Several preparative bitumen fractionation methods based on initial precipitation of asphaltenes
by an n-paraffin followed by solvent elution from silica gel and refluxing on Attapulgus clay are
reviewed. These methods are based on the ASTM D2007 standard and have been collectively
designated as SARA (saturates, aromatics, resins, asphaltenes). In actual fact, there are numerous
variations of SARA. In this paper, the results from the standard ASTM method are compared to
a variation developed by Syncrude. One alternative to SARA was developed at Alberta Research
Council (ARC) and is called SAPA (saturates, aromatics, polars, asphaltenes). It is compared to
SARA, and some advantages and disadvantages of each are described. An analytical thin layer
chromatographic (TLC) method, producing only component-type data, was also developed at ARC
as a faster alternative to SAPA. The TLC approach has recently been modified to produce results
similar to those of SAPA, in order that the results from the two techniques may be used
interchangeably. Results and comparisons between SAPA and TLC will be described for two
different bitumen samples.
Solvent mass transfer plays a key role in a thermal gravity drainage process involving solvent. The diffusion coefficients of solvent in such a process are not well studied. This article presents the effective diffusion coefficients of solvent in bitumen‐saturated sands under high temperature/pressure conditions measured using a CT scanning technique. Experimental results show that the effective diffusion coefficient of n‐hexane in bitumen‐saturated sands varied with the solvent concentration or with the viscosity of solvent–bitumen mixture (i.e., De ∝ c0.4 or De ∝ μm−0.46). The solvent concentration weighted diffusion coefficient of n‐hexane in the bitumen under the condition 160–170°C/1,900 kPa had an order of magnitude of about 10−5 cm2/s for solvent volume concentration less than 0.2. The penetration distance of n‐hexane in bitumen‐saturated sands depended on the nonlinearity of diffusion and had a value of −2 cm after 1‐day diffusion. The stronger the nonlinearity of diffusion, the shorter the penetration distance.
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