Refining separation: Which solvent is conventionally used in the deasphalting of petroleum residua to separate asphaltenes from deasphalted oil?

Introduction / Context:
Deasphalting is a key residue conversion/separation step that splits heavy vacuum bottoms into deasphalted oil (DAO) and an asphaltene-rich pitch. The choice of solvent critically affects selectivity, quality of DAO, and yield of pitch.

Given Data / Assumptions:

• Feed is a petroleum residue (e.g., vacuum bottoms).
• We seek the commonly used solvent in deasphalting units.
• Options include polar and nonpolar solvents used elsewhere in refining.

Concept / Approach:
Propane deasphalting (PDA) is a long-established technology. Light paraffinic solvents such as propane (and sometimes butane/pentane variants) selectively dissolve maltenes while rejecting asphaltenes. In contrast, furfural and liquid SO2 are used for extractive processes on distillates (e.g., aromatic extraction), and MEK commonly appears in dewaxing blends (often with toluene), not deasphalting.

Step-by-Step Solution:

Verification / Alternative check:
Standard process diagrams and vendor literature universally refer to “Propane Deasphalting” for residue separation, confirming the solvent choice.

Why Other Options Are Wrong:

• Furfural: Aromatics extraction for lube/distillate improvement, not residue deasphalting.
• Methyl ethyl ketone: Common in solvent dewaxing (paired with toluene), not PDA.
• Liquid sulphur dioxide: Historical extractive solvent for aromatics, not the residue deasphalting standard.

Common Pitfalls:
Mixing up extraction services (dewaxing vs deasphalting vs aromatics extraction) due to overlapping “solvent” terminology.

Final Answer:
Propane