ISO-6326-1-2007.pdf

Reference number ISO 6326-1:2007(E) © ISO 2007 INTERNATIONAL STANDARD ISO 6326-1 Second edition 2007-06-15 Natural gas Determination of sulfur compounds Part 1: General introduction Gaz naturel Détermination des composés soufrés Partie 1: Introduction générale Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products 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, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT © ISO 2007 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 writing from either ISO at the address below or ISO's 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.org Web www.iso.org Published in Switzerland ii © ISO 2007 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) © ISO 2007 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references. 2 3 Sampling 2 3.1 General. 2 3.2 Safety precautions 3 4 Methods for determination of total sulfur content 3 4.1 Wickbold combustion method (ISO 4260) 3 4.2 Lingener combustion method (ISO 6326-5) . 4 5 Methods for determination of individual sulfur compounds or groups of sulfur compounds 5 5.1 Gas chromatography method (ISO 19739). 5 5.2 Potentiometric method (ISO 6326-3). 5 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) iv © ISO 2007 All rights reserved Foreword ISO (the 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 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 electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies 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 document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 6326-1 was prepared by Technical Committee ISO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. This second edition cancels and replaces the first edition (ISO 6326-1:1989), which has been technically revised due to the replacement of ISO 6326-2:1981 and ISO 6326-4:1994 by ISO 19739:2004, Natural gas Determination of sulfur compounds using gas chromatography, which gives the requirements needed to perform a sulfur analysis by gas chromatography. This second edition also provides a general introduction to ISO 19739. ISO 6326 consists of the following parts, under the general title Natural gas Determination of sulfur compounds: Part 1: General introduction Part 3: Determination of hydrogen sulfide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry Part 5: Lingener combustion method Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) © ISO 2007 All rights reserved v Introduction Sulfur compounds can occur naturally in natural gas and remain as traces after treatment, or they may have been injected deliberately to allow subsequent olfactory detection for safety reasons. The standardization of several methods for the determination of sulfur compounds in natural gas is necessary in view of the diversity of these compounds hydrogen sulfide, carbonyl sulfide, tetrahydrothiophene (THT), etc. and the requirements of the determinations (required uncertainty, measurement at the well head, at clean-up plant or in the transmission pipes, etc.). In order to enable the user to choose the method most appropriate to his needs and to perform the measurements under the best conditions, ISO 6326 has been prepared in several parts. This part of ISO 6326 gives a rapid comparison of standardized methods and therefore provides information for the choice of the method. The other parts of ISO 6326 and ISO 19739 describe in detail the various standardized methods. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISO 6326-1:2007(E) © ISO 2007 All rights reserved 1 Natural gas Determination of sulfur compounds Part 1: General introduction WARNING The majority of sulfur compounds are extremely toxic and thus present a serious health hazard if handled without precautions. 1 Scope This part of ISO 6326 gives a brief description of standardized methods that can be used for the determination of sulfur compounds in natural gas. The principle of each method is described generally, the range of concentrations for which the method is suitable is indicated, and the analytical range and precision of each method is given. It should enable the user to select judiciously the proper method for the application being considered. Sulfur analysis is performed in order to determine a) total sulfur, b) sulfur contained in specific groups (e.g. thiol sulfur), c) individual sulfur compounds, and d) specific groups of sulfur compounds. The standardized methods available in the field of sulfur analysis are the Wickbold combustion method: for total sulfur determination (ISO 4260), the Lingener combustion method: for total sulfur determination (ISO 6326-5), gas chromatography: for determination of individual sulfur compounds (ISO 19739), and potentiometry: for determination of hydrogen sulfide, carbonyl sulfide and thiol compounds (ISO 6326-3). Other methods for the determination of sulfur compounds are available but are not considered here. Table 1 gives an overview of the standardized methods which can be used for the determination of total sulfur, hydrogen sulfide, carbonyl sulfide, tetrahydrothiophene, thiol sulfur, individual thiols, individual thiophenes, individual organic sulfides and disulfides. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) 2 © ISO 2007 All rights reserved Table 1 Methods for the determination of sulfur compounds in natural gas Concentration range a Determination Method mg/m3 Reference Total sulfur Wickbold combustion method 1 to 20 000 ISO 4260 Lingener combustion method 0,5 to 1 000 ISO 6326-5 Potentiometry W 1 ISO 6326-3 Hydrogen sulfide (H2S) Gas chromatography 0,1 to 100 (or 0,5 to 600 depending on the detector used) ISO 19739 Gas chromatography 0,1 to 30 ISO 19739 Carbonyl sulfide (COS) Potentiometry W 1 ISO 6326-3 Tetrahydrothiophene (THT) Gas chromatography 0,1 to 100 ISO 19739 Thiol sulfur Potentiometry W 1 ISO 6326-3 Individual thiols Gas chromatography 0,1 to 100 ISO 19739 Individual thiophenes Gas chromatography 0,1 to 100 ISO 19739 Individual organic sulfides and disulfides Gas chromatography 0,1 to 100 ISO 19739 a For the determination of total sulfur, the sulfur content is expressed as milligrams of sulfur per cubic metre of gas. For the determination of sulfur compounds, the mass concentration of sulfur compounds is expressed as milligrams of sulfur compound per cubic metre of gas. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 4260, Petroleum products and hydrocarbons Determination of sulfur content Wickbold combustion method ISO 6326-3, Natural gas Determination of sulfur compounds Part 3: Determination of hydrogen sulfide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry ISO 6326-5, Natural gas Determination of sulfur compounds Part 5: Lingener combustion method ISO 10715, Natural gas Sampling guidelines ISO 16664, Gas analysis Handling of calibration gases and gas mixtures Guidelines ISO 19739:2004, Natural gas Determination of sulfur compounds using gas chromatography 3 Sampling 3.1 General The sampling procedures are very important in the analysis of sulfur compounds. Sulfur compounds have a strong tendency to adsorb on to, or to chemically react with, different materials of construction. Low contents of sulfur compounds in samples and calibration gas mixtures put demands on the sampling procedure in order to ensure that the sulfur compounds in correct quantity reach the analytical device. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) © ISO 2007 All rights reserved 3 Carry out representative sampling in such a way that the sample represents the bulk of the gas at the time of sampling. Sampling and sample transfer shall be in accordance with ISO 10715. Purge time should be long enough to obtain replicate stable analytical results within the acceptable standard deviation of the analyser. The purge time needed depends on the type and concentration of the sulfur compound, materials in contact with the gas, and the gas flow rate through the sample loop. Sampling of the gas can be carried out in two different ways: at atmospheric pressure in a silanized glass vessel, equipped with polytetrafluoroethylene (PTFE) plugs or a sampling bag made of material inert to sulfur compounds, such as polyvinylfluoride (PVF) or PTFE, which has been flushed with dilute hydrochloric acid, subsequently flushed with distilled water and dried; after the glass vessel is filled with the gas under study, it should be shielded from daylight; under pressure in a stainless steel or aluminium cylinder, if the sulfur content exceeds 50 mg/m3. 3.2 Safety precautions Safety precautions required in handling gas cylinders with pressurized flammable gas mixtures are described in ISO 10715. If a pressure regulator is to be connected to the cylinder, always use a regulator whose materials of construction are recommended by the producer of the calibration gas. For other precautions and advice for the use, sampling and handling of gas mixtures containing sulfur compounds, see Clause 3 of ISO 19739:2004 and ISO 16664. 4 Methods for determination of total sulfur content To carry out the analyses, reference should be made to the specific methods which are described in detail in ISO 4260, ISO 19739, ISO 6326-3 and ISO 6326-5. 4.1 Wickbold combustion method (ISO 4260) 4.1.1 Scope This method is applicable to products having sulfur content on the order of 1 mg/m3, and is particularly suitable for gases with total sulfur content in the range 1 mg/m3 to 20 000 mg/m3 and for distillates with total sulfur content of less than 300 mg/m3. 4.1.2 Principle The natural gas is supplied to the burner of a hydrogen-oxygen flame, where the sulfur compounds undergo combustion with a considerable excess of oxygen. The resulting sulfur oxides are converted into sulfuric acid by absorption in hydrogen peroxide solution. Depending on the sulfur content of the sample, the sulfate ions in the absorption solution are determined by colorimetric, nephelometric, turbidimetric or conductometric titration (see Table 2). Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 06/18/2007 23:45:49 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 6326-1:2007(E) 4 © ISO 2007 All rights reserved Table 2 Concentration range an