Low-pressure Ziegler process for polyethylene: select the single correct statement about operating/features.

Introduction / Context:
The Ziegler (and later Ziegler–Natta/Phillips) processes revolutionized polyethylene by enabling polymerisation at relatively low pressures with specific catalysts, yielding high-density grades.

Given Data / Assumptions:

• We compare pressure, yield, density of product, and catalyst requirements.
• Only one statement should be correct.

Concept / Approach:
Low-pressure processes use specialized catalysts to obtain HDPE with high conversion. They do use catalysts; they do not target very low-density PE (that is characteristic of high-pressure free-radical LDPE). Operating pressures vary (often a few to a few tens of bar), so asserting a single fixed value like 30 kgf/cm2 as “the” standard is too specific for a universal statement.

Step-by-Step Solution:
Eliminate (c): product is HDPE, not very low density.Eliminate (d): catalysts are essential (Ziegler/Phillips).Treat (a) as over-specific; conditions vary by technology and reactor.Select (b) as the broadly correct and general statement.

Verification / Alternative check:
Process summaries show high single-pass conversions and high overall ethylene utilisation in Ziegler-based HDPE plants.

Why Other Options Are Wrong:
(a) Not universally true; pressure is not a single fixed value.(c) Misstates product density class.(d) Incorrect—catalyst is fundamental.

Common Pitfalls:
Conflating high-pressure LDPE (radical) with low-pressure catalytic HDPE.

Final Answer:
Achieves a high ethylene conversion/yield of roughly 95–98%.