“…This pretreatment stage is known as esterification and is usually catalyzed by sulfuric acid, with reaction yields over 95% (Canacki and Van Gerpen 2001). Solid-acid catalysts, such as Dowex monosphere 550A, Dowex upcore Mono A-625, Amberlyst-15, Amberlyst-16, Amberlyst-35, Dowex HCR-W2, mesoporous aluminosilicates, Amberlyst 131, Relite CFS, ZrO 2 -supported metal oxide and mesoporous organosilicas, have also been considered (Özbay et al 2008, Carmo et al 2009, Tesser et al 2010, Morales et al 2010, Kim et al 2011). More recently layered bismuth carboxylates, has also been used in esterification of fatty acids (Rosa da Silva et al 2013).…”