CO2 Adsorption on Supported Molecular Amidine Systems on Activated Carbon

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Abstract
The CO2 capture capacities for typical flue gas capture and regeneration conditions of two tertiary amidine N‐methyltetrahydropyrimidine (MTHP) derivatives supported on activated carbon were determined through temperature‐controlled packed‐bed reactor experiments. Adsorption–desorption experiments were conducted at initial adsorption temperatures ranging from 29 °C to 50 °C with temperature‐programmed regeneration under an inert purge stream. In addition to the capture capacity of each amine, the efficiencies at which the amidines interact with CO2 were determined. Capture capacities were obtained for 1,5‐diazo‐bicyclo[4.3.0]non‐5‐ene (DBN) and 1,8‐diazobicyclo[5.4.0]‐undec‐7‐ene (DBU) supported on activated carbon at a loading of approximately 2.7 mol amidine per kg of sorbent. Moisture was found to be essential for CO2 capture on the amidines, but parasitic moisture sorption on the activated carbon ultimately limited the capture capacities. DBN was shown to have a higher capture capacity of 0.8 mol CO2 per kg of sorbent and an efficiency of 0.30 mol CO2 per mol of amidine at an adsorption temperature of 29 °C compared to DBU. The results of these experiments were then used in conjunction with a single‐site adsorption model to derive the Gibbs free energy for the capture reaction, which can provide information about the suitability of the sorbent under different operating conditions.