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Special
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Written by Sabrina Deparine
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Tuesday, 15 September 2009 13:45 |
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Page views: 2867 |
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Page 1 of 2
Ever since talks about ethanol fuel had surfaced, we all know that ethanol has to be anhydrous or free of water. It should be in its purest form to make it suitable for use as transport fuel. Purifying ethanol to its anhydrous form helps inhibit its corrosive property.
However, with all the modern-day technologies and knowledge that we have now, even the impossible can actually become possible. One of the researchers at Process Design Center Inc. (PDC), a Netherlands-based company, was first interested in challenging the current ethanol dehydration methods like the use of molecular sieves. The main objective was to find alternatives that can reduce the costs and the energy used for the dehydration process. PDC owner, Hans Keuken was not impressed by this proposal so he suggested that instead of challenging the conventional process, maybe the researcher can focus on finding a new way to separate water from ethanol using gasoline. The reason why Keuken chose gasoline as the dehydrator is because gasoline is full of aromatic contents which will work well for azeotropic distillation. Technically, the process for this is to use a liquid-liquid extraction column to extract the ethanol content and purge to the gasoline stream. What Keuken was not able to realize then was that this process will only work if ethanol and water can be totally separated. Quite unfortunately, they cannot. This is because the densities of these two are almost equal and it will take a long time to separate one from the other. To make Keuken’s process possible, there will be large extractor volumes that will make ethanol production more operationally expensive. So the next idea that Keuken thought of was: “If we can’t get the water out, why not leave it in?”
 Now this new idea is possible because in Brazil, anhydrous and hydrous blends of ethanol exist in the fuel industry. However, oil companies, which were PDC clients, were not sold to the idea because they were loyal subscribers to the old-school idea that water in ethanol is bad.
According to ASTM standards, fuel-grade ethanol should contain less than 1% water. But the procedure for testing was they put anhydrous ethanol in the gasoline and then add some water. The effects of this process are actually different than when the water comes chemically-bound in the ethanol.
Among the mixtures tested by PDC researchers, it was concluded that the mid-level hydrous ethanol blend (with 96% ethanol and 4% water) does not phase separate and can absorb five times more water than the anhydrous ethanol blends. This means that this ethanol-water mixture is even less corrosive because it can absorb the water content better.
PDC’s research was able to catch the attention and perk the interest of an ethanol plant-builder in Minnesota. He has agreed to conduct a pro bono study to establish the energy savings that result from skipping the dehydration process. Based on the results garnered by Keuken’s team, the energy savings range from 10% to 45%, depending on the technology or method employed. Other savings include avoided capital and the operating and energy costs associated with the dehydration process. It was also noted that aside from reduced energy consumption and costs, there was a 4% increase in product volume. As a whole, the elimination of the hydrous-to-anhydorus step in ethanol production can make a significant contribution to the cost-efficiency of ethanol fuel. It will also contribute to the enhancement of fuel cycle net energy balance and greenhouse gas emission profiles.
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