Adsorption Kinetics of Asphaltenes at the Heptol–Water Interface

Abstract

The dynamic pendant drop method was employed to better understand the adsorption kinetics at the oil/water interface. Various volume ratios of n-heptane/toluene (heptol) have been chosen as solvents to represent the model of crude oil systems. The results show that an increase in the asphaltene concentration reduces the interfacial tension and this reduction is much more pronounced at higher fractions of n-heptane. The Ward–Tordai short-time model was used to estimate the diffusion coefficient of asphaltenes for dilute solutions of asphaltenes in heptol (up to 0.01 wt %). The results show that the asphaltene adsorbed as monomers onto the interface and the bulk nanoaggregates do not contribute to the adsorption process. Furthermore, the results reveal that the asphaltene diffusion coefficient decreases with increasing its concentration and decreasing solvent aliphaticity. The Langmuir adsorption isotherm was used to study the asphaltene behavior at the oil/water interface and to predict the parameters of adsorption kinetics. It was shown that asphaltenes were adsorbed as monomers onto the interface. The results show that at higher n-heptane fractions, more asphaltene molecules are adsorbed onto the interface. A higher concentration of n-heptane in solvent results in faster and more asphaltene adsorption on the oil/water interface leading to lower interfacial tension and thus promotes emulsification. These findings improve our understanding of adsorption kinetics of asphaltenes at the oil/water interface and find applications in oil/water separation and solvent-aided recovery of heavy oil and bitumen.

An Analytical Model for Estimation of the Self-Diffusion Coefficient and Adsorption Kinetics of Surfactants Using Dynamic Interfacial Tension Measurements

“…21 The interfacial tension data has been measured using the pendant drop technique, and details of the experiments have been reported elsewhere. 21 Figure 3 shows the equilibrium interfacial tension versus concentration of asphaltenes for four different solvents obtained using Langmuir and Frumkin isotherms as compared to the experimental data. As can be seen, both isotherms can predict the experimental data with acceptable accuracy.…”

“…Table 1 summarizes the estimated equilibrium parameters using the Langmuir and Frumkin isotherms and the equilibrium interfacial tension data. 21 The interfacial tension data has been measured using the pendant drop technique, and details of the experiments have been reported elsewhere. 21 Figure 3 shows the equilibrium interfacial tension versus concentration of asphaltenes for four different solvents obtained using Langmuir and Frumkin isotherms as compared to the experimental data.…”

“…As noted earlier, the details of IFT measurements have been reported elsewhere. 21 The reduction in the interfacial tension during the droplet formation (35 μL, R s = 2.03 mm) is significant at concentrations above 0.01 wt %.…”

“…The surfactant diffusion coefficients can also be estimated using the Ward− Tordai model during the diffusion-controlled stage. 21 However, the Ward−Tordai model does not consider the dynamics of surfactant adsorption at the interface. In addition, the Ward− Tordai model does not allow estimation of the adsorption kinetics at the interface.…”

“…The results shown in Figure 5 reveal that the estimated diffusion coefficients for asphaltenes using the developed model are between 2 and 5 times higher than those predicted using the Ward−Tordai model. 21 Ahmadi et al 25 have used the molecular dynamics simulations to obtain the selfdiffusion coefficient of asphaltene. The self-diffusion coefficients have been reported to be 3.6 × 10 −10 and 3.8 × 10 −10 m 2 /s for heptol (90:10) and n-heptane at infinite dilution, respectively.…”