Batch reaction experiment for CO2

[serhatttt]

Hi Everyone,

I am doing a batch reaction experiment. My aim is to compare changes in pH with respect to CO2 concentration for high saline geothermal water. Also, I will measure pH values after the reactor experiment and compare pH values with experimental data.

I assign gas volume and pressure, but after running the code, pH values are not reasonable.

Can you help me with this?

Thank you.
Here is the code.

SOLUTION 1
    temp      25
    pH        7  charge
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Cl        1008.57
    Na        769.56
    -water    1 # kg
END

USE SOLUTION 1
   
REACTION 1
    CO2(g)     1
    0.065 moles in 100 steps
   
GAS_PHASE 1
    -fixed_pressure
    -pressure 6.95 #atm
    -fixed_volume
    -volume 0.3557 #liter V=m*R*T/P
    -temperature 25
     CO2(g) 0
     H2O(g) 0
     
 REACTION_TEMPERATURE
     188
   
USER_GRAPH 1
-headings RXN Gas_volume pH
-axis_titles "CO2 addition, mol" "Gas volume, L" "pH"
10 GRAPH_X RXN
20 GRAPH_Y GAS_VM * GAS("CO2(g)")
30 GRAPH_SY -LA("H+")
END

[dlparkhurst]

Look at your output for the initial solution.

[serhatttt]

Hi David,

Thank you so much for your quick reply.

I checked my output file, but the ph values are still not reasonable. They are at around 3.7

Also, I looked at the graphs; pH values seem to be 0.8 in the y2 axis.

[dlparkhurst]

You are charge balancing your initial solution with pH, which results in a pH less than 1 to start your calculation. Because Cl > Na in your initial solution, to charge balance, H+ is added by lowering the pH.

Set the initial solution to a pH that fits your conceptual model, and either don't charge balance or charge balance on another element.

[serhatttt]

Thank you so much! Now it works.