EPA-600/4-77-007
JANUARY 1977
Environmental Monitoring Series
DETERMINATION OF HYDROGEN SULFIDE IN
REFINERY FUEL GASES
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL MONITORING series.
This series describes research conducted to develop new or improved methods
and instrumentation for the identification and quantification of environmental
pollutants at the lowest conceivably significant concentrations. It also includes
studies to determine the ambient concentrations of pollutants in the environment
and/or the variance of pollutants as a function of time or meteorological factors.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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DETERMINATION OF HYDROGEN SULFIDE IN REFINERY FUEL GASES
BY
Joseph E. Knoll and M. Rodney Midgett
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and
Support Laboratory. U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not con-
stitute endorsement or recommendation for use.
n
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ABSTRACT
EPA Test Method 11 has been evaluated. In this study, the cadmium
hydroxide/cadmium sulfate gas absorbing solution was found to be an
efficient collector of thiols. Since thiols are iodimetrically active and
often found present together with hydrogen sulfide in refinery fuel gases,
they cause a serious interference in the method. The same problem was found
to exist when several other gas absorbing solutions were studied. These in-
cluded neutral cadmium sulfate, neutral zinc acetate, as well as buffered
cadmium acetate, cadmium formate and zinc acetate solutions. Large inter-
ferences occurred when thiols were simultaneously present with hydrogen
sulfide and coprecipitation took place. Further investigation produced an
absorbing solution that is essentially free from thiol interference. This
has been achieved using 0.16M CdSCL solution, adjusted to pH 3.Q with HpSO.,
which is effective for the collection of H?S in the 70-700 mg/m range, in
the presence of up to 1800 mg/m of CH3SH.
Sulfur dioxide in the 1300 mg/m range was found to be effectively re-
moved by the single midget impinger of 3 percent H?®? sPec''f''ec' ^n Method 11.
Less than 0.2% of the H^S was removed by this reagent and interferences
resulting from its evaporative entrainment were negligible. The peroxide
solution also was shown to serve as a physical trap for other unwanted
substances.
Compatibility of the absorbing solutions under study with iodimetric
measurement was shown and cadmium sulfide precipitates aged for ten days did
not differ from freshly prepared samples when analyzed.
Further studies were also made employing other substances often
present in refinery fuel gases. No measurable interference resulted from
the presence of carbon oxysulfide, dimethyl sulfoxide, ethene or thiophene.
Acetaldehyde and acetone were observed to interfere at the 24000 and 48000
mg/m level, respectively. The former substance was largely removed by the
air flush procedure and the latter substance was trapped, to a large extent,
in the peroxide solution.
A revised version of the test method is presented.
This report covers a period from January 1, 1974 to December 31, 1975
and work was accomplished as of December 31, 1975.
m
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CONTENTS
Abstract iii
Figures vi
Tables vii
Acknowledgments viii
1. Introduction 1
2. Conclusions 2
3. Experimental 4
4. Results and Discussion 6
References 15
Appendices
A. Method for the determination of hydrogen sulfide emissions
from petroleum refinery fuel gases 16
B. Chemical processes relevant to Method 11 28
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FIGURES
Number Page
1 HpS Absorption Flow Apparatus 3
2 Collection efficiency of H2S and Ci-LSH in zinc acetate
solutions at various pH values. (CJ, H~S collection
efficiency, O. CH-jSH collection efficiency.) 7
3 Collection efficiency of HpS and ChUSH in cadmium sulfate
solution at various concentrations. (^, H?S collection
efficiency, O» CHgSH collection efficiency.: 8
4 H2S Sampling Train 27
vi
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TABLES
Number Page
1 Interference Levels of Methanethiol in Hydrogen Sulfide
Measurements 9
2 Test of Removal of SCL Interference by 3% H202 Solution . 12
3 Entrainment of Peroxide 13
4 Sulfide Recovery as Percent of Added Na^S 14
vii
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ACKNOWLEDGMENTS
The authors wish to thank Drs. J. B. Clements, W. J. Mitchell, and
Mr. F. P. Scaringelli of this Agency, and Dr. G. W. Scheil of Midwest
Research Institute for helpful discussions during the course of this
research.
viii
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SECTION 1
INTRODUCTION
In view of the increasing national concern about toxic sulfur compounds
in the atmosphere, the U.S. Environmental Protection Agency (EPA) has issued
regulations that deal with the emission of sulfur dioxide into the atmosphere
from the combustion of petroleum refinery fuel gases and process gases that
contain hydrogen sulfide. In March 1974, a standard was promulgated that
limited the emission of sulfur gases from fuel gas combustion devices by
specifying that the fuel gas combusted contain no more than 230 mg/dscm of
H2S, or optionally, that the gases resulting from the combustion of fuel gas
be treated in a manner which limits the release of S02 into the atmosphere.
The applicable performance test method for H2S, designated EPA Method 11,
utilizes an alkaline CdSO* solution to collect H2S, which is later regenerated
and measured iodimetrically. Other methods have also been developed for the
analysis of gases containing hLS, and recently the literature has been review-
ed. Two iodimetric procedures that have also been widely employed are the r
ASTM Method D2385-65-T, which uses CdS04 and a method which uses Zn(C2H302)2.
In recognition of the acute need for accurate techniques, EPA's Environ-
mental Monitoring and Support Laboratory (EMSL) has been given the task of
evaluating the standardizing test procedures in current use. This task has
included the investigation of interferences in Method 11. lodometry is not
specific for H2S; other substances that are often found present in refinery
gases are also iodimetrically active. Among these, for example is S02 and
Method 11 includes a H202 solution for the removal of S02 from the gas under
analysis, prior to its passage through the H,,S absorption solution.
Recent attention to the fact that thiols may also be important constit-
uents of refinery fuel gases, prompted the present study which is mainly con-
cerned with the elimination of interferences resulting from these substances.
To this end, collection efficiences of H2S and CH-SH were measured in several
reagents, and the effects of varying concentration and pH were determined.
Serious levels of interferences were found in all three of the methods cited
above, ' but a useful H?S absorbing medium was developed. Some informa-
tion was also obtained on tne efficacy of removal of SOp by the H202 absorb-
ing solution. And further, since entrained Hfl? may itself interfere in
subsequent analytical processes, a study was also made of the minimum
quantity transported as a result of evaporation and its fate in the H?S
absorbing solution. Interferences resulting from several other substances
commonly found in fuel gases were also briefly considered. These data are
presented below.
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SECTION 2
CONCLUSIONS
This investigation has produced an absorbing solution that is
essentially free from thiol interferences for use in the measurement of
H?S in refinery gases. This has been achieved using 0.16 M CdSO* solution
aajusted to pH 3.0 with H2SO», which is effective for the collection of
H2S in the 70-700 mg/m range, in the presence of up to 1,800 mg/m of
CH3SH. Recommendation of this solution as a substitute for the collecting
meaium now employed in EPA Method 11 is planned. (A revised version of
the method is contained in Appendix A of this report.)
Serious thiol interferences were uncovered when neutral cadmium
sulfatec* alkaline cadmium sulfate (current EPA Method 11), neutral zinc
acetate as well as when buffered cadmium acetate, cadmium formate and zinc
acetate solutions were used.
o
Sulfur dioxide in the 1,300 mg/m range is effectively removed by a
single impinger of 3 percent hLOo. Interferences caused by the evaporative
entrainment of the latter compound are negligible.
No measurable interference resulted from the presence of carbon
oxysulfide, ethene, dimethyl sulfoxide, or thiophene. Acetaldehyde and
acetone were observed to interfere at the 2,400 and 48,000 mg/m level,
respectively.
Equations pertaining to the relevant chemical processes are tabulated
in Appendix B.
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HASTINGS MASS FLOW METER
MODEL ALF-2KX
o o
SAMPLE PORT
-ROTAMETERS
!!
UL
SAMPLE PORT
^MIXING CHAMBERS-*
NEEDLE VALVES
CH3SH/N2
Figure 1. H2S absorption flow apparatus.
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SECTION 3
EXPERIMENTAL
Since refinery fuel gases consist of mixtures of light hydrocarbons
which cannot easily be duplicated in the laboratory, C2Hg was selected as
a diluent to prepare feed gases containing the sulfur compounds of interest.
Hydrogen sulfide/ethane, methanethiol/nitrogen, sulfur dioxide/ethane
mixed gases and ethane gas for further dilution obtained from a commercial
supplier, were employed. The gas cylinders used were connected to the
laboratory gas dilution system (shown in Figure 1) by means of 1/4" I.D.
stainless steel tubing and joined with stainless steel Swagelock connectors.
In each case, the gas passed through a Hoke Type 1335g4Y metering valve
and into a Dwyer 1 to 9 1/min rotometer-type flow meter. The three gas
inputs connected into the manifold through a T-joint and the combined gases
passed through two, 200 ml mixing chambers. A second T-joint afforded
symmetrical sampling ports to which the sampling trains could be connected
and duplicate samples withdrawn. The system was operated slightly above
atmospheric pressure and exhausted through a Hastings Model ALF-2KX Flow
Meter, which was used to monitor flow and compute dilution factors. The
sampling trains are described in Appendix A.
Cadmium sulfate/cadmium hydroxide, cadmium acetate, cadmium formate,
cadmium sulfate/sulfuric acid and zinc acetate absorbing solutions were
prepared from analytical grade reagents. Buffered absorbing solutions
were prepared by mixing appropriate quantities of salt and acid and
determining pH with a pH meter. Collection efficiencies of H?S and CH^SH
were measured in these solutions over a range of pH values, employing gas
streams containing diluted H?S and CH.,SH (separately) and mixtures of
H2S and CHgSH. J
o
The gas sampling and analytical procedures described in Method 11
were followed, except as noted below. In practice, feed gas passed through
a midget bubbler containing 15 ml of 3 percent H202 solution and then
through three midget impingers, each containing T5 ml of the absorbing
solution under investigation. The gas was collected for 10 minutes at a
flow rate of approximately one 1/min, which was followed by a 15 minute
air flush at the same flow rate. This is typical of the procedure followed
in practical stack sampling. Impingers containing the absorbed sulfur
compounds were extracted with acid-iodine solution and analyzed iodimet-
rically. An identical impinger extraction procedure was followed when
measuring reagent blanks. In some instances, the contents of the hydrogen
peroxidg-containing impinger was analyzed for sulfate by the barium thorin
method.
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Possible interferences resulting from the vaporization and
collection of H?CL were studied by passing 28.3 liters of air through
15 ml of 30 percent HpO? solution (cooled to 0°C) and then through three
impingers containing acid CdS04 solution. The latter were then analyzed
by the Method 11 procedure, which was modified as follows: Several drops
of 1.0 N ammonium molybdate were added along with the acid-iodine solution
to catalyze the reaction of peroxide with iodide ion. Though this reaction
goes nearly to completion under the prevailing analytical conditions, the
addition of catalyst was made to avoid variations resulting from incom-
pleteness of reaction.
Interferences from substances other than thiols of sulfur dioxide
were investigated as follows: Gases were introduced pure or diluted with
nitrogen into the sampling train at a flow rate of 1 1/min for 10 minutes,
followed by a 15 minute air flush at 1 1/min. Liquid substances were
introduced directly into the CdSO, absorbing solution and analyzed
iodimetrically. When a significant analytical difference resulted, an
atmosphere of the substance in question was generated by passing nitrogen
gas through the liquid at 0°C and estimating gas phase concentrations
from the vapor pressure. Approximately 10 liters of the resulting mix-
ture were sampled, followed by a 15 liter air flush. When large quantities
of active materials were collected, the recovered absorbing solution was
diluted prior to analysis.
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SECTION 4
RESULTS AND DISCUSSION
Several reagents were studied as absorption media for H2S'to determine
suitability for use in the quantitative collection and separation of H2S
from thiols. Collection efficiencies of H2S and CH,SH were measured at
various pH values. Figure 2 shows results obtained using zinc acetate/acetic
acid solutions. Over the pH range of approximately 5 to 6, the collection
efficiency of H2S is near unity while that of CHoSH is essentially negli-
gible. Howeverf when Zn(C2H302)2 solutions buffered in this pH range were
employed for the measurement of gas streams containing mixtures of H2S and
CHLSH, considerable thiol was collected along with the HLS, apparently as a
result of the coprecipitation of ZnS and mercaptide. These data are shown
in Table 1 along with the results of similar measurements made employing
alkaline cadmium sulfate (EPA Method 11), buffered cadmium acetate, and
cadmium formate solutions. The levels of interference encountered are un-
acceptably large for any of these reagents to be employed for the collection
and separation of H2S from thiols. Further these results demonstrate that
unbuffered zinc acetate (pH 6.6) takes up large quantities of thiols, even
when hLS is absent. Since this reagent is occasionally employed in source
sampling tests, potentially large thiol interferences must be expected
from its use.
Collection efficiencies of H2S and CH-SH in neutral cadmium sulfate
solutions were also measured and are shown in Figure 3. Neutgal CdSO*
hSs been previously studied, and the ASTM Method (D2385-65-T) employs 0.57
M CdSO« td separate HLS frora CH.,SH when concentrations of the latter com-
pound do not exceed 23 mg/mi. However, in the CH3SH range employed in the
present study (0 - 900 mg/m ), significant CH3SH collection was observed at
that CdSO* concentration, even in the absence of H2S. Therefore, the ASTM
Method does not work at these high thiol levels.
A study was also made of CdS04/H2SO, solutions for the absorption of
H2S from CHUSH-hLS feed gas mixtures. Table 1 lists results obtained
using 0.16 M CdSO. at several pH values, which show that thiol interference
decreases with decreasing pH and at pH 3.0 does not exceed 4 percent of the
H2S~concentration under analysis. The use of 0.16 M CdSO* was also found
to have additional advantages. It is sufficiently concentrated to assure
essentially quantitative H^S collection at pH 3.0 while at the same time
providing some buffering against the acidity produced during CdS formation.
Sulfate ions have only a weak buffer capacity, but at the concentration and
pH employed, it is sufficient to assure that the pH of the absorbing
solution is not reduced below the value at which H2'S absorption becomes in-
efficient, provided that the quantity of H2S collected does not exceed 0.3
millimoles.
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1.00
0.80
oO.GO
o
iZ
u_
UJ
2
o
u
gO.40
0.20
D
D
OCH3SH COLLECTION EFFICIENCY . Q
O H2S COLLECTION EFFICIENCY
D
D
1
3.0 4.0 5.0 6.0 7.0
PH
Figure 2. Collection efficiency of H2S and CHsSH in zinc acetate solutions at various pH values.
7
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1.00
0.80
o
io.eo
o
o.40
o
CJ
0.20
0.10
A H2S COLLECTION EFFICIENCY
O CHsSH COLLECTION EFFICIENCY
1
0.20 0.30 0.40
CADMIUM SULFATE CONCENTRATION, m/l
0.50
0.60
Figure 3. Collection efficiency of H2S and CHsSH in cadmium sulfate solution at various
concentrations.
8
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TABLE 1. INTERFERENCE LEVELS OF METHANETHIOL IN HYDROGEN SULFIDE MEASUREMENTS
Absorbing Solution
Reagent
CdS04/Cd(OH)2
Cd(OAc)2/HOAc
Cd(OOCH)2/HOOCH
CdS04/H2S04
CdS04/H2S04
CdS04/H2S04
CdS04/H2S04
Zn(OAc)2/HOAc
Zn(OAc)2
M
0.017
0.04
0.04
0.16
0.16
0.16
0.16
0.08
0.09
pH
7.2
4.2
3.5
4.0
3.3
3.0
3.0
5.4
6.6
Feed Gas Composition
mg H0S/tir ,
H0S
0
172
153
333
333
106
333
355
106
"" CH-SH"
329b
279
295
129
129
308
129
147
308
Quantity
Detected as
mg HpS/nT
391
323
202
346
342
110
337
382
317
Excess as Percent
of Added CH,SH
118
54
17
10
7
1
3
19
69
aCH?SH concentrations are listed as equivalent mg of H2S/m at 20°C and 1 atm., and may be converted to
mg CH3SH/m3 values by multiplying by 2.82.
bValue specified by compressed gas supplier.
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The results shown in Table 2 indicate that Spercent H202 solutions
are effective for the removal of SCL interferences in H2S measurements.
Values measured after SCL removal are statistically equivalent to the con-
centration of HpS introduced into the feed gas. (The latter quantity had
been determined by substituting an equivalent amount of C?Hg diluent gas
for the SCL/CpHg employed.) A small but statistically significant quantity
of SOo remains, after passage through H^CL in gas streams where H2S is
absent. Marked SCL interferences result when the peroxide absorbing
solution is omittea. In further studies, barium-thorin analysis of H202
solutions after passage of H?S-containing feed gases showed that less
than 0.2 percent of the quantity of H2S sampled had been converted to
sulfate by the peroxide.
No evidence was found that entrained peroxide is destroyed after it
has been collected by acid cadmium sulfate solution. The quantity
evaporated from 3 percent peroxide solution was too small to measure
accurately, but could be detected. To test for these effects, a more con-
centrated solution was employed. Entrained peroxide from a 30 percent H202
solution was collected in acid CdSO* solution and measured iodimetrically.
Results are listed in Table 3 and a?e compared with a theoretical value.
The latter quantity is the quantity of H202 that would completely saturate
a volume equal to the volume of gas passed through the peroxide solution
during a typical sampling run (28.31), at the temperature (0°C) and con-
centration of interest. This value was determined, employing values of
the vapor pressure (0.272 mm) and activity coefficient (0.513) of H202,
calculated from equations given by Scatchard et.al.- The measured results
are approximately 40 percent of the calculated value; it is therefore
possible that complete saturation of the gas stream may not have taken place
during the sampling process. However, if the results of these observations
are extrapolated, peroxide equivalent to approximately -4 mg H^S/m must be
expected to be entrained by evaporation from the 3 percent H202 solution
employed in Method 11. This quantity is less than 2 percent of the applic-
able standard and of the same order of magnitude as the reagent blank and
standard deviations, examples of which are given in Table 2. However, much
larger interferences will result if portions of the hydrogen peroxide
solution are transferred into the HpS collecting impingers, so that caution
must be exercised during sampling to avoid this occurrence.
No detectible iodometric measurement resulted from sampling carbon
oxysulfide (20 percent in N,), undiluted ethene, dimethyl sulfoxide, ethanol-
amine or thiophene. Acetalaehyde and acetone react with iodine and produce
unstable titration endpoints. However, the sampling process did not result
in the complete collection of these compounds in the absorbing solution sub-
jected to analysis. Acetone vapor was largely retained in the peroxide
solution while some acetaldehyde was removed by the air flush. Based on
the quantities actually measured, acetaldehyde at 2,400 mg/m and acetone at
48,000 mg/m concentrations would be required to produce an interference
level equivalent to 10 percent of the applicable H2S standard. The fore-
going compounds were studied as examples of substances that might be found
in refinery process gases.
10
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Method 11 was further investigated by adding measured quantities of
sodium sulfide to the absorbing solution. The resulting mixture contain-
ing CdS precipitate was then analyzed iodimetrically. These measurements
enabled us to study the completeness of sulfide recovery in the analytical
part of the method, i.e., in that part that includes processes such as the
conversion of CdS to free H^S, its partial escape into the gas phase, its
reabsorption and its subsequent reaction with iodine. It separated out
those effects that might have resulted from sampling. Some information
about the aging of CdS precipitate also resulted from this investigation.
These results are listed in Table 4. The quantities of sulfide employed
correspondedoto that which would have resulted from feed gases of from 85-
280 mg H^S/m . Recoveries differ from 100 percent by amounts that do not
exceed 3 percent for all but one determination. The latter corresponded
to an HpS concentration that was only a third of the value of the pro-
mulgatea standard. Table 4 also contains the results of the measurement
of samples that were aged for ten days. No appreciable difference between
aged and unaged samples could be found. The foregoing served as a check
on the compatibility of the absorbing solution with iodimetric measurements
and to show the absence of problems resulting from the time interval between
sampling and analysis.
11
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TABLE 2. TEST OF REMOVAL OF S02 INTERFERENCE BY 3% H202 SOLUTION
Feed Gas Composition lodimetrically Active Materials
mg HpS/m"5 a c"""'4 ™ u c/m
Sample
1
2
3
4
5
6
£
H.2i
0
0
234
234
234
234
S0b
L
176
176
176
176
318
318
HpOo Employed
4.5
4.5
239
243
232
239
• — -e. - —
H000 Omitted
£. £-
178
174
280
263 v.
340
317
u
Standard deviations of H2S values in Runs 3-6, S02 in Runs 1-4 and S02
in Runs 5 and 6 were 5, Z and 6 mg H2S/m , respectively.
b 3
S02 concentrations are listed as equivalent mg of H2S/m at 2Q°C and
1 atm., and may be converted to the corresponding mg of S0?/m values
by multiplying by 1.88.
c 3
Average Reagent Blank: 12 mg hLS/m ; std. dev. 3.
12
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TABLE 3. ENTRAPMENT OF PEROXIDE3
lodometrically Active
Materials Detected
Run Micromoles HpOp
1 20.5
2 31.0
3 25.9
4 28.4
mean 26.5 + 4.5
theoretical 65.1
From 30% H202 solution at 0°C.
b
Standard Deviation.
c
Calculated using following constants: volume 28.3 1; vapor pressure,
0.272 mm; mole fraction, 0.3; activity coefficient, 0.513.
13
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TABLE 4. SULFIDE RECOVERY AS PERCENT OF ADDED Na2$
Na^S taken
miflimoles
0.1885
0.1885
0.0943
0.0566
0.1885
0.1885a
0.18853
Sulfide measured
millimoles
0.1940
0.1933
0.0954
0.0612
0.1829
0.1829
0.1839
Percent
recovery
102.9
102.5
101.1
108.1
97.0
97.0
97.6
a
Samples aged for ten days.
14
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SECTION V
REFERENCES
1. Federal Register, 39(47):9308-9323, March 8, 1974.
2. Ibid., pp. 9321-9323.
3. Kniebes, D. V., "Sulfur-Containing Gases," in The Analytical Chemistry
of Sulfur and its Compounds, Part I, J. H. Karchmer, pp. 145-181,
Wiley-Interscience, N. Y., 1970.
4. Annual Book of ASTM Standards, Part 24, D2385-65T, American Society
for Testing and Materials, Philadelphia, Pa., 1974.
5. Wilson, A. J., "New Test Methods Submitted by the South Coast Air Basin
Technical Advisory Committee," Stack Sampling News, 3(4):2-6, 1975.
6. Federal Register, 36(247):24890-28891, December 23, 1971.
7. Riensenfield, F. C., and Orbach, H. K., Petroleum Engineer, 25,
c-32, c-34, c-38, June 1953.
8. Scott, W. W., "Standard Methods of Chemical Analysis" Vol. II,
Fifth Ed., 2180, D. Van Nostrand Co., N. Y., 1939
9. Scatchard, G., Kavanagh, G. M., and Ticknor, L. B., J. Am. Chem.
Soc., 74:3715, 1952.
15
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APPENDIX A
METHOD FOR THE DETERMINATION OF HYDROGEN SULFIDE EMISSIONS
FROM PETROLEUM REFINERY FUEL GASES
DISCLAIMER
This method has been assembled from available information
based upon extensive laboratory and field evaluations
followed by interlaboratory collaborative testing. How-
ever, it does not represent an official EPA position at
this time.
16
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1.0 Principle and Applicability
1.1 Principle
Hydrogen sulfide (H2S) is collected from a source in a series of
midget impingers and absorbed in pH 3.0 cadmium sulfate solution to form
cadmium sulfide (CdS). The latter compound is then measured iodometrically.
An impinger containing hydrogen peroxide is included to remove SC>2 as an
interfering species.
1.2 Applicability
This method is applicable for the determination of hydrogen sul-
fide emissions from stationary sources only when specified by the test pro-
cedures for determining compliance with the new source performance standards.
2.0 Range and Sensitivity
The limit of detection is approximately 8 mg/m^ (6 ppm). The
maximum of the range is 740 rng/m^ (520 ppm).
3.0 Interferences
Any compound that reduces iodine or oxidizes iodide ion will
interfere in this procedure, provided it is collected in the cadmium sul-
fate impingers. Sulfur dioxide in concentrations of up to 2,600 mg/m is
eliminated by the hydrogen peroxide solution. Thiols coprecipitate with
hydrogen sulfide. In the absence of H2S, only traces of thiols are col-
lected. When methane- and ethane-thiols at a total level of 300 mg/m^
are present in addition to I^S, the results vary from 2% low at an H2S
concentration of 400 mg/m^ to 14% high at an I^S concentration of 100
mg/m^. Carbon oxysulfide of 20% does not interfere. Certain carbonyl-
containing compounds react with iodine and produce recurring end points.
However, acetaldehyde and acetone at concentrations of 1 and 37», respec-
tively, do not interfere.
Entrained hydrogen peroxide produces a negative interference
equivalent to 100% of that of an equimolar quantity of hydrogen sulfide.
Avoid the ejection of hydrogen peroxide into the cadmium sulfate impingers.
4.0 Precision and Accuracy
Collaborative testing has shown the within-laboratory coeffi-
cient of variation to be 2.2% and the overall coefficient of variation to
be 5.0%. The method bias was shown to be -4.8% when only ^S was present.
17
-------
In the presence of the interferences cited in 3.0 above, the bias was posi-
tive at low H2S concentrations and negative at higher concentrations. At
230 mg H2S/m3, the level of the compliance standard, the bias was +2.7%.
Thiols had no effect on the precision.
5.0 Apparatus
5.1 Sampling Train
5.1.1 Sampling line - Six to 7 mm (1/4 in.) Teflon* tubing to
connect sampling train to sampling valve. Depending on sampling stream
pressure, a pressure-reduction regulator may be required just prior to
the Teflon sampling line.
If significant amounts of water or amine are present in the
sample stream, a corrosion-resistant cold trap should be used immediately
after the sample tap. The trap should not be operated below 0°C to avoid
condensation of €3 or 64 hydrocarbons.
5.1.2 Impingers - '~ve midget impingers, each with 30 ml capacity.
The internal diameter of the impinger tip must be 1.00 mm ± 0.05 mm. The
impinger tip must be positioned 4 to 6 mm from the bottom of the impinger.
5.1.3 Glass or Teflon connecting tubing for the impingers.
5.1.4 Ice bath container - To maintain absorbing solution at a
low temperature.
5.1.5 Silica gel drying tube - To protect pump and dry gas meter.
5.1.6 Sampling valve - Needle valve or equivalent to adjust gas
flow rate. Stainless steel or other corrosion-resistant material.
5.1.7 Dry gas meter - Sufficiently accurate to measure sample vol-
ume to within 1% and calibrated with a wet test meter over the range of flow
rates used in sampling. Gas volume for one dial revolution must not be more
than 10 liters. The gas meter should have a gas petcock or equivalent on
the outlet connector which can be closed during the leak test.
5.1.8 Flow meter - Rotameter or equivalent, to measure a 0.5 to
2.0 liters/min (1 to 4 CFH) flow rate.
* Mention of trade names of specific products does not constitute endorse-
ment by the Environmental Protection Agency.
18
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5.1.9 Graduated cylinder -25 ml size.
5.1.10 Barometer - To measure atmospheric pressure to within
± 2.5 mm (0.1 in.) Kg.
5.1.11 U-Tube manometer - 0-30 cm water column. For leak check
procedure.
5.1.12 Rubber squeeze bulb - To pressurize train for leak check.
5.1.13 Tee, pinchclamp, and connecting tubing - For leak check.
5.1.14 Vacuum pump - Required for air purge.
5.1.15 Needle valve or orifice - To set air purge flow to 1 liter/
min.
5.1.16 Tube packed with activated carbon - To filter air during
purge.
5.1.17 Volumetric flask - One 1,000 ml.
5.1.18 Volumetric pipette - One 15 ml.
5.2 Sample Recovery
5.2.1 Sample container - Iodine flask, glass-stoppered; 500 ml
size.
5.2.2 Pipette - 50 ml volumetric type.
5,2.3 Graduated cylinders - One each 25 and 250 ml.
5.2.4 Flasks - 125 ml, Erlenmeyer.
5.2.5 Wash bottle.
5.2.6 Volumetric flasks - Three 1,000 ml.
5.3 Analysis
5.3.1 Flask - 500 ml glass-stoppered iodine flask.
5.3.2 Burette - 50 ml.
5.3.3 Flask - 125 ml Erlenmeyer
19
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5.3.4 Pipettes, volumetric - One 25 ml; two each 50 and 100 ml.
5.3.5 Volumetric flasks - One 1,000 ml; two 500 ml.
5.3.6 Graduated cylinders - One each 10 and 100 ml.
6.0 Reagents
Unless otherwise indicated, it is intended that all reagents
conform to the specifications established by the Committee on Analytical
Reagents of the American Chemical Society, where such specifications are
available. Otherwise, use best available grade.
6.1 Sampling
6.1.1 Cadmium sulfate absorbing solution - Dissolve 41.0 g of
3CdS04'8 H20 and 15.0 ml of 0.1 M sulfuric acid in a 1-liter volumetric
flask that contains approximately 3/4 liter of deionized distilled water.
Dilute to volume with deionized water. Mix thoroughly. pH should be 3.0
±0.1. Add 10 drops of Dow-Corning Antifoam B.* Shake well before use.
If Antifoam B is not used, the alternate acidified iodine extraction pro-
cedure must be used.
6.1.2 Hydrogen perioxide, 3% - Dilute 30% hydrogen peroxide to
3% as needed. Prepare fresh daily.
6.1.3 Water - Deionized, distilled, to conform to ASTM specifi-
cations D1193-72, Type 3.
6.2 Sample Recovery
6.2.1 Hydrochloric acid solution (HCl), 3 M - Add 240 ml of
concentrated HCl (specific gravity 1.19) to 500 ml of deionized, distilled
water in a 1-liter volumetric flask. Dilute to 1 liter with deionized
water. Mix thoroughly.
6.2.2 Iodine solution, 0.1 N - Dissolve 24 g of potassium iodide
(KI) in 30 ml of deionized, distilled water. Add 12.7 g of resublimed
iodine (l£) to the potassium iodide solution. Shake the mixture until the
iodine is completely dissolved. If possible, let the solution stand over-
night in the dark. Slowly dilute the solution to 1 liter with deionized,
distilled water, with swirling. Filter the solution if it is cloudy.
Store solution in a brown-glass reagent bottle.
Mention of trade names of specific products does not constitute endorse-
ment by the Environmental Protection Agency.
20
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6.2.3 Standard iodine solution, 0.01 N - Pipette 100.0 ml of
the 0.1 N iodine solution into a 1 liter volumetric flask and dilute to
volume with deionized, distilled water. Standardize daily as in Section 8.1.
This solution must be protected from light. Reagent bottles and flasks
must be kept tightly stoppered.
6.3 Analysis
6.3.1 Sodium thiosulfate solution, standard 0.1 N - Dissolve
24.8 g of sodium thiosulfate pentahydrate (^28203-51^0) or 15.8 g of
anhydrous sodium thiosulfate (^28203), in 1 liter of deionized, distilled
water and add 0.01 g of anhydrous sodium carbonate (Na2C03> and 0.4 ml of
chloroform (CHC13) to stabilize. Mix thoroughly by shaking or by aerating
with nitrogen for approximately 15 min and store in a glass-stoppered, re-
agent bottle. Standardize as in Section 8.2 below.
6.3.2 Sodium thiosulfate solution, standard 0.01 N - Pipette
50.0 ml of the standard 0.1 N thiosulfate solution into a volumetric flask
and dilute to 500 ml with distilled water.
6.3.3 Starch indicator solution - Suspend 10 g of soluble starch
in 100 ml of deionized, distilled water and add 15 g of potassium hydroxide
(KOH) pellets. Stir until dissolved, dilute with 900 ml of deionized dis-
tilled water and let stand for 1 hr. Neutralize the alkali with concen-
trated hydrochloric acid, using an indicator paper similar to Alkacid test
ribbon, then add 2 ml of glacial acetic acid as a preservative.
(Note 1: Test starch indicator solution for decomposition by titrating
with 0.01 N iodine solution 4 ml of starch solution in 200 ml
of distilled water that contains 1 g potassium iodide. If
more than 4 drops of the 0.01 N iodine solution are required
to obtain the blue color, a fresh solution must be prepared.)
7.0 Procedure
7.1 Sampling
7.1.1 Assemble the sampling train as shown in Figure 1, connect-
ing the five midget impingers in series. Place 15 ml of 3% hydrogen per-
oxide solution in the first impinger. Leave the second impinger empty.
Place 15 ml of the cadmium sulfate absorbing solution in the third, fourth,
and fifth impingers. Place the impinger assembly in an ice bath container
and place crushed ice around the impingers. Add more ice during the run,
if needed.
21
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7.1.2 Connect the rubber bulb and manometer to first impinger,
as shown in Figure 1. Close the petcock on the dry gas meter outlet.
Pressurize the train to 30-cm water pressure with the bulb and close off
tubing connected to rubber bulb. Train must hold a 30-cm water pressure
with not more than a 1 cm drop in pressure in a 1-min interval. Stopcock
grease is acceptable for sealing ground glass joints.
7.1.3 Purge the connecting line between the sampling valve and
the first impinger. Close valve and connect the sample line to the train.
Open the petcock on the dry gas meter outlet. Record the initial reading
on the dry gas meter.
7.1.4 Open the sampling valve and then adjust the valve to
obtain a rate of approximately 1 liter/min. Maintain a constant flow
rate during the test. Record the meter temperature.
7.1.5 Sample for at least 10 min. At the end of the sampling
time, close the sampling valve and record the final volume and temperature
readings.
7.1.6 Disconnect the impinger train from the sampling line.
Connect the charcoal tube and the pump, as shown in Figure 1. Purge
the train with clean ambient air for 15 min to ensure that all I^S is
removed from the hydrogen peroxide. For sample recovery, cap the open
ends and remove to a clean area that is away from sources of heat. The
area should be well lighted, but not exposed to direct sunlight.
7.2 Sample Recovery
7.2.1 Discard the contents of the hydrogen peroxide impinger.
Carefully rinse the contents of the third, fourth, and fifth impingers into
a 500 ml iodine flask.
(Note 2: The impingers normally have only a thin film of cadmium sulfide
remaining after a water rinse. If Antifoam B was not used or
if significant quantities of yellow cadmium sulfide remain in
the impingers, the alternate recovery procedure must be used.)
7.2.2 Pipette exactly 50 ml of 0.01 N iodine solution into a
125-ml Erlenmeyer flask. Add 10 ml of 3 M HCl to the solution. Quanti-
tately rinse the acidified iodine into the iodine flask. Stopper the
flask immediately and shake briefly.
7.2.2 (Alternate) Extract the remaining cadmium sulfide from
the third, fourth, and fifth impingers using the acidified iodine solution.
Immediately after pouring the acidified iodine into an impinger, stopper it
and shake for a few moments, then transfer the liquid to the iodine flask.
22
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Do not transfer any rinse portion from one impinger to another; transfer it
directly to the iodine flask. Once the acidified iodine solution has been
poured into any glassware containing cadmium sulfide, the container must
be tightly stoppered at all times except when adding more solution, and
this must be done as quickly and carefully as possible. After adding any
acidified iodine solution to the iodine flask, allow a few minutes for
absorption of the I^S before adding any further rinses. Repeat the iodine
extraction until all cadmium sulfide is removed from the impingers. Ex-
tract that part of the connecting glassware that contains visible cadmium
sulfide.
Quantitatively rinse all of the iodine from the impingers, con-
nectors, and the beaker into the iodine flask using deionized, distilled
water. Stopper the flask and shake briefly.
7.2.3 Allow to stand about 30 min in the dark for absorption of
the ILjS into the iodine, then complete the titration analysis as in Sec-
tion 7.3.
(Note 3:CAUTION! Iodine evaporates from acidified iodine solutions.
Samples to which acidified iodine have been added may not be
stored, but must be analyzed in the time schedule stated above
in 7.2.3.)
7.2.4 Prepare a blank by adding 45 ml of cadmium sulfate absorb-
ing solution to an iodine flask. Pipette exactly 50 ml of 0.01 iodine
solution into a 125-ml Erlenmeyer flask. Add 10 ml of 3 M HCl. Follow
the same impinger extracting and quantitative rinsing procedure carried
out in sample analysis. Stopper the flask, shake briefly, let stand 30
min in the dark, and titrate with the samples.
(Note 4: The blank must be handled by exactly the same procedure as that
used for the samples.)
7.3 Analysis
(Note 5: Titration analyses should be conducted at the sample-cleanup area
in order to prevent loss of iodine from the sample. Titration
should never be made in direct sunlight.)
7.3.1 Using 0.01 N sodium thiosulfate solution, rapidly titrate
samples in iodine flasks using gentle mixing, until solution is light yel-
low. Add 4 ml of starch indicator solution and continue titrating slowly
until the blue color just disappears. Record Vt, the volume of sodium
thiosulfate solution used (ml).
7.3.2 Titrate the blanks in the same manner as the samples. Run
blanks each day until replicate values agree within 0.05 ml. Average the
replicate titration values which agree within 0.05 ml.
23
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8 -0 Calibration and Standards
8.1 Standardize the 0.01 N iodine solution daily as follows: Pipette
25 ml of the iodine solution into a 125 -ml Erlenmeyer flask. Add 2 ml of
3 M HCl. Titrate rapidly with standard 0.01 N thiosulfate solution until
the solution is light yellow, using gentle mixing. Add four drops of starch
indicator solution and continue titrating slowly until the blue color just
disappears. Record Vfc, the volume of thiosulfate solution used (ml). Re-
peat until replicate values agree within 0.05 ml. Average the replicate
titration values which agree within 0.05 ml and calculate the exact normal-
ity of the iodine solution using Equation 9.1. Repeat the standardization
daily.
8.2 Standardize the 0.1 N thiosulfate solution as follows: Oven-dry
potassium dichromate (I^C^Oy) at 180 to 200°C. Weight to the nearest
milligram, 2 g of potassium dichromate into a 500 ml volumetric flask,
dissolve in deionized, distilled water and dilute to exactly 500 ml. In
a 500 ml iodine flask, dissolve approximately 3 g of potassium iodide (KI)
in 45 ml of deionized, distilled water, then add 10 ml of 3 M hydrochloric
acid solution. Pipette 50 ml of the dichromate solution into this mixture.
Gently swirl the solution once and allow it to stand in the dark for 5 min.
Dilute the solution with 100 to 200 ml of deionized distilled water, wash-
ing down the sides of the flask with part of the water. Titrate with 0.1 N
thiosulfate until the solution is light yellow. Add 4 ml of starch indi-
cator and continue titrating slowly to a green end point. Record Vt, the
volume of thiosulfate solution used (ml). Repeat until replicate analyses
agree within 0.05 ml. Calculate the normality using Equation 9.2. Repeat the
standardization each week.
9.0 Calculations
Carry out calculations retaining at least one extra decimal fig-
ure beyond that of the acquired data. Round off results only after the
final calculation.
9.1 Normality of the Standard Iodine Solution.
N V
N =
VI
where N-j- = normality of iodine, g-eq/liter;
V-r = volume of iodine used, ml;
N™ = normality of sodium thiosulfate, g-eq/liter; and
VT = volume of sodium thiosulfate used, ml.
24
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9.2 Normality of the Standard Thiosulfate Solution.
NT = 2.04 _
T VT
where W = weight of K2Cr207 used, g;
V^ = volume of Na2S203 used, ml;
Nrp = normality of standard thiosulfate solution, g-eq/liter; and
2.04 = conversion factor.
(6 eq I2/mole K2Cr2<)7) (1,000 ml/liter)
(294.2 g K2Cr207/mole) (10 aliquot factor)
9.3 Dry Gas Volume - Correct the sample volume measured by the dry
gas meter to standard conditions (20°C) and 760 mm Hg.
IP
V = V - bar
vm , vm ^f p
"std I Tm I lpstd
where Vm , = volume at standard conditions of gas sample through
the dry gas meter, standard liters;
Vm = volume of gas sample through the dry gas meter (meter
conditions), liters;
Tst(j = absolute temperature at standard conditions, 293 K;
Tm = average dry gas meter temperature, °K;
I?bar = barometric pressure at the orifice meter, mm Hg; and
Pstd = abs°lute pressure at standard conditions, 760 mm Hg.
9.4 Concentration of H2S - Calculate the concentration of l^S in
the gas stream at standard conditions using equation:
CHoS
K[(VINI - VTNT) sample - (V-j-Nj - VTNT) blank]
mstd
where (metric units):
Cu0g = concentration of H2S at standard conditions, mg/dscm;
K = converstion factor = 17.0 x 10^
(34.07 g/mole H2S) (1,000 liters/m3) (1,000 mg/g)
(1,000 ml/liter) (2H2S eq/mole)
25
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Vj = volume of standard iodine solution, ml;
Nj = normality of standard iodine solution, g-eq/liter;
VT = volume of standard sodium thiosulfate solution, ml;
N™ = normality of standard sodium thiosulfate solution,
g-eq/liter; and
Vm , = dry gas volume at standard conditions, liters.
o L. ^1
10.0 Stability
The absorbing solution is stable for at least 1 month. Sample
recovery and analysis should begin within 1 hr of sampling to minimize
oxidation of the acidified cadmium sulfide. Once iodine has been added
to the sample, the remainder of the analysis procedure must be completed
according to Sections 7.2.2, 7.2.3, and 7.3.
11.0 References
11.1 "Determination of Hydrogen Sulfide, Ammoniacal Cadmium Chloride
Method, API Method 772-54." In: Manual on Disposal of Re-
finery Wastes, Vol. V; Sampling and Analysis of Waste Gases
and Particulate Matter, American Petroleum Institute, Washington.
D.C., 1954.
11.2 Tentative Method of Determination of Hydrogen Sulfide and Mer-
captan Sulfur in Natural Gas, Natural Gas Processors Associa-
tion, Tulsa, Oklahoma, NGPA Publication No. 2265-65, 1965.
11.3 Knoll, J. E., M. R. Midgett, "Determination of Hydrogen
Sulfide in Refinery Fuel Gases," Environmental Monitoring
Series, Office of Research and Development, U.S. EPA, NC 27711.
11.4 Scheil, G. W., and M. C. Sharp, "Standardization of Method 11 at
a Petroleum Refinery," Midwest Research Institute Draft Report
for U.S. EPA, Office of Research and Development, RTF, NC 27711,
EPA Contract No. 68-02-1098, August 1976.
26
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Used for
Air Purge
SAMPLING VALVt
Used for
Leak Check
TEFLOfJ SAMPLING LINE
•
/ MIDGET IMPINGERS
r—SILICA GEL TUBE
FUEL GAS
LINE
DRY GAS METER
Used for
Air Purge
Figure 4 - H2S Sampling Train
27
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APPENDIX B
CHEMICAL PROCESSES RELEVANT TO METHOD 11
28
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Appendix II. Chemical Processes Relevant to Method 11.
The following are the reactions pertinent to the processes
in the main body of this report.
discussed
Sample analysis:
K0S + CdSO. = CdS + H.SO. collection
2 4 24
CdS + 2HC1 = H2S + CdCl2 acidification
H2S + I2 = 2HI + S reaction
0 + I = NaS0 + 2KaI measurement
Standardization:
14K
+
3I
61 = 31
= 61
2Cr
3S4°6
Sulfur dioxide removal;
S0
Interference
S0
2HI
2CH3SH
2HI
= 2HI
CH3S(0)SCH3 + 4HI
= 3S
(CH3)2CO + I2 = CH3C(0)CH2I + HI
(CH3)2S + I2 + H20 = (CE3)2SO + 2HI slowly
slowly
Q + 4III = 2I2 + 2H20
29
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION>NO.
4. TITLE AND SUBTITLE
DETERMINATION OF HYDROGEN SULFIDE IN REFINERY FUEL
GASES
5 RFPDRT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Joseph E. Knoll and M. Rodney Midgett
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Quality Assurance Branch
Environmental Monitoring and Support Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
1HD621
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Several widely employed test methods for the iodimetric measurement of hydrogen
sulfide in refinery fuel gases are shown to suffer from serious thiol interferences.
An absorbing solution consisting of 0.16 M cadmium sulfate/sulfuric acid at pH 3.0,
is shown to be effective for the collection of hydrogen sulfide in the 70-700 mg/m
range and to be essentially free from interference by up to 1800 mg/m of methane-
thiol. When combined with a single 3 percent hydrogen peroxide impinger, sulfur
dioxide interferences of up to 1,300 mg/m are also removed. No measureable inter-
ference results from the presence of carbon oxysulfide, ethene, dimethyl sulfoxide,
or thiophene. Acetaldehyde and acetone are observed to interfere at the 2,400 and
48,000 mg/m level, respectively. It is proposed that the absorption solution
described here be substituted for the cadmium hydroxide/cadmium sulfate mixture used
in the EPA test method (Method 11) for determining the hydrogen sulfide content of
refinery fuel gases.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
Air pollution
Hydrogen sulfide
Iodimetric measurement
Refinery fuel gases
Thiols
c. COSATI Field/Group
13b
8. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
37
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
30
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