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 degrees C), compressed (5.0 MPa, 30.0 degrees C), liquid (15.0 MPa, 25.0 degrees C), gaseous (0.1 MPa, 30.0 degrees C) and atmospheric (0.1 MPa, 30.0 degrees 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. (C) 2012 Elsevier B.V. All rights reserved.