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Phase separation

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Ethanol / Water Solubility Table

  • Ethanol is very sensitive to water with water solubility of 100% at 70˚F.
  • A 10 v% ethanol blend has a water tolerance of ~ 0.45% at 60˚F
    • and less at lower blend levels
  • The table shows tolerance of 3 comon fuel blends
  • Once a gasoline ethanol blend reaches water saturation,
    • The water and alcohol will “phase separate”
  • This results in a lower phase of alcohol and water and an upper phase, of predominantly hydrocarbon fuel.  

ethanol_tolerance.jpg

  • The amount of water that the three common ethanol blend levels can tolerate Before phase separating (at 60˚F) is
        • 0.20 v% at 5.7 v%  Ethanol,
        •  0.33 v% at 7.7 v% Ethanol 
        • 0.45 v% at 10 v%   Ethanol.  

    Source: Oak Ridge National LaboratoryEthanol Project Subcontract No. 4500010570

  • PHASE SEPARATION

    • If a 10% ethanol blend is contaminated with over .5%water,
    • The ethanol and water mixture will separate from the gasoline and fall to the bottom of the gas tank.
    • This is an inconvenience, because the fuel system must then be drained and new fuel added.
    • Before using ethanol blended fuel for the first time in an older small engine, it is recommended that the fuel tank be drained to assure that there is not water accumulation.
      • Since many outboard motor carburetor problems result from water in the fuel system, continuous use of an ethanol blend will prevent water accumulation, breakdowns,and maintenance.

    <SOURCE>

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    PHASE SEPARATION IN STORAGE TANKS

    • Ethanol blends require a water free environment. 
    • Before converting to ethanol blends stations must first prepare their storage tanks and dispensers to ensure that they are compatible with ethanol blends and are tight against water entry.  
    • The system must always be maintained free of water.
    • This is extremely important since ethanol will bond with the water and pull it up into the fuel.
    • Once there it can remain in this cloudy state until the temperature of the fuel cools or the water and ethanol saturation becomes so heavy that it drops away from the lighter gasoline hydrocarbons.
    • The water or water and ethanol mixture settles to the bottom of the container leaving the lighter gasoline on top.
      •  This is known as phase separation.

    <SOURCE >