The properties of final product strongly depend on the yield of
methyl ester (purity of methyl ester phase). The presence of glyceride
types, in particular, in the fuel can cause serious problems
in commercial applications. According to EN 14214 biodiesel standard,
there are strict limitations for both free and total glyceride
contents of biodiesel and the level of methyl ester content.
Although the amounts of free glyceride and total glyceride were
not measured, the purity of biodiesel can be determined by using
the viscosity measurement [7,13]. Regarding the measured viscosity
of the biodiesel, the calculated methyl ester content in this
study was approximately 91–92%. This was slightly lower than
the minimum level of methyl ester content, which is 96.5%. Once
again, this explained the formation of high carbon residue of the
biodiesel mentioned in the previous section