Freeze-Drying kinetics in synthesis of biological hydroxyapatite-supported catalyst

Abstract

Kinetics of freeze-drying for the preparation of high performance bone-derived-hydroxyapatite (BDHAp) supported iron catalyst has been experimentally evaluated and modeled using standard drying models. The BDHAp was economically derived from Rohu fish (Labeo rohita) bone, which is considered as a municipal solid waste (MSW). After wet-impregnation of Fe2(SO4)3 .H2O on BDHAp, the precipitated mass was freeze-dried using three types of radiation viz. grey body radiation (GBR), infrared radiation (IRR) and tungsten halogen lamp radiation (THLR).Freeze-drying kinetics for all the different heating systems were evaluated and compared with standard drying models. THLR-assisted-freeze-drying (THLRAFD) rate was found maximum among all the thermal radiation. Midilli model was found to corroborate the experimental freeze-drying kinetics of THLRAFDoperation. The acidity of the catalysts prepared through THLRAFD (10.27, 10.36 and 11.21 mmol KOH/g catalyst) was found higher than their air-dried counter parts (8.14, 9.01 and 9.60 mmol KOH/g catalyst) corresponding to 65, 75 and 85°C drying temperatures at 1.75 Fe2(SO4)3 .H2O to BDHAp weight ratio. The prepared Fe-BDHAp catalyst developed through THLRAFD possessed appreciable acidity making it suitable for application as an efficient heterogeneous acidic catalyst.