Crystallization from solution is a promising unit operation to separate linear and branched isomers. To reduce the number of experiments, a thermodynamic modeling approach is proposed to calculate the required phase equilibria. Hereby, the thermodynamic data of pure substances are required to fit model parameters, but the branched isomers are often not available. Therefore, a methodology which allows for the prediction of phase equilibria of systems containing branched molecules was developed in this contribution. The basic idea is to fit the model parameters to experimental data of linear molecules and combine these parameters with information about the molecular architecture of the branched isomers to predict the phase equilibria of these isomers. For this purpose the lattice cluster theory which considers directly the molecular architecture was applied in combination with the chemical association lattice model. As model systems linear and branched alkanes dissolved in an alcohol were investigated. The developed methodology is able to predict the binary liquid liquid equilibria of the branched alkanes dissolved in an alcohol in good agreement to experimental data. Furthermore, the thermodynamic model is able to simultaneously calculate the liquid liquid equilibrium and the solid liquid equilibrium with the same model parameters in good agreement with experimental data.