The influence of bromide-based ionic liquids on solubility of {LiBr (1) + water (2)} system. Experimental (solid + liquid) phase equilibrium data. Part 2

Abstract

The main aim of the work is to investigate ionic liquids (ILs) or zwitterionic compound (ZI) as anti-crystallization additives for {LiBr (1) + water (2)} system, conventionally used as a working pair in absorption refrigeration technology. In this study, solubility of lithium bromide in water has been determined at wide temperature and composition range and compared to the literature data. The transition temperature and enthalpy between lithium dihydrate and lithium monohydrate forms were calculated using the van't Hoff plot. The main purpose of this work is to determine and discuss the solubility of lithium bromide in water in presence of IL, or ZI as an additive. The solubility measurements have been carried out using dynamic method within temperature range from (230 to 370) K. In this work, new ILs namely: N-methyl-N-(2-hydroxyethyl)morpholinium bromide, [MOR1,2OH][Br], N-(2-acetyloxy)ethyl-N-methyl-morpholinium bromide, [MOR1,2(OOC)1][Br], N-methyl-N-(2-ethoxy-2-oxoethyl)-morpholinium bromide, [MOR1,1(COO)2][Br], 1-methyl-3-(2-hydroxyethyl)imidazolium bromide, [Im1,2OH][Br], N-methyl-N-(2-hydroxyethyl)-pyrrolidinium bromide, [PYR1,2OH][Br], 2-hydroxyethypyridinium bromide, [Py2OH]Br], N-(2-hydroxy-ethyl)-N,N,N-triethyl-ammonium bromide, [N2,2,2,2OH][Br], N-(cyanomethyl)-N,N,Ntriethylammonium bromide, [N2,2,2,1CN][Br], N-(2-hydroxyethyl)-N,N-dimethyl-N-butyl-ammonium bromide, [N1,1,2OH,4][Br], N,N-di(2-hydroxyethyl)-N,N-dimethylammonium bromide, [N1,1,2OH,2OH][Br] and ZI namely: 3-(1-methylmorpholinium)propane-1-sulfonate, [MOR1,3SO3] were investigated. All compounds have been synthesized and characterized using NMR analysis. The thermophysical characterization of pure compounds, including: temperature of phase transition (Ttr), enthalpy of phase transition (∆trH), melting temperature (Tm) and enthalpy of melting (∆mH) have been measured using differential scanning calorimetry technique (DSC) at pressure p = 100 kPa. The experimental phase equilibria measurements for {LiBr (1) + IL, or ZI (2) + water (3)} ternary systems, with fixed IL to LiBr mass fraction w = 0.3 for all ILs and w = 0.1 and 0.2 for ammonium-based ILs and [MOR1,3SO3] have been performed by dynamic method. For all of the tested systems the transition point between lithium bromide dihydrate and monohydrate form was observed. Significant solubility enhancement of lithium bromide in water was obtained by adding ionic liquid, or zwitterionic compound to the lithium bromide + water solution. The experiment shows, that the greatest increase in solubility of LiBr in water was observed when [MOR1,3SO3], or [N1,1,2OH,2OH][Br] were added. This work is the first step of the experimental work in this area and further research will be carried out.