Plant Analytical Techniques Gas Analysis: Determination of Hydrogen Sulfide by Cadmium Sulfide Precipitation SCOPE AND FIELD OF APPLICATION This method is suitable for the in situ determination of hydrogen sulfide in ammonia plant gas streams when testing is required during catalyst reduction. PRINCIPLE Hydrogen sulfide present in the gas precipitates cadmium sulfide from a cadmium solution. The precipitate is filtered then reacted with iodine; the excess iodine is then titrated with sodium thiosulfate.

1. GBH Enterprises, Ltd.
Plant Analytical Techniques
Gas Analysis: Determination of Hydrogen Sulfide by Cadmium
Sulfide Precipitation
Information contained in this publication or as otherwise supplied to Users is believed to be
accurate and correct at time of going to press, and is given in good faith, but it is for the User to
satisfy itself of the suitability of the information for its own particular purpose. GBHE gives no
warranty as to the fitness of this information for any particular purpose and any implied warranty
or condition (statutory or otherwise) is excluded except to the extent that exclusion is prevented
by law. GBHE accepts no liability for loss or personnel injury caused by or resulting from reliance
on this information. Freedom under Patent, Copyright and Designs cannot be assumed.
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com

2. GAS ANALYSIS:
1
Determination of Hydrogen Sulfide by
Cadmium Sulfide Precipitation
SCOPE AND FIELD OF APPLICATION
This method is suitable for the in situ determination of hydrogen sulfide in
ammonia plant gas streams when testing is required during catalyst reduction.
2
PRINCIPLE
Hydrogen sulfide present in the gas precipitates cadmium sulfide from a
cadmium solution. The precipitate is filtered then reacted with iodine; the
excess iodine is then titrated with sodium thiosulfate.
3
REAGENTS
During the analysis, use only reagents of analytical reagent grade, unless
otherwise specified, and water which has been deionized and then distilled
from an all glass apparatus, or water of equivalent purity.
3.1
Cadmium acetate solution, 2% m/v solution in 5% v/v acetic acid: Dissolve
2g of cadmium acetate dihydrate in 100 mL of 5% v/v acetic acid.
CADMIUM ACETATE IS POISONOUS AND SHOULD BE REGARDED AS A
CANCER SUSPECT AGENT (CARCIONOGEN).
3.2
Iodine, standard volumetric solution, C(I,)-0.10 mol/L.
3.3
Sodium thiosulfate, standard volumetric solution, C(Na2S2O3) = 0.10
mol/L.
Hydrochloric acid (SG 1.18).
3.4
THIS REAGENT IS CORROSIVE AND CAUSES BURNS
3.5
Hydrochloric acid, 5 mol/L solution in water: Add 44.5 mL of hydrochloric
acid (3.4) to 55.5 mL of water, mixing thoroughly.
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com

3. 3.6
Starch indicator solution, 0.2% m/v: Add 40 mg of mercuric iodide to
approximately 800 mL of water, and heat to dissolve. Mix 2.0 g of soluble
starch to a thin cream with a small quantity of water and pour into the
boiling mercuric iodide solution. Boil for two minutes, cool and dilute to
1L with water.
THIS REAGENT SHOULD BE STABLE FOR SEVERAL WEEKS.
4
APPARATUS
4.1
Standard volumetric glassware, class A.
4.2
Absorption train consisting of two Dreschel bottles and a rotary gas
meter.
5
PROCEDURE
5.1
Measure 30 mL of cadmium acetate solution (3.1) into one of the Dreschel
bottles, and dilute to 100 mL with water. The second Dreschel bottle is
employed as a moisture trap.
5.2
Purge the sample line and connect it to the Dreschel bottles. Allow the
gas to pass through the cadmium acetate solution until a suitable quantity
of precipitate has been formed. Pass approximately 100 L of gas.
5.3
Disconnect the apparatus and filter the precipitate through a No 31
filter paper, washing all the precipitate from the bottle onto the filter
paper with cold water. Ensure that all the precipitate is transferred to the
filter, then wash thoroughly with cold water.
5.4
Place in a 500 mL conical flask, 50.0 mL of iodine solution (3.2). 10 mL
of hydrochloric acid solution (3.5) and 50 mL of water.
5.5
Transfer the filter paper retaining the precipitate of calcium sulfide
to the conical flask and shake well until dispersion is complete.
5.6
Wash down the inside of the conical flask with water and titrate the
excess iodine with sodium thiosulfate solution (3.3), adding a few drops of
starch indicator solution (3.6) near the end point, indicated by the
pale-straw color of the solution.
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com

4. 6
EXPRESSION OF RESULTS
6.1
The hydrogen sulfide, expressed as ppm v/v, is given by the expression
where
V1 is the volume of iodine solution used for the determination (in mL; ie 50);
V2 is the titre of sodium thiosulfate solution used in the determination (in mL);
1.2 is the volume (in mL) of hydrogen sulfide gas, at normal temperature and
pressure, which corresponds to 1 ml, of a 0.1 mol/L solution of iodine:
V3 is the volume of gas sample passed (in L).
7
NOTES
7.1
During sampling, the gas sample should not be hot as it comes into
contact with the absorption system; a cooling coil (condenser) should
therefore be incorporated into the sampling process.
Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com

5. Refinery Process Stream Purification Refinery Process Catalysts Troubleshooting Refinery Process Catalyst Start-Up / Shutdown
Activation Reduction In-situ Ex-situ Sulfiding Specializing in Refinery Process Catalyst Performance Evaluation Heat & Mass
Balance Analysis Catalyst Remaining Life Determination Catalyst Deactivation Assessment Catalyst Performance
Characterization Refining & Gas Processing & Petrochemical Industries Catalysts / Process Technology - Hydrogen Catalysts /
Process Technology – Ammonia Catalyst Process Technology - Methanol Catalysts / process Technology – Petrochemicals
Specializing in the Development & Commercialization of New Technology in the Refining & Petrochemical Industries
Web Site: www.GBHEnterprises.com