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 M a t e r i a l s , D 129-34, p. 974, 1A3ii. (3) G i b s o n , 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
VOL. 10, NO. 4
INDUSTRIAL AND ENGINEERING CHEMISTRY
208
cient for all oil samples analyzed in this laboratory. Less destabilizer is sufficient with some oils, but since the use of this material does not interfere with subsequent analyses for halogens and cations, it is safer to use the amount given. Use of too little of this destabilizer results in poor separation of the oil and water and incomplete extraction of the brine. TABLEI. EFFECTOF AGITATIOXo s EXTRACTED
. ~ M O U S T OF
SALT
(Total halogen as mg. of NaCl per liter of crude) .4gitation Time 3 min. 5 min. 10 min. 15 min. From Shuler Crude 906 931 855 925
147 144 145
975 1006 969 956
1000 994 988
..
From Oklahoma Crude 145 151 145 143 153
149
1000 1013
.. ..
.. ..
..
Since the calcium and magnesium salts of most sulfonic acids are partially soluble in oil, it was feared a t first that much of the calcium and magnesium would be lost by solution in the form of sulfonates in the oil phase. The destabilizer called for in the procedure is equivalent to roughly 30 mg. of calcium chloride or 25 mg. of magnesium chloride, which often is more than is present in 100 ml. of crude. T o determine whether or not this occurred, the following test was made: A solution was prepared containing about 1 gram of calcium chloride per liter and 100 ml. of this solution were analyzed for calcium by the usual gravimetric method (1). Another 100-ml. portion was shaken for 10 mlnutes with a mixture of 100 ml. of kerosene and 100 ml. of xylene (which has about the same solvent pro erties as a mixture of crude oil and xylene) to which had been ad&d 4 ml. of a 5 per cent xylene solution of Destabilizer A. The aqueous phase was separated and analyzed for calcium.
The solution so treated was in all casesfound to contain the same amount of calcium, within experimental error, as the original solution. Apparently, a t the dilution obtained in the extraction, the calcium sulfonate remains almost completely in the aqueous phase. Since the magnesium sulfonates are generally more mter-soluble and less oil-soluble than the calcium sulfonates, i t is concluded that magnesium also is left nearly completely in the aqueous phase. Xylene is recommended as a diluent for the oil, since it has good solvent action on most petroleums, a 1017 vapor pre,,w r e with consequent low fire and poison hazards, and a low specific gravity, a property which gives a larger specific gravity differential between the oil and water phases and thus permits faster and more complete settling out of the water. Benzene, toluene, or gasoline may be used if xylene is not available. The efficiency of salt extraction by this method depends greatly on the agitation given to the mixture after addition of the water. The shaking time of 5 minutes given in the above procedure has been found sufficient to extract a t least 95 per cent of the salt from even the most difficult samples. Usually, in the determination of the salt content of oils, extremely accurate analyses are not required, and some sacrifice may be made in accuracy in order to permit a more rapid determination. TYithin 5 per cent of the true salt content value is generally considered sufficiently accurate. I n order to determine the extent to which the efficiency of the extraction depends upon the time of agitation, analyses for total halogen were made on several crude oils, varying the time of agitation. The shaking was done by hand a t the rate of from 150 to 200 shakes per minute. Halogen was determined by the Mohr method ( I ) , with corrections for the blank being applied. Table I s h o w the results obtained on a
typical high salt content crude from Shuler, Ark. Very little increase in accuracy is obtained by shaking more than 5 minutes, but values nearly 15 per cent low may be obtained with only 3 minutes’ agitation. This oil contained 0.4 per cent of emulsified brine and is considered difficult to analyze by other methods. Results are expressed in milligrams of sodium chloride per liter of crude. In the petroleum industry, chloride contents of crude oils are often expressed as grams of sodium chloride per barrel (of 42 gallons) or as pounds of sodium chloride per 1000 barrels. The relations between these units and the metric units employed here are as follows: Grams per barrel (42 gallons) = mg. per liter X 0.1590 Pounds per 1000barrels = mg. per liter X 0.3505 Similar tests were made on an oil of low salt content from Oklahoma. This oil contained 0.2 per cent of dispersed brine and is considered easy t o extract by other methods. Table I also gives the results of these tests. With this oil, 3 minutes’ agitation gives satisfactory extraction. These same oils were analyzed also by theT;. 0.P. method, three extractions being made of each sample. Results of these analyses are given in Table 11. DETERMIXED BY C . 0. P. METHOD T.LBLE11. HALOGEN (ME. of NaCl per liter of crude) 1 1 s t extraction 2nd extraction 3rd extraction Total
In Shuler Crude 2 3
868
77 3 548
-
881 86
811 120
973
934
6 -
23
I n Oklahoma Crude 1 2 3 135 8
2 -
145
134 8
4 -
146
141 6
2 -
149
I n the case of the Shuler crude, the salt removed by three extractions using the U.0. P. method was 2 to 8 per cent belox the maximum values and averaged less than the &minute values shown in Table I. With the Oklahoma oil, the values obtained after three extractions by the U.0. P.method agree with those of Table I. Ho-ivever, with both oils, the first extractions by the U.0. P. method gave values 10 to 20 per cent below the maximum values obtained by the new method.
Rapid %lethod I n routine analysis for halogens only, it has been found possible to niodify the procedure described above to permit more rapid determinations. The volume of sample used in the procedure described below is in general too small to permit accurate analysis for cations, K i t h many oils, the cation ratio, sodium to calcium to magnesium, remains constant over long periods of time and, after this ratio has been established, analysis for total halogens gives sufficient information for control work. I n this procedure, a different destabilizer from that used in the longer procedure is employed-a mixture of isomeric compounds obtained by the acylation of polyhydroxy glycerides known under the trade name of Destabilizer B. The exact chemical structure of these compounds is not known. This material is much more effective than the sulfonic acid salts in flocculating the dispersed water droplets, but the coarse flocs formed do not easily coalesce under the influence of gravity, and for this reason cannot be used with the first method. I n the centrifuging procedure, as employed in this rapid method, the coarse flocs are quickly coalesced and a clear aqueous layer is formed. Into a 100-ml. standard A. 8. T. b l . 011 centrifuge tube, pour 25 ml. of the crude oil and add 2 ml. of a 2 per cent xylene solution of Destabilizer B. Then add xylene t o fill to the 50-ml. graduation mark. Shake for a f e x seconds and add 50 ml. of boiling, chloride-free, distilled water. Stopper and shake vigorously for 2 or 3 minutes, and centrifuge for 1 minute. Pour the contents
APRIL 15, 1938
ANALYTICAL EDITION
of the tube into a small separatory funnel, draw off the aqueous layer, filter, and titrate an aliquot amount for halogens.
Discussion of Rapid Method If the graduations on the centrifuge tube are used to measure the volumes of oil and water added, results on a given oil may be expected to vary by 4 or 5 per cent a t least, since volumes of fluid in the tube cannot be estimated to much closer than 1ml. Again, one should correct for the decrease, on cooling, in the volume of water added. K h e n the oil sample contains only small amounts of chloride, the experimental error may become greater than 5 per cent, because of the proportionately larger end-point error in the titration. Where the amount of salt present is small, the mercury nitrate method ( 2 ) of halogen determination is to be recommended in place of the bIohr method. T.4BLE
111. TOTAL HALOGEX BY RAPIDi\'IETHOD O l g . of Sac1 per liter of crude) Oklahoma
Sliuler Crude 975 103s 931
944
Crude 133 153 162 155
Table I11 shows the results obtained using this rapid method on samples of the two oils previously analyzed by the longer method. Graduations on the centrifuge tube were used to measure the volumes of oil, xylene, and water used. Halogen was determined by the Mohr nietliotl. T2ie.e rehiiltS may be compared n-it11 those given in Table 1.
209
Acknowledgment The author is indebted to R. B. Perkins, Jr., of the Petroleum Rectifying Company for testing these two methods of analysis on a number of different crude oils.
Summary For quantitative extraction of inorganic salts from crude oils, i t is desirable to employ a destabilizing agent' which causes coalescence of the particles of emulsified brine present in the oil and prevents permanent emulsification of the extraction water. A new met'hod of extraction of inorganic salts from crude oil is presented. This method employs a mixture of ammonium salts of high molecular weight sulfonic acids as a destabilizing agent, and gives nearly quantitat'ive removal of the salts in one extraction. A rapid method of extraction is presented, which permits analyses for total halogens sufficiently accurate for control work. This rnet'hod employs a destahilizer consisting of a mixture of isomeric compounds obtained b y the acylation of polyhydroxy glycerides.
Literature Cited (1) Fales,
"Inorganic Quantitative Analysis," New York, Century
co., 19".
(2) Miller, C. F., Citemisf-Analyst, 26, 83 (1937). (3) Universal Oil Products Co.. "1,aboratory Tost Methods for Petroleunii and Its Protluc I : i : < , ~ , r r ~Sovelnber n ?!I, l ~ l ; l 7
Approximate Specific Gravity Determination A Rapid Method for Use with Pecans and Similar Small Objects JOHN G. W24UGH,Bureau of Plant Industry, U. S. Department of Agriculture, i u s t i n , Texas
T THE present' time there seems to be no satisfactory method for the rapid deterniination of the approxjniate specific gravity of pecans and similar small objects. I n determining the specific gravity of individual pecan nuts, it was found that gravimetric methods n-ere slow and the apparatus described herein was constructed to facilitate more rapid measurements. It may be used for the det'erniination of the approximate specific gravity of small objects whose specific gravity is less than unity, and which are unaffected by inimersion in wat'er or other liquids of the same density. The apparatus is simple and is easily and cheaply constructed.
Method and Apparatus The method involves x-eighing the object to 0.01 gram and subsequently measuring its buoyancy directly in distilled water at room temperature by the hydrometerlike apparatus shown to scale in Figure 1, a. It consists of a 50-ml. bulb, A , from a pipet, to the lower end of which is sealed a bulb, B , to hold lead shot. To the upper end of bulb A a thin-xyalled glass tube of uniform 8-mm. outside diameter is sealed with a bend at C. A scale is constmcted and fitted in the tube at, D. A copper wire carriage, E, made of S o . 20 gage wire, is fitted t o the tube to depress the object, F , xhose specific gravity is to be determined. -1phosphor-bronze clip, G, x-ith a sliding collar may be added to hold tmheobject in the carriage. The instrument is neighted so that when it floats without load, the water level or zero point, is at H . Its over-all length is 43 em. and it niny be uied in a 1liter gradiiatrd cyIin(1c~i~. b'CJr the t i h J V t . i l l S t I ' l l l l l C ' l l t , the I ' H I l g e ui' bilc,j'all('Jr dt!tt;l'mination is 8 grams with a scale calibratd for distilled n-ater
a t 20" C. to 0.1 gram which can be read to 0.05 gram. By altering the dimensions of the instrument and adjusting its sensitivity with an appropriate diameter of scale-tube, i t can be adapted to measure the specific gravity of objects with other ranges of weight and volume. By adding the phosphorbronze spring clip, G, to hold the object in the carriage and extending the scale upward, measurements of specific gravity of objects heavier than water may be made. Using a mixture of ligroin and carbon tetrachloride or some other suitable liquids having the density of water, the specific gravity of objects which would be affected by immersion in water iiiay be obtaiued. The formulab f u r calculating the bpecific gravity are as follows
where It' is the weight in grams, I- the volume in ml., B tlic buoyancy in grams. and cl the density of the liquid used. If the demity of the liquid is unity, d = 1, and the formula rcduces to Specific gravity
=
11-
TT
~
i-
B
Sime the specific gi,avity tletcminntions are nppwximatr, c*orreutionis made for the density of' tlist,illed w t e r (O.CJYX, 1 ) at room temperature (20' C.jand 1 ' ~ m i u l : tL' i i usecl i l l ( I N . calculations. For objects heavier t,lian water E'orniula 2 still
IIO
