Biodiesel From Tallow

Biodiesel can be easily made from tallow using very similar processes to plant oils. However, and according to a paper by Miller-Klein Associates, it has some advantages and disadvantages that are agreed between different studies.

 Advantage

Biodiesel from tallow has a higher cetane number than plant oil biodiesel. This means cleaner and more efficient burning in diesel engines.

Cetane numbers rate the ignition properties of diesel fuels, just as octane numbers determine the quality and value of petrol. It’s a measure of a fuel’s ability to ignite when it’s compressed. The higher the cetane number, the more efficient the fuel. Biodiesel has a higher cetane number than petrodiesel because of its oxygen content. The ignition quality affects engine performance, cold starting, warm up and engine combustion roughness. A high cetane fuel also may lead to incomplete combustion and smoke if the fuel ignites too soon by not allowing enough time for the fuel to mix with air for complete combustion.

 Disadvantage

Higher cloud point. Because of the high levels of saturates, biodiesel from tallow tends to crystallise out at much higher temperatures than biodiesel from plant oils. In Northern Europe this makes tallow biodiesel unsuitable for winter use apart from blending at low rates into conventional diesel. Tallow diesel cannot meet the required DIN standard for 100% biodiesel, but as a 5% mix with conventional diesel it meets the required standards.

Conclusions

There are no environmental advantages to using tallow as a biodiesel feedstock instead of plant oils. Total availability of tallow as a feedstock is limited and cannot be increased, and in some instances is declining.

Use of tallow for biodiesel competes with existing commercial outlets where the properties of the specific fatty acid composition bring advantages.

Tallow is not the best feedstock for biodiesel, especially for fuel use in areas with cold winters as it congeals. High cloud is more of a problem than higher cetane number is a benefit.

Exploitation of tallow will make economic sense for companies who are vertically integrated into rendering, but it will always be a minor component of the whole biodiesel picture.