Fly Ash-MgO infused CaO-based sorbent for high-temperature CO2 capture under realistic carbonation and harsh calcination conditions

Abstract

Calcium Looping (CaL) technologies suffer from sintering-induced agglomeration, which reduces their performance under repeated carbonation and calcination cycles. The drawback has attracted extensive research towards modifying the sorbent by adding different inert materials through various synthesis techniques. Among various inert materials, fly ash (FA) emerges as a low-cost and abundantly available candidate containing refractory material that can resist sintering. The current work investigates the infusion of an optimized proportion of FA and MgO precursor (MgO_P) into a calcium-based organic precursor (CaAc) through the sol–gel combustion synthesis to enhance carbonation conversion (X_CBN) and stabilize cyclic performance. The study includes characterizing as-synthesized and spent sorbent while evaluating cyclic capture performance thermo-gravimetrically under realistic carbonation (CO₂ = 20v/v%, t_CBN = 20 mins, T_CBN = 650 °C) and harsh calcination (CO₂ = 80v/v%, t_CALC = 10 mins, T_CALC = 900 °C) conditions with shorter transition time. The sorbent performance was optimized based on the FA/inert ratio (FA_y) and CaAc/sorbent ratio (CaAc_x_CaAc). The result showed comparatively better performance of FA_0.4 with deterioration of only 10.38 % over 5 cycles. Despite a lower X_CBN (55.77 %) of CaAc_0.8 in the 1^st cycle compared to CaAc_0.9 (79.74 %), the former exhibited more excellent cyclic stability, losing only 6.04 % in X_CBN after 5 cycles compared to the latter (38.75 %). Temperature sensitivity studies on CaAc_0.8 established 650 °C as the most suitable carbonation temperature, incurring lower deterioration than 700 °C and 750 °C. Overall, CaAc_0.8 (8 wt% FA, 12 wt% MgO_P) yielded the most stable cyclic performance (10 cycles) under realistic carbonation and harsh calcination conditions, proving its efficacy for CO₂ capture.