INDUSTRIAL AND ENGINEERIKG CHEMISTRY
86
If Formula 3 is substituted into 1 and the resulting eauation into the original inverton formulas, and the resulting equations are simplified, Formulas 4 and 5 are obtained: I
log1 = 1.0667 log
F
+ 1.1690
_
(4)
for values of Z up to 7.50 log I
=
F
0.8299 B- - 0.4490
(5)
for values of I greater than 7.50 Formulas 4 and 5 are easily represented by nomograms, which were constructed by the usual method (Figures 10 and 11). The inverton values are read by aligning the point representing initial polarization with that representing fall in polarization and noting the point a t which the line crosses the inverton scale. ACKNOWLEDGMENT The authors wish to thank Charles N. Frey for his aid and interest in this work.
Vol. 7, No. 2
LITERATURE CITED (1) Brown, A. J., J . Chem. Soc., 81,373-88 (1902). (2) Clark, W. M., "Determination of Hydrogen Ions," 2nd ed., Baltimore, Williams & Wilkins Co., 1922. Fassnacht, H. H., Dissertation, Columbia University, 1930. Gore, H. C., IND. E m . CHEM.,Anal. Ed., 4, 367 (1932). Henri, V., Z. physik. Chem., 39, 194-216 (1901). Michaelis, L., and Menten, M. L., Biochem. Z . , 49, 333-69 (1913). Nelson, J. M., and Hitchcock, D. I., J . Am. Chem. Soc., 43, 2632-55 (1921). Nelson, J. M., and Vosburgh, W. C., Ibid., 39, 790-811 (1917). O'Sullivan, C.. and T o m w o n . F. W., J . Chem. Soc., 57. 834931 (1890). Vosburgh, W . C., J . Am. Chem. Soc., 43, 1693-1705 (1921). Weidenhapen. R.. Chem.-Zta.. 58. 185-7 11934). WillstLtter, R., Graser, J., ahd K u h n , R., 2. physiol. Chem., 123, 1-78 (1922). Willstiitter, R., and K u h n , R., Be?., 56,509-12 (1923). RECEIVED October 8, 1934. Presented before the Division of Agricultural and Food Chemistry a t the 88th Meeting of thc American Chemical Society, Cleveland, Ohio, September 10 t o 14, 1934.
Determination of Mercaptans in Hydrocarbon Solvents An Improvement of the Silver Nitrate Method WILLIAM M. MALISOFF'AND CLAUDEE. ANDING,JR., The Atlantic Refining Co., Philadelphia, Pa.
A
PROCEDURE has been described by Borgstrom and Reid (1) for determining mercaptans, involving the formation of silver mercaptide by excess silver nitrate
15 mm. and melting points of 41" to 43" C., respectively. The inorganic reagents were Baker's c. P. analyzed.
PROCEDURE. The tests are performed in glass-stoppered Erlenmeyer flasks. To known (weighed) amounts of mercaptan solutions kept in the dark for as short a period as possible, add 5 to 10 cc. of methanol and an excess of standard 0.005 N silver nitrate. Shake well and add 2 cc. of standard ferric alum indicator. Titrate with 0.005 N ammonium thiocyanate to a very faint pink. Then add a small excess of silver nitrate solution and titrate back again with thiocyanate until the pink appears. The final result is taken as the end point. Constant shaking is necessary throughout, and care must be taken not t o confuse the IN NAPHTHA faint color of the end point with the slight tint due to the presence TABLEI. ANALYSISOF n-hdYL MERCAPTAN of ferric alum. If in doubt, repeat the treatment with excess of FOR MERCAPTAN SULFUR silver nitrate and titration with thiocyanate. MERCAPTAN SULFURFOUND Stock ferric alum solution is made up of 40 grams of ferric Borgetrom-Reid Modified CONCBNTRATION methoda methodb alum and 20 cc. of 6 N nitric acid per 100 cc. It is boiled to ( CALOD.) remove any free nitrogen oxides and then diluted with 3 parts of % % % water to 1 of stock to make up the actual standard indicator. 0.158-0.166 0.196-0.199 0.162
which is titrated back with ammonium thiocyanate, using ferric alum as an indicator. This analog of a known method of chloride determination revealed some difficulties in use, as reported by Malisoff and Marks (3) and in private communications (2). An example of the oscillation in results when the method is applied literally is given in Table I.
0.316 0.738 b
0.314-0.324 0.730-0.750
0.315-0.399 0.664-0.762
Range of from 4 to 6 analyses (each analysis Two or more analyses.
=
2 titrations).
At the higher mercaptan concentrations the averages seem to line up better, but one must have more than two analyses per sample and even then may be in doubt. An effort has been made to set up a series of safeguards and a sharper definition of conditions to insure a better degree of reproducibility.
EXPERIMENTAL MATERIALS.The mercaptans and solvents have been described by Malisoff and Marks ( 3 ) . Besides these, phenyl and p-tolyl mercaptans were obtained from the Eastman Kodak Company and had boiling points of 70" to 71" C. a t 1 Present address, Department of Physiological Chemistry, University of Pennsylvania, Philadelphia, Pa.
Using the procedure as outlined, analytical data have been obtained as shown in Table 11. PURITY OF MERCAPTANS. The purity and the stability of the mercaptans were tested in hydrocarbon solution under varying conditions. Amyl mercaptan was the purest and most reliable of those studied. The principal impurities are disulfides which themselves do not affect the analytical method, Mercaptans, especially the aromatic ones, change readily to disulfides by oxidation. The effect is marked in sunlight, and is sufficient to account for discrepancies in analyses carried on before and after exposure to ordinary daylight, The effect also appears to be greater in naphtha solutions than in benzene. Table I11 indicates the effect of exposure to direct ordinary daylight in a southeast window, It is apparent that within a month it is possible to miss all of certain mercaptans in a hydrocarbon solution containing originally about 0.3 per cent of mercaptan sulfur.
March 15, 1935
ANALYTICAL EDITION
TABLE 11. DETERMINATIOS O F MERCAPTAN SULFUR MODIFIEDMETHOD
MEROAPTAX n-Amyl
MERCAPTAN SULFUR Deviation of check determinaPresent Found tions (calcd.)
SOLVENT Naphtha Naphtha Naphtha Naphtha Amylene Heptane
+ I
Isoamyl n-Butyl Isobutyl n-Propyl n-Heptyl Benzyl Phenyl p-Tolyl 0.013 per b 0.011per 0.020per
(I
BY
%
%
%
0.748 0.322 0.162 0.063 0.301
0.733 0.319 0.164 0.063 0 302
11.6 11.8 12.4 10.8 10.5
0,324 Octane 0.285 Benzene 0.164 Benzene 0.337 Naphtha 0.070 Naphtha 0.325 Naphtha 0.309 Naphtha 0.060 Naphtha 0.311 Naphtha 0.060 Naphtha 0.320 Naphtha 0.063 Naphtha 0.347 Naphtha 0.063 Naphtha 0.302 Benzene 0.356 Naphtha Bensene 0.318 0.329 Naphtha Benzene 0.321 cent of sulfur Sound to be R2Sz. cent sulfur found to be RzSz. cent sulfur found to be RzSs,
0.319
10.4
0,280 0.161 0.328 0,067 0.301a 0.306 0.060 0.308 0.059 0.318
*2.0 11,o 10.8 10.9 h1.3 f1.6 f0.2 11.6 11.4 *l.O 11.5 12.2 11.7 11.0 f5.0
0.064
0.350 0,064 0.310 0.3126 0,290 0.275C 0.283
*o. 1
15.3 f3.0
T A B L11 ~1. EFFECTOF LIGHTEXPOSURE ON MERCAPTAKS [Solutions exposed in sealed 120-cc. (4-02.) cylindrical glass bottles] MERCAPTAN SULFUR Final Changed SOLVENT EXPOSURE^ Original
RSH
n-Amyl
Isoamyl n-Butyl Isobutyl n-Propyl n-Heptyl Benzyl
Benzene
~~~~~~] Naphtha Naphtha SOY Naphtha 208 Amylene Naphtha Naphtha Naphtha Naphtha Naphtha Naphtha Naphtha Naphtha Naphtha Benzene
~~~~~~)
1
Days
%
%
%
27 27 17 5
0.282
0.009 0.015
l7 17
0.061 0.335 0.067 0.29s 0 060 0.300 0.060 0.310 0.059 0.064 0.310 0.319 0.064 0.287 0.298 0.304
0.273 0.297 0.274 0.005 0,002 0.304 0.005 0.181 0.007 0.268 0.003 0.162 0.003 0.004 0.307 0.228 0.000 0.169 0,220
0.282 0.276
0.225
14
27 14 17 14 27 14 14 26 26 37 27 17
Naphtha Benzene Benzene Naphtha 24 Benzene 27 p-Tolyl Naphtha 27 Exposed at relatively the same time. Phenyl
0.312 0,330 0.066
0.000
0.000
0.056
0.061 0.059 0.031 0.062 0.117 0.053 0.032 0.057 0.148 0.056
EMULSION BREAKING.The precipitation of silver mercaptides favors emulsion formation. This is counteracted by working with the low dilutions recommended and by the addition of methanol prior to that of silver nitrate. In some cases it may be wise to increase the amount of methanol. MASKINGOF ENDPOINT. Colored mercaptides or the oil itself may occasionally introduce difficulty in reading the end point. In such cases an actual physical separation of the oil is made and the mercaptide precipitate is filtered off and washed, The original solution and the wash liquor are titrated. TABLEIV. EFFECTOF STORAGE OF NAPHTHA SOLUT~ONS OF MERCAPTANS IN LABORATORY CABINET KIND
Table IV indicates that prolonged storage in a laboratory cabingt with glass doors and no direct sunlight results in serious changes and explains the provision for dark storage for the shortest possible time. CONCENTRATION OF MERCAPTANS. When the concentration of mercaptan sulfur is 0.150 per cent or greater the weighed sample is diluted to a definite volume and an aliquot portion used for analysis. A 5- or 10-cc. portion of a mercaptan sulfur concentration of about 0.075 per cent is convenient, since in this range the quantity of silver mercaptide precipitated is moderate and the volume of solution in the 250-cc. Erlenmeyer flask is a convenient one. I ~ L U E N T SMethanol . is preferred as a diluent, since it is soluble in both water and oil and therefore improves mutual interpenetration and because it is readily available in a pure state.
I
TIME
-MERCAPTAN Original
Months 2
Phenyl n-Butyl n-Amyl
10 14 1
9
6 a 0.055 per cent sulfur as RzSz. b 0.029 per cent sulfur as RrSr. Dark storage.
Final
SULFUR-Changed
%
?.&-
0.368
0.295a 0.185 0.241 0.3296 0.181 0.261C
0.368 0.311 0,366 0.366 0.275
%
,I
0.073 0.183 0.070 0.037 0.185 0.014
LIGHTFOR TITRATION. Precision is gained by working in bright daylight. Reproduction may be poor on gray days unless a daylight lamp is used. The standardization of the ferric alum indicator is advantageous. DISCUSSION The principal changes in the Borgstrom and Reid procedure are : inclusion of precautions concerning the storage of mercaptan samples, adoption of a uniform dilution method, employment of more dilute standard solutions, standardization of the ferric alum indicator,. provisions for minimizing emulsions, provision for minimizing masking of color, and reduction of the time of operation (direct titration, without shaking period). The erratic results when the above factors are not considered are thus eliminated. TABLEV MERCAPTAN SULFUR MERCAPTANCalculated Found
%
0.060
0.003 0.091 0.064 0.118 0.078 0.304 0.057 0.275
87
a
b
p-Tolyl 0.1895 Phenyl 0.2104 Average of 3 analyses. Average of 2 analyses.
RzSz
TOTALSULFUR FOUND
%
%
%
0.118b o.iz5b
0.077 0.094
0.195 0.219
Working with this procedure, using known solutions of aliphatic mercaptans, it is possible to account for 97.3 to 102.7 per cent of the mercaptan present with a maximum deviation of less than 2.4 per cent. In the case of the aromatic mercaptans only 83.6 to 91.2 per cent was determined because part of the mercaptans had changed to disulfides. An effort made to check this by slow reduction with zinc and acetic acid, followed by titration of the resulting mercaptan, led to a satisfactory sulfur balance as shown in Table V. TABLEVI. DUPLICATE ANALYSES OF COMMERCIAL NAPHTHAS KIND Straight run Cracked distillate
Vapor phase cracked
MERCAPTAN SULFUR
%
%
0.004 0.008 0.008 0.001
0.008
0.004
0.007 0.001
0.008
0.008
0.017 0.036 0.052 0.017 0.031
0.016 0.039 0.054 0.018 0.035
The results are a little high, probably on account of the method for determining disulfides. This was proved by
88
INDUSTRIAL AND ENGINEERING CHEMISTRY
extracting the mercaptans with caustic-methanol and redetermining them in the extract. The results were for p tolyl mercaptan, 0.118 per cent on both samples, and for phenyl 0*125per cent and per cent in the extract. Experiences with commercial naphthas are appended (Table VI). These show the breakdown of sensitivity a t 0.001 per cent of mercaptan sulfur a t very low concentrations and a
Vol. 7, No. 2
variation of 0.004 per cent a t a concentration of 0.035 per cent. LITERATURE CITED (1) Borgstrom and Reid, ENe. CHEM.,Anal. Ed,, 1, 186-7 (1929). (2) Duffey, private communication.
(3) Malisoff and Marks, IND.ENQ.CHEM., 23, 1114 (1931). RECEIVED December 19, 1934.
Determination of Gas, Coke, and By-Products of Coal Evaluation of Laboratory Assay Tests W. A. SELVIG AND W. H. ODE, Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa. Two small-scale, laboratory, high-temperature assay tests and one low-temperature assay test f o r determination of yields of gas, coke, and by-products of coal have been applied to 20 to 30 coals. Check limits have been established for duplicate determinations on the same coal by the same laboratory. Yields of gas, coke, and by-products by the laboratory tesls have been correlated with yields obtained by the BM-AGA carbonization test. The factors for converting the yields obtained by the small-scale laboratory tests into those obtained by the BM-AGA carbonization test vary appreciably with different coals.
progressively up to 900" C. in a gas-fired combustion furnace. A transparent quartz tube was substituted for the glass tube specified, because glass tubes often failed a t the carbonization temperature. After charging, a well-fitting Pyrex-glass tube, 95 mm. in length, is inserted into the open end of the quartz tube. The inner glass tube collects that portion of the tar and combined ammonia that does not pass into the recovery train. When the test is completed, the quartz tube with its contents is weighed. The inner glass tube is removed, boiled in water to dissolve combined ammonia, immersed and scrubbed in acetone t o remove tar, and ignited. The open end of the quartz tube is ignited t o burn off any tar that may have collected. The glass tube is replaced and the quartz tube with its contents is weighed. The decrease in weight represents the tar and combined ammonia present in the distillation tube and is added to that recovered in the tar filter.
When the published method was used tar yields were low, because of excessive cracking of the tar in the end of the quartz tube. At the suggestion of the Central Laboratory of N CONNECTION with a survey of gas-, coke-, and by- the Illinois Steel Company, - - Joliet, Ill., the temperature of the t a r - e n d of t h e product-making properties of American coals being made quartz tube, which a t the Pittsburgh Experiment Station of the United projects out of the States Bureau of Mines (g, S), the following small-scale labofurnace, was lowratory assay tests have been applied to 20 to 30 coals (Table ered by means of I) : United States Steel Corporation dry-distillation test (8), an asbestos shield Fuel Research Board (British) high-temperature assay (6), provided with a and Fischer low-temperature assay ( 5 ) . The bureau studied hole to fit snugly the duplicability of the tests and their correlation with the around the distilBureau of Mines-American Gas Association (BM-AGA) lation tube a t the test (S),in which charges of 36 to 45 kg. (80 to 100 pounds) of outer end of the coal are carbonized in a cylindrical retort 32.5 em. (13 inches) furnace. With in diameter. this modification, A correlation of the yields of gas, coke, and by-products as tar yields were obobtained by these various methods should permit evaluation tained which were of these small-scale laboratory tests for predicting the probable yields from a given coal in commercial carbonization FIGURE 1. TIME-TEMPERATURE CURVE more comparable FOR FISHERLOW-TEMPERATURE TEST to thoseobtainedin practice. An advantage of this correlation is that the BMcoke-oven practice. AGA carbonization tests were conducted under closely conThe freezing method for determination of light oil was trolled and comparable conditions and not under varying conditions, as would occur in different commercial gas and used in this investigation. coking plants. FUELRESEARCHBOARDTEST UNITEDSTATESSTEELCORPORATION TEST I n the Fuel Research Board test the coal is heated in an The procedure used was that published by the Chemists' electric furnace to 900" C. A 10-gram sample of air-dry Committee of the United States Steel Corporation (8), in coal, passing a No. 60 sieve, was used instead of the 20-gram which 20 grams of dry coal passing a No. 35 sieve are heated sample specified in the published method, as trouble was ex-
I
