Determination of Unsaturation in Heavy Hydrocarbon Gases by Catalytic Hydrogenation Boiling Water-Jacketed Catalj-st JESSE II. SHIVELY, FLOYD IWILCREES, \ \ I ) I I i H H Y l,k:\.IS The Texas Company, neacort, V. 1..
HE catalytic hydrogenation method described by RlcMillan, "Cole, and Ritchie ( I ) has been widely used for the determination of unsaturates in normally gaseous hydrocarbons. Refinements of this method, involving corrections for the nonideality of gases, have been described by Robey and Morrell (S), who also extended the method to include CS hydrocarbons which they rendered gaseous by diluting with hydrogen 1 to 2. Other methods commonly used for determining gaseous unsaturates are based on bromine number determination or absorption of the unsaturates in aqueous solutions of various reagents. These methods supplement catalvtic hydrogenation, which is the only rapid method giving a reliable indication of the total number of unsaturated linkages per average molecule of gascoinmonly expressed as "per cent unsaturation," as though the molecule contained one double bond. The value obtained in the preliniinary hydrogenation run is (Ii*carded, its purpose being only to establish adsorption equilih-
Table I.
Analyses of Simple Mixtures of CCHydrocarbons
-__ Present
Unsaturation, P e r Cent Found Run Preliminary run 1
Run 2
Using Unheated Catalyst Sample 1 99.9% mixed pentanes 0.17"pentenes Sample 2 20 8% Z-methylbutane 54 0% n-pentane 25 2% 1-pentene
0 1"
25
zc
5.0
1.2b
29
0.3
25
24
Using Boiling Water-.Jacketed Catalyst Sample 3 2-Pentenes Sayple 4 ( 7 . 6 % n-pentane 2 2 . 4 % 2-pentenes
C.P.
99
98
98
22 4 c
23
22
22
13
13
Sample 5 8 7 . 9 % n-pentane 1 2 . 1 V0 2-pentenes 12.1c 13 4 Determined by bromine titration. b Catalyst apparently not adequately presaturated. discarded. c Blended.
This value should be
Table 11. Per Cent Unsaturation of Complex Cs Low Temperature Fractional Distillation Fractionsc (Boiling Range 18' t o 50' C.) Boiling Water-Jacketed Unheated Catalyst Catalsst PW. ._
liminary run 117 129 114 110
Run Cut 1 1 104 2 116 3 109 4 108 5 117 110 6 113 102 a Chiefly pentenes
PW. .~ ~
Run Run Run 2 3 4 108 111 117 114 116 106 115 103 109 ... 109 ... .. 94 100 and pentadienes.
liminary run 10.5
107 108 106 106 96
Run 1 103 107 102
Run 2 103 107 104
Run 3 103
105 95
...
...
105
. .. ,_ .
,..
104 . .
.. ..
rium between the catalyst and the residual gasesthat is, to saturate the Occasionally c a t a1 y s t one preliminary run is insufficientand i t is necessary to discard the results IITURNS 2 4 G A of two runs on a sample. N I C H R O M E WIR Initial attempts t o utilize the conventional room temperature hydrogenation method as a step in the complete analysis C A T A L Y STof certain complex Cb cuts from analytical low G L A S S WOOL temperature f r a c t i o n a l d i s t i l l a t i o n s met with little success (Table 11). though the unsaturation of simple mixtures preBMM OD pared from pure Cg h)d r o c a r b o n s w a s determined moderately w l l Figure 1. Water-Jacketed (Table I), Hydrogenation Catalyst The apparatus (it M c M i l l a n , Cole. anti Ritchie ( 1 ) was used after modifying it so the catalyst \vas equipped Ivith a boiling water jacket (Figure 1). IVheii reducing the catalyst boiling triethylene glycol (280" t o 290" C.) was used instead of wat,er. All stopcocks were luhricated with hydrocarbon-insoluble lubricant ( 2 ) , which is esseiitial in CSanalysis. The better precision obtainable with the heated cat,alyst is apparent from Table 11. The high values for unsaturation found in preliminary runs with unheated catalyst, in contrast to niuch lower values found in succeeding runs on the same sample, indicate that adsorption on the catalyst was excessive. When the temperut,ure of the catalyst was maintained a t 100" C. througho u t the analysis, the Cs hydrocarbons exhibited low adsorption characteristics similar to lighter hydrocarbons at room trmperature, and though the exact compositions of these samples are unknown the results with the heated catalyst are probably more reliable for this reason. Even the saturating run generally aprws very well with subsequent runs under these conditions. I n the analysis of simple Csmixtures acceptable results were obtained by either method (Table I), but those from the preliminary runs were usable only with the hot catalyst. The time required with the latter was generally about half that necessary with the conventional catalyst tube. The original method called for presweeping the catalyst with hydrogen before every determination. It subsequently proved more practical t o eliminate this step between duplicate determinations on the same sample, inasmuch as after the first test the catalyst is in equilibrium with residual reaction gases, and
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AIR OR W A T E R CONDENSER
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V O L U M E 21, NO. 12, D E C E M B E R 1 9 4 9 Table 111.
Effect of Hydrogen Presweeping of Catalyst
Composition
Total Unsaturation, Per CentFound Preliminary Run Run Present run 1 2
1. (Swept catalyst with hydrogen) 2. 2-Rlethylpropene 99.5a
100.7 99.7 99.6 3. 1,a-Butadiene 196.4b 197.7 1 9 7 . 5 197.5 ... 4. 1-Butene 99.9a 100.0 99.8 5. (Swept catalyst with hydrogen) 6. n-Butane 1-Butene 10.1c 11.2 10.3 10.4 7. n-Butane 1,3-Butadiene 49.1C 49.5 49.5 49.3 8. n-Butane 0.0a 0.0 0.3 0.3 9, n-Butane 1-Butene 1,3-Rutadiene 128.8C 128.6 128 6 1 2 8 . 5 10. (Swept catalyst with hydrogen) 11. Ethene, commercial Unknown 95.2 95.6 95.5 12. n-Butane 1-Butene 128.8C 129.2 128.6 ... 1.3-Butadiene 13. (Swept catalyst with hydrogen) 14. 2 0 . 8 % 2-methylbutane 2 5 . 2 % 1-pentene ,i4.0% n-pentane 25.2c 24.8 24.6 25.0 15. 9 9 . 9 % mixed pentanes 0 , l pentenes 0 .l a 0.0 0.3 -0.3 a Determined by bromine titration. b Minimum unsaturation; determined with maleic anhydride. c Blended.
the latter technique was employed in the present work except where otherwise stated. The data in Table I11 were obtained with the hot catalyst in the order in which they appear. The catalyst was not swept with hydrogen except as indicated, and then only to ascertain the effect. When the catalyst had not been swept with hydrogen as a prior step, the results of preliminary runs Lvere never significantly different from succeeding runs, even though the composition of successive samples varied widely-for example, Cp preceded Cq hydrocarbons and O", unsaturation preceded 128%. Even with prior hydrogen sweeping of the catalyst, preliminary runs gave values which differed little
from subsequent runs, in contrast to large differences when Cc hydrocarbons were run a t room temperature with conventional presweeping (Table 11). Catalyst life has been so good that the authors suspect it may undergo a certain amount of autoregeneration. Unlike hydrogenation a t room temperature, the present method has been used successfully on undried gases with aqueous solutions or moist mercury in the burets of the hydrogenation apparatus. This proved particularly convenient in hydrogenating moist gases left from Orsat analyses. However, it is considered good practice to avoid exposing the catalyst to moisture unnecessarily when cold and not in use and this is accomplished by closing the stopcocks a t its base, t,hereby isolating the wet burets. The hot water-jacketed catalyst has also been applied to the analysis of gaseous mixtures containing cyclopentene, cyclopentadiene, ethylacetylene, and vinylacetylene. The reaction with cyclopentene proceeds normally. That cleavage of the ring did not occur a t the temperature of boiling water was established by mass spectrometric examination of the reaction products. Slightly exaggerated analytical results are obtained, however, when essentially pure cyclopentadiene or ethylacetylene is subjected to catalytic hydrogenation over the heated catalyst. The high values probably result from dimerization followed by absorption of gaseous hydrocarbon in the condensed dimer. Liquid product has actually been observed on the confining mercury following A determination on pure ethylacetylene. Mixtures containing less than lOYG ethyl- or vinylacetylene have been analyzed xith satisfactory results. ACKNOW LEDGII ENT
The authors express their appreciation to W. L. Slater for suggestions on the design of the boiling water-jacketed catalyst. LITERATURE CITED
(1) McMillan, Cole, and Ritchie, ISD. EXG.CHEM..A s . 4 ~ED., . 8, 105 (1936). (2) Melochc and Frederick, J . Am. Chem. Soc., 54, 3264 (1932). (3) Robey and Morrell, IXD.EKG.CHEY.,ASAL.ED.,14, 880 (1942).
RECEIVED December 26, 1947.
Purification of 0,O-Diethyl O-p-NitrophenylThiophosphate (Parathion) for Use as a Primary Standard FRED I. EDWARDS AND S. A. HALL Bureau of Entomology and Plant Quarantine, U . S . Department of Agriculture, Beltsville, M d .
HE increased use of the new insecticide, parathion, has Tcreated an urgent need for a simple method of obtaining the pure compound from technical grade material for use as an analytical standard. The only published criterion for evaluating the purity ( 1 ) of parathion has as its basis a nitrogen analysis. The presence of any contaminant containing nitrogen would make this procedure questionable. The following method has been used in this laboratory to prepare parathion in a pure state for use as a standard. PROCEDURE
A 30-gram sample of technical parathion (a dark brown oil with a strong garliclike odor) was washed by decantation with small portions of petroleum ether (Skellysolve A), using a total of 200 ml. The parathion was then taken up in 50 ml. of ether and shaken with 25-ml. portions of 10% sodium carbonate until the aqueous solution was no longer colored. This required about 200 ml. of the wash solution. The ether solution was then dried over anhydrous sodium sulfate and was finally passed through a plug of dried cotton. The dried ether solution was filtered, using mild
suction, through a column (8 cm. long and 3 cm. in diameter) containing a mixture (I) of 2 parts of Attapulgus clay (an attapulgite clay) and 1 part of Hyflo Super-cel (a diatomaceous earth), previously made wet with ether. The ether was removed on the steam bath and the last traces were removed by a strwm of dried nitrogen, leaving a yellow oily residue. To test the purity a t this point, a portion of this residue was chilled in dry ice for one hour. Scratching soon induced crystallization. The melting point of the pale amber crystalline mass was about 1O C. The main body of the oil was dissolved in 25 ml. of ether, and Skellysolve A was added a t room temperature to the point of incipient turbidity. This solution was placed overnight in the freezing compartment of a refrigerator a t a temperature of -15" C. I n the morning there was a mass of white needles, which were freed from the amber mother liquor by decantation and washed twice with 10-ml. portions of a precooled mixed solvent consisting of equal parts of Skellysolve A and ether. The crystals were taken up in about 50 ml. of ether, dried over anhydrous sodium sulfate, and passed through dried cotton; the ether was removed on the steam bath, and the last traces of solvent were removed by a current of dried nitrogen. The parathion thus obtained (about 5 grams) was a very pale yellow liquid without odor, which crystallized into almost colorless long needles melting sharply a t 6' C.
