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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/advances Page 1 of 9 Journal Name RSC Advances Dynamic Article Links ► Cite this: DOI: 10.1039/c0xx00000x www.rsc.org/xxxxxx ARTICLE TYPE New Technology for Post-Combustion Abatement of Carbon Dioxide via in situ Generated Superoxide Anion-Radical Uri Stoin *a, Zach Barnea b and Yoel Sasson c Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX 5 DOI: 10.1039/b000000x A novel chemistry for the efficient sequestration of carbon dioxide via swift nucleophilic attack by superoxide anion is disclosed. Relatively stable aqueous solution of the latter is generated in situ by contacting alkali hydroxide solution with hydrogen peroxide at pH 11. Using a simple gas liquid scrubber containing the above blend, carbon dioxide is quantitatively absorbed from a gas stream under ambient 10 conditions and is totally converted to aqueous carbonate. The aqueous solution containing the in situ generated superoxide specie was found to be far more effective for absorbing CO 2 than the standard ethanolamine or soda caustic solutions. Manuscript Introduction technologies in two main groups of abatement methods, reversible process (absorption/desorption) and mineralization Climate change is considered to be one of the greatest 1 technologies. However, relatively few reversible methods have 15 environmental threats of our times. The atmospheric 50 gained any measure of acceptance from an industrial viewpoint. concentration of greenhouse gases has increased steadily over the 12 Currently, CO can be removed from flue gas and waste gas past century and is approaching disturbing levels. 2 Current 2 streams by absorption into amine solutions such as mono- research shows that there is an excess of approximately 3.9% ethanolamine (MEA) to form the ammonium carbamate, this is a CO with respect to the natural ‘‘carbon cycle’’. 3 The 2 well understood and widely used reversible technology. 13 MEA 20 atmospheric warming is associated with a global climate change 55 has a high CO absorption capacity and it readily reacts with CO Accepted and a planetary temperature increase. 4 The growing evidence that 2 2 under normal conditions. Nevertheless, there are still several links the greenhouse gas, carbon dioxide and global climate serious drawbacks to this methodology: the uptake of water into change highlights the need to develop cost effective carbon the gas stream causes serious corrosion in the process sequestration schemes. 5 infrastructure, the loss of volatile amines and evaporation of 25 The largest source of CO 2 emission (nearly sixty percent) comes 60 water during the driving-off of CO results in an increase in from power generation, public electricity and heat production 2 operating costs. 14 In addition, the thermal release of CO from using fossil fuel combustion. 6 The International Energy Agency 2 the carbamate solution requires a substantial energy input. The (IEA) predicts that fossil fuels will remain the dominant source of thermal instabilities of both MEA and the carbamate lead to energy until 2030. 7 Other pollution sources are combustion decomposition which can cause environmental problems. 15 30 systems such as cement kilns, furnaces in industries and iron 65 Additionally, flue gases coming from coal combustion will and steel production plants. In these large-scale processes, the Advances contain not only CO , N , O and H O, but also air pollutants direct firing of fuel with air in a combustion chamber has been 2 2 2 2 such as SOx, NOx, HCl, HF, particulates and other trace organic (for centuries) the most economic technology to extract and and inorganic contaminants. 16 Those contaminants can react with use the energy contained in the fuel. Therefore, the strategic MEA to from non sedimentary and heat stable salts such as 35 importance of post-combustion capture systems becomes 17 70 ammonium nitrate, ammonium sulfate etc. Nonetheless, MEA evident when confronted with the reality of today’s sources RSC is currently the industry standard for CO and other acidic gasses of CO emissions. 8 2 2 reversible absorption technologies, but it is certainly not an The removal of a gaseous component through contact with a optimized reagent, rather one of convenience. 18 liquid is known as wet scrubbing. Wet scrubbing can be divided The alternative, irreversible (mineralization) technology for 40 into processes where there is a chemical reaction between the 75 carbon dioxide abatement from flue gas is by aqueous alkaline sorbate and the sorbent and others where the sorbate is just solutions to generate inorganic carbonates. These processes are physically dissolved into the sorbent phase. 9 known since the 70s of last century. 19 The absorption of CO A wide range of different methods for carbon dioxide treatment 2 10 into strong hydroxide solutions was shown to proceed via an already exists. Adsorption, absorption, ionic liquid - irreversible second order reaction between CO 2 and OH ions. 45 technologies were reported and even biological and membrane 20 80 Unfortunately, this absorption technology is effective only, treatment was suggested. 11 We can characterize these This journal is © The Royal Society of Chemistry [year] [journal] , [year], [vol] , 00–00 | 1 RSC Advances Page 2 of 9 under conditions of strong caustic solutions, with low humidity, at high temperature and long liquid/gas contact time. 21 Consequently CO 2 absorption by alkali did not develop into a practical method for carbon dioxide post-combustion capture. 22 5 In the last decades researches have proposed scores of different 23 interesting technologies for complete mineralization of CO 2. However these technologies have several serious drawbacks. The main drawbacks are slow reaction rates and special reaction conditions. Consequently they cannot be applied as industrial 10 technologies. In this study we advocate the in situ generated superoxide anion radical as a unique reagent for the swift capture, abatement and total mineralization of carbon dioxide. Reactive oxygen species 55 Figure 1: Schematic assembly of the CO 2 absorption system. 1- (ROS) such as peroxide and superoxide reagents were tested Carbon dioxide cylinder, 2- flow meter, 3-magnetic stirrer, 4- 24 15 previously as traps for carbon dioxide. Currently, potassium scrubber, 5- CO 2/O 2 gas analyzer with data logger, 6-computer, superoxide is utilized in self-contained breathing equipment for 7-bypass. the generation of oxygen gas. 25 The superoxide radical anion is an ROS that possesses both anionic and free-radical properties. Physical Measurements The latter is a powerful and effective nucleophile in polar aprotic 26 60 FTIR (Fourier transform infrared spectroscopy) studies were 20 solvents such as dimethyl sulfoxide. Conversely, in protic conducted using Peact IR 4000, manufactured by Mettler-Toledo solvents, e.g. water, it is presumed inactive, owing to its strong Ltd. XRD (X-ray diffraction) studies were conducted using X-ray solubility by this medium and its rapid hydrolysis. Aqueous diffractometer, Range: 1100 <2 θ°> 1680 , D8 advance by Bruker superoxide is therefore not an obvious candidate for practical Manuscript AXS. EPR spectra were recorded using a Bruker EMX-220 X- applications. 65 band ( υ = 9.4 GHz) EPR (electron paramagnetic resonance 25 We have recently described a novel method for the in-situ spectroscopy) spectrometer equipped with an Agilent 53150 A generation of a remarkably water stable superoxide anion by frequency counter at room temperature (RT, T = 295 K). To reacting sodium or potassium hydroxide with hydrogen peroxide achieve a better signal-to-noise ratio for weak fast decaying under ambient conditions. 27 This reagent was effectively utilized signals, each 1024 point EPR spectrum was recorded in over- for the total mineralization of carbon tetrachloride and other 28 70 modulation mode using magnetic field modulation frequency of 30 polyhalogen compounds. In this manuscript, we demonstrate 100 kHz and modulation amplitude of 0.3 mT, microwave power the unique nucleophilic properties of the as-prepared superoxide of 10 mW and 16 fast (10 s) coherent acquisition scans. anion in water and its instantaneous reaction with carbon dioxide Processing (base line correction, digital filtering etc.) of EPR which renders it most likely, the superb reagent for abatement of Accepted spectra was performed by using Bruker WIN-EPR software, CO 2 from flue gas. 75 simulations of spin adducts were performed using Bruker 35 It should be noted that a technologies for H S and CO absorption 2 2 WINEPR SimFonia and NIEHS/NIH P.E.S.T. WinSim2002 and into alkaline solutions containing an oxidizing agent are already OriginLab Corp. Origin software. CO concentration was known. 29 However, our new proposed technology has a different 2 determined using a gas analyzer with IR detector (the range are reactive species (superoxide) and different final products. The 1% - 100%) manufacture by Emproco Ltd. end products of this proposed process are carbonate salt and 40 oxygen that can be used in various processes and products in the 80 CO absorption system chemical and food industry.