1、 IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TO DETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH AND SAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE IN THE MANNER PRESCRIB
2、ED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS (MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT1969, 1986, 2011 UOP LLC. All rights re
3、served. Nonconfidential UOP Methods are available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959, USA. The UOP Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service at serviceastm.org, 610.832.9555 FAX, or 6
4、10.832.9585 PHONE. Sulfide in Refinery Waste Water UOP Method 683-11 Scope This method is for determining the sulfide content in refinery waste water using cadmium chloride. The range of quantitation is from 1 mg/kg (mass-ppm) to 2 mass-% as sulfur. It is not applicable to caustic solutions. If pres
5、ent, polysulfides may interfere with the analysis. Reference UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method A known amount of representative sample is mixed with water containing a small amount of ammonium hydroxide. This solution is then titrated potentiometri
6、cally with standard cadmium chloride using a combination silver/glass Titrode electrode and the result calculated as mass-percent sulfur. Apparatus References to catalog numbers are included as a convenience to the method user. Other suppliers may be used. Balance, readability 0.0001 g Beakers, 100-
7、 and 250-mL, VWR, Cat. Nos. 89000-200 and -204, respectively Beaker, electrolytic, 250-mL, Metrohm USA, Cat. No. 020212209 Bottle, Boston round, 120 mL, VWR, Cat. No. 16152-427 (for prepared sodium sulfide solution) Bottle, wash, 250-mL, VWR, Cat. No. 16551-573 Cylinder, graduated, Class B, 100-mL,
8、VWR, Cat. No. 89000-270 Desiccator, 160-mm ID, and porcelain plate, VWR, Cat. Nos. 25035-005 and 89038-068, respectively Dish, evaporating, nominally 60-mm diameter, VWR, Cat. No. 89038-076 Electrode, combination silver/glass Titrode 6.0430.100, Brinkmann Instruments, Cat. No. 020948507, available f
9、rom Metrohm USA. The electrode should be dedicated to sulfur analysis. 2 of 6 683-11 Flask, volumetric, Class A, 1000-mL, VWR, Cat. No. 89090-710 Oven, drying, capable of operation at 105C, Fisher Scientific, Cat. No. 13-245-506G Pipets, volumetric transfer, Class A, 1 and 100-mL, VWR, Cat. Nos. 890
10、45-056 and -088, respectively Refrigerator, flammable-materials storage, Fisher Scientific, Cat. No. 97-938-1 Spatula, micro, Fisher Scientific, Cat. No. 21-401-15 Stirrer, magnetic, VWR, Cat. No. 12365-380, with stir bar, VWR, Cat. No. 858948-230 Titrator, potentiometric, recording, 2000 mV range,
11、1-mV resolution, capable of reducing the titration rate to a minimum in the vicinity of the endpoint, with dispenser having a volume readout of 0.00-99.99 mL and 0.0005 of the buret volume resolution, Metrohm, Model 904 Titrando with optional sample changer, and 20-mL buret, Methrohm USA. A second b
12、uret is required, Cat. No. 6.3026.220. Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Unless otherwise specified, references to water mean deionized or distilled water. Ammonium hydroxide, concentrated
13、, certified ACS Plus grade, Fisher Scientific, Cat. No. A669-212 Cadmium chloride, anhydrous, primary standard, Sigma-Aldrich, Cat. No. 438900, or equivalent. Oven dry 5 g in an evaporating dish for eight hours at 105oC; cool and store in a desiccator. CAUTION: Cadmium is a known carcinogen. All ope
14、rations involving its use must be performed in a properly ventilated area while wearing appropriate personal protective equipment. Cleaning pad, synthetic, mildly abrasive, Scotch-Brite, Runco Office Supply, Cat. No. MMM-96 Desiccant, indicating Drierite, 8-mesh, Fisher Scientific, Cat. No. AC21905-
15、0020 Hydrochloric acid, concentrated, certified ACS plus grade, Fisher Scientific, Cat. No. A144212 2-Propanol, 99% minimum purity, Fisher Scientific, Cat. No. A451-4 Silver nitrate, 0.1-M solution, Fisher Scientific, Cat. No. SS72-4 Silver nitrate, 0.01-M alcoholic solution. Pipet 100 ml of 0.1-M s
16、ilver nitrate solution into a 1000-mL volumetric flask. Dilute to the mark with 2-propanol, cap and invert several times to mix thoroughly. When capped, this solution is stable for two months at room temperature, after which a new solution is prepared. Sodium sulfide, anhydrous, Sigma-Aldrich, Cat.
17、No. 407410 Sodium sulfide, 1-% solution. In a 250-mL beaker, dissolve 1.00 g 0.01 g of sodium sulfide in 100 mL of water. Store in a 120-mL bottle. This solution is stable for two months under refrigeration. Water, deionized or distilled Wiper, Kimwipes Ex-L, VWR, Cat. No. 21905-026 3 of 6 683-11 Pr
18、ocedure The analyst is expected to be familiar with general laboratory practices, the technique of titration, and the equipment being used. Dispose of used reagents, materials, and samples in an environmentally safe manner according to local regulations. Preparation of Cadmium Chloride Solutions For
19、 the purpose of this method, anhydrous cadmium chloride is considered to be a primary standard. Care should be taken to protect the solid reagent from excess exposure to air. Prepare a solution of approximately 0.010-M cadmium chloride as follows: 2. Weigh 1.83 g 0.01 g, to the nearest 0.0001 g, of
20、dried anhydrous cadmium chloride into a clean dry 100-mL beaker. 3. Quantitatively transfer with water the contents of the beaker to a 1000-mL volumetric flask. 4. By pipet, add 1 mL of concentrated hydrochloric acid and make up to volume with water. Discard after two months or if the solution becom
21、es cloudy or a precipitate forms. Prepare a solution of approximately 0.025-M cadmium chloride as follows: 1. Weigh 4.60 g 0.01 g, to the nearest 0.0001 g, of dried anhydrous cadmium chloride into a clean dry 100-mL beaker. 2. Quantitatively transfer with water the contents of the beaker to a 1000-m
22、L volumetric flask. 3. By pipet, add 1 mL of concentrated hydrochloric acid and make up to volume with water. Discard after two months or if the solution becomes cloudy or a precipitate forms. Calculate the exact molarity of the titrants prepared, using the Equation 1: M = 31.183W (1) where: M = mol
23、arity of the cadmium chloride solution W = mass of dried cadmium chloride, g 183.31 = molecular weight of cadmium chloride, g/mole, multiplied by one liter Electrode Preparation and Reconditioning Proper electrode preparation is essential to obtain reproducible and noise-free titration curves having
24、 good endpoints. The electrode should be reconditioned on a weekly basis when in use, and should be reconditioned if it is used for any titrations other than sulfur compounds. It is recommended that an electrode be dedicated to sulfur analysis. Prepare and recondition the silver-silver sulfide elect
25、rode as follows: 1. Clean the silver surface with a cleaning pad. Rinse with water and dry with a wiper. 2. Immerse the electrode in a solution consisting of 2 mL of concentrated ammonium hydroxide, 90 mL of 2-propanol, and 8 mL of the aqueous sodium sulfide solution. Add a stir bar. 3. Slowly add a
26、pproximately 10 ml of 0.01-N alcoholic silver nitrate solution over a period of 10 minutes while stirring at a moderate speed. A film of silver sulfide will be deposited on the silver electrode. 4. Wipe off the excess silver sulfide from the electrode with a wiper. The electrode should be cleaned af
27、ter each titration by rinsing with water. 4 of 6 683-11 Determination of Sulfide emf Inflection Point 1. Assemble and operate the titrator and the electrode according to the manufacturers instructions. 2. Fill the dispenser reservoir of the titrator with the 0.025-M cadmium chloride solution. 3. Usi
28、ng a pipet, transfer 1 mL of 1-% sodium sulfide solution into a 250-mL beaker. Add 100 mL of water by graduated cylinder. Add a stir bar. 4. Place the beaker on the titration stand, immerse the electrodes and buret tip, and stir. If using the automatic sample changer, place the beaker in the rack an
29、d start the program. Obtain a stable reading before proceeding to Step 5. If using sample changer, this is part of the program 5. Titrate the sodium sulfide solution using the 0.025-M cadmium chloride. Determine the emf of sulfide at the inflection point of the titration curve. If more than one infl
30、ection occurs, the sulfide inflection is defined as the one occurring at approximately the established sulfide emf value. Confirm the sulfide emf inflection point periodically or when operating parameters or equipment such as electrodes and titrator are changed. A typical titration curve is shown in
31、 the Figure. Figure Typical Titration Curve Sample Analysis 1. Prepare the titrator and the electrode for operation according to the manufacturers instructions. 2. Weigh into a tared beaker, to the nearest 0.0001 g, a mass of sample appropriate to the expected sulfur concentration, see Table 1. The
32、volume of titrant to be used should be 5 mL or greater. 3. Add water, if needed, see Table 1. Using a pipet, add 1 mL of concentrated ammonium hydroxide to the beaker. Add a stir bar. If the expected sulfide concentration is low, less than 10 ppm, direct titration of waste water is recommended witho
33、ut additional water, see Table 1. 5 of 6 683-11 If the expected sulfide concentration is not known, analyze as though the sample concentration is 1000 mg/kg. Once an estimated concentration is obtained, reanalyze the sample, if necessary, using the recommended conditions in Table 1. Table 1 Recommen
34、ded Sample Mass and Titrant Concentration in Accordance with Expected Sulfur Concentration Expected S concentration, mg/kg Recommended sample mass, g Water added, mL Molarity of titrant, M 1-10 150 0 0.010 10-50 100 50 0.010 50-100 50 50 0.025 100-1000 10 100 0.025 1000 4 100 0.025 4. Set the beaker
35、 containing the sample on the titrator stand, insert the electrode and disperser tip, and stir. 5. Select either the 0.010-M or 0.025-M, see Table 1, cadmium chloride solution for titrating. Start the titration, observe the inflections, and record the corresponding volume of titrant dispensed. If mo
36、re than one inflection occurs, use the emf determined in Determination of Sulfide emf Inflection Point to define the sulfide inflection and the corresponding volume. Calculations Calculate the concentration of sulfide as sulfur using Equation 2. Report the result to the nearest mg/kg. Note, the resu
37、lts are good to only two significant figures, see Precision. Sulfide, as sulfur, mg/kg = S MV32065 (2) where: M = molarity of the cadmium chloride solution S = sample mass, g V = volume of cadmium chloride used to reach endpoint, mL 32065 = 361010065.32 (2a) where: 32.065 = molecular weight of sulfu
38、r 103 = conversion of mL to L 106 = factor for mg/kg If the result exceeds 10,000 mg/kg, divide the result by 10,000 and report as mass-% to the nearest 0.01 mass-% Precision Precision statements were determined using UOP Method 999, “Precision Statements in UOP Methods.” Repeatability and Site Prec
39、ision A nested design was carried out for determining sulfide on three samples by two analysts, with each 6 of 6 683-11 analyst performing analyses on two separate days, performing two analyses each day for a total of 24 analyses. Using a stepwise analysis of variance procedure, the within-day estim
40、ated standard deviations (esd) were calculated at the concentration means listed in Table 2. Two analyses performed in one laboratory by the same analyst on the same day should not differ by more than the repeatability allowable differences shown in Table 2 with 95% confidence. Two analyses performe
41、d in one laboratory by different analysts on different days should not differ by more than the site precision allowable differences shown in Table 2 with 95% confidence. Table 2 Repeatability and Site Precision, mg/kg Repeatability Site Precision Sample Mean Within- Day esd Allowable Difference With
42、in- Lab esd Allowable Difference A 7 0.1 1 0.5 2 B 890 6.8 27 8.8 54 C 9436 87.6 344 122.7 552 The data in Table 2 represent short-term estimates of the repeatability of the method. When the test is run routinely, use of a control standard and a control chart is recommended to generate an estimate o
43、f long-term repeatability. Reproducibility There is insufficient data to calculate the reproducibility of the test at this time. Time for Analysis The elapsed time and the labor requirement is 0.4 hour. Suggested Suppliers Fisher Scientific, 711 Forbes Ave., Pittsburgh, PA 15219-4785, USA (412-490-8
44、300) Metrohm USA, 6555 Pelican Creek Circle, Riverview, FL 33578, USA (813-316-4700) Runco Office Supply, 1655 Elmhurst Road, Elk Grove Village, IL 60007, USA (847-437-4300) Sigma-Aldrich, Milwaukee, WI 53201, USA (414-438-3850) www.sigma- VWR International, 1310 Goshen Parkway, West Chester, PA 19380 (610-431-1700)
