Gas–solid carbonation of Ca(OH)2 and CaO particles under non-isothermal and isothermal conditions by using a thermogravimetric analyzer: Implications for CO2 capture

Abstract

a b s t r a c tThe gas-solid carbonation of alkaline sorbents has been actively investigated as an alternative method to CO 2 capture from industrial combustion sources and CO 2 contained in the air. This study has a twofold objective: firstly, quantify the gas-solid carbonation extent and the carbonation kinetics of Ca(OH) 2 and CaO; and secondly, propose a reaction mechanism of gas-solid carbonation for CaO under dry conditions (relative humidity close to 0), i.e., when the action of water is negligible. The main results of our study have revealed that a high proportion of Ca(OH) 2 nanoparticles were transformed into CaCO 3 particles by gas-solid carbonation (carbonation extent, > 0.94) under non-isothermal conditions. Moreover, this gas-solid reaction requires low activation energy (E a ≈ 6 kJ/mol) at a constant heating rate of 5 or 10 K/min. A similar carbonation extent was determined for gas-solid carbonation of in situ synthesized CaO under non-isothermal conditions. However, the gas-solid carbonation of CaO takes place in a broader temperature range, implying a more complex thermokinetic behavior (overlapping of carbonation regimes or steps). Concerning the gas-solid carbonation of Ca(OH) 2 and CaO under isothermal conditions, a high carbonation extent (>0.9) was determined for CaO at 600 (873 K) and 800 • C (1073 K). Conversely, the gas-solid carbonation of Ca(OH) 2 particles was relatively low (<0.56) at 400 • C (673 K) after 6 h of reaction. This case is in agreement with the formation of a dense non-porous layer of carbonate mineral around the core of the reacting Ca(OH) 2 particles, thereby limiting the transfer of CO 2 .Finally, an alternative reaction mechanism is proposed for the gas-solid carbonation of CaO, when the relative humidity is close to 0. This macroscopic control at high temperature avoids CO 2 dissociation with molecular water at the CaO-CO 2 interface. For these specific conditions, the mineralization of adsorbed CO 2 on CaO particles implies a solid state transformation, i.e., CaCO 3 formation from CaO-CO 2 interactions. This could be explained by an atomic excitation than at high temperature allows the local migration of one oxygen atom from the solid toward the adsorbed CO 2 leading to its mineralization into carbonate (porous or non-porous layer) around the reacting particles; chemically the mineralization of CO 2 also implies the breaking of one covalent bond in the CO 2 molecule.

Mechanism of Calcium Incorporation Inside Sol–Gel Silicate Bioactive Glass and the Advantage of Using Ca(OH)2 over Other Calcium Sources

“…As a result, the gel time of the BG−CE sol decreased from 2 h 40 min with a freshly opened CE (Gelest) to 1 h 30 min after several openings, which is the typical gel time measured for BG−CH sols (Table 1). Likewise, CH is known to progressively partially form CaO (upon dehydration) 43 and CaCO 3 (via carbonation) 44 under storage until a thermody namic equilibrium is reached. According to our experiments, the carbonation of CH is, however, very slow since its FTIR spectrum remains unchanged after 2 months of storage under ambient atmosphere (Figure 2b).…”

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)2

“…13,15,30 Note that the step increase in the CaCO 3 growth curve is not accompanied by an equivalent disappearance of CaIJOH) 2 . 350°C.…”

Solid sorbents for in-situ CO 2 removal during sorption-enhanced steam reforming process: A review

“…At high temperature atomic excitation allows the local migration of oxygen atoms from CaO toward the adsorbed CO 2 leading to its mineralization into carbonate around CaO particles; chemically the mineralization of CO 2 also implies the breaking of one covalent bond in the CO 2 molecule [24]. Typical optimal carbonation/regeneration parameters and details for different CaO-based sorbents are summarized in Table 1 [25][26][27][28][29][30][31][32][33][34][35][36][37].…”