D6560_(17)_11
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Estimate the asphaltene content
of the sample or residue
obtained from the procedure
in annex A1 of the written
standard, and weigh the quantity
to the nearest 1 milligram
per masses above 1 gram and
to the nearest 0.1 milligrams
for masses of 1 gram
and below into a flask
of appropriate capacity.
Add heptane into
the test portion
in the flask at a
ratio of 30 milliliters
to each 1 gram of sample if
the expected asphaltene content
is below 25% mass for mass.
For samples with an
expected asphaltene
content of above
25% mass for mass,
a minimum heptane volume of
25 milliliters shall be used.
Boil the mixture under reflux
for 60 minutes plus or minus
5 minutes.
Remove the flask and contents
at the end of this period.
Cool, close with a
stopper, and store
in a dark cupboard for 90
minutes to 150 minutes,
calculated from the time
of removal from reflux.
Place the filter paper,
folded as shown here
so as to prevent loss of
asphaltenes by creeping,
in the filter funnel
using forceps.
Thereafter, handle the filter
paper only with forceps.
Without agitation, decant the
liquid into the filter paper.
And then transfer the
residue in the flask
as completely as possible
with successive quantities
of hot heptane.
Using a stirring
rod as necessary,
give the flask a final
rinse with hot heptane,
and pour the rinsings
through the filter.
Set the flask aside
without washing for use
as specified in section 11.6
of the written standard.
Remove the filter
paper and contents
from the funnel and place
in the reflux extractor.
Using a flask different
from that used initially,
reflux with heptane at a
rate of 2 drops per second
to 4 drops per second from
the end of the condenser
for an extraction period
of not less than 60 minutes
or until a few drops of
heptane from the bottom
of the extractor
leave no residue
on evaporation on a glass slide.
Replace the flask by
the one used initially
and to which has been added 30
milliliters to 60 milliliters
of toluene, and
continue refluxing
until all the asphaltenes have
been dissolved from the paper.
Transfer the
contents of the flask
to a clean and dry
evaporating vessel.
Weigh to the nearest
0.2 milligrams
by tare against a similar dish.
Wash out the flask with
successive small quantities
of toluene to a total not
exceeding 30 milliliters.
Remove the toluene by
evaporation on a boiling water
bath or by evaporation
in a Rotavapor
under an atmosphere
of nitrogen. Warning--
perform the evaporation
in a fume hood.
Dry the dish and contents in
the oven at 100 to 110 degrees
Celsius for 30 minutes.
Cool in the cooling vessel
for 30 minutes to 60 minutes,
and reweigh by tare against
the dish used previously
for this purpose and
which has been subjected
to the same heating and
cooling procedure as
was the dish
containing asphaltenes.
Asphaltenes are very
susceptible to oxidation,
and it is important that
the procedure specified
in the final drying stage
is adhered to exactly as
regards to the temperature and
time plus or minus 1 minute.