Sulphur emissions from cars and aircraft could be virtually eliminated using low-cost materials.
Researchers at the University of Michigan are investigating ‘molecular sieves’ – adsorbent materials that they claim will significantly reduce sulphur levels in petrol, diesel and aircraft fuel. The materials, which can be developed from either copper or more expensive silver ions, bond strongly with sulphur compounds when added to fuel during the refining process.
Sulphur emissions cause acid rain and can lead to respiratory disorders. By carefully designing the adsorbents, the researchers claim that the materials could reduce sulphur concentrations from hundreds of parts per million to less than 0.2, and take up about 40 times more sulphur than the best previously known adsorbent materials. ‘After treatment the fuel is essentially sulphur-free,’ said Ralph Yang, professor of chemical engineering at the university.
The materials could help countries to meet increasingly strict air pollution regulations, said Yang. ‘All government regulations, including those from the EU, are going to be very stringent on sulphur levels in liquid fuels, so getting those levels down will be very important.
‘Sulphur is currently removed during the refinery stage, under high temperature and pressure, using a brute force approach. But some sulphur compounds are very hard to remove using conventional processes. Our materials have been designed to target these.’
The materials would be very simple and cheap to produce, costing around $2 (£1.20) per pound, said Yang. ‘These materials are very selective in finding sulphur compounds, and can take them out at room temperature and pressure.’
The technology could also help realise the concept of fuel cells that convert petrol into hydrogen onboard the vehicle, said Yang. The catalysts within fuel cells are extremely sensitive, and would be damaged by the sulphur in petrol, he added. ‘Fuel cells have a lot of platinum catalysts, which would be poisoned by sulphur, meaning any [liquid] fuel has to be sulphur-free.’
GM and Toyota are working with Exxon Mobil to develop fuel cell technology for onboard conversion, which GM claims will act as a bridge to a pure hydrogen fuel-based economy. But critics claim it would be difficult to sequester the CO2 produced by the process, undermining its green credentials.