Sorption-enhanced water gas shift reaction by sodium-promoted calcium oxides

The water gas shift reaction was evaluated in the presence of novel carbon dioxide (CO2) capture sorbents, both alone and with catalyst, at moderate reaction conditions (i.e., 300–600 °C and 1–11.2 atm). Experimental results showed significant improvements to carbon monoxide (CO) conversions and production of hydrogen (H2) when CO2 sorbents are incorporated into the water gas shift reaction. Results suggested that the performance of the sorbent is linked to the presence of a Ca(OH)2 phase within the sorbent. Promoting calcium oxide (CaO) sorbents with sodium hydroxide (NaOH) as well as pre-treating the CaO sorbent with steam appeared to lead to formation of Ca(OH)2, which improved CO2 sorption capacity and WGS performance. Results suggest that an optimum amount of NaOH exists as too much leads to a lower capture capacity of the resultant sorbent. During capture, the NaOH-promoted sorbents displayed a high capture efficiency (nearly 100%) at temperatures of 300–600 °C. Results also suggest that the CaO sorbents possess catalytic properties which may augment the WGS reactivity even post-breakthrough. Furthermore, promotion of CaO by NaOH significantly reduces the regeneration temperature of the former.