Adsorption Kinetics and Thermodynamics of Vanadyl Etioporphyrin on Asphaltene in Pentane

The interaction between vanadyl porphyrins and asphaltene in alkane solvents is important to increase the removal rate of metals during the solvent deasphalting process. Thus, the adsorption kinetics and thermodynamics of vanadyl etioporphyrins on a Canadian oil sands bitumen vacuum tower bottom (VTB) asphaltene in n-pentane were investigated. After adsorption, asphaltene was analyzed via transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). A certain amount of vanadyl porphyrins was adsorbed by the VTB asphaltene. This adsorption process was affected by the asphaltene dosage (0.01 and 0.02 g), the concentration of the n-pentane solution containing vanadyl porphyrins (10 and 15 mu g/ mL), and the temperature (288, 293, and 298 K). The adsorption rate was initially distinctly high. However, this rate became much slower after around 300 min, until equilibrium was reached after 1800 min. A comparison of four kinetic models of the overall adsorption rate showed that the adsorption process can be well-described by a pseudo-first-order equation. Furthermore, the adsorption equilibrium fit the Freundlich isotherm. The Delta G degrees and Delta H degrees values of the adsorption process between vanadyl porphyrins and asphaltenes had been regressed at different temperatures. The absolute value of Delta G degrees was less than 20 kJ/mol, whereas that of Delta H degrees was greater than 40 kJ/mol.