Absorption behaviour and diffusivity of ammonia in ionic liquids.

Research on the use ionic liquid as an absorber for natural refrigerant has been significantly progressing in recent years. Having unique characteristics, the working fluids involving natural refrigerant and ionic liquid mixtures, including ammonia/ionic liquid pairs are able to overcome the drawback of conventional working fluids such as crystallization problem and the necessity of rectification process. Some ionic liquids that may be suitable as absorbent for ammonia refrigerant are 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([EtOHmim][BF4]) and 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide ([EtOHmim][NTf2]). These ionic liquids are considered as suitable candidate ionic liquid based absorbent due to their favourable properties and their viability as absorbent for ammonia refrigerant. In this paper, an experimental investigation to study the absorption behaviour and mass diffusivity of ammonia into ionic liquids is reported. This investigation is essential in order to fundamentally identify the absorption performance and characteristic of refrigerant in absorbent before heading to the detail study on heat and mass transfer performance of these working pairs. The ionic liquids studied in this work are combinations of two different cations ([EtOHmim]+ and [emim]+) and anions ([BF4]-, and [NTf2]-). The detail methodology and experimental setup are explained in this paper and measurement parameters of ammonia absorption into ionic liquid are discussed.