solubility of hydrogen in water and in brines

[IliasBouchkira]

Hi everyone, is it possible to predict hydrogen solubility in water and in H2O-NaCl. To be more clear, I am triying to model H2-H20 and H2-NaCl-H2O systems. I have made this code but its not working.

Code: [Select]

# Definition of the solution and equilibria
SOLUTION 1
    pH 7
    pe 4
    temp 25
    H+ 10^(-7)
    -water 1 # kg
END

EQUILIBRIUM_PHASES 1
    H2(g) 0.1
END

# Definition of the pressure range
USER_PUNCH
    -headings Pressure (bar) Hydrogen (mol/kgw)
    -start
      P     = 10
      DP    = 10
      NP    = 10
    -loop
      -pressure P
      SELECTED_OUTPUT
        -reset false
        -solution 1
        -high_precision true
        -punch TOT("H2(g)")/1e-3 # mol/L to mol/kgw
      END
    P = P + DP
    -end
END

# Plotting of the results using user_graph
USER_GRAPH
    -headings Pressure (bar) Hydrogen (mol/kgw)
    -chart_title "Solubility of Hydrogen in Water as a Function of Pressure"
    -axis_titles "Pressure (bar)", "Hydrogen Concentration (mol/kgw)"
    -plot_concentration_vs x
    -start
    10 3.1623e-08
    20 6.3246e-08
    30 9.4869e-08
    40 1.2649e-07
    50 1.5811e-07
    60 1.8974e-07
    70 2.2136e-07
    80 2.5299e-07
    90 2.8461e-07
    100 3.1623e-07
    -end
END

many thanks in advance,

[dlparkhurst]

Come on. You didn't even try.

If you at least define the SOLUTION correctly, I will help you.

You can also do a search in this forum for H2(g) and Hdg(g). There have been quite a few posts recently about hydrogen solubility. Hdg and Hdg(g) is in the phreeqc.dat and pitzer.dat databases and represents H2 as inert, that is, there are no redox reactions as there are with H2.

[IliasBouchkira]

Hi Dr, Sorry for my question! it's been long time I have not used PhreeqC and I was always using it for solid liquid equilibria, which I assume more flexible than modeling vapor liquid equilibria. Thank you for the reference, I have found some previous discussions on solubility of hydrogen in NaCl

I am wondering which models are used for the modeling of the vapor pase (phi).

I also have an other question is there any way to find molar volume of hydrogen in phreeqc databases as we are using a pointing approach for high pressure that needs it.

Many thanks in advance.

[dlparkhurst]

In phreeqc.dat and pitzer.dat, the gas phase is modeled with the Peng-Robinson equation of state.

Here is a script that calculates solubility of Hdg (inert H2) as a function of pressure. The solubility and molar volume are plotted with USER_GRAPH. The calculation uses a large enough volume of GAS_PHASE so that the gas phase does not dissolve completely. The molar volume of the Peng-Robinson gas phase (L/mol) is given by the Basic function GAS_VM. Other functions that may be of interest are GAS("Hdg(g)"), moles of Hdg in the gas phase; GAS_P, gas pressure; PR_P("Hdg(g)"), partial pressure of Hdg(g); SI("Hdg(g)"), log fugacity of Hdg(g); and PR_PHI("Hdg(g)"), fugacity coefficient of Hdg(g).

Code: [Select]

SOLUTION 1
    temp      25
    pH        7
    units     mol/kgw
    Cl        1
    Na        1
GAS_PHASE 1
    -fixed_pressure
    -pressure 1
    -volume 10
    -temperature 25
    Hdg(g)     1
REACTION_PRESSURE
10 100 in 10
USER_GRAPH 2
    -headings Pressure Mol(Hdg) Gas_molar_volume
    -chart_title "Solubility of Hydrogen in Water as a Function of Pressure"
    -axis_titles "Pressure, atm", "Hdg(aq), mol/kgw" "Gas molar volume, L/mol"
    -plot_concentration_vs x
    -start
10 GRAPH_X PRESSURE
20 GRAPH_Y MOL("Hdg")
30 GRAPH_SY GAS_VM
    -end
END


[IliasBouchkira]

Many thanks Dr! all is great now.