Before washing with water, the crude biodiesel is analysed to
evaluate conversion and the total soap content. Crude biodiesel is
finally washed with distilled water, in a ratio of 1:1 v/v to biodiesel,
five times and total soap content is again measured.
All final product analyses were confirmed by INNOVHUB, stazioni sperimentali per l’industria innovazione e ricerca, Laboratorio
Sostanze Grasse e Derivati (Milan, Italy).
A simple routine qualitative test to evaluate FAME content was
carried out after each experiment by adding methanol (27 mL) to
the biodiesel sample (3 mL) in a test tube and shaking it for about
30 s, at room temperature; since biodiesel is soluble in methanol,
good FAME conversion implies no visible precipitate or cloudiness.
The total soap content test is performed by adding biodiesel (10 g)
to isopropyl alcohol (100 mL) under stirring in a beaker, then dil.
HCl (0.01 N) is added dropwise until pH 4.5. Total soap content is
evaluated by the following equation