224
ANALYTICAL CHEMISTRY
1.0 molal in hydrogen ion, 0.1 molal in hydrocyanic acid, that the iodine monocyanide formed is 0.01 molal, and that the iodine a t the end point is 10-0 molal; the iodine-iodine monocyanide potential in such a solution would be -0.74 volt. Considering only equilibrium conditions, this potential value indicates that the oxidation could be effected by electrolytically generated bromine, chlorine, or tetrapositive cerium; in addition, under similar conditions, quantitative oxidation of tripositive arsenic and antimony should be obtained. Qualitative experiments have indicated that these predictions ran be realized and quantitative studies are in progress. LITERATURE CITED
(1) Davies, .\I.. and Gwynne, E., J . Am. Chem. SOC.74, 2748
(1952). (2) Gaugin, K., BuZl. soc. chini. P’rance 1948, 1052.
(3) Hildebrand, J. H., J . A m . Chem. SOC.35, 847 (1913). (4) Kolthoff, I. l f .and , Laitinen, H. -1., “pH and Electro Titi-+ tions,” p. 90, Wiley, Sew York. 1944. (5) Kovach, L., 2. p h y s i k . Chern. 80, 107 (1912). (6) Latimer, W. AI., ”Oxidation Potentials,” p. 63, Kew T o r k , Prentice-Hall, 1952. (7) Lewis, G. X., and Keyes, D . B., J . A m . Chem. SOC. 40, 472 (1918). (8) Lorrh, A . E., ISD. Esc. CHEW.,ASAL. ED. 6, 164 (1934). (9) Noyes, .i..I.,and Garner, C. S., J . Am. Chem. SOC.58, 1266 (1936). (10) Oesper, R. E., and Bottger, W., ”Sewer Methods in Volumetric Analysis,” Tan Nostrand, Sew York, 1938. (11) Robinson, R. A . . and Stokes, li. H., Trans. Faraday SOC.45, 619 (1949). (12) Swift, E. H., J . Ani. C h e m . SOC.52, 897 (1930). (13) Yost, D. XI., and Stone. W . E., Ibid., 5 5 , 1889 (1933). RECEIVED for review August 8, 1955. Accepted November 18, 1955. Contribution S o . 2025 from the Gates and Crellin Laboratories of Chemistry, California Institute of Technology.
Determination of Sulfuric and Sulfonic Acids in Sour Oil L. 1. CALI and 1. WEST LOVELAND Sun
Oil Co., Marcus Hook, Pa.
In the sulfonation of lubricating oils a sour oil lajer is obtained which contains sulfonic acids and a small amount of sulfuric acid. Methods of analysis were needed for both acids in order to follow the processing of the sour oil to a finished sulfonate. The aniline precipitation method, used b> others on acid sludges where ~ proied to sulfuric acid contents w e r e 20 to 9 0 7 ~has work satisfactorilj on sour oils where the concentration is 0.01 to 0.25qc. This method has been extended so that sulfonic acids can be determined on the same sample. The presence of sulfur dioxide in the sour oil does not appear to interfere in either analjsis. A t least 10 moles of water for everj mole of sulfuric acid plus sulfonic acid should be present to obtain quantitatiie results. For sour oils the repeatabilitj standard deFiation for and for sulfuric acid is 0.007% in the range 0.01 to 0 , 2 5 7 ~ sulfonic acid it is 0.0977~in the range of 3 to 8 7 ~ .
T
HE sulfonation of lubricating oils produces commercially valuable oil-soluble sulfonates, usually called mahogany sulfonates. The sour oil layer contains not only the mahogany sulfonic acids but also small amounts of sulfuric acid and sulfur dioxide which are salt formers. Methods were needed t o folloiv the removal of the salt. formers, to predict yields of the finished product, and to determine losses of sulfonic acid during processing. Alethods have been published for the determination of sulfuric acid in acid sludges or spent acids ( 2 , 6, 10); however, the sulfuric acid concentrations were very high, usually 20 to 90%. The sour oils the authors are concerned Tvith contain 0.01 to 0,3070 of sulfuric acid. Bacon ( 8 ) investigated a number of methods for determining sulfuric acid and acid sludges. One of these methods used aniline in chloroform to precipitate the sulfuric acid. The aniline sulfate was dissolved and titrated with potassium bromate. Parke and Davis (8) studied this same method on sulfuric acid in the presence of organic acids and mineral acids. Quantities as small as 1 mg. of sulfuric acid were analyzed with an accuracy of 0.2 mg. These workers improved the method of Bacon ( 2 )by dissolving the precipitate in hot water and titrating the sulfuric acid released with base to a phenolphthalein end point.
More recently, Keiss and others (10) used this technique to det,ermine sulfuric acid in spent acids and acid sludges. Holzman and Suknarowski (6) have determined sulfuric acid in acid sludges by making use of the partition of sulfuric acid and sulfonic acid between water and amyl alcohol. The sulfuric acid in the water layer is precipitated as barium sulfate and weighed. There is little or no information in the literature on the direct determination of sulfonic acids in sour oils. However, methods are available for the indirect determination of sulfonic acids as the neutralized product. Sodium sulfonates have been analyzed by Marron and Schifferli ( 7 ) using the p-toluidine hydrochloride method. Epton ( 5 ) and Barr, Oliver, and Stubbings ( 3 ) have titrated t’he sodium sulfonates with cetyl pyridinium bromide. Brooks, Peters, and Lykken (4)have proposed a scheme for analyzing petroleum sulfonates, but t’his is a rather lengthy method. The ASTM procedure (1) can also be used on oilsoluble sodium sulfonates. Weiss and others (11)have suggested an improved ‘4STll method, but both of these methods are very time-consuming. Sulfonic acids have been determined in spent acids and acid sludges where concentrations of from a few per cent to more t,han 50% are involved. Holzman and Suknarowski (6) have determined the sulfonic acids in the amyl alcohol extract h>removing the alcohol under reduced pressure and weighing the dried acids. This method has the disadvantage of being t,imeronsuming. Von Pilat and Starkel (9) determined total acidity and corrected for the sulfuric acid present to give a measure of the sulfonic acids plus other acidic materials. Any sulfur dioxide present would cause an appreciable error in the results. JTeiss and others (10) determined sulfonic acids in acid sludges by correcting total acidity for sulfuric acid (determined by the aniline precipitation method) and sulfur dioxide (determined by iodine-thiosulfate titration). Their results, however, were not too satisfactory because of uncertainty in equivalent weights. They recommend the use of the ASTM analysis for determination of the sulfonic acids. This work extends the aniline precipitation procedure to t,he analysis of sour oils for sulfuric acid concentrations of 0.01 to 1.0%. I n addition, the same sample is used to determine sulfonic acids in the range of 3 to 8%. The method has the advantage of simplicity and it requires no special equipment. Sulfur dioxide in acid sludges and spent acids has been de-
V O L U M E 2 8 , N O . 2, F E B R U A R Y 1 9 5 6
225
termined by the iodine-thiosulfate method ( I O ) . The authors have found no trouble in adapting this titration to the determination of sulfur dioxide in sour oils.
increment of titrant. The normality (S,) and the milliliters required ( B ) for the sample are recorded. CALCULATIONS
APPARATUS 4ND REAGENTS
Erlenmeyer flask, 125-ml. Suction flask, 250-ml. Graduated cylinder, 50-ml. Beaker, 250-ml. Pipet, 1-ml., graduated to 0.1 ml. Buret, 25-ml., graduated to 0.05 ml. Buchner funnel with fritted-disk filter, medium porosity. pH Meter. Chloroform. Aniline in chloroform, 10% by volume. Distilled water. Isopropyl alcohol. Phenolphthalein indicator. Potassium hydroxide, 0.2N in isopropyl alcohol. Sodium hydroxide, 0.05.V in water. PROCEDURE
Weigh accurately about 10 g r a m of sour oil sample (20 grams if sulfuric acid content is less than O.lyo)into a 250-ml. beaker. Add 15 ml. of chloroform from a graduated cylinder and 0.4 ml. of distilled water from a 1-ml. pipet. Stir until homogeneous. With constant stirring add from a graduated cylinder 50 ml. of 10yoaniline in chloroform solution that has been heated to boiling on a steam bath. Break up any large lumps of aniline sulfate with the flattened end of a stirring rod. After allowing the mixture to cool to room temperature, filter the mixture through a Buchner funnel fitted with a medium porosity fritted-glass disk. Apply vacuum to the suction flask and filter off the liquid. Wash the reaction beaker with three 10- to 15-ml. portions of chloroform, adding each washing to the funnel. Continue washing the precipitate while breaking up the precipitate into fine particles until a t least 100 ml. of chloroform have been used. Attach the funnel to a clean 250-ml. suction flask. Save the filtrate for the determination of sulfonic acid. Wash the precipitate with 2 to 3 nil. of acetone and then appl). suction until the precipitate is dry. Add 10 to 15 ml. of hot natei to the reaction beaker t o dissolve any precipitate n-hich \\as not previously washed out, and pour into the funnel. Wash a second time if necessary. Dissolve the remaining precipitate in the funnel by adding four 25-ml. portions of hot distilled water, sucking each portion into the flask. If lumps of the precipitate are still present, wash with a little acetone to free the oil, and continue washing with hot water. Titrate the contents of the flask containing the dissolved precipitate with 0.05N sodium hydroxide to the phenolphthalein end point, recording the volume ( A ) and normality (1V) of the base.
Table I.
Analysis of Known Blends of Sulfuric and Toluenesulfonic Acids in Oil
W t ', '5 Sulfuric Acid .kdded Found Dern. 0.063 0.062 0.212 0.225 0,022 0.020 0.097 0.096
0.064 0.072 0.205 0.219 0.025 0.024 0.107 0.106
Standard deviation 95c/, confidence limits of duplicates
+0.001 +0.010 -0.007
-o.ooc,
-0.003 f0.004 f0.010 tO.O1O
IVt. "c Toluenesulfonic .kcid .4dded Found Devn. 1.92 1.94 +0.02 1.94 1.98 +0.04 1.93 1.92 -0.01 1.95 1 96 tO.01 2:04 2.10 2.09
2103 2.06 1 98
...
-0.01 -0.04 - 0 11
0.007
0,048
0 023
0.10
Place the filtrate containing the sulfonic acids on a steam bath and evaporate to approximately 20 ml. or until all of the chloroform has been evolved. Transfer the residue quantitatively to a 250-ml. beaker, washing the flask alternately with approximately equal increments of distilled water and isopropyl alcohol. The total volume of washings plus sample should be about 150 ml. Titrate the contents of the beaker potentiometrically &h 0.2N alcoholic potassium hydroxide using glass-calomel electrodes. When approaching the end point the increments of titrant should be 0.10 ml. Determine the end point a t the greatest e.m.f. change for a 0.10-ml.
Weight yo sulfuric acid =
.-I
xsx
49
n hei c 49 is t h c sample w i g h t X 10 eouivalent weight of sulfuric acid. B X 'VL X equivalent n-eight Weight % sulfonic acid = sample weight X 10 Y
where equivalent weight is determined on the sodium niahogani sulfonate by ,\ST11D 855-52T (1) and corrected for the sodium. If good accuracy is not needed, a fair approximation of equivalent weight can be made bj- adding 80 (for the SO, group) to the average molecular weight of the aromatics of the charge to the sulfonation. R E SU LT S
Accuracy on Blends of Sulfuric and Toluenesulfonic Acids. JTeiss and others (10) report that the sulfonic acids of lower niolecaular weight cause the most trouble in their sulfuric acid determinations. Therefore, it was felt that if the proposed method \yere applicable for determination of sulfonic acid of low molecular i\-eight-i.e., toluenesulfonic nc.id-lrw interference would be cbncountered from the mahogsny sulfonic*acids of higher molerular n-eight. Known hlends of sulfuric wid m d toluei?i,slili'onicarid (TS.I) u w e made in a typical sulfonation ch:irgt~oil :is follom: Weighed cjnantities of 60Oj, siilfuric. acid wei'(x added to ii 150-ml. beaker. .l weighed amount of about 20Yo toluciieeuiionic~acid in isopropyl :tlttohol was lare red i n the s:inic 1)rako. It uas necessary to tlissolve t,he tohienesulf'onir acid i n isopropyl alvohol because of the low solubility of the acid i n the charge oil. To this was atlded known :mounts of sulf'on:iti& t~hargestork oil and the 1,lend vas thoi,oiighly mixed.
Tahle 11. Addition o f Known Quantities of Sulfuric Acid to Sour Oils 7; Sulfuric Acid _ _ _ _ _ ~ ~ IVt. ~ _ _ ~ _ _ _ ~ Sour Oil 0.02 0.02 0.13 0.02 0.13 0.13 0.13
ldded
Expected
Found
0 17 0 34 0.28 0.51 0.40 0.76 1.11
0 19 0 36 0 41 0.53 0 53 0 89 1 24
0.18 0 34 0.42 0.52 0.53 0.90 1. "7
Standard deviation
Devn. -0
01 -0.02 01 - 0 01 0.00 +Q 01 +o 03
to
0 0lii
The blended samples contained 2% of sulfonic and 0.02 to 0.2% of sulfuric acid. The data obtained on these synthetic blends are given in Table I. For sulfuric acid the standard deviation is 0.007% over the range of 0.02 to 0.22%. For toluenesulfonic acid it is 0 . 0 4 8 ~ oa t the 2% concentration level. These data indicate that the aniline precipitation method Jvorks xell on mixtures of sulfuric and toluenesulfonic acids and that there should be little difficulty in applying the method to sour oils. Accuracy of Sulfuric and Sulfonic Acid Values in Sour Oils. The accuracy of sulfuric acid vzlues in sour oils was determined by adding known quantities of this acid to previoualy anall-zed sour oils. The data obtained are given in Table 11. The amounts of sulfuric acid added cover the range of 0.17 to 1.1 weight %. The standard deviation from known values is 0.016%. I t is possible to predict the salt value due to sulfuric acid in the final product to about Z I = O . ~ ~ assuming ~, that no desalting step is performed.
ANALYTICAL CHEMISTRY
226 Mahogany sulfonate acids in sour oil are reasonably stable, but in pure form they become somewhat unstable. Therefore, they cannot be used for determining the accuracy of the method. However, based on the authors' analyses of toluenesulfonic acid in sulfuric acid-toluenesulfonic acid mixtures, the accuracy for the mahogany sulfonic acid should be within *3% relative. It has been possible to predict actual plant yields to within 2% on 60% sodium mahogany sulfonates from data obtained by this procedure.
Table 111. Repeatability of Sulfuric and Sulfonic Acid Determinations on Plant Sour Oils Wt. 7% Sulfuric Acid R t "r Sulfonic Acid sample 2
1
NO.
5 6 7 8
0.18 0.22
9 10
Diff. 0.00 0.01 0.02 0.00 0.01 0.00 0.00 0.01 0.01 0.00
0.01 0.04 0.11 0.17 0.19 0.18 0.05 0.14
0.01 0.05 0.09 0.17 0.20 0.18 0.05 0.13
1 2 3 4
0.19
0.22
2
1
Diff.
5.15 5.08 7.71 6.82 8.20
5.11 4.90 7.5.5 6.70 8.40
0.04 0.18 0.16 0.06 0.20
3100
3 : io
0 10
..
..
..
. .
...
Standard deviation
0.007
0. 0 9 i
95% confidence limits
0.02
0.34
of duplicates
Repeatability Data on Sour Oils. Table I11 shows duplicate results obtained on actual plant samples, taken a t various stages of the processes and on different days. The charge oil is the same in all cases.
6
Table IV.
Sulfur Dioxide Interference in Sulfuric and Sulfonic Acid Determinations Sample before Purging
with Nitrogen _______Sola, wt.
7LW
H ~ S O Iwt. . /c Sulfonic acid, n t . '3 a
A
B
0.45 0.20 7.17
0.40 0.23 6.94
Sample after P u r g i n g w i t h Kitroycn A B 0.001
0.19
7.07
0.033 0.20 6.97
By iodine-thiosulfate titration
The repeatability standard deviation for sulfuric acid is 0.007% in the range 0.01 to 0.25%. For mahogany sulfonic acid it is 0.097% in the range 3 to 8%. The good repeatability f'ol both determinations indicates that other acidic materials, sucli as sulfur dioxide, do not interfere. Sulfuric acid ester content is probably negligible in the sour oils. In many instanceb sulfur dioxide was not determined, but from previous experience it is hnom-n that some samples contain as much as 0.5y0 of sulfur dioxide.
Table V.
Interference Studies. Weiss and others (IO) state that sulfur dioxide does not interfere in the aniline precipitation method for sulfuric acid, but give no supporting data. Parke and Davis (8) indicate that 0.4 ml. of saturated sulfurous acid gives a precipitate with aniline. -4study was made to determine whether or not sulfur dioxide would interfere in either the sulfuric or the sulfonic acid determinations. Sour oil samples from plant production were analyzed for sulfur dioxide and sulfuric and sulfonic acids before and after purging r i t h dry nitrogen for approximately 2 hours. The data obtained are given in Table IV. The sulfur dioxide content decreases in one case more than one hundredfold, yet the sulfuric and sulfonic acid values are within the established repeatability limits a t the 95% confidence level. In the second case the sulfur dioxide content decreases about tenfold; however, here again the sulfuric and sulfonic acid determinations agree rather well. In order to firm the authors' conclusion as to the extent of interference by sulfur dioxide, 50 ml. of the aniline-chloroform precipitating solution were bubbled with sulfur dioxide and diluted to 100 ml. A 25-m1. aliquot was acidified with hydrochloric acid and titrated by the iodine-thiosulfate method. This aliquot contained 0.18 meq. of sulfur dioxide. For a 10-gram sample of sour oil this would be equivalent to 0.23% of sulfur dioxide. Another 25 ml. aliquot showed 0.19% of sulfur dioxide by acid-base titration. Two other aliquots were evaporated on the steam bath to a loa. volume. The sulfur dioxide content mas less than 0.01% on both of these samples as determined by iodine-thiosulfate on one aliquot and acid-base titration on the other. Thus, evaporating the aniline-chloroform sample to a low volume drives off any sulfur dioxide which might otherwise result in high sulfonic acid values. Minimum Water Required for Quantitative Results. Weiss and others (IO)report that if less than 1 mole of water is present for every mole of sulfuric acid, poor results are obtained. Parke and Davis (8) show data that indicate that a much larger ratio of water to sulfuric acid should be used. The maximum recovery for a 0,004-gram sample of sulfuric acid was obtained a t a mole ratio of about 350% of water to 1 of sulfuric acid. I n the present work, water requirement was studied on mixtures containing xylenesulfonic and sulfuric acids. These mixtures were analyzed by the proposed procedure, except that the amount of water added was varied. The data of Table V show that, contrary to expectation, poor iesults are obtained even when the ratio of water to sulfuric acid is much greater than one. In fact, in some cases, results become worse as this ratio increases. The data indicate that sulfonic acid plays a predominant role in water requirement. Probably the most important factor to be considered is the mole ratio of mater to sulfonic acid plus sulfuric acid. This ratio should be a t least 10 to 1 in order to obtain good results. The exart reasons for the need of water is not clear. One wason ma\ be that a partially soluble aniline-sulfonic acid complex is formed which is broken up only by the presence of a
Minimum Water Requirements Xiole Ratio
HnOa 0.0104 0,0055 0.0037 0,0206 0.0193 0 0181 0.0326 0.0301 0.0287
Mole Present HnSO4 0.0028 0.0012 0.0006 0.0025
0.0019
0.0015 0.0027 0.0018 0.0014
XSA 0.0006 0.0011 0 0015 0 0005 0.0013 0.0013 0.0005 0.0010 0.0015
-_ F1IlO i r_ - -
H~SOI L S O a 3 7 4 6
6.2
8.2 10.2 12.1 12.1 16 7 20.5
+ XSL
3.1 2.4 1.8
6.9 6.0
6.0 10.2 10 7
9 9
H~POI5 Calcd. Found 47.0 28.3 14.4 48.0 31.7 27.0 48 9 35.1 25.1
47.5 31.6 25.4 48.6 32.9 28.7 49.1 35 2
26.0
XSi SC Calcd.
Found
19.6 48.0
17.9 35.7 27 1 16.0 37.6 43.1 17 7 38 6 53.6
69.2 18.2
42.9
49.9 16.8 37.7 52.9
Includes water present in sulfuric and x5-lenesulfonic arids used in makins blends plus water added. _..__
V O L U M E 28, NO. 2, F E B R U A R Y 1956 large excess of water. Another reason may be that the anilinesulfonic acid complex is stable but it is made more soluble in the aniline-chloroform medium with increased amounts of water. When analyzing plant sow oil samples, the amounts of sulfuric and sulfonic acid present in a sample are much less than those used in these experiments. For plant samples, the 0.4 ml. of water recommended in the procedure gives a mole ratio of water to total acids of about 20 to 1.
227
About eight samples can be analyzed in 1man-day; the easeand rapidity of determination make this method a desirable one for plant control. The estimation of plant yields of finished product based on sulfonic acid values agrees well with yields actually obtained. The determination of the small amounts of sulfuric acid in the sour oil layer has made it possible to follow desalting operations. QCKNOWLEDGMENT
con-cLusIo>s
The data obtained have shown that the determination of sulfuric and sulfonic acids in sour oils is possible. Sulfur dioxide does not interfere in the determinations. RIinimum water requirement studies have shown that controlling the mole ratio of water to sulfuric acid, as previously reported ( f O ) , is not the determining factor in obtaining good results. The water requirements are higher, mainly because of the presence of sulfonic acids. More work is needed t o determine the elact rolc the amount of water plays in this determination. It is believed that the aniline precipitation procedure described here can be used t o determine not onlv sulfuric acid in acid sludges, as suggested bj- Weiss and others (fa),but for sulfonic acids as well. If the equivalent w i g h t of the sulfonic acid is k n o w and there is negligible sulfuric acid ester present, this method should be applicable t o both acid sludgep and spent acids. I t should be pal ticularly useful on alkylarenesulfonic acids. Thc authors have successfully analyzed a large number of “green acids”-Le., the bottom layer produced during the sulfonation of lubricating oils-for both of these constituents. For this type sample about 1 gram is taken. Typical analyses would be 15% sulfuric and 609; siilfonir acids.
The authors wish to express their thanks to the Sun Oil Co. for the privilege of publishing this paper and to acknowledge the help of Paul Congdon. LITERATURE CITED
(1) Am. SOC.Testing Materials, D 855-52T, ‘Standards on Petroleum Products and Lubricants,” (D-2), p. 335, 1954. ( 2 ) Bacon, F. S., IND.Ero. CHEM.,AXAL.ED. 1, 89 (1929). (3) Barr, T., Oliver, J., and Stubhings, W. V., .J. SOC.Chem. Ind. 67, 45 (1938). (4)Brooks, F., Peters. E. D., and Lykken, L.. ISD. ENG.CHEM., A N A L . ED. 18, 544 (1946). ( 5 ) Epton, S.K., Trans. Faraday soc. 44, 226 (1948). ( 6 ) Holzrnan, E., and Suknarowski, S., IHD.ENG. CHEM.,A s . 4 ~ . ED. 7, 378 (1935). ( 7 ) Xlarron, T. E.. and Schifferli,
