July 15, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
the contactpoints on the relay so that the pump motorwould operate when the relay actuating circuit was completed. LITERATURE CITED (1) Cox, IXD.EKG.CHEM.,Anal. Ed., 1, 7 (1929).
319
RECEIVEDMarch 3, 1932. This work was oarried out a t The Johns Hopkins University, and the apparatus described was developed in connection with Research Project No. 28 of the American Petroleum Institute The work was supported by a research fund of the Inatitute donated by John D. Rockefeller and administered b y the Institute with the cooperation of the Central Petroleum Committee of the National Research Council.
Determination of Olefins by Bromine Titration J. C. MORRELL AND I. M. LEVINE, Universal Oil Products Co., Chicago, Ill.
T
.
HE present procedure has been developed as a rapid method for the determination of olefins in a mixture of hydrocarbons, particularly in cracked hydrocarbon distillate. It is based upon the idea that a solution containing olefins will absorb bromine in proportion to the olefin concentration. This idea is, of course, not new; it is the factor which governs the determination of the bromine number. Instances of direct bromine titration also appear in the literature. A chloroform solution of ice-cold nerol (4) has been so titrated, bromine entering both double bonds quantitatively. The degree of unsaturation of ethyl stilbene (5) has been determined in like manner. Similarly, Kurt Meyer (3) titrated a keto-enol mixture (methyloxaloacetate) for the determination of the enol portion. Although the application to nerol and ethyl stilbene is satisfactory, the method has potential sources of error which prevent its general adoption, The errors involved, as a result of substitution, incomplete additions, etc., have vitiated the usefulness of the bromine or iodine number as applied to cracked petroleum distillate ( 2 ) . Some of the objections are overcome when the olefin concentration of an oil is calculated from the ratio of its bromine titer to that of a standard solution containing a known concentration of known olefins. This is the basis of the present work. PROCEDURE The titration of the experimental standard and unknown is carried out under the same conditions of light and heat in the following manner: The oil (2 cc. or a volume which requires 1 to 5 cc. of the bromine solution) is diluted with olefin-free naphtha to a volume of 10 cc., and a 4 per cent solution by volume of bromine in carbon tetrachloride is added from a buret, five drops (0.1 cc.) a t a time, stirring after each addition. The end point of the titration is that point where a definite orange color persists for 30 seconds. This end point is one which each operator has to fix in his own mind. The titration should be carried out in diffused light, since direct sunlight causes the production of excessive hydrogen bromide. All values of concentration in this paper are expressed in terms of volume per cent. For the case in which the standard and unknown solution contains the same single olefin, Equation 1 is used to calculate the olefin content of the solution.
where U
olefin content of solution olefin content of standard titer of solution Tz = titer of standard = = T1 =
S
Solutions containing various amounts of octylene in olefin-free cleaner's naphtha were titrated. Tables I and I1 indicate the results obtained. TABLEI. TITRATION OF SOLUTIONS CONTAININQ OCTYLENE VOL. 12% CsHle SOLN.
VOL.Brz SOLN,
10 5 4 3 2
5.1 2.6 2.2 1.5 0.98
cc.
cc.
VOL.Br? SOLN. VOL. CeHie SOLN. 0.51 0.52 0.55 0.50 0.49
A volume of 1 cc. gave results that were entirely too low. TABLEI1 CSHMIN SOLN.
VOL. TITRATED
cc.
VOL. Brz SOLUTION USED (TITER)
cc.
VOL. Brz SOLN. FOR
2 00. OF 1% CsHis
cc.
The amount of bromine that can be absorbed by 2 cc. of a 1 per cent octylene solution is 0.00664 cc. This corresponds to 0.166 cc. of a 4 per cent solution. The average quantity of bromine solution actually used is 0.166 cc. The standard may also consist of an oil which contains the same type of olefin mixture as that in the oil under investigation. Equation 1 will apply in this case also. I n a concurrent paper it is shown that the olefins in cracked gasolines are probably of the same type in approximately the same relative proportion. Thus a cracked gasoline in which the olefin content has been accurately determined may be used as a standard. Results are shown in Table 111. OF BROMINE AND SULFUR MONOTABLE111 COMPARISON CHLORIDE METHODS r
No. 1 2 3 4 5
VOL. Brz SOLN.
Brz method
cc
%
. 6.74
6.14 8.72 6.90 13.0
OLEFINS SzClz method (8)
29.6 standard 27.0 38.2 30.4 57.0
% 29.6 28.0 35.0 29.8 61.4
These analyses indicate that the distribution of various olefins (including those of various types, as well as of different molecular weights) is the same in cracked distillate from various charging stocks and operations. Equation 1 has also been found to give good results when small concentrations of olefins are to be determined. I n cases of this kind larger samples are used for analysis. The method may also be used where the solution contains known olefins different from that contained in the standard. I n this case the specific gravities and the molecular weights of the olefins must be known. If the solution contains a
ANALYTICAL EDITION
320
mixture of olefins, the average molecular weights and specific gravities will apply. The olefin content is then calculated by use of the equation
MI,DI,and N1 are the actual or average molecular weight and density of and number of olefin bonds in the olefin or mixture being determined, while M,, D,,and N , are the corresponding properties of the standard olefin. If the olefin in the standard and solution is octylene and T X in Equation 2 amylene, respectively, the expression gives the concentration of amylene in the solution in terms of octylene, while the expression in the brackets is the amylene equivalency of octylene. To test Equation 2, solutions of 2-pentene, pinene, and allyl sulfide were titrated. An octylene solution was used as a standard with the results shown in Table IV. In the process of titration of the allyl sulfide, the tetrabromide was precipitated as fine white needles. Solids were deposited from solutions of pinene (and limonene) also, but they are more or less gummy.
&
TABLEIV. TITRATION TO TESTEQUATION 2 OLEFIN
Ti8
AMT. PREaENT
TP
OLEFIN EQUIV. OF OLEFIN OCTYLENE FOUND
% Amylene
%
4.8 7.0 15.0
7.2 10.9 22.6
0.69 0.09 0.69
5.0 7.5 15.6
Vol. 4, No. 3
where U,is the olefin concentration in terms of the standard, and U,,U2,etc., are the concentration of the various olefins in the mixture. The factors for amylene, pinene, limonene, and allyl sulfide in terms of octylene as the standard are calculated to be 1.44,1.97,1.92,and 2.43, respectively. DETERMINATION OF OLEFINSAND TERPENES The bromine titration method cannot be used for olefin mixtures unless the average molecular weights and specific gravities of the olefins are known. If in a simple mixture containing two known olefins one of the olefins may be removed, however, the concentration of each olefin can be determined by this means. Mixtures of octylene and limonene were analyzed by titrating the oils before and after removal of most of the limonene. The limonene was separated from the octylene by selective polymerization. The reagents tried were metallic sodium and the following acids : nitric, phosphoric, phosphorous, mono-, di-, and trichloroacetic, and sulfuric, All except the last polymerized limonene to a limited extent only. Table VI shows the proportions of the terpene remaining in the oil after a 9.36 per cent solution of limonene in olefin-free cleaner's naphtha was treated with the various reagents and distilled to the original end point. Phosphoric, phosphorous, and the chloroacetic acids polymerized only 30 per cent of the limonene as determined by bromine titration (the original solution being used as a standard) or by observation of the refraction of the distillate. TABLEVI. TERPENE IN OIL AFTER TREATMENT REAQENT
REFRACTIVE INDEX OF DIBTILLATIU
LIMONENE POLYMERIZED
% 49 "01 8 9 8 HIPOI
TABLEV. PER CENTOLEFINSIN MIXTURE No. 1 2 3 4 5 0 7 8 9
CALCD. AB LIMOAMY- ALLYL OCTYOCTYLENENENE PINENE LENE SULFIDELENE FOUND
%
%
4.56 10.18 17.00 8.33 9.72 6.85 19.34 3.42 3.42
4.39 3.07 5.69
......
.... ..
%
..*.
.. 1:i3 6.28 3.14 4.61 3.14
%
.... *.
..
5:32 2.66 2.66 2.06
% ... ...
i:o
... ... ... ... 5.0
%
%
13.0 17.2 28.4 20.5 12.1 26.9 29.3 16.3 25.0
12.7 16.8 28.4 19.8 12.1 28.0 28.4 10.0 24.0
The two double bonds in allyl sulfide and the two potential double bonds in pinene are thus saturated quantitatively, as they are in nerol, Under the conditions of the titration, no bromine is added to the sulfur in the allyl sulfide. This inactivity is analogous to the nonreplacement of the hydroxyl group in nerol. According to Faragher, Gruse, and Garner ( I ) , diolefins absorb halogen very rapidly in the beginning. This was observed also in this work. For example, a pinene solution absorbed 60 per cent of the needed bromine before a yellow color appeared which persisted for 30 seconds, whereas an octylene solution of double the concentration of the pinene became yellow almost from the beginning. It is of interest to note that the cracked gasolines behave as if they contained a large concentration of polyolefins, since a considerable proportion of bromine reagent was added before a yellow color was produced. It is sometimes useful to determine the value of a mixture of olefins in terms of a standard o l e k such as octylene. To determine if interfering reactions arise, Equation 3 has been applied.
1.4157 a7 1.4179 27 1.4179 23 1.4170 1.4179 1.4167 (terpineol formation noted)
Ha 01 CICHnCOIH ClzCHCOzH
*... ..
ClrC. COzH
Sulfuric acid gave much better results. The best results were obtained as follows: The oil was shaken with threetenths its volume of sulfuric acid of 80 per cent concentration for 30 minutes, allowed to stand for 1 hour, the acid layer withdrawn, and the oil distilled to the original end point. The distillate from the treatment of the limonene solution retained an olefin content equivalent to 7 per cent of the limonene in the untreated oil. This residual olefin is not limonene, since it is not further reacted upon by retreatment, but for the sake of calculation it may be so considered. Under the same conditions 11.0 per cent of octylene is removed, That the relative proportion of octylene remaining after treatment is almost independent of the octylene concentration is shown in Table VII. TABLEVII. EFFECTOF OCTYLENECONCENTRATION CONCENTRATED OCTYLENE Before treatment After treatment
OCTYLENE UNAFFECTED
%
%
%
5.17 6.20 12.25 16.67 22.8
4.63 4.08 10.5 13.82 20.76
89.5 89.0 86.0 88.2 91.0
The average proportion of the octylene remaining after treatment is 89 per cent. According to Equation 3, the olefin Concentration, M , of a mixture of octylene and limonene in terms of octylene is given by the expression M = E + 1.92 L (4) where E and L are the volume percentages of octylene and limonene, respectively.
July 15, 1932 TABLE
INDUSTRIAL AND ENGINEERING CHEMISTRY
L = 0.56 M - 0.63 D E = M - 1.92 L
VxII. ANALYSISO F MIXTURESFROM TABLE v
MIXTURE
M
D
OLEFINFOUND
12.7
4.6
16.8 28 4
9 6 16.1
4 . 7 octylene 4 . 2 limonene 10.3 3 4limonene octylene 1 7 . 3 octylene 5 . 8 limonene
% 4.56 octylene 4 . 3 9 limonene 10.18 3.67 limonene octylene 17.60 octylene 5.60 limonene
%
As already stated, a solution containing octylene and limonene, upon treatment with sulfuric acid under the specific conditions given, results in a distillate containing the equivalent of 7 per cent of the limonene and 89 per cent of the octylene added. The olefin content, D,in terms of octylene is then D = 0.89 E (0.07 X 1.92) L (5)
+
By the simultaneous solution of Equations 4 and 5, the values of E and L are obtained.
321 (6) (7)
Mixtures 1, 2, and 3, Table V, were analyzed with satisfactory results, shown in Table VIII. The method can be applied to pinene and linalool, and probably to other terpenes and terpene alcohols. However, it is very limited in its scope as, for example, trimethyl ethylene is wholb Polymerized and 3-methYlcYclohexene is two-thirds polymerized. LITERATURE CITED Faragher, Gruse, and Garner, J. IND.E m .CHEM, 1 3 , 1 0 4 4 (1921). Faragher, Morrell, and Levine, Ibid., Anal. E d . , 2, 18 (1930). Meyer, Ann., 380, 212 (1911); Ber., 45, 2860 (1912). Soden and Zeitschel, Ibid.. 36, 266 (1903). (5) Stoermer and Becker, Ibid., 56, 1447 (1923).
(1) (2) (3) (4)
RECEIVED February 23, 1932.
Approximate Determination of Olefin and Aromatic Hydrocarbons J. C. MORRELL AND I. M. LEVINE, Universal Oil Products Co., Chicago, Ill.
A
METHOD has been described for the determination of olefin and aromatic hydrocarbons (2) in cracked gasolines involving the determination of the sum of the concentration of these hydrocarbons, the removal of the olefins by means of sulfur monochloride and distillation from the reaction products, and finally, the determination of the aromatic hydrocarbons in the olefin-free oil. Where the work is of such nature that an absolute error of 1 to 3 per cent is acceptable, the time may be shortened considerably by the use of the method described herein. The sum of the olefins and aromatic hydrocarbons is determined in a manner in which the technic is modified slightly from that described in the previous article. The olefin concentration may then be calculated from the weight of residue remaining after distillation of the oil obtained upon treatment with 91 per cent sulfuric acid by the use of empirical formulas developed in this work. Obviously, the aromatic hydrocarbon content constitutes the difference between the total volume per cent of olefin and aromatic hydrocarbons and the olefin concentration. All values of concentration in this work are expressed in terms of volume per cent.
ice in the condenser and with the receiver in an ice-water bath, the loss may be assumed to be 1 cc., which is the average loss sustained in the many distillations made in this work. The distillate is transferred to the same funnel used for the 91 per cent sulfuric acid treatment, and treated with 3 volumes of 98 per cent sulfuric acid in the manner described above. The treated oil is measured and weighed in the graduate used heretofore, and its specific gravity calculated. The total volume per cent of olefins and aromatic hydrocarbons is calculated according to the formula
s
=
v, - (V, + I )
(1)
where VI is the volume of the original oil, VZ the volume of oil remaining after the second acid treatment, and I the average distillation loss. The following equations showing the relationship between the weight of the distillation residue and olefin content were developed empirically : A: For gasolines with a olefin content)
P
factor of 10 t o 25 (15 to 35 per cent
P U = 1.3 (2) D OF TOTAL OLEFIN-AROMATIC HYDROCARBON DETERMINATION P CONTENT or U = D- + 6 (3) The oil (100 cc.), measured in a weighed graduate, is P shaken with 3 volumes of 91 per cent sulfuric acid for 30 factor of 25 to 35 (35 t o 50 per cent minutes in a 500-cc. separatory funnel. The mixture is B: For gasolines with a olefin content) allowed to settle for 30 minutes, the acid layer withdrawn, and the oil permitted to stand 30 minutes longer, any sludge P U = 1.4 accumulating being withdrawn in the meantime. The D stopcock and stem of the separatory funnel are also freed from U = BP + l 3 or sludge. The oil is transferred directly into a weighed 200-cc. short-neck round-bottom flask, from which the oil is distilled P to a temperature 5" above the end point of the original oil, C: For gasolines with a 3 factor of 35 to 40 (50 to 60 per cent as previously determined in a similar manner. The flask is olefin content) provided with a small uninsulated Hempel column (effective P size 3 by 0.5 inches). The weighed graduate is used as a U = 1.5 (61 D receiver. P The distillation loss may be determined from the weight U D L,+ 15 (7) or loss and the density. If the distillation is carried out with
+
