Making Biodiesel: A Lengthy Process
How to Make Biodiesel at Home
Reading Time: 4 minutes
When James began looking into the process of making biodiesel as opposed to buying petrodiesel (what we buy at the gas station), he was hoping for a cheaper alternative to the $4 per gallon that he was spending at the pump. While he did not find that cheaper alternative, biodiesel is much better for the environment. Just for that reason, he continues to make his own biodiesel.
The chemical reaction of making biodiesel is actually very similar to soap making. You start with oil and add either potassium hydroxide or sodium hydroxide that has been mixed with methanol. In the end, you have biodiesel with glycerin as a byproduct. The oil you use can impact the consistency of the finished biodiesel product, such as animal fats like lard making a biodiesel that congeals at higher temperatures than biodiesel made with liquid oil, but other than that, it doesn’t matter so much what you use. James gathers used fryer oil from local restaurants. He states that even after the oil has been processed into biodiesel and used in his truck, you can smell the food that was cooked in that oil. He has had people literally follow his truck just to tell him that the diesel fumes from his truck made them hungry as opposed to the normal disgust at the stench of burning diesel.
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If you want to explore making your own biodiesel, do your research. There are quite a few upfront costs such as for the large drum in which to mix your ingredients. That drum must be stainless steel to avoid chemical reactions with your potassium or sodium hydroxide. The highly caustic nature of the lye can erode or react with many other metals. That drum also needs to have a method of circulating the liquid inside and a drain at the bottom. A window in the side is also helpful. James has a condenser coil at the top of his setup to catch the methanol that evaporates off. He can catch and reuse roughly 80% of the methanol that was used in a batch of biodiesel.
James’ process for making biodiesel goes as follows:
He collects the oil from local restaurants and places it in his 300-gallon tank. He allows that oil to settle so any water can separate to the bottom. He then drains off that water, hence why you need a drain valve at the bottom.
Then James pumps oil from the middle of the tank, avoiding contaminants that either float at the top or settle to the bottom. He filters that again then heats it to 13 degrees F. He turns on his mixer so that the oil circulates in a slow whirlpool.
James mixes his potassium hydroxide and methanol and allows it to very slowly trickle into the tank as the oil circulates. If you dump it in too quickly, the reactants will combine explosively. You must allow the mixture to react slowly. Everything must be allowed to circulate and mix together for 12-14 hours with constant heat.
The next day, James turns off the circulation and heat to allow everything to settle for another day. When you can see the separation through your side window, it is ready. You can then drain off the glycerin from the bottom. At this point, you would want to then heat and circulate everything then allow it to settle once again to separate out any remaining glycerin.
At this point, James mists water on top of the biodiesel. This water mist grabs any contaminants in the biodiesel as it moves through the biodiesel to settle at the bottom of the tank. The water is then drained off.
Finally, the biodiesel is filtered one last time with a desiccant to pull out any remaining water before being stored for use.
As you can see, making biodiesel is a labor and time-intensive process. James’ method costs him approximately 48 hours of labor, not including the times in which the biodiesel is settling. In our society, time is money. This must be factored into your calculations of whether or not it is worth it to make your own biodiesel. The methanol, or wood grain alcohol, is also pricey. James buys his methanol in 50-gallon drums to be cost-effective. If you use the same method of collecting used fryer oil from restaurants as James does, you can at least save the cost of the oil itself.
Another consideration in regards to biodiesel is the fact that it has a tendency to gel in cooler temperatures faster than petrodiesel does. Even living in South Carolina, James mixes his biodiesel 50% with petrodiesel during the winter.
If you do choose to switch to biodiesel, whether or not you make your own, realize that it is a solvent. While petrodiesel has a tendency to leave deposits in your fuel system, biodiesel loosens and breaks up those deposits. There is a period of transition in which the biodiesel is cleaning out the fuel line, and it may clog your fuel filter. As long as you change out your fuel filter several times in the first couple months of using biodiesel, the transition shouldn’t be too hard on your vehicles or equipment.
Now that you know more about making biodiesel, will you be making the switch?