Fish bone derived natural hydroxyapatite-supported copper acid catalyst: Taguchi optimization of semibatch oleic acid esterification

Natural hydroxyapatite (NHAp) derived from waste fish (Lates calcarifer) bone has been effectively utilized as a support for preparation of low-cost, recyclable, heterogeneous copper acid catalyst. The novel catalyst has been prepared through wet-impregnation method involving tungsten-halogen-irradiation assisted freeze-drying. The catalyst was characterized through TGA, SEM, XRD, BET-BJH and FTIR analyses. The catalyst possessed 16.78 m(2)/g specific surface area, 0.0313 cc/g pore volume and 33.14 nm modal pore size with an acidity of 11.22 mmol KOH/g catalyst. The developed acid catalyst demonstrated excellent efficacy in the semibatch esterification of oleic acid with ethanol. The Taguchi robust design method (L-9 orthogonal array) was applied to optimize process parameters governing oleic acid conversion. The maximum oleic acid conversion over a span of 1 h was 91.86% corresponding to the parametric values viz. 90 degrees C freeze-drying temperature, 1.0 weight ratio of copper nitrate to NHAp, 0.8 mL/min ethanol flow rate and 1000 rpm stirrer speed. Moreover, in situ water removal within the reactor through use of silica-gel desiccators could significantly enhance oleic acid conversion. The innovative Cu-NHAp catalyst demonstrated excellent reusability and regeneration characteristics. Thus, the article explores an innovative and environmentally-benign utilization avenue of waste fish bone as a promising heterogeneous catalyst support. (C) 2012 Elsevier B.V. All rights reserved.