Asphaltene models

Yen et al. (1961) examined the structure of isolated petroleum asphaltenes by using XRD. From the diffraction pattern they were able to calculate the aromaticity, defined as the number of aromatic carbon atoms over the total carbon atoms. The aromaticity ranged from 0.26 to 0.53 for petroleum asphaltenes. In addition, the characteristic dimensions of an asphaltene were obtained by the XRD method. The asphaltene model developed by Yen et al. (1961) from these observations is presented in Fig. 6 with characteristic molecular dimensions. The model consists of... 

The removal of metals with the asphaltenic sulfur is observed in Figure 4. This response is consistent with an asphaltene model in which vanadium and nickel are buried as porphyrins or sandwich compounds (9). The slightly higher removal of vanadium reflects a general tendency for vanadium to deposit on the catalyst more readily than nickel. 

Demelallization of Asphaltenes Modelling Feed and Product Molecular Size Dislributfons and Metal Distribution Parameters... 

DEMETALLIZATION OF ASPHALTENES MODELLING FEED AND PRODUCT MOLECULAR SIZE DISTRIBUTIONS AND METAL DISTRIBUTION PARAMETERS,... 

The concept of an asphaltene model that incorporates smaller polynuclear aromatic systems is more in keeping with the types of systems that occur in nature. Indeed, smaller polynuclear aromatic (and pseudoaromatic) systems are capable of producing high yields of thermal coke either because of the heteroatom content (87) or because of the presence of pendant alkyl moieties that have the capability of forming the internuclear cross-links (88) that can lead to coke. In this latter case, it is likely that the indigent alkyl chains can interact in this manner, or shorter alkyl chains, formed by thermolysis, can play the role of cross-linking agents. 

The IFPYV is defined as the shear stress at zero shear rate (72). The IFPYV of the film is related to its stractural strength. From Fig. 9, it is revealed that the IFPYV or strength of the film increases with increased asphaltene concentration in the oil phase. Both IFPYV and interfacial viscosity of the films between water and asphaltene model oils increases with reduced aromaticity of the oil phase. 

Nordgard Erland L., Serland Geir, And Sjoblom Johan, (2009). Behavior of Asphaltene Model Compounds at W/O Interfaces. Langmuir Article 2010, 26(4), 2352-2360 Normura, m. Artok, 1. SU, Y. Hirose, Y. Hosokwa, M. Murata, S., (1999). structure and reactivity of Petroleum-Derived asphaltene. Energy Fuels, 13 92), 287-2%... 

Based on the previous studies, a new asphaltene model has been codified in the "modified Yen model" and stipulates the dominant structme of asphaltene molecules, nanoaggregates and clusters of nanoaggregates (Mullins, 2010). This model was built upon the Yen Model,... 

Preliminary work showed that first order reaction models are adequate for the description of these phenomena even though the actual reaction mechanisms are extremely complex and hence difficult to determine. This simplification is a desired feature of the models since such simple models are to be used in numerical simulators of in situ combustion processes. The bitumen is divided into five major pseudo-components coke (COK), asphaltene (ASP), heavy oil (HO), light oil (LO) and gas (GAS). These pseudo-components were lumped together as needed to produce two, three and four component models. Two, three and four-component models were considered to describe these complicated reactions (Hanson and Ka-logerakis, 1984). 

Figure 18.13 Experimental and calculated concentrations of Coke (COK) "A , Asphaltene (ASP) o" and Heavy Oil + Light Oil (HO+LO) "a" at 50 °C for the low temperature oxidation of North Bodo oil sands bitumen using model l.

This paper reviews the experiences of the oil industry in regard to asphaltene flocculation and presents justifications and a descriptive account for the development of two different models for this phenomenon. In one of the models we consider the asphaltenes to be dissolved in the oil in a true liquid state and dwell upon statistical thermodynamic techniques of multicomponent mixtures to predict their phase behavior. In the other model we consider asphaltenes to exist in oil in a colloidal state, as minute suspended particles, and utilize colloidal science techniques to predict their phase behavior. Experimental work over the last 40 years suggests that asphaltenes possess a wide molecular weight distribution and they may exist in both colloidal and dissolved states in the crude oil. 

In part II of the present report the nature and molecular characteristics of asphaltene and wax deposits from petroleum crudes are discussed. The field experiences with asphaltene and wax deposition and their related problems are discussed in part III. In order to predict the phenomena of asphaltene deposition one has to consider the use of the molecular thermodynamics of fluid phase equilibria and the theory of colloidal suspensions. In part IV of this report predictive approaches of the behavior of reservoir fluids and asphaltene depositions are reviewed from a fundamental point of view. This includes correlation and prediction of the effects of temperature, pressure, composition and flow characteristics of the miscible gas and crude on (i) Onset of asphaltene deposition (ii) Mechanism of asphaltene flocculation. The in situ precipitation and flocculation of asphaltene is expected to be quite different from the controlled laboratory experiments. This is primarily due to the multiphase flow through the reservoir porous media, streaming potential effects in pipes and conduits, and the interactions of the precipitates and the other in situ material presnet. In part V of the present report the conclusions are stated and the requirements for the development of successful predictive models for the asphaltene deposition and flocculation are discussed. 

Suspension Model of Interaction of Asphaltene and Oil This model is based upon the concept that asphaltenes exist as particles suspended in oil. Their suspension is assisted by resins (heavy and mostly aromatic molecules) adsorbed to the surface of asphaltenes and keeping them afloat because of the repulsive forces between resin molecules in the solution and the adsorbed resins on the asphaltene surface (see Figure 4). Stability of such a suspension is considered to be a function of the concentration of resins in solution, the fraction of asphaltene surface sites occupied by resin molecules, and the equilibrium conditions between the resins in solution and on the asphaltene surface. Utilization of this model requires the following (12) 1. Resin chemical potential calculation based on the statistical mechanical theory of polymer solutions. 2. Studies regarding resin adsorption on asphaltene particle surface and... 

Figure 3. Molecular weight distributions of asphaltenes before and after flocculation predicted by our continuous mixture model.

Figure 4. Asphaltene particle peptization effected by adsorbed resin molecules. This physical model is the basis of our asphaltene Thermodynamic-Colloidal Model.

Figure 36. Proposed structural models of asphaltene molecules.

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