Published: June 06, 2011 r2011 American Chemical Society 2988 dx.doi.org/10.1021/ef200556j | Energy Fuels 2011, 25, 2988–2996 ARTICLE pubs.acs.org/EF Desorption Kinetics of the Monoethanolamine/Macroporous TiO 2 -Based CO 2 Separation Process Zhuoyan Sun, † Maohong Fan,* ,† and Morris Argyle †,‡ † Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071, United States ‡ Department of Chemical Engineering, Brigham Young University, Provo, Utah 84602, United States ABSTRACT: Monoethanolamine (MEA)/macroporous TiO 2 sorbent is a promising material for CO 2 separation because of its low energy demand. Similar to other CO 2 separation technologies, CO 2 desorption from the MEA/macroporous TiO 2 sorbent is the most energy-intensive step in the overall CO 2 separation process. The presence of water during the CO 2 desorption process leads to a significant increase in energy consumption. Therefore, CO 2 desorption in the absence of water is an important method to reduce energy consumption of CO 2 separation using MEA/macroporous TiO 2 , which is determined by several major factors, including desorption kinetics. However, the study on CO 2 desorption kinetics of supported MEA is lacking. This research was designed to make progress in this area. The CO 2 desorption kinetic model of the MEA/macroporous TiO 2 sorbent is experimentally derived with the data collected within the water-free desorption environment and theoretically proven by the pseudo-steady-state theory. The AvramiErofeyev mechanism controls the CO 2 desorption process, which is first-order with respect to RNH 3 + RNHCOO  , RNH 3 + , or RNHCOO  . The activation energy of the CO 2 desorption process is 80.79 kJ/mol. The kinetic characteristics of the CO 2 desorption are much superior to those associated with aqueous MEA-based CO 2 separation. The energy savings because of the use of MEA/macroporous TiO 2 for CO 2 separation not only results from avoiding the use of water, with its high specific heat capacity and high vaporization enthalpy, but also from the favorable desorption kinetics of the MEA/macroporous TiO 2 -based CO 2 separation. 1. INTRODUCTION People are increasingly concerned about the continuous eleva- tion of the atmospheric CO 2 concentration. Fossil-fuel-based power generation plants have been and will continue to be among the major CO 2 emission sources because of their availability and prices. 14 Therefore, cost-effective technologies should be devel- oped and adopted for capture of CO 2 from fossil fuel power plants, while renewable or low-carbon-emission fuels are sought. 57 Amine compounds have been considered to be good candi- dates for CO 2 separation because of their good reactivity with CO 2 . 8,9 Monoethanolamine (MEA) has high potential as a CO 2 - capture agent because it has a high mass-based CO 2 sorption capacity and fast reaction rate with CO 2 . The reaction associated with the conventional method for CO 2 absorption with aqueous solutions can be expressed as RNH 2 + CO 2 +H 2 O r s f k R1 , k R1 RNH 3 + HCO 3  ðR1Þ MEA has been commercially used for separation of CO 2 in the natural gas, synthesis gas, and refinery industries. However, to date, conventional coal-fired power plants still can not use aqueous MEA for CO 2 separation because of the high operating cost of the technology, resulting from its energy-intensive desorption process. In addition, thermal and oxidative degrada- tions are issues of CO 2 separation with aqueous MEA because CO 2 desorption needs to be operated within a relatively high- temperature range, which leads to the loss of MEA during multiple sorptiondesorption cycles. To overcome the shortcomings of aqueous MEA-based CO 2 separation processes, two major methods have been investigated. The first is to mix MEA with other amines to use their advantages to overcome the shortcomings of MEA. For example, the CO 2 absorption rate can be enhanced significantly when MEA is blended with N-methyldiethanolamine (MDEA), while the associated CO 2 desorption is improved. 10,11 However, these CO 2 sorption systems are still aqueous-phase. People have been interested in this type of method for a long time; thus, the thermodynamic and kinetic characteristics of CO 2 separation with blended aqueous amines have been well-studied. 1217 The second method is to replace water with organic solvents. Jou et al. found that diethylene glycol (DEG) can dissolve much more CO 2 than water. 18 Glycol compounds, includ- ing ethylene glycol (EG), DEG, and triethylene glycol (TEG), have shown high CO 2 solubility and low vapor pressure, which is desired for reducing the total energy consumption needed for the overall CO 2 separation process. 19 Essentially, replacing water with organic solvents is used to eliminate the dissociation of protonated MEA or the formation of carbonate or carbamate within the aqueous environment or recombination of water and MEA and, thus, reduce energy consumption. 20 Recently, researchers have been very interested in developing solid CO 2 sorbents with various amines, making significant progress in increasing CO 2 sorption capacities and lowering CO 2 desorption temperatures. 2129 When used for separation of CO 2 from flue gases in power plants, they could save much energy by avoiding circulation of large amounts of water. One of the methods used for preparing those solid sorbents is to Received: April 12, 2011 Revised: June 1, 2011