Processes > Oxidation and reduction equilibria

H2S solubility

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ehsan:
hey dears
i have problem with h2s solubility in pure water
and I ask you to help me please
my phreeqc is attachment
thanks

--- Code: ---SOLUTION 1
PHASES 1
REACTION 1
    H2S(g)     1;0 23*1
GAS_PHASE 1
    -fixed_volume
volume 5
    H2S(g)    0
h2o(g) 0
REACTION_TEMPERATURE 1
    40
INCREMENTAL_REACTIONS True
GAS_PHASE_MIX 1
1 0.2
USER_GRAPH 1
-headings 40C
-plot_tsv_file h2s2.tsv
 -axis_titles "Pressure, in atmospheres" "H2S concentration"   
 -axis_scale x_axis 0 500
 -axis_scale y_axis 0 4
 -connect_simulations false
 10 graph_y TOT("S(-2)")
 20 graph_x pressure
end
USE gas_phase 1
USE reaction 1
USE solution 1

REACTION_TEMPERATURE 2
    60
USER_GRAPH 1
-headings 60C
end
USE gas_phase 1
USE reaction 1
USE solution 1
REACTION_TEMPERATURE 3
    90
USER_GRAPH 1
-headings 90C
end

--- End code ---

dlparkhurst:
I don't see anything wrong with your calculation. The extent of the graph will change when you use GAS_PHASE_MIX to make total gas volume 1 L as opposed to 5 L, but the basic curve will be the same.

There are not that many parameters involved in the calculation. I think the Peng-Robinson parameters should be relatively well known--critical temperature, critical pressure, and acentric factor.  You can check in the literature. I think there may be a reference for H2S in
"Equations for calculating hydrogeochemical reactions of minerals and gases such as CO2 at high pressures and temperatures",CAJ Appelo, DL Parkhurst, VEA Post - Geochimica et Cosmochimica Acta, 2014

H2S(aq) is by far the dominant species, and being uncharged, there is no activity coefficient effect available unless the medium has other ions contributing to the ionic strength.

That leaves only the Henry's law equilibrium constant as a function of temperature. Using the analytical expression compared to the Van't Hoff seems to bracket the solubility. sit.dat has a different delta_H for H2S(g) (the analytical expression is equivalent to Van't Hoff).

So, you are on your own to decide which parameters could be adjusted, or how your data compares to other experiments.

ehsan:
excuse me dr
can you send to me a few phreeqc file of H2S solubility please?
because i'm not have a reference for this

dlparkhurst:
You will need to search the literature. One reference in CAJ Appelo, DL Parkhurst, VEA Post - Geochimica et Cosmochimica Acta, 2014 is the following:

Peng-Robinson predictions for hydrocarbons, CO2, N2, and H2 S with pure water and NaCI brine
I Søreide, CH Whitson - Fluid Phase Equilibria, 1992 - Elsevier

ehsan:
thanks dr
i have three question more
one : How does phreeqc analyze analytic parameter in PHASES when we commented it with a #?  in code
two : Why do break occur in the solubility diagram when dissolved? in attachment pic
three : Where can I find Pitzer parameters(a0,...,a5) for H2S?

--- Code: ---# DATABASE c:\phreeqc\database\llnl.dat # has S5- etc species
# Compare expt data of H2S solubility at high H2S pressure and
#   Peng-Robinson calc's with initial solution equilibria.
PHASES
H2S(g)
H2S  =  H+ + HS-
log_k    -7.97
-delta_h   9.1
# -analytic -9.7354e+001 -3.1576e-002 1.8285e+003 3.7440e+001 2.8560e+001
-T_c  373.2
-P_c  88.2
-Omega 0.1

SOLUTION 1
 pH 7 charge
 S(-2) 1# H2S(g) 0
SELECTED_OUTPUT; -reset false; -file H2S_71.prn
USER_PUNCH
  1 sc$ = chr$(59)
 10 for i = 1.1 to 220 step 5
 20   punch 'SOLUTION 1' + sc$ + ' -temp 71' + sc$ + ' pH 3 charge' + EOL$ + 'S(-2) 1 H2S(g) ' + str$(log10(i)) + EOL$ + '-pressure ' + str$(i) + EOL$ + 'END' + EOL$
 30 next i
END

SELECTED_OUTPUT 1; -active false
PRINT; -reset false; -echo_input true
USER_GRAPH
 -plot_csv_file H2S_71C.dat
 -axis_titles "Pressure / atm" "H2S / (mol/kgw)" " phi_H2S"
 -axis_scale x_axis 0 210
 -initial_solutions true
 10 x = PR_P("H2S(g)")
 20 graph_x x # tot("Na")
 30 graph_y tot("S(-2)")
 40 graph_sy PR_phi("H2S(g)") #mol("H2S") / tot("S")
 -end
INCLUDE$ H2S_71.prn
END
--- End code ---

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