A novel sorbent consisting of NaOH/CaO was developed for CO 2 capture at 315 °C suitable for hightemperature CO 2 -capture applications, such as coal gasification systems. The sorbent is regenerable at 700 °C, and steam does not affect the sorbent performance. A multicycle test conducted in the atmospheric reactor at 315 °C indicated that the sorbent improved the performance with an increased number of cycles. The sorbent can also capture CO 2 at a wide range of temperatures from ambient to 500 °C. However, the mechanism of CO 2 capture is different at ambient temperature. The sorbent is unique because it has a high CO 2 -capture capacity of more than 3 mol/kg at 315 °C and is regenerable at 700 °C.

Chemical-looping combustion (CLC) is a combustion technology for clean and efficient utilization of fossil fuels for energy production. This process which produces sequestration ready CO2 systems is a promising technology to be utilized with coal gasification systems. In the present work, chemical-looping combustion has been studied with an oxygen carrier, NiO/bentonite (60 wt % NiO) for the gasification systems utilizing simulated synthesis gas. Global reaction rates of reduction and oxidation as a function of conversion were calculated for oxidation−reduction cycles utilizing the thermogravimetric analysis (TGA) data on multicycle tests conducted with NiO/bentonite at atmospheric pressure between 700 and 900 °C. The rate of reduction increased slightly with an increase in temperature, while the rate of oxidation decreased at 900 °C. The effect of particle size of the oxygen carrier on CLC was studied for the particle size between 20 and 200 mesh. The rates of reactions depended on the particle size of the oxygen carrier. The smaller the particle size, the higher the reaction rates. The multicycle CLC tests conducted in a high-pressure flow reactor showed stable reactivity for the production of CO2 from fuel gas at 800 and 900 °C and full consumption of hydrogen during the reaction. The data from a one cycle test on the effect of the pressure on the performance with NiO/bentonite utilizing the tapered element oscillating microbalance (TEOM) showed a positive effect of the pressure on the global rates of reduction−oxidation reactions at higher fractional conversions. The X-ray diffraction (XRD) analysis confirmed the presence of the NiO phase in NiO/bentonite with the oxidized sample in the high-pressure reactor and Ni phase with the reduced sample. The presence of a small amount of NiO in the reduced sample detected by X-ray photoelectron spectroscopy (XPS) may be due to its exposure to air during sample transfer from the reactor to XPS. Scanning electron microscopy (SEM) analysis showed no significant changes in morphology of NiO/bentonite reacted in the temperature range 700−800 °C in an atmospheric TGA for 10 oxidation−reduction cycles, but some loss of surface area and porosity was observed at 900 °C. This effect was found to be greater with increase in the particle size of the oxygen carrier.

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The effect of various additives on the decomposition of sodium carbonate (Na2CO3) was evaluated using temperature-programmed desorption, thermogravimetric analysis, X-ray diffraction, and X-ray photoelectron spectroscopy. Incorporation of additives, CaO and Ca(OH)2, had a significant effect on lowering the decomposition temperature of Na2CO3, while CaCO3, SiO2, and Al2O3 had no effect. The amount of additive, sweep gas flow rate, and heating rate were also found to play a significant role in altering the decomposition temperature of Na2CO3. The formation of a carbonate-type intermediate in the presence of CaO and Ca(OH)2 may have promoted the decomposition of Na2CO3.