Advanced simulation to choose a cheaper membrane process for salt removal from complex mixtures

Most of chemical reactions have — as a final result — a large mixture of end products out of which the main one represents a small rate when compared with secondary products. One of these reactions results in a mixture of products that takes place in the process obtaining ethylene amines. The reaction occurring at elevated pressure and temperature, between dichloroethane and ammonia, conducts to amino-chlorohydrates intermediate products which are then neutralized by means of NaOH. Finally the amines and NaCl are formed. Then excess ammonia is removed resulting in a mixture of NaCl, water and amines. Currently a procedure separated the amines from the rest of the components by evaporation and centrifugation. Since this desalting method causes many problems regarding steam consumption, clogging, corrosion and erosion of the equipment, it was suggested in a previous paper, based on pilot scale calculations (100 l/h), to solve these problems by using membrane technology, i.e. ED or PV. The study pointed out that PV appeared to be more advantageous than ED. The new paper takes into account the same membrane processes as the previous study using advanced simulation for the variables involved in the process, including the sensitivity cost analysis as well. The scale of the current plant is an industrial one (5400–7200 kg/h) and therefore the results can be a more realistic support for a potential investor.

The study had as its basis a practical existing case in one chemical plant and tried to stress the importance of hybrid processes for solving different problems of chemical engineering by combining the classical unitary processes with membrane ones. The replacing of some classical steps for separation purposes with membrane processes can be an important decision both for existing owners of the process and the producers of membrane units and/or equipment. The present paper is a new attempt at a higher scale to demonstrate the reliability of such membrane processes making at the same time a cost comparison between two processes. The made assumptions help to simplify the computations but some other variables, including sensitive analysis can be taken in account. However, it is very clear for an investor that for any new mixture to be separated by a membrane process, pilot or labor tests have to be performed in order to obtain reliable data for industrial plant. Chemical branches offer wide opportunities of applications for membrane technologies and this attempt try to stress once again upon the impor- tance of hybrid processes to be applied in the future.