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Troubleshooting Failed Biodiesel Reactions

Solving Biodiesel Problems


photo of glycerin separation of biodiesel

Good biodiesel reaction with proper separation on right.

photo © Adrian Gable

The process of biodiesel making is fraught with potential “gone wrongs,” but play by the rules and things will generally go very well. The three most important points to remember are:

  • Keep it clean and pure
  • Keep it accurate
  • Be patient - haste does make waste

Sometimes though, things do go wrong. After all the careful weighing and measuring … the numerous titrations and test batches … the meticulous scrubbing of processing vessels and mixing tools … after all that, the occasional batch of biodiesel will go belly-up. It’s disheartening to open up the bucket (or barrel, or tub) only to find that instead of rich amber biodiesel awaiting your gaze, you ‘re greeted with thick “soup,” or worse yet, a nearly solid gel. What gives?

Lots of little things can go wrong, from a misread scale to lost count when doling out ingredients. But sometimes it’s just unexplainable—you’re sure you’ve done everything just so—but the reaction failed anyway. Over the hundreds and hundreds of batches of biodiesel that we’ve made, just about every conceivable failure has come our way. Some of them we recognized instantly as a mistake that we made, or perhaps a contaminated ingredient. Some failures though, seem to defy explanation. Sometimes it is just “bad” (highly acidic or deteriorated) WVO (waste vegetable oil). Some restaurants add chemical stabilizers to increase fryer oil life, and it often disrupts biodiesel reactions. Excessive water or animal fat from food that was cooked in the oil can throw off a reaction as well.

In the final analysis, making biodiesel (transesterification) is really just a chemical reaction, so if a batch has failed, it is generally a problem with the amount or condition of chemicals and ingredients used.

Failed batches generally fall into one of three main categories:

No reaction - No Separation

This is when there’s no visible reaction (after mixing, the vegetable oil remains unchanged with no separation) and is usually an indication that too little lye was used. On occasion, we’ve been able to rescue these non-reactions by adding a bit more lye and then remixing. Be aware though that at this point, any further chemical additions will be guesswork and the efforts may or may not be successful. At times, we’ve had batches of oil that were so heavily used and acidic that they would not react no matter what strength of ingredients was used. It doesn’t happen often, but it’s frustrating when no matter what efforts are extended, the oil won’t work. When this happens to us, we use the oil in our converted straight vegetable oil (SVO) Benz. If you don’t have an SVO converted vehicle, it’s certainly worth considering. Conversion kits are available for as little as $1000, and this cost is quickly recaptured since burning straight veggie oil incurs no processing costs. If a conversion is not in the cards, then it’s probably best to discontinue using this oil supply.

Partial Reaction – Soupy

A thick soupy result is usually caused by one of several things: too little methanol used, mixing time not long enough, or a tad too much lye used. Sometimes it’s caused by lye that has become contaminated. If the lye container is accidentally left open for several hours (or worse, overnight), the lye itself will absorb moisture from the atmosphere. Lye that has absorbed excessive moisture will almost certainly adversely affect a biodiesel reaction. Sometimes this can be remedied by further mixing for another half hour or so—but if this doesn’t help, “soup” is generally a lost cause. However, if you suspect that the soupiness is the result of too little methanol, the batch may be salvageable by the addition of more alcohol and then remixing. As indicated above, it’ll be guesswork and may prove fruitless, but then again it might turn a wasted batch into useable fuel. Just keep in mind that methanol is quite expensive and balance that against the possibility of a lost effort and further wasted supplies.

Over Reaction – Congealed to a Solid

If upon opening the reaction vessel, you find a thick and nearly solid mass, give your head a wry shake and curse lightly. This situation is almost always caused by too much lye and means that this particular biodiesel batch is a goner. In essence, it’s turned into a big chunk of soap. On the bright side, let this mass air-out (to allow residual methanol to evaporate) for a few weeks and you have yourself a nice big supply of “work around the house all purpose cleaner.” We have a few spackle buckets filled with this very substance and have been using it for years to clean everything from engine blocks to lawn mower decks.

All in all, failed reactions are not always so bleak, since most problems and failures are part of being a newbie—and are fewer and further between as experience and knowledge grows. Yes, as practice and experience hones your skills, you’ll be able to spot potential problems long before they show up as a “glop of slop” in your brew pot.

Learn How to Dispose of "Can't be Salvaged" Failed Batches

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