perometric methods for the determination of halide ions recovered from petroleum products are discussed by Parks and Lykken (8). Titrations were performed a t about 5 C. to take advantage of the lorver solubility of d y e r chloride (5) at lower temperatures. This allows greater accuracy in the titration and improves the appearance of the titration curve. Four of these apparatus in use in this laboratory operate in pairs from the same set of gas cylinders and airpurification systems. Individual vacuum pumps are attached to each unit. For more than one year these
units have been in continuous use for the determination of micro- and milligram quantities of sulfur and chlorine. ACKNOWLEDGMENT
The author wishes to express his thanks to hlildred 0. Corley for diligently operating the apparatus during the course of this investigation. LITERATURE CITED
(1) Agazzi, E. J., Peters, E. D., Brooks, F. R., ANAL.CHEW25,237 (1953). (2) .4m. SOC. Testing Materials, Philadelnhia. Pa.. “Standards on Petroleuk P6d;cts and Lubricants,” p. 23, 1955.
(3) Granatelli, L., ASAL. CHERI.27, 266 (1955).
(4) Kolthoff, I. If., Kuroda, P. K., Ibid., 23, 1306 (1951).
(5) Kolthoff, I. M., Sandell, E. B., “Textbook of Quantitative Inorganic Analysis,” 3rd ed., p. 60, Macmillan, New York, 1952. ( 6 ) Ibid., p. 541.
(7) . Lieeett. L. M.. ANAL. CHEW26. 748 I
.I.,
(1954). (8) Parks, T. M., Lykken, L., Ibid., 22, 1444 (1950). (9) Pecherer, B., Gambrill, C. If., Wilcox, G. W., Ibid., 22,311 (1950). (10) Wear, G. E. C., Quiram, E. R., Ibid., 21, 721 (1949).
RECEIVED for review -4ugust 9, 1956. Accepted November 23, 1956.
Determination of Trace Amounts of Chlorine in Naphtha J. G. BERGMANN and JOHN SANIK, Jr. Research Department, Standard Oil Co. (Indiana), Whiting, Ind.
,A method has been developed for determining less than 10 p.p.m. of chlorine in naphthas. Lamp combustion or sodium biphenyl reduction is used to convert organic chlorine to chloride ion; for most naphthas, lamp combustion i s preferred. Of several ways investigated for determining less than 100 y of chloride, only a ferric thiocyanate colorimetric procedure provided sufficient accuracy. With lamp combustion, the method has a standard deviation of 0.1 p.p.m, and an analysis can be completed in 3 hours.
A
the trace elements found in light petroleum fractions are arsenic, iron, nickel, vanadium, chlorine, nitrogen, and sulfur. hlethods for determining some of these elements in the parts-per-million range have been published (3, I S ) , but no method has been available for determining less than 10 p.p.m. of chlorine in naphthas within 0.5 p.p.m. Two types of methods are possible: direct and indirect. In the first, the chlorine is determined directly in the naphtha; in the second, it is first separated from the naphtha and then determined in aqueous solution. Direct methods include neutron activation, x-ray fluorescence, and flame photometry. Neutron activation analyses of several naphthas containing known amounts of chlorocyclohexane shot\-edan accuracy within 1.5 p.p.m., which was unsatisfactory for the purposes of this investigation. However, the analyses showed the presence of only negligible MONG
quantities of halogen other than chlorine. Other direct methods either do not apply to trace amounts of chlorine or apply only to specific chlorine compounds. Hence, procedures were needed for separating chlorine from the naphtha as chloride ion, and for determining trace amounts of chloride ion in aqueous solution. Two general procedures exist for converting organic chlorine to chloride ion: oxidation of the entire sample (1, W), and reduction with sodium in various media (5, 14-16, 18). Most of the procedures require excessive reaction time for the more refractory chlorine compounds or cannot accommodate large enough samples. Exceptions are lamp combustion ( 1 ) and sodium biphenyl reduction (14, 16). Both are rapid and permit the use of 10 to 15 grams of sample-enough to provide sufficient chloride ion for accurate measurement. Procedures for determining small quantities of chloride ion in aqueous solution include nephelometry ( I I ) , amperometry (IO, l a ) , differential potentiometry (4) mercuric nitrate titrimetry ( 6 ) , and a microdiffusioncolorimetric method (‘7, 8, 17). Each procedure was investigated for measuring less than 100 y of chloride-the amount obtained from 10 to 15 grams of naphtha. However, accuracies were not sufficient, particularly below 50 y , because the amount of chloride approaches the sensitivity limits of these procedures. A new and more sensitive procedure (9) depends upon displacement of thiocyanate ion from mercuric I
thiocyanate by chloride ion; in the presence of ferric ion, a highly colored ferric thiocyanate complex is formed, 2C1-
+ Hg(SCN)t + 2Fe+++ HgClz + 2 Fe(SCN)++ -+
the color of which is stable and proportional to the original chloride ion concentration. The procedure can detect as little as 0.5 y of chloride and is accurate within 0.5 y in the range of 1 to 100 y . A method has been developed for determining trace amounts of chlorine in naphtha. Organic chlorine is converted t o chloride ion by lamp combustion or sodium biphenyl reduction. After either method of isolation, the ferric thiocyanate colorimetric procedure determines the chloride ion. LAMP-COMBUSTION PROCEDURE
Combustion is carried out in apparatus identical in principle to the ASTbl lamp sulfur apparatus (1). It consists essentially of a means for burning the sample from a wick in a synthetic atmosphere, composed of 70% carbon dioxide and 3001, oxygen, and for absorbing the hydrogen chloride from the combustion products. The apparatus is designed to accommodate a blank and one or more samples.
Two modifications to the apparatus were made: inclusion of Fischer-Porter C-type rotameters to indicate the gas flow to each burner, and the use of water, rather than hydrogen peroxide, in the VOL. 29, NO. 2, FEBRUARY 1957
241
scrubber, chimney-manifold manometer, and absorber. The rotameters (calibrated from 0 to 0.2 cubic foot per minute) aid in the initial adjustment of the apparatus and improve the control of gas flow during combustion. Water quantitatively absorbs the hydrogen chloride produced and simplifies the subsequent determination of chloride. All water used is ion-exchanged; distilled water passed through Amberlite MB-3 resin is satisfactory. To avoid contamination from the hands, lamp wicks are handled only with clean forceps. Preliminary adjustments of the apparatus are made to provide the proper pressures ( I ) , and the burner vacuum valve is set so that the rotameter indicates a flow rate of 3 liters (0.1 cubic foot) per minute of the carbon dioxideoxygen mixture through the absorber. A weighed sample of about 20 ml. is taken for combustion. With minor adjustments of the control valves to provide a stable and nonsmoking flame, the rotameter shows a flow rate of about 1.5 liters per minute. After nearly all the naphtha has burned, combustion is stopped and the flask is reweighed to determine the amount of naphtha burned. A blank must be run concurrent with the combustion (1). The aqueous solutions from both absorbers are transferred to 50-ml. volumetric flasks. Absorbers, chimneys, and spray traps are rinsed three times with small quantities of water. The washings are added to the absorber solutions, and final solutions are adjusted to volume. SODIUM BIPHENYL PROCEDURE
Sodium biphenyl reagent is prepared by the reaction of 14.5 grams of sodium and 98 grams of biphenyl in 480 ml. of ethylene glycol dimethyl ether (14). These concentrations of sodium and biphenyl are lower than those used by Liggett (14) and give a reagent that is easier to pipet and provides more uniform blanks. Ten to 20 ml. of the naphtha in a separatory funnel is shaken for 30 seconds with sufficient sodium biphenyl to maintain a green color (usually no more than 10 ml.). The excess reagent is decomposed with 10 ml. of water; 20 ml. of hexane is added, and the mixture is agitated and allowed to settle. The aqueous layer is withdrawn into a 60-ml. nickel beaker (Nickelware is used because it is alkali-resistant and because nickel does not interfere in the colorimetric procedure.) The funnel and contents are washed with 10 ml. of water, which is added to the initial extract. To remove interfering substances extracted by the sodium biphenyl, the combined extracts are adjusted to a p H of 10 to 12 with concentrated nitric acid, evaporated to dryness on a hot plate, and ignited in a muffle furnace a t 500' to 550' C. for 30 minutes. (Hydrogen peroxide or ammonium persulfate oxidizes most interfering substances except thiophene and its homologs, which have been found in some naphthas.) The residue is dissolved in a minimum amount of water, and the solution is transferred to a 25-ml. volumetric flask
242
ANALYTICAL CHEMISTRY
Table 1.
Precision and Accuracy with Lamp Combustion
n-Heptane Added Found
0.0 2.12 2.31 2.33 2.43 2.30
Av . Recovered Table It.
Chlorine, P.P.M. Mid-continen t Kaphtha
8.65 10.64 10.94 11.01 11.09 10.92 2.30 8.62
-
0.0 1.79 1.88 1.90 1.97 1.89
Treated Midcontinent Naphtha 0.0 0.77 0.87 0.87 1.20 0.92
4.07 5.87 5.96 5.97 5.99 5.95 1.89 4.06
-
3.98 4 93 4 95 4.96 5 24 5.02 0.92 4 10
Comparison of Combustion and Sodium Biphenyl Reduction
Naphtha n-Heptane plus added C1 hfid-continent lus added C1 Mid-continent ~160'-390' F.) Mid-continent ~100"-360' F.) Mid-continent (190'-400' F.) Mid-continent (200"-370" F.) Mid-continent, treated (190"-360" F.) Gulf Coast, naphthenic (23Oo-41O0 F.) Mid-continent, treated ( 180"-380' F.)
and diluted to volume with water. A blank is carried through the entire procedure. COLORIMETRIC PROCEDURE
A 20-ml. aliquot of the chloride solution obtained by either lamp combustion or sodium biphenyl reduction is transferred to a 25-ml. volumetric flask. Two milliliters of a 0.25M ferric ammonium sulfate [Fe(NH4)(S04)2.12H20 ] solution in 9M nitric acid is added, followed by 2 ml. of a saturated solution of mercuric thiocyanate in ethyl alcohol. The solutions are mixed, diluted to volume with water, and mixed again. The blank is treated in the same manner. Ten minutes after developing the color, the absorbances of both solutions are measured in a spectrophotometer against water in a 5-cm. cell a t 460 mp; a Beckman Model R is satisfactory. (Because any chloride present in the air is slowly absorbed, these measurements are made as promptly as possible, and water is used in the reference cell instead of the blank.) The amount of chloride in the aliquot corresponding to the difference between the two absorbances is then obtained from a calibration curve, and the original concentration of chlorine in the naphtha is calculated, To prepare the calibration curve, a t least five aliquots of a standard sodium chloride solution containing 10 y of chloride per ml. are taken to cover the range from 0 to 50 y ; color development and absorbance measurement follow the outlined procedure. dbsorbance is plotted against micrograms of chloride.
Chlorine. P.P.M. Sodium bi henyl Lamp reJuction combustion 10.6, 1 0 . 8 5.6, 5.9 6.1, 6 . 3 1.9. 2 . 1 1.9; 2 . 4 0.9, 1 . 5 0.9, 1 . 9 1.1, 1 . 4 1.3, 1.6
10.9,ll.O 5.9, 6 . 0 6.6, 6 . 7 1.8, 1 . 9 1.4, 1 . 5 1.5, 1.8 1.0, 1 3 1.0, 1.2 0.8, 0 . 9
method were tested in three ways. Lamp combustion was used t o study the recovery of chlorine added tu naphthas. The two methods of isolating chloride were compared with the same naphthas. Several naphthas of different origins were analyzed in duplid cate with lamp combustion. Table I shows the virtually complete recovery of chlorine from naphthas to which chlorine had been added as chlorocyclohexane. Four burnings were made on each sample. The standard devia; tion of the results is 0.1 p.p.m., and the average difference is 0.1 p.p.m. Kine naphthas with chlorine con. tents established by lamp combustion were analyzed by sodium biphenyl reduction. The results in Table I1 show a standard deviation of 0.3 p.p.m. and an average difference of 0.3 p.p.m. Duplicate routine analyses of typical naphthas are shown in Table 111. Lamp combustion was used for isolating chloride. The results show a standard deviation of 0.1 p.p.m. of chlorine, The method thus gives as precise results with naphthas of widely different origins as it does with synthetic blends. To obtain accurate results, two precautions must be observed. The analyses must be conducted in a room from which fumes of interfering substances are excluded. The lamp-combustion apparatus and all glassware used must be reserved solely for determining trace chlorine. CONCLUSION
DISCUSSION OF RESULTS
The accuracy and precision of the
Kith either lamp combustion or sodium biphenyl reduction, the method
Table 111. Duplicate Analyses of Typical Naphthas with Lamp Corn bustion
Alid-continent (l6O0-39O0F.) Mid-continent (140"-390' F.) Mid-continent (10Oo-39O0F.) Arkansas West Texas coker Mid-continent (250°-3800 F ) Gulf Coast. naphthenic (210"-360" F.) Mid-continent (210"-390" F ) Kuwait Mid-continent (200"-310" F ) Wyoming, treated
Chlorine, P.P.M. 6 59,6 70 4 00,4 28 3 46,3 58 2 32,2 39 1 2 3 , l 63 1 1 1 , l 27 1 0 0 0 0
04,l 17 76,O 89 58,O 67
56,O 58 23,O 23
is well suited to multiple analysis by nontechnical operators. The absorber solutions from lnmp combustion are ideally suited t o the colorimetric procedure because of the absence of interfering ions. A 15gram sample can be burned in about 2 hours, and the total analysis can be completed in about 3 hours. Lamp combustion is therefore recommended for isolating chloride from naphthas. Although chloride can be separated from the naphtha in 10 minutes by
sodium biphenyl reduction, the time advantage is negated by the subsequent manipulations required. These steps increase the chances of chloride cont,amination and make the determination of chloride by the sodium biphenyl procedure less precise and accurate than by lamp combustion. Sodium biphenyl reduction is therefore recommended only for materials that do not burn cleanly in a lamp. The method should be applicable t o trace-chlorine analysis of other petroleum fractions. Some heavier materials can be burned satisfactorily when blended with a low-chlorine diluent; others can best be analyzed by sodium biphenyl reduction. LITERATURE CITED
Am. SOC.Testing Materials, ".1STM Standards on Petroleum Products and Lubricants," D 1266-551', p. 679 (1955). Ibid., ASTlI D 808-52T, p. 308 (1955). Barney, J. E., ANAL.CHEM.27, 1283 (1955). Blaedel,' W. J., Lewis, W. B., Thomas, J. W.,Ibid., 24, 509 (1952) (1952). Chabloy, E., Ann. chim. 1, 469 ( 5 ) Cl (1914).
(6) Clarke, F. E., ANAL.CHERI.22, 553 (1950). ( 7 ) Conway, E. J., "Micro Diffusion Analysis and Volumetric Error," rev. ed., chap. XXII, C. Lockwood, London, 1947. (8) Gordon, H. T., ANAL. CHEm 24, 857 (1952). (9) Iwasaki, I., Utsumi, S., Ozawa, T., Bull. Chem. SOC.Japan 2 5 , 226 (1952). (10) Kolthoff, I. bl., Kuroda, P. K., ANAL.CHEW23, 1306 (1951). (11) Kolthoff, I. M., Yutzy, H., J . Am. Chem. SOC.5 5 , 1915 (1933). (12) Laitinen, H. *4.,Jennings, W. P., Parks, T. D., IND.EKG.CHEM., ANAL. ED. 18, 355 (1946). (13) Lake, Y. R., XlcCutchan, P., Van Meter, R., Neel, J. C., ANAL. CHEX.23, 1634 (1951). (14) Liggett, L. M., Ibid., 26, 748 (1954). (15) Lohr, L. J., Bonstein, T. E., Frauenfelder, L. J., Ibid., 25, 1115 (1953). (16) Pecherer, B., Gambrill, C. XI., Wilcox, G. W., Ibid., 22,31,f (1950). (17) Rodden, C. J., Ed., Analytical Chemistry of the Manhattan Project," p. 297, McGraw-Hill, New York, 1950. (18) Umhoefer, R. R., IXD.ENG.CHCM., A N A L . ED. 15, 383 (1943). RECEIVEDfor review June 27, 1956. -4ccepted September 20, 1956. Division of Petroleum Chemistry, 130th Meeting, ACS, Atlantic City, N. J., September 1956.
Determination of Vanadium in Titanium Tetrachloride and Titanium Alloys WILLIAM H. OWENS', CHARLES L. NORTON, and J. ALFRED CURTIS Cramet, Inc., Chattanooga, Tenn.
A spectrophotometric procedure has been developed for the determination of trace amounts of vanadium in titanium tetrachloride. It is also applicable to the determination of vanadium in alloying amounts in titanium-base alloys. The procedure is very simple, rapid, and accurate to within 270 relative. Chromium offers the only interference found in a limited investigation.
A
and accurate control method is necessary in the production of titanium tetrachloride of high purity. Most methods for determining vanadium, including the peroxide and phosphotungstic acid (2,3)methods, are subject to interference from titanium. Volumetric methods ( 1 ) are suitable for alloying amounts of vanadium but are 1 Present address, Yational Refearch Metals Corp., Cambridge, Mass. RAPID
not accurate enough for 0.100% and less. Lengthy procedures involving chemical separations are, of course, undesirable. Upon evaporation of a sulfuric acid solution of titanium tetrachloride containing vanadium with nitric acid. an intense yellow color was produced, which became more intense on further evaporation. As the color n a s found t o be reproducible if the evaporation was carried to fumes of sulfuric acid, it was used as a basis for determining vanadium in titanium tetrachloride. The method was also applicable to the determination of vanadium in titanium alloys. REAGENTS
Standard vanadium solutions, 0.05 and 0.50 mg. per ml. Sulfuric acid, concentrated and 1 to 1. Nitric acid, concentrated. Vanadium-free titanium tetrachloride.
APPARATUS
Beckman 1Iodel DU or Model B spectrophotometer with 5-mm. cells Glass hypodermic syringes, 2-mi. and 10-ml. PROCEDURES
1. Vanadium in Titanium Tetrachloride. Pipet a 2-ml. aliquot of vanadium-free titanium tetrachloride into a clean, dry 250-ml. beaker. Slowly and carefully add 40 ml. of 1 t o 1 sulfuric acid. Rinse down the sides of the beaker with dilute sulfuric acid and then add 10 ml. of nitric acid. Cover and place on a hot plate. When most of the water and nitric acid have evaporated, remove the tvatch glass and continue heating. After all the water and nitric acid have evaporated, there is a short time before the fumes of. sulfuric acid appear. As soon as these fumes appear, remove the beaker from the hot plate. Allow the beaker to cool to about 50" to 60' C. and then VOL. 29, N O . 2, FEBRUARY 1957
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