Ionic liquid based absorption chillers for usage of low grade waste heat in industry

Abstract

SUMMARY The standard working pairs for absorption chillers, ammonia/water and water/lithium bromide show problematic behaviours like crystallisation and corrosiveness. Because of their convenient solving properties and their low vapour pressure, ionic liquids are a new promising class of sorbents for absorption cooling purposes. In this study, the working pairs water/1,3‐dimethylimidazolium dimethylphosphate ([MMIM][DMP]) and water/1‐ethyl‐3‐methylimidazolium dimethylphosphate ([EMIM][DMP]) are implemented in AspenPlus. The performance of a single effect cycle with these pairs is simulated and compared to results of a cycle with water/LiBr. For [EMIM][DMP] a coefficient of performance (COP) comparable to that of LiBr or even higher (up to 0.85) is found. [MMIM][DMP] shows a smaller maximum COP but a largely wider operating temperature range than LiBr. Results are compared with those of other groups, discrepancies discussed and improvements suggested. Copyright © 2013 John Wiley & Sons, Ltd.

Crystallization Temperature, Vapor Pressure, Density, Viscosity, and Specific Heat Capacity of the LiNO3/[BMIM]Cl/H2O Ternary System

“…On the basis of measured thermophysical properties, they predicted the performance of an absorption heat pump using [MMIM]­[DMP] (1,3-dimethylimidazolium dimethylphosphate)/H 2 O as a working pair, showing that the problems of crystallization and corrosion were relieved, although the performance was slightly lower than that with LiBr/H 2 O as the working pair. − Zheng et al also reviewed the research on the working pairs based on imidazolium IL with particular focus on the methods of evaluation and selection, thermophysical property measurement and modeling, future prospect assessment, and developing potential in the applications . The thermophysical properties of ILs/H 2 O as well as performance predictions of the absorption heat pump based on ILs/H 2 O have also been reported in other studies. − Generally, compared with LiBr/H 2 O and LiNO 3 /H 2 O, ILs/H 2 O have much lower crystallization temperatures and corrosivity while with much higher working absorbent mass fractions and viscosities, leading to a reduction in the performance of the absorption heat pump …”

Analysis of the Potential for Improvement of Chemical‐Energy Transformation Processes

“…The working fluid in AHPs is always a working pair, which consists of a solute that serves as the refrigerant, and a solvent into which the refrigerant is dissolved and evaporated within the working cycle. Ionic liquids (ILs) are potential new solvents that are currently under research for their applicability as solvents in AHPs . The main feature of ILs in this context is that their properties can be tailored to the demands of the respective application by the choice of the constituting cations and anions.…”

Enhancing the solar energy conversion and harvesting characteristics of multiwalled carbon nanotubes‐modified 1‐hexyl‐3‐methyl‐imidazolium cation ionic liquids

“…8 In this group of salts, charges of the organic compound cause a noticeable lower vapor pressure compared to the other substances. 9,10 Typically, this kind of molten salts have a melting temperature around room temperatures; however, the decomposition temperature of these compounds varies from 500 to 700 C. 11,12 Furthermore, the negligible vapor pressure of the RTILs leads to simplifying thermal and structural design in the system when used as a working fluid because ionic liquids (ILs) cannot evaporate at atmospheric pressure, which means no undesirable emission. 13,14 However, negligible vapor pressure is not the only reason to apply ILs in the thermal system.…”

“…A group of low melting salts was developed with negligible vapor pressure over three decades ago, which are referred to as room‐temperature ionic liquid (RTIL) 8 . In this group of salts, charges of the organic compound cause a noticeable lower vapor pressure compared to the other substances 9,10 . Typically, this kind of molten salts have a melting temperature around room temperatures; however, the decomposition temperature of these compounds varies from 500 to 700°C 11,12 .…”