The Roles of 02 and SO2 in the Degradation of Monoethanolamine during CO2 Absorption from Industrial Flue Gas Streams Teeradet Supap Petroleum and Petrochemical College, Chulalongkorn University, Pathumwan, Bangkok, Thailand, 10330 Raphael Idem# Process Systems Engineering Laboratory, Faculty of Engineering, University of Regina, Regina, Saskatchewan, Canada S4S OA2 Paitoon Tontiwachwuthikul Process Systems Engineering Laboratory, Faculty of Engineering, University of Regina, Regina, Saskatchewan, Canada S4S OA2 Chintana Saiwan Petroleum and Petrochemical College, Chulalongkorn University, Pathumwan, Bangkok, Thailand, 10330 ABSTRACT The roles of 02 and S02 in the degradation of aqueous monoethanolamine (MEA) in the concentration range of 5 - 7 kmol/m3 were investigated using simulated flue gas containing 02 of 6 - 100 %, and S02 concentration in the range of 10-11 - 11 ppm, as typically present in polished flue gas streams, at degradation temperatures in the range of 328 - 393 K. An analysis of a power law rate expression formulated to represent the degradation process showed that the degradation was most susceptible to 02 followed by MEA and then SO2. SO2 played a significant role by giving rise to additional MEA oxidative degradation. An increase in °2 and S02 concentrations, the initial MEA concentration, and temperature all resulted in an increase of the degradation rate. Keywords: Degradation, SO2, 02, MEA Introduction Approximately, 90% of the world's primary energy is currently derived from the use of fossil fuels (Gupta et al., 2003). In terms of measurable reserves, the distribution is in the order of oil, natural gas and coal, respectively having shares of 38, 31, and 28% (Speight, 1994). Although fossil fuels contribute to such a significant energy supply, an environmental concern over the emission of carbon dioxide (CO2), a major greenhouse gas, can limit their use. The product of the combustion of coal in air gives rise to the flue gas stream, which contains considerable concentration of CO2 (Berkowitz, 1994). Research has shown that coal alone, is globally responsible for 28 - 36 % of CO2 emission (Smith and Thambimuthu, 1993). With a lack of proper control technique, the emitted CO2 can aggravate the enhanced greenhouse effect causing a rise of the global temperature. In addition, coal-fired flue gas streams used in industrial processes such as the manufacture of ammonia and coal gasification must meet the CO2 concentration targets to respectively avoid catalyst poisoning and dilution of the fuel gas products. These environmental and quality control concerns give rise to the significance of CO2 capture from large point sources of coal-fired flue gas streams. Absorption with chemical reaction using aqueous amine solutions is the most attractive technique for the extraction of CO2 from low pressure flue gas streams. Its commercial use in coal-fired power plants has been summarized in the literature (Chakma et al., 1995). A more recent semi-commercial technology demonstration unit for CO2 extraction from coal- power station, a unit of the International Test Center for C02 Capture (ITC), University of Regina, has been in operation since 2000 for performance and reliability evaluation of alkanolamine-based CO2 capture technology (Wilson et al., 2004). Nonetheless, there still exist operational burdens that continuously upset absorption plants. One of them is that the considerable quantity of 02 in flue gas streams chemically induces the break-down of amines during the capture process. These fragmentations, known as oxidative degradation, are extremely undesirable since they result in solvent losses and the introduction of unwanted degradation products which need to be periodically removed to maintain the CO2 removal capacity in the absorption cycle, thus, increasing operational cost and energy consumption. In some severe cases, heavily contaminated solvents must be eventually replaced with fresh ones giving rise to additional cost of disposal and amine make-up. An additional burden also imposed is corrosion problems. Degradation products have been periodically implicated for their negative corrosive effect towards plant equipment (Rooney et al., 1997; Veldman, 2000). In the early stage of the oxidative degradation research, it was mainly focused on detection of the existence of the oxidation and qualitative analysis of the oxidation products. A study indicated the oxidation resistance in the order of monoethanolamine (MEA) > triethanolamine (TEA) > diaminoisopropanol (Gregory and Scharmann, 1937). Due to a limitation of analytical technique, individual acid product of MEA oxidation in MEA alone or in glycol solution 1-4244-0218-2/06/$20.00 C)2006 IEEE.