摘要:

A better understanding of colloidal macrostructure of the heavy petroleum products and their complex fractions is of great importance in the context of industrial problems that arise during the crude oil production, refining and transport. Much effort has been devoted to the chemical structure studies, but there is a need for more precise data regarding parameters that characterize those complex systems. For instance, the molecular weight of heavy molecules, the composition and size of aggregates formed during the industrial processing and their evolution upon the variation of temperature, pressure and with the addition of solvent have not been well known. In this paper we present new results obtained using several powerful techniques. Scattering methods (using X-rays and neutrons) are applied to study both the fractionated products (asphaltene and resin solutions in more or less good solvents) and the real systems (Safaniya vacuum residue). The lamellar structural model for asphaltenes and resins is confirmed and the molecular weight of these species determined using a polydisperse size distribution. Discussion is presented concerning the specificity of X-ray and neutron scattering : X-ray experiments are more sensitive to the aromatic-rich regions, whereas the neutron scattering data provide information about all the particle volume. Viscosimetry measurements provide information on the molecular shape of asphaltene and confirm the disk-like model. Critical micellar concentration has been obtained using Vapour Pressure Osmometry (VPO) for asphaltene suspensions in toluene and in pyridine. The resin molecules are smaller than asphaltenes, and appear to be a good solvent for asphaltenes. One of the major conclusions of this work is the wide-spread presence of density heterogeneities in diluted solutions of asphaltenes and resins as well as in the pure product (Safaniya vacuum residue). This was deduced from the scattering experiments and cryo-scanning electron microscopy data. The heating effects. were studied: a temperature increase leads to the decrease of molecular weight, but heterogeneities remain present. The structure of vacuum residue exhibits large density fluctuations which are thermally stable. These dense regions remain connected into a network up to 393°K and determine the yield value of the rheological behaviour.

ISSN:0884-3759    

DOI:10.1080/08843759608947569

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

It has been observed that there is a dispersed phase of particles in vacuum residue that is associated with the heptane insoluble asphaltenes. The particles are in the size range of 100 Aˇ. In this paper we present rheological and small angle X-ray scattering(SAXS) data for the vacuum residue of Arabian Medium/Heavy crude oil that suggests the dispersed particles flocculate at elevated temperatures. We find the asphaltenic particles are stabilized below 200°C against the attractive dispersion forces between asphaltenic particles by an adsorbed layer of non-asphaltenic molecules. However the strength of the interaction holding the adsorbed layer to the particles is only about 1.8 kcal/mole(3kT), and so this layer is dissipated as the temperature is increased. We estimate the particles are unprotected at 200°C. The strength of the attraction due to the dispersion force is about 7kT in this state, and so the dispersion becomes thermodynamically unstable with respect to flocculation. Additionally, the driving force for flocculation is augmented by the formation of particles in the non-asphaltenic phase at elevated temperatures. The appearance of these particles increases the osmotic pressure, and forces the asphaltenic particles together. We suggest the asphaltenic phase formed by flocculation, well below the temperatures at which chemical reactions occur, is the precursor to the coke-producing phase in the reacting residue discussed by Wiehe.

ISSN:0884-3759    

DOI:10.1080/08843759608947570

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Petroleum asphaltenes have been precipitated in solvent mixtures of n-heptane and toluene at various temperatures, likewise n-heptane asphaltenes have been dissolved in under similar conditions. This give added evidence to apparent hysteresis phenomenon between the two processes. The Asphaltenes have been characterized showing that although data is scattered convergence to certain structural parameters as incipient flocculation is approached. The asphaltenes are seen to consist of an associating and a non-associating part. The solubility of asphaltenes has been correlated/modelled using the Flory-Huggins equation using two different terms for the Flory parameter. A process for evaluation of best choice of solubility parameter and molar volume for the asphaltenes is proposed. Dissolution processes are seen to be best fitted by the equations. Based on these findings the asphaltenes are proposed to be formed by a colloidal and a true solution part.

ISSN:0884-3759    

DOI:10.1080/08843759608947571

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The solubility and insolubility of heavy oils and their fractions in dilute mixtures with various solvents were used to characterize heavy oil interactions. A two-dimensional solubility parameter, developed for the selection of solvents for organic polymers, was found to group all the solvents for each heavy oil fraction in polygon areas when the complexing solubility parameter component was plotted against the field force solubility parameter component. All fractions of Cold Lake vacuum residua, except for the saturate fraction, form concentric solubility areas. Therefore, in going in the direction of decreasing aromaticity from coke to asphaltenes to resins to aromatics, all solvents for the previous fraction in the series are also solvents for all subsequent fractions in the series. As a result, asphaltenes can be precipitated, but not extracted, from heavy oils. This is attributed to the interaction among polynuclear aromatics being the dominate interaction in petroleum that causes insolubility in hydrocarbon liquids. However, the paraffinic chains on the same petroleum molecules limit their solubility in highly complexing liquids. In contrast, even vacuum gas oils from the Exxon Donor Solvent coal liquefaction process are insoluble in aromatic liquids but soluble in moderately complexing liquids because of hydrogen bonding, resulting from oxygen functionality. Hydrotreating of these coal derived vacuum. gas oils reduces their oxygen functionality and increases their solubility areas so that they become compatible with petroleum liquids.

ISSN:0884-3759    

DOI:10.1080/08843759608947572

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Precipitation of asphaltenes in crude oil has been measured both as a function of pressure and composition. The onset of precipitation has been determined by the measurement of conductivity. A specially designed high pressure conductivity cell has been constructed. Due to the low conductivity of most crude oils the electrode spacing has to be very narrow and the effective electrode area as large as practical. The cell has a coaxial design with inlet and outlet on opposite sides on the cylinder. The cell is rated to 700 bar and 120 deg.C but can be constructed for both higher pressure and temperature. The onset of precipitation is detected by a maximum in the weight normalized conductivity, i.e. the conductivity divided by the weight fraction of oil

ISSN:0884-3759    

DOI:10.1080/08843759608947573

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0884-3759    

DOI:10.1080/08843759608947574

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0884-3759    

DOI:10.1080/08843759608947575

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0884-3759    

DOI:10.1080/08843759608947576

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0884-3759    

DOI:10.1080/08843759608947577

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0884-3759    

DOI:10.1080/08843759608947578

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor