UOP 481-2010 Water in Liquid Hydrocarbons and Heavy Hydrocarbons by Vaporizer using Coulometric Titration.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. 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). COPYRIGHT 1970, 1977, 1980, 1991, 2009, 2010 UOP

3、 LLC. All rights reserved. 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

4、.832.9555 FAX, or 610.832.9585 PHONE. Water in Liquid Hydrocarbons, and Heavy Hydrocarbons by Vaporizer, using Coulometric Titration UOP Method 481-10 Scope This method is for determining the water content of liquid hydrocarbons (naphtha, gasoline, kerosene, diesel), or other petroleum products (sul

5、folane and other solvents) that are liquid at room temperature using coulometric Karl Fisher titration. The lower limit of quantitation for the titrator is 10 g of water. This results in an applicable concentration range for a sample of 10 mg/kg (mass-ppm) to 2 mass-% water. Heavy hydrocarbons (inso

6、luble oils and waxes) and other hydrocarbons that are viscous or solid at room temperature can be accommodated using a vaporizer for determining dissolved trace water and is applicable to samples over a concentration range of 20 mg/kg to 2 mass-% water. Samples containing less than 500 mg/kg of wate

7、r can be collected in prepared dry bottles or syringes as described in the Appendix. Other applications for moisture and common interferences are discussed in Notes 1 and 2. References ASTM Method D1364, “Water in Volatile Solvents (Karl Fischer Reagent Titration Method),” www.astm.org ASTM Method D

8、6304, “Determination of Water in Petroleum Products, Lubricating Oils, and Additives by Coulometric Karl Fischer Titration,” www.astm.org UOP Method 163, “Hydrogen Sulfide and Mercaptan Sulfur in Liquid Hydrocarbons by Potentiometric Titration,” www.astm.org UOP Method 344, “Moisture in Hydrocarbon

9、Streams Using an On-Line Analyzer,” www.astm.org UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Outline of Method For liquid hydrocarbon samples, the sample is injected directly into a coulometric Karl Fischer titrator that determines micrograms of water. No standardization is r

10、equired since 96,000 coulombs is 2 of 13 481-10 equivalent to 1/2 mole of water. Once prepared, the instrument can be used for repeated sample titrations without additional reagents. The concentration of water in the sample is calculated using the mass of the sample injected. This technique is descr

11、ibed in Procedure, Part A. For heavy hydrocarbon samples, a head-space analysis that carries volatilized water from a sample in a dry nitrogen stream to a Karl Fischer titration cell is used. The titration of the water in the nitrogen carrier gas operates as described in Part A. This technique is de

12、scribed in Procedure, Part B. Samples containing less than 500 mg/kg water can be collected in prepared dry bottles or syringes. Dry bottle sampling is recommended since there is less opportunity for moisture contamination from the environment, and the integrity of the sample is preserved for a long

13、er period of time. Syringe sampling, although more convenient, can only be used if the analysis is to be completed within two hours. These techniques are described in the Appendix. Apparatus References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers

14、 may be used. Balance, readability 0.1-mg Beaker, 150-mL, VWR, Cat. No. 89000-202 Crimper, Cosa Instruments, Cat. No. VABH06 Desiccator, plastic, VWR, Cat. No. 24987-026 Hot plate / magnetic stirrer, VWR, Cat. No. 12365-452, includes PTFE-coated stir bar Pipets, volumetric transfer, Class A, 100-mL,

15、 VWR, Cat. No. 89045-088 Pipet filler, VWR, Cat. No. 53497-055 Regulator, nitrogen, two-stage, high purity, delivery pressure range 15-200 kPa (2-30 psi), Matheson, Model 3121-580 Syringe, glass, with PTFE plunger tip, 100-L, VWR, Cat. No. 60376-252 Titrator, coulometric-amperometric, designed to pe

16、rform titrations to pre-set endpoints with a polarizing current capable of maintaining approximately 1 V across two platinum electrodes and a sensitivity capable of indicating an endpoint based on a 50 mV change. The Mitsubishi, Model CA-200 with fritless cathode is satisfactory, Cosa Instruments, C

17、at. Nos. MC64917 and MC74917. Tweezers, VWR, Cat. No. 63042-970 Vaporizer, Model VA-230, Cosa Instruments Cat. No. MC64930 Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. References to water mean double

18、 deionized or triple distilled, unless otherwise specified. Acetone (2-propanone), 99.5% minimum purity, VWR, Cat. No. VW0330-3 Cleaning pad, synthetic, mild abrasive, Scotch-Brite, Runco Office Supply, Cat. No. MMM-96 Cleanser, mild abrasive, Comet, Runco Office Supply, Cat. No. PAG-02255 3 of 13 4

19、81-10 Crimp cap with septum, Cosa Instruments, Cat. No. VABH04 and VABH05, respectively Desiccant, 8-mesh, indicating, VWR, Cat. No. 22891-040 Hydrogen peroxide, 30%, VWR, Cat. No. VW3742-1 Karl Fischer reagent, Aquamicron FLS, Cosa Instrument, Cat. No. MC02032 (see Note 1) Nitrogen, 99.999% minimum

20、 purity Pipets, disposable transfer, VWR, Cat. No. 16001-188 Reference Standard (Part A), Hydranal Water Standard 0.10, Aldrich, Cat. No. 34847-40ML Reference Standard (Part B), Reference Material 8507 Mineral Oil, NIST Silicone rubber, nominally 10 x 10 x 5 mm blocks, Cosa Instrument, Cat. No. 0217

21、0, to stopper syringe needle tips Sulfuric acid, concentrated, 95-98%, VWR, Cat. No. VW6840-3 Syringes, disposable, all PP/PE, 3-, 5-, 10-, 20-, and 50-mL, VWR, Cat. Nos. 53548-002, -004, -006, -008, and -010, respectively, with needle, VWR, Cat. No. BD305187 Tissue, Kimwipes, VWR, Cat. No. 21905-02

22、6 Vials, Cosa Instruments, Cat No. VABH03 Water, double deionized or triple distilled Water, tap, warm Procedure The analyst is expected to be familiar with general laboratory practices, the technique of titration, and the equipment being used. Instrument Setup The instrument should be set up as per

23、 manufacturers specifications. General guidelines for operating conditions for the instrument referred to under Apparatus are shown in Tables 1 and 2. However, these conditions may be optimized to meet the users specific needs/requirements. Sampling Samples containing greater than 500 mg/kg water ca

24、n be collected in glass screw-cap containers without special precautions. If a liquid hydrocarbon sample is expected to contain less than 500 mg/kg, collect the sample as described in the Appendix. Electrode Preparation and Cell Conditioning Clean the double platinum electrode, initially and when th

25、e drift continues to exceed 0.15 g/s with fresh titration solvent using the following procedure: 1. Use a mild abrasive cleanser to prepare a “paste” with warm tap water. 2. Load a wiper or a cleaning pad with the paste. Polish the platinum tips of the detector electrode with the paste and wiper or

26、cleaning pad. 3. Rinse the residue off the electrode with warm tap water, then with deionized water. If required sensitivity is not achieved with cleaning, the electrode tip can be immersed in a solution of equal parts of concentrated sulfuric acid and hydrogen peroxide in a small beaker and 4 of 13

27、 481-10 stirred for approximately one hour or more to remove any residual organic coating on the platinum. Safety Caution: Great care should be taken with this acidic solution; work in a hood and use appropriate personal protection equipment. 4. Place the electrode in the titration cell. Pipet 100 m

28、L of the coulometric titration solvent (Karl Fisher reagent) into the 250-mL titration cell. Adjust the stirring speed to create a vortex in the solvent such that bubbles do not develop at its center. Condition the titration cell using the 100-L syringe to titrate a 10-L injection of water. 5. Allow

29、 the drift to stabilize to less than 0.15 g/s. The electrode and titration cell must be properly conditioned to obtain reproducible and noise-free titration curves. Condition the cell at the beginning of each day that samples are analyzed, as well as each time the titration solvent is replaced. Repl

30、ace the titration solvent when the solution becomes cloudy or the drift exceeds 0.15 g/s. Table 1 Typical Operating Conditions (Part A Liquid Hydrocarbons) Coulometric Titration Delay 10 seconds Minimum titration time 1 minute End sensitivity 0.1 g/s Table 2 Typical Operating Conditions (Part B Heav

31、y Hydrocarbons) Coulometric Titration Delay 1 minute Minimum titration time 12 minutes End sensitivity 0.1 g/s Vaporizer temperature 180 C Nitrogen flow rate 250 mL/min Instrument Performance Verification 1. Verify the performance of the iodine generation (direct injection coulometric titration) by

32、following the Part A procedure and titrating 1 gram of the Reference Standard (Part A). 2. Verify the performance of the vaporizer by following the Part B procedure and titrating 3 grams of the Reference Standard (Part B). If the determined water concentration is not within 3% of the calculated theo

33、retical value for either reference standard, replace electrolyte/titration solutions or adjust the titration parameters based on manufacturer recommendations. The generating current for coulometric electrodes can vary. Experience gained in the titration of water reference standards will provide guid

34、ance in the choice of optimal settings for titration. Part A: Liquid Hydrocarbon Samples 1. If not already filled, pipet 100 mL of the coulometric titration solvent (Karl Fisher reagent) into the 250-mL titration cell. Replace the titration solvent when the solution becomes cloudy, or the drift (Ste

35、p 2 below) exceeds 0.15 g/s. After replacing the titration solvent, condition the cell as described in Electrode Preparation. 5 of 13 481-10 2. Adjust the stirring speed to create a vortex in the solvent such that bubbles do not develop at its center. Allow the drift reading of the solution to stabi

36、lize to less than 0.15 g/s. 3. Flush a disposable syringe (with needle) at least three times and draw an aliquot of sample for analysis. Quickly remove any liquid adhering to the outside of the needle with a tissue and stopper the tip of the needle with a small piece of silicone rubber. The sample s

37、ize needed is dependent on the expected water concentration. The optimum sample amount contains approximately 100 g of water. Use Table 3 as a guide in determining the sample amount needed. Table 3 Sample Sizes Guidelines for Expected Water Content Expected Water Concentration, mg/kg Sample Amount,

38、g 1 to 100 2 to 10 100 to 500 1 500 to 1000 0.5 1000 to 2000 0.2 4. Weigh the stoppered syringe plus sample to the nearest 0.1 mg. 5. Remove the silicone rubber stopper and inject the sample aliquot into the coulometric Karl Fischer titrator according to the manufacturers instructions. The needle ti

39、p is inserted directly above the level of the Karl Fischer reagent to ensure that the entire sample dissolves in the solution and does not adhere to the cell walls. 6. Replace the stopper and reweigh the stoppered syringe to the nearest 0.1 mg. Calculate the mass of the sample injected by difference

40、 and record. 7. Record the g water present in the sample as indicated by the coulometric Karl Fischer titrator. 8. Calculate the water content (see Calculations). Part B: Heavy Hydrocarbon Samples 1. Place an empty vial on the balance and tare. 2. Transfer sample by disposable pipet into the vial us

41、ing Table 4 as a guide and record the weight to the nearest 0.1 mg. If the sample is solid or viscous at room temperature, warm the sample on a hot plate until fluid. If an expected water concentration is not known, add approximately three grams of sample to the vial. After an approximate water conc

42、entration is determined, a more appropriate sample size is selected and the sample is reanalyzed to obtain a precise result. Table 4 Sample Sizes Guidelines for Expected Water Content Expected Water Concentration, mg/kg Sample Amount, g 20 to 100 3 100 to 500 1 to 2 500 to 1000 0.5 1000 0.1 to 0.2 6

43、 of 13 481-10 3. Crimp cap tightly onto the vial. 4. Also prepare two “conditioning blank” vials, empty vials with crimped septum caps that are prepared the same day as the samples. 5. Turn on vaporizer and nitrogen gas and allow the temperature to stabilize with nitrogen flowing through the vaporiz

44、ers warming chamber. An empty vial with a crimped septum cap should be kept in the vaporizer when a sample is not present. The dual needle should be inserted in the vial to allow dry nitrogen to flow through the titration cell at all times. 6. If not already filled, pipet 100 mL of the coulometric t

45、itration solvent into the 250-mL titration cell. Replace the titration solvent when the solution becomes cloudy, or the drift (Step 7 below) exceeds 0.15 g/s. After replacing the titration solvent, condition the cell as described in Electrode Preparation and Cell Conditioning. 7. Adjust the stirring

46、 speed to create a vortex in the solvent such that bubbles do not develop at its center. Allow the drift reading of the solution to stabilize to less than 0.15 g/s with nitrogen flowing through the titration cell prior to starting any analysis. 8. Remove the empty vial from the vaporizer using tweez

47、ers and insert a conditioning blank. The blank is performed in duplicate. The blank value should be within the range of 30-120 g of water and duplicate values should agree within 5%. 9. Insert the sample vial into the vaporizer and puncture the septum with the dual needle. 10. Record the g water gen

48、erated for the sample as indicated by the coulometric titrator. 11. Calculate the water content (see Calculations). Calculations Calculate the water concentration to the nearest mg/kg using Equation 1: Water, mg/kg = BA (1) where: A = instrument reading, g H2O B = mass of sample, g When the water co

49、ncentration is greater than 2000 mg/kg (0.2 mass-%), calculate the water concentration to the nearest 0.01 mass-%, using Equation 2: Water, mass-% = B10A4 (2) where: A, B = previously defined, Equation 1 104 = factor to convert mass-ppm to mass-% Notes 1. Common interferences include: aldehydes, ketones and mercaptans. Special Karl Fischer reagents may be purchased to allow for water determination in the presence of ketones and aldehydes. Such reagents include Aquamicron AU and Aquamicron CK, Cosa Instrument, Cat. Nos. MC02012 an