Reducing bulk solvents in the process industries

Bulk solvents used in the process industries can pose a serious threat to human and environmental health.

But now a team of international researchers is attempting optimise a technique known as mechanochemistry that avoids the use of these solvents altogether.

Mechanochemistry is the general name applied to the field of reactions caused by mechanical energy.

In recent years, ball milling has become increasingly popular mechanochemistry method for the production of highly complex chemical structures.

In such synthesis, steel balls are shaken with the reactants and catalysts in a rapidly vibrating jar.

Although it is well known that mechanical action can break chemical bonds, for example in tear and wear of textile fibres, it is much less known that mechanical force can also be used to synthesise new chemical compounds and materials.

This is difficult to model and, without access to real time reaction monitoring, mechanochemistry remained poorly understood.

These results could improve understanding of processes central to pharmaceutical, metallurgical, cement and mineral industries

Scientists have, for the first time studied, a milling reaction in real time, using highly penetrating X-rays to observe the surprisingly rapid transformations as the mill mixes, grinds and transforms simple ingredients into a complex product.

“When we set out to study these reactions, the challenge was to observe the entire reaction without disturbing it, in particular the short-lived intermediates that appear and disappear under continuous impact in less than a minute”, said Tomislav Friš?i?, a Professor at McGill University in Montreal.

The team of scientists chose to study mechanochemical production of the metal-organic framework ZIF-8 (sold as Basolite Z1200?) from the simplest and non-toxic components.

Materials such as ZIF-8 are rapidly gaining popularity for capturing large amounts of CO2 and, if manufactured cheaply and sustainably, could become widely used for carbon capture, catalysis and even hydrogen storage.

“The team came to the European Synchrotron Radiation Facility (ESRF) because of our high-energy X-rays capable of penetrating 3 mm thick walls of a rapidly moving reaction jar made of steel, aluminium or plastic.

“The X-ray beam must get inside the jar to probe the mechanochemical formation of ZIF-8, and then out again to detect the changes as they happened”, said Simon Kimber, a scientist at the ESRF in Grenoble.

This methodology enabled the real-time observation of reaction kinetics, reaction intermediates and the development of their respective nanoparticles.

This technique is not limited to ZIF-8. In principle, all types of chemical reactions in a ball mill can now be studied and optimised for industrial processing.

“These results hold promise for improving the fundamental understanding of processes central to pharmaceutical, metallurgical, cement and mineral industries and should enable a more efficient use of energy, reduction in solvent and optimise the use of often expensive catalysts,” said Tomislav Friš?i?.

The international team included scientists from McGill University, the University of Zagreb, from University of Cambridge, the Max-Planck-Institute for Solid State Research and the ESRF.