By-products of high-temperature coal carbonisation: Which of the following is <em>not</em> recovered as a by-product from a conventional high-temperature coke-oven plant?

Introduction / Context:
High-temperature coal carbonisation (around 1000–1100°C) yields metallurgical coke, coke-oven gas, tar, and liquor. From these, by-product plants recover valuable chemicals. Recognizing which products are typically recovered guides economic evaluation and environmental compliance.

Given Data / Assumptions:

• Coke-oven gas contains H2, CH4, CO, CO2, small higher hydrocarbons, NH3, H2S, and light aromatics (“benzol”).
• Coal tar is distilled to naphthalene, creosote oil, pitch, etc.
• Ethylene is negligible in conventional coke-oven gas and is not a standard recovered by-product in these plants.

Concept / Approach:

Standard by-product recovery includes benzol by absorption from gas, ammoniacal liquor from gas scrubbing, naphthalene from tar/gas, and pitch/creosote from tar distillation. Ethylene is not typically recovered; it is a core product of steam cracking of naphtha/ethane, not coal carbonisation.

Step-by-Step Solution:

Verification / Alternative check:

Block flow diagrams for coke plants confirm benzol recovery trains, ammonia recovery, tar distillation, but no ethylene separation units.

Why Other Options Are Wrong:

Benzol, PCM, naphthalene, and ammoniacal liquor are well-established by-products in integrated coke-oven by-product recovery schemes.

Common Pitfalls:

Assuming all hydrocarbon gases include recoverable ethylene; conflating petrochemical steam-cracking with carbonisation.

Final Answer:

Ethylene