August 14 – Advanced plastic waste recycling technologies, such as pyrolysis and gasification, are touted by the chemicals industry as the solution to the ever-growing plastic waste epidemic, because they can tolerate mixed plastics and films, which can’t be handled through traditional mechanical recycling.
But their heavy energy usage, emissions of toxic pollutants, and low levels of conversion into new plastics have put a question mark around their environmental credentials.
A UK company, Mura Technology, is aiming to change all that with a technology that uses water heated to supercritical temperatures to break down the bonds in waste plastic, instead of combusting the plastic itself.
The company’s first commercial-scale plant, at Wilton on Teesside, will open later this year, recycling an initial 20,000 tonnes per year of plastic waste, such as films, pots, tubs and trays, which are currently sent to landfill or incinerated.
The company claims the process creates a “true circular plastics economy” because the oils derived from the waste can be used to produce new food-grade plastic, with no limit to the number of times it can be reprocessed.
Geoff Brighty, the UK company’s chief sustainability officer, told a recent conference in London that Mura’s HydroPRS technology works in a similar way to pyrolysis, which is the thermal processing of a substance in the absence of air. But instead of applying heat directly to plastics, it heats water under supercritical conditions to crack the polymeric material in plastic back into short-chain hydrocarbons. “You aren’t creating a char or a waste material, meaning we have very high conversion efficiencies (high 80s or maybe even low 90s) and you are putting less energy into the system,” said Brighty.
A lifecycle assessment by the European Commission’s Joint Research Centre this year found that HydroPRS had a global warming potential about 50% lower than pyrolysis, and 80% lower than incineration. Researchers at the University of Warwick, found that the process doesn’t create the same harmful byproducts, such as dioxins, “and helps to maximise higher product yields” of recycled plastics.
“By diverting plastics from energy from waste,” Brighty said, “we estimate a net saving of 1.8 tonnes of CO2 for every tonne we process.”
The system is tolerant of mixed, contaminated plastic waste, including polystyrene and agricultural plastic waste.
“Millions of tonnes of plastic waste in this country go to incineration each year,” Brighty said. “We want to change that. The point is to complement the existing mechanical recycling infrastructure by diverting it away from energy from waste.”
Besides producing different grades of plastic, one byproduct of the process is a heavy wax residue, the result of stripping off the waxes in waste plastic packaging.
“It’s effectively a bitumen binder that can be used to decarbonise road-making,” said Brighty.
Mura has partnered with large chemicals companies including Dow and Chevron Phillips Chemical, which has an equity stake, and has a pipeline of projects in Europe and the U.S, with four 100,000 tonnes per annum sites under development in Germany and four of the same capacity under development in the U.S. It has also licenced Mitsubishi to use its technology. By 2025 the company says it will have 1 million tonnes of capacity in operation or being constructed globally.
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