How to Perform a Biodiesel
Dry Wash

Biodiesel dry wash is made simple with ion exchange resins. They can also be used when making biodiesel at home, however they are used up quicker when they are used with waste vegetable oil (WVO).


What are Ion exchange Resins?

• Ion exchange resins are composed of small polymer beads, usually just 1 or 2 mm in diameter. Some types are porous in order to have more surface area for ion exchange to take place on during the biodiesel dry wash. The resins are designed to attract the biodiesel waste products to themselves.

• Ion exchange resins last longer on biodiesel made from straight vegetable oil.

• WVO uses these products up faster due to all the extra impurities contained in it. Resin beads are typically used up 3 to 5 times as fast when using WVO. This effects the cost per batch for those of us making biodiesel at home with WVO.

• Ion exchange resins eventually 'expire'. They can be regenerated by washing the beads with methanol... but eventually they are DONE-done.


Benefits of Dry Washing:

• It decreases production time by knocking out several steps incurred by water washing.

• Biodiesel dry wash takes up less space because no large water wash tanks or extra settling tanks are needed.

• It is less expensive because there is no effluent water to dispose of, no water removal equipment or extra settling tanks, and no water to pay for.

• It is easier to comply with ASTM D6751. Water washing WVO usually results in a fuel with water content more than double ASTM’s cut off of 500 ppm.


A General Overview of How to Use Ion Exchange Resins:

• First the biodiesel is left to separate and the glycerin is drained off.

• Methanol is removed.

• Resin is loaded into a tower.

-The towers are usually made of steel and having a screen supported at the bottom.

-Different resins require different depths of beds.

-The tower needs to be tall enough to allow room for when the beads expand.

• The flow rate of the biodiesel passing through the resin is adjusted to that which is specified by the manufacturer.

-A diaphragm pump can be used to control the rate of flow through the tower. Or a centrifugal pump coupled with a ball valve could be used to control the flow rate.


...and When resin beads are 'used up'?

-Either perform a free glycerin test, a soap titration, or utilize a site glass to determine when they are spent.

• To regenerate the resin beads:

-Flush the resin bed with methanol several times until it passes a soap test.

-To dry them of remaining methanol, spread them out to dry in an area where the methanol vapors will not be a problem, or use nitrogen gas to dry them in the tower.
How to Flush an Ion Exchange Resin Tower with Methanol:

• The purpose of this is to remove glycerin, soaps other impurities that have collected on the resin beads.

• Flush with methanol until it looks very clear (around 4-5 times).

• Test the methanol for soaps and other contaminants:

-Fill a graduated cylinder with 100ml of the flushed methanol.

-Lower an alcohol thermometer into the graduated cylinder (which reads the % methanol). It should be very near 100%.

-Now, in a beaker dissolve 10 ml of the final flush methanol sample into 100 ml of 99% or better isopropyl alcohol.

-To test for soaps, add approximately 15 drops Bromophenol Blue or until it is a medium/deep blue.

-Add 0.01 normality hydrochloric acid one drop at a time until mixture turns a bright clear yellow.

-Write down how many ml of acid it took to turn the mixture yellow.

-Determine how much soap is present by using this formula:

Ml of hydrochloric acid used × 304 parts per million (ppm) = how much soap is present.

-It is good if it is under 60 ppm.

-Otherwise flush them again.

• Once it passes the test, drain out the methanol

• Dry the beads... and now they're ready to perform a biodiesel dry wash again!


What’s Different About Using Magnesol D-SOL?

• Instead of having the biodiesel flow through a bed, the Magnesol is mixed into the biodiesel for 25 minutes.

• The biodiesel is then filtered by flowing through wash columns.

• Biodiesel is then run through a final polish tank.


In Summary:

Biodiesel dry wash is effective whether used in a factory or at home. It tends to produce a better finished product than water washing. Dry washing is becoming more popular with those making biodiesel at home due to increasing water prices and speed factors.

Click here for a list and description of each of the chemicals commonly used in biodiesel dry wash.

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