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sample add 15 grams of U. S. P. X I fusion mixture and mix thoroughly. Superimpose a layer of fusion mixture, using 5 grams for each ram of sample. Continue with method as given above. d h e n neutralizing the alkaline solution of the flux with hydrochloric acid (1 4), use about 20 cc. of hydrochloric acid and 80 cc. of water for each 20 grams of fusion mixture employed in the assay. From the amount of iodine found, calculate to per cent of labeled amount on basis of U. S. P. mean (0.200 per cent) iodine content of thyroid.
+
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 5th ed., XXVII, 57, p. 368, 1940. (2) Burnett, R. S., and Warkow, R. F., IND.ENQ.CHEM.,ANAL.ED., 12,734 (1940). (3) Hilty, W. W., and Wilson, D. T., Ibid., 11, 637 (1939). (4) Hojer, J. W., Biochem. Z.,205,273 (1929). (5) Johnson, F.F., and Nelson, H. A., Am. Drug. Mfrs. Assoc., Proc. 30th Annual Meeting, p. 186 (1941).
Determination of Salts in Crude Oil CLARENCE A. NEILSON, J. STEWART HUME, AND BERT H. LINCOLN Continental Oil Company, Ponca City, Okla.
T
HE presence of salts in crude oil is one of the most seri-
ous problems confronting the petroleum refiner. These salts may contribute to (1) the mechanical clogging of furnace tubes, condensers, and lines by deposition; (2) the corrosion of equipment by the hydrolysis of salts producing hydrogen chloride; and (3) high ash content of still residues. In predetermining the amount of salt in crude oil for the purpose of plant control, a quick and easy analytical method is of prime importance. A brief review of some of the many analytical methods now in use has been given by Blair (1). The more popular methods are essentially alike, in that they involve an intimate mixing of the oil with water, followed by the addition of a n emulsion breaker. Frequently a n organic solvent for hydrocarbons is added to reduce the viscosity of the oil. Essential differences lie in the manner of mixing the oil and water and in the demulsifying agents employed ( 3 , 4 ) . The aim of all extraction procedures is the quantitative removal of all the inorganic salts contained in the crude. This extraction is often difficult because the salts may be contained in brine-in-oil emulsions, rendered very stable by naturally occurring emulsifiers in the crude, or they may be present in the form of wax- or asphalt-protected crystals. Analysis of the extract may involve the quantitative determination of sodium, calcium, magnesium, sulfate, and chloride; but for most plant control work, only the chloride is determined. The chlorides are of first importance because of the hydrochloric acid released by the hydrolysis of the calcium and magnesium chlorides by crude oil distillation. The following procedure for extracting salt from crudes and for determining chloride in the extract has been in use for some time in Continental Oil Company laboratories and has proved to be reasonably accurate. It has the advantage of being rapid, since only one extraction is required. Procedure Thoroughly mix the oil sample under test; then transfer exactly 125 ml. of the homogeneous sample to a 1-liter separatory funnel, If the oil is viscous, add 125 ml. of hot xylene, benzene, or toluene and shake until thoroughly mixed. Gasoline has always proved to be a very unsatisfactory diluent. The solvent is unnecessary with most crude oils lighter than 34 A. P. I. gravity, though it may always be used, particularly if an especially clear water extract is desired. For very light crudes, where the addition of a hot diluent may be hazardous, it is preferable to mix the oil and solvent at room temperature, then heat carefully to 60' C. (140" F.). Add 200 ml. of boiling distilled water and shake gently for 3 minutes, frequently relieving the pressure. (Invert the sephratory funnel and release pressure through stopcock.) Add 20 ml. of phenol in 30 ml. of boiling distilled water and shake gently for 5 minutes. Better extraction and a cleaner break of the emulsion have been found to result from this stepwise addition of the water and phenol. Allow the mixture t o stand until more than 100 ml. of clear water have separated out. Filter off exactly 100 ml. of the water
into a graduated cylinder through two sheets of heavy, qualitative filter paper. If negligible quantities of hydrogen sulfide and mercaptans are present, transfer the 100 ml. of filtered solution to an Erlenmeyer flask, adjust to a pH of 6.5 to 7.0, using 1 ml. of Continental indicator, add 0.5 ml. of a saturated solution of potassium chromate, and readjust the pH to 6.5 to 7.0. The advanta e at this point of the use of a universal indicator of the nature of Continental indicator is its clear yellow color at this particular pH range. Experience has shown that a careful pH control a t this stage is very important for a satisfactory chromate end point. Exact pH control for this titration has been found necessary in the presence of ammonium salts ( 8 ) ,and seems desirable in the presence of phenol. N o interference by the pH indicator with the chromate titration has been observed. Cool the solution to 29.4" C. (85" F:) and titrate withO.0;38 N silver nitrate to a light orange end point. Vigorous agitation of the solution during titration is absolutely necessary to ensure complete precipitation of the silver halide before the appearance of the silver chromate end point (2). A blank titration may be carried out on 92 ml. of water plus 8 ml. of phenol, the whole having been neutralized to a pH of 6.5 to 7.0 before addition of the chromate indicator. If either hydrogen sulfide or mercaptans or both are present, they must be removed before the halides can be determined. The method of acidifying and boiling is not applicable, since loss of hydrogen chloride may result. Transfer the 100 ml. of filtered extract to a 250-ml. beaker, add 1 ml. of Continental indicator, and adjust the pH to 6.5 to 7.0 (light yellow). Precipitate the sulfides and mercaptans with an excess of cadmium nitrate. Allow to stand 1 hour, then transfer to a centrifuge tube. Centrifuge until the solution is clear and the precipitate is a dense firm mass. Decant the clear solution into an Erlenmeyer flask, filtering if necessary. Rinse the beaker with 10 ml. of distilled water into the centrifuge tube. Thoroughly wash the precipitate by shaking, and recentrifuge. Decant the clear wash water into the solution in the Erlenmeyer flask and adjust to 6.5 pH (yellow). Titrate for halides. If a centrifuge is not available, filtration through Whatman No. 44 filter paper may be substituted. An alternate method for chlorides in the presence of sulfides and mercaptans is the Volhard procedure.
CALCULATIOK. (Ml. of AgNOs - ml. of blank) X 10 = grams of NaCl per barrel This relationship is true only if the exact volumes and concentrations specified are used. If the determination is desired in other units, the silver nitrate solution may be adjusted accordingly. If an appreciable amount of water is present initially in the crude, results will be too low unless corrected as follows: 250 1.25 X % water NaCl X
+
250
where the per cent of water is determined by A. S. T. M. method D-95-40. Discussion of Procedure The use of phenol promotes the extraction of asphalt- or wax-protected crystals from the crude; hence phenol is essen-
June 15, 1942
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465
values. I n solutions with a p H but slightly lower than 6.5, TABLEI. EFFECT OF QUANTITY OF PHENOL O N SALTEXTRAC- the precipitation of the mercaptans is not complete; and some TION OF OKLAHOMA CITY-EDMOND, OXLA.,CRUDESAMPLES chloride may be carried down with the sulfide. The general Phenol Used Water Used NaCl effectiveness of phenol as a demulsifier has not been checked MI. M1. Grams/hhZ. on all varieties of crude oils, but it has been used with success 0 250 28 on many crudes from Oklahoma, Kansas, Texas, and Louisi5 245 33 240 39 10 ana. If slow breaking emulsions are encountered, the 20 230 43 25 225 43 difficulty may be due to too vigorous shaking, or it may be that phenol is not the proper demulsifier for the crude. Frequently the addition of a larger proportion of diluent is helpOF CONOCO AND BLAIRSALT-EXTRACTABLE11. COMPARISON ful. TION METHODS The following Continental indicator mixture has been found Salt Extracted Oklahoma Cityvery useful in this procedure, particularly for p H adjustment Lucien-Crescent to 6.5 to 7.0. At this value, the indicator gives a clear yellow Method Edmond crude crude Grams/bbl. Groms/bbE. color which does not interfere with the chromate indicator. Conoco no diluent 33 75 If, after the addition of the chromate, the solution is not a Conoco: no diluent 34 74 bright yellow, readjustment to pH 6.5 to 7.0 can be made by Conoco + 200 ml. of hot xylene 34 75 Conoco + 125 ml. of hot benzene 35 75 comparing the color with a blank of water and potassium chroConoco. no diluent (HzS added to crude) 76 (HtS and mercaptan mate. Exact pH adjustment is very important, as is the Conoco; no diluent added to crude) 74 quantity of potassium chromate indicator specified. Con34 75 Blair destabilizer A 73 36 Blair destabjlizer A tinental indicator has an advantage over p H paper in that 74 34 Universal Oil Productsa i t is more sensitive to slight variations of pH. It is more cona Triple extraction with gravimetric chlorine analysis for control. veniently prepared, and is generally very useful. tial for complete salt extraction, even when the oil and water do not form an emulsion. Twenty milliliters of phenol have been found to be a n optimum quantity, as shown by Table I. Actual separation of the oil and water layers was equally good in all the extractions shown in Table I, but the salt extraction was not, c p w l e t e when less than 20 ml. of phenol was , used. The volume change in mixing phenol and water may be disregarded in these tests. To check the phenol distribution between the water and crude, 125 ml. of a dry sample of Oklahoma City-Lucien-Crescent fields crude were extracted with 230 ml. of water and 20 ml. of phenol; 209 ml. of water- henol mixture immediately separated and were drawn off (no &ter paper used) and measured. On centrifuging, 38 ml. more of the water-phenol mixture were recovered, thus giving a total recovery of 247 ml., or a volume loss of 1 per cent. This loss is largely due to cooling and in a lesser degree t o evaporation. Evidently very little henol remains dissolved in the crude. Similar results were ogtained with a variety of Kansas and Oklahoma crudes.
It will usually be observed that a blank made up of the same proportions of phenol and water as used in the extraction procedure will show a higher acidity than a n actual extract water. This effect is attributed to the buffer action of the salts extracted from the crude, rather than to solution of the phenol in the crude. The use of a centrifuge to hasten or secure a more complete separation of the oil and water phases has been found to have no effect on the efficiency of salt extraction. The data in Table I1 indicate good agreement between the Conoco and Blair methods, and a similar agreement was found between the Conoco method and triple extraction by the Universal Oil Products method (4). I n the Conoco method, the use of an oil diluent is frequently unnecessary, as shown in Table 11; but with viscous oils, the diluent simplifies the extraction. The hydrogen sulfide and mercaptans were added in the instances noted to check the accuracy of the halide analysis in their presence. I n the case of most “sweet crudes” the cadmium separation is unnecessary. If, however, a dark precipitate appears a t the start of the silver nitrate titration, the presence of hydrogen sulfide is indicated. I n the case of unknown crudes, a second small aliquot portion of the extract water may be checked with cadmium nitrate solution before proceeding with the determination The success of the cadmium removal of the hydrogen sulfide and mercaptans depends upon the exact adjustment of the pH
FORMULA FOR CONTINENTAL INDIC.4TOR Sodium salt of methyl red (Eastman) 0 . 2 0 gram Bromothymol blue (Eastman) (dibromothymolsulfonphthalein) 0 . 6 0 gram Phenolphthalein (Merck or hlallinckrodt) 0 . 6 4 gram
Dissolve the indicators in order in 1 liter of 50 per cent (by volume) ethanol and add sufficient dilute (0.1 N ) sodium h droxide to produce a green color (pH = 8). Store in tightfy stoppered brown bottles of 100- to 250-ml. capacity. For a pH determination, use 0.10 ml. of indicator per 10 ml. of water sample. The color changes are as follows: pH pH pH pH pH pH pH
up to 3.0
4.0 5.0 5.5 6.0 6.5 7.0-7.5
Red Deeper red Orange red Orange Orange yellow Yellow Greenish yellow
pH pH pH pH pH pH pH
8.0 8.5 9.0 9.5
10.0 10.5 11.0
Green Bluish reen Greenis% blue Blue Violet Reddish vio!et Deeper reddish violet
The shaking times specified are minimum. Special care should be exercised in shaking the hot water and oil mixture. If highly volatile fractions are present in considerable quantities in the oil, a cloth should be wrapped around the funnel before shaking and the pressure frequently released. For calcium and magnesium determination on a crude, the same general procedure may be employed; however, a 200ml. sample of crude should be used and extracted with 365 ml. of water and 35 ml. of phenol. As large an aliquot as obtainable of the extract water should be drawn off for analysis.
Summary A simple and rapid method for the quantitative extraction of inorganic salts from crude oils is presented, in which phenol serves as the destabilizing agent. Provision is made for the separation of hydrogen sulfides and mercaptans, a precaution not taken in some of the common methods for salt extraction and analysis. Details are given for easy regulation of the p H in the determination of extracted chlorides by the Mohr t,itration in the presence of phenol. A formula is given for a simple and generally useful universal indicator to be used in the procedure.
Literature Cited (1) Blair, C. M . , IND.ENG.C H E M ANAL. ., ED.,10, 207 (1938). (2) Kolthoff a n d F u r m a n , “Volumetric Analysis”, Vol. 11, pp. 214, 225, New York, John Wiley & Sons, 1929. (3) Roberts and Stenzel, Petroleum Engr., 10, 35 (1939). (4) Universal Oil Products Co., “Laboratory Test Methods for Petroleum and Its Products”, Method A-22-40.
