Investigation on sediment formation in residue thermal conversion based processes

The thermal conversion of fifteen vacuum residual oils (VROs) having different properties was investigated in a modified high-temperature-high-pressure batch autoclave reactor. It was found that the sediment level (toluene insoluble) in the unconverted residual oil demonstrated a behavior typical for presence of induction period. The sediment level at the end of the induction period was mostly influenced by feedstock colloidal stability. The rate of sediment formation after the induction period was mostly influenced by VRO resin content. The results in this study do not support the assumption that the more aromatic VROs generate more coke-like sediments during thermal conversion. The higher density and aromatic VROs generated less sediment. The addition of high aromatic fluid catalytic cracking (FCC) slurry oil to a VRO decreased the thermal reactor surface deposit. The effect of this coke-like reactor sediment reduction is attributed to improvement in VRO asphaltene solubility by the high aromatic FCC slurry oil and a possible hydrogen donating properties of this gas oil. The use of a synthetic dispersant was found to improve the asphaltene solubility limit and extend the period of conversion without forming coke-like deposit in the thermal cracking reactor. The FCC slurry demonstrated a stronger inhibition effect on sediment formation than the synthetic dispersant probably because it is a stronger solvent and/or because it possesses hydrogen donating properties.