Thermodynamic and Kinetic Study of Carbon Dioxide and Mercury Removal from Flue Gas in Coal Combustion Power Plants by Kun Liu B.Sc. Chemical Engineering, Tianjin University, 2007 A Dissertation submitted in partial fulfillment of the requirements for the degree Doctor of Philosophy in the School of Energy, Environmental, Biological & Medical Engineering of the College of Engineering and Applied Science University of Cincinnati Cincinnati, OH 2012 Dissertation Committee: Stephen W. Thiel, Ph.D (Chair) Junhang Dong, Ph.D Yuen-Koh Kao, PhD Neville G. Pinto, Ph.D Drew C. McAvoy, Ph.D Abstract Carbon dioxide and mercury from anthropogenic emissions pose a significant threat to our environment and human health. Removal from their major source – coal- fired power plants – is one of the most effective approaches to control their emissions. Traditional removal technologies are usually cost-intensive and low-efficient. Many studies have been focused on the novel capture approaches that are cost-effective while keeping a high performance. Thermodynamics and kinetics are critical to these studies as they provide fundamental knowledge of the capture process. In this work, the thermodynamics and kinetics of CO2 and Hg capture through absorption using aqueous amines solutions and adsorption using supported ionic liquid sorbents were investigated. A vapor-liquid equilibrium (VLE) data reduction method developed by Barker [1] that simplifies experimental measurements while maintaining accuracy was applied for the first time to the thermodynamic study of CO2 absorption in aqueous amine systems. The method eliminates the measurements of speciation in liquid phase and vapor phase by applying a layer of mass balance iteration in the correlation. Incorporating the electrolyte non-random two liquid (eNRTL) model and the Soave–Redlich–Kwong (SRK) model, the data reduction method was used to correlate VLE and heat of absorption data collected in a modified batch calorimeter for ethanolamine (MEA) - H2O - CO2 system and piperazine (PZ) - H2O - CO2 systems. The optimized model with the best-fit eNRTL model parameters was used to predict vapor pressures under the conditions reported in the literature; the predicted values were consistent with the independent literature results, indicating successful application of the Barker data reduction method and the mathematical model in the thermodynamic study of CO2- ii aqueous amine systems. The importance of combined correlation of VLE and heat of absorption data in the accurate prediction of the two properties was also confirmed by comparing the prediction from single and multiple data sets correlation. With the current technologies, capture of CO2 and Hg from coal combustion flue gas requires additional air pollution control devices that can only do a single task (for example, a gas scrubber for CO2 or duct entrainment adsorption for Hg). To reduce the cost, a new approach to capture both CO2 and Hg from coal combustion flue gas in an integrated adsorbent system was discovered. In this approach, a task-specific amino acid ionic liquid is supported on silica gel particles with high surface area and pore volume. CO2 capture for these sorbents was studied in simplified fixed-bed experiments. The CO2 capacity for was found to be 0.4 mol of CO2/ mol of ionic liquid. The ionic liquid loading was optimal for CO2 capture at 40 wt%. Mass transfer in fixed-bed trials was slow at high ionic liquid loadings due to the decreasing in contact surface area. Limited change of CO2 capacity was observed after four adsorption/desorption cycles, which indicates good regenerability. Hg capture performance was assessed for the same material in fixed-bed adsorption tests under a nitrogen environment. These sorbent systems had a total Hg uptake of more than 14 mg/g. Slipstream testing of the sorbents, along with other novel Hg sorbents developed previously, using coal combustion flue gas showed promising and competitive results in Hg removal rate and Hg capacity compared with competing technologies. When both CO2 and Hg are present in the gas phase, it is expected that Hg (present in trace quantities in flue gas) accumulates and fixes in the sorbent via strong chemical bonding over an extended time, while CO2 (present in large quantities in flue gas) can reversibly be adsorbed and desorbed on the sorbent. This hypothesis was iii validated by the experimental evidence that the present of CO2 has limited effect on the capture of elemental Hg vapor and the theoretical evidence that oxidized Hg has a stronger bonding with the ionic liquid than CO2. In summary, the thermodynamic and kinetic behaviors of CO2 and Hg capture from coal combustion flue gas were successfully investigated through experimental and theoretical methods. The obtained experimental results and modeling framework will advance the design and optimization of pollution control process. [1] Barker, J., Determination of activity coefficients from total pressure measurements. Australian Journal of Chemistry, 1953. 6(3): p. 207-210. iv Copyright © 2012 by Kun Liu All rights reserved v Acknowledgements I would like to express my deep appreciation and gratitude to my academic advisor, Dr. Stephen W. Thiel, for all the support, instruction, and encouragement that he provided to me throughout my graduate study. His in-depth knowledge and experience in chemical engineering is a tremendous help in my research. In 2008 and 2009 when my research had some resistance, his patience and continuous encouragement helped me overcome the difficulties. In the stage of dissertation writing, his timely and helpful comments and suggestions are also greatly appreciated. I am truly fortunate to have had the opportunity to work with Dr. Thiel. I would also like to express my heartfelt appreciation to Dr. Neville G. Pinto for his valuable suggestion and encouragement to my research. His effort on helping the slipstream testing of mercury sorbent project moving forward is also greatly appreciated. I would like to thank the other members in my dissertation committee: Dr. Junhang Dong, Dr. Yuen-Koh Kao, and Dr. Drew C. McAvoy for their helpful comments and suggestions to my research work and their valuable time on reviewing my dissertation. This work was supported by the following agencies, companies, and organizations: Ohio Coal Development Office, Babcock & Wilcox Co., US Environmental Protection Agency, Duke Energy Co., Oxford Mining Inc, ARCADIS Co., and The University of Cincinnati. Their financial and technical supports are gratefully acknowledged. I highly appreciate and would like to thank my research colleagues: Juan He, Rebecca J. Desch, Amina Darwish, Jungseung Kim, Poornima Rao, Shada Salem, Taylor vi Robie, Ali Gitipour, and Salem Shehadeh. The experience of working with them was enjoyable and memorable. I greatly appreciate the help by Juan on the bench-scale mercury adsorption tests. Her excellent work provided very valuable support to the slipstream tests in this work. Finally, I would like to thank my family: my parents, the loveliest couple in the world, and my wife, the most beautiful woman in the world. Their trust and love are the greatest momentums to my graduate study. vii Table of Content List of Figures ................................................................................................................. xiii List of Tables ................................................................................................................ xviii List of Symbols ................................................................................................................ xx Chapter 1 - Introduction and Objectives ........................................................................ 1 1.1 Major flue gas pollutants and control technologies .................................................. 3 1.1.1 Carbon dioxide ................................................................................................... 3 1.1.2 Mercury ............................................................................................................ 15 1.1.3 Other pollutants ................................................................................................ 18 1.1.4 Process Integration ........................................................................................... 20 1.2 Key thermodynamic and kinetic properties in pollutant gas removal from flue gas ...................................................................................................................................... 21 1.2.1 Vapor liquid equilibrium .................................................................................. 22 1.2.2 Energy demand for regeneration ...................................................................... 23 1.2.3 Heat capacity .................................................................................................... 23 1.2.4 Mass transfer and dispersion in fixed-bed adsorption ..................................... 24 1.3 Objectives ............................................................................................................... 26 Chapter 2 - Materials and Methods .............................................................................. 28 2.1 Materials and Preparation ....................................................................................... 28 2.1.1 Aqueous CO2 solvents ..................................................................................... 28 2.1.2 Amino acid (AA)-based room temperature ionic