ABSTRACT
One of the most important tasks in the chemical industry is the separation of
multicomponent liquid mixtures into one or more high-purity products. Several
technologies are feasible for this task, either alone or in combination, such as
distillation, extraction, crystallization, ect. Among these, distillation is by far the most
widely spread and has a long history in chemical technology. However, until recently,
there has been no systematic approach for understanding the separation of complex
mixtures where azeotropes and multiple liquid phases may occur.
There has been a growing interest in the use of residue curve and column profiles for
the preliminary design of distillation columns. Residue curves and column profile are
not only used to predict the composition changes in the distillation column but also to
determine the feasibility of the proposed separation. Recently, theory underlying
column profile maps has been developed by Tapp, Holland and co-workers. However
there has been no direct experimental validation of the predictions of the column
profile map theory. The main aim of this thesis is to experimentally verify some of
the predictions of column profile map theory.
A simple experimental batch apparatus has been developed to measure residue curve
maps (RCMs) by Tapp and co-workers, the apparatus was modified so that it could
be used to measure column profile maps (CPMs) in this thesis. CPM theory has
shown that CPMs are linear transforms of the residues curve maps (RCMs). A stable
node which was the apex of a mass balance triangle (MBT) was introduced inside the
MBT, this was done by transforming the RCMs to CPMs using the appropriate
distillate composition xd and reflux ratio R. It was also shown that the saddle point
which was on the boundary of the triangle of the RCM can be shifted inside the MBT
by transforming the RCM to CPM. This is again in accordance with theoretical
predictions of CPM theory.
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Residue curves (RCs) and pinch point curves (PPCs) are used to determine the
operation leaves and hence the feasible region for distillation columns operating at a
specific distillate and bottoms composition for all fixed reflux ratio. The operating
leaves were expanded beyond the pinch point curve by varying the reflux ratio from a
higher reflux to a lower reflux ratio. This showed that one can effectively cross the
pinch point curve hence expanding the operating leave.
Finally the importance of experimentally measuring CPMs is demonstrated. Two
thermodynamic models were used to predict the profiles of a complex system. The
binary vapor-liquid equilibrium (VLE) diagrams and the residue curves produced
from using these two thermodynamic models did not predict the same topology. The
composition of the profiles were not the same because there were multiple liquid
phases involved in this system, which made it difficult for the researchers to measure
the correct profiles. Column profile maps were simulated using the different
thermodynamic models, they also showed that there is some discrepancy between the
predictions of the two models.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/4713 |
| Date | 27 March 2008 |
| Creators | Modise, Tshepo Sehole David |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1161249 bytes, application/pdf, application/pdf |
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