Surya Chandra TIWARI1, Sreedevi UPADHYAYULA1, Kamal Kishore PANT1
1Indian Institute of Technology Delhi, New Delhi, India
CO2 capture using benign cost-effective solvents is an essential unit operation not only in the process industry for CO2 separation and recovery from industrial off-gas streams but also for direct capture from air to clean the environment. Several solvents are identified, by researchers, with high CO2 capture efficiency due to their favorable chemical and physical properties, interaction mechanism with CO2, and low regeneration energy cost. However, N-Methyldiethanolamine (MDEA) is the most frequently used solvent for CO2 capture with promoters such as piperazine (Pz) and monoethanolamine (MEA). These promoters have several issues, such as low thermal stability, heat-stable salt formation, and being highly degradable. Therefore, new class promoters need to be used to overcome these issues. Dual-functionalized ionic liquids (DFILs) have the potential to overcome these limitations. Hence, in this work, two new class dual-functionalized ionic liquids (DFILs) were used as promoters and determined their role in enhancing CO2 absorption performance. The CO2 absorption is performed at different pressure (2 bar, 4.4 bar, and 7 bar) and different temperature (303, 313,323, and 328K). The results confirmed that CO2 loading increases around 18 to 22% after 5wt% FILs blended in the MDEA. It was noticed that the CO2 loading increases with increasing pressure and decreases with increasing temperature for all absorbent systems. Further, the equilibrium CO2 solubility data are correlated using a semi-empirical model and an equilibrium-based Modified Kent-Eisenberg model, which shows a better agreement with the generated experimental data. The accuracy in terms of %ADD for T-Im, and D-Im blend systems were found, and 1.63% and 1.90%, respectively. These data were further used to determine the concentration profile of ions with respect to CO2 loading and the result showed that bicarbonate formation is much higher for both systems, which is also confirmed in the 13C NMR result. Additionally, for the thermodynamics study of these systems, the heat of absorption, Gibbs free energy, and entropy is calculated. It was noticed that the heat of absorption of T-Im blend system is slightly lower than D-Im blend system, which is 50.32 and 52.06 (kJ/mol), respectively. Typically, lower heat of absorption reduces the energy required for the regeneration process. Since Gibbs free energy and entropy increase with increasing temperature, therefore, high temperature is not favorable for effective CO2 absorption. Overall, this work will provide a systematic insight that will assist researchers and engineers in understanding an absorption solvent’s efficacy for CO2 capture comprehensively.