Small Scale Biodiesel Production

By Terry McGleish

Making biodiesel from waste vegetable oil (WVO) is accomplished by a procedure called transesterification. The procedure requires the proper amounts of methanol (CH3OH) and sodium hydroxide (NaOH) commonly known as lye or caustic soda, combined to form a mixture known as sodium methoxide (Na+ CH3O-). The sodium methoxide, when mixed with WVO causes a chemical reaction which breaks the WVO into glycerin and esters or biodiesel.

Locating WVO is fairly easy, small local restaurants or bars who offer fried foods seem very willing to let you take their WVO. A trick I use is to take my 10 yr. old daughter with me when asking the manager or head cook, I haven't been turned down yet. I use a 1 gallon milk jug with the top cut off as a "dipper" to dip the WVO from their container to mine, which is a 15 gallon plastic drum. This drum is transported home and poured into my 55 gallon storage drum.

55 gallon plastic storage drum

You will also need methanol, usually available at race shops or tracks. Small amounts can sometimes be found at local hobby shops who deal with radio controlled planes or cars. Lye or caustic soda, I have found to be harder to locate than methanol. The caustic properties have caused grocery stores to discontinue carrying the product. I located the "Red Devil" brand at a local hardware store.

"Red Devil Lye" can be found at most hardware stores.

Once you have located all the materials needed to make biodiesel, you will need a mixer, a mixing container and a heat source to warm the WVO. For the mixer you can use a 3/8 or 1/2 inch drill with a paddle type mixer, similar to paint or plaster mixers. I used a 3/8" steel rod with two pieces of 1" flat stock welded near the end to form paddles. A mixing container can be anything from an old stainless steel cooking pot to a 55 gallon drum. A drum which works well for small batches is a 15 gallon, steel, motor oil or bearing grease container. These can be found at local shops which specialize in oil changes. I installed a drain valve near the bottom of the container to drain off the glycerin.  Their are several ways to heat the WVO, I have found a "hot plate" works well. Try not to use an open flame if possible, methanol is highly flammable and can cause severe burns.

A 15 gallon steel drum with a valve mounted near the bottom for draining off the glycerin and esters.

Safety First!

Make sure you are using protective gear when making biodiesel. Methanol and lye can be dangerous if not handled properly, and when mixed to form sodium methoxide they are very caustic. Do not breathe the vapors of any of the above and keep them from coming in contact with your skin. Wear a proper respirator, chemical resistant gloves, eye protection and a long sleeve shirt. Always keep a source of running water available when working with methanol, it can burn your skin with out feeling any pain.

Wear a respirator and chemical resistant gloves when working with lye and methanol to make sodium methoxide.

The Procedure:

Before making larger batches of biodiesel, small test batches should be mixed to determine the proper amounts of methanol and lye needed for a successful reaction. The most common way is to perform a titration on the WVO, but I have found that this extra step is unnecessary if you make small batches noting the amounts of lye and methanol used in each batch. Then taking the amounts used in the successful test batch and doing the math for a larger batch.

A successful test batch showing the separation of esters and glycerin.

Four- one liter test batches can be performed using only 1 gallon of WVO and just under 1 qt. of methanol. Below are the measurements for four test batches.

I have found that after several batches using WVO from different sources that between  6.25 - 6.75 grams of lye per liter of WVO is about average, yielding about 80% product.  Depending on the condition of the WVO from your source, you may have to experiment with the amount of lye used to get satisfactory results.

Once you have determined the proper amounts of lye and methanol in your test batches,  multiply those amounts for larger batches.  Below are average measurements I use for 5 gallon batches.

Whether you are mixing a test batch or larger batch, the procedure is the same.  The WVO should be filtered if it contains food particles or other foreign matter. If the WVO contains water, it can be boiled off by raising the temperature to 212 degrees until the water has boiled off.  Once the WVO has been filtered it can be placed in the mixer and heated to around 120 degrees if you are in a cool climate. If the outside temperature is above 80 degrees, I do not heat the oil at all if it is in a liquid state. I have had successful results using both methods.

Allow 1 hour of mixing time with the mixer set at a speed which just forms a vortex at the top of the WVO.

Once the WVO is heated, you are ready to mix the lye and methanol to form sodium methoxide. Add the lye to the methanol, mixing thoroughly until all lye is dissolved. Keep the lye and all utensils dry. Immediately add the sodium methoxide to the WVO and mix for a minimum of one hour. After mixing is complete, let settle for at least 8 hours. The heavier glycerin will settle to the bottom of the container, leaving the esters (biodiesel) on top. The biodiesel can then be pumped off and the glycerin drained out the bottom. If the outside temps are cool, the glycerin will solidify to a cake like substance, and will have to be re-heated to allow for draining. On batches under 5 gallons, the biodiesel can be poured off the top, leaving the hardened glycerin, which can be cut into "pizza" slices and taken out by hand.

Glycerin byproduct from a five gallon batch.

The glycerin byproduct can be used as a degreaser/hand soap. Heat the glycerin to 150 degrees to boil off the remaining methanol, and allowing it to settle to remove any excess impurities. Or, allow the glycerin to sit for up to three weeks to evaporate the remain methanol, then use as a compost.

Multiple filters help remove any impurities from the bio-diesel.

The biodiesel should be allowed to set for at least 24 hours, preferably longer, then filtered and washed before using it in your engine or fuel applications. I only filter the biodiesel before running it through my diesel genset, skipping the wash procedure, because I have two pre-filters and a water separator on the gen-set. This method has worked well for me and I have run the genset over a hundred hours without any ill effects. For more information on washing biodiesel, see Mike Pellys recipe for straight washing and the Idaho bubbler technique.

This is a simple straight forward method I use to produce biodiesel. Although what works for me may not work for everyone. There are several good articles and books on making biodiesel available on the web, and should be consulted for more detailed information on this subject.

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