United States
Environmental Protection
Agency
Atmospheric Research and
Exposure Assessment Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-90/054 Aug. 1990
&EPA Project Summary
Laboratory Method to Estimate
Hydrogen Chloride Emission
Potential Before Incineration of a
Waste
Max R. Peterson, John R. Albritton, and R. K. M. Jayanty
A laboratory method has been
developed to provide an estimate of
the amount of hydrogen chloride gas
that will form during incineration of a
waste. The method involves heating
of a sample of the waste to 900°C in
a tube furnace, removal of particles
from the resulting gases by filtration
at 250°F (120°C), collection of hydro-
gen chloride gas in a water-filled
impinger, and measurement of the
collected HCI as chloride using a
standard ion chromatography/con-
ductimetric detection method. Dupli-
cate experimental runs were conduc-
ted with quartz and with INCONEL
components in the furnace zone of
the apparatus. The two materials
gave quite different results, which
indicates some surface phenomenon
may be involved.
Results with quartz components
indicated that organochlorine is es-
sentially completely converted to HCI.
Very ionic inorganic chlorides (e.g.,
KCI and NaCI) formed little or no HCI
when heated in zero grade air (<3
ppm water and <1 ppm total
hydrocarbon) but gave large amounts
of HCI (20-80% conversion) if the
atmosphere inside the apparatus
contained 2.4-5.0% water vapor,
which contains hydrogen for HCI
formation. Results with less ionic
inorganic chloride (FeCI3) and with
chlorine in a positive oxidation state
(NaCIO solution) indicated significant
conversion to HCI, especially in the
presence of hydrogen from water
vapor. In all cases, the presence of
water vapor increased the amount of
HCI formed, but INCONEL gave low
recovery of organohalogen as HCI.
This Project Summary was devel-
oped by EPA's Atmospheric Research
and Exposure Assessment Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Current U.S. EPA regulations for
permitted hazardous waste incinerators
require analysis of the waste feed for
total organochlorine content. At present,
no adequate analytical method is known
that will accomplish this. Furthermore, a
method to measure hydrogen chloride
emission potential in waste feed would be
preferable since the purpose of the
regulations is to control emission of HCI.
The current method assumes that
organochlorine is the dominant source of
HCI emissions from hazardous waste
incinerators. Chlorine-containing organic
molecules contain atoms of both elem-
ents required to form hydrogen chloride:
For this reason, chlorine-containing
organic compounds form HCI when
burned in air.1 Without a source of
hydrogen, inorganic chlorides do not
form HCI when heated to high
temperatures in dry air. The result of
heating an inorganic chloride to high
temperature in the presence of" a
hydrogen-containing species (e.g., water)
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apparently has not been investigated in
previous work.
The ultimate goal of the work
described here is to develop a laboratory
method to estimate, from analysis of a
waste, the maximum amount of HCI that
could form during incineration of that
waste, regardless of the chemical envi-
ronment of chlorine in the waste. The
analytical approach chosen for evaluation
involved heating a sample of chlorine-
containing waste in a tube furnace,
filtering particulate chloride from the hot
gas stream, and trapping hydrogen
chloride (HCI) gas by bubbling the
filtered gas through water in an impinger.
The collected HCI was measured as
chloride (CO by ion chromatography
(ICJfconductimetric analysis of the water
solution.
Experimental parameters evaluated
included the effect on HCI formation of
(1) the bonding environment of chlorine in
the waste, (2) the furnace temperature,
(3) the presence of water vapor, and (4)
the composition of the components of the
furnace zone. A total of 35 experimental
runs were conducted.
Experimental Procedures
The following sections describe (1) the
laboratory apparatus, (2) the procedures
for injecting waste samples, and (3) the
collection and analysis of HCI samples.
Apparatus
The laboratory apparatus used for the
study is shown schematically in Figure 1.
The components included (1) an injection
assembly, (2) a furnace zone (tube
furnace), (3) a heated filter zone (to
remove paniculate matter), and (4) hydro-
gen chloride sample collectors.
The injection assembly consisted of a
movoablo boat mechanism sealed inside
a glass housing located immediately
upstream from the furnace zone. The
design of this assembly allowed for
injection of a waste sample into a
completely sealed system exposed only
to the controlled atmosphere inside the
apparatus. The boat mechanism was
made from either quartz or INCONEL
components to match the composition of
the furnace tube. A hand-held magnet
(outside the glass tube) was used to push
the boat, which had a piece of magnetic
material on the upstream end, into the
furnace zone and to withdraw it after
volatilization and/or incineration of the
sample.
The furnace zone was inside a quartz
or INCONEL combustion tube that was
healed in a tube furnace. Waste samples
were volatilized and/or thermally oxidized
in the furnace zone. Chlorine, if present in
the waste, then combined with hydrogen
to form hydrogen chloride.
A thermocouple was used to deter-
mine temperature profiles of the furnace
zone at tube-center temperatures of
400°C and 900°C. The profiles indicate
that (1) the furnace zone was maintained
at the desired temperature setting for at
least 1 in. on either side of the center and
(2) the temperature of the gas stream at
the exit of the tube furnace was greater
than 100°C. The latter condition prevent-
ed condensation of water vapor during
transfer of gases to the heated filter zone.
The heated filter zone was located im-
mediately downstream from the furnace
zone. The filter apparatus consisted of a
quartz-fiber filter supported by a per-
forated Teflon disk and was used to
remove particulate material from gaseous
material. The filter apparatus was similar
to the one used in U.S. EPA's Modified
Method 5 Sampling Train.2 The entire fil-
ter apparatus and associated connectors
were housed in an insulated box and
maintained at a temperature of 250°F
(120CC) to prevent condensation of
gases.
Sample collectors were located
immediately downstream from the heated
filter zone. The filtered gases were
bubbled through two midget impingers
connected in series. The first impinger
contained deionized water to remove
gaseous HCI; trie second, 0.1 N NaOH
solution to remove any chlorine gas
present in the gas stream.
Experimental Run Procedure
Several initial runs using quartz
components were conducted with the
assembled apparatus to determine op-
timum sample size (actually, mass of
chlorine which must be injected to obtain
a reasonable percent recovery) and heat-
tracing requirements. Wastes containing
organochlorine, assumed converted
completely to HCI when heated to 900°C,
were used to monitor accuracy (percent
recovery) as improvements were made in
the apparatus and as the chlorine content
of the waste and the injection volume
were adjusted to achieve acceptable
results.
Each experimental run consisted of (1)
a single injection of a blank (referred to
as the prerun blank), (2) three to five
separate injections of the waste, and (3) a
second injection of a blank (referred to as
the postrun blank). The blanks were
made up of the same matrix (ethanol
and/or water) as the sample but
contained no chlorine-containing species.
The prerun and postrun blanks were used
to monitor background concentrations of
HCI. Each injection (waste or blank)
generated a single liquid sample
(collected in the first impinger) that was
subsequently analyzed for chloride by 1C
with conductimetric detection.
The procedure used for each injection
(waste or blank) into the laboratory
apparatus is given in the full report.
Sample Preparation and
Analysis
After volatilization and/or incineration
of an injection of material (waste or
blank), the deionized water in the first
midget impinger was analyzed for chlo-
ride on a Dionex Model 14 ion chromato-
graph with conductimetric detection.
Solutions to be analyzed were diluted, if
necessary, to obtain a CI" concentration
in the range of 0.06 to 15 ppm, the
optimum working range for the
measurement method. The conductivity
meter had a detection limit of 0.01 ppm
cr.
Wastes Studied
The compounds selected for use in
synthetic wastes were methylene
chloride, an organohalogen compound;
ferric chloride, a predominantly molecular
inorganic compound; and sodium
chloride and potassium chloride, two very
ionic inorganic compounds. In addition, a
solution of sodium hypochlorite was used
as a synthetic waste containing chlorine
in a positive oxidation state. Table 1
gives the composition and chlorine
concentration of the synthetic wastes
used in the study.
Two real-world wastes were used in
the study. The first was an aqueous
waste containing a large amount of
organochlorine. The second was also
aqueous and contained large amounts of
inorganic chlorine.
For the purposes of this evaluation,
blank values were determined by
injecting pure ethanol or a water-ethanol
mixture, as appropriate, into the
apparatus and measuring the background
CI' concentration in the water-impinger
solution. Blanks were the first and last
injections of each experimental run. The
blank value was computed as the
average of the chloride concentrations
from the prerun and postrun blank
injections.
Tesf Atmospheres
Four different test atmospheres were
investigated: (1) 100% zero grade air, (2)
zero grade air containing 0.5% propane,
(3) zero grade air containing 2.4% water
vapor, and (4) zero grade air containing
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Tube Furnace
(900-1000 °C)
II
Injection
Assembly
J I
Air
Sample
Collectors
Figure 1. Laboratory apparatus used in the study.
Table 1. Synthetic Waste
Chlorine
Synthetic Concen-
Waste Composition tration
9.5%
WaC//H2O
11.8%
KC//H2O
6.6%
CH2CI2/EfOH
6.2%
FeCI3/H2O
4-6%
WaC/O/H2O
705 mg NaCI per
mL of H2O
134 mg KCI per
mL of H2O
56. 1 mg CH2CI2
per mL of EtOH
66.5" mg FeCI3
per mL of H2O
Unknown
5.8%
5.6%
5.5%
4.1%'
' Calculated from chloride concentration
measured by ion chromatography.
5.0% water vapor. The last three atmo-
spheres were investigated to determine if
the presence of a hydrogen-containing
species would affect the recovery of
inorganic chlorine as HCI.
An airflow of 200 mL/min was used to
sweep material through the furnace tube
and sampling train. This flow rate gave a
residence time of 3-4 sec in the hottest
part of the tube. At the 900°C setting,
residence time in the region heated
above 700 °C was 8-10 sec.
Results and Discussion
A furnace tube and boat mechanism
made of quartz were used for all prelim-
inary runs. The test atmosphere was
100% zero grade air and the temperature
in the furnace zone was 900 "C. Results
of those runs appeared straightforward:
Organohalogen was converted to HCI;
inorganic chloride was not. Runs at
1000°C gave similar results.
A gas-mixing system was then added
to the laboratory apparatus. It allowed the
preparation of a test atmosphere contain-
ing a small amount of propane (0.5%) in
zero grade air. Under the new conditions,
30-50% of inorganic chloride was
converted to HCI.
Other hydrogen sources were then
considered because of the safety hazards
associated with handling propane. Water
vapor was the obvious choice. Approx-
imately 40% of inorganic chloride heated
in an atmosphere containing water vapor
was recovered as HCI. The presence of
large amounts of HCI gas was confirmed
by gas-filter correlation infrared spectros-
copy (HCI analyzer). Likewise, 1C analysis
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of an impinger solution from a laboratory
run with a sodium chloride waste
indicated 52.7% recovery of CI' as HCI,
whereas analysis of the same solution by
inductively coupled argon plasma
indicated only 3.8% recovery of Naf.
Table 2 summarizes recovery of chlo-
ride (from NaCI) as HCI with furnace
temperatures of 900 °C and 1000°C in (1)
100% zero grade air, (2) zero grade air
containing 0.5% propane, and (3) zero
grade air containing 2.4% water vapor.
Tho concentrations of propane and water
vapor above gave approximately the
same concentration of hydrogen in the
test atmosphere and gave very similar
recoveries of chloride as HCI. Increasing
the water vapor concentration to 5.0%
had no appreciable effect on recovery of
chloride as HCI. Water vapor (2.4%) was
used for all subsequent runs requiring a
source of hydrogen.
Table 2. Recovery from Sodium Chloride at
900"C and WOO°C
Zero Grade Air Mean Recovery of CI-
Containing as HCI
Propane
no
0.5%
no
Water
no
no
2.4%
900°C
0.6%
30.7%
38.5%
1000°C
5. 1%
48.5%
38.5%
Addition of water vapor to the test
atmosphere led to problems with deg-
radation of quartz components. The boat
was a brownish-red at the end of the
ferric chloride runs presumably because
of the presence of iron in the degraded
quartz. This provides additional evidence
that metal cations may remain, perhaps
as silicates, on the walls of the tube and
boat following conversion of chloride to
HCI.
A furnace tube and boat made of
INCONEL 600 (76.0% nickel, 15.5%
chromium, and 8.0% iron) were used to
determine if HCI formation was affected
by the chemical composition of the tube
and boat. Consequently, experimental
runs with synthetic and real-world wastes
were repeated with INCONEL com-
ponents.
The INCONEL tube withstood the
900°C temperatures of the furnace
without sagging. The interior of the tube
became discolored after several runs.
The surface of the INCONEL boat
mechanism slowly deteriorated during
the study. The boat eventually became
pitted and cracked, and material
resembling iron filings collected in the
tube. This material was attracted to a
magnet, the INCONEL components were
not.
Table 3 gives the results of all
experimental runs at 900 °C with quartz
components and with INCONEL compo-
nents, with water vapor present and
without. The following observations may
be made about the results in Table 3.
1. Comparison of results with and without
a source of hydrogen (water vapor) in
the test atmosphere:
a. Predominantly covalent chlorine-
containing compounds (CH2CI2 and
FeCI3) gave a higher percent
conversion of chlorine to HCI when
water vapor was present in every
experimental run except one. The
exception was CH2CI2 with quartz
components.
b. Predominantly ionic chlorine-
containing compounds (NaCI and
KCI) gave a higher percent
conversion of chlorine to HCI when
water vapor was present in every
experimental run.
2. Comparison of results with quartz
components and with INCONEL com-
ponents:
a. Predominantly covalent chlorine-
containing compounds (CH2CI2 and
FeCI3) gave a higher percent
conversion of chlorine to HCI with
quartz components.
b. Predominantly ionic chlorine-con-
taining compounds (NaCI and KCI)
gave a higher percent conversion of
chlorine to HCI with INCONEL
components.
3. Comparison of prerun and postrun
blank concentrations:
a. For 6 of the 15 quartz tube runs at
900°C and 10 of the 17 INCONEL
runs, the HCI concentration of the
blank at the end of the run was at
least twice the concentration of the
blank at the beginning of the run.
b. For 1 quartz tube run and 6
INCONEL runs, the HCI
concentration of the blank at the
end of the run was lower than the
concentration of the blank at the
beginning of the run.
Conclusions
The results of this study have shown
that formation of hydrogen chloride from
incineration of a waste depends upon (1)
the chemical bonding environment of
chlorine in the waste, (2) the presence of
hydrogen in the test atmosphere, and (3)
the composition of the walls and other
surfaces in the furnace zone.
In a quartz tube, organochlorine tends
to be completely converted to HCI and
does not require an external source of
hydrogen. Heating of the organochlorine
compound in an INCONEL 600 tube gave
no measurable amount of HCI in the
collection impinger. Ionic inorganic chlo-
ride is not converted to HCI, in quartz or
INCONEL 600, unless a source of hydro-
gen (e.g., water vapor) is present. Ferric
chloride results more closely resemble
those obtained with organochlorine than
those obtained with very ionic chlorides.
The presence of hydrogen (from water
vapor) increased conversion of inorganic
chlorine to HCI. This was true with both
quartz and INCONEL components in the
tube furnace.
Recommendations
The purpose of this method
development activity was to develop a
procedure that would allow estimation of
the release of HCI during incineration of a
hazardous waste feed stock. This project
showed that such a method is impractical
since the conversion of inorganic chlo-
rine-containing compounds to HCI is
incomplete and variable. Accordingly, it is
recommended that the Agency can
estimate the maximum hydrogen chloride
concentration either by assuming total
conversion of both organic and inorganic
chlorides to HCI or by making a direct
stack gas measurement.
To measure the acid gas control
device efficiency an emission test both
before and after the scrubber will be
needed, because estimates of the max-
imum hydrogen chloride emission from
feed data will lead to overestimation of
scrubber efficiency.
,Many additional studies could be
performed to better define the param-
eters affecting the conversion of chlorides
to hydrochloric acid. Experiments on pilot
and full-scale incinerators would be inter-
esting and potentially useful to regulators
as well as those regulated. It is currently
thought, however, that the conversion
process is probably sensitive to enough
parameters that accurate quantitative
prediction by any test method is unlikely.
References
1. Peterson, M. R., Gaskill, A., Jr., and
Jayanty, R. K. M. Total organohalogen
(Phase I). EPA Contract Number 68-
02-4442, Work Assignment 41,
Research Triangle Institute, Research
Triangle Park, North Carolina, 1988. 16
pp.
2. U.S. EPA, Method 0010, Test methods
for evaluating solid waste, Vol. II field
manual, physical/chemical methods,
3rd. ed. EPA-SW-846. U.S. Environ-
mental Protection Agency, Washing-
ton, DC, 1986.35pp.
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Table 3. Recovery of Chlorine as HC
Mass Cl
Injected
Composition of Sample (mg)
6.6% CH2C\2/BOH 0.234
9.5% NaCI/H2O 0.319
11.8%KCI/H2O 0.319
6.2% FeC!3/H2O 0.436
4-6% NaOCI Soln. Unknown
Real-World Waste Unknown
(Organic)
Real-World Waste Unknown
(Inorganic)
:/af900°C
Water Quartz
Vapor Run Mass Cl Percent
Cone. No. Recovered (mg) Recovery (%)
0% 1 0.242 103.%
2.4% 2 0.1755 75.0%
0% 3 0.0063 2.0%
4 0.0018 0.55%
2.4% 8 0.1227 38.5%
0% 11 0.0018 0.56%
2.4% 12 0.0755 23.7%
0% 13 0.3349 76.8%
2.4% 14 0.4044 92.8%
2.4% 15 0.1442
0% 16 0.1810
2.4%
2.4% 18 0.0590
Run
No.
19
20
21
22
23
24
25
26
27
29
30
31
32
33
34
35
INCONEL
Mass Cl
Recovered (mg)
0.0060
0.0023
0.0833
0.0949
0.1501
0.0160
0.1447
0.2649
0.266
0.0059
0.0593
0.0226
0.2969
0.2934
0.3191
0.0840
Percent
Recovery (%)
2.6%
1.0%
35.6%
40.6%
64.1%
5.0%
45.4%
83.1%
83.4%
1.8%
18.6%
5.2%
68.1%
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Max R. Peterson John R. Albritton, and R. K. M. Jayanty are with Research
Triangle Institute, Research Triangle Park. NC 27709.
Robert G. Fuerst is the EPA Project Officer (see below).
The complete report, entitled "Laboratory Method to Estimate Hydrogen Chloride
Emission Potential Before Incineration of a Waste," (Order No. PS 90-235
854IAS; Cost: $15.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Atmospheric Research and Exposure Assessment Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-90/054
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