Oxidative Stability of Biodiesel by P-DSC

Although biodiesel is an excellent source of fuel, it has some disadvantages which include relatively poor cold flow properties and dilficulty in maintaining fuel quality during long-term storage. The latter is a matter of oxidation stability and will be discussed in this part. 

Degradation of the quality of this alternative fuel leads to an increase of deposits on injectors and pump parts and therefore an increase in pressure across filters [31]. Biodiesel is easily subject to oxidation under ambient conditions. This is mainly due to the presence of double bonds in the chains of fatty compounds. However, these unsaturated chains with low melting points lead to a good cold flow behavior (see Sect. 13.1), which is essential for a biodiesel. 

Other factors can have an impact on the oxidative stability of fatty oils and/or esters, such as, water, metals and light, etc. The presence of water can cause hydrolysis reactions and damage the fuel quality. Moreover, water can be dispersed in the biodiesel by mono-, di-glycerides and glycerol (co-products of the esterification). These compounds can play the role of emulsifier [3]. Furthermore, the presence of metals, even trace levels, can catalyze the oxidation reaction. Copper [30] has the 

Some AOs can be naturally present in vegetable oils (VOs), such as tocopherols, or chemically synthesized. Tocopherol is a phenolic compound that is found in four isomeric forms (a, P, Y, and S). They all occur naturally in VOs but not in animal-derived fats (except at trace levels). Several studies have shown that the naturally-occurring levels of tocopherols are optimized with respect to AO ability. In general, further addition of tocopherols has either no further benefit or may even decrease the oxidative stability [42], The commonly synthesized AOs are  

AO effectiveness is generally measured by stressing a fatty oil or ester both with and without AO and comparing the results. The methods used will be discussed in the following paragraphs. 

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