A bio-inspired heterogeneous catalyst for the transformation of limonene from orange peel waste biomass into value-added products

The kinetic study of limonene oxidation using an iron hexadecachlorinated phthalocyanine immobilized on modified silica catalyst (FePcCl16-NH2-SiO2) with the oxidizing agent t-butyl hydroperoxide (TBHP) is developed. Experimental reaction rates from a batch reactor were fitted with the kinetic expression based on Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanisms with the adsorption of both reactants and the main reaction products (carvone, limonene 1,2-epoxide and carveol) on the surface of the phthalocyanine with 99% accuracy. A similar kinetic expression fitted the carveol oxidation to carvone with a 96% exactness. Limonene conversion of 74% was obtained after 23 h with a carvone selectivity of 10% and apparent activation energy of 38.6 kJ mol(-1); whereas at 78% carveol conversion the selectivity to carvone was 87% after 10 h. The catalyst can be recycled up to seven times without losing neither limonene conversion nor carvone selectivity and these results do not depend on the treatment of the catalyst before reusing. Leaching of the active species was not observed at the reaction conditions and the influence of liquid-phase free-radicals was demonstrated, concluding that the reaction includes heterogeneous and homogeneous paths.