1、SULFUR COMPONENTS IN LPG OR C5MINUSHYDROCARBON FRACTIONS BY GC-SCDUOP Method 791-94SCOPEThis method is for determining trace amounts of sulfur species in liquefied petroleum gases (LPG) or inC5minus hydrocarbon streams using a gas chromatograph equipped with a sulfur chemiluminescencedetector (GC-SC
2、D). Individual components are determined quantitatively from approximately one to 50mass-ppm sulfur. Higher concentrations can be determined by increasing the concentration of sulfur in thestandard. If the entire sample elutes, the individual sulfur concentrations can be summed to report totalsulfur
3、 in the sample. Identified components can also be calculated and reported as mass-ppm of thecomponent.OUTLINE OF METHODA reproducible sample volume is introduced into a gas chromatograph equipped with a fused silicacapillary column internally coated with methyl silicone, a sulfur chemiluminescent de
4、tector, and cryogenicoven cooling. The sulfur chemiluminescence detector (SCD) is sulfur specific and responds to all sulfurcompounds on an equimolar basis. The mass-ppm sulfur concentration of each sulfur species in an LPGsample is calculated using the gas chromatographic external standard method o
5、f quantitation. The mass-ppm sulfur concentration for each sulfur species in the C5minus hydrocarbon fraction is obtained by theinternal standard method of quantitation, wherein the peak area for each sulfur compound is compared tothe peak area for a known amount of internal standard.APPARATUSRefere
6、nces to catalog numbers and suppliers are included as a convenience to the method user. Othersuppliers may be used.Balance, electronic, readability 0.1-mg, 200-g capacityBucket, 9.5-liter, Fisher Scientific, Cat. No. 03-687-30Caps. open hole, screw, to fit 22-400 threaded scintillation vial, Alltech
7、 Associates, Cat. No. 95331IT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIVE HEALTH ANDSAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THISPROCEDURE
8、 IN THE MANNER PRESCRIBED HEREIN CAN BE HAZARDOUS. MATERIAL SAFETY DATA SHEETS(MSDS) OR EXPERIMENTAL MATERIAL SAFETY DATA SHEETS (EMSDS) FOR ALL OF THE MATERIALS USED INTHIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE). COPYRIGHT 1980, 1994 UOP LLC
9、ALL RIGHTS RESERVEDUOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken PA 19428-2959,United States. The Methods may be obtained through the ASTM website, www.astm.org, or by contacting Customer Service atserviceastm.org, 610.832.9555 FAX, or 61
10、0.832.9585 PHONE.2 of 14791-94Chromatographic column, 30 m of 0.32-mm ID fused silica capillary, internally coated to a filmthickness of 4-m with methyl silicone, Supelco, Cat. No. 2-4158MClamp, for ring stand and sample cylinders. minimum opening 38.1-mm, Scientific Products, Cat. No.C6088-12Clamp
11、holder, for ring stand and clamp, Scientific Products, Cat. No. C6088-2Cylinder, for sample collection, type 316 or 304 stainless steel, high pressure, 12,400 kPa gauge (1800psig) maximum working pressure, 500-mL capacity, Whitey, Cat. No. 304L-HDF4-500. Equip thecylinder with 2 stainless steel valv
12、es, Whitey, Cat. No. 16DKM4-F4.Flowmeter housing, stainless steel, 3.175-mm (1/8-inch) FPT, 1725 kPa gauge (250 psig), Matheson GasProducts, Cat. No. JI-4C101-J010Flowmeter tube, 65-mm, 20- to 300-sccm air, Matheson Gas Products, Model No. J010Freezer, laboratory, Model SLF518A, Scientific Products,
13、 Cat. No. R3863-1AGas chromatograph, temperature programmable, capable of cryogenic cooling, built for capillary columnchromatography utilizing a split injection system having a deactivated glass injection port insert andequipped with a sulfur chemiluminescence detector (Sievers Instruments, Model 3
14、55B) that will give aminimum peak height response of 10 times the background noise for 1.0 mass-ppm of ethyl methylsulfide as sulfur when operated at the recommended conditionsIntegrator, electronic, for obtaining peak areasOven, drying, capable of 160COxygen remover, disposable Getter Cartridge, R&
15、D Separations, Cat. No. GC1Pipet, Pasteur, disposable, 146-mm, Fisher Scientific, Cat. No. 13-678-20APipet bulb, 1-mL, Fisher Scientific, Cat. No. 13-678-9ARecorder, 1-mV full scale, 1-sec or less full-scale responseRegulator, air, two-stage, high purity, Matheson Gas Products, Model 3104-590Regulat
16、or, helium, two-stage, high purity, Matheson Gas Products, Model 3104-580Regulator, hydrogen, two-stage, high purity, Matheson Gas Products, Model 3104-350Regulator, nitrogen, two-stage, high purity, Matheson Gas Products, Model 3104-580Ring stand, with rectangular base, 140- 229-mm with 610-mm rod,
17、 Scientific Products. Cat. No.S9135-30Sample injector, any syringe or injector capable of introducing 1.0-L volume of sample, such as theHamilton 701-NWG syringe, Alltech Associates, Cat. No. 80307 (required for C5minus samples)Septa, 20-mm, TFE lined, for 22-400 caps, Alltech Associates, Cat. No. 9
18、5333Syringe, 2-mL, gas tight, Alltech Associates, Cat. No. 830943 of 14791-94Tubing, stainless steel, 1.59-mm (1/16-inch) OD, Alltech Associates, Cat. No. 300010Tubing, Tygon, 6.35-mm (1/4-inch) ID, Scientific Products, Cat. No. T6010-3Valve, injection, 1.0-L internal sample volume injector, stainle
19、ss steel, UWP series, with 1.59-mm(1/16-inch) fittings, manual with standoff, Valco Instruments. Cat. No. C14UWP1 (required foranalysis of LPG)Valve, metering, 3.175-mm (1/8-inch), Swagelok, straight, stainless steel, Nupro, Cat. No. M-2MGValve, relief, low pressure, externally adjustable, stainless
20、 steel, range 0 to 1540 kPa gauge (0 to 225psig) set at maximum relief pressure, Nupro, Cat. No. SS-RL3M4-F4Valve, toggle on/off, brass, 3.175-mm (1/8-inch), Swagelok, Alltech Associates, Cat. No. 2328Vial, scintillation, 20-mL, glass, with 22-400 GPI thread finish, Scientific Products, Cat. No. R25
21、48-21REAGENTS AND MATERIALSAll reagents shall conform to the specifications established by the Committee on Analytical Reagents ofthe American Chemical Society, when such specifications are available, unless otherwise specified.References to catalog numbers and suppliers are included as a convenienc
22、e to the method user. Othersuppliers may be used.Air, zero-gas, total hydrocarbons less than 2 mass-ppm as methaneBlend, LPG, calibration, certified standard, containing nominally 50 mass-ppm of ethyl methyl sulfide(21 mass-ppm sulfur) in isobutane, size No. 3 treated aluminum cylinder, with eductor
23、 tube,pressurized with an inert gas to 1437 kPa gauge (210 psig), Matheson Gas Products (required foranalysis of LPG streams). The calibration blend life is estimated at 6 months. The blend must bemonitored regularly and replaced when changes in concentration or species present are noted.Carbon diox
24、ide, 99.5% purity, compressed gas, equipped with dip tubeEthyl methyl sulfide, 99% minimum purity, Aldrich Chemical, Cat. No. 23,831-7Ethyl methyl sulfide solution, approximately 1%, in heptane. Dissolve 0.05 g of ethyl methyl sulfide in 5g of heptane.Ferric chloride, anhydrous, 98% purity, Aldrich
25、Chemical, Cat. No. 15,774-0Helium, zero-gas, total hydrocarbons less than 2 ppm as methanen-Heptane, 99% minimum purity, Aldrich Chemical, Cat. No. 27,051-2 (required for C5minus samples)Hydrochloric acid, 37% minimum purity, ACS reagent, Aldrich Chemical, Cat. No. 25,814-8Hydrogen, zero-gas, 99.95%
26、 minimum purity, total hydrocarbons less than 0.5 ppm as methanePhenyl sulfide, 98% purity, Aldrich Chemical, Cat. No. P3,531-6 (required for C5minus samples)Water, distilled4 of 14791-94PREPARATION OF APPARATUSChromatographic Technique1. Install the oxygen remover in the supply line between the car
27、rier gas source and the carrier gas inletson the gas chromatograph. Column life is significantly reduced if an oxygen remover is not used.2. Install the fused silica capillary column in the gas chromatograph.3. Install the injection valve in the carrier gas line just ahead of the injection port and
28、connect the valveports according to the manufacturers instructions (see Fig. 1). An injection valve is required only if LPG samples are to be analyzed.4. Establish the recommended operating conditions as given in Table 1. Other conditions may be used provided they produce the required sensitivity an
29、d chromatographicseparations equivalent to those shown in the Typical Chromatograms (Figs. 2 and 3).Table 1Carrier gas heliumColumn head pressure 70 kPa gauge (10 psig)Split flow 40 mL/minInjection port temperature 250CColumn temperature programInitial temperature -10CInitial time 3 minProgramming r
30、ate 1 15C/minIntermediate finaltemperature150CIntermediate time 0 minProgramming rate 2 20C/minFinal temperature 250CFinal time 10 minSCD Detector *Chart speed 5 mm/minSample size 1.0 L (reproducible for LPG)_*The sulfur chemiluminescence detector is set up and operated according to themanufacturers
31、 instructions.5. Program the column oven to 250C and maintain this temperature until a stable baseline has beenobtained at the required sensitivity.6. Cool the column oven to a stabilized - 10C.7. Condition the chromatographic system (septum, injection port, column, SCD) by sequential multipleinject
32、ions (10 times) of a 1% ethyl methyl sulfide in heptane solution at an oven temperature of5 of 14791-94200C. After the final injection, reset the conditions as indicated in Table 1 and monitor the baselineto verify that no extraneous sulfur species elute. Repeat the Table 1 conditions until a flat b
33、aseline isobtained and then proceed. Conditioning should be repeated whenever there is a replacement of a chromatographic systemcomponent or if the sulfur area counts of the standard are seen to decrease steadily in successiveinjections (10%). An instrument must be dedicated to sulfur determination
34、to maintain repeatability.CALIBRATION OF APPARATUSC5Minus HydrocarbonsQuantitative results are based on the comparison of the area response of each sulfur compound of interestto that of an internal standard that is added to the sample. Because the sulfur chemiluminescence detectorresponds to all sul
35、fur compounds on an equimolar basis, the response for all sulfur compounds is the sameand no additional factors are required.LPGQuantitative results are based on the injection of a reproducible volume of a sample and a calibrationblend (external standard). A response factor is then used to relate th
36、e peak area obtained for the ethyl methylsulfide in the blend to the peak areas of all sulfur impurities in the LPG sample. The sulfurchemiluminescence detector responds to all sulfur compounds on an equimolar basis.1. Connect the valve on the eductor tube of the LPG calibration blend containing eth
37、yl methyl sulfide inisobutane to the sample injection valve.2. Analyze the blend in triplicate as described under Analysis of LPG Samples, Steps 6 through 15.3. Average the peak areas of the ethyl methyl sulfide from the triplicate runs. The peak area from each of the three runs should not deviate f
38、rom the average by more than 3% of thevalue. If greater deviations occur, make certain that there are no problems with the equipment and thenmake further runs until the required repeatability is obtained on two consecutive runs.4. Determine a response factor to be used for all sulfur species to 3 de
39、cimal places using the followingformula:LQK= (1)where:K = average peak area for ethyl methyl sulfide in the blendL = concentration of ethyl methyl sulfide, as sulfur, in the blend, mass-ppmQ = response factor for sulfur species, mass-ppm/area countSAMPLINGPreparation of Sample CylinderSulfur species
40、 readily react with cylinder walls. Steps must be taken to reduce this reactivity. Use thefollowing procedure to passivate sample cylinders:6 of 14791-941. Evacuate the cylinder.2. Prepare passivating solution by dissolving approximately 3 g of ferric chloride in a mixture of 300 mLof distilled wate
41、r and 300 mL hydrochloric acid for each one-liter cylinder to be passivated. The exact amount of ferric chloride used is not critical. The amount of solution required is dependent on the number and size of cylinders to be passivated (seeStep 3).3. Aspirate 600 mL of the solution prepared in Step 2 i
42、nto each one-liter sample cylinder or 300 mL toeach 0.5-liter sample cylinder and close both valves.4. Place the sample cylinder into a 9.5-liter bucket filled with hot tap water so that one valve is above thewater.5. Open the cylinder valve that is above the water.6. Condition the cylinder in this
43、position for 30 5 minutes.7. Close the valve and invert the cylinder in the bucket.8. Open the cylinder valve above the water and condition the cylinder for 30 5 minutes.9. Close the valve, remove the cylinder from the bucket, shake the cylinder vigorously for severalminutes and then drain the conte
44、nts.10. Flush the cylinder with hot tap water for 25 minutes.11. Flush the cylinder with cold tap water for 25 minutes.12. Dry the cylinder in a 160C oven for 25 minutes.13. Cool and purge the cylinder with nitrogen for 20 minutes. The passivated cylinders are stored under nitrogen with both valves
45、closed.Sample CollectionObtain samples according to UOP Method 516. Analysis must be performed as soon as possible aftersampling to minimize sulfur adsorption on cylinder walls, and to minimize reactions that produce changesin the composition of sulfur compounds in the cylinder.PROCEDUREPreparation
46、of Internal StandardA phenyl sulfide internal standard blend is required for addition to C5minus liquid samples. An internalstandard technique is used because the volatility of C5minus hydrocarbons in the injection syringe results innon-reproducible injection volumes. Other sulfur compounds can be u
47、sed in place of the phenyl sulfideinternal standard, provided they are stable and are not originally in the sample. A large quantity of stockstandard, required for accuracy, is prepared first and the concentration reduced to the desired workingconcentration by serial dilution as follows:7 of 14791-9
48、4Phenyl Sulfide Stock Standard,Nominally 1700 mass-ppm as Sulfur1. Weigh approximately 10 g of n-heptane, to the nearest 0.1 mg, into a tared vial using a Pasteur pipet,then tare the vial and contents again.2. Add approximately 0.1 g of phenyl sulfide to the vial using a Pasteur pipet, and quickly r
49、eweigh to thenearest 0.1 mg.3. Install a septum, cap the vial and mix thoroughly by inverting several times.4. Calculate the concentration of the phenyl sulfide as sulfur, to three significant figures, to the nearestmass-ppm as follows:632.1(10 )MY186 P= (2)where:M = mass of phenyl sulfide weighed into vial, gP = total mass of final solution (phenyl sulfide plus n-heptane) weighed into vial, gY = phenyl sulfide, as sulfur, in standard, mass-ppm32.1 = relative molecular mass of sulfur in phenyl sulfide186 = relative molecular mass of pheny
