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Metal Porphyrin Adsorption onto Asphaltene in Pentane Solution: A Comparison between Vanadyl and Nickel Etioporphyrins

Chen, Feifei, Zhu, Qiushi, Xu, Zhiming, Sun, Xuewen, Zhao, Suoqi
Energy & Fuels 2017 v.31 no.4 pp. 3592-3601
X-ray diffraction, adsorption, bitumen, heat, models, nickel, nitrogen, oil sands, pentane, porphyrins, solvents, sorption isotherms, temperature, transmission electron microscopy
In the solvent deasphalting process, it is necessary to study the interaction between metal porphyrins and asphaltene for improving demetallization efficiency (vanadyl or nickel). Therefore, the main aim of this study is to investigate the adsorption kinetics and thermodynamics of nickel etioporphyrins onto Canadian oil sands bitumen vacuum tower bottom (VTB) asphaltene, and to compare the results with that of vanadyl etioporphyrins onto VTB asphaltene in pentane. Asphaltene was characterized by transmission electron microscopy (TEM), N₂ adsorption, and X-ray diffraction technique (XRD). The results showed that vanadyl/nickel porphyrins were adsorbed onto the VTB asphaltene. The adsorption rate varied as the dosage of asphaltene, the concentration of vanadyl/nickel porphyrins, and the adsorption temperature changed. By comparison of the pseudo-first-order adsorption kinetics model of the two adsorption processes, the adsorption rate for nickel octaethylporphyrin (Ni-OEP) was faster than that for vanadyl octaethylporphyrin (VO-OEP). Furthermore, the equilibrium adsorption capacity of Ni-OEP was greater than that of VO-OEP. Moreover, the adsorption equilibriums of vanadyl/nickel porphyrins both wonderfully fitted to the Freundlich isotherm. In addition, the ΔG° and ΔH° values of two adsorption processes had regressed at different temperatures. Compared with Ni-OEP, in the same conditions it was easier for VO-OEP to be adsorbed and more heat was released in the process.