V O L U M E 22, NO. 4, A P R I L 1 9 5 0
555
V X 35,460.YS
ierence, the coloriiiietric I est htts an estimated accuracy of r O . 5 p.p.m. The titrimetric test has the same accuracy up to 200 p.p.m. Khen extended beyond that range by dilution of the sample, the estimated error in parts per million is 50/S.
C1-, p,p.m. C1-, e.p.ni. =
T.'
x
____-
1000 s
S
wheie V = milliliters of mercuric nitrate consumed, S = normality of mercuric nitrate, and S = milliliters of sample water. If titration must be made on solutions which consistently eyceed 1000 p.p.m. of chloride, it will be preferable to employ a higher concentration of mercuric nitrate. EXPERILMENTAL DATA
The precision and accuracy of the colorimetric and titrimetric tests 1%ere evaluated by various laboratory personnel, using gravimetrically standardized solutions of C.P. potassium chloride in distilled water. The results are shown in Tables I1 and 111. On completion of these analyses of pure chloride solutions, additional titrimetric tests Rere made on solutions contaminated Kith positive and negative ions apt to be encountered in industrial naters. KOeffort was made to overcome effects of the ions by modification of the titration. When used individually, 1000 p.p.m, of nitrate, sulfate, phosphate, magnesium, calcium, and aluminum did not significantly affect the titration. The heavy metal ions, zinc, lead, ferrous, nickel, and chromium, affected solution colors, but 100 p.p.m. concentrations of these ions did not reduce accuracy. cupric ion was tolerable in concentrations to 50 P,P.m. On the Other hand, chromate and ferric ions ruined the titration in concentrations as low as 10 p.p,m. These two ions must be removed Or Otherwise counteracted before determination of chloride by this method. In the absence of inter-
CONCLUSIONS
The improved analytical methods described in t,his papel' are applicable to the determination of chloride ion in all types of waters. They require only standard laboratory equipment and can be effectively applied by personnel with very limited laboratory experience. When implemented with slide-comparator equipment, the colorimetric test is ideally suited to field testing. The titrimetric method is independent of practically all common interferences. ACKNOWLEDGMENT
Acknowledgment is made to Genevieve Ziurys, who conducted most of the development tests concerned with the colorimetric method, and to Mary Q.Garner, who conducted the performance tests connected with the t,itrinietric method. The service of W. A. Taylor & Company in preparing a slide comparator for use with the colorimetric method, also is acknowledged. LITERATURE CITED
(1) Dubsky, J. Lr., and Trtilek, J., Mikrochemk 12, 315-20 (1933). (2) Ibid., 15, 302 (1934). (3) Roberts, Irving, IND.ENG.CHEM.,ANAL.ED.,8, 365-7 (1936). RECEIVED October 31, 1949.
The opinions expressed in this paper are those
of the author and are not necessarily official opinions of the U.S.N. Engineering Experiment Station or the yavyDepartment.
Water Content of Hydrocarbons Modi$ed Karl Fischer Method W. S. HANNA AXD A. B. JOHNSON California Research Corporation, Richmond, Calif. .4 niodification of the Karl Fischer method applicable to the determination of
water in hydrocarbons or petroleum fractions is described. The method involves extraction of the water from the hydrocarbon by dry ethylene glycol and subsequent titration of the glycol extract with Fischer reagent. Under normal conditions, over 90% of the water present is absorbed in one extraction. The method is elastic in that, when properly used, equally accurate determinations can be made on very dry or relatively very w e t stocks.
N
U?\IEROUSanalytical methods haye been deyeloped for the determination of Rater in hpdrocarbons, These Illethods mav be roughly classified into those that employ physical means for measurement and thosr that use chemical means. Some physical methods are: thc il.S.T.11. distillation procedure (4), t h r cloud 23), alld the electrical conductivity 11, method (6, 9). A fen- of the methods that employ chemical means are: titration of acid resulting from the action of water on arptyl chloride (15, 20) 2.i), measurement of the volunie of gas ]ibel.ated by the action of J7-ater on (lg, 26), methyl magnesium iodide (14, Z-$)>.01' metallic. sodium ( 8 ) , and the Karl Fischer method. With the exception of the A4.S.T.lI.distillation procedure, t,he Karl Fischer method is by far the most widely used because of its grcJatrr accuracy in the determination of Rater content over the range 0.0005 to 0.5%. There are, however, certain difficulties encountered in the conventional use of this method on petroleum frwtions.
The Fischer reagent is not miscible with hydrocarbons. This property in conjunction with the relatively low solubilitv of n ater in hydrocarbons produces an indefinite titration end point. The visua] end point is difficultto detect in colored fiactions. Because of the low solubility of water in hydrocarbons, t,he actual quantities of water are very small if samples of convenient size are taken. Some method of concentration of the water from :I large volume of sample into a relatively small volume of estract for analysis is required for accurate determinations. The conventional method cannot be emploged on stocks of high vapor pressure, such as butane, propane, isopentane, etc. Certain compounds, notably ketones, aldehydes, and mercaptans (thiols). interfere n-ith the determination bv combining directly with the Fischer reagent. In view of the above-mentioned difficulties various modifications of the Fischer method have been proposed: elimination of the two-phase condition in the t,itration by addition of a solvent to the hydrocarbon phase-e.g., chloroform, pyridine, methanol, or Gertain mixtures of these compounds (1, IS, 22), and elimination
556
ANALYTICAL CHEMISTRY
of visual end point di5culties by electrometric titration (f, 3,16, 67,B).
These modifications do not, however, provide for concentration of the water from a large volume of hydrocarbon into an extract suitable for titration, nor do they permit the use of the Fischer reagent in the determination of water in volatile stocks. Thus, when i t became necessary, in the course of some laboratory investigations, to determine the water content of propane and butane more accurately than was possible by the change in color of oobaltous bromide (is)), the need of a method of extracting the water from these materials hy a suitable solvent was indicated. Ethylene glycol wsa found t o be i d 4 for this purpose. It is relatively insoluble in hydrocarbons, it is inert to Fiscber reagent but completely miscible in it, and in a dry stste i t has a high affinity for water.
I
Commercid ethylene glycol ueed in the extraction is rendered practically anhydrous by fractional distillation. The crude product is charged to an all-glass still fitted with a packed distillation column, reflux condenser, and overhead take-off line. The glycol is refluxed for 30 minutes, and,&!O% overhead put is removed. This is discarded, and the distillation is continued until a cut equal to SO% of the still charge is obtained. This procedure reduces the water content of the glycol to approrimately 0.0002 gram per ml. APPARATUS
The apparatus is shown in Figure 1. The titration vemel is cone-shaped with the apex a t the bottom, and it is equipped with a drain cock. The base of the inverted cone is fitted with five openings for the following equipment: (1) Fischer reagent buret, (2) sample buret, (3) standard methanol solution buret, (4) vent, and (5) spiral alass stirrer connected throueb - a mercurv seal to an i i r mitor. All reagent bottles, burets, and the vent are protected from atmospheric moisture by Drierite tubes. The samDle containers are usuallv m a r t bottles. each fitted with a dhwh tube reaching t o the loweit D O h t in the bottom of
are used for volatile stocks such aiprop"&e, butane, et;.
~... .
shakei~oft h e t y p e of Precision Scientific Compan , C&og 5855. The shaker is used to agitate the sample anJglyco1.
~~
No.
DETERMINATIONOF WATER CONTENT IN HYDROCARBONS .i mensurd amount oi ihc d r i d ethylrue glycol, iivuull,y 200 wl., i q e h a r p d tu rLe I-qurm s.mple vontsincr. The I m t t l e nnil the YIWOIarc shaken io remow 11.e adiorlr:d moisture from ihc
insi&"af the container. Twentv-milliliter Dartions of the alvcol ~~
~~~~~
may be~d&mined either by weight differenee or by subtr&ting the total volume used for t h e blanks from the volume charged. The sample container is weighed before and after transferring the sample t o it. The sample and glycol are then shakeu for 15 minutes in a mechanical shaker of the type mentioned above. T h e glycol-water extract settles out when allowed to stand for a few minutes after shaking. The sample buret (Figure 1) arid sample oontainer are then connected by dry tubing. The wn,lls e t,obinz .. . . of . ~ .i h ~ .~~ ~ are broueht to the same condition of moisture content as the ex&t by pkging w i t h ~ aportion of t h e extract. The sample taken into t h e sample buret. . ^^ fpr analysis ,~~is then ALL..L., > "le titration vessel t o B water content of the ows: ~~
~~~~
ID
Weight % water in sample = Figure 1. Titration Equipment
\"
- A) x c x v x vxw 1
100
where The proposed modification of the Karl Fischer method may be briefly summarized sa follows: The dissolved or suspended water in the hydrocarbon is extracted by shaking with a known quantity of dry ethylene glycol, and aliquot portions of the glycol solution ace titrated with standard Fischer reagent. The data reported by Gester (7), in his work on hexane, were obtained in the authors' laboratory by the method described in detail in the sections that follow. REAGENTS
Standardiaation is & d e against a methanolkate; solution by
~~~~~~
~
The methanol-water soluGon uyed to stilndardiae the Fischei reagent is prepared with about 0.002 gram of water per ml.
of Y ml. of ethylene glycol after extraction A = ml. of Fisober reagent usled in titration of v ml. of ethylene glycol before extractioL1 C = water equivalent of Fischer reagent in grams of water per ml. of reagent V = total volumeof ethylene]Jycol shaken with sample W = weight of sample ih grams v = volume of sample of glycol used in each titration B
= ml. of Fischer reagent used in titration
If greater a c c u r a y is required, or if the water content of the materid is very low, the sample size should be increased to tm much aa 1 gallon. The glycol-hydrocarbon ratio should not be less than 10 ml. per 100 grams for the average sample. However, i t may be necessary to increase this ratio for stocks with entrained or suspended water. Likewise for very dry stocks, the accuracy of the determination may be increased by decreasing the ratio sufficiently to widen the dieerential between the blank and find titrations. Under such conditions longer shaking periods will be necessary to ensure complete ahsorption of the water by the glycol.
V O L U M E 2 2 , NO. 4, A P R I L 1 9 5 0 Table I .
in Ethylene Glycol a t 75' F. 7
4
2 1.3 1 0 1 2 0.5 1.5 1
+
Boiling Range, F. 300-400
Petroleum paint thinner l l i x e d hexanes
the glycol extraction method, it is necessary to correct for the increase in volume of the glycol which results from contact with the hydrocarbons. The approximate relative solubilities of various hydrocarbons are shown in Table I.
Relative Solubility Vol. % Solubility of Hydrocarbon
Hydrocarbon Benzene Toluene Xylenes (mixed) n-Hexane Iso-octane n-Decane Cyclohexane I-Pentene Petroleum paint thinner 15% benzene Petroleum paint thinner Alixed hexanes 30% benzene
+
557
PRECAUTIONS
Approximate Composition
%
paraffin? 13 77
110-160
%
Both the Fischer reagent and the dried ethylene glycol are hygroscopic and therefore must be prevented from coming into contact with moist air. The air used in pressuring the various solution reservoirs for charging the burets must be dried by passing through drying tubes. The titration vessel as well as all the vents from the burets must also be protected in the same way. I t is essential to keep the tubing connecting the saniplr cont,ainer holding the glycol-nater extract as short as consistent with good operation and to purge it with the estract before a sample is taken into the sample buret. In the field, it is necessary to use extreme care to obtain truly representative samples and avoid contamination. Lines should be t'horoughly purged, and there should he no appreciable temperature drop in the line from the source to the bomb. This is important, because the solutility of water in hydrocarbons decreases rapidly with tlwreasing temperature, Petroleum fractions containing interfering compounds such as hydrogen sulfide, mercaptans, ketones, etc., cannot a t prrsent be analyzed for ivater by this mpthod. Although the ethylene glycol does rJxtrart the xater, these cornpounds are likewise absorbed to sonip r2stent and consequrntly intmluce errors in the determinations.
~
%
naphthenes 70 19
aromatic17 4
Khen liquefied petroleum gases are sampled, steel sample bombs are substituted for the glass containers, and the samples :Ire taken without venting. To ensure complete extraction of the \vater from these stocks, the shaking period is increased to atlout 25 minutes. When the glycol is removed from the bomb after shaking, it usually is necessary to allow the glycol to weathe], in the glycol (sample) buret-that is, to allow entrained and dissolved hydrocarbons to distill out of the solution. With the esrrption of these three differences, the method of analysis is the wine as t.he procedure followed with higher boiling stocks. The solubility of glycol in hydrocarbons is very Ion-; conversely, the solubility of nonaromatic hydrocarbons in glycol is also low. Benzene and toluene are! however, appreciably soluble in glycol, $0 that in determining the nater content of these compounds by
EXPERIMENT4 L
Tables 11, 111, and I V show the extraction efficiericy of ethylene glycol when used a ith various hydrocarbons. . _ The procedure followed in obtaining the data given in Table I1 Table 11. Efficiency of Eth:-lene Glycol A s Water was as follows: The hydrocarbons were dried by agitation a i t h Absorbent dry glycol, weighed quantities of water were added, and the Petrolerirn samples were well shaken. Finally, the water contents were dePaint Hydrocarbon Benzene Decane Thinner termined by the modified method. The extraction efficiencies of TTeight of dry sample. graills G88 1862 2348 the three samples were 96.6, 93.8, and 94.7%, respectively. Weight of water added, gram 0.2646 0.5224 0.2364 Glycol-liydrocarbon ratio, m1./100 grams 18 7.5 I n order to determine the effect of repeated extractions on the 8.8 Shaking time, min. 15 15 15 same sample, benzene saturated with water was subjeeted to Weight of water recovered. gram 0.2X 0.490 0,224 7c of water found as shown by F'ischer three successive extractions Kith dry glycol. If we consider the reagent titration of glycol 96.6 93.8 94.7 sum of the three extractions as being the total n-ater content of the benzene, then 99% of the water was ahsorhed i n the first extraction. These results are given in Table 111. Tahle 111. Effect of Repeated Contacts w-ith Ethylene Glycol on Water Content of Henzene Saturated at 70" F. On the same basis, Table I V shows the efficiency of extracting First extraction water from benzene and prltroleum paint thinner with water conGlycol-hydrorarbon ratio, 1111.,'lo0 grams lG.5 tents varying from 0.005 to 0.08%. In this series, the extraction Shaking time. min. 20 R water by first ahsorption 0.062 efficiency for a single treatment with glycol ranged from 92 to Second extraction 98%. The number of determinations was, however, insufficient to Glycol-hydrocarbon ratio, nl1./100 grams 9.0 20 Shaking time. min. establish a relation between the extraction efficiency and the 70mater by second absorption 0.00054 Third extraction glycol-hydrocarbon ratio or the water content, of the stock. Glycol-hydrocarbon ratio, nil. /IO0 grains 4.0 Shaking time. min. 15 From the foregoing data, it may be concluded that, employing % water by third ahsorption 0,00008 o n l y one e x t r a c t i o n , t h i s method can he used to determine the water content of Tahlr I\-. Efficiency of Ethylene Gl>-col as Water .Absorbent hydrocarbons with an accuracy Benzene, C.P. Petroleum Paint Thinner -~ of a t least 92%. SuperPartially -
~
~
~~
~~
~
~
~
~ .~
~
~~
~
First extraction Glycol-hydrocarbon ratio, d . / l O O grams Shaking min. 7% water time, by first extraction Second extraction Glycol-hydrocarbon ratio, m1./100 grams Shaking time, m n . ' by second extrac-
%,?;L
Total % water % of total water shown by first extraction
-~
. .-
~
Saturated a t 75' E.
Saturated saturated Saturated a t 70' F. a t 75' F. a t 75' F.
16.3 15 0.0644
15 10 0.06
14.7 12 0.074
10.5
...
14.8
11.3
10
12
9.0 15
... ... ...
0.002 0.062 !li
0.004 0.078 9 :
1d
0.021
0.0022 0.023
saturated a t 75O F. 5.3 15 0.0049
10.5 15 0,0525
11.2 15 0,0680
6.2 15 0.00014
16.5 15 0.0041
15.4 13
0.0050
98
CI 2 ~
Supersaturated a t 75' F.
0.0566 93
0,OOBX
0.0719
95.5
OTHER APPLICATIONS OF METHOD
The data given in Tables 11, 111, and IV are for hydrocarbons w h i c h a r e c l e a r a n d have low vapor pressures-i.e.i are stable liquids at. room temperature. However, t h e m e t h o d h a s a l s o been
558
ANALYTICAL CHEMISTRY
used for several years in the authors' laboratory with very satisfactory results in the following special applications: Determination of water in stocks of high vapor pressure such as propane and the butanes. Determination of water in colored stocks such as lubricating oils, transformer oils, etc., in which the color bodies are not solubla in the glycol. Studies of the water solubility-temperature relationship for hydrocarbons over the temperature range 60" to 180" F. There seems no reason to doubt that the upper temperature may not be further increased. SUMMARY
-4modified Karl Fischer method for determining the water content of hydrocarbons and petroleum fractions involves extraction of the water from the hydrocarbon by dry ethylene glycol and subsequent titration of the glycol with Fischer reagent. With one extraction, over 90% of the watc,i present in the hydrocarbon is absorbed by the glycol. Increased accuracy with stocks of low water content mav be obtained by concentration of the water from a large volume of hydrocarbon in a small volume of extract. The difficulty of titration in a two-phase liquid is eliminated. The method is applicable t o high vapor pressure stocks such as liquefied petroleum gases. Colored stocks, such as lubricating oils, transformer oils, etc., in which the color bodies are not soluble in glycol, may be analyzed for water without difficulty. This method may be used to determine the solubility of water in hydrocarbons and petroleum frartions at temperatures up to about 350" F.
Ackci and Frediani, ISD. Esc,. ( ' H E M . , ANAL. ED., 17, 793 (1945). Aepli and McCarter,Ibid.,1 7 , 3 1 6 (1945). Almy, Griffin, and Wilcox, I / , i d . , 12, 3 9 2 (1940). Am. SOC.Testing Materials, Conmiittee D-2, "Standards uf Petroleum Products and Lubricants," Philadelphia, 1948. Boeke. J., P h i l l i p s Tech. Rea., 9, S o . 1, 13 (1947). Fischer, Karl, Angew. Chcm., 48, 304 (1935). Gester, C . G., Cheni. Eng. Progress, 43, 117 (1947). Graefe, E., J . SOC.Chem. Ind., 25, 1035 (1906). Gremeko, B., S m o s t i T t k h n i k i , 6 , 43 (1938). Griswold and Kasch, Iiid. E i i g . C'hem., 34, 804 (1942). Groschuff. E., 2. Elektrochon.. 1 7 , 348 (1911). Hachmuth, K. H., WerterrL(;ria. 8, 55 (1931). Johansson, A , , Svensk Pappo'atidn,, 50, 11B, 124 ( 1 9 4 7 ) . Larsen, R. G., ISD. E x .
