ISO 3735 Crude petroleum and fuel oils - Determination of sediment - Extraction method
4 Reagents and materials
4.1 Methylbenzene (toluene), (C6H5CH3), conforming to grade 2 of ISO 5272.
5 Apparatus
Usual laboratory apparatus and glassware, together with the following:
5.1 Extraction apparatus, as illustrated in figures 1 and 2, and consisting of the elements described in 5.1.1 to 5.1.6.
5.1.1 Extraction flask, consisting of a wide-necked conical (Erlenmeyer) flask of 1 litre capacity, conforming generally to the requirements of ISO 1773, but with a minimum external neck diameter of 50 mm.
5.1.2 Condenser, in the form of a metal coil approximately 25 mm in diameter and 50 mm in length attached to, and with the ends projecting through, a lid of sufficient diameter to cover the neck of the flask as shown in figure 1. The coil shall be made from stainless steel, tin, tin-plated copper or tin-plated brass tubing having an outside diameter of 5 mm to 8 mm and a wall thickness of approximately 1.5 mm. If constructed of tin-plated copper or brass, the tin coating shall have a minimum thickness of 0.075 mm.
NOTE The exposed area of the coil for cooling purposes is approximately 115 cm2.
5.1.3 Extraction thimble, of a refractory porous material, pore size index P 16 according to ISO 4793, 25 mm in diameter by 70 mm in height, weighing not less than 15 g and not more than 17 g. The thimble shall be suspended from the condenser coil by means of a basket so that it hangs approximately mid-way between the surface of the extracting solvent (4.1) and the bottom of the condenser coil (see 5.1.2).
5.1.4 Thimble basket, corrosion-resistant, made of platinum, stainless steel, nickel-chromium alloy, or similar material. It shall meet the design and dimension requirements of figure 2.
5.1.5 Water cup, for use when testing a sample with a water content in excess of 10 % (V/V) [see figure 1 b)]. The cup shall be made of glass, conical in shape, approximately 20 mm in diameter and 25 mm deep, having a capacity of approximately 3 ml. A glass hook shall be fused onto the rim on one side and shaped so that, when hung on the condenser, the cup hangs with its rim reasonably level.
In these procedures, the thimble basket is suspended either as shown in figure 1 a), by means of the corrosion-resistant wire looped over the bottom of the condenser coil and attached to the basket supports, or as in figure 1 b), where the wire supports of the basket are attached to hooks soldered to the underside of the condenser lid.
5.1.6 Heater, suitable for vaporizing the toluene.
NOTE A hotplate is preferred.
5.2 Analytical balance, with an accuracy of 0.1 mg.
5.3 Non-aerating mixer, meeting the verification of mixing efficiency requirements specified in ISO 3170 and ISO 3171.
NOTE Both insertion mixers and circulating external mixers are acceptable, provided they meet the above criteria.
5.4 Oven, capable of maintaining a temperature of 115 °C to 120 °C.
5.5 Cooling vessel, consisting of a desiccator without desiccant.
5.6 Thermometer, capable of measuring the temperature of the sample to the nearest 1 °C.
6 Samples and sampling
6.1 Unless otherwise specified, samples shall be taken by the procedures specified in ISO 3170 or ISO 3171.
6.2 Test portions from the laboratory samples shall be drawn immediately after thorough mixing. Heat viscous samples to a temperature which renders the sample liquid, and homogenize, using the mixer (5.3) as necessary (see 6.3).
The difficulties of obtaining a representative test portion for this determination are unusually great, hence the need for great attention to the mixing and aliquoting stages.
6.3 Record the temperature of the sample before mixing. Mix the laboratory sample in its original container, using the mixing time, mixing power (speed) and position relative to the bottom of the container appropriate to the crude petroleum or fuel oil being analysed, and as established by the verification of mixing efficiency requirements given in ISO 3170 and ISO 3171. To avoid the loss of light ends from crude petroleum or other samples containing volatile material, operate the mixer through a gland in the closure of the sample container. Take the test portion for analysis immediately after mixing. Record the temperature of the sample immediately after mixing. If the rise in temperature during mixing exceeds 10 °C, cool the sample, and repeat the mixing at a lower energy input.
NOTE A rise in temperature of greater than 10 °C may result in a decrease of viscosity that is sufficient for the sediment to settle.
7 Selection of thimbles and preparation
7.1 Selection of thimbles
Select either a new or used thimble for the test. Requirements for new thimbles are given in 5.1.3.
New thimbles shall be used in the event of dispute.
NOTE Used thimbles may be employed when carrying out routine tests. When reusing thimbles, the extraction to constant mass for one determination should be considered as the preliminary extraction for the succeeding determination. After several determinations, the accumulated sediment may be sufficient to interfere with further determinations, and the procedure described in 7.3 should then be followed.
7.2 Preparation of a new thimble
Rub the outside surface of the thimble with fine sandpaper and remove all loosened material with a stiff brush. Place the thimble in the extraction flask (5.1) and extract with toluene (4.1), allowing the solvent to drip from the thimble for at least 1 h. Dry the thimble for 1 h in the oven (5.4), cool in the cooling vessel (5.5) for 1 h, and weigh to the nearest 0.1 mg. Repeat the extraction and cooling steps until the masses of the thimble after two successive extractions do not differ by more than 0.2 mg.
7.3 Preparation of a used thimble
Remove the combustible portion of the accumulated sediment by heating the thimble to dull red heat for 20 min. Extract, cool and weigh to constant mass by following the procedure described in 7.2.
NOTE An electric furnace maintained at approximately 750 °C is suitable for heating the thimble.
