10.1 Introduction

• • In this lecture, we present two important processes that are used to upgrade the residue product obtained from the vacuum distillation unit.

• Significant amounts of vacuum residue is obtained from various crude oils.  For instance Arabian heavy oil produces 23.2 vol% vacuum residue product.

• The residue consists of heavier hydrocarbons with molecular weights ranging from 5000 – 10000.

• Thermal cracking is most preferable for the vacuum residue.

• The vacuum residue also consists of other metals such as vanadium and nickel.

• Typically, vacuum residue is subjected to six different operations namely

• Vacuum residue desulphurization (VRDS)

• Residue fluid catalytic cracking (RFCC)

• Visbreaking

• Coking

• Deasphalting

• Gasification

• Amongst these, Viskbreaking and Coking are prominent operations that exist in many refineries and we restrict our discussion to these processes only.

10.2 Visbreaking

• • In Visbreaking operation, a mild thermal cracking is carried out.
• • Visbreaking produces Naphtha, Gasoil and a residue. The residue has lower viscosity and pour point and hence can easily meet the requirements of the fuel oil specifications in the fuel oil blending pool.
• • Visbreaking basically breaks the long paraffinic side chains attached to aromatic structures. Due to this the residue pour point and viscosities are considerably reduced.
• • Two classes of reactions occur during visbreaking