Assessment of CO_2 Adsorption Capacity on Activated Carbons by a Combination of Batch and Dynamic Tests

摘要

In this work, batch and dynamic adsorption tests are coupled for an accurate evaluation of CO_2 adsorption performance of three different activated carbons (AC) obtained from olive stones by chemical activation followed by physical activation with CO_2 at varying times (i.e., 20, 40, and 60 h). Kinetic and thermodynamic CO_2 adsorption tests from simulated flue gas at different temperatures and CO_2 pressures are carried out under both batch (a manometric equipment operating with pure CO_2) and dynamic (a lab-scale fixed-bed column operating with a CO_2/N_2 mixture) conditions. The textural characterization of the AC samples shows a direct dependence of both micropore and ultramicropore volume on the activation time; hence, AC60 has the higher contribution. The adsorption tests conducted at 273 and 293 K showed that when CO_2 pressure is lower than 0.3 bar, the lower the activation time, the higher CO_2 adsorption capacity; a ranking of ω_(eq)(AC20) >ω_(eq)(AC40) >ω_(eq)(AC60) can be exactly defined when T = 293 K. This result is likely ascribed to the narrower pore size distribution of the AC20 sample, whose smaller pores are more effective for CO_2 capture at higher temperature and lower CO_2 pressure, the latter representing operating conditions of major interest for decarbonation of flue gas effluent. Moreover, the experimental results obtained from dynamic tests confirm the results derived from the batch tests in terms of CO_2 adsorption capacity. It is important to highlight the fact that the adsorption of N_2 on the synthesized AC samples can be considered to be negligible. Finally, the importance of proper analysis for data characterization and adsorption experimental results is highlighted for the correct assessment of the CO_2 removal performance of activated carbons at different CO_2 pressures and operating temperatures.