Determination of Water-Extractable Sodium in Liquid Hydrocarbons KURT H. NELSON and M. D. GRIMES Phillips Petroleum Co., Bartlesville, Okla.
b A procedure permitting the use of flame photometers which do not have integral atomizer-burners has been developed for the determination of 0 to 10 p.p.m. of sodium in liquid hydrocarbons. The sodium i s extracted b y shaking the hydrocarbon with an equal volume of sodium-free distilled water. Sodium in the aqueous phase i s then determined b y flame photometry. The method has been applied to samples boiling from 135" to 900' F. with an accuracy of the order of &4%.
by modifying one of these methods, a procedure which would permit the use of any flame photometer was desired. The developed method consists of extracting the sodium from the hydrocarbon sample by shaking the hydrocarbon with an equal volume of sodiumfree distilled water, and measuring the extracted sodium in the aqueous phase flame photometrically. This procedure permits the use of flame photometers which do not have an integral atomizerburner. APPARATUS
G
gas oils, fuel oils, and other liquid hydrocarbons may become contaminated by saline water during shipment and storage. This contamination is not prevalent in domestic handling, but may readily occur during overseas shipments. Usually the contamination is of the order of only a few parts of sodium per million. Because of the adverse effects of contaminants in the use of the petroleum products, a measure of the amount of sodium present in the liquid hydrocarbons is highly desirable. The amount of sodium present in hydrocarbons has been determined directly using flame photonietcrs having integral atomizer-burnrrs. Lubricating oils have been diluted u i t h various solvents and aspirated directly into the flame (2, 3). Likewise, crude oil has been diluted with chloroform before determining various metals by flame photometry (6). Although 0 to 10 p.p.m. of sodium in liquid hydrocarbons could be determinrd directly AROLINE,
Any flame photometer may be used. A mechanical shaker (1) and 4ounce polyethylene bottles fitted with polyethylene screw caps are required. Other types of screw caps are unsatisfactory. REAGENTS
Standard Sodium Solutions. A sodium stock solution is prepared by dissolving 2.5412 grams of reagent grade sodium chloride in distilled water in a 100-ml. volumetric flask. A set of standard sodium solutions containing 0 t o 0.1 mg. of sodium per 100 ml. is prepared by diluting 0-, I-, 2-, 3-, 4-, and 5-ml. aliquants of a 1 t o 500 dilution of t h e sodium stock solution, Another set of standard sodium solutions containing 0 t o 1.0 mg. of sodium per 100 nil. is prepared b y diluting 0-, 2-, 4,6-, 8-, and 10ml. aliquants of a 1 to 100 dilution of t h e sodium stock solution. All polyethylene \Yare and glasmare used in the preparation of standard solutions and in the analysis of samples must be washed with distilled water,
Table I. Analyses of Petroleum Distillates Containing Added Sodium Jet Fuel, Reformer Charge, Kerosine, Gas Oil, 135-460' F. 331403" F. 488-900" F. 146-367' F. Added, Found, Added, Found, Added, Found, .4dded, Found, p,p.m. p p.m. p.p.m. p.p.m. p.p.m. P P ~ . P P ~ p.p.ni. 0 0 0 0 , o o 0.0 0.0, 0.0 0.0 0.0, 0.0 0 0 00, 0 0 0 3 0 3 0.4 0.4, 0.4 04, 0 4 0.5 0.4, 0.5 0 4 0 5 0 5 0.0 0.8, 0.8 0.9 0.9, 1.0 0 8 08, 0 8 1.1, 1.2 1.2 0 8 0 8 , 0 8 , 0 8 1.3 1.3, 1 . 3 13, 11 1 2 1 1 1 2 2 9 27. 2 8 3.1 3.1, 3.0 3.3 3.1, 3.5 1 3 1:,14,13 6.2 6.2, 6.1 6.6 6 , 5 , 6 . 2 5 8 5 5 ; 5 7 2 7 21 9.3 9.3, 9.2 9 . 9 10.0, 9 . 8 8 7 85, 8 4 5 3 5 2 , 5 . 5 , 5 , 3 13.2 1 2 . 9 , 1 2 , 8 1 2 , 4 1 2 . 1 , 1 2 . 3 11 6 11 3, 11 6 8 0 7 6 10 6 10 0, 10.3
594
ANALYTiCAL CHEMISTRY
rinsed with acetone, and air-dried. Care should be taken at all times to avoid contamination of equipment and solutions by sodium salts from the hands. PROCEDURE
Accurately weigh 25.0 ml. of the hydrocarbon into a 4-ounce polyethylene bottle, add 25.0 ml. of distilled water, and shake the tightly capped bottle for 30 minutes on the shaker. Then pipet a portion of the water layer into a clean container and analyze by flame photometry, using the 0- to 1.0nig,. standard sodium solutions for calibration. If the water layer contains less than 0.1 mg, of sodium per 100 ml., reanalyze using the 0- to 0.1mg. standard sodium solutions. After correcting the emission readings for that of distilled water, read the concentration of sodium in the rvater layer from the calibration curve which is prepared from the appropriate set of standard sodium solutions. Then calculate the sodium content of the hydrocarbon from: Sodium, p.p.ni. by weight =
A (1000) 4 IY ~
where A is the milligrams of sodium in the water layer and Ti' is the grams of hydrocarbon. DISCUSSION
Ordinarily, when trace amounts of sodium are added to hydrocarbons, a small volume of a n aqueous or aqueousalcoholic sodium chloride solution is shaken with a large volume of the hydrocarbon to produce a homogeneous solution. This procedure is not entirely satisfactory a t times because of the low solubility of the sodium chloride and n t e r in the hydrocarbons. An examination of solubility data (4, 5 ) for the sodium halides revealed that sodium chloride and sodium bromide have low solubilities in most organic liquids. I n contrast, sodium iodide is very soluble in organic solvents such as methanol, ethanol, acctonc, ethylenediamine, cthylcnc glycol, and monoethanolnniinc. Of thcscl solvents, acetone is very soluble in hydrocarbons. Some preliminary cspcrinients slio\\ cd that a sodium iodide-wctonr solution was a simple means of nccur:ttely adding traces of sodium to liquid h!.rlroc:u.boiis.
The resulting sodium iodide-acetonehydrocarbon solutions were stable for a t least 24 hours. Manual shaking of hydrocarbon samples with distilled water for as long as 15 minutes \vas unsat’isfactory, giving incoinplcte extraction and generally rrratic sodium analyses. HoTvever, a 30-minute vigorous mechanical shaking ( I ) proved sufficient, a second 30minute extraction yielding only a minute trace of sodium. T o t’est the procedure: four series of hydrocarbon samples were prepared by adding k n o m amounts of sodium iodide-acetone solution to a jet fuel, a reformer chargp, a kerosine, and a gas oil as shown in Tahle I. This was accomplished hy dissolving 6.500 grams of reagent grade sodium iodide in acetone in a 100-ml. volumetric flask. Then 1.0 nil. of this solution was diluted with acetone to 100 ml. Aliquants of this
second solution were diluted with the hydrocarbon in 100-ml. volumetric flasks. These solutions of the jet fuel, the reformer charge, and the kerosine were then analyzed b y the described procedure. The analysis of the gas oil solutions was identical, escept that 25 ml. of cycloheaane was added to the gas oil in each polyethylene bottle before shaking. This reduced the viscosity of the gas oil phase during the extraction. The analytical data for these four series of hydrocarbon samples are tabulated in Table I. On the basis of these results, the relative error of the method is =t4% and the precision is *2%.
LITERATURE CITED
(1) .4m. SOC. Testing Materials, 1916 Race St., Philadelphia, Pa., ASTM Committee -D-2, Method D 1019-56T, Amendix I1 (2) Zoniad, A.L., Johnson, W. C., ANAL. CHEM.2 2 , 1530-3 (1950). (3) Curtis, G. IT., Knauer, H. E., Hunter, L. E.. Am. SOC. Testing Materials.’ Spec. Tech. Publ. 116, 67-74 (1951). (4) Seidell, A,, “Solubilities of Inorganic and Metal Organic Compounds,” 3rd ed., Vol. I, Van Sostrand, Xew York, 1940. ( 5 ) Seidell, A,, Linke, K. F., “Solubilities of Inorganic and Organic Compounds,”
Supplement to 3rd ed., Van Kostrand, Xew York, 1952. (6) Whisman, ?*I.,Eccleston, B. H., ANAL. CHEM.27,1861-9 (1955).
ACKNOWLEDGMENT
The authors thank F. TIr. Blanton for performing the analyses required during this investigation.
RECEIVEDfor review March 16, 1959. Accepted January 7, 1960. Thirteenth Annual Southwest Regional Meeting, ACS, Tulsa, Okla., 1957.
Effects Due to Chemical State of the Samples in X-Ray Emission and Absorption PAUL D. ZEMANY Research laboratory, General Electric Co., Schenectody,
b Experimental results show that the chemical state of an element can affect the structure and position of an absorption edge and both the wave length and intensity of an emission line. The measurements were made with a conventional x-ray spectrograph. In some cases it may be necessary to consider these effects in x-ray emission analysis.
N. Y.
tude and significance in typical situations encountered in x-ray, emission spectrography. If they can be detected and are neglected, they will limit the accuracy of analytical results. The effects described here result from the valence state of the atom, and differ from the effects ascribed to hpterogeneity by Claisse ( 2 ) . ABSORPTION EFFECTS
T
HE valence state of an element in a series of compounds has a relatively small effect on both Tvave length (6) and intensity in x-ray absorption and emission. These effects are so small that it was possible to neglect them in the early work on x-ray methods for chemical analysis ( 1 ) 6 ) . Several years ago, when this conclusion was first reached, it probably ivould not h a w been possible to demonstrate these chemical effects. However, more recent developments, which r e s u l t d in improved stability and prcci4on of measurements, extension of the nicasurPnients of intensity to longer na1-e lengths, and improvements in resolution suggest that the possibility of effects due to chemical state should be re-examined. The experiments descrilicd below were designed to sec if these effects could be detected and t o detcmiinr their magni-
Both the absorption and emission spectra are significant in x-ray emission spectrography. A change in the magnitude of the absorption coefficient will result in a corresponding change in the emitted intensity in thin samples, if the fluorescent yield is unchanged. I n thick samples, the resultant fluorescent intensity is modified by absorption effects and the geometry of the system. which complicate the simple result obtained with thin samples. The change in position of the absorption edge will result in the absorption of more or less of the exciting radiation a t the corresponding wave length, again causing a directly corresponding change in emitted intensity for thin samples, and a more complicated result for thick samples. Recently Van Sordstrand ( 7 ) showed the fine structure of the absorption edge
for several series of compounds. He found considcrable detail in the spectra, and correlated some of the detail to the degree of coordination of the elements involved. By using techniques similar to his, the spectra shown in Figure 1 and 2 vier(’ obtained. Figure 1 s h o w the absorption coefficient, pz, for a sample of potassium permanganate; the particular sample was furnished by him. Figure 2 s h o m a spectrum of hSnSO4 H10. The sample was prepared by moistening a sheet of capacitor paper (a very thin kraft paper of high purity) with a solution of the salt, and allowing it to dry. These absorption spectra were obtained on the General Electric XRD-5 spectrograph, set up for diffraction, and using the white radiation from a (2.4-7 copper target tube operated at 50 kv., 15 ma. A 3” source slit, 0.05” exit slit, and high resolution Soller slits vere used, rvith a topaz crystal (2d = 2.712 -4.).The samples were inserted as filters in place of those nornially used to attenuate the K Oline of a tube used for diffraction. Values of pz, the product of the mass absorption coefficient and sample thickness, rather than p are given, as it was not possible t o determine the thickness of the films with significant accuracy. It is evident, from the difference betrreen the two examples given, that substantial differences in VOL. 32 NO. 6, MAY 1960
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