Turning Plastic into Fuel with the Help of Chromatography
Apr 25 2019
Plastics have been making the news. The environmental impact of waste plastics is highlighted as a growing disaster. Waste plastics are found the remotest places on Earth - buried in Arctic ice and on the highest peaks. Marine animals in particular have been found to contain the waste plastics that humans have discarded. Is there a better way to treat plastic waste?
In a recent paper published in Current Journal of Applied Science and Technology - Catalyst Screening for Conversion of Waste Polyethylentherphtalate Plastic in to Liquid Fuel - researchers from Ethiopia have investigated the option of turning waste plastic into liquid fuel. Take a closer look at plastic and see if it could be the new fuel in your car’s tank.
Plastics and recyclability
Plastics can be categorised into one of two main types. Thermosetting plastics and thermoplastics. Thermoplastics are produced by carrying out polymerisation reactions converting monomers (the individual building blocks of polymers) into long chain-like molecules. Once formed, these chain structures are not held in a rigid fixed formation. When the conditions are changed, for example if heat or pressure is applied, the plastics become soft and flexible - allowing the plastic to be moulded easily. Examples include nylon, PET and HDPE - drinking bottles.
Thermosetting plastics are generally produced in two main stages or reactions. The initial stage produces long chains of molecules which have reactive branches sticking out from the main chain. When the chains are reacted again, the branches crosslink making a fixed and rigid plastic. These plastics cannot be softened again after the initial cooling from reaction temperature. Epoxies, polyester and melamine - kitchen worktops.
Making fuel from PET
PET plastic is used the world over and causes major environmental problems. It does not degrade easily in landfills when it isn’t recycled. Instead, after photodegradation it forms the miniscule plastic fragments that are finding their way into the bodies of fish and into the frozen wastelands of the Arctic. Researchers are looking for ways to reuse the plastic and turning it into fuel is one option being explored.
The researchers in Ethiopia investigated a process called pyrolysis which involves heating the plastic to a very high temperature in the presence of a catalyst. They compared PET with other widely used plastics including HDPE and LDPE and used different catalysts (Ca(OH)2, Fe2O3 and an activated carbon-zinc oxide mix).
The different fuels produced by the process were analysed by chromatography to determine the fuel composition and the effect of the different catalysts and plastic combinations. The use of chromatography to analyse plastics is discussed in the article, HPLC Analysis of Melamine and Related Substances in Fertilisers. The team found that on its own PET only had a low yield, but that this increased when PET was combined with other plastics like HDPE and LDPE.
It seems though that there is still a long way to go before we’ll be filling up our cars with plastic bottles.
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