Why don't you try NRTL and UNIQUAC?

The two sub-process models for the GTL process, i.e., the syngas generation process and the Fischer Tropsch synthesis (FTS) process, are analyzed in detail with ASPEN Plus. The autothermal reforming process (ATR) is analyzed using Aspen Plus based on the Gibbs reactor model, while FTS is simulated with ASPEN Plus based on detailed kinetic models for industrial iron and cobalt catalysts. Proven process integration techniques for thermal management and resource conservation will be employed to optimize the system design. The flexibility offered by changing parameters such as reflux ratio, etc. has also been investigated through parametric studies .As an extension of the previous works, a methodology is now proposed to design a RD column for FTS in Aspen Plus, utilizing the kinetic and thermodynamic models reported previously. Slurry reactor simulations are performed initially to form a design basis and a simple RD column is configured.

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Article Reactive Distillation for Fischer−Tropsch Synthesis: Simulat...

Article Reactive Distillation for Fischer−Tropsch Synthesis: Feasibl...

My "Project" located at:

  https://www.researchgate.net/project/Gas-to-Liquids-Fischer-Tropsch

may help you defining your product distribution and/or determine your "equilibrium theoretical" product distribution.

I believe your current question is how to model your F-T product distribution in Aspen plus.  I would be surprised if Nonane is actually the highest boiling N-Paraffin you can define in Aspen plus but you probably should consider lumping at least some of the heavier components together and defining them with a Boiling Point and gravity or K-Watson for your VLE simulations.  I normally use Peng-Robinson but the SRK methods are probably also reasonable choices.

I would not try to model the individual reactions in Aspen.  All you need to do is consume the H2 and CO reactants with a component separator and produce and equal mass of the entire F-T (and other reactions) product distribution and add the heat of reaction. 

I have developed several F-T simulations over the past 30+ years let me know if you need any help.

Thank you everyone for your suggestions.

Answering Rick Manner,

Actually, I have defined parafins and olefins up to C20. But I will try to lump heavier components. But I would like to simulate the reaction in itself using a Rgibbs, I want to know what is the maximum thermodinamic composition but using this methods and RGibb Aspen provides me not more C9 in the outlet stream.

I think Rgibbs is equivalent to a Gibbs Reactor in Hysys/PetroSim.  A Gibbs reactor will minimize gibbs free energy among all of the components youallow it to consider giving essentially th same results as an equilibrium reactor.  I do not believe a Gibbs reactor is appropriate for a F-T reactor simulation.  I believ a Gibbs reactor gien a syn-gas feed will  produce a lot of CH4  and H2O and some CO and CO2 but very little else.

I do not beleive there is a prepackaged  reactor model in Aspen plus ir Hysys that will poduce a Shulz-Flory distribution of products.  

In the properties estimation setup section you can add experimental data. Also in reactor modules and chemical section you can specify which products should be produced.

Fischer Tropsch has a principle intermediate, that should be included in the component list and properties selections. If the component is not found in a data set, then it can be sketched in the estimator section and calculated in the physical chemistry routines.