EN ISO 16591:2010

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Mineralölerzeugnisse - Bestimmung des Schwefelgehaltes - Oxidatives mikrocoulometrisches Verfahren (ISO 16591:2010)Produits pétroliers - Dosage du soufre - Méthode par microcoulométrie oxydante (ISO 16591:2010)Petroleum products - Determination of sulfur content - Oxidative microcoulometry method (ISO 16591:2010)75.080Naftni proizvodi na splošnoPetroleum products in generalICS:Ta slovenski standard je istoveten z:EN ISO 16591:2010SIST EN ISO 16591:2011en01-marec-2011SIST EN ISO 16591:2011SLOVENSKI
STANDARD
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN ISO 16591
December 2010 ICS 75.080 English Version
Petroleum products - Determination of sulfur content - Oxidative microcoulometry method (ISO 16591:2010)
Produits pétroliers - Dosage du soufre - Méthode par microcoulométrie oxydante (ISO 16591:2010)
Mineralölerzeugnisse - Bestimmung des Schwefelgehaltes - Oxidatives mikrocoulometrisches Verfahren (ISO 16591:2010) This European Standard was approved by CEN on 10 December 2010.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations 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 CEN-CENELEC Management Centre or to any CEN member.
This European Standard exists 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 CEN-CENELEC Management Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
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Reference numberISO 16591:2010(E)© ISO 2010
INTERNATIONAL STANDARD ISO16591First edition2010-12-15Petroleum products — Determination of sulfur content — Oxidative microcoulometry method Produits pétroliers — Dosage du soufre — Méthode par microcoulométrie oxydante
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ii © ISO 2010 – All rights reserved
ISO 16591:2010(E) © ISO 2010 – All rights reserved iii Contents Page Foreword.iv 1 Scope.1 2 Normative references.1 3 Principle.2 4 Reagents and materials.2 5 Apparatus.3 6 Samples and sampling.5 7 Apparatus preparation.5 7.1 Titration cell.5 7.2 Microcoulometer and recorder.6 7.3 Heating tape.6 7.4 Typical operating conditions.6 8 Apparatus verification and calibration curve construction.6 9 Procedure.7 10 Calculation.8 11 Expression of results.8 12 Precision.8 12.1 General.8 12.2 Repeatability, r.9 12.3 Reproducibility, R.9 13 Test report.9 Annex A (informative)
Determination of sulfur contents below 1 mg/kg — Standby technique.10 Annex B (informative)
Troubleshooting.11 Annex C (informative)
Calculation of sulfur content from electrochemical data.13 Bibliography.15
ISO 16591:2010(E) iv © ISO 2010 – 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 16591 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants.
INTERNATIONAL STANDARD ISO 16591:2010(E) © ISO 2010 – All rights reserved 1 Petroleum products — Determination of sulfur content — Oxidative microcoulometry method WARNING — The use of this International Standard may involve hazardous material, operations and equipment. This International Standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this International Standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 1 Scope This International Standard specifies a method for the determination of the sulfur content by oxidative microcoulometry of petroleum light and middle distillates with a final boiling point not higher than 400 °C. It is applicable to materials with sulfur contents in the range of 1 mg/kg to 100 mg/kg. Products with sulfur contents above 100 mg/kg can be analysed after dilution with a suitable sulfur-free solvent. Products with sulfur contents below 1 mg/kg can also be analysed by a modified technique described in Annex A. The precision quoted only applies to measurements in the 1 mg/kg to 100 mg/kg range. Nitrogen interferes with the analysis at concentrations above 0,1 % (m/m), and chlorine interferes at concentrations above 1,0 % (m/m), but these interferences are overcome by the addition of sodium azide to the cell electrolyte. Bromine and organometallic compounds also interfere with the analysis at concentrations above approximately 500 mg/kg. NOTE 1 The microcoulometric method is capable of analysing light liquid hydrocarbons boiling in the range from 26 °C to 274 °C (for example, naphtha and MS samples) that undergo pyrolysis at 900 °C to 1 200 °C. The combustion of high boiling components (for example, diesel) can result in the formation of carbonaceous deposits in the inlet portion of the combustion tube, which need to be removed frequently. NOTE 2 The results obtained using this International Standard on light and light-middle distillates generally approximate to those obtained using ISO 4260. NOTE 3 For the purposes of this International Standard, the term “% (m/m)” is used to represent the mass fraction of a material. 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 3170, Petroleum liquids — Manual sampling ISO 3171, Petroleum liquids — Automatic pipeline sampling ISO 3675, Crude petroleum and liquid petroleum products — Laboratory determination of density — Hydrometer method ISO 3696, Water for analytical laboratory use — Specification and test methods ISO 12185, Crude petroleum and petroleum products — Determination of density — Oscillating U-tube method SIST EN ISO 16591:2011

ISO 16591:2010(E) 2 © ISO 2010 – All rights reserved 3 Principle A test portion is burned in a combustion tube under a flowing stream of oxygen plus an inert gas. The combustion products are swept into a titration cell, where the sulfur dioxide reacts with tri-iodide ion present in the electrolyte. The tri-iodide ions that are consumed are coulometrically replaced, and the current required for replacement is a direct measure of the sulfur content of the sample. The reactions are: I3ø + SO2 + H2O → SO3 + 3Iø + 2H+ (1) 3Iø → I3ø + 2eø (2) 4 Reagents and materials All reagents shall be of recognized analytical grade, and water shall conform to the requirements of Grade 3 of ISO 3696. 4.1 Electrolyte Dissolve 0,5 g ± 0,01 g of potassium iodide (KI) and 0,6 g ± 0,01 g of sodium azide (NaN3) in approximately 500 ml of water in a 1 000 ml volumetric flask. Add 5 ml of glacial acetic acid (CH3COOH) and make up to the mark with water. Store in a dark glass bottle or in a dark place. CAUTION — Sodium azide is highly toxic in contact with the skin. Wear protective clothing at all times when handling sodium azide. Crystalline sodium azide decomposes explosively under conditions of heat, shock, concussion and friction. Ensure adequate precautions are taken to prevent these conditions occurring. NOTE The shelf life of bulk electrolyte has been found to be approximately three months. 4.2 Oxygen, of high-purity grade, minimum purity of 99,995 %. 4.3 Carrier gas, of high-purity grade argon, helium or nitrogen, with a minimum purity of 99,995 %. If nitrogen is used, it should be tested in the apparatus for baseline stability. 4.4 Iodine, resublimed. 4.5 Sulfur-free solvent, preferably a sulfur solvent which is essentially sulfur-free (< 0,5 mg/kg) or has an accurately known low (< 5 mg/kg) sulfur content, similar in characteristics to the sample being analysed. Alternatively, a high-purity grade of cyclohexane, 2,2,4-trimethylpentane, toluene or hexadecane is suitable, as appropriate. 4.6 Sulfur stock solution 4.6.1 General A certified reference material (CRM), or a prepared stock solution with a sulfur content in the range 200 mg/kg to 500 mg/kg. 4.6.2 Preparation Select a solvent-soluble sulfur compound (see the note in this subclause) of accurately known sulfur content, preferably appropriate to the boiling range and sulfur type expected to be present in the sample. Weigh, to the nearest 0,1 mg, a quantity of this compound into a weighed 100 ml volumetric flask. Add solvent (4.5), swirl to ensure dissolution, make up to the mark with solvent and reweigh to the nearest 0,1 mg. Calculate the exact sulfur content to the nearest 0,000 1 % (m/m) (1 mg/kg). SIST EN ISO 16591:2011

ISO 16591:2010(E) © ISO 2010 – All rights reserved 3 NOTE Suitable sulfur compounds include: a) thiophene, of nominal sulfur content 38,103 % (m/m); b) dibutyl sulfide (DBS), of nominal sulfur content 21,915 % (m/m); c) dibenzothiophene (DBT), of nominal sulfur content 17,399 % (m/m); d) thionaphthene (TNA), of nominal sulfur content 23,89 % (m/m). 4.7 Sulfur standard solutions Prepare a range of sulfur standard solutions to cover the range of concentrations expected in the samples being analysed, by dilution of the stock solution (4.6) with solvent (4.5) calculated on the basis of mass fraction. At least three standard solutions are required for each concentration level, or a range of not less than five standard solutions to cover a set of sample analyses within the total scope of this International Standard. 5 Apparatus 5.1 Microcoulometric apparatus 5.1.1 General The microcoulometer and associated apparatus are described in 5.1.2 to 5.1.7, and the general arrangement is shown in Figure 1. ab12345678 Key 1 sample injection septum 5 mirocoulometer 2 inlet zone 6 potentiometric recorder 3 oxidizing combustion zone 7 titration cell 4 outlet zone 8 pyrolysis furnace a Oxygen, O2. b Carrier gas. Figure 1 — General arrangement of microcoulometric apparatus SIST EN ISO 16591:2011

ISO 16591:2010(E) 4 © ISO 2010 – All rights reserved 5.1.2 Pyrolysis furnace, electrically powered, consisting of two or three independently controlled temperature zones. The first, or inlet, zone shall maintain a temperature sufficient to volatilize the entire organic sample. The second zone, or oxidizing combustion zone, shall maintain a temperature sufficient to pyrolize the organic matrix and oxidize all the organically bound sulfur. The third, or outlet, zone for further pyrolysis, is optional. The manufacturer's instructions should be consulted for optimum temperatures. 5.1.3 Pyrolysis tube, of quartz, constructed in such a way that the test portion is completely vaporized in an inert gas atmosphere in the inlet section and swept into the oxidation zone, where it mixes with oxygen and is burned. The inlet end of the tube shall hold a septum for syringe introduction of the test portion, and side arms for the admission of oxygen and carrier gas. The oxidizing combustion zone(s) shall be of sufficient volume to ensure complete pyrolysis of the test portion. The outlet section of the tube may be closed by a 20 mm length of quartz-wool if desired. Typical designs of pyrolysis tube are shown in Figure 2. Some manufacturers recommend the use of a chemical scrubber in line between the pyrolysis furnace and the titration cell. This scrubber is used for the removal of soot, water and heavy metals, and aids the stability of the titration cell. For the analysis of products with a substantial portion boiling above 230 °C, a boat inlet system may give better recovery. 1ab a)
TOT tube 1ab b)
COT tube Key 1 septum a Oxygen, O2. b Ar, He or N2. Figure 2 — Typical designs of pyrolysis tube 5.1.4 Boat inlet system, sealed to the combustion tube, with boats made from platinum or quartz, and with a drive mechanism that advances and withdraws the boat at a controlled and repeatable rate. 5.1.5 Titration cell, containing a sensor-reference pair of electrodes to detect changes in tri-iodide ion concentration, and a generator anode-cathode pair of electrodes to maintain constant tri-iodide ion concentration in the cell electrolyte. For the description of the sensor electrodes used, consult the manufacturer's operating manual. SIST EN ISO 16591:2011

ISO 16591:2010(E) © ISO 2010 – All rights reserved 5 Shielding of the cell from electrical interferences by means of an earthed (grounded) Faraday cage is recommended by some manufacturers and should be described in the manufacturer's operating manual, particularly in the determination of very low milligram per kilogram levels of sulfur. The cell shall be provided with a suitable inlet for the combustion gases from the pyrolysis tube, and supplied with appropriate stirring. If a magnetic stirrer is used, the stirring rate should not be excessive, to ensure that the stirring bar does not rise in the cell and damage the electrodes. The creation of a slight vortex is adequate. Some instruments rely on the agitation caused by gas bubbling through the solution. 5
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