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

Abstract

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 16.78m2/g specific surface area, 0.0313cc/g pore volume and 33.14nm modal pore size with an acidity of 11.22mmol KOH/g catalyst. The developed acid catalyst demonstrated excellent efficacy in the semibatch esterification of oleic acid with ethanol. The Taguchi robust design method (L9 orthogonal array) was applied to optimize process parameters governing oleic acid conversion. The maximum oleic acid conversion over a span of 1h was 91.86% corresponding to the parametric values viz. 90°C freeze-drying temperature, 1.0 weight ratio of copper nitrate to NHAp, 0.8mL/min ethanol flow rate and 1000rpm 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 andenvironmentally-benign utilization avenue of waste fish bone as a promising heterogeneous catalyst support.