Gas guzzler

A pioneering catalyst technology could transform carbon dioxide emissions from power stations into a key component of battery electrolytes, carrier bags and fuel-improving additives.

A Newcastle University team led by Prof Michael North has developed a process using highly active dimetallic aluminium (salen) complexes to produce useful cyclic carbonates that could save a great deal of energy.

The process can be carried out at room temperature, normal atmospheric pressure and with concentrations of CO_² found in power stations' exhaust gases. Existing catalysts for this reaction only work at very high temperatures — in excess of 100ºC — and at anything up to 100 atmospheres of pressure.

'Simple thermodynamics tells you you're going to generate much more carbon dioxide to make the heat and the pressure that you need than you're going to consume in making the cyclic carbonite,' said North. 'Instead of using carbon dioxide, the current processes are net generators of carbon dioxide.

He added: 'The big breakthrough is having a catalyst that works well at atmospheric pressure and temperature, and is compatible with the CO_² concentrations that come out of the effluent stream of a power station. Overall we can turn the process from one which is a net producer of CO_² into one that is a net consumer of CO_².'

The team settled on dimetallic aluminium complexes as a target material through a combination of previous literature in the area, 'a bit of chemical know-how' and the fact that out of the suitable metals, aluminium is the most environmentally benign. It has a low toxicity, is cheap and is less toxic than alternatives such as chromium and cobalt.

North said the technology is designed for fixed-site CO_² producers such as power stations, steam reforming plants or oil refineries.

The researchers proved their technology in the lab using an artificial waste stream, made by burning methane and generating a stream of carbon dioxide, water and the other impurities similar to an industrial output mixture, and passing it over the catalyst.

The cyclic carbonates produced by the process have a number of applications. One growth market is in the manufacture of ethylene carbonate, a component of electrolytes used in rechargeable lithium ion batteries.

Cyclic carbonates are already used as industrial solvents, and North believes a greater proportion of less environmentally sound solvents could be replaced by solvents made using his method. They can also be polymerised to make biodegradable polycarbonate carrier bags from renewable sources instead of the commonly used polyethylene variant, whose use is being discouraged.

Cyclic carbonates are used as chemical intermediates for other useful chemicals. Dimethyl carbonates, made from dimethylene carbonates, can be used as an anti-knocking agent for petrol. At present they cannot be made cheaply enough to be viable, but North believes the new technology will bring the price down significantly.

'The moment you say to people we're going to burn it in petrol, they say that's not very green,' said North. 'But of course if you're getting 100mpg rather than 40mpg, it is making a big contribution to reducing oil usage.'

One method of dealing with CO₂ is to capture and store it. North said although he is not against carbon capture and storage, he believes it makes more economic sense to turn the CO₂ into a useful product, which could also represent a more viable long-term solution.

'The projections are that worldwide production of oil and gas is going to peak by 2020, so we're going to have to redesign the entire chemicals industry to take alternative feedstocks in anyway. Obviously the ideal solution would be for one for those feedstocks to be carbon dioxide,' he said.

North believes his method could find a use for 48 million tonnes of CO₂, which is four per cent of the UK's emissions, based on UN figures. 'You wouldn't even need to fit our device to every power station in the country to produce all the cyclic carbonates that we need,' he said.

The team is now securing follow-on funding from suitable sources to allow it to study pre-pilot and pilot plants. It will then consider business models with a view to commercialising the technology.

Berenice Baker