1、 COPYRIGHT 1972, 1975, 2000, 2003 UOP LLC ALL RIGHTS RESERVED uop, UOP, and Molex are trademarks and/or service marks of UOP LLC. Marks of other proprietors may appear incidentally AROMATICS IN MOLEX PROCESS n-PARAFFIN PRODUCTS BY ULTRAVIOLET SPECTROPHOTOMETRY uop Method 495-03 SCOPE This method is
2、for estimating total aromatics in Molex process n-paraffin products. The method determines an average amount of naphthalenes and alkylbenzenes that may be present, provided the concentration of the alkylbenzenes is at least ten times greater than the naphthalenes. In practice, this condition is sati
3、sfied for the specified applications. Other samples with similar compositions may also be suitable for this analysis. The lower limit of detection is 0.0003 mass-%. REFERENCES API Project 44, American Petroleum Institute, 1220 L Street, N.W., Washington, DC 20005 (202-682-8000) www.api.org ASTM Meth
4、od D 4052, “Density and Relative Density of Liquids by Digital Density Meter,” www.astm.org UOP Method 999, “Precision Statements in UOP Methods,” www.astm.org OUTLINE OF METHOD The ultraviolet absorbance spectrum of the sample is measured. Average absorptivities from published spectral data are use
5、d to compute the concentrations of the naphthalenes and alkylbenzenes. Sample complexity does not permit experimental calibration. APPARATUS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Absorption cells, matched pairs, sil
6、ica, 10-, 5- and 1-cm, Fisher Scientific, Cat. Nos. 14-385-930F, -930E, and -904C, respectively 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 F
7、OLLOWED WHEN UTILIZING THIS PROCEDURE. FAILURE TO UTILIZE THIS PROCEDURE 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 IN THIS PROCEDURE SHOULD BE REVIEWED FOR SELECTION OF THE AP
8、PROPRIATE PERSONAL PROTECTION EQUIPMENT (PPE). in this method for purposes such as product or service identification, but no claim is made to any other proprietors mark used. UOP Methods are available through ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194428-2959,
9、United States. The 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 PHONE. 2 of 8 Balance, readability 0.1-mg Flasks, volumetric, Class A, 25-mL, Fisher Scientific, Cat. No. 10-210-5A, several requ
10、ired Spectrophotometer, capable of scanning and operation in the 360-220-nm region with a spectral bandwidth of 1 nm and capable of 0.5% precision in absorbance measurements at the 1.0 level at this resolution Vacuum source, a water aspirator, Fisher Scientific, Cat. No. 09-960-2, is sufficient REAG
11、ENTS AND MATERIALS References to catalog numbers and suppliers are included as a convenience to the method user. Other suppliers may be used. Isooctane, spectroscopic grade, Fisher Scientific, Cat. No. 0300-4 CALIBRATION Instead of directly calibrating the spectrophotometer with known naphthalenes,
12、the average absorptivities of the C10through C13naphthalenes at 285 nm, 33.7 L/g-cm, and, near 270 nm, 30.0 L/g-cm, are used in this method (see Table 1). Similarly, the average absorptivity of available C10to C20alkylbenzenes near 270 nm, 3.01 L/g-cm, is used (see Table 2). Absorptivities of indivi
13、dual naphthalene and alkylbenzene hydrocarbons at their respective wavelengths are derived from data in the API catalog of ultraviolet spectral data issued by Research Project 44, and are listed in Tables 1 and 2. Table 1 Naphthalene Absorptivities, L/g-cm Compound API Serial Number 285 nm Near 270
14、nm Naphthalene 1-Methylnaphthalene 2-Methylnaphthalene 1,2-Dimethylnaphthalene 1,3-Dimethylnaphthalene 1,4-Dimethylnaphthalene 1,5-Dimethylnaphthalene 1,6-Dimethylnaphthalene 1,7-Dimethylnaphthalene 1,8-Dimethylnaphthalene 2,3-Dimethylnaphthalene 2,6-Dimethylnaphthalene 2,7-Dimethylnaphthalene 1-Iso
15、propylnaphthalene Average 605 539 572 215 216 217 218 219 220 221 222 226 224 203 28.5 32.0 22.9 37.3 36.4 43.5 54.0 36.4 36.0 46.0 22.0 21.3 23.5 31.7 33.7 32.6 32.0 31.8 26.5 26.5 26.0 29.0 35.0 32.5 30.0 30.0 27.5 29.5 31.7 30.0 495-03 3 of 8 Table 2 Alkylbenzene Absorptivities, L/g-cm Compound A
16、PI Serial Number Near 270 nm Tetralin 2-Methyltetralin 5-Methyltetralin 6-Methyltetralin 6-n-heptyltetralin n-Butylbenzene 1,4-Diethylbenzene n-Hexylbenzene 1,4-Diisopropylbenzene n-Octylbenzene n-Undecylbenzene n-Tetradecylbenzene 1,1-Diphenylethane 1,1-Diphenylbutane 1,4-Diphenylbutane Average 133
17、 398 134 135 287 176 188 143 191 144 146 394 199 200 283 4.45 3.83 1.89 5.41 4.96 1.82 3.05 1.40 2.19 1.40 2.50 2.39 2.65 2.72 4.50 3.01 PROCEDURE The size of the cells to be used (10-, 5- or 1-cm) is determined by the concentration expected in the samples. If an estimate is not available, use the 1
18、-cm pair first, and switch to the 5- or 10-cm pair only if greater sensitivity is required. The detection limit for this method is based upon the use of a 10-cm cell for alkylbenzenes. 1. Fill a matched pair of absorption cells with isooctane and place them in their respective beam paths. Perform a
19、background correction by scanning in the region from 360 to 220 nm. 2. Empty the sample cell and dry it using the vacuum. 3. Transfer the sample, as received, into the cell and return it to the spectrophotometer. 4. Obtain the spectrum from 360 to 220 nm. Typical examples are shown in Figures 1 and
20、2. 5. If the absorbance maximum near 270 nm exceeds 1.0, sample dilution is required. (Some instrument manufacturers may recommend a different maximum; follow the manufacturers recommendations.) Proceed to Step 7 if the sample requires dilution. 6. If the sample does not require dilution, obtain the
21、 density of the as received sample using ASTM Method D 4052, Density and Relative Density of Liquids by Digital Density Meter (or equivalent), see NOTE 1. If the absorbance maximum near 270 nm is less than 0.1, proceed to Step 11, otherwise, proceed to Step 12. 7. Dilute sequentially with isooctane
22、until the absorbance is within the recommended range (0.1 to 1.0). Weigh a portion of the sample to the nearest 0.1-mg, into a 25-mL volumetric flask. Dilute to volume, cap, and invert several times to thoroughly mix the contents. 8. Empty the sample cell, clean with isooctane, and dry. 495-03 4 of
23、8 9. Fill the sample cell with the diluted sample and return the cell to the instrument sample beam. 10. Obtain the spectrum of the diluted sample from 360 to 220 nm. Go to Step 12. 11. If greater sensitivity is required, use the 5- or 10-cm matched pairs of cells. Perform Steps 1 through 4 with the
24、 longer path length cells. Then go to Step 12. Use 10-cm cells if the absorbance using the 1-cm cell is well below 0.1. Use 5-cm cells if the absorbance using the 1-cm cell is near 0.1 or the supply of sample is limited. Do not use 5- or 10-cm cells for diluted samples. 12. Calculate the naphthalene
25、 and alkylbenzene concentrations in the sample. CALCULATIONS Significant Figures When using the equations that follow, carry a minimum of three significant figures through all calculations. When reporting final alkylbenzenes and naphthalenes, report a single significant figure for data below 0.1 mas
26、s-% and two significant figures at or above 0.1 mass-%. Baseline Correction The procedure below describes the determination and use of baseline correction by mathematical means. If it is desired to perform the baseline correction manually, see NOTE 2. Calculate the baseline corrected absorbances (Fi
27、gures 1 and 2) by the following equations: ( )360320320270270bA- A1.25 - A- A A = (1) ( )360320320285285bA- A0.88 - A- A A = (2) where: A270= maximum absorbance measured near 270 nm A285= absorbance measured at 285 nm A320= absorbance measured at 320 nm A360= absorbance measured at 360 nm Ab270= bas
28、eline corrected absorbance near 270 nm (at A270maximum) Ab285 =baseline corrected absorbance at 285 nm 1.25 = constant = (320 - 270)/(360 - 320) 0.88 = constant = (320 - 285)/(360 - 320) Calculations for as received samples, and for samples requiring dilution, are different. Naphthalenes interfere w
29、ith the alkylbenzenes determination and a correction is made for their effect. As Received Samples Spectra of samples run as received may be obtained using 1-, 5- or 10-cm cells; the longer path lengths are used to maximize sensitivity 495-03 5 of 8 Naphthalenes, mass-% =33.7BDA285b100 )3(where: Ab2
30、85= previously defined, Equation 2 B = cell path length, cm D = density of as received sample, g/L (see NOTE 1) 33.7 = average absorptivity, or calibration coefficient, of naphthalenes listed in Table 1, L/g-cm 100 = conversion factor, g/g to mass-% Alkylbenzenes, mass-% =BD01.3A89.0A285b270b100 )4(
31、 where: Ab270= previously defined, Equation 1 Ab285= previously defined, Equation 2 B = previously defined, Equation 3 D = previously defined, Equation 3 0.89 = constant, ratio of average naphthalene absorptivities at 270 nm over 285 nm (30.0/33.7), from Table 1 3.01 = average absorptivity, or calib
32、ration coefficient, of alkylbenzenes listed in Table 1, L/g-cm 100 = factor to convert g/g to mass-% Diluted Samples Spectra of diluted samples are obtained using 1-cm cells. Naphthalenes, mass-% =33.7BFA285b100 )5( where: Ab285= previously defined, Equation 2 B = previously defined, Equation 3 F =
33、concentration of sample in dilution, g/L (see NOTE 1) 33.7 = average absorptivity, or calibration coefficient, of naphthalenes listed in Table 1, L/g-cm 100 = conversion factor, g/g to mass-% Alkylbenzenes, mass-% =BF01.3A89.0A285b270b100 (6) where: Ab270= previously defined, Equation 1 Ab285= previ
34、ously defined, Equation 2 B = previously defined, Equation 3 F = previously defined, Equation 4 495-03 6 of 8 0.89 = constant, ratio of average naphthalene absorptivities at 270 nm over 285 nm (30.0/33.7), from Table 1 3.01 = previously defined, Equation 3 100 = factor to convert g/g to mass-% NOTE
35、1. The units of density used in this method are g/L, not the common g/mL. Multiply the values obtained from ASTM Method D 4052 by 1000 to obtain g/L. 2. For Manual Baseline Correction, draw a straight baseline from approximately 360 nm to 320 nm, extrapolating beyond 270 nm, see Figures 1 and 2. Det
36、ermine the baseline corrected absorbances, in absorbance units, of the sample at 285 nm and at the maximum absorbance near 270 nm. Define the absorbance at 285 nm, above the background baseline, as Ab285. Define the maximum absorbance near 270 nm, above the background baseline, as Ab270. Proceed wit
37、h the calculations under As Received Samples or Diluted Samples. PRECISION The precision statements were determined using UOP Method 999. ASTM and UOP Repeatability A nested design was carried out for determining alkylbenzene and naphthalene in n-paraffins with two analysts in one laboratory. Each a
38、nalyst carried out four tests at each of two concentrations on two separate days. The total number of tests at each concentration was 16. Using a stepwise analysis of variance procedure, the within-day estimated standard deviation (esd) was calculated for each concentration and is listed in Table 3.
39、 Two tests performed by the same analyst on the same day should not differ by more than the ASTM allowable difference shown in Table 3 with 95% confidence. Two tests performed in one laboratory by different analysts on different days should not differ by more than the UOP allowable difference shown
40、in Table 3 with 95% confidence. Table 3 ASTM and UOP Repeatability ASTM Repeatability UOP Repeatability Mean Concentration Within-Day esd Allowable Difference Within-Lab esd Allowable Difference Sample 1 Alkylbenzene, 11 mass-% 0.015 0.05 0.038 0.2 Naphthalene, 0.2 mass-% 0.00057 0.002 0.00112 0.004
41、 Sample 2 Alkylbenzene, 0.01 mass-% 0.000038 0.0001 0.0001 0.0005 Naphthalene, 0.003 mass-% 0.000004 0.00001 0.00001 0.00006 The data in Table 3 are a short-term estimate of repeatability. When the test is run routinely, a control standard and chart should be used to develop a better estimate of the
42、 long-term repeatability. Reproducibility There is insufficient data to calculate the reproducibility of the test at this time. 495-03 7 of 8 TIME FOR ANALYSIS The elapsed time and labor requirement for a single analysis are identical, 0.7 hours. SUGGESTED SUPPLIER Fisher Scientific Co., 711 Forbes Ave., Pittsburgh, PA 15219-4785 (412-490-8300) 495-03 8 of 8 495-03
