Reprocessing Bad Batches

By Rick Da Tech


Beginners and Experts alike will sometimes take shortcuts that result in bad batches, like skipping the test batch, or not checking their oil for water. When we make a bad batch we want to fix it. After all, we have invested time and money in this oil and want to get it back in the form of biodiesel. There are cures that let you salvage the oil and sometimes even the methanol. To look at those cures we need to look at each of the three types of bad batches individually, the Soapy Mess, Barely Biodiesel, and Almost ASTM.

Almost ASTM is the most common form of bad batch. You can follow the instructions exactly to a tee and still make a batch of Almost ASTM. Almost ASTM is a batch that almost meets ASTM specifications for free and total glycerin. It will often have small droplets of oil in the 3/27 test. Most of us go ahead and use this fuel anyway. We did for years before we had the 3/27 test without any problems. Note, if you sell your biodiesel, you are required by law to meet the full ASTM specifications. If you do not sell your biodiesel, then you can make it to whatever standard you feel is proper for you. The ASTM standards are not set in stone; they were developed by a committee of industry experts. There has been no scientific testing proving that a specific level of conversion is required for any specific engine. It is possible to reprocess, just be warned that test batches do not accurately predict the results of the full size batch. You can reprocess a test batch, have it turn out perfect, and still end up with a reactor full of jello rather than biodiesel. After Draining the Glycerin and before any water is added or any washing (dry or wet) you can reprocess. Dissolve 1 gram of NaOH into 35ml of methanol for each liter of oil. Mix for an hour and test using the 3/27 test. You may not have any glycerin to fall out after processing. It will come out in the wash. If you waited until after you washed to decide you need to reprocess, then your best bet will be blending, described later in this article.

Barely Biodiesel is a low conversion biodiesel. It will have a good glycerin separation, but will badly fail the 3/27 test. Sometimes it will have some soap blobs floating in the biodiesel. If you had made a test batch before continuing with the larger batch, the low conversion would have become apparent. It is biodiesel as the early adaptors made it, low conversion, simple, and used in very robust diesel engines, often as unwashed biodiesel. You may want to take a lesson from commercial producers and blend in the bad biodiesel with a lot of good biodiesel. Large Scale biodiesel producers will bring in a large tanker of oil, process a batch, and test it for conversion. The first batch may not meet their in house standards for conversion. Pass or fail, they will still pump the finished batch into the finished biodiesel tanker. They will adjust the recipe on the next batch to meet their conversion standards. Even if they have several bad batches in the beginning, by the time they have processed the whole tanker of oil, the finished biodiesel will meet conversion standards.

The soapy mess is the worse case, with little or no biodiesel made. The glycerin does not separate and fall out to the bottom. The methanol usually soaks up trash that makes it dark and floats to the top of the batch. The catalyst is consumed making soap, so you have lots of soap. The oil could be liquid, or it could be a gel depending on which type of lye you used, how much lye you used and how much methanol you used. It is most often caused by very wet oil. Sometimes it is caused by oil contaminated with detergents or other unidentified junk. Normally a test batch will show a problem before the large batch is started. The methanol can be decanted off, but it can not be used without further distillation. If you are recovering methanol from the glycerin layer, you can save most of the methanol by decanting it off the batch and adding it to a batch of glycerin about to be distilled. To salvage the oil, wash out the soap. There is a lot of soap it normally takes a long time to wash it out. I like to throw it in a drum, top it off with water, add a few cups of table salt, and let it sit for several weeks. If you used NaOH, the mix will usually form three layers. The bottom will be salty water, the top will be good clean WVO, the middle will be soap. Once the WVO is washed and dried, it can be reprocessed like it was fresh WVO just collected.

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