Difficulty: Medium
Correct Answer: Lubricating oils to improve viscosity index and stability
Explanation:
Introduction / Context:
Solvent extraction with polar solvents like furfural, phenol, or NMP is a classic refining step for improving base oil quality. The process removes aromatics and polar compounds that degrade viscosity index, oxidation stability, and color in lubricating oils.
Given Data / Assumptions:
Concept / Approach:
A two-phase extraction contacts lube distillate with furfural. Aromatics preferentially partition into the solvent-rich extract, while the raffinate is enriched in paraffinic and naphthenic molecules that possess higher viscosity index and better oxidative behavior. Downstream, solvent is recovered and streams are further finished by dewaxing and hydrotreating.
Step-by-Step Solution:
Verification / Alternative check:
Refining schemes show furfural extraction units in lube trains prior to solvent dewaxing and hydrofinishing. Performance metrics include viscosity index gain and Conradson carbon reduction.
Why Other Options Are Wrong:
Naphtha: Typically reformed or hydrotreated; not extracted by furfural for octane uplift. Wax: Upgraded by deoiling and dewaxing, not aromatic extraction. Cracking feed: Quality is adjusted by hydrotreating; extraction is uncommon for FCC feed prep.
Common Pitfalls:
Confusing solvent extraction for aromatics with solvent dewaxing that targets high pour point paraffins; they are distinct steps.
Final Answer:
Lubricating oils to improve viscosity index and stability
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