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Thermogravimetric apparatus (TGA) and X-ray diffraction (XRD) have been used to study the characteristics of potassium-based sorbents for CO 2 capture. The carbonation reactivity of K 2 CO 3 · 1.5H 2 O and K 2 CO 3 dehydrated from K 2 CO 3 · 1.5H 2 O was weak. However, K 2 CO 3 calcined from KHCO 3 showed excellent carbonation capacity and no deactivation of sorbents during multiple cycles. The XRD results showed that the sample dehydrated from K 2 CO 3 · 1.5H 2 O was K 2 CO 3 with structure of monoclinic crystal (PC#1). The carbonation products of PC#1 included K 2 CO 3 · 1.5H 2 O and KHCO 3 , and K 2 CO 3 · 1.5H 2 O was the main product. Correspondingly, K 2 CO 3 with structure of hexagonal crystal (PC#2) was the product calcined from KHCO 3 , and the main carbonation product of PC#2 was KHCO 3 . The byproduct of K 4 H 2 (CO 3 ) 3 · 1.5H 2 O for PC#2 would affect the carbonation processes. Hydration tests confirmed the two hypotheses: the hydration reaction will first occur for K 2 CO 3 with structure of monoclinic crystal, and the carbonation reaction will first occur for K 2 CO 3 with structure of hexagonal crystal. The reaction principles were analyzed by product and the relevant reactions. This investigation can be used as basic data for dry potassium-based sorbents capturing CO 2 from flue gas.

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Considerable studies have been reported on the coal pyrolysis process and the formation of SO 2 and NO x processors such as H 2 S, COS, SO 2 , HCN, and NH 3 in inert atmospheres. Similar studies in CO 2 atmosphere also need to be accomplished for better understanding of the combustion characteristics and the SO 2 /NO x formation mechanism of oxy-fuel combustion, which is one of the most important technologies for CO 2 capture. In this study, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) analysis was employed to measure the volatile yield and gas evolution features during coal pyrolysis process in CO 2 atmosphere. Results show that replacing N 2 with CO 2 does not influence the starting temperature of volatile release but seems to enhance the volatile releasing rate even at 480 °C. At about 760 °C, CO 2 prevents the calcite from decomposing. In CO 2 atmosphere, the volatile yield increases as the temperature increases and decreases as the heating rate increases. COS is monitored during coal pyrolysis in CO 2 atmosphere while there are only H 2 S and SO 2 formed in N 2 atmosphere. The COS is most likely formed by the reaction between CO 2 and H 2 S. No NH 3 was monitored in this study. In CO 2 atmosphere, the gasification of char elevates the conversion of char-N to HCN. The HCN yield increases as the temperature increases and decreases as the heating rate increases.