213
V O L U M E 20, NO. 3, M A R C H 1 9 4 8 Table VIII. Determination of Ethylacetylene and Vinylacetylene in Samples Containing 1,a-Butadiene
spmple
9 10 11
Ethylacetylene Blended Found 3 3 7.6 5 3
0 2 3.3 2.1
Vinylacetylene Blended F O I ~ I’olume Per C m f 3 5 0.7 4 4 0 6 06 3.6
for many helpful suggestions and criticisms in the initial stages of this work. LITERATURE CITED
1,2-Butadiene Blended
Altieri, V. J., “Gas dnalysis,” p. 329, New York, American Gas Association, 1945. Chavastelon, R., Compt. rend., 125, 245-6 (1897). Hillyer, J. C., and Webber, L. A., Phillips Petroleum Co., private communication. McMillan, W. A,, IND.ENG.CHEM.,A N ~ L ED., . 9, 511-14
2.1 2 5 2 5
(1937).
McMillan, W. A., J . Znst. Petroleum Tech., 22, 616-45 (1936) McMillan, W. A., Cole, H. A., and Ritchie, A. V., IND.ENG. CHEM.,ANAL.ED.,8,105-7 (1936). Percgud, E., Caoutchouc and Rubber (U.S.S.R.), No. 7-8, 63-70
stantiated in Table 111, runs 9, 10, anli 11, which contain 1,2butadiene along with other C, hydrocarbons. Samples of 1,2-butadiene of 97+% purity showed 0.6 and 1.0% absorption in maleic anhydride, whereas 1,3-butadiene is completely absorbed, as indicated in ‘Table V. No method is available for determining 1,2-butadiene, except those employing spectrographic procedure; hence no correction for its presence can be made in a (chemical analysis of this type. The catalytic hydrogenation step will indicate the presence of an extra double bond, which is not accounted for otherwise and will be considered as originating in vinylacetylene. The vinylacetylene result will therefore be high and the ethylacetylene content low by the amount of the 1,a-b~tadienepresent. Table VI11 s h o w this t o be approximately so on samples which contain 1,2-hutadiene.
(1937).
Robey, R. F., and Morrell, C. E., IND. ENG.CHEX,ANAL.ED., 14, 880-3 (1942).
Robey, R. F., Morrell, C. E., and Vanderbilt, B. M., “Symposium on Analytical Methods Used in the Petroleum Industry,” St. Louis Meeting A.C.S., April 7-11, 1941, Preprint, p. 122.
Ross, W. H., and Trumbull, H. L., J . Am. Chem. Soc., 41, 11809 (1919). Stanerson, B. R., and Levin, H., IXD. ENG.CHEM.,ANAL.ED., 14,782-4 (1942).
Tropsch, H., and Mattox, W. J., Ibid., 6, 104-6 (1934). Vaughn, T. H., Hennion, G. F., Vogt, R. R., and Nieuwland,
J.A,, J . Org. Chem., 2, 1-22
(1937).
Young, W. G., and Lucas, H. J., J . Am. Chem. Soc., 52, 1964-70 (1930).
ACKNOWLEDGMENT
The authors wish to express their appreciation t o H. Levin
RECEIVEDDecember 21, 1945. Presented before the Division of Petroleum Chemistry at the 109th Meeting of the BMERICAXCHEMICALSOCIETY, Atlantic City, N. J.
Determination of Cyclopentadiene and Methylcyclopentadiene in Admixtures with Other Hydrocarbons .I. S. POWELL, K. C. EDSON,
E. L. FISHER Butadiene Production D e p a r t m e n t , Southern Calijornia Gas C o m p a n y , Los Angeles, Calif. A method is described for quantitatively depolymerizing the dimers of cyc1opr:ntadiene and methylcyclopentadiene and determining individually the concentrations of the monomers in the resulting mixture. The method is based on the rate of condensation of cyclopentadiene and of methylcyclopentadiene with acetone in an alkaline solution to form the dimethyl fulvenes; and benzaldehyde in an alkaline solution to form the phenyl fulvenes. After
I
N T H E pyrolysis of hydrocarbons
a,t high temperature, two of the many compounds that are formed are cyclopentadiene and methylcyclopentadiene. These two products in turn dimerize, forming the cyclopentadiene and methylcyclopentadiene dimers, and cross dimerize, forming the codimer. I n industrial processing it has been found very difficult t o separate these two compounds economically and thus it is desirable to be able to differentiate between the two basic components by chemical analysis. Of the methods mentioned in the literature, none were devised for this purpose nor were they readily adaptable. Sefton (5’) devised a method for determining cyclopentadiene, using the heat of reaction with maleic anhydride. He states that his method is not specific for cyclopentadiene, but he expects little interference, as the other dienes present in the same boiling range react more slowly. Methvlcvclopentadiene would
AND
neutralization with acetic acid, the intensity of the color produced is measured by means of a spectrophotometer. The concentrations of cyclopentadiene and methylcyclopentadiene are calculated from the extinction coefficients which differ under the conditions of fulvene formation. The determination is not affected by the presence of paraffins, aromatics, naphthenes, mono-olefins, or aliphatic diolefins.
be expected to react more slowly than the cyclopentadiene, but utilizing this difference in rate of reaction would be complicated by the other dienes present. Ultraviolet light absorption may offer a basis for a method. Pickett, Paddock, and Sackter ( 2 ) made a study of the spectrum for cyclopentadiene but have not used it for the determination of this compound. h study of the spectrum of methylcyclopentadiene made by the authors revealed a shift in the absorption curve of this compound as compared with that of cyclopentadiene. However, the use of such a method may be subject to interference from such constituents as aromatics and other conjugated diolefins. The condensation reaction between cyclopentadiene and aldehydes or ketones forming the highly colored fulvenes as observed by Thiele ( 4 ) was utilized by Uhrig, Lynch, and Becker (5). One
A N A L Y T I C A L CHEMISTRY
214
unpublished method investigated involved the reaction of cyclopentadiene with acetone t o form the colored compound dimethyl fulvene. Uhrig et al. used benzaldehyde in place of the acetone, thus forming the colored compound phenyl fulvene. As a result of earlier work in which pure methylcyclopentadiene was separated from hydrocarbon mixtures and its properties were determined, it was observed that methylcyclopentadiene reacts more slowly than cyclopentadiene in forming fulvenes with both acetone and benzaldehyde ( 1 ) . The reaction rates of methylcyclopentadiene and cyclopentadiene with acetone are slower than their reactions with benzaldehyde. Table I indicates that the reactions of methylcyclopentadiene and cyclopentadiene with benzaldehyde are complete for both compounds in less than 20 minutes, whereas with acetone neither reaction is complete; however, the cyclopentadiene reaction is considerably more complete than the methylcyclopentadiene reaction. These data suggested that by determining for a mixture of cyclopentadiene and methylcyclopentadiene the optical density of the fulvenes formed with acetone for a 15-minute reaction time and -4th benzaldehyde for a 20-minute reaction time, the composition of the mixture could be calculated. The stable form of both cyclopentadiene and methylcyclopentadiene is in the form of the dimers. Therefore, for any analytical method for the determination of the monomers, it is essential that a preliminary step be employed in which the dimers are converted to the monomers. Uhrig et al. have proposed such a method involving the destructive distillation of cyclopentadiene. This method is time-consuming and requires certain precautions, and, where two compounds with different boiling points are involved, it becomes more difficult to carry out. I t was found that when a hydrocarbon sample containing dimers of cyclopentadiene and methylcyclopentadiene is passed through a tube heated to appi-oximately 340" to 360' C., the dimers will decompose quantitatively, forming the monomers.
table, determine the dilution of the sample, the volume of diluted sample to depolymerize, and size of volumetric flask receiver for the depolymerized sample to use. Approximate Weight % ' of Dimer
Dilution of Sample
0.0 to 0 . 9 0 . 8 to 2 . 8 2 . 6 to 9 . 0 9 . 0 to t o 28 28 to 90
None None 3/10 l/ l/ 66
air0
Mixture t o Depolymerize MI. 15 5 5
5
5
Receiver
M1. 50 50 50 100 100
To dilute the sample, place approximately 20 ml. of toluene in the appropriate volumetric flask and weigh. Pipet the correct volume of sample into the flask and reweigh. Record the weight of sample, and dilute to the mark with toluene. Place the outlet tube, extending from the bottom of the depolymerization apparatus, in a second volumetric flask containing approximately 20 ml. of toluene cooled by an acetone-dry ice bath. Transfer the diluted sample into the funnel a t the top of the depolymerization apparatus. When the funnel is empty, add 5 ml. of toluene, washing down the sides of the funnel during the addition. After all the toluene has passed through, allow the tube to drain for approximately 1 minute; remove the volumetric flask; allow the flask and the contents to come to room temperature, and dilute to the mark with toluene. Aliquots of this solution are analyzed for cyclopentadiene and methylcyclopentadiene using the following procedure.
1/2 MM. I.D. CAPILLARY TUBING
REAGENTS
Toluene, C.P. Acetone, technical. Dry ice. Anhydrous sodium sulfate. Alcoholic potassium hydroxide solution. Dissolve 5 grams of potassium hydroxide in 100 ml. of 95% ethanol. Acetic acid, 4y0solution. Dilute 40 ml. of glacial acetic acid to 1000 ml. with distilled water. Benzaldehyde, .20% solution. Dilute 20 ml. of C.P. benzaldehyde to 100 ml. with 95y0 ethanol.
-8
MM. I.D. HEAVY WALL
INTERNAL HEATING COIL, 24-GAGE WIRE,
APPARATUS
Depolymerization apparatus as shown in Figure 1. Beckman spectrophotometer. Constant-temperature bath. Interval timer. Pipets, 1-, 2-, 5-, lo-,15-, and 20-ml. Volumetric flasks, 50- and 100-ml. Glass-stoppered bottles, 125-ml. Beakers, 50-ml. PROCEDURE
No preliminary fractionation of the sample is necessary unless it is known that interferences exist which can be removed by this operation, The dimers of cyclopentadiene and methylcyclopentadiene do not form fulvenes; therefore, if these compounds are not all in the monomeric state, a preliminary depolymerization treatment is necessary. If the sample contains both monomers and dimers, they can be determined individually by making the fulvene analysis on both the sample as received and the depolymerized sample. Depolymerization of Sample. Adjust the power input t o the depolymerization apparatus to have the depolymerized sample vapor leave the heating coil a t 340" to 360' C. This is accomplished by predetermining the setting of a variable-voltage transformer to give the above temperature of vapors immediately leaving the heating coil as indicated by a test thermocouple inserted within the depolymerization tube. While heating the apparatus, dry the sample with sodium sulfate. From the estimated weight per cent of dimer present, from the following
1u Figure 1. Depolymerization Apparatus
Determination of Cyclopentadiene and Methylcyclopentadiene Monomers. The depolymerized sample should be analyzed as soon as possible to minimize errors from the redimerization of the monomers. It has the proper dilution for the acetone reaction and for the benzaldehyde reaction should be diluted one to five.
In a pair of 125-ml. bottles for the acetone reaction and in another pair of 125-m1. bottles for the benzaldehyde reaction, prepare the following mixtures. In bottle 1 (to be used for reaction)
215
V O L U M E 20, N O . 3, M A R C H 1 9 4 8 mix 5 ml. of C.P. acetone and 5 ml. of alcoholic potassium hydroxide. I n bottle 2 (to be used for blank) mix 5 ml. of C.P. acetone, 5 ml. of alcoholic potassium hydroxide, and 10 ml. of 4y0 acetic acid. In bottle 3 (to be used for reaction) mix 5 ml. of 20y0 benzaldehyde and 5 ml. of alcoholic potassium hydroxide. In bottle 4 (to be used for blank) mix 5 ml. of 20y0 benzaldehyde, 5 ml. of alcoholic potassium hydroxide, and 10 ml. of 4y0 acetic acid. Immerse the bottles in the water bath and allow them to come to a bath temperature of 32” C. Add 5 ml. of properly diluted sample to each bottle and swirl the contents without allowing any sample to contact the stopper. After allowing the acetone reaction t o proceed for exactly 15 minutes and the benzaldehyde reaction to proceed for exactly 20 minutes, neutralize the contents of the corresponding bottles with 10 ml. of 4y0 acetic acid. Add 20 ml. of toluene to each bottle, mix thoroughly, and decant the hydrocarbon layers into 50-ml. beakers. ,4dd approximately 1 gram of sodium sulfate to each beaker and cover them with watch glasses. After dehydrating the toluene solution, determine the optical density with the spectrophotometer. Use a wave length of 425 mp and a slit width of 0.03 mm.
Table I. Specific Extinction Coefficients of Cyclopentadiene and Methylcyclopentadiene Fulvenes as Function of Formation Reaction Time Reaction Time, Min. 15 30 45 60 5 10 20 30 a
K a t 32” C. and 425 m r a Methylcyclopentadiene
Fulvene Acetone
Cyclopentadiene 0,345 0.370 0.403 0.430 0.950 0,930 0.896 0 . Si4
Benzaldehyde
0.085 0.140 0.194 0.234 0.732 0,744 0,759 0.759
Units, liters per mole per cm.
Calculations. First calculate the extinction coefficients from the optical densities observed for the two reactions, using the f ol lowing equation :
k ’ = -D
CL
where
K = extinction coefficient D = opticaldensity C = concentration of sample in grams per liter of solution L = optical path in em. Making K I = K acetone reaction K1 = K benzaldehyde reaction The nTeight per cent of the two components present in the sample may be calculated as follows:
X = weight yoof cyclopentadiene = 100 (klK1 - k2K2) Y = weight % of methyl cyclopentadiene = 100 (krK,
- krK1)
The constants, k l , k?, k,, and ka in the above equations must be determined by carrying out the above procedure, using pure cyclopentadiene and methylcyclopentadiene separately, determining the extinction coefficients for the two compounds in both reactions, and substituting these values in the following equations:
Table 11. Determination of Cyclopentadiene and Methylcyclopentadiene in Hydrocarbon Samples Cyclopentadiene Present, Found, wt. % wt. %
Methylcyclopentadiene Present, Found, wt. 70 wt. 5% 10.6 10.4 10.4 10.1 5.3 5.3 0.4 0.4
PRECpUTIONS
Extreme care must be taken to keep acetone out of the reagents used in the benzaldehyde test. Benzaldehyde and acetone react to give the colored compound benzal-acetone which will interfere with the spectrophotometer readings. Separate sets of pipets must be used for the acetone and benzaldehyde reactions. Uhrig et al. reported that the yellow color of phenyl fulvene, the reaction product of benzaldehyde and cyclopentadiene, was stable and did not change with time. Contrary to this, the authors found that the color faded gradually as shown in Table I. Thus in this reaction as well as that using acetone, it is necessary to hold time and temperature constant. ACCURACY OF METHOD
The results of a series of analyses on synthetic samples containing both compounds in known concentrations are given in Table 11. As indicated, this test method has a high degree of accuracy. The widest variation from the actual percentage of either compound is 0.30/0. This method has been applied to numerous plant hydrocarbon streams which vary considerably in cyclopentadiene and methylcyclopentadiene content and in admixtures with various types of paraffinic, naphthenic, and aromatic hydrocarbons with satisfactory results. The only type of hydrocarbon compound found to interfere with this test method is indene. However, it would be expected that any other compounds forming fulvenes would interfere, such as higher homologs of indene and other substituted cyclopentadiene compounds with the substitution in the 1 and 2 positions only. Indene having the same type structure as cyclopentadiene will undergo fulvene condensation; however, its rate of reaction is slow. The rate of reaction with acetone is so low that it does not interfere. With benzaldehyde, the rate of reaction is rapid enough to cause an error in the methylcyclopentadiene content, as calculated in this method, equal to approximately one fourth of the indene content present. Therefore, if more than a small quantity of indene is known to be present, a preliminary fractionation is necessary to remove it. LITERATURE CITED
Edson, K. C., Powell, J. S., and Fisher, E. L., “Properties of Methylcyclopentadiene,” Ind. Eng. Chem., to be published. (2) Pickett, L. W., Paddock, E., and Sackter, E., J . Am. Chem. Soc., (1)
63, 1073 (1941).
(3) Sefton, R., J . SOC.Chem. Ind., 64, 104 (1945). (4) Thiele, J., Ber., 33, 666 (1900). (5) Uhrig, K., Lynch, E., and Becker, H. C., ISD. ENG.CHEX., ANAL.ED.,18,550 (1946). RECEIVED July 10, 1947.
where
A = K. = extinction coefficient of cyclopentadiene in the acetone reaction Kb = extinction coefficient of methylcyclopentadiene in the acetone reaction K , = extinction coefficient of cyclopentadiene in the benzaldehyde reaction Kd = extinction coefficient of methylcyclopentadiene in the benzaldehyde reaction
Correction. In the report of the Eighth Conference on Applied Spectroscopy [AN.4L. CHEM.,19,1045 (1947) 1, the word “Quantometer” appears as a general designation for direct reading instruments. It should have been used only in connection TTith the instrument manufactured by the Applied Research Laboratories for which it is a trade name.
