8.4 Petrochemicals: Manufacture of Plastics

Author: Victoria Lindo

ABSTRACT: Plastic is one material that has a very high demand all over the world. The process of manufacturing plastics is important to understand before knowing why plastics are harmful to our environment, from manufacturing to the point of disposal.

MAIN:

There are two main types of plastics:

  1. Synthetic plastics are the most common type of plastics being used. This plastic is made from petroleum-based raw materials.
  2. Bio based plastics are types of plastic made from renewable materials like vegetable fats, oils, carbohydrates, starch, and other biological substances.

Chart A shows the advantages of Bio-Based plastics, which are reducing the use of fossil fuel resources and helping to create a smaller carbon footprint and has faster decomposition. Bio-based plastics are also less toxic and do not contain harmful chemicals that are often found in traditional plastics.

Plastic can be grouped into two main polymer families:

  1. Thermoplastics – which soften when being heated and then harden again when being cooled. An example representing this process could be demonstrated by an “ice cube” which will melt when heated but hardens again when cooled. Like a thermoplastic this process may be repeated numerous times.
  2. Thermosets – which never soften once they have been heated and molded. This can be similar to cooking an egg, once that egg has been cooked it cannot be reverted back to its original form, and a thermoset polymer cannot be softened once it is “set”.

So, how is plastic made?

The process can be broken down into five categories: (1) Raw material extraction, (2) Preparing the raw materials, (3) Chemical processing, (4) Melting, and (5) Cooling.

What is plastic made from?

Plastic is made of fossil fuels, oil, or natural gas. Plastic can also be made from coal, however it isn’t very common. Oil is extracted from the Earth using a pump and Natural gas is most commonly extracted by drilling vertically from the Earth’s Surface. Once these fossil fuels have been extracted, they need to be transported to a petroleum refinery.

Inside the refinery

Crude oil must be separated into different components based on weight and boiling points. This is done by heating the oil in a furnace and then distilling it. This process separates a mixture of chemical compounds. Each fraction of the chemical compound evaporates and then condenses in its very own section.

The Chemical Reaction

The next process uses energy and water to alter their structure. The hydrocarbon starting points are further refined into ethane and propane. Both gases are then “steam cracked” into ethylene and propylene, a process in which the gases are mixed with steam at temperatures of 900 degrees Celsius or higher and break down into their lighter, unsaturated monomers for use in production. By adding a chemical called catalysts, a polymer “fluff” is created, which looks like powdered laundry detergent.

Heating and Cooling

This fluff is then fed into an extruder, where it begins to melt. As it travels through this pipe the plastic begins to cool, forming a long tube. That tube is then cut into small, tiny pellets and voila you have made plastic! Those pellets then get shipped to factories to be melted down into and modeled into endless possibilities using numerous methods.

Carbon Calculations According to the EPA, approximately one ounce of carbon dioxide is emitted for each ounce of polyethylene (PET) produced. Worldwide, we consume approximately 100 million tons of plastic each year. From the EPA’s more conservative estimate to be anywhere from 100 million tons of carbon dioxide emitted to 500 million tons. Also using the conservative estimate of 30 percent carbon savings for recycled plastic, recycling could save between 30 and 170 million tons of carbon each year, or the approximate equivalent of removing between six and 30 million vehicles from roads. Carbon from fossil fuel feedstocks is locked into plastic products and emitted when plastic is being incinerated or decomposed. In 2015, 25 percent of global plastic waste was incinerated; in the U.S., emissions from plastic incineration were equivalent to 5.9 million metric tons of CO2, equivalent to the emissions from heating 681,000 homes for a year (R., & Cho, R., 2020).

RESOURCES

20, R., & Cho, R. (2020, February 20). More plastic is on the way: What it means for climate change. Retrieved April 13, 2021, from https://news.climate.columbia.edu/2020/02/20/plastic-production-climate-change/

Guide to manufacturing processes for plastics. (n.d.). Retrieved April 13, 2021, Retrieved from https://formlabs.com/blog/guide-to-manufacturing-processes-for-plastics/

How plastics are made. (n.d.). Retrieved April 13, 2021, Retrieved from https://plasticseurope.org/plastics-explained/how-plastics-are-made/   

P. (2020, January 06). How are plastics made? Retrieved April 13, 2021, Retrieved from https://thisisplastics.com/plastics-101/how-are-plastics-made/

BIOGRAPHY

Victoria Lindo is a third-year Interior Design student studying at the Ryerson University and lives in Ontario, Canada. Her passion is to learn, understand and help spread the awareness of environmental health, as this planet we live on needs to be taken care of in order for a future. Within her designs, she pays attention to ways any design project of hers can be greener. Incorporating the importance of reusing and reducing waste, material choice, and how these designs will affect our planet.

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