Coke formation tendencies: Choose the correct statement about coking in refinery/thermal processes considering molecular weight, pressure effects, and reaction heat.

Introduction / Context:
“Coking” refers to the formation of solid carbonaceous material in thermal and catalytic processes (e.g., visbreaking, coking, FCC). It deactivates catalysts, plugs equipment, and reduces liquid yields. Understanding factors that drive coking helps in selecting severity and feed quality windows.

Given Data / Assumptions:

• Comparison across hydrocarbon feeds from light naphtha to residua.
• General trends rather than unit-specific anomalies.
• Reaction heat refers here to net heat effects of the overall pathway to solid carbon.

Concept / Approach:
Heavier feeds (higher molecular weight, higher Conradson carbon/asphaltenes) contain more precursors for condensation and polyaromatic growth, thus showing stronger coking propensity. Pressure effects are complex and unit-dependent; “always enhances coke formation” is too absolute. Coking itself results from polymerisation/condensation and dehydrogenation steps; while cracking is endothermic, overall pathways to carbon are not characterised simply as exothermic in specifications. Moisture control helps but does not “eliminate” coking when heavy precursors are present.

Step-by-Step Solution:

Verification / Alternative check:
Unit operations literature correlates coke make with feed CCR/asphaltenes and severity; heavy feeds inherently show greater coke formation under similar severities.

Why Other Options Are Wrong:

Common Pitfalls:
Treating a multivariate phenomenon with single-factor absolutes; always consider feed CCR, asphaltenes, and severity together.

Final Answer:
Coking tendency increases with increasing molecular weight.