Homogeneous catalysts can be base catalysts, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) (Shimada et al. 2002), or acid catalysts, such as sulfuric, sulfonic, phosphoric, and hydrochloric acids (Georgogianni et al. 2009). Base catalysts possess higher catalytic efficiency, lower cost (Wen et al. 2010), and lower reaction temperature and pressure (Freedman et al. 1984) so they are preferred over acid catalysts. Heterogeneous catalysts also classified as acidic and basic. Such as sulfated metal oxide, heteropolyacids, acidic ion exchange resin, and sulfonated amorphous catalysts (Sakai et al. 2009) Ni-Ca-hydroxyapatite solid acid catalyst (Chakraborty and Das 2012) zinc oxide (ZnO), calcium oxide (CaO), stron­tium oxide (SrO) (Lam and Lee 2011), and Na/SiO2 (Akbar et al. 2009) and (Yusuf et al. 2012). Researchers used calcined washed Rohu fish scale (Labeo rohita) as a heterogeneous base catalyst with a maximum biodiesel yield of 97.73 % and up to six reuses (Chakraborty et al. 2011). Fly-ash-supported CaO catalyst from eggshell waste shows a performance of 96.5 % for biodiesel production (Chakraborty et al.

2010) . Some of the commonly used heterogeneous base catalysts are K/y-Al2O3 catalyst (Alonso et al. 2007), HTiO2 hydrotalcite catalyst (Barakos et al. 2008),

Ca and Zn mixed oxide (Ngamcharussrivichai et al. 2008), Al2O3 supported CaO and MgO catalysts (Umdu et al. 2009), alkaline earth metal oxides (Mootabadi et al. 2010), KF/Ca-Al, basic zeolites, alkali metal loaded alumina (Narasimharao et al. 2011). Basic heterogeneous catalysts have higher activity than acidic catalysts owing to shorter reaction times lower temperatures requirement in comparison to acidic catalyst.