## 4 Discussion  
Our previous experience documented in [2; 11; 17] showed that the sediment content in the ATB (atmospheric tower bottom) product and the fouling rate are within the acceptable limits during processing Urals or Siberian Light vacuum residues when the conversion is not higher than 60%. This can also be seen from the data shown in Figures 1 and 2. For the investigated period of time, as apparent from the data in Figure 5, the periods when 100% Urals and Siberian Light vacuum residues were processed were between 17 May 2022 and 15 August 2022, and between 15 October 2022 and 28 November 2022. Table 2 summarizes the main performance indicators extracted from the data in Figures 6-9 and 12. The data in Table 2 indicate that, similar to the previous experience [2; 11; 17] with processing Urals and Siberian Light vacuum residues at a conversion level of 67 wt.% (17 May 2022), although the sediment content in the ATB was not higher than the acceptable limit of 0.40 wt.%, the fouling rate was unacceptably high, suggesting a need for reaction temperature reduction. The HDM extent for that date was the lowest for the four cases in Table 2--58.2%. The \(\Delta\)T of the first reactor was also the lowest--58 \({}^{\circ}\)C. The end of the first period (15 August 2022) demonstrated a 9.1 wt.% higher conversion due to the reaction temperature enhancement by 11 \({}^{\circ}\)C. Irrespective of reaction temperature augmentation, no magnification in ATB sediment content was observed. The HDM extent, however, showed a remarkable enhancement of 27.5% (abs.). This data suggests that the HDM enhancement may be responsible for the much better performance on 15 August 2022 relative to that registered on 17 May 2022. The second period with the processing of 100% Urals and Siberian Light vacuum residues between 15 October 2022 and 28 November 2022 shows  
Figure 13: Relation of hydrodeasphaltization to vacuum residue net conversion. further improvement of the hydrocracker's performance, reaching the conversion level of 82.7 wt.% at the lowest ATB sediment content of 0.12 wt.% and the remarkably high HDM extent of 97.9%. The data in Table 2 exhibits that although the case 28 November 2022 was characterized by the highest asphaltene content in the hydrocracked vacuum residue, the fouling rate and sediment content were not affected by this fact. This observation is in line with the finding reported in our recent research [16] that the asphaltene content in the hydrocracked residual oils does not correlate with sediment formation or fouling rates. As reported by [PERSON] et al. [37], the sediment content is dependent on asphaltene content and asphaltene stability. The data in Table 2 may suggest that the asphaltenes in the case 28 November 2022 should have the highest stability because they have the highest concentration, which in principle facilitates precipitate formation, but on the other hand, this case exhibited the lowest ATB sediment content. A possible explanation for this observation is the highest HDM extent of that case. The metals in vacuum residues are mainly concentrated in asphaltenes and resins [38; 39; 40]. [PERSON] [41], and [PERSON] et al. [42] reported that approximately 80% of total asphaltene vanadium presents in the form of nanoaggregates. They conclude that the intercommunication of metalloporhyrins concentrated in the asphaltene fraction seems to have a crucial role in the association of asphaltenes. Their results suggest that the association of metal porphyrins with asphaltene molecules is a general form of metal-containing compounds present in asphaltenes [41; 42]. Thus, the higher extent of metal removal from the vacuum residue during hydrocracking may contribute to the reduction of the content of these compounds, which facilitate aggregation with asphaltene molecules, which eventually leads to a lower extent of aggregation, precipitate formation, and fouling. Data shown in Figures 5 and 7-9 were extracted in the form of Table S2 and processed by the intercriteria analysis (ICrA).