4 | RESULTS OF pKa AND DISCUSSIONS
Table S4 in the SI section is an example of the recorded pH values and the calculation steps for the pKa of MDEA at 298.15K. In particular, the first column is the number of moles of neutral MDEA which remained in the solution after adding the hydrochloric acid. The second column is the total volume of the acid added. The third column represents the moles of the protonated amine which are assumed as the same as the moles of added HCl. The pH column is the recorded stable pH value at each step. The last three columns are the dissociation constant values before the thermodynamic correction, the value of the thermodynamic correction and the dissociation constant values after thermodynamic correction, respectively. Equation 6 represents the relationship between the three quantities:
\begin{equation} {pK}_{a}=\ {pK}_{a}^{M}-TC\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (6)\nonumber \\ \end{equation}
The measurements of pKa values of MDEA in the temperature range varying from 298.15K to 313.15K are summarized and compared with literature data14-16 in Figure S1 and Table S3. The values of this study and literature are in excellent agreement. The dissociation constants of the eight studied amines in addition to MDEA and monoethanolamine (MEA)9 in the same temperature range were determined. In the eight amines studied, three amines (DMAOEOE, DBEA and PEA) are monoamines while two (2DMAOEE and 2-MPMDA) were diamines. Final the remaining three amines (2AOE13PDA, DMAPAPA and DAOMDPA) were triamines. The first, second and third dissociation constants of the amines were reported in Tables 1 to 3 and Figures 1 to 3, respectively.
Table 1 pKa1­ values for the eight studied amines, MDEA and MEA at various temperatures a