There has been an increased interest in the use of solid sorbents for CO2 capture from flue gases to reduce emissions from fossil energy. This work uses a simple Carnot engine-like model to compare the energy requirements for a CO2 capture process using a solid adsorbent in a circulating fluidized bed with its minimal thermodynamic needs and with the performance of a conventional liquid solvent process. The energy requirements for CO2 capture using thermal swing separation sorption are dominated by the standard Gibbs free energy of separation from the sorbent (Δg0,sep), the sensible heat needed to reach the desorption temperature, and loading optimization to avoid thermodynamic pinching effects. The Δg0,sep is an invariant of the system, so only its value at reference conditions is required and it is independent of the desorption temperature or the heat of evaporation of a liquid solvent. A baseline is established using the Δg0,sep as well as the equivalent work for a well-established amine process. In all cases the energy requirements are found to be well above the minimum thermodynamic values and those of conventional liquid absorption. Higher-capacity solid sorbents and challenging improvements on heat recovery will be needed to close the gap.