Is Homemade Biodiesel a Realistic Proposition?

Tired of high diesel prices? Ever think you could make your own fuel cheaper? With options from home-made labs to turn-key systems available to would-be fuel producers, it begs the question: Does making your own biodiesel make sense?

What is biodiesel?

A triglyceride, the basic molecule of fat, is made up of three fatty acid chains connected to a glycerin (glycerol) backbone. Through the process of transesterification, a chemical reaction breaks the glycerin away from the molecule and adds atoms at the end of the fatty acid chains to form esters. These alcohol esters can be burned by diesel engines, hence the name "biodiesel."

How is biodiesel made?

The fat is mixed with a catalyst, usually a strong base like lye, and an alcohol, usually methanol. Once fully mixed, the reaction combines the fat and methanol into methyl esters and crude glycerol. The mixture is left to settle, with the glyerol sinking to the bottom of the tank. The esters and glycerol are separated, and the esters are washed by mixing with it with water; this removes any remaining glycerol and catalyst. Finally, the esters are dried, creating biodiesel.

Is making biodiesel safe?

The chemicals involved are dangerous, particularly methanol, which is poisonous and highly flamable. An AR (alcohol resistant) fire extinguisher should be on hand in case of fire. Lye is extremely caustic. However, biodiesel itself is relatively safe, being both non-poisonous and inflammable except at very high temperatures.

The crude glycerol coming straight from the process still contains methanol and catalyst, which will need to be safely disposed of or refined into pure glycerin which can be used to make soap.

Is it safe to use in a diesel engine?

Modern diesel engines are built using biodiesel-compatable hoses and fittings, but older rubber may swell when it comes in contact with biodiesel. Most new engines are designed from the start to run blends of up to 20% biodiesel, and using this fuel may improve overall engine life because it lubricates better than mineral diesel. However, biodiesel that hasn't been washed properly will still contain methanol and catalyst that can damage the fuel system.

Biodiesel is hydroscopic, so it will need to be stored in a sealed container to keep it from gathering water from the air.

Is it economical?

It depends entirely on the cost of the ingredients used. When calculating costs, keep in mind that it takes about one part methanol for every 5 parts fat and a typical yield will be 80% biodiesel and 20% glycerol. Taxes vary from state to state: off-road use biodiesel is not taxed, but taxes may need to be paid for use in road-legal vehicles. A sustainable profit from small scale manufacture is unlikely.

What kind of fat works best?

Just as mono- and poly-unsaturated fats are liquid at lower temperatures than saturated fats, so will biodiesel made from these fats. This makes virgin vegetable oils the best choice for colder climates.

Used oils have a lot of mono- and diglycerides, waxes and impurities which can react incompletely, bonding with the catalyst causing saponification, the formation of soap.

What about running straight oil?

Pure oil is much thicker than diesel or biodiesel, which is hard on fuel pumps and injectors, and can lead to clogging. Used oil is particularly risky as it can contain impurities that will clog the fuel system and leave deposits in the engine.


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