ABSTRACT: In this study, Al-pillared white bentonite (Ordu- Unye, Turkey) was used for cottonseed oil bleaching. Pillaring process parameters were optimized in terms of bleaching effi- ciency as the bleaching capacity of cottonseed oil. The initial cation concentration, hydrolyzing agent ratio, and thermal treat- ment temperature were chosen as major process parameters. Pil- lared clays were characterized by FTIR and differential thermal analysis. The bleaching efficiency of bentonite increased from 11.8 to 17.5% by acid activation and to 33.5% by further Al pil- laring. The optimal pillaring process conditions for cottonseed bleaching were an initial concentration of AlCl 3 of 0.5 M, a OH - /Al 3+ molar ratio of 0.3, and a thermal treatment tempera- ture of 700°C. Paper no. J10945 in JAOCS 82, 599–602 (August 2005). KEY WORDS: Al-pillared clay, bleaching, cottonseed oil. Acid-activated clays [i.e., activated bleaching earths (ABE)], which are traditionally activated by an inorganic acid, are widely used to bleach edible oils. Montmorillonitic clays natu- rally have the crystal lattice distortion to contain active sites and have a high cation-exchange capacity (CEC). Such clays are generally modified by applying a known type of activation (i.e., acidic, cationic, anionic, organo-cationic, or thermal) to form new active sites and/or to reinforce existing ones. In the acid-activation mechanism (e.g., dry or wet process), the free protons formed attack the –OH groups that exist in tetrahedral and octahedral layers to increase the number of Lewis and Brønsted acid sites over the lattice (1). β-Carotene, a red pigment, is the major colorizing agent in cottonseed oil. It has a slightly alkaline character and a rela- tively high aspect ratio (i.e., rodlike). Based on the size and acidity of β-carotene, acidic adsorbents having mezopores are needed to remove this species from cottonseed oil by the bleaching process (2). However, the adsorption capacities of naturally occurring low-grade bentonites cannot be increased to levels as high as those of commercial products by acid acti- vation alone (e.g., Tonsil; Südchemie, Hilden, Germany). For these types of clay minerals, combined activation methods (i.e., a combination of acid and organo-cationic activation with fur- ther thermal treatment) may result in better oil bleaching ca- pacities compared with the traditional activated clays. A number of studies appear in the literature about applying almost all types of activated clays to cottonseed oil bleaching (3). Characteristic differences between β-carotene and α- chlorophyll (the major colorants in cottonseed and olive oil, re- spectively) have motivated the development of cheaper and more active adsorbents for bleaching. Silicon-based adsor- bents, hectorite-based activated clays, and organo-cationic clays are the groups of adsorbents most often studied for re- moving colorants from oils (4). In the last decades, catalyst re- searchers have investigated new approaches for developing heterogeneous (clay-based) catalysts by using clay minerals as a substrate. Pillaring clay (bentonite, hectorite, etc.) by altering the basal spacing with polycations of group IVB (Ti, Zr), group VB (V), group VIIB (Fe, Ni, Pd), groups I and IIB (Cu, Zn), or group IIIA (Al) cations have been examined the most. The pil- lared clays have been shown to have higher surface areas with selective activity. The mechanism of the pillaring process in- volves two subprocesses: cation exchange and further stabiliza- tion. The process can be performed either by inserting initially formed polycations into the basal space by a cation-exchange mechanism or by forming polycations in situ at CEC sites of the layered clay structure. These hydrated polycation pillars can be stabilized by severe heat treatment (e.g., at over 400°C) (5). These types of structures, called pillared clays (PILC), and Keggin-type polycations are the inorganic pillaring compo- nents most widely studied in the literature (6–9). Al 13 -polyca- tions can be formed by forced hydroxylation of either AlCl 3 (with or without crystalline H 2 O) or Al(NO 3 ) salts by reacting them with a hydrolyzing agent (i.e., NaOH) in aqueous solu- tion with or without a buffer (8,10,11). Although the compo- nents vary widely in their clay-pillaring properties, they are generally inorganic cations. A few studies can be found in the literature concerning organic pillars (12). Al-pillared clays having large surface areas with high cat- alytic activity have been reported previously (13). These higher surface area (>200 m 2 /g) clays could be intended for use in bleaching vegetable oils. In this study, preactivated (i.e., acidic and thermal) clay was pillared with Al-polycations by investigating the effect of major parameters assumed in the pillaring process (i.e., hy- drolyzing agent ratio, initial cation concentration, and thermal treatment temperature). Al-pillaring conditions and the effects of major parameters on the bleaching process were optimized by comparing the bleaching efficiencies of each adsorbent type as a measure of the activity of the clay. EXPERIMENTAL PROCEDURES Preactivation of bentonite. Original white bentonite (Ordu- Unye, Turkey) having a CEC of 103 mequiv/100 g clay (de- noted as “O”), which was dried and crushed to less than 63 μm, was activated without purification (i.e., organic compounds and Copyright © 2005 by AOCS Press 599 JAOCS, Vol. 82, no. 8 (2005) *To whom correspondence should be addressed at Hacettepe University, Chemical Engineering Department, Beytepe, Ankara, 06800, Turkey. E-mail: oguzhanc@hacettepe.edu.tr Al-Pillared Clay for Cottonseed Oil Bleaching: An Optimization Study Mustafa Oguzhan Caglayan*, Suleyman Kafa, and Nevzat Yigit Cumhuriyet University, Chemical Engineering Department, 58140, Sivas, Turkey Preview