10.4.9 Shut off the reflux valve and the heating system. Allow the contents to cool to such a temperature that the distillation can be commenced at a lower pressure without boiling. This temperature can be estimated by adding the AT between the liquid and vapor temperatures found for the column during operation to the expected initial vapor temperature at the lower pressure, or by subtracting the AT from the last recorded liquid temperature.

10.4.10 Weigh all fractions and determine their densities at 15°C.

10.5 Distillation at Lower Pressures:

10.5.1 If the final cut point has not been reached, distillation can be continued at a lower pressure subject to the same limitation as before (see 10.4.1). Only one pressure level between 13.3 kPa (100 mm Hg) and 0.266 kPa (2 mm Hg) is permitted. Where the maximum cut point is 400°C AET, the minimum pressure is recommended.

10.5.2 Adjust the pressure to the desired level. If the liquid boils before the pressure is reached, increase the pressure and cool further until the desired pressure can be achieved without boiling. Follow the procedure in 10.4.4.

10.5.3 Circulate cooling water in the condenser and liquid cooler either at ambient temperature or warmed to a temperature that will ensure that wax does not crystallize in the condenser or takeoff lines. Alternatively, leave the cooling coils full of water but vented and not circulating, or else circulate a stream of air instead of water as a coolant.

10.5.4 Continue vacuum operation as in 10.4.5 through 10.4.8. During this operation, a reflux ratio of 2:1 is allowed if mutually agreed upon in advance and noted in the report. Correct observed and corrected vapor temperatures to AET using the equations given in Annex A8. Table 4 and Table 5 are provided only as a guide in estimating the cutpoints during distillation.

10.5.5 Check periodically that the condensate drips normally in the condenser and that the distillate flows smoothly into the takeoff line. If crystallization is observed, allow the coolant in the condenser to warm as in 10.5.3.

10.5.6 When the final cut point has been reached, or when limits of boiling liquid temperature and column pressure prevent further distillation, turn off the reflux valve and heating system and allow to cool with the vacuum still applied.

10.5.7 When the temperature of the residue in the flask has fallen below 230°C, shut off the vacuum pump. Vent the fractionating unit with nitrogen or other inert gas. Do not use air. (Warning—Air is suspected of initiating explosions in fractionating units that are vented while too hot, such as at the end of a run.)

10.5.8 Stop circulation of coolant in the condenser and ancillary equipment. Disconnect the flask. Recover the static holdup of the column (wettage) by distilling a small quantity of solvent such as toluene in a separate flask to wash the column, condenser, and takeoff system. Evaporate the solvent from the collected residue at 10°C above the boiling point of the solvent, using a small purge of nitrogen. For distillations not involving disagreement, or by mutual consent, the holdup can be estimated using a graph similar to Fig. 4. The density of the holdup is estimated by extrapolation of the density line for the preceding cuts. The static holdup can be treated as a separate small cut or blended into the bottoms before inspections are made. The latter must be done if other analyses besides density are to be performed on the residue.

10.5.9 Weigh all fractions and the residue in the flask and determine their densities at 15°C by Test Method D 4052 or by another suitable method. Convert the density to 15°C, if necessary.

Note 4—Heavier flasks, such as those for 50 and 70-mm diameter columns, are not normally removed for weighing. In these cases the residue can be discharged at a temperature not over 200°C into a tared container for weighing. Nitrogen pressure of approximately 6.7 kPa (50 mm Hg) will be sufficient for this. Wettage in these cases will include that of the column and the flask together.

TABLE 4 Conversion of Temperatures to Atmospheric Equivalent from Measurements at 1.33 kPa (10 mm Hg)

Note 1—Numbers calculated by Eq A8.1 and Eq A8.3, using 10.00 mm Hg as pressure input.

TABLE 4 Conversion of Temperatures to Atmospheric Equivalent from Measurements at 1.33 kPa (10 mm Hg)

Note 1—Numbers calculated by Eq A8.1 and Eq A8.3, using 10.00 mm Hg as pressure input.

Temperature, °C

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