UOP 868-1988 TRACE SATURATES IN HIGH PURITY AROMATICS BY GC.pdf

1、TRACE SATURATES IN HIGH PURITY AROMATICS BY GCUOP Method 868-88SCOPEThis method is for determining trace paraffins and naphthenes by carbon number from C3through C10inolefin-free C6, C7or C8aromatics or mixtures thereof (see Note 1). The range of detection for C3to C8paraffins or naphthenes is 2 to

2、2,000 mass-ppm. The range of detection for C9and C10paraffins andnaphthenes is 100 to 2,000 mass-ppm.OUTLINE OF METHODA repeatable sample volume is injected into a gas chromatograph that is equipped with a two-columnchromatographic system and a flame ionization detector. The first column is polar, p

3、acked with OV-275 onChromosorb, and the second column is selective, packed with specially treated 13X molecular sieves.Initially, the two columns are connected in series. Immediately before the elution of benzene from the polarcolumn, the polar column is backflushed to vent while the eluted saturate

4、d hydrocarbons are analyzed onthe selective column. The external standard method of quantitation is used.APPARATUSBalance, readability 0.1-mgChromatographic columns:Column 1: 3 m of 2-mm ID (1/8-inch OD) stainless steel tubing, packed with 30% OV-275 on 60-80mesh Chromosorb PNAW, Alltech Associates,

5、 or equivalentColumn 2: 1.6 m of 2-mm ID (1/8-inch OD) stainless steel tubing, packed with specially treated 13Xmolecular sieves, Analytical Controls, Part No. 50.06.530Gas Chromatograph, built for dual packed column operation, with dual flow controllers, pressure gaugesand a single flame ionization

6、 detector, capable of column temperature programming to 400 C, andequipped with a separate isothermal heated zone large enough to contain 2 rotary valves, 2 restrictorvalves and a column. The detector must be capable of producing a minimum peak height response of10 times the background noise for 2 m

7、ass-ppm of n-hexane when operated at the recommendedconditions (see Note 2).Integrator, electronic, or equivalent for obtaining peak areasIT IS THE USERS RESPONSIBILITY TO ESTABLISH APPROPRIATE PRECAUTIONARY PRACTICES AND TODETERMINE THE APPLICABILITY OF REGULATORY LIMITATIONS PRIOR TO USE. EFFECTIV

8、E HEALTH ANDSAFETY PRACTICES ARE TO BE FOLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THISPROCEDURE 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 SHOUL

9、D BE REVIEWED FOR SELECTION OF THE APPROPRIATE PERSONAL PROTECTIONEQUIPMENT (PPE). COPYRIGHT 1986, 1988 UOP LLCALL 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 throu

10、gh the ASTM website, www.astm.org, or by contacting Customer Service atserviceastm.org, 610.832.9555 FAX, or 610.832.9585 PHONE.2 of 7868-88Oxygen remover, Oxy-Trap, Alltech Associates, Cat. No. 4001, or equivalent. (An oxygen remover in thecarrier gas line ensures optimum column life.)Recorder, 1-m

11、V full scale, 1-sec or less full-scale responseRegulator, air, two-stage, high purity, Matheson, Model 3104-590, or equivalentRegulator, hydrogen, two-stage, high purity, Matheson, Model 3104-350, or equivalentRegulator, nitrogen, two-stage, high purity, Matheson, Model 3104-580, or equivalentRestri

12、ctor, fine metering valve, Nupro, Cat. No. SS-1-SG, or equivalent, 2 required (see Note 2).Sample injector, any syringe or injection system capable of injecting a 1.0-L volume of sample, such asa Hamilton 701-NWG syringe, Alltech Associates, or equivalentStopwatch, electronic, digital, Alltech Assoc

13、iates, Cat. No. 4061, or equivalentValve, 6-port rotary, Valco Instruments Co., Model C6UWP, or equivalent, 2 required (see Note 2).REAGENTS AND MATERIALSAll reagents shall conform to the specifications established by the Committee on Analytical Reagents ofthe American Chemical Society, when such sp

14、ecifications are available, unless otherwise specified.References to water mean deionized or distilled water, except where noted.Air, zero gas, total hydrocarbons less than 2.0 ppm as methaneBenzene, 99.9% minimum purity, Wiley Organics, Cat. No. 0160.84, or equivalentButylcyclohexane, 99.9% minimum

15、 purity, Wiley Organics, Cat. No. 0419.71-1, or equivalent (C10naphthene)Cyclohexane, 99.9% minimum purity, Wiley Organics, Cat. No. 0679.02, or equivalent (C6naphthene)n-Decane, 99.9% minimum purity, Wiley Organics, Cat. No. 0812.57, or equivalent (C10paraffin)Ethylcyclohexane, 99.9% minimum purity

16、, Wiley Organics, Cat. No. 2442.00, or equivalent (C8naphthene)n-Heptane, 99.9% minimum purity, Wiley Organics, Cat. No. 3111.00, or equivalent (C7paraffin)n-Hexane, 99.9% minimum purity, Wiley Organics, Cat. No. 3442.00, or equivalent (C6paraffin)Hydrogen, zero gas, total hydrocarbons less than 0.5

17、 ppm as methaneMethylcyclohexane, 99.9% minimum purity, Wiley Organics, Cat. No. 4082.00, or equivalent (C7naphthene)Nitrogen, zero gas, total hydrocarbons less than 0.5 ppm as methanen-Nonane, 99.5% minimum purity, Wiley Organics, Cat. No. 6782.00 or equivalent (C9paraffin)n-Octane, 99.9% minimum p

18、urity, Wiley Organics, Cat. No. 7056.50, or equivalent (C8paraffin)Propylcyclohexane, 99.8% minimum purity, Wiley Organics, Cat. No. 8260.05-1, or equivalent (C9naphthene)Toluene (methylbenzene), 99.9% minimum purity, Wiley Organics, Cat. No. 3829.90, or equivalent3 of 7868-88PROCEDUREInstall the ox

19、ygen remover in the supply line between the hydrogen source regulator and the carrier gasinlet on the gas chromatograph.The recommended operating conditions for this analysis are given in Table 1. Other conditions may beused provided they produce the required sensitivity and chromatographic separati

20、ons equivalent to thoseshown in the Typical Chromatogram (Fig. 2).Table 1Operating ConditionsCarrier gas hydrogenCarrier gas flow rate 15 mL/minDetector flame ionizationDetector temperature 250 CInjection port temperature 200 CHydrogen flow rate* 15 mL/minAir flow rate* 400 mL/minMakeup gas nitrogen

21、Makeup gas flow rate* 30 mL/minColumn 1 temperature 120 CColumn 2 temperature programInitial temperature 100 CProgramming rate 6 C/minFinal temperature 400 CFinal time 10 minChart speed 0.5 cm/minSample size 1.0 L repeatable*Consult the manufacturers instrument manual for suggested flow rates.Prepar

22、ation of ApparatusInstrument Set-upInstall Column 1 (OV-275), the rotary and restrictor valves in a separately heated zone with the flowsconfigured as shown in Fig. 1. In the oven of the gas chromatograph install Column 2 (molecular sieve).CAUTION: Leakage of hydrogen into the confined volume of the

23、 column and valve compartments cancause a violent explosion. It is, therefore, mandatory to test for leaks each time a connection is made andperiodically thereafter. All connecting lines are to be of minimum diameter and length and must be heated.The restrictors are required to minimize any flow dis

24、ruption when the flow positions of the rotary valves arechanged and must be set to provide the same back pressure as Column 2.Establish the column flows in the following manner. Rotate Valve No. 1. to the broken-line position andfully open Restrictor No. 1. Measure flow through Column 1 (OV-275) at

25、the vent exit of Valve No. 1.Adjust Flow Controller No. 1 to produce the recommended flow rate of 15 mL/min. Measure the flowthrough Column 2 (molecular sieve) at the inlet to the FID. Adjust Flow Controller No. 2 to produce thesame flow as Column 1. Return Valve No. 1 to the solid-line position and

26、 proceed with the restrictoradjustment.4 of 7868-88Restrictor AdjustmentStart with Valve No. 1 and No. 2 in the solid-line position. Note the pressure reading on Pressure GaugeNo. 1. Rotate Valve No. 2 to the broken-line position and adjust Restrictor No. 2 until Pressure Gauge No. 1indicates the sa

27、me value as noted earlier. Return Valve No. 2 back to the solid-line position and rotateValve No. 1 to the broken-line position and note the pressure reading on Pressure Gauge No. 2. ReturnValve No. 1 to the solid-line position and adjust Restrictor No. 1 until Pressure Gauge No. 2 indicates thesame

28、 value as noted earlier.Column ConditioningWith Valve No. 1 in the broken-line position, condition Column 2 (molecular sieve) at 100 C for onehour. Then program the column temperature up to 400 C at 6 C/min and hold that temperature until a stablerecorder baseline is established at the required sens

29、itivity. At the same time condition Column 1 (OV-275)at 120 C in the heated zone. Allow Column 2 to cool to 100 C and rotate Valve No. 1 to the solid-lineposition.Cut-Time DeterminationWith Valve No. 1 in the solid-line position and Valve No. 2 in the broken-line position, inject 1.0 L ofbenzene int

30、o Injection Port 1. Determine the time from injection at which benzene begins to elute, andsubtract six seconds from this value. This time is defined as T. Redetermine time, T, daily during the firstweek of operation and weekly thereafter.Chromatographic TechniqueInject a repeatable volume of sample

31、, nominally 1.0 L, into Injection Port 1 of the gas chromatographwith both valves in the solid-line position. Immediately start the temperature programmer, integrator andrecorder. At time T, rotate Valve No. 1 to the broken-line position. A typical chromatogram is shown in Fig.2.Determine the relati

32、ve density of the sample by ASTM Method D 4052 or other suitable technique.CalibrationThe external standard technique is used for calibration. Quantitative results are based on the injection of arepeatable volume of sample and standard, and the use of response factors to relate peak areas obtained t

33、omass-ppm. Prepare a calibration blend as described in ASTM Method D 4307 to contain representativeparaffin and naphthene components (see REAGENTS AND MATERIALS) in toluene at approximately theconcentrations expected in the samples. Determine the relative density of the blend by ASTM Method D4052 or

34、 other suitable technique. Analyze the blend in duplicate as described under ChromatographicTechnique and determine the average area for each paraffin and naphthene peak. In the same manneranalyze the toluene and make appropriate corrections to the blend if any paraffins and naphthenes arepresent in

35、 the toluene. Calculate the mass response factor for each component using the following equation:AFB=5 of 7868-88where:A = concentration of component in blend, mass-ppmB = average peak area of componentF = response factor for component, mass-ppm/unit areaDetermine response factors, as directed above

36、, daily for each instrument used. Use the response factor ofC6paraffins for C3, C4and C5paraffins. Use the response factor of C6napthenes for C5naphthene.CALCULATIONSCalculate the concentration of each component to the nearest mass-ppm using the following equation:EFSComponent, mass-ppmD=where:D = r

37、elative density of sampleE = component peak areaF = response factor, previously definedS = relative density of calibration blendNOTES1. C3and C4paraffins can be calculated but the determined concentrations may be in error due to theinstability of these compounds in the sample. If samples are known t

38、o contain C3and C4paraffins, and areliable value is required, precautions must be taken in the handling of the sample to maintain its integrity.2. A suitable gas chromatograph is a Hewlett-Packard Model 5880A with HP 19358D Option 601. Thisoption includes the separate isothermal heated zone, the two

39、 required valves and one of the two requiredrestrictors. This gas chromatograph also includes a recorder and, if the Level 4 option is specified, anintegrator.PRECISIONRepeatabilityBased on two tests performed by each of two analysts, on each of two days (8 tests) in one laboratory, thewithin-labora

40、tory estimated standard deviations (esd) were calculated for components at specificconcentrations and are listed in Table 2. Two tests performed in the one laboratory by different analysts ondifferent days should not differ by more than the allowable difference values listed in Table 2 at theconcent

41、rations shown.6 of 7868-88Table 2ComponentConcentration,mass-ppmWithin-Lab esd,mass-ppmAllowable Difference,95% Probability,mass-ppmC5Paraffins 29 1.5 5C6Naphthenes 96 1.9 6C6Paraffins 100 2.4 8C7Naphthenes 180 3.3 11C7Paraffins 201 4.9 16C8Naphthenes 207 3.7 12C8Paraffins 307 5.1 17C9Naphthenes 334

42、 3.7 12C9Paraffins 477 5.3 17C10Naphthenes 451 5.7 19C10Paraffins 378 7.0 24ReproducibilityThere is insufficient data to calculate the reproducibility of the test at this time.TIME FOR ANALYSISThe elapsed time for one analysis is 1.4 hours. The labor requirement is 0.6 hour.REFERENCEASTM Methods D 4

43、052 and D 4307, www.astm.orgSUGGESTED SUPPLIERSAlltech Associates, Inc., 2051 Waukegan Rd., Deerfield, IL 60015Analytical Controls, Inc., 3448 Progress Dr., Bensalem, PA 19020Hewlett-Packard, 1200 E. Diehl Road, Naperville, IL 60566Matheson, P.O. Box. 96, Joliet, IL 60434Nupro Company, 4800 East 345th St., Willoughby, OH 44094Valco Instruments Co., Inc., P.O. Box 55603, Houston, TX 77055Wiley Organics, Inc., 4654 Kenny Road, Columbus, OH 432207 of 7868-88Figure 1Flow DiagramFigure 2Typical Chromatogram