Improved Hydrotalcite-type Compounds for Post-Combustion CO2 Abatement

摘要

Among the greenhouse gasses, CO2 emissions are of great concern. Releasing 4Gt fossil carbon results in an annual increase in the atmospheric concentration of CO2 by 1 ppm. As the demand for fuel increases progressively with worldwide economic progress, CO2 emissions become a stringent problem; scientists are looking for solutions to deal with this problem. CO2 capture and storage is one of the only viable options for capturing CO2 emissions from stationary point sources. Post-combustion CO2 capture systems could be retrofit to existing and new point CO2 sources, such as power plants. The current state of the art technology utilizes an aqueous amine solution in a temperature swing for CO2 capture. There are several potential advantages of using solid materials, such as a lower specific heat capacity and less evaporation of moisture. However, significant improvements in sorbent performance are still necessary. Specifically, the cost, stability, attrition, and interaction with flue gas constituents are of concern. This work exploits the possibility to change the characteristics of the hydrotalcite-type materials by increasing their CO2 physisorption properties in order to make them more suitable for the post-combustion technologies. By inducing changes during the preparation of hydrotalcite-type compounds and/or addition of dopants such as Zr~(4+) it has been possible to modify the structure of these materials by lowering the strength of the water bonding to the surface of the material. This leads to the decrease of the temperature where the dehydration takes place. Moreover, this gives higher than normal CO2 capacities at low temperatures which are explained through the existence of weak basic sites. This behaviour is temperature dependent and gives scope to exploit the structural characteristics of the hydrotalcite type compounds for developing new materials which to compete with amine based systems in terms of energy efficiency. The hydrotalcites have been evaluated at the laboratory scale. The importance of activation temperature, moisture, and testing procedure has been highlighted. The deactivation is only related to the dehydration process and the process is reversible as no structural modification at the level of octahedral layers can be observed.