Propylene: the molecule hiding in everything you own

Open your car door. The dashboard, the bumper, the battery case, the seat fabric. All polypropylene. The yogurt cup in your fridge, the surgical mask in your glovebox, the bottle cap you twist off without thinking. All polypropylene. And polypropylene starts as propylene.

The United States produces roughly 48 billion pounds of propylene per year. About half of that comes from the Gulf Coast. And unlike ethylene, which has one dominant production route, propylene arrives three different ways, which is what makes its supply chain one of the more interesting puzzles in petrochemicals.

What propylene is and where it goes

Propylene is a three carbon gas. Colorless, flammable, slightly sweet smelling if you could get close enough to notice, which you should not. Like ethylene, it is almost never sold as a finished product. It exists to become something else.

About 65% of all propylene becomes polypropylene, the most versatile commodity plastic in the world. Polypropylene shows up in packaging, automotive parts, medical devices, textiles, and consumer goods. Another 7 to 10% becomes acrylonitrile, which feeds into ABS plastics, acrylic fibers, and carbon fiber precursors. About 8% goes to oxo alcohols for plasticizers and solvents. 7% becomes propylene oxide, which becomes polyurethane foam, propylene glycol, and a long list of industrial intermediates. The remaining 10% splits among cumene (which becomes phenol and acetone), acrylic acid (superabsorbent polymers), and a tail of specialty derivatives.

If ethylene is the building block of modern packaging, propylene is the building block of modern everything else.

How it is made: three routes, one corridor

This is where propylene gets interesting. Ethylene has one dominant route: steam cracking. Propylene has three, and each one tells a different story about how the Gulf Coast petrochemical economy works.

Steam cracking byproduct

When a steam cracker runs on heavier feeds like naphtha or gas oil, propylene comes out as a significant co-product, about 14 to 18% of the output stream on a liquids fed cracker. For decades, this was the primary source of propylene worldwide. But when the US shale revolution made ethane cheap and abundant, Gulf Coast crackers switched to ethane feeds. Ethane gives more ethylene per pound of feed, but it produces almost no propylene. The Gulf Coast got more ethylene and less propylene at the same time, and the gap had to be filled.

Today, steam cracking still supplies about 45% of US propylene, but the share has been falling for over a decade.

Refinery FCC units

Fluid catalytic cracking units in oil refineries were originally designed to make gasoline, but they also produce significant propylene as a co-product. Refinery grade propylene from FCC units accounts for roughly 29% of US supply. The quality is lower than polymer grade. It needs further purification before it can feed a polypropylene reactor, but the volume matters.

When a refinery shuts down, the propylene supply chain feels it. LyondellBasell closed its 268,000 barrel per day Houston refinery in early 2025, removing a source of refinery grade propylene from the Gulf Coast supply picture.

On purpose PDH

The third route is the newest and the most consequential for the Gulf Coast. Propane dehydrogenation takes propane, abundant and cheap thanks to shale gas, and converts it directly to propylene and hydrogen in a catalytic reactor running above 650 degrees Celsius.

PDH is called "on purpose" because propylene is the primary product, not a byproduct. The selectivity is 85 to 90%, meaning almost all the propane converts to propylene. Compare that to 15% propylene yield from a naphtha steam cracker. PDH plants exist for one reason: to make propylene.

On purpose production currently supplies about 16% of US propylene, and that share is growing. The industry projects it will reach 20% within the next several years. The Gulf Coast propylene supply dynamics have shifted toward more seasonal volatility as PDH maintenance schedules increasingly drive spot pricing swings.

The Gulf Coast operator map

Four PDH plants on the Texas Gulf Coast are the swing supply factor for polymer grade propylene pricing across the United States. When one goes down for maintenance, the market notices.

The PDH producers

• —Enterprise Products Mont Belvieu. PDH 1 started 2017, PDH 2 started August 2023. Combined capacity 3.3 billion lb/yr of polymer grade propylene. Both units use Honeywell UOP Oleflex technology and consume 35,000 barrels per day of propane each. Enterprise's total propylene supply platform, integrating PDH with fractionation, exceeds 9 billion lb/yr.
• —Dow Freeport. 1.65 billion lb/yr PDH unit, the largest Honeywell UOP Oleflex unit in the world at the time it was built. Started December 2015. Sits within the largest single chemical site in the Western Hemisphere, alongside multiple ethylene crackers that produce additional propylene as a co-product.
• —Flint Hills Resources Houston Ship Channel. 658,000 MT/yr. Originally built by PetroLogistics in 2010 as the first PDH plant in North America. Acquired by Flint Hills Resources (Koch Industries) in 2014.

Steam cracker and refinery producers

• —ExxonMobil Baytown. Produces propylene alongside roughly 10 billion lb/yr of total petrochemical products from its olefins plant. The adjacent 584,000 barrel per day refinery generates additional refinery grade propylene from its FCC units.
• —INEOS Chocolate Bayou. 475,000 MT/yr propylene capacity across two olefins crackers, feeding two polypropylene units on site.
• —LyondellBasell Channelview. Approved a new 400,000 MT/yr metathesis unit in March 2025 that will convert ethylene to propylene. Construction starts Q3 2025 with startup projected for late 2028. The Channelview complex also hosts the world's largest propylene oxide plant at 1 billion lb/yr.
• —Chevron Phillips Cedar Bayou. Propylene co-product from its 3.4 billion lb/yr ethylene crackers.
• —BASF/TotalEnergies Port Arthur. Joint venture steam cracker producing over 1 million MT/yr of ethylene plus propylene and butadiene co-products.
• —Formosa Plastics Point Comfort. Commissioned the largest horizontal polypropylene reactor in North America in September 2025, adding 550 million lb/yr of PP capacity.
• —Phillips 66 Sweeny. FCC units at the 265,000 barrel per day refinery generate refinery grade propylene.

The PDH technology behind the growth

Two licensed technologies dominate PDH on the Gulf Coast.

Honeywell UOP Oleflex uses a platinum based catalyst in four vertical moving bed reactors with continuous catalyst regeneration. It achieves about 36% propane conversion per pass with 85% propylene selectivity. Every Gulf Coast PDH plant built by Enterprise and Dow uses Oleflex.

Lummus Technology CATOFIN uses a chromium oxide catalyst in horizontal fixed bed parallel reactors with cyclic operation. It achieves about 40% conversion per pass with 88% selectivity. CATOFIN has nine PDH plants and six isobutane dehydrogenation plants globally, producing over 5 million MT/yr of propylene.

Both technologies exist because of the same economic reality: the US shale revolution made propane cheap and abundant on the Gulf Coast, while the shift to ethane cracking reduced propylene co-production from steam crackers. PDH filled the gap.

What is next

Propylene is the molecule that connects ethylene crackers, oil refineries, and dedicated PDH plants into a single supply picture. The next piece in this series covers benzene, the aromatic that connects refineries, steam crackers, and an entirely different set of downstream chemistry, and that carries regulatory complexity unlike anything else in the corridor.

For more on the ethylene side of the equation, see Ethylene: the molecule that built the Gulf Coast.

If you sell into the operators running these PDH units, crackers, and refineries, ExecGraph maps the decision chains at each facility. Book a 1 hour walkthrough.

Last verified 2026-05-12.