The ASPEN simulation software was used to investigate the control of reaction temperature. The simulation was set up with the following unit operations: two Reactors (RSoic, B1&B2), Cooler (Heater, C1), and Heat exchanger (HeatX, H1). The reactor B1 is adiabatic which means there is no heat. Then, a cooler (C1) was generated to cool the sodium hydroxide solution to 25 C. A second reactor (RStoic, B2) then was used for the incoming aqueous HCL stream (S5). The stoichiometric reactor was operating adiabatically to carry out the neutralization. Finally, a two-stream heat exchanger (HeatX, H1) was used using water as cold stream.
The electrolytes feature was used due to working with aqueous solutions. The ionic compounds and ionic components were defined which are NaOH, NaCl, HCl, WATER, H+, OH-, Na+, and Cl-. Then, a reaction set was created by specifying dissolution reactions of NaOH, NaCl, and HCl which give the following reaction:
NaOH à OH- + Na+
HCl à Cl- + H+
NaCl à Cl- + Na+
Sodium hydroxide solution preparation tank (RSoic, B1) using dissolution of NaOH in water as the reaction.
The outlet stream (S3) of the first reactor (B1) was checked and adjusted to give a Molar flow rate of 2 mole/s for both OH- and NA+. Then, the outlet stream (S3) goes to a cooler (C1) to cool down the solution to 25 C (1 barg). Then, the outlet stream (S4) of the cooler goes to the second reactor (B2) as well as another stream (S5) of known molar concentration (6 M), mass flow rate (1 tonne/h), temperature (20 c), and Pressure (1 barge) enters the reactor. The solvent was chosen to be water. The operating conditions of the second reactor (B2) was set to zero due to it is adiabatic with a pressure of 1 barge. The stoichiometry reaction is H+ + OH- à H2O with a fractional conversion of 1 of component H+. After running the model, the molar flow rates of OH- and H+ was checked regularly as they should be close to zero to make sure that HCL is completely neutralized. The molar flow rate of H+ was zero whereas the molar flow rate of OH- was 2.10E-07 mole/h. The pH can be calculated using the following equation:
pOH = -log[OH]= – log[2.10E-07] = 6.67
pH+pOH=14
pH=14- pOH=14-6.67=7.32
Therefore, the pH of OH- was calculated to be 7.32 and this is close enough to confirm that HCL is completely neutralized. After all, the outlet stream (S7) went to a hot inlet heat exchanger (H1) with a temperature of 46 C. The temperature of the heat exchanger was set to be 30 C as specified and the temperature of the neutralised stream coming out of the heat exchanger was ensured to be 30 C. The cold inlet heat exchanger (S6) had a temperature of 20 C, a pressure of 1 barge and it was given a mole fraction of 1 as it is only water. The mass flow of the water was assumed to be 4254 kg/hr as an initial guess which was the value of the mass flow rate from stream (S7). The value then was reduced regularly unit its lowest value that can give the neutralised stream coming out of the heat exchanger at 30
(S8) which was 2500 kg/hr.
