In petroleum refining, the visbreaking process is a mild thermal cracking step primarily used to reduce residue viscosity for downstream handling and sales. Visbreaking is mainly employed to make which commercial product stream?

Introduction / Context:
Visbreaking is a common thermal conversion process in refineries designed to mildly crack long, heavy hydrocarbon molecules found in vacuum or atmospheric residues. The primary business goal is to reduce viscosity so the heavy stream can be sold or blended as fuel oil and handled without excessive heating.

Given Data / Assumptions:

• The process target is viscosity reduction rather than deep conversion.
• Feed is usually atmospheric residue or vacuum residue.
• Operating severity is intentionally limited to minimize coke formation.

Concept / Approach:

Under moderate temperatures and short residence times, visbreaking breaks some long chains into slightly lighter molecules. This lowers viscosity and pour point of the bottoms stream while making small yields of naphtha, light gas oil, and gases. The main volume product remains a heavy fuel oil suitable for bunkers or industrial firing.

Step-by-Step Solution:

Verification / Alternative check:

Process flow schemes and refinery LP models show visbreaker bottoms routed to fuel oil blending. Units like FCC or hydrocrackers, not visbreakers, are used to maximize gasoline or diesel qualities like octane or cetane.

Why Other Options Are Wrong:

High octane gasoline / High cetane diesel: Only small side yields from visbreaking; not the main purpose. Smoke-free kerosene: Kerosenes are controlled by cut point and hydrotreating, not visbreaking severity.

Common Pitfalls:

Confusing visbreaking with deep thermal cracking or catalytic cracking; overestimating light product yields; assuming it is a gasoline-making process.

Final Answer:

Fuel oil with reduced viscosity for storage and pumping