Thermodynamic study on the prevention of B30 biodiesel wax crystallization by γ-Al2O3 nanoparticles and sorbitan monooleate

Abstract

This paper reports a thermodynamic investigation on the role of γ-Al2O3 nanoparticles and sorbitan monooleate (SMO) as cold-flow improver additives for B30 biodiesel blend. Here, the two additives were able to improve fuel’s cold-flow properties and responsible for reducing wax crystallization temperature as low as 6.42 °C. Based on DCS analysis, the addition of individual SMO or γ-Al2O3 nanoparticles gave rise to the increase in crystallization enthalpy and entropy. However, the opposite effect was observed when they were used in combination. This synergistic effect was found to be responsible for making them effective in the prohibiting the spontaneity of wax crystallization, which was proven by the increase in crystallization Gibbs free energy (ΔGxtal) value from −72.9 to −35.7 J/g. This is primarily due to that the ability of SMO to stabilize wax nuclei and the role of γ-Al2O3 nanoparticles as an additional nucleation site. Furthermore, DLVO analysis also revealed that γ-Al2O3 nanoparticles exhibited high colloidal stability, enabling them to facilitate stable Pickering emulsion formation. Finally, microscopic observations demonstrated that both additives could suppress the formation of insoluble paraffinic “house of cards” crystals.