Understanding visbreaking outcomes: Which statement correctly describes the purpose and operating result of the visbreaking process applied to vacuum residue?

Introduction:
Visbreaking is a mild thermal cracking process. Refineries employ it to reduce the viscosity of heavy residual oils so that they can be used or blended as lower-grade fuel oils without excessive cutter stock. This question focuses on the core purpose and outcome of visbreaking.

Given Data / Assumptions:

• Feed: atmospheric residue or vacuum residue.
• Severity: lower than coking; aims to limit coke formation.
• Operating conditions: elevated temperature and modest pressure, often with short residence time.

Concept / Approach:
By slightly cracking very large molecules, visbreaking lowers viscosity and pour point of the residue, increasing the yield of distillates marginally and enabling production of lower-viscosity fuel oils. It is not designed to produce only gasoline, nor does it use natural gas as feed, nor does it run strictly at 1 atm; mild pressure is typically maintained to keep the stream in the liquid phase.

Step-by-Step Solution:

Verification / Alternative check:
Refinery flow schemes list visbreaking as a residue-upgrading step that avoids the high coke make of full coking while achieving fuel oil spec targets.

Why Other Options Are Wrong:

• Natural gas as feed: Incorrect; feeds are heavy liquid residues.
• Atmospheric pressure only: Units typically operate above atmospheric to suppress flashing.
• Produces gasoline only / converts all to LPG: Overstated; small light ends are formed but not exclusively.

Common Pitfalls:
Confusing visbreaking (mild) with coking (severe) or FCC (catalytic).

Final Answer:
Produces fuel oil of lower viscosity