Previous studies have shown that hybrid distillation processes using either pervaporation or
vapor permeation can be very attractive for the separation of mixtures. In this paper, a
comparison between these two hybrid processes has been made. A tool has been presented that
can assist designers and engineers to decide which process is more convenient for a specific
application. Water removal from acetonitrile has been used as an example. A hybrid process
with vapor permeation is preferred when the membrane is used either for water removal at
high water concentration or just for overcoming the azeotropic composition. When the membrane
removes water at water concentrations lower than the azeotropic point, pervaporation is more
effective. Recycling part of the product as permeate (product sweep) and applying different
pressures in the distillation columns and the membrane unit strongly reduce the required
membrane area and the total cost of the process. Relatively low membrane selectivities are
required for an economically optimal hybrid membrane-distillation process.
Distillation–pervaporation
in a single unit is a novel concept
where the pervaporation membrane is located inside the distillation
column as a packing bed. In this work, a simplified model, based on
phase equilibrium and membrane selectivity, is derived for a DPSU
column. The model provides the separation trajectories inside the
column, where distillation and pervaporation mechanisms simultaneously
occur. A Serafimov’s topological classification (1.0–2),
specifically acetone–isopropanol–water, is evaluated.
The results show that a feasible separation is achieved with product
compositions separated by a distillation boundary. The stationary
points are modified as compared to conventional distillation overcoming
the distillation boundaries. General aspects of a DPSU column are
identified to provide fundamentals in the DPSU column design.
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