Shea nut shell based catalysts for the production of ethanolic biodiesel

This work focused on the synthesis of charcoal as carbonaceous catalyst support for the ethanol transesterification of vegetable oil to produce biodiesel. Shea (Vitellaria paradoxa) nut shells (SNS) were used as raw material to prepare an activated carbon based catalyst by chemical activation with potassium hydroxide (KOH). A central composite design of the response surface methodology (RSM) was used to investigate the interactive effect of the SNS-K catalyst synthesis parameters (pyrolysis temperature, residence time and KOH impregnation ratio) and its catalytic activity in sunflower ethanol transesterification. Experimental yields reached > 90% ester content in the biodiesel, with a catalyst prepared under mild pyrolysis conditions. Results showed that the temperature of pyrolysis and the KOH ratio used to impregnate SNS are the most important factors influencing the SNS-K catalytic activity. Catalyst prepared between 400 °C and 650 °C, with 120 min residence time and a biomass: KOH ratio of between 14% and 17.5% produced the highest ethyl ester content (96%) with an optimal catalyst prepared at 650 °C, with 120 min residence time and 14% KOH loading. SNS-K catalyst characterization by X-ray diffraction (XRD) showed potassium carbonate to be the main active potassium species responsible for catalytic activity. Recyclability tests showed that the catalyst can be reused after a thermal post treatment without catalytic activity loss. Thus, this new simple catalytic process allows biodiesel production under mild conditions, using local reactant (i.e. bioethanol, vegetable oils and char from local agricultural residues). This can be a realistic alternative process for a shift towards sustainable energy in sub-Saharan Africa.