Exploring metal nanocomposites for asphaltene removal: the role of Cu-BTC, CoMn2O4 and K-OMS-2 in the adsorption and oxidation of asphaltenes†

Asphaltenes, the most polar and complex class of compounds in petroleum crude oils, pose significant challenges in refining processes due to their tendency to precipitate, causing fouling, clogging, and corrosion in pipelines and reactors. These issues are further increased by their solubility behaviour, making their removal difficult. The present study investigates the synthesis of metal nanocomposites focused on a metal–organic framework (Cu-BTC), a spinel oxide (CoMn₂O₄) and an octahedral molecular sieve (K-OMS-2) for the adsorption and oxidation of asphaltenes from model solutions. The prepared nanocomposites were characterised using FE-SEM, EDX, HR-TEM, FT-IR, XRD, and BET surface area analysis. Furthermore, they were tested for their ability to adsorb asphaltenes using batch adsorption studies, and the equilibrium data obtained were interpreted using Langmuir, Freundlich, Temkin, Redlich–Peterson, and Hill isotherm models. Thermodynamic studies were performed, and changes in enthalpy (ΔH⁰), entropy (ΔS⁰) and free energy (ΔG⁰) were determined from the data. Kinetic studies were conducted, and the data were analysed using pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich, intraparticle diffusion, and Boyd diffusion models. Adsorption studies revealed that asphaltenes’ adsorption onto Cu-BTC was best explained by the Freundlich adsorption isotherm, while CoMn₂O₄ followed the Langmuir model and K-OMS-2 was governed by the Hill isotherm. The monolayer adsorption capacities of the prepared nanocomposites varied in the order: K-OMS-2 (245 mg g⁻¹) > CoMn₂O₄ (77 mg g⁻¹) > Cu-BTC (50 mg g⁻¹). Kinetic studies indicated that the adsorption process was rapid, and the Boyd diffusion model suggested that the rate-limiting step was the external mass transfer of asphaltenes onto the adsorbent. CoMn₂O₄ exhibited the highest catalytic activity among the prepared nanocomposites for asphaltene oxidation, achieving a 140 °C reduction in oxidation temperature. The findings indicated that K-OMS-2 is an effective material for adsorption, while CoMn₂O₄ is efficient in the catalytic oxidation of asphaltenes.