Hi Farid

What about Comsol? Comsol is useful for this purpose?

Aspen plus works well for most simple electrolyte processes, using ENRTL thermo, and making sure to generate the proper ionic species, check that the necessary equilibrium chemistry is in place, etc.  You can mix solutions of electrolytes, have it predict a pH. OLI is a more advanced electrolyte package, with data for more systems, & should be used if you happen to have access to it.

Aspen Plus allows you to define a flow sheet section in which the electrochemical property set is selected. If you place a mixer block with two or more input streams and a single out put stream, then you can place an analyzer block in the output stream and in as many input streams as you like. Near the bottom of the set up menu there are design spec modules that allow you to specify a pH in the output stream by changing one parameter of one input stream like flow rate of a caustic solution.

To be practical if you are trying to neutralize a weak acid by adding a strong base, the process may be unstable as it is in nature. Then you could add upstream dilution blocks for the caustic, and additional meters to report the resulting pH.

Thanks, Mr.Decker. I am trying to simulate my bench scale setup in Aspen and get data from it to see pH change in the different flow rates of my titrant agents because I am looking for a way. unfortunately, I do not have Aspen OLI License. 

Mr.Decker to see pH property in Aspen we must define reactions and I could not implement your solution can you send me a sample file, please?

Regards