How Oil Becomes Plastic – A Step-By-Step Process
Plastics are ubiquitous to modern life. From cell phone cases to plastic cups to the so many components in a modern car, plastic is everywhere. Did you know that most of it is made from oil? Though manufacturers are now beginning to delve into bio plastics, the vast majority of plastic product we produce start as either crude oil or natural gas.
Plastic being a petroleum product explains why it can be challenging to recycle. A company like Tennessee-based Seraphim Plastics can reduce plastic scrap, like buckets and dunnage trays, to a regrind material that can be mixed with virgin plastic pellets in the manufacturing process. But apart from this sort of mechanical recycling, there aren’t many other options. Chemical and thermal depolymerization are generally too cost prohibitive to utilize on a wide scale.
At any rate, recycling isn’t the point of this post. Rather, the point is to help you understand how plastic is made. Below is a simplified step-by-step process that should give you a basic understanding. Remember that it all starts with oil.
Step #1: Oil Is Extracted
The first step is to extract oil from underground. Note that oil companies generally don’t drill just so that they have the raw materials for plastics. They drill to produce crude, which can then be converted into all sorts of things. Their main priority is fuel. Crude oil can be refined to make gasoline, diesel, and other fuels. Following extraction, oil is transported to a refinery for the next step.
Step #2: Oil Is Refined
At the refinery, crude oil is converted into a variety of petroleum products by way of high heat and distillation. Heating the crude oil prepares it for the distillation process, a process that has been used for millennia to separate molecules from liquids based on boiling point. It is the same process companies rely on to distill spirits, cannabis compounds, and even essential oils.
Crude oil is heated and then transferred to a distillation unit were additional heat and pressure are applied. As the various components reach their boiling point, they evaporate. The evaporated material is immediately cooled in order to return it to its liquid state. It is then collected and taken out.
Step #3: Polymerization
Refining oil produces what are known as monomers. These are essentially the building blocks of plastic. Monomers are individual molecules. The lightest monomers, including propylene and butylene, can be utilized to create polymers by bonding individual molecules together to create long chains. Doing so is known as polymerization.
Think of polymers as long chains of links in a chain-link fence. Each polymer is pretty strong on its own. Combining polymers makes them all stronger as a set. To bond polymers together, you need a catalyst. Peroxide is a pretty common catalyst for making polyethylene, PVC, and polystyrene.
Step #4: Compounding
The final step is to take the polymer groups and combine them with additives to create the particular type of plastic you’re after. This is done with heat. The polymers and additives are combined and heated to melting point. They are then blended and forced through an extruder to create the finished product. In most cases, you are looking at pellets. Those pellets are utilized to manufacture end products by way of injection molding.
In principle, making plastic is not very hard at all. In practice though, it can be difficult to get it right. Polymerization is the key. How you convert monomers to polymers plays a crucial role in the type of plastic you’ll end up with. Interestingly enough, it also partially determines how easily recycled plastic is.