Selective Adsorption using Flexible Hybrid Solids – SAFHS

One of the technological problems that face society today is the environmentally friendly and economically favourable separation and recovery of fluids (gases, liquids or vapours). Several examples are currently of interest : the separation of alkane/alcenes, the selective recovery of solvents, the preparation of alcohols with a high degree of purity for the synthesis of biofuels or even the purification or capture of gases (hydrogen, carbon dioxide...). Many of the above processes include an adsorption step in which microporous adsorbents such as activated carbon and zeolites are used. In such cases, it is the thermal regeneration step that is most costly in terms of energy. Recently a new class of porous materials have found interest in the literature. These 'Metal Organic Frameworks', or 'Metal Coordination Polymers' are formed of metallic centres which are linked to each other through organic chains which are often polycarboxylates. Several of these organic-inorganic hybrid porous solids have the interesting feature, during the adsorption process, of being selectively flexible (breathing) as a function of the nature of the adsorptive fluid. Examples discovered in Versailles include flexible porous carboxylates formed with chains of metallic centres (MIL-53, -69) or with meal centre trimers (MIL-88-A, -B, -C, -D). These solids have shown to be able to 'breath' with an unprecedented amplitude between 50 and 220% in volume according to the nature of the fluid. A consequence of this particular property is the possibility to develop novel selective separation and storage processes with a favourable energetic cost with respect to existing processes. Indeed, the specific adsorption – desorption cycles that these materials give allow the possibility regenerate these solids by a simple heating or vacuum process or using a mechanical piston effect. This project exhibits a fundamental character whose purpose is to study the olefins or alcohols sorption properties of a series of hybrid flexible porous solids. Finally, a combination of experimental (XRD, microcalorimetry, IR and UV spectroscopy) and theoretical (quantum and classical) tools will be used to gain a greater understanding of the specific interactions between the adsorptive molecules and the adsorbent pore surface. This will allow the a posteriori synthesis of tailor-made porous solids with optimal separation properties. In a second step, the adsorption properties of these hybrid solids will be optimised via a modification of the carboxylate ligand (direct synthesis) The aim of this present project is the understanding of separation phenomena of hydrocarbons and alcohols by the abovementioned porous hybrid breathing phases which show huge flexibility to selective fluids. This field of application brings together a number of fundamental challenges that current microporous solids have not been able to overcome. The novel materials prepared within the framework of the present project can lead to both geometric and energetic selectivity via their recently characterised surface properties. They are therefore very promising candidates with respect to a number of fundamental problems which equally have a marked industrial interest.