Ethylene (C2H4) gas is the basis of the polymer industry since approximately 60% of the world’s ethylene is used to produce polyethylene (PE), whose (-CH₂-CH₂-) repeat units in the molecular chain structure directly determine material properties. The world’s total polyethylene production in 2023 was 130 million tons (34% of the total plastics production), of which high-density polyethylene (HDPE) 45% (density 0.94-0.97g/cm³, tensile strength 21-37 mpa), low density polyethylene (LDPE) 25% (density 0.91-0.94g/cm³, low density polyethylene (LDPE) 25% (density 0.91-0.94g/cm³, low density polyethylene (LDPE)). Elongation at break 500%-700%). Ethylene is polymerized by free radical polymerization (high pressure, 150-300 mpa) or coordination polymerization (Ziegler Natta catalyst) to give polymers having different properties, e.g., the INSITE™ technology of Dow Chemical, which improves the toughness of LLDPE (linear low density polyethylene) by 40% (impact strength of 80kJ/m²).
The cost and efficiency advantages are impressive, ethylene cracking units (i.e., steam cracking furnaces) single-line capacity 1.2 million tons/year (Saudi Aramco Jubail plant), and the production cost per ton of ethylene is around US $500-700 (60%-70% naphtha feedstock). Coal-to-ethylene (CTO) is up to $900-1,100 / ton (China Shenhua project data). The gas phase polymerization process of ethylene (e.g., Unipol process) conversion rate is greater than 99.5% (reaction time <2 hours), with energy consumption 30% less (800kWh vs. 1,200kWh per ton of PE) compared with the liquid phase process (conversion rate 85-90%). Basf 2022 data show that the use of highly selective catalysts, i.e., metallocene catalysts, can enhance the transparency of PE films from 88% to 94% (fog <5%), which meets the high demands of food packaging.
Control of the material properties is based on the precise addition of ethylene purity (≥99.95%) and copolymers (e.g., 1-butene, hexene). For example, with every 1% increase of 1-butene copolymer in HDPE, the environmental stress cracking resistance (ESCR) increases by 50% (test standard ASTM D1693). The Exceed™ series PE of ExxonMobil reduces the tensile modulus from 1,100MPa to 600MPa by introducing hexene (6-carbon monomer), which is suitable for flexible packaging (thickness error ±0.5μm). In auto lightweight, DSM’s Stanyl® PA46 (which has ethylene containing segments) with 230°C temperature resistance (60°C higher than regular nylon) is used for the reduction of hood weight by 30%.
Environmental protection and circular economy drive innovation, c2h4 gas cracking has CO₂ emissions of 1.8 tonnes/tonne ethylene (naphtha route), while bio-based ethylene (e.g., sugarcane ethanol route in Braskem, Brazil) emits only 0.5 tonnes/tonne carbon and produces 100% biodegradable PE (e.g., NatureWorks Ingeo™, NatureWorks). Compost cycle 6 months. Chemical recovery processes, i.e., Eastman’s carbon regeneration process, depolymerize waste PE to ethylene monomer (85% recovery) more effectively than mechanical recovery (30% performance loss). EU Plastics Strategy 2030 target of 30% recycled plastic content spurs growth in vinyl recycling capacity (estimated CAGR of 12%).
Case studies include:
Saudi Basic Industries Corporation (SABIC) ethylene cracking plant produces 13 million tons per annum ethylene capacity, facilitating Middle East petrochemical exports of $32 billion (2023 figures).
PE packaging film (containing 30% recycled ethylene monomer) developed by P&G and Dow reduces the product’s carbon footprint by 25% (carbon emissions per ton of packaging material from 3.2 tons to 2.4 tons).
Lyondellbasell’s Hyperzone™ polyethylene technology has increased single-line capacity to 500,000 tons/year (20% lower investment costs) and increased catalyst efficiency 15-fold.
The starring role of C2H4 gas is a result of its unmatched reactivity, economies of scale production and material designability, and ethylene will lead the green transformation of the polymer industry with the future development of bio-based and recycling technologies.