Developing a novel theory for the synthesis and design of membrane-based separations
Date
2009-04-01T13:11:37Z
Authors
Peters, Mark George Dominic
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Abstract
A novel approach for the design and synthesis of membrane separation systems has
been developed. The theory is shown to be applicable to both batch and continuous
membrane operations, and has been formulated in such a way that it is valid for any
type of membrane. In this thesis, however, only vapour permeation and pervaporation
membranes are incorporated for illustration purposes. The method, which employs a
graphical technique, allows one to calculate and visualise the change in composition
of the retentate. An integral part of the approach was the derivation of the Membrane
Residue Curve Map (M-RCM), and the related differential material balance which
describes it. By definition, this plot shows the change, in time, of the retentate
composition in a batch still. However, it has been shown that the M-RCM is
applicable to conventional continuously-operated membrane units, as well as infinite
reflux membrane columns. Finite reflux columns and cascades have been examined
by using column sections (CS): any column, or arrangement, no matter how complex,
can be broken down into smaller units, namely CS. The development of the
Difference Point Equation (DPE) for non-constant flow allowed one to generate, and
interpret, profiles for individual CS’s, which can ultimately be connected to form a
membrane column arrangement. The profiles, which are more complex than those
obtained in the M-RCM, exhibit a unique behavior. Since there is varying flow, the
reflux is continually changing, orientating the profile so as to seek a stable node that
is “mobile”. Thus, the movement of CS profile is dictated by the location and
direction of the pinch point locus. Finally, having membrane permeators examined in
an analogous manner to other separation methods, allows for easy synthesis and
design of combinations of different processes. Hybrid distillation-membrane systems
are analyzed by incorporating CS’s and the appropriate DPE’s which describe each.
Investigating the arrangement as a thermally-coupled column introduces a novel way
of synthesizing hybrids. Regions of feasibility, which are dictated by the relevant
pinch point loci of each separation method, are ultimately sought.
Description
Keywords
Membrane, Residue curve map, Hybrids