Impact of pressure on coking of vacuum residue

Thermal conversion of vacuum tower bottoms (VTB) and its narrow‐cut distillation fractions were studied at 530°C between 0.1 and 2 MPa pressure to assess the effect of the reaction pressure on coking. Coke yield in the VTB conversion increased with pressure, which was found to be mostly due to the enhanced coking of the 700°C+ narrow cut. The microcarbon residue in the liquid remained unaffected. The yield of products with a boiling point below 510°C, including distillate and by‐product lights, decreased with the pressure increase. The trend was a cumulative effect of the increased yields from the VTB cuts boiling below 635°C and the decreased yields from the heavier cuts. Admixing different VTB cuts into the VTB feed resulted in the weighted average changes with no synergistic or antagonistic effects.