HDPE via Ziegler (Ziegler–Natta) solvent polymerisation: typical low-pressure conditions for producing high-density polyethylene are approximately what pressure–temperature pair?

Introduction / Context:
Ziegler–Natta catalysis revolutionized polyethylene by enabling high-density polyethylene (HDPE) at low pressures and moderate temperatures compared with earlier high-pressure free-radical LDPE processes. Recognizing the order of magnitude of process conditions helps distinguish catalyst families and product structures (branching, density, crystallinity).

Given Data / Assumptions:

• Solvent/slurry polymerisation using organo-aluminium and transition-metal catalysts.
• Objective: HDPE with high crystallinity and low branching.
• “Typical” refers to exam-standard representative values.

Concept / Approach:
HDPE with Ziegler–Natta catalysts is produced at low pressure (roughly 1–10 kgf/cm²) and relatively low temperatures (around 60–80 °C in many solvent processes). These mild conditions contrast starkly with LDPE free-radical methods that require hundreds to over a thousand kgf/cm² and elevated temperatures. Options listing extremely high pressures or unrealistically high temperatures do not match Ziegler low-pressure technology.

Step-by-Step Solution:

Verification / Alternative check:
Process descriptions for slurry/solution loop reactors cite pressures on the order of a few atmospheres and temperatures near 70 °C for HDPE grades with Ziegler catalysts.

Why Other Options Are Wrong:

• 1000 kgf/cm²: characteristic of LDPE radical processes, not Ziegler HDPE.
• 7 kgf/cm² & 700 °C: temperature far exceeds polymer stability.
• 1 kgf/cm² g: pressure too low for typical industrial solvent systems in exam context.
• 200 kgf/cm² & 300 °C: mismatched to low-pressure catalysis.

Common Pitfalls:
Conflating LDPE autoclave/tubular conditions with Ziegler–Natta processes.

Final Answer:
7 kgf/cm² and 70 °C