Maximum Bleaching of Vegetable Oils by Acid-activated Bentonite: Influence of Nanopore Radius

The optimum conditions necessary for preparing a bleaching earth (BE) with maximum bleaching power (BP) towards soybean oil (SO) and cottonseed oil (CSO) were investigated. BEs were obtained by H2SO4 activation of a white calcium bentonite (CaB) sample from the Kutahya region of Turkey. After drying for 4 h at 105 degrees C, the CaB samples were activated by heating their acidic aqueous suspensions for 6 h at 97 degrees C, the acid content of the dry bentonite/acid mixture being varied in the 0-70% mass range. The respective specific surface area (S) and specific nanopore volume (V) of the BEs were determined from nitrogen adsorption/desorption data obtained at -196 degrees C. For natural CaB, the values of S and V were 44 m(2)/g and 0.11 cm(3)/g, respectively. These values attained a maximum of 135 m(2)/g and 0.30 cm(3)/g for the BE sample prepared employing 40% H2SO4 for acid activation. Interestingly, the maximum BP was not associated with the maximum S and V values. The optimum values for the percentage H2SO4, S and V for attaining the maximum BP were 20%, 100 m(2)/g and 0.17 cm(3)/g, respectively.