ZAFAR Sadain : CO2 hydrates as an alternative solution to water desalination & greenhouse gas mitigation

Résumé de thèse : The annual global emissions of CO₂ have escalated by approximately 80% between 1970 and 2004.¹ Such greenhouse gases (GHG) emissions are produced from a variety of industrial activities, from power generation to manufacturing. Power generation is currently one of the major sources of CO₂ emission and contributes to about 41%.² Natural gas will remain the main bridge in the transition period from conventional fossil fuels (oil, natural gas and coal) to alternative energy sources for more than 50 years. A better understanding of the structure and chemical composition of combustion residues, as well as the implementation of capture and sequestration processes for flue gases such as CO₂ are necessary to mitigate the environmental impact. One approach to reduce CO₂ emissions is to capture CO₂ in post-combustion. One breakthrough solution proposed within this project is to use gas hydrate technology for CO₂ capture, separation, and subsequent valorization. Hydrates are nano-porous crystalline materials, consisting of aqueous cages encapsulating molecular species (CO₂). These compounds keep attracting increasing interest due to their numerous applications (gas transport, refrigeration, H₂ storage, desalination, etc.), and in particular, as an alternative solution to reduce greenhouse gas emissions (ex: CO₂) in the atmosphere. Meanwhile, it has been demonstrated that certain ion elements dissolved in water (e.g. sodium ion) are naturally excluded from the aqueous cages constituting the sedimentary hydrates. By combining the work carried out on natural hydrates and the knowledge acquired on CO₂ capture, it becomes possible to combine the double operation of capturing and purifying water, in the optics of optimizing the environmental benefit of this technology, also of interest for gas transportation. This technology constitutes a sustainable approach for simultaneous water treatment and CO₂ capture, which may additionally require low energetic costs if the right formation conditions are found.

The prime directive of the present project is to understand the influence of ions in saline environments on the physicochemical properties of hydrates (stability, kinetics, composition, separation of CO2 from industrial smokes) for CO2 capture and transport, and water purification. It includes laboratory syntheses of CO2 hydrates with varying salt concentrations (possibly with promoter additives) and spectroscopic (Raman) analyzes of these synthetic hydrates. The parameters will thus be varied to evaluate the performance of capture, storage, and desalination. The results will provide a better understanding of the hydrate formation mechanism and the accompanying salt exclusion phenomenon. A high-pressure optical cell coupled to 3D-optical microscopy and micro-Raman spectroscopy will be used to monitor the hydrates crystallization process. 

ZAFAR Sadain

Directeur(s) de thèse :  B. Chazallon, C. Pirim