Letter Re: Advice on Storing E85 Ethanol Fuel

Regarding your statement: :”Even E10 (10% ethanol) blended gasoline is highly hygroscopic and can absorb 50 times more water than traditional non-blended gasoline.”
E10 is much more sensitive to the water/alcohol solution separating from the gasoline than E85 is. E10 undergoes separation at around 0.5% water. E85 can absorb about 20% water before separation occurs. – PNG

JWR Replies: That is not entirely correct. An explanatory note from the L.U.S.T. Line Report (on Leaking Underground Storage Tanks): “Ethanol will mix with gasoline,
but it does so reluctantly. Although gasoline is nonpolar, it can only hold up to 0.2 percent dissolved water before the water “drops” out of solution to the bottom of the storage vessel as free water. Conversely, hydrogen bonding allows E10 fuel to hold much more dissolved water than gasoline—approximately 0.5 percent. This is because the energy needed for ethanol and water to hydrogen bond is much lower than the higher energy required to keep ethanol evenly distributed with gasoline. Because of this, ethanol and water will continue to preferentially bond until the ethanol and water drop out of solution, a process known as “phase separation.” A Wikipedia entry on 85 mentions that phase separation of E85 can occur with as little as 1% water contamination: The article states: “In addition to corrosion, there is also a risk of increased engine wear for non-FFV engines that are not specifically designed for operation on high levels (i.e., for greater than 10%) of ethanol. The risk primarily comes in the rare event that the E85 fuel ever becomes contaminated with water. For water levels below approximately 0.5% to 1.0% contained in the ethanol, no phase separation of gasoline and ethanol occurs. For contamination with 1% or more water in the ethanol, phase separation occurs, and the ethanol-water mixture will separate from the gasoline. This can be observed by pouring a mixture of suspected water-contaminated E85 fuel in a clear glass tube, waiting roughly 30 minutes, and then inspecting the sample. If there is water contamination of above 1% water in the ethanol, a clear separation of ethanol-water from gasoline will be clearly visible, with the colored gasoline floating above the clear ethanol-water mixture.” Temperature is a major determining factor in the threshold for phase separation. The lower the temperature, the less tolerance for water. (Phase separation is more likely in cold weather.)

OBTW, later in the same article, there is this useful tidbit of information for wound-be still builders: “For those making their own E85, the risk of introducing water unintentionally into their homemade fuel is relatively high unless adequate safety precautions and quality control procedures are taken. Ethanol and water form an azeotrope such that it is impossible to distill ethanol to higher than 95.6% ethanol purity by weight (roughly 190 proof); regardless of how many times distillation is repeated. Unfortunately, this proof ethanol contains too much water to prevent separation of a mixture of such proof ethanol with gasoline, or to prevent the formation of formic acid during low temperature combustion. Therefore, when making E85, it becomes necessary to remove this residual water. It is possible to break the ethanol and water azeotrope through adding benzene or another hydrocarbon prior to a final rectifying distillation. This takes another distillation (energy consuming) step. However, it is possible to remove the residual water more easily, using 3 angstrom (3A) synthetic zeolite pellets to absorb the water from the mix of ethanol and water, prior to mixing the now anhydrous ethanol with gasoline in an 85% to 15% by volume mixture to make E85. This absorption process is also known as a molecular sieve. The benefit of using synthetic zeolite pellets is that they are essentially comparable to using a catalyst, in being reusable and in not being consumed in the process, and the pellets require only re-heating (perhaps on a backyard grill, in a solar reflector furnace, or with heated carbon dioxide gas collected and saved from the fermentation process) to drive off the water molecules absorbed into the zeolite.

Also BTW, I found the following at a Mercury Marine web site that confirms my assertion that ethanol tanks should be kept as full as possible for long term storage: “A partially full tank is not recommended because the void space above the fuel allows air movement that can bring in water through condensation as the temperature cycles up and down. This condensation potentially becomes a problem.”