2 into an aqueous solution, which converted to hydrogen carbonate via hydrogen evolution at the cathode. Simultaneously, aluminum was oxidized at the anode instead of hydrogen, releasing aluminum ions into the solution, which reacted with hydrogen carbonate to fix CO2 in the form of an aluminum hydroxycarbonate mineral. The authors predicted that this technology could be used to mineralize 20–45 million tons of CO2 annually, according to the annual production and recycling rates of aluminum. Additionally, the authors proved that the steel can also be used for CO2 mineralization, which could mineralize 822 million tons of CO2 by using non-recycled scrap steel. This finding opens a much more expansive resource pool for CO2 capture. The corresponding energy consumption reported is between 1,200 and 2,400 kWh/ton CO2, higher than that of using wallastonite or portlandite as feedstock. However, the calculated
Gibbs free energy of such a reaction under the standard state conditions is about 1,680.52 kJ/mol, releasing up to 3,536.5 kWh per metric ton of CO2, which is far more than that of using other feedstocks (Figure 1). Moreover, the standard redox potential for aluminum oxidation is 1.68 V, which is more negative than that of hydrogen evolution in a CO2 solution ( 0.463 V) and is capable of generating electricity theoretically rather than consuming it. This means that CO2 mineralization using scrap aluminum as feedstock has a lot of room to improve energy efficiency and is theoretically an energyoutputting strategy. Despite the large number of resources available for CO2 mineralization and the clear advantages over geological storage, the costs of CO2 mineralization are currently too high for a large application of this technology. Compared with traditional mineralization processes, electrochemical mineralization is more energy efficient. There
is still a long way to go before the cells are optimized with, for example, improved electrodes and enhanced gas-liquid and liquid-solid mass transfers, and we should be concerned about the influence of the nitrogen oxide, sulfur oxide, and carbon monoxide contained in flue gases. However, generally speaking, electrochemical mineralization couples waste processing and carbonation reaction and appears to be a promising process for CO2 sequestration. 1. Seifritz, W. (1990). CO2 disposal by means of silicates. Nature 345, 486. ´ ., 2. Matter, J.M., Stute, M., Snæbjo¨rnsdottir, S.O Oelkers, E.H., Gislason, S.R., Aradottir, E.S., Sigfusson, B., Gunnarsson, I., Sigurdardottir, H., Gunnlaugsson, E., et al. (2016). Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions. Science 352, 1312–1314. 3. Lamb, K.J., Dowsett, M.R., Chatzipanagis, K., Scullion, Z.W., Kro¨ger, R., Lee, J.D., Aguiar, P.M., North, M., and Parkin, A. (2017). Capacitance-assisted sustainable electrochemical carbon dioxide mineralisation. ChemSusChem. Published online November 24, 2017. https://doi.org/10. 1002/cssc.201702087.
Chem 4, 16–26, January 11, 2018
25
4. House, K.Z., House, C.H., Schrag, D.P., and Aziz, M.J. (2007). Electrochemical acceleration of chemical weathering as an energetically feasible approach to mitigating anthropogenic climate change. Environ. Sci. Technol. 41, 8464–8470.
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Chem 4, 16–26, January 11, 2018
5. Xie, H., Liu, T., Hou, Z., Wang, Y., Wang, J., Tang, L., Jiang, W., and He, Y. (2015). Using electrochemical process to mineralize CO2 and separate Ca2+/Mg2+ ions from hard water to produce high value-added Carbonates. Environ. Earth Sci. 73, 6881–6890.
6. Xie, H., Liu, T., Wang, Y., Wu, Y., Wang, F., Tang, L., Jiang, W., and Liang, B. (2017). Enhancement of electricity generation in CO2 mineralization cell byusing sodium sulfate as the reaction medium. Appl. Energy 195, 991–999.
Carbon Dioxide Capture by Electrochemical Mineralization Heping Xie,1,* Bin Liang,1,2 Hairong Yue,2 and Yufei Wang1,* Recently in ChemSusChem, Lamb et al. reported a novel electrochemical cell comprising a dual-component graphite and earth-crust-abundant-metal anode, a hydrogen-producing cathode, and an aqueous sodium chloride electrolyte for sustainable carbon dioxide mineralization and hydrogen production. The natural global carbon cycle cannot counteract the ever-increasing levels of anthropological carbon dioxide (CO2), which brings about great challenges in reducing CO2 emissions for sustainable development in both energy and the environment. CO2 capture and utilization is an ideal way to convert CO2 to highvalue chemical products to tackle the environmental concerns of increasing global CO2 levels, particularly in the transition from a fossil-fuel-based economy to a renewable-energy-based economy. The chemical utilization of CO2 has remarkably increased over the past decade, and mineralization is one of the most efficient methodologies given that it is thermodynamically favorable and could reduce CO2 emissions with a relatively low overall cost and energy expenditure. CO2 mineralization is the chemical carbonation of CO2 with metal ions, such as calcium and/or magnesium, for the formation of stable carbonates.1 It is a permanent and safe way to store CO2 and does not garner potential concerns over long-term monitoring and liability issues, such as geological storage.2 In recent years, natural minerals (serpentine, olivine, and K-feldspar) and industrial wastes (phosphogypsum, steel slag, and fly ash) have been extensively investigated as candidates for fixing CO2 through mineralization. Because of the low reactivity of natural minerals, CO2 mineralization by natural
24
weathering is too slow to match the increasing atmospheric CO2 level. Therefore, the pretreatment of natural ores, such as acid dissolution and thermal activation, is necessary for accelerating the mineralization process, contributing to mineralization’s high energy consumption and high cost. Using industrial wastes that are normally chemically active makes CO2 mineralization practical; on the other hand, it is an alternative way to cut waste discharge. Recently in ChemSusChem, Lamb et al. reported a capacitance-assisted electrochemical process for sustainable CO2 mineralization.3 Electrochemical mineralization has already been proposed to intensify the carbonation of CO2 with earth-abundant silicates,4 soluble magnesium and/or calcium salts,5 and industrial alkaline wastes6 and has the advantage of directly mineralizing CO2 from flue gas and generating valuable products. In the present study, electrochemical mineralization based on two hydrogen electrodes was highly efficient at CO2 mineralization. It generated hydroxide to remove CO2 from flue gas by hydrogen evolution at the cathode as follows: 2CO2 + 2H2O + 2e = 2HCO3 + H2, E0 = 0.463 V. The formed hydrogen carbonate was precipitated by metal ions. Simultaneously, hydrogen produced by the cathode was electro-oxidized to pro-
Chem 4, 16–26, January 11, 2018 ª 2017 Published by Elsevier Inc.
2e = tons by giving electrons (H2 2H+, E0 = 0 V) at the anode. The proton was exploited for producing acid or dissolving ores to provide calcium and magnesium ions for the mineralization of CO2. Compared with traditional electrolysis used in the chlor-alkali industry, this process can reduce the energy consumption of CO2 mineralization by over 50% by displacing the chloride ion oxidation reaction with a hydrogen oxidation reaction at the anode, which changed the standard redox potential of the anode from 1.36 to 0 V. The energy requirement for electrochemical CO2 mineralization highly depends on the alkalinity and reactivity of the feedstock. Figure 1 summarizes the theoretical and actual energy consumption of electrochemical CO2 mineralization with different feedstocks. It should be noted that electricity can be harvested by electrochemical CO2 mineralization when the feedstock is alkali and reactive enough, such as portlandite in industrial alkaline wastes. In contrast to such approaches, Lamb et al. reported a fundamentally distinct electrochemical CO2 mineralization process that uses scrap aluminum or steel as the feedstock in place of natural minerals or industrial alkaline wastes. In this process, the authors constructed an electrochemical cell comprising a graphite-lined aluminum anode and a hydrogen-evolving cathode with sodium chloride as the electrolyte. The graphite acted as a supercapacitive
1Institute
of New Energy and Low-Carbon Technology, Sichuan University, Chengdu 610207, China
2School
of Chemical Engineering, Sichuan University, Chengdu 610065, China *Correspondence: [email protected] (H.X.), [email protected] (Y.W.) https://doi.org/10.1016/j.chempr.2017.12.024
Figure 1. Theoretical and Actual Energy Requirement for Electrochemical CO2 Mineralization with Different Feedstocks
reagent concentrator by pumping CO2 into an aqueous solution, which converted to hydrogen carbonate via hydrogen evolution at the cathode. Simultaneously, aluminum was oxidized at the anode instead of hydrogen, releasing aluminum ions into the solution, which reacted with hydrogen carbonate to fix CO2 in the form of an aluminum hydroxycarbonate mineral. The authors predicted that this technology could be used to mineralize 20–45 million tons of CO2 annually, according to the annual production and recycling rates of aluminum. Additionally, the authors proved that the steel can also be used for CO2 mineralization, which could mineralize 822 million tons of CO2 by using non-recycled scrap steel. This finding opens a much more expansive resource pool for CO2 capture. The corresponding energy consumption reported is between 1,200 and 2,400 kWh/ton CO2, higher than that of using wallastonite or portlandite as feedstock. However, the calculated
Gibbs free energy of such a reaction under the standard state conditions is about 1,680.52 kJ/mol, releasing up to 3,536.5 kWh per metric ton of CO2, which is far more than that of using other feedstocks (Figure 1). Moreover, the standard redox potential for aluminum oxidation is 1.68 V, which is more negative than that of hydrogen evolution in a CO2 solution ( 0.463 V) and is capable of generating electricity theoretically rather than consuming it. This means that CO2 mineralization using scrap aluminum as feedstock has a lot of room to improve energy efficiency and is theoretically an energyoutputting strategy. Despite the large number of resources available for CO2 mineralization and the clear advantages over geological storage, the costs of CO2 mineralization are currently too high for a large application of this technology. Compared with traditional mineralization processes, electrochemical mineralization is more energy efficient. There
is still a long way to go before the cells are optimized with, for example, improved electrodes and enhanced gas-liquid and liquid-solid mass transfers, and we should be concerned about the influence of the nitrogen oxide, sulfur oxide, and carbon monoxide contained in flue gases. However, generally speaking, electrochemical mineralization couples waste processing and carbonation reaction and appears to be a promising process for CO2 sequestration. 1. Seifritz, W. (1990). CO2 disposal by means of silicates. Nature 345, 486. ´ ., 2. Matter, J.M., Stute, M., Snæbjo¨rnsdottir, S.O Oelkers, E.H., Gislason, S.R., Aradottir, E.S., Sigfusson, B., Gunnarsson, I., Sigurdardottir, H., Gunnlaugsson, E., et al. (2016). Rapid carbon mineralization for permanent disposal of anthropogenic carbon dioxide emissions. Science 352, 1312–1314. 3. Lamb, K.J., Dowsett, M.R., Chatzipanagis, K., Scullion, Z.W., Kro¨ger, R., Lee, J.D., Aguiar, P.M., North, M., and Parkin, A. (2017). Capacitance-assisted sustainable electrochemical carbon dioxide mineralisation. ChemSusChem. Published online November 24, 2017. https://doi.org/10. 1002/cssc.201702087.
Chem 4, 16–26, January 11, 2018
25
4. House, K.Z., House, C.H., Schrag, D.P., and Aziz, M.J. (2007). Electrochemical acceleration of chemical weathering as an energetically feasible approach to mitigating anthropogenic climate change. Environ. Sci. Technol. 41, 8464–8470.
26
Chem 4, 16–26, January 11, 2018
5. Xie, H., Liu, T., Hou, Z., Wang, Y., Wang, J., Tang, L., Jiang, W., and He, Y. (2015). Using electrochemical process to mineralize CO2 and separate Ca2+/Mg2+ ions from hard water to produce high value-added Carbonates. Environ. Earth Sci. 73, 6881–6890.
6. Xie, H., Liu, T., Wang, Y., Wu, Y., Wang, F., Tang, L., Jiang, W., and Liang, B. (2017). Enhancement of electricity generation in CO2 mineralization cell byusing sodium sulfate as the reaction medium. Appl. Energy 195, 991–999.