Marcos,

This topic has been studied pretty extensively. Almost any introductory book on separation processes in the chemical engineering curriculum will talk about this. Often, you can find graphs for determining distribution coefficients in the appendices. Often these are based on the work of Depriester

C.L. Depriester, Chem. Eng. Progr. Symp. Ser. 49(7), 1 (1953).

https://en.wikipedia.org/wiki/DePriester_chart

You can find these programmed up with some simple web searches.

I send you the attachement file to calculaye Liquid-Vapour Equilibrium for Ethane, Propane and Butane on a mix of heavier hydrocarbons.

Here is a very good article written in 1957 in the subject - Hydrogen is mmuch more interesting than the other light hydrocarbons .

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/37292/690030219_ftp.pdf?sequence=1

Thank you very much for your answers. They have been extremely helpful. 

Duraid Fadhil Ahmed could you provide references for that file? I am finding the method quite accurate, but I need to reference it. Do you have a source? Thank you in advance.