Determining the Kinetics of Asphaltene Adsorption from Toluene: A New Reaction–Diffusion Model

Abstract

8Fouling by asphaltene, which constitutes the densest, most polar fraction of crude oil, poses a serious 9 problem for the oil production industry. In order to obtain a fundamental understanding of asphaltene 10 deposition it is necessary to determine both the thermodynamics and kinetics that govern this process. In 11 recent years, there have been numerous studies of the kinetics of asphaltene adsorption, however, a 12 consensus on the model that best describes asphaltene adsorption remains elusive. In this paper the 13 adsorption of asphaltene from solution in toluene onto a gold surface is investigated using a quartz crystal 14 microbalance inside a flow cell. The kinetics of adsorption depends on the state of asphaltene in solution 15 and the adsorption behaviour alters with long-time aging of asphaltene solutions. A model is developed 16 that links the kinetics of asphaltene adsorption to the bulk solution properties in terms of coexisting 17 monomer and multimer states. A large portion of deposited asphaltene is effectively irreversibly bound 18 and not easily removed by rinsing with toluene. The model suggests that asphaltene-asphaltene 19interactions play an important role in the formation of irreversibly bound deposits, which could lead to 20 fouling problems. 21 22

Deposition of Asphaltene from Destabilized Dispersions in Heptane–Toluene

“…n.b. Previously, we investigated the adsorption of this same asphaltene onto Au from solution in toluene over a concentration range of 0.001 to 1 gL⁻¹ at 20°C and found that it followed the Langmuir adsorption isotherm giving the mass of complete monolayer as 804 ngcm⁻² [46]. In this study, this pre-existing asphaltene monolayer simplifies our analysis, since throughout the deposition experiments we are always dealing with asphaltene-asphaltene interactions, i.e.…”

On the use of nanomechanical atomic force microscopy to characterise oil-exposed surfaces

“…Understanding the nature of these deposits and their interaction with the relevant surfaces is the rst step towards being able to mitigate against them. A wide variety of characterisation techniques have been employed in recent years [1][2][3][4][5][6][7][8][9] to explore these deposits including electron microscopy and spectroscopy, infra-red spectroscopy, QCM and AFM.…”

Mechanism of an asphaltene inhibitor in different depositing environments: Influence of colloid stability

“…The minimum concentration of inhibitor required to prevent floc formation in our studies (0.1 gL⁻¹ = 143 ppm) is within the typical range of treat rates for this inhibitor in the field (100 -200 ppm), see Table 1. 3.2 Inhibition behaviour at surface: Adsorption and deposition of asphaltene inhibitor onto a gold surface QCM-D experiments were carried out to monitor adsorption of Inhibitor A onto gold surface from solution in toluene. Gold is used as a model metallic surface (piping systems in the Oil and Gas industry are typically constructed from stainless steel) since it is relatively inert, easily-cleaned under oxygen-plasma and has previously been found to give reproducible results in asphaltene adsorption studies (Campen et al, 2017). When inhibitor is flowed through the cell, negative shifts in frequency are observedthese are indicative of adsorption of molecules onto the gold surface, Fig 5. After an adsorption time of 30 min, the surface is rinsed by flowing toluene; the frequency does not return to its baseline value, suggesting that the inhibitor molecules are strongly adsorbed to the surface, as expected due to their polar head groups.…”

“…Previously we have used QCM-D to investigate the adsorption from toluene (Campen et al, 2017) and the deposition from heptane-toluene (Campen et al, 2018) of asphaltene samples extracted from the same crude oil onto gold. In brief, asphaltene adsorbs from toluene forming a thin film of monomer-nanoaggregates which remains upon toluene-rinsing.…”

“…The deposition behaviour of asphaltenes strongly depends on the environmental conditions encountered. In toluene, asphaltenes exist as a stable colloid of small nanoaggregates and individual molecules, and monolayer adsorption is observed (Campen et al, 2017). However, in heptane-toluene, asphaltenes exist as a destabilized colloid and multilayer deposition of asphaltenes occurs.…”