Hussein Alboudwarej

Asphaltene self-association and water-in-hydrocarbon emulsions

The configuration of asphaltenes on the water-oil interface was evaluated from a combination of molar mass, interfacial tension, drop size distribution, and gravimetric measurements of model emulsions consisting of asphaltenes, toluene, heptane, and water. Molar mass measurements were required because asphaltenes self-associate and the level of self-association varies with asphaltene concentration, the resin content, solvent type, and temperature. Plots of interfacial tension versus the log of asphaltene molar concentration were employed to determine the average interfacial area of asphaltene molecules on the interface. The moles of asphaltenes per area of emulsion interface were determined from the molar mass data as well as drop size distributions and gravimetric measurements of the model emulsions. The results indicate that asphaltenes form monolayers on the interface even at concentrations as high as 40 kg/m(3). As well, large aggregates with molar masses exceeding approximately 10,000 g/mol did not appear to adsorb at the interface. The area occupied by the asphaltenes on the interface was constant indicating that self-associated asphaltenes simply extend further into the continuous phase than nonassociated asphaltenes. The thickness of the monolayer ranged from 2 to 9 nm.

Estimation of SARA Fraction Properties With the SRK EOS

One approach to modelling asphaltene solubility is regular solution theory. The key parameters for this approach are the molar volume and solubility parameters of each constituent. However, these parameters are largely unknown for crude oils. Some authors have used cubic equations of state (CEOS) to estimate the solubility parameters and molar volumes of solvents and C 7 + fractions, but CEOS have yet to be applied in this way to asphaltenes due to their high molar mass and unknown critical properties. In this work, a modified Soave-Redlich-Kwong EOS with the Peneloux correction is used to estimate the molar volumes and solubility parameter of the four solubility classes (saturates, aromatics, resins, and asphaltenes) of bitumens. The EOS is modified for the asphaltenes, which are assumed to be polymeric-like compounds consisting of aggregates of monodisperse asphaltene monomers. Correlations are developed for the critical properties and acentric factor of each solubility class. The EOS-predicted properties are tested against density measurements of SARA fractions from several bitumens. The predicted parameters are used to determine the onset of asphaltene precipitation from bitumen upon the addition of heptane and the predictions are compared with measured onsets.

Spectrophotometric Measurement of Asphaltene Concentration

Abstract Typically, when ultraviolet and visible absorbance of asphaltenes is employed to measure asphaltene concentration, linear calibrations of absorbance vs. asphaltene concentration are prepared from a sample of asphaltenes in a given solvent. This calibration is shown to be sensitive to: (a) the inorganic solids content of the asphaltenes; (b) physical–chemical differences between asphaltenes from different sources or extracted with different methods; and (c) selective adsorption of asphaltenes on liquid–liquid or solid–liquid interfaces. Calibration constants were determined at wavelengths of 288 and 800 nm for samples of Athabasca and Cold Lake asphaltenes obtained using different extraction methods, from precipitation experiments, and from adsorption experiments on water-in-hydrocarbon emulsions and on powdered metals. It was found that the inorganic solids content did not affect absorbance but the asphaltene concentrations must be corrected to a solids-free basis for accurate results. Calibration constants were found to correlate to the average associated molar masses of the asphaltenes. Therefore, any change in molar mass of asphaltenes during the course of an experiment may change the calibration constant. Partial precipitation and the selective adsorption of asphaltenes can lead to a change in the molar mass of asphaltenes left in solution. The corresponding change in the calibration constants can lead to errors of 5–25% in the estimated concentration.

A pipe-loop apparatus to investigate asphaltene deposition

Abstract A circulating pipe-loop has been designed to measure asphaltene deposition under flowing conditions. Bitumen and n-heptane are combined to induce asphaltene precipitation at the entrance of a test section in which deposition is to be measured. The n-heptane is separated from the bitumen at the exit of the test section allowing the asphaltenes to redissolve in the bitumen before it is pumped back to the test section. In the test section, solid deposits are measured nonintrusively with X-ray tomography using a computer assisted tomographic (CAT) scanner. A segment of the test section is also removable for direct gravimetric measurement and collection of deposits. The pipe-loop is designed to investigate the effect of flow rate, solvent type, solvent-to-bitumen ratio, metal type, temperature, and pressure on asphaltene deposition. The effect of additives can also be assessed. The system is rated for pressures upto 7 MPa, temperatures from 25 to 100°C, and flow rates up to 0.1 m3/h.