Polycaprolactam (nylon-6) via ring-opening/condensation of caprolactam at 240–280 °C typically reaches what overall monomer conversion under steady industrial operation?

Introduction / Context:
Nylon-6 is produced by hydrolytic ring-opening polymerisation of caprolactam. Knowledge of typical conversion informs downstream finishing, devolatilisation, and monomer recovery (e.g., lactam extraction and recycle).

Given Data / Assumptions:

• Process temperature: 240–280 °C.
• Industrial reactors often operate with water as a chain-transfer/initiating species.
• We seek approximate conversion in primary polymerisation before finishing.

Concept / Approach:
Primary polymerisation yields high but not complete conversion; typical values are around 85–95%. Residual monomer is removed in finishing to meet product specs. Hence “about 90%” is a representative figure for the main reaction stage.

Step-by-Step Solution:
Match operating range to known conversion band (high but not near 100%).Select the closest listed value: about 90%.Note that final product may have lower residual monomer after post-treatment.

Verification / Alternative check:
Process monographs show significant monomer removal steps (extraction/stripping), evidencing incomplete in-reactor conversion.

Why Other Options Are Wrong:
50% or 75%: too low for practical productivity.99%: unusually high for the main reactor without extensive finishing.

Common Pitfalls:
Assuming condensation polymerisations reach full conversion in one pass; equilibrium and kinetics limit this.

Final Answer:
About 90%