Development of Advanced Amine Systems with Accurate Vapour-liquid Equilibrium Measurement Danlu Tong A thesis submitted for the degree of Doctor of Philosophy of the University of London and Diploma of Membership of Imperial College Energy Engineering Group Department of Chemical Engineering and Chemical Technology Imperial College London London SW7 2AZ, United Kingdom 2012 2 Declaration of Originality I, Danlu Tong, hereby certify that this thesis has been written by me, based on the original work conducted by me in the Department of Chemical Engineering at Imperial College London between 2008 and 2012, except where specifically acknowledged in the text. 3 Abstract Imperative pressure on containing anthropogenic greenhouse gas (GHG) emissions, particularly CO , has led to the development and deployment of low-carbon technologies 2 across the globe. Carbon capture and storage (CCS) is widely considered as an indispensible part of the technology portfolio alongside energy efficiency, renewables and nuclear. Due to its operational flexibility and technology maturity, post-combustion capture (PCC) is most likely to be one of the first adopted capture processes. However, the associated capital expenditure (CAPEX) and operating cost (OPEX) of the current state-of-the-art PCC process are seemed as the major barriers for its commercialisation. This thesis investigated the relationship between the chemical structure of the amines and their CO cyclic loading capacity through solubility measurements with two types of 2 apparatuses: a static-analytical apparatus and a static-synthetic setup. The former was first validated by measuring the solubility of CO in 30 mass% aqueous monoethanolamine (MEA) 2 solutions at = (313 and 393) K and a total pressure range between (11 and 415) kPa. After successful validation of the apparatus, new CO solubility data for a sterically-hindered 2 amine, 2-Amino-2-Methyl-1-Propanol (AMP) were obtained at temperatures between (313 and 393) K and a total pressure range of (23 to 983) kPa. CO solubility data for a tertiary 2 amine, 2-Dimethylaminoethanol (DMMEA) were also measured with the analytical apparatus from = 313 K to = 393 K and a total pressure of (6 to 616) kPa. Apart from the three single amines studied, this work investigated the blended amine systems and the influence of an activator (piperazine or PZ) on the promoted amines. For AMP + PZ blends, solubility measurements of CO in 25 mass% AMP + 5 mass% PZ and 20 mass% AMP + 10 mass% 2 PZ were conducted from (313 to 393) K; while for the DMMEA + PZ mixture, 25 mass% DMMEA + 5 mass% PZ system was studied. The static-synthetic setup employed in this work was first validated through measuring the solubility of CO in water from (313 to 393) K. A calculation algorithm implemented in 2 Microsoft Excel as VBA was used to convert the experimental data to Henry‘s constants which were then compared with literature data. After the validation, CO solubility of 25 2 mass% MDEA was measured at 313 K. 4 Another aspect of this work involved building quasi-chemical thermodynamic models to interpret the experimental data obtained in both apparatuses. This work used two different methods including Deshmukh-Mather model based on activity (γ)-fugacity (φ) approach and a more simplified Kent-Eisenberg model to represent the single and mixed amine systems respectively. Despite the compromise in the correlation quality compared to the γ- φ approach, Kent-Eisenberg model has received wide popularity due to its simplicity. In this work, the correlation results from the two models were compared. The applications of the models to predict solution phase speciation and CO solubility behaviour not measured in this work 2 were also discussed. 5 Acknowledgements Spending three-and-half years on a PhD project is a significant commitment. This experience is an invaluable asset in my life and will not be so rich and colourful without the contributions from numerous people, to whom I would like to express my sincere appreciation. First and foremost, my sincere gratitude undoubtedly goes to my supervisors: Paul, Martin and Geoff. Your immense support and encouragement throughout my PhD were always the sources of momentum that led me through the obstacles. Thank you also Jon, Niall, and Mathieu, for the inspiring and thoughtful discussions on the CCS-related issues. Thank you Nigel and John, for your patience and kind guidance on any query I had. And to all the fellow colleagues in Paul‘s and Martin‘s groups, thank you for the inspiring discussions as well as fun social activities that made my life more colourful. Thank you very much the Granthams, for providing the financial assistance that allow me to complete my PhD. Thank you all the people from the Grantham Institute, Brian, Simon, Neil, and Ajay, for the invaluable discussions on the climate change and energy-related issues. Finally, special thanks to Zheng, your tremendous support is very much appreciated. 6 ―Success is the ability to go from one failure to another with no loss of enthusiasm.‖ -Winston Churchill 7 Contents Chapter 1 Introduction.......................................................................................................... 18 1.1 Motivation for carbon capture ........................................................................................ 18 1.2 Scope and objectives of this work .................................................................................. 21 1.3 Outline of thesis ............................................................................................................. 22 1.4 Key contributions of this work ....................................................................................... 23 Chapter 2 Literature Review: Amine Scrubbing in the Context of Carbon Capture ..... 25 2.1 Carbon capture technologies .......................................................................................... 26 2.1.1 Post-combustion capture .......................................................................................... 26 2.1.2 Pre-combustion capture ........................................................................................... 28 2.1.3 Oxy-combustion capture .......................................................................................... 31 2.1.4 Other capture technologies ...................................................................................... 32 2.2 Types of amines ............................................................................................................. 35 2.3 Experimental apparatus for VLE measurement ............................................................. 36 2.3.1 Static-analytical apparatus ....................................................................................... 38 2.3.2 Static-synthetic apparatus ........................................................................................ 43 2.3.3 Flow systems ........................................................................................................... 45 2.3.4 Other methods.......................................................................................................... 46 2.4 Thermodynamic models ................................................................................................. 47 2.4.1 Solution chemistry ................................................................................................... 48 2.4.2 Thermodynamic framework .................................................................................... 48 2.4.3 Important VLE model .............................................................................................. 50 8 Chapter 3 Solubility Measurements for CO in Aqueous Amines with a Static-analytical 2 Apparatus ............................................................................................................................... 59 3.1 Introduction .................................................................................................................... 60 3.2 Original design of the apparatus..................................................................................... 60 3.2.1 Layout of the static-analytical apparatus ................................................................. 60 3.2.2 Gas and liquid sampling systems ............................................................................. 62 3.3 Revised design of apparatus ........................................................................................... 68 3.4 Experimental procedures ................................................................................................ 69 3.5 Validation of the apparatus ............................................................................................ 70 3.5.1 Validation of the pressure and temperature sensors ................................................ 70 3.5.2 Calibration of the GC system .................................................................................. 71 Chapter 4 Experimental Results from the Static-analytical Apparatus for CO solubility 2 in aqueous amines .................................................................................................................. 76 4.1 Introduction .................................................................................................................... 77 4.2 Experimental uncertainty ............................................................................................... 78 4.3 Validation of the static-analytical apparatus by measuring CO solubility in aqueous 30 2 mass% MEA solutions ......................................................................................................... 78 4.3.1 MEA in the context of carbon capture..................................................................... 78 4.3.2 Validation results ..................................................................................................... 82 4.4 Solubility of CO in aqueous AMP and AMP+PZ solutions ......................................... 84 2 4.4.1 Sterically-hindered amines in the context of carbon capture .................................. 84 4.4.2 Experimental results on CO solubility in aqueous AMP solutions ........................ 91 2 4.4.3 Experimental results on CO solubility in aqueous mixtures of AMP and PZ ........ 93 2 4.5 Solubility of CO in DMMEA and DMMEA solutions ................................................. 95 2 4.5.1 Tertiary amines in the context of carbon capture .................................................... 96 9 4.5.2 Experimental results on CO solubility in aqueous DMMEA and DMMEA+PZ 2 solutions .......................................................................................................................... 100 4.6 Comparisons of the CO solubility in amines solutions ............................................... 102 2 4.6.1 30 mass% MEA vs 30 mass% AMP ..................................................................... 103 4.6.2 30 mass% AMP vs 25 mass% AMP + 5 mass% PZ vs 20 mass% AMP + 10 mass% PZ.................................................................................................................................... 104 4.6.3 30 mass% MEA vs 30 mass% AMP vs 30 mass% DMMEA ............................... 107 4.6.4 30 mass% DMMEA vs 25 mass% DMMEA + 5 mass% PZ ................................ 110 Chapter 5 Thermodynamic Models for the Solubility of CO in Single and Blended 2 Amine Systems ..................................................................................................................... 112 5.1 Introduction .................................................................................................................. 113 5.2 γ-φ model for CO solubility in single amine solutions ............................................... 114 2 5.2.1 Physical and chemical equilibria ........................................................................... 114 5.2.2 Phase nonideality ................................................................................................... 117 5.2.3 Balance equations .................................................................................................. 119 5.2.4 γ-φ model for MEA-H O-CO ............................................................................... 119 2 2 5.2.5 γ-φ model for AMP-H O-CO ............................................................................... 123 2 2 5.3 Kent-Eisenberg model for AMP-based and DMMEA-based blended amine systems 126 5.3.1 Physical and chemical equilibria ........................................................................... 126 5.3.2 Phase nonideality ................................................................................................... 128 5.3.3 Balance equations .................................................................................................. 129 5.3.4 Kent-Eisenberg model for AMP-PZ-H O-CO ..................................................... 130 2 2 5.3.5 Kent-Eisenberg model for DMMEA-PZ-H O-CO .............................................. 135 2 2 5.4 Thermodynamic models for CO solubility in aqueous MDEA solutions ................... 139 2 5.4.1 Kent-Eisenberg model for MDEA-H O-CO ........................................................ 139 2 2 5.4.2 γ-φ model for MDEA-H O-CO ............................................................................ 142 2 2 10 Chapter 6 Solubility Measurements for H O-CO and MDEA-H O-CO Systems with 2 2 2 2 Synthetic Apparatus ............................................................................................................ 145 6.1 Introduction .................................................................................................................. 146 6.2 Apparatus and experimental procedures ...................................................................... 149 6.2.1 Apparatus ............................................................................................................... 149 6.2.2 Experimental procedures ....................................................................................... 153 6.3 Results and discussions ................................................................................................ 156 6.3.1 Calculation of the Henry‘s constant with graphical interpretation ........................ 156 6.3.2 Results from the ‗graphical interpretation‘ method ............................................... 158 6.3.3 Calculation of the Henry‘s constant with theoretical modelling ........................... 159 6.3.4 Sources of uncertainties ......................................................................................... 165 6.3.5 Uncertainty analysis .............................................................................................. 165 6.4 Measurement of the solubility of CO in aqueous MDEA system with the synthetic 2 apparatus............................................................................................................................. 166 6.4.1 Methodology for the calculation of CO solubility from experimental 2 measurements ................................................................................................................. 167 6.4.2 Results ................................................................................................................... 170 6.4.3 Other sources of uncertainties and limitations ...................................................... 174 Chapter 7 Conclusions and Future Work ......................................................................... 175 7.1 Summary of this work .................................................................................................. 176 7.1.1 Static-analytical apparatus ..................................................................................... 176 7.1.2 Quasi-chemical modelling ..................................................................................... 178 7.1.3 Synthetic apparatus ................................................................................................ 179 7.2 Conclusions .................................................................................................................. 180 7.2.1 CO absorption in 30 mass% aqueous AMP and AMP+PZ blends ...................... 181 2 7.2.2 CO absorption in 30 mass% aqueous DMMEA and DMMEA+PZ blends ......... 183 2