UOP 202-2014 Disulfide Sulfur in Light Petroleum Distillates and LPG.pdf

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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. SAFETY DATA SHEETS (SDS) OR EXPERIMENTAL SAFETY DATA SHEETS (ESDS) FOR ALL OF THE MATERIALS USED IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). COPYRIGHT 1967, 1998, 2000, 2014 UOP LLC. All rights reserved. Nonco

3、nfidential 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 610.832.9585 P

4、HONE. Disulfide Sulfur in Light Petroleum Distillates and LPG UOP Method 202-14 Scope This method is for determining disulfide sulfur in gasoline, liquefied petroleum gas (LPG), and other light petroleum distillates. Part A of the method, an acid stirring procedure, is used for low molecular weight

5、disulfides usually found in LPG and for distillates that do not contain tertiary disulfides. Because of its rapidity, the acid stirring procedure is recommended for routine work where tertiary disulfides are not a factor. Part B of the method, an acid reflux procedure, is reserved for samples contai

6、ning tertiary disulfides. This method is applicable to samples containing a disulfide sulfur concentration of 10 mass-ppm or greater. References ASTM Method D4052, “Density and Relative Density of Liquids by Digital Density Meter,” www.astm.org Hubbard, R.L., Haines, W.E., and Ball, J.S., Anal. Chem

7、., 30, (1958) UOP Method 163, “Hydrogen Sulfide and Mercaptan Sulfur in Liquid Hydrocarbons,” www.astm.org UOP Method 516, “Sampling and Handling of Gasolines, Distillate Fuels, and C3-C4 Fractions,” www.astm.org UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method P

8、art A - Acid Stirring Procedure The mercaptan sulfur content of the sample is first determined by a potentiometric titration with silver nitrate, according to UOP Method 163, “Hydrogen Sulfide and Mercaptan Sulfur in Liquid Hydrocarbons.” The disulfides in the sample are reduced to mercaptans with z

9、inc metal and acetic acid in methanol by stirring at room temperature for 30 minutes. Then the mixture is decanted and filtered quickly into a titration beaker. The reaction flask and filter paper are washed with titration solvent and the washings are added to the titration beaker. This is followed

10、by a potentiometric titration of the solution with alcoholic silver nitrate. The mercaptan sulfur titrated is equal to the original mercaptan present plus the mercaptan sulfur resulting from the reduction of the disulfides. The 2 of 10 202-14 disulfide sulfur present in the sample is determined from

11、 the difference between the mercaptan sulfur content before and after reduction. Part B - Acid Reflux Procedure The mercaptan sulfur content of the sample is first determined by a potentiometric titration with silver nitrate, according to UOP Method 163. The disulfides in the sample are reduced to m

12、ercaptans by refluxing in the presence of acetic acid and zinc in a reaction flask. Part of the mercaptans are vaporized, and are carried from the reaction flask with nitrogen and collected into a potassium hydroxide solution for a subsequent potentiometric titration with alcoholic silver nitrate. A

13、n aliquot is taken from the liquid in the reaction flask and is also titrated potentiometrically with silver nitrate. The mercaptan sulfur titrated is equal to the original mercaptan present plus the mercaptan sulfur resulting from the reduction of the disulfides. The disulfide sulfur present in the

14、 sample is determined from the difference between the mercaptan sulfur content before and after reduction. Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. In addition to the equipment listed below, the apparatus spe

15、cified in UOP Method 163 is also required for this method. For LPG samples, the apparatus specified in UOP Method 516, “Sampling and Handling of Gasolines, Distillate Fuels, and C3-C4 Fractions,” is also required. Balance, 5-kg maximum capacity, readable to 0.5 g Balance, readable to 0.0001 g Beaker

16、s, tall form, 300-mL, Fisher Scientific, Cat. No. 10-310-8 Boiling flask, 1000-mL, round bottom, center neck with 24/40 standard taper female joint, side neck 19/38 standard taper female joint; fitted with an inlet tube extending to the bottom of the flask for nitrogen purging, Kimble Chase Kontes,

17、Cat. Nos. 605020-1419 and 479101-0000, respectively Bottle, gas-washing, 250-mL, with a coarse fritted glass cylinder, Fisher Scientific, Cat. No. 03-040B Condenser, Allihn, reflux, with 24/40 standard taper male joint to fit boiling flask, Kimble Chase Kontes, No.:431000-2430, Fisher Scientific, Ca

18、t. No. K431000-2430 Connector, with a 24/40 standard taper connector on one end, and a hose connector on other end, for top of condenser, Sigma-Aldrich, Cat. No. Z11,908-3 Desiccator, glass, Fisher Scientific, Cat. No. 08-595D Dry ice condenser trap, Sigma-Aldrich, Cat. No. Z15,426-1 Electrode, comb

19、ination glass/silver Titrode, Metrohm, Cat. No. 20948507. This electrode should be dedicated to sulfur analysis. Flasks, Erlenmeyer, 125- and 250-mL, glass-stoppered, Fisher Scientific, Cat. Nos. 10-100D and 10-100E, respectively Flasks, volumetric, 100- and 1000-mL, Fisher Scientific, Cat. Nos. 10-

20、209D and 10-209H, respectively, several of each required 3 of 10 202-14 Flow meter, capable of measuring gas flow in the 100- to 200-mL/min range, Sigma-Aldrich, Cat. No. 20432 Funnels, glass, short-stem, Fisher Scientific, Cat. No. 10-322D, several required Heating mantle, 1000-mL, Fisher Scientifi

21、c, Cat. No. 11-473-22 Oven, laboratory drying Pans, to hold water ice bath and dry ice bath Pipets, volumetric, Class A, 1-, 2-, 5-, 10-, 50-, and 100-mL, Fisher Scientific, Cat. Nos. 13-650-2B, -2C, -2F, -2L, -2S, and -2U, respectively Regulator, nitrogen, two-stage, high purity, Matheson Tri-Gas,

22、Model 3122-580 Scotchbrite abrasive cleaning pads, or equivalent, local supply Stirrer, magnetic, Fisher Scientific, Cat. No. 11-300-49S Stirring bar, magnetic, Teflon-covered, 8-mm x 32-mm (5/16-inch x 1.25-inch), Fisher Scientific, Cat. No. 14-511-94 Titrator, potentiometric, recording, 2000-mV ra

23、nge, 1-mV resolution with a dispenser having a volume readout of 0.00 to 20.00 mL and 0.01% resolution, Titrando, Metrohm, Cat. No. 29040020 Tube, stainless steel, 3.2-mm (1/8-inch) OD x 300-mm (12-inch) long, local supply Valve, needle, to fit LPG sample cylinders, local supply Reagents and Materia

24、ls References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. References to water mean deionized or distilled water. In addition to the reagents and materials listed below, the reagents and materials specified in UOP Method 163 are also

25、 required for this method. For LPG samples, the reagents and materials specified in UOP Method 516 are also required. Acetic acid, glacial, Fisher Scientific, Cat. No. A38-212 Acetone, Fisher Scientific, Cat. No. A18-4 Ammonium hydroxide, concentrated, Fisher Scientific, Cat. No. A669-212 Calcium su

26、lfate, anhydrous, Drierite, 4-mesh, Fisher Scientific, Cat. No. 07-577-1B Chelating solution, a solution of chelating agents found effective in reducing the deterioration of sulfides and mercaptides in caustic solutions. The recommended usage is 2 mL/100 mL of caustic solution. This chelating soluti

27、on is made up from the constituent chemicals: Diethylenetriamine pentaacetic acid, sodium salt (Na5DTPA), 40% aqueous solution, Acros Organics, Fisher Scientific, Cat. No. 40729-0010 Diethylenetriamine pentaacetic acid, sodium salt, 20 mass-% solution. Dilute diethylene-triamine pentaacetic acid, so

28、dium salt, 40% aqueous solution, with water to make a 20 mass-% solution. N-(2-hydroxyethyl) ethylenediaminetriacetic acid, sodium salt, (Na3HODTA), Sigma-Aldrich, Cat. No. 16,153-5, or Acros Organics, Fisher Scientific, Cat. No. 34870-0010 4 of 10 202-14 N-(2-hydroxyethyl) ethylenediaminetriacetic

29、acid, sodium salt, 20 mass-% solution. Dissolve N-(2-hydroxyethyl) ethylenediaminetriacetic acid, sodium salt, in water to make a 20 mass-% solution. Ethylenediaminetetraacetic acid, sodium salt (Na4EDTA), Sigma-Aldrich, Cat. No. E2,629-0, or, Acros Organics, Fisher Scientific, Cat. No. 14786-5000 N

30、,N-bis(2-hydroxyethyl)glycine (Bicine), Sigma-Aldrich, Cat. No. 16,379-1, or, Acros Organics, Fisher Scientific, Cat. No. 17265-1000 Mix 1:1 by weight ethylenediaminetetraacetic acid, sodium salt, and N,N-bis(2-hydroxyethyl) glycine. Dissolve in water to make a 20 mass-% solution. Mix equal volumes

31、of each of the three 20 mass-% solutions to make the final chelating solution. Congo red, indicator test paper, Fisher Scientific, Cat. No. 14-861 Dry ice, crushed Filter paper, coarse, 110-mm, Whatman 41, Fisher Scientific, Cat. No. 09-850C Isooctane, pesticide grade, Fisher Scientific, Cat. No. O2

32、97-4 Methanol, certified ACS grade, Fisher Scientific, Cat. No. A412-4 Nitrogen, high purity, local supply Potassium chloride, primary standard. NIST Standard Reference Material 999b. Before each use, oven dry at 105C for 2.5 hours and cool in a desiccator. Potassium hydroxide, 10 % (mass/vol), 1-L,

33、 Fisher Scientific, Cat. No. 50-823-5157 Potassium hydroxide-chelating solution. Add 10.0 0.1 g of the chelating solution mixture (see below) directly to the 1-L bottle of 10% potassium hydroxide, cap and invert several times to thoroughly mix. 2-Propanol, certified ACS grade, Fisher Scientific, Cat

34、. No. A416-4 Silver nitrate concentrate, Fisher certified grade, Fisher Scientific, Cat. No. SS73 Silver nitrate, alcoholic solution, nominally 0.1N. Quantitatively transfer the silver nitrate concentrate to a 1000-mL volumetric flask using several washes of 2-propanol. Fill to the mark with 2-propa

35、nol, cap and invert several times to thoroughly mix the contents. Standardize this solution following the stepwise instructions in Procedure. Mark the actual normality thus determined on the volumetric flask. Silver nitrate, alcoholic solution, nominally 0.01N. Pipet 100 mL of the nominally 0.1-N al

36、coholic silver nitrate solution into a 1000-mL volumetric flask. Add 80 mL of water to the flask. Fill to the mark with 2-propanol, cap and invert several times to thoroughly mix the contents. The normality of this solution will be exactly one-tenth the normality of the nominally 0.1-N alcoholic sil

37、ver nitrate solution as determined in Procedure. Mark this actual normality on the volumetric flask. Sodium sulfide, 9-hydrate, Fisher Scientific, Cat. No. S425-500 Sodium sulfide, 1% solution. Dissolve 1.0 g + 1.0 mg of sodium sulfide in 100 mL of water. Sulfuric acid, concentrated, Fisher Scientif

38、ic, Cat. No. A300-212 Sulfuric acid, dilute. Prepare by mixing equal volumes of concentrated sulfuric acid and water. 5 of 10 202-14 Titration solvent, oxygen free. Purge a freshly opened bottle of 2-propanol with nitrogen for 30 minutes. Add 1% by volume of concentrated ammonium hydroxide. Store un

39、der nitrogen. Tubing, plastic, appropriate size to connect pieces of acid reflux apparatus Water, deionized or distilled Water ice Water, tap Wipers, Kimwipes Ex-L, VWR, Cat. No. 21905-026 Zinc, powder, Fisher certified grade, Fisher Scientific, Cat. No. Z5-500 Zinc, granular, 20-mesh, certified ACS

40、 grade, Fisher Scientific, Cat. No. Z15-500 Procedure The analyst is expected to be familiar with general laboratory procedures, the technique of titration, and the equipment being used. Dispose of used supplies and samples in an environmentally safe manner according to local regulations. Electrode

41、Preparation and Reconditioning Proper electrode preparation is essential to obtain reproducible and noise-free titration curves having 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 c

42、ompounds. It is recommended that an electrode be dedicated to sulfur analysis. Prepare and recondition the silver-silver sulfide electrode as follows: 1. Clean the silver surface with a Scotchbrite pad. Rinse with water and dry. 2. Immerse the electrodes in a solution containing 90 mL of 2-propanol,

43、 2 mL of ammonium hydroxide and 8 mL of 1% sodium sulfide solution. 3. Slowly titrate approximately 10 mL of 0.1N 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 the excess silver sulf

44、ide from the electrode with a wiper or a soft paper towel. The electrode should be cleaned after each titration by rinsing with water. LPG Sample Preparation 1. Obtain a sample of LPG from the process sampling point by following the instructions in UOP Method 516, including the cleaning of the 1000-

45、mL cylinder, and transport it to the laboratory. Trace sulfur applications require the use of a specially coated cylinder as described in UOP Method 516. 2. Connect a needle valve to the LPG cylinder and attach an approximately 300-mm length of 3.2-mm (1/8-inch) tubing to the outlet of the needle va

46、lve. 3. Weigh the sample cylinder to the nearest 0.5 g. 4. Add 75 mL of isooctane to a 250-mL Erlenmeyer flask. 5. Place the flask into a pan containing crushed dry ice in a hood and ground the sample cylinder and pan by attaching a length of copper wire from the valve and pan to a metal water outle

47、t in 6 of 10 202-14 the hood. If the water pipes are not metal, establish a connection to another suitable ground. 6. Position the cylinder such that liquid will be withdrawn through the attached valve and that the outlet of the tubing is placed below the surface of the isooctane. Direct, slowly and

48、 carefully, a flow of LPG from the cylinder into the flask. Take approximately 200 g of sample and swirl to mix. The flow may be stopped and restarted several times to control the boiling of the LPG. 7. Reweigh the cylinder to the nearest 0.5 g to determine the actual sample size taken. 8. Allow the

49、 LPG to boil off at room temperature in a fume hood. 9. Transfer the isooctane now containing the disulfides (they do not evaporate under these conditions) from the flask to a 100-mL volumetric flask. This method is not appropriate for quantitation of mercaptans in LPG. 10. Wash the Erlenmeyer flask with 20 mL of isooctane and add the washings to the volumetric flask. 11. Dilute to the mark with isooctane. Cap and invert the flask several times to ensure proper mixing. This solution is hereafter referred to as the LPG-isooctane concentrate. 12. Proceed to Sample Analysis, Pa