Using WVO as a Fuel

Using waste vegetable oil (WVO) as a fuel, both commercially and environmentally speaking is an all round good idea, food producers spend less money on waste and recycling charges and the biodiesel producers can get hold of feedstock for a low price, or in some cases - free!

Most biodiesel is made from WVO. This needs to be treated before it is reacted and turned into biodiesel in order for the oil to reach any recognized standard of cleanliness by getting rid of any free fatty acids (FFA), oil contaminants and moisture so that the reaction can work successfully. WVO usually contains around 2-5% of FFA, any higher than 5% then you will face problems after the settling and reaction processes. A common problem that biodiesel producers face is that once the have reacted the vegetable oil, there is no clear separation between the glycerin by-product and the biodiesel, instead, they are left with a gooey substance that cannot be purified and used as fuel. If this happens it means that the FFA and/or moisture content was too high at the time of reaction.

All WVO contains fatty acids, moisture and solid particles, all of which can be removed providing you use the correct methods of filtration.

First of all, you should heat the oil to 100˚C (this is because it is the boiling point of water whereas oil has a higher boiling point) and wait for it to stop boiling, this mean all of the water has evaporated, after this, the oil needs to be left to settle for a couple of days until white skins have formed on the bottom of the storage containers; the oil can be drawn off the top, through a filtration rig which will remove solid particulate up to a certain size, depending on the filter you are using' micron rating (I would not advise using a very low rated filter as it will clog very quickly, especially if you have quite low quality WVO, I would say 15-20 micron will do the job), doing it this way will increase your overall quality of biodiesel by removing most of the FFAs and impurities both through what is left at the bottom of the storage container and also whatever has been picked up by the filters.

Once the oil has been filtered, it needs to go through esterification, in order to turn the FFAs into methyl esters, this is a process by which you react your WVO with methanol and 95% concentrated sulphuric acid, this is because the oil has been reheated so many times that the fatty acids have broken away from the glycerin and now move freely in the oil (hence the name free fatty acids), these react with the catalyst during transesterification (the process in which vegetable oil is reacted with methanol to produce biodiesel).

Now, transesterification, the oil now needs to be transferred into a reactor, you can do this using a filtration rig again, but this time you can use a filter with a lower micron rating (around 10 micron) just to make it that little bit cleaner. Once this is done, you're clean(ish) oil needs to be reacted with methanol and a catalyst, this is required to increase the rate of the reaction, this needs to be an alkaline, either Sodium Hydroxide or Potassium Hydroxide. This can be recovered unaffected by the reaction along with the glycerol that was separated from the vegetable oil.

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This process is reversible, this means that the reaction works in both directions until there is equilibrium between vegetable oil and biodiesel. This means that as the biodiesel producer, you must ensure that biodiesel is being created all the time rather than having the reaction stall when there is a balance between vegetable oil and biodiesel.

In commercial production, you would tap off the output biodiesel as it is created to make sure that there is more oil than there is biodiesel, therefore, the reaction will continue.

With smaller production lines it is easier to just add more methanol than you need to ensure that the reaction carries on producing biodiesel.

After the reaction you will be left with a mix of: biodiesel, glycerol, unused catalyst, excess methanol and traces of water, all of these need to be removed from the biodiesel in order for it to be used as a fuel.
First off the glycerol is much denser than the biodiesel, so all you need to do is wait for a couple of days for it to separate and drain off the glycerol by-product from the bottom of the tank, this can be sped up using a centrifuge.
The water and methanol is removed by using either flash evaporation or distillation.
Then all that is left is the unused catalyst, this is removed from the biodiesel by gently washing it with warm water until the wash water goes clear. After this, it is advised to filter your product through a 5 micron filter to make sure all contaminants have been removed, then you need to dry the biodiesel and put your finished product into storage.



The key to successful biodiesel production is to make sure that the base feedstock you are getting is of a high standard. If you collect poor quality WVO, there will be a considerable amount of shrinkage due to the high FFA content, which HAS to be removed. Most WVO is sold by weight so its best to stay away from poor quality oil - especially if you are paying for it!
It is possible to measure how much FFA is in your WVO by using a Free Fatty Acid Measuring Strip, these can be found on the Filtertechnik website for you to buy, not only this but you can find a whole range of analytical equipment that are ready for you to buy, such equipment allows you to view what is contaminating your oil and how much is present including water content.
Another thing to watch out for is that the term WVO doesn't necessarily mean waste vegetable oil anymore, food producers are selling hydrogenated, semi-hydrogenated veg oils, rendered tallow and animal fats (AKA brown grease) as WVO, not to try and scam you, its just that the term has lost its meaning (FYI, in this post, when I say WVO, I mean WVO!), these can cause serious problems because they contain high levels of solid contamination, fats and water, which if used in a motor vehicle, can cause big problems with the fuel delivery system.

WVO can also be used for power generation, but to do so, your oil has to be exceedingly clean, so it may need a filtration system that incorporates an anti-bacterial conditioning system and a polishing filter. Again, such systems can be found on the Filtertechnik website in varying sizes, from small home brew systems to big industrial size rigs.

Thanks for reading!