In hydrofining (catalytic desulfurization/sweetening) of petroleum fractions, what is the functional role of adding hydrogen to the process?

Introduction:
Hydrofining (hydrotreating) removes sulfur, nitrogen, oxygen, and metals from petroleum streams, improving product quality and protecting downstream catalysts. Hydrogen is fundamental to both the chemistry and the stability of the process.

Given Data / Assumptions:

• Catalysts: typically CoMo/NiMo on alumina.
• Feeds: naphtha, kerosene, diesel, or other middle distillates.
• Targets: H2S formation (from organosulfur), saturation of olefins, and coke suppression.

Concept / Approach:
Hydrogen participates in hydrodesulfurization (HDS) converting organosulfur compounds to H2S and saturated hydrocarbons. Maintaining sufficient hydrogen partial pressure also suppresses polymerization/condensation reactions, minimizing coke on catalyst surfaces.

Step-by-Step Solution:
1) Recognize hydrogen’s role as a reactant in HDS/Hydrogenation.2) Understand hydrogen keeps the environment reducing, limiting coking.3) Conclude both enhancement of desulfurization and coke minimization are valid.

Verification / Alternative check:
Operating guidelines require adequate hydrogen-to-oil ratio to sustain activity and cycle length; low hydrogen leads to rapid deactivation due to coke and poorer desulfurization.

Why Other Options Are Wrong:
a or b alone: Incomplete—both benefits are realized.d/e: Contradict process fundamentals; hydrogen directly enables sulfur removal and catalyst stability.

Common Pitfalls:
Assuming hydrogen only improves color/smell; its primary roles are chemical conversion (HDS) and preventing deactivation via coke suppression.

Final Answer:
Both (a) and (b)