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 m2/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 (L9 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 °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.

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• Natural hydroxyapatite (NHAp) was derived from fish (Lates calcarifer) bone.
• NHAp supported efficient, cost-effective, reusable copper Lewis acid catalyst.
• Catalyst preparation through Tungsten–halogen-irradiation-assisted freeze-drying.
• Optimization of semibatch ethyl oleate synthesis through Taguchi robust design.
• Enhanced oleic acid conversion by in situ water removal employing adsorbent.