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