I'm sure we can help with the computational steps. Here's what I would expect:

1) get partial pressure of each component in the vapor phase. What kind of data do you have for H2SO4 VLE?

1a) The data I have for H2SO4 is in from Perry's and is in a tabulated format -- partial pressure of each species at different temperature and composition values. If I choose conditions at any one of the tabulated points, I can read the partial pressures off of the table. If I choose conditions at other points, I have to figure out how I want to interpolate/extrapolate from the tabulated values to my chosen conditions.

1b) Or, perhaps you have a mathematical model to describe the VLE of H2SO4 -- maybe an activity coefficient equation with chemical equilibrium equations and ionization equations and so on. Solve the equations for partial pressure of each component.

2) Once you have partial pressures for each component, then you add in the partial pressure of any blanket gas and get the total system pressure. Divide partial pressures by total system pressure to get vapor phase concentration (mole basis) of each species.

3) The example in the OP assumes that the blanket gas making up the bulk of the vapor phase does not significantly impact the VLE of the solvent. There is probably value in questioning that assumption to see if further effort is needed to compute the impact of the blanket gas on the VLE of the system.

At this point, the main question is what data for the VLE of H2SO4 do you have?

**Edited by MrShorty, 21 March 2018 - 11:10 AM.**