High-pressure gas–solid carbonation route coupled with a solid ionic liquid for rapid synthesis of rhombohedral calcite

A novel carbonation route for the synthesis of CaCO3 is reported with high pressure CO2 scintillated into dry Ca(OH)2 powder containing a solid ionic liquid (SIL, tetra-n-heptyl-ammonium bromide). Results show that calcite structure with rhombohedral lattice is produced at all CO2 conditions investigated: supercritical (15.0 MPa, 50.0 °C), compressed (5.0 MPa, 30.0 °C), liquid (15.0 MPa, 25.0 °C), gaseous (0.1 MPa, 30.0 °C) and atmospheric (0.1 MPa, 30.0 °C). Furthermore, rapid and complete conversion is achieved under the supercritical condition with the production of nano-sized calcite particles, suggesting that coupling SIL with CO2 could be an effective system for enhancing traditional gas–solid reactions. A mechanism for the rapid gas–solid carbonation reaction is proposed with emphasis on the initialization of the reaction by tiny adsorbed water and CO2 dissolved in the SIL.