Comprehensive analysis of alkaline earth metal ion removal from biodiesel using amino polycarboxylate chelating agents: Performance and mechanistic insights

Abstract

The presence of alkaline earth metal ions in biodiesel can exacerbate engine wear, impair fuel oxidation stability, and substantially reduce combustion efficiency. Improving the quality of biodiesel is therefore crucial for promoting its adoption as a viable alternative to conventional fossil fuels. This study investigates the removal of alkaline earth metal calcium (Ca²⁺) and magnesium (Mg²⁺) from Jatropha biodiesel using four amino polycarboxylate chelating agents: ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), 1,2-cyclohexanediaminetetraacetic acid (CDTA), and N-(2-hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA). The results showed that CDTA demonstrated the highest removal efficiency and selectivity for Ca²⁺ and Mg²⁺ among the four chelating agents, resulting in removal rates of 98.6% and 94.3%, respectively. Furthermore, the oxidative stability of biodiesel, measured as induction period, increased from 3.38 to 8.31 h after treatment with EDTA solution and reached a maximum of 8.68 h after treatment with CDTA. Density functional theory (DFT) calculations were performed to analyze Mulliken charges, electrostatic potential, frontier molecular orbitals, and interaction energies. The results indicate that the four chelating agents form cyclic structure complexes by simultaneously coordinating with a metal ion through multiple coordination atoms (N atom in amino group and O atom in carboxyl group). CDTA has the strongest interaction energies with Ca²⁺ and Mg²⁺, calculated at –826 and –915 kcal/mol, respectively, corroborating its superior chelation performance.

Graphical abstract

Keywords

chelation mechanism / Jatropha biodiesel / impurity ions / oxidation stability

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