## 4 Wax Problems and Use of Solvents in the Oil Industry
### Pour Point Depressants (PPDs)  
Pour point depressants (PPDs) are a solution in heavy or extra-heavy crude oils where the main problem is flowability, especially from offshore to ground facilities [92; 93]. A crystal candle modifier, also called a PPD, is a chemical that determines the solubility of wax, adsorption, and nucleation. The modification of wax crystallization may help depress the crude oil's pour point, viscosity, and yield stress appreciably [94]. Many polymers have been used as pouring depressants. In heavy waxed oils, high-branched poly-\(\alpha\)-olefins, long-chain fatty acid amides, poly-n-alkyl, acrylates, methacrylate copolymers [95], alkyl ester copolymer carboxylic acids, unsaturated \(\alpha\)-olefin, ethylene-vinyl fatty acid esters, vinyl acetate-\(\alpha\)-olefins, and maleic anhydride copolymers are used. A number of patents have been generated for these polymers [92]. Examining the effect any different PPDs on the viscosity, pouring point, and temperature of the candle selection proved that PPD substances are able to reduce the wax crystals, changing the growth \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Characteristic**} & \multicolumn{4}{c}{**Slack Waves**} \\ \cline{2-4}  & **Light** & **Middle** & **Heavy** \\ \hline \multirow{3}{*}{Congealing point, \({}^{\circ}\)C} & 48 & 59 & 62.5 \\  & Kinematic viscosity, 98.9 \({}^{\circ}\)C & 3.04 & 4.30 & 6.00 \\  & Refractive index, 98.9 \({}^{\circ}\)C & 1.4224 & 1.4270 & 1.4402 \\  & Density, 70 \({}^{\circ}\)C & 0.7920 & 0.8035 & 0.8107 \\  & Mean molecular weight & 384 & 446 & 477 \\  & Oil content, wt.\% & 5.32 & 6.23 & 23.05 \\  & Cone penetration, 25 \({}^{\circ}\)C & 17 & 13 & 28 \\  & Needle penetration, \({}^{\circ}\)C & 43 & 40 & 59 \\  & Sulfur content, wt.\% & 0.09 & 0.10 & 0.22 \\  & Color (ASTM D-1500) & 1.0 & 1.5 & 3.0 \\ \hline \multicolumn{4}{c}{**Carbon Distribution Analysis**} \\ \hline \% C\({}_{\rm A}\) & 5.93 & 8.41 & 10.46 \\  & \% C\({}_{\rm N}\) & 12.85 & 14.20 & 29.44 \\  & \% C\({}_{\rm R}\) & 18.78 & 22.61 & 39.90 \\  & \% C\({}_{\rm P}\) & 81.22 & 77.39 & 60.10 \\ \hline \multicolumn{4}{c}{**Molecular Type Composition**} \\ \hline \multicolumn{4}{c}{Total saturates, wt.\%} & 97.63 & 96.97 & 86.18 \\  & n-paraffin content, wt.\% & 74.71 & 62.89 & 35.07 \\  & Iso- and cyclo-paraffin content, wt.\% & 22.92 & 34.08 & 51.11 \\  & Total aromatics, wt.\% & 2.37 & 3.03 & 13.82 \\  & Mono- aromatics, wt.\% & 2.37 & 3.03 & 11.52 \\  & di- aromatics, wt.\% & - & 2.30 \\ \hline \multicolumn{4}{c}{\% C\({}_{\rm A}\)—percentage of aromatic carbon per average molecule = \% C\({}_{\rm R}\)– \% C\({}_{\rm A}\)} \\  & \% C\({}_{\rm R}\)– \% C\({}_{\rm N}\) + \% C\({}_{\rm A}\) \\  & \% C\({}_{\rm P}\)—percentage of paraffinic carbon per average molecule = 100\% C\({}_{\rm R}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical characteristic carbon distribution analysis and molecular type composition of slack wax crudes [91]. characteristics and surface of the crystal at metal surfaces that are attached like pipe walls [96], as shown in Figure 3. Studies were able to reduce crude oil from 1000 cP to 10 cP at 10 C-20 C in all of these additives, which increased the flow of crude oil. The following effect on the viscosity of crude oil was successfully modeled by regulating lower melting temperatures for wax molecules in the range of C\({}_{21}\) to C\({}_{45}\) in the presence of additives that increase flow [95]. Several studies have been conducted in Mexico to test the rheological properties of light and heavy oils by measuring pouring depressant performance using a combination of vinyl acetate, styrene, and n-butyl acrylate, and viscosity was reduced at 25 C and 50 C[97]. In other studies, the viscosity in heavy crude oil dropped at 25 C and in light crude oil at 313 K due to the depressant pour point [92]. Figure 4 shows the effect of concentration on the depressant pour point. The pour point can be reduced at 11 C and a dose of 400 ppm.