UOP 1021-2017 Determination of Trace Methyl and Ethyl Mercaptan in Polymer Grade Ethylene & Propylene by Gas Chromatography Mass Spectrometry.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

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3、tial UOP Methods are available from ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 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. Determination of Trace Methyl and Ethyl Mercaptan in Polymer Grade Ethylene & Propylene by Gas Chromatography Mass Spectrometry UOP Method 1021-17 Scope This method is for determining trace methyl and ethyl mercaptans in high purity polymer grade ethylene and propylene gas or liquid using a

5、gas chromatograph equipped with a mass spectrometer run in selected ion monitoring mode. The specific instrument is preconfigured and is capable of determining typical impurities in polymer grade ethylene or propylene, however this method only outlines the procedure for determining methyl mercaptan

6、and ethyl mercaptan. Methyl and ethyl mercaptan elute on the propylene tail but are readily extracted by unique ions. The lower limit of quantitation for each component is 0.05 mol-(or mass-) ppm. References UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org Wasson ECE Instrumentati

7、on, Application 460-SP instrument manual Wasson ECE Instrumentation, Dynamic Blender instrument manual Outline of Method The method requires the use of a dedicated gas chromatographic mass spectrometer system that is configured for automated analysis which is capable, via valving and an on-board vap

8、orizer, of determining impurities in polymer-grade ethylene or propylene gas or liquid. For the trace mercaptan analysis, a reproducible sample volume is injected into a gas chromatograph (GC) that is equipped with a polar fused silica capillary column (Figure 1, column 2), a mass spectrometer detec

9、tor, and control and quantitation software. The concentrations of methyl mercaptan and ethyl mercaptan are determined by a multi-point external standard calibration curve for each component that represents the area of each selected ion versus its concentration, analyzed under identical conditions an

10、d injection volumes. Significance and Use High purity ethylene and propylene are used as feedstocks for production of polyethylene and polypropylene, respectively. The quality of the monomer is critical to successful polymerization. The presence of trace amounts of certain impurities can have detrim

11、ental effects on the catalyst and 2 of 13 1021-17 product yields. This test method is suitable for setting specifications, for use as an internal quality control tool, and for use in development or research work. Apparatus References to catalog numbers and suppliers are included as a convenience to

12、the method user. Other suppliers may be used. Analyzer Wasson-ECE Instrumentation Application 460-SP “GC/MS Analysis of Impurities in Polymer-grade Propylene”, other vendors also supply similar systems. Confirm with the selected vendor that the required separations are provided for the specific samp

13、le types to be analyzed. Pre-configured systems are available from Wasson-ECE for determining only mercaptans, the application specified can determine other impurities. The Wasson-ECE analyzer includes: Chromatographic column, 60 meters, PLOT, part# 60 m 2358, Wasson-ECE Instrumentation Chromatograp

14、hic column, 60 meters, polar, part# 60 m 2318, Wasson-ECE Instrumentation Gas chromatograph, capable of multiple temperature ramping, built for capillary column chromatography utilizing a split injection system with electronic pressure control (EPC), having a glass injection port insert. Three chann

15、els of additional electronic pressure control is required. Agilent Technologies, Model 7890. Mass Spectrometer Detector, capable of selected ion monitoring and equipped with inert EI source, performance turbo pump, ion gauge controller kit and data system. Agilent Technologies, Model 5977B. On-board

16、 Vaporizer, converts LPG to the gas phase prior to injection, Wasson-ECE Instrumentation Clamp, for ring stand and sample cylinders, Fisher Scientific Cat. No. 02-217-000 Clamp holder, for ring stand and clamp, Fisher Scientific Cat. No. 02-217-005 Data System, for computerized instrument control of

17、 data acquisition and data reduction, ChemStation, Agilent Technologies. Dynamic Blender with mass flow controller, model DB302, Wasson-ECE Instrumentation Flowmeter, Mass/VLM, Agilent Technologies, Model ADM 2000. Leak detector, gas, Fisher Scientific, Cat. No. 0.-251-702 Tubing, Sulfinert, .030-in

18、 ID x 1/16-in OD, Cat# 29230, Restek Tubing, translucent, FEP Teflon, 3.2-mm (1/8-inch) OD, 1.6-mm (1/16-inch) ID, 3450 kPa (500 psi), Thomas Scientific, Cat. No. 9567K20 Regulator, helium, two-stage, high purity, delivery pressure range 30 to 700 kPa (4 to 100 psi), Matheson Tri-Gas, Model 3122-580

19、, Cat. No. SEQ3122A580, 2 required Regulator, nitrogen, two-stage, high purity, delivery pressure range 30 to 700 kPa (4 to 100 psi), Matheson Tri-Gas, Model 3122-580, Cat. No. SEQ3122A580 Regulator, 2 component mercaptan blend, two-stage, high purity, delivery pressure range 30 to 1700 kPa (0 to 25

20、0 psi), Matheson Tri-Gas, Model 3810-350, Cat. No. SEQ3816A350 Ring stand, with rectangular base, 140- x 229- mm with 610- mm rod, Fisher Scientific, Cat. No. 14-679Q 3 of 13 1021-17 Reagents and Materials References to catalog numbers and suppliers are included as a convenience to the method user.

21、Other suppliers may be used. Calibration blends, Gas, quantitative, containing methyl mercaptan and ethyl mercaptan at the 3 mol-ppm level in helium, local supply. Gas purifier, for carrier gases, to remove moisture, VICI Mat/Sen, Cat. Nos. P100-1(helium), P300-1(nitrogen), local supply. Helium, UHP

22、, 99.9995% minimum purity, total hydrocarbons less than 0.5 ppm as methane, local supply. Nitrogen, zero gas, 99.99% minimum purity, total hydrocarbons less than 0.5 ppm as methane, local supply. Procedure The analyst is expected to be familiar with general laboratory practices, the technique of gas

23、 chromatography, mass spectrometry and the equipment being used. Dispose of used reagents, materials, and samples in an environmentally safe manner according to local regulations. Sampling Obtain the sample by following the procedures described in ASTM Practice D 1265, “Sampling Liquefied Petroleum

24、(LP) Gases (Manual Method),” ASTM Practice D 5287, “Automatic Sampling of Gaseous Fuels,” UOP Method 516, “Sampling and Handling of Gasolines, Distillate Fuels, and C3-C4 Fractions,” or other reliable technique. Chromatographic Technique 1. Follow the instrument site preparation checklist provided b

25、y the manufacturer and arrange for installation by the manufacturers service engineer to establish recommended operating conditions as listed in Table 1. The Wasson-ECE analyzer comes with on-site installation and training by a Wasson-ECE engineer in the continental U.S., inquire with Wasson-ECE for

26、 other locations. 2. Install the gas purifier in the supply line between the carrier gas source and the carrier gas inlets on the gas chromatograph. Column life is significantly reduced if the gas purifier is not used. Replace the gas purifier at intervals determined by good laboratory practice. An

27、indicating oxygen trap may be placed downstream of the gas purifier. When the indicator shows one-half used, replace both the gas purifier and the indicating trap. 3. When a major change is made to the system, such as the power to the GCMS is interrupted, the GCMS needs to be tuned in accordance wit

28、h the manufacturers instructions. A new calibration curve should then be established. Operating Conditions It is recommended to use the manufacturer operating conditions for this analysis to produce the required sensitivity and chromatographic separations equivalent to those shown in the Total Ion C

29、hromatogram as shown in Figure 2. 4 of 13 1021-17 Table 1 Recommended Operating Conditions Carrier gas helium Mode constant flow Flow rate 1.5 mL/min Head pressure 8.2 psig 40C Linear velocity 31.4 cm/sec 40C Split flow 15 mL/min Injection port temperature 200C On-board Vaporizer temperature 80C Col

30、umn temperature program Initial temperature 40C Initial time 6 min Programming rate 15C/min Final temperature 150C Final time 3 min Detector Ion Source EI Source temperature 230C Quad temperature 150C Transfer line temperature 280C Fixed Electron energy 70 eV Acquisition Type SIM Sample size 1.0 mL,

31、 repeatable Gas Samples and Blends 1. Choose and load appropriate method for gas sample analysis, ensuring valve 1 is in the on position to bypass the on-board vaporizer, see Figure 1. 2. Connect the sample cylinder or calibration blend cylinder to the sample inlet with Sulfinert tubing and purge th

32、e system with the gas to be analyzed for 20 seconds. Stop the flow, allow 5 to 10 seconds for the pressure to equilibrate, and start the analysis. If connecting the dynamic blender to the system, significantly more time (about 60 seconds) should be used to purge the inlet due to the decreased flow r

33、ate. The stop flow technique is described however constant flow while injecting can also be used, especially when using the dynamic blender. The technique which provides the best precision between multiple injections should be used. 3. Identify methyl and ethyl mercaptan by matching retention time a

34、nd their target ion as listed in Table 2. Record the area of each target ion from the extracted ion chromatogram. A typical total ion chromatogram is shown in Figure 2 for reference. Retention times of components may be influenced by the amount of propylene or diluent in the calibration blend or sam

35、ple. 4. Repeat steps 1 and 2 for each sample until the peak areas from each run do not deviate by more than 10%. 5 of 13 1021-17 Liquid Petroleum Gas (LPG Stream Samples) 1. Place the LPG sample cylinder in a vertical position in a hood or well-vented area. If the cylinder has an outage tube, the ou

36、tage tube must be at the top. Briefly open the bottom valve to check that no water or sediment is present in the LPG. If water or sediment is determined to be present, discontinue the analysis and obtain a clean sample. LPG samples are usually contained in a cylinder having valves on both ends or, i

37、n some cases, a cylinder where one of the valves is connected to an eductor tube. If the sample cylinder contains an eductor tube, invert the cylinder and briefly open the valve not connected to the eductor tube to check that no water or sediment is present. See Figure 3 for diagram of common LPG cy

38、linders. 2. Pressurize the LPG cylinder containing the sample (or blend) to approximately 1400 to 2068 kPa gauge (200 to 300 psig) with nitrogen or helium. 3. Mount the cylinder securely on a ring stand in a vertical position. If the cylinder has an outage tube, the outage tube fitting must be at th

39、e top. Connect the bottom valve to the liquid sample inlet tubing. If the cylinder is fitted with an eductor tube, connect the eductor tube outlet to the sample injection inlet tubing in such a manner that the eductor tube is sampling liquid LPG. The connecting tubing between the cylinder and the li

40、quid sample inlet must be as short as possible. 4. Choose and load appropriate method for LPG sample analysis, ensuring valve 1 is in the off position and the vaporizer is in line with the inlet of the system. Refer to Figure 1. 5. Ensure that the back pressure restrictor valve is closed. 6. Fully o

41、pen the bottom valve or eductor valve of the sample cylinder. 7. Partially open the back pressure restrictor to permit LPG flow through the sampling system. 8. Continue the flow until the flow emitting from the liquid sample vent is liquid and no bubbles are observed through translucent Teflon tubin

42、g. CAUTION: Inspect the translucent tubing regularly. Replace at first signs of wear or kinking. Pressure rating on the translucent tubing must be rated higher than pressure on sample or blend cylinder. 9. Stop the sample flow by closing the back pressure restrictor valve. 10. With the back pressure

43、 restrictor valve closed monitor the gas vent bubbler and wait 1 minute to ensure vaporized sample has flushed the sample loop. 11. Stop the flow, allow 5 to 10 seconds for the pressure to equilibrate, and start the analysis, the integrator and the column temperature programming sequence. 12. Close

44、the LPG cylinder valve and open the back pressure valve to vent the sampling system. 13. Identify methyl and ethyl mercaptan by matching retention time and their target ion as listed in Table 2. Record the area of each target ion from the extracted ion chromatogram. A typical total ion chromatogram

45、is shown in Figure 2 for reference. Retention times of components may be influenced by the amount of propylene or diluent in the calibration blend or sample. 14. Repeat steps 4 through 13 for each sample until the peak areas from each run do not deviate by more than 10%. Typically, 3-5 times when in

46、strument is run daily. 6 of 13 1021-17 Calibration A calibration curve is required to relate the detector response of ion 47 for methyl mercaptan and ion 62 for ethyl mercaptan to mol-ppm. Each calibration curve is generated by the analysis of gas calibration blends as described under Chromatographi

47、c Technique in triplicate and plotting the average area of each selected ion versus its concentration. Three or more component concentration levels are required to generate the plot. The different calibration levels can be obtained using the specified gas standard and the Wasson dynamic blender. See

48、 Appendix for the steps needed to use the blender. The calibration blend concentrations should bracket the expected concentration of the samples to be analyzed and not have a range of more than 2 orders of magnitude. Determine experimentally how long the calibration curve is valid, typically more th

49、an 2 months for the instrument specified if no major change were made to the system. A linear regression model should be used for the calibration curves, with the intercept not forced through zero. The R-squared (R2) for the regression should be 0.99. The peak areas from each of the triplicate blend runs should not deviate from the average by more than 10% (relative). If greater deviations occur, make certain that there are no problems with the equipment and then make additional runs unt