Biodiesel The Easy Way

If you are or have ever been interested in making your own biodiesel, you have probably noticed that the only simple instructions to be found deal with making a tiny, one liter batch using 2-liter drink bottles; hardly enough to be worth the bother, except as a means of getting your mind around exactly what it is you are trying to do. The rest of the readily available instructions are full of science, require a fully-equipped laboratory, and stress a need for perfection in measuring and testing.

Many people have been turned off entirely from the prospect of making their own fuel by the seeming requirement for a PhD and thousands of dollars’ worth of equipment and chemicals. Others wonder, if the simple method can make a liter of acceptable fuel, why can’t it make 5 gallons?

It can, and I’m here to tell you how. Consider this: while the various instructional articles about home biodiesel production stress the importance of performing an accurate titration to determine exactly how much additional lye (NaOH) to add to your specific batch of used cooking oil, over and above what is necessary for fresh clean oil, the quoted starting amount for fresh clean oil varies from 3.5 grams per liter, to 5 grams per liter. That is the amount of lye prescribed to achieve transesterification of new, unused cooking oil; that is, to break it down into a layer of glycerin and a layer of biodiesel. The equipment, chemicals and effort needed to titrate are simply for the purpose of determining how much additional lye must be added to neutralize fatty acids created when the oil was heated for cooking purposes.

Here is the secret no one is talking about: that 1.5 gram-per-liter difference is about the most you will normally see between batches of used cooking oil. What this means is that if you find an amount of lye to add that works, using that amount for future batches will in all likelihood, also work. So make that one liter test batch, then just scale up the proportions if you have good results.

In my testing (and I have titrated several times), I usually arrive at 8 grams of lye per liter of used cooking oil if I use 5 grams as the starting point. I have extrapolated this 8 grams per liter and come up with 30.28 grams per gallon. One volumetric ounce, or two tablespoons, is slightly under 30 grams by weight of lye. That is one of the scoops that is included in every can of some brands of coffee. So it is a happy coincidence that a coffee scoop of lye is just about the right amount to make a gallon of biodiesel! That is exactly the way I do it too, and I have yet to have a batch fail to convert.

OK, with that out of the way, let’s get to the brass tacks of what you need to produce your own 5-gallon batch of biodiesel:

8 gallon stock pot. One of the cheap aluminum ones is fine, as long as you are careful about pouring in the methoxide (described later). A 10 gallon steel drum of the type some oils and solvents are sold in, would be even better. A 5-gallon stock pot is too small, but if that is all you have, you can scale it to 3-gallon batches. Never reuse this pot for cooking, by the way!

A thermometer for checking the temperature of the hot oil.

A source of heat. The kitchen stove is fine, but it may stink up the house. You can get a “turkey cooker” set that includes a propane-fueled cooker and the 8-gallon stock pot you need, as well as a thermometer, for well under $100. The price of one tank of fuel, nowadays.

5 gallon HDPE plastic bucket.

Drill motor.

Paint stirrer attachment for the drill motor.

2 gallon gas can.

Siphon pump, of the variety used for filling kerosene heaters.

Old T-shirt or something similar, for filtration.

Safety gear: full-length pants, long-sleeve shirt, heavy-duty, long rubber gloves, eye protection, and a chemical apron. Boots would be a good idea too.

And finally, the aforementioned coffee scoop.

And your consumables:

5 gallons of used cooking oil.

1 gallon of methanol. The standard proportion is 20% of the volume of oil. The best place to find methanol is a local racetrack, drag strip, or automotive speed shop.

Lye. Best bought online, from dealers like Utah Biodiesel Supply.

Water, for washing the resultant biodiesel.

OK, let’s get started. Don your safety gear, pour 5 gallons of filtered, waste cooking oil into your stock pot. Put it on low heat. I generally run it up to at least 180 degrees F, to drive out any moisture; but if you’re sure it’s dry, 130-140 F is sufficient. While it is heating, add 5 (one ounce/2 tablespoon) scoops of lye to the 1 gallon of methanol, in a 2 gallon (or larger) plastic gas can. Replace cap, make sure the vent is closed, and swirl gently, then set it down and let it dissolve for awhile. Do this outdoors and do not breathe the fumes nor allow any to get on your skin, as it is highly toxic and caustic!

Check every 30-45 minutes, momentarily (and carefully!) open the vent, then re close and give it another swirl.

Monitor the temperature of your oil. It should be 130 F, no higher, when you add the methoxide (methanol/lye mixture). The methoxide should be ready within a couple of hours. It is ready when the lye is fully dissolved into the methanol. At this point, it is much more toxic than methanol alone, so take all precautions.

Carefully pour the methoxide into the 130 degree oil, being careful not to splash. If the oil is much above 130 degrees F, it will erupt; so check the temperature. Also, especially if using an aluminum stock pot, be sure to pour the methoxide directly into the oil, avoiding direct contact with the aluminum. Methoxide attacks aluminum, eroding it and producing hydrogen gas in the process.

Now stir for 20 minutes, using the paint stirrer and drill motor. I have done this (once) holding the drill motor by hand; now I use a jig I made of scraps of 2×4 lumber.

After 20 minutes, turn off and remove the stirrer. Allow the biodiesel to settle for at least an hour.

Using your siphon pump, carefully siphon the biodiesel into your 5 gallon pail, leaving the glycerin layer behind. Pour the glycerin into another container for later use or disposal, then pour the biodiesel back into the stock pot. Add a gallon of water, and stir vigorously with the paint stirrer for a couple of minutes. Allow to settle overnight, then siphon biodiesel into the 5 gallon pail, and discard the water. Repeat a couple more times until the waste water comes out clear, then allow the biodiesel to settle until it clears, 3 days to 3 weeks. Filter your biodiesel however much or little you deem necessary, and pour it in your fuel tank!