Measurements and correlation of high pressure densities of protic ionic liquids

J. Coutinho1, P. Carvalho1, S. Mattedi2, M. Iglesias2, I. Fonseca3 and A. Ferreira3

1CICECO, Departamento de Química, Universidade de Aveiro, Aveiro, Portugal
2Programa de Pós Graduação em Engenharia Química, Escola Politécnica, Universidade Federal da Bahia (UFBA), Salvador-BA, Brazil
3Departamento de Engenharia Química, Faculdade de Ciências a Tecnologia, Universidade de Coimbra, Coimbra, Portugal

Keywords: high pressure
property: density
material: ionic liquids

Until now, studies concerning ionic liquids have been based on the imidazolium cation and, to a lesser extent, on the alkyl pyridiniums and trialkylamines. Protic ionic liquids (PILs) have, however, received limited attention from the academia. The first PIL reported, ethanolammonium nitrate, was reported by Gabriel and Weiner in 1888, followed by ethylammoniumnitrate (EAN), in 1914, synthesized by Walden. These PILs were produced by a stoichiometric acid–base Brønsted reaction and their main difference, compared to aprotic ILs (AILs), is the presence of at least a proton, which is/are able to promote extensive hydrogen bonding. These liquids present some characteristics, such as a slightly lower conductivity and stability, which may reduce, at first, their interest for a number of applications. However, their low cost, simple synthesis and purification methods, low toxicity and high biodegradation character, among other set of appealing characteristics, overcomes those limitations for many different purposes. This work focus on measuring high-pressure densities of the N-methyl-2-Hydroxyethylammonium- and 2-Hydroxyethylammonium-based protic ionic liquids in order to investigate the relationship between ionic structures and their densities, establishing principles for the molecular design and interconnect and/or solidify the knowledge acquired on previous works.

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