Esterification Esters 10 Biodiesel 6 Catalysts 6 Fatty acids 6 Palm fatty acid distillate 6 Fatty acid methyl ester 4 Carbon 3 Heterogeneous solid acid catalysts 3 Methanol 3 Molar ratio 3 Supercritical methanol 3 Additives 2 BIODIESEL PRODUCTION 2 Carbohydrate-derived solid acid catalyst 2 Carbonization 2 Catalysis 2 Catalyst activity 2 Energy conservation 2 Heterogeneous catalyst 2 Heterogeneous solid acid catalyst 2 High free fatty acids 2 Methyl esters 2 OPTIMIZATION 2 Palm oil 2 Physico-chemical characterization 2 Physicochemical properties 2 Reaction temperature 2 Reusability 2 Scanning electron microscopy 2