Effects of Triethylamine- or Ammonium-Hydroxide-Impregnated Activated Carbon on Carbon Dioxide Capture

The adsorption of carbon dioxide (CO₂) in activated carbon modified by either physical or chemical treatments was investigated in this study. The physical treatment was treated with nitrogen at room temperature and then heated to 850^oC under CO₂ gas. The chemical treatment was carried out by impregnation with either triethylamine (TEA) or ammonium hydroxide (NH₄OH). Porous properties of original and modified activated carbons were determined from N₂ adsorption isotherm at 77K. The nitrogen adsorption analysis revealed that the physical treatment increased the mesopore volume of activated carbon. Conversely, for chemically impregnated with TEA samples, the Brunauer-Emmett-Teller surface area decreased with increasing TEA concentration compared to the original activated carbon. Fixed-bed adsorption experiments demonstrated an increase of CO₂ uptake with TEA-impregnated activated carbon, while physically treated carbon exhibited similar CO₂ adsorption capacity as the original material. It was found that the maximum breakthrough time was observed for activated carbon impregnated with 1% by weight TEA solution, and then it decreased with an increase in TEA concentration (3 and 5% by weight in this study). In the study of the effect of NH₄OH on the adsorption of CO₂ on activated carbons at 298K, the isotherm obtained from the original carbon was compared with carbon impregnated with 0.05, 0.25 and 0.5% by weight of NH₄OH solutions. The adsorption in activated carbon treated with 0.05% NH₄OH solution had the maximum adsorption capacity and the adsorption capacity obtained from chemically treated activated carbons was greater than that of the original one. We also analyzed the pore volume obtained from CO₂ adsorption in carbon with and without NH₄OH, the pore volume derived from CO₂ adsorption at 298K and 1 atm was less than that obtained from N₂ adsorption isotherm at 77K. Because the saturated pressures of CO₂ at 298K and nitrogen at 77K are 64 and 1 atm, respectively, the condensation inside the pore may not be observed in the case of CO₂. The pore volume of activated carbons with NH₄OH was greater than that without NH₄OH, and this led to a greater adsorbed amount in the case of activated carbon in the presence of NH₄OH. The adsorption of CO₂ in the activated carbon with and without NH₄OH at 273K was greater than that at 298K, due to its physical adsorption behavior. In the simulation study, an early onset in the adsorption isotherm can be observed for the heterogeneous pore, especially for a smaller pore width less than 0.8 nm. The simulation result and experimental data for CO₂ adsorption at 298K agreed quite well and they could be used to describe the adsorption behavior in heterogeneous carbon. Despite this, the study identified an approach for enhancing CO₂ capture selectivity using a cost-effective preparation method that is scalable for industrial applications and real-world CO₂ capture processes.