05.10.2020 change 05.10.2020

Polish prof’s ‘inventive and beautiful’ images of rotating chemical reactors on cover of Nature magazine

Stunning images by a Polish scientist of ‘self-organizing chemical factories’ which use centrifugal force and liquids of different densities have made it on to the front cover of the prestigious journal Nature.

The rotating reactors by Professor Bartosz Grzybowski and his team at the UNIST University in South Korea and the Institute of Organic Chemistry of the Polish Academy of Sciences, which show how to carry out a whole series of complex chemical reactions at once by using centrifugal force, could be used to recover, among other things, lithium from battery liquid.

That liquids of different densities can form immiscible layers can be observed even during lunch, by staring at the eye of the broth in soup. The fat in soup rises to the top, as it is less dense than the watery part of the soup.

You can also do a more complex experiment at home by slowly pouring many liquids of different densities into one vessel. You can start with the thickest honey, through maple syrup, washing up liquid, water, vegetable oil and the least dense kerosene. If it is done slowly enough, in this (inedible) density column, you can see the differently coloured, separate, unmixed layers.

But if you now start to spin such a density column very, very quickly by turning the vessel around its vertical axis (like on a potter's wheel, but much faster, for example 2,600 revolutions per minute), the subsequent layers will form concentric rings. The lightest liquids will have a smaller diameter and will be arranged closer to the centre of this centrifuge, and the densest ones will form large rings closer to its periphery. 

The centrifugation is an important factor as the centrifugal force begins to dominate over the surface tension of the liquid. So you can get very thin layers of liquid (0.15 mm, and maybe even thinner) without the risk that they will mix. If the density of the liquid is properly selected, scientists show that up to 20 coloured rings rotating around a common axis in the centrifuge can be obtained.

A spinning density column is an extremely aesthetic physical experiment in itself. But Professor Grzybowski and his team have shown how much chemists can benefit from it. Rotating liquids of different densities can be prepared in such a way that each of them contains a different reagent needed for a chemical reaction.

Since the rings are very thin and their contact area is large, diffusion of compounds between successive rings takes place in a relatively short time (much shorter than if the column did not move).

Professor Grzybowski points out that such self-organizing chemical factories can find industrial applications, for example to separate ingredients from mixtures. In the publication in Nature, the researchers show how to recover amino acids (protein components) from fermentation broth in such a spinning experiment.

Grzybowski said: “It could be done similarly in the case of lithium recovery from the battery mixture. Now that would be a business. After all, there are no good methods for that yet.”

The research was carried out largely in Korea and partially at the Institute of Organic Chemistry PAS. In addition to Professor Grzybowski, several other Polish scientists were involved: Dr. Olgierd Cybulski, Dr. Mirosław Dygas, Barbara Mikulak-Klucznik, Dr. Marta Siek and Dr. Tomasz Klucznik.

PAP - Science in Poland, Ludwika Tomala

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