Novel aluminum-pectin/bentonite pellets for continuous biodiesel production in a packed bed reactor

The development of structurally stable and catalytically active materials is essential for continuous biodiesel production. In this work, aluminum–pectin (ALP) catalysts were mixed with bentonite clay in varying proportions to overcome the poor compactability of pure ALP powder and produce stable pellets. The resulting composites were shaped by extrusion, dried, and calcinated to yield mechanically stable pellets suitable for packed bed reactor applications. Structural and textural analyses revealed that the incorporation of bentonite altered the material properties, where ALP_72 pellets possess a specific surface area of 4.51 m² g⁻¹ and a pore volume of 5.9 × 10⁻³ cm³ g⁻¹, while CO₂-TPD analysis demonstrated a high density of strong basic sites responsible for the enhanced transesterification activity. Mechanical compression tests confirmed enhanced pellet strength for ALP_33 (33 wt% ALP) formulations, whereas ALP_72 (72 wt% ALP) demonstrated fragility. Catalytic activity was initially screened in batch reactions, confirming an increase in basicity and fatty acid methyl esters (FAME) yield with higher ALP content. In continuous flow experiments, ALP_33 and ALP_72 pellets achieved biodiesel yields above 95% under mild conditions (50 °C, 1:1 MeOH:oil ratio), with ALP_72 maintaining stability for over 24 h of operation. GC–MS analysis confirmed that the transesterification process preserved the molecular structure of methyl esters, with no signs of rearrangement. These results reveal the promise of ALP-based pellets as efficient and durable catalysts for sustainable biodiesel production.