Challenging channels

Three UK universities are collaborating to devise a way of making environmentally-friendly microreactors, which hold the promise of efficient screening and synthesis of new chemicals.

Researchers from Liverpool, Bath and Durham are combining to make tiny chemical reactors. The goal is to find environmentally friendly ways of making the microreactors, which hold the promise of efficient screening and synthesis of new chemicals and drugs.

Microreactors are miniaturised chemical plants, where fluids are pumped through channels only micrometres across into equally tiny reaction chambers. Devoid of turbulence and using only small quantities of chemicals, they are proving useful for testing new reaction routes for the process industries and for screening chemical compounds for toxicity or pharmaceutical activity.

Although environmental friendliness is a major advantage, the methods of making them are anything but green. Microreactor design is based on the circuitry of microprocessors and similar techniques are used to make them; corrosive chemicals are used to etch the channels from blocks of metal or alloy. The project, due to begin in October, uses rapid prototyping techniques, making the reactors by building material up rather than taking them away.

A team from the University of Liverpool will use high-powered lasers to melt powders of steel or alloys to build the complex geometries layer by layer. These reactors will be riddled with channels about 100µm across, designed to carry reactants and heat exchange fluids.

Then a team from Durham, led by Jas Badayal, will bombard the channels with plasma to ‘functionalise’ their surfaces to allow them to be coated with polymeric materials.

The microreactors will be passed to project leader Pawel Plucinski at BathUniversity. In the non-functionalised systems, whose channels are designed to act as a static mixer, the team will use experimental catalysts based around magnetic nanoparticles coated with ceramics or polymers with catalytic functions; their magnetism makes them easy to recover from reaction mixtures and recycle.

The functionalised surfaces will be further converted to make them catalytically active, by coating them with polymers with catalytic activity. ‘There are coated micro-reactors now, but they are designed for gas-phase experiments; they are coated using vapour deposition and work at very high temperatures. We want to do liquid-phase work, so we need the mixing function as before and we can use polymer catalysts because the reaction temperatures are so much lower,’ Plucinski said.

To test the devices, chemical engineers are developing new sensors. ‘We need to have IR and UV to tell what’s going on, and we’re looking at piezoelectric devices we can install in the channels for information about the flow rates,’ Plucinski said. ‘Existing sensors only work on single-channel devices.’