D6560_(17)_11

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.