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 ------- 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 ------- |