Contact crystallization of substances from solutions using evaporating refrigerants

Abstract

Objectives. The aim of this study was to analyze the possibility of using contact crystallization with evaporating refrigerants for the isolation of substances from their aqueous solutions using salts [KNO3, NaI, and (NH2)2CO] as extraction examples and sucrose. Isobutane was used as a refrigerant.Methods. The analysis of the influence of the main technological parameters (i.e., solution’s cooling temperature, initial concentration, and compressed refrigerant vapor pressure) on the separation process and identification of its regularities was performed using mathematical dependencies previously developed by N.I. Gelperin and G.A. Nosov for each stage of the contact crystallization process. The authors studied the influence of these parameters on the yield of crystalline and liquid phases, refrigerant consumption, and compressor power.Results. The study showed that the use of evaporating refrigerants can significantly intensify the process of separating the mixture and spent refrigerant from the resulting crystalline suspension. This occurs owing to the evaporation of the liquid refrigerant that is in contact with the solution, which is accompanied by intense cooling. This process can be carried out at the temperature difference between the refrigerant and crystallizing mixture in the range of 0.5–1.0°C.Conclusions. Contact crystallization with evaporating refrigerants can be successfully applied to separate various substances from aqueous solutions. An important advantage of this process is the relatively low refrigerant consumption because heat removal from the solution is carried out as a result of changes in the aggregate state of the refrigerant. The use of contact crystallization can also considerably simplify the equipment.