Study of water absorption by anhydrous ethanol from different sources

Abstract:

Anhydrous ethanol presents a very important property that is hygroscopicity, i.e., ethanol is able to absorb water vapor from the atmosphere. This property must be taken into consideration for conducting corrosion tests in the laboratory because the amount of water absorbed by ethanol during this type of tests can cause a water intake in amount higher than the limit established by ethanol current specifications which is 1% (v/v) maximum. This is particularly significant for laboratory tests, because they use a small volume. In this work, a study was done to verify, in a comparative manner, the capacity of water absorption property by ethanol from different sources exposed to the atmospheric air in different conditions. This was done by testing three ethanol samples obtained from sugar cane, another obtained from corn and an analytical grade pure ethanol sample. Two exposure conditions were considered: semi-open and open. For the semi-open system, a 550-mL glass bottle provide with a metallic cover was used. Three holes were made on the cover to allow contact of tested ethanol sample with the atmospheric air. The bottle was filled with sample volume (250 mL, 375 mL, 550 mL). For the open systems, a 250mL graduated cylinder and a volume of 250 mL of sample were used. The water content as a function of exposure time was determined. The determination of water content was made by potentiometric titration, i.e., the Karl Fischer method. For the semi-open system, it was observed that, when the bottles were not completely filled, the water absorption rate of the studied samples was the same regardless of the source of ethanol. However, when the system was completely filled, the highest purity ethanol sample presented the highest absorption rate. It was also found that the bigger the empty space, the higher the rate of water absorption. For the open system, the rate of water absorption of the three ethanol sample was the same order of magnitude. Finally, it was found that the water absorption rate of semi-open system conducted with the highest empty space were of the same order of magnitude of the rates obtained in the open system.


Reference:
NUNES, Gislaine Maria Bragagnolo; PANOSSIAN, Zehbour; SANTOS, Célia Aparecida Lino dos; PIMENTA, Gutemberg de Souza . Study of water absorption by anhydrous ethanol from different sources. In: RIO PIPELINE CONFERENCE & EXPOSITION, 2011, Rio de Janeiro. Proceedings… 6 p.

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