Determination of Hydrogen Sulfide, Sulfur Dioxide, Carbonyl Sulfide, Carbon Disulfide, and Carbon Dioxide in a Gas Mixture Arthur Schwartz Development Center, Chemical Construction Corporation (CHEMICO), New Brunswick, N. J . 08903 The objective of the work undertaken was to determine hydrogen sulfide in the presence of other sulfur gases which usually interfered. A cupric sulfate solution quantitatively removes hydrogen sulfide as a cupric sulfide precipitate, while another cupric sulfatesolution in the presence of chloride ions oxidizes sulfur dioxide to sulfur trioxide. These gases are then determined by applying simultaneous equations to reactions involving the increase of acid and the loss of copper. Carbonyl sulfide and carbon dioxide, which are acidic gases, and carbon disulfide, which is not soluble in water solutions, are not absorbed in the aqueous acidiccopper solutions. Simultaneous equations are applied to results obtained by an iodination and by a bromination to determine these sulfur gases, while a standard acid-base analysis determines carbon dioxide. An accuracy of better than 3% and a precision of 0.5% is possible for the determination of hydrogen sulfide and sulfur dioxide.
THIS WORK was originally begun after studying anomalous results obtained by a standard procedure for the determination of hydrogen sulfide in the presence of sulfur dioxide using aqueous ammoniacal cadmium chloride solutions as the absorbent ( I ) . Although carbonyl sulfide is not very soluble in aqueous solutions, and carbon disulfide even less so, sufficient quantities remain in the high concentration of ammonia and react with cadmium chloride to precipitate as cadmium sulfide, thus falsely indicating a high concentration of hydrogen sulfide. Although a method has been described for the determination of these gases by gas chromatography, (2), water interferes with the determination of H,S. In addition, in order to separate COS from SOU, the required flowrate and temperature were such that it took more than an hour before the CS2 peak was observed, making it impractical to take samples from several points within a short period of time. EXPERIMENTAL
Scope. The normal amount of copper sulfate recommended in the procedure, 50 ml of 0.5N, should oxidize a maximum of 50 cc of sulfur dioxide at standard temperature and pressure within a reasonably short time of gas-liquid contact. Either the volume of inert gas taken must be adjusted to contain this maximum of sulfur dioxide, or the volume of 0.5N copper sulfate must be increased for larger amounts of SO2. The capacity of copper sulfate for hydrogen sulfide removal is greater than that for sulfur dioxide-about 100 cc per 50 ml of 0.5N CuS04. The amount of copper sulfate and/or the volume of inert gases taken must be adjusted accordingly for any combination of these two gases. (1) V. J. Altieri, “Gas Analysis and Testing of Gaseous Materials,” The American Gas Association, Inc., 420 Lexington Avenue, New York, N. Y . , 1945, p 346. ( 2 ) H. M. McNair and E. J. Bonelli, “Basic Gas Chromatography,” Vuriun Aerogruph, Varian Associates, Palo Alto, Calif., March 1969, p 64.
Apparatus used consisted of a wet-test meter or water displacement gas-measuring apparatus (similar to Reich test apparatus); a nitrogen cylinder; 12.5-cm Whatman No. 541 filter paper; 24-cm Whatman No. 2 filter paper; a 80 mm long stem funnel; a 150-mm powder funnel; 3 Fleming gas purifier jars with tapered internal inlets, each 150 mm high; a 500-ml plastic storage bottle with rubber stopper through which a glass tube is inserted for making dropwise additions of 4 0 x NaOH; and a 2-inch length of Kel-F tubing for making connection to a hot sample line. Reagents. 0 . 5 N COPPERSULFATE.Weigh 250 g of reagent grade, fine crystal cupric sulfate 5 H 2 0 (mol wt 249.686) into a clean, dry, tared 3-liter beaker; add 1600 ml of water while stirring the mixture. Quantitatively transfer the clear solution to a 2-liter volumetric flask and add distilled water to the mark. After thoroughly mixing the solution, filter it through a 24-cm Whatman No. 2 filter paper supported by a large powder funnel resting on a 2-liter Erlenmeyer flask. Stopper the flask and label it: “0.5NCopper Sulfate for SO?Reduction.” To obtain 25 sodium chloride, 25 potassium bromide, 25 potassium iodide, and 25 barium chloride, dissolve 250 g of each salt, respectively, in water, and dilute each to 1 liter in a graduate. 2.5 SODIUM CHLORIDE.Fifty ml of 25 sodium chloride plus 450 ml of distilled water was stored in a plastic wash bottle. 40 % SODIUMHYDROXIDE. Use standard aqueous solution on a weight to weight basis. 0.05N HYDROCHLORIC ACID. Dilute 100 ml of 0.5N hydrochloric acid to 1 liter with water. ACIDINDICATOR “A” was prepared by using 0.1 gram 444dimethylamino-l-napthylazo)-3-methoxybenzenesulfonicacid (E.K. No. 1954) in 100 ml of water. Add 0.1N sodium hydroxide dropwise, until a solution results. (A small amount of precipitate is acceptable.) Store in a brown bottle. BROMATE INDICATOR “B.” One-tenth gram of 4-(p-ethoxyphenylazo)-m-phenylene-diamine monohydrochloride (E.K. No. 5314) in 100 ml of water. Store in a brown bottle. CARBONATE INDICATOR “C.” Dissolve 0.06 gram of bromcresol green and 0.04 gram of methyl red in 100 ml of ethanol. Store in a brown bottle. ALCOHOLIC POTASSIUM HYDROXIDE SOLUTION.Weigh 100 grams of potassium hydroxide pellets into a dry 1-liter beaker. Add 950 ml of absolute ethanol. Stir the mixture by magnetic agitation, using a large Teflon-coated spin bar. Occasionally a glass rod may be required to stir KOH pellets that have accumulated near the walls of the beaker. When the bulk of the pellets is in solution (potassium carbonate remains as a residue), filter the mixture through a piece of glass wool in a large, plastic powder funnel supported by a 1-liter Erlenmeyer flask. Add 50 ml of distilled water directly to the flask, and stir the solution. Stopper the flask loosely with a rubber stopper; when the solution has cooled, stopper the flask tightly and store it in a refrigerator when not in use. Procedure. A. SAMPLING.Three Fleming gas purifier jars were filled as follows: Jar 1-as indicated in Table I; Jar 2-25 ml of 0.5N copper sulfate, 40 ml of 25% sodium chloride; Jar 3-75 ml of alcoholic potassium hydroxide. They were connected in order, directly to the sample source 3
ANALYTICAL CHEMISTRY, VOL. 43, NO. 3, MARCH 1971
Table I. Composition of First Jar H2S 0 . 5 N CuSO4 25% NaCl 25 ml 25 ml
Hz0 15 ml 30 0
Table 11. Volume of Inert Gas Sample Estimated concentrationa % H2S so,
5 10 20 30