STEM Takes on Environmental Issues: CAT-HTR & Plastic Pollution

Plastic is everywhere, and yet, as we discussed here, it is hardly ever recycled. But a recent innovation might change that – the CAT-HTR (catalytic-hydrothermal reactor).

How Does CAT-HTRs Work?

So how does it work? Plastic is shredded, heated, then combined with supercritical water before being heated again. It then enters the CAT-HTR, where the supercritical water breaks the polymeric bonds of the plastic. This releases the hydrogen atoms, leaving behind stable hydrocarbons which can be made into new plastic. There are a lot of neat things about this technology:

It can recycle film plastics, which are notoriously hard to recycle.
It can recycle food-contaminated plastic, something that can’t be achieved my most recycling processes.
Since no combustion is used, the toxic byproducts that come from combustion processes are not produced.
Impurities in the plastics, like additives and colorants, are separated and can be used in other things such as construction.

This technology is relatively new, and as of now, no commercial-scale plants exist. This won’t be the case for long, though, as the first recycling plant to use this technology is currently being built in the UK. When it is up and running, it is estimated that the plant will recycle 80,000 tonnes of plastic annually, and that approximately 85% of the mass of plastic recycled will be turned into hydrocarbons (the rest is lost in the process).

CAT-HTR is a form of chemical (or feedstock) recycling. This refers to recycling methods that aim to break down plastic into its individual components (basic chemical elements). It’s useful because it allows for the recycling of plastics that are typically hard to recycle due to quality, lack of value, or other reasons. Moreover, plastic that is broken down using these methods can be remade into plastic that has the same quality as new plastic. This differentiates it from typical mechanical recycling, in which the quality of plastic is degraded each time it undergoes the recycling process.

While chemical recycling seems promising, it does have some drawbacks, such as being energy-intensive and expensive. Another issue lies in what the hydrocarbons produced are used for – if they are repurposed into fuel, they will act as pollutants just like fossil fuels.

Some chemical recycling methods in themselves also result in pollution, such as pyrolysis and hydrogenation. A report by the GAIA (Global Alliance for Incinerator Alternatives) found that the environmental impact of such technologies is way too energy-intensive and will not be scalable in the near future. However, this report did not speak to the feasibility of CAT-HTR specifically.

Benefits and Challenges

Proponents of CAT-HTR claim that this technology is more energy-efficient. They claim that the use of supercritical water allows for more efficient heat transfer, and that the gas produced by the process will be used to heat the water, even further reducing energy use. They also claim that CAT-HTR will strive to use renewable energy whenever possible.

Whether or not CAT-HTR lives up to its claims remains to be seen, but it could be a major step forward in ensuring that our plastic ends up reused, rather than in a landfill.

While the potential of CAT-HTR is promising, it’s crucial that we acknowledge that this technology it would only be a temporary step. The only way to truly end plastic pollution is to drastically reduce its use in the first place.

If you’d like to learn more about the various types of chemical recycling, check out this infographic here.