33 1
V O L U M E 20, NO, 4, A P R I L 1 9 4 8 Table V.
Accuracy and Precision of hletho'd
Weight of Mixture, Grams
Volume, RI1.
0.3125
100
0.625
100
1.250
50
Photometric Readings Standard Vnknown 186 184 181 171 186
186 184 179 172 186 184
184
Amoiint of Phenothiazine Actual, Found, mg. 26 25
mg. 25.0
50 50 200 200
49.4 50.3 200 200
25.0
Table \-I. Comparison of Bromine and Copper Methods, Same Samples of Commercial Phenothiazine Guarantee,
Bromine Method,
Copper Method.
98.84 97.00
98.39 96.53 98.39 98.16 33.15
98.13 96.00 98.84 97.62 33.43 98.20 98.00
7i
98:84 33.33 98.00 08.00
70
98,82 98.62
7c
Table V illustrates that results tound are in close agreement with the actual amount of phenothiazine. A neight of sample should be taken such that the aniount of phenothiazine present is apprownately equal to that in the standard solution. The recommendations given for us? of the Klett-Summerson photoelectric coloiimeter were followd in , estimating phcnothiazinr in the iegular raniples. 'Concentration of unknon n equals concentration of itandard divided hv reading of standard and multiplied by reading of unknown.
Several samples of commercial phenothiazine xvere simultaneously tested by the copper and bromine methods. I n both methods, the above formula was used instead of the standard curve for calculation of the amounts of phenothiazine. The results of both methods are in fairly good agreement, as indicated in Table VI. DISCUSSIOn
hlthough the copper method is not so rapid as the bromine method, it is more convenient, and the actual time consumed for running it is less. By the copper method a close agreement of results can be obtained on duplicate samples. The sensitivity of the copper method is greater than that of the bromine method. LITERATURE CITED
(1) Assoc. Official hgr. Chem., Official and Tentative Methods of Analysis, 6th ed., p. 721, 1946. (2) Cupples, H. L., IND.ENG.CHEY.,ANAL.ED.,14, 53 (1942). (3) Mellor, J. W., "Comprehensive Treatise on Inorganic and Theoretical Chemistry," 1'01. 111, pp. 153, 160, 161, 178, London. New York. Lonemans. Green and Co., 1938. (4) Kat. Formulary, p. 332, 1642.
(5) Orerholser, L. G., and Yoe, J. H., IND.ENG.CHEM.,ANAL.ED., 14, 646 (1942). (6) PaSEei, R., and Marshall, C. V., J . Assoc. OflciaE Ag?. Chem., 28, 429 (1945). (7) Ychnitzer, R. J., Siehenmann, C., and Bett, H. D., Can. Pub. Health J . , 17, 24 (1942). (8) Smith, L. E., ISD.ENG.CHEN.,.%SAL. E D ,10, 60 (1938). KECEJYEUFebruary 24, 1947.
Determining the Purity of Dicyclopentadiene Concentrates A Cryoscopic Method G-IRDNER C . RAY, Phillips Petroleum Co., Bartlewille, Okla. A cryoscopic procedure is described for determining the dicyclopentadiene content of concentrates having purities of the order of 50 to 80Yo. Analyses of synthetic samples and of dicyclopentadiene concentrates produced from certain hydrocarbon cracking operations indicate that accuracies of the order of 1 to 2% can be obtained. Within the limits of experimental error, solid solution behavior was not observed in the analyses of these mixtures.
C
OMMERCIAL quantities of dieyclopentadiene are available as a by-product from certain petroleum refinery operations in which natural gas, petroleum, or its fractions are pyrolyzed. This compound is formed by the dimerization of cyclopentadiene, which is a component of the cracking efftuent. In plant-scale operation the dicyclopentadiene is often recovered in concentrates ranging in purity from 50 to 807,. This paper presents a rapid and simple analytical procedure for determining the purity of such concentrates.
sample can be calculated from a knowledge of the freezing point of the 93 to 97% mixture described above, freezing point of the added high-purity dicyclopentadiene, relative weight of the concentrate sample to the added dicyclopentadiene, and molecular weight of the concentrate sample. The principles of this method were described by Streiff and Rossini (3) and applied t o the determination of individual aromatic hydrocarbons in mixtures of aromatics. APPARATUS
DESCRIPTION OF METHOD
The high niolal depression constant (Kp = 50.7) and the convenient freezing point (33.6' C.) of dicyclopentadiene (.;?) makes it particularly suited t o cryoscopic analysis. However, the usual equations derived from dilute solution laws may not be accurately applied to freezing point data obtained on dicyclopentadiene concentrates having purities as low as 50 t o 80%. I n the method described in this paper high-purity dicyclopentadiene is added to the concentrate sample in a n amount sufficient to raise the purity of the resultant mixture t o 93 t o 97%. In this concentration range the dilute solution laws hold with reasonable accuracy. The dicyclopentadiene rontent of the 50 to 8041, concentrate
The equipment used in this work is schematically diagrammed in Figure 1. It is essentially the same as that described by Mair, Glasgow, and Rossini ( 1 ) . The main parts are: A , freezing cell (clear glass). B, constant-speed stirring motor, 108 r.p.m. C, drying tower. D,thermometer, -10" t o +50" C. graduated in 0.1" C. divisions and calibrated for partial immersion. E, aluminum stirrer. F , clear glass Dewar. CHE.MICALS
High-purity dicyclopentadiene (97 to 100%). PKOCEDURE
The freezing point of the high-purity dicyclopentadicne (97 t o 100%) is determined on a separate portion of this material in the
ANALYTICAL CHEMISTRY
332 Table I.
Sample No.
Analysis of Dicyclopentadiene Concentrates Having Purities of the Order of 60 to 70 Per Cent
Hydrocarbon Added, as Impurity
Mol. Wt. of Samplea
p-Cymenee m-Xylenee CumeneC Dodeoaned
1
2
3 4
132.9 123.7 127.4 142.9
Computed from sample synthesis.
Table TI.
1 2d
3 4
5 6'
b
Supplied by Phillips Petroleum Co.
Dioyclopentadiene in Freezing Point 14ixture
F.P. ,of Freeiing Point Mixture
Synthesis of Freezing Point Mixture High-Purity Dicyclopentadieneb Synthetic Purity sample Grams .VIole % Grams 32,6220 99.02 4.9281 34,5432 98.45 4.2167 37,1717 98.60 3,6779 30.8838 98.50 5.0869
c.
Difference
Mole %
7
11.9 13.0 13.7 13.3 c
Dicyclopentadiene in Sample BY Experisynthesis mental
94.50 94.78 94.95 94.85
Eastman pure grade.
-1.55 +0.23 -0.27 -0.03 A v . -0.4 d Connecticut Hard Rubber Co., best grade. 65.97 66.42 59.66 70.93
64,42 66.65 59.39 70.90
Cryoscopic .4nalyses of Dicyclopentadiene Concentrates Obtained from Hydrocarbon Cracking Operations
Mol. Wt. of
Sample
pentadiene
140" 135.5C 1340 1420 145.3" 141.4C
Drams 3.6786 10.5293 5.0426 3.7677 3.8657 12.7744
Grams 35.7790 27.3916 26.6825 36.0064 35.1514 26.3079
Dioyolopentadiene Added Mole % 98.53 98.48 98.99 98.99 98.58 98.53
, of Freezing Point Mixture
c.
Dicyclopentadiene in Freezing Point Mixture
Dicyclopentadiene in Sample Determined Independently Mole % 51.41 32 O b '78.17 78.27C 69.34 69.0b 52.13 52.86 78.68 84.79 84'iRC
--
94.36 92.94 94,33 94.83 96.77 04.24
11.3 5.5 11.2 13.2 21.0 10.8
Difference -0.6 -0.1
+0.3 -0 7 +0:2 h v . -0.2
Determined bv Beckmann method in benzene. b Determined by method based on thermal depolymerization of dioyolopentadiene. C Computed from previous analysis and sample synthesis. d Known increment of high-quality dicyclopentadiene added t o sample 1 t o prepare sample 2. Known increment of relatively pure dicyclopentadiene added t o sample 5 t o prepare sample 6. a
manner described below. If solid a t room temperature, it is melted prior to introduction into the fieezing cell.
A sample of about 4 t o 10 grams of 50 t o 80% dicyclopentadiene concentrate is weighed on the analytical balance. T o this material is added a weighed quantity of the high-purity dicyclopentadiene in such an amount that the concentration of the resultant mixture is about 93 t o 97 mole %. The freezing point of this mixture is measured t o the nearest 0.1 O , and the highest temperature recorded after the first appearance of crystals is taken t o be the freezing point. Supercooling of the order of 0.05' t o 0.1' C. may be observed. Cold water serves as a satisfactory cooling bath and should be adjusted to a
temperature such that a cooling rate of about 0.1" to 0.2" C. per minute is obtained in the freezing cell. An independent molecular weight determination is made on a separate portion of the 50 t o 80% dicyclopentadiene concentrate using the Beckmann method. C4LCULATION OF RESULTS
The purities of the 93 t o 97% mixture (subsequently referred to as the freezing point mixture) and of the high-purity dicyclopentadiene used in its preparation are computed from thP following relation: A logic, P = 2 - 2.303 ( T p o - TFI
where P = purity, mole per cent dicyclopentadiene TF, = freezing point of pure dicyclopentadiene, 33.6" C T F = experimentally determined freezing point, a C A = - AH = 0.002605
R T F' ~
[This value of A was calculated using a value for AH of 487 calories per mole, computed from the molal depression constant (KF= 50.7) reported by Smoker and Burchfield @).I The purity of the 50 to 80% concentrate sample is calculated from the following expression derived from a weight balance on dicyclopentadiene: Z
P
WC
- BM -(E
- PI
where 2 = mole per cent dicyclopentadiene in 50 to 80% concentrate sample B = grams of concentrate sample taken for analysis C = molecular weight of concentrate sample taken for analysis W = grams of high-purity dicyclopentadiene used in preparing freezing point mixture E = mole per cent purity of dicyclopentadiene W M = mole weight of dicyclopentadiene W (assumed to be 132.2 when E = 97 100) P = mole per cent dicyclopentadiene in freezing point mixture
-
EXPERIMENTAL DATA
Figure 1. Diagram of Equipment
Several synthetic mixtures of essentially pure dicyclopentadiene with variouq hydrocarbons Tvere analyzed by the procedure de-
333
V O L U M E 20, NO. 4, A P R I L 1 9 4 8 ic,ribed. Data from these experiments are summarized in Table I. A number of commercial products available from hydrocarbon cracking operations were also analyzed. Results from these experiments are summarized in Table 11. DISCUSSION
Ideal behavior is assumed for the mixtures on which the freezing point measurements are made. Data obtained on samples 2 and 6 in Table I1 show Oormal freezing point depressions for the added dicyclopentadienc. This indicates that within the limits of experimental error the formation of solid solutions did not ocvur. In the analysis of dicyclopentadiene concentrates of the order o f 50 to 80% purity, accuracy of the order of 1 or 2% may be obt ained \yith the equipment and procedure described. With the use of more elaborate cryoscopic equipment and 1 rrhniques, such 9s the utilization of a platinum resistance ther-
inometer for temperature measurements and time-temperature melting or freezing curves for the determination of the true freezing point (4),better accuracies could perhaps be realized. ACKNOWLEDGMENT
The author is indebted t o H. J. Hepp and to M. R. Cines for helpful suggestions while conducting this work and to the Phillips Petroleum Company for permission to publish this paper. LITERATLIKE CITED
(1) Mair, B. J., Glasgov, A. R., Jr., and Kossini, E’. D., J . Research S a t l . Bur. Standards, 26, 591 (1941). (2) Smoker, E. H., and Burchfield, P. E., IND.ENG.CHEM.,ANAL. ED.,15, 128 (1943). (3) Streiff, A. J., and Rossini, F. D., J . Research A’atl. Bur. Standards, 32, 185 (1944). (4) Taylor, IT.J., and Rossini, F.D., Ibid., 32, 197 (1944). RECEIVED July 28, 1947. Presented before the Division of Petroleum Chemistry a t the Midwest Regional Meeting. Kansas City, blo.. June 23 t o 25, 1947.
Determination of Total Aromatic Plus Olefin By Sulfonation in the Presence of Phosphorus Pentoxide I. W. MILLS, S. S . KURTZ, JR., A. H. A. HEYN, AND &.I.R. LIPKIN Sun Oil Company, Norwood and Marcus Hook, Pa. A procedure is presented for the determination of the total olefin and aromatic content of hydrocarbon mixtures in the gasoline and kerosene boiling range by absorption in sulfuric acid containing 30% by weight of phosphorus pentoxide. The method consists of treating the sample with the sulfonation mixture at ice temperature, which converts the unsaturated hydrocarbons (olefins and aromatics) to acid-soluble compounds and leaves the paraffins and naphthenes in a separate phase that can be measured quantitatively.
T
HERE is corisiderable information in the literature on the use of sulfuric acid as a means of determining olefin and aromatic content. The previous methods, although satisfactory fon some mixtures, are not equally accurate for all types of hydrocarbon mixtures (7, 8, 20). Fisher and Eisner (8)have shown that adjustment of acid concentration and experimental csonditions to overcome this failing has not been entirely successful. If fuming sulfuric acid is used, complete sulfonation of unsaturated compounds is usually obtained, but some of the saturated components may also be sulfonated (19, 21). If less concentrated acid is used, the reaction Kith saturated hydrocarbons is decreased but aromatics may be incompletely sulfonated @,IO) and olefins tend to produce polymers or alkylates which are not completely absorbed by the acid layer (6, 11, 15, 18).
The uhe of sulfuric acid modified with various added “catalysts” has also been proposed. Silver sulfate has been used for this purpose (17). Kattwinkel ( I d ) proposed a mixture of concentrated sulfuric acid containing 14y0 by weight of phosphorus pentoxide. Although these reagents were an improvement over sulfuric acid alone, they were not entirely successful. Berg and Parker ( 4 ) recently suggested the use of fuming sulfuric acid and glacial acetic acid. The purpose of the present paper is to show that if the sulfonation mixture contains 30% by weight of phosphorus pentoxide and 707, by weight of 95 to 9670 sulfuric acid, and the reaction is carried out under carefully controlled conditions on hydrocarbon mixtures boiling under 600” F., side reactions are virtually eliminated and an accurate measure of the total olefin and aromatic content is obtained.
This method of determining total olefin and aromatic content has been used in this laboratory for some time and during the war was submitted to the American Society for Testing Materials and incorporated in emergency method ES-45A (g), and more recently in tentative method D875-46T (3). This procedure was also used for analysis of gasoline by Kurtz, Mills, Martin, Harvey, and, Lipkin (14). However, a detailed evaluation of the method is not given in any of these references. I n brief, the method involves treating the sample with the sulfonating mixture a t ice temperature t o convert the unsaturated hydrocarbons to acid-soluble compounds. The saturated hydrocarbons are not sulfonated and can be centrifuged from the reaction mixture and measured quantitatively as “raffinate.” Since the sulfonating mixture described herein is a strong corrosive chemical, the operator should take suitable safety precautions. A safety mask should be worn during the test period, and the mechanical shaker should be equipped with a safety hood. APPARATUS
Sulfonation Flask. The flask used in this work ( 1 ) is shown in Figure 1. The calibrated neck of the 10-ml. flask is graduated in 0.1-ml. increments and readings can be estimated t o 0.02 ml., a precision of 0.2%. A modified Babcock bottle (5) can also be used if precision of 1%is sufficient. Centrifuge. A centrifuge should be suitable for handling the type of sulfonation flask described above. Mechanical Shaker, A mechanical shaking device. is required that has a horizontal stroke 7.5 * 1.25 em. (3 * 0.5 inches) in length and a speed of 250 * 25 cycles per niinute, each cycle consisting of one forward and one return stroke. [Shaking by hand is practical only for samples of low olefin content (8, S).] The bottles or flasks are supported in a vertical position during
