Thermodynamic Studies on CO2 Capture through Gas Hydrate Formation Technology Poorandokht Ilani-Kashkouli MSc. Analytical Chemistry (Shiraz University, Shiraz, Iran, (Sept2009-Jan2012)) This dissertation (ENNO8RPH1) is submitted for the degree of doctorate of philosophy in Engineering (Ph.D. Eng) in the School of Chemical Engineering at the University of KwaZulu- Natal. Supervisor: Prof. Deresh Ramjugernath Co-supervisor(s): Prof. Amir H. Mohammadi, Dr. Paramespri Naidoo April 2015 Declaration I, Poorandokht Ilani-Kashkouli, declare that: i. The research reported in this dissertation, except where otherwise indicated is my original work. ii. This dissertation has not been submitted for any degree or examination at any university. iii. This dissertation does not contain other person’s data, pictures, graphs or other information, unless specifically acknowledged as being sourced from other persons. iv. This dissertation does not contain other person’s writing, unless specifically acknowledged as being sourced from other researchers. Where other written sources have been quoted then: a) Their words have been re-written but the general information attributed to them has been referenced; b) Where their exact words have been used, their writing has been placed inside quotation marks, and referenced. v. Where I have reproduced a publication of which I am an author or co-author I have indicated in detail which part of the publication was actually written by myself alone and have fully referenced such publications. vi. This dissertation does not contain text, graphics or tables copied and pasted from the internet, unless specifically acknowledged, and the source are detailed in the dissertation and in the References sections. ________________________ P. Ilani-Kashkouli (candidate) As the candidate’s supervisor/co-supervisor I agree/ do not agree to the submission of this dissertation. ________________________ Prof. D Ramjugernath (supervisor) ________________________ _______________________ Dr. P Naidoo (co-supervisor) Prof. A.H Mohammadi (co-supervisor) I Abstract CO2 capture and sequestration or storage (CCS) is one of the important area of research mainly due to the increased public and governmental awareness of carbon dioxide’s drastic green-house effects. The use of gas hydrate technology for the capture of CO2 from flue gas is generating much attention in the literature. Gas hydrates are non-stoichiometric, ice-like crystalline compounds formed from water and suitably sized guest molecule(s) generally under low-temperatures and elevated pressures. As the pressure required for gas hydrate formation is generally high, aqueous solutions of particular chemicals are added to the system as gas hydrate promoters. These promoters generally reduce the required hydrate formation pressure and increase the formation temperature leading to the possibility of modifying the selectivity of hydrates cages to capture various gas molecules. Some ionic liquids (ILs) such as tetra butyl ammonium bromide (TBAB), tetra butyl ammonium nitrate (TBANO3), tetra butyl phosphonium bromide (TBPB), etc. can be applied as hydrate formation promoters, in which the anion portion participates in the hydrogen- bonded cages formed by networks of water molecules and the cation part can be trapped in the hydrate cavities. Such compounds are called "semi-clathrate" hydrates. In the present work, the thermodynamic knowledge of semi-clathrate hydrates of various gases including different hydrate types, and their properties were studied. New efficient gas hydrate promoters (TBPB, TBANO3 and TBAF) were used to reduce the system pressure required for hydrate formation. Thereafter, new phase equilibrium data of semi-clathrate hydrates for (CO2/CH4/N2/Ar) in the presence of (TBPB / TBANO3 / TBAF) at varying concentrations (0.05, 0.075, 0.10, 0.15, 0.20 and 0.30 mass fraction TBPB), (0.05, 0.10, 0.15, 0.20 mass fraction TBANO3) and (0.041, 0.067 mass fraction TBAF) were generated. Measurements were undertaken in the temperature range of (275.1 to 293.3) K and in the pressure range of (1.07 to 9.90) MPa. All the measurements were performed using a static high pressure cell using the isochoric pressure search technique. The results indicate that the addition of the quaternary ammonium salts moderate the hydrate dissociation conditions. Increasing the TBPB concentration increases its promotion effect on CO2/CH4/N2/Ar semi- clathrate hydrate, i.e. the formation conditions were shifted to low pressures and high temperatures in comparison with the clathrate hydrates of corresponding gases in the presence of water. TBANO3 shows both hydrate inhibition and promotion effect. TBANO3 acts as a hydrate promoter at low concentrations (e.g. 0.05 mass fraction) and low pressure and as well as an inhibitor at higher pressure. II A comparison of hydrate phase equilibrium data in the presence or absence of TBAF shows drastic promotion effect of TBAF on CO2 hydrate formation. These effects may lead to separation of CO2 from gas mixtures using hydrate crystallization and for economic studies, the optimum value of salts concentration are required. A thermodynamic model was presented to calculate/predict the dissociation conditions of semi-clathrate hydrate of CO2/CH4/N2/Ar in the presence of TBPB/TBANO3/TBAF. The solid solution theory of the vdW-P (J.H. van der Waals, 1959) with modification of the expressions to determine the vapour pressure of water in empty hydrate lattice and the Langmuir constants was used to develop the model. Additionally the PR-EoS along with the Mathias-Copeman alpha function (Mathias and Copeman, 1983) including re-tuned parameters were used for calculation of the fugacity of the gaseous hydrate formers in the gas phase. The Nelder-Mead optimization algorithm (Nelder and Mead, 1965) was used to determine the optimal value of the model parameters. The model used for the CO2 + promoters system to obtain the optimal value and the tuned parameters was later used to estimate the semi-clathrate hydrate dissociation conditions of CH4/N2/Ar in the presence of promoters. Determination of accurate experimental phase equilibrium data is essential for industrial applications in order to design efficient processes and estimation of the optimal parameters of the thermodynamic models for prediction of the phase equilibria of the systems of interest at various operational conditions. In order to assess the reliability of experimental phase equilibrium data, the Leverage approach was used. This method consists of numerical and graphical algorithms to detect the outliers in different phase equilibrium data of the systems containing gas hydrates. III تقدیم به همسرم فرهاد و پدرم و مادرعزیزم که در پس هر کلمه این کتاب حضور دارند ، چه ، هر کلمه اي در این کتاب ، نه لفظي ، که پاره اي از " بودن " من بوده است. Acknowledgements I would like to express my gratitude to the many people who supported me for the successful achievement of this research project. My deepest gratitude goes to God for everything that happens for me and for what I have. I would like to express greatest thank to my thesis supervisors, Prof. Deresh Ramjugernath, Prof Amir H. Mohammadi and Dr. Paramespri Naidoo who gave me the golden opportunity to do this wonderful project. Without their guidance and help this dissertation would not have been possible. I also would like to thank the staff members of the thermodynamic research unit including the head, technicians, and secretaries. I must express my profound gratitude to my parents for their supports in all aspects of my life. My husband, Farhad Gharagheizi, deserves to be highly acknowledged. He makes me familiar with important scientific aspects. This accomplishment would not have been possible without him. IV List of Publications 1. P. Ilani-Kashkouli, Hashemi, H., F. Gharagheizi, Babaee, S., A. H. Mohammadi, D. Ramjugernath, Gas Hydrate phase Equilibrium in Porous Media: An Assessment Test for Experimental Data. Fluid Phase Equilibria. 360, 161–168, 2013. 2. P. Ilani-Kashkouli, Babaee, S., F. Gharagheizi, Hashemi, H., A. H. Mohammadi, D. Ramjugernath, Assessment Test of Phase Equilibrium Data of Water Soluble and Insoluble Clathrate Hydrate Formers. Fluid Phase Equilibria. 360, 68-76, 2013. 3. P. Ilani-Kashkouli, Babaee, S., F. Gharagheizi, Hashemi, H., A. H. Mohammadi, D. Ramjugernath, Evaluation of Experimental Data for Gas Solubility in Liquid Water in Equilibrium with Gas Hydrates, In book: Advances in Chemistry Research (Volume 24)., Publisher: Nova Science Publishers, Inc., NY, USA, Editors: James C. Taylor. 4. P. Ilani-Kashkouli, A. H. Mohammadi, P. Naidoo, D. Ramjugernath, Hydrate dissociation data for CO2, CH4 or N2 in the presence of Tetrabutylphosphonium Bromide (TBPB). Submitted to The Journal of Chemical Thermodynamics. 5. P. Ilani-Kashkouli, A. H. Mohammadi, P. Naidoo, D. Ramjugernath, Experimental phase equilibrium data for semi-clathrate hydrates of CO2, CH4, or N2 in the presence of Tetrabutyl Ammonium Nitrate (TBANO3). Submitted to Fluid Phase Equilibria. 6. P. Ilani-Kashkouli, A. H. Mohammadi, P. Naidoo, D. Ramjugernath, Experimental phase equilibrium data for semi-clathrate hydrates of Ar in the presence of Tetrabutyl Ammonium Nitrate (TBANO3) and Tetrabutylphosphonium Bromide (TBPB). Submitted. 7. P. Ilani-Kashkouli, F. Gharagheizi, A. H. Mohammadi, P. Naidoo, D. Ramjugernath, CO2 Capture by Hydrate Formation: State of the Art. (Review). Submitted. 8. F. Gharagheizi, P. Ilani-Kashkouli, A. H. Mohammadi, D. Ramjugernath, A Group Contribution Method