Dynamics and molecular properties of clathrate hydrates of carbon dioxide and hydrocarbons

This dissertation is based on research I have been conducting under supervision of Prof. Dr hab. Joanna Sadlej in Laboratory of Inter- molecular Interactions at the Department of Chemistry, Univeristy of Warsaw during my PhD studies in 2009-2013. There are two main parts of it. First is devoted to description of NMR properties of clathrate hydrates of methane, ethane, propane and carbon dioxide. Second is concentrated on processes connected with formation and dissociation of clathrate hydrates. Clathrate hydrates are inclusion compounds resembling ice. They are built of water molecules organised in cages, in which guest molecules may reside. As naturally occuring deposits of clathrate hydrates con- tain vast amounts of lower hydrocarbons, thay may become important energy resource in the future. Interest in NMR properties of clathrate hydrates is directed toward characterisation of basic aspects of properties of those structures. At the same time it may provide useful tool to analyse concentration of guest molecules in crystalline structures, distinguished between possible structure types as well as determine what kind of guest molecules are enclathrated. Those information are of crucial importance for future development of technologies enabling extraction of enclathrated lower hydrocarbons (mainly methane) from naturally occuring deposits. My research was devoted to fill gaps in this field - thank to systematic calculations of very high accuracy I was able to predict NMR properties (absolute shielding constants and spin-spin coupling constants) for all atoms forming most abundant crystal types (sI and sII) containing most abundant guest molecules (methane, ethane and propane). Thank to my results it will be possible to credibly interpret experimental spectra of natural clathrate hydrates containing mixtures of guest molecules. My calculations in this area were partially conducted in coopera- tion with professor Kenneth Ruud from University of Tromso, Norway. Their results were already published in two papers (for methane as a guest), one was already sent for publication (for carbon dioxide as a guest) and one is in preparation (methane, ethane and propane as guests). Second area of my research was concentrating around formation and dissociation related phenomena. Those processes are still not well un- derstood on molecular level. I have used Molecular Dynamics method- ology to study nucleation and growth of methane clathrate hydrate from liquid solution of water. To mimic natural environment clay lay- ers were introduced to the system. I was studying influence of sev- eral parameters (concentration of methane solution, temperature, ionic strength of the solution, type of the clay) on the nucleation and crystal growth processes. To trace those processes I have modified already ex- isting programs and have written my own code giving opportunity to trace with single-molecule resolution process of formation of clathrate hydrate crystal. Finally I was able to observe not only nucleation, but also growth of methane clathrate hydrate crystal from liquid solution near to the clay surface. That is the first time ever such a phenomenon was the- oretically obtained. I am still working on this subject trying to trace the influence of clay, which may be of great importance to unveil the details of molecular mechanism of clathrate hydrate crystal formation. Working on this part of the project I was cooperating with dr Eugene Myshakin and Professor Kenneth Jordan from University of Pittsburgh, Pennsylvania, USA.