Yicheng Long

Stability and settling characteristics of solvent-diluted bitumen emulsions☆

When bitumen emulsions are diluted with aliphatic solvents at solvent-to-bitumen ratios above a certain value, water droplets, solids, and precipitated asphaltenes tend to form clusters that are much larger than the individual components. This work demonstrates that bitumen emulsions diluted with aliphatic solvent exhibit settling behavior distinctly different from that of bitumen emulsions diluted with aromatic solvent. The aliphatic system exhibits a zone settling mode with sharp interfaces. A characteristic interface appears as a discontinuity between the clean oil phase and the hindered settling zone. Laboratory techniques have been developed for measuring settling rates by tracking the interface positions with time. As an example, an experimentally observed settling curve was modeled by solving the conservation law hyperbolic equations.

Asphaltene Self-Association and Precipitation in Solvents—AC Conductivity Measurements

Techniques used for investigating asphaltene self-association are reviewed. The principles, fundamental differences, and limits of each technique are briefly discussed. A new approach using AC conductivity measurement for detecting asphaltene self-association is proposed and demonstrated using Alberta bitumenderived asphaltene as a model system. Preliminary results show that the AC conductivity measurement is sensitive to subtle capacitance change arising from asphaltene self-association but only within a certain frequency range. A percolation model with parallel capacitor–resistor circuit is adopted to establish the theoretical basis for this approach. This model predicts the functional behavior of the AC conductivity and exhibits phase transition-like behavior upon asphaltene self-association. The conductivity measurements show functional forms similar to the predicted ones and exhibit discontinuity near 120 mg/L in toluene where self-association is believed to occur. This value agrees (on the same order of magnitude) with earlier surface tension,1 laser thermal lensing,2 and ultrasonic3 measurements. In addition to detecting asphaltene self-association, AC conductivity is also applicable to characterization of asphaltene precipitation in toluene upon addition of nonsolvent such as heptane. The sensitivity is high and the method is simple. These two experiments suggest that AC conductivity method can be a good option for measuring flocculation, precipitation, and phase separation of petroleum complex fluids, provided the right frequency range is chosen. Further validation of this method is needed for other complex fluids. Asphaltene is a heavy end component of petroleum material commonly defined as the solvent class that is soluble in toluene but insoluble in aliphatic solvent (e.g., heptane, pentane, etc.). It is an undesired component in many petroleum processes (production, transportation, refining) and engine operation using heavy oils.

Selective Solvent Deasphalting for Heavy Oil Emulsion Treatment

Solvents are often used to treat heavy oil emulsions such as bitumen froth produced in the recovery of bitumen from oil sands. It has been found that the aromaticity of the solvent and the solvent-to-bitumen dilution ratio (S/B, by wt) have profound effects on the stability of water-in-bitumen emulsions. An aliphatic solvent at a certain S/B not only partially precipitates asphaltenes from the solvent-diluted bitumen solution, but also, at the same time, promotes aggregation of the emulsified water droplets (WD), dispersed solids (DS), and precipitated asphaltenes (PA). The WD/DS/PA aggregates exhibit zone settling in solvent-diluted bitumen, and various distinct zones and corresponding interfaces develop during settling. Typically, the top zone is a clean oil phase containing less than 0.1 wt% water– plus–solids, the middle is an emulsion zone containing the WD/DS/PA aggregates, and the bottom is a compaction zone of the settled WD/DS/PA aggregates. The position of the sharp interface that develops between the oil phase and the emulsion zone can be tracked by visual observation with the help of proper illumination. An in-line transflectance probe coupled with a spectrophotometer via a fiber-optic cable is also developed for monitoring the settling of the WD/DS/PA aggregates. The settling rate depends on many factors and conditions including solvent type, S/B, temperature, and mixing conditions. Treatment of bitumen emulsions with aliphatic solvents not only produces clean bitumen but also leads to significant reductions in asphaltene content, coking propensity, and the concentrations of metals, sulfur, and nitrogen. The viscosity of the bitumen is also reduced, which, in turn, significantly reduces the amount of light diluent that must be blended with the bitumen in order to meet the pipelining specification for viscosity. Therefore, proper selection of solvent, S/B, and other process conditions make it possible to produce bitumen products to satisfy a variety of specifications. The term heavy oils usually refers to crudes with API gravity of less than 20◦. Heavy oils with API gravity less than 10◦ are also called extra heavy oils