## 2 Methodology
### Experimental Procedure  
#### 2.4.1 Absorption of CO\({}_{2}\)  
The equipment for the absorption experiment is shown in Figure 2, including the bubble column, cooling circulator, tubing pump, CO\({}_{2}\) detector, heater, mass flow controller, and pressure gauge. The sodium glycitane solution absorbs the CO\({}_{2}\) in the bubble column, under a constant pH environment, then the simulated blue gas concentration (15%) and temperature (50 \({}^{\circ}\)C) from the coal-fired power plant are pumped into the column. First, the absorbent concentration for the experiment is prepared--the CO\({}_{2}\) detector (Guardian Plus, D600, Hartford, CT, USA), pressure indicator (SR-321), pH controller (Suntex, PC-310, New Taipei City, Taiwan), and heating controller (5020 Data Acquisition System) are switched on; the mass flow controller (N\({}_{2}\) and CO\({}_{2}\)) (Bronkhorst, F-201 CB DMFC) is adjusted to the correct flow for the experiment; and the CO\({}_{2}\) concentration is changed to 15%. The heater is switched on, and the temperature is controlled at 50 \({}^{\circ}\)C. The cooling circulator ([PERSON], D-620, New Taipei City, Taiwan) is switched on and the temperature for the experiment is set. When the gas inlet temperature is fixed at 50 \({}^{\circ}\)C, the CO\({}_{2}\) concentration is fixed at 15%, and the corrected pH electrode is plugged in the bubble column for operation. The initial CO\({}_{2}\) concentration, pH, liquid temperature, gas temperature, gas inlet pressure, and absorbent feed volume are recorded.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **pH** & \(Q_{g}\) & \(T\) & \(C_{L}\) \\ \cline{2-5}  & **(-)** & **(L min\({}^{-1}\))** & **(\({}^{\circ}\)C)** & **(M)** \\ \hline
1 & 9.5 & 3 & 25 & 3 \\
2 & 9.5 & 5 & 30 & 4 \\
3 & 9.5 & 7 & 35 & 5 \\
4 & 9.5 & 9 & 40 & 6 \\
5 & 10 & 3 & 30 & 5 \\
6 & 10 & 5 & 25 & 6 \\
7 & 10 & 7 & 40 & 3 \\
8 & 10 & 9 & 35 & 4 \\
9 & 10.5 & 3 & 35 & 6 \\
10 & 10.5 & 5 & 40 & 5 \\
11 & 10.5 & 7 & 25 & 4 \\
12 & 10.5 & 9 & 30 & 3 \\
13 & 11 & 3 & 40 & 4 \\
14 & 11 & 5 & 35 & 3 \\
15 & 11 & 7 & 30 & 6 \\
16 & 11 & 9 & 25 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Orthogonal array in the absorption study.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multicolumn{1}{c}{**Factor**} & **1** & **2** & **3** & **4** \\ \hline (A) pH & 9.5 & 10 & 10.5 & 11 \\ (B) \(Q_{g}\) [L min\({}^{-1}\)] & 3 & 5 & 7 & 9 \\ (C) \(T\) [\({}^{\circ}\)C] & 25 & 30 & 35 & 40 \\ (D) \(C_{L}\) [M] & 3 & 4 & 5 & 6 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Parameters and levels in the absorption study. \(Q_{g}\)—gas flow rate; \(C_{L}\)—solvent concentration.  
Subsequently, the solvent is poured into the column until it overflows, and the initial solution volume in the column is recorded. The tubing pump controller (EASY-LOAD, 7518-00) and pH electrode controller are switched on for timing. As the pH decreases after the solution absorbs CO\({}_{2}\), the pH controller injects the sodium glycinate solution into the column automatically, so that the pH is controlled. The experimental data are recorded once every 5 min, and 10 mL of solution is taken as the sample every 10 min. When the CO\({}_{2}\) concentration measured by the CO\({}_{2}\) detector reaches a steady state, the experiment can be ended.