Cooking up a transport solution

Fuel cell cars could one day run on hydrogen made from cooking oil now research into a novel way of producing hydrogen is to take a step forward. If the process is proved to have commercial potential, other sources of the gas could include scrap tyres and waste industrial oil.

A team at the Energy and Resources Research Institute of Leeds University is perfecting the making of liquid fuels by reforming unmixed steam. Put simply, fuel is reacted with steam to release hydrogen from both.

The process was invented 10 years ago in the US but not made public until 1999. Now researchers around the world are trying to make it commercially viable so that it can play a significant role in the much-touted ‘hydrogen economy’.

It claims to be a convenient way to distribute fuel for hydrogen production, which is difficult and expensive to store and transport.

Speciality chemicals company Johnson Matthey and scrap tyre recycler Tyrolysis of Wales, are supporting the work at Leeds. The idea is that fuel can be distributed in liquid or compressed gas form to filling stations, where it is reformed into hydrogen.

General Electric has a large demonstrator in place but it uses methane and pulverised coal. The Yorkshire team is, instead, investigating the basic science for the process so that other fuels, particularly those from biomass and the waste stream, can also be used.

‘The science is not well understood in detail,’ said Dr Valerie Dupont, principal investigator at Leeds. ‘In the last three years we have looked at the chemistry of the process and there is still more to do to make sure that it is optimised and reliable.’

In laboratory experiments, up to 76 per cent of the available hydrogen has been produced from the methane fuel and steam combined, and 44 per cent from sunflower cooking oil and steam combined. Higher efficiencies could be achieved with improved steam conversion, which is now the main limiting factor.

The laboratory reformer has a total capacity of 80cc and contains a granulated nickel/alumina catalyst, which is fed first with air. Oxygen from the air binds with the nickel in an exothermic reaction that generates heat for the process. Then some vaporised fuel is fed into the reformer to help complete reduction of the nickel.

Finally, with the reformer now running at about 800ºC, a mix of vaporised fuel and steam are fed in so that dolomite can absorb the carbon dioxide, effectively separating out the hydrogen. The process is repeated and is regenerative. Sulphur in the fuel is claimed to also undergo oxidation under the airflow rather than irreversibly poisoning the reforming catalyst.

The nickel material and the dolomite are sometimes described as catalysts for the process but Dupont also refers to them as ‘mass transfer materials’ because they facilitate the movement of atoms and do not largely accelerate the reaction themselves.

The process goes under different guises and is known as ‘chemical looping combustion’ when used in a different type of reactor. Whatever its name, it clearly works well with methane although there are many questions to be answered, particularly if it is to be used with other fuels.

‘One question we want to answer is what are the optimum periods for the air feed, fuel feed and fuel/steam feed,’ said Dupont. Now the air feed takes six minutes, as does the fuel/steam feed but more experiments in the next three years will identify the best times.

During the next three years the Leeds team will also investigate what happens when waste cooking oil, waste tyre pyrolysis oils, pine wood forestry material and industrial waste oil are used.

There is optimism that the Leeds process may be better suited to local production of hydrogen at, say, filling stations, because its reformer dimensions are more compact than the tall structures being tested elsewhere.

fuel companies dream that tankers may one day collect old cooking oil from local factories, instead of petrol or diesel from the middle east, and transport it to filling stations to be reformed on demand into hydrogen for fuel cell cars. This is decades away from reality but the work at Leeds is bringing it closer.