1、CEN EN*2794L 93 3404589 0074773 534 BS EN 27941 : BRITISH STANDARD 1994 BS 2000 : Part 405 : 1994 IS0 7941 : 1988 Methods of test for Petroleum and its products Part 405. Commercial propane and butane - Analysis by gas chromatography (Identical with IP 405/94) The European Standard EN 27941 : 1993 h
2、as the status of a British Standard CEN EN*Z794L 93 W 3404589 0074774 470 = BS 2000 : Part 405 : 1994 National foreword This British Standard, having been prepared under the direction of the Petroleum Standards Policy Committee, was published under the authority of the Standards Board and comes into
3、 effect on 31 March 1994. It is the English language version of EN 27941 : 1993 Commercial propane and butane - Analysis by gas chromatography, published by the European Committee for Standardization (CEN), which endorses IS0 7941 : 1988, published by the International Organization for Standardizati
4、on (ISO). This British Standard supersedes BS 7276 : 1990, which is withdrawn. Due to the implementation of IS0 7941 : 1988 as a European Standard and as a Part of BS 2000, this British Standard has been given a different number to BS 7276 : 1990. However, there are no other differences between this
5、 British Standard and BS 7276 : 1990. BS 2000 comprises a series of test methods for petroleum and its products that are published by the Institute of Petroleum (IP) and have been accorded the status of a British Standard. Each method should be read in conjunction with the preliminary pages of IP St
6、andard methods for analysis and testing of petroleum and related products which gives details of the BSI/IP agreement for publication of the series, provides general information on safety precautions, sampling and other matters, and lists the methods published as Parts of BS 2000. The numbering of t
7、he Parts of BS 2000 follows that of the corresponding methods published in IP Standard methods for analysis and testing of petroleum and related products. Under the terms of the agreement between BSI and the Institute of Petroleum, BS 2000 : Part 405/BS EN 27941 will be published by the IP (in Stand
8、ard methods for analysis and testing of petroleum and related products and as a separate publication). BS 2000 : Part 405 : 1994 is thus identical with IP 405/94. Compliance with a British Standard does not of itself confer immunity from legal obligations. 0 The institute of Petroleum values above 1
9、 imply separation of the components. 4.3 Retention 4.3.1 adjusted retention time or volumel: The time elapsed or the volume of gas emerged from the column1 be- tween the moment of elution of unretained components (e.g. air or methane) and the moment of elution of the component in question, both refe
10、rring to peak maxima. 1) To be published. 1 CEN EN*Z7941 73 3404587 0074778 OLb m IS0 7941 : 1588 (E) When a flame ionization detector is used, the air peak time may be calculated from uncorrected retention times of three con- secutive normal paraffins as follows: 6.2 Injection device A liquid sampl
11、e valve capable of delivering a liquid test portion of 0,5 to 1 pl, or a gaseous sample valve capable of delivering a gaseous test portion of up to 0.5 ml. 6.3 Column where The types of column described in this clause have been found suitable and are recommended. Other columns may be used provided t
12、hat the resolution performance quoted in 6.3.3 is achieved and provided that the relative retentions of other hydrocarbons are well known. to is the retention time for the unretained component; t1 is the retention time for component 1 ; i2 is the retention time for component 2; i3 is the retention t
13、ime for component 3. 6.3.1 Column material 4.3.2 relative retention: The ratio of the adjusted retention time or volume of a component to that of a standard reference component. The column should be made from glass, copper, stainless steel or aluminium tubing and have the following dimensions and fo
14、rm. 4.4 internal normalization technique: The technique by which the concentration of a component is found by comparing its corrected peak area (the product of its peak area and correc- tion factor) with the sum of the corrected peak areas of all com- ponents. 6.3.1.1 Dimensions al For commercial pr
15、opane, 8 m of di-n-butyl maleate packing + 3 m of Bp-oxy-dipropionitrile packing. bi For commercial butane, 8 m of di-n-butyl maleate. 5 Materials c) For both applications, alternatively 6 m of sebaconitrile (1,8-dicyano-octane) packing. Tubing with an internal diameter between 2 mm and 5 mm is reco
16、mmended. The external diameter of the tubing should be appropriate to the chromatograph. 5.1 Carrier gas Hydrogen (see warning on page 11, helium or nitrogen, free of hydrocarbons, oxygen and water impurities. 5.2 Reference gases Pure gases or a mixture of gases with certified compositions, boiling
17、in the LPG range. 6.3.1.2 Form Any suitable coil shape that will fit into the oven without acute bends. 6 Apparatus 6.3.2 Packing 6.1 General 6.3.2.1 Solid support Chromosorb Pl, acid washed and sieved to obtain the portion between 180 pm and 250 pm (see IS0 565). Apparatus for gas phase chromatogra
18、phy, or chromatograph, containing the following main elements and satisfying the requirements defined in 6.2 to 6.7: a) device for the control of the flow of carrier gas; b) injection device (see 6.2); c) oven with suitable column or columns; d) detector (see 6.4); 6.3.2.2 Stationary phase Chemical
19、identity: - . di-n-butyl maleate and fl/l-oxy-dipropionitrile 6.3.1.1 al and 6.3.1.1 b)l e) 6.5). recorder and, generally, integrator or computer (see - sebaconitrile (1 , RAB is the resolution for the two peaks A and B; R,A, and SR, are the adjusted retention times for com- ponents A and B respecti
20、vely, the times being ex- pressed as chart distances in millimetres; wA and wB are the peak widths of components A and B respectively. 6.4 Detector The detector may be a thermal conductivity type (hot-wire type or thermistor type1 or a flame ionization type. The system should be capable of detecting
21、 0,l % concentration of any Peak 0 NOTE - The diagram shows an air peak, but this would not be seen with a flame ionization detector. Figure 1 - Measurements for determination of resolution 3 CEN ENu2794L 93 sl 3404589 0074780 774 IS0 7941 : 1988 (E) component that is resolved. If a recorder is used
22、 and the peaks are measured subsequently, the peak height for this concentra- tion should be at least 5 chart divisions above the noise level on a O to 100 division chart. The noise level should be restricted to a maximum of 1 chart division. If electronic integration is employed, the signal for a c
23、omponent present at 0.1 % should be measurable with a repeatability of not greater than 20 % relative when the sample is analysed. Check the linearity of response of the apparatus by injecting a series of reference gas mixtures with widely varying but known concentrations or by injecting mixtures of
24、 pure gases at dif- ferent known partial pressures. 6.5 Recorder and optional integrator or computer The potentiometric recorder should have the following characteristics : a) a maximum full scale response time of 1 s; b) an available chart speed such that the first peak width to be measured will be
25、 at least 3 mm at half height. Peak areas are measured either manually, as described in 8.4.3, or by using electronic integration. Both techniques have been used to establish the precision quoted in clause 10. The integrator should have the following characteristics : ai wide range (0-1 Vi input; bi
26、 capable of baseline tracking and of measuring peaks on a sloping baseline. 6.6 Attenuator If peak areas are to be measured from the recorder chart, a multistep attenuator for the amplified detector output should be used to maintain the peak maxima on the recorder chart. 6.7 Sintered metal filter If
27、 a liquid sample valve (6.2) is used, it is recommended that a suitable sintered metal filter should be inserted before the injec- tor, to prevent the introduction of solid particles into the injec- tor. This filter should be located just after the outlet valve from the sampling container or cylinde
28、r. 7 Sampling See IS0 4257. 8 Procedure 8.1 Control of the apparatus 8.1.1 Injector port For liquid injection, adjust the injection port temperature to 40 I 5 OC but maintain the liquid sample valve at ambient temperature, For gaseous injections, the sample valve and loop may be warmed (e.g. to 70 O
29、C) to avoid condensation of higher boiling components at the column pressure. 8.1.2 Oven Depending on the choice of column, maintain the oven temperature at - 40 I 1 OC for columns 6.3.1.1 ai and 6.3.1.1 bi; - 20 k 1 OC for column 6.3.1.1 cl. 8.1.3 Flowrate Adjust the flow to a value such that the c
30、onditions required for the resolution (see 6.3.3) are obtained. 8.1.4 Detector Thermistor type conductivity detectors should be operated at 40 to 50 oc. Hot-wire type conductivity detectors should be operated at 100 to 150 oc. The flame ionization detector should be operated at 100 to 150 OC. 8.1.5
31、Recorder Select the chart speed to obtain the conditions set out in 6.5. 8.2 Calibration 8.2.1 Qualitative analysis The identification of components may be obtained by passing through the column a standard reference mixture or pure hydrocarbons, or by comparison with typical chromatograms and relati
32、ve retentions (see 4.3.2) shown respectively in figures 2, 3 and 4 and table 1. 8.2.2 Quantitative analysis 8.2.2.1 Thermal conductivity detector The calibration method is an internal normalization method. The peak area correction factors used” are given in tables 2 li The peak area correction facto
33、rs used have been taken from the following publication: KAISER, Gas phase chromatography, vol. 111, p. 91, Butteworths (1963). the values in which were taken from: VAN DE CRAATS, Gas chromatography 1958, Butteworths (1958) Ifor hydrogen gas vector); MESSNER and ROSIE, Analytical chemistry, 1959, vol
34、. 31, p. 230 Ifor helium gas vector). The precision given in clause 10 was based on the use of these correction factors. 4 CEN ENx27941 93 H 3404589 0074783 600 H and 3. They should be used only as a guide or approximation; laboratories who have both the equipment and the experience to prepare calib
35、ration gas mixtures should determine their own correction factors. 8.2.2.2 Flame ionization detector FID) If the linearity is satisfactory for FID detection (see 6.41, peak area correction factors FI for component masses are calculated according to the following formula : where nc, is the number of
36、carbon atoms in component i; nHI is the number of hydrogen atoms in component i; 0,826 5 is the mass factor of carbon in butane, its use serving only to make F, (butane) = 1 ; the factors for other components are given in table 4. 8.3 Introduction of test portion Volume of test portion injected: 0.5
37、 to 1 pl for liquid injection; up to 0.5 mi for gaseous injection. The size of test portion chosen for the test should be such that linear response is ensured (see 6.4). 8.3.1 Liquid injection (preferred method1 Place the sampling container or the gas cylinder in an upright position, with the outlet
38、 valve at the bottom. Connect this valve through the metal filter (6.71 to the injector, using a non- plasticized or plastic, transparent, armoured or pressure- resisting tube which should be earthed (see figure 5). Downstream of the purge system of the injection device, use a pressure-reducing valv
39、e to avoid any vaporization upstream when the flow equilibrium is reached. Open the outlet valve and control the flow through the transparent tube so that the latter becomes completely filled with liquid. Inject the test portion into the column. Close the outlet valve. 8.3.2 Gaseous injection (less
40、desirable) Use one of following alternative procedures: 8.3.2.1 Connect a sampling container of 2 ml capacity (see figure 6) in an upright position, with the inlet valve at the bot- tom, directly to the liquid sample source or to a larger sampling container containing the liquid sample. Purge the 2
41、ml con- tainer until liquid appears at the outlet. Close the outlet valve, IS0 i941 : 1988 (E) and after approximately 10 min (to establish equilibrium), close the inlet valve. Close the sample source valve and disconnect the 2 ml sample container. Support the container in the upright position, open
42、 the bottom valve, and run off approximately 20 % of the contents. Vaporize the sample completely into an empty vessel of a suffi- cient capacity to contain the sample at a pressure slightly greater than atmospheric pressure. Mix the sample thoroughly. Connect this vessel to the injection device, fl
43、ush the loop and then inject the test portion into the column. 8.3.2.2 Use a normal sampling container, in a vertical position with the ullage tube at the top. Connect a Drechsel bottle, con- taining sufficient water to give a 6 mm seal, to the outlet of the sample loop of the injector. Connect the
44、bottom sampling con- tainer valve to the inlet of the sample loop, open it slightly and allow the vapour to purge the loop at the rate of two bubbles per second (as indicated at the Drechsel bottle). Care should be taken not to open the valve on the sampling container excessively, or the lighter hyd
45、rocarbons will vaporize at a faster rate than the heavier ones and the test portions injected will not be representative of the liquid in the sampling container. Purge the sample loop with about ten times its volume, and then close the valve on the sampling bomb. Allow the vapour in the loop to come
46、 to atmospheric pressure and inject the test portion into the column. Disconnect the Drechsel bottle to prevent water being sucked back into the chromatograph. 8.4 Examination of the chromatograms 8.4.1 Typical chromatograms Figures 2, 3 and 4 represent typical chromatograms obtained with samples of
47、 commercial propane, commercial butane and a reference mixture containing LPG components. The columns usedare thosedescribedin6.3.1.1 ai,6.3.1.1 band6.3.1.1 ci respectively and under the conditions as described in 8.3.1. 8.4.2 Qualitative analysis 8.4.2.1 Identification of components Identify the co
48、mponents by comparison with a reference mixture or by relative retention times (see 8.2.1). 8.4.2.2 Interferences Under the conditions recommended in this International Stan- dard, there is no separation between the following pairs of components: - air and methane, with the columns 6.3.1.1 ai, b) an
49、d cl; - and cl; ethane and ethene, with the columns 6.3.1.1 a), b) - butane and isobutene, with the columns 6.3.1.1 ai and b). 5 CEN EN*2794L 93 W 3404589 0074782 547 W IS0 7941 : 1988 (E) 8.4.3 Quantitative analysis Evaluate the peak area for each component (Ai) as follows, depending on whether a recorder or an integrator or a com- puter is used. 9.2 Flame ionization detector The mass percentage, x, % (mlm), of component i in the sam- ple is given by the equation x; = x 100 8.4.3.1 Using a recorder Measure each peak height and peak width at half height (see 6.3.3) and calcula
