Friday, February 8, 2008

Membranes to Replace Distillation

Distillation is by far the most energy intensive step in the production of ethanol and it consumes large amounts of coal or natural gas (depending on the plant), which comes at a high cost to the company. A group of researchers in the Netherlands has developed a membrane that can separate the water out of ethanol; bypassing a lot of the energy needed for distillation and potentially being a great step forward both for ethanol economics but also for the energy balance/GHG emissions that people have pointed out so vocally in the press. Although the idea of developing a selective membrane to filter the water out of ethanol is not new, (a group in Canada has also done this, among others), tests on these membranes has shown that their effectiveness can not climb about 40% pure anhydrous ethanol.

Although the Dutch group was able to develop a stable membrane capable of separating large amount of ethanol from water, the procedure requires temperatures above 150C. This plus the fact that the membrane is unstable below 60C and their claims that the process is energy efficient seems hard to prove. Keep in mind that the boiling point of ethanol is 78C, which is the temperature currently needed for distillation. Although using current technology this still only results in approximately 96% ethanol and necessitates an additional step in anhydrous ethanol is needed, the Dutch team claims to be able to displace some of the energy needed for distillation, which I can not verify and have some large doubts. Either way, a cool technology with big potential but it may be a few more years off before the engineers can get a better handle on it.

A computer generated image of these nano-sieves.

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