Abstract
AbstractAcid activation was carried out by heating muds prepared from Ca-rich bentonite (CaB), sulfuric acid (H2SO4) and distilled water, yielding various bleaching earths (BEs). The roles of each of the process variables, namely mass fraction of H2SO4 (x) in the dried CaB and pure H2SO4 mixture, heating temperature (T) and contact time (t), in the activation were tested. The raw CaB and each BE were examined with X-ray diffraction, chemical analyses, N2 adsorption/desorption, pH-metry and tintometry. The BE contents in both the aqueous and oily suspensions were set to 2% by mass in order to measure the pH value and the bleaching power, respectively. The optimum conditions for the activation to obtain a BE having the same bleaching power (0.60) as Tonsil® Optimum Bleaching Earth for soybean oil were determined as x = 0.35, T = 100°C and t = 2 h. The bleaching power increased only marginally upon increasing the activation time from 2 h up to 10 h at a given x and T. After 10 h, significant changes did not take place in the bleaching power of the BE. The mass fraction of total structural metal oxide (y), pH value, specific pore volume (V), specific surface area (S) and mean internal diameter (D) of the mesopores for the optimized BE are y = 0.10, pH = 3.0, V = 0.31 cm3 g–1, S = 225 m2 g–1 and D = 7 nm. The pH and D values were more important for bleaching the alkaline refined soybean oil compared to the other parameters tested.
Highlights
Crude vegetable edible oils are produced by compression or solvent extraction of soybean, cottonseed, sesame, coconut, olive, safflower, sunflower, corn, rapeseed, mustard seed, peanut and palm oils
Of acid-activated montmorillonite on its bleaching efficiency was studied by Falaras et al (1999), who showed that bleaching efficiency increases with increasing acidity and specific surface area, where medium activation of montmorillonite is the most efficient way to bleach cottonseed oil, producing the best colour index and lowest peroxide value
Falaras et al (2000) investigated the physical and chemical properties of pillared materials to understand their effects on bleaching efficiency in the processing of cottonseed oil and concluded that the Al-pillared acid-activated material was comparable to Tonsil® Optimum Bleaching Earth (TOBE)
Summary
Crude vegetable edible oils are produced by compression or solvent extraction of soybean, cottonseed, sesame, coconut, olive, safflower, sunflower, corn, rapeseed, mustard seed, peanut and palm oils They are processed by both chemical and physical refining techniques (Mounts, 1981; Zschau, 1999). Previous studies on the kinetics of the bleaching of vegetable oils (Brimberg, 1982) showed that the catalytic effect of the bleaching earth (BE) causes lengthy chemisorbed β-carotene molecules to immediately decompose to form shorter molecules As this decomposition causes a colour change from white to greyblue, the bleaching power (BP) is more conveniently measured by the adsorption of chlorophyll rather than β-carotene. Because every clay sample has slightly different mineralogical and geochemical properties, bleaching powder that is produced through acid activation of the clay may result in variation in adsorption properties such as porosity, specific surface area and pore-size distribution
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