Partial Pressure of CO2 with respect to pressure

[serhatttt]

Hi Everyone.

I did an experiment about rock-water-CO2 interaction in a batch reactor. My brine composition is very saline.
I want to calculate dissolved CO2 during my experiment with respect to the partial pressure of CO2 and pH of the solution.

Here is the code. However, the results are not reasonable. Can you help me with this?
My experiment conditions in reactor:
Temperature: 200 C
Pressure: 44 bar
pH of the solution after injection CO2 into the reactor: 4.83
Na: 24426 mg/l
Cl: 40875 mg/l


SOLUTION 1
-temp 25
-pressure 44
-water 0.065
units mg/l
    Na       24426
    Cl        40875
END
GAS_PHASE 1
-fixed_pressure
CO2(g) 0
END

EQUILIBRIUM_PHASES 1
CO2(g) 1.64 10

USE solution 1
USE gas_phase 1
REACTION_PRESSURE
44
REACTION_TEMPERATURE
200
REACTION 1
CO2 1
3.563e-01 in 20
USER_GRAPH 1
    -headings               rxn P(CO2) pH
    -axis_titles            "CO2 added" "P(CO2)" "pH"
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  x
  -start
10 GRAPH_X RXN
20 GRAPH_Y SI("CO2(g)")/PR_PHI("CO2(g)")
30 GRAPH_SY -LA("H+")
  -end
 
USER_PUNCH
-headings CO2 PCO2 pH
10 PUNCH RXN
20 PUNCH SI("CO2(g)")/PR_PHI("CO2(g)")
30 PUNCH -LA("H+")
 
SELECTED_OUTPUT
-reset false
-file Exp.txt
END

[dlparkhurst]

If your reactor has a constant volume, you probably want a -fixed_volume GAS_PHASE. If it is constant pressure, you may not need a GAS_PHASE and you can simply set the CO2(g) partial pressure with EQUILIBRIUM_PHASES.

Code: [Select]

SOLUTION 1
-temp 200
-density 1 calc
pH 7
-pressure 44
-water 0.065
units mg/l
    Na       24426
    Cl        40875
END
EQUILIBRIUM_PHASES
CO2(g) 1.64 10
END
USE solution 1
USE equilibrium_phases 1
 
Any way you do the calculation, I think 4.8 will be too high for the pH.