The determination of active filter aid adsorption sites by temperature-programmed desorption

Temperature programmed desorption (TPD) was used to evaluate the active sites of several filter aids that have been promoted for use by the deep-frying industry: activated carbon, aluminas, bleaching earths, diatomaceous earth, silica and synthetic magnesium silicate. TPD analysis determines both the total surface concentration of the active sites and the details of their intensity distribution. A correlation analysis was made between the adsorbents' oil treatment performance and the observed acidic/basic sites. For some of the adsorbents, the adsorption of free fatty acids and the percent change in the color of the oil was shown to relate to the total basic sites and acid sites, respectively. The study also showed that other factors might affect these adsorptivities.