《ISO-6145-10-2002.pdf》由会员分享，可在线阅读，更多相关《ISO-6145-10-2002.pdf（24页珍藏版）》请在三一文库上搜索。
1、 Reference number ISO 6145-10:2002(E) ISO 2002 INTERNATIONAL STANDARD ISO 6145-10 First edition 2002-02-01 Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 10: Permeation method Analyse des gaz Prparation des mlanges de gaz pour talonnage laide de mthodes vo
2、lumtriques dynamiques Partie 10: Mthode par permation ISO 6145-10:2002(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and in
3、stalled on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobes licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software pr
4、oducts used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found
5、, please inform the Central Secretariat at the address given below. ISO 2002 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in w
6、riting from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.ch Web www.iso.ch Printed in Switzerland ii ISO 2002 All rights reserved ISO 6145-1
7、0:2002(E) ISO 2002 All rights reserved iii Contents Page Foreword.iv Introduction.v 1 Scope1 2 Normative reference1 3 Principle1 4 Reagents and materials 2 5 Apparatus.2 6 Procedure.5 6.1 Preliminary checks and operating conditions5 6.2 Determination of mass loss6 7 Expression of results7 7.1 Calcul
8、ation .7 7.2 Sources of uncertainty8 7.3 Estimation of uncertainties.10 7.4 Example calculation of uncertainties13 Annex A (informative) Example of uncertainty calculation for a two-pan continuous weighing system14 Bibliography16 ISO 6145-10:2002(E) iv ISO 2002 All rights reserved Foreword ISO (the
9、International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee
10、 has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnic
11、al standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bo
12、dies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this part of ISO 6145 may be the subject of patent rights. ISO shall not be held responsible for identi
13、fying any or all such patent rights. ISO 6145-10 was prepared by Technical Committee ISO/TC 158, Analysis of gases. It cancels and replaces ISO 6349:1979 which has been technically revised. ISO 6145 consists of the following parts, under the general title Gas analysis Preparation of calibration gas
14、mixtures using dynamic volumetric methods: Part 1: Methods of calibration Part 2: Volumetric pumps Part 4: Continuous injection method Part 5: Capillary calibration devices Part 6: Critical orifices Part 7: Thermal mass-flow controllers Part 9: Saturation method Part 10: Permeation method Diffusion
15、will be the subject of a future part 8 to ISO 6145. Part 3 to ISO 6145, entitled Periodic injections into a flowing gas stream, has been withdrawn by Technical Committee ISO/TC 158, Analysis of gases. Annex A of this part of ISO 6145 is for information only. ISO 6145-10:2002(E) ISO 2002 All rights r
16、eserved v Introduction This part of ISO 6145 is one of a series of standards dealing with various dynamic volumetric methods used for the preparation of calibration gas mixtures. INTERNATIONAL STANDARD ISO 6145-10:2002(E) ISO 2002 All rights reserved 1 Gas analysis Preparation of calibration gas mix
17、tures using dynamic volumetric methods Part 10: Permeation method 1 Scope This part of ISO 6145 specifies a dynamic method using permeation membranes for the preparation of calibration gas mixtures containing component mole fractions ranging from 109 and 106. A relative expanded uncertainty of 2,5 %
18、 of the component mole fraction can be achieved using this method. In the mole fraction range considered, it is difficult to maintain some gas mixtures, for example in cylinders, in a stable state. It is therefore desirable to prepare the calibration gas immediately before use, and to transfer it by
19、 the shortest possible path to the place where it is to be used. This technique has been successfully applied in generating low content calibration gas mixtures of, for example, sulfur dioxide (SO2), nitrogen dioxide (NO2) and benzene (C6H6) in air. If the carrier gas flow is measured as a gas mass-
20、flow, the preparation of calibration gas mixtures using permeation tubes is a dynamic-gravimetric method which gives contents in mole fractions. 2 Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this part of ISO
21、 6145. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of ISO 6145 are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. F
22、or undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 6145-1, Gas analysis Preparation of calibration gas mixtures using dynamic volumetric methods Part 1: Methods of calibrat
23、ion 3 Principle The calibration component for example SO2, NO2, ammonia (NH3), benzene, toluene, xylene is permeated through an appropriate membrane into the flow of a carrier gas, i.e. the complementary gas of the mixture obtained. The calibration component, of known purity, is contained in a tube,
24、 which is itself contained in a temperature- controlled vessel. This vessel is purged at a known and controlled flow rate by the carrier gas. The composition of the mixture is determined from the permeation rate of the calibration component as well as the flow rate of the high quality carrier gas, f
25、ree from any trace of the calibration component and from any chemical interaction with the material of the permeation tube. The permeation rate of the calibration component through the membrane depends upon the component itself, the chemical nature and structure of the membrane, its area and thickne
26、ss, the temperature, and the partial pressure gradient of the calibration component across the membrane. These factors can be kept constant by proper operation of the system. The permeation rate can be measured directly by mounting the tube on a microbalance and weighing the tube either continuously
27、 or periodically. ISO 6145-10:2002(E) 2 ISO 2002 All rights reserved 4 Reagents and materials 4.1 Permeating substances for calibration, of the highest possible purity so as to avoid any effect of impurities on the permeation rate; if this is not possible, the nature and quantities of the impurities
28、 shall be known and allowance made for their effect. 4.2 Carrier gas, of known purity, established by an appropriate analytical technique, for example, gas chromatography (GC) and/or Fourier transform infrared (FTIR) spectrometry. 5 Apparatus 5.1 Permeation apparatus, typically consisting of one of
29、two modes (5.1.1 and 5.1.2) of application of the permeation method. The materials of the permeation apparatus shall be chosen so as to avoid any effect on the content of the calibration component by sorption (chemical or physical). The smaller the desired final content, the greater the effect of ad
30、sorption phenomena. If possible, use glass as the housing of the temperature-controlled permeation tube. Choose flexible and chemically inert tube materials and metals, especially having regard to the transfer of the gas between the permeation apparatus and the analyser. Pay special attention to all
31、 junctions so as to keep them free from leaks. The flow range of the carrier gas is kept constant by a control system and is monitored by a flowmeter. The value of the flow rate can, for example, be controlled by means of a mass flow controller and determined using a mass flowmeter. The existence of
32、 an outlet for surplus gas enables the analyser under calibration to take the gas flow rate necessary for its proper operation, the remainder of the flow of gas being vented to atmosphere. 5.1.1 Periodic-weighing-mode permeation apparatus, consisting of a permeation tube kept in a temperature- contr
33、olled enclosure, swept by carrier gas. The permeation tube is periodically removed from the enclosure to be weighed. Typical examples are given in Figures 1 and 2. 5.1.2 Continuous-weighing-mode permeation apparatus, consisting of a permeation tube kept in a temperature-controlled enclosure, swept b
34、y carrier gas. The permeation tube is suspended from a weighing device and weighed continuously. A typical example is given in Figure 3. ISO 6145-10:2002(E) ISO 2002 All rights reserved 3 Key 1 Flowmeter 5 Thermometer 2 Carrier gas 6 Permeation tube 3 Drier 7 Outlet for surplus gas 4 Filter 8 Analys
35、er Figure 1 Example 1 of a periodic-weighing-mode permeation apparatus Key 1 Outlet for surplus gas 2 Sampling system 3 Mixing bulb 4 Flowmeter 2 5 Diluent gas 6 Thermometer 7 Permeation tube 8 Copper tubing 9 Water bath 10 Flowmeter 1 11 Carrier gas 12 Drier Figure 2 Example 2 of a periodic-weighin
36、g-mode permeation apparatus ISO 6145-10:2002(E) 4 ISO 2002 All rights reserved Permeation tube Mass flow controller Tare mass Key 1 High purity air/N2 2 Temperature controller 3 Water 4 Microbalance controller 5 Gas blender 6 RS232 link 7 PC (acquisition, analysis and diagnostics) 8 16-bit ADC 9 Flo
37、w rate calibration facility 10 Gas analyser 11 Stable mixture requiring certification Figure 3 Continuous-weighing-mode permeation apparatus ISO 6145-10:2002(E) ISO 2002 All rights reserved 5 5.2 Permeation membrane, made from polymers and having sufficient chemical and mechanical resistance, e.g. s
38、uitable polytetrafluoroethylene (PTFE), polyethylene, polypropylene or a copolymer of tetrafluoroethylene and hexafluoropropylene (FEP). Take into account variations of the material characteristics which occur with a change of temperature. 5.3 Permeation tubes, or containers, made of stainless steel
39、 or glass, fitted with a permeation membrane (5.2) and capable of holding the calibration component in the liquid phase and gaseous phase; the membrane through which the permeation takes place may be in contact with the liquid phase only, or with the gaseous phase only, or with both. See examples gi
40、ven in Figure 4. Before use, keep the permeation tube in an airtight container under an anhydrous atmosphere in a cold place (e.g. in a refrigerator at approximately 5 C) so as to maintain the diffusion rate as low as possible, hence to minimize loss of the calibration component and avoid any conden
41、sation on the tube. a) Cylindrical tube fitted with a membrane in contact with both phases b) Tube fitted with a membrane in contact with only the liquid phase c) Container fitted with a membrane in contact with only the gaseous phase Key 1 Membrane 2 Stainless steel 3 Liquid level 4 Glass Figure 4
42、Examples of permeation tubes and container 6 Procedure 6.1 Preliminary checks and operating conditions 6.1.1 Permeation tube Before use, assess the purity of the product of the permeation tube by collecting a sample of the permeated gas for analysis by an appropriate analytical technique e.g. GC or
43、FTIR so as to quantify any likely major contaminants. This information may be provided by the suppliers of the tube and, if so, a certificate of analysis by an accredited body shall be provided. Periodically check the permeation rate of the tube at a known, fixed temperature by measuring the mass lo
44、ss. This gives a good indication as to the purity of the permeated gas. If the permeation rate changes by more than 10 % at the known, fixed temperature, discard the permeation tube. When first using the permeation tube, allow the system to reach a state of equilibrium before carrying out the first
45、weighing so as to ensure that the permeation rate is well stabilized at the constant value. The time needed to reach ISO 6145-10:2002(E) 6 ISO 2002 All rights reserved equilibrium is dependant on the component contained within the permeation tube, but a value of 72 h is applicable to most species. F
46、or most applications, it is essential to control the temperature of the enclosure to within 0,1 K because of the very strong dependence of the permeation rate upon temperature. The tube diffusion rate may, for example, double for an increase in temperature of approximately 7 K. Under certain circums
47、tances, in which the diffusing gas is highly soluble in the membrane polymer, an increase in temperature may reduce the permeation rate. During the period of use, maintain the permeation tube at constant temperature, principally to avoid the delay, sometimes very lengthy, which is necessary to resto
48、re equilibrium. Avoid any rapid changes in temperature. If the operating conditions change significantly (e.g. a change in operating temperature), allow a period of 72 h for the permeation tube to re-equilibrate before resuming measurements. 6.1.2 Carrier gas flow configuration Before the carrier ga
49、s reaches the tube, it is essential that its temperature be controlled at that of the permeation tube. Any system which enables the carrier gas to remain in the temperature-controlled enclosure for a sufficient period of time is satisfactory. To change the content of the calibration mixture, adjust the carrier gas flow rate and the diluent gas flow rate (avoiding any change of the tube permeation rate as a result of temperature change); in this case, equilibrium is rapidly obtained. R