Solutizer sweetening processes in refining: In the context of “solutizer” sweetening, which solutizer solutions are correctly matched with their respective processes?

Introduction:
Sweetening processes in petroleum refining aim to remove or convert odorous, corrosive sulphur compounds (especially mercaptans) to produce “sweet” products. A special subset, called solutizer processes, employs a co-solvent (the solutizer) to enhance the distribution and reactivity of mercaptans or their salts between hydrocarbon and treating phases. This question tests recognition of the correct solutizer–process pairings for two classic routes: Unisol and Mercapsol.

Given Data / Assumptions:

• Unisol and Mercapsol are established names for solutizer-style mercaptan treating.
• Solutizers are additives that improve phase behaviour and reaction efficiency.
• We need to identify the correctly matched solutizer with each named process.

Concept / Approach:
In the Unisol process, methanol is employed as the solutizer. It improves the transfer of mercaptans into the treating phase and facilitates formation and handling of mercaptides for subsequent conversion/stripping. In the Mercapsol process, naphthenic acid acts as the solutizer (forming soaps/naphthenates in alkaline media), similarly enhancing the separation and conversion behaviour of mercaptans. Recognising these canonical pairings is a common refinery-operations trivia point.

Step-by-Step Solution:

Verification / Alternative check:
Older refinery handbooks and training notes list Unisol (methanol) and Mercapsol (naphthenic acid) as example solutizer systems distinct from straight caustic extraction or catalytic oxidation-only schemes (e.g., Merox).

Why Other Options Are Wrong:

• Methanol in Unisol alone: Incomplete, misses the Mercapsol pairing.
• Naphthenic acid in Mercapsol alone: Incomplete for this multi-select style stem.
• Neither (a) nor (b): Contradicts standard references.
• Aqueous ammonia in both: Not a canonical solutizer pair for these named processes.

Common Pitfalls:
Confusing Merox (mercaptan oxidation with caustic) with solutizer-enhanced extraction schemes; assuming any alcohol or acid qualifies as a solutizer without considering the specific trademarked process.

Final Answer:
Both (a) and (b)