Plastic waste could be recycled through new pyrolysis process

Although householders currently spend a great deal of effort separating out their plastic waste for recycling, typically only 12 per cent of the so-called municipal plastic solid waste is truly recycled.

It is often simply too time consuming to separate out and clean the various types of plastic, as that requires significant laborious human intervention. An additional problem is that often objects are made of more than one plastic that would require different treatments.

However, the Warwick engineers have come up with a simple process that they claim can cope with every piece of plastic waste and can even break some polymers such as polystyrene back down to its original monomers (styrene in the case of polysterene).

To demonstrate the effectiveness of their recycling process, the researchers have designed a system which uses pyrolysis (using heat in the absence of oxygen to decompose of materials) in a fluidised bed reactor.

Tests completed in the last week have shown that the system can reclaim from the plastic mix a wide range of products. These include wax that can be used a lubricant; original monomers such as styrene, which can be used to make new polystyrene; terephthalic acid that can be used in PET plastic products; methylmetacrylate that can be used to make acrylic sheets; and carbon which can be used as carbon black in paint pigments and tyres. Even the char left at the end of some reactions can be sold as activated carbon at a value of at least £400 a tonne.

This research could have a significant impact on the budgets of local authorities and produce considerable environmental benefits. The lab-scale tests have successfully produced distilled liquids and solids that can be processed into new products.

The Warwick University engineers are now working with the university’s technology transfer arm, Warwick Ventures, who expect their work will be of great interest to local authorities and waste-disposal companies who could use the technology to create large-scale reactor units at municipal tips that would produce tanker loads of reusable material.

The lead researcher on the project, engineering professor Jan Baeyens, said: ’We envisage a typical large-scale plant having an average capacity of 10,000 tonnes of plastic waste per year. In a year, tankers would take away from each plant over £5m worth of recycled chemicals and each plant would save £500,000 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 a year, the system will be commercially very attractive and give a rapid payback on capital and running costs.’