What is the SOLU parameter?

A question came from a user: I was trying to add an organic compound to the database and I came across the coefficients for sol(T) (keyword: SOLU) in the vapor phase section. I can find the meaning of this entry in the help files, but I cannot find the function for which the parameters should be given. Could you please tell me which function OLI uses in SOLU?

The answer:

The functional form of the SOLU parameters is

Log₁₀ SOLU = a + b/T + cT + dT² where SOLU is the solubility of the species in a non-aqueous liquid in mole %.

Having said that, we use this record to estimate the solubility of a neutral species such as CO2 in a hydrocarbon liquid. This estimate is used to initialize our solver to get the phase equilibria correct. It is not a required parameter and can be ignored especially in the MSE thermodynamic framework. We originally used the parameter in the AQ thermodynamic framework. This parameter is only used as an initial guess.

We also only use this parameter for neutral compounds that are very soluble in both water and hydrocarbons and especially if the critical temperature is low, near ambient conditions.

So you can use this parameter if you wish but you don’t really need it unless your results are behaving badly with respect to the solubility in the hydrocarbon phase.