Biodiesel from Tallow: Tallow is rendered mutton, beef or other bovine fat, processed from suet. (Rendered fat obtained from pigs is known as lard.) Tallow can be stored for extended periods without the need for refrigeration to prevent decomposition, provided it is kept in an airtight container to prevent oxidation.
Tallow is used in animal feed, to make soap, for cooking, as a bird food, and was once used for making candles. It can be used as a raw material for the production of biodiesel and other oleochemicals.
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.
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.
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.
Miller-Klein Associates also suggest other studies have been much more measured in their conclusions, and that using tallow for biodiesel only makes sense if there is genuinely no other outlet for the tallow (Government of Ontario study), or that the GHG savings from tallow biodiesel are less than for plant oils because of the additional impacts of animal production. A study published in 2004 by Climate Change Central assembled data from several LCA studies on the use of different feedstocks for biodiesel. These included substitution effects in their analysis, and concluded that the GHG savings are very similar across all feedstocks. Given the data uncertainties we should regard them as the same.
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. For example, in Australia sheep stock rates are at an all time low, and the Bureau of Statistics says cattle numbers are also down. As climate changes with hotter drier conditions, stocking rates could continue to fall and dependence on this feedstock could well be an ongoing issue.
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.
Reference: Miller-Klein Associates 2006, Use of Tallow in Biodiesel
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