Heterogeneous Fenton-like oxidation of phenalkamine condensate using iron oxide nanoparticles: catalytic performance, kinetics, and reusability

Graphical abstract showing Fenton-like oxidation of phenalkamine condensate using FeNP, achieving 85.11% COD removal from an initial COD of 140,000 mg/L. SEM analysis shows agglomerated spherical particles, while FTIR confirms Fe–O and other characteristic bonds. XRD identifies danalite, spinelloid, hematite, and iron oxide phases. Catalyst reusability was evaluated over four treatment cycles. Phenalkamine, a reaction product of cardanol, formaldehyde, and amines, is a highly valuable commercial product. The phenalkamine condensate is characterized by high pH, high chemical oxygen demand (COD) (140,000 mg/L), and comparatively low biochemical oxygen demand (BOD), making it challenging to degrade. In this study, heterogeneous Fenton-like oxidation using commercially obtained iron oxide nanoparticles (FeNPs) was investigated for treating real phenalkamine condensate. The FeNPs were characterized using SEM-EDS, XRD, FTIR, and BET techniques. XRD analysis confirmed hematite (Fe2O3) as the dominant crystalline phase with minor mixed crystalline reflections. The investigation also explored the influence of different parameters, including initial pH, H2O2 dosage, catalyst dosage, reaction time, and temperature. Optimal conditions are as follows: pH = 3.5, H2O2/COD ratio = 2, H2O2/FeNP ratio = 10, reaction period of 300 min at 313 K, and the maximum COD removal efficiency reached 85.11%. The degradation followed pseudo-first-order kinetics with a reaction rate constant of 0.00591 min−1 and an activation energy of 15.75 kJ/mol, indicating diffusion-controlled reaction. Comparison with conventional Fenton's oxidation demonstrated the superior performance of the FeNP catalyst. Furthermore, catalyst reusability studies revealed that the FeNPs could be reused for up to three cycles. This research contributes significant insights into the utilization of FeNPs as efficient catalysts for the degradation of phenalkamine condensate.