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Title: Batch Recovery of Acetonitrile/Toluene Mixture by Hybrid Distillation-Pervaporation Process
Authors: Ooms, Tom
Vandezande, Pieter
Vreysen, Steven
Parvez, Ashak Mahmud
Van der Bruggen, Bart
Vermeulen, Geert #
Issue Date: Sep-2012
Conference: Eurmembrane location:Londen date:23-27 September
Abstract: Many fine chemicals, pharmaceuticals and speciality chemicals are produced in batch
processes, which generate large volumes of solvent mixtures as ‘waste’. Due to the
interactions between the solvents in these waste mixtures, azeotropes frequently occur.
Hence, these solvents cannot be easily recovered by conventional distillation, and the
solvent mixtures are usually incinerated. It is clear that the recovery of spent solvents
from these azeotropic solvent mixtures could offer a direct cost saving to many
chemical manufacturing companies and a large benefit for the environment.
The increased world-wide competitiveness in production has forced the chemical
industry to improve their current processes. Consequently, the reorganization of existing
process designs and the development of new processes, with the possible integration of
new technologies, is of growing importance to industry. Membrane technologies have
emerged as an additional category of separation processes to the well-established mass
transfer processes. The advantages of membrane separations include high selectivity,
low energy consumption, moderate cost to performance ratio, and compact and modular
design.
In recent years, pervaporation has established itself as one of the most promising
membrane technologies. It offers potential solutions in a wide range of applications
from the well-established dehydration of solvents to the recovery of organics from water
and the separation of organic/organic mixtures. Within these applications, pervaporation
as a stand-alone process has often to compete with conventional, reliable separation
processes like distillation, liquid-liquid extraction, adsorption and stripping, the cost of
which can be readily calculated. Despite its clear advantages related to its energyefficient
character, in many cases pervaporation alone may not supply products suitable
for further processing or waste disposal in accordance with environmental standards.
Therefore, hybrid processes are regarded as a means of overcoming these limitations.
In an attempt to combine the advantages of robust standard thermal separation processes
and an alternative, energy-efficient separation technology, a hybrid distillationpervaporation
process was developed for the separation of azeotropic batch solvent
mixtures. This hybrid concept is an innovative combination of separation techniques
that, in many cases, individually fail in satisfactorily and/or efficiently separating
azeotropic solvent mixtures and purifying the solvents to the requisite level. While
azeotropic distillation is regarded as expensive and insufficiently sustainable due to the
addition and recovery of entrainers, pervaporation as a stand-alone process does often
not offer sufficient selectivity in the separation of solvent mixtures, especially since
there are almost no pervaporation membranes for organic-organic separations on the
market. By combining both separation techniques in a hybrid process, however, it is
anticipated that solvents could be recovered from waste streams and purified to the
targeted quality in an energy-efficient, thus competitive way.
This hybrid separation concept was applied to several industrially relevant binary
solvent mixtures. In general, an entrainer forming a heteroazeotrope with one of the
solvents in the mixture was added first. The search for suitable entrainers was based on
residue curve analysis using RegSol software. The ternary solvent mixture was then
separated by heteroazeotropic distillation in which the two liquid phases constituting the
heteroazeotrope were split by a decanter. Finally, the separated solvents, i.e. the light
and heavy phases of the formed heteroazeotrope, were further purified by pervaporation.
This contribution will focus on the heteroazeotropic distillation of a acetonitrile/toluene
mixture using hexane as entrainer, and the subsequent processing of the obtained
acetonitrile-rich heavy phase by pervaporation.
Publication status: accepted
KU Leuven publication type: IMa
Appears in Collections:Health Care - KAHO Sint-Lieven
Process Engineering for Sustainable Systems Section
Health Care and Chemistry Department - Geel Campus - TM K
# (joint) last author

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