environmental engineering

Christmas trash gets a second chance

U. WARWICK (UK) — Most plastic packaging on gifts is almost impossible to recycle. A new technique could process 100 percent of household plastics instead of the tiny fraction currently recycled.

Sorting household plastic and putting it into the recycling bin doesn’t guarantee it won’t end up in a landfill. Typically only 12 percent of such waste is truly recycled. Such materials are often simply too time consuming to separate, and often objects are made of more than one plastic, making the job even more challenging.

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

The researchers devised a unit that utilizes pyrolysis (using heat in the absence of oxygen to decompose of materials) in a “fluidised bed” reactor. They literally shovel in a wide range of mixed plastics that are then reduced down to useful products, many of which can be retrieved by simple distillation.

The reclaimed materials include:

  • wax that can then be used as a lubricant
  • original monomers such as styrene that can be used to make new polystyrene
  • terephthalic acid which can be reused in PET plastic products
  • methylmetacrylate that can be used to make acrylic sheets
  • carbon which can be used as Carbon Black in paint pigments and tyres
  • char left at the end of some of the reactions can be sold to use as activated carbon.

The team expects 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 which would produce tanker loads of reusable material.

“We envisage a typical large scale plant having an average capacity of 10,000 tons of plastic waste per year,” says engineering professor Jan Baeyens, the project’s lead researcher. “In a year tankers would take away from each plant over £5 million worth of recycled chemicals and each plant would save £500,000 a year in landfill 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.”

More news from the University of Warwick: www2.warwick.ac.uk/newsandevents

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