HTL – the new kid on the block turning plastics back into oil

Seventy per cent. That’s the target needed to be reached for plastic packaging to be recycled, as set out in the 2017-2022 Strategic Plan for the Australian Packaging Covenant. We are at 16 per cent, with the 2025 target looking unlikely, according to Dr Len Humphreys from biotechnology company Licella.

What is needed are various strategies. A number of companies – RePlas is one example – are trying to convert hard-to-dispose-of plastics into products such as bench seats and tables.

Another way of recycling plastics is to turn them back into their basic building blocks – oil. There are several ways this can be done, with pyrolysis and gasification being the two most common methods. There is a third – hydrothermal liquefaction, or HTL.

The brainchild Humphreys, HTL is in its infancy in Australia, but Humphreys and his team are in the throes of ramping up its capabilities in Australia. What exactly is HTL? It uses hot, pressurised water to recycle carbon from plastic, while using less energy than pyrolysis and gasification. It also moves hydrogen from the water into the newly created oil, making the oil easier to upgrade in a conventional refinery.

“When you introduce water into the equation, it suspends the reaction to stop it going back to carbon. That means that more of the carbon in plastic gets to oil, so we can convert 75 per cent of the plastics back to oil,” said Humphreys. “We have about three times greater conversion compared to gasification, and probably about a 70 per cent increase in conversion compared to pyrolysis.

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“We work at temperatures of around 400˚C, not 600˚C or 900˚C that are needed for gasification and pyrolysis. It’s lower energy, higher conversion, and water controls the reactions to give you more oil and less wasted carbon. It happens at a low temperature because water is chemically contributing. It’s the modern manifestation of advanced recycling.”

What made Humphreys think of this technology to turn plastic back into oil?

“Those already in the industry were stuck in the tradition of what they do,” he said. ”I think like a chemist [Humphreys is an organic chemist with a PhD], not a plastic processor. I think in a different way. I’ve done pyrolysis and gasification before, so I stood on the shoulders of pyrolysis, and then jumped higher.”

One of the benefits of HTL is that costs are less due to the amount of oil that can be converted from plastic, compared to other methods. Another plus for HTL is that when it comes to feedstock it can convert more different types of plastics.

“With a method such as pyrolysis, you have to take out a lot of the layered plastics and films and even PET can be a problem,” said Humphreys, “because both plastics, films and PET can block up the pyroliser. We don’t care. We can take a larger range of more contaminated plastics. We can also take post-consumer biomass and tyres.”

Which is good news for those who hate the idea of plastics going to landfill. A study commissioned by Licella and other third parties found that in Victoria alone, there is potentially 897,000 tonnes of gross plastics being produced by both commercial operations and other consumers.

“We look at the almost 900,000 tonnes and about 500,000 tonnes of it is being buried due to contamination and other reasons,” said Humphreys. “The paper recyclers have to be choosy with what they take. However, because we’re using HTL, we don’t have to be picky, which means we can take a broader range of plastics and biomass.”

In 2021, Licella, supported by Amcor, Coles, iQ Renew, LyondellBasell and Nestlé, released a report highlighting the potential for establishing an advanced recycling facility using Licella’s Cat-HTR HTL platform.

The report highlighted economic and environmental benefits using advanced recycling with HTL to enable a local circular economy for plastic. It found that compared to imported conventional crude, the oil made using HTL delivers a 64 per cent reduction in CO2.

One of the systems is up and running on New South Wales’ Central Coast, while another five commercial plants are to be built around the world. The first commercial plant in Australia is planned for Altona in Victoria, under Licella’s subsidiary Advanced Recycling Victoria (ARV). The advanced recycling facility would be an Australian first and presents the opportunity to divert up to 120,000 tonnes, or 24 per cent, of the waste plastics sent to landfill every year in Victoria.

And what about maintenance? 

“It’s all in a contained system. There is no smoke. It’s a hot, pressurised system – think of it like a pressure cooker,” said Humphreys. “We have spent 15 years reducing maintenance. Every time we did a scale-up, we made it simpler. We only have one moving part in the whole system, which is the part that delivers the plastics or the biomass into the reactor. In the world of pressure and temperature, we’re working in quite a moderate range.

“At the end of the day, we’ve developed an advanced recycling technology that’s more applicable to a carbon constrained world.”