Researchers at Purdue University have developed a new chemical process to convert polypropylene and other polyolefin waste plastic into fuel and other new products.
Polypropylene is used in everything from food containers to furniture and makes up around 23 per cent of all plastic waste. The conversion process relies upon selective extraction and hydrothermal liquefaction. In the study, model polypropylene (PP) was converted into oil using supercritical water at 380−500°C and 23MPa. Up to 91 per cent of the model PP was converted into oil at 425°C with a 2−4 hour reaction time or at 450°C with a reaction time of around one hour.
Once the plastic is converted into naphtha (a mixture of hydrocarbons), it can be used as a feedstock for other chemicals or further separated into specialty solvents or other products. According to the researchers, clean fuels derived from the polyolefin waste generated each year could theoretically satisfy four per cent of the annual demand for petrol or diesel fuel.
“Our strategy is to create a driving force for recycling by converting polyolefin waste into a wide range of valuable products, including polymers, naphtha, or clean fuels,” said research lead Linda Wang, a Professor in the Davidson School of Chemical Engineering at Purdue University. “Our conversion technology has the potential to boost the profits of the recycling industry and shrink the world’s plastic waste stock.”
Wang was inspired to develop the technology after reading about the extent of plastic pollution humanity has created. Around 8.3 billion tons of plastics have been produced over the past 65 years, with just nine per cent recycled and about 12 per cent incinerated. The remaining 79 per cent have gone into landfills or the oceans. According to the World Economic Forum, by 2050 the oceans will hold more plastic waste than fish if current rates of dumping persist.
“Plastic waste disposal, whether recycled or thrown away, does not mean the end of the story,” said Wang. “These plastics degrade slowly and release toxic microplastics and chemicals into the land and the water. This is a catastrophe, because once these pollutants are in the oceans, they are impossible to retrieve completely.”