Analysis of Halide Mixtures by Ion-Exchange Chromatography RICHARD C. DEGEISO',WILLIAM RIEMAN 111, and SIEGFRIED LINDENBAUM N. J.
School o f Chemistry, Rutgers University, N e w Brunswick,
The quantitative analysis of a mixture of chloride, bromide, and iodide has always been a difficult task, especially when the heavier halides predominate. The application of ion-exchange chromatography to the problem has yielded a procedure by which satisfactory results can be obtained even for a minor constituent of a halide mixture. The complete analysis requires only 3 hours.
THE
ion-exchange procedure previously recommended by this laboratory ( 3 ) for the separation of chloride and bromide is not satisfactory for the analysis of mixtures containing iodide because the iodide is removed from the column too slowly. By applying a more concentrated solution of sodium nitrate as eluant as soon as the chloride is removed from the column, the removal of iodide is greatly hastened. Further improvement is achieved by substituting Dowex 1-X10 (100-200 mesh) for Amberlite XE-67. This permits the use of a column only 7 cm. long instead of the 17-em. column previously used. Thus, smaller volumes of eluate and less time are required for the separation. Since these are both strong-base resins, the finer particle size of the Dowex 1 is probably responsible for its better performance in chromatographic separations
r
COLUMN A
electrode of low resistance was used with a salt bridge of 2.OM sodium nitrate. A slide-wire potentiometer reading to 0.1 mv. was used in these titrations, and nitrogen was bubbled through the solution during the titration. Iodide titrations were done with a platinum electrode, a Beckman saturated calomel electrode, and a Beckman p H meter, Model G. Reagent-grade sodium chloride was used without further purification. Potassium bromide, free from chloride, was prepared by the recrystallization and heating of reagent-grade potassium bromate (1). Reagent-grade potassium iodide was recrystallized. Eluant solutions of 0.50 and 2.OM sodium nitrate were prepared by weighing and diluting the reagent-grade compound. Silver nitrate, approximately O.O5iV, for the chloride titrations was standardized by titrating about 2.0 meq. of sodium chloride, accurately weighed and dissolved in TO ml. of 0.5031 sodium nitrate. A blank correction was applied for the chloride content of the sodium nitrate. The same solution of silver nitrate was used for the bromide titrations but was then standardized by the titration of about 2 meq. of potassium bromide dissolved in 70 ml. of 2.0M podium nitrate. In order to prevent the precipitation of the trace of chloride found in the reagent-grade sodium nitrate, 1.4 ml. of l . 0 X ammonia was added before the titration. The results of the two different titrations did not check exactly. For example, a solution of silver nitrate was 0.04883N by sodium chloride and 0.04860N by potassium bromide. The difference is probably due to the greater coprecipitation of silver nitrate by the silver bromide in the presence of 2.0M sodium nitrate. Ceric ammonium sulfate, approximately O.O5iV, for the iodide titrations was standardized by dissolving about 2.0 meq. of potassium iodide in 260 ml. of 2.OM sodium nitrate, adding 1.0 gram of sulfamic acid, acidifying with 50 ml. of 3 M sulfuric acid (added slowly with stirring), and titrating. The sulfamic acid was added to destroy the nitrite present in the nitrate, which would otherwise oxidize iodide ion. In all the potentiometric titrations, the end point was located by finding the volume a t which A2E/Av2 is zero. EXPERIMENTAL WORK
; 100
M
I n order to select the best conditions for the separation, several preliminary elutions were performed as previously described (3) but with variations in the kind of resin, dimensions of the column, flow rate, and concentration of eluant. The conditions selected involve the u8e of either of the columns described above, a flow rate of 1.0 em. per minute, the passage of 55 ml. (column A ) or 70 ml. (column B ) of 0.50M eluant, and continuation with 2.OM eluant. The change of eluant is effected without permitting air to enter the column. An elution graph obtained under these conditions is shown in Figure 1. The use of an initial eluant much more concentrated than 0.50M fails to separate chloride and bromide with the columns used. Elution with sodium nitrate above 2.OM after the removal of chloride from the column causes a more rapid removal of bromide and iodide from the column. Although perfect separations of bromide and iodide are obtained under these conditions, the concentrated eluant causes considerable shrinkingof the resin. Then there is danger of cracking the glass tube when the resin swells on subsequent treatment with 0.50M nitrate. For these reasons, 0.50 and 2.0M sodium nitrate were selected as eluants. Analysis of Halide Mixtures. Samples of halide mixtures, containing not more than 2.6rneq. of any one halide, were weighed and dissolved in about 2 ml. of 0.50M sodium nitrate. This solution was poured carefully upon the column, p,reviously equilibrated with 0.5031 sodium nitrate, and drained within a few millimeters of the upper level of the resin. .4 few milliliters of 0.50M sodium nitrate were used to rinse the sample into the column. The stopcock beneath the column was opened to drain the liquid almost to the level of the resin. Then 0.50M sodium nitrate was passed through the column a t a flow rate of 1.0 em. per minute until a total of 55 ml (column A ) or 70 ml. (column B )
150
200
250
3CO
350
VOLUME OF ELUATE, ML.
Figure 1. Elution Graph
Greater accuracy in the titration of the isolated halides is obtained by using the potentiometric technique instead of chromate ion as indicator. The use of wetting agents in the eluants is not recommended, since they were found to cause a slight decrease in the accuracy of the titrations. APPARATUS AND REAGENTS
Column A , 6.7 em. X 3.4 sq. cm., was prepared as previously described ( 3 ) except that Dowex 1-X10 (100-200 mesh) was used, and 0.50M sodium nitrate was used for the removal of the chloride originally present in the resin. Column B, 7.4 cm. X 3.7 sq. em., was prepared similarly. Siphon pipets (S), delivering 3.54 and 15.75 ml., were used in the preliminary work. Bromide titrations and most of the chloride titrations were done with a silver electrode, a glass reference electrode, and a Beckman pH meter, Model G. The silver electrode was prepared by electroplating silver on a Beckman platinum electrode from a bath of potassium cyanoargentate. For the titration of quantities of chloride under 0.2 millimole, a saturated calomel 1 Present address, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Mass.
1840
1842
V O L U M E 2 6 , N O . 11, N O V E M B E R 1 9 5 4 Table I.
Analysis of Approximately Equimolar Mixtures of Three Halides
h1ixture No. 1 2 3 4
iYaC1, Mmoles. Taken Found 2.223 2.241 2.480 2.472 2.164 2.166 2.393 2.387
KBr, Mmoles. Taken Found 2.184 2.177 2.205 2.207 2.478 2.473 2.471 2.462
XI, Mmoles. Taken Found 1.831 1.835 1.950 1.946 1.984 1.981 2.066 2.067
A or 70 ml. for column B, was also collected in a graduate. The third fraction of 260 or 330 ml. was similarly collected. Finally, 100 ml. of 0.50114 sodium nitrate was passed through the column to prepare it for the next separation. This effluent was rejected. As indicated in Figure 1, the three fractions of effluent contain the isolated chloride, bromide, and iodide, respectively. These fractions were titrated with the same techniques as used in the standardizations. RESULTS
Then the 2.OM Podium nitrate was passed through the column a t the same rate. The change in eluant is indicated by the dotted line in Figure 1. The reservoirs of eluant solutions were Mariotte flasks ( d ) , so that constant heads and hence constant flow rates could be easily maintained. The second fraction of effluent, 55 ml. for column
of effluent was collected in a graduated cylinder.
Table 11. Determination of One Halide in the Presence of Large Amounts of the Other Halides Series A = , NaC1, Micromoles Taken Found
Series Ba, KBr, Micromoles Taken Found
Seriea CC, K I , Micromoles Taken Found
..
9 9 5 4 KBr and KI, 2.3 millimoles of each. NsCl and KI, 2.3 millimoles of each. NaC1 a n d KBr, 2.3 millimoles of each. 10
C
LITERATURE CITED
(1) Kolthoff, I. M., and Stenger, 5’. A , , “Volumetric Analysis,” Voi. 2 , p. 252, New York, Interscience Publishers, 1947. (2) Kiederl, J. B., and Niederl, V., “Organic Quantitative Microanalysis,” 2nd ed., p. 114, X e w York, John Wiley & Sons, 1942 (3) Rieman, W., and Lindenbaum, S.,ANAL.CHEM.,24, 1199 (1952).
10
a
Four mixtures of approiimately equivalent, weighed amounts of the three halides were analyzed by this procedure. The results, Table I, indicate that the average error in the determination of any one halide is k O . O 9 % of the total halide. Three series of determinations were run in which the samples consisted of 2.3 millimoles each of two halides, while the amount of the third halide was decreased throughout the series. These results are listed in Table 11. The average error, bithout regard to sign, in the determination of the trace halide, was 0.0207, of the total halide content of the mixture.
RECEIVED for review October 6, 1953. rlccei)ted January 26, 1954. Taken from a thesis submitted by R. C. DeGeiso t o the faculty of Rutgers University in partial fulfillment of the rerluireinents for the degree of bachelor of science with honors.
Chromatographic Fractionation of Total Crude Shale Oil CLARENCE KARR,
JR.,
W. D. W E A T H E R F O R D , JR., T. R. KENDRICK Ill’, and R. G. C A P E L L
Mellon Institute, Pittsburgh, Pa.
Fractionation of total crude shale oil by elution chromatography on activated alumina or activated bauxite gives 40 to 45 weight %of a colorless, color-stable, pleasant-smelling oil which is free of nitrogen compounds and substantially reduced in sulfur content. About 4 weight % can be recovered as a yellow, color-stable, pleasant-smelling oil which is free of nitrogen compounds, and essentially all the remaining constituents can be recovered from the adsorbent as a brown-black semisolid enriched in nitrogen and sulfur compounds.
S
HALE oil production has existed on a commercial scale for
some time in certain countries that have insufficient or depleted petroleum reserves. Production of oil from shale is contemplated for the United States, when the increasing demand for fuels and petrochemicals rises appreciably above the petroleum supply. The oil shales in the known reserves of this country could supply a t least 224 billion barrels of shale oil (8). However, shale oil presents an entirely new set of analytical and refinery problems because of the very high proportions of unsaturates (about 20%)and of nitrogen compounds (about 40%) ( 3 ) . Shale oil naphthas (up t o 200” C. a t 760 mm.) may contain from 0.8 to 1.1% sulfur and 0.5 to 0.9% nitrogen. Although these naphthas are only light yellow immediately after distillation, they turn black within a few days ( 1 ) . The poor color stability and unpleasant odor of shale oil distillates are believed to be caused by the presence of nitrogen compounds (10). Very little separation with respect to sulfur and nitrogen is 1
Present address, Callery Chemical Co , Callery, Pa.
achieved by distilling total ciude shale oil as exemplified by the data of Stevens, Dinneen, and Ball (11) in Table I. These data also illustrate that nearly half of the crude shale oil cannot he distilled by the usual distillation procedures. Hence, it is logical to seek a technique which might answer the major prohlems peculiar to shale oil. The present work was undertaken to dptermine whether 01 not elution chromatography could aid 111 the development of satisfactory assay methods for crude shale oils.
Table I.
Distillation of Colorado Total Crude Shale Oil Obtained from N-T-U Retort [Stevens, Dinneen, and Ball ( 1 1 ) ] B P. Distillation Range, Pressure, Weight, ‘(2. Mm H g %
Sulfur, Nitrogen,
%
%
‘Totnl c r i i d e s h a l ~
Residuum
...
...
48.0
. 0.70
WORK O F PREVIOUS INVESTIGATORS
Apparently no previous work has been done o n chroniatographic fractionation of total crude shale oil. Some chromatography of shale oil distillates has been carried out, but these distillates and the total shale oil are very dissimilar. Conventional total crude shale oil is a heavy, thixotropic, black, high-boiling liquid with a high pour point and a high asphaltic content.
