ANALYTICAL CHEMISTRY
1770 origin and was used without purification. Ground (20-mesh) and unground specimens gave the same oxidimetric results. The three samples of purified cellulose were prepared and contributed by C. M. Conrad, Southern Regional Research Laboratory, and were used without further treatment. The high- and low-viscosity celluloses n-ere commercially purified and derived from cotton; the viscose rayon, from wood. The latter had been extracted with hot ethyl alcohol to remove resins, etc., a t the Southernal Regional Research Laboratory. Moisture in the celluloses was determined with a vacuum oven a t 3 mm. of mercury and 110" C. for 20 hours. Ash was determined for all materials at 550" C. for 16 hours, after precharring with infrared. -4sh values for the celluloses in the order of Table I were 0.04, 0.13, 0.02, and 0.05%. The starch and glucose have been described ( 6 ) .
The latter is thus oxidized through heat of dilution; subsequent external heating completes the oxidation of resins. Errors in the alkali-soluble fraction are the only critical ones-; those in the alpha fraction cancel out, practically speaking, inasmuch as a 1.5% error therein would result in an error of only 0.1% in an CYcellulose value near 90%, as calculated from total cellulose. CONCLUSION
Cellulose can be determined rapidly and with slight error, in the presence of moisture and usual inorganic impurities, by applying the theoretical factor 0.01240 gram of cellulose per ml. of 1.835 AT (90.00 grams per liter) potassium dichromate solution, with the dichromate heat-of-dilution method.
RESULTS AND DISCUSSION
The results by the two methods on the celluloses, starch, and glucose are shown in Table I. The yield values were calculated as in previous work ( 6 ) . Of the sources of error previously discussed, only two need be stressed. Moisture in cellulose is particularly difficult to determine because the last traces of water are tenaciously retained by such high polymers. Both sets of values are probably too low, by the same amount, because of this effect. Nelson and Hulett (6) found by extrapolation to 250" C. that 0.41% water remained in their cellulose a t equilibrium a t 115" C. and 0.001 mm. of mercury. If such a value could be applied to the celluloses of Table I, the heat-of-dilution method could be assumed to give truly theoretical yields for celluloses. The high yield for surgical cotton would then have to be ascribed to oxidizable impurities of a more reduced nature than cellulose.
Table I.
Comparison of Results by Two Methods on Celluloses, Starch, and Glucose
Substance High viscosity cotton Surgical cotton Viscose rayon Low vlscoslty cotton Starch Glucose
Heat-of-Dilution h l s d External Heating Method Yield, Standard No. of Yield, Standard No. of Yo of devia- repli% of devia- replitheory tions cates theory tions cates 99.70 100.05 99.65
0.18 0.27 0.12
6 12 6
98.50 98.20 98.50
0.24
6
0.08
4
0.24
6
99 60 99 35 99 40
0 21 0 21
16
9 8 45 98 25 99 20
0 18 0 22 0 21
8 8 8
0 12
10 12
The other error is due to carbon monoxide formation and escape. Segal, Tripp, Tripp, and Conrad (9) have shown that 1.0 to 1.6% of glucose and cellulose was converted to carbon monoxide when they used the same method of external heating applied herein for comparison. They measured the amount of carbon monoxide which escaped from solution and thus accounted for their low results, which were in essential agreement with those in Table I, column 5, the glucose value of which fits into their range of values (their Table IV). It appears reasonable to account for the difference between the two sets of yield values as being due to smaller quantities of carbon monoxide formed or escaping in the heatrof-dilution method. This could be the result of the much more rapid heating, together with the two- to fivefold greater concentrations of acid and dichromate in the present method over t h a t of external heating. Furthermore, in the latter method, some oxidation, approximately 9%, occurs during the addition of dichromate to the cellulose solution. Since under these conditions cellulose is in excess a part of the time, carbon monoxide formation may be favored. Both procedures are combined in the a-cellulose determination developed a t the National Bureau of Standards ( 4 ) and used as ASTM and TAPPI standard methods ( 1 , IO). Solution of cellulose by 12M acid, followed by dichromate, is used in the alpha fraction. whereas addition of concentrated acid to the dichromate-cellulose mixture is used for the alkali-soluble fraction.
ACKNOWLEDGMENT
The authors take pleasure in thanking C. M. Conrad for the purified celluloses. LITERATURE CITED
(1) American Society for Testing Materials, ASTM Standard hlethod No. 588. (2) Burton, J. O., and Rasch, R. H., Bur. Standards J . Research, 6, 603 (1931). (3) Kettering, J. H., and Conrad, C. M,, IND.ENG.CAEM.,A N ~ L . ED.,14, 432 (1942). (4) Launer, H. F., J . Research Natl. Bur. Standards. 18, 333 (1937); 20, 87 (1938). (5) Launer, H.F..and Tomimatsu. Y.. b x a ~CHEM.. . 25.1767 (1953). (6) Nelson, 0. A , , and Hulett, G. A , , J . I n d . Eng. Chem., 12, 40 (1920). (7) Scribner, B. W., P a p e r I n d . a n d P a p e r W o r l d , 30, 2 (1948). (8) Scribner, B. W., and Wilson, W. K., J . Research ~2'atl. Bur. Standards, 39, 21 (1947). (9) Segal, L., Tripp, R. C., Tripp, V. W., and Conrad, C. AI., ASAL. CHEM.,21, 712 (1949). (10) Technical A4ssociationof the Pulp and Paper Industry, TAPPI Standard Method No. 42911. ~I
RECEIVED for review June 1, 1953. Accepted August 10, 1953. Presented before the Division of Cellulose Chemistry a t the 123rd Meeting of the Los Angeles. Calif. AMERICAN CHEMICAL SOCIETY,
Infrared Determination of Total Aromatics In Naphthas and Catalytic Reformates Boiling between 200' and 400' F. JOSEPH BOMSTEIN Sinclair Research Laboratories, Inc., Harvey, I l l . of total aromatics in hydrocarbon fractions is D of considerable interest to petroleum refiners, and has been the subject of many investigations Methods have been deETERMISATION
veloped through use of several techniques, including acid absorption ( 1 , 5 ) , ultraviolet (8), Raman ( 6 ) , mass spectrometry (g), and adsorption (3). The infrared method was developed to overcome difficulties encountered in several of these techniques, and is found to provide a rapid, reasonably accurate analysis, with limitations, interference. and errors as discussed below. APPARATUS AND MATERIALS
All spectra were obtained with a Perkin-Elmer Model 21 spectrometer, using rock salt cells and prism. The maker's recommended quantitative conditions were used throughout (9). Recordings were linear in wave length. All pure compounds were obtained from the National Bureau of Standards and were of better than 99% purity, except o-tertbutyltoluene, which was obtained from the National Advisory Committee for Aeronautics, Washington, D. C., and was of unknown purity.
vo L U M E
2 5 , NO. 11, N O V E M B E R 1 9 5 3
1771
Values of K for Pure Compounds
Table 11. Composition of Aromatic Blend for Calibration
Table I.
( h r e a i n square centimeters
x
molecular weight diyided b y 100) Deviation from Boiling , K Extrapolated Average Point, ' F,
Compound Ben7ene Toluene Ethylbenzene o-Xylene m-Xylene p-Xylene o-Methylethylbenzene m-Methylethylbenzene p-hfethylethylbenzene n-Propylbensene IsopropSlbenzene 1 2 3-Trimethylbenzene 1'2'4-Trimethylbenzene 1:3:5-Trimethylbenzene n-Butvlbenzene Isobutylbenzene sec-Butylbenzene fert-Butylbenzene o-Cymene m-Cymene p-Cymene 1-Methyl-2-n-propylbenzene 1-hlethyl-3-n-propylbenzene 1- M Phvl-4-n-~ro~vlbenzene ~ 1,2.3,4-i;etrameth;benzene 1 2 3 5-Tetramethylbenzene 1:2:4:5-Tetramethylbenzene 1 2-Dimet;hyl-3-ethylbenzene 1 :3-Dimethy1-2-ethylbenzene 1 2-Dimethyl-4-ethylbenzene 1'3-Dimethyl-4-ethylbenzene 1'4-Dimethyl-Z-ethylbenzene 1'3-Dimefhyl-5-ethylbenzene o1Diethylbenzene m-Diethylbenzene p-Diethylbenzene Indane o-tert-Butyltoluene m-tert-But yltoluene p-tert-Butyltoluene Tetralin Average of all aromatics Extrapolated value Value obtained b y actual analysis Standard deviation b y method of summation of squares Relative standard deviation Standard error
176 232 277 291 282 282 323 325 32:3 318 305 351 338 329 356 345 340 336 347 349 349 360 351 363 399 387 383 381 374 374 371 368 363 363 358 360 350 393 373 379 405
22 ,5
-4
6
30.8 t3.7 27.8 -0.7 25.8 -1.3 32.2 -3.9 Not available h-ot available Not Not available -4.5 22.6 27.2 +0.1 Not available Not available Not available 3-ot available S o t available 26.4 -0.7 26.1 -1.0 25.8 -1.3 21.1 -fi.o 27.6 +O.j 30.5 +3.4 -2.7 24.4 +I .5 28.6 7-3.1 30.2 26.3 27.1
-0.8
28.9
+1.8
Weight Toluene Ethylbenzene m-Xylene m-Methylethylbenzene p-Methylethylbenzene Isopropylbenzene I ,2,4-Trimethylbenzene 1,3,5-Trimethylbenzene m-Cymene p - C ymene 1 2 3 &Tetramethylbenzene 1;3~Dimethyl-5-ethylbenzene
6.27 6.34 6.36 6.62 6.14 5.80 6.48 6.19 5.77 5.91 6.27 5.85
Indane
7.64
p-Xylene
1 ,19
o-Xylene
1.18
Analysis, % '
Blend ilB-3 AB-5
Table IT.
I582 1583 1599 1600 1624
Table V. Cut KO. 2
3 4
DEFINITIONS AND SYMBOLS
THEORY AND DEVELOPMENT O F METHOD
The measurement region is 5.00 to 5.85 microns, where absorption bands are probably due to overtones and combinations (7, 10). S o theoretical treatment is at present available. The reIationPhips b e h een substitution types and spectral patterns in the 5- to 6-micron region were first described by Young, DuVall, and Wright (10). This method utilizes a value which is related t o integrated intensity (4). The latter was not calculated, as measurements were made on a linear wave-length instrument, and convenient and reproducible "wing" measurements could not be made. Initial attempts to develop a method by measurements of band absorbances and areas failed, because of the high specificity of the infrared method for substitution types. Inspection of the 6-micron region showed that the areas under the curves between 5 and 6 microns were fairly constant for a given molecular weight. Subsequent calibration proved the approximate constancy of K for aromatics in the 200" to 400' F. range. In order to minimize olefin interferences, the 5.85-micron value was arbitrarily selected as the boundary on the long wave-length side. "Background" effects were satisfactorily handled through use of a standard raffinate solvent, discussed later. Molecular weight may be obtained by any suitable procedure, but in this work values were obtained by mass spectrometry ( 2 ) . At this time the authors are studying application of the method
Infrared 98.1
70
Ll5 1.12 0,72 1.29 1.21 1.21 1.10 1.02 1.20 1.28 1.17 1.19 1 18
1.13
Ultraviolet 96.7
Weight % Found in R u n 1 2 3 39.0 39.0 39.0 59.5 59.6 59.8
Weight % ' Aromatics 40.4 61.7
Total -4romatics in Blends of Corpus Christi Naphtha Weight Per Cent
Sample KO.
10.4% 0,55
A = area in square centimeters bounded by 5.00 microns, 100% transmittance, 5.85 microns, and the absorption curve .If = average molecular weight of the aromatics in a given sample, determined by mass spectrometry or other means K = AM /lo0 for a theoretical 0.100-mm. cell
Artual 100
Weight Compound Isobutylbenzene n-Propylbenzene 1-Methyl-2-ethylbenzene 1,2,3-Trimethylbenzene n-Butylbenzene sa-Butylbenzene tert-Butylbenzene p-Diethylbenzene n-Diethylbenzene o-Diethylbenzene o-Cymene 1-Methyl-3-tert-butylbenzene l-l\lethyl-4-ter~-hutylbenzene 1-Methyl-2-tert-butylbenzene
Tahle 111. Reproducibility of I< by Repeated Analyses
...
?.8
70
Compound
.5 6
7 8 9 10 11 12 13
Boiling Range, O F. 297-340 340-37.5 202-248 248-297 375-399
Infrared 17.8 25.1 4.2 13.2 27.3
Ultraviolet 21.2 21.8 7.6 18.1 22.3
Acid absorption 20.8 24.5
..
2i:o
Total -4romaticsin Cuts of Rangely, Colo., Crude Boiling Range, O F. 207 215 232 243 251 260 271 280 292 300 311 320 331 341 349 I61 (15 mm) 173 (15 mm)
Infrared 0.0 3.0 5.8 0.0 0.0 1 .n
Weight Per Cent UltraMass violet spec. 1.0 ... 5.9 ... ... 6.4 1.3 ... 0.6 ... 4.3 ... 13.6 ,.. 17.6 ... 8.0 ... 3.7 , . . 8.3 ... 15.9 ,.. 18.0 ... 15.5 ... 13.3 ... 12.9 ... 13.6 8.7 9:1
Acid absorption
16.3 14.3 3.4 0.3 7.0 14.0 14 15.0 16 14.3 10.7 16 14.3 17 14.8 18 Blend 2-18" 9.2 a Weighted average of individual cuts based on infrared shows 7.9
%.
... ...
... ...
... 9.4 weight
to higher boiling aromatics. Initial results indicate that extension is valid for mononuclear aromatics, as, for example, in the cases of C1&9 compounds, whose K's fall into the range shown in Table I. Biphenyls and naphthalenes have different K's, although for the limited number of compounds examined, each group is approximately constant as a class. In addition, a relationship may exist between classes. This is a subject of present investigation, but is not reported here because of insufficient data. CALIBRATION
Calibration was accomplished in several steps. The 5- to µn spectrogram was obtained for available aromatics in the 200' to 400' F. range. Areas within the previously described boundaries were measured in square centimeters with a compensating polar planimeter. Measurements were repeated, until three readings agreed within 0.1 sq. cm., and the average of these three was taken. Areas obtained were multiplied by molec-
ANALYTICAL CHEMISTRY
1772
__
__
fins, thiophenes, and pyridine, and (2) aromatics whose K varies from the established values, such Weight % Weight % by BR benzene, naphthalene, and polyphenyls. InfraMass Acid Infrahlass .4ciciObviously, the extent of the interference will red spec. absorption Saniple KO, red spec. absorption vary with the absorptivity and concentration of 11007 28041 55.2 55.5 65 8 28042 1,033 the interfering compound. In practice, small 68.0 68.9 78.2 17082 58.0 54.4 65.7 28043 amounts of olefins and naphthalenes do not in17084 28044 65.5 64.0 75 .O 17021 28046 59.6 52.0 47.6 terfere seriously. Many of the samples in Table 17024 62.0 28047 71 .O 59.5 17029 V I were known to contain both. 51.0 46.2 28051 57.0 28031 62.5 68.8 59.1 28052 d particular advantage of the method is that 28032 45.2 28054 46.0 53 1 28034 64 8 53.1 28053 56.5 the identity of an interfering compound may often 47.3 28035 59 2 28067 52.0 80.0 be established from the spectrogram and suitable 28039 28037 75.0 correction made, based on its concentration and contribution to the area measurement. Table 1-11, Total Aromatics i n Synthetic Blends Inspection of the data shows that indane and Wt. % Added Aroinaticsa Tetralin (1,2,3,4-tetrahydronaphthalene)K’s are within the Present Found Deviation. % general range. -4lthough no substituted indanes and Tetralins 49.7 48.5 -1.2 were available, there is no apparent reason for nonconformity. 34.8 33.6 -1.2 26.9 28.2 +1.3 Errors based on deviations of single compounds from the aver20.1 21.7 4-1.6 10.8 12.9 +2.1 age are computed and shown in Table I. These values indicate that the method is reliable. Errors based on deviations from a Original contained 6.8 wt. Yo aromatics by infrared. Beer’s law are negligible for concentrations between 10 and 9575, as shown by the straight line obtained. Errors based on synTable Y I I I . Errors Caused by Contamination thetic blends are shown in Table VII, indicating a slight curvature Theoretical y t . % Wt. % to the calibration curve. Contaminant Aromatic3 Found Deviation, % Errors caused by inclusion of typical impuritiea are shown for 1.65% benzene 67.2 70.0 +2.8 4 . 9 4 % benzene 68.3 74.0 +5.7 the cases of benzene, naphthalenes, and olefins in Table VIII. 0 . 5 1 7 naphthalenes 76.0 76.5 +0.5 The naphthalene contaminant was composed of l i % naphthalene, 1 , 7 6 4 naphthalenes 76.5 77.6 +1 .o 5 . 0 % olefins 76.0 76.5 +0.5 65% 1-methylnaphthalene, and 17%2-methylnaphthaIene. The 9 . 9 % olefins 68.4 69.5 +1.1 olefin contaminant was a Cs-Clocut of propylene polymer, and by infrared analysis contained a large proportion of terminal olefin. It is apparent from this that approximately 1% benzene, 2y0 naphthalenes and 10% olefin can be tolerated. ular weights and the product was corrected to give K for a theoretical 0.100-mm. cell. Values of K for pure compounds are listed in Table I. RAFFINATE PREPARATION -4 raffinate was prepared as described below, and a blend of available calibration samples was made, with composition shown A 200’ to 400” F. fraction of a mid-continent crude was acidin Table 11. A series of blends of aromatics in raffinate was treated, washed, dried, and percolated through silica gel: until it made, and their spectra were obtained. K was calculated and contained less than 0.0050/0 total aromatics by ultraviolet absorpplotted against theoretical weight per cent aromatics, giving a straight line. The extrapolation to both ordinates gives reasontion methods. A second raffinate was similarly prepared from a able agreement with calculated values (see Table I). Individual reformate. deviations are small, so that large changes in molecular distriValues of K deviated by less than the magnitude of analytical bution can be tolerated. error anticipated, so that the first prepared raffinate was used Two blends were run repeatedly under identical conditions to check reproducibility. Deviations are listed in Table 111. throughout the calibration. Table VI.
Total ironlatics in Reformates
ANALYTICAL PROCEDURE
ACKNOWLEDGMENT
A sample is placed in a O.lO&mm. cell, and its spectrogram is obtained between 5.00 and 5.85 microns. The area under the curve is measured, and K is calculated, using mass spectrometry for molecular weight. Reference to the calibration curve gives weight per cent total aromatics directly. Time required for a single analysis is less than 30 minutes, including molecular weight determination.
The author is grateful to the Sinclair Research Laboratories, Inc., for permission to publish this work, and takes this opportunity to express appreciation to James Nee1 for his capable assistance throughout, and to various other groups who cooperated. LITERATURE CITED
APPLICATIONS TO PETROLEUM-BASED MATERIALS
Many determinations have been made by this method, and values were compared t o those of other methods when possible. Table IV shows results from blends of Corpus Christi naphtha. Table V lists data for Rangely, Colo., naphtha. Table VI shows data for cuts of two different catalytic reformates. Mass spectrometer data were obtained by the method of Brown (#), with slight modification; ultraviolet data by the method of Kinder (8); and acid absorption data by ASTM method (1). Data by the LeTourneau method (3)were not available.
American Society for Testing Materials, “Standards on Petroleum Products and Lubricants,” p. 323 (D 875-461T), November 1950. Brown, R..4., A N ~ LCHEM., . 23,430(1951). Criddle, D.W., and LeTourneau, R. L., I b i d . , 23, 1620 (1951). Francis, 5. A., J . Chem. Phys., 18,861 (1950). Gross, -4. V.,and Wackher, R. C., IND.ENO.CHEM.,ANAL.ED., 11, 614 (1939). Heigl, J. J., Black, J. F., and Dudenbostel, B. F., Jr., ANAL. CHEM.,21,554 (1949).
Herrberg, G., “Infrared and Raman Spectra,” p. 365,New York, D.Van Nostrand Co., 1945. Kinder, J. F., ANAL.CHEM.,23,1379 (1951). Perkin-Elmer Corp., “Instruction Manual,” Vol. 3B, p. 42, 1952.
INTERFERENCES AND ERRORS
Young, C. W., DuVall, R. B., and Wright, N., ANAL.CHEM., 23, 709 (1951).
Interferences are generally of two types: (1) nonaromatics which absorb in the 5- t o 6-micron region, such as carbonyls, ole-
RECEIVSD for review April 25, 1953.
Accepted August 7, 1953.
