Lube refining: Which treatment produces appreciable improvement in the viscosity index (VI) of lubricating oil by selectively removing low-VI components?
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AAcid treatment
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BSolvent extraction
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CAlkali treatment
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DClay treatment
Answer
Correct Answer: Solvent extraction
Explanation
Introduction / Context:Lubricating oil base stocks require good viscosity-temperature behavior. Refining steps aim to remove components that degrade VI, oxidation stability, or low-temperature flow.
Given Data / Assumptions:
- Objective: appreciable increase in VI.
- Processes considered: acid, solvent extraction, alkali, and clay treatment.
- Feed: lube distillates prior to dewaxing/finishing.
Concept / Approach:Solvent extraction (e.g., with furfural or N-methyl-2-pyrrolidone) removes aromatics and polar compounds that depress VI. This yields raffinate with higher VI, often followed by dewaxing and hydrotreating/ hydrofinishing.
Step-by-Step Solution:
Step 1: Identify components harmful to VI (aromatics, polars).Step 2: Use selective extraction to move these into the extract phase.Step 3: Resulting raffinate shows appreciably higher VI.Verification / Alternative check:Process data consistently show VI uplift after solvent extraction compared to untreated distillates.
Why Other Options Are Wrong:
- Acid treatment: Historical sludge/asphaltene removal and color improvement; limited VI uplift.
- Alkali treatment: Neutralizes acidic impurities; does not appreciably raise VI.
- Clay treatment: Adsorptive finishing mainly for color/trace impurities; small VI effect.
Common Pitfalls:Assuming dewaxing alone defines VI; dewaxing targets pour point, while extraction targets solvency profile affecting VI.
Final Answer:Solvent extraction