Isothermal study of asphaltene adsorption over 4A, 13X, ZSM-5, clinoptilolite zeolites, and phoslock

The paper reports the adsorption studies of asphaltenes of Iran's heavy crude oil on some natural and synthetic alumino-silicates. Asphaltenes were precipitated using n-heptane. Toluene was used as a precipitating solvent of asphaltenes and several zeolites including 4A, ZSM-5, Clinoptilolite, and La-modified bentonite (Phoslock) as adsorbents. FTIR analysis indicated the asphaltenes which comprise a complex of aromatic, aliphatic, and polar compounds. The pore size and outer surface area of the adsorbents were determined by BET method and the following order was found between outer surface areas: ZSM-5 (238.27 m(2) g(-1)) > Clinoptilolite (28.75 m(2) g(-1)) > Phoslocks (27.92 m(2) g(-1)) > zeolite 4A (21.11 m(2) g(-1)) > Zeolite 13X (317.24 m(2) g(-1)). Besides, the adsorption isotherms were investigated with the conventional isotherm models and it was indicated that the Langmuir isotherm fitted the experimental data. Zeolite 13X with the highest specific surface area and pore size exhibited the maximum adsorption capacity, indicating that there is a direct relationship between surface area and adsorption capacity. However, it seems that the pore size effect is more prominent because of the large size of asphaltene's molecules.