How green are my solvents?

Volatile organic solvents that damage the atmosphere are the normal media for the industrial synthesis of organic (petrochemical and pharmaceutical) products, with a current worldwide use of about 10 billion Australian dollars. The Montreal protocol ban on the use of many solvents has resulted in a compelling need to re-evaluate many chemical processes that have proved otherwise satisfactory for many years.

Offering a green alternative to conventional molecular solvents, ionic liquids are involatile - they have no effective vapour pressure, which means they do not escape into the environment and cause the problems that many molecular solvents do. As well as that, they are easy to recycle.

Among other potential benefits, ionic liquids remain liquid over a temperature range of 300°C (for instance, remaining liquid at temperatures as low as -96°C), allowing excellent process control. At the same time they have proved to be outstandingly good solvents for a range of inorganic, organic and polymeric materials. Their high solubility implies small reactor volumes and - in technical terms - they exhibit Brønsted, Lewis and Franklin acidity, as well as superacidity.

They range from hydrophilic to hydrophobic to hydrophilic varieties (with or without an affinity for water), in water-sensitive to air-stable forms, and they are thermally stable up to 200°C. Very importantly, they are relatively cheap and easy to prepare.

Unlike water and other hydroxylic solvents, ionic liquids can dissolve a range of organic molecules: exploratory work has demonstrated that groups of catalysed organic reactions "are serious candidates for commercial processes". The reactions they have observed, say the researchers, all indicate that "room-temperature ionic liquids are the basis of a new industrial technology. They are truly designer solvents."

The Queen's University Ionic Liquids Laboratories (Quill) centre in Belfast creates designer solvents that, it is claimed, will also improve working conditions for millions of people and significantly enhance job and wealth creation.

Working with a range of industrial partners, including BP, ICI and Shell, Quill is a global player in its field, and the UK representative on the recently formed International Green Network - a scientific consortium focused on developing green chemistry to meet environmental concerns - formed by eight research centres, one based in each of the G8 countries.

The university's Professor Martin Atkins said: "A power mix of industry representatives from sectors as diverse as healthcare products to energy companies has provided a unique forum for discovery and exploitation of the main innovations in the rapidly moving field of ionic liquids. I am unaware of any such industrial research cooperative of this diversity operating in Europe at present."

Centre director Professor Ken Seddon explained: "It is absolutely vital for the future of mankind that we develop ways of tackling pollution. The potential of ionic liquids (liquids composed entirely of ions - electrically charged atoms or molecules) is immense. For example, one of the companies we have worked with, the German chemical giant BASF, reported an 80,000 times increase in productivity after introducing ionic liquids to one of its processes.

"These liquids act as solvents for a broad spectrum of chemical processes and can dissolve a wide range of materials - even rocks, coal and almost anything organic - amazingly well. However, unlike conventional solvents, they do not emit vapours. Put quite simply, they have remarkable properties which have tremendous applications in the development of clean technology for manufacturing processes. They are the basis of a whole new industrial technology.

"Quill is unique in the world in existing to prevent pollution being created in the first place," added Professor Seddon. "The scope of the research is so large that the industry partners cannot afford to develop it individually; Quill provides the perfect mechanism for industry-industry collaboration with an academic nexus. Quill is demonstrably leading the world in ionic liquids for green chemistry, one of the hottest topics in scientific research today.

"Ionic liquids are not intrinsically green," he pointed out. "We could, in fact, prepare some extremely toxic ones, but we can design them to be green, and 'design' is an essential element of green chemistry. While they contribute no VOCs [volatile organic compounds] to the atmosphere, and are non-flammable, if these were the only reasons for using ionic liquids, they would represent a worthy, but rather boring, area of research - green, but a dull green!

"However, ionic liquids have a wide range of other properties that make them fascinating. There are at least a million simple ionic liquids possible and a trillion ternary ionic liquids. It is thus possible to design and tune the solvent to suit very specific requirements."

Solving solutions: "designer solvents" can tackle primary sources of pollution. Professor Ken Seddon (left) and Professor Jim Swindall demonstrate ionic liquids developed in the word-leading research centre at Queen's University, Northern Ireland. The ion-packed solvents can also improve working conditions for millions of people and significantly enhance job and wealth creation.