Pre-esterification of FFA in plant oil transesterified into biodiesel with the help of solid acid catalysis of sulfonated cation-exchange resin

One of the ways for the economically reasonable biodiesel production is to use the low quality plant oil as the cost advantageous feedstock. However, a large amount of free fatty acids (FFA) contained in the low quality plant oil causes the various problems: slowdown of the base-catalyzed transesterification, loss of the produced biodiesel and so on. Therefore, much interest has been taken in esterifying FFA into their methyl esters preliminarily with the help of solid acid catalysis of sulfonated cation-exchange resin. In the present research work, the resin catalysts of two types differing in textile structure of the matrix were employed for esterification of oleic acid with methanol at 333 K. For both the gelular resin and the macro-reticular one, the original bead shape provided the lower conversion ratio than the powder form prepared by grinding. The difference in the conversion ratio between the original bead shape and the powder form was larger for the gelular resin than for the macro-reticular one. On the other hand, the gelular resin was more active in catalyzing the esterification than the macro-reticular one. Also, for the purpose of examining the influence of the liquid–liquid interfaces formed between oil and methanol phases, soybean oil and methyloleate were used as a vehicle for the source oil of oleic acid. Additionally, a relation between the reusability of the resin catalyst and the by-production of water was investigated from a data collected by repeating the esterifying batches with reusing the resin catalyst.

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► Esterification of oleic acid with methanol was carried out at 333 K in the presence of sulfonated cation-exchange resin.
► The macro-reticular type was superior in the internal mass transfer, while the gelular type was more catalytically active.
► Liquid–liquid interfaces formed between oil and methanol phases were advantageous to the acid-catalyzed esterification.