Natural clays for biodiesel purification: Adsorption of glycerol and functionalization of polymeric membranes for polar phase removal

Efficient and sustainable purification methods are essential not only to ensure biodiesel quality but also to reduce environmental impacts and production costs. In this study, natural clays (pink, green, and white) were evaluated as sustainable materials applied in two distinct stages of the purification process: adsorption of free glycerol from the ester‐rich phase and incorporation as additives in polymeric membranes for the separation of the reaction mixture. Characterization showed that green clay had the highest specific surface area (112 m 2 g −1 ), greater amorphous character, mesoporosity, and silica content, all of which favoured the adsorption of free glycerol. In batch tests, green clay outperformed the other clays, achieving approximately 60% free glycerol removal and a maximum adsorption capacity of 524 mg g −1 within 60 min. In the membrane separation process, the incorporation of clays into the polymer solution promoted morphological changes, resulting in an increase in average pore diameter and higher hydraulic permeability compared with the pristine membrane. With the addition of 2.5% acidified water to the reaction mixture, the membrane containing 1% green clay reduced the polar phase content in the permeate to 8% (75.8% removal), compared with 15% in the permeate (54.5% removal) for the unmodified PES membrane. These results demonstrate that natural clays, particularly green clay, are effective both as adsorbents and as membrane additives, representing a new and sustainable alternative for biodiesel purification.