石油烃类中溴指数检测方案(自动电位滴定)

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APAT-0198en京都電子工業株式会社KYOTO ELECTRONICSMANUFACTURING CO.，LTD. APAT-0180en Application Note Determination of the Bromine Index of PetroleumHydrocarbons Using Electrometric Titration IndustryChemicalsInstrumentAutomatic potentiometric titratorMeasurement methodConstant voltage polarization titrationStandardsASTMD 2710 1.Scope The bromine index indicates the amount of a component with unsaturated bonds. It is defined as thenumber of mg of bromine that reacts with 100 g of a sample. In ASTM D 2710， measurement of thebromine index is stipulated as an index of the amount of an unsaturated trace compound in a petroleumfraction at 288℃ (550°F) or lower. In these standards， only samples that satisfy all of the followingconditions can be used. · The bromine index is under 1.000. · The sample does not contain a substance less dense than isobutane. ·Petroleum fraction at 288C(550°F) or lower · The main component must be olefin-free hydrocarbons or mixtures. In the example in this Application Note， a sample solution of cyclohexene dissolved in isooctane ismeasured in accordance with ASTMD 2710. 2. Apparatus Main unit Automatic potentiometric titrator (polarization titration preamplifier ：POT)Electrode Twin platinum electrode， Temperature compensation electrode 3.Reagents Titrant 0.05 mol/L Bromide-Bromate Standard Solution (potassium bromide andpotassium bromate)Titration solvent Solution consisting of a mixture of 714 mL of acetic acid， 134 mL of 1，1，1- trichloromethane or dichloromethane， 134 mL of methanol， and 18 mL ofsulfuric acid (1+5) 4.Procedure -Calibration- 1) Place approximately 8 g of the sample in a beaker and add 110 mL of titration solvent. 2) While stirring， cool the sample in an ice bath until the temperature reaches 5 ℃ or lower. 3) Set the voltage applied to the twin platinum electrodes to 300 mV. 4) Immerse the twin platinum electrodes in the sample solution and calibrate. -Blank test- 1) Add 110 mL of titration solvent to a beaker. 2) While stirring， cool the sample in an ice bath until the temperature reaches 5°C or lower. 3) Titrate with 0.025 mol/L of bromine solution. -Measurement- 1) Weigh out precisely 8 g of the sample and place it in a beaker. 2) Add 110 mL of titration solvent to the beaker. 3) While stirring， cool the sample in an ice bath until the temperature reaches 5°C or lower. 4) Titrate with 0.025 mol/L of bromine solution. 5. Calculation Bromine index (mgBr2/100g)=(EP1-BL1)×TF×0.05×7990/S EP1 Titration amount (mL) BL1 Titration amount (mL) of Blank test=0.0645(mL) TF Factor of Titrant =1.0265 S Sample size (g) 6. Example 一Parameter— 一Example of Titration curve 一 京都电子工业株式会社-可睦电子(上海)商贸有限公司 上海市徐汇区宜山路333号1201室电话：021-54488867 电邮： kemu-kem@163.com 网址： http：//www. kem-china.com Table 1 Measurement result Sample (g) Titration (mL) Bromine index(mgBr2/100g) 1 8.1746 7.6665 381.4 2 8.1535 7.6065 379.3 3 8.3814 7.8517 381.0 Mean - 380.6 SD 1.1 RSD (%) - 0.3 7. Summary The repeatability RSD was less than 1 %，showing that excellent accuracy can be achieved. In ASTM D 2710， constant voltage polarization titration is stipulated as the measurement method. Inthis measurement method， a constant voltage is applied between the twin platinum electrodes， and thechange in current as titration progresses is monitored. Before the end point， the bromine is consumed through addition to the unsaturated bonds， so there isessentially no flow of current and a constant current value is shown. When the titration reaction iscomplete， if there is even a slight amount of excess bromine， a current will flow in the twin platinumcathode due to bromine reduction， and a sharp increase in the current value will be observed. Thehigher the bromine concentration， the longer the increase in the current value continues， so noinflection point appears in the titration curve. In this Application Note， automatic intersection detectionwas used as the end point detection method. This function automatically detects the end point at theintersection of two tangent lines drawn at the bend of the titration curve. If the end point cannot bedetected automatically， there is also a function that uses the intersection of two manually drawn tangentlines as the end point. KEM’s titrators allow users to perform measurements in accordance with ASTMD2710. 8.Reference ASTM D 2710 Standard Test Method for Bromine Index of Petroleum Hydrocarbons byElectrometric Titration. / 京都電子工業株式会社KYOTO ELECTRONICSMANUFACTURING CO.，LTD 石油烃类溴指数的测定 应用资料(英文版)根据ASTM D2710 石油烃类溴指数测定法(电位滴定法)。将已知量的试样溶解在规定的溶剂中，用溴化钾-溴酸钾标准溶液进行电位滴定。当试样中能与溴作用的物质反应完毕，溶液中有游离溴出现时，溶液的电位突然变化。终点以"死停点"电位滴定仪指示或以电位滴定曲线(E-V曲线)的电位突跃来判断。