Biodiesel 2 Catalysts 2 Esterification 2 Esters 2 Fatty acids 2 High free fatty acids BET surface area 1 Biodiesel production 1 Carbon dioxide 1 Catalyst loadings 1 Environmental problems 1 Fatty acid methyl ester 1 Feedstocks 1 Fossil fuels 1 Fourier transform infrared spectroscopy 1 Fuel oils 1 Heterogeneous base catalyst 1 Heterogeneous catalyst 1 Heterogeneous solid acid catalysts 1 High fatty acids 1 Infrared spectroscopy 1 Low cost methods 1 Low grade 1 Low grade feedstock 1 Methanol 1 Palm fatty acid distillate 1 Proven reserves 1 Scanning electron microscopy 1 Shells (structures) 1 Sulfated calcium oxide 1