Multiobjective Evaluation of Amine-Based Absorbents for SO2 Capture Process Using the pKa Mathematical Model

Abstract

The screening of high-efficiency and low-energy consumption absorbents is critical for capturing SO2. In this study, absorbents with better performance are screened based on mechanism, model, calculation, verification, and analysis methods. The acidity coefficient (pKa) values of ethylenediamine (EDA), piperazine (PZ), 1-(2-hydroxyethyl)piperazine (HEP), 1,4-bis(2-hydroxyethyl)piperazine (DIHEP), and 1-(2-hydroxyethyl)-4-(2-hydroxypropyl)piperazine (HEHPP) are calculated by quantum chemical methods. A mathematical model of the SO2 cyclic absorption capacity per amine (αc) in the amine-based SO2 capture process is built based on the electroneutrality of the solution. Another model of desorption reaction heat (Qdes) is also built based on the van’t Hoff equation. Correspondingly, αc and Qdes of the above five diamines are calculated and verified with the experimental data. The results show that αc of the diamine changes with the increase in the pKa value, and the increase in the pKa value directly leads to changes in Qdes. The order of αc of the above five diamines is EDA > PZ > HEHPP > HEP > DIHEP, and the order of Qdes is EDA > PZ > HEHPP > DIHEP > HEP. The multiobjective analysis between αc and Qdes suggests that it is not advisable to simply pursue a higher αc while ignoring Qdes. The compound quaternary system absorbent has a wider range of αc than the single ternary absorbent, which is the direction of absorbent development. This study is expected to strengthen absorbent screening for the amine-based SO2 capture process from flue gas.