Ethylene
Properties
| State | Gas |
| Color | Colorless |
| Solubility | Slightly soluble in water (131 mg/L at 25°C); soluble in organic solvents |
| Melting Point | -169.2°C |
| Boiling Point | -103.7°C |
About Ethylene
Ethylene is the smallest alkene and the largest-volume organic chemical on the planet — global production sits above 200 million tonnes a year, and steam-cracker capacity is one of the standard proxies economists use to track petrochemical demand. The C=C double bond is the entire story: 614 kJ/mol total bond energy split into a sigma and a pi bond, planar D2h geometry, sp²-hybridized carbons with H–C–H angles of 117°. The pi bond is what reacts — Ziegler–Natta and metallocene catalysts coordinate ethylene through that pi system and insert it into a growing alkyl chain, producing every grade of polyethylene from soft LDPE shopping bags to UHMWPE in artificial hip joints (the latter being the tonnage end use, with HDPE pipe second). Ethylene is also the feedstock for ethylene oxide (and downstream ethylene glycol and detergent surfactants), vinyl chloride monomer for PVC, ethylbenzene for styrene, vinyl acetate for EVA copolymers, and a long tail of smaller derivatives. Industrially it's made almost entirely by steam cracking of ethane (in the US, after the shale-gas boom) or naphtha (in Europe and Asia), at 800–900°C with millisecond residence times in radiant tube coils, then quenched and separated cryogenically from methane, propylene, butadiene, and the C5+ pyrolysis gasoline. Ethylene is also the original plant hormone, identified in 1934 as the volatile signal that triggers fruit ripening — which is why a banana ripens faster sealed in a paper bag with an apple, and why ethylene scrubbers (KMnO4 on alumina) line the holds of refrigerated banana ships.
Where you'll encounter it
If you've ever bought a green tomato in winter and watched it turn red on the counter, you've watched commercial ethylene chemistry: those tomatoes were picked green, shipped under refrigeration with ethylene scrubbers running, then gassed with 100–150 ppm ethylene in a ripening room for 24–72 hours before shelf delivery. On the industrial side, an ethylene cracker is one of the largest single-train chemical plants in the world — typical world-scale units run 1.5 million tonnes of ethylene a year through compressors the size of houses, fed by pipeline networks linking US Gulf Coast crackers, downstream polyethylene reactors, and ethylene oxide units in a tightly coupled chemistry park.
Common Uses
- Polyethylene production (HDPE, LDPE, LLDPE, UHMWPE) via Ziegler–Natta and metallocene catalysis
- Feedstock for ethylene oxide (then ethylene glycol and detergent ethoxylates)
- Vinyl chloride monomer synthesis (oxychlorination route to PVC)
- Ethylbenzene production for styrene and polystyrene
- Commercial fruit ripening (bananas, tomatoes, avocados) at 100–150 ppm in ripening rooms
- Oxyethylene cutting and welding gas where high flame temperature is needed
Safety Information
GHS: H220 extremely flammable gas, H280 gas under pressure, H336 may cause drowsiness or dizziness. Simple asphyxiant displaces O2 in enclosed spaces. Flammable range in air 2.7–36% — wide enough that any leak in an enclosed area is essentially guaranteed to be in the explosive range somewhere. Autoignition 450°C. No exposure limit set by OSHA but ACGIH TLV is 200 ppm TWA. Industrial handling is by pipeline at 30–40 bar; cylinder use is rare outside flame work and is always with regulators rated for the wide flammable range.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.