1、 ICS 75.060 DEUTSCHE NORM Determination of sulfur compounds in natural gas Part 3: Determination of hydrogen sulfide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry (ISO 6326-3 : 1989) Enqlish version of DIN EN ISO 6326-3 Descriptors: Natural gas, sulfur compounds, testing. Erdgas - B
2、estimmung von Schwefelverbindungen - Teil 3: Bestim mung von Schwefelwasserstoff, Mercaptanschwefel und Kohlenstoff oxidsulfidschwefel durch Potentiometrie (ISO 6326-3 : 1989) April 1998 DIN EN ISO 6326-3 Supersedes parts of DIN 51855-6, March 1989 edition. European Standard EN ISO 6326-3: 1997 has
3、the status of a DIN Standard. A comma is used as the decimal marker. National foreword This standard has been published in accordance with a decision taken by GEN/TC 19 to adopt, without alteration, International Standard ISO 6326-3 as a European Standard. The responsible German body involved in its
4、 preparation was Technical CommitteeAnforderungen an und Prufung von Brenngasen of theNormenausschuB Materialprufung (Materials Testing Standards Committee). The DIN Standards corresponding to the International Standards referred to in clause 2 of the EN are as follows: ISO 385-1 ISO 1042 ISO 4260 A
5、mendments DIN 12700-1 DIN 12664-1 DIN EN 24260 DIN 51855-6, March 1989 edition, has been superseded by the specifications of EN ISO 6326-3, which is identical to ISO 6326-3. Previous editions DIN 51615: 1956-03; DIN 51855-6: 1972-02, 1977-01, 1989-03. National Annex NA Standards referred to (and not
6、 included in Normative references) DIN 12664-1 One-mark volumetric flasks with flanged rim, conical socket and conical joint, for laboratory use Burettes for laboratory use - General requirements DIN 12700-1 DIN EN 24260 Determination of sulfur content in petroleum products and hydrocarbons by the W
7、ickbold combustion method (ISO 4260 : 1987) No part of this standard may be reproduced without the prior permission of DIN Deutsches lnstitut fur Normung e. V . Berlin. Beuth Verlag GmbH, D-10772 Berlin, has the exclusive right of sale for German Standards (D/N-Normen). EN comprises 7 pages. Ref. No
8、. DIN EN ISO 6326-3 : 1998-04 English price group 0 7 Sa/es No. 110 7 09.98 EUROPEAN STANDARD NORME EUROPEENNE EUROPAISCHE NORM EN ISO 6326-3 December 1997 ICS 75.060 Descriptors: Natural gas, sulfur compounds, testing. English version Natural gas Determination of sulfur compounds Part 3: Determinat
9、ion of hydrogen sulfide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry (ISO 6326-3 : 1989) Gaz naturel - Determination des composes soufres - Partie 3: Determination du sulfure dhydrogene, des thiols et du sulfure de carbonyle par potentiometrie (ISO 6326-3 : 1989) Erdgas - Bestimmun
10、g von Schwefel verbindungen - Teil 3: Bestimmung von Schwefelwasserstoff, Mercap tanschwefel und Kohlenstoffoxid sulfidschwefel durch Potentiometrie (ISO 6326-3 : 1989) This European Standard was approved by CEN on 1997-11-06. CEN members are bound to comply with the CEN/CENELEC Internal Regulations
11、 which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. The European
12、Standards exist in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national
13、standards bodies of Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. CEN European Committee for Standardization Comite Europeen de Normalisation
14、 Europaisches Komitee Hir Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1997. GEN - All rights of exploitation in any form and by any means reserved worldwide for GEN national members. Ref. No. EN ISO 6326-3: 1997 E Page2 EN ISO 6326-3 : 1997 Foreword International Standard ISO 63
15、26-3 : 1989 Natural gas - Determination of sulfur compounds - Part 3: Determination of hydrogen sulfide, mercaptan sulfur and carbonyl sulfide sulfur by potentiometry, which was prepared by ISO/TC 193 Natural gas of the International Organization for Standardization, has been adopted by Technical Co
16、mmittee CEN/TC 19 Petroleum products, lubricants and related products, the Secretariat of which is held by NNI, as a European Standard. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, and conflicting national stan
17、dards withdrawn, by June 1998 at the latest. In accordance with the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Greece, Icelan
18、d, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. Endorsement notice The text of the International Standard ISO 6326-3 : 1989 was approved by CEN as a European Standard without any modification. Introduction Page3 EN ISO 6326-3 : 19
19、97 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, thiols (mercaptans), tetrahydrothiophene (THT), etc. and the pur poses of the determinations (required accur
20、acy, measurement at the drilling head 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. ISO 6326-1 gives a rapid comparison of sta
21、ndardized methods and therefore provides information for the choice of the method. The other parts of ISO 6326, including this part, describe in detail the various stan dardized methods. The determination of total sulfur is specified in ISO 4260 : 1987, Petroleum products and hydrocarbons - Determin
22、ation of sulfur content - Wickbold combustion method. 1 Scope This part of ISO 6326 specifies a potentiometric method for the determination of hydrogen sulfide, mercaptan sulfur, and car bonyl sulfide sulfur in natural gas in the concentration range equal to or above 1 mg/m3. The gas must be free of
23、 dust, mist, oxygen, hydrogen cyanide and carbon disulfide. The hydrogen sulfide/ mercaptan sulfur ratio and also the mercaptan sulfur/hydrogen sulfide ratio should not exceed 50 : 1. The method is not recommended for gases containing more than approximately 1,5 % (VI VJ carbon dioxide. NOTE - In al
24、l parts of ISO 6326, 1 m3 of gas is expressed at normal conditions (0 C; 101,325 kPa). 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this part of ISO 6326. At the time of publication, the editions indicated were vali
25、d. All standards are subject to revision, and parties to agreements based on this part of ISO 6326 are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and ISO main tain registers of currently valid International Standards.
26、ISO 385-1 : 1984, Laboratory glassware - Burettes - Part 1 : General requirements. ISO 648 : 1977, Laboratory glassware - One-mark pipettes. ISO 1042: 1983, Laboratory glassware One-mark volumetric flasks. 3 Principle Hydrogen sulfide and mercaptans are absorbed in a 35 % (m/m) aqueous potassium hyd
27、roxide solution and carbonyl sulfide in a 5 % (m/m) ethanoholic monoethanolamine solu tion. The solutions are titrated potentiometrically using silver nitrate solutions with a silver/silver sulfide electrode system to indicate the end point. 4 Reagents and materials During the analysis, use only rea
28、gents of recognized analytical grade and only distilled water or water of equivalent purity. 4.1 Potassium hydroxide, solution. Dissolve 35 g of potassium hydroxide (KOH) in 65 g of water. NOTE - In order to prevent interference by heavy metal ions, 0,5 g of a mixture of polyaminoacetic acids is add
29、ed for each 50 ml of absorp tion solution to inactivate the heavy metal ions. The mixture consists of equal parts of the pentasodium salt of diethylenetriamine pentaacetic acid (Na5DTPA); the trisodium salt of N-hydroxyethylenediamine triacetic acid (Na3HEDTA); the sodium salt of N,N-di(2-hydroxyeth
30、yl-glycin) (NaDHEG); the tetrasodium salt of ethylenediamine tetraacetic acid (Na4EDTA). Page4 EN ISO 6326-3 : 1997 4.2 Monoethanolamine, solution. Dissolve 5 g of monoethanolamine (C2H70N) in 95 g of ethanol. 4.3 Nitrogen, purity better than 99,95 %, oxygen-free, under pressure. 4.4 Silver nitrate,
31、 standard volumetric solution, c(AgN03) = 0,01 mol/I. For the preparation of the silver nitrate solution use boiled distilled water, cooled to 20 C while bubbling with nitrogen (4.3), to remove all traces of oxygen. Dissolve about 1,7 g of silver nitrate in 200 ml of water in the 1 000 ml one-mark v
32、olumetric flask (5.6) and make up to the mark with water. Standardize the solution with hydrochloric acid c(HCI) = 0,01 mol/IJ. 4.5 Ammonium hydroxide solution (e20 oc = 0,90 g/ml). 4.6 Electrolyte solution. Mix 1 000 ml of methanol and 25 ml of ammonium hydroxide solution (4.5). 4.7 Cotton-wool, fo
33、r the removal of dust. 5 Apparatus Ordinary laboratory apparatus and 5.1 Test apparatus, (see figure 1 ), cons1st1ng of three washing bottles (high-speed absorbers of any suitable design), maximum pore diameter 90 m to 150 m; 1 washing bottle for the removal of dust, if required; gas meter, wet desi
34、gn, tolerance 0, 1 litre, with thermometer and water manometer. The thermometer shall have a measuring range of 0 C to at least 30 C. The scale intervals shall be not less than 0,5 C. The connections between the three washing bottles shall be glass to glass sealed by fluorelastomer tubing. NOTE - Fo
35、r low levels of sulfur compounds, butt connections and stop cocks with polytetrafluoroethylene plugs instead of the screw clamps are recommended. 5.2 One-mark pipette, of capacity 10 ml, complying with ISO 648. 5.3 Microburette, of capacity 10 ml, complying with ISO 385-1. 5.4 Beaker, of capacity 30
36、0 ml. 5.5 Measuring cylinder, of capacity 50 ml. 5.6 One-mark volumetric flask, of capacity 1 000 ml, complying with ISO 1042. 5.7 High-resistance voltmeter, range 1 000 mV, accuracy better than 5 mV. (An automatic titrimeter may be used, providing that it meets the above specification.) 5.8 Silver/
37、silver sulfide measuring electrode NOTE - Ion-selective silver/silver sulfide crystal membrane electrodes are commercially available and allow faster and more precise titration, especially at low sulfur concentrations. If such an electrode is not available, a conventional silver I silver sulfide ele
38、ctrode may be prepared according to the following procedure. Prepare a solution of sodium sulfide and sodium hydroxide by dissolv ing 1,2 g of sodium sulfide nonahydrate (NazS,9H20) and 40 g of sodium hydroxide in 1 litre of water. Clean the silver metal of the electrode with fine abrasive paper and
39、 im merse it in 100 ml of the sodium sulfide/sodium hydroxide solution, stir the solution and add 10 ml of the silver nitrate solution (4.4) over a period of 10 min to 15 min. Remove the electrode from the solution, wash it with water and wipe it lightly with a clean cloth. The coating should last f
40、or several weeks. Before use, soak the electrode for at least 5 min in 100 ml of the elec trolytic solution (4.61 to which 0,5 ml of silver nitrate solution (4.4) has been added. Store the electrode in this solution. 5.9 Silver/silver chloride reference electrode. 5.10 Electric stirrer. 6 Sampling O
41、n-line sampling is recommended. In the case where indirect sampling is indispensable, use sampling cylinders in accord ance with clause 3 of ISO 6326-1 : 1989. 7 Procedure 7.1 Preliminary operations Assemble the absorbers in series, as shown in figure 1. Place 50 ml of potassium hydroxide solution (
42、4.1) in the washing bottle (E), and 50 ml of monoethanolamine solution (4.2) in each of the two washing bottles (F). In order to remove the oxygen dissolved in the absorption solutions, purge the assembly with nitrogen (4.3) for a period of 5 min to 10 min, at a rate of 1 I/min to 2 I/min. Transfer
43、the washing bottles, closed hermetically with screw clamps (D), to the sampling point and assemble the testing apparatus as shown in figure 1. If required, connect an additional washing bottle filled with cotton-wool (4.7) between the sam pling cock (B) and the T-piece (C) to intercept any solid par
44、ticles. 7.2 Absorption (see figure 1) Flush the sampling line and the T-piece (C) with gas. Open the screw-clamps (D) at the inlet and outlet of the washing bottles (E and Fl and record the initial reading of the gas meter (G). A Gas line B Sampling valve c T-piece D Screw-clamp E Washing bottle for
45、 potassium hydroxide solution F G H J Pages EN ISO 6326-3 : 1997 Washing bottles for mono-ethanolamine solution Gas meter Thermometer Water manometer Figure 1 - Test apparatus The gas is passed through the absorption solutions at a flow rate of 120 l/h 20 l/h. Read the temperature and pressure of th
46、e gas and the atmospheric pressure during the absorption period. The amount of gas depends on the content of sulfur compounds; 100 litres to 200 litres are sufficient in most cases. Close the sampling valve (B) and read the amount of gas passed through the solutions on the gas meter (G). By the free
47、 end of the T-piece, pass 10 litres of nitrogen (4.3) through the washing bottles to transfer the dissolved carbonyl sulfide from the potassium hydroxide into the monoethanolamine solution. Close the washing bottles (E and F) hermetically and titrate the solutions containing the absorbed sulfur comp
48、ounds im mediately. 7.3 Potentiometric titration 7.3.1 Determination of hydrogen sulfide and mercaptan sulfur Flush the 300 ml beaker (5.4) with nitrogen (4.3). Quantitatively transfer the contents of the washing bottle (E) into the beaker and dilute with approximately 200 ml boiled distilled water,
49、 cooled to 20 C. While bubbling with nitrogen (4.3), add 2 ml of concentrated ammonium hydroxide solution (4.5) using the pipette (5.2). CAUTION - Ammonia must not be added after the titration has commenced because of possible formation of explosive compounds. The dilution of the absorption solution is necessary to reach a fast response of the voltmeter (5.7). Immerse the electrodes (5.8 and 5.9) in this mixture. Start a nitrogen purge of the liquid surface and continue this throughout the titration. Stir the solution with the el
