Carbazole - motor fuel of the future?

By Stefanie Koller and Sebastian Raabe Jul 20, 2011, 3:06 GMT

Stuttgart - The toxic organic chemical carbazole is being touted as the fuel of the future for the motor industry by two German researchers because of its ability to store hydrogen.

Senior government transport official Rainer Bomba has gone so far as to refer to a 'miracle substance,' although major German carmakers remain unimpressed.

Research currently being conducted by two professors at the University of Erlangen-Nuremberg, Wolfgang Arlt and Peter Wasserscheid, is still in its infancy, but there are hopes the brownish liquid in the form n-ethylcarbazole will replace petrol and diesel.

The little-known chemical is capable of storing hydrogen for release in a car fuel cell or even in a normal internal combustion engine.

By contrast with petrol and diesel, the carbazole can then be recycled and charged with hydrogen once more. The used carbazole is pumped out of the car at the filling station and replaced with fresh product enriched with hydrogen - the actual fuel.

Arlt says that drivers would see very little difference, apart from the nozzle, and that the rest of the filling station infrastructure would remain largely unchanged.

The aim is to generate hydrogen from solar or wind energy, enriching the carbazole with hydrogen on site where the energy is generated to avoid transporting the highly explosive gas. Tanker trucks would deliver the finished product directly to the filling stations.

The idea is seductive, because the dangers involved in handling pure hydrogen have caused the biggest headaches for engineers working on hydrogen fuel cell technology. Hydrogen can be stored only at extremely low temperatures or under high pressure.

The new carbazole idea is in competition with the alternative of storing hydrogen under high pressure in a car fuel tank. This is the technology being used by Daimler, makers of the Mercedes Benz range, for its fuel cell cars, which the Stuttgart company hopes to bring onto the market in 2014.

'We have looked thoroughly into the options for using carbazole,' a Daimler spokeswoman said, adding immediately that the disadvantages outweighed the advantages. In Daimler's view, carbazole is currently not suitable for use in cars powered by fuel cells.

Rival BMW has also turned away from this technology, after looking into it for years. 'It sounds really good,' a spokesman for the Munich-based company said, noting that the research was still in its infancy.

However, what appeared good in theory did not always work in practice, and there were 'many, many problems', he said, casting doubt on whether carbazole would ever power a production car.

The main difficulty is that a considerably higher temperature is required than the 80 degrees Celsius at which the Daimler fuel cell car operates, according to the spokeswoman.

The car would need additional temperature control equipment necessitating considerable technical effort. In addition, the hydrogen released by the carbazole would not be of sufficiently high purity and would have to be purified to ensure that the sensitive membranes built into the fuel cell were not damaged.

Another problem is tank capacity. A car using carbazole charged with hydrogen would need to carry twice as much fuel to travel the same distance as one using petrol.

There would also be a considerable change in driving behaviour, with acceleration taking much longer, as the carbazole gives up its hydrogen only relatively slowly, according to Daimler.

'That's unacceptable,' Arlt acknowledges. But he and Wasserscheid plan to iron out some of these problems. 'We've been working on this issue for a year and we're still at the laboratory stage. There are no prototypes yet.'

The two professors acknowledge there is a long road to travel before the technology is ready for mass production, perhaps as long as 10 years.