Catalyst selection is a key factor in order to design a biodiesel
production process using acid raw materials. Hydroxides are less
efficient to catalyze transesterification than methoxides, compared
in a molar basis. Potassium catalysts form lower amount of soaps
than the sodium one. This is an advantage in order to process acid
raw materials. In the case of oils with acidity higher than 1%,
KOCH3 is more active than NaOCH3. This is explained by a lower
soaps formation by the former. KOH is the less active catalyst independently
of the oil acidity.