Porous material could purify bioethanol with less waste.

Mar 18, 2013

Shigematsu, A, T Yamada and H Kitagawa. 2012. Selective separation of water, methanol, and ethanol by a porous coordination polymer built with a flexible tetrahedral ligand. Journal of American Chemical Society http://pubs.acs.org/doi/pdfplus/10.1021/ja306401j.

Synopsis by Marty Mulvihill

Chemists have debuted a unique, porous material they say separates ethanol from contaminants that lower its performance. Separating ethanol from the water and methanol that form during distillation currently takes many steps and lots of energy. The new material may simplify this procedure, creating a better fuel with fewer resources.

A new material holds promise to improve the performance of bioethanol fuel by removing the trace amounts of water and methanol that remain in the end product, a problem that has long plagued the industry. The chemical filter would produce a pure ethanol that would boost performance of the gasoline alternative. 

Remarkably, the novel material can selectively take out the contaminants without removing any of the valuable ethanol.

This is one of the first materials that is able to distinguish the very similar chemicals from each other.

The unique material combines copper with a molecule called tetrakis(m-pyridyloxymethylene)methane (mtpm). This combination creates a porous network with different sized and shaped "holes" that can absorb methanol and water but not ethanol. The advances make the material – called a porous coordination polymer (PCP) – more flexible, simpler to use and cleaner than activated carbon and other micropores currently used to separate the bioethanol mixture.

Ethanol is the most commonly used bio-based fuel, with over 5.4 billion gallons consumed in 2008 alone. In California and other states with strict air quality standards, most ethanol is blended with gasoline to help minimize pollution from car exhaust.

Ethanol is distilled from molasses, corn or other plant material. Some methanol and water remain in the end product, but both must be taken out before the biofuel can safely burn in a car.

Currently, ethanol is separated from methanol and water by distillation with chemical additives. This process takes large amounts of energy and often requires multiple steps.

The chemists report the findings of their initial laboratory experiments in the Journal of the Chemical Association. More study, testing and application are needed before these preliminary results can be verified and the PCP material widely applied in industry.