Researchers have developed a low-temperature process converting plastic waste into liquid fuel as a way to re-use discarded plastic bags and other products. The most common waste we all see worldwide is the standard polymer, low-density polyethylene (LDPE), which is used to make many types of containers, medical and laboratory equipment, computer components and, of course, the ubiquitous plastic bags.
Plastic Bag Beach.
Recycling efforts are in place in many parts of the world, but much of the polyethylene waste ends up in landfills, dispersed out in the environment or floats in the sea. There are likely billions of tons of the stuff cluttering up the planet.
Chemist Achyut Kumar Panda of Centurion University of Technology and Management Odisha, India is working with chemical engineer Raghubansh Kumar Singh of the National Institute of Technology, Orissa, India, to develop a commercially viable technology for efficiently rendering LDPE into a liquid fuel.
Given that most plastics are made from petrochemicals, this solution to plastic recycling brings the chemical life cycle full circle allowing a second use as an oil substitute. The process could, if implemented on a large enough scale, reduce pressures on landfills as well as ameliorating the effects of dwindling oil supplies in a world with increasing demands on petrochemicals for fuel.
The study paper has just appeared in the journal International Journal of Environment and Waste Management.
The team’s process is to heat the plastic waste to between 400 and 500º C (750 to 930º F) over a kaolin catalyst. This causes the plastic’s long chain polymer chains to break apart in a process known as thermo-catalytic degradation. This releases large quantities of much smaller, carbon-rich molecules. The team used the analytical technique of gas chromatography coupled mass spectrometry to characterize these product molecules and found the components of their liquid fuel to be mainly paraffins and olefins 10 to 16 carbon atoms long. This, they explain, makes the liquid fuel very similar chemically to conventional petrochemical fuels.
The catalyst, Kaolin, is a clay mineral containing aluminium and silicon. It acts as a catalyst by providing a large reactive surface on which the polymer molecules can sit and so be exposed to high temperature inside the batch reactor, which breaks them apart. The team optimized the reaction at 450º C, a temperature with the lowest amount of kaolin at which more than 70% of the liquid fuel is produced. In other words, for every kilogram of waste plastic they could produce 700 grams of liquid fuel. The by-products were combustible gases and wax. They found boosting the yield to almost 80% and minimized reaction times required a lot more catalyst, 1 kg of kaolin for every 2 kg of plastic.
The Indian team’s efforts are welcome. The polyethylene scattered about the planet is going to get worse, much worse as time goes by. Some incentive to recycle this and other materials is going to be a matter of simple cleanliness before long. Returning this family of petrochemicals for reuse is a needed enterprise. Drive by any landfill if you’re unconvinced.
This is a better start than many ideas. Let’s hope the economics are favourable and the incentives make the effort to clean up worthwhile.
Your humble writer is getting pretty tired of collecting these used bags from fences, bushes, up in the trees, from under the car . . . ugh. Better they’re made into jet and diesel fuel. Imagine the difference if it were worth it to pick ‘em up.
By. Brian Westenhaus