Ethylene: the molecule that built the Gulf Coast

If you have driven I-10 between Houston and Lake Charles at night, you have seen the flares. Most of them are burning ethylene. It is the highest volume chemical produced in the world, the building block for plastics, antifreeze, and a long list of things you touch every day. The Gulf Coast makes more of it than anywhere else on the planet.

This is what ethylene is, how it is made, what comes with it, and who makes it.

What ethylene is and where it goes

Ethylene is a small, simple gas. Two carbon atoms, four hydrogen atoms. Lighter than air, colorless, flammable, and almost never sold as a finished product. It exists to be turned into something else.

About sixty percent of all ethylene becomes polyethylene, the plastic in milk jugs, grocery bags, water pipes, and shrink wrap. Another fifteen percent becomes ethylene glycol, which is the antifreeze in your engine, the fiber in your polyester shirt, and the resin in your water bottle. Ten percent becomes PVC, the white pipe in every plumbing aisle in America. The rest becomes solvents, detergents, synthetic rubber, and a long tail of specialty chemicals.

Without ethylene, modern packaging, transportation, and construction would all look very different. It is the most consequential industrial chemical of the past hundred years.

How it is made

Ethylene is made by steam cracking. The name describes the process. You take a hydrocarbon (usually ethane on the Gulf Coast), mix it with steam, and send it through tubes inside a very hot furnace. The heat breaks the carbon to carbon bonds in the feed, and the steam keeps the tubes from clogging up with soot.

What comes out is a hot mixture of gases that has to be cooled, compressed, and separated. The separation happens in tall distillation columns running at temperatures cold enough to liquefy each product. Ethylene boils at minus 155 degrees Fahrenheit, which is why steam crackers run some of the largest refrigeration systems in any industry.

The Gulf Coast picked ethane as its feedstock because shale gas made ethane cheap and abundant. Ethane gives the highest yield of ethylene per pound of feed: about eighty pounds of ethylene out of every hundred pounds of ethane in. That is why every major Gulf Coast cracker built in the last fifteen years runs on ethane, while crackers in Europe and Asia run on naphtha, a heavier feedstock that yields less ethylene but more byproducts.

What comes with it

A steam cracker does not produce pure ethylene. For every hundred pounds of ethane fed in, you get roughly:

• —80 pounds of ethylene (the main product)
• —4 pounds of hydrogen
• —6 pounds of methane (recycled as fuel gas)
• —1 to 2 pounds of propylene
• —A few pounds of mixed C4s
• —A small amount of pyrolysis gasoline, a stream rich in benzene and toluene

These byproducts are not waste. They are the reason petrochemical plants cluster together. The propylene from a steam cracker feeds a polypropylene plant next door. The hydrogen feeds a refinery hydrocracker down the road. The benzene becomes styrene, which becomes polystyrene. Every pound of byproduct has a buyer within a mile or two of the cracker, which is why the Gulf Coast looks like one continuous industrial corridor instead of a scatter of isolated plants.

The Gulf Coast operator map

The U.S. Gulf Coast is the densest concentration of steam cracker capacity in the world. The corridor produces roughly 35 billion pounds of ethylene per year, about sixty percent of all U.S. capacity.

In Texas:

• —ExxonMobil Baytown — 4.2 billion lb/yr across two crackers
• —Dow Freeport — 3.5 billion lb/yr across multiple units, the largest single chemical site in the Western Hemisphere
• —Chevron Phillips Cedar Bayou (Baytown) — 3.4 billion lb/yr
• —INEOS Chocolate Bayou (Alvin) — 2.4 billion lb/yr
• —LyondellBasell Channelview — 2.0 billion lb/yr
• —ExxonMobil/SABIC Gulf Coast Growth Ventures (Corpus Christi) — 1.8 billion lb/yr, started 2022
• —LyondellBasell Corpus Christi — 1.7 billion lb/yr
• —Formosa Point Comfort — 1.6 billion lb/yr
• —Total Petrochemicals Port Arthur — 1.0 billion lb/yr
• —ExxonMobil Beaumont — 0.7 billion lb/yr

In Louisiana:

• —Sasol Lake Charles — 3.4 billion lb/yr, the newest cracker in this group, started 2019
• —Westlake Lake Charles — 2.6 billion lb/yr across multiple units
• —NOVA/Indorama Geismar — 1.95 billion lb/yr
• —Dow St. Charles (Hahnville) — 1.8 billion lb/yr
• —Shell Norco — 1.4 billion lb/yr

These fifteen sites are the foundation of the Gulf Coast petrochemical economy. Every polyethylene reactor, every PVC plant, every ethylene oxide unit between Corpus Christi and Norco depends on one of these crackers running.

What is next

Ethylene is the headline molecule. The next pieces in this series cover polypropylene and the three different reactor technologies running at Gulf Coast plants, LNG liquefaction and the four dominant licensor processes, and polyethylene and why one cracker feeds three different reactor lines at the same site.

If you sell into Gulf Coast operators and want to know who makes the procurement, maintenance, and engineering decisions at each cracker, that is what ExecGraph Energy maps.