Recrystallization of substances from solutions using heat pumps

Аuthors

Yakovlev D. S., Nosov G. A., Uvarov M. E.

MIREA — Russian Technological University (Lomonosov Institute of Fine Chemical Technologies), 78, Vernadsky prospect, Moscow, 119454, Russia

Abstract

A process of recrystallization using various solvents is widely used to clean many substances from impurities. Commonly this process consists of several stages: dissolution of the starting material, crystallization, separation of the resulting suspension, washing the crystalline phase,regeneration of solvents, etc. Moreover, the technical and economic indicators of separation strongly depend on the costs of solvents and energy costs associated with its implementation.

Evaporative crystallization process can be used to crystallize substances the solubility of which is weakly dependent on temperature. The advantages of this recrystallization option in- clude the fact that in this case it becomes possible to combine the crystallization and solvent re- generation stages. Herewith the secondary vapors of solvents formed at the stage of evaporative crystallization can be returned to the stage of dissolution of the starting materials. As a result, the cost of fresh solvents can be significantly reduced. However, applying of evaporative crys- tallization is usually associated with significant heat costs. Considering this, the possibility of using vapor compression heat pumps in the process of recrystallization of a number of sub- stances from aqueous solutions by evaporative crystallization was investigated in this article.

As a result of theoretical analysis, the influence of the main theoretical parameters on the energy indicators of the separation process under consideration was established. Moreover, to characterize the energy efficiency of the separation process, the specific consumption of equiva- lent fuel was used.

The calculations showed that the lowest energy consumption during the process under con- sideration occurs when solutions are fed to the crystallization stage at a temperature close to their boiling point. It was also established that it is unprofitable to carry out the crystallization stage at excess pressure.

Studies have shown that, depending on the selected separation parameters and the physico- chemical properties of the substances to be purified, when using a heat pump, the equivalent fuel consumption is 2 to 5 times lower than conventional separation.

Keywords:

purification of substances, evaporative crystallization, recrystallization, energy costs, regeneration of solvents, heat pumps, equivalent fuel consumption.

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