1、NORMAL PARAFFINSBY CAPILLARY GAS CHROMATOGRAPHYUOP Method 915-92SCOPEThis method is for determining total normal paraffins (TNP) and individual normal paraffins inhydrocarbons, such as the UOP Molexprocess streams, including samples containing the Molex processdesorbent. Samples are typically in the
2、 C8to C20carbon number range. By preheating the sample andadding a suitable solvent, the range can be extended up to C40. The mass-% TNP at the high and lowconcentrations tend to be biased slightly high because of incomplete compensation for non-normals at thenormal paraffin sites. A slightly more a
3、ccurate TNP value would be expected using UOP Method 411 (seeNOTE). The lower limit of detection is 0.01 mass-% for any compound.OUTLINE OF METHODThe sample to be analyzed is injected into a gas chromatograph that is equipped with a fused silicacapillary column, internally coated with DB-17 (bonded)
4、 methylphenyl-polysiloxane, and with a flameionization detector (FID). To determine the total normal paraffins at all concentrations requires analysis bytwo different procedures, designated Method A and Method B.In Method A, samples containing less than 75 mass-% TNP are injected using the appropria
5、te operatingconditions. The integrator events are programmed to force a baseline at the valley point before and aftereach normal paraffin to compensate for the underlying non-normals at the normal paraffin site (Figs. 1 and2). The mass-% of each normal paraffin is obtained by the internal standard m
6、ethod of quantitation, whereinpeak areas are compared to the peak area of a known amount of an internal standard. The individual normalparaffins are summed to obtain TNP.In Method B, samples containing 75 mass-% or greater concentrations of total normal paraffins areinjected using the appropriate op
7、erating conditions. The mass-% composition of the sample is obtained bythe internal normalization technique. The individual normal paraffins are summed to obtain TNP.APPARATUSReferences to catalog numbers and suppliers are included as a convenience to the method user. Othersuppliers may be used.Bala
8、nce, readability 0.1-mgIT 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 IN
9、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 1992 UOP LLCALL RIGHTS
10、 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 610.832.9585
11、 PHONE.2 of 10915-92Chromatographic column, 30 m of 0.32-mm ID fused silica capillary, internally coated to a filmthickness of 0.25 m with DB-17 (bonded) 50% methyl-50% phenyl-polysiloxane, J therefore, it is mandatory to check for leaks each time a connection is made and periodicallythereafter.3. E
12、stablish the operating conditions listed in Table 1; except, set the column oven to 260C until thebaseline is stable. Other conditions may be used provided they produce the required sensitivity and chromatographicseparations equivalent to those shown in the Typical Chromatograms. If the carbon numbe
13、r range is significantly different from that shown in the Typical Chromatograms, thestarting temperature, final temperature or programming rate (Table 1) can be adjusted to optimizecomponent elution.4. Cool the column oven to a stabilized 32C.Method A: Normal Paraffins by Internal Standard Less Than
14、 75 Mass-% TNP1. Inject 0.5 L of the sample to be analyzed into the gas chromatograph and start the recorder,integrator and column temperature programming sequence. Typical chromatograms are shown inFigs. 1 and 2. Better precision is obtained when an autoinjector is used. This experimental run deter
15、mines the carbon number distribution of the sample, the internal standard to beused, and the approximate TNP composition. For samples containing equal to or greater than 75 mass-% TNP, use Method B.2. Choose an internal standard having one less or one more carbon number than the lowest or highestcon
16、tained in the sample.3. Add approximately 0.5 g of the internal standard, weighed to the nearest 0.1 mg, to approximately 5 gof the weighed liquefied sample. Samples containing solids at ambient temperature are heated in an oven at 85C until the entire sample isliquefied. A solvent such as n-hexane
17、can be added to the weighed sampleinternal standard solution, if necessary,to maintain a liquefied state at ambient temperature.4. Set the integrator events to force a baseline at the valley points before and after each normal paraffin(see Figs. 1 and 3). The baseline must be set in this way to comp
18、ensate for the underlying non-normals at the n-paraffin sites.5. Inject 0.5 L of the sample with the internal standard added and start the recorder, integrator andcolumn temperature programming sequence.4 of 10915-92 If the sample has been diluted, inject a proportionately larger sample volume.6. Id
19、entify the normal paraffins from the resultant chromatogram by comparing the chromatogramobtained to the Typical Chromatograms (Figs. 1 or 2), or to a known blend of normal paraffinsanalyzed under identical conditions.Method B: Normal Paraffins by Normalized Composition Equal To or Greater Than 75 M
20、ass-% TNP1. Set the integrator events to ensure that a true baseline, from the beginning to the end of thechromatogram, is maintained (see Fig. 3). A horizontal forward or equivalent baseline event must be used to prevent the integrator from establishinga new baseline during data processing of unres
21、olved groups of non-normals.2. Inject 1.0 L of the sample to be analyzed and start the recorder, integrator and column temperatureprogramming sequence. Heat the sample and add solvent, if necessary, to maintain a liquefied state at ambient temperature. Set the integrator events to inhibit peak detec
22、tion while the solvent peak is eluting.3. From the resultant chromatogram, identify the normal paraffins by comparing the chromatogram tothe Typical Chromatogram (Fig. 3) or to a known blend of normal paraffins analyzed under identicalconditions.Table 1Carrier gas hydrogenCarrier gas velocity 40 cm/
23、sec (1.5 mL/min at 50C)Column head pressure 32 kPa gauge (5 psig)Split flow rate 150 mL/minInjection port temperature 275CColumn temperature programInitial temperature 32CInitial time 8 minProgramming ratea2C/minFinal temperatureb260CFinal TimebHoldDetectorflame ionizationDetector temperature 300CHy
24、drogen flow rateC30 mL/minAir flow ratec275 mL/minMakeup gas nitrogenMakeup gas flow ratec30 mL/minChart speed10 mm/minSample size, Method A 0.5 LMethod B 1.0 LaProgram rate should be increased to 3C/min for carbon number ranges exceeding C24.bHold until all peaks have eluted or abort program ramp e
25、arly when all peaks have eluted.cConsult the manufacturers instrument manual for suggested flow rates to ensure detector linearitybetween small and large peaks.5 of 10915-92CalibrationSince all the sample components have essentially the same detector response on a mass basis, no relativeresponse fac
26、tor calibration is required (area-% is equivalent to mass-%). The internal standard method ofquantitation is used for Method A, wherein the n-paraffin peak areas are compared to the peak area of aknown amount of internal standard. The internal standard technique is required because the non-normalsth
27、at underlie the normal paraffins are not measured. The internal normalization technique is used forMethod B where area contribution from non-normals is minimal.CALCULATIONSUsing the peak areas for each sample component or group of components, calculate the composition ofeach sample using the appropr
28、iate formula.Method ANormal Paraffins by Internal StandardCalculate the mass-% of each normal paraffin in the sample to the nearest 0.01 mass-% using thefollowing formula:100 ABCDE= (1)where:A = peak area of the specific normal paraffinB = mass of the internal standard added, gC = concentration of t
29、he specific normal paraffin, mass-%D = peak area of the internal standardE = mass of the sample to which the internal standard was added, g100 = factor to convert to mass-%Calculate the total normal paraffin (TNP) content of the sample to the nearest 0.1 mass-% by summingthe individual normal paraff
30、ins. The total non-normals are calculated by difference, 100TNP.Method BNormal Paraffins by Normalized CompositionCalculate the mass-% of each normal paraffin in the sample to the nearest 0.01 mass-% using thefollowing formula:100 ACF= (2)6 of 10915-92where:A = previously defined, Eq. 1C = previousl
31、y defined, Eq. 1F = sum of all peak areas including n-paraffins and non-normals100 = previously defined, Eq. 1Calculate the total normal paraffin (TNP) content of the sample to the nearest 0.1 mass-% by summingthe individual normal paraffins. Total non-normals are calculated by difference, 100TNP.NO
32、TEUOP Method 411 is limited to samples having a carbon number range ending at C30. Also, the methodrequires a customized arrangement of two gas chromatographs, connected in series, utilizing molecularsieve extraction of normal paraffins, and extensive calibrations.PRECISIONRepeatabilityBased on 2 te
33、sts performed by each of 2 analysts on each of 2 different days (8 tests), the within-laboratory estimated standard deviations (esd) were calculated for components at specific concentrations intypical process streams and are listed in Table 2. Two tests performed in one laboratory by differentanalys
34、ts on different days should not differ by more than the allowable differences in Table 2 at theconcentrations listed (95% probability).ReproducibilityThere is insufficient data to calculate reproducibility of the test at this time.TIME FOR ANALYSISThe elapsed time for one analysis is 1.0 hour for ca
35、rbon numbers to C16and 2.5 hours for carbon numbersto C40. The labor requirement is 0.5 hour and 1.0 hour, respectively.REFERENCEUOP Method 411, “Normal Paraffins by Subtractive Gas Chromatography”SUGGESTED SUPPLIERSAlltech Associates, 2051 Waukegan Rd., Deerfield, IL 60015 (708-948-8600)J & W Scien
36、tific, Inc., 91 Blue Ravine Rd., Folsom, CA 95630 (961-351-0387)Matheson Gas Products, Inc., P.O. Box 96, Joliet, IL 60434 (815-727-4848)Wiley Organics, 1245 South 6th St., Coshocton, OH 43812 (614-622-0755)7 of 10915-92Table 2ProcessStream ComponentConcentration,mass-%Within-Labesd,mass-%AllowableD
37、ifference,mass-%Extract TNP 98.4 0.07 0.2TNN 1.6 0.07 0.2n-C105.10 0.094 0.31n-C1110.00 0.122 0.41n-C1214.87 0.093 0.31n-C1324.53 0.037 0.12n-C1424.40 0.116 0.39n-C1514.60 0.130 0.44n-C164.95 0.060 0.20Feed TNP 26.3 0.37 1.2TNN 73.7 0.37 1.2n-C101.43 0.013 0.04n-C112.63 0.024 0.08n-C123.75 0.074 0.2
38、5n-C136.84 0.116 0.39n-C146.41 0.108 0.36n-C153.88 0.083 0.28n-C161.34 0.037 0.12Raffinate TNP 7.3 0.17 0.7TNN 92.7 0.17 0.7n-C100.46 0.005 0.02n-C110.88 0.010 0.03n-C121.27 0.050 0.20n-C131.61 0.077 0.30n-C141.78 0.037 0.15n-C150.97 0.021 0.08n-C160.32 0.008 0.038 of 10915-92Figure 1Typical Chromatogram, Molex Process Feed9 of 10915-92Figure 2Typical Chromatogram, Molex Process Raffinate10 of 10915-92Figure 3Typical Chromatogram, Molex Process Extract
