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Electrochemically-Mediated Separations for CO Capture

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Electrochemically-Mediated Separations for CO Capture Electrochemically-Mediated Separations for CO2 Capture Fritz Simeon, Mike Stern, Howard Herzog and T. Alan Hatton Department of Chemical Engineering and the MIT Energy Initiative (MITei) Massachusetts Institute of Technology Cambridge, MA 02139, USA Page | 1 CarbonCarbon CCaptureapture aandnd MMitigationitigation Coal to play a major role in world’s energy future: lowest-cost for base-load electricity generation coal resources distributed around the world. Adverse environmental effects accompany its mining, transport and utilizations. Carbon Capture and Storage (CCS mitigate contribution of carbon-based fuel emissions to climate change, capture carbon dioxide (CO2) from point sources, e.g., power plants and other industrial facilities, and store it in deep subsurface geological formations for indefinite isolation from the atmosphere. World Primary Energy Consumption, World Electricity Generation by Fuel, 2005-2025 2005-2030 Petawatt-hours (1015 watt-hours) Trillion Kilowatt-hours Sources:Sources: 2005: 2005: Energy Energy Information Information Administration Administration (EIA),(EIA) InternationalInternationalEner Energygy Annual Annual 2005 2005 (June-(June Sources: 2005: Energy Information Administration (EIA), International Energy Outlook 2005, website October 2007), website www.eia.doe.gov/iea. Projections: EIA, System for the Analysis of Global www.eia.doe.gov/iea. Energy Markets/Global Electricity Module (2006). http://www.tobacco-facts.net/2009/12/coal-will-be-harder-to-quit-than-tobacco Page | 2 CoalCoal CCombustionombustion CCaptureapture TTechnologyechnology Post-combustion Challenges: Dilute CO2 concentration in flue gas. Pre-combustion Challenges: Other flue gas components. Low operational temperature of existing CO2 removal technology. N2, O2 High capital and operational costs. More economical to combust syngas before fully shift (reducing fraction of CO2 captured). CO2 Flue Gas COC 2 Capture Unit Air Post-Combustion PowerP & Heat CO2 Pre-Combustion CO2 Reformer & H2 Compression/ CO Separator PowerP & Heat Sequestration 2 DeDehydrationhydra Air PowerP r & Heat CO2 Coal O Oxy-Combustion 2 Oxy-combustion Challenges: AirA Separation N Expensive cryogenic air separation. Air 2 High operational temperature of pure oxy Unit combustion requires new materials for boiler. Page | 3 Gas Separation Technology for Post-Combustion CCS Alkanolamines, Blended alkanolamines Zeolites Gas/liquid contractors Piperazine, Amino acids Carbon Permselective membranes Second generation amine Silica High-temperature polymeric Third generation sorbent, Alumina Potassium carbonate, Chilled ammonia Absorptionorp Membranee AdsorptionA Flue Gas R&D Pathways ExploratoryEx Biologicalcal Reactivetive Solid Adsorption Algae Metal Oxides Metal Organic Frameworks (photosynthesis) Sodium Bicarbonate CO2 Hydrates Carbonic anhydrase Sodium Hydroxide Liquid crystals (enzyme-catalyzed CO2 capture) Lithium Zirconate Ionic Liquids Lithium Silicate Thermal-Swing Processes Energy for Separation Pressure-Swing ProcessesIsothermal Processes Electrochemical-Swing Processes Page | 4 Gas Separation Technology for Post-Combustion CCS Excellent CO2 selectivity over N2 Increase CO2 permeation rates Reduce capital & operational costs Increase CO2/N2 selectivity Lower energy consumed Increase selectivity Increase CO2 capacity Improve economies of scale Minimize oxidative degradation Minimize Sox & Nox degradations Absorptionorp Membranee AdsorptionA Flue Gas R&D Pathways ExploratoryEx Biologicalcal Reactivetive Solid Adsorption Challenge in economies of scale Required highly porous materials Increase CO2 capacity Long term biological activity/stability Improve long term stability Improve CO2 selectivity Improve long term performance Thermal-Swing Processes Energy for Separation Pressure-Swing Processes Isothermal Processes Electrochemical-Swing Processes Page | 5 ObjectiveObjective ofof CCSCCS RR&D&D ooff DDOEOE iinn TThehe UUnitednited ofof SStatestates “Energy Cost + Retrofitting Cost” Minimum CO2 capture = 90% Maximum increase in COE = 35% “Capital Cost + Cost” Operational DOE/NETL-2009/1366 – Existing Plants, Emissions and Capture – Setting CO2 Program Goals CCS technology requires new approaches to achieve target of 35% maximum increase in COE. Page | 6 TraditionalTraditional Wet-ScrubbingWet-Scrubbing ProcessProcess With extensive energy integration, The theoretical minimum work is 0.11 MWh/ton CO2 Rochelle, G. T., Science 2009, 325:1652-1654 Developed over 70 years ago as non-selective acid gas removal processes Today, the only real option for deploying CCS technology Recent solvent R&D focuses on solvent degradation and equipment corrosion Need significant improvement to meet 35% maximum increase in COE Page | 7 PotentialPotential BenefitBenefit ofof EElectrochemical-Swinglectrochemical-Swing ProcessesProcesses Significant decrease in total energy consumption for CCS Ease of integration with existing power plants Decrease in indirect cost of CCS Applicable to other large-scale carbon emitters with no possibility for energy integration for thermal swing processes Cement and chemical industries Page | 8 ElectrochemicalElectrochemical SeparationSeparation ProcessesProcesses Advantages of electrochemical processes in waste treatment industry: Versatile Energy efficient Lower temperature requirements Cell optimization to minimize power losses caused by overpotential and side reactions Cost effective Electrochemical-Swing Gas Separation Technologies Electrochemical Reaction Electrochemical Reaction of Target Molecules of Carrier Molecules Mode 1 Mode 2 Ox ne Red Red Ox ne Ox ne Reded RedRe Ox ne A Red A Red A-RedA - A Red Oxx Red Ox A A-Red A influx outflux influx outflux Page | 9 Electrochemical Separation Processes 1970 – Electrochemical pumping of NO through thin films (Mode 2) 1974 – Molten carbonate electrochemical CO2 concentrator (Mode 1) 1979 – Aqueous carbonate electrochemical CO2 concentrator (Mode 2) 1981 – Flue gas desulfurization using an electrochemical SO2 concentrator (Mode 1) 1984 – Electrochemical removal and concentration of H2S from coal gas (Mode 1) Electrochemical heterocyclic nitrogen compound separation – 1993 (Mode 2) Electrochemically-modulated complexation: CO concentrator – 1995 (Mode 2) Electrochemically-modulated complexation: ethylene/ethane separator – 1997 (Mode 2) Electrochemically-modulated complexation: CO2 air capture – 2003 (Mode 2) Separation of CO2 from flue gas using electrochemical cells – 2010 (Mode 2) Page | 10 ElectrochemicalElectrochemical SwingSwing GasGas SeparationSeparation ProcessesProcesses Electrochemical-Swing Gas Separation Technologies Electrochemical Reaction Electrochemical Reaction of Target Molecules of Carrier Molecules Mode 1 Mode 2 Ox ne Reded RedRe Ox ne Oxx Red Ox A A-Red A influx outflux influx outflux Page | 11 Electrochemical Gas Separation of CO2 Molten Carbonate Electrochemical Cell (1974) Winnick, J. et al., AIChE Journal 1982, 28(1):103-111 Considered for CO2 removal in a manned spacecraft Electrochemical reactions: 2- Cathodic reaction: CO2 + ½O2 + 2e = CO3 2- Anodic reaction: CO3 = CO2 + ½O2 + 2e High temperature operation ~ 700°C 60% CO2 removal efficiency CO2 removal efficiency increases with increasing current density Current efficiency decreases with increasing applied current density (still remaining challenge) H2 H H2O 2 CO2 + H2 CO + H2O CO2-AIR CO2-AIR 2- CO 2- CO3 CO2 + ½O2 + 2e CO2 + ½O2 + 2e CO3 CO2 Porous Porous Electrodes Electrodes 2- 2- CO2 + ½O2 + 2e CO3 CO3 CO2 + ½O2 + 2e N2 CO2-AIR CO2-AIR N2 CO2 Molten Carbonate Fuel Cell Molten Carbonate CO2 Separation Cell (Hydrogen Mode) (Driven/Nitrogen Mode) Page | 12 Electrochemical Gas Separation FGD using electrochemical SO2 concentrator (1981) Townley, D. and Winnick, J. Ind. Eng. Chem. Process. Des. Dev. 1981, 20(3):435-440 Electrochemical reactions: “Driven” mode: 2- Cathode: SO2 + O2 + 2e = SO4 2- Anode: SO4 = SO3 + ½O2 + 2e “Reducing-gas” mode: 2- Cathode: SO2 + O2 + 2e = SO4 2- Anode: SO4 + 5H2 = 4H2O + H2S+ 2e Cell configuration for electrochemical SO2 concentrator Page | 13 Electrochemical Gas Separation FGD using electrochemical SO2 concentrator (1981) Townley, D. and Winnick, J. Ind. Eng. Chem. Process. Des. Dev. 1981, 20(3):435-440 Electrochemical reactions: “Driven” mode: 2- Cathode: SO2 + O2 + 2e = SO4 2- Anode: SO4 = SO3 + ½O2 + 2e “Reducing-gas” mode: 2- Cathode: SO2 + O2 + 2e = SO4 2- Anode: SO4 + 5H2 = 4H2O + H2S+ 2e Cell configuration for electrochemical SO concentrator Operational condition: 2 Concentrate SO2 from 0.03% at the cathode to 10% at the anode at 600°C. Operational energy costs: For a 500 MWe plant burning 3.5% sulfur coal of 9000 Btu lb heating value, the total electrical energy required is about 2% of the plant power, comparing to other FGD processes requiring up to 6% of plant power. Operating costs: ~ 0.05 cents/kWh in the driven mode and ~ 0.15 cents/kWh in the reducing-gas mode (wet scrubbing processes cost 0.14 to 0.20 cents/kWh). Experimental result: Nearly all SO2 was scrubbed from the flue gas, with less than 5 ppm remained. Page | 14 Electrochemical Gas Separation Electrochemical removal of H2S from coal gas (1984) Electrochemical reactions: Current Sources 2– Cathode: H2S + 2e = H2 + S Sweep N2 H2S 2– S Vapor Anode: S = ½ S2 + 2e Contaminate 2 d Fuel Gas Feasible H S removal at high temperature S2 2 H2 S 98% removal efficiency of H2S with Polished Fuel Gas H Sweep reasonable levels of polarization 2 N2 Favorable capital and operational costs Porous Electrolyte Porous for the H2S
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