Chemical process design is a creative
step of engineers that should
be supported by different computer-aided design tools. Such tools
should be simple and easy to use because process synthesis often means
the investigation of a huge number of alternatives. During the design
of the separation of liquid mixtures, among many others, distillation
and pervaporation are usually simultaneously considered because pervaporation
is frequently considered as an alternative to distillation. To easily
compare the efficiencies of continuous pervaporation and flash distillation,
we propose a new and simple method, the so-called membrane flash index
(MFLI). The comparison is based upon vapor–liquid equilibrium
data and the permeation data of a pervaporation membrane and therefore
can be plotted on a common chart in the case of binary mixtures. The
permeation values of organophilic and hydrophilic pervaporations can
be calculated with the help of known separation factors and feed concentrations.
The MFLI is dimensionless and can be determined by dividing the permeate
concentration by the corresponding vapor equilibrium data obtained
from a simple flash distillation. Only the feed concentration, separation
factor, and refereed equilibrium data are necessary for the calculations.
If the MFLI is <1, the application of pervaporation can be worse
than that of flash distillation. In our study, the efficiencies of
pervaporation and flash distillation are compared using three mixtures,
methanol/water, ethanol/water, and isobutanol/water. After determining
the MFLI for different types of membranes, we can conclude that the
separation capability of hydrophilic membranes is significantly better
than that of the organophilic ones and also better than that of flash
distillation by far. Apart from azeotrope braking, the MFLI, as a
single number, gives clear information about the separation capabilities
of pervaporation and flash distillation in the course of process design.
The carbon dioxide capture is a more and more important issue in the design and operation of boilers and/or power stations because of increasing environmental considerations. Such processes, absorber desorber should be able to cope with flue gases from the use of different fossil primary energy sources, in order to guarantee a flexible, stable, and secure energy supply operation. The changing flue gases have significant influence on the optimal operation of the capture process, that is, where the required heating of the desorber is the minimal. Therefore special considerations are devoted to the proper design and control of such boiler and/or power stations equipped with CO2 capture process.
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