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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.

The CO 2 capture characteristics of dry potassium-based sorbents were investigated with thermogravimetric analysis (TGA) and a bubbling fluidized-bed reactor. Potassium-based sorbents were prepared by impregnation with potassium carbonate on supports such as coconut activated charcoal (AC1), coal active carbon (AC2), silica gel (SG), and activated alumina (Al 2 O 3 ). Sorbents such as K 2 CO 3 /AC1, K 2 CO 3 /AC2, and K 2 CO 3 /Al 2 O 3 showed excellent carbonation capacity; The total conversion rates of those sorbents were 97.2, 95.9, and 95.2%, respectively in the TG test, and 89.2, 87.9, and 87.6%, respectively, in the fluidized-bed test. However, K 2 CO 3 /SG showed poor carbonation capacity, the total conversion rates were only 34.5 and 18.8%, respectively, in TG and fluidized-bed tests. The differences in carbonation capacity of those sorbents were analyzed by studying the microscopic structure and crystal structure of the supports and the sorbents with X-ray diffraction, scanning electron microscopy, and N 2 adsorption tests.

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