What’s cracking? Producing plastics from natural gas

What do toys, drain pipes, helmets, playgrounds, and clothing have in common? They are all everyday plastic items made possible by natural gas.

Ethane molecules are “cracked” into ethylene by breaking a single bond and releasing two hydrogen atoms. Graphic by Penn State Extension Marcellus Education Team.

Plastics are a large part of what makes our everyday lives safe and comfortable. We store our food, safely contain our cleaning supplies, and protect our families with plastic products. The molecules in natural gas can create a vast lineup of plastics, but the materials have a long journey ground to your home.

The natural gas retrieved from miles underground is primarily made of methane, but also contains molecules called ethane. The ethane is separated from the natural gas, and can be “cracked” to make major ingredients for plastics manufacturing.

Ethane cracker plants make it possible to harvest the potential power of the natural gas liquid (NGL). The ethane, a liquid under pressure, is carried to the plants by pipes. The molecules are heated, and when they reach around 1,500 degrees Fahrenheit their bonds begin to stretch, weaken, and eventually crack. That’s where the name “cracking” comes from.

A new molecule called ethylene is created when the ethane cracks. Light and easy to bond with, these ethylene molecules form long chains to create the famous plastic base polyethylene.

Polyethylene, or simply PE, can be changed to meet the requirements of different types of plastic; does it need to be rigid or pliable? Strong or breakable?

In fact, you can often see what kind of polyethylene your plastics are made of right on the product. For example, High Density Polyethylene (HDPE) can be used for everyday items like milk jugs and garbage bins. The HDPE and other resin codes are often visible right underneath a recycling symbol, and determines if or how the product can be recycled. As you can see below, coffee cup lids, baby bottles, and microwaveable plastics are made of a thermoplastic polymer called polypropylene. It is marked by the number “5” and often the letters “PP.”

Many plastic products bear a resin code that shows the type of material.

Polyethylene can make dozens of different types of plastics for everyday use in households, businesses, healthcare, and industry. These plastics can also be recycled into products like like shipping envelopes, furniture, trashcans, and floor tile.

Next time you grab a carton of milk from the fridge, thank natural gas for helping make plastics possible.

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Madison Weaver

Madison Weaver is a creative writing and communications double major at Bucknell University. As the external affairs intern at Cabot Oil & Gas Corporation for summer 2018, Madison will be creating blog posts and video content for Well Said.

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