Approccio Combinato di Metalli e Poliammine per la Cattura e Conversione della CO2

The continuous increase in global energy demand and the over-exploitation of fossil fuels have brought a dramatic growth in the outflows of CO2 in the atmosphere in the last centuries, with dramatic effects on global warming. In the last decades the scientific community has focused on Carbon Capture Utilization and Storage, a range of technologies applied to cover the complete life cycle of CO2, from its capture from flue gases to its transportation and following storage or utilisation, in an effort to limit the environmental damages during the transition from a fossil fuel-based economy to a renewable energy-based one. The main technology developed to this day for Post Combustion Capture is amine scrubbing, the chemical absorption of CO2 by aqueous amine solutions. One of the main issues of this solvent-based process, limiting its appliance on the industrial scale, is the great amount of heat necessary for sorbent regeneration after capture. Many efforts are being done to find the ideal sorbent, capable at the same time of efficiently and selectively binding CO2and easily releasing it. Drawing inspiration from nature, the advantages of cooperative absorption, such as haemoglobin towards O2, are evident. Cooperative absorbents show a sudden shift from a low to a high loading state, which can be described by a step-shaped isothermal plots: small temperature increases allow to reach higher working capacities in cooperative systems compared to classic sorbents. In this work CO2 absorption by a 0.5 M solution of Diethylenetriamine is completely elucidated in methanol and shows cooperativity. The cooperative shift towards the high loaded state of DETA depends on a supramolecular assembly between two carbamated species, similar to DNA's double strand folding. Yet, the cooperative behaviour is strongly attenuated in water, pointing out the need for additives to restore this feature in this eco-friendly medium used in industrial facilities. The preferential affinity of a hard metal towards polycarbamated species can be exploited to maximise the amount of CO2 loaded per amine molecule. The influence of 1/12 equivalents of CoCl2*6H2O on the absorption system in methanol is presented: the addition of Cobalt does not modify the maximal loading in CO2 of DETA but induces a disproportionation equilibrium, accompanied by the spontaneous oxidation of the metal center, which favours bicarbamate formation against monocarbamates. This system looks promising towards the development of an aqueous cooperative CO2 sorbent. The same system has been studied with FeCl3, but the reactive features of the two-component metal-amine system make it not suitable for CO2 capture. In fact, in absence of CO2 a ring closure metathesis between two polyamine molecules with Iron, which plays at the same time the role of redox agent and template, is discovered. The main product is Cyclen, a tetraazamacrocycle of pharmaceutical relevance. Although the current preparation methodology needs to be optimized, it constitutes a cost-effective, sustainable alternative to the current manufacturing procedure of Cyclen. The results presented in this thesis show the great versatility of the chemistry of polyamines with transition metals, systems which can efficiently contribute to cost reduction of both CO2 capture and chemical synthesis.