Preparation and characterization of some ionic liquids and their use in the dimerization reaction of 2-methylpropene

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>This study concentrates on the preparation and characterization of some ionic liquids and their use in dimerization reaction of 2-methylpropene. Ionic liquids consist of cations and anions, and are commonly understood as green solvents. By definition their melting points should be lower than 100 °C. Prepared ionic liquids were used as catalytic solvents in dimerizations of 2-methylpropene to a high octane compound, isooctene. The monograph consists of two parts: the literature survey and the practical work. The literature survey reviews the preparation and characterization of ionic liquids as well as their environmental aspects, such as toxicity, biodegradability and recyclability. In addition, the acid catalyzed dimerization of butenes is discussed together with the dimerizations of light olefins carried out in ionic liquids. The practical work consists of three entities: The environmentally benign preparation of 1-alkyl-3-methylimidazolium-based ionic liquids under microwave activation, the characterization of ionic liquids and the use of the ionic liquids in the dimerization reaction.</p><p>Ionic liquids absorb efficiently microwave irradiation and the most beneficial aspect in the microwave-assisted preparations was the considerably shortened reaction time compared to the conventional methods. In addition to the microwave-assisted preparations, [C_nmim][InCl₄] ionic liquids were prepared successfully without microwave irradiation. A special attention was paid to the characterization of ionic liquids since impurities are known to affect on the properties of the ionic liquids. Ionic liquids were analysed with the following methods: ¹H and ¹³C NMR, MS(ESI⁺ and ESI^-), GC and elemental analysis. Characterization of ionic liquids was done by determining the thermal stability, the melting point and the crystal structure of each solid ionic liquid. The determination of the liquid range of ionic liquid is necessary in order to know the temperature limits for each ionic liquid.</p><p>Novel InCl₃-based ionic liquids revealed to be the more efficient than Brønsted acidic ILs as a catalytic reaction media in the dimerization of 2-methylpropene. It was preferable to apply [C₆mim]Cl/InCl₃ (x(InCl₃) = 0.55) as a catalytic IL since then the conversion of 2-methylpropene and the product distribution revealed to be good. In order to maximize the production and the separation of dimers reaction should be carried out continuously at temperature high enough, such as 160 °C. Neutral InCl₃-based ionic liquid did not catalyze reaction of 2-methylpropene, but it had to be acidic x(InCl₃) > 0.5. Excess of InCl₃ did not leach out from the IL and the recycling of IL was possible. </p></div>