1404
ANALYTICAL CHEMISTRY
VOL. % DISTILLED Figure 12. Analysis of Sail Joaquin Valley Crude 30' API Equilibrium flash distillation a t atmospheric pressure
IO
Figure 13.
LITERATURE CITED
66,33 (1947). (2) Dean, E. W.. Hill. H. H.. Smith, K. A. C.. and Jacobs, W. A.. U.S. Bur. Mines, Bull. 207 (January 1922).
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40
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70
VOL. X DISTILLED
of W. R. Doty, head glassblower of the California Research Corp. The helpful cooperation of G. R. MacPherson in the preparation of this paper is gratefully acknowledged.
(1) Birch, S. F., Gripp, V., and Kathan, W. S., J . SOC.C h m . I?kd.,
i
Analysis of Sun Joaquin Valley Crude 30' API Equilibrium flash distillation Viscosity of bottoms
(3) Mithoff, R. C., MacPherson, G. R., and Sipos, F., Oil Gas J . , 40, S O . 26, 81-5, 187 (1941). ( 4 ) Smith, R. B., Dresser, T., Hopp, H. F., and Paulsen, T. H., I ? d Eng. Chem., 43, 766 (1951). RECEIVEDMay 14, 1951.
Direct Determination of Oxygen in Organic Compounds Carbon Reduct ion-Manometric Met hod JOSEPH HOLOWCHAK
AND
G. E. C. WEAR
Esso Laboratories, Research Division, Standard Oil Development Co., Linden, N . J .
A
T THE present time, there is no entirely satisfactory method
for the direct determination of oxygen in organic substances, especially in samples of low oxygen content. The most promising method, currently used by most laboratories in this country and exclusively in European countries (16), is based on the thermal decomposition of the organic compound over carbon, first proposed by Schdtze ( 16) and later improved by Unterzaucher (20). Elving and Ligett ( 4 ) in their review of the direct determination of oxygen critically examined the available methods and presented a complete literature survey on the subject. Since this review was written, practically all the publications on the direct determination of oxygen have been based on the Unterzaucher carbon-reduction procedure, Among these are the excellent papers by Aluise et a[.(I), Dinerstein and Klipp (S),and Maylott and Lewis ( l a ) of this country, Deinum and Schouten ( 2 ) of the Netherlands, and Kirsten (9) of Sweden. A recent publication by Grosse el al. (6) describes an entirely new procedure, an isotopic method, which does not require the quantitative separation and quantitative recovery of the ouygen-containing compound 01 any of its reaction products.
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Considerable difficulties are encountered by many laboratories in adapting the titrimetric Unterzaucher method to the direct determination of oxygen. The major cause of the uncertainty of the method has not been established. At present, it is not known exactly what reactions the iodine pentoxide undergoes under varying conditions. It has been the experience of this and other laboratories that hydrogen, produced during the pyrolysis of the organic compound, reacts with iodine pentoxide, as shown in Table I, with liberation of iodine, which leads to high results. This effect, coupled with the variation in the operating blank, makes it extremely difficult to obtain reliable results on substances of low oxygen content, especially petroleum product8. I t is particularly desirable, however, to have a reliable method for the determination of small amounts of oxygen in petroleum materials, as a sninll amount of oxygen may represent an appreciable quantity of an oxygenated impurity of high molecular weight in the petroleum fraction. Knowledge of the oxygen content is important, because trace amounts of oxygen may affect the stability of petroleum materials during storage and use.
1405
V O L U M E 23, NO. 10, O C T O B E R 1 9 5 1 Table I.
Effect of Hydrogen on Iodine Pentoxide
Gas 30% hydrogen in nitrogen Seaford nitrogen (approx. 1% hydrogen) Prepurified nitrogen, Matheson
Volume of Gas Used, 111. 340 445 330 380 360 510 420 370 650
0.02016 .V Thiosulfate Required Total, BII. per ml. 100 ml. gas 4.52 1.33 7.45 1.67 3.17 0.96 0.22 0.06 0.24 0.07 0.35 0.07 0.00 0.00 0.00 0.00 0.00 0.00
A manometric method (13) has been applied to the determination of carbon and hydrogen in organic compounds. Such a manometric procedure utilizing a sensitive manometer and two closed systems, one for the determination of oxygen in substances of low oxygen content, the other for substances of high oxygen content, would be inherently simpler and more advantageous for the determination of carbon dioxide produced than the other methods cited above. This paper deals with the adaptation of a manometric method to the determination of oxygen in organic compounds in conjunction with the Unterzaucher carbon-reductiori procedure. M'PARATU S
It would appear necessary, in view of the fact that iodine pen-
A diagram of the apparatus is shown in Figure 1, and a detailed sketch of the manometric cystem is given in Figure 2.
toxide may be sensitive to hydrogen, either to devise a method for the removal of hydrogen from the reaction products or to use Nilropen other methods for the determination of carbon monoxide or, after oxidation, the carbon dioxide, in which hydrogen would not n interfere. Harris et at. ( 8 )describe the construction of a hydrogen diffuser, consisting of a heated palladium membrane xhich will selectively remove the hydrogen by diffusion and which can readily be incorporated in the conventional Unterxaucher apparatus. Several methods for the determination of the carbon monoxide or carbon dioxide produced have been used with some measure of success. The National Bureau of Standards To M ~ r t o l t lB o t t l e ( 1 7 ) has developed a coloriAll metric method for detecting Hiqh small amounts of carbon monoxide in air. This method has been applied to the determination of oxygen in polymers by the Unterzaucher method ( 2 0 ) and is designed primarily for compounds that contain less Figure 1. .ipparatus for Determination of Oxygen than 2% oxygen. The Texas Co. (19) resorted to a graviThe apparatus is the conventional Unterzaucher apparatus ubed metric microdetermination of the carbon dioxide with apparent in this country, which is adequately described by Aluise et al., success. Deinum and Schouten applied the titrimetric deterDinerstein and Klipp, and Maylott and Lewis, with the following mination of carbon dioxide described by Pieters (14). Harris et substitution and addition: The iodine pentoxide tube is replaced al. employed a physicochemical technique in which the carbon with a tube containing copper oxide vire (of the type customarily used in the Dumas nitrogen microprocedure) heated a t 300' C., monoxide was determined by a thermal conductivity method. and the addition of the manometric system. Another procedure, which has been tried by this laboratory The liquid nitrogen trap located a t the exit end of the quartz without much success, is the determination of carbon monoxide reaction tube is an essential part of the apparatus and serves by use of red mercuric oxide (11). effectively to remove all reaction products formed during pyrolysis and carbon reduction with the exception of carbon monoxide, hydrogen and methane. The absorption tube filled with Ascarite situated between the liquid nitrogen trap and the copper An apparatus and procedure have been developed for oxide reaction tube acts as a protective measure, as a side stream the direct determination of oxygen in organic coniof nitrogen (which may contain carbon dioxide) added through pounds by a manometric modification of the Unterthe adjacent three-\Tag stopcock is .used for filling and flushing zaucher carbon reduction method, in order to cirthe manometric system after evacuation. The manometric system comists of three U-type traps sepacumvent difficulties due to reaction of hqdrogen rated by stopcocks so that each system can be isolated. The formed by pyrolysis and reduction of organic matemanometer consists of two base tubes connected to form a U. rial with'iodine pentoxide. Interference of hydrogen A 1-mm. capillary tube, 450 mm. in length, is attached to one was especially troublesome in the analysis of hydroend of the base tube and by means of 9-mm. tubing and a stopcock is connected to the pressure leg of the manometer. The base carbons containing small amounts of oxygen. The tubes are filled with mercury to about half of their volume. Ocmodified procedure involves oxidation of the carbon toil-S (2-ethylhexyl sebacate) is added to the capillarv leg of the monoxide to carbon dioxide by means of copper manometer. Bn oil-soluble dye may be added to the Octoil-S to oxide, collection of the carbon dioxide in a liquid nifacilitate reading of the manometer. A three-way stopcock connects the U-type traps with the manometer. A glass-mirrored trogen trap, and, after the residual gases have been millimeter scale is placed behind the capillary tube for reading the pumped out by means of a vacuum pump, deterprefisures. mination of the carbon dioxide manometrically in a PROCEDURE standard volume. Hydrogen is concurrently removed The procedure for the proper manipulation of the Unterzaucher as water and frozen out in a dry ice trap. The apparatus, handling of the sample, and the pyrolysis step is method is self-contained, has greater sensitivity, and essentially the same as that described by Aluise et al., Dinerstein is not subject to erroneously high results on samand Klipp, and Maylott and Lewis. The methods differ only ples of low. ovygen content due to hydrogen inin the final step. Instead of using iodine pentoxide and subterference. sequently determining the liberated iodine, copper oxide is used
I
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~~
1406
ANALYTICAL CHEMISTRY
as the okidant and the carbon dioxide is determined manonietrically. Therefore, only the manometric step is described here. Piior to the first determination, the manometric system is isolated from the rest of the apparatus, and the entire system including the manometer is completely evacuated. During the evacuation, the lower stopcock on the manometer is kept open. After complete evacuation, it is closed, and the manometer is isolated from the U-traps by proper manipulation of the threeway stopcock. While still evacuating the system, the U-trap nearest the copper oxide tube is immersed in an acetone-dry ice bath to remove the water formed by oxidation of the hydrogen with copper oxide. The other t n o traps are immersed in liquid nitrogen baths. The center (liquid nitrogen) trap retains the carbon dioxide which is produced. The last (liquid nitrogen) trap serves as a guard trap to remove any carbon dioxide or water vapor which may be drawn in from the atmosphere during manipulation of the stopcock attached to the Mariotte bottle. The svJtem is then isolated from the vacuum pump and filled with nitrogen gas by connecting this system with the rest of the apparatus. The stopcock that connects the manometric system with the atmosphere is attached to a Mariotte bottle by means of rubber tubing. After the svstem has been filled w-ith nitrogen, this stopcock is opened and the flow of nitrogen regulated to give a rate of 12 to 15 ml. per minute. The sample is then pyrolyzed by the prescribed procedure. After a saeeping-out period of 20 minutes, the U - t r a p immersed in liquid nitrogen are isolated from the rest of the apparatuq by cloping the stopcocks to the coppc'i oxide tube and Mariotte bottle.
i j~ 1
High Vacuum Type
I I~ ~I
A l l dimensions ore in millimeters unless other.
>
'J W
,9mm
A11 Absorkrlubes
some dimensions
Thc manometer is empirically calibrated in terms of milligrams of oxygen per millimeter of carbon dioxide pressure by running a seriep of determinations on benzoic acid as described by Saughton and Frodyma ( I S ) . A method for an absolute calibration of the system is discussed by the above author8. The manometric system can also be calibrated by making use of a common procedure in high vacuum technique for calibration of U-tubes b j the careful decomposition of a known amount of pure sodium bicarbonate to sodium carbonate, carbon dioxide, and watclr. RESULTS AYD DISCUSSIOh
Tablc~I shons the effect of hydrogen in reducing iodine pentoxide. These results were obtained by allowing the gases to by-pass the quartz reaction tube. ii number of pure compounds were used to check the method (Table 11). Results obtained on two samples of oxygen-free material are presented in Table 111. This method has just been developed to the point of yielding acceptable results; it is believed that the present relative accuracy within 2% could be improved to yield results with a relative accuracy within 1%. One determination by the manometric method requires about the same time as the titrimetric Unterzaucher procedure.
Boll Join1
-T--T
making an appropriate correction for an operating blank and for temperature changes. This system is used for samples of low oxygen content. For samples of high oxygen content, the procedure is the same up to the point of closing the stopcock betveen the two U-traps immersed in liquid nitrogen. After this stopcock is closed, the liquid nitrogen bath surrounding the last C-trap is replaced by a beaker of water a t room temperature, and the system is completely evacuated. After the trap has been warmed to approximately room temperature, the system is isolated from the vacuum pump, and the stopcock between the two traps is opened. ThL allows the frozen carbon dioxide to vaporize into the larger volume provided by the third trap and expansion chamber with a corresponding reduction in the manometer premure reading. The rest of the procedure is the same as that described above.
Tubina
1
1 ~
IJ d
For the apparatus shown in Figure 1, the factor for conversion of pressure readings to milligrams of oxygen is 0.00279 mg. of oxygen per millimeter of carbon dioxide pressure for the svstem used for samples of lox oxygen content, and 0.00936 mg. of 0x5 gen per millimeter for the system for Sam les of high oxygen content. The operating blanks for the smalyand large systems are 20 and 5 . 5 mm. of carbon dioxide pressure, respectively. As shown in Figure 1, the total volume of the large system was increased by means of an expansion bulb. K i t h the present apparatus, it is possible to determine up to 1 mg. of oxygen in the small system and 4 mg. of oxygen in the large system. A comparison of the operating blanks obtained by the manometric and titrimetric methods indicates that high blank values do not arise from the iodine pentoxide when properly conditioned. The pressure reading of the operating blank for the manometric method is equivalent to approximately 0.5 ml. of 0.02 S thiosulfate. This figure is equivalent to about the best value the authors were able to obtain by the titrimetric Unterzaucher method on the apparatus. This operating blank without sample should not be confused nith actual runs made on ouygen-free mateIials. In the latter case, the hydrogen released during pyrolysis of the sample results in erroneously high apparent oxygen values due to the reducing effect of the hydrogen on iodine pentoxide. The manometric method does not suffer from this disadvantage. Data illustrating this point were presented in Tables I and 111.
-31-
Figure 2.
Details of Manometric System
After the isolated system has been completely evacuated, the stopcock between the second and third U-traps is closed and the second trap is connected to the manometer. A reading of the manometer is taken. The frozen carbon dioxide is then evaporated by replacing the liquid nitrogen bath with a beaker of water a t room temperature. After the gas has reached room teniperature, a manometer reading is again taken. The difference hetween the two readings is a measure of the amount of carbon dioxide produced. The percentage of oxygen is calculated after
This procedure has been in use on a routine baqis in this laboratory for several months, and the operating blank has remained constant for the entire period, with a variation of no more than 2-mm. pressure on the small system (equivalent to approximately 0.05 ml. of 0.02 S thiosulfate). A blank value would be constant only for a definite apparatus and method. Factors that enter into the operating blank are the ash content and type of carbon used, the temperature and material of t h e tube, the length of the determination, and the oyygen content of the nitrogen. Two other factors which probably affect the blank unfavorably
V - O L U M E 23, NO. 10, O C T O B E R 1 9 5 1
1407
copper oxide were not substantiated in this laboratory. The effect of reduction of the carbon zone on the Weight, Sniall Large Absolutemagnitude of the blank has not been completc~lyinCompound Mg. system system Calcd. Found error vestigated. Kirsten (16)has been able to obtain exBenzoic acid, NBS standard 9.76 272.5 26.20 26.13 -0.7 sample 39F 7.71 214.8 28.98 -0.22 cellent results for the past several years employing +0.07 11.42 320.5 26.27 the Uriterzaucher procedure vrith a carbon zone 3,55 334.8 26.3 +O.l 3.18 296.5 26.0 -0.2 of appro\imatrly 5 em. Acetanilide, E.K. Go. reagent, 21.3i 271.0 11.84 11.87 -0 03 The manometric procedure shows promise of bcrecrystallized 14.45 184,s 11.95 +0.11 5.92 253.6 11.95 10.11 coming an accurate and simple procedure for the -0.08 7.49 315.7 11.76 diiect determination of oxygen in all types of organic 6.61 280.3 11.84 0.00 compounds. It has rever:iI advantages over other Antipyrinu. hlerck reagent 39.92 362.3 8.50 8.50 0.00 30.48 278.7 8.56 +O.OB modifications of the Unterzaucher method. I t is 7.03 212.7 8,44 -0.06 self-contained, has greater hensitivity, and eliminates 205.0 8 40 -0.lU 6.81 7.65 234.2 8.54 +o 01 preparation and standardization of leagents for Correcred f o r blank a n d for temperature changes. titrimetric methods. Some of the objections to the ~microgravinietiic method are the small weight of Table 111. Results Obtained on Oxygen-Free Materials carbon dioxide involved, uauallv less than 1 mg., - . the by Manometric and Titrimetric RIethods time spent in weighing, and the exacting procedure Manometric __ -~~~ - - _ . TirrinEtzc wtailed in the handling of the absorption tubes. Pressure. 0.02016 .Y Even TTith the removal of hydrogen from the gas Sample mm." Sample thiosulfate wt.. (small Apparent wt., required. .il)parent stream by diffusion through a heated palladium tube Comi~oulid me. system) '6 oxygen nig. inl. b c; oxygen in the conventional titrimetric method, there is still 0.00 38,62 1.63 Cetane 32.5 -0.2 0.57 purified 65.0 -0.5 0.00 27.47 1.10 0.54 the problem of complete removal of hydrogen, the 81.5 0.5 O.OO(2) 39.34 1.73 0.59 proper conditioning, and the unpredictability of the 112.1 1.6 0 . 0 0 (4) 40.37 2.04 0.68 0.41 iodine pentoxide. 0.0 Saplitlialene 42. 1 0.00 29.93 0.91 -1.2 0.00 51.51 1.42 purified 71.1 0.3; Another advantage is t h e ease with which the sys86.4 1.0 O.OO(1) 31.44 0.93 0.40 103.2 -0.5 0.00 49 12 1.7i 0 48 teni can be conditioned a t the beginning of the daj-'s a Corrected for blank and for temperature cliangez. run by evacuatian of the entire system. This prob Corrected for blank. cedure facilitates the removal of the carbon dioxide and carbon monoxide adsorbed on the surface of the carbon ( 5 , 16). :ti'(' ~ ] I C rc.:iction > of the quartz tube \\-ith the carbon, and thts reEsperimental work involving further s t u d - of the reduction :wtion 01 the quartz tube and quartz chips if used in back of the, or elimination of the blank value is now in progress. The factors car1,on pxcking with the carbon deposits formed during pyrol! to be evaluated consist of reduction of the carbon zone from the Grub? and Spietiel ( 7 ) ha\ .ho\vn that the rea(-tion products of present 12 to 5 em., complete removal of the last traces of oxygen silicon dioxide and carbo11 :it 1200" C. arc Yilicwri monoxide. carby chemical means, suhstitution of purified helium for nitrogen, bon monoxide. and silicon caibide. 1,uriclquist (10 ) draw-b and possible replacement of the quarts: tube with a tube ron:ittention to the fact that a rractiori betiwen quartz and carbon structcd from zirconia. btllow 1200" C. should 1 x 3 considered possible. Kirsten ( 9 ) ACKNOWLEDGRIENT point?; out t h r possibilit!- of this reaction and asserts that the tube is also attacked by thc carbon drposits formed during The authors a.ish to express their appreciation to H. R . Derry pyrolysis. Ileinum and Schouteii showed that carbon formed and T. J. Dcvlin for assistance in carrying out much of the during pyrolysis does affect the blank adversc,ll-. Similitr data analytical work. obtainrd in thk laboratory dit1 not substnntiatr thwc findings LITERATURE CITED conclusively. (1) Aluise, 1.. A., Hall, R. T., Staats, F. C., and l
