Chloroaluminate Ionic Liquids: from their Structural Properties to their Applications in Process Intensification

Abstract : The structural properties of new organochloroaluminate ionic liquids based on mixtures of (Ethyl)nAlCl$_{(3-n)}$ (n = 1 to 3) with 1-methyl-3-butyl-imidazolium chloride (BMIC) have been studied by Raman spectroscopy. With this technique, the mono and polynuclear anions present in these melts have been identified and quantified. The mixed salts formed with AlCl3 and EtAlCl2 or [ EtAlCl2 and Et2AlCl] together with BMIC are also considered. All behave as regular chloroaluminates; in particular, their acid-base properties depend on their compositions. Thanks to this study, it has been possible to anticipate and to optimize the composition of an ionic liquid based on EtAlCl2, with the aim of performing industrially the Ni-catalyzed olefin oligomerization in chloroaluminates. The influence of the solvent composition on the overall mechanism of the catalysis is now basically understood. The resulting ionic liquids play the dual role of solvents and nickel activator (or co-catalyst).