New technique recycles 100 percent of household plastic
By Ben Coxworth
December 15, 2010
This Christmas, chances are you’ll save the plastic film and blister packs that your presents come encased in and send it all off for recycling. According to scientists from the University of Warwick, however, only about 12 percent of plastic sent to depots actually gets recycled. Because of problems such as glued-on paper labels, or different types of plastic being combined in one product, the rest of it goes to the landfill or is burnt as fuel. Those same scientists have now devised a system that could recycle 100 percent of household plastic.
The Warwick system is based around a unit that utilizes pyrolysis within a fluidized bed reactor. Pyrolysis is the use of heat in the absence of oxygen for the decomposition of materials, while fluidized bed reactors pass a gas or liquid through solid granular material at high velocity, causing it to behave like a liquid.
The researchers shoveled a wide variety of mixed plastics into the reactor, which were then broken down into useful elements that could be retrieved (in some cases) through distillation. Those elements included wax, which could be used a lubricant; original monomers such as styrene, that could be used to make new polystyrene; terephthalic acid, which could be repurposed in PET plastic products; methylmetacrylate, that could be used to produce acrylic sheets; and carbon, which could be used as Carbon Black in paint pigments and tires. The char left over at the end of the process could reportedly also be sold as activated carbon.
“We envisage a typical large scale plant having an average capacity of 10,000 tonnes of plastic waste per year,” said lead researcher Prof. Jan Baeyens. “In a year, tankers would take away from each plant over £5 million (US$7.7 million) worth of recycled chemicals and each plant would save £500,000 (US$777,291) a year in land fill taxes alone. As the expected energy costs for each large plant would only be in the region of £50,000 (US$77,729) a year, the system will be commercially very attractive and give a rapid payback on capital and running costs.”