United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S7-90/012 June 1990
&EPA Project Summary
Development of Infrared
Methods for Characterization
of Inorganic Sulfur Species
Related to Injection
Desulfurization Processes
M. M. Thompson and R. A. Palmer
The report gives results of using
photoacoustic (PA) and diffuse
reflectance (DR) detection methods
in Fourier transform infrared
spectroscopy (FTIRS) to evaluate the
reaction of particulate CaO, CaCO3
and Ca(OH)2 samples with SO2 at
temperatures ranging from 25 to
900°C.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research 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).
Three Types of Studies
Photoacoustic (PA) and diffuse
reflectance (DR) detection methods in
Fourier transform infrared spectroscopy
(FTIRS) were used to evaluate the
reactions of particulate CaO, CaCO3, and
Ca(OH)2 samples with SO2 at
temperatures ranging from 25 to 900°C.
More specifically, this work involved three
types of studies: 1) post-exposure FTIR-
PAS (25-900°C); 2) in situ FTIR-DRS (25-
700°C); and 3) in situ FTIR-PAS (25-
400°C). The emphasis of this work was
on determining the utility of FTIR-PA and
FTIR-DR techniques for understanding
the mechanisms by. which S02 is
captured by particulate samples of CaO,
Ca(OH)2, and CaCO3.
Post-exposure FTIR-PAS experiments
involved obtaining spectral
measurements of particulate CaO,
CaCO3, and Ca(OH)2 samples after they
had been exposed to 1.5% SO2 in He as
a function of exposure time, temperature,
and gas composition. These data indicate
that : 1) the initial product formed is
CaSO3; 2) at temperatures above 500°C,
CaSO3 is converted to CaS04
predominantly through the reaction of
CaSO3 with SO2; 3) additional CaSO4
production, as well as the production of
CaS2O3, occurs via CaSO3 dis-
proportionation; 4) the formation of
CaSO4 is not as extensive for exposures
of 900°C as it is at 750°C; 5) in the
presence of O2, the production of
CaS2O3 is reduced; 6) the products form
as a thin layer on the surface of the 50-
lOOum particles; and 7) the extent of SO2
capture by the reactants decreases in the
order Ca(OH)2 > CaCO3 > CaO.
In situ FTIR-DRS experiments
confirmed post-exposure FTIR-PAS
results. In addition, the inherent
sensitivity and in situ capabilities of FTIR-
DRS enabled the detection and
identification of: 1) two different SO3 =
species and 2) an intermediate
monodentate SO4 = species. FTIR-DRS
also indicated that the formation of
S203 = depends on the concentration of
CaO, CaC03, or Ca(OH)2 in the NaCI
diluent.
To be able to perform in situ high
temperature FTIR-PAS measurements
the development of a photoacoustic cell
with elevated temperature and
atmospheric control was necessary. The
design of the cell is described. The
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interaction of 1.5% SOz in N2 with
Ca(OH)2, CaC03, and Na2C03 as a
function of time and temperature of
exposure was monitored. Preliminary
data, depicting the presence of
physisorbed SO2 on the CaC03 surface
at 360°C, demonstrated the sensitivity of
in situ FTIR-PA detection methods for
both gas- and solid-phase reaction
intermediates.
M. Thompson and R. Palmer are with Duke University, Department of Chemistry,
Durham, NC 27706.
Frank £ Brlden is the EPA Project Officer (see below).
The complete report, entitled "Development of Infrared Methods for
Characterization of Inorganic, Sulfur Species Related -to- Injection
Desulfurization Processes," (Order No. PB 90-231-275AS; Cost: $23.00,
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:
Air and Energy Engineering Research 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/S7-90/012
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