Exploring the Structure–Activity Relationship of Bentonites for Enhanced Refinement of Recycled Vegetable Oil

The use of bentonite for recycling vegetable oils presents challenges, as even minor variations in the clay composition and structure can lead to significant differences in its ability to retain various chemical groups. This study investigates the structure–activity relationship of four bentonites—two hydrophilic and two hydrophobic (both in commercial and ground forms)—to better understand these effects. Solid-state NMR spectroscopy revealed subtle differences between hydrophobic and hydrophilic materials, as well as distinctions between ground and unground hydrophilic clays, through 29Si and 27Al experiments. These structural variations directly influenced the bentonites’ capacity to retain specific chemical groups, which in turn affected the pour point and volatile profile of the processed oils. A simplex lattice design of experiments, combined with multivariate analysis, facilitated the development of a predictive model to optimize process efficiency. Remarkably, this model achieved an improvement in pour point of up to 14.5 °C (from −2 °C to −16.5 °C) for oils treated with hydrophilic unground bentonite. This research underscores the critical role of bentonite morphology in enhancing the efficiency of vegetable oil recycling.