Plastics are made from fuel-like products. Just like fuel, plastic is a product of refining crude oil. However, to make polymers, more refining steps are necessary than for making fuel. So in a way, fuels are the precursor to making plastic. Because of the many refining steps in which heavy metals are removed the polymers are rather clean. Thus fuels can be obtained from plastic by essentially reversing the polymer making process. Pyrolysis is a very simple way to achieve this.
The plastic waste is heated to above 450 °C. Normally, when plastics are heated to these temperatures, they start burning, which means that they react with oxygen to produce CO2 and CO. However, if this is done in an airtight chamber, the oxygen is quickly used up and the polymer chains are broken into liquids and gasses that resemble the products used to make the plastic in the first place. Therefore, pyrolysis is arguably the simplest way to chemically recycle plastic. Chemical recycling refers to all methods of recycling in which the chemical bonds of the plastic are broken.
Which products are obtained and thus the properties of the fuel, depend on the temperature, whether a catalyst is used and residence time. One goal of this project is to find simple, easy-to-apply methods to tune the fuel properties, like octane number and burning value.
Next up: How pyrolysis could provide a solution to plastic waste while providing a living for poor families »
Or read our diary on building a small-scale model for domestic use.