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.
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