Polarographic Dete rminat ion of EIemental Sulfur in liquefied Petroleum Gases 1. B. GREGORY and GEORGE MATSUYAMA Research Department, Union O i l Co. o f California, Brea, Calif.
i method has heen developed for the polarographic determination of elemental sulfur present in liquefied petroleum gases in concentrations as low as 0.01 p.p.m. Samples of liquefied petroleum gases are collected in specially fitted stainless steel bombs. After volatilization of the saniple, elemental sulfur remaining in the *amplebomb is dissolved in a pyridine-methanol-hydrochloric acid solvent and the resulting solution elecI rolyzed polarographically.
1,I;MI:STAL sulfur in petroleum products presents an iniportant problem in the industry because of the ease with nhlch it is formed and its corrosive nature. I n contact a i t h moit mr.ta1.. elemental sulfur reacts to form the metal sulfidps
nation of elemental sulfur in liquefied petroleum gases (LPG) by weathering off the liquid sample, dissolving the residue in a hydrocarbon, and determining the amoiint of sulfur present by the procedure of Uhrig and Levin ( 1 6 ) . Another property of elemental sulfur which has been utilized for its determination is its reaction with alkali metal cyanide to form thiocyanate ( 1 2 ) . Recently, Bartlett and Skoog (3) developed a rapid, accurate method for the determination of as little as 2 p.p,m. of elemental sulfur in hydrocarbons based on this reaction, combined JT-ith a colorimetric determination of the thiocj.anate with ferric iron. This technique has so far not been extmded to the analysis of liquefied petroleum gas samples. T h e polarographic reduction of elemental sulfur has been used for its determination in hydrocarbon liquids (4, 7 , 11). I n the authors' laboratories this method has been found t o be the simplest and most sensitive for the determination of elemental sulfur in crude oils, gasolines, and intermediate distillates. Less than 1 p.p.m. of elemental sulfur in gasoline can be determined accurii tely . T h e present study was undertaken t o extend the use of the polarographic method to the quantitative determination of elemental sulfur present in liquefied petroleum gases a t concentration levels normally associated with the sensitivity limit of the mercury corrosion test (0.1 p.p.m.). Investigation has shown that it is possible to determine polarographically a few hundredths of 1 p.p,m. of elemental sulfur in liquefied petroleum gases. APPARATUS A X ) REAGENTS
Polarographic measurements vere made m-ith a Sargent hlodel X X I polarograph. H-type polarographic cells containing a saturated calomel reference electrode separated from the solution compartment by a 1-cm. fine sintered-glass disk and a potassium chloride-agar plug were employed. Oxygen was removed from the analyzed solutions b y bubbling with prepurified nitrogen (99.9 %) previously saturated with pyridine-methanol solvent. Polarograms were run with the solutions maintained a t a constant temperature of 26.0" C. in a therniostatically controlled water bath. All chemicals used \T-ere of reagent grade. Sampling containers used were 1-liter, two-valved, stainless steel bombs (Hoke Style No. L D 1000) fitted as s h o r n in Figure 1 with an outage tube a t one end and an O-ring closure a t the other to facilitate rinsing of the bomb.
+
HOKE
NO323
lrEEDLE VALVI
Figure 1.
Sample container
R E c o m r E s n E n PRocEnuRE r .
1I i ( . corrosive action of eienieiitai sulfur on mercury, copper, and silwr has been used for some time as a seiniquantitative test for srilfiir in petroleum products ( 1 , 6, 9). During recent years more wcurate quantitat,ive methods have become increasingly important in the development and evaluation of new refinery proc. Levin and Stehr (8) determined elemental sulfur in petroleiim oils by shaking them with copper gauze and determinirig iodonietrically the copper sulfid roduced. To increase the +eii.r acknowledged. LITERATURE CITED
Am.8oc. Testing Materials. Designation D 130-5OT, "Tentative 1Iethod of Test for Free and Corrosive Sulfur in Petroleum Products." Ibid., D 1265-63T, "Tentative 1\Iethod of Sampling Liquefied Petroleum Gases." Bartlett, J. K., Skoog, D. -1.. ASAI.. ('HEY. 26, 1008 (1954). Eccleston, B. H., 11orrisou. AI., Smith, H. AI., I b i d . . 24, 1745 (1952).
Fouretier, G.. Compt. r e n d . 218, 194 (1944). Garner, F. H., Evans, E. B., J . Inst. P&de7ml. Technol. 17, 451 (1931).
Hall, 11.E., ANAL.C m Y . 22, 1137 (1950). Levin, H., Stehr, E., I s n . ENG.(,'HEM.. ANAL. ED. 14, 107 (1942). Mapstone, G. E., Ibid., 18, 498 (1946). .\Iit(.hell, 0 . li., P e t d e r m Refiner 31, S o . 6, 148 (1952). Proske, G., .4ngeus. Chem. A59, 121 (1947). Schulek, E., Z. anaZ. Chew. 65, 352 (1925). Shively. J. E€., Levin, H., Petroleum Processir~g8, 913 (1953). Taillade, AI., Compt. rend. 218, 836 (1944). Uhrig, K., Levin, H., dsar..CHEM. 23, 1334 (1951).
ACKNOWLEDGMENT
The authors wish to express their :rppreciation to TT'. \T. Howland and G. IT. Uroivn, who wpplied the necessary samples for
R E C E I V E for D review March 1, 1936. Acct7pted April 30, 1956. Symposium on Methods for Testing Liquefied Petroleiini Gases, St. Louis, Mo., September 27 and 28, 1954.
Dry Combustion and Volumetric Determination of Isotopic Carbon and Hydrogen in Organic Compounds Removal of Nitrogen Dioxide, and Gas Temperature Correction Factors DAVID R. CHRISTMAN, JOAN E. STUBER,
and
AKSEL A. BOTHNER-BY
Chemistry Department, Brookhaven N a t i o n a l Laboratory, Upton,
Small aniounts of nitrogen dioxide in the presence of excess oxygen will pass through a dry ice-cooled radiator trap at low pressures, making possible the freezing out of water before the removal of nitrogen dioxide by external means during the dry combustion of organic compounds. In applying a temperature correction to the gas pressure measurements of carbon dioxide and water by means of a two-liquid manometer, an empirical correction of greater magnitude (about 0.5% per degree) than that calculated by means of the gas law gives the most consistent results.
N. Y.
W
HILE the nitrogen oxide is successfully removed by nian-
ganese dioxide from the gas stream during the dry comhnstiustion of nitrogen-containing organic compounds ( 2 ) , nitrogcri d'ioaide .' (the oxide normally present below 150' C . ) (6) would not be expected to pass cleaiily through a radiator trap at dry icc. tcniperature. Such :L trap is used in the present system to hold the water formed during the combustion, placed before the manganese dioxidr ti,ap for the removal of nitrogen dioxide. A question [vas raised as to whether the nitrogen oxidc present is actually nitrogen dioxide, which has a vapor pressure of 0.03 mm. a t -80" C. ( 4 ) , or is nitric oxide, which docs not freeze at -80" hiit h u l d
