ASTM D6560 Test Method for Determination of Asphaltenes (Heptane Insolubles)
ASTM D6560 Standard Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum and Petroleum Products
11. Procedure
11.1 Estimate the asphaltene content of the sample, or residue obtained from the procedure in the Annex A1, and weigh the quantity, to the nearest 1 mg for masses above 1 g and to the nearest 0.1 mg for masses of 1 g and below (see Table 1), into a flask (see 6.4) of appropriate capacity (see Table 1).
11.2 Add heptane (see 7.2) to the test portion in the flask at a ratio of 30 mL to each 1 g of sample if the expected asphaltene content is below 25 % m/m. For samples with an expected asphaltene content of above 25 % m/m, a minimum heptane volume of 25 mL shall be used (see Table 1).
11.3 Boil the mixture under reflux for 60 ± 5 min. Remove the flask and contents at the end of this period, cool, close with a stopper (see 6.5), and store in a dark cupboard for 90 to 150 min, calculated from the time of removal from reflux.
11.4 Place the filter paper, folded as shown in Fig. 2 (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 the residue in the flask as completely as possible with successive quantities of hot heptane, using the using the stirring rod (see 6.14) 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 11.6.
11.5 Remove the filter paper and contents from the funnel, and place in the reflux extractor (see 6.3). Using a flask different from that used initially, reflux with heptane (see 7.2) at a rate of 2 drops/s to 4 drops/s from the end of the condenser for an extraction period of not less than 60 min, or until a few drops of heptane from the bottom of the extractor leave no residue on evaporation on a glass slide.
11.6 Replace the flask by the one used initially, and to which has been added 30 to 60 mL of toluene (see 7.1), and continue refluxing until all the asphaltenes have been dissolved from the paper.
11.7 Transfer the contents of the flask to a clean and dry (see Section 10) evaporating vessel (see 6.6), weighed to the nearest 0.2 mg by tare against a similar dish. Wash out the flask with successive small quantities of toluene to a total not exceeding 30 mL. Remove the toluene by evaporation on a boiling water bath (Warning - Perform the evaporation in a fume hood.), or by evaporation in a rotovapor under an atmosphere of nitrogen.
11.8 Dry the dish and contents in the oven (see 6.12) at 100 to 110°C for 30 min. Cool in the cooling vessel (see 6.15) for 30 to 60 min 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.
NOTE 4 - 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 temperature and time ± 1 min.
12. Calculation
12.1 Calculate the asphaltene content, A, in % m/m, of petroleum products as follows:
A = 100 (M/G)
where:
M = is the mass of asphaltenes, in grams, and
G = is the mass of test portion, in grams.
12.2 Calculate the asphaltene content, C, in % m/m, of crude petroleum prepared in the manner described in the Annex, as follows:
C = 100 (MR/GD)
where:
M = is the mass of asphaltenes, in grams,
R = is the mass of the residue from distillation, in grams,
G = is the mass of the residue aliquot, in grams, and
D = is the mass of crude petroleum sample distilled, in grams.
