Biodiesel is made from renewable resources like vegetable oil or waste products such as fish oil and can be blended in any ratio with mineral diesel (gasoline) for use in most diesel engines. However, car manufacturers advocate using blends up to 20% biodiesel (B20). Only some German car manufacturers offer adaptation sets for 100% biodiesel use. There are only a very few pump stations left nowadays that still sell 100% biodiesel.

Biodiesel or FAME is biodegradable and has a lower CO₂ footprint than ordinary diesel. Except for NOx, the tailpipe emissions are also favourable. Because of its higher flash point it is safer in use and storage than mineral diesel. Long term storage of biodiesel and other biofuels however, needs special attention. Biodiesel is strongly hygroscopic and can absorb moisture from the air, giving rise to all kinds of problems.

Fungi and bacteria can and did cause problems in big storage tanks while in the presence of condensed water. Polymerization due to oxidation is another common problem with biodiesel. The resulting gums do clog the fuel filters rather quickly.

Methanol fumes can also be formed as a result of decomposition or polymerization of biodiesel and can lead to higher risk levels of explosions in combination with static electricity. Static electricity build-up must be prevented by proper grounding and other precautions.

This is our process description of making biodiesel from vegetable oil:

• First the oil which forms your feedstock may need pre-treatment such as the removal of dirt or water using equipment like centrifuges or oil driers. Water is the worst enemy for any biodiesel process and must be evaporated.
• The oil is heated in pre-heating tanks.
• Methanol and sulphuric acid are added to start the esterification step.
• The mixture of oil and biodiesel is dried and neutralized.
• Methanol and NaOH (or KOH) dissolved in alcohol are added to the oil (we prefer a liquid 30 percent sodium or potassium methylate). The total amount of chemicals (the catalyst) you need is dependent on the level of Free Fatty Acid remaining. This is determined by using a simple chemical procedure called titration to test for the acid value (AV).
• While the temperature is raised to 65 Celsius the processor operates under 3 bar pressure to prevent loss of methanol vapour and facilitate rapid transesterification.
• After the correct temperature has been reached, the processor automatically maintains it during the chemical reaction. The whole process finishes in approximately 60 minutes.
• The mixture of biodiesel/glycerol is purged from the processor.
• The process of separating the biodiesel and glycerol using centrifuges or settling tanks starts here. Following the removal of glycerine from the biodiesel, it is transferred to a washing station where the biodiesel is passed through a centrifuge or filter press to remove dissolved contaminants like soap, MAG and glycerol.
• A Methanol Recovery Unit completes the extraction of most of the Methanol from the Glycerine and the Biodiesel.
• Glycerol must be neutralized and can be sold as a soap feedstock.
• In order to be sure that the biodiesel is 100% clean, it is polished, including a filtration down to 1 micron. The resulting biodiesel will conform to EN14214.

Every producer of biodiesel needs some basic laboratory equipment to do some chemical tests on both the oil and the produced biodiesel in order to guarantee a high quality standard. For this a GC and a NIR spectrometer are highly recommended.

Some basic wet chemical tests you need to perform are:

• Dirt/water content in the oil and biodiesel
• FFA and other polar components in the oil
• Dissolved metals in both oil and biodiesel
• Ester content in biodiesel
• Mono, di- and triglyceride content in biodiesel
• Methanol content in biodiesel

In the animation below we put a glass of fresh produced biodiesel from the reactor on a container. Immediately you can see the heavier glycerol settling out to the bottom. The raw, unwashed and lighter biodiesel stays on top. This process is called gravity separation. A centrifuge will speed up this process.