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.     

Water‐in‐Crude Oil Emulsions in the Burgan Oilfield: Effects of Oil Aromaticity,Resins to Asphaltenes Content (R/(R+A)), and Water pH

Asphaltenes and resins separated from emulsion samples collected from Burgan oil field were used with heptane‐toluene mixtures as model oil to study the effect of oil aromaticity, resin content, and pH of the aqueous phase on the stability of water in model emulsions. It was confirmed that, as long as the asphaltenes are completely solubilized, increasing aromaticity leads to less stable emulsions. A consistent correlation between emulsion stability and relative resin mass content (R/(R+A)) was observed for all three of the field samples. There was a sharp decrease in stability when the R/(R+A) value exceeded 0.75. Emulsion stability was enhanced at high pH and possibly at very low pH (<2).     

Water-in-Hydrocarbon Emulsions Stabilized by Asphaltenes at Low Concentrations

The role of Athabasca asphaltene particles and molecules in stabilizing emulsions was examined by measuring the surface area of water-in-toluene/hexane emulsions stabilized by various asphaltene fractions, each with a different proportion of soluble and insoluble asphaltenes. The stabilized interfacial area was found to depend only on the amount of soluble asphaltenes. Furthermore, the amount of asphaltenes on the interface was consistent with molecular monolayer coverage. Hence, at low concentrations, asphaltenes appear to both act as a molecular surfactant and stabilize emulsions. The effect of the hexane : toluene ratio on emulsion stability was examined as well. At lower hexane : toluene ratios, more asphaltenes were soluble but the surface activity of a given asphaltene molecule was reduced. The two effects oppose each other but, in general, a smaller fraction of asphaltenes appeared to stabilize emulsions at lower hexane : toluene ratios. The results imply that the emulsifying capacity of asphaltenes is reduced but not eliminated in better solvents. Copyright 2000 Academic Press.     

Temperature change from isenthalpic expansion of aqueous triethylene glycol mixtures for natural gas dehydration

In natural gas dehydration units, rich TEG solutions are decompressed before the TEG regeneration stage and the direction of the temperature change during the decompression has been debated. The temperature change from an isenthalpic expansion from (7000 kPa to 440 kPa was measured for the following aqueous mixtures: pure water, 99% pure triethylene glycol (TEG), aqueous TEG (99 wt% TEG + 1% water), aqueous TEG saturated with methane, aqueous TEG saturated with n-pentane, and aqueous TEG saturated with n-heptane. In all cases, the temperature increased upon expansion with the magnitude of the temperature change ranging from 1.4 K for pure water to 2.4 K for TEG. A simple equation of state model predicted the correct direction for the temperature change and the predicted values were within ±1 K of the experimental data.