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Experimental
Samples
Experiments have been carried out with asphaltene-rich
model oil (asphaltene concentration 12.3 g/l). The light hydrocar-
bon fractions were represented by toluene, the heavy oil fractions –
by 11.6 wt. % of a vacuum residue from Western Siberian crudes
(density at 20
0
C – 979 kg/m
3
; pour point - 18
0
C; boiling point –
342
0
C; asphaltenes – 10.9 wt. % ). The components were mixed at
room temperature 1 month before the experiments and were stored
at RT (18–20°C) in a dark glass vessel, in air.
Measurements of heavy organic deposition were performed at
metal substrates – two 1 mm thick steel plates with the total sur-
face area of 256.1 cm
3
.
Apparatus and Procedure
Deposition studies were conducted in a temperature controlled
(±0.1°C) glass cell with steel substrates vertically immersed into
the model oil, to minimise sedimentation effects. The mass of de-
posits was determined with an analytical balance (100 g capacity,
0.1 mg precision). Oil viscosities were measured in a temperature
controlled Hoppler-type viscometer.
Between deposition/viscosity experiments, the model oil was
stored at RT (18–20°C). Each individual experiment commenced
with pre-heating the entire quantity of the model oil to the re-
quired measurement temperature for 15–20 minutes. Afterwards
several ml of the liquid were transferred either to the deposition
cell or to the viscometer. A standard deposition time was 20 min-
utes. Steel samples covered with deposits were dried in warm air
and weighted. Before a new experiment the samples were washed
in toluene, wiped with a cotton cloth and dried in warm air. This
procedure restored the mass of steel plates to within 1 mg of its
initial value.
It should be noted, that we had no strict scenario for choosing
the individual measurement temperatures (i.e. no prescribed “de-
scending order” or “ascending order”). To improve statistics, each
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