Dutch scientists have made molecular sieves that are stable at high temperatures for over a year. The stability of these nanosieves means that they could replace conventional separation techniques in the petrochemical industry.

Much research has been carried out to develop stable membranes for industrial separation. However, until now the silica-based membranes could not be used in industrial applications because they would not operate at both high temperatures and in the presence of water. This is because the Si-O-Si bonds in the silica are open to attack by water.

Hessel Castricum from the University of Twente and co-workers have replaced some of the Si-O-Si bonds with organic linkers such as -Si-CH₂-CH₂-Si- which do not hydrolyse. The materials produced act as effective sieves even after 18 months at very high operating temperatures.

At the moment, industrial separations involve techniques such as distillation that require large amounts of energy and can have efficiencies as low as 10%. Instead of distilling to obtain a pure product, a nanosieve could be used to filter small molecules, such as water or hydrogen, leaving behind the larger ones. Biofuels, such as bioalcohols, could be dried using this technology. According to Castricum, the vast energy needs of current distillation plants are proving to be a major stumbling block in implementing biofuel technologies.

Henk Verweij, an expert in ceramic engineering from Ohio State University, Columbus, US, said that the membranes 'could be used for dehydration of industrial alcohol-water mixtures at temperatures up to 150°C'.

Castricum feels that his nanosieves have removed the 'serious limitations for industry to become involved in membrane technology and it should be seen as a highly energy-efficient alternative for existing processes.'

'The next challenges are to confirm our findings in an industrial-scale pilot test and to develop materials that withstand even more extreme conditions, such as strong bases and very high temperatures,' he said.

Ruth Doherty