Esterification of free fatty acids in biodiesel production with sulphonated pyrolysed carbohydrate catalysts

The pre-treatment of free fatty acids in oils and fats in biodiesel production is of pivotal importance, and esterification in acidic medium must be done prior to basic transesterification of glycerides. The free fatty acids may be converted over an acidic catalyst of sulphonated pyrolysed carbohydrates. These were prepared by pyrolysis of the carbohydrates in inert atmosphere at 300-450°C in 1-15 h and sulphonation in concentrated or fuming sulphuric acid at 150°C. A monophasic fatty model mixture of lauric acid, tricaprylate and methanol was subsequently treated with the prepared catalysts. Conversion of free fatty acids to methyl esters were monitored by gas chromatography. Sulphonated pyrolysed sugar or starch showed free fatty acid conversions of about 75% in 1 h and about 95% in 3 h.