courtesy Penn State Extension Shale Team
Purity ethane (at least 90% ethane, but usually higher) then travels in a pipeline to its destination, an ethane cracker plant. At the cracker plant, which has access to a large energy source, ethane is heated to about 1500 degrees Fahrenheit. This process is called cracking, because heat energy is used to break apart or crack molecules to form new molecules. At that temperature ethane (C2H6) molecules lose two hydrogen molecules, which split off to form a separate, stable hydrogen molecule (H2), leaving molecules which are about 80 percent ethylene (C2H4). (See graphic).
The ethylene formed in the cracking process is next transported by pipeline to another facility to be converted to usable products, the most common of which is polyethylene. Ethylene is at this point still a gas and needs pressure and a catalyst to turn it into polyethylene, a resin. The process by which polyethylene is made from ethylene is known as polymerization.
The term "plastic" suggests one material, but there are actually hundreds of different plastic polymers. Polymerization occurs when a chemical reaction causes molecules to react together to form polymer chains. These polymer chains can be engineered to control the specific physical properties of the resulting plastic resin, thus allowing the product to be designed for many different uses. For example, some plastic products may require extra strength, some require maximum flexibility, and others need to be resistant to solvents. All of these requirements can be accounted for by the polymers used in the process.
Polyethylenes may be labeled as low density or high density polyethylenes (LDPE or HDPE), or other designations that can be seen at the bottom of household containers.
Polyethylene resin can be transported by truck, barge, or train to a manufacturing facility to make end products. Cracker plants, therefore, usually have access to a lot of transportation options and warehouse facilities to store and ship resins and liquid products.
Ethane is a valuable NGL, which is an important and economical feedstock for plastics. While ethane is produced in numerous shale regions, it has major value nationally and worldwide in its use.
See first part of news item: How Plastic is Made from Natural Gas - Part 1
Dan Brockett, Extension Education, Penn State Extension