Table II.
throughout t h e time inteir-a1 studied (Figure 4 ) . T e n minutes TI as chosen as t h e time for standing so t h a t samples would not overlap if several were being run a t 1-minute intervals. Interference of Other Chlorinated Compounds. T h e following chlorinated compounds mere checked for possible interference in t h e method. T h e compounds, not purified before use, were added t o carbon tetiachloride in concentrations of 1000 p.p.m.
Precision of Method
CHCls Found,
Std. Dev., %c 0.00255, Standard 0.0025 0.0025 0.0001-L 0.0027 0.020‘ Stantiard 0 020 0 019 0 023 0 018 0 019 0 023 0 020 0 021 0 020 0 0OlT 0.060( Standard 0 061 0 060 0 059 0 058 0 062 0 0015
5%
Methylene chloride Ethyl chloride 1,l-Dichloroethane 1,2-Dichloroethane 1,1,l-Trichloroethane 1,1,2-Trichloroethane
The concentration of pyridine directly influences the intensity of the color produced. With this in mind, the concentration of pyridine that was to be used in the procedure was chosen so that concentrations of chloroform varying from 0.00 to 0.097, would have an absorbance varying from 0.0 to about 90. Color Stability. One sample was prepared using t h e 0.02Y0 standard. T h e regular procedure was followed u p t o t h e dilution with methanol. After dilution t h e absorption was measured a t regular intervals from 2 t o 20 minutes. T h e intensity of t h e color decreased in a uniform manner
1,1,1,2-Tetra-
chloroethane 1,1,2,2-Tetrachloroethane Pentachloroethane Hexachloroethane 1,l-Dichloroethl lmr Perchloroethylene
The experiments showed that 1,1,1,2and 1,1,2,2-tetrachloroethane,pentachloroethane, and 1,l-dichloroethylene reacted in the same manner as chloroform. 90 attempt was made to measure the intensity of the deep red color produced with these compounds. However, they should not be present in significant amounts in carbon tetrachloride. Interference of Carbon Disulfide. Carbon disulfide, if present in a n excess of about 20 p . p . n i , also interferes. However, t h e presence of this compound is readily apparent, as i t causes a n instant yelloning of t h e mixture before i t is placed into t h e boiling water, after \vhich it turns t o a very deep red. Reagent Purity. A blank qhould be run on all new lots of pyiidine and methanol. If a n y color or turbidity
appears, the reagents are not satisfactory a n d must be redistilled. If a supply of carbon tetrachloride cannot be found t h a t is lorn in chloroform, t h e carbon tetrachloride must be redistilled several times on a high efficiency fractionating column, in each case taking t h e heart cut. PRECISION
The precision of the method u a s found b y analyzing three of the standards several times. Standard deviation was calculated for each series. The results are given in Table 11. ACKNOWLEDGMENT
The author wishes to thank J. H. Brumbaugh, C. L. Dunning, and D . E. Stallard of this laboratory for their valuable criticism and advice, and in particular, R. E. Knapp for the infrared analyses of some samples. LITERATURE CITED
Adanis. IT. L.. J . Phartnacol. 74. 11-17 (1942). ’ Brain, F. H., dnalyst 74, 555-9 (1949). Cole, W. H., J . Bid. Chem. 71, 173 (1926). Daroea. R. R.. Pollard. A. G.. J . SOC. Crhzm,’.I n d . 60. 218-22 (1941) Freidman, M. R’I., Calderone,’ F. -I., J. Lab. Clin. M e d . 19, 1332 (1934). Fuiiwara, K., Sztz. -Vat. Ges. Rostock 6, 33-43 (1916). Gettler, -4. O., Blume, €I., Arch. Pathol. 11, 554-60 (1931). ~
RECEIVED for review Kovember 5, 1956. Accepted February 23, 1957. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1957.
Removal of Elemental Sulfur from Hydrocarbon Fractions MAX BLUMER Shell Developmenf
Co., Explorafion
and Production Research Division, Houston, Tex.
b The presence of elemental sulfur interferes seriously with the analysis of hydrocarbon mixtures obtained from sedimentary rocks or petroleum. The method described is capable of quantitative removal of sulfur from such mixtures by simple percolation through a column of active copper powder.
E
sulfur is often present in sedimentary rocks. I n the extraction procedures commonly used for the isolation of hydrocarbons from such LEMEKTAL
samples (8, 11) the sulfur i. alco recovered, and it often exceeds the small amounts of hydrocarbons. The sulfur interferes with the analysis of the hydr+ carbons by absorption- and mass spectroscopy and leads to erroneous results in molecular-weight determinations. Especially objectionable is the presence of sulfur in samples that are to be distilled because it reacts a t e l e n t e d temperatures with hydrocarbons to form hydrogen sulfide and dehydrogenated products.
To eliminate these interferences n method was developed for the removal of elemental sulfur from hydrocarbon fractions. It seemed most promising to base such a method on the rapid and quantitative reaction between elemental sulfur and certain heavy metals like silver, copper (6, 7 ) . or mercury ( 2 , 5). Such a procedure would have the advantage of great rapidity and simplicity over methods which make use of the extraction of sulfur from a n organic into a n aqueous phase containing reVOL. 29, NO. 7, JULY 1957
* 1039
agents like cyanides ( S ) , hydroxides (9), sulfides (6),and sulfites (10). Copper in a finely divided state reacts uith elemental sulfur even a t room temperature. and it is prepared easily as a spongy precipitate nith a very large surface. Precipitated silver on the other hand can be made to react with sulfur only a t elevated temperatures and has a tendency to precipitate in a dense form n hich packs tightly and obstructs the flon of liquids through H column.
REAGENTS A N D APPARATUS
CUPRIC SULFATE, crystal, reagent grade. ZISC &TAL, powder, reagent grade. HYDROCHLORIC ACID, reagent grade, 2 _-A- . WETTIXG AGEST,0.5% solution (aerosol may be used). ACETONE,reagent grade, redistilled. BENZEXE,reagent grade, redistilled. ~-PEKTANE, reagent grade, redistilled. Preparation of Copper Powder. Dissolve 45 grams of copper sulfate crystals in 500 ml. of cold, distilled water containing 20 ml. of 2-1- hydrochloric acid. Prepare a thick slurry of 15 grams of pure zinc ponder in 25 mi. of rvater containing a sinal1 amount of rvetting agent, and slow-l~-add to this the copper sulfate solution n hile stirring rapidly. Continue to stir until the copper which precipitates turns a red to redbroxn color. Decant the supernatant liquid, allowing some of the finer particles of precipitate to be removed. R a s h the copper repeatedly with distilled water, transfer it into a plastic ice-cube tray, cover i t with water, and freeze. Preparation of Column. For samples containing less than 150 mg. of elemental sulfur use a column with a bed volume of about 10 ml. of copper powder. Kse a smaller or larger column depending on the amount of sulfur to be removed. The shape of the column is not critical; the ratio of length to the square of the diameter of the column used for the work reported here was 16 cm.-I Lubricate the stopcock with a soh ent-insoluble lubricant-e.g., concentrated sugar-dextrin solution-and support the copper bed by a glass-wool Plug. Melt enough ice cubes to pack the column. Wash the copper into the column. Replace the 11-ater by mashing with distilled acetone, and replace the acetone with benzene or pentane, depending on which sol\ ent is required to elute the sample.
lect the eluate and remove the solvent by distillation or evaporation with a rotating evaporator.
DISCUSSION
Dissolve the sample in n-pentane; use benzene if large amounts of crystallized sulfur are present. Add the solution to the column, regulating the f l o ~ rate t o 1 t o 2 drops per second. Wash the walls of the column with a small amount of solvent, and elute the sample Fvith 40 ml. of the same solvent. Col1040
ANALYTICAL CHEMISTRY
The finely divided precipitated copper powder tends to be inactivated rapidly by oxidation if stored a t room temperature longer than a few hours. For this reason a column should never be allon-ed to run dry. If stored under ice ac: described above, the copper retains its activity for a t least 6 months. On an active, well-packed column the absorption of the sulfur takes place in an even zone with a sharp lower boundary. A bed ~ o l u m eof 10 ml. will retain about 200 to 300 mg. of sulfur; the column should be repacked when two thirds of its volume has been converted into th? black copper sulfide. Attempts to remove sulfur from very complex mixtures, like whole extracts that have not been subjected to chromatographic separations, lead to difficulties. The sulfur removal is incomplete and some of the more polar components of the mixture are strongly retained on the copper bed. The method should be used only after distillation or chromatography on alumina or silica gel on fractions containing saturated and the more simple aromatic hydrocarbons up to three ring numbers. Hunt and Jamieson ( 8 ) have recently described a method Tyhich involves stirring of the sample over a pool of mercury. It is useful for the treatment of large samples, while the method using active copper is universally applicable, is especially suited for the rapid treatment of very small samples, and eliniinates the hazards which are involved in handling and regenerating mercury. S o experimental data are available on the removal of organic sulfur coni-
EXPERIMENTAL RESULTS
To evaluate the efficiency of sulfur removal, solutions containing 2, 20, and 100 mg. of elemental sulfur and 10 ml. of benzene were passed through bhe copper column as outlined above. The amount of sulfur left in the solution after passage through the bed was determined LJ- polarography (j),and in each instance, was found to be less than the limit' of t'he detection of the method (0.01 mg.). Samples of eleniental sulfur, 20 mg. each, Lvere dissolved in a saturate fraction of a petroleum distillate boiling between 325" and 400" C. Ten milliliters of benzene was added to each mixture and the solutions were passed through t'he column. The benzene in the eluate was removed by distillation, and the sulfur content' in the residue was determined. The same procedure n-as repeated, substituting a ~vliolepetroleum distillate boiliiig between 325" and 400" C. The residual sulfur concentration was below the limit, of detection of the polarographic method in all samples except one (see Table I ) , Chromatographic fractions of extracts from sedimeiits which contain elemental sulfur were carried t'hrough the sulfurremoval procedure. The residual sulfur in the eluates (saturated hydrocarbons containing a total of about 10% of nioiio-, di-, and tricyclic aromatics) \vas determined by ultraviolet spectroscopy. The very intense ultraviolet absorption ( 1 ) of sulfur can be used as a basis for its determination, with a sensitivity of O.OOO:! mg. per nil. I n no instance
Table
I.
Removal of Sulfur from Petroleum Fractions
Fraction Saturates boiling between 325" and 400' C. Total distillate boiling between 325" and 400' C. Table
PROCEDURE
could residual sulfur be detected (see Table 11).
Fraction
II.
S Added,
17
20 20 20 20 20 20
Residual S in Eluate,
Mg.
llg. 86
860 17 86 860
Mg. 50.01 50.01
