ISO 3405 Petroleum products - Determination of distillation characteristics at atmospheric pressure
6 Samples and sampling
6.1 Determine the nature of the product to be sampled, and place it in the appropriate group according to Table 1, which also gives general guidance on sampling conditions.
6.2 Unless otherwise specified, sampling shall be carried out by the procedures described in ISO 3170 or ISO 3171, bearing in mind the special conditions described in Table 1. Maintain samples prior to testing at the specified temperatures given in Table 1, away from sources of direct heat or sunlight.
6.2.1 Group 0. Collect the sample in a container previously cooled to below 5 °C. Clean the container, preferably by immersing it in the liquid, where possible, and discarding the first sample. Where immersion is not possible, the sample shall be drawn off into the previously cooled container in such a manner that agitation is kept at a minimum. Close the container immediately with a tight-fitting stopper, and place the sample in an ice bath or refrigerator to maintain the sample below the specified temperature.
6.2.2 Groups 1 and 2. Collect the sample in a container previously cooled to below 10 °C. Condition the container and sample in the manner described in 6.2.1. Maintain the sample below 10 °C prior to testing, and preferably store at or below this temperature. Where maintenance and/or storage at below 10 °C is not possible or practicable, a temperature up to 20 °C is acceptable provided that the sample is always conditioned to a temperature below 10 °C before the container is opened.
6.2.3 Groups 3 and 4. Maintain the sample at ambient temperature. If the sample is not fluid at ambient temperature, maintain it at a temperature of 9 °C to 21 °C above its pour point. Shake the sample vigorously prior to subsampling to ensure homogeneity, and disregard the temperature range shown in Table 2 for the receiving cylinder. Prior to analysis, heat the receiving cylinder to approximately the same temperature as the sample, and pour the heated test portion precisely to the 100 ml mark. Transfer the test portion as rapidly and completely as possible to the distillation flask.
CAUTION - A tightly-sealed, full, cold container of sample is likely to break if heated.
6.3 Samples of materials that visibly contain water are not suitable for testing.
6.3.1 Groups 0, 1 and 2. If the sample is not dry, obtain another sample for testing that is free from suspended water. If such a sample cannot be obtained, add a sufficient amount of anhydrous sodium sulfate or other suitable drying agent to the sample maintained at 0 °C to 10 °C, and physically remove the water by shaking. Once the sample shows no visible signs of water, use a decanted portion of the sample, maintained at 0 °C to 10 °C, for the analysis. Record that the sample has been dried by desiccant.
NOTE Data from a round-robin exercise show that suspended water in hazy samples in group 1 and group 2 can be removed by the above procedure without statistically affecting the results of the test.
6.3.2 Groups 3 and 4. In cases where a water-free sample is not practical, remove the suspended water by shaking the sample with anhydrous sodium sulfate or another suitable drying agent, and separate it from the drying agent by decantation.
7 Preparation of apparatus
7.1 Refer to Table 2 and prepare the apparatus by choosing the appropriate distillation flask, temperature-measurement system and flask-support board as directed for the indicated group. If gas heating is used, use a Type 1 flask-support (5.6.1); if electric heating is used, use a Type 2 flask-support (5.6.2). Bring the temperature of the graduated cylinder, the flask, the temperature sensor and the cooling bath to the indicated temperature.
7.2 Make any necessary provisions so that the temperature of the cooling bath and graduated cylinder will be maintained at their specified temperatures. The graduated cylinder shall be positioned in a bath such that either the liquid level is at least as high as the 100 ml mark, or the entire graduated cylinder is surrounded by an air-circulation chamber.
7.2.1 Groups 0, 1, 2 and 3. Suitable media for low temperature baths include chopped ice and water, refrigerated brine and refrigerated ethylene glycol.
7.2.2 Group 4. Suitable media for ambient and higher bath temperatures are cold water, hot water and heated ethylene glycol.
7.3 Remove any residual liquid in the condenser tube by swabbing with a piece of soft, lint-free cloth attached to a cord or wire.
7.4 For samples in groups 0, 1, 2 and 3, fit a low-range temperature sensor, provided with a snug-fitting cork or silicone rubber stopper, tightly into the neck of the sample container, and bring the temperature of the sample to that specified in Table 2.
7.5 When the temperature of the sample is confirmed, measure the test portion precisely to the 100 ml mark of the receiving graduated cylinder, and then transfer it as completely as practical to the distillation flask, taking care that none of the liquid flows into the vapour tube.
NOTE Any material which evaporates during the transfer will contribute to the loss; any material which remains in the graduated cylinder will contribute to the observed recovery volume at the time of the initial boiling point.
7.5.1 If irregular boiling (bumping) is expected, add a small volume of clean and dry boiling chips to the test portion.
NOTE Although theoretically the volume of deposit on the chips is part of the residue, this figure is negligible and can be disregarded.
7.6 Fit the appropriate temperature sensor through a centring device (5.9). In the case of a mercury-in-glass thermometer, the bulb is centred in the neck and the lower end of the capillary is level with the highest point on the bottom of the inner wall of the vapour tube (see Figure 9). In the case of a thermocouple/resistance thermometer, follow the manufacturer’s instructions as to placement so that the sensing position will be just below the level of the side arm of the distillation flask.
7.6.1 Use a small quantity of vacuum grease on the mating surface of the polytetrafluoroethylene (PTFE) centring device to facilitate dismantling after use.
7.7 Fit the flask vapour tube, provided with a snug-fitting, well-rolled cork or silicone rubber stopper, tightly into the condenser tube. Adjust the distillation flask in a vertical position so that the vapour tube extends into the condenser tube for a distance of 25 mm to 50 mm. Raise and adjust the flask-support board to fit snugly against the bottom of the flask.
7.8 Place the graduated cylinder that was used to measure the test portion, without drying, into the bath under the lower end of the condenser tube so that the end of the condenser tube is centred in the graduated cylinder and extends therein for a distance of at least 25 mm, but not below the 100 ml mark. For manual distillations, cover the graduated cylinder closely with a piece of blotting paper or similar material, that has been cut to fit the condenser tube snugly.
7.9 Record the room temperature and prevailing barometric pressure. Proceed at once with the distillation, as described in clause 9.