Biodiesel from fried vegetable oils via transesterification by heterogeneous catalysis

Three solid catalysts have been tested in the transesterification of fried oils: CaO, SrO, K3PO4. For CaO and SrO the different efficiency, between their use as powder or granules, has been examined. Another investigated aspect has been the catalytic activity at different catalyst loadings and recycles. At the end granules have been employed in a catalytic bed reactor, comparing results with batch systems. Results have shown that using catalyst as granule does not affect the yields after 3 h of reaction. The use of the catalytic bed reactor has given the possibility to perform the transesterification maintaining the catalyst separated from the reactants, without loss of efficiency; in fact the comparison between trials in batch reactor and in catalytic bed system has not shown differences in yields. After 3 h of reaction, at 65 °C, 5 wt% of catalyst, we have had the following FAME yields: 92% for CaO, 86% for SrO, 78% for K3PO4. The transesterification reaction has shown a sensitive influence respect to K3PO4 granules amount used; in fact the yield has reached the 85% using 10 wt% of catalyst. The reutilization of the catalyst, without regeneration, has shown a loss of efficiency of about 10–20% in decreasing yield.

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► CaO, SrO and K3PO4 heterogeneous catalysts in transesterification reaction to produce biodiesel.
► Exhausted frying oil as triglycerides source to achieve biodiesel production more profitable.
► A catalytic bed reactor employing catalysts as granules form.