Dry regenerable sorbent technology is one of the emerging technologies as a cost-effective and energyefficient technology for CO 2 capture from flue gas. Six sodium-based dry regenerable sorbents were prepared by spray-drying techniques. Their physical properties and reactivities were tested to evaluate their applicability to a fluidized-bed or fast transport-bed CO 2 capture process. Each sorbents contained 20-50 wt% of Na 2 CO 3 or NaHCO 3 . All sorbents except for Sorb NX30 were insufficient with either attrition resistance or reactivity, or both properties. Sorb NX30 sorbent satisfied most of the physical requirements for a commercial fluidizedbed reactor process along with good chemical reactivity. Sorb NX30 sorbent had a spherical shape, an average size of 89 µm, a size distribution of 38-250 µm, and a bulk density of approximately 0.87 g/mL. The attrition index (AI) of Sorb NX30 reached below 5% compared to about 20% for commercial fluidized catalytic cracking (FCC) catalysts. CO 2 sorption capacity of Sorb NX30 was approximately 10 wt % (>80% sorbent utilization) in the simulated flue gas condition compared with 6 of 30 wt % MEA solution (33% sorbent utilization). All sorbents showed almost-complete regeneration at temperatures less than 120 °C.
Potassium-based sorbent was prepared by impregnation with potassium carbonate on activated carbon. The role of water and its effects on pretreatment and CO 2 absorption was investigated in a fixed bed reactor. K 2 CO 3 could be easily converted into K 2 CO 3 ·1.5H 2 O working as an active species by the absorption of water vapor as the following reaction: K 2 CO 3 +3/2 H 2 O→K 2 CO 3 ·1.5H 2 O. One mole of K 2 CO 3 ·1.5H 2 O absorbed one mole of CO 2 as the following reaction: K 2 CO 3 ·1.5H 2 O+CO 2 → ← 2KHCO 3 +0.5 H 2 O. The K 2 CO 3 ·1.5H 2 O phase, however, was easily transformed to the K 2 CO 3 phase by thermal desorption even at low temperature under low relative humidity. To enhance CO 2 capture capacity and CO 2 absorption rate, it is very important to maintain the K 2 CO 3 ·1.5H 2 O phase worked as an active species, as well as to convert the entire K 2 CO 3 to the K 2 CO 3 ·1.5H 2 O phase during CO 2 absorption at a temperature range between 50 o C and 70 o C. As a result, the relative humidity plays a very important role in preventing the transformation from K 2 CO 3 ·1.5H 2 O to the original phase (K 2 CO 3 ) as well as in producing the K 2 CO 3 ·1.5H 2 O from K 2 CO 3 , during CO 2 absorption between 50 o C and 70 o C.
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