Ionic liquids – ILs, TRILs, TSILs

High energy ionic liquids

Ionic liquids are substances that are molten salts with a low melting point (below 100°C). They consist of a large and asymmetric organic cation and an organic or inorganic anion. Their advantages include low vapor pressure, a wide temperature range in which they exist in liquid form, high stability, the ability to dissolve many compounds, and high conductivity. In recent years, there has been growing interest in ionic liquids as an environmentally friendly alternative to organic solvents and in areas such as organic synthesis, electrochemistry, separation and analytical techniques, materials chemistry and others.

By selecting an appropriate compound structure, high-energy ionic liquids can be obtained, which can find applications as explosives or rocket fuels. Thus, they can successfully replace the currently used hydrazine, which is a volatile, toxic and carcinogenic substance. Ionic liquids also have the advantage of being easy to work with due to their low toxicity and very low volatility. Many ionic liquids exhibit spontaneous ignition (hypergolic) on contact with some oxidizers. This feature is very desirable in rocket propulsion because ignition of both components occurs spontaneously and no additional ignition system or catalyst is required. An important parameter characterizing hypergolic fuel is its ignition delay. This is the initiation time that elapses from the moment the fuel (e.g. ionic liquid) and the oxidizer come into contact with each other. It is preferable for this parameter to be as low as possible. Properly selected substances and oxidant can achieve very low ignition delay times. Currently, the typical hypergolic system used is dimethylhydrazine and diazotium tetroxide or fuming red nitric acid. All of these compounds are highly irritating, poisonous and dangerous. Ionic liquids are a much more advantageous alternative, especially since some compounds show ignition with highly concentrated hydrogen peroxide, which is a fairly safe, but mostly non-toxic substance.

We will design for you an ionic liquid with the expected properties – TSILs (task specific ionic liquids).

The table below presents frequently used groups of cations and anions for creating high energy ionic liquids. The cations used are often suitable derivatives of heterocyclic compounds (like imidazole), for this purpose products containing substituents like 1-butyl-3-methylimidazole, 1-ethyl-3-methylimidazole, 1-allyl-3-ethylimidazole etc. are obtained by chemical synthesis. Similarly, the anions used can be suitably modified from the borohydride to form cyanoborohydride or dicyanoborohydride. This means that the number of possible ionic liquids that can be formed is essentially unlimited.

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