ASTM D721 Standard Test Method for Oil Content of Petroleum Waxes
8. Procedure
8.1 Melt a representative portion of the sample, using a water bath or oven maintained at 70 to 100°C (158 to 212°F). As soon as the wax is completely melted, thoroughly mix. Preheat the pipet or equivalent measuring device in order to prevent the solidification of wax in the tip, and withdraw a portion of the sample as soon as possible after the wax has melted. The mass of wax transferred to the test tube must be 1.00 +/- 0.05 g. Allow the test tube to cool, and weigh to the mearest 1 mg.
NOTE 3 - The weight f a test tube which is cleaned by means of solvents will not vary to a significant extent. Therefore, a tare weight may be obtained and used repeatedly.
8.2 Pipet 15 mL of methyl ethyl ketone into the test tube and place the latter just up to the level of its contents in a hot water or steam bath. Heat the solvent wax mixture, stirring up and down with the wire stirrer, until a homogenous solution is obtained. Exercise care to avoid loss of solvent by prolonged boiling.
NOTE 4 - Very high-melting wax samples may not form clear solutions. Stir until the undissolved material is well dispersed as a fine cloud.
8.2.1 Plunge the test tube into an 800-mL beaker of ice water and continue to stir until the contents are cold. Remove the stirrer. Remove the test tube from the ice bath, wipe dry on the outside with a cloth, and weigh to the nearest 0.1 g.
NOTE 5 - During this operation the loss of solvent through vaporizations should be less than 1%. The weight of the solvent is, therefore, practically a constant, and, after a few samples are weighted, this weight, approximately 11.9 g, can be used as a constant factor.
8.3 Insert the thermometer into the test tube and place the test tube containing the wax-solvent slurry in the cooling bath, which is maintained at -34.5 +/- 0.3°C (-30 +/- 2°F). During this chilling operation it is important that stirring by means of the thermometer be almost continuous, in order to maintain a slurry of uniform consistency as the wax precipitates. Do not allow the wax to set up of the walls of cooling vessel nor permit any lumps of wax crystals to form. Continue stirring until the temperature reaches -31.7 +/- 0.3°C (-25 +/- 0.5°F).
8.4 Remove the thermometer from the tube and allow it to drain momentarily into the tube; then immediately immerse in the mixture the clean dry filter stick which has previously been cooled by placing it in a test tube and holding at -34.5 +/- 1°C (-30 +/- 2°F) in the cooling bath for a minimum of 10 min. Seat the ground-glass joint of the filter so as to make an air-tight seal. Place an unstoppered weighing bottle, previously weighed together with the glass stopper to the nearest 0.1 mg, under the delivery nozzle of the filtration assembly.
NOTE 6 - Take every precaution to ensure the accuracy of the weight of the stoppered weighing bottle. Prior to determining this weight, rinse the clean, dry, weighing bottle and stopper with methyl-ethyl ketone, wipe dry on the outside with a cloth, and place in the evaporation assembly to dry for about 5 min. Then remove the weighing bottle and stopper, place near the balance, and allow to stand for 10 min prior to weighing. Stopper the bottle during this cooling period. Once the weighing bottle and stopper have been dried in the evaporation assembly, lift only with forceps. Take care to remove and replace the glass stopper with a light touch.
8.5 Apply air pressure to the filtration assembly, and immediately collect about 4 mL of filtrate in the weighing bottle. Release the air pressure to permit the liquid to drain back slowly from the delivery nozzle. Remove the weighing bottle immediately, and stopper and weigh to the nearest 10 mg without waiting for it to come to room temperature. Unstopper the weighing bottle and place it under one of the jets in the evaporation assembly maintained at 35 +/- 1°C (95 +/- 2°F), with the air jet centered inside the neck, and the tip 15 +/- 5 mm above the surface of the liquid. After the solvent has evaporated, which usually takes less than 30 min, remove the bottle, stopper, and place near the balance. Allow to stand for 10 min and weigh to the nearest 0.1 mg. Repeat the evaporation procedure, using a 5-min evaporation period instead of 30 min, until the loss between successive weighings is not over 0.2 mg.
9. Calculation
9.1 Calculate the amount of oil in the wax as follows:
Oil in wax, weight % = (100 AC/BD) - 0.15
where:
A = weight of oil residue, g,
B = weight of wax sample, g,
C = weight of solvent, g, obtained by subtracting weight of test tube plus wax sample (8.1) from weight of test tube and contents (8.2), and
D = weight of solvent evaporated, g, obtained by subtracting weight of weighing bottle plus oil residue from weight of weighing bottle plus filtrate (7.5).
0.15 = average factor correcting for the solubility of wax in the solvent at -32°C (-25°F)
