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Saturated fatty acid adsorption by acidified rice hull ash
Author(s) -
Farook Adam,
Ravendran Supramaniam
Publication year - 2000
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/s11746-000-0070-0
Subject(s) - adsorption , chemistry , monolayer , fatty acid , nuclear chemistry , langmuir adsorption model , langmuir , volume (thermodynamics) , chromatography , organic chemistry , biochemistry , physics , quantum mechanics
Rice hull ash (RHA) was treated with 1.0 M HNO 3 (RHA‐A1) and another batch was treated with 14.0 M HNO 3 (RHA‐A14). RHA‐A1 and RHA‐A14 had a pH of 6.58 and 6.13, respectively. Adsorption of saturated fatty acids (C 8 , C 10 , C 12 , C 14 , C 16 , and C 18 ) was carried out on RHA‐A1 and RHA‐A14 at 32±1°C. The adsorption data conformed to the Langmuir isotherm. The specific surface area of RHA‐A1 was 183.84 m 2 g −1 while that of RHA‐A14 was 174.67 m 2 g −1 . The specific pore volume of RHA‐A1 was 0.216 cm 3 g −1 while that of RHA‐A14 was 0.234 cm 3 g −1 . The acid‐treated ash, RHA‐A14 ( q m =0.43±0.03 mmol g −1 where q m is the amount of adsorbate adsorbed to form a monolayer coverage on the ash particles) showed a twofold increase in the adsorption of fatty acid per gram ash compared to RHA‐A1 ( q m =0.25±0.03 mmol g −1 ). The free energy of adsorption, Δ G° ads , was determined to be −7.06±0.10 and −6.75±0.11 kcal mol −1 for RHA‐A1 and RHA‐A14, respectively. The reduced Δ G° ads values observed for RHA‐A14 were attributed to the electrostatic repulsion of the hydrophobic chain of the fatty acid adsorbed on adjacent sites and brought into close proximity of each other. The Δ G° ads values showed that the process of adsorption took place through physisorption on both RHA.