Phospholipids are commonly found in biological membranes. They have a polar head group and two ester linked fatty acids tails. Different methods such as thin layer chromatography and high performance liquid chromatography coupled with ultraviolet, refractive index, flame ionization detector, and mass spectrometry (MS) detection have long been used in the study of phospholipids. These methods were time-consuming and lacked quantitative accuracy. In this work, phosphatidylcholine, phosphatidyl-ethanolamine, phosphatidylinositol and phosphatidylserine have been studied by supercritical fluid chromatography (SFC) coupled with evaporative light scattering detection (ELSD) and mass spectrometry (MS). Four different silica-based stationary phases were studied: 2-ethylpyridine, 4-ethylpyridine, diol and conventional cyanopropyl. The influence of different mobile phase additives on the elution of phospholipids has been studied. The results have shown that isopropylamine is a better additive compared with ammonium acetate, tetrabutyl-ammonium acetate, and trifluoroacetic acid for the elution of phospholipids. All phospholipids have been eluted with baseline separation in less than 15 minutes although there is some partial overlap on the pyridine columns. The second goal for this work was fractionation of phospholipids from lecithin (a by-product from soybean) by using supercritical fluid extraction (SFE) with methanol-modified CO2. Neutral lipids were first removed from the crude sample using pure CO2. Partrial fractionation of PE and nearly pure fractionated PC were obtained by varying the modifier concentration in the extraction fluid at 460 atm and 40oC with silica gel inside the extraction vessel. A total of six components were isolated from crude soybean lecithin. / Master of Science

With current energy demands globally and locally, nuclear energy remains one of the top competitors for cleaner and sustainable energy. The nuclear industry requires more inherent safety and proliferation resistance in reactor design. Thorium has therefore been identified as a possible fuel for future nuclear reactors that can comply with these requirements. However current extraction techniques are expensive, time consuming and generate large quantities of hazardous waste. A possible alternative to conventional solvent extraction of thorium is SFE (Supercritical Fluid Extraction). A monazite sample from the Steenkampskraal mine was investigated using SEM (Scanning Electron Microscope) analysis methods to determine the distribution of thorium in the grains that could potentially complicate the effectiveness of the SFE extraction method if zoning is present. The results show a homogeneous distribution with no discernable zonation in the grains. The concentration of Th, Ce and Nd was determined by quantitative MPA (Micro Probe Analysis). The results obtained from the MPA point analysis on several grains show average Th, Ce and Nd concentrations of 6.5 wt. %, 24.1 wt. % and 9.7 wt. % respectively. The extraction of Th+4 from a filter paper was conducted to verify the extraction procedure and extractability of transition elements employing SFE. The extraction was conducted using supercritical CO2 and methanol as co-solvent with TBP (Tributyl Phosphate) and HFA (Hexafluoroacetylacetone) added in situ as chelates. ICP-MS results for the Th+4 extraction procedure showed extraction efficiency of 53 % compared to 83 % in literature (Kumar et al. 2009). This marked difference in extraction efficiency is attributed to ineffective trapping methods employed and lack of prior maintenance and support on the extraction apparatus. Subsequently all further extracted samples of Th from monazite were tested using XRF analysis methods. Due to the lack of prior maintenance on the extraction apparatus several technical breakdowns were encountered and addressed from a mechanical engineering standpoint. The operational effectiveness of the modified apparatus was verified through the extraction of marula seed oil and compared with another supercritical fluid (SF) extractor to show 50 % extraction efficiency in each case. A review of the literature indicated that the crystal chemical requirements for substitution of trivalent (Ce+3) for tetravalent (Th+4) may be fulfilled during SFE processes. Experimental substitution extractions were conducted by addition of different chelates and were conducted by subjecting the monazite samples to 20 MPa pressure for 180 min static flow and 10 min continuous flow extraction times with a CO2 flow rate of 2 mL/min with 10 % co-solvent flow rate. The results of the two sets of substitution extractions namely α and β show no clear indication of Th extraction. The maximum theoretical efficiency obtainable under current extraction equipment limitations was calculated as 12%. The XRF analysis error margin was given by the analytical laboratory as 10 %. The literature has shown the substitution of trivalent cations for tetravalent cations in the monazite structure to be a valid reaction mechanism. The experimental results showed little or no success in extracting thorium from monazite. In order to prove the practical feasibility of thorium extraction several changes to the experimental operating conditions is required. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

With current energy demands globally and locally, nuclear energy remains one of the top competitors for cleaner and sustainable energy. The nuclear industry requires more inherent safety and proliferation resistance in reactor design. Thorium has therefore been identified as a possible fuel for future nuclear reactors that can comply with these requirements. However current extraction techniques are expensive, time consuming and generate large quantities of hazardous waste. A possible alternative to conventional solvent extraction of thorium is SFE (Supercritical Fluid Extraction). A monazite sample from the Steenkampskraal mine was investigated using SEM (Scanning Electron Microscope) analysis methods to determine the distribution of thorium in the grains that could potentially complicate the effectiveness of the SFE extraction method if zoning is present. The results show a homogeneous distribution with no discernable zonation in the grains. The concentration of Th, Ce and Nd was determined by quantitative MPA (Micro Probe Analysis). The results obtained from the MPA point analysis on several grains show average Th, Ce and Nd concentrations of 6.5 wt. %, 24.1 wt. % and 9.7 wt. % respectively. The extraction of Th+4 from a filter paper was conducted to verify the extraction procedure and extractability of transition elements employing SFE. The extraction was conducted using supercritical CO2 and methanol as co-solvent with TBP (Tributyl Phosphate) and HFA (Hexafluoroacetylacetone) added in situ as chelates. ICP-MS results for the Th+4 extraction procedure showed extraction efficiency of 53 % compared to 83 % in literature (Kumar et al. 2009). This marked difference in extraction efficiency is attributed to ineffective trapping methods employed and lack of prior maintenance and support on the extraction apparatus. Subsequently all further extracted samples of Th from monazite were tested using XRF analysis methods. Due to the lack of prior maintenance on the extraction apparatus several technical breakdowns were encountered and addressed from a mechanical engineering standpoint. The operational effectiveness of the modified apparatus was verified through the extraction of marula seed oil and compared with another supercritical fluid (SF) extractor to show 50 % extraction efficiency in each case. A review of the literature indicated that the crystal chemical requirements for substitution of trivalent (Ce+3) for tetravalent (Th+4) may be fulfilled during SFE processes. Experimental substitution extractions were conducted by addition of different chelates and were conducted by subjecting the monazite samples to 20 MPa pressure for 180 min static flow and 10 min continuous flow extraction times with a CO2 flow rate of 2 mL/min with 10 % co-solvent flow rate. The results of the two sets of substitution extractions namely α and β show no clear indication of Th extraction. The maximum theoretical efficiency obtainable under current extraction equipment limitations was calculated as 12%. The XRF analysis error margin was given by the analytical laboratory as 10 %. The literature has shown the substitution of trivalent cations for tetravalent cations in the monazite structure to be a valid reaction mechanism. The experimental results showed little or no success in extracting thorium from monazite. In order to prove the practical feasibility of thorium extraction several changes to the experimental operating conditions is required. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

Thesis (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: In this study the deoiling and fractionation of paraffin wax using supercritical fluid extraction (SCFE) has been investigated. SCFE was compared with state-of-the-art processes such as wax crystallisation, static crystallisation and short path distillation. Ethane and carbon dioxide were investigated as supercritical solvents for the supercritical fluid extraction of paraffin wax. Supercritical phase equilibrium data for ethane - n-alkane and CO2 - n-alkane systems close to the mixture critical region were obtained from the literature, and were correlated with several equations of state. Statistical mechanical equations of state failed to correlate the data close to the mixture critical region due to the neglect of density fluctuations which influences phase behaviour close to critical points, or due to inadequate mixing rules. It was found that simple cubic equations of state such as Soave-Redlich-Kwong, Peng-Robinson and Patel-Teja could correlate the data using two interaction parameters. This can be attributed more to their flexibility as correlating tools than to their fundamental accuracy. The Patel-Teja EOS was modified by fitting it to predict low vapour pressure data for long-chain n-alkanes. This modified Patel-Teja EOS was then fitted to the phase equilibria by adjusting two interaction parameters per binary system. The interaction parameters for each solvent (ethane or CO2) system were then fitted to generalised correlations to enable extrapolation to solvent - n-alkane systems for which no equilibrium data were available. The Simplified Perturbed Hardchain theory (SPHC) equation of state was used to correlate lower-pressure solubility data used to model the extract separator. A pilot plant SCFE unit was constructed and used to obtain experimental fractionation data of a low-molecular weight Fischer-Tropsch wax. The experimental results indicate that fractionation of the wax is possible and that the separation efficiency is enhanced by returning some of the extract to the column as reflux. An equilibrium stage model was constructed and used to simulate the extraction experiments. It was possible to obtain good agreement between the experimental results and model predictions. Deoiling of petroleum waxes with a low n-paraffin content (which are not currently deoiled commercially) was investigated. Experimental SCFE and SPD results indicated that selective deoiling is not possible, since the separation is based on differences in molecular weight (or vapour pressure). Simulations of wax crystallisation or solvent extraction and practical tests indicate that deoiling is possible, based on differences in structure and therefore melting point of the components in the wax. Practical problems associated with crystallisation or solvent extraction such as filtration, the use of chlorinated solvents and low yields currently prevent the commercial deoiling of these waxes. During crystallisation of these waxes a soft wax cake is formed which impedes the operation of static crystallisation. A detailed study of the economics of n-paraffin wax deoiling using SCFE was conducted. Flow sheets were proposed to minimise the energy consumption of the SCFE process. Comparison of SPD, static crystallisation and SCFE indicates that a SPD plant will be the cheapest option for deoiling the wax feed investigated. Fractionation of heavier waxes using SPD might not be economically feasible, since the distillation temperature increases dramatically with increasing molecular weight, which leads to higher energy cost. For medium to long chain n-paraffin waxes SCFE should be very competitive, since the capacity of the supercritical solvent can be manipulated to extract longer chain waxes without increasing the extraction temperature. Static crystallisation appears to be the more expensive deoiling option, due primarily to the large initial capital investment cost. / AFRIKAANSE OPSOMMING: Die olieverwydering en fraksionering van paraffienwasse met behulp van superkritiese ekstraksie is in hierdie studie ondersoek. Die modellering van moderne olieverwyderings- en fraksioneringsmetodes soos waskristallisasie, statiese kristallisasie en kortpad distillasie is ook ondersoek. Etaan en koolstofdioksied is ondersoek as superkritiese oplosmiddels vir die superkritiese ekstraksie van paraffienwasse. Literatuurdata van superkritiese fase-ewewigte vir etaan - n-alkaan en CO2 - n-alkaan stelsels naby die mengselkritiese punt is versamel en gekorreleer met verskeie toestandsvergelykings. Statisities-meganiese toestandsvergelykings kon nie data naby mengselkritiese punte korreleer nie, moontlik weens digtheidsvariasies wat afwykings van klassieke gedrag teweegbring, of onakkurate mengreëls. Eenvoudige kubiese toestandsvergelykings soos Soave-Redlich-Kwong, Peng-Robinson en Patel-Teja kon op die ewewigsdata gepas word deur gebruik van twee interaksieparameters. Dit kan eerder toegeskryf word aan hulle buigsaamheid eerder as hulle fundamentele akkuraatheid. Die Patel-Teja toestandsvergelyking is gemodifiseer deur dit te pas op lae dampdruk data van langketting n-alkane. Hierdie gemodifiseerde toestandsvergelyking is gepas op die fase-ewewig data deur twee interaksieparameters te gebruik per binêre sisteem. Die interaksieparameters vir die oplosmiddel stelsels (etaan of CO2) is gekorreleer met algemene vergelykings sodat dit vir ekstrapolasie na oplosmiddel - n-alkaan stelsels gebruik kan word waarvoor ewewigsdata nie beskikbaar is nie. Die "Simplified Perturbed Hardchain" teorie (SPHC) toestandsvergelyking is gebruik om laer druk oplosbaarheidsdata te korreleer vir gebruik in die modellering van die ekstrak skeier. In Superkritiese ekstraksie loodsaanleg is gebou en gebruik om eksperimentele fraksioneringsdata van 'n lae molekulêre massa Fischer- Tropsch was te genereer. Vanaf die eksperimentele resultate blyk fraksionering van was moontlik te wees. Die doeltreffendheid van die skeiding kan verhoog word deur terugvloei van ekstrak na die kolom. 'n Ewewigsmodel is opgestel en gebruik om die ekstraksie eksperimente te modelleer. Deur die ekstraksiedruk en aantal stadia te verander kon goeie ooreenstemming met eksperimentele resultate verkry word. Die verwydering van olie uit petroleumwasse met In lae n-paraffien inhoud (wat nie tans kommersiëel ontolie word nie) is ondersoek. Eksperimentele resultate vir superkritiese ekstraksie en kortpad distillasie dui daarop dat selektiewe olieverwydering nie moontlik is nie, omdat die skeiding gebaseer is op verskille in molekulêre massas en dus (of dampdrukke). Simulasies van waskristallisasie dui op die moontlikheid van olieverwydering gebaseer op verskille in strukture van die komponente in die was. Praktiese probleme geassosieer met kristallisasie of oplosmiddel ekstraksie soos filtrasie, lae opbrengste en gebruik van gechlorineerde koolwaterstowwe as oplosmiddel belemmer die kommersialisering van olieverwydering vir hierdie tipes wasse. 'n Gedetaileerde studie van die ekonomiese lewensvatbaarheid van superkritiese olieverwydering is uitgevoer. Vloeidiagramme is voorgestelom die energieverbruik van die superkritiese ekstraksieproses te minimeer. Vergelyking van kortpad distillasie, statiese kristallisasie en superkritiese ekstraksie dui daarop dat kortpad distillasie die goedkoper opsie vir die olieverwydering van die spesifieke was is. Fraksionering van swaarder wasse met kortpad distillasie sal moontlik nie haalbaar wees nie omdat die distillasietemperatuur drasties toeneem met molekulêre massa. Die skeiding van medium tot langketting wasse met superkritiese ekstraksie behoort meer mededingend te wees, want die kapasiteit van die superkritiese oplosmiddel kan maklik verstel word om langer kettinglengtes wasse te ekstraeer sonder om die temperatuur te verhoog. Statiese kristallisasie blyk die duurder olieverwyderingsopsie te wees hoofsaaklik weens die hoë kapitaalkoste van so 'n aanleg.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Long-chain hydrocarbons are of value to numerous lucrative industries. Due to the low volatility and close melting and boiling points of these solutes, traditional fractionation methods lack the required selectivity for separation and cause thermal degradation of the product. This project investigates the feasibility of Supercritical Fluid Extraction (SFE) for processing these systems, with the primary objective of modelling the high-pressure vapour-liquid equilibrium (VLE) properties of hydrocarbon solutes with a light-weight solvent using a semiempirical equation of state (EOS). Pure component vapour pressures and saturated liquid volumes are also investigated. A thorough investigation into the phase behaviour of the n-alkanes, 1-alcohols, carboxylic acids and esters in light weight supercritical solvents CO2, ethane and propane revealed that the solute structure and temperature largely influence the solute solubility and process feasibility. Good selectivity amongst the various solutes was observed for all three solvents, but very high pressures were required for complete miscibility using CO2 (exceeding 30 MPa). The quadrapole moment of CO2 further leads to complexities in phase behaviour such as temperature and density inversions (CO2/alkanes and CO2/alcohols) and 3-phase regions within the operating range. Simple linear trends in pressure vs. carbon number and temperature were observed for all the considered series using ethane and propane and these solvents were thus selected for conducting the modelling for this study. A thorough review of semi-emperical EOS models from literature revealed that the simple cubic equations of state (CEOSs) provide a promising modelling approach for SFE applications due to their simplicity, flexibility and reliability. The simple Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) EOSs provide good correlation of vapour pressure (%AAD below 5 %) for all the series over a large carbon number range (up to nC20), provided a two parameter alpha function is used. A 3rd parameter in the volume dependence for Patel-Teja (PT) EOS provides considerable improvement over the PR and SRK EOSs for satureate liquid volume correlations of the non-polar solutes (alkanes and esters), but offers virtually no advantage for the more polar alcohols and acids. The CEOSs therefore suffer clear limitations in simultaneous representation of these saturation properties (vapour pressure and liquid molar volume) for the systems of interest. Good correlations of high pressure binary VLE data were obtained using CEOSs available in the Aspen Plus ® simulator (% AAD in P, T and X2 generally below 1 % and ranging from 4 to 12 % for Y2 for all series) provided that two binary interaction parameters (BIPs) are used in the model mixing rules, irrespective of the model used. Aspen Plus ® was further validated as a reliable thermodynamic tool by comparing model fits using the RK-ASPEN model with parameters obtained from the Aspen Plus ® data regression routine and computational methods used in self-developed MATLAB software. Very similar results were obtained for both computational methods, which encourages the use of Aspen Plus ® for process modelling in SFE applications. A statistical sensitivity analysis into the relative effect and interactions between 6 modelling factors in applying the CEOSs revealed that the mixing rules, temperature and solute structure had the largest effect on the correlation of the high pressure VLE, with the pure component limit having negligible effect once BIPs are fitted to data. A significant interaction was, however, observed between the pure component model and the solute structure and temperature, which suggest that accurate correlation of mixture VLE does not solely rely on appropriate mixing rule selection, but also the pure model. Binary interaction parameters (BIPs) in model mixing rules were found to become intercorrelated when more than one are used, greatly impeding the development of generalized correlations. BIPs were also found to be sensitive to the pure component limit (alpha function and pure constants used), the temperature, the combining rules used and possibly the fluid density. These factors should all be taken into account systematically for developing generalized correlations which therefore fell outside the scope of this study. Recommendations were, however, made on how the MATLAB software developed in this study can be used to both expand the size of the statistical analysis already conducted into relevant modelling factors and to develop new generalized correlations for BIPs and new mixing rules. / AFRIKAANSE OPSOMMING: Lang-ketting koolwaterstowwe is van waarde in talle winsgewende industriële toepassings. Vanweë die lae vlugbaarheiden ooreenstemmende kook- en smeltpunte van hierdie molekules, toon tradisionele fraktioneringsmetodes nie die nodige selektiwiteit vir ekstraksie nie en veroorsaak bonop termiese degradering van die produk. Hierdie projek ondersoek dus die lewensvatbaarheid van superkritiese ekstraksie vir die prosesering van hierdie sisteme, met primêre fokus op die modellering van die hoë-druk damp-vloeistof ewewig eienskappe van koolwaterstowwe opgelos in ‘n lae-massa oplosmiddel met gebruik van ‘n semi-empiriese toestandsvergelyking. Suiwer-komponent dampdrukke en versadigde vloeistof volumes word ook ondersoek. ‘n Deeglike ondersoek na die fasegedrag van die n-alkane, 1-alkohole, korboksiel-sure asook esters in lae-massa superkritiese oplosmidds CO2, etaan en propaan toon dat die struktuur van die opgeloste stof en die temperatuur ‘n groot invloed het op die oplosbaarheid en proses lewensvatbaarheid. Goeie selektiwiteit tussen die verskillende koolwaterstowwe was waargeneem vir al drie oplosmiddels, alhoewel baie hoë drukke nodig was vir totale vermenging van die fases in CO2 (hoër as 30 MPa). Die quadrupool moment van CO2 veroorsaak verder ongewenste kompleksiteite in fase gedrag soos temperatuuren digtheid inversies (CO2/alkane en CO2/alkohole) en 3-fase-gebiede in die bedryfs-kondisies. Eenvoudige lineêre tendense in druk tenoor die koolstofnommer van die opgeloste stof asook die temperatuur was waargeneem vir al die ondersoekte koolwaterstof reekse in etaan en propaan en hierdie oplosmiddels was dus gekies vir die modellering vir hierdie studie. 'n Deeglike oorsig van semi-empiriese toestandsvergelykings uit die literatuur het getoon dat die eenvoudige kubiese toestandsvergelykings ‘n belowende modelleringsbenadering bied vir superkritiese ekstraksie toepassings vanweë hul eenvoudigeid, buigsaamheid enbetroubaarheid. Die eenvoudige Peng-Robinson (PR) en Soave-Redlich-Kwong (SRK) toestandsvergelykings bied goeie korrelasie van suiwer dampdruk (foute laer as 5 %) vir alle koolwaterstowwe oor ‘n groot koolstofnommer gebied (tot by nC20), met die voorwaarde dat ‘n 2 parameter alpha funksie gebruik word. ‘n 3rde parameter in die volume afhanklikheid van die Patel-Teja (PT) toestandsvergelyking bied ‘n beduidende verbetering in die passing van die versadigde vloeistof volume vir die nie-polêre koolwaterstowwe (n-alkane en die esters), maar bied geen voordeel vir die meer polêre alkohole en karkoksiel sure nie. Die kubiese modelle toon dus duidelike beperkings vir die gelyktydige voorstelling van hierdie versadigingde eienskappe (dampdruk en vloeistof volume) vir die sisteme van belang. Goeie korrelasie van hoë druk binêre damp-vloeistof ewewig data was verkry deur gebruik van die kubiese toestandsvergelykings beskikbaar inAspen Plus ® (fout in P, T en X2 tipies laer as 1 % en van 4 tot 12 % vir Y2 vir alle sisteme), met die voorwaarde dat 2 binêre interaksie parameters gebuik word in die model mengreëls, onafhanklik van die model. Aspen Plus ® was verder bekraktig as ‘n betroubare termodinamiese hulpmiddel deur model passings te vergelyk met die RK-ASPEN model tussen gevalle waar parameters verkry is deur die beskikbare regressie metode in Aspen Plus ® en metodes gebruik in self-ontwikkelde MATLAB sagteware. Eenderse resultate was verkry vir beide berekeningsmetodes, wat die gebruik van Aspen Plus ® vir prosesmodellering in superkritiese ekstrasie toepassings aanmoedig. ‘n Satistiese sensitiwiteits analise op die relatiewe effek en interaksies tussen 6 modelleringsfaktore in die toepassing van die kubiese toestandsvergelykings het gevind dat die mengreëls, temperatuur en die stuktuur van die opgeloste stof die grootste effek op die korrelasie van hoë druk binêre damp-vloeistof ewewig het, met ‘n weglaatbare effek vandie suiwerkomponent limiet waargeneem sodra binêre interaksie parameters gepas is aan data. ‘n Beduidende interaksie was wel waargeneem tussen die suiwerkomponent model en die struktuur van die opgeloste stof asook die temperatuur, wat daarop dui dat akurate korrelasie van mengsel damp-vloeistof ewewig nie slegs afhanklink is van ‘n gepaste keuse van mengreëls nie, maar ook die suiwer-komponent model. Binêre interaksie parameters in die model mengreëls ondergaan inter-korrelasie wanneer meer as een interaksie parameter gebruik word, wat die ontwikkeling van algemeen toepaslike korrelasies grotendeels belemmer. Binêre interaksie parameters was ook bevind om sensitief te wees tot die suiwer component limiet (alpha funksie en suiwer konstantes wat gebruik is), die temperatuur, die kombineringsreëls en moontlik die vloeistof digtheid. Hierdie faktore moet dus almal sistematies in ag geneem word wanneer algemeen toepaslike korrelasies ontwikkel word, wat dus buite die omvang van die huidge studie val. Aanbevelings was wel gemaak vir hoe die MATLAB sagteware ontwikkel vir hierdie studie gebruik kan word om beide die betaande statistiese analise uit te brei, asook nuwe korrelasies vir binêre interaksies parameters en nuwe mengreëls te ontwikkel.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2001. / Current methods for wax fractionation result in products with large polydispersity, and due to the high temperatures required, thermal degradation of the wax is often incurred. The need for an alternative process thus exists. The purpose of this project is to investigate the technical viability of supercritical fluid processing as an alternative wax fractionation technology. The main aims of this project are to select a suitable supercritical solvent, to conduct binary phase equilibrium experiments, to determine if the process is technically viable and to investigate the ability of various equations of state to correlate the phase equilibrium data. Based on limited data from the literature, propane and a propane rich LPG (Liquefied Petroleum Gas) were selected as suitable solvents. Literature data for propane and high molecular weight alkanes is scares and incomplete, thus necessitating experimental measurements. A phase equilibrium cell was designed, constructed and commissioned. The cell was designed for pressures up to 500 bar and temperatures to 200 oC, and with the aid of an endoscope, the phase transitions were detected visually. The measurements correspond well to literature values from reliable research groups. Phase equilibrium data sets for propane with nC32, nC36, nC38, nC40, nC44, nC46, nC54 and nC60 as well as LP Gas with nC36 were measured. At temperatures just above the melting point of the alkanes, the phase transition pressures can be considered to be moderate, which will positively impact the economics of the process. The phase transition pressure increases with increasing carbon number, the relationship being found to be linear when the pressure is plotted as a function of carbon number at constant mass fractions and temperature. The increase in phase transition pressure with increasing carbon number indicates that the solvent will be able to selectively fractionate the wax. At higher temperatures the gradient of the line is larger and may thus lead to improved selectivity. The higher temperatures will also lead to better mass transfer. The linear relationship indicates that limited extrapolation to higher carbon numbers may be possible. However, this needs to be verified experimentally. The inability to measure the critical point and vapour pressure curves of the higher molecular weight normal alkanes, as well as the inability of cubic equations of state to predict liquid volumes and to capture the chain specific effects such as internal rotations, results in cubic equations of state requiring large interaction parameters to fit the data. The alternative, statistical mechanical equations of state, have difficulty in predicting the critical point of the solvent correctly and thus overpredicts the mixture critical point, yet require smaller interaction parameters to fit the data. Further work is required to improve the predictability of these non-cubic equations of state. This project has proven that wax fractionation by supercritical extraction with propane is technically feasible.

Thesis (MScEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Supercritical extraction is being investigated as a possible alternative to the processes currently used in the fractionation of paraffinic waxes. By removing the lighter carbon fractions from the wax, the wax hardness will be improved and its melting temperature range reduced, hence improving the performance of the wax product in certain applications. In order to evaluate and operate such an extraction process optimally, it is necessary to have a thermodynamic model that accurately represents the process system. There are, however, currently no predictive models available for these systems. In order to fit present models to the systems, accurate phase equilibrium data of the supercritical solvent - n-alkane systems are needed. Unfortunately, the amount of reliable published data on these systems in the required operating range is very limited. A view cell was designed and developed with which these high pressure equilibria could be studied. The binary phase equilibria of supercritical CO2 with n-CI2, n-CI6, n-C20, n-C24, n-C28 and n-C36 and of supercritical ethane with n-CI6, n-C24 and n-C28 were measured in the temperature range 313 - 367 K. It was found that the systems with these two solvents have very different types of phase behaviour. The n-alkane solubility is much higher in ethane, but supercritical CO2 will provide a much better degree of control over the selectivity achieved in an extraction process. Of the various equations of state investigated, it was found that the Patel Teja equation of state provided the best fit of the CO2 - n-alkane systems and that the Soave-Redlich- Kwong equation fitted the ethane - n-alkane systems the best. The interaction parameters of both these equations of state display a functional relationship with temperature and nalkane acentric factor, making it possible to determine parameter values for application at other operating temperatures and with other n-alkane systems. It was found that the current equations of state were not able to represent the phase equilibria accurately over the entire range of operating conditions. The poor performance of the equations of state can be attributed to inherent flaws in the existing equations of state. / AFRIKAANSE OPSOMMING: Superkritiese ekstraksie word tans ondersoek as 'n moontlike altematief vir die prosesse wat huidiglik gebruik word om paraffiese wasse te fraksioneer. Die Iigter koolstofwasse word verwyder om die washardheid te verhoog en die temperatuurgebied waaroor die was smelt te verklein. Dit verbeter dan die was se kwaliteit en werkverrigting. Modelle wat die superkritiese ekstraksie proses akkuraat kan voorstel word egter benodig om die ekstraksie proses te kan evalueer en optimaal te bedryf. Daar is tans geen modelle beskikbaar wat die proses direk kan voorstel nie. Akkurate fase-ewewigsdata word benodig om bestaande modelle aan te pas vir gebruik in hierdie sisteme. Daar is egter baie min betroubare faseewewigsdata vir die superkritiese oplosmiddel - n-alkaan sisteme beskikbaar in die literatuur. 'n Sig-sel, waarrnee hierdie hoe druk data gemeet kan word, is ontwerp en ontwikkel. Die volgende binere fase ewewigte is in die temperatuur gebied 313 - 367 K gemeet: superkritiese CO2 met n-CI2, n-CI6, n-C20, n-C24, n-C28 en n-C36, en superkritiese Etaan met n-CI6, n-C24 en n-C28. Daar is gevind dat hierdie twee superkritiese oplosmiddelsisteme verskillende tipes fase-ewewigsgedragte openbaar. Die n-alkane het 'n baie boer oplosbaarheid in Etaan, maar deur superkritiese C02 in 'n ekstraksie kolom te gebruik, sal tot beheer oor die selektiwiteit van die ekstraksieproses lei. Uit die verskillende toestandsvergelykings wat ondersoek is, is daar gevind dat die Patel- Teja vergelyking die CO2 sisteme die beste kon beskryf en dat die Soave-Redlich-Kwong vergelyking die beste vergelyking was om die Etaan sisteme mee te modelleer. Beide die toestandsvergelykings se interaksie parameters het 'n funksionele verband met temperatuur en die n-alkaan asentrise faktor getoon. Dit is dus moontlik om waardes vir die parameters vir sisteme by ander temperature en met ander n-alkaan tipes te bepaal. Daar was gevind dat die bestaande toestandsvergelykings nie die die fase-ewewigte oor die hele eksperimenele gebied akkuraat kon voorstel nie. Dit kan toegeskryf word aan foute wat inherent is aan die vergelykings.

Ionic liquid/scCO₂ biphasic systems have been studied as a possible solution to the main problems concerning homogeneous catalysis reactions such as, the product/catalyst separation, the catalyst retention in the reaction medium and the use of organic solvents. The hydroformylation of long chain alkenes (1-octene) has been carried out as a continuous flow reaction using [OctMIM]Tf₂N (OctMIM = 1-octyl-3-methylimidazolium, Tf = CF₃SO₂) as the reaction solvent and scCO₂as the mobile phase to extract the products. The performance of the rhodium complexes formed with the ionic ligands [PentMIM][TPPTS] (1-pentyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) and [OctMIM][TPPTS] (1-octyl-3- methylimidazolium tri(m-sulfonyl)triphenylphosphine) is described under different sets of experimental conditions. Continuous flow hydroformylation of 1-octene was also carried out using a SILP (Supported Ionic Liquid Phase) catalyst formed with the TPPTS-based ionic ligands named above. The SILP system described in this work has the peculiarity of introducing the “without gases” approach: syn gas was synthesised in situ by the decomposition of formaldehyde. The performance of both systems is compared in the end. The extension of the continuous flow ionic liquid/scCO₂ biphasic system is shown with the optimisation of the silver-catalysed heterocyclisation of furans. A comparison is carried out with a previously developed and optimised continuous flow heterogeneous system.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The Supercritical Fluid Extraction (SFE) technique was used to fractionate Suwannee River reference fulvic acid (FA). The fractions were characterized by gas chromatography (GC) and reversed-phase high performance liquid chromatography (RP-HPLC). A SFE fractionation method was developed using stepwise gradient of supercritical CO₂ and methanol. Three FA fractions were separated. The average mass recovery was 102% with the coefficient of variation of 2.8%. The fractionation dynamics and the difference in the ratios of UV absorption to fluorescence emission indicate the real fractionation of the FA. The HPLC chromatographic peak patterns and the spectra of the corresponding peaks were almost indistinguishable. The overall results of this research support the argument that FA exhibits polymer-like molecular structure.