Browsing by Author "Ramjugernath, Deresh."
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Item Activity of complex multifunctional organic compounds in common solvents.(2009) Moller, Bruce.; Ramjugernath, Deresh.; Rarey, Jurgen.The models used in the prediction of activity coefficients are important tools for designing major unit operations (distillation columns, liquid-liquid extractors etc). In the petrochemical and chemical industry, well established methods such as UNIFAC and ASOG are routinely employed for the prediction of the activity coefficient. These methods are, however, reliant on binary group interaction parameters which need to be fitted to reliable experimental data. It is for this reason that these methods are often not applicable to systems which involve complex molecules. In these systems, typically solid-liquid equilibria are of interest where the solid is some pharmaceutical product or intermediate or a molecule of similar complexity (the term complex here refers to situations where molecules contain several functional groups which are either polar, hydrogen bonding, or lead to mesomeric structures in equilibrium). In many applications, due to economic and environmental considerations, a list of no more than 20 solvents is usually considered. It is for this reason that the objective of this work is to develop a method for predicting the activity coefficient of complex multifunctional compounds in some common solvents. The segment activity coefficient approaches proposed by Hansen, MOSCED and the NRTL-SAC models show that it should be possible to “interpolate” between solvents if suitable reference solvents are available (e.g. non-polar, polar and hydrogen bonding). Therefore it is useful to classify the different solvents into suitable categories inside which analogous behaviour should be observed. To accomplish this, a significant amount of data needs to be collected for the common solvents. Data with water as a solvent was freely available and multiple sources were found with suitable data. Both infinite dilution activity coefficient (y∞) and SLE (Solid-Liquid Equilibrium) data were used for model development. The y∞ data were taken from the DDB (Dortmund Data Bank) and SLE data were taken from Beilstein, Chemspider and DDB. The limiting factor for the usage of SLE data was the availability of fusion data (heat of fusion and melting temperature) for the solute. Since y∞ in water is essentially a pure component property it was modelled as such, using the experience gained previously by this group. The overall RMD percentage (in ln y∞) for the training set was 7.3 % for 630 compounds. For the test set the RMD (in ln y∞) was 9.1 % for 25 fairly complex compounds. Typically the temperature dependence of y∞ data is ignored when considering model development such as this. Nevertheless, the temperature dependence was investigated and it was found that a very simple general correlation showed moderate accuracy when predicting the temperature dependence of compounds with low solubility. Data for solvents other than water were very scarce, with insufficient data to develop a model with reasonable accuracy. A novel method is proposed for the alkane solvents, which allows the values in any alkane solvent to be converted to a value in the solvent hexane. The method relies on a first principles application of the solution of groups concept. Quite unexpectedly throughout the course of developing the method, several shortfalls were uncovered in the combinatorial expressions used by UNIFAC and mod. UNIFAC. These shortfalls were empirically accounted for and a new expression for infinite dilution activity coefficient is proposed. This expression is however not readily applicable to mixtures and therefore requires some further attention. The method allows for the extension of the data available in hexane (chosen since it is a common solvent for complex compounds). In the same way as the y∞ data in water, the y∞ data in hexane were modelled as a pure component property. The overall RMD percentage (in ln y∞) for the training set was 21.4 % for 181 compounds. For the test set the RMD (in ln y∞) was 11.7 % for 14 fairly complex compounds. The great advantage of both these methods is that, since they are treated as pure component properties, the number of model parameters grows linearly with the number of groups, unlike with mixture models (UNIFAC, ASOG, etc.) where it grows quadratically. For both the water and the hexane method the predictions of the method developed in this work were compared to the predictions of UNIFAC, mod. UNIFAC, COSMO-RS(OL) and COSMO-SAC. Since water and hexane are not the only solvents of practical interest, a method was developed to interpolate the alcohol behaviour based on the water and hexane behaviour. The ability to predict the infinite dilution activity coefficient in various solvents allowed for the prediction of various other properties, viz. air-water partition coefficient, octanol-water partition coefficient, and water-alcohol cosolvent mixtures. In most cases the predictions of these properties were good, even for the fairly complex compounds tested.Item Adsorption studies for the separation of light hydrocarbons.(2014) Govender, Inbanathan.; Ramjugernath, Deresh.; Naidoo, Paramespri.; Nelson, Wayne Michael.Traditionally, the separation of ethylene from ethane is undertaken using a fractionation sequence. The distillation is performed at low temperatures and elevated pressures in conventional trayed fractionators. For economic feasibility, the separation scheme must be heat integrated to produce the low temperatures needed for separation – as low as 243 K. Low temperature distillation units are expensive to build and are typically only economically feasible for feed streams containing high amounts of ethylene. Adsorption provides a favourable alternative to the traditional low temperature distillation process. The availability of accurately measured adsorption data over a wide range of temperatures and pressures is vital in the design of efficient separation processes. However, reproducible binary adsorption data are not readily available in the literature due largely to the uncertainties involved in measuring adsorption equilibria. This project involved the measurement of adsorption equilibria using two techniques – the gravimetric and the volumetric technique. Particular focus was placed on the design and commissioning of a volumetric apparatus capable of measuring binary adsorption equilibria over a range of temperatures and pressures. The gravimetric apparatus is not capable of measuring multicomponent adsorption equilibria. The Thermodynamic Research Unit (TRU) has extensive capabilities in the field of phase equilibria with specialized expertise in the field of vapour liquid equilibria (VLE). The objective of this project is to develop competence in the field of adsorption equilibria by designing and commissioning new apparatus. This forms part of a larger objective to extend the capabilities of TRU. The volumetric apparatus designed and commissioned in this study uses an innovative gas mixer to prepare binary mixtures for adsorption equilibrium measurements. The measured data were compared to literature to validate the measurement reproducibility of the apparatus and accuracy of measurement techniques used. Adsorption equilibrium data were measured for pure components and a binary system. Pure component adsorption data were measured for methane, ethane and ethylene. The binary system of ethane + ethylene was also investigated. Measurements were performed at pressures up to 15 bar, at temperatures of 298 K and 323 K, on an adsorbent zeolite 13X. The gravimetric and volumetric apparatus both showed good reliability and reproducibility. Uncertainties in temperature and pressure were 0.1 K and 4×10-3 bar for the gravimetric apparatus and 0.03 K and 0.002 bar for the volumetric apparatus respectively. The measured equilibrium data were fitted to the Langmuir, Sips and Vacancy Solution Model (VSM) adsorption models. The regressed parameters were used to predict binary adsorption equilibria. The Langmuir model performed the poorest across the pressure range investigated, with an average absolute deviation (AAD) as high as 5%. The deviation however, was comparable with the experimental uncertainties reported in literature. The Sips model improved upon the Langmuir model with the VSM model generally performing the best with an AAD of approximately 1%. The Extended Langmuir, Extended Sips and VSM all provided good predictions of the binary adsorption equilibria. The Extended Langmuir model performed best with an AAD of 3%. The Extended Sips model performed marginally poorer with an AAD of 3.05%. The VSM model performed satisfactorily with an AAD of 6%, marginally higher than the reported experimental uncertainties of 5%.Item Application of a non-linear transformation to the surface fraction of the UNIQUAC model and the performance analysis of the subsequent model (FlexQUAC-Q).(2007) Naidoo, Thishendren.; Ramjugernath, Deresh.GE-model and equations of state are used to describe and predict phase equilibria. Current models have varying capabilities and some display selectivity for certain special mixtures. While many models are superior to others in their performance, all models share a common deficiency, the inability to simultaneously describe vapour-liquid (VLE) and liquid-liquid equilibria (LLE). Current models require separate parameters to describe the two equilibria. This formed the motivation for a non-linear transformation which was formulated by Rarey (2005). The transformation was applied to the concentration space. The clear advantage of such a transformation was that it could be easily applied to any model. The flexibility of the model was drastically increased. The effects were investigated on the local composition models, in particular the UNIQUAC model resulting in the FlexQUAC model. The model was used to regress a host of VLE and LLE data sets contained in the Dortmund Data Bank (DDB). The transformation had the desired effect on the flexibility of the model and the model was now able to describe VLE and LLE. However a symmetric transformation applied to the concentration space might not be effective in the description of systems exhibiting large difference in molecular size. This is a clear disadvantage of the proposed FlexQUAC model. In order to allow the model to cater to asymmetric systems, the transformation is now applied to the surface fraction of the residual contribution of the UNIQUAC model. The Guggenheim-Staverman expression in the combinatorial part was not transformed. Both the original combinatorial term and the more suitable modification of Weidlich and Gmehling (1987) were used. The newly formed model was called the FlexQUAC-Q model. The development of the FlexQUAC-Q model, derivation of activity coefficient expressions, model implementation and its performance analysis form the basis for this research study. The activity coefficient of the new model had to be re-derived due to the application of the transformation to the residual contribution of the UNIQUAC equation. The computation of the activity coefficient was programmed in FORTRAN and integrated into the regression tool (RECVAL) of the Dortmund Data Bank (DDB). The RECVAL tool was used to regress data sets contained in the DDB. Results obtained were comparable to those obtained using the GEQUAC model. The regression was also performed in EXCEL for the three models (UNIQUAC, FlexQUAC, FlexQUAC-Q). The regression in EXCEL was more rigorous and was used for the comparison of the objective functions and to obtain a set of unique model parameters for each data set. The performance of the FlexQUAC-Q model was assessed utilizing the same data sets used to analyse the performance of the FlexQUAC model. The model's performance was assessed in the regression of 4741 binary VLE data sets, 13 ternary VLE data sets and carefully select ternary LLE cases. The minor mean relative reduction of about 3% of the objective function using FlexQUAC-Q compared to FlexQUAC was observed compared to a reduction by about 53% relative to the UNIQUAC-results. It was necessary to illustrate that the new model does not degenerate the model's existing capabilities (e.g. ability to predict multi-component mixtures from binary data) and that the model performs as well as or superior to the UNIQUAC model. FlexQUAC-Q performed similarly to FlexQUAC. However the improvement in the qualitative description of data sets exhibiting asymmetry is apparent. Herein lies the justification of such a modification and this illustrates the preference of such a model when asymmetric systems are being considered. In addition, the FLEXQUAC-Q model can be adapted to be implemented into a group contribution method, a distinct advantage over the previous model FlexQUAC. The equations for the application of a non-linear transformation to a functional group activity coefficient model, UNIFAC are also explored in this study. The resulting model is referred to as FlexFaC.Item Application of gas hydrates in cold storage technology : experimental study and thermodynamic modeling.(2015) Hashemi, Hamed.; Ramjugernath, Deresh.The ever-increasing demands for air conditioning technology especially in residential areas results in a severe imbalance between power generating utilities, especially during peak usage hours. To provide the required peak capacity, expensive peak-generators are compulsory. Hence, researchers are compelled to find an effective air conditioning system which can be utilized during peak-hours with the minimum of electrical consumption. One solution to this problem is to shift the electrical consumption from peak-hours to off-peak hours by a combination of a cold storage technology with the air conditioning system. In the cold storage system, the cold energy can be stored by a medium during off-peak hours (e.g. ice or water) and it can be released for use at peak hours. An air conditioning system which operates with cold storage technology usually consists of a storage medium, a storage tank, a coolant circulator, a pump and a condenser. Due to the fundamental role of storage medium in cold storage systems, various investigations have been performed in order to design an applicable storage tank. Ice, eutectic salt, and water are the most common materials being used as storage materials in cold storage applications. However, the application of these conventional materials as storage medium is not practical, due to their formation at low temperatures, their low enthalpy of dissociation and their low density of cold storage. It was found that most refrigerant hydrates can be utilized as a suitable cold storage medium in air conditioning systems due to their significant properties such as high enthalpy of formation/dissociation close to that of ice, and temperatures of formation above the freezing point of water. In this study an extended review on the application of clathrate/semiclathrate hydrates in cold storage systems is performed. The gas hydrate dissociation conditions of refrigerants R23, R134a, R125a, R22, R116, R410A, R407C, R408A, R508B, R404A, R406A, R427A and R507C have been measured experimentally using an isochoric pressure search method. From the measured experimental dissociation data, the enthalpies of hydrate dissociation are evaluated. Results indicate that R507C has the highest enthalpy of dissociation amongst the other refrigerant blends. R134a, R410A, R407C and R427A with low pressure of hydrate formation/dissociation, show the most suitable behaviour to be used in cold storage applications. A thermodynamic model with the ability to correlate dissociation conditions of refrigerant hydrates in the different phase equilibrium boundaries (Hydrate-Ice-Vapour, Hydrate-Aqueous solution-Vapour, Hydrate- Hydrate-Aqueous solution-Liquid refrigerant) has been proposed. The difference between model predictions and experimental data is reasonable. Furthermore, in order to examine the rate of the refrigerant hydrate formation, an experimental study has been performed on the kinetics of the hydrate formation of the refrigerant blends namely R407C, R410A, R507C, R404A, R406A, R408A and R427A. The induction time of hydrate formation, apparent rate constant of the hydrate reaction, water to hydrate conversion during hydrate nucleation and growth, storage capacity and the rate of hydrate formation of above mentioned refrigerants at different initial conditions (pressures and temperatures) have been calculated using a kinetic model. The results demonstrate that in the presence of pure water R407C has the maximum apparent rate constant, appropriate induction time, and highest storage capacity at temperate pressures and temperatures amongst the eight refrigerants studied. The effect of sodium dodecyl sulfate (SDS) with different concentrations of 400, 500 and 600 ppm on hydrate nucleation and growth rate was investigated. In contrast to the refrigerants R406A, R404A, R408A and R427A an inhibition effect of SDS on gas hydrate nucleation rate was found for the refrigerants R407C, R410A and R507C. The most relevant kinetic results were found for the system R406A + 400 ppm SDS solution.Item The application of non-thermal plasma-catalysis in Fischer-Tropsch synthesis at high pressure.(2016) Govender, Byron Bradley.; Ramjugernath, Deresh.Abstract available in PDF file.Item Applications of fluorocarbons for supercritical extraction in the petroleum industry.(2016) Williams-Wynn, Mark Duncan.; Ramjugernath, Deresh.; Naidoo, P.The majority of supercritical processes utilise carbon dioxide (CO2) as the principal solvent, because CO2 has many attributes that make it an ideal supercritical fluid (SCF) solvent. This study investigates the possibility of replacing CO2 with trifluoromethane or hexafluoroethane, because of the poor performance of CO2 in cases where more polar and heavier molecular weight solutes must be extracted. Several applications in the petroleum industry, such as oil sludge treatment and the treatment of contaminated soils, are discussed. Due to the large number hydrocarbons present in such applications, a selection of solutes that could be used to simulate a simplified stream were chosen for these investigations. These selected solutes were n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, 1-hexene, 3-methylpentane, methylcyclohexane, toluene and water. High-pressure vapour-liquid equilibria and vapour-liquidliquid equilibria for binary systems containing either trifluoromethane or hexafluoroethane, with these solutes were measured using a static-analytic apparatus at temperatures of between (272.9 and 313.2) K. For several systems, the phase equilibria data were verified using bubble-point pressures measured with a static-synthetic, variable-volume cell. Parameters for thermodynamic models were obtained by regression of the experimental data for the binary systems. The models provide a good representation of the majority of the systems investigated, and were therefore also used to estimate portions of the critical locus curves. These critical locus curves were compared to the critical loci that were extrapolated from the sub-critical coexistence data as well as critical loci that were measured with a critical point determination apparatus. There is satisfactory agreement between the calculated, the extrapolated and the measured critical loci. The thermodynamic models were used to simulate the separation of several hydrocarbon-water emulsions using either CO2, trifluoromethane, hexafluoroethane or mixtures thereof. The simulations confirmed that trifluoromethane, hexafluoroethane as well as mixtures thereof, provide improved performances (recoveries and yields) when used as alternative solvents in the SCF extraction of these systems. An economic analysis of a SCF extraction process was performed to investigate the performance of the solvents, and if such SCF extraction processes, using a mixture of trifluoromethane and hexafluoroethane, would provide an economically competitive treatment process for hydrocarbon-water emulsions.Item Automation of a static-synthetic apparatus for vapour-liquid equilibrium measurement.(2012) Moodley, Kuveneshan.; Naidoo, P.; Ramjugernath, Deresh.; Raal, Johan David.The measurement of vapour-liquid equilibrium data is extremely important as such data are crucial for the accurate design, simulation and optimization of the majority of separation processes, including distillation, extraction and absorption. This study involved the measurement of vapour-liquid equilibrium data, using a modified version of the static total pressure apparatus designed within the Thermodynamics Research Unit by J.D. Raal and commissioned by Motchelaho, (Motchelaho, 2006 and Raal et al., 2011). This apparatus provides a very simple and accurate means of obtaining P-x data using only isothermal total pressure and overall composition (z) measurements. Phase sampling is not required. Phase equilibrium measurement procedures using this type of apparatus are often tedious, protracted and repetitive. It is therefore useful and realizable in the rapidly advancing digital age, to incorporate computer-aided operation, to decrease the man hours required to perform such measurements. The central objective of this work was to develop and implement a control scheme, to fully automate the original static total pressure apparatus of Raal et al. (2011). The scheme incorporates several pressure feedback closed loops, to execute process step re-initialization, valve positioning and motion control in a stepwise fashion. High resolution stepper motors were used to engage the dispensers, as they provided a very accurate method of regulating the introduction of precise desired volumes of components into the cell. Once executed, the control scheme requires approximately two days to produce a single forty data points (P-x) isotherm, and minimizes human intervention to two to three hours. In addition to automation, the apparatus was modified to perform moderate pressure measurements up to 1.5 MPa. Vapour-liquid equilibrium test measurements were performed using both the manual and automated operating modes to validate the operability and reproducibility of the apparatus. The test systems measured include the water (1) + propan-1-ol (2) system at 313.15 K and the n-hexane (1) + butan- 2-ol system at 329.15 K. Phase equilibrium data of binary systems, containing the solvent morpholine-4-carbaldehyde (NFM) was then measured. The availability of vapour-liquid equilibrium data for binary systems containing NFM is limited in the literature. The new systems measured include: n-hexane (1) + NFM (2) at 343.15, 363.15 and 393.15 K, as well as n-heptane (1) + NFM (2) at 343.15, 363.15 and 393.15 K. The modified apparatus is quite efficient as combinations of the slightly volatile NFM with highly volatile alkane constituents were easily and accurately measured. The apparatus also allows for accurate vapour-liquid equilibrium measurements in the dilute composition regions. A standard uncertainty in the equilibrium pressure reading, within the 0 to 100 kPa range was calculated to be 0.106 kPa, and 1.06 kPa for the 100 to 1000 kPa pressure range. A standard uncertainty in the equilibrium temperature of 0.05 K was calculated. The isothermal data obtained were modelled using the combined (-) method described by Barker (1953). This involved the calculation of binary interaction parameters, by fitting the data to various thermodynamic models. The virial equation of state with the Hayden-O’Connell (1975) and modified Tsonopoulos (Long et al., 2004) second virial coefficient correlations were used in this work to account for vapour phase non-ideality. The Wilson (1964), NRTL (Renon and Prausnitz, 1968), Tsuboka-Katayama-Wilson (1975) and modified Universal Quasi-Chemical (Anderson and Prausnitz, 1978) activity coefficient models were used to account for the liquid phase non-ideality. A stability analysis was carried out on all the new systems measured to ensure that two-liquid phase formation did not occur in the measured temperature range. A model-free method based on the numerical integration of the coexistence equation was also used to determine the vapour phase compositions and activity coefficients from the measured P-z data. These results compare well with the results obtained by the model-dependent method. The infinite dilution activity coefficients for the systems under consideration were determined by the method of Maher and Smith (1979b), and by suitable extrapolation methods. Excess enthalpy and excess entropy data were calculated for the systems measured, using the Gibbs-Helmholtz equation in conjunction with the fundamental excess property relation.Item Binary vapour-liquid equilibria for oxygen-containing compounds.(2009) Pillay, Jeremy Clive.; Ramjugernath, Deresh.; Naidoo, P.In this study, there was a need for VLE data for systems of oxygen-containing organic compounds. Experimental VLE data are presented for the following binary systems: a) 2-propanone (1) + 2-butanol (2) at 333.15K, 353.15K and 373.15K b) 2-propanone (1) + n-propanoic acid (2) at 333.15K, 353.15K and 373.15K c) 1-propanol (1) + n-butanoic acid (2) at 333.15K and 353.15K A test system (cyclohexane + ethanol at 323.15K) was measured to confirm the accuracy of the method and apparatus. With the exception of the test system, data for all the other binary systems investigated in this study are currently not available in the open literature. The dynamic recirculating stills of Joseph (2001) and Reddy (2006) were utilised to undertake the measurements. The experimental vapour pressure data measured in this study and the results obtained for the highly non-ideal test system were in excellent agreement with the literature data. It was thus concluded that the apparatus and operating procedures used were capable of producing highly accurate VLE data and confidence in the new data measured was obtained. Thermodynamic consistency testing was performed on the experimental VLE data using the point test (Van Ness et al., 1973), which provided an indication of the data’s quality and reliability. The data were thereafter subjected to data correlation to enable interpolation of the data and extrapolation to conditions other than those measured. Appropriate thermodynamic models (taking into account vapour-phase association in particular) were correlated to the data using the combined approach to VLE ( - method). For the calculation of the fugacity coefficients, three methods were used viz. the virial EOS and the Hayden-O’Connell correlation (1975); chemical theory and the Nothnagel et al. Formulation (1973); and the VPA/IK-CAPE EOS (Abbott and Van Ness, 1992). Three activity coefficients models were also used viz. the Wilson (1964) model; the NRTL model (Renon and Prausnitz, 1968); and the UNIQUAC model (Abrams and Prausnitz, 1975). In general, the models fitted the data well and the model parameters that were acquired are included. Theoretical developments involving associating components are ongoing.Item Binary vapour-liquid equilibrium for systems of industrial importance.(2015) Avoseh, Funmilola Elizabeth.; Ramjugernath, Deresh.; Narasigadu, Caleb.Most industrial chemical engineering separation processes such as distillation, extraction, absorption and adsorption rely absolutely on accurate phase equilibrium data for effective design, optimization and simulation. Carbonyls and alcohols are known to be of important use in the petrochemical industries. Ketones alongside with alcohols and carboxylic acids are found both in the product stream and waste stream of the Fischer-Tropsch process. 4-methyl-2-pentanone forms parts of these by-products and it is used in a number of industrial applications. It is generally used as solvent, as chemical intermediate in the production of paints, rubber products, chemicals, resins and drugs to mention a few, due to its low solubility in water; it is used for liquid-liquid extraction. This work focuses on measurement of new vapour-liquid equilibrium (VLE) data for binary mixtures of : 1-Propanol (1) + 4-methyl-2-pentanone (2) (at 338.15 K, 353.15 K, and 368.15 K), 2-propanol (1) + 4-methyl-2-pentanone (2) (at 323.15 K, 338.15 K, and 353.15 K) and 2-pentanone (1) + 2-methylpropan-1-ol (2) (at 343.15 K, 358.15 K, and 363.15 K). A modified (Bhownath, 2008) low pressure dynamic VLE glass recirculating still originally designed by Raal (Raal & Mühlbauer, 1998) was used for the measurements. This work also presents the infinite dilution activity coefficients and the excess thermodynamic properties (i.e. molar excess Gibbs energy GE, heat of mixing HE, and excess entropy SE). These properties were derived from the measured isothermal VLE data. A highly non-ideal system comprised of cyclohexane + ethanol was chosen as a test system and was used to verify the reproducibility and repeatability of the apparatus. The test system had been measured in our laboratory (Joseph, 2001) and the data were found to agree excellently with those of Morachevsky and Zharov (1963) and were reported to be thermodynamically consistent according to Gmehling and Onken (1977). The results for the test system measured in this work were in excellent agreement with literature. Thus, there was confidence in the new data measured since the apparatus and the operating procedures used for the test system were able to give accurate results. The vapour pressures measured in this study were also in good agreement with literature. The temperature, pressure and composition measuring devices were well calibrated and the uncertainty acquired for each is included. The uncertainty in the pressure measurement was estimated to be ± 0.02 kPa and controlled within 0.01 kPa. The uncertainty in the temperature measurement was estimated to be ± 0.06 K (Type B uncertainty, NIST) and was controlled within 0.04 K during manual operation. The uncertainty in the composition measurement was estimated as ± 0.002. The 1-propanol (1) + methyl isobutyl ketone (2) system was found to exhibit a minimum boiling azeotrope at 353.15 K. The gamma-phi (γ-Φ) or combined method was used for the regression of the measured VLE data. Three activity coefficient models were investigated to account for the liquid phase deviation of the mixture from ideality: NRTL (Renon and Prausnitz, 1968), Wilson (1964) and the UNIQUAC (Abrams and Prausnitz, 1975) models. Two equation of state models were used to account for the vapour phase non- ideality: the virial EoS with the Hayden O’ Connell (Hayden & Connell, 1973) correlation for the calculation of the second virial coefficient, and the Nothnagel (Nothnagel, Abrams, & Prausnitz, 1973) formulation. The maximum likelihood regression technique was used to determine the regressed parameters of the activity coefficient models. These models were found to fit the measured data well. The measured VLE data passed the point test of Van Ness(et al., 1973) and the direct test (Van Ness, 1995).Item Carbon dioxide capture methods for industrial sources.(2010) Osman, Khalid.; Ramjugernath, Deresh.In order to reduce the rate of climate change, particularly global warming, it is imperative that industries reduce their carbon dioxide (CO2) emissions. A promising solution of CO2 emission reduction is Carbon dioxide Capture and Storage (CCS) by sequestration, which involves isolating and extracting CO2 from the flue gases of various industrial processes, and thereafter burying the CO2 underground. The capture of CO2 proved to be the most challenging aspect of CCS. Thus, the objective of this research was to identify the most promising solution to capture CO2 from industrial processes. The study focussed on capturing CO2 emitted by coal power plants, coal-to-liquids (CTL) and gas-to-liquids (GTL) industries, which are common CO2 emitters in South Africa. This thesis consists firstly of an extensive literature review detailing the above mentioned processes, the modes of CO2 capture, and the various CO2 capture methods that are currently being investigated around the world, together with their benefits and drawbacks in terms of energy penalty, CO2 loading, absorption rate, capture efficiency, investment costs, and operating costs. Modelling, simulation, and pilot plant efforts are also described. The study reviewed many CO2 capture techniques including solvent absorption, sorbent capture, membrane usage, hydrate formation, and newly emerging capture techniques such as enzyme based systems, ionic liquids, low temperature cryogenics, CO2 anti-sublimation, artificial photosynthesis, integrated gasification steam cycle (IGSC), and chemical looping combustion The technique of solvent absorption was found to be the most promising for South African industries. Vapour-liquid-equilibrium (VLE) measurements of solvent absorption using amine blends were undertaken, using blends of methyl-diethanol amine (MDEA), diethanol amine (DEA) and water (H2O) with composition ratios of 25: 25: 50 wt% and 30: 20: 50 wt% respectively, and with CO2 and N2 gases at CO2 partial pressures of 0.5 to 10.5 bar. Experiments were conducted under system pressures of 5 to 15 bar and temperatures of 363.15 and 413.15 K, using a static analytic apparatus. CO2 liquid loading results were analysed and discussed. The experimental data were regressed in Matlab (R2009b) using the Posey-Tapperson-Rochelle model and the Deshmukh-Mather model. The Matlab programmes are presented along with the regressed binary interaction and model parameters. The accuracy of model predictions are discussed. Thereafter an Electrolyte-NRTL model regression and simulation of the absorption process was conducted using Aspen Plus V 7.1. for flue gas compositions, solvent compositions, temperature, and pressure conditions similar to that of process operating conditions. CO2 loading, design factors, CO2 recovery, and CO2 purity results were analysed and compared where appropriate, with experimental results. Finally a general preliminary energy efficiency and cost analysis was conducted based on the simulation results. The main conclusions reached are that the amine solvent blend containing 25:25:50 wt% of MDEA:DEA:H2O, produced higher CO2 loadings for its respective system conditions than other solvents studied and those found in literature. However, absorption of CO2 was found to be highly dependent on system temperature and pressure. The Deshmukh-Mather model provided higher accuracy than the Posey-Tapperson-Rochelle model, producing CO2 loading predictions with a relative error not exceeding 0.04%, in 1.5 to 3 minutes using a dual core processor. Aspen absorption simulations provided significantly lower CO2 loading results than those experimentally obtained, due to the low contact time achieved and higher temperature dependence in the proposed absorption process. Process improvements were highlighted and implemented to increase CO2 recovery and purity. Energy penalty values were found to be higher than those found in literature, but room for process and design improvement was identified and recommendations were given. Investment cost estimates were found to be justifiable and within reason. Limitations of the simulation were also identified and discussed.Item Carbon dioxide removal from coal power plants : a review of current capture techniques and an investigation of carbon dioxide absorption using hybrid solvents.(2014) Osman, Khalid.; Ramjugernath, Deresh.; Coquelet, Christophe.The aim of this project was to identify and assess all possible solutions to reduce carbon dioxide (CO2) emissions from coal power plants in South Africa, identify the most likely solution to be implemented industrially in the short to mid-term future, and contribute towards its development through lab measurement and further research. This thesis thus contains a substantial literature review conducted on the current state of CO2 emissions in South Africa, conventional and novel coal power plant processes, modes of CO2 capture, criteria regarding the implementation of CO2 capture techniques, and the various CO2 capture techniques currently investigated with varying levels of development. The study found gas absorption using solvents to be the most likely mid-term CO2 capture technique to reach industrial implementation. However, certain challenges still need to be overcome, particularly due to numerous limitations of current solvents, to make this technique feasible for CO2 capture. In an attempt to overcome the main challenge of solvent absorption capacity, it was decided to investigate the use of ionic liquids for CO2 absorption. An in-depth review of ionic liquids was conducted, as well as a review of measurement techniques and modelling of gas absorption in alkanolamine and ionic liquid solvents. Four ionic liquids, namely methyl trioctyl ammonium bis(trifluoromethylsulfonyl)imide [MOA][Tf2N], 1-butyl-3-methyl imidazolium bis(trifluoromethylsulfonyl)imide [Bmim][Tf2N], 1-butyl-3-methyl imidazolium tetrafluoroborate [Bmim][BF4], and 1-butyl-3-methyl imidazolium methyl sulphate [Bmim][MeSO4] were tested for CO2 and O2 absorption by measuring equilibrium Pressure-Temperature-Liquid mole fraction (P-T-x) data. Measurements were conducted using an Intelligent Gravimetric Analyser (IGA-01) at 303.15, 313.15, and 323.15 K. CO2 partial pressures of 0.05 to 1.5 MPa and O2 partial pressures of 0.05 to 0.7 MPa were investigated. Furthermore, density and refractive index measurements were conducted for all solvents. The ionic liquids were benchmarked against other ionic liquids and conventional alkanolamine solvents for CO2 absorption capacity and selectivity. The study found that ionic liquids achieved higher CO2 absorption capacity at high pressure than conventional alkanolamine solvents, but very low absorption capacity at low pressure. Of the ionic liquids studied, [Bmim][BF4] and [Bmim][Tf2N] achieved high CO2 absorption and high CO2 selectivity over O2. Therefore, these two ionic liquids were selected to be combined with conventional alkanolamine solvents, namely Monoethanolamine (MEA), Diethanolamine (DEA), and Methyl Diethanolamine (MDEA), in order to form hybrid solvents. P-T-x data was obtained for CO2 absorption in alkanolamine-ionic liquid hybrid solvents containing various compositions of the above alkanolamines and ionic liquids, by gravimetric analysis, under temperature and pressure conditions as described above. CO2 absorption in the hybrid solvents was analysed, compared, and benchmarked against absorption in pure ionic liquids and conventional alkanolamine solvents. Absorption data for pure ionic liquid systems was modelled using the Redlich-Kwong equation of state (RK-EOS), while absorption in hybrid solvents was modelled using the RK-EOS for the ionic liquid components and the Posey-Tapperson-Rochelle model for the alkanolamine components of each hybrid solvent. All modelling was programmed using MatlabTM R2012B engineering programming software. Further composition analysis was intended using Fourier transform infrared (FTIR) spectroscopy. The design and development of this apparatus is described herein. The apparatus possessed limitations in achieving the desired measurements. Recommendations are described for future modifications to make the apparatus more applicable for the systems in this work. The most important conclusion was that the hybrid solvents successfully achieved higher equilibrium CO2 absorption than conventional alkanolamine solvents and pure ionic liquids, at low pressure. Absorption increased with higher temperature, lower pressure, and alkanolamine concentrations lower than 40wt%. Modelling of CO2 absorption in hybrid solvents using the above stated model proved inadequate, with deviations nearly as high as 10% of measured data. A process of CO2 capture was simulated using the engineering software Aspen Plus V8.0. CO2 absorption in the hybrid solvent containing MEA:DEA:[Bmim][BF4] at 31.8:12.1:56.1 wt% was benchmarked against CO2 absorption in a conventional alkanolamine solvent. The simulation revealed a significant improvement in CO2 absorption using the hybrid solvent at low system pressure. However CO2 selectivity and solvent recycle heat duty results were undesirable. Finally, recommendations are listed for future research endeavours, simulation and apparatus development.Item Commissioning of a refrigerant test unit and assessing the performance of refrigerant blends.(2017) Ndlovu, Phakamile.; Naidoo, Paramespri.; Raal, Johan David.; Narasigadu, Caleb.; Ramjugernath, Deresh.This study has two major purposes; to commission and to demonstrate that a new refrigerant test rig can be used for investigating the performance of different refrigerants and refrigerant blends. The motivation for this work is the need for testing new refrigerants or refrigerant blends to replace current refrigerants which are on the verge of being phased out due to environmental concerns (Montreal and Kyoto protocols). These protocols seek to implement refrigerants without any environmental impacts such as global warming potential and ozone depletion. In literature, several refrigerant test rigs that have been assembled and used in the investigation of different refrigerants are outlined, but there is limited coverage of refrigerant blends due to technical difficulties associated with the use of blends. Consequently, this places restrictions on their application, necessitating further research into properties, operating procedures, and equipment development. A refrigerant test rig was designed and assembled at the University of KwaZulu-Natal to operate on the following cycles; simple vapour compression cycle, two-stage vapour – compression cycle, cascade system and vapour –compression cycle with a suction-line heat exchanger. In this study, the simple vapour compression cycle was used, with the refrigerant R134a being employed to validate the reliability and reproducibility of the refrigerant test rig. The main components of the cycle were the evaporator, the condenser, the compressor and the throttle valve. Water was used as the heat load and heat sink medium in the evaporator and the condenser, respectively. The temperature was measured by thermocouples and; pressure transducers were used for the measurement of pressure, and their combined expanded uncertainties were 0.1 ℃ and 0.026 MPa respectively. Commercial blends R507a and R413a, as well as a laboratory synthesised blend R134a/R125 in the ratio (66/34) and (50/50) by wt-%, were used in the investigation. The simulation of the refrigeration cycles was carried out using the Reference Fluid Properties Package (REFPROP) property method, which is a component within Aspen Plus ® V8.6. This software package allowed the prediction of the theoretical performance of the refrigerants, and refrigerant blends studied. One objective of this study was to compare the performance of the test rig against the simulated results to assess the extent of the deviation between the practical and theoretical (ideal) results. Mollier charts were used to analyse experimental data. Refrigerant blend R507 displayed the best performance when compared to the refrigerants investigated in this study, with a coefficient of performance (COP) value of 5.00, while R413a had the lowest COP value of 4.00. Considering environmental aspects, R134a/R125 (66/34 wt %) with COP value of 4.88 has the least negative impact. The deviation between the theoretical and experimental values was within the experimental uncertainty, with a notable difference occurring in the evaporator inlet temperature. The results show that the test rig is fit for use in refrigeration experimental work. Furthermore, refrigerant blends showed good performance on the vapour compression cycles employed in this study proving that it is feasible to use the test rig in the investigation of refrigerant blending.Item Degradation studies of carbamazepine and escherichia coli in wastewater using a non-thermal electrical discharge reactor.(2021) Gwanzura, Emmanuel.; Iwarere, Samuel Ayodele.; Ramjugernath, Deresh.Over the last 30 years, there has been increasing detection of emerging chemical pollutants and biological contaminants in the aquatic environment. As Wastewater Treatment Plants (WWTP) are considered the primary gateway for chemical and biological contaminants into water bodies, it can be inferred that WWTP in their current configuration are ineffective against the emerging contaminants. Therefore, it is imperative to investigate new technologies capable of removing emerging chemical and biological contaminants. With this background, Advanced Oxidation Processes (AOP) are a candidate technology that can be utilised for wastewater remediation. This study explores the potential application of an AOP electrohydraulic discharge as a non-conventional tertiary stage technology for the inactivation of Escherichia coli (ATCC 25922) (E. coli) and degradation of carbamazepine (CBZ) as representative contaminants in wastewater. A reactor geometry with vertical copper electrodes with a 2 mm electrode gap in a point-to-plane configuration, connected in negative polarity to a high voltage direct current power supply, was utilised. Separate semi-batch studies were conducted for E. coli and CBZ. All the experiments were conducted using synthetic wastewater. For the E. coli studies, the effects of the electrode gap on the electric discharge, the influence of initial bacterial density, copper electrode material on bacterial inactivation were investigated. The target treatment criterion in the study was the total bacterial inactivation of E. coli. For an electrode gap of 2 mm, total inactivation for E. coli cell density ranging from 3.96 × 104 to 2.5 × 107 CFU/mL was achieved in 180 seconds. Short inactivation times can probably be attributed to the synergy of shockwaves, radicals, and Ultraviolet radiation within the reactor. Control reactor experiments confirmed the anti-bacterial properties of the copper ions in solution. However, bacteria inactivation can be attributed primarily to plasma discharges in water due to the observed higher inactivation in plasma-treated cells. For example, at 3.96 × 104 CFU/mL initial E. coli density, 4.5 log reduction by plasma treatment was observed at 180 seconds compared to 1.7 log reduction in 300 seconds for copper control. The bacterial cell walls were damaged by plasma treatment as observed for plasma-treated cells through the Scanning Electron Microscope imaging. Thus, the destruction of the cell wall can be proposed as one of the possibly numerous contributing mechanisms resulting in E. coli inactivation by plasma. In preliminary benchmarking against chlorination and ozonation, the electrohydraulic discharge reactor used in this study had considerably higher treatment costs per cubic metre of wastewater. For CBZ degradation, discharge current, air flow rate, and initial concentration were investigated, with removal efficiency and energy consumption being the response variables. CBZ degradation experiments utilised Liquid-liquid chromatography for extraction followed by GC-FID and GC-MS for quantitative and qualitative analysis, respectively. Discharge current, air flow rate, and initial concentration all influenced the removal efficiency to different degrees. However, for energy consumption, only current and air flow rate were significant variables. The highest removal efficiency obtained was 93% ± 4% for 10 and 40 mg/L initial CBZ concentration after 10 minutes of plasma treatment at a current of 0.45 A and no air flow rate. The high removal efficiency could be attributed to higher currents (0.45 A), resulting in an improved generation of highly reactive and high energy species and UV generation. Additionally, no air could also improve discharge stability resulting in an uninterrupted discharge. The experimental setup and plasma reactor used in this study show a prospect for sectors where the concentration level of the contaminants in the effluent is above 10 mg/L based on the investigations carried out within the context of this research. Treatment cost per cubic metre benchmarking of the reactor against established technologies revealed that the reactor still requires significant optimisation. The research on the reactor demonstrated its capability to treat high chemical and biological contaminants in wastewater with possible applications being in pre-concentrated wastewater remediation. However, there is still room for optimisation. One key area of focus being reducing treatment cost, which may be achieved theoretically, pending further experimental investigation, by the introduction of an AC power supply.Item Design of a static micro-cell for phase equilibrium measurements : measurements and modelling = Conception d'une micro-cellule pour mesures d'é́́́quilibres de phases : mesures et mod́élisation.(2011) Narasigadu, Caleb.; Ramjugernath, Deresh.; Naidoo, P.; Coquelet, Christophe.; Richon, Dominique.Vapour-Liquid Equilibrium (VLE), Liquid-Liquid Equilibrium (LLE) and Vapour-Liquid-Liquid Equilibrium (VLLE) are of special interest in chemical engineering as these types of data form the basis for the design and optimization of separation processes such as distillation and extraction, which involve phase contacting. Of recent, chemical companies/industries have required thermodynamic data (especially phase equilibrium data) for chemicals that are expensive or costly to synthesize. Phase equilibrium data for such chemicals are scarce in the open literature since most apparatus used for phase equilibrium measurements require large volumes (on average 120 cm3) of chemicals. Therefore, new techniques and equipment have to be developed to measure phase equilibrium for small volumes across reasonable temperature and pressure ranges. This study covers the design of a new apparatus that enables reliable vapour pressure and equilibria measurements for multiple liquid and vapour phases of small volumes (a maximum of 18 cm3). These phase equilibria measurements include: VLE, LLE and VLLE. The operating temperature of the apparatus ranges from 253 to 473 K and the operating pressure ranges from absolute vacuum to 1600 kPa. The sampling of the phases are accomplished using a single Rapid-OnLine-Sampler- Injector (ROLSITM) that is capable of withdrawing as little as 1μl of sample from each phase. This ensures that the equilibrium condition is not disturbed during the sampling and analysis process. As an added advantage, a short equilibrium time is generally associated with a small volume apparatus. This enables rapid measurement of multiple phase equilibria. A novel technique is used to achieve sampling for each phase. The technique made use of a metallic rod (similar in dimension to the capillary of the ROLSITM) in an arrangement to compensate for volume changes during sampling. As part of this study, vapour pressure and phase equilibrium data were measured to test the operation of the newly developed apparatus that include the following systems: • VLE for 2-methoxy-2-methylpropane + ethyl acetate at 373.17 K • LLE for methanol + heptane at 350 kPa • LLE for hexane + acetonitrile at 350 kPa • VLLE for hexane + acetonitrile at 348.20 K New experimental vapour pressure and VLE data were also measured for systems of interest to petrochemical companies. These measurements include: • VLE for methanol + butan-2-one at 383.25, 398.14 and 413.20 K ABSTRACT • VLE for ethanol + butan-2-one at 383.26, 398.23 and 413.21 K • VLE for ethanol + 2-methoxy-2-methylbutane at 398.25 and 413.19 K • VLE for ethanol + 2-methylpent-2-ene at 383.20 K These measurements were undertaken to understand the thermodynamic interactions of light alcohols and carbonyls as part of a number of distillation systems in synthetic fuel refining processes which are currently not well described. Two of these above mentioned systems include expensive chemicals: 2-methoxy-2-methylbutane and 2-methylpent-2-ene. The experimental vapour pressure data obtained were regressed using the extended Antoine and Wagner equations. The experimental VLE data measured were regressed with thermodynamic models using the direct and combined methods. For the direct method the Soave-Redlich-Kwong and Peng-Robinson equations of state were used with the temperature dependent function (α) of Mathias and Copeman (1983). For the combined method, the virial equation of state with the second virial coefficient correlation of Tsonopoulos (1974) was used together with one of the following liquid-phase activity coefficient model: TK-Wilson, NRTL and modified UNIQUAC. Thermodynamic consistency testing was also performed for all the VLE experimental data measured where almost all the systems measured showed good thermodynamic consistency for the point test of Van Ness et al. (1973) and direct test of Van Ness (1995).Item The design of two apparati to measure solid-liquid and liquid-liquid equilibria data.(2010) Tadie, Margreth.; Naidoo, Prathieka.; Ramjugernath, Deresh.Two new apparati have been developed to measure solid-liquid and liquid-liquid equilibria via a synthetic visual method by determination of thermal signatures. One apparatus adopts a technique of using Peltier modules for cooling, and the other is a well-known design that uses a cryogenic fluid in a thermostatted glass cell for cooling of the sample. The Peltier design is for small sample volumes, with a 10 cm3 aluminium equilibrium cell and has a minimum operating temperature of 253.15 K. The glass design is developed to complement the Peltier and has a larger volume of 140 cm3 and a minimum operating temperature of 223.15 K. Both apparati have been semi-automated in order to increase the accuracy and improve the efficiency of data measurements. Therefore the experimenter no longer has to wait for many hours for the determination of equilibrium. This was done by incorporating software, which was specially designed for the apparati using Labview8TM, for controlling the cooling and heating rates. The uncertainty of the temperature measurements was found to be ±0.03 K for the Peltier apparatus and ±0.02 K for the Glass apparatus. Liquid-liquid equilibria data has also been measured on the Peltier apparatus, to demonstrate its versatility. This was done using a digital camera, controlled through the Labview software to identify cloud points. The results have been found to be comparable with literature values. For solid-liquid equilibria new systems of n-alkyl carboxylic acid binary mixtures have also been measured: heptanoic acid + butyric acid and heptanoic acid + hexanoic acid. These systems were measured using both apparati and both systems exhibited eutectic behaviour. All eutectic temperatures were measured on the Glass apparatus. Experimental data for these systems was modelled using the local composition models: Wilson, NRTL and UNIQUAC models. The NRTL model was found to give the best results for both systems with root mean square deviations (RMSD) of 2.16 K and 1.27 K and absolute average deviations (AAD) of 0.61 K and 0.49 K, between temperature measurements of this work and those calculated from the models, for the heptanoic acid + butyric acid and heptanoic acid + hexanoic acid systems, respectively.Item Determination of activity coefficients at infinite dilution using the inert gas stripping technique.(2008) George, Salvannes.; Ramjugernath, Deresh.; Raal, Johan David.; Naidoo, P.The determination of limiting activity coefficients in liquid mixtures has become an important tool in chemical engineering. It has been investigated intensively during the past in order to find new alternatives and improved methods for its accurate detennination. The limiting activity coefficient is a fundamental thermodynamic quantity which measures the solution non-ideality and acts as a correction factor to deviations from Raoult's Law. This dissertation involves the determination of limiting activity coefficients using the inert gas stripping (IGS) technique only. It is considered to be the best method as it is a direct method involving exact concentrations of components in the mixtures encountered in industry. A comprehensive study of activity coefficients at infinite dilution for various systems, using the inert gas stripping (IGS) method has been undertaken. Various other methods and their suitability have also been discussed but preference is given to the superior quality of measurements obtained using the inert gas stripping technique. Extensive research has been conducted into the background and origination of the technique. Various improvements of the equilibrium cell designed by various authors for different types of systems have been outlined along with the various equations derived by the authors. The equipment was designed for use with the double-cell technique as well as the single-cell technique and in some cases both techniques were used. The techniques involve the use of a dilutor cell in which the highly diluted, volatile solute is stripped from a liquid solution using the inert gas nitrogen, introduced into the cell through capillaries and dispersed through the solution as small bubbles, at a constant flow rate. Analysis of the stripped solution is accomplished through the use of a gas chromatograph; the peak areas obtained from these analyses as well as the residence times and other system data such as temperature, pressure, mass and flow rate were used to compute the infinite dilution activity coefficient through the use of the various equations available in literature. The original equipment was designed for the use of the single cell technique by Soni (2004). Various modifications have been made to the equipment in order to measure limiting activity coefficients of more diverse systems with high accuracy. A major change to the equipment was the introduction of a second saturation cell of similar design to the dilutor cell. This enabled the determination of activity coefficients at infinite dilution of difficult systems i.e. systems where the solvent volatility is high and for higher order systems. The equipment was redesigned and built using ideas and improvements by previous researchers in the field and commissioned using test systems that have been classed as easy systems for this technique. The new equipment is now applicable to almost all systems, however good separation in the GC column could be a problem for complex systems. The determination of infinite dilution activity coefficients for one-component solute + onecomponent solvent systems and multi-component solvent systems were accomplished. The systems that were investigated consisted of a mixture of components of alkanes, alkenes, phenols and ketones, mostly in binary mixtures. Multi-component mixtures have also been investigated in the form of ternary systems involving a binary solvent mixture at varying concentrations, and a solute in order to show the diversity, uniqueness and efficiency of the IGS technique. Major variables affecting the system (the dilutor cell), namely the stripping gas flow rate and the dilutor cell temperature, were also investigated for all systems. Two test systems, cyclohexane in 1-methyl-2-pyrrolidone (NMP) and n-heptane in NMP were used to determine if the equipment is operating properly by comparing values obtained, to literature values where the inert gas stripping technique was used to determine the activity coefficients at infinite dilution. Another test system n-hexane in NMP was used to compare the two techniques, Le. the results of the single cell technique with the results of the double cell technique. The experimental results were thereafter compared to published literature values. Systems where the inert gas stripping technique has not been used to determine activity coefficients at infinite dilution were also investigated. These systems include 1-hexene in 0- cresol as well as the ternary systems '-hexene in various concentrations of NMP + o-cresol. A thorough literature survey has been completed and the relevant theory has been summarized. The validity of the equations proposed by Bao and Han (1995), Duhem and Vidal (1978), Leroi et a!. (1977), Hovorka and Dohnal (1997) and Krummen et al. (2000) for the determination of activity coefficients at infinite dilution were investigated. The experimental values obtained were consistent with literature values, with percentage errors of less than 1 % where the same equation was used to determine the limiting activity coefficient. Comparing limiting activity coefficients with the values obtained from other equations proposed by other authors mentioned above resulted in deviations no greater than 2.5 %, and where possible limiting activity coefficients were compared to values obtained from the single-cell technique. The theory section of this thesis covers all the various formulae (and where possible a summary of their derivation) used in the analysis of results. Some limiting activity coefficients for the systems involving n-heptane, n-hexane, n-hexene, cyclohexane, o-cresol and n-methyl-2-pyrrolidone under various experimental conditions have been reported making it readily available for use in other works. The effect of two major variables temperature and inert gas flow rate on the limiting activity coefficients with regard to all the systems studied have also been investigated and reported. This was also done in order to check that the data was reproducible. A sensitivity analysis was also performed in order to check the effect that certain measured variables would have on the limiting activity coefficient. These errors are estimated possible errors and may not exist at all, so not much consideration was given to this when reporting limiting activity coefficients for the various systems. The maximum error range for any given limiting activity coefficient as determined by the sensitivity analysis is ±11 %. The inert gas stripping technique is also extended to the determination of Hendry's constants. The actual values for the Hendry's constants were not determined but a comprehensive study of its determination was undertaken by Miyano et al. (2003) and summarized here. In addition the suitability and diversity of the inert gas stripping technique has been outlined, along with the advantages and disadvantages of the technique. The various designs of equilibrium cells have been outlined taking into account mass transfer considerations as proposed by Richon et al. (1980). The assumptions and limits of the method have also been outlined and must be taken into consideration when using the technique. A detailed description of the equipment setup and experimental procedure has been provided. The purpose, suitability, operation and applicability, of the various pieces of equipment used to make up the final equipment have been discussed in detail. Details for consideration when designing the equilibrium cells have also been provided.Item The determination of petroleum reservoir fluid properties : application of robust modeling approaches.(2016) Kamari, Arash.; Ramjugernath, Deresh.; Mohammadi, Amir Hossein.Abstract available in PDF file.Item Determination of phase equilibria for long-chain linear hydrocarbons by Monte Carlo simulation.(2005) Du Preez, Nicholas Bruce.; Ramjugernath, Deresh.; Bolton, Kim.The focus of this study was to determine the coexistence phase equilibria for three groups of long-chain linear hydrocarbons (n-alkanes, 1-alkenes and 1-alcohols) using Monte Carlo simulation. Three common transferable united-atom force fields were used in the simulations: OPLS-UA (Jorgensen et al., 1984), TraPPE-UA (Martin and Siepmann, 1998) and NERD (Nath, Escobedo, de Pablo and Patramai, 1998). Isothermal phase equilibria was calculated over a temperature range from approximately the normal boiling point up to just below the critical temperature. The liquid and vapour densities and vapour pressures were determined from the simulations. The density results were then fitted using least-squares regression to the scaling law and the law of rectilinear diameters in order to estimate the critical properties. The vapour pressure data were fitted using least-squares to the Clausius-Clapeyron equation to estimate the normal boiling points. The NVT-Gibbs ensemble method was used to simulate the pure-component coexistence of the vapour and liquid phases. The NPT-Gibbs ensemble was used to simulate the n-alkane binary mixtures. Two forms of configurational-bias Monte Carlo (standard CBMC and coupled-decoupled CBMC) were used to increase the number of swap moves accepted during the simulations. Dual-cutoff CBMC was implemented with a second cut-off of sA in order to speed up the CBMC calculations. Minimum image and a spherical potential truncation after 14A were implemented with standard tail corrections. BICMAC and TOWHEE were the two Fortran-77 codes used to simulate the hydrocarbon compounds. BICMAC was used in the simulations of non-polar molecules and TOWHEE was used in the simulations of polar molecules. System sizes ranged from 300 (for the CB'S) down to 100 molecules (for the Czo's). The simulations were typically equilibrated for at least 30000 cycles and production runs ranged from 50000 to 120000 cycles for the different hydrocarbon groups. Standard deviations of the calculated thermophysical properties were between 1-3% for the liquid densities and 10-20% for the vapour densities and vapour pressures. It was found that the coexistence density curves were generally in good agreement with experiment for all the hydrocarbon groups investigated (the OPL5-UA force field being the exception). The chain-length appeared to have littl e effect on the quality of the calculated thermophysical properties. The chain-length did however increase the time required to perform the simulations substantially. The va pour pressures were consistently over-predicted by NERD and TraPPE-UA. The normal boiling pOints were typically under-predicted by 2-5%. The critical tempe ratures and densities were predicted to within 1-5% of experimental values. The n-alkane mixtures were satisfactorily predicted using the NPT-Gibbs ensemble. While both the NERD and TraPPE-UA force fields were shown to be substantially more accurate compared to the OPLS-UA force field, there was little difference between their predictions. Thus, it is likely that the added complexity of using the bond-stretching potential (used by NERD) is unnecessary. The results of this study show that Monte Carlo simulation may be used to predict vapour-liquid coexistence properties of long-chain hydrocarbons and to approximate critical properties. However, current force fields require more refinement in ord er to accurately predict the hydrocarbon thermophysical properties. Plus, faster computing speeds are required before Monte Carlo simulation becomes an industrially viable method.Item Development and critical evaluation of group contribution methods for the estimation of critical properties, liquid vapour pressure and liquid viscosity of organic compounds.(2006) Nannoolal, Yash.; Ramjugernath, Deresh.; Rarey, Jurgen.Critical properties, liquid vapour pressures and liquid viscosities are important thermophysical properties required for the design, simulation and optimisation of chemical plants. Unfortunately, experimental data for these properties are in most cases not available. Synthesis of sufficiently pure material and measurements of these data are expensive and time consuming. In many cases, the chemicals degrade or are hazardous to handle which makes experimental measurements difficult or impossible. Consequently, estimation methods are of great value to engineers. In this work, new group contribution methods have been developed for the estimation of critical properties, liquid vapour pressures and liquid viscosities of non-electrolyte organic compounds. The methods are based on the previous work of Nannoolal (2004) & Nannoolal et al. (2004) with minor modifications of structural group definitions. Critical properties, viz. critical temperature, critical pressure and critical volume, are of great practical importance as they must be known in order to use correlations based on the law of corresponding states. However, there is a lack of critical property data in literature as these data are difficult or in many cases impossible to measure. Critical property data are usually only available for smaller molecules of sufficient thermal stability. The proposed group contribution method for the estimation of critical properties reported an average absolute deviation of 4.3 K (0.74%), 100 kPa (2.96%) and 6.4 cm3.mol1 (1.79%) for a set of 588 critical temperatures, 486 critical pressures and 348 critical volumes stored in the Dortmund Data Bank (DDB (2006)), respectively. These results were the lowest deviations obtained when compared to ten well known estimation methods from literature. In addition, the method showed a wider range of applicability and the lowest probability of prediction failure and leads to physically realistic extrapolation when applied to a test set of components not included in the training set. For the estimation of the critical temperature using the new method, knowledge about the normal boiling point is required. If there is no information on the latter property, then the previous group contribution estimation method can be employed for estimation. Because of their great importance in chemical engineering, liquid vapour pressures have received much attention in literature. There is currently an abundance of experimental data for vapour pressures, especially for smaller molecules, but data are scarce or of low quality for larger and more complex molecules of low volatility. The estimation of liquid vapour pressures from molecular structure has met with very limited success. This is partly due to the high quality predictions required for vapour pressures for use in the design of for example distillation columns. This work presents a new technique for the estimation of liquid vapour pressures by developing a two-parameter equation where separate parameters model the absolute value and slope while at the same time the equation is able to approximate the nonlinearity of the curve. The fixed point or absolute value chosen was the normal boiling point for which a large amount of experimental data is available. A group contribution estimation of the slope was then developed which showed nearly no probability of prediction failure (high deviation). Employing experimental normal boiling points in the method, an absolute relative deviation of 6.2% in pressure for 1663 components or 68835 (68670 from DDB and 165 from Beilstein) data points was obtained. This result is in comparable accuracy or slightly higher in deviation than correlative models such as the Antoine and DIPPR equations (direct correlations). A test of the predictive capability by employing data that were not used in the training set also showed similar results. Estimations are possible up to the inflection point or a reduced normal boiling temperature of ±1.2. If there is no information about the experimental normal boiling point, two options are recommended to obtain this value. The first and more reliable is back-calculation using the known boiling point at other pressures and the estimated slope of the vapour pressure equation. Results in this case are similar to cases where experimental normal boiling points were used. The second possibility is to estimate the normal boiling point using the method developed previously. In this case, an absolute relative deviation of 27.0% in pressure is obtained. The saturated liquid viscosity is an important transport property that is required for many engineering applications. For this property, experimental data are limited to mostly simple and more common components and, even for these components the data often cover only a small temperature range. There have been many different approaches to estimate liquid viscosities of organic compounds. However, correlative and empirical methods are often the only or preferred means to obtain liquid viscosities. The technique used for the estimation of the liquid viscosity is similar to that in case of liquid vapour pressures, i.e. a two-parameter equation models the absolute value, slope and the non-linearity of the curve. As there was no convenient reference point at a standard viscosity available to model the absolute value (viscosity reference temperature), an algorithm was developed to calculate this temperature which was chosen at a viscosity of 1.3 cP. This work then presents a group contribution estimation of the slope and using calculated or adjusted reference temperatures, an absolute relative deviation of 3.4% in viscosity for 829 components or 12861 data points stored in the DDB was obtained. This result is in comparable accuracy or slightly higher in deviation than correlative models such as the Andrade and Vogel equations (direct correlations). The estimation method has an upper temperature limit which is similar to the limit in case of liquid vapour pressures. If no data are available for a viscosity close to 1.3 cP then, as in case of the vapour pressure estimation method, the temperature can be back calculated from data at other viscosity values. Alternately, the viscosity reference temperature can be estimated by a group contribution method developed in this work. This method reported an average absolute deviation of 7.1 K (2.5%) for 813 components. In case both the slope and absolute value were estimated for the liquid viscosity curve, an average absolute deviation of 15.3 % in viscosity for 813 components or 12139 data points stored in the DDB was obtained. The new method was shown to be far more accurate than other group contribution methods and at the same time has a wider range of applicability and lower probability of prediction failure. For the group contribution predictions, only the molecular structure of the compound is used. Structural groups were defined in a standardized form and fragmentation of the molecular structures was performed by an automatic procedure to eliminate any arbitrary assumptions. To enable comparison, chemical family definitions have been developed that allow one to automatically classify new components and thus inform the user about the expected reliability of the different methods for a component of interest. Chemical family definitions are based on the kind and frequency of the different structural groups in the molecule.Item Development of a continuous process for the production of hexafluoropropyl methyl ether.(2015) Domah, Ashveer Krishen.; Lokhat, David.; Ramjugernath, Deresh.Partially fluorinated dialkyl ethers are valuable intermediates for organofluorine syntheses. These compounds can be used for the preparation of perfluoroacrylic acids or the anhydrides, amides and esters thereof. They also serve as very effective solvents, particularly for the extraction of essential oils. A continuous process for producing 1,1 ,2,3,3,3-hexafluoropropyl methyl ether by reacting a liquid mixture of potassium hydroxide and methanol with gaseous hexafluoropropene in one or more microstructured devices was developed. The reaction of hexafluoropropene and potassium methoxide is highly exothermic, with higher operating temperatures favouring the formation of hexafluoropropyl methyl ether. The reactants are contacted for a prescribed time within a reaction zone having a high heat transfer area to reaction volume ratio and in intimate contact with a cooling medium, facilitating efficient dissipation of the exothermic reaction heat. The product mixture is contacted with water at below ambient temperature to extract the residual methanol and the raffinate is further purified by means of conventional distillation. The water and methanol mixture is fed to a distillation column that recovers methanol at a purity of 99%. The HME-methanol mixture is fed to another distillation column which produces HME at 98% purity. The methanol recovered from both distillation columns is recycled to the start of the process. The synthesis of hexafluoropropyl methyl ether using the aforementioned process was demonstrated experimentally using a falling film microreactor. Quadratic response surface methodology was used to probe for optimal reaction conditions for the yield of hexafluoropropyl methyl ether as well as the purity of the raw product.