490
ANALYTICAL CHEMISTRY 10
IO 7-
::= 5 E l-
2-
g6 .7I -
5).
‘H-
The results pertained here to the specific lots of powder used; hon-ever, limited investigation indicated only minor variation in both parameters.
-2
-’
.5
-3
-5
3-
=
-4
were prepared, with and without agglomerates. From the results it is possible to see that, for all sizes, agglomeration is taking place within the powder resulting in a distribution with the same standard deviation but different mean volume diameter (Figure
-7
1
-7
I I I I I I I 1 I I t .5
01 I 2 5 IO 20 50 80 9095 99 CUMULATIVE PERCENTAGE UNDERSIZE
Figure 5. Cumulative size distribution of tracer 2266 obtained by sedimentation method (Andreasen pipet) A. B.
ACKNOWLEDGRIENT
This work was sponsored by the Air Force Cambridge Research Center, Geophysics Research Directorate, Contract No. A F 19(122)-472, C. E. Anderson, Scientific Oficer. The assistance of M. A. Fisher, Supervisor of Fine Particles Research, Armour Research Foundation, in valuable discussions of particle size analysis and of Andrew Ungar in consultation and advice in the statistical field is gratefully acknowledged.
Aggregates present Aggregates broken LITERATURE CITED
The particles of S o . 2205 dust are very close to spheres. This is the main reason that the results from calculations based on microscopic examination and sedimentation are in better agreement. The direct count (dilution method) gives a result of about the amount of the other results. This is easily foreseen because the size distribution is one-sided truncated at about l micron. The cnrve of niicroscopic count indicates 12y0below 1 micron, whereas the count distribution curve derived by sedinientation indicates 42% less than 1 micron. This illustrates the necessity of the degree of truncation of the distribution when converting distribution from one basis t o another (Figure 2). Powder NJZ 2266 as used in qualitative experiments in high altitude cloud tracing. Because of the qualitative nature of the teats, only Sedimentation analysis was used. Two suspensions
Bostock, W., J . Sci.Instr. 29, 209 (1952). Braham, R. R., Seely, B. IC., Croeior, W.D., Trans. Am. Geophys. UniOTk 33 (NO. 6), 825-33 (1952).
Dalla Valle, J. hI., “Jlicromeritics: Tho Technology of Fine Particles,” pp. 47, 60, Pitman Publishing Corp., New York, 1948.
Herdan, G., Smith, bl. L., “Small Particle Statistics,” pp. 33, 66, Elsevier, Now York, 1953. Loomis, G. A,, J . Am. Ceram. SOC.21, 393-9 (1938). RIcCully, C. R., others, Armour Research Foundation, Illinois Inst. of Technol.Sci. Rept., No. 15, Contract No. AF19(122)472 (Oct. 26, 1954). Odon, S., Proc. Roy. SOC.Edinburgh 36, 219 (1915). Perkins, W. A., Leighton, P. A., Crinnell, S. W., Webster, F. X., Proc. Nall. Air Pollution Symposium, 2nd Symposium, Pasadena, Calif., 1952, p. 42.
RECEIVED for review September 1, 1955. Accepted January 17, 1956.
Determination of Six- and Seven-Carbon Naphthenes in Catalytic Reforming Feed Report of the Subcommittee on Determiaation of Naphthenic Hydrocarbons, Committee on Analytical Research, Division of Refining, American Petroleum Institute C. C. MARTIN and S. S. KURTZ, JR., Chairmen, Sun O i l Co., Marcus Hook, Pa. G. R. LAKE Union O i l Co. G. R. BOND, Houdry Process Corp. R. L. LETOdRNEAU, California Research Corp. 1. A. GRANT Pan American Refining Corp. RALPH GRIFhTH Sinclair Research Laboratories, Inc. D. R. LONG Universal O i l Products Co. A. A. RAWLINGS, British Petroleum Company, Ltd. C . E. HEADINGTbN, Atlantic Refining Co. (formerly Anglo-lranian) B. J. HEINRICH, Phillips Petroleum Co. E. B. TUCKER, Standard O i l Co. of lndiana C . W. KEY, RichfieM O i l Corp.
Cooperative w-ork in twelve laboratories has shown that there are several methods for accurate analysis of Cg and Ci naphthcnes in reformer charge stock. Mass spectrometry, infrared spectrometry, refractivity intercept, and catalytic dehydrogenation methods have all been successfully used. In one California naphthenic charge stock, the individual Cr, naphthenes-cyclohexane and nicthylcyclopentane-have been determined with a standard deviation of only 0.5%. The C7 naphthenes-niethylcyclohexane and the sum of the six cyclopcntane isomers-have been determined with a little less precision, but generally within 1% of the mean.
T
HE accurate determination of naphthenic hydrocarbons
(cycloparaffins) has grown in importance to the petroleum industry -with the expanding use of the catalytic rcforming process. Naphthenes are converted to aromatics as the primary chemical reaction over various catalysts (15). By this means, the petrochemicals, benzene, toluene, and xylenes, and ethyl benzene, are produced in relatively large volumes from light naphtha fractions. High octane gasoline blending components are also made from virgin or straight-run distillates. Good analytical methods have been available for aromatic hydrocarbons in gasoline range materials. At present, absolute accuracies from 2 t o 3% down to 0.1 to 0.20/, are available, depending upon what one can afford in manpower and elapsed
V O L U M E 28, NO. 4, A P R I L 1 9 5 6
49 1 The following inspection data were obtained on the sample:
Table I. Boiling Poin tsa of Individual Cj to CS Naphthenes No. of Carbons
Boiling Point
Naplithone
c.
0
F.
5
Cyclopentane
49.3
120.7
6
LMethylcyclopentane Cyclohexane
71.8 80.7
161.3 177.3
hf ethylcyclohexane Ethylcyclopentane
87.8 90.8 91.7 91.9 99.5 100.9 103.5
190.1 195.4 197.1 197.4 211.2 213.7 218.2
Trimethyloyclopentanes (eight) hlethylethylcyclopentanes (five) Isopropylcyclopentane n-Propylcyclopentane Dimethylcyclohexanes (seven) E t hylcyclohexane
105-123 121-128 12G.4 130.9 119-130 131.8
221-253 249-262 259.6 267.7 247-266 269.2
7
8
D a t a from (1).
time. hletliods vary from those involving relatively simple equipment available in any laboratory to those involving large and expensive equipment and usually permitting economy in manpower. Considerably less attention has been paid to developing accurate methods for naphthenes. In 1952, the American Petroleum Institute Committee on Analytical Research appointed a subcommittee for the comparieon of methods of naphthene determination and development of iiew or improved methods where necessary. As its first assignment, the group undertook the comparison of methods in the C6 and C7 range. This was a logical starting point because more methods were available and greater accuracy was needed than in the higher boiling range. Table I lists the various possible Cg and C, naphthenes and their boiling points. Information is also given on the adjacent CS and CS naphthenes. There have been several reports (6, 8, 19) on the relative amounts of naphthenes in this boiling range covering a number of widely different crudes. The two major classes of naphthenes in the gasoline range are the cyclohexane (six-membered ring) derivatives and the cyclopentane (fivemembered ring) derivatives. API Research Project 6 has shown that the relative proportions of these two classes differ among naphthas (8, 17). In reforming processes, benzene and toluene are produced from cyclohexane and methylcyclohexane by dehydrogenation, and from metliylcyclopentane and seven-carbon cyclopentanes by isomerization and dehydrogenation. It is important to know the degree of conversion of naphthenes to aromatics by various catalytic reforming processes. Confronted with this problem, most petroleum analytical laboratories have felt the need for checking the accuracy of their naphthene methods. The basic data and standard samples supplied by research projects sponsored by the American Petroleum Institute made possible the naphthene data and methods discussed in this paper. The spectroscopic methods are completely dependent upon calibrations made with API-NBS standard hydrocarbon samples supplied by ilPI Research Project 6. The accurate physical property and spectroscopic correlations could not have been developed without the physical data and spectra on hydrocarbons provided by API Research Project 44 ( 1 ) . EXPEKIMENTAL
Sample. A 170" t o 220' F. charge stock from a California crude was chosen for the comparison of methods. Five drumn of this particular stock were supplied by the California Research Corp., San Francisco, Calif. This material has been stored in a cold room by the Houdry Process Corp. a t Linwood, Pa., and is still available for use in testing naphthene methods.
10% 50%
90% E n d point
177 190 112 25.5
This sample proved to contain more than 85% Cg and C7 hydrocarbons. Less than 1% of the sample mas 1ightt.r hydrocarbons and a little over 10% was heavier hydrocarbons. There were 24 individual compounds in the CS and C7 groups. Bctually, the six dominant hydrocarbons consituted as much as 50% of the sample. Twelve hydrocarbons made up 75% of the sample. The over-all hydrocarbon type distribution wae about 52% naphthenes, a little over 40%) paraffins, and about 7% aromatics. The sample can be classed as a moderately high naphthene stock. Data. Tables I1 through VI1 summwize the experimental data obtained on this saniple by the 12 laboratories which participated in the study. All determined the CS naphthenes, 10 determined the C7 naphthenes, and sevei al determined the other naphthenes, the paraffins, and the aromatics as well. Methods Used. Each laboratory v a s requested to use its best method, no matter how time-consuming this might be. The emphasis was placed upon referee-type methods to see whether different laboratories could agree under the most favorable conditions. Results by Ehort-cut methods were also to be submitted where feasible. hlost of the laboratories chose to use either the mass spectrometer or the infrared spectrometer or a comhiriatiou of the two. A few laboratories performed the detailed analyses using physical property correlations; two laboratories m d e use of Rampton's analytical dehydrogenation technique (16 ) . Most of the shortcut analyses relied on the refractivity intercept correlation. It is not the purpose of this paper to describe details of experimental methods. A brief discussion of the various procedures for the preliminary separations and for the determinations follows.
DEAROMATIZATION. Saturated hydrocarbon fractions can be more easily analyzed after the aromatic hydiocarbons are removed from the mixture. For use of physical property correlations, quantitative removal of the aromatics is essential. For infrared spectrometry, removal is preferable because it simplifies the absorption spectra. For mass spectrometry, there is very little interference of the aromatics with the saturates; some cooperators dearomatized the sample and others did not. Aromatics were removed either by treating with acid, such a8 the sulfuric acid-phosphorus pentoside mixture (b), or by adsorption on silica gel ( 3 ) . Saturated hydiocarbon mixtures obtained from either type of processing appear to be satisfactory for further analysis. DISTILLATION.Sharp separation of the hydrocarbon mixture into fractions containing a limited number of compounds was necessary for accurate analysis. Most laboratories used 3-, 4, or 6-foot Podbielniak high-temperature distillation columns. Reflux ratios varied from 33 to 1 up t o 100 t o 1 and columns were operated a t throughputs equivalent to 45 to 100 theoretical plates a t total reflux. A distillation curve for the saturates from this sample is shown in Figure 1. I n this example a 200-m1. saniple was distilled in a Podbielniak column 3 feet X 13 mm. a t a throughput of 330 ml. per hour and a 45 to 1 reflux ratio. An aromatic hydrocarbon chaser was used. The boiling points of the predominant saturated hydrocarbons in the California naphtha are shown in Figure 1. Among the 12 laboratories the number of fractions taken depended on the method of analysis and varied from three or four up t o 30 or more. MASSSPECTROMETRY. Mass spectra are useful for determining either individual hydrocarbons or groups of similar hydrocarbons ( 6 , 7). For individual hydrocarbons, it is best to work with distillation fractions narrow enough t o contain only one isomeric group for any given type of hydrocarbon. For example, accurate determination of cyclohexane and methylcyclohexane in the
492
ANALYTICAL CHEMISTRY
250
I20
Lc
100
I,t-2- Dirnethylcyclopentane I, 1-3-Dimethylcyclopentane
0
c
g
wide differences in refractive indices of paraffins and naphthenes, individual compounds were quantitatively determined in fractions obtained by distillation a t 200 theoretical plates. Physical property correlations are more frequently applied to the determination of groups of similar hydrocarbons than to the determination of individual compounds. Functions of refractive index and density such as refractivity intercept (12, IS, 21, 12) and specific refraction ( 1 6 ) are used for determining proportions of paraffins and naphthenes. Special correlation charts must be used for each fraction when highest accuracy is desired (10, 22). The two different types of naphthenes-namely, cyclohexanes and cyclopentanes-are not separately determined by such physical property correlations except where they can be first separated by distillation. An auxiliary chemical method for determining cyclohexane derivatives is the catalytic dehydrogenation technique of Rampton (14, 16). Cyclohexanes are converted t o aromatics, which are determined in the product. Cyclopentanes remain unchanged and are calculated as the difference between total naphthenes and total cyclohexanes. Laboratories A, F, L, and ill determined the cs and C7 naphthenes by various combinations of physical property correlations and other methods. Two of them determined the cyclohexanes by dehydrogenation and one by infrared spcc-
200
.”: c
H
a
(3
(3
z
2
Cyclohexane
0
m
z
-
i
-Methylcyclopentane I50
-3-Methylpentune 2- Methylpentane IO
0
20
30
40
i 50
60
70
00
90
=!
80
60
100
VOLUME PER CENT DISTILLED
Figure 1. Distillation curve for riaphtheiie-paraffiin California naphthenic charge stock
prirtion from
same fraction would be difficult because of interference by other ~ ~ 11. b Determillation l ~ of IndividL1al Cs Naphthellcs components a t the significant mass numbers. Determination of individual close-boiling isomers such as some of the dimethylVolume % of Whole Sample Methoda of’ Analyzing cyclopentanes is almost impossible. MethylFor group analysis, correlations are derived based on sunimaFractions tions over certain sDccific mass numbers. For example, cyclocyclopentane Cyclohexane 6.5 Spec. refraction 9.3 A hexane and cyclopenbne derivatives can be calculated separately 7.0 hls 10.6 by using different mass peaks (9). The sum of the dimethyl6.4 10.3 I R , hlS cyclopentanes is easily determined even though the individual 6.0 10.2 hIS E 5.7 10.0 (n-d/2), I R F compounds mag not be determined. 7.6 9.4 MS Laboratories B, J, I
