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
                  900C.
                   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 900C.
                  More specifically, this work involved three
                  types of studies: 1) post-exposure FTIR-
                  PAS (25-900C); 2) in situ FTIR-DRS (25-
                  700C); and  3) in situ FTIR-PAS (25-
                  400C). 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 500C,
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 900C as it is at 750C;  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 360C, 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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