A Computational and Experimental Stndy of Mercury
Speciation as Facilitated by the Deacon Process
Jack R. Edwards
North Carolina State University
Department of Mechanical and Aerospace Engineering
Campus Box 7910
Raleigh, NC 27695
Ravi K. Srivastava*, Chun Wai Lee, and James D. Kilgroc
U.S. Environmental Protection Agency
Office of Research and Development
National Risk Management Research Laboratory
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
S. Behrooz Ghorishi
ARCADIS Geraghty & Miller, Inc.
P.O. Box 13109
Research Triangle Park, NC 27709
Prepared for presentation at:
The A&WMA Specialty Conference on Mercury Emissions:
Fate, Effects, and Control
Chicago, IL
August 21-23,2001
1
-------
A Computational and Experimental Study of Mercury
Speciation as Facilitated by the Deacon Process
Jack R. Edwards
Department of Mechanical and Aerospace Engineering, Campus Box 7910, North
Carolina State University, Raleigh, NC 27695
Ravi K. Srivastava, Chun Wai Lee, and James D. Kilgroe
U.S. Environmental Protection Agency. Office of Research and Development, National
Risk Management Research Laboratory, Research Triangle Park, NC 27711
S. Behrooz Ghorishi
ARCADIS Geraghty & Miller, Inc., P.O. Box 13109, Research Triangle Park, NC 27709
ABSTRACT
It is known that fly ashes that contain trace CuO or Fe203 are effective catalysts for
elemental mercury conversion to HgCl2 in the presence of HC1, even at low reactor
temperatures (less than 250 °C), As these same trace metals promote chlorine gas
formation through the Deacon process, it is possible that this process, combined with gas-
phase mercury chlorination pathways, can explain such speciation trends. In support of
this hypothesis, experiments are conducted to determine whether direct reactions of
mercury with chlorine gas are possible at low temperatures and whether appreciable
mercury is captured onto the model fly ash surface. These results are used to develop and
refine a chemical kinetics model for mercury speciation as driven by chlorination induced
by the Deacon process.
Much recent attention has been focused toward explaining observed gas-phase mercury
speciation trends through the use of detailed kinetics mechanisms.'"3 Such mechanisms
combine elemental mercury chlorination pathways with reactions describing interactions
of chlorine-containing compounds with other flue-gas constituents. The dominant path
for elemental mercury conversion to HgCN has been identified as:1
with the production of atomic chlorine being the controlling factor. Studies have shown
that such mechanisms do explain high temperature (> 500 °C) speciation trends quite
well, but at lower temperatures (< 500 °C), they tend to underpredict observed conversion
trends quite significantly.2,3 The reason is that, without the introduction of arbitrary
concentrations of trace radical species, the proposed pathways do not produce enough
INTRODUCTION
Hg + CI => HgCl
HgCl + CI => HgCl2,
(1)
(2)
2
-------
atomic chlorine at low temperatures to effect high levels of mercury conversion. These
results may point to the importance of heterogeneous chlorination pathways, possibly
involving other reactive species (such as Cl2), as key elements in the conversion process
at low temperatures.
This paper examines one possible heterogeneous mechanism for low-temperature
mercury speciation based on the occurrence of the well-known Deacon process.4"6 The
Deacon process involves the oxidation of HC1 in the presence of a metal catalyst to
produce CI? and H20. The process can be represented by the global gas-phase reaction
2 HC1 + '/2 02 <=> H20 + Ch (3)
but is actually composed of a sequence of heterogeneous reactions representing the steps
of HC1 sorption, chlorination, and oxidation5,6. The chlorination steps result in the
formation of intermediate metallic compounds on the sorbent surface, while the oxidation
step releases Cl2 into the gas phase and results in the regeneration of the catalyst. Hisham
and Benson5 note that the most active catalyst (of the many that they studied) is CuO and
that the chlorination steps in general are exothermic.
Ghonshi7 conducted several experiments that measured steady-state mercury conversion
for simulated flue gas passing through a fixed bed of model fly ash particles. Ghorishi
observed that the baseline fly ash (composed of 22 wt% AI2O3 and 78 wt% Si02) did not
promote mercury conversion, but when trace metal oxides, such as Fe20;i and CuO, were
added to the fly ash, a significant amount of mercury was converted over time. As these
metal oxides promote the Deacon process, it was conjectured that this process played a
role in mercury conversion. In this work, we develop further this conjecture, which
hinges on the hypothesis that the mercury conversion observed is primarily a result of
gas-phase reactions with Cl2 formed through the Deacon process. To this end, new
experimental results on the homogeneous reaction of elemental mercury with molecular
chlorine are reported, as are mass balance data indicating the degree of surface capture of
mercury by model fly ash particles. A new rate coefficient for the gas-phase reaction
Hg + Cl2 <=> HgCl2 (4)
is derived, and the results used to determine new rate coefficients for a two-step global
mechanism for the Deacon process as catalyzed by CuO.8 The ability of the proposed
three-step mechanism to predict the speciation trends observed by Ghorishi7 is assessed,
and some conclusions and directions for future work are drawn.
GAS-PHASE MERCURY-CHLORINE REACTIONS
A key requirement in the above hypothesis is the ability of elemental mercury (Hg°) to
react directly with Cl2 vapor at low (< 500 °C) temperatures. The most comprehensive
study, by Hall et al.9, indicates that the two gases can react at any temperature and that
the relatively slow reaction rate is independent of temperature. Skare and Johansson10
monitored the mercury vapor concentration in mixtures of mercury vapor, air, and
3
-------
chlorine gas, enclosed in a gas bag at room temperature. They reported a 40 % drop in the
initial mercury vapor concentration over 24 hours. Their results may have been
influenced by the decay of chlorine gas concentration due to other factors, which
precluded obtaining data at higher temperatures.
To attempt to characterize the degree of reactivity of mercury and chlorine vapor more
precisely, experiments were performed in an empty reactor (described in Ref. 7) at
temperatures of 150 and 250 °C with a gas mixture consisting of 40 ppbv IIg° and 2 ppm
Cl2 in N2. The effluent of the reactor was sampled for 90 minutes using a modified
Ontario Hydro (OH) mini-impinger train in which each KC1 impinger was spiked with 10
mg sodium thiosulfate (Na2S203).u The samples were analyzed according to the OH
method instruction" to obtain mercury speciation. Each test was duplicated. At the
reactor temperature of 150 °C, Hg° oxidation was 85±5 %, while at the reactor
temperature of 250 °C, Hg° oxidation was 88±4.5 %. These results were reproducible and
indicate that significant gas-phase oxidation of Hg° does occur in the presence of Cl2.
This oxidation is relatively independent of temperature in the range considered. Total
mercury recoveries were within an acceptable range of 80 - 120%.
Given these data and the quenching pattern characteristic of this reactor2, an Arrhenius
rate coefficient for the reaction Hg + Cl2<=> HgCl2 was determined as follows. The
evolution of the molar concentration of Hg° is given by
where:
p„ = molar concentration of Hg° (kmol/m3)
Pen - molar concentration of Cl2 (kmol/m3)
A = pre-exponential factor
B = characteristic temperature (K)
T = temperature (K)
p^= pressure (101325 Pa)
R= universal gas constant (J/kmol-K)
XCI2= mole fraction of Cl2
In the above, it is assumed that the mercury chlorination reaction being elementary
follows the law of mass action. Equation (5) is integrated over the residence time of the
fluid within the reactor, with each stage of the quench treated as a plug-flow reactor
(5)
kf - Aexp(-B/T)
(6)
(7)
4
-------
characterized by its own average temperature and residence time. The mole fraction of
Cl2 is assumed to be constant over the reactor, as it is well in excess of the initial mercury
mole fraction. With these assumptions, Eq. (5) integrates to
= (8,
R *=i Tk
where
Z = conversion of Hg°
Tk= average temperature of the kth reactor stage
Atk - residence time for the kti, reactor stage
Table 1 gives the parameters for each of the reactor temperatures considered.
Table 1. Temperatures and residence times for different reactor stages.
Reactor
temperature (K)
r,(K)
T2( K)
T,(K)
?;(K)
A/,(s)
At 2 (s)
At As)
At4 (s)
423.15 (150 °C)
423.15
378.87
322.21
302.49
2.350
0.225
0.154
1.260
523.15 (250 °C)
523.15
446.31
345.27
308.11
1.890
0.174
0.144
1.200
Equation (8) is evaluated at both reactor temperatures, and the resulting nonlinear system
is solved to yield the pre-exponential factor A and the characteristic temperature B. The
result is the following Arrhenius rate coefficient:
kf = 2x10s exp(-1248/F) (units of meters, kilomoles, seconds, K) (9)
This may be contrasted with Hall's temperature-independent rate of kf = 3.4xlO6 (same
units) as given in Ref. 1. At room temperature (25 °C), the new rate coefficient yields a
value of 3.04 x 106 m3/ kmol-s, in qualitative agreement with that of Hall. Regression of
the data of Skare and Johansson10 gives a much smaller rate coefficient of 72 m3/ kmol-s,
but this result must be considered suspect in view of their described difficulties in
maintaining the stability of Cl2 in N2 without mercury. Table 2 presents predicted levels
of mercury conversion for Ghorishi's test conditions.
Table 2. Predicted mercury conversion versus experimental data.
Temperature (K)
Z (%, new rate)
Z (%, Hall)
Z (%, experiment)
423.15
84.74
58.87
85 (+/- 5)
523.15
87.74
49.62
88 (+/-1)
5
-------
The Hall rate coefficient results in an underprediction of mercury conversion levels. The
best-fit rate as determined from the analysis above performs well and is used in
subsequent calculations.
MERCURY MASS BALANCE DATA
A second consideration in validating the hypothesis of a primarily gas-phase mercury
conversion process is the amount of mercury captured by the fly ash versus that released
back into the flue gas stream. To close this mass balance and obtain the extent of surface
mercury adsorption, the fixed bed reactor described in Ref, 7 was loaded with model fly
ash consisting of 22 wt% AI2O3, 77 wt% Si02, and 1 wt% CuO at temperatures of 150
and 250 °C. Flue gas consisting of 40 ppbv Hg°, 50 ppmv HCI, 2% 02, and 5% C02 in N2
was passed through the reactor and the effluent sampled using the spiked OH method.11
The exposed model fly ash was recovered and analyzed according to the OH method to
obtain the amount of mercury captured by the surface. Each test was duplicated. At a
reactor temperature of 150°C, 86±5% of the inlet Hg° was present in an oxidized state
(probably HgCl?) in the gas phase, while 6.3±1.5% of the inlet Hg° was captured by the
fly ash. The remainder was unreacted Hg°. The total mercury mass balance across the
reactor was 98±1%. At a reactor temperature of 250 °C, 98±0% of the inlet Hg° was
present in oxidized form in the gas-phase, while 1.1 ±0.5% of the inlet Hg° was adsorbed
by the model fly ash. The remainder was unreacted Hg°. The total mercury mass balance
across the reactor was 99±0.3%. As expected from the earlier work7, significant oxidation
of mercury vapor was observed in the presence of CuO.
These results show that the fly ash surface is not inert to mercury and that some
consideration of the details of adsorption/desorption processes, as well as possible surface
reactions of mercury and chlorine, may be necessary. Without more experimental data, it
is difficult to conjecture whether the majority of the mercury conversion takes place
within the fly-ash bed itself or in the gas stream. However, given the degree of mercury
reactivity with chlorine in the gas phase as evidenced above, it seems logical to maintain
the initial premise that the gas-phase reactions are the more important, and that the fly ash
simply catalyzes the production of the gas-phase reactant CI2 from HCI.
DEACON PROCESS MODELING
Though much recent progress has been made in developing thermodynamically feasible
elementary reactions for the Deacon process5'6, there exists no comprehensive set of rate
data for these reactions. A two-step global reaction scheme for the Deacon process as
driven by a CuO catalyst has been proposed by Nieken and Watzenberger8 and is used as
the basis for the present work.. The Nieken-Watzenberger mechanism subdivides the
process into a chlorination step (which results in the formation of the intermediate surface
species CuCl;> and the release of gas-phase H20), and a dechlorination step (which results
in the formation of Cl2 and the regeneration of the catalyst CuO):
6
-------
Chlorination
2 HC1 + CuO => CuCl2 + H20, (10)
kf = 4.16x 1()97"exp(-12000/7') (units of meters, kilomoles, seconds, K)
Dechlorination
CuCI2 + '/a 02 => CuO + Cl2, (11)
y
kf - 1.44772 exp(-2000/7') (units of meters, kilomoles, seconds, K)
The chlorination reaction is first order with respect to CuO and HC1 concentration, while
the dechlorination reaction follows the law of mass action. The Nieken-Watzenberger
mechanism is written on a per-volume basis, though surface species CuO and CuCl2 are
involved. The reaction mechanism thus depends on the initial concentration of CuO in the
sorbent and on the voidage of the fixed bed.
This mechanism is solved simultaneously with the mercury chlorination reaction (4) with
rate coefficient from Eq. (9) using a plug-flow reactor code. The voidage is a function of
spatial distance within the reactor and is set to 0.93 within the fly ash bed and 1.0 outside
the bed. The Nieken-Watzenberger mechanism is assumed to apply only within the extent
of the bed. while the mercury chlorination reaction is assumed to apply everywhere
within the reactor. Test conditions are from Ghorishi7 and involve CuO concentrations of
0.1 and 1 % by weight of sorbent and temperatures of 150, 200, and 250 °C. The
superficial gas velocity and quenching pattern are functions of the temperature, as
indicated in Ref. 2. The initial flue gas composition is 40 ppbv Hg°, 50 ppmv HC1, 2%
02, and 5% C02 in N2.
Table 3 shows the results of applying Nieken and Watzenberger's mechanism for
chlorine formation (with original rate coefficients) with the mercury chlorination reaction
(4).
7
-------
Table 3. Mercury conversion for Ghorishi7 experiments (original Nieken-Watzenberger
rates).
Case
% Hg conversion
at 150 °C
% Hg conversion
at 200 °C
% Hg conversion
at 250 °C
Original Nieken-
Watzenberger rates,
0.1 wt% CuO
1.07
20.2
91.0
Experiment,
0.1 wt% CuO
66.5
86.8
91.8
Original Nieken-
Watzenberger rales,
1 wt% CuO
10.2
87.9
100
Experiment,
1 wt% CuO
95.1
91.6
94.2
As indicated in Table 3, the Nieken-Watzenberger mechanism results in a significant
underprediction of mercury conversion levels at the lower temperatures of 150 and 200
°C and at the lower CuO concentration of 0.1 % by weight of sorbent. Agreement
improves for the highest temperature of 250 °C and for the higher CuO concentration of 1
% by weight of sorbent. No explanation is given in Ref. 8 as to how the reaction rates
were determined, but it is likely that they are representative of a more industrial-scale
Deacon-type process, involving much larger HC1 concentrations and probably higher
temperatures.
This uncertainty as to the validity of the mechanism for the present situation led initially
to a sequence of experiments designed to measure actual Cb production in the reactor in
the absence of mercury and with a CuO catalyst. The intent was to provide data suitable
for refitting the rate coefficients of the Nieken-Watzenberger scheme for the present
range of conditions. However, substantial difficulties were encountered in trying to
measure sub-pprn Cl2 concentrations accurately. The experiments did indicate the
presence of chlorine vapor at relatively low reactor temperatures, indicating that a
Deacon-type process was in effect, but results could not be quantified. As such, an
alternative procedure was devised, based on the heterogeneous chlorination results
presented earlier.7
The procedure starts by determining the amounts of molecular chlorine necessary to
effect the levels of mercury conversion observed in Ref. 7, given the gas-phase pathway
Hg + Cl2=> HgCI? (with the new rate coefficient) as the only reaction involved.
As the data for 1 wt% CuO display more scatter and do not exhibit the anticipated
increase in conversion with increasing temperature, attention is focused on the 0.1 wt%
data. The second step is to determine the rate coefficient(s) for the Nieken-Watzenberger
mechanism that best (in a least-squares sense) produce the desired chlorine
concentrations in the steady-state limit, given the bed length and voidage (0.93). This step
8
-------
is facilitated by realizing that, at steady-state, the net production of the surface species
CuO and C11CI2 is zero, meaning that the forward rate of the chlorination step must equal
the forward rate of the dechlorination step. This simplification enables the analytic
integration of the plug-flow advection/reaction equations across the extent of the bed:
Mass fractions of the reactive species at the end of the bed are thus determined by
YHClF = YHCtl zxV{-2kfpCu0LIU u) (12)
Y0/ = Y(P' -1 12—^LYHa(/)[! — exp(-2£f pCu0L/U )] (13)
Mhc,
r M 1
Ycn = 1/2—~^Ylia [I-exp(-2k f pCu0L/ U )] (14)
Mhci
Y/no' = ^^~7T^~YHa'[l~exp(-2kypCu0L/U )] (15)
where :
Yt = mass fraction of species k
F = conditions at the end of the fixed bed
/ = conditions at the beginning of the fixed bed
Paio ~ molar concentration of CuO, referenced to unit total volume (kmol/m3)
L = length of the bed (2 cm)
U = superficial gas velocity (m/s)
M k = molecular weight of species k (kg/kmol)
kf= rate coefficient of the chlorination step, expressed in general Arrhenius form as
Ai ( expi-BlT).
It is of note that the steady-state mass fractions at the end of the bed are dependent only
on the rate coefficient of the chlorination step. Mole fractions of the reactive species are
Y. / M
determined by X , given initial concentrations of the inert species C02 and
1
N2. The predicted mole fraction of Cl2 at the end of the fixed bed is then compared to the
target value for each of the three temperatures (150, 200, and 250 °C), with the unknowns
being the pre-exponential constant A, the characteristic temperature B, and the exponent
C. This closed nonlinear system could not be solved, indicating that the assumed
functional form for the rate coefficient is not precise enough. This is of little concern, as
the data are not that precise either, and a least-squares solution was found by setting C to
0 and performing the required analysis. The result is a rate coefficient of the form:
9
-------
k, -11716exp(-2040/7") (units of meters, kilomoles, seconds, K)
(16)
Table 4 compares results obtained from the Nieken-Watzenberger mechanism with re-
fitted chlorination rate coefficient with the data of Ghorishi.7 Reasonable agreement is
evidenced across the range of temperatures for the 0.1 wt % CuO concentration. The
model predicts complete conversion for the 1 wt% CuO concentration, while the data
indicate that some mercury remains unreacted.
Table 4. Mercury conversion for Ghorishi7 experiments (refitted Nieken-Watzenberger
chlorination step).
Case
% Hg conversion at
150 °C
% Hg conversion at
200 °C
% Hg conversion at
250 °C
Refitted rates,
0.1 wt% CuO
67.7
82.5
90.9
Experiment,
0.1 wt% CuO
66.5
86.8
91.8
Refitted rates,
1 wt% CuO
100
100
100
Experiment,
1 wt% CuO
95.1
91.6
94.2
Figures 1 and 2 present steady-state chlorine and mercury mole fractions versus distance
along the reactor for the three-step mechanism described above (with refitted rate
coefficients). Chlorine is formed within the fly ash bed, while chlorine due to reaction
with elemental mercury is depleted downstream of the bed. Mercury is depleted within
and downstream of the bed; concentrations at the exit of the straight-section reactor are
higher than those in Table 4, indicating that further reaction takes place during the
quench of the flue gas stream and in the sampling train.
10
-------
Figure 1. Chlorine mole fractions versus distance along the reactor.
4E-06
3.5E-06
3E-06
c
.2 2.5E-06
o
S
« 2E-06
O
E
_f 1.5E-06
O
1E-06
5E-07
0
0,1 %CuO,T = 150*C j
0.1 * CuO, T = 200 *C I
0.1 %CuO,T = 250*C;
0
Note: fixed bed between
X = 0.127 and X = 0.147 m
-1 11 I. I I
0.1
X(m)
0.2
Figure 2. Mercury mole fraction versus distance along reactor.
4E-08
3.5E-08
3E-08
0.1 %CuO,T = 150*C
0.1 %CuO,T = 200'C
0.1 %CuO,T = 250*C
2.5E-08
2E-08
Note; ftxed bed between
X = 0,127 »ndX = 0.147 m
1E-08
5E-09
0
0.2
0
0.1
X(m)
-------
CONCLUSIONS
This paper examines one possibility of low-temperature mercury speciation as facilitated
by a Dcacon-type process for producing CI2. The viewpoint taken is that elemental
mercury and chlorine vapor react primarily in the gas phase, with the production of
chlorine vapor from HC1 catalyzed by metal oxides (CuO in this work) present in fly ash.
New experimental data for the gas-phase reaction of mercury and chlorine vapor have
been obtained and used to determine a new temperature-dependent rate coefficient for the
reaction Hg + CI2 <=> HgCk Mass balance analyses have established that, under the
present experimental conditions, mercury capture by the surface is a secondary effect.
These experimental results give some credence to the premise raised above. An existing
chemical kinetics model for chlorination/dechlorination stages of the Deacon process has
been refitted to describe existing heterogeneous chlorination data better and, when
combined with the mercury-chlorine reaction, has been shown to predict observed
speciation trends reasonably well. Future work is planned to conduct an independent
validation of the chemical kinetics model through direct measurements of Cl2. Work is
also planned to extend the model to account for more realistic situations, which may
include the presence of inhibitory agents (such as H2O and S02) in the flue gas and other
trace metal oxides (such as Fe203).
ACKNOWLEDGMENTS/DISCLAIMER
Portions of this work were conducted under EPA Purchase Order OC-R377-NASE with
Jack R. Edwards of North Carolina State University and under EPA Contract No. 68-C-
99-201 with ARCADIS Geraghty and Miller, Inc. The research described in this article
has been reviewed by the Air Pollution Prevention and Control Division, U.S.
Environmental Protection Agency, and approved for publication. The contents of this
article should not be construed to represent Agency policy nor does mention of trade
names or commercial products constitute endorsement or recommendation for use.
REFERENCES
1. Sliger, R.N., Kramlich, J.C., and Marinov, N.M. Fuel Process. Tech. 1982, 65-66,
423-438.
2. Edwards, J.R., Srivastava, R.K, and Kilgroe, J.D. J. A&WMA 2001, in press.
3. Niksa, S., Helble, J.J., and Fujiwara, N. Environ. Sci. Tech. 2001, submitted.
4. Deacon, H. U.S. Patent 165 802, 1875; see also U.S. Patent 85 370, 1868; U.S.
Patent 118 209, 1871; and U.S. Patent 141 333, 1875.
5. Hisham, M.W.M., and Benson, S.W. J. Phys. Chem. 1995, 99, 1995, 6194-6198.
6. Pan, IJ.Y, Minet, R.G., Benson, S.W., and Tsotsis, T.T. Ind. Eng. Chem. Res.
1994, 33, 2996-3003.
7. Ghorishi, B. "Fundamentals of Mercury Speciation and Control in Coal-Fired
Boilers," EPA-600/R-98-014 (NTIS PB98-127095), Air Pollution Prevention and
Control Division, February 1998.
-------
8. Nieken, U., and Watzenberger, O. Chem. Eng. Sci. 1999, 54, 2619-2626.
9. Hall, B., Schager, P., and Lindqvist, O. Water, Air, and Soil Pollution 1991,56, 3-
14.
10. Skare, I., and Johansson, R. Chemosphere 1992, 24, 1633-1644.
11. Linak, W.P., Ryan, J.V., Ghorishi, S.B., and Wendt, J.O.L. J. A&WMA 2001,51,
688-698.
13
-------
TECHNICAL REPORT DATA
NRMRL-RTP-P-612 (Please read Instructions on the reverse before completing)
1 REPORT NO. 2.
EPA/600A-01/111
3. RECIPIENTS ACCESSION NO.
4 TITLE AND SUBTITLE
A Computational and Experimental Study of Mercury
Speciation as Facilitated by the Deacon Process
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7 author- J.R.Edwards (NCSU); R.K.Srivastava, C.W.Lee, and
J.D.Kilgroe (EPA); and S.B.Ghorishi (ARCADIS)
8. PERFORMING ORGANIZATION REPORT NO
9 PERFORMING ORGANIZATION NAME AND ADDRESS
North Carolina State Univ. ARCADIS Geraghty &
Dept. of Mech./Aerospace Engrg. Miller, Inc.
Campus Box 7910 P.O. Box 13109
Raleigh, NC 27695 RTP, NC 27709 ^
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
EPA P.O. 0C-R377-NASE (NCSU)
68-C-99-201 (ARCADIS)
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 1-5/01
14. SPONSORING AGENCY CODE
EPA/600/13
15 supplementary notes Ravi « # Srivastava is APPCD project officer, Mail Drop 65, 919/541-
3444. For presentation at AWMA Conference, Mercury Emissions: Fate, Effects, and Control
Chicago, IL, 8/21-23/01.
,6 abstract paper gives results of a computational and experimental study of mercury
(Hg) speciation as facilitated by the Deacon process. Fly ashes that contain trace
cupric or ferric oxide are effective catalysts for elemental mercury (Hg) conversion to
mercuric chloride in the presence of hydrogen chloride, even at low reactor tempera-
tures (less than 250 C). Since these same trace metals promote chlorine (C12) gas for-
mation through the Deacon process, it is possible that this process, combined with gas-
phase Hg chlorination pathways, can explain such speciation trends. In support of this
hypothesis, experiments were conducted to determine if direct reactions of Hg with C12
gas are possible at low temperatures and if appreciable Hg is captured onto the model
fly ash surface. These results are used to develop and refine a chgmical kinetics mo-
del for Hg speciation as driven by chlorination induced by the Deacon process.
17. KEY WORDS AND DOCUMENT ANALYSIS
a DESCRIPTORS
b. IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
Pollution Kinetics
Mercury (Metal)
Fly Ash
Copper Oxides
Iron Oxides
Catalysis
Chlorination
Pollution Control
Stationary Sources
Deacon Process
13B 20K
07B
21B
07D
07C
18. DISTRIBUTION STATEMENT
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
20. SECURITY CLASS (This Page)
22. PRICE
EPA Form 2220-1 (Rev 4-77 ) PREVIOUS EDITION IS OBSOLETE forms/admin/techrpt frm 7/8/99 pad
------- |