Determination of Inorganic Salts in Crude Oils E. P. RITTERSHAUSEN AND R. J. DEGRAY, Socony-Vacuum Oil Co., Brooklyn,
VU.
N. Y.
of 3 per cent hydrogen peroxide should be added, .the solution boiled for 5 minutes and cooled, prior to neutralization.
ARIOUS methods have been advocated for determining the salt contents of crude oils such as those described by S. Bureau of Mines (S),Universal Oil Products Comthe pany ( 5 ) ,and Blair (8). Recently a cooperative program was initiated among the laboratories of this company to determine the most accurate and reproducible method concomitant with reasonable speed and ease of manipulation. This led to the development of a new method rather than to a recommendation of any of those previously used. This method has been in use in routine work, for over a year, with satisfactory results. Practically all previous methods agree on one step a t least, wherein the sample, diluted with a hydrocarbon solvent, is shaken by hand with boiling distilled water. This involves the obvious difficulties of handling hot glass apparatus, and development of high vapor pressures in a closed container. A second step common to all methods is the separation of the aqueous and hydrocarbon phases after extraction, though the means by which this is accomplished vary. The tetraethyllead extraction apparatus (1) consists of a separatory funnel in which aqueous and hydrocarbon layers can be mixed intimately by boiling and refluxing. The application of this apparatus to the subject determination is readily apparent.
Calculation of Results. The salt content of the crude is usually reported as pounds of sodium chloride per thousand barrels of crude. Correction must be made for any acid present. If desired, the extracts may be analyzed for calcium, magnesium, or other chlorides, and the salt content reported in other terms. I n terms of sodium chloride, however, Salt content = 410 (VANA- V K N K ) where V A is total volume in milliliters of silver nitrate used, corrected for the blank V K is total volume in milliliters of potassium hydroxide used N A is the normality of the silver nitrate N K is the normality of the potassium hydroxide
Discussion EMULSIFICAT~ON. Butyl alcohol has broken all emulsions encountered to date. If this were not effective in some cases, it is expected that one of the Tretolites (3) could be used instead, being added a t the same point as was the alcohol. If added before refluxing, the Tretolite so prevents emulsification that quantitative extraction of the chlorides is much more difficult. BUMPING. With some samples, bumping may be serious. The addition of boiling water and regulation of heat input help to minimize this difficulty. One laboratory has installed an apparatus which is twice the size of the standard tetraethyllead apparatus, so that bumping, even when serious, does not result in loss of sample. ACIDITYADJUSTMENT.The Mohr titration of chlorides (4) must be conducted in a neutral solution. The Bureau of Mines method (3) uses phenolphthalein as the indicator for this adjustment. When the titration medium was distilled water, the ratio of the strength of the silver nitrate solution to that of the potassium chloride solution used was 0.999 to 1. If the acidity was adjusted with sodium carbonate and acetic acid to the phenolphthalein end point, the ratio was 0.964 to 1. The error caused by the use of this indicator is thus 3.5 per cent. Adjusting with carbonate and nitric acid to this end point gave a ratio of 0.999 to 1. However, if the salt of a weak acid were present, the use of nitric acid would give the same error as that obtained with acetic acid. When adjusted to the litmus end point, both acetic and nitric acids gave the ratio 0.999 to 1. If an acid indicator such as 2,4dinitrophenol is used, the ratio drops to 0.944 to 1. If the extract is far from neutral, it is convenient to adjust to the phenolphthalein end point first and then to the litmus end point. The second adjustment requires only a few drops of the nitric acid. SULFIDESAND MERCAPTANS. The standard potassium chloride solution was saturated with hydrogen sulfide and titrated. A black precipitate formed, as would be expected. One milliliter of glacial acetic acid was added and the solution was boiled for 5 minutes, cooled, adjusted to litmus, and titrated. This procedure is recommended by the Bureau of Mines (3). No black precipitate formed, but the ratio obtained was 0.922, an error of 7.7 per cent. Instead of the acetic acid, 5 ml. of hydrogen peroxide were added to the potassium chloride solution, boiled, cooled, neutralized, and titrated as before. The ratio obtained in this case was 0.999 to 1. SOAPS. The Bureau of Mines method (3) recommends the addition of a few drops of 5 per cent zinc acetate solution to
Recommended Procedure APPARATUS. Hydrochloric acid reflux apparatus (A. S. T. M. D526-41T), 300-ml. Erlenmeyer flask, 50-ml. burets, and a 100-ml. graduate. CHEMICALS (c. P.). %-Butyl alcohol, potassium chloride, potassium chromate, silver nitrate, and xylene (20' or better). SOLUTIONS. Potassium chloride, 0.05 N , 3.7280 grams of pure, dry potassium chloride per liter. Silver nitrate, 0.05 N, about 8.5 grams of silver nitrate er liter. Chromate indicator, about 65 grams of potassium ctromate dissolved in 100 ml. of distilled water, and sensitized by the addition of a few drops of the silver nitrate solution, followed by filtration. STANDARDIZATION. The determinations involve the titration of about 50 ml. of sample in a 300-ml. Erlenmeyer flask. Consequently, the blank and the standardization of the silver nitrate solution against the standard potassium chloride solution, should be determined under the same conditions. Three drops of chromate indicator are used. ANALYSIS. Eztraction. The sample is shaken thoroughly, 50.0 ml. are measured into a graduate and poured into the extractor, and graduate and thistle tube are rinsed with xylene until about 100 ml. of xylene have been used. Fifty milliliters of distilled water are then introduced into the extractor, the heat is turned on, and refluxing is continued for 15 minutes. (The use of water already heated t o boiling saves considerable time and minimizes bumping.) At the end of this time the heat is turned off, and the layers are allowed t o separate. If the separation is slow, or an emulsion has formed at the interface, the addition of about 5 ml. of butyl alcohol and the judicious application of heat will cause a sharp separation. The water extract is drained into a 300-ml. Erlenmeyer flask, and cooled to room temperature. Another 50-ml. portion of distilled water is added to the apparatus, and the extraction is repeated. Each 50-ml. extract is titrated separately. If a recision of 1.8 kg. (4pounds) of sodium chloride per 1000 barrefs is desired, a titration of 0.2 ml. of 0.05 N silver nitrate may be considered as indicating complete extraction. Generally, the second extractions will require only 0.2 ml. of silver nitrate. Titration. Each 50-ml. extract should be tested with litmus paper. If alkaline, it should be made slightly acid by the dropwise addition of approximately 1.6 N nitric acid. If acid, it should be titrated with 0.2 N potassium hydroxide until neutral t o litmus paper and the volume recorded. It is then made acid by the dropwise addition of the nitric acid, and the extract is titrated with the silver nitrate solution, using 3 drops of the chromate indicator. If sulfides or mercaptans are present, 5 ml. 947
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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TABLEI. SALTCONTENT OF CRUDE (Pounds of S a C l per 1000 barrels of crude. method.) A B C D r y O P O P O P O P 7 4 77 73 76 54 59 65 67 70 72 65 67 54 53 60 62 68 70 74 7 4 48 53 53 63 73 79 72 76 58 51 49 67 5 .. 67 . . 65 51 .. 63 Av. 71 73 71 72 54 53 57 64
Lrtborat o 1 2 3 4
..
0, own method. O 118 109 116 107
...
113
E
P 114 110 109 117 109 112
O 77 79 64 62
F
P , proposed P O 79 73 77 70 78 78 76 68
. . . . ..
71
78 72
G
P 76 73 72 74 68 73
coagulate the soap and prevent a pink coloration. When the soap was added to the standard potassium chloride solution, followed by the zinc acetate, and adjustment to the litmus end point, titration gave a ratio of 0,999 to 1.
Experimental The adaption of the tetraethyllead extraction apparatus to the determination of the salt content of crude oil is obvious, and requires no detailed description. The balance of the work consisted of a n exchange of samples between five laboratories of this company. Each laboratory was asked to supply samples of crude representative of the general run handled, choosing as troublesome samples as possible. Seven samples n-ere circulated, and were analyzed both by the procedure then in use a t each laboratory and by the proposed method. Table I gives the results. The proposed method was new to the operators. The reproducibility may be expected to improve with practice.
Vol. 14, No. 12
The time required for the proposed method is longer, for one sample, than that required for the other methods studied. The other methods, however, require constant activity on the part of the operator, while with the proposed method, the extraction is made without attention. With three sets of apparatus, one operator can analyze three samples every 45 minutes. Duplicate determinations by one operator check to within 2 pounds of sodium chloride per thousand barrels of crude oil. The variations shown in Table I are considerably larger than this, but inexperience with the method and difficulties in sampling prevent an exact evaluation of the reproducibility.
Acknowledgment The authors wish to thank the personnel of the other laboratories for their cooperation in the preparation and analysis of the crude oil samples.
Literature Cited (1) A. S. T. M. Designation D52641T. (1) (2) Blair, C. M., Jr., IND.ENQ.CHEM., CHEM.,ANIL. ED.,10, 207 (1938). (3) Horne, J. W., and Christianson, L. F., U . S . BUT.Mines Rept.
3517 11940).
Scott, “Standard Methods of Chemical Analysis”, 6th ed., Vol. I, p. 272, D. Van Nostrand Co., New York, 1939. ( 5 ) Universal Oil Products Co., “Laboratory Test Methods for Petroleum and Its Products”, Procedure A-3, 1940. (4)
PRESENTED before the Division of Petroleum Chemistry at the 102nd CHEMICAL SOCIETY, Atlantic City, N. J. Meeting of the AMERICAN
Colorimetric Determination of Vitamin C 3x. L. ISAACS DeLamar Institute of Public Health, Columbia University, New York, N. Y.
V
ITAMIY C as a moderately strong reducing agent is
capable of producing colored reduction products from a number of the phospho- and silico- molybdates and tungstates. One of these reactions has been adapted by Brand and Kassell to a quantitative determination of the vitamin ( 1 ) . Another, which offers certain advantages under suitable conditions, is the reaction between vitamin C and silicomolybdie acid produced by the reaction of ammonium molybdate and sodium silicate in acid solution. The reaction is sensitive, 0.01 mg. of the vitamin in 50 ml. of solution producing a discernible color; the reagent is stable and can be kept for long periods; and the blue reduction product is not reoxidized by exposure to air. I n the procedure described below, using the photoelectric colorimeter, natural coloring matter in the yellow and red part of the spectrum does not interfere with the test. The method described is suitable for determining the vitamin C content of fruits, vegetables, and other materials in which the content of other reducing substances is low-e. g., bananas and lemon juice. In other materials it gives results more nearly comparable to the iodine titration and therefore tends to run higher than the indophenol method. The molybdate reagent is easily reduced by ferrous and stannous ions and more slowly by cysteine, sulfites, and thiosulfates. PREPARATIOX OF REAGENT. Two grams of ammonium molybdate are dissolved in 50 ml. of water at about 55’ C., and 10 ml. of 1 per cent sodium silicate solution (Na&3iOa.9Hz0) freshly prepared are added, followed by 5 ml. of glacial acetic acid. The volume of the solution is then made up to 100 ml. After standing overnight the reagent is ready for use. The reagent keeps indefinitely. After several weeks a white
precipitate forms (probably molybdic acid) but the loss of this material does not interfere with the use of the reagent. PROCEDURE. An extract of the material to be examined is prepared by grinding a weighed quantity with 5 per cent acetic acid and sand in a mortar. After filtration and washing of the residue with fresh 5 per cent acetic acid, the filtrate is made up to a suitable volume. An extract of this type is stable for approximately 3 or 4 hours. If kept overnight, even in a refrigerator, loss of vitamin may run as high as 10 per cent. With some materials, such as bananas, extraction may be made directly with a measured quantity of diluted reagent and sand. In making a determination, a suitable quantity of filtrate containing up to 1 mg. of vitamin C is placed in a 50-ml. volumetric flask with approximately 25 ml. of water; 5 ml. of reagent are added, followed by distilled water up to the graduation mark. One milliliter of reagent is sufficient in the range of 0.01 to 0.1 mg. The contents of the flask are thoroughly mixed and allowed to stand for 15 minutes before making a reading. If the solution is turbid it may be filtered. The 50-ml. volume was chosen for convenience in measuring reagents; any smaller volume, however, may be used with proportionate decreases of reagent and dilution water. The depth of color may be estimated in two ways, using standards in Nessler tubes or a photoelectric colorimeter, the latter method being preferred. The Duboscq colorimeter is not suitable in this procedure because of the presence in the final product of varying amounts of excess of the yellow reagent. For the preparation of standards in Nessler tubes, solutions of pure ascorbic acid may be used. The convenient range contains 0.01 to 1 mg. per 50-ml. h a 1 volume, in steps ranging from 0.01 or 0.02 to 0.2 mg. In this higher range the colors may be matched from the side. The fact that the final color results from the partial disappearance of yellow and the formation of a blue color accentuates the difference between the standards. During the course of 2 days after preparation, the standards tend to increase in color. If at the end of this time they are readjusted with diluted reagent, they remain unchanged for several weeks. Further storage results in a gradual loss of the blue color.
