Prof. Jan Baeyens with plastic for the fluidized bed
reactor (Photo: University of Warwick)
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.”