Na,Ca-based catalysts supported on activated carbon for synthesis of biodiesel from soybean oil

Abstract

Different catalysts containing CaO particles dispersed in commercial activated carbon were prepared by wet impregnation followed by heat treatments. The catalytic efficiency of the prepared materials was investigated by evaluating their performance in biodiesel production by the transesterification reaction of soybean oil with methanol. The catalysts were prepared by three different routes; the first two routes involved the use of co-precipitation, with Ca(NO3)2·4H2O as the source of calcium and either NaOH (route 1) or NH4OH (route 2) as the precipitating agent, which were mixed with the activated carbon in aqueous suspension; in the third method (route 3), NaOH and CaO were directly mixed with the activated carbon in aqueous suspension. In all cases, the as-prepared materials were heat-treated at 800 °C for 3 h under argon flow. The best catalytic efficiency was achieved for the Na,Ca-based catalyst prepared by route 3, which was mainly composed of a mixture of CaO and Na2CO3 crystals dispersed in the porous carbon network. Catalytic recycling tests were also performed to evaluate the possibility of catalyst reuse, which revealed a drop in efficiency after 3 cycles; however the reused catalysts still showed significant activity, attributed to the permanence of Na+ ions within the porous carbon structure. Analysis of the Ca and Na contents in biodiesel samples synthesized in the three reaction cycles revealed low concentrations of metals; in the case of Ca, the concentration leached into the biodiesel after the 3rd cycle was 9 times lower than that of a biodiesel sample synthesized using pure CaO. The results obtained showed that the chosen methodology is a promising route for the development of heterogeneous carbon-supported Na,Ca-based catalysts with considerable surface area and good catalytic efficiency in the transesterification reaction for biodiesel production.