# Purification of Produced Water by Solvents to Enhance Oil Recovery and Reuse Separated Droplets
## 4 Discussion
### Hansen Solubility Parameters and Produced Water
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Number** & **Solvent** & \(\mathbf{d_{D}}\) & \(\mathbf{d_{P}}\) & \(\mathbf{d_{H}}\) & **“Effective Destabiliser”** \\ \hline
1 & Acetonitrile & 15.3 & 18.0 & 6.1 & 0 \\
2 & Acetic acid & 14.5 & 8.0 & 13.5 & 0 \\
3 & Isopropyl myristate & 14.4 & 4.0 & 4.3 & 0 \\
4 & Glyerin & 17.4 & 12.1 & 29.3 & 0 \\
5 & Tetrachloroethylene & 18.3 & 5.7 & 0.0 & 1 \\
6 & Toluene & 18.0 & 1.4 & 2.0 & 0 \\
7 & Diethanolamine & 17.2 & 10.8 & 21.2 & 0 \\
8 & 2-Phenylethylanol & 19.0 & 5.8 & 12.8 & 0 \\
9 & n-Butyl acrylate & 15.6 & 6.2 & 4.9 & 0 \\
10 & Dimethyl sulfoxide & 18.4 & 16.4 & 10.2 & 0 \\
11 & Chloroform & 17.8 & 3.1 & 5.7 & 1 \\
12 & Acetone & 15.5 & 10.4 & 7.0 & 0 \\
13 & Ethanol & 15.8 & 8.8 & 19.4 & 1 \\
14 & Dichloromethane & 18.2 & 6.3 & 6.1 & 1 \\
15 & Methanol & 15.1 & 12.3 & 22.3 & 1 \\
16 & Isobutyl methacrylate & 15.8 & 4.9 & 10.7 & 0 \\
17 & Cyclohexane & 16.8 & 0.0 & 0.2 & 1 \\
18 & n-Heptane & 15.0 & 1.1 & 2.6 & 1 \\
19 & Butanone & 16.0 & 9.0 & 5.1 & 0 \\
20 & Limonene & 17.2 & 1.8 & 4.3 & 0 \\
21 & Benzene & 18.4 & 0.0 & 2.0 & 1 \\
22 & 2-Propanol & 15.5 & 6.1 & 16.4 & 1 \\
23 & 1-Butanol & 16.0 & 5.7 & 15.8 & 1 \\
24 & Polyethylene glycol 400 & 25.9 & 11.2 & 12.9 & 0 \\
25 & Decyl oleate & 19.6 & 1.6 & 10.7 & 0 \\
26 & Ethyl acetate & 15.8 & 5.3 & 7.2 & 0 \\
27 & Diproylene glycol & 16.5 & 10.6 & 17.7 & 0 \\
28 & Propylene glycol & 16.8 & 9.4 & 23.3 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Hansen solubility parameters of the tested solvents, MPa\({}^{1/2}\), and ability to destabilise oil emulsions in produced water. After entering this information into the Techne Solubility 3S software, it was found that, exceptionally, produced water exhibits three solubility spheres (Figure 9). This explains why solvents with very different cohesion energies are capable of effectively destabilising oil emulsions in produced water and purifying it. The most lipophilic solvents are grouped within the sphere with the lowest hydrogen-bonding solubility parameter (sphere L). In contrast, the most hydrophilic solvents, with the highest hydrogen-bonding parameter, are in sphere H, while those with an intermediate hydrogen-bonding parameter are found in sphere LH. The figure presents two- and three-dimensional representations of the spheres, while Table 5 displays the solubility parameters of the centres of the spheres and their radii. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Number** & **Solvent** & \(d_{D}\) & \(d_{P}\) & \(d_{M}\) & **“Effective Destabiliser”** \\ \hline
29 & Polypropylene glycol 2000 & 15.0 & 6.3 & 10.6 & 0 \\
30 & Vaseline (liquid) & 18.6 & 0.3 & 3.4 & 0 \\
31 & Liquid paraffin & 16.4 & 0.1 & 0.2 & 0 \\
32 & Petroleum ether & 14.4 & 0.0 & 0.0 & 0 \\
33 & Xylene & 17.6 & 1.0 & 3.1 & 1 \\
34 & N,N-Dimethyl formamide & 17.4 & 13.7 & 11.3 & 1 \\
35 & Isocatne & 15.2 & 0.0 & 0.0 & 0 \\
36 & Dietibly ether & 14.5 & 2.9 & 5.1 & 1 \\
37 & Tetrahydrofuran & 16.8 & 5.7 & 8.0 & 1 \\
38 & Ethylene glycol & 17.0 & 11.0 & 26.0 & 1 \\
39 & Cyclohexanone & 17.8 & 6.3 & 5.1 & 1 \\
40 & 1-propanol & 16.0 & 6.8 & 17.4 & 1 \\ \hline \end{tabular}
\end{table} 
Table 4: _Cont._  
Figure 9: Graphical representation of the solubility spheres of produced water. On the axes, according to the nomenclature provided by the Techne Solubility 3S software, D, P, and H represent \(\delta\)D, \(\delta\)P, and \(\delta\)H, respectively. The red points represent solvents that are effective destabilisers, while the white points represent those that are not. In the 2D representations, there are white points that may appear to be inside the spheres; however, other than a few exceptions, they are actually located in front of or behind the spheres.