Recycling Atoms With Supercritical Water

You can light stuff on fire in supercritical water?!

Dec 27, 2023

Quaise is a company making science fiction a reality. As Eli Dourado describes it, “[t]he company is developing a drilling system that uses gyrotron-generated mm-wave directed energy to vaporize granite.”

But that’s not even the best part. By drilling deep enough, Quaise can produce supercritical water anywhere on Earth. They promote this as a way to produce renewable energy, but like most clean technologies, we’re thinking too small.

Supercritical water (SCW) is special, at about 400C and 200 atmospheres of pressure, water becomes completely different. It can transfer heat efficiently, dissolve new substances, and light things on fire.

undefined — Past the critical point, water becomes a supercritical fluid (source)

This last property is the most interesting. Using only water, you can burn any organic matter into simple molecules like N2, O2, CO2, and H2O. In fact, supercritical water is one of the only ways we know of to break down “forever chemicals”.

We can use this trick to recycle our trash. All sewage, paper, plastic, yard waste, and food can go into a supercritical water oxidation system and get broken down. Even better, the process generates additional energy from burning trash. This atomic recycling system can even help with the future carbon shortage.

Carbon shortage? I thought we had too much carbon in our atmosphere? We do, but notice how little carbon there is relative to the other elements needed for life like nitrogen (80% of our air), oxygen (20% of air), and hydrogen (water). Every time we burn carbon and scatter it to the wind we make the problem worse. This is why Austin Vernon and Eli Dourado point to a coming carbon shortage in Energy Superabundance:

Once any materials manufacturing process using CO2 from the air becomes competitive, our tragedy-of-the-commons problem reverses. Each ton of polyethylene produced sequesters over three tons of CO2 (see appendix). Cement production would also be carbon negative. If these processes become economical, it becomes inevitable that we will have a carbon shortage in the atmosphere.

But supercritical water oxidation fixes all of that. Every bit of carbon in our waste can get broken down into simple molecules. And there’s already significant effort devoted to converting CO2 back into chemical products1.

But wait! There’s more! Supercritical water can perform a wide range of chemical processes. Electrolysis is easier in supercritical water, providing green hydrogen. Paradoxically, salts have low solubility in supercritical water, meaning that it can be used for desalination. And finally, SCW is also a green solvent that can support a wide range of chemical reactions. Imagine a system that took all sorts of sewage and spat out clean water, hydrogen, and carbon-neutral fuel. On site facilities could transform those inputs into plastics, fertilizer, and pharmaceuticals. We would be one step closer to a system that uses local energy to transform organic matter however we want2.

Unfortunately, supercritical water oxidation lags far behind other clean technologies. Research on supercritical chemistry is just beginning, and using supercritical water in an industrial process is challenging because supercritical fluids are corrosive. On the bright side, coal and nuclear power plants use supercritical water to generate energy, so perhaps this process could be adapted to a more complex reaction mixture.

I think this approach deserves more attention, and enhanced geothermal companies should consider it as part of their pitch. Most other clean technologies are seeing exponential growth, but if we want to recycle atoms in time to cope with climate change, we need to move faster.

Splitting Infinity

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Splitting Infinity

Recycling Atoms With Supercritical Water

You can light stuff on fire in supercritical water?!

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