Useful sulfur | Science and life

Can a mineral turn into useless? Despite the fact that at first glance, such a thought seems absurd, there are many examples of such “miracles”. Recently, we have seen negative futures oil prices. And those who like to go mushrooming and berries in the summer probably know that the mountains brought from the forest of boletus and strawberries promise some problems. With mushrooms, berries or oil, it is easier in this regard – when there are too many of them, their collection and production can be limited by force. But this method does not work with all minerals. And one of them is sulfur.

Native sulfur has been known to mankind since time immemorial. And pure sulfur deposits have long been the main source of this valuable element for industry. However, over time, oil and gas refineries became the main “deposit” of sulfur. The fact is that in natural oil and gas contains a certain amount of sulfur compounds – various substances in the molecules of which there are sulfur atoms. Oil and gas from different deposits differ in sulfur content – in some it is very small, but in others, on the contrary, very much.

You can’t just leave sulfur in oil or gas. If gasoline or diesel fuel is made from crude oil that is not purified from sulfur, then all exhaust gases obtained from burning this fuel will contain a large amount of poisonous gas – sulfur oxide. Not only is it harmful in itself, it also contributes to the formation of acid rain. The situation with natural gas is similar. In addition, if we process oil and gas into petrochemical raw materials, the high sulfur content in it will disable complex catalytic systems of chemical plants, since sulfur is a poison that poisons catalysts. Therefore, excess sulfur is disposed of at the earliest stages of hydrocarbon processing – even at oil refineries and gas refineries. As a result of cleaning hydrocarbons from sulfur compounds, huge volumes of sulfur are formed, with which it is not always clear what to do.

Most of the sulfur goes to the production of sulfuric acid and mineral fertilizers, but still there is too much “unnecessary” sulfur. It is cheap, it is usually stored in the open air in the form of real sulfur mountains several tens of meters high. And this creates problems: firstly, the wind carries dust particles of sulfur, and secondly, sulfur is gradually oxidized up to sulfuric acid under the influence of atmospheric oxygen and various microorganisms. In all this there is nothing good either for the environment, or for people and animals living near such places. Therefore, many chemists have been struggling over the problem of what is useful from sulfur. And great success in this was achieved by a group of researchers from the University of Liverpool.

Last year, they published an article in Nature Communications that described the method of “reverse vulcanization” – the synthesis of an unusual polymer based on sulfur. The essence of “ordinary” vulcanization is that long mobile polymer molecules, for example, natural rubber are crosslinked by short “bridges”, for example, of the same sulfur, making the material more durable. This method is the basis for rubber production. During vulcanization, sulfur acts as a kind of molecular bond.

However, sulfur has a unique feature – it itself can form quite long chains. And here it becomes possible to do the opposite – to use sulfur not as paper clips for polymers, but as the polymer itself. True, such sulfur chains in their pure form turn out to be short-lived and quickly fall apart into fragments. This is where “reverse vulcanization” comes in handy, the purpose of which is to crosslink long and brittle polymer sulfur molecules into small molecules.

Thanks to reverse vulcanization, it is possible to turn large volumes of “useless” sulfur into a completely useful polymer material. Recently, researchers from the University of Liverpool and Flinders University presented new results – they were able to significantly improve the characteristics of the “sulfur polymer” by developing the technology for its production in two separate stages (they allow you to obtain a polymer with the required characteristics), and in addition, show that such polymer materials can be repaired after damage and even recyclable.

If such a technology develops, then we can not only solve the problem of an overabundance of sulfur obtained from oil and gas, but also create completely new and cheap polymer materials.