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.

Oiling-out is an unwanted phenomenon during crystallization processes since it influences the product properties negatively and should, therefore, be avoided. To reduce the time of process development, thermodynamic modeling is usually applied. In the course of fitting model parameters, thermodynamic data of the present molecules are required. In case of branched molecules these thermodynamic data are often not available. To overcome this limitation, a methodology, which allows for the prediction of liquid–liquid equilibria (LLE) of binary systems containing branched molecules was developed recently. The developed methodology was applied in this contribution in order to predict the superposition of ternary LLE and solid–liquid equilibria (SLE) of the system n-hexadecane + 2,2,4,4,6,8,8-heptamethyl­nonane + ethanol. To consider the influence of the molecular architecture on phase equilibria, the lattice cluster theory in combination with the chemical association lattice model was applied. The prediction of the ternary phase equilibria was based on the binary subsystems. It could be shown that the ternary LLE and the ternary SLE can be predicted in very good agreement with experimental data using the same set of model parameters. All model parameters were fitted using only binary LLE data of linear alkanes dissolved in ethanol. Neither binary experimental data of the branched alkane nor ternary ones were used for parameter fitting.

No abstract

No abstract

Liquid–liquid equilibrium (LLE) and therefore interfacial tension are highly dependent on molecular architecture. In processes, where branched molecules are involved, these properties often cannot be measured; therefore, there is a need for thermodynamic modeling to make these properties accessible. A methodology, which allows for the prediction of liquid–liquid equilibria of systems containing branched molecules, was developed recently, where the lattice cluster theory is combined with the chemical association lattice model. In this contribution, it was proved whether the methodology can consider small changes in molecular architecture. Therefore, binary LLE of methanol and four hexane isomers were estimated and predicted. All predicted LLE showed a very good agreement with the experimental data. Additionally, the interfacial tension and interfacial concentration profiles were estimated for the investigated systems and calculated by the density gradient theory. For that, its influence parameter was adjusted to a single data point.

No abstract

To separate linear and branched molecules in a liquid state, adsorption on porous materials is a promising separation method. To calculate the adsorption isotherms, a combination of lattice cluster theory and density functional theory was introduced recently, allowing the prediction of branched molecules' adsorption isotherms based on the knowledge of the adsorption isotherms of the pure linear substances. However, these models are not practicable for process simulation and optimization because of their high numerical effort. Therefore, a simpler adsorption model based on the lattice cluster theory was developed to provide the results of the density functional theory approach for process development. In addition to the adsorption isotherm calculations, the model also considers the overall mass balance of the adsorption process. The model was validated for the adsorption of two binary, liquid alkane systems on three different adsorbents. Therefore, adsorption isotherms of these mixtures on activated coal, zeolite, and silica gel were measured. A good agreement of experimental and calculated adsorption isotherms was observed for all systems.

No abstract