Self-activation and effect of regeneration conditions in CO2–carbonate looping with CaO–Ca12Al14O33 sorbent

Abstract

CO2 capture by solid sorbents through uptake–regeneration cycling is a promising option for high temperature removal of CO2 from combustion gases and synthesis/fuel gases. The present study investigates the influence of regeneration atmosphere and temperature on the CO2 uptake capacity during repeated cycling of CaO-based solid sorbents. The sorbents were synthesised to contain 75 and 85% w/w of active phase (CaO) and binder (Ca12Al14O33) and were then subjected to cycling tests with repeated CO2 uptake and release in a thermogravimetric analyser TGA for up to 200 cycles. Test conditions were chosen to test high temperature CO2 capture at 600°C in an atmosphere containing 14 and 25% v/v CO2 (N2 balance). Three different regeneration conditions were tested:(a)mild condition: regeneration at 900°C in 14% CO2 or 100% N2;(b)moderate condition: regeneration at 1000°C in 14% CO2; and(c)severe condition: regeneration at 1000°C in 86% CO2.Hydration of the sorbent during synthesis and prolonged carbonation prior to the cycling tests significantly improved the stability of the uptake capacity. Interestingly, the pretreated 75% w/w CaO synthetic sorbent maintained a good uptake capacity up to the 150th cycle under severe regeneration conditions and even showed continuously increasing CO2 uptake capacity throughout the 150 cycle test with 25% CO2. The 75% w/w CaO sorbent is thus an interesting candidate for future work on high temperature CO2 capture.