Propylene
Properties
| State | Gas |
| Color | Colorless |
| Solubility | Slightly soluble in water; soluble in organic solvents |
| Melting Point | -185.2°C |
| Boiling Point | -47.6°C |
About Propylene
Propylene (propene, CH3CH=CH2, 42.08 g/mol) is the second-largest-volume petrochemical building block on the planet — global production sits around 130 million tonnes annually, second only to ethylene. Roughly two-thirds of that volume comes out of steam crackers as a co-product of ethylene cracking from naphtha or LPG feeds; the rest comes from FCC off-gas at oil refineries and from on-purpose routes (propane dehydrogenation, methanol-to-olefins) that grew sharply through the 2010s as the U.S. shale boom shifted ethylene crackers toward ethane feedstock and starved the propylene co-product stream. The molecule's defining feature is the asymmetric C=C double bond between C1 and C2, with a methyl group hanging off C3. That asymmetry created the Nobel-Prize-winning chemistry of stereoregular polymerization — Karl Ziegler and Giulio Natta won in 1963 for the catalysts that lock the methyl side groups into a single isotactic orientation, producing the high-crystallinity, high-melting polypropylene that is now the second most-produced plastic globally. Beyond polypropylene, propylene feeds the value chain to propylene oxide (polyurethane), acrylonitrile (acrylic fiber and ABS), cumene (the Hock route to phenol and acetone), 2-propanol, and acrolein.
Where you'll encounter it
If you've ever poured boiling water into a polypropylene yogurt cup without it deforming, sutured a wound with monofilament Prolene, or sterilized a centrifuge tube in an autoclave, you've used isotactic polypropylene downstream of propylene polymerization on a Ziegler-Natta or single-site metallocene catalyst. In a refinery, the propylene fraction off the FCC unit is what splitter columns separate from propane to feed the polypropylene plant next door — usually a Spheripol or Unipol process running at 65-75 °C and 30-40 bar. In an organic chemistry teaching lab, the addition of HBr to propylene under radical conditions versus polar conditions is the worked example for Markovnikov versus anti-Markovnikov regiochemistry — peroxide-initiated radical addition gives 1-bromopropane, while polar acid-catalyzed addition gives 2-bromopropane. And in a working ammonia-fiber plant, the SOHIO process oxyammonates propylene with NH3 and O2 over a bismuth-molybdate catalyst to make acrylonitrile, the monomer for acrylic carpet fiber and ABS plastic.
Common Uses
- Isotactic polypropylene production via Ziegler-Natta or metallocene catalysts for fibers, films, and rigid containers
- Propylene oxide manufacture via the chlorohydrin or HPPO route for polyurethane polyols
- Acrylonitrile production through SOHIO oxyammonation for acrylic fiber and ABS resin
- Cumene synthesis via Friedel-Crafts alkylation of benzene en route to phenol and acetone (Hock process)
- 2-Propanol manufacture via direct or indirect hydration for solvent and disinfectant markets
- Acrolein and acrylic acid feedstock for superabsorbent polymer production in diaper cores
Safety Information
GHS classification: Extremely flammable gas Category 1 (H220), Compressed gas (H280, may explode if heated). Simple asphyxiant — displaces oxygen in confined spaces without producing warning symptoms before unconsciousness. No substance-specific enforceable exposure limit applies; handling follows simple-asphyxiant guidance, and in practice the flammable range binds long before any toxicity limit does. Vapor explosion limits 2.0-11.1 vol% in air, autoignition temperature 455 °C. Stored as a liquefied gas under its own vapor pressure (about 9 bar at 20 °C), so cylinders need pressure-rated regulators and outdoor or ventilated storage. Industrial handling means continuous combustible-gas monitoring at the LEL/4 level and nitrogen-purged piping during start-up and shutdown. Not classified as carcinogenic or mutagenic.
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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.