Carboxylic acid and formaldehyde separation from aqueous solutions using ionic liquids

A series of hydrophobic ionic liquids (ILs) have been employed to extract acetic acid (AcOH) or formaldehyde (HCHO) from aqueous solutions at atmosphere pressure. The ILs, mainly trihexyl(tetradecyl)phosphonium ([P6,6,6,14]+) carboxylate based ILs, were tested as a function of the anion chain length, which ranges from isobutyrate ([IB]-) to dodecanoate ([D]-). Most of these ILs show a large two-phase region and high extraction efficiency. Furthermore, tetraoctylphosphonium ([P8,8,8,8]+) and trihexyl(tetradecyl)ammonium ([N6,6,6,14]+) based ILs were also investigated to study the effect of the cation on extraction performance. Besides pure IL extraction, the mixture of IL and other chemicals, such as matched carboxylic acid, alkane and ester, were also investigated on extraction. The matched carboxylic acid could enhance the extraction performance and thus could be called ‘enhancer’. A balance point could be found for the ratio IL/enhancer to obtain a better extraction in each {H2O + AcOH + IL/enhancer} system, compared with the corresponding pure IL liquid-liquid equilibrium (LLE). Several ILs, including [P6,6,6,14]+ based ILs and imidazolium based ILs, were investigated on extraction of HCHO. Among these ILs, the imidazolium based ILs performed better than the [P6,6,6,14]+ based ILs in terms of two-phase region, hydrophobicity of IL-rich phase and partition coefficient/relative selectivity. <br/>The UNIQUAC method was employed to correlate the LLE data for pure IL systems. Some physical property data, such as density and viscosity, of ILs were correlated. The Joback group contribution method was used to predict the heat capacities of some ILs in this work. These correlations with low deviations made it possible for ILs to be further studied in Aspen process modelling.<br/>

Name dc:type.qualificationname

Doctor of Philosophy

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

Queen's University Belfast

Year dc:date.issued

2017

Author dc:creator

• Qi, Fei

Advisor dc:contributor.advisor

• Rooney, David

• ionic liquids
• acetic acid
• carboxylic acid
• LLE
• phosphonium

Language dc:language

eng

Identifier

oai:pure.qub.ac.uk/portal:studenttheses/56aa0414-73e4-4f2e-9622-a9d3cd88ff4e

OAI identifier oai:identifier

oai:pure.qub.ac.uk/portal:studenttheses/56aa0414-73e4-4f2e-9622-a9d3cd88ff4e