Chemical & Engineering NewsKey insightsThe demand for desalinated water is high and still growing. Reverse osmosis, one of the most common desal...

Chemical & Engineering News
Key insights
The demand for desalinated water is high and still growing. Reverse osmosis, one of the most common desalination methods, isn't meeting the need.
Researcher Juan Felipe Torres has developed a method for desalinating water that relies on an old technology called thermodiffusion.
Thermodiffusion harnesses a temperature gradient to separate sodium chloride ions from seawater.
Vitals
Hometown: Medellín, Colombia

Current position: Associate professor, Australian National University, and founder and CEO of Soret Technologies

Education: Bachelor of engineering, mechanical and aerospace engineering, 2009, and master of engineering, mechanical systems and design, 2011, Tohoku University; doctor of philosophy, fluid mechanics/mechanical systems and design, Tohoku University and École Centrale de Lyon, 2014

Professional highlights: Worked as a research scientist at Toshiba from 2014 to 2016; founded Soret Technologies in May of 2025

Favorite molecule: H2 because it’s abundant in the universe and it forms the basis of life, but at the same time it could be the key to solving the energy crisis

Hobbies: Scuba diving, camping with his family

Artistic or nonscientific work that inspires you: Yojijukugo (the Japanese art of conveying ideas in a few characters); the Bible; fractals

As climate change drives hotter, drier weather and a population boom strains the limited water supply in arid regions, a growing number of cities and countries are turning to desalination to meet their freshwater needs. The global demand for desalinated seawater is expected to double by 2030. More than 21,000 desalination plants are currently in operation, up from 14,000 in 2008.

But the process that powers most of these plants, called reverse osmosis, is energy intensive and can be damaging to the marine environment. It requires large amounts of electricity (most often supplied by burning fossil fuels) to push water through a membrane and separate salt from H2O molecules, producing a heavy saline brine as a by-product that’s released back into the ocean.

Juan Felipe Torres, a researcher at the Australian National University, has developed a technique for desalinating seawater that he believes can address all these issues at once. It’s based on a method called thermodiffusion, which has been known to science since the 1850s but operates too slowly to be practical for most real-world applications. With Torres’s engineering tweaks, the method is much faster. He’s now working on patenting it and spreading it to various industries through his company, Soret Technologies.

Diana Kruzman spoke with Torres about how thermodiffusion could outcompete reverse osmosis in certain cases and how it can be applied to lithium mining and chemical engineering. This interview was edited for length and clarity.

What’s the current state of desalination technology?

The industry worldwide right now is relying on a very old technology. It’s called reverse osmosis, and the first commercial plant in the world opened in California 60 years ago. Fast-forward 60 years, and you would think this technology took over and solved our problems. But in reality, we’ve satisfied less than 0.5% of our freshwater needs by desalination, and more than a billion people worldwide are suffering from water scarcity. So the technology that we're using now is old, and it does not meet the needs we have.

Although the energy efficiency of reverse osmosis is outstanding, there are risks of long-term use—membranes degrade, and they're difficult to maintain. And there's also the brine problem. The recovery rate, which is how much water we can purify from seawater for a given technology, for reverse osmosis is 50%. That means that for every cubic meter of fresh water that is produced, a cubic meter of brine is produced as well. And that brine is hypersaline, double the salt concentration [of seawater]. And when it’s dumped into the ocean, it sinks to the seabed and has a big environmental impact.

What exactly is thermodiffusion?

Thermodiffusion is the transport of species, either ions or dissolved solids, when there's a temperature gradient. So one side is hot, the other side is cold, and those species would move either to the hot or to the cold. And sodium chloride ions, in the case of seawater, move spontaneously to the cold side.

How thermodiffusion desalinates water
Thermodiffusion works by leveraging the natural properties of sodium chloride ions, which move spontaneously toward the cold side of a channel (shown). In Torres’s device, multiple channels are combined to enhance thermodiffusive separation.
A 2D illustration of a thermodiffusion device. Saline water flows left to right between a hot water bath (top) and a cold water bath (bottom), and small circles representing ions in the saline water are shown moving down toward the cold water bath. At the right side of the device, the saline water exits via a low-salinity stream and a high-salinity stream.
Credit: Yang H. Ku/C&EN
How did you start working on it?

I started working at Toshiba a couple of years after the Fukushima [Daiichi Nuclear Power Plant] disaster. At the time, Toshiba was in charge of cleaning all this contaminated water [from the nuclear meltdown]. And while doing research, I found that thermodiffusion was used in the Manhattan Project to enrich uranium; the first bomb was actually enriched halfway through thermodiffusion. This background, and the need to clean and purify water that had this nuclear waste content, led me to study a bit more about the potential of thermodiffusion as a separation technology.

Why haven’t we used thermodiffusion for desalination before?

Thermodiffusion has never been used for desalination because it's a weak phenomenon. It takes a long time to produce small concentration differences. So this is where the engineering challenge is. How can we enhance thermodiffusive separation while keeping recovery rates of 50% or more, and without compromising energy efficiency?

This is where our invention comes into play. It's called multichannel thermodiffusion, which is a network of channels that enhance thermodiffusive separation. We arrange them in a cascaded structure that can be 3D printed or produced en masse using injection molding.

Water flows through a rectangular channel where the top wall is hot and the bottom wall is cold. The ions move spontaneously to the cold bottom wall. Once the flow reaches the end of the channel, the high-concentration [stream] goes to the right, and the low-concentration [stream] moves to the left. We use neighboring channels to reconnect . . . low-concentration streams [which we then run through thermodiffusive separation again]. So at the end, we're able to enhance the separation substantially.