Bomb-Volumetric Method for Sulfur in Refined Petroleum Products ROBERT E. KREIDER and J A M E S G. F O U L D S Standard O i l Co. of California, Richmond,
Calif. ductioii of the concentrated sulfate to sulfide, which is collected as cadmium sulfide and det,ermined iodonietrically.
The bomb-gravimetric procedure for sulfur is too lengthy to be considered a rapid control method. .4 bomb-volumetric procedure has been developed for refined petroleum products which can be performed in 2 hours. The method involves the hydriodic acid reduction of sulfate and the iodometric titration of the resultant sulfide in an improved manner. Phosphorus presents no difficulty as it does in most other volumetric methods. The method is not applicable to oils containing barium, selenium, or nitrogen in significant amounts. Accuracy is &2%, which is believed to be an advantage of the method.
APPARATUS
Parr oxygen bomb, 36C!-rnI., for the decomposition of samples. .4II-glass distillation apparatus, as shown in Figure 1, consisting of a 250-ml. Erlenmeyer flask with a gas delivery tube, a spray trap, and a Liebig condenser with a removable delivery tube tip. The flask is marked a t the lower meniscus when it contains 35 nil. REAGENTS
+4cidmixture. Mix 400 ml. of hydriodic acid (47%), 400 n?l. of hydrochloric acid (35%), and 100 ml. of hypophosphorous acid (50%). Boil the mixture for 5 minutes, cool, and place in brown reagent bottles. Ammoniacal cadmium chloride solution. Dissolve 4 grams of cadmium chloride dihydrate in distilled water. Add 300 ml. of ammonium hydroxide (28%), and dilute to 2 liters. Standard Dotassium iodate, 0.0100N. Accuratelv weigh 0.7134 gram of pure dry potassium iodate, and dissolie in dystilled water. Bdd 2 grams of sodium hydroxide and 10 grams of potassium iodide. Dilute to 2 liters. Starch indicator solution, 0.5%, freshly prepared. Sodium thiosulfate solution, 0.01OOW. Dissolve 2.5 grams of sodium thiosulfate pentahydrate and 0.1 gram of sodium carbonate in 1 liter of water. Standardize weekly as follows: To 40.0 ml. of standard potassium iodate solution add 100 ml. of water and 20 nil. of hydrochloric acid. Titrate with thiosulfate solution, adding starch indicator a8 the end point is approached. Calculate the normality of the thiosulfate solution.
T
HE bomb-gravimetric method for sulfur in petroleum products ( 1 ) involves decomposition of the sample in an oxygen liomb, followed by gravimetric determination of the sulfate as barium sulfate. The primary disadvantage of the method is the gravimetric determination which makes the method longer than clesirable for rapid control testing. Another disadvantage is the \yell-known contamination of the barium sulfate precipitate. Volumetric procedures for sulfur have been reported (6, 9, IO), but are subject to interference from phosphorus.
I5O M
M
y
PROCEDURE
NITROGEN IN
35-ML.MARK
u
)
1{1 \
REMOVABLE TIP
Figure 1. Apparatus
Colorimetric procedures ( 7 . 8 ) and volumetric procedures (S, 4, 6 ) for sulfur have been described using the hydriodic acid reduc-
tion of sulfate. For the analysis of lubricating oil additives in particular, a volumetric method was desired. Oxidation by fuming nitric acid alone (3) is time-consuming and subject to losses when applied to oils. The evaporation of sulfate solutions to near dryness ( 6 )is not reliable when applied to bomb washings directly. A procedure has been developed using a distillation apparatus for increasing the concentration of sulfate obtained from bomb washings, and the simultaneous hydriodic acid re-
Oxidize from 0.3 to 0.8 gram of sample, depending on sulfur coiiteiit, in an oxygen bomb and prepare the sulfur solution according to ASThI method D 129 (1). Collect the sulfur solution by thorough, but not excessive, washing of the bomb, arid hydrochloric acid treatment of the sample cup if an ash remains. Treat the sulfur solution with bromine water to ensure complete conversion of sulfur compounds to sulfate. After removal of bromine by boiling, cool, and transfer the solution to a 250-ml. volumetric flask, and dilute to the mark. Pipet a 50-ml. aliquot into the special Erlenmeyer flask. S d d a few boiling chips of coarse Carborundum and 35 ml. of the acid mixture. Attach a nitrogen line to the flask and start the flow of gas a t the rate of approximately two bubbles per second. ,Idd 100 ml. of ammoniacal cadmium chloride solution to a 500-ml. iodine flask, and immerse the tip of the condenser tube until it touches the bott,om of the flask. Assemble the apparatus as shown in Figure 1 and start the distillation with the Erlenmeyer flask on a hot plate and cooling water in the condenser. Remove t,he effluent gases with a vacuum line placed over the receiver or conduct t,he distillation in a hood. Proceed with the distillatiori until the level of liquid in the distillation flask is 2 mm. below the 35-m1.mark. (The volume of li uid remaining should be approximately 25 ml. when it has coole8.) Lower the receiver, remove the t,ip of the condenser delivery tube, and place it in the receiver. Add a few boiling chips to the receiver and boil for 2 minutep. (ilvoid prolonged boiling, as the solution should remain ammoniacal.) Disconnect the gas line and disassenible the apparatus. If iodide in the condenser and spray trap should become oxidized on standing, as indicated by the appearance of an iodine color, rinse the parts before conducting another distillation. Retain the distillation bottoms for later recovery of hydriodic acid if desired. Remove the receiver from the hot plate and cool in a stream of water until just warm. -4dd a measured amount of standard iodate solution in excess of that anticipated to be required to watt with the cadmium sulfide precipitate (see Figure 2). Inimediately add 20 nil. of hydrochloric acid, swirl, wash down the sides of the flask, and let stand momentarily. Titrate the excess iodine, using standard thiosulfate and starch indicator as the end point is approached.
1983
ANALYTICAL CHEMISTRY
1984 In case an excess of iodate was not added prior to acidification, add more iodate from the buret until in excess. Stopper the flask and shake gently to consume any hydrogen sulfide; then titrate the ewess iodine as above. I t is desirable to repeat the distillation on a second aliquot, using the quantity of iodate found to be necessary. Carry a reagent blank through the entire procedure using 5 ml. of iodate solution. The blank should be less than 0.002 meq.
shorter boiling time required when the acid mixture was added to a dry or nearly dry sulfate salt. Results on precipitates in unboiled solutions were approximately 0.1 mg. of sulfur higher t h m theoretical. Results on precipitates filtered from the ammoniacal solution were low by approximately the same amount. The latter is believed to be due to the solubility of cadmium sulfide in ammonia. The evolution method for sulfur is generally conducted by CALCULATION titrating an acid solution with iodate. There is always the posBlank = nil. of iodate X N - ml. of thiosulfate X N sibility of loss of hydrogen sulfide. When the solution is acidified after the addition of iodate in excess of require8 02[(n11 of iodate X N ml. of thiosulfate X N ) blank] yo sulfur = L---L ments, there is no loss. This is believed to be an imgrams of original sample provement ovei the procedure of pouring the cadmium sulfide precipitate into an acid solution of iodine ( 4 ) ,since there DISCUSSION is no transfer of the precipitate, The solution should be acidiThe ASTM method ( 1 ) is to be considered an integral part fied immediately following the addition of iodate to preclude any of this method for decomposition of the sample and preparation possible reaction between iodate and sulfide ion derived from of the sulfur solution. By using an aliquot of the sulfur solution, the solubility of cadmium sulfide in ammoniacal solution. the solution is still available for checking by this method, or As a control method this procedure would generally be used the remainder can be finished gravimetrically. An aliquot conon stocks the sulfur content of which is known approximately. tains sufficient sulfate for an accurate determination and is The titration guide (Figure 2) is a convenient means for ensuring faster than boiling d0a.n the whole of the bomb washings. If addition of a 5-ml. excess of iodate. I n case insufficient iodate it were desirable to use a whole sample, stronger reagents would is preqent, the losses are no greater after acidification than is b e in order (4). generally the case with the evolution method, for more iodate can be added following acidification. However, it is advisable PERCENT SULFUR in such cases to distill another aliquot, using the amount of iodate I 3 4 5 found necessary in the first distillation.
-
INTERFEREhCES
15
ML. 0.010 N
25
IODATE
Figure 2.
35
PER
50/250
45
55
ML. ALIQUOT
Titration Guide
Distillation of the aliquot takes about 0.5 hour and the titration is rapid. Elapsed time is about 2 hours per determination. Working time is about the same as for the gravimetric procedure. The test is particularly suitable for multiple operation where a large number of determinations are required for control testing. The distillation apparatus is easily assembled from standard items by a glass blower. The spray trap is to prevent carry-over of hypophosphorous acid while the condenser decreases the loss of ammonia from the solution in the receiver which would otherwise become hot. The condenser tip is made removable (6) so that traces of cadmium sulfide which adhere to it may be easily recovered. Assuming an oxygen bomb to be available, the additional equipment is inexpensive. Stopping the distillation a t the proper time is probably the most critical part of the test. Although there is partial reduction of the sulfate in dilute solution, the solution must be concentrated to complete the reaction. Further, the last traces of hydrogen sulfide must be swept into the receiver. If the distillation is carried too far, the receiver becomes acid and sulfide may be lost. The procedure described has proved to be satisfactory for complete recovery. The ammoniacal solution of cadmium sulfide must be boiled to remove traces of phosphine which result from the decomposition of hypophosphorous acid. Others (3,4, 6) have obtained satisfactory results without this step, possibly because of the
The method is not suitable for samples containing barium because of the slow rate of decomposition of barium sulfate. It is satisfactory for samples containing lead, if provision is made for using the whole sample rather than an aliquot. The method is not satkfactory for oils containing selenium, as hydrogen selenide will distill to some extent. The method is satisfactory for refined petroleum products, since only traces of nitrogen are normally prescnt in such samples. I t is not applicable to oils of significant nitrogen content because of the oxidation of sulfide by nitrogen acids, causing incomplete recovery of sulfur and poor end points during the titration ( 4 ) . If an aliquot containing a significant amount of nitrogen were evaporated to dryness in the presence of an excess of zinc oxide. the distillation would then be essentially that described by Luke ( 3 ) . EXPERIMENTAL
Aliquots of a standard solution of potassium sulfate were subjected to the distillation procedure with results as shown in Table I. Tests in the presence of other elements are shown in Table 11.
Table I.
Sulfur Recovery from Standard Potassium Sulfate Solution
Sulfur Taken, Mg.
1.00 3.00
6.00 5.00
7.00 7.00
Table 11.
5.04 6.98 6.98
Error,
%
+2.0 0 -0.6 +0.8
-0.3 -0.3
Sulfur Recovery in Presence of Other Elements
Sulfur Present as Known 1.01% Fuel oil 1 Fuel oil 2 3.91% Mixture 1 5 .OO mg. Mixture 2 7 . 0 0 mg. Mixture 3 7 . 0 0 mg. Mixture 4 6.86 mg. Mixture 5 6 . 2 0 mg. Equivalent to sulfur. Stock
Sulfur Found, Mg. 1.02 3.00 4.97
Other Element N,0 . 9 2 % N, 0.64% N, 5 . 0 mg. N. 7 . 0 mg. Se, 7 . 0 mg. Baa Pba
Present Sulfur as Found Organic 0 . 9 7 , 0 . 7 5 % Organic 2 . 1 6 , 3 . 7 7 % KKOs 4.R2 mg. Indeterminate KNOa HzSeO4 7 . 7 6 mg. Bas04 5 . 8 0 rng. PbSOi 6 . 1 7 mg.
V O L U M E 26, NO. 12, D E C E M B E R 1 9 5 4 Table 111. Sample Dibenayl sulfidea Sulfosalicylic acida Additive 1 Additive 2 Additive 3 hlotor oil 1 hlotor oil 2
1985
Comparison of Methods Grarinietric Sulfur,
Volumetric Sulfur,
Difference,
15.04,15.09 12.37,12.33 6.60, 6 . 5 8 4 . 7 8 . 4.85 2 . 5 6 , 2.62 0.59. 0.62 0.54, 0 . 5 7
14.73, 14 81 12.15,12.21 6.44, 6 . 4 4 4.71. 4 . 7 3 2.52, 2.54 0.62. 0.62 0 . 2 2 , 0.55
-2.0 -1.4 -2.3 -2.1 -2.4 i-1.6 13.6
%
70
%
hypophosphorous acid is poisonous and spontaneously combustible. The fraction betyeen 117” and 128” C. is collected as hydriodic acid (SO%), specific gravity 1.55. Crystals of phosphonium iodide may appear in the condenser. Recovery of 90% can be achieved by adding 50 ml. of phosphoric acid per liter of collected distillation bottoms. The stream of carbon dioxide should not he cut off until the residue has cooled considerably. ACKNOW LEDGMEIYT
Eastman white label.
The method has been applied to compounded motor oils and lubricating oil additives containing calcium and phosphorous and to organic compounds as shown in Table 111. The bombgravimetric procedure gives results slightly higher in general than the proposed bomb-volumetric procedure. The primary reason for this is believed to be the contamination of barium sulfate precipitates. A precipitate from an additive was analyzed spectroscopically and showed significant amounts of sodium, magnesium, aluminum, copper, iron, and silicon. RECOVERY OF HYDRIODIC ACID
Hydriodic acid may be recovered if desired by collecting the distillation bottoms and distilling them in an all-glass apparatus blanketed with a rapid stream of carbon dioxide ( 2 ) . The apparatus should be properly shielded and the distillation conducted in a hood since phosphine produced by the decomposition of
Thanks are due to R. E. Ramsay of the California Research Corp. for spectroscopic analyses and to F. H. Dempster and H. E. St. George of the Standard Oil Co. of California for review of the manuscript. LITERATURE CITED
-Am. Soc. Testing Materials, Philadelphia, Pa., “1952 Book of ASTlf Standards,” Part 5, D 129-52, p. 7 7 , 1953. Clark, E. P., “Semimicro Quantitative Organic Analysis,” p. 71, New York, Academic Press, Inc., 1943. Luke, C. L., ISD.ENG.CHEM.,ANAL.ED.,15, 6 0 2 (1943). Ibid., 17, 298 (1945). RIilner, 0. I., A N ~ LCHEM., . 24, 1247 (1952). Rodden, C. J.. “Analytical Chemistry of the Manhattan Project,” p. 307, New York, NcGraw-Hill Book Co., 1950. Roth, H., Mzkrochemie w r . Mikrochim. Acta, 36/37, 379 (1951). St. Lorant, I., and Kopets, L., Biochem. Z . , 238, 67 (1931). Siegfriedt, R. K., Wiberley, J. S.,and Moore, R. W,, -ANAL.
CHEM.,23, 1008 (1961). Wagner, E. C., and Miles, S. H., Ibid., 19, 2 7 4 (1947). RECEIVED for review November 2 , 1953.
.4ccepted August 23, 1954.
X-Ray Diffraction Identification of Alcohols By Their Xanthate Derivatives G. G. WARREN and F. W. MATTHEWS Central Research laboratory, Canadian Industries (1954), ltd., McMasterville, Quebec, Canada
Potassium xanthate derivatives of some of the common alcohols have been prepared. Tables of their x-ray diffraction powder data are given as a means of identification.
so.
CZ C8 c 4
C6
Ca
c7 C8
ClO ClZ C,, CIS ClS
CS CS Ca
C‘
A
LCOHOLS are among the most commonly used organic compounds in the laboratory and in industry. While pure alcohols in their solid form can be identified by their powder diffraction data ( 5 ) , when encountered in solvent mixtures their identification is often difficult and time-consuming. In previous papers from this laboTable I. Index Lines of the Potassium Xanthate Derivatives of .4lcohols ratory, the authors have described the identification of Strongest Lines, A . Innermost Alcohol 1st 2nd 3rd 4th Line, 4. fatty acids hy means of the xEthql alcohol 7 . 5 (1.00) ray diffraction data of various 3.55(0.60) 3.19 (0.30) 3.24 (0.25) 1 8 . 3 (0.02) 1-Propanol 1 0 . 1 (1.00) 2 . 2 1 (0.50) 3 . O O (0.70) 2 . 6 5 (0.45) 16.4 (0.10) derivatives (2, S). This paper 2-Propanol 9 . 6 (1.00) 3 . 0 6 (0.50) 3 . 1 9 (0.30) 7 . 6 (0.25) 9.6(1.00) 1-Butanol 3.32(0.80) 10.0 (1.00) 2 . 2 5 (0.40) 3 . 8 1 (0.40) 1 0 . 0 (1.00) discusses the use of x-ray dif2-Rletliyl-1-propanol 1 1 . 6 (1.00) 3 . 0 6 (0.60) 2 . 7 8 (0.40) 7 . 5 2 (0.30) 1 1 , 6 (1.00) 2-Butanol 1 0 . 9 (1.00) fraction patterns for the identi3.18(0.50) 6 . 2 3 (0.45) 3 . 1 3 (0.45) 1 0 . 9 (1.00) 1-Pentanol 1 2 . 2 (1.00) 4.57(0.40) 4.04(0.40) 3.15 (0.20) 1 2 . 2 (1.00) fications of crystalline deriva3-Methyl-1-butanol 1 2 . 8 (1.00) 4 . 8 6 (0.50) 3 . 2 1 (0.30) 3 . 1 7 (0.30) 1 2 . 8 (1.OO) 2-Methyl-1-butanol 1 2 . 5 (1.00) 3.09 (0.60) 4 . 1 4 (0.40) 3 . 1 9 (0.30) 12.5(1.00) tives of alcohols. In choosing 3-Methyl-2-butanol 11.9 (1.00) 4 . 9 2 (0.25) 3 . 1 8 (0.30) 6.37 (0.20) 11.9 (1.00) 3-Pentanol 12.1 3.17 (0.40) a derivative for identification 4.62 0 30) 4 . 0 7 (0.30) 1 2 . 1 (1.00) 1-Hexanol 14.0 4 . 0 7 [0:15) 4.59 (0.20) 3 . 1 8 (0.10) 1 8 . 0 (0.05) by means of x-ray diffraction 1-Heptanol 15.6 (1.00) 4 . 6 2 (0.50) 4 . 0 6 (0.40) 3.14(0.30) 1 5 . 6 (1.00) 1-Octanol 4.27 1 6 . 8 (0.90) 6 . 5 (0.60) 3.38(0.50) 1 6 , s (0.90) powder patterns, the emphasis 1-Decanol 4.29 7 . 3 (0.50) 3 . 6 7 (0.40) 5 . 1 4 (0.30) 14.6 (0.20) 1-Dodecanol 4.32 (1.00) may he on ease of preparation, 3.68(0.40) 3.82 (0.70) 1 6 . 5 (0.30) 16.5(0.30) 1-Tetradecanol 4 . 3 3 (1.00) 3 . 8 1 (0.80) 18.2 (0.60) 3 . 6 8 (0.50) 18.2 (0.60) as the ease of purification and 1-Hexadecanol 4 . 3 5 (1.00) 3.70(0.70) 3 . 8 3 (0.50) 2 0 . 5 (0.40) 2 0 . 5 (0.40) I-Octadecanol2 2 . 1 (1.00) 4.35(0.90) 1 4 . 7 (0.80) 3 . 8 1 (0.70) 2 2 . 1 (1.00) sharpness and dispersion of 2-Propen-1-01 3 . 0 1 (0.80) 9 . 6 (1.00) 2.27(0.40) 4 . 0 1 (0.30) 9.6(1.00) C yclohexanol melting points are no longer of 3 . 0 5 (0.15) 4 . 9 0 (0.10) 1 2 . 8 (1.00) 3.16(0.10) 1 2 . 8 (1.00) 2-hfethoxyethanol 3 . 0 4 (0.80) 9 . 4 (1.00) 4 . 3 2 (0.40) 2 . 8 8 (0.35) 9 . 4 (1.00) importance. 2-Ethoxyethanol l o . , (1.00) 3.12 (0.60) 3 . 6 6 (0.30) 3.28(0.25) 1 0 . 7 (1.00)
1:. :E{
1E3
2-Methoxymethoxyethanol
11.4(1.00)
3.16(0.50)
4.44(0.40)
3.26(0.35)
11.4(1.00)
The potassium xanthate derivatives of alcohols are easily
