Polyethylene (LDPE, LLDPE): Production route
Crushing pressure versus clever catalysts
What this tab covers How it is made: the main production routes or, for product families, the main product types and technologies, compared on share of supply, inputs per tonne, plant scale, yield, co-products and unit cost.All LDPE and LLDPE starts from ethylene. LDPE uses free-radical polymerisation at very high pressure, which gives branched chains, clarity and easy processing. LLDPE uses catalysts at low pressure and a short-chain comonomer, which gives linear chains with short branches and much higher toughness at the same thickness. Metallocene LLDPE (mLLDPE) is the premium end. Bio-based and recycled-feed PE use the same reactors with different ethylene or mass-balance feed.
Routes compared
| Route | Share of supply | Inputs per tonne | Typical scale | Yield | Co-products | Unit cost |
|---|---|---|---|---|---|---|
| High-pressure LDPE (tubular and autoclave) | about 35-40% of LDPE plus LLDPE supply (indicative) | about 1.01 t ethylene and about 0.8-1.1 MWh electricity per t (indicative) | typical tubular line 300-400 kt/yr (indicative) | over 99% of ethylene ends up in polymer after recycle (indicative) | small wax and purge streams | ethylene cost plus about $150-250/t conversion (indicative) |
| Gas-phase LLDPE (e.g. Unipol, Spherilene) | about 40% of LDPE plus LLDPE supply (indicative) | about 0.92 t ethylene, 0.08-0.10 t butene or hexene, about 0.4-0.5 MWh per t (indicative) | 300-650 kt/yr per line (indicative) | about 99% (indicative) | vent gas recovered | ethylene and comonomer cost plus about $80-150/t conversion (indicative) |
| Solution LLDPE (including octene and metallocene grades) | about 20-25% (indicative) | about 0.88-0.92 t ethylene and 0.08-0.12 t octene; more steam than gas phase (indicative) | 200-500 kt/yr (indicative) | about 99% (indicative) | solvent recycled | higher than gas phase; premium grades sell above commodity LLDPE (indicative) |
| Bio-based and circular-feed PE | well under 1% (indicative) | about 1.7 t ethanol per t ethylene for bio-PE (ethylene tile) | Braskem Triunfo about 260 kt/yr (indicative) | as fossil PE | as fossil PE | bio-PE about 30-50% above fossil PE (indicative) |
How each route works
High-pressure LDPE (tubular and autoclave)Ethylene is compressed to about 1,500-3,000 bar and polymerised with peroxide or oxygen initiators at 150-300°C. Conversion per pass is only 20-35%, so large hypercompressors recycle unreacted gas. Autoclaves make coating and EVA grades; tubular reactors make film grades at larger scale.
Unique clarity and melt strength, but power-hungry and capital-intensive; little new capacity outside China (Argus 2025).
indicative (industry standard); Argus Polyethylene Outlook, Sep 2025 Gas-phase LLDPE (e.g. Unipol, Spherilene)Ethylene and comonomer are polymerised in a fluidised bed at about 20-25 bar and 80-100°C over Ziegler-Natta, chromium or metallocene catalysts. Many lines are swing plants that make either LLDPE or HDPE.
Lowest-cost, flexible swing process; butene grades are commodity, hexene and metallocene grades earn premiums.
indicative (industry standard) Solution LLDPE (including octene and metallocene grades)Ethylene and octene-1 or hexene-1 are polymerised in a hydrocarbon solvent at 150-250°C with metallocene or constrained-geometry catalysts, then the solvent is flashed off. Short residence time allows fast grade changes and very tough, clear films.
Best performance for thin, strong films and mono-material recyclable packs; fewer licensors and higher energy use.
indicative (industry standard) Bio-based and circular-feed PEEthylene from sugarcane ethanol (Braskem) or cracker feed from pyrolysis oil or bio-naphtha is polymerised in standard plants; circular feed is allocated by ISCC Plus mass balance.
Drop-in for converters and recyclable with fossil PE, but costly and supply-limited.
ethylene tile; indicative Unit economics are indicative ranges from the sources named; costs move with feedstock and energy prices, plant size and region.