UOP 988-2011 Low Trace Sulfur in LPG and Gaseous Hydrocarbons by Oxidative Combustion with Ultraviolet Fluorescence Detection.pdf

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 2011 UOP LLC. All rights reserved. Non

3、confidential 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

4、 PHONE. Low Trace Sulfur in LPG and Gaseous Hydrocarbons by Oxidative Combustion with Ultraviolet Fluorescence Detection UOP Method 988-11 Scope This method is for determining sulfur in liquefied petroleum gas (LPG) and gaseous hydrocarbons at concentrations ranging from 10 to 1400 ng/g (0.01 to 1.4

5、0 mass-ppm). A trap approximately twice that amount for a 3.2-L bag). For gas samples, fill until the bag expands, but is not completely full. 4. Close the valve on the gas sampling bag and remove from the cylinder. 5. Analyze the sample within 3 hours of transferring to the gas sampling bag. Prepar

6、ation of Apparatus 1. Set up the instrument according to the manufacturers instructions for the trap and release unit. 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

7、Operating Conditions for the Mitsubishi TS-100V analyzer are listed in Table 1. The same trap time must be used for the calibration and the samples use the longest trap time if calibrating for multiple ranges. A 25-mL syringe is installed in the GI-220 gas injector. Table 1 Operating Conditions for

8、Mitsubishi TS-100V/SD-100/TRU-100 Upper temperaturea 900C Lower temperatureb 1000C Argon main 170 mL/min Oxygen main 150 mL/min Argon auxiliary 50 mL/min Oxygen auxiliary 400 mL/min GI-220 carrier argon 80 mL/min Gain Ultra Normal end Off Minimum area 40000 Base line 75% GI-220 Syringe 25 mL Absorpt

9、ion rate 50 mL/min Injection rate 20 mL/min aCombustion tube, upper portion bCombustion tube, lower portion Table 2 Recommended Sample Size and Instrument Timing Concentration Range (ng/g) Sample Volume (mL) Trap Time (s) Timer Start (s) Timer End (s) 10 - 200 80 532 535 835 200 - 500 40 296 310 610

10、 500 - 1400 10 250 270 570 Calibration Calibrate weekly when in use. Check the calibration daily when in use, by analyzing one of the calibration standards or a reference material. 1. Transfer the calibration standard to a gas sampling bag, and then connect to the GI-220 gas injector module. The sam

11、e gas sampling bag can be re-used for the standard. Empty the bag before refilling. 5 of 8 988-11 2. Set up the sample table for multiple sample volumes and replicate injections of the sulfur standard. Three or four injections are recommended for volumes below 10 mL and two injections for volumes ab

12、ove 10 mL. Use the trap time and timer start/end from Table 2. If calibrating for multiple ranges, use the trap and integration times for the longest method that will be used for all standards and samples. For a low level calibration, use 1-, 2-, 3-, 5-, and 10-mL volumes. For a mid or high level ca

13、libration, use 5-, 10-, 20-, and 30-mL volumes. Do not exceed 30 mL of the standard, or the trap may be saturated. See Note 4. 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 measurement

14、s on the same material automatically, and the S content and response areas can be entered in manually. See Note 5. 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. 3.

15、 Analyze the standard according to the instrument manufacturers instructions. 4. Create a regression line using the instrument software using 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

16、of the sample, see the Appendix. 2. Attach the gas sampling bag with the first sample to the GI-220 gas injector module. 3. Add the sample to the sample table. If unsure of concentration, start with a small volume such as 5 mL; otherwise, select the volume based on Table 2. The amount of sulfur inje

17、cted should not exceed 50 ng per measurement. Analyze samples above 100 ng/g in duplicate. For samples below 100 ng/g, 3 or more measurements should be made. Enter the sample average molecular weight to calculate the results as mass-ppm. 4. Analyze the sample replicates according to the instrument m

18、anufacturers instructions. 5. Repeat Steps 1 through 4 for each additional sample. If the detector becomes contaminated (trace off scale), disconnect the gas sampling bag and analyze air blanks until the response stabilizes. Then, confirm that the sensitivity has not changed by analyzing a calibrati

19、on standard or a control standard. Integration and calculations are done automatically. The average of the replicate injections is calculated by the instrument software. Calculations All calculations are performed by the software, and results are displayed and printed in mass-ppm (mg/kg) or mass-ppb

20、 (ng/g). 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 the same sample are averaged by the instrument software. Report Report results as mg/kg (mass-ppm) to two decimal place

21、s. 6 of 8 988-11 Notes and Precautions 1. The membrane drier is used to remove the water produced during combustion. If not removed, the water vapor would enter the detector and result in a reduction of the chemiluminescence intensity. The membrane drier consists of a thin walled Nafion tube within

22、a larger plastic tube. The combustion product gas flows through the Nafion tube. Dry air or other dry gas flows counter-current through the outer 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

23、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 as a short section of silicone tubing, should be used to make the connection. Samples should be analyzed within 3 hours of transfer into the gas sampling bag

24、 3. The use of passivated cylinders (e.g. Silcosteel, Sulfinert, etc) is required to prevent the loss of S compounds to the cylinder wall. The internal components of the cylinder valves should be similarly treated. 4. Do not exceed 50 ng of S for the TRU-100 trap and release unit. If a single measu

25、rement contains more than 50 ng S, it may be necessary to bake out the trap and release unit to remove excess sulfur. Follow the manufacturers instructions if the bake out is needed. 5. When running the calibration as “samples,” type in the calibration data manually to create a calibration. Run the

26、sample report to print the individual measurements. Calculate the sulfur content for each injection volume 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.

27、Precision Precision statements were determined using UOP Method 999, “Precision Statements 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 determini

28、ng impurities in three LPG samples and one gas sample by two analysts on two separate days, 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 list

29、ed in Table 3. 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 3 with 95% confidence. Two analyses performed in one laboratory by different analysts on different days should not differ

30、by more than the site precision allowable differences shown in Table 3 with 95% confidence. Table 3 Repeatability and Site Precision for Procedure, mg/kg Repeatability Site Precision Sample Mean Within- Day esd Allowable Difference Within- Lab esd Allowable Difference LPG 1 0.68 0.013 0.05 0.015 0.0

31、6 LPG 2 0.26 0.002 0.01 0.002 0.01 LPG 3 0.01 0.001 0.01 0.001 0.01 Gas 0.06 0.001 0.01 0.001 0.01 7 of 8 988-11 The data in Table 3 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 gene

32、rate an estimate of long-term repeatability. Reproducibility There is insufficient data to calculate the reproducibility of the test at this time. Time for Analysis The elapsed time for the calibration is approximately 4 hours. When performed as in “calibration” mode, then the labor requirement for

33、calibration is identical to the elapsed time, 4 hours. In “sample” mode, the labor requirement is approximately 1 hour. Each sample analysis requires 0.5 hour for duplicate measurement. Suggested Suppliers COSA Instrument Corp., 55 Oak St., Norwood, NJ 07648, USA (201-767-6600), distributor for Mits

34、ubishi Chemical Analytech, 370 Enzo, Chigasaki, Kanagawa Pref., 253-0084, Japan (+81-467-86-3864) Fisher Scientific, 711 Forbes Ave., Pittsburgh, PA 15219, USA (412-562-8300) Matheson Tri-Gas, 166 Keystone Dr., Montgomeryville, PA 18936, USA (215-641-2700) Perma Pure Inc., 8 Executive Dr., Toms R

35、iver, NJ 08754, USA (732-244-0010) 8 of 8 988-11 Appendix Calculation of the Average Molecular Weight of a Gas Scope This appendix may be used to calculate the average molecular weight of a gaseous material from its known composition. References ASTM Method D2163, Hydrocarbons in Liquefied Petroleu

36、m (LP) Gases and Propane/Propene Mixtures by Gas Chromatography,” www.astm.org UOP Method 373, “Composition of C2 through C5 Hydrocarbon Mixtures by GC,” www.astm.org UOP Method 539, “Refinery Gas Analysis by Gas Chromatography,” www.astm.org Calculations If the composition of the material is not kn

37、own, analyze it using the following test methods. Other similar methods may be used. For gas samples: UOP Method 539, “Refinery Gas Analysis by Gas Chromatography” For LPG samples: UOP Method 373, “Composition of C2 through C5 Hydrocarbon Mixtures by GC,” or ASTM Method D2163, Hydrocarbons in Liquef

38、ied Petroleum (LP) Gases and Propane/Propene Mixtures by Gas Chromatography” Calculate the average molecular weight of the gas sample (after expansion if the sample was an LPG), from its known composition, using Equation A1. M =n1iii100WP (A1) where: M = average molecular weight of the gas Pi = conc

39、entration of each component in the sample, vol-% Wi = molecular weight of that component, Table A1 100 = correction for % Table A1 Molecular Weights of Gas Sample Components Component Molecular Weight Hydrogen 2.02 Nitrogen 28.01 Methane 16.04 Ethane 30.07 Ethylene 28.05 Propane 44.10 Propylene 42.08 C4 Paraffins 58.12 C4 Olefins 56.11