1、THIOSULFATE IN LEAN AMINE SOLUTIONSUOP Method 818-81SCOPEThis method is for determining thiosulfate in lean amine solutions. Thiosulfate is calculated and reportedas either apparent H2S in grains/gal or as sodium thiosulfate in g/100 mL. The lower limit of detection isapproximately 25 grains/gal.OUT
2、LINE OF METHODThe amine sample is diluted with water, boiled to eliminate hydrogen sulfide and acidified. Thethiosulfate in the acidified solution is treated with an excess of standard iodine solution. The excess iodineis back-titrated to the starch indicator endpoint with standard sodium thiosulfat
3、e solution.APPARATUSBalance, torsion or top loading type, capacity 500 g, capable of weighing to 0.01 gBeaker, 100- and 250-mLBoiling chipsBuret, 50-mLCylinder, graduated, 25- and 250-mLFlask, Erlenmeyer, 250-mLFlask, volumetric, one-liter (2 required)Flask, volumetric, 100-mLHot platePipets, volume
4、tric, 1-, 5- and 10-mLStirrer, magnetic, with Teflon-covered stirring barStirring rod, glass, 150-mm lengthIT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH ANDSAFETY PRACTICES AR
5、E TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THISPROCEDURE IN THE MANNER PRESCRIBED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS(MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED INTHIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF
6、THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE). COPYRIGHT 1981 UOP LLCALL RIGHTS RESERVEDUOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken PA 19428-2959,United States. The Methods may be obtained through the ASTM website, www.astm.org, or
7、 by contacting Customer Service atserviceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.2 of 3818-81REAGENTS AND MATERIALSUnless otherwise indicated, all reagents shall conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society, where such specifications
8、 exist. References towater, unless otherwise indicated, mean distilled or deionized water.Hydrochloric acid, concentratedIodine solution, 0.05-M. To prepare, dissolve 25 g of potassium iodide in 200 mL of water. Warm slightlyto dissolve. Cool and add 12.69 g iodine crystals. Stir the solution to dis
9、solve the reagents and transferquantitatively to a one-liter volumetric flask. Dilute to volume with water. Store in an amber bottle.Standardize against the 0.1-M sodium thiosulfate. If samples are analyzed infrequently, the iodinesolution must be standardized prior to use.Lead acetate paperMethyl o
10、range indicator solution, 0.1 wt-% concentration. Dissolve 0.1 g of methyl orange in 100 mL ofwater.Salicylic acidSodium thiosulfate solution, 0.1-M. To prepare, dissolve 24.82 g of sodium thiosulfate (Na2S2O3 5H2O)in 200 mL of warm water. Quantitatively transfer to a one-liter volumetric flask, coo
11、l, and dilute tovolume with water. Standardize in any acceptable fashion such as by the iodine or arsenious oxidetechnique.Starch, arrowroot, Leco Corp., Cat. No. 051-061, or equivalentStarch solution. Stir with a glass rod while slowly adding 0.25 g of starch to 10 mL of water in a 100-mLbeaker. Qu
12、antitatively transfer the resulting solution to a 100-mL volumetric flask containing 60-70mL of hot, 100 C, water. Swirl the flask to mix. Add 0.12 g of salicylic acid, predissolved in 5 mL ofwarm water, to the flask as a preservative. Cool the flask and contents to room temperature and diluteto vol
13、ume with water. A fresh solution must be prepared if a mold appears or when a definite bluecolor is not obtained with iodine solution.PROCEDUREArrange the apparatus in an efficient hood. Hydrogen sulfide is an extremely poisonous gas. Pipet 10 mLof the lean amine sample into a 250-mL Erlenmeyer flas
14、k containing boiling chips. Dilute to a volume of75-100 mL with water. Place the flask and contents on a hot plate and carefully boil at a slow rate. Makeadditions of water, as required, to keep the volume greater than 25 mL. Occasionally test the vapors withmoist lead acetate paper until no darkeni
15、ng of the paper is observed, thereby indicating that the hydrogensulfide has been removed. Continue boiling the solution 15 minutes longer.Cool the flask and contents to room temperature and adjust the volume to 100 mL with water. Place amagnetic stirring bar in the flask and place on magnetic stirr
16、er. Pipet one milliliter of concentratedhydrochloric acid into the flask and turn on the magnetic stirrer. Add a measured excess of the standardizediodine solution to the flask from either a buret or pipet. The volume of iodine solution added will varydepending upon the thiosulfate content of the am
17、ine solution. It should be enough to require at least a 10mL back titration with the sodium thiosulfate solution.3 of 3818-81If the acidified sample is not darkly colored before the addition of the iodine solution, titrate with thestandard sodium thiosulfate solution until the sample-solution is alm
18、ost colorless, then add 2 mL of starchindicator solution and continue the titration until the sample-solution is colorless. If the acidified samplewas colored, add starch immediately and titrate with the standard sodium thiosulfate solution until the bluecolor disappears. Test the sample-solution wi
19、th methyl orange indicator to verify that the solution wassufficiently acid. If the solution is not acid (red colored), repeat the analysis but this time add 25% moreconcentrated hydrochloric acid.CALCULATIONSCalculate the amount of thiosulfate contained in the amine sample as follows:IT2995(2A B )T
20、hiosulfate, as apparent H S, grains/galVMM=where:A = standard iodine solution added, mLB = standard sodium thiosulfate solution added, mLMI= molarity of the iodine solutionMT= molarity of the sodium thiosulfate solutionV = sample volume, mLThe thiosulfate concentration may also be expressed as follo
21、ws:Sodium thiosulfate, g/100 mL = 0.0159 T0.0159 T Sodium thiosulfate, wt-%S=where:S = specific gravity of lean amine sample, g/mLT = thiosulfate, as apparent H2S, grains/galPRECISIONInsufficient data are available to calculate an esd with at least 4 degrees of freedom. It is estimated thatduplicate analyses should agree within 25 grains/gallon.TIME FOR ANALYSISThe elapsed time for one analysis is approximately 1 hour. The labor requirement is 1 hour.REFERENCEGirdler Method SM-3, The Girdler Corp., Louisville, KYSUGGESTED SUPPLIERLeco Corp., 300 Lakeview Ave., St. Joseph, MI 49085
