V O L U M E 2 6 , N O . 6, J U N E 1 9 5 4
1087 ACKSOWLEDGMENT
cannot be estimated with mercuric acetate by any of these methods, as they do not quantitatively react with mercuric acetate under the conditions employed. Mercury addition products are, in general, unstable toward halogen acids. I n some cases, they are so very susceptible to acidity that titration with hydrochloric acid is not possible. This has been observed with or-methylstyrene, cinnamic acid, and diisobutylene, where the addition products undergo quick decomposition in the course of titration with hydrochloiic acid. In other cases that have been studied, the decomposition is very slow, and at the end point, the acid color of the indicator persists for several minutes, so that no difficulty is involved i n detecting the correct end point.
The author is indebted to Santi R. Palit for his kind intereit in the work. LITERATURE CITED
(1) Birks, A. II.,arid Wright, G. F..J . A m . Chrm. Soc., 62, 2412 (1940). ('2) Das, AI. Ii.,J . I n d i a n C/~c.?n. SOC.,31, 39 (1954). (3) Hornstein, I.,ANAL.CHEM.,23, 1329 (1951). ( 4 ) JIsrquardt, R. P., and Luce, E. X,, Ibid., 20, 751 (194s). (5) Ibid., 21, 1194 (1949). (6) Martin, K. W., Ibid., 21, 921 (1949). (7) Palit, 8 . R., Ih-n. E m . C H E Y . ,ANAL.ED.,18, 246 (1946). (8) Wright, G. F., J . .4m. ('hem. S O C . , 62, 3993 (1935). RECEIVED f o r review October 14, 19.53. -4ccepted RIarch 30, 1931
Determination of Cyclohexane-T y pe Naphthenes by Analytical Dehydrogenation A. T. POLISHUK, C. K. DONNELL, and J. C. S. WOOD Research
and Development Department,
Son O i l Co.,
T
Norwood, Pa.
HE i n c r t ~ ein the use of catalytic reforming proccsses to improve motor gasoline and to produce benzene, toluene, and xylenes has stimulated interest in analytical procedures for determining naphthenes (cycloparaffins) in the gasoline boiling range, since naphthenes are converted to aromatics in their forming proce$>. Most naphthenes in this range are cyclopentane or cyclohexane derivatives. -4 method for determining cyclohexane-type naphthenes in petroleum naphthas has been described by Rampton (4). Thid method consists of dearomatizing the petroleum fraction; selectively dehydrogenating the reactable cyclohexanes in the saturates over n platinum catalyst to the corresponding aromatics (q~m-sul IF t i t u t ed cyclohexanes, such as 1 1-dimethylcyclohexane. are not dehydrogenated); determining the aromatics produced: nnd c~;tlr*ulatingthe amount of reactable cyclohexanes present. ~
THERMOCOUPLE RATE
INOICATINO BUBBLER
The successful application of this method and some modification* of the apparatus and procedure are reported here. APPARATUS MODIFICATIONS
The modified apparatus, employed to obtain the data herein reported, is shown in Figure 1. The sample reservoir is graduated to aid in measuring the feed rate, and is water-jacketed to prevent the vapor pressure of low boiling samples from interfering ith the feed rate. The reactor tube is inserted into a solid block of aluminum alloy, which is heated by electrical windings. This block is insulated and uniform temperature is maintained by a pyrometer controller actuated from a thermocouple in the alloy block. Several reactor tubes can be installed in the same block, thus increasing the efficiency of operation. The feed inlet tube has been redesigned to assure a continuous f l o of ~ sample to the preheater, which is a short section of 4-mm. borosilicate glass heads incorporated within the reactor tube. These changes provide a more constant vapor flow through the catalyst bed than is provided with dropwise feed. S o hydrogen is passed through the unit during operation, as additional hydrogen may tend to reverse the reaction and limit the rate of throughput. The modifications permit higher feed rates and result in essentially complete dehydrogenation in one pass. CATALYST TREATMENT
NOSTEN WIRE
ELECTRODES
ELECTROLYTIC
CELL
2 - 1% NaOH
2Sml ORADUATED SAMPLE RESERVOIR CAPILLARY RESERVOIR
TUBINQ FROM REACTOR
TO
GLASS BEAD ( 4 m m )
PREWEATER
6 0 ~ 0OF IS% PLATINUM ON ACTIVATED CARBON (10-20 MESH) ALUMINUM ALLOY CYLINDER 11"I 2 4 " ) QLASS
BEADS
OLASS REACTOR
(4mrnI
TUBE ( I S m m I 3 0 " )
CONDENSER
25nl
ORAOUATED R E C E I V E R
Figure 1. Glass Dehydrogenation Apparatus
The catalyst was prepared in accordance with the detailed instructions given by Rampton (4). I n this work Darco Corp. :ic*tivatedcarbon, 10- to 20-mesh, was used as the catalyst support. \\hen a new catalyst is flushed with hydrogen, the flow must be csontinued until no more hydrochloric acid is given off as evidenced by a test for chlorides in the exit gases. This step is essential if a highly active catalyst is to be obtained. I t has heen found in another laboratory ( 3 ) that considerable time is qnved by hydrogenating the catalyst a t 425' C., then reverting to 325" C. for operation. These worker6 have also been successful 111 regenerating a t this higher temperature some catalysts which had been contaminated hy sulfur compounds. The activated vntalyst must be maintained in a hydrogen atmosphere, especial11 at elevated temperatures. PROCEDURE CHANGES
Samples may be dearomatized either by large scale acid absoi ption similar to the A4STMmethod ( 1 ) or by adsorption on silica gel. The authors have found it convenient to dearomatize by acid absorption. If this method is used, the raffinates must he percolated through a small amount of silica gel-e.g., 1 part of gel for 2 to 5 parts of sample-to remove any sulfur contaminants before dehydrogenation. Using samples prepared in this manner and maintaining the catalyst in a hydrogen atmosphere, it has been possible to maintain tn-o tuhes of active catalyst for 18
'ANALYTICAL CHEMISTRY
1088 months. During this time 50 volumes of hydrocarbons per volume of catalyst have been charged, with no decrease in catalyst activity. Catalyst activity is checked daily, by dehydrogenating pure cyclohexane which is relatively difficult to dehydrogenate. A 97% or higher conversion t o benzene is an acceptable activity test. R A T E STUDIES
Rate studies were made to determine the effect of these apparatus modifications and procedure changes on the conversion of cyclohexanes t o aromatics. Figure 2 shows that for feed rates up to 20 ml. per hour (equivalent to 1 volume of sample t o 3 volumes of catalyst per hour), the amount of dehydrogenation is unaffected by rate and is essentially quantitative. Above 20 ml. per hour the conversion tends to decline; however, it is still a t least 9701, up to 10 ml. per hour. In addition to reducing operation time, the increased feed rate reduced the amount of ring opening in the methylcyclopentane molecule. While the opening of cyclopentane rings does not affect the analysis of cyclohexanes, which is the primary object of this procedure, it is undesirable if the saturates remaining after dehydrogenation are t o be analyzed further. Infrared analysis of the saturated hydrocarbons remaining after dehydrogenation of a pure hydrocarbon blend containing 35% cyclohexane, 15% methl Icl-clopentane, and three paraffins proved that methylcyclopentane was lost by ring opening to form methylpentanes. Data in the following table show that at a rate of 20 ml. per hour the loss of methylcyclopentane was reduced to about 5y0 in the case investigated. Rate, hll./Hour 6 12 20
The data obtained from runs with naphtha fractions in the sixto eight-carbon range were compared with infrared analyses. Table I1 compares cyclohexanes by dehydrogenation of the whole sample to the sum of the individual cyclohexanes by infrared analysis of a series of distillate fractions. The agreement between cyclohexanes determined by these two independent methods was generally better than 1%. This comparison could not be extended beyond the eight-carbon range because infrared methods have not been extended bevond this range..
Table 11. Comparison of Cyclohexanes b y Dehydrogenation and Infrared -Methods in Straight-Run Naphtha Fractions Boiling Range, ('nrbon N o . , o r . Range 60-80 C&7
60-92 60 105
Ce-C; C6-CS
80-90
Ca-Ci
90-105
Cy-cs
Table I. Dehydrogenation for Determining Cyclohexanes in Hydrocarbon Blends ~
a
Deviations"
49.2
f 0 . 2 , +0.8
43 0
f 2 . 2 ,+2.8
32 3
+0.8
42 9
+1.0
38.2
-0.3
62.7
f2.4
81.8
f0.6. f 0 . 6
63 8
+0.7,+0.8
15.8
-1.3
21 9 fl.O, f 1 . l Average deviation 1.1
Experimental value minus theoretical value.
7
Difference
ti i -1.0 ,
-0.5 -0.4 +o 4 -0 9 -0 9 i l 9
f0.8 -0.1 -0.1 fO.2 +1.6
-1.1 .4verage difference 0 . 7
g o
E l
0
P
0
0
I
Runs made on known blends of six- and seven-carbon hydrocarbons which consisted of the major components present in narrow boiling gasoline fractions showed deviations from the known values of about 1%. Table I s h o w the composition of ten blends and the deviation of the experimental results from the known values. Where dehydrogenation analyses were carried out in duplicate, the reproducibility was about 0.5%.
Theoretical Cyclohexanes
Rfi ~.
20 5 38 0 24 4 40 1 39 9 8 9 10 H 8.2 54.4 53.6 54.8 52.9 33.1
9 54.5 53 5 55 54 5 32
C;-Cs
ISB
DISCUSSION OF RESULTS
Blend Composition, Number, and Type of Compounds ParNaphthenes affins Cyclopentanes Cyclohexanes Ilethylcyclouentane Cyclohexane JI&hylcycloCyclohexane pentane AlethylcycloCyclohexane pentane IlethylcycloCyclohe~ane pentane 4 &Iethylcyclopentane Cyclohexane 1 ... Ilethylcyclohexane 1 ... Ilethylcyclohexane 2 4 dimethylcyclo- Ilethylcyclopentanes hexane 1 4 dimethylcyclo- Alethylcyclopentanes hexane 1 ... Ethylcyclohexane
19.5 3,s 5 24 40 .i 39 8
% Infrared; 27.7
Summation of analyses of a series of distillate fractions.
Ilethylcyclopentane Loss, % 30 12 5
By operating a t 20 ml. per hour, a yield of dehydrogenated material sufficient for analysis is obtained in 1 hour.
27 -.
12 5. ._
105-130
0
Cyclohexanes, Dehydrogenation 28
0 0
PURE
CYCLOHEXAME OR YETHYLCYCLOHEXANL
KNOWN BLEND-
X NAPHTHA SO
0
40%
fRACTION
CYCLOHEXANE
- 20.1. I
1
10
20
30
F E E D RATE.
Figure 2.
CYCLOHEXANE
I
YL. PER
1 4.3
I
sa
HOUR
Effect of Rate on Dehydrogenation on Cyclohexanes
The experimental values for cyclohexanes by dehydrogenation, given in Tables I and 11, were calculated from the aromatic content of the dehydrogenation product back to an original sample basis using the formula given by Rampton (4). The aromatic contents of the products were determined by rlST3I method (1) although any method yielding aromatic contents with an accuracy of f1 % is satisfactory. The accuracy achieved in the range studied indicates that dehydrogenation of cyclohexane rings is practically the only reaction occurring, and there is no appreciable amount of interfering reactions such as cracking or isomerization-for example, isomerization of alkylcyclopentanes to form cyclohexanes would have produced high values for cyclohexanes. To establish the amount of cracking, several samples of the exit gases were analyzed by the mass spectrometer. These gases contained about 98% hydrogen, produced by dehydrogenation of cyclohexanes, and less than 2% hydrocarbons, showing that very little cracking occurs. This method has already proved to be a valuable analytical tool for the determination of cyclohexane type naphthenes in the sixto eight-carbon range. By using fractional distillation and
V O L U M E 26, NO. 6, J U N E I 9 5 4
1089
proper choice of cut points, cyclohexane, methyleyelohexane, and total CScyclohexanes (excluding 1,l-dimethyloycloheusne) have been determined in petroleurn fractions. I n addition to its use in the lower maleoular weight range, the dehydrogenation method may he extended to the Cr range and higher. Decahydronaphthalene, a dicyclic, has been quantitatively dehydrogenated in the presence of n-decane. There are, however, two complications to be considered when the method is applied t o the higher range: The possible number of gemsubstituted cyclohexane isomers increaaes rapidly, so t h a t the reactable cyclohexane8 should not be confused with total cyclohexanes, and there is at present no independent method for checking the ac-
curacy of results. The few results obtained so far have appeared to be logical, but further investigation is needed. LITERATURE CITED
(11 Am. Sac. Testing Msterials. "ASTM Standards on Petroleum products and LI.L.:---'" n o m c 1cm 3 3 , n r n (2) .'bid., Designstion (3) Tiarriz. C. G., Hc
communication. (4) Rampton, H. C.. P
RECE~VED for review September 17. 19G3. locepted February 2G, 1954. Presented at the Meeting-in-~liniatureof the Philadelphia Seotion of the .A,rnnrC.~N CHEMICAL SOCIETI. January 27, 1953.
rature Refractometry with an Abbe-Type Instrument E. P. BLACK, W. T. HARVEY, and S. W. FERRIS Sun Oil Co.. Marcus Hook, Pa.
- - _..
. J index
1 measurements have been used O l l r G * L l V L n W U VY UIC: l Y a b l U 1 1 9 1 UUI*&.U VI UbLLIIUaIUP, &llU \\~aS of petroleum wares, found to agree, after emergent stem correotion, uithin 0.1" a t there has been little uniformity in testing temperatures. Many 212mF, wax technologists have used 176" F. (80"C.) since 1929, fallowing Temperature-Control System. The water jacket of the refractometer wm connected to a source of low pressure steani and llie suggestion of Ferris, Cowles, and Henderson (S),who reported colinked with a I-liter water tank in such a way that,either water refractive indices at that temperaturein oonnection with their from the tank or steam could be admitted to the jacket. The work on the composition of paraffin wax. Until recently 176" F. unter tank wa8 equipped with 8. heater, was generally acceptable, since it fulfilled a primary requisite of ITater from the jacket outlet was recirculakd, but the steam maintaining any available petroleum TVZX in the molten state. Lately, hou.ever, many petroleum waxes are being produced that melt in the neighborhood of 200" F. and, consequently, 176" F. is no longer adequate for general wax refractometry. The temoerature 212' F. is niieeested herewith BR R suitahle ~.~~ ~.~~ .~~~~~ i,eniperature for refractive index measurements, since it exceecIS the melting point of any current petroleum wax product and it is conveniently attainable by the use of low pres~uresteam 8.8 a. heating medium. The adaptation and use bf an Abhd-type r(?frnctorneter for 212' F. refractometry is described below.
A-riim ~ " yyears far the &racte"zatiou
~
~~
~~~
__~
~~~~~
~~~
~~
~
APPARATUS
Refractometer. The instrument shown in Figures 1 and 2 was manufactured by the Valentine Technical Instrument Carp. and is designat,ed as the Improved Precision model. I n order th,t tem~ ~ ~ . . . L . . ~ ~ ~ f -L , ~ ~~~1~~~ . ~
EO.no
Y7
~
~
,~~~ ~
~ ~ ~ : - . ~ ~ ~ ~ ,
~
7
~
,
. ~ ~ I L
In preparing the instrument for use, the tank n,ater tva8 hentcd from room temperature to 200" F. while being circulated through the jacket to raise the prism temperature gradually, thus avoiding the damage by thermal shock t h a t is likely to result from too rapid heating. When the temperature had reached 200' F. or above, over a period of a t least 30 minutes, the u-ater was shut off m d steam a t about 1-pound gage pressure was turned on. After 5 minutes of Steam flow with the temperature remaining constant ( i 0 . l ' F.) the instrument was considered to he itt temperature equilidrium and ready for index determinations. The jacket temperature in this appamtus held well within + O . l ' F. for an hour or more. Although occaBiona1 drift of 0.1" or 0.2" \vas observed, it r a 6 too slow to he significsnt during
