Deasphalting step choice: Which solvent is most suitable for solvent deasphalting of vacuum residue to produce deasphalted oil (DAO)?

Introduction:
Solvent deasphalting (SDA) separates asphaltenes from vacuum residue to yield a cleaner deasphalted oil (DAO) for further upgrading (e.g., hydrocracking, FCC). The choice of solvent controls selectivity and yield.

Given Data / Assumptions:

• Feed: vacuum residue rich in asphaltenes/resins.
• Goal: maximize DAO quality while rejecting asphaltenes/metals.

Concept / Approach:
Light paraffinic solvents (propane, butane, pentane) dissolve maltenes while precipitating asphaltenes. Propane is the classic SDA solvent, offering good selectivity for DAO quality. MEK is used in dewaxing, not SDA. Doctor’s solution is for sweetening (H2S/mercaptans). Methanol amine is for gas treating (acid gas removal).

Step-by-Step Solution:

Verification / Alternative check:
Refinery flowsheets list propane deasphalting units as common SDA installations.

Why Other Options Are Wrong:

• MEK: Dewaxing solvent, not SDA.
• Doctor’s solution: Sweetening, not SDA.
• Methanol amine: Amine treating for gases, not SDA.
• Toluene-only: Aromatic solvent dissolves asphaltenes, defeating precipitation.

Common Pitfalls:
Confusing dewaxing or sweetening chemistries with SDA.

Final Answer:
Propane