Coal-tar products: Which of the following is <em>not</em> obtained by distillation of coal tar in a by-product recovery plant?

Introduction / Context:
High-temperature coal carbonization produces coke, coke-oven gas, and coal tar. Valuable aromatics are recovered from these streams by cooling, scrubbing, and fractionation. Some compounds are primarily recovered from coal tar, while others are recovered from the gas phase using wash oils. Distinguishing their origins is important for by-product plant design and operation.

Given Data / Assumptions:

• Source streams: coal tar (liquid by-product) and coke-oven gas (gaseous by-product).
• Typical coal-tar distillation fractions include light oils (phenolic), middle oils (naphthalene), creosote oil, and pitch; higher polycyclic aromatics like anthracene are enriched in heavier tar cuts.
• “Benzol” commonly refers to a benzene/toluene (and related light aromatics) mixture recovered from gas via wash oil, not from the tar still.

Concept / Approach:

Coal tar is distilled to yield specific fractions rich in phenolic compounds, naphthalene, creosote oil, anthracene oil, and finally pitch. Meanwhile, “benzol” (benzene/toluene/xylene range) is typically absorbed from the coke-oven gas using a wash oil and then stripped—this is a gas-treatment operation rather than tar distillation.

Step-by-Step Solution:

Verification / Alternative check:

Process-flow diagrams for by-product recovery show parallel trains: tar decanting/distillation for heavy aromatics and pitch; gas cooling/scrubbing for ammoniacal liquor and light aromatics (benzol). This separation by stream origin is standard practice.

Why Other Options Are Wrong:

Phenol, naphthalene, creosote oil, and anthracene are classic coal-tar derivatives obtained via fractional distillation and crystallization.

Common Pitfalls:

Assuming all aromatics come from tar; forgetting that the lightest aromatics are preferentially recovered from the gas by absorption rather than from the tar column.

Final Answer:

Benzol (benzene/toluene mixture recovered from coke-oven gas)