Aspen simulation of the pH value of ammonia solution as a function of ammonia concentration — turning point

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Dear experts: I am using Aspen’s mixer to simulate the pH changes resulting from variations in the mass fraction of ammonia water. 1. Establish the process. 2. Enter the components; for H2O and NH3, use Electronic Wizard to select the electrolyte and automatically generate the reaction equation. Add a PH option to the Prop-sets in the properties section, and include it in the report options under setup. 3. For sensitivity analysis, set NH3, H2O, and PH as variables, with NH3 ranging from 1 to 99; use Fortran statements to set H2O = 100 – NH3. 4. Run the simulation to obtain the sensitivity analysis results. 5. Use Plot to create a graph, with NH3/(NH3+H2O) on the horizontal axis and PH on the vertical axis. Here’s the problem: (1) The maximum concentration of ammonia solution is 12; however, it seems that in industrial and laboratory settings, the pH of ammonia solutions can be higher than 12. (2) Ammonia water reaches a minimum turning point around 8%, and its pH first decreases before increasing again. (3) I simulated the addition of ammonia to an aqueous sulfuric acid solution, and a similar situation occurred. Seeking help from experts