Reactive Absorption of CO2 Using Ethylaminoethanol Promoted Aqueous Potassium Carbonate Solvent

Atmospheric concentration of CO2, which is considered as one of the major greenhouse gases (GHGs), has increased up to 398 ppmv as of 2015. CO2 concentration in atmosphere was 280 ppmv in pre-industrial era, and due to the continuous discharge, it is expected to increase up to 550 ppmv by 2050. Many of the major industrial sources of CO2 emissions are natural gas fired power plants, synthesis gas used in integrated gasification combined cycle (IGCC) and power generation, gas streams produced after combustion of fossil fuels or other carbonaceous materials, and oxyfuels. Reactive absorption of CO2 from the industrial off gases by using chemical solvents is considered as one of the most common, efficient, and cost effective technologies utilized by the industry for CO2 capture. The captured CO2 can be stored by using the geological or oceanic sequestration approaches. As an alternative to geological or oceanic sequestration, the captured CO2 can be re-energized into CO by using solar energy and combined with H2, which can be generated from different methods, to produce syngas. The syngas produced can be further processed to liquid fuels such as methanol, gasoline, jet fuel, etc. via the catalytic Fischer-Tropsch process. In past, a variety of chemical solvents (mostly aqueous amines and there derivatives) have been used for CO2 capture from different gaseous streams via reactive absorption. Though the amines are attractive for the CO2 capture application, there are several disadvantages such as very strong corrosion to equipment and piping, high energy requirement during the stripping of CO2 and they are prone to oxidative and thermal degradation. Recently, use of aqueous potassium carbonate (K2CO3) as a solvent for the absorption of CO2 has gained widespread attention. The usage of K2CO3 has been employed in a number on industries for the removal of CO2 and H2S. Due to its high chemical solubility of CO2, low toxicity and solvent loss, no thermal and oxidative degradation, low heat of absorption, and absence of formation of heat stable salts, K2CO3 seems to be more attractive compared to the conventional amines towards CO2 capture. However, K2CO3 solvent shows slow rate of reaction with CO2 and, consequently, low mass transfer in the liquid phase as compared to the amine solvents. Hence, several investigators are focused towards improving the rate of reaction of CO2 in K2CO3 solvent with the help of different types of promoters. In this paper, the kinetics of absorption of CO2 into an aqueous K2CO3 (20 wt %) promoted by ethylaminoethanol (EAE) solution (hereafter termed as APCE solvent) was studied in a glass stirred cell reactor using a fall in pressure method. Reactive absorption of CO2 in EAE promoted aqueous K2CO3 solution (APCE solvent) was studied at different initial EAE concentrations (0.6 to 2 kmol/m3) and reaction temperatures (303 to 318 K). The reaction between the CO2 and APCE solvent was very well represented by the zwitterion mechanism. The N2O analogy was employed for the determination of H_(CO2) in the APCE solvent. The H_(CO2) was observed to be decreased by 5 and 31% due to the increase in the EAE concentration from 0.6 to 2 kmol/m3 and reaction temperature from 303 to 318 K, respectively. The D_(CO2) in the APCE solvent was also decreased by 21% due to the similar increase in the initial EAE concentration. In contrast, the D_(CO2) increased with the rise in the reaction temperature from 303 to 318 K by a factor of 1.678. The rate of absorption of CO2 in the APCE solvent was observed to increase by 35.10% and 47.59% due to the increase in EAE concentration (0.6 to 2 kmol/m3) and reaction temperature (303 to 318 K). The absorption kinetics was observed to be of overall second order i.e. first order with respect to both CO2 and EAE concentrations, respectively. The rate constant (k_2) for the absorption of CO2 in the APCE solvent was observed to be equal to 45540 m3/kmol√s at 318 K. The temperature dependency of k_2 for the CO2 – APCE solvent system was experimentally determined as: k_2 = (1.214 × [10]^18)√exp(( − 9822.7)/T). Findings of this study indicate EAE as a promising promoter for the aqueous K2CO3 solution.qscienc

Solar Thermochemical CO2 Utilization via Ceria Based Redox Cycle

According to the recent studies, it is expected that the global energy requirement will increase from 14 TW to 30 TW by the year 2050. Currently, fossil fuels are the major energy source utilized for the fulfillment of the energy requirement. Due to the excessive utilization of fossil fuels, the concentration of greenhouse gases in the atmosphere is increasing day by day and hence there is a pressing need to develop technologies to produce carbon free renewable fuels. The liberated CO2 can be re-energized into CO via ferrite based thermochemical looping process using concentrated solar energy. The CO produced via solar thermochemical CO2-splitting can be combined with H2 derived from ferrite based solar thermochemical water-splitting process to produce solar syngas which can be further processed to liquid fuels such as Methanol, Diesel, and Kerosene via the Fischer-Tropsch process. The current research trends in solar thermochemical community are focused towards high and constant levels of solar fuel production in multiple cycles and it is believed that non-volatile mixed metal oxides such as undoped and doped ceria will significantly improve the production of solar fuels. Ceria based redox cycle comprises of two steps. First step belongs to solar endothermic reduction of ceria at higher temperatures releasing O2. The second step corresponds to the non-solar exothermic re-oxidation of the reduced ceria at lower temperatures by H2O, CO2, or a mixture of the two producing H2, CO or syngas. In this investigation, Zr and Hf doped ceria based redox nanoparticles (various doping combinations) were synthesized using a co-precipitation method. The respective metal precursors were dissolved in water. Upon complete dissolution, excess ammonium hydroxide (NH4OH) was added drop-wise to the mixture under vigorous stirring to precipitate the mixed-metal hydroxides (final pH = ?9). The obtained precipitates were filtered, washed with water until free from anion impurities and oven dried at 100 C for 8-10 h. Subsequently calcination was performed at different temperatures in air. The calcined powders were characterized by powder X-ray diffraction, BET surface area analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The compositional purity of the derived Zr/Hf doped ceria was identified using powder XRD and the obtained results indicate phase pure composition of the derived materials (based on the stoichiometry selected during synthesis). The derived Zr/Hf doped ceria also possess high specific surface area (SSA) and porosity which is confirmed by BET analysis. The SEM and TEM analysis indicate formation of Zr/Hf doped ceria nanoparticles in the range of 10 to 50 nm. Synthesized Zr/Hf doped ceria nanoparticles were further tested for thermochemical CO2-splitting by using a high-temperature thermogravimetric analyzer (TGA). Multiple thermal reduction and oxidation (by CO2) cycles were performed at various operating conditions by using TGA while the O2 and CO was quantified by gas chromatography. Results obtained indicate that the derived Zr/Hf doped ceria is capable of producing higher amounts of solar CO as compared to previously investigated undoped and doped ceria materials. Also, the Zr/Hf doped ceria was examined in 20 thermochemical cycles towards successive thermal reduction and CO2 splitting reactions and the obtained findings indicate stable redox reactivity and thermal stabilityQscienc