UOP 989-2014 Trace Sulfur in LPG and Gaseous Hydrocarbons by Oxidative Combustion with Ultraviolet Fluorescence Detection.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 2014 UOP LLC. All rights reserved. Nonconfidential UOP Met

3、hods 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 PHONE. Trace Sulfur

4、 in LPG and Gaseous Hydrocarbons by Oxidative Combustion with Ultraviolet Fluorescence Detection UOP Method 989-14 Scope This method is for determining sulfur in liquefied petroleum gas (LPG) and gaseous hydrocarbons at concentrations ranging from 0.2 to 100 mg/kg (mass-ppm). LPG samples are expande

5、d into the gas phase before analysis. If any heavy sulfur compounds are present in the LPG that do not volatilize quantitatively with the LPG, they may be under-reported. The method can also be applied to the analysis of hydrogen and other gas samples. Halogens interfere at concentrations greater th

6、an approximately 0.3%. This method is similar to ASTM Method D6667, “Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases by Ultraviolet Fluorescence,” and ASTM Method D7551, “Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases and Natural Gas by Ultrav

7、iolet Fluorescence,” but uses a different sample introduction system which may improve precision and accuracy. References ASTM Method D6667, “Total Volatile Sulfur in Gaseous Hydrocarbons and Liquefied Petroleum Gases by Ultraviolet Fluorescence” www.astm.org ASTM Method D7551, “Total Volatile Sulfu

8、r in Gaseous Hydrocarbons and Liquefied Petroleum Gases and Natural Gas by Ultraviolet Fluorescence,” 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 M

9、ethod A commercial instrument is set up and calibrated with different volumes of LPG standards. The gas or LPG materials are dispensed into fluoropolymer gas sampling bags and, if LPG, are allowed to evaporate. The atmospheric pressure gas sample is injected into an argon carrier flow using a syring

10、e-based gas injector. The gas mixture is combined with oxygen at high temperature. The organic material is converted to carbon dioxide and water. The sulfur in the sample is converted to sulfur dioxide. The signal is proportional to the total volatile sulfur in the sample. 2 of 7 989-14 Apparatus Re

11、ferences to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Regulator, argon, single-stage, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3231. This regulator is installed downst

12、ream of the two-stage regulator to provide better flow control. Regulator, argon, two-stage, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3122-580 Regulator, oxygen, single-stage, with stainless steel diaphragm, delivery pressure range 30

13、-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3231. This regulator is installed downstream of the two-stage regulator to provide better flow control. Regulator, oxygen, two-stage, with stainless steel diaphragm, delivery pressure range 30-700 kPa (4-100 psi), Matheson Tri-Gas, Cat. No. 3122-540 S

14、ulfur analyzer, with attached furnace, autosampler, controls and computer, Model TS-100V, with SD-100 Sulfur Detector and GI-220 Gas Injector, Mitsubishi Chemical Analytech, available from COSA Instrument. This method was developed and validated using the Mitsubishi analyzer. The procedure for analy

15、sis may be different for other instruments and other instruments need to be validated before using for this method. Not all combustion/UV fluorescence instruments are capable of running this analysis. The Mitsubishi analyzer must be equipped with the following accessories: Gas Injector, Mitsubishi G

16、I-220, COSA Instruments Membrane drier, Perma Pure MD-110-24F-4 or Tube Dryer, Mitsubishi, Cat. No. TN6RPC, COSA Instruments (see Note 1) Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. The following it

17、ems are required to perform the analysis. Additional reagents and materials may be required depending on the specific instrument. Air, compressed, dry, oil-free, for membrane drier (if the instrument does not purge the drier with argon), local supply Alumina balls, Mitsubishi, Cat. No. TS3CAT, COSA

18、Instruments Argon, compressed gas, 99.99% minimum purity, UHP, Matheson Tri-Gas or local supply Gas sampling bags, 1.6-L or 3.8-L, Cat. No. 10-923-10 or -11, Fisher Scientific (see Note 2) LPG standards, 1.5, 15, 75, and 150 mass-ppm methyl mercaptan (methanethiol) in n-butane, Matheson Tri-Gas Oxyg

19、en, compressed gas, 99.98% minimum purity, UHP, Matheson Tri-Gas or local supply Quartz wool, Mitsubishi, Cat. No. TNQWL, COSA Instruments Procedure The analyst is expected to be familiar with general laboratory practices, the technique of sulfur 3 of 7 989-14 analysis using ultraviolet fluorescence

20、, and the equipment being used. Dispose of used supplies and samples in an environmentally safe manner according to applicable regulations. Preparation of Standards The calibration standard of methylmercaptan in n-butane is purchased as a certified standard from gas suppliers. A 1.5 mass-ppm methylm

21、ercaptan in n-butane standard is 1.0 mass-ppm S. When expanded to atmospheric pressure in the gas sampling bag, it contains 2.592 ng/mL (as S) at 0 C or 2.375 ng/mL (as S) at 25 C. Calculate the gaseous sulfur concentration in the vaporized standard from the concentration of the methylmercaptan in n

22、-butane LPG standard using Equation 1. A = T15.273C728.1 (1) where: A = gaseous sulfur concentration of the vaporized standard, at specific temperature, ng/mL C = concentration of methylmercaptan in LPG blend, g methylmercaptan/g of LPG (mass-ppm) T = absolute temperature, K 1.728 = 414.22124.58107.

23、48064.32 (1a) where: 32.064 = atomic mass of S, g/mol 48.107 = molecular mass of methylmercaptan, g/mol 58.124 = molecular mass of butane, g/mol 22.414 = volume of ideal gas at STP, L/mol Calculate the mass of sulfur injected from the injection volume and the gaseous sulfur concentration using Equat

24、ion 2. B = A V (2) where: A = previously defined, Equation 1 B = mass of injected sulfur, ng V = gaseous volume of expanded calibration blend injected, mL Sampling The sample should be collected according to UOP Method 516, “Sampling and Handling of Gasolines, Distillate Fuels and C3-C4 Fractions.”

25、The use of a passivated cylinder (e.g. Silcosteel, Sulfinert, etc.) is required (see Note 3). The transfer of the LPG or gas sample to the gas sampling bag should be performed in a fume hood. A new bag should be used for each sample to prevent contamination. 1. Flush the sample cylinder outlet with

26、sample for a few seconds before connecting to the gas sampling bag. 2. Open the valve on the gas sampling bag. 3. Open the cylinder valve briefly, allowing sample to flow into the bag. Do not overfill the bag. For LPG samples, transfer a small volume of LPG (2 - 4 mL) and allow it to vaporize (this

27、is for a 1.6-L bag; approximately twice that amount for a 3.2-L bag). For gas samples, fill until the bag expands, but is not completely full. 4 of 7 989-14 4. Close the valve on the gas sampling bag and remove from the cylinder. 5. Analyze the sample within two hours of transferring to the gas samp

28、ling bag. Preparation of Apparatus Set up the instrument according to the manufacturers instructions. Connect the membrane drier in series between the combustion tube and the detector. Allow the instrument to warm up and the baseline to stabilize before injecting samples. Suggested Operating Conditi

29、ons for the Mitsubishi TS-100V analyzer are listed in Table 1. A 25-mL syringe is installed in the GI-220 gas injector. Table 1 Operating Conditions for Mitsubishi TS-100V/SD-100/TRU-100 Upper temperaturea 900 C Lower temperatureb 1000 C Argon main 170 mL/min Oxygen main 150 mL/min Argon auxiliary 5

30、0 mL/min Oxygen auxiliary 400 mL/min GI-220 carrier argon 80 mL/min Gain Middle Normal end Off Minimum area 40000 Baseline 75% GI-220 Syringe 25 mL Absorption rate 50 mL/min Injection rate 20 mL/min aCombustion tube, upper portion bCombustion tube, lower portion Calibration Calibrate weekly when in

31、use. Check the calibration daily when in use, by analyzing one of the calibration standards or a reference material. If the results deviate from the known concentration by more than the repeatability allowable difference shown in Precision, recalibrate. 1. Transfer the calibration standard to a gas

32、sampling bag, and then connect to the GI-220 gas injector module. The same gas sampling bag can be re-used for the standard. Empty the bag before refilling. 2. Set up the sample table for multiple sample volumes and replicate injections of the sulfur standard. Three or four injections are recommende

33、d. 3. Analyze the standard according to the instrument manufacturers instructions. If run as a “calibration” method, the “START” button will need to be pressed for each new sample volume. If run as a “sample” method, the instrument will run all measurements on the same material automatically, and th

34、e S content and response areas can be entered in manually (see Note 4). Relative standard deviation (RSD), as calculated by the instrument for the standards, should be within 15% for the 1- or 2-mL injections and within 10% for 3-mL or larger injections. 4. Create a regression line using the instrum

35、ent software and the appropriate volumes of the standards. Set the regression line to “y=bx+c” for this calibration. Sample Analysis 1. Determine the average molecular weight of the sample, see the Appendix. 5 of 7 989-14 2. Attach the gas sampling bag with the first sample to the GI-220 gas injecto

36、r module. 3. Add the sample to the sample table. Set the sample injection volume to 5 mL. If unsure of concentration, start with a 1-mL sample volume to avoid overloading the system. Analyze samples above 5 mg/kg in duplicate. For samples below 5 mg/kg, three or more measurements should be made. Ent

37、er the sample average molecular weight to calculate the results as mass-ppm. 4. Analyze the sample replicates according to the instrument manufacturers instructions. 5. Repeat Steps 1 through 4 for each additional sample. If the detector becomes contaminated (trace off scale), disconnect the gas sam

38、pling bag and analyze air blanks until the response stabilizes. Then confirm that the sensitivity has not changed by analyzing a calibration standard or a control standard. Integration and calculations are done automatically. The average of the replicate injections is calculated by the instrument so

39、ftware. Calculations All calculations are performed by the software and results are displayed and printed in mass-ppm (mg/kg). The molecular weight of the sample is input during sample data entry and is used by the instrument to convert results from mass/volume to mass/mass. Multiple injections of t

40、he same sample are averaged by the instrument software. Report Report results as mg/kg (mass-ppm) to one decimal place below 10 mg/kg and the nearest whole number above 10 mg/kg. Notes and Precautions 1. The membrane drier is used to remove the water produced during combustion. If not removed, the w

41、ater vapor can react with the sulfur dioxide to form H2SO3 with a resultant loss of signal. The membrane drier consists of a thin walled Nafion tube within a larger plastic tube. The combustion product gas flows through the Nafion tube. Dry air or other dry gas flows counter-current through the oute

42、r plastic tube. The Nafion membrane allows water to pass through, and be carried away by the air stream on the other side. 2. Gas sampling bags are made of Tedlar or other fluoropolymers. The fitting on the gas sampling bags may not match the connector on the GI-220. In that case, an adapter, such a

43、s a short section of silicone tubing, should be used to make the connection. Samples should be analyzed within two hours of transfer into the gas sampling bag. 3. The use of passivated cylinders (e.g. Silcosteel, Sulfinert, etc.) is required to prevent the loss of sulfur compounds to the cylinder wa

44、ll. The internal components of the cylinder valves should be similarly treated. 4. When running the calibration as “samples,” type in the calibration data manually to create a calibration. Run the sample report to print the individual measurements. Calculate the sulfur content for each injection vol

45、ume using the equations in “Preparation of Standards.” Under the “System” menu, select “Default Calibration Curve.” Click “Edit” and enter all of the calibration data points. Save the calibration. 6 of 7 989-14 Precision Precision statements were determined using UOP Method 999, “Precision Statement

46、s in UOP Methods.” As described in the Procedure and Calculations, two to four replicate injections were averaged for each analysis. Repeatability and Site Precision A nested design was carried out for determining impurities in three LPG samples and one gas sample by two analysts on two separate day

47、s, performing two analyses each day for a total of 32 analyses. Using a stepwise analysis of variance procedure, the within-day estimated 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 d

48、ay should not differ by more than the repeatability allowable differences shown in Table 2 with 95% confidence. Two analyses performed 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% confidenc

49、e. Table 2 Repeatability and Site Precision, mg/kg Repeatability Site Precision Sample Mean Within- Day esd Allowable Difference Within- Lab esd Allowable Difference LPG 1 1.0 0.02 0.1 0.03 0.1 LPG 2 5.7 0.23 0.9 0.29 1.3 LPG 3 19.8 0.21 0.8 0.19 0.8 LPG 4 53.4 0.22 0.9 0.64 3.9 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 of long-term repeatability. Reproducibility There i