Simulation for determination of optimal conditions for salt removal from aqueous amine solution

Abstract

Some chemical reactions are conducted to form — as final results — a versatile mixture of end products and other components which are difficult to be further separated. One of these reactions, having as a result a mixture of desired products together with secondary or by-products, takes place in the process of ethylediamine production. The reaction occurs between dichloroethane and ammonia solution leading to the amino-chlorohydrates followed by neutralization in the presence of sodium hydroxide, with formation of free amines and sodium chloride, at about 70 bar and 100°C. The mixture to be separated is introduced first in a double-column system in order to remove the excess of ammonia. The next step — on which the work is focused — is the removal of sodium chloride salt from the mixture, while the last steps are mainly classical separation columns. Since the removal of salt raises a lot of problems regarding crystals separation, high rate of steam consumption for water/amines evaporation, clogging, corrosion and erosion of the equipment due to high rate of recirculation, the author sought to solve the problem using membrane technology for separation of species, i.e. to remove the salt and to obtain an aqueous solution of amines. The characteristics of the mixture show the possibility to use one of the following membrane processes: electrodyalisis or pervaporation. The paper presents the comparative simulated results obtained by engineering and economic analysis for both systems.