Honeycomb-structured materials offer new hydrogen purification method

February 16th, 2009 - 2:42 pm ICT by ANI  

Washington, Feb 16 (ANI): A team of chemists in the US has offered a new hydrogen purification method, by developing a class of new porous materials, structured like honeycomb, that is very effective at separating hydrogen from complex gas mixtures.

The materials, developed by Northwestern University chemist Mercouri G. Kanatzidis, together with postdoctoral research associate Gerasimos S. Armatas, exhibit the best selectivity in separating hydrogen from carbon dioxide and methane, to the best of the researchers knowledge.

The materials are a new family of germanium-rich chalcogenides.

A more selective process means fewer cycles to produce pure hydrogen, increasing efficiency, said Kanatzidis, Charles E. and Emma H. Morrison Professor of Chemistry in the Weinberg College of Arts and Sciences and the research papers senior author.

Our materials could be used very effectively as membranes for gas separation. We have demonstrated their superior performance, he added.

Current methods of producing hydrogen first yield hydrogen combined with carbon dioxide or hydrogen combined with carbon dioxide and methane.

The technology currently used for the next step removing the hydrogen from such mixtures — separates the gas molecules based on their size, which is difficult to do.

Kanatzidis and Armatas offer a better solution.

Their new materials do not rely on size for separation but instead on polarization the interaction of the gas molecules with the walls of the material as the molecules move through the membrane.

This is the basis of the new separation method.

Tests of one form of the family of materials - this one composed of the heavy elements germanium, lead and tellurium - showed it to be approximately four times more selective at separating hydrogen from carbon dioxide than conventional methods, which are made of lighter elements, such as silicon, oxygen and carbon.

We are taking advantage of what we call soft atoms, which form the membranes walls, said Kanatzidis.

These soft-wall atoms like to interact with other soft molecules passing by, slowing them down as they pass through the membrane. Hydrogen, the smallest element, is a hard molecule. It zips right through while softer molecules, like carbon dioxide and methane take more time, he added.

Kanatzidis and Armatas tested their membrane on a complex mixture of four gases.

Hydrogen passed through first, followed in order by carbon monoxide, methane and carbon dioxide. As the smallest and hardest molecule, hydrogen interacted the least with the membrane, and carbon dioxide, as the softest molecule of the four, interacted the most.

Another advantage is that the process takes place at what Kanatzidis calls a convenient temperature range - between zero degrees Celsius and room temperature. (ANI)

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