Doping of metal oxides increases basic strength. Potassium ions
being highly basic, when added to the calcium ions, become a competitive
base catalyst with high conversions of WCO to biodiesel at
lower reaction conditions. Potassium salts like potassium hydroxide
(KOH), potassium iodide (KI), potassium fluoride (KF) and
potassium chloride (KCl) have already been studied as a source of
potassium ions [16–19]. The current work is based on potassium
bromide (KBr) impregnated calcium oxide as a heterogeneous solid
base catalyst for transesterification. Studies report that the catalyst
had granular and porous structures with high basicity and superior
catalytic performance for the transesterification reaction after
impregnation [20].