Thesis (PhDEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: Separation processes are an integral part of chemical engineering. The
purity of a chemical product is among the principal factors influencing its
value. Therefore, any method that can increase the purity of a product or
decrease the cost of purification will have a direct effect on the
profitability of the entire plant.
An important class of separation processes is the solvent-based
separations. This includes processes like extractive distillation, liquid-liquid
extraction and chromatographic separation. Heterogeneous azeotropic
distillation is closely related to these processes. The most important
variable in the design of a solvent-based separation process is the choice
of solvent.
A genetic algorithm for the computer-aided molecular design of solvents
for extractive distillation had been previously developed by the author.
This algorithm was improved and expanded to include liquid-liquid
extraction, heterogeneous azeotropic distillation, gas-liquid
chromatography and liquid-liquid (partition) chromatography. At the same
time the efficiency of the algorithm was improved, resulting in a speed
increase of up to 500% in certain cases. An automatic parameter tuning
algorithm was also implemented to ensure maximum efficiency of the
underlying genetic algorithm.
In order to find suitable entrainers for heterogeneous azeotropic distillation
a method is required to locate any ternary heterogeneous azeotropes
present in a system. A number of methods proposed in the literature were
evaluated and found to be computationally inefficient. Two new methods
were therefore developed for ternary systems. A methodology for
applying these methods to quaternary and higher systems was also
proposed. Two algorithms to design blended solvents were also developed. Blended
solvents allow the use of simpler and thus cheaper solvents by spreading
the active functional groups over several molecular backbones. It was
observed in a number of cases that the blended solvents performed better
than their individual components. This was attributed to synergistic
interactions between these components. Experimental evidence for this
effect was also found.
The algorithm was applied to a number of industrially important separation
problems, including the extremely difficult final purification process of
alpha olefins. In each case solvents were found that are predicted to
perform substantially better than those that are currently used in industry.
A number of these predictions were tested by experiment and found to
hold true. / AFRIKAANSE OPSOMMING: Skeidingsprosesse is 'n integrale deel van chemiese ingenieurswese. Die
suiwerheid van 'n chemiese produk is een van die hoof faktore wat die
waarde daarvan bepaal. Derhalwe sal enige metode wat die suiwerheid
van 'n produk kan verbeter, of die koste van die suiwering daarvan kan
verlaag, 'n direkte effek op die winsgewendheid van die hele aanleg hê.
'n Belangrike groep skeidingsprosesse is die oplosmiddel-gebaseerde
skeidings. Dit sluit prosesse soos ekstraktiewe distillasie, vloeistofvloeistof
ekstraksie en chromatografiese skeidings in. Heterogene
azeotrope distillasie is nou verwant aan hierdie prosesse. Die belangrikste
veranderlike in die ontwerp van so 'n oplosmiddel-gebaseerde proses is
die keuse van oplosmiddel.
'n Genetiese algoritme vir die rekenaargesteunde molekulêe ontwerp van
oplosmiddels vir ekstraktiewe distillasie is voorheen ontwikkel deur die
skrywer. Hierdie algoritme is verbeter en uitgebrei om vloeistofvloeistofekstraksie,
heterogene azeotrope distillasie, gas-vloeistof
chromatografie en vloeistof-vloeistof (verdelings) chromatografie in te
sluit. Ter selfde tyd is die doeltreffendheid van die algoritme verbeter, wat
'n verbetering in spoed van tot 500% in sekere gevalle tot gevolg gehad
het. 'n Algoritme om die parameters van die onderliggende genetiese
algoritme outomaties te verfyn is ook geïm plementeer om die optimale
werksverrigting van die algoritme te verseker.
Om gepaste saamsleepmiddels vir heterogene azeotrope distillasie te vind,
word 'n metode benodig om enige ternêre heterogene azeotrope aanwesig
in 'n stelsel op te spoor. 'n Aantal sulke metodes wat in die literatuur
voorgestel is, is geëvaluEer en daar is gevind dat hierdie metodes
ondoeltreffend is. Twee nuwe metodes is derhalwe ontwikkel vir ternêre stelsels. 'n Metodiek om hierdie metodes op kwaternêre en hoër stelsels
toe te pas, is ook voorgestel.
Twee algoritmes vir die ontwerp van gemengde oplosmiddels is ook
ontwikkel. Gemengde oplosmiddels laat die gebruik van eenvoudiger en
dus goedkoper oplosmiddels toe, deur die aktiewe funksionele groepe oor
'n aantal molekulêe strukture te versprei. Daar is 'n aantal gevalle
waargeneem waar die mengsel beter skeiding bewerkstellig het as die
individuele oplosmiddels waaruit dit bestaan. Dit is toegeskryf aan 'n
sinergistiese wisselwerking tussen die komponente van die mengsel.
Eksperimentele getuienis vir hierdie effek is ook ingewin. Die algoritme is toegepas op 'n aantal belangrike skeidingsprobleme vanuit
die bedryf, insluitende die uiters moeilike finale suiwering van alfa
olefiene. In elke geval is oplosmiddels gevind wat volgens voorspelling
aansienlike beter skeidings sal bewerkstellig as dié wat tans in die bedryf
gebruik word. 'n Aantal van hierdie voorspellings is eksperimenteel
getoets en korrek bewys.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52171 |
| Date | 12 1900 |
| Creators | Van Dyk, Braam |
| Contributors | Nieuwoudt, I., Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 230 p. |
| Rights | Stellenbosch University |
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