Determination of Sulfur in Oil Tetrahydroxyquinone As an Indicator in Direct Titration ROBERT T. SHEEN
AND
H. LEWIS KAHLER, W. H. & L. D. Betz, Philadelphia, Pa.
S
MATERIALS AND REAGEKTS.Standard barium chloride solution, I ml. = 0.0004 gram of sulfur, standardized gravimetrically by precipitation as barium sulfate Potassium hydroxide 0.02 iV (approximately) Hydrochloric acid 0.02 N (approximately) Phenolphthalein indicator, 1 per cent solution Tetrahydroxyquinone indicator Ethyl alcohol, or ethyl denatured by formula 30 or 3-A, or isopropyl alcohol Measuring dipper, capacity 0.15 gram of indicator PROCEDURE. Take a sample of oil weighing from 0.6 to 0.8 gram, record the w-eight, and burn in an oxygen bomb. Treat the sample thus obtained with bromine water in the conventional manner ( 2 ) . Evaporate sufficient,water t o bring the total volume of the sample below 100 ml., cool, and make up in a volumetric flask to 100 ml. Transfer 25 ml. of sample by pipet t o a 125ml. Erlenmeyer flask, add a few drops of phenolphthalein indicator, and neutralize just t o the alkaline side of the phenolphthalein end point with approximately 0.02 N potassium hydroxide. Discharge the red coloration with approximately 0.02 N hydrochloric acid. Add 25 ml. of alcohol, and 1 dipper of indicator (0.15 gram). Titrate the sample with standard barium chloride solution until the solution changes sharply from yellow to red that is permanent with strong shaking. Shake the flask throughout the titration to establish equilibrium conditions.
ULFUR in oil is usually determined by the barium sul-
fate precipitation method as prescribed by the American Society for Testing Materials (2). Analytical chemists have long sought a substitute to allow savings in time, and the investigators feel that the method presented here fulfills this requirement. Previous publications ( 5 , 6 , 7 )specified a dispersion of tetrahydroxyquinone in potassium chloride. Further research on the method of preparation of the indicator indicates that with certain other dispersing agents the end point of the titration was materially improved, the end-point range was sharpened, and the color change was intensified. The use of tetrahydroxyquinone dispersed in an organic medium (THQ) has been found to overcome the difficulties mentioned by Ampt ( I ) , Manov (4, and Gibson (3). The determination of sulfur in oil is important in the examination of petroleum and there is a wide field of application for a rapid and accurate method. In the method proposed the oxidation of sulfur in a bomb according to standard methods is followed by complete oxidation by bromine (2), concentration of sample to a definite volume, and direct titration of an aliquot with standard barium chloride solution, using tetrahydroxyquinone as a n internal indicator. The color change is sharp from yellow to red. The method requires only about 0.75 hour as compared with 3 or 4 hours for a gravimetric analysis, and gives results obtainable within the limits as specified by the A. S. T. M. (2) and by most laboratories. The indicator used throughout this study is a dispersion of the disodium salt of tetrahydroxyquinone in a solid organic medium, and is manufactured in the Beta laboratories with the modifications mentioned. This product is anhydrous and stability tests for sensitivity and color reaction have indicated no changes in its properties in 8 months.
CALCULATION OF RESULTS. From the total volume of the barium chloride required, 0.1 ml. should be subtracted for a blank. The amount of sulfur present in the original sample may then be calculated from the following formula: MI. of BaClz x strength of BaClz (in grams of sulfur per ml.) X weight of oil sample in prams 100 4 = p e r cent of sulfur in oil
X
I n the examination of this method, duplicate samples were burned in a bomb, and the sulfur content of the oil was determined gravimetrically on one set in accordance with the usual A. S. T. M. procedure, while the other set was analyzed for sulfur by the method presented here. Results obtained are presented in Table I. Samples 9 to 15, inclusive, were evaporated to below 200ml. volume and made u p to 200 ml.. and 25 ml. were taken for titration. I n this case, a factor of 8 was required. While results obtained with the use of a 200-ml. volume are acceptable, the increased time required for evaporation to the 100nil. volume is justified by finer results. The variance in practically each case with the 100-m1. sample mas less than half the limits as set by A. 8.T. &I. for different operators and in all cases less than the variance allowed for the same operator, and a t the same time well within limits allowed by the oil companies. After evaporation and adjustment to the proper volume, the time required for a determination is less than 5 minutes. On the basis of these data, this method can be used by oil laboratories for the routine control of sulfur in oil, expecting checks a t all times within acceptahle limits. While the data presented cover only petroleum oils, the method should be applicable to marine and vegetable oils and possibly to certain other organics.
TABLEI. COMPARISON OF METHODS --Sulfur-.
Sample
Gravimetric analysis
THQ
%
%
1
0.67
2
1.09
0.68
3
1.08 0.55
4
0.18
5
0.23
6
0.31
7
1.97 0.17
8
Average difference
%
100-ml. Sample 0.67 0.68 0.00 1.08 1.08 0.01 0.32 0.51 0.03 0.20 0.20 0 02 0.24 0.23 0.01 0.29 0.28 0.02 1.90 1.9,o 0 07
0.1,
0.16 0.15
0.01
Difference Allowed, A . 8 . T. M. Same Different operator operator
70
%
0.05
0.07
0.06
0.11
0.04
0.06
0.03
0.04
0.03
0.04
0.03
0.04
0.10
0.18
0.02
0,08
200-ml. Sample 9
0.71
10
0.15
11
1.94
12
1.47
13
0.43
14
0.28
15
1.97
0.67 0.71 0.1; 0.17 1.86 1.80 1.40 1.37 0.39
0.02
0.05
0.08
0 02
0.03
0.03
0 11
0.10
0.17
Summary
0.08
0.08
0.13
0.43
0.02
0.04
0.05
0.25 0.28 1 89 1.89
0.01
0.03
0.04
0.08
0.10
0.18
Sulfur in oil can be determined following the usual oxidation of a n oil sample in a bomb, by direct titration using tetrahydroxyquinone as an internal indicator. Results obtained are well within the limits as prescribed by the Ameri206
IK.4LTTIC.IIL EDIT101
APRIL 15, 1938
can Society for Testing Materials anti maintained by most oil companies; and the method is suggested for routine determination of sulfur in oil t,o effect, a saving in time without. sacrifice of accuracy.
hclinowledgiiieiit The authors gratefully acknoi1-1edge the generous aid of W.H. R L. D. Beta anti their permission to publish this study. The collaboration of George -4.Shaner and his assistance in preparing the oil samples is sincerely appreciated.
307
Literature Cited (1) A m p t , G . A , , duatralian Chem. Inst. J . 6: Proc., 2, 10 (1935). ( 2 ) A m . SOC. Testing hlaterials, S t a n d a r d s , Part 11, Kon-metaiiic Materials, D 129-34, p. 974, 1A3ii. (3) Gibson, D. T., and Caulfieid, T. H., A n a Z y s t , 60, 522 (1935). ( 3 ) hlanol-, G. G., a n d K i r k , P. L . , ISD. ESG. CHmf.. Anal. Ed., 9, 10s (1937). (5) Pchroeder. TT-. C . , Ihid.. 5, 303-G (19 (6) Sheen, R . T., a n d Kahler, H. I,., I h l d , , 8, 127 [ lOSCj. ( 7 ) Sheen, R . T., Kahler, H. L . . and Cline. D. C., 15id., 9, 69 (1937). RECEIVED Sol-eniber 13, 1937
Determination of Inorganic Salts in Crude Oils CHliRLES .\I. B L k I R . JR., Tretolite Company. St. Louis, 310.
S U N B E R of different methods of extracting the inorganic salts from crude oil for their subsequent analysis are in use. all of which seem to be either long and tedious, unreliable, or both. The most widely used procedure for extracting the salt from crude oil is the so-called C.0. P. method (3). I n this method, the salt is removed by agitating the oil n-ith benzene, water, and acetone, the acetone presumably being used to cause coalescence of the emulsified particles of brine in the oil and to prevent emulsification of the extraction water added. This method is capable of giving sufficiently accurate results for most practical purposes if two or three extractions of the oil sample are made. K i t h some crudes, one extraction may be sufficient, but the time required for complete separation of the oil and water phases and the necessity for drawing off and analyzing all the aqueous phase are objectionable features. An aliquot portion of the separated aqueous phase cannot immediately be taken for analysis, since the total volume of the aqueous phase is unknown until it has been completely separated and measured, which usually takes some time. The acetone added is distributed between the oil and water and the distribution ratio varies with the specific kind of oil under examination. Also, some of the acetone is added after agitation of the mixture and before drawing off the aqueous phase, and may or may not become distributed between the oil and n-ater in equilibrium amounts. I n another frequently used method, the oil is shaken with benzene and water for several minutes and the mixture is then centrifuged to separate the aqueous layer, which is draivn off and analyzed. Since a definite amount of water may be added, a measured portion of the separated aqueous extract may be analyzed and the total salt content calculated. HOKever, i t has been found by repeated tests in this laboratory that this method is completely unreliable. The salt content determined by analysis of this extract is almost invariably low, with one crude giving as little as 18 per cent of the actual salt content. T o remove the salt completely from most oils, agitation alone with water is not sufficient. The presence of salts in crude oil almost invariably means t h a t the oil contains emulsified brine. The 1 per cent or less of emulsified brine contained in refinery stocks generally consists of extremely fine droplets (often less than lo-' cm. in diameter) which are highly stabilized by a n adsorbed film of emulsifying agent normally occurring in the oil. These droplets do not coalesce readily with one another or with added water unless they are destabilized in some manner. A method of extraction has been developed in this laboratory which is fairly rapid and gives nearly quantitative removal of the salt in one extraction. With this method, de-
stabilization of the brine emulsion and prevention of emulsification of the extraction water are brought about by the use of a small aniount of a destabilizing chemical compound, From tests n-ith a large number of different destabilizing chemicals and many different oils, it has been found that the most generally useful compound is a mixture of the ammonium salts of isomeiic sulfonic acids of high mcilecular weight, the exact structures of which are unknown. These sulfonic acids are characterized by the fact that their calcium and magnesium salts have appreciable water solubility. The mixture of ammonium salts of these acids is available under the trade name of Destabilizer -4.1
Procedure Into a 750- or 1000-ml. separatory funnel put 100 ml. of the crude oil, 100 ml. of xylene, and 4 ml. of a 5 per cent xylene solution (or the equivalent if other than a 5 per cent solution is used) of Destabilizer A. Shake for 30 seconds and add 100 ml. of boilmg, chloride-free, distilled TT ater. Stopper the funnel and shake, releasing the pressure occasionally at first, for a total time of 5 minutes. Then allow to stand. Break up any loose emulsion nhich may collect at the oil-sater interface by gentle agitation mith a long stirring rod. Draw off as much of thf, aqueous layer as is required for analqsis, filter t o remove any oil film, and analyze measured portions of the extract b) conventional methods (1). When the salt content of an oil is Ion, it is adliiable to extract larger samples of oil, using proportionately larger amounts of xylene, ater, and destabilizer. Since the distilled nater is added a t a temperature near 100" C. and since the tempeiature of the separated aqueous extract nil1 have fallen nearly to room temperature by the time the portions are taken for analysis, the volume of the water added will have decreased by about 4 per cent by this time. Therefore, the total volume o f the aqueous layer a t the time of measurement of the portions taken for analysis will be 96 ml. plus the small yolunie of brine originally dispersed in the oil. Account of this fact should be taken in calculating the total amount of any constituent in the sample based on the analysis of a measured portion of the aqueous extract.
Discussion of Procedure Use of the large separatory funnel is recommended in order that a large free space may be present to permit violent agitation of the liquids during shaking. The amount of the destabilizer used is very important. T h e amount called for in the procedure has been found suffi1 Analysts ma> obtain reasonable amounts of this material and of Destabilizer B gratis from t h e Tretolite Company
