How to Perform a Biodiesel
Dry Wash

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Biodiesel dry wash is made very simple with ion exchange resins. These resins are commonly used by large producers of biodiesel, but can also be used by those making biodiesel at home. Most home brewers use waste vegetable oil (WVO), which requires changing the resin more frequently.

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 when used with biodiesel made from straight vegetable oil. The resin is typically used up 3 to 5 times faster when used with WVO due to the extra impurities contained in it.

Ion exchange resins will eventually 'expire'. They can be regenerated by washing the beads with methanol but eventually they must be disposed of and replaced.

Benefits of Dry Washing:

• Dry washing 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 has the potential to be 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 Ion Exchange Resins are Used:

First the biodiesel is left to separate.

Next, the glycerine is drained off and the methanol is extracted.

The biodiesel is run through the dry wash resin tower to remove any remaining glycerin, catalyst and soap.

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

In order to tell if the resin beads have expired, a free glycerin test, a soap titration, or a site glass is used.

Typically, to regenerate the resin beads, the resin bed is flushed with methanol several times until it passes a soap test. Next they must be dried. They can be spread out to dry in an area where the methanol vapors will not be a problem, or nitrogen gas can be used to dry them in the tower.

How to Flush an Ion Exchange Resin Tower with Methanol:

The purpose of flushing a resin tower is to remove glycerin, soaps other impurities that have collected on the resin beads.

First the tower is flushed with methanol until it looks very clear (around 4-5 times).

The methanol would then be tested for soaps and other contaminants by filling a graduated cylinder with 100ml of the flushed methanol.

An alcohol thermometer is lowered into the graduated cylinder (which reads the % methanol). It should be very near 100%.

Next, 10 ml of the final flushed methanol sample is dissolved into 100 ml of 99% or better isopropyl alcohol.

It is tested for soaps by adding approximately 15 drops Bromophenol Blue or until it is a medium/deep blue.

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

The mL of acid it took to turn the mixture yellow is recorded.

The amount of soap present is calculated by using this formula:

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

They have been successfully regenerated if the soap content is under 60 ppm.

If the soap content is greater than 60 ppm, the resin is flushed again and then re analyzed.

Once it passes the test, the methanol is drained.

The beads are dried and ready to be used 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 product of higher quality than water washing. Dry washing is becoming more popular with those making biodiesel at home due to increasing water prices and the time saved.

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