Hierarchical CaO catalyst derived from rape pollen for high-efficiency glycerol-free biodiesel production via tri-component coupling transesterification

Abstract

This study develops a hierarchical calcium oxide (CaO) catalyst, designated as CaO(I), synthesized via the impregnation of a calcium acetate precursor onto porous hollow rape pollen templates. The catalyst demonstrates exceptional efficacy in glycerol-free biodiesel production through the tri-component transesterification of rapeseed oil with methyl acetate and methanol. Under optimized conditions (60 °C, 2 h reaction time, 1 : 1 : 8 oil/methyl acetate/methanol molar ratio), CaO(I) achieves a near-quantitative fatty acid methyl ester (FAME) yield of 99.72%. Comprehensive characterization (SEM, XRD, N₂-physisorption, FT-IR, TG, and CO₂-TPD) confirms that CaO(I) possesses a well-defined hierarchical pore structure with superior textural properties—including enhanced basic site density (14.6161 mmol g⁻¹) and BET surface area (34.8607 m² g⁻¹, versus 4.8 m² g⁻¹ for commercial CaO)—attributed to high active-phase dispersion and favorable pore architecture. Parameter optimization reveals 700 °C as the optimal calcination temperature, and it is observed that the precursor concentration critically influences the catalytic performance. The catalyst maintains robust reusability over multiple cycles with negligible activity loss. This novel templating approach leverages sustainable biomass resources to simultaneously address glycerol surplus issues in conventional biodiesel synthesis and enhance catalytic efficiency, establishing an environmentally conscious pathway for high-performance biofuel production.