The effect of relative humidity on CO_2 capture capacity of potassium-based sorbents

摘要

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_2CO_3 could be easily converted into K_2CO_3·1.5H_2O working as an active species by the absorption of water vapor as the following reaction: K_2CO_3+3/2 H_2O→K_2CO_3·1.5H_2O. One mole of K_2CO_3·1.5H_2O absorbed one mole of CO_2 as the following reaction: K_2CO_3·1.5H_2O+CO_2↔2KHCO_3+0.5 H_2O. The K_2CO_3·1.5H_2O phase, however, was easily transformed to the K_2CO_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_2CO_3·1.5H_2O phase worked as an active species, as well as to convert the entire K_2CO_3 to the K_2CO_3·1.5H_2O phase during CO_2 absorption at a temperature range between 50 ℃ and 70 ℃. As a result, the relative humidity plays a very important role in preventing the transformation from K_2CO_3·1.5H_2O to the original phase (K_2CO_3) as well as in producing the K_2CO_3·1.5H_2O from K_2CO_3, during CO_2 absorption between 50 ℃ and 70℃.