## 2 Materials and Methods  
During this study, vacuum residues derived from three crude oils: Urals, Siberian Light, and Basraha heavy with properties summarized in Table 1 were processed in a commercial ebullated bed hydrocracker. The processing diagram of the commercial ebullated bed vacuum residue hydrocracker is presented in Figure 3. The operating conditions of the studied vacuum residue hydrocracker are detailed in our earlier research [11; 12]. The properties of crude oils under study are presented in Table S1. The SARA composition of straight run, and hydrocracked vacuum residues was analyzed by two procedures: that described in [29], and the SAR-AD\({}^{\text{TM}}\) method, described in [30]. The relationships between both methods are described in our recent investigation [16]. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & & **Urals** & \begin{tabular}{c} **Basrah** \\ **Heavy** \\ \end{tabular} & \
\begin{tabular}{c} **Siberian** \\ **Light** \\ \end{tabular} &
\begin{tabular}{c} **VTB** \\ **Recycle** \\ \end{tabular} \\ \hline VR density at 15 C & & 0.997 & 1.071 & 0.993 & 1.0359 \\ VR Concarbon & wt.\% & 17.5 & 28.9 & 14 & 23.5 \\ VR sulphur & wt.\% & 3.0 & 7.1 & 1.58 & 1.15 \\ Sat (ref. [29]) & wt.\% & 25.6 & 12.3 & 25 & 23.5 \\ Aro (ref. [29]) & wt.\% & 52.5 & 54.1 & 61.1 & 50.8 \\ Res (ref. [29]) & wt.\% & 7.8 & 5.8 & 6.1 & 7.7 \\ C\({}_{7}\)-asp (ref. [29]) & wt.\% & 14.1 & 27.7 & 7.8 & 18.0 \\ C\({}_{5}\)-asp (ref. [29]) & wt.\% & 17.6 & 37 & 15.5 & 25.7 \\ Kin. vis. * & mm\({}^{2}\)/s & 220.9 & 731.9 & 149.1 & 114 \\ Soft point,\({}^{\circ}\)C & wt.\% & 40.1 & 68.6 & 28.9 & 38.9 \\ Sat (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 18.2 & 7.4 & 21.2 & 21.5 \\ Aro 1 (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 7.0 & 6.5 & 9.4 & 8.4 \\ Aro 2 (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 20.7 & 23.9 & 19.4 & 20.3 \\ Aro 3 (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 33.0 & 38.9 & 32.2 & 39.7 \\ Resins (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 14.0 & 13.4 & 13.4 & 4.2 \\ CyC\({}_{6}\) (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 2.4 & 3.0 & 1.3 & 0.14 \\ Toluene (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 4.4 & 6.6 & 2.9 & 5.28 \\ CH\({}_{2}\)Cl\({}_{2}\) (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 0.1 & 0.3 & 0.1 & 0.53 \\ Total Asp (SAR-AD\({}^{\text{TM}}\); ref. [30]) & wt.\% & 6.9 & 9.9 & 4.4 & 5.95 \\ Vanadium content & ppm & 255 & 187 & 116 & 45 \\ Nickel & ppm & 79 & 48 & 46 & 28 \\ \hline \hline \end{tabular}  
* These are viscosities of blends consisting of 70% vacuum residue, and 30% fluid catalytic cracking heavy cycle oil. A reduction of viscosity may be also obtained as described in [31; 32].  
\end{table} 
Table 1: Properties of vacuum residue fractions processed in the hydrocracker during the study. During the study the cascade catalyst system to add fresh catalyst was replaced by a parallel one as shown in Figure 4.  
Figure 4: Cascade and parallel modes of fresh catalyst addition employed in this study. Figure 3: Process flow diagram of the commercial ebullated bed residue hydrocracker under study. The net 540 \({}^{\circ}\)C+ vacuum residue conversion was calculated using Equation (1). \[\text{Conversion}(\text{wt.}\%)=\frac{\text{HOilFeed}_{\text{540}^{\circ}\text{C +}}-\text{HOilProduct}_{\text{540}^{\circ}\text{C+}}}{\text{HOilFeed}_{\text{540}^{ \circ}\text{C+}}} \tag{1}\]  
where,  
HOilFeed\({}_{\text{540}^{\circ}\text{C+}}\) = mass flow rate of the H-Oil feed fraction boiling above 540 \({}^{\circ}\)C determined by the high temperature simulated distillation method ASTM D 7169 of the feed and multiplied by the mass flow rate of the feed in t/h;  
HOilProduct\({}_{\text{540}^{\circ}\text{C+}}\) = mass flow rate of the H-Oil product fraction boiling above 540 \({}^{\circ}\)C determined by high temperature simulated distillation. method ASTM D 7169 of the liquid product multiplied by the flow rate of the liquid product in t/h.