About the Acidity-Catalytic Activity Relationship in Ionic Liquids: Application to the Selective Isobutene Dimerization

作者：Magna L^*; Bilde J; Olivier Bourbigou H; Robert T; Gilbert B

来源：Oil & Gas Science and Technology-Revue de l Institut Francais du Petrole, 2009, 64(6): 669-679.

DOI：10.2516/ogst/2009041

About the Acidity-Catalytic Activity Relationship in Ionic Liquids: Application to the Selective Isobutene Dimerization - The Bronsted acidity level was evaluated for ionic liquids to which a strong acid has been added. As a first approach, the evaluation method was based on the determination of the Hammett acidity functions H-0, using UV-Visible spectroscopy. The acidity of protons is mainly determined by their solvation state and consequently, the properties of protons depend on, both the nature of the solvent and the nature and concentration of the acid. An apparent acidify scale was defined following this principle. It was found that, for the investigated ionic liquids, the cation does not play a dominant role on the acidity level ([BMIm] similar to [BHIm] similar to [HNEt3]), whereas changing the nature of the anion of the ionic liquid may lead to very different acidities ([SbF6] > [PF6] > [BF4] > [NTf2] > [OTf]). This "acidity scale" was tentatively compared with an "activity scale" obtained for the dimerization of isobutene into isooctenes. The tendencies concerning the cation effect were confirmed ([BMIm] similar to [BuMePyrr] similar to [HNEt3]). The anion effect in only partially validated with a different behaviour for NTf2 type ionic liquids ([NTf2] similar to [SbF6] > [PF6] similar to [BF4] > [OTf]). By an adequate choice of the ionic liquid, selectivity for isobutene dimers can reach 88 wt% (at 70% isobutene conversion) with possible recycling of the catalytic system without loss of activity and selectivity.

• 出版日期2009-12