An important phenomenon that must be controlled during the resids conversion is the possible phase separation that might occur if the reacting mixture reaches the instability condition, that is to say the condition that gives rise to the asphaltene precipitation into the reactor. In fact, during conversion, the thermal decomposition of the asphaltenes generates dealkylated and more aromatic intermediates which are less soluble in the original hydrocarbon phase. Over a certain level of conversion, asphaltenes become incompatible with oil matrix and precipitate producing an "unstable oil" which can cause fouling problems and coke deposition (Figure 1).
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