The esterification reactions conducted using IL concentrations in the range of 4.0e
6.0 wt.% for ILs 1-butyl-3-methyl-imidazolium hydrogensulfate (BMIMHSO4), 1-butylimidazolium hydrogensulfate (BIMHSO4), and 1-methylimidazolium hydrogensulfate (MIMHSO4) at 170 C were optimized with the highest achievable mixing degree
(800 rpm) and an excess molar ratio of methanol to crude palm oil (CPO) (21:1) for 4 h.