Fabrication of novel Ca-based solid sorbents for sorption-enhanced gasification processes
Date
2019-04-30
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Abstract
Calcium (Ca) based sorbents as high-temperature performance sorption materials in the carbon dioxide (CO2) capture process have been investigated due to their high CO2 capacity, low cost, and environmental benignity. Unfortunately, commercialized applications of these materials have been hindered by their severe capacity loss during cycling operation. However, refractory zirconium-based ceramics have shown excellent performances as thermal barrier coatings in many high-tech applications, and the recent doping of zirconia in Ca-based sorbents has exhibited excellent sustainability in the activity stability in cyclic CO2 capture operations. This study examined the effects of a number of mixed metal oxide supports, such as alkaline earth metal zirconate (calcium zirconate, CaZrO3), which has the chemical structure of perovskite, and rare earth metal zirconates, which have the chemical structure of pyrochlore on the performance of Ca-based sorbents. These materials were prepared through the wet co-precipitation method, in order to increase the CO2 uptake stability in cyclic CO2 capture operations. The interaction between two metal oxides was also examined. This study focused on 1) the determination of the optimal crystalline structure of mixed oxide ceramics, 2) analysis of the effect of a second metal oxide support on sorbent activity, and 3) the investigation of the influence of a high number of cycles (over 60) carbonation-calcination cycles on sorbent durability and activity. The results indicated considerable sorbent stability and capacity improvement for mixed metal oxide zirconia-stabilized CaO over those of pure CaO, which showed significant cyclic capacity decay under similar conditions. Among the studied materials, aluminum zirconate and zirconium molybdate stabilized sorbents showed the best performances in severe operating conditions. In another attempt to overcome the activity loss of Ca-based sorbents, this study investigated highly crystalline zirconium dioxide (ZrO2) layers derived from the hydrolysis of zirconium butoxide and coated on pelletized sorbents to control the growth of ZrO2 crystals. The zirconia-coated sorbent showed excellent cycling stability corresponding to a capacity of retention of 78% after 30 cycles at high temperatures. More importantly, the highly crystalline ZrO2-coated sorbents exhibited a significantly lower capacity decay compared to the uncoated sorbents, which could be attributed to the formation of a layered high-temperature-resistant ceramic through the solid-state reaction of the compact and highly crystalline ZrO2 layer with CaO. The carbonation reaction of the modified sorbents is a first-order reaction. Also, the carbonation rate increased with increasing the temperature up to 700°C and decreased with further increases. The global kinetic study confirms that the grain model is more reliable compare to the unreacted shrinking core model to investigate the behavior of the sorbents under the various operating conditions.
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Keywords
CO2 capture, Environmental engineering, Calcium looping, Gasification, Sorbents, pre-combustion
Citation
Soleimani Salim, A. H. (2019). Fabrication of novel Ca-based solid sorbents for sorption-enhanced gasification processes (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.