1、APPARENT HYDROGEN SULFIDE IN AMINE SOLUTIONSUOP Method 827-81SCOPEA Control and a Precision method are used for the determination of apparent hydrogen sulfide in aminesolutions. Hydrogen sulfide is determined by oxidation with standard iodine solution in an acid medium.Thiosulfate, if present, is al
2、so titrated and is included as apparent H2S in the calculation. Thiosulfate may bedetermined by using UOP Method 818, and the value thus obtained subtracted from the apparent H2Sconcentration. The lower limit of detection is approximately 25 grains/gallon.OUTLINE OF METHODControl MethodFor plant con
3、trol work with lean amine solutions containing low levels of hydrogen sulfide, a directtitration method may be used. A portion of the amine sample is pipeted into water, acidified with HCl, andimmediately titrated with a standard iodine solution using starch solution as the indicator.Precision Metho
4、dFor solutions containing more than 100 grains of H2S per gallon, or where better precision is required, aportion of the amine sample is pipeted into an acidified water solution containing an excess of standardiodine solution. The excess iodine is back titrated with standard sodium thiosulfate solut
5、ion using starchsolution as the indicator.APPARATUSBalance, torsion or top loading type, 500 g capacity, capable of weighing to 0.01 gBeakers, 100- and 250-mLBuret, 50-mL (2 required) with Teflon stopcock, 0.1-mL subdivisionsCylinder, graduated, 50-mL, glass, 1.0-mL subdivisionsFlask, Erlenmeyer, 25
6、0-mLFlask, volumetric, one-liter (2 required)IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH ANDSAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTI
7、LIZE 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 THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE). COPYRIGHT
8、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 by contacting Customer Service atserviceastm.org, 610.832.955
9、5 FAX, or 610.832.9585 PHONE.2 of 4827-81Flask, volumetric, 100-mLHot plate, adjustable heat, Sargent-Welch Scientific Co., Cat. No. S-41000A, or equivalentPipet manipulator, Sargent-Welch Scientific Co., Cat. No. S-69793, or equivalentPipets, serological, calibrated for blow-out, 1-, 5- and 10-mL c
10、apacity, Sargent-Welch Scientific Co., Cat.Nos. S-69625-C, G and H, or equivalentStirrer, magnetic, with Teflon covered stirring bar, Sargent-Welch Scientific Co., Cat. No. S-76490, orequivalentREAGENTSAll reagents shall conform to the specifications established by the Committee on Analytical Reagen
11、ts ofthe American Chemical Society, when such specifications are available, unless otherwise specified.References to water mean deionized or distilled water.Hydrochloric acid, concentratedIodine solution, 0.05 M. To prepare, dissolve 25 g of potassium iodide in 200 mL of water. Warm slightlyto disso
12、lve. Cool and add 12.69 g of iodine crystals. Stir the solution to dissolve the reagents andtransfer quantitatively to a one-liter volumetric flask. Dilute to volume with water. Store in an amberbottle. Standardize against the 0.1 M sodium thiosulfate. If samples are analyzed infrequently, theiodine
13、 solution must be standardized prior to use.Methyl orange 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) in200 mL of warm water. Quantita
14、tively transfer to a one-liter volumetric flask, cool, and dilute tovolume with water. Standardize in any acceptable fashion such as by the iodine or arsenious oxidetechnique.Starch, arrowroot, Leco Corp., Cat. No. 501-061, or equivalentStarch solution. Stir with a glass rod while slowly adding 0.25
15、 g of starch to 10 mL of water in a 100-mLbeaker. Quantitatively transfer the resulting solution to a 100-mL volumetric flask containing 60-70mL of hot, 95-100 C, water. Swirl the flask to mix. Add 0.12 g of salicylic acid, predissolved in 5 mLof warm water, to the flask as a preservative. Cool the
16、flask and contents to room temperature anddilute to volume with water. A fresh solution must be prepared if a mold appears or when a definiteblue color is not obtained with iodine solution.PROCEDUREArrange the apparatus in an efficient hood to avoid any hazard from the evolution of gaseous H2S.Deter
17、mine the amount of sample to be taken for analysis from the following table:3 of 4827-81Apparent H2Sconcentration expected inthe sample, grains/gallonSample size,mL 100 1.0 100 5.0-10.0Control MethodPipet the appropriate size sample into a 250-mL Erlenmeyer flask containing a magnetic stirring bar a
18、nd100 mL of water. With viscous samples, rinse the pipet with water and add the rinsings into the flask. Pipeta volume of concentrated HCl, equal to the sample size taken, into the flask. Add approximately 2 mL ofstarch indicator solution. Turn on the magnetic stirrer and titrate immediately with st
19、andard 0.05 M iodinesolution until a deep-blue color persists.Precision MethodTo a 250-mL Erlenmeyer flask containing a magnetic stirring bar, add 50 mL of water and 25 mL ofstandard iodine solution (measured to the nearest 0.1 mL from the iodine buret). Add a volume ofconcentrated HCl to the flask
20、equal to the volume of amine solution to be taken (see Notes 1, 2 and 3). Turnon the magnetic stirrer and pipet the amine sample into the flask. With viscous samples, rinse the pipet withwater and add the rinsing into the flask.If the acidified sample is not darkly colored before the addition of the
21、 iodine solution, titrate with thestandard sodium thiosulfate solution until the sample-solution is almost colorless, then add 2 mL of starchindicator solution and continue the titration until the sample-solution is colorless. If the acidified sample iscolored, add starch immediately and titrate wit
22、h the standard sodium thiosulfate solution until the blue colordisappears. Test the sample-solution with methyl orange indicator to verify that the solution is sufficientlyacid. If the solution is not acid (red colored), repeat the analysis but this time add 25% more concentratedhydrochloric acid (s
23、ee Note 3).CALCULATIONSCalculate the concentration of apparent hydrogen sulfide in the sample solution as follows:Control Method121991 AApparent H S, grains/gallon VM=where:A = standard iodine solution added, mLM1= molarity of the iodine solutionV = sample volume, mLPrecision Method1221991 (A 0.5B )
24、Apparent H S, grains/gallon VMM=4 of 4827-81where:B = standard sodium thiosulfate solution, mLM2= molarity of the sodium thiosulfate solutionA, M1and V are as previously definedThe apparent hydrogen sulfide concentration in grains/gallon may be converted to volumes of hydrogensulfide, as a dry gas a
25、t 15.6 C (60 F) and 101.3 kPa (760 mm), to volume of solution by dividing by 84.The apparent hydrogen sulfide concentration may be converted to wt-ppm as follows:217CApparent H S, wt - ppm S=where:C = apparent H2S content, grains/gallonS = specific gravity of sample, 60/60 F (15.6/15.6 C)NOTES1. The
26、 volume of standard iodine solution is varied with the hydrogen sulfide content of the aminesolution sample. Sufficient iodine solution should be taken so that about 10 mL of standard sodiumthiosulfate solution are required for back titration.2. When the amine sample solution is concentrated and vis
27、cous, it is preferable to pipet the sample into anErlenmeyer flask, containing 50 mL of water. Rinse the pipet with water into the flask. The diluted sampleis then mixed with the acidified iodine solution. This procedure prevents the local neutralization of theiodine by strong amine solution.3. Free
28、 amine reacts quite rapidly with iodine solution and it is, therefore, necessary that the aminesolution come in contact with the iodine only in the presence of excess acid.PRECISIONAn estimated standard deviation is not reported since insufficient data are available at present to permitthis calculat
29、ion with at least 4 degrees of freedom. It is estimated that duplicate analyses should agreewithin 25 grains/gallon for both the control and precision methods.TIME FOR ANALYSISThe elapsed time for one analysis is 1.0 hour. The labor requirement is 0.5 hour.REFERENCESMethod SM-6, The Girdler Corp., Louisville, KYSUGGESTED SUPPLIERSLeco Corp., 300 Lakeview Ave., St. Joseph, MI 49085Sargent-Welch Scientific Co., 7300 N. Linder Ave., Skokie, IL 60076
