Targeting unsaturates and BTX: Which refining/chemical process is specifically aimed at producing higher yields of gaseous unsaturated hydrocarbons and aromatics such as benzene and toluene?

Introduction:
Different refinery and petrochemical processes emphasise different product slates. When the objective is to maximise light olefins (ethylene, propylene) and generate aromatics like benzene/toluene (BTX range), high-severity thermal processes are typically used. This question asks you to select the process most closely associated with producing unsaturates and BTX.

Given Data / Assumptions:

• Product targets: gaseous olefins and BTX aromatics.
• Candidate processes: reforming, pyrolysis, alkylation, hydrocracking, isomerisation.

Concept / Approach:
Pyrolysis (e.g., steam cracking) is an extremely high-temperature thermal cracking process that breaks larger hydrocarbons into smaller fragments rich in unsaturated molecules (ethylene, propylene, butadiene) and also forms aromatics (benzene, toluene) via cyclisation and dehydrogenation pathways in the pyrolysis gasoline by-product. By contrast, catalytic reforming (reforming) increases aromatics primarily from naphthenes but does not target gaseous olefins; alkylation consumes olefins; hydrocracking saturates and cracks to make paraffins; isomerisation rearranges without increasing unsaturation.

Step-by-Step Solution:

Verification / Alternative check:
Petrochemical complexes use steam crackers (pyrolysis) as the primary source of ethylene/propylene and as a route to pyrolysis gasoline for BTX extraction units.

Why Other Options Are Wrong:

• Reforming: Produces aromatics from naphtha but not high gaseous olefins yield.
• Alkylation: Consumes olefins; produces saturated isoparaffins.
• Hydrocracking: Hydrogen-rich, yielding saturated distillates.
• Isomerisation: Rearranges without significantly changing saturation level.

Common Pitfalls:
Assuming reforming equals maximum aromatics and thus best answer; the question emphasises gaseous unsaturates, which points to pyrolysis.

Final Answer:
Pyrolysis