Computational Chemistry Study of Solvents for Carbon Dioxide Absorption Eirik Falck da Silva Doctoral Thesis Norwegian University of Science and Technology Fakultet for Naturvitenskap og Teknologi Institutt for Kjemisk Prosessteknologi Trondheim, August 2005 Contents List of Papers................................................................................................................5 Abstract.........................................................................................................................7 Acknowledgements ......................................................................................................9 1 Introduction........................................................................................................11 1.1 Purpose.................................................................................................... 11 1.2 Global Warming...................................................................................... 12 1.3 Mitigation................................................................................................ 13 1.3.1 Background ..................................................................................... 13 1.3.2 CO2 Capture and Storage ................................................................ 13 2 CO2 Absorption..................................................................................................17 2.1 Introduction............................................................................................. 17 2.2 Solvents................................................................................................... 19 2.3 Challenges............................................................................................... 20 2.4 Current Understanding of the CO2 Absorption Process.......................... 21 3 Computational Chemistry.................................................................................25 3.1 Introduction............................................................................................. 25 3.2 Quantum Mechanics ............................................................................... 26 3.2.1 Introduction..................................................................................... 26 3.2.2 The Born-Oppenheimer Approximation......................................... 28 3.2.3 Hartree-Fock Self-Consistent Field Method................................... 28 3.2.4 Post-HF Methods............................................................................ 28 3.2.5 Density Functional Theory.............................................................. 29 3.2.6 Basis Sets........................................................................................ 30 3.2.7 Basis Set Superposition Error ......................................................... 31 3.2.8 Temperature .................................................................................... 32 3.2.9 Performance .................................................................................... 32 3.3 Molecular Mechanics.............................................................................. 33 3.3.1 Introduction..................................................................................... 33 3.3.2 Force Field Parameterization .......................................................... 35 3.3.3 Atomic Charges...............................................................................36 3.3.4 Polarizable Force Fields.................................................................. 38 3.4 Simulations ............................................................................................. 39 3.4.1 Introduction..................................................................................... 39 3.4.2 Free Energy Perturbations............................................................... 41 3.5 QM/MM.................................................................................................. 43 3.6 Computational Chemistry and Experiment............................................. 43 3.7 Review of Computational Chemistry Work on CO2 Absorption............ 45 4 Modeling of Solvation Energy...........................................................................47 4.1 Introduction............................................................................................. 47 4.2 The liquid state........................................................................................ 48 1 4.3 Statistical Mechanics.............................................................................. 49 4.4 Models to Calculate the Free Energy of Solution................................... 52 4.4.1 Introduction..................................................................................... 52 4.4.2 Equation of State and Lattice Models............................................. 53 4.4.3 Continuum Models.......................................................................... 56 4.4.4 Molecular Simulation...................................................................... 62 4.4.5 RISM and RISM-SCF..................................................................... 63 4.4.6 Supermolecule Approach................................................................ 64 4.4.7 Hybrids of Computational Chemistry approaches.......................... 65 4.4.8 Descriptor Models........................................................................... 66 4.4.9 Other Models...................................................................................67 4.4.10 Hybridization of Gibbs Energy Models and Computational Chemistry Based Models ................................................................................ 68 4.5 Comparison of Methods to Calculate the Free Energy of Solution ........ 69 4.5.1 Methods........................................................................................... 69 4.5.2 The Basicity.................................................................................... 71 4.5.3 Amines ............................................................................................ 72 4.5.4 Results............................................................................................. 73 4.5.5 Conclusion ...................................................................................... 79 5 Reaction Mechanisms and Equilibrium...........................................................81 5.1 Introduction............................................................................................. 81 5.2 Reaction Mechanisms ............................................................................. 81 5.2.1 Introduction..................................................................................... 81 5.2.2 Bicarbonate Formation.................................................................... 82 5.2.3 Carbamate formation....................................................................... 84 5.2.4 Bases ............................................................................................... 87 5.2.5 Alcohol-Group Bonding to CO2 ..................................................... 87 5.2.6 Carbamate as Reaction Intermediate............................................... 88 5.2.7 Molecules with Multiple Amine Functionalities ............................ 89 5.2.8 Shuttle Mechanism.......................................................................... 91 5.2.9 Summary and Conclusion ............................................................... 92 5.3 Determining Equilibrium........................................................................ 94 5.3.1 Equilibrium and Kinetics................................................................ 94 5.3.2 Temperature Dependency of Equilibrium Constants...................... 95 5.3.3 Activity Coefficients....................................................................... 96 5.3.4 Process Energy Consumption ......................................................... 97 5.3.5 Summary ......................................................................................... 98 6 Other Solvent Properties...................................................................................99 6.1 Introduction............................................................................................. 99 6.2 Solubility in Water.................................................................................. 99 6.3 Solvent Degradation.............................................................................. 100 6.4 Corrosion............................................................................................... 101 2 6.5 Foaming ................................................................................................ 102 6.6 Toxicology ............................................................................................ 103 6.7 Cost ....................................................................................................... 103 6.8 Precipitations......................................................................................... 104 7 Present and Potential Solvents........................................................................105 7.1 Introduction........................................................................................... 105 7.2 Solvents in Use..................................................................................... 105 7.2.1 Ethanolamine ................................................................................ 105