Phase Separation

Water and gas do not mix.  Traditionally, as water accumulates in a tank of pure gas, it will fall quickly to the bottom and stay there.  This is not the case with gas containing an ethanol mixture..

Ethanol and water do mix and when the two liquids come together, they become attached and bind together. 

Because water is considerably heavier than gas, when enough water saturates the ethanol, gravity will pull the ethanol/water mixture to the tank bottom. This is called phase separation.

In a recent article in the PEI Journal it states that any more water than 1/2 of 1% is an invitation to phase separation.  For example, if you have 6,000 gallons of fuel you might get by with up to 30 gallons of water.  Any more than that could be troublesome.

Most phase separation occurs when fuel is low and there is not enough ethanol to absorb any influx of water. Premium tanks are vulnerable because they are usually kept at a low volume of fuel.

Phase separation will reach customer tanks when phased fuel reaches tank pump levels. This is usually at the 4-6" level. Phase separation will stall engines and require costly repairs.

Even 1 or 2 inches of phase separation in a tank can be dangerous. Phase separation, like plain water, can reach a customer’s tank if some phased ethanol is stirred up during a fuel drop and a customer is fueling at the same time.

Phase separation is also harmful to tanks, pumps, and lines as it is much more corrosive than pure gas or pure water. Phase separation is about one part water and three parts ethanol.

When phase separation occurs, it will usually show on a central meter (Veeder Root) as water. Also, phase separation can be measured by “sticking” the tank using a paste for oxygenated fuels.

All phase separation will be sitting on the bottom and should be removed asap by a complete bottom sweep system. (Straight suck systems at the probe or fill help, but this method will not remove all the phasing because tanks are usually tilted and there are low spots.)

If phase separation reaches the submersible pump, the pump and all lines involved should be flushed out to protect equipment and the customer.

Fuel remaining after phase separation is removed can be used, however, this fuel will be lowered in octane and should not be sold until octane levels are increased to desired levels. Pure ethanol is approximately 113 octane. Premium gasoline is about 92 octane.

To bring your octane to legal levels, the following factures must be considered:

- The base octane of the fuel before ethanol was added.
- The volume of fuel in the tank.
- The desired octane you wish to achieve.
- The octane of the fuel used to “boost” the depleted fuel.

You should work with your supplier. He knows the base octane of the e-ten you had and can also help with the formula needed to bring the fuel to a saleable condition.

Remember, phase separation is not likely to occur if proper maintenance is observed. Old caps and poor maintenance will invite problems. It looks like ethanol is here to stay, so we must all learn to handle it properly.