Operation of a small scale demonstration plant for Biodiesel synthesis under supercritical conditions

A small scale demonstration plant was designed, set up and operated for the heterogeneously catalysed synthesis of biodiesel under supercritical conditions. An ASPEN plus model was applied to minimise the energy demand for the product purification stages, which were identified as the point of highest energy consumption of the process owing to the high molar excess of methanol required for the process (40:1 molar excess, 1.45:1 on a mass basis). Vacuum distillation followed by a small rectification column was identified as the optimum solution. The determination of the energy demand of the plant revealed the economic viability of the process as far as the energy consumption is concerned. The plant could be operated at full conversion of the feed (not raffinated rapeseed oil). The catalyst incorporated into the plant had been selected out of a large number of possible formulations through a screening procedure applying tricaprin as model substance. g-Al2O3 modified by acid treatment and La2O3 supported by g-Al2O3 were identified as most promising candidates. The stability of these formulations was proven through long term stability tests. They revealed stable conversion for different feed stock such as raffinated rapeseed oil, not raffinated rapeseed oil and Used Cooking Oil (UCO), while for partially fermented rapeseed oil severe catalyst deactivation was observed after 250 h test duration.