A better understanding of the hydrodynamics related to flooding conditions in distillation column... more A better understanding of the hydrodynamics related to flooding conditions in distillation columns is required in order to provide optimised designs for new plants and plant retrofits. Current flooding prediction correlations are predominantly based on air/water systems and tend to diverge at high vapour capacities. In this work an experimental setup was designed and constructed to test the hydrodynamic characteristics of random – and structured packing as well as sieve – and valve trays. The experimental setup is used to develop a better understanding of the influence of gas and liquid properties on entrainment and column flooding. The experimental setup was tested with an air/water system and the tray entrainment data followed the trends from Bennett et al. 1 quite well. The packed column yielded the correct trends on both pressure drop and liquid hold-up data which correlated reasonably well with the general model proposed by Piché et al. 2 .
The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carb... more The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carbon atoms in supercritical ethane were studied to determine if the phase equilibrium pressure can be predicted from the number of carbon atoms and system temperature. It has previously been shown that for the phase equilibria of heavy n-alkanes in supercritical propane there exists, at constant temperature and mass fraction, a linear relationship between the number of carbon atoms and the bubble/dew point pressure. Published data in the temperature range 310-360 K was obtained from a literature survey and, where required, additional data was measured using a high-pressure equilibrium cell. It was found that linear relationships exist and that these relationships can be used to predict the phase equilibrium pressure within 4% of experimental values.
Proceedings of the 32nd International Symposium on Ballistics
In interior ballistic simulations, the burn time can be affected by the burn rate, propellant dim... more In interior ballistic simulations, the burn time can be affected by the burn rate, propellant dimensions and flame spread. Standard IB models assume that grains are symmetric with no variation in dimensions, with instantaneous homogeneous ignition. This paper evaluates the contribution of grain dimensional variation (specifically the web), asymmetry and flame spread in a single base propellant with a single perforated grain geometry. It is shown that flame spread has the dominant effect on burn time, followed by web dimensional variation and lastly asymmetry. The implementation of these effects also leads to a simulated result that is more representative of the experimental curve in the closed vessel especially in the burnout phase.
Mathematical thermodynamic models capable of predicting phase equilibria behaviour are used to de... more Mathematical thermodynamic models capable of predicting phase equilibria behaviour are used to design, operate and optimise industrial separation and extraction equipment. Developing state of the art thermodynamic models requires accurate laboratory-scale phase equilibria data. The shortage of information and guidelines on equipment design and construction available in literature hampers the output of such data. A critical review of published equipment designs and discussions on, amongst others, mixing, sampling, sample homogenisation, analysis, pressure control, temperature control and observation windows are presented. This review enabled the authors to decide on a variable-volume, dual-phase circulation cell with multi-port sampling valves and online chromatographic analysis and density measurements. This will benefit other research groups, and thus the chemical industry, in a similar fashion but only in combining said review with future reports on equipment construction and oper...
Please help populate SUNScholar with the full text of SU research output. Also - should you need ... more Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please snd us the details and we will try to get hold of the full text as quick possible. E-mail to scholar@sun.ac.za. Thank you.NatuurwetenskappeToegepaste Wiskund
Fast pyrolysis of Eucalyptus grandis was carried out using different reactor configurations and s... more Fast pyrolysis of Eucalyptus grandis was carried out using different reactor configurations and scale setups, a 0.1 kg/h bubbling fluidised bed (BFB) reactor, a 1 kg/h BFB reactor and a 10 kg/h twin-screw reactor. The influence of lignocellulosic composition, process configuration (reactor configuration, separation and condensation system) and their feed capacity on yields and quality of pyrolysis products was discussed. The increasing reactor scale study had constraints such as the availability of biomass feedstock with inherent changes in the chemical composition and the practicality of the condensation chain. Although the methods employed for phase separation and liquid collection differ from plant to plant limiting the repeatability of results, it was clearly identified that the implementation of efficient solid separation and use of mineral oil as the coolant system were crucial aspects of the mass production of organics. These results suggest that yields and quality of fast pyrolysis at a larger scale are all process-related rather than feedstock conditioned. A comparison of energy balances indicated that fast pyrolysis retained the same energy yield at scales of 1 and 10 kg/h.
A process model developed in Aspen Plus®, was used for the thermodynamic modelling of supercritic... more A process model developed in Aspen Plus®, was used for the thermodynamic modelling of supercritical water gasification (SCWG) using a wide variety of biomass materials as feedstock. The influence of the composition of the biomass material (in terms of carbon, hydrogen and oxygen content) on various performance indicators (such as gas yields, cold gas efficiency, calorific value of product gas and heat of reaction), were determined at various temperatures (600, 700 and 800°C) and biomass feed concentrations (5, 15 and 25wt.%). Generalised contour plots, based on the biomass composition, were developed for these performance indicators to provide the thermodynamic limits at various operating conditions. These plots can aid in the selection or screening of potential biomass materials and appropriate operating conditions for SCWG prior to conducting experimental work.
Eucalyptus grandis is a fast growing hardwood that is extensively used in the paper and pulp indu... more Eucalyptus grandis is a fast growing hardwood that is extensively used in the paper and pulp industry of South Africa (Godsmark, 2010). Pyrolysis has been shown to be an effective method for condensing bulky biomass such as wood into valuable and easily ...
ABSTRACT The phase equilibria of high molecular mass 1-alcohols in supercritical propane is measu... more ABSTRACT The phase equilibria of high molecular mass 1-alcohols in supercritical propane is measured to investigate the relationship between the phase equilibrium pressure and the number of carbon atoms and by comparison with n-alkanes, to show the effect of the hydroxyl group. Binary phase equilibrium measurements of high molecular mass 1-alcohols (with 10, 12, 16, 18 and 22 carbon atoms) in supercritical propane are measured between 378 and 408 K for 1-alcohol mass fractions of 0.0175–0.600. Complete solubility below 100 bar, with no region of liquid–liquid immiscibility, is observed and the phase transition pressure increases with increasing number of carbon atoms. By plotting the number of carbon atoms as a function of the phase transition pressure at constant temperature and mass fraction 1-alcohol, a linear relationship is realized. This linear relationship can be used to estimate the phase equilibrium of 1-alcohols with 10–22 carbon atoms in propane. When the measured 1-alcohol–propane data is compared to published n-alkane–propane data it can be seen that the hydroxyl group has the effect of increasing the phase equilibrium pressure of the 1-alcohol in comparison to the n-alkane.
High pressure phase equilibria measurements of long chain saturated methyl esters (methyl decanoa... more High pressure phase equilibria measurements of long chain saturated methyl esters (methyl decanoate, methyl dodecanoate, methyl tetradecanoate, methyl hexadecanoate, methyl octadecanoate and methyl docosanoate) in supercritical ethane have been measured for temperatures between 312 K and 355 K and for methyl ester mass fractions from 0.65 to 0.018. The results show a generally linear relationship between the phase equilibria pressure and the temperature with complete mutual solubility above 17 MPa. No three-phase regions or temperature inversions (change in sign of gradient of temperature-pressure relationship at constant composition) were observed while maxima in the phase transition pressures were found for methyl ester mass fractions usually between 0.2 and 0.3. When the phase transition pressure is plotted as a function of carbon number at constant temperature and mass fraction methyl ester, a linear relationship is realised. This linear relationship can be used to determine the solubility of any saturated methyl ester with between 10 and 22 carbon atoms, with limited extrapolation being possible. Thermodynamic modelling of the measured phase equilibria with the sPC-SAFT and Peng Robinson equations of state showed that, even with the use of an interaction parameter, these equations of state are not able to model the phase behaviour and the linear pressure-carbon numbers provide more accurate predictions.
The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyar... more The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyard annual prunings were investigated for their potential as soil amendments and compared to biochar from sugar cane bagasse. Biochar from sugar cane bagasse seems to be a promising sorbent and soil conditioner due to its high surface area, high surface acidity and microporous structure. This biochar can be applied to a wide pH range of soils for enhancing nutrient and water retention. On the other hand, the biochars from black wattle and vineyard possessing high concentrations of aromatic carbon, nutrients, and alkalinity are potential soil amendment agents. Black wattle biochar is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. Therefore, this study recommends the utilization of biochars from black wattle as soil amendment agents especially in subtropical regions.
In the analysis of a ballistic evaluation motor (BEM) for extruded double base motors, an irregul... more In the analysis of a ballistic evaluation motor (BEM) for extruded double base motors, an irregular burning phenomenon was encountered. The irregular burning manifested as a drop in pressure. This was not combustion instability as acoustic instability is associated with high frequency pressure oscillations 2 , usually a mean pressure rise and steep fronted shock waves. L* instability is also eliminated as a possibility as the pressure is much higher than the pressure associated with this phenomena (>5MPa), and the pressure did not oscillate at the frequencies associated with L*-instability 3 . The reason for this phenomenon lies in the unique design of the motor. An internal/external burning cylindrical grain, inhibited on one end, was used. The external grain initially vented onto the cold steel wall, resulting in a significant heat loss. Experimental measurements of the steel wall temperature indicated that the heat losses to the wall were in the order of 14-15kJ or 4-6% of the heat released by combustion. This heat loss is also only experienced by the external burning surface of the propellant, thus amplifying the heat loss effect for the outside wall of the propellant. Inserting a silica-phenolic sleeve eliminated the irregular burning. This indicated that the heat transfer at the external wall surface is the most likely source of the irregular burning. This was also confirmed by the increase in severity of the irregular burning for cold firings, where the total heat loss was increased due to the lower temperature of the motor wall and more energy was absorbed by the casing to heat the surface. The burn rate was measured from the pressure/time curve because pressure was the only practical parameter that could be measured. It is not, however, the mechanism that drives the burn rate but is directly related to it. The propellant decomposes at the surface when the surface temperature reaches the ignition temperature. This mass flux from the surface moves into the flame zone and then combusts releasing heat. This heat is then absorbed by the surface, speeding up the decomposition (usually, some form of the Arrhenius equation applies to the surface decomposition), increasing the mass flux and finally increasing the heat released by the combustion. The increased mass addition and flame temperature resulted in the increase in pressure. In most cases the propellant is an internally burning grain that is axis symmetric. In the case of this BEM motor it is also burning from the outside. This has a significant effect on the heat transfer within the motor. In an internally burning axis symmetric motor the radiative heat transfer away from the surface is the same as the incoming energy from the surface directly opposing it. Thus, both surfaces transfer energy to each other. This may not be significant in terms of conductive as most of the conductive heat transfer to the surface comes from the combustion nearest the surface, but can be significant in terms of radiation. Basic propellant combustion theory states that radiation can account for up to 25-30% of the heat transfer to the surface. The energy radiated from the propellant surface should be the same as the energy radiated from the opposing surface. In the case of the motor burning inwards the opposing surface (in this case a steel wall) is not another source of radiant heat but will only be a heat sink. This, combined with the cooling of the combustion gasses, causes the propellant surface not to heat up at the same rate as the propellant surface in the internally burning grain. Thus, its burn rate is lower, resulting in a drop in pressure. This phenomenon warranted a more fundamental approach in the burn rate calculation and heat transfer modeling to confirm the above assertions. To accomplish this, a complete heat transfer calculation was performed. In parallel a CFD simulation with radiation and conduction effects was performed. The results of the two approaches showed remarkable similarity and both pointed to the heat losses as the origin of the irregular burning.
Internal ballistic design of solid rocket motors (SRMs) is a well-established field. Most grain d... more Internal ballistic design of solid rocket motors (SRMs) is a well-established field. Most grain designs have been well characterized throughout the industry. However, generating and evaluating different grain design options can be quite tedious and time-consuming. Thus, it was endeavored to create a preliminary design tool which can be used in a workshop with a client to promptly establish the most likely and suitable grain and performance design for the particular missile application, starting with a system definition. This tool was developed in the MATLAB environment. This tool also serves as an input for the more detailed design. As part of the larger program it was endeavored to create an internal ballistic tool that allows for more detailed analyses. It was endeavored to use the rapidly expanding open source tools available to develop a fully coupled CFD internal ballistic tool. The grain regression and CFD modules have been developed to date.
Corn cobs and sugar cane bagasse are two of the most important agricultural residues in South Afr... more Corn cobs and sugar cane bagasse are two of the most important agricultural residues in South Africa in terms of availability and potential for use as a bioenergy resource. The thermal devolatilization of samples of these two fuels in an inert atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range of 10-50 • C min −1. Friedman's isoconversional method was applied using the AKTS Thermokinetics software to obtain the dependence of activation energy on conversion. The same method was also applied to the kinetic analysis of lignocellulosic pseudocomponents derived from the mathematical deconvolution of the original DTG curves. The results showed that apparent activation energy in the 0.1-0.8 conversion interval ranged from 170-225 kJ mol −1 to 75-130 kJ mol −1 for sugar cane bagasse and corn cobs respectively. The range of apparent activation energy obtained for the pseudocomponents representing hemicelluloses, cellulose and lignin derived from sugar cane bagasse were given as 200-300 kJ mol −1 , 163-245 kJ mol −1 , and 80-180 kJ mol −1 , while for corn cobs the values were 85-110 kJ mol −1 , 80-140 kJ mol −1 , and 10-60 kJ mol −1 respectively. The derived thermokinetic parameters from both global and pseudocomponent analyses satisfactorily reproduced the experimental curves used for the analysis and could also successfully predict reaction progress at a heating rate outside what was used in the analysis. The fits obtained between simulated and experimental results were comparable to what has been reported in the literature based on conventional model-fitting techniques.
Experimental phase equilibrium data for the systems CO 2 + n-dodecane, CO 2 + 1-decanol and CO 2 ... more Experimental phase equilibrium data for the systems CO 2 + n-dodecane, CO 2 + 1-decanol and CO 2 + 3,7-dimethyl-1-octanol were used to determine values for binary interaction parameters for use in the RK-ASPEN thermodynamic model in Aspen Plus ®. Bubble and dew point data of the mixtures CO 2 + (n-dodecane + 1-decanol), CO 2 + (n-dodecane + 3,7-dimethyl-1-octanol), CO 2 + (1decanol + 3,7-dimethyl-1-octanol) and CO 2 + (n-dodecane + 1-decanol + 3,7-dimethyl-1-octanol) were measured experimentally in a static synthetic view cell, and compared to the data predicted by the RK-ASPEN model. The model predicted the phase equilibrium data reasonably well in the low solute concentration region; significant deviation of model predictions from experimental data occurred in the mixture critical and high solute concentration regions due to the exclusion of solute-solute interaction parameters in the model. Distribution coefficients and separation factors were determined for the multicomponent mixture and separation of the alkane from the alcohol mixture with a supercritical fluid extraction process was found to be possible.
High pressure phase equilibrium measurements of long chain 1-alcohols (1-decanol through 1docosan... more High pressure phase equilibrium measurements of long chain 1-alcohols (1-decanol through 1docosanol) in supercritical ethane and their prediction are presented. The data were measured in a high pressure view cell above the melting points of these alcohols, i.e. between 308 and 356 K, and with 1alcohol mass fractions ranging from 0.0173 to 0.648. The results show a linear relationship between the phase transition pressure and the system temperature. The phase transition pressure increases with increasing molecular mass of 1-alcohol at constant temperature and composition. Furthermore, a linear relationship exists between the phase transition pressure and the number of carbon atoms of the 1-alcohol, making it easy to predict phase transition by simple interpolation within the experimental boundaries. Additionally, the state-of-the-art sPC-SAFT EOS model, as now typically included in process simulators, is unable to predict the phase equilibria, although it tends to give better results than the classic Peng Robinson EOS.
The ability to model and predict the behaviour of high-pressure alcohol and carbon dioxide mixtur... more The ability to model and predict the behaviour of high-pressure alcohol and carbon dioxide mixtures is important for industrial purposes. The phase equilibria behaviour of four 8-carbon alcohols in supercritical carbon dioxide are measured to determine the effect of the hydroxyl group position on alcohol solubility. Experimental bubble-and dew point data are generated on a high pressure phase equilibrium cell for the systems 1-octanol, 2-octanol, 3-octanol and 4-octanol in supercritical carbon dioxide between 35 • C and 75 • C. 1-Octanol is shown to be the least soluble and, at 35 • C, exhibits a phase transition pressure 85 bar higher than that of 2-octanol. 1-Octanol also exhibits a temperature inversion near the critical temperature of carbon dioxide in the mixture critical region. 2-Octanol possesses marginally higher phase transition pressures than 3-octanol which, in turn, possesses marginally higher phase transition pressures than 4-octanol. This difference in phase equilibria is believed to result from a difference in polarity. Shifting the hydroxyl group from the first to the second carbon atom causes a large decrease in polarity and increase in solubility. Further movements toward the molecule centre result in progressively smaller polarity reductions and solubility increases, producing phase boundaries that coincide or differ minimally.
This paper is the continuation of a previous study on the investigation of the separation of dete... more This paper is the continuation of a previous study on the investigation of the separation of detergent range alkanes and alcohols with supercritical fluids. Specifically this paper presents results on the optimisation of the process parameters for the separation of n-tetradecane and 1-dodecanol with supercritical carbon dioxide and ethane. The optimum operating conditions were determined from the results of a study of the influence of the process parameters, as well as an investigation into the size of the operating range. The results showed that the optimum temperature is a balance between good separation at lower temperatures and better control at higher temperatures. The solvent-to-feed ratio should be kept low (within the range of vapour-continuous operation) as lower solvent-to-feed ratios result in improved separation, as well as lower energy requirements. The use of reflux is necessary for good separation when using carbon dioxide as solvent, but is not required with ethane as solvent. An analysis of the operating range showed that a process using ethane is easier to control. Ethane as solvent is technically superior to carbon dioxide yet, depending on the exact process and location, costs, safety and logistics may favour the use of carbon dioxide.
The past decade has seen the development of high-performance epoxyacrylate coatings. Some of thes... more The past decade has seen the development of high-performance epoxyacrylate coatings. Some of these coatings are used exclusively as can coatings. To improve chemical resistance, emulsion polymerization in the presence of the dispersed epoxy resin can be conducted. Replicated factorial designs were designed to investigate some of the factors that contribute to the performance and stability of the epoxyacrylate coating. The factors investigated in this study were: the type and amount of neutralizing amine, the type of initiator, the presence or absence of salt, and the stirring speed of the impeller. The measured responses for the experimental design were particle size, particle size distribution, and conversion. It has been shown in this study that the type of amine used to neutralize the polyacrylic stabilizer significantly influenced the observed responses probably by acting as chain transfer agent during polymerization. The addition of salt significantly affected the observed responses by shielding the surface charges on the particle surface that impart stability to the latex through electrostatic repulsion. Stirring speed of the impeller and the type of initiator as factors in the range investigated do not influence the kinetics or the particle size and polydispersity to any great extent either on their own or in combination with other factors.
A better understanding of the hydrodynamics related to flooding conditions in distillation column... more A better understanding of the hydrodynamics related to flooding conditions in distillation columns is required in order to provide optimised designs for new plants and plant retrofits. Current flooding prediction correlations are predominantly based on air/water systems and tend to diverge at high vapour capacities. In this work an experimental setup was designed and constructed to test the hydrodynamic characteristics of random – and structured packing as well as sieve – and valve trays. The experimental setup is used to develop a better understanding of the influence of gas and liquid properties on entrainment and column flooding. The experimental setup was tested with an air/water system and the tray entrainment data followed the trends from Bennett et al. 1 quite well. The packed column yielded the correct trends on both pressure drop and liquid hold-up data which correlated reasonably well with the general model proposed by Piché et al. 2 .
The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carb... more The available sets of data for the phase equilibrium of long chain n-alkanes with 10 or more carbon atoms in supercritical ethane were studied to determine if the phase equilibrium pressure can be predicted from the number of carbon atoms and system temperature. It has previously been shown that for the phase equilibria of heavy n-alkanes in supercritical propane there exists, at constant temperature and mass fraction, a linear relationship between the number of carbon atoms and the bubble/dew point pressure. Published data in the temperature range 310-360 K was obtained from a literature survey and, where required, additional data was measured using a high-pressure equilibrium cell. It was found that linear relationships exist and that these relationships can be used to predict the phase equilibrium pressure within 4% of experimental values.
Proceedings of the 32nd International Symposium on Ballistics
In interior ballistic simulations, the burn time can be affected by the burn rate, propellant dim... more In interior ballistic simulations, the burn time can be affected by the burn rate, propellant dimensions and flame spread. Standard IB models assume that grains are symmetric with no variation in dimensions, with instantaneous homogeneous ignition. This paper evaluates the contribution of grain dimensional variation (specifically the web), asymmetry and flame spread in a single base propellant with a single perforated grain geometry. It is shown that flame spread has the dominant effect on burn time, followed by web dimensional variation and lastly asymmetry. The implementation of these effects also leads to a simulated result that is more representative of the experimental curve in the closed vessel especially in the burnout phase.
Mathematical thermodynamic models capable of predicting phase equilibria behaviour are used to de... more Mathematical thermodynamic models capable of predicting phase equilibria behaviour are used to design, operate and optimise industrial separation and extraction equipment. Developing state of the art thermodynamic models requires accurate laboratory-scale phase equilibria data. The shortage of information and guidelines on equipment design and construction available in literature hampers the output of such data. A critical review of published equipment designs and discussions on, amongst others, mixing, sampling, sample homogenisation, analysis, pressure control, temperature control and observation windows are presented. This review enabled the authors to decide on a variable-volume, dual-phase circulation cell with multi-port sampling valves and online chromatographic analysis and density measurements. This will benefit other research groups, and thus the chemical industry, in a similar fashion but only in combining said review with future reports on equipment construction and oper...
Please help populate SUNScholar with the full text of SU research output. Also - should you need ... more Please help populate SUNScholar with the full text of SU research output. Also - should you need this item urgently, please snd us the details and we will try to get hold of the full text as quick possible. E-mail to scholar@sun.ac.za. Thank you.NatuurwetenskappeToegepaste Wiskund
Fast pyrolysis of Eucalyptus grandis was carried out using different reactor configurations and s... more Fast pyrolysis of Eucalyptus grandis was carried out using different reactor configurations and scale setups, a 0.1 kg/h bubbling fluidised bed (BFB) reactor, a 1 kg/h BFB reactor and a 10 kg/h twin-screw reactor. The influence of lignocellulosic composition, process configuration (reactor configuration, separation and condensation system) and their feed capacity on yields and quality of pyrolysis products was discussed. The increasing reactor scale study had constraints such as the availability of biomass feedstock with inherent changes in the chemical composition and the practicality of the condensation chain. Although the methods employed for phase separation and liquid collection differ from plant to plant limiting the repeatability of results, it was clearly identified that the implementation of efficient solid separation and use of mineral oil as the coolant system were crucial aspects of the mass production of organics. These results suggest that yields and quality of fast pyrolysis at a larger scale are all process-related rather than feedstock conditioned. A comparison of energy balances indicated that fast pyrolysis retained the same energy yield at scales of 1 and 10 kg/h.
A process model developed in Aspen Plus®, was used for the thermodynamic modelling of supercritic... more A process model developed in Aspen Plus®, was used for the thermodynamic modelling of supercritical water gasification (SCWG) using a wide variety of biomass materials as feedstock. The influence of the composition of the biomass material (in terms of carbon, hydrogen and oxygen content) on various performance indicators (such as gas yields, cold gas efficiency, calorific value of product gas and heat of reaction), were determined at various temperatures (600, 700 and 800°C) and biomass feed concentrations (5, 15 and 25wt.%). Generalised contour plots, based on the biomass composition, were developed for these performance indicators to provide the thermodynamic limits at various operating conditions. These plots can aid in the selection or screening of potential biomass materials and appropriate operating conditions for SCWG prior to conducting experimental work.
Eucalyptus grandis is a fast growing hardwood that is extensively used in the paper and pulp indu... more Eucalyptus grandis is a fast growing hardwood that is extensively used in the paper and pulp industry of South Africa (Godsmark, 2010). Pyrolysis has been shown to be an effective method for condensing bulky biomass such as wood into valuable and easily ...
ABSTRACT The phase equilibria of high molecular mass 1-alcohols in supercritical propane is measu... more ABSTRACT The phase equilibria of high molecular mass 1-alcohols in supercritical propane is measured to investigate the relationship between the phase equilibrium pressure and the number of carbon atoms and by comparison with n-alkanes, to show the effect of the hydroxyl group. Binary phase equilibrium measurements of high molecular mass 1-alcohols (with 10, 12, 16, 18 and 22 carbon atoms) in supercritical propane are measured between 378 and 408 K for 1-alcohol mass fractions of 0.0175–0.600. Complete solubility below 100 bar, with no region of liquid–liquid immiscibility, is observed and the phase transition pressure increases with increasing number of carbon atoms. By plotting the number of carbon atoms as a function of the phase transition pressure at constant temperature and mass fraction 1-alcohol, a linear relationship is realized. This linear relationship can be used to estimate the phase equilibrium of 1-alcohols with 10–22 carbon atoms in propane. When the measured 1-alcohol–propane data is compared to published n-alkane–propane data it can be seen that the hydroxyl group has the effect of increasing the phase equilibrium pressure of the 1-alcohol in comparison to the n-alkane.
High pressure phase equilibria measurements of long chain saturated methyl esters (methyl decanoa... more High pressure phase equilibria measurements of long chain saturated methyl esters (methyl decanoate, methyl dodecanoate, methyl tetradecanoate, methyl hexadecanoate, methyl octadecanoate and methyl docosanoate) in supercritical ethane have been measured for temperatures between 312 K and 355 K and for methyl ester mass fractions from 0.65 to 0.018. The results show a generally linear relationship between the phase equilibria pressure and the temperature with complete mutual solubility above 17 MPa. No three-phase regions or temperature inversions (change in sign of gradient of temperature-pressure relationship at constant composition) were observed while maxima in the phase transition pressures were found for methyl ester mass fractions usually between 0.2 and 0.3. When the phase transition pressure is plotted as a function of carbon number at constant temperature and mass fraction methyl ester, a linear relationship is realised. This linear relationship can be used to determine the solubility of any saturated methyl ester with between 10 and 22 carbon atoms, with limited extrapolation being possible. Thermodynamic modelling of the measured phase equilibria with the sPC-SAFT and Peng Robinson equations of state showed that, even with the use of an interaction parameter, these equations of state are not able to model the phase behaviour and the linear pressure-carbon numbers provide more accurate predictions.
The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyar... more The physico-chemical properties of biochars from the vacuum pyrolysis of black wattle and vineyard annual prunings were investigated for their potential as soil amendments and compared to biochar from sugar cane bagasse. Biochar from sugar cane bagasse seems to be a promising sorbent and soil conditioner due to its high surface area, high surface acidity and microporous structure. This biochar can be applied to a wide pH range of soils for enhancing nutrient and water retention. On the other hand, the biochars from black wattle and vineyard possessing high concentrations of aromatic carbon, nutrients, and alkalinity are potential soil amendment agents. Black wattle biochar is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. Therefore, this study recommends the utilization of biochars from black wattle as soil amendment agents especially in subtropical regions.
In the analysis of a ballistic evaluation motor (BEM) for extruded double base motors, an irregul... more In the analysis of a ballistic evaluation motor (BEM) for extruded double base motors, an irregular burning phenomenon was encountered. The irregular burning manifested as a drop in pressure. This was not combustion instability as acoustic instability is associated with high frequency pressure oscillations 2 , usually a mean pressure rise and steep fronted shock waves. L* instability is also eliminated as a possibility as the pressure is much higher than the pressure associated with this phenomena (>5MPa), and the pressure did not oscillate at the frequencies associated with L*-instability 3 . The reason for this phenomenon lies in the unique design of the motor. An internal/external burning cylindrical grain, inhibited on one end, was used. The external grain initially vented onto the cold steel wall, resulting in a significant heat loss. Experimental measurements of the steel wall temperature indicated that the heat losses to the wall were in the order of 14-15kJ or 4-6% of the heat released by combustion. This heat loss is also only experienced by the external burning surface of the propellant, thus amplifying the heat loss effect for the outside wall of the propellant. Inserting a silica-phenolic sleeve eliminated the irregular burning. This indicated that the heat transfer at the external wall surface is the most likely source of the irregular burning. This was also confirmed by the increase in severity of the irregular burning for cold firings, where the total heat loss was increased due to the lower temperature of the motor wall and more energy was absorbed by the casing to heat the surface. The burn rate was measured from the pressure/time curve because pressure was the only practical parameter that could be measured. It is not, however, the mechanism that drives the burn rate but is directly related to it. The propellant decomposes at the surface when the surface temperature reaches the ignition temperature. This mass flux from the surface moves into the flame zone and then combusts releasing heat. This heat is then absorbed by the surface, speeding up the decomposition (usually, some form of the Arrhenius equation applies to the surface decomposition), increasing the mass flux and finally increasing the heat released by the combustion. The increased mass addition and flame temperature resulted in the increase in pressure. In most cases the propellant is an internally burning grain that is axis symmetric. In the case of this BEM motor it is also burning from the outside. This has a significant effect on the heat transfer within the motor. In an internally burning axis symmetric motor the radiative heat transfer away from the surface is the same as the incoming energy from the surface directly opposing it. Thus, both surfaces transfer energy to each other. This may not be significant in terms of conductive as most of the conductive heat transfer to the surface comes from the combustion nearest the surface, but can be significant in terms of radiation. Basic propellant combustion theory states that radiation can account for up to 25-30% of the heat transfer to the surface. The energy radiated from the propellant surface should be the same as the energy radiated from the opposing surface. In the case of the motor burning inwards the opposing surface (in this case a steel wall) is not another source of radiant heat but will only be a heat sink. This, combined with the cooling of the combustion gasses, causes the propellant surface not to heat up at the same rate as the propellant surface in the internally burning grain. Thus, its burn rate is lower, resulting in a drop in pressure. This phenomenon warranted a more fundamental approach in the burn rate calculation and heat transfer modeling to confirm the above assertions. To accomplish this, a complete heat transfer calculation was performed. In parallel a CFD simulation with radiation and conduction effects was performed. The results of the two approaches showed remarkable similarity and both pointed to the heat losses as the origin of the irregular burning.
Internal ballistic design of solid rocket motors (SRMs) is a well-established field. Most grain d... more Internal ballistic design of solid rocket motors (SRMs) is a well-established field. Most grain designs have been well characterized throughout the industry. However, generating and evaluating different grain design options can be quite tedious and time-consuming. Thus, it was endeavored to create a preliminary design tool which can be used in a workshop with a client to promptly establish the most likely and suitable grain and performance design for the particular missile application, starting with a system definition. This tool was developed in the MATLAB environment. This tool also serves as an input for the more detailed design. As part of the larger program it was endeavored to create an internal ballistic tool that allows for more detailed analyses. It was endeavored to use the rapidly expanding open source tools available to develop a fully coupled CFD internal ballistic tool. The grain regression and CFD modules have been developed to date.
Corn cobs and sugar cane bagasse are two of the most important agricultural residues in South Afr... more Corn cobs and sugar cane bagasse are two of the most important agricultural residues in South Africa in terms of availability and potential for use as a bioenergy resource. The thermal devolatilization of samples of these two fuels in an inert atmosphere was studied by non-isothermal thermogravimetric analysis in the heating rate range of 10-50 • C min −1. Friedman's isoconversional method was applied using the AKTS Thermokinetics software to obtain the dependence of activation energy on conversion. The same method was also applied to the kinetic analysis of lignocellulosic pseudocomponents derived from the mathematical deconvolution of the original DTG curves. The results showed that apparent activation energy in the 0.1-0.8 conversion interval ranged from 170-225 kJ mol −1 to 75-130 kJ mol −1 for sugar cane bagasse and corn cobs respectively. The range of apparent activation energy obtained for the pseudocomponents representing hemicelluloses, cellulose and lignin derived from sugar cane bagasse were given as 200-300 kJ mol −1 , 163-245 kJ mol −1 , and 80-180 kJ mol −1 , while for corn cobs the values were 85-110 kJ mol −1 , 80-140 kJ mol −1 , and 10-60 kJ mol −1 respectively. The derived thermokinetic parameters from both global and pseudocomponent analyses satisfactorily reproduced the experimental curves used for the analysis and could also successfully predict reaction progress at a heating rate outside what was used in the analysis. The fits obtained between simulated and experimental results were comparable to what has been reported in the literature based on conventional model-fitting techniques.
Experimental phase equilibrium data for the systems CO 2 + n-dodecane, CO 2 + 1-decanol and CO 2 ... more Experimental phase equilibrium data for the systems CO 2 + n-dodecane, CO 2 + 1-decanol and CO 2 + 3,7-dimethyl-1-octanol were used to determine values for binary interaction parameters for use in the RK-ASPEN thermodynamic model in Aspen Plus ®. Bubble and dew point data of the mixtures CO 2 + (n-dodecane + 1-decanol), CO 2 + (n-dodecane + 3,7-dimethyl-1-octanol), CO 2 + (1decanol + 3,7-dimethyl-1-octanol) and CO 2 + (n-dodecane + 1-decanol + 3,7-dimethyl-1-octanol) were measured experimentally in a static synthetic view cell, and compared to the data predicted by the RK-ASPEN model. The model predicted the phase equilibrium data reasonably well in the low solute concentration region; significant deviation of model predictions from experimental data occurred in the mixture critical and high solute concentration regions due to the exclusion of solute-solute interaction parameters in the model. Distribution coefficients and separation factors were determined for the multicomponent mixture and separation of the alkane from the alcohol mixture with a supercritical fluid extraction process was found to be possible.
High pressure phase equilibrium measurements of long chain 1-alcohols (1-decanol through 1docosan... more High pressure phase equilibrium measurements of long chain 1-alcohols (1-decanol through 1docosanol) in supercritical ethane and their prediction are presented. The data were measured in a high pressure view cell above the melting points of these alcohols, i.e. between 308 and 356 K, and with 1alcohol mass fractions ranging from 0.0173 to 0.648. The results show a linear relationship between the phase transition pressure and the system temperature. The phase transition pressure increases with increasing molecular mass of 1-alcohol at constant temperature and composition. Furthermore, a linear relationship exists between the phase transition pressure and the number of carbon atoms of the 1-alcohol, making it easy to predict phase transition by simple interpolation within the experimental boundaries. Additionally, the state-of-the-art sPC-SAFT EOS model, as now typically included in process simulators, is unable to predict the phase equilibria, although it tends to give better results than the classic Peng Robinson EOS.
The ability to model and predict the behaviour of high-pressure alcohol and carbon dioxide mixtur... more The ability to model and predict the behaviour of high-pressure alcohol and carbon dioxide mixtures is important for industrial purposes. The phase equilibria behaviour of four 8-carbon alcohols in supercritical carbon dioxide are measured to determine the effect of the hydroxyl group position on alcohol solubility. Experimental bubble-and dew point data are generated on a high pressure phase equilibrium cell for the systems 1-octanol, 2-octanol, 3-octanol and 4-octanol in supercritical carbon dioxide between 35 • C and 75 • C. 1-Octanol is shown to be the least soluble and, at 35 • C, exhibits a phase transition pressure 85 bar higher than that of 2-octanol. 1-Octanol also exhibits a temperature inversion near the critical temperature of carbon dioxide in the mixture critical region. 2-Octanol possesses marginally higher phase transition pressures than 3-octanol which, in turn, possesses marginally higher phase transition pressures than 4-octanol. This difference in phase equilibria is believed to result from a difference in polarity. Shifting the hydroxyl group from the first to the second carbon atom causes a large decrease in polarity and increase in solubility. Further movements toward the molecule centre result in progressively smaller polarity reductions and solubility increases, producing phase boundaries that coincide or differ minimally.
This paper is the continuation of a previous study on the investigation of the separation of dete... more This paper is the continuation of a previous study on the investigation of the separation of detergent range alkanes and alcohols with supercritical fluids. Specifically this paper presents results on the optimisation of the process parameters for the separation of n-tetradecane and 1-dodecanol with supercritical carbon dioxide and ethane. The optimum operating conditions were determined from the results of a study of the influence of the process parameters, as well as an investigation into the size of the operating range. The results showed that the optimum temperature is a balance between good separation at lower temperatures and better control at higher temperatures. The solvent-to-feed ratio should be kept low (within the range of vapour-continuous operation) as lower solvent-to-feed ratios result in improved separation, as well as lower energy requirements. The use of reflux is necessary for good separation when using carbon dioxide as solvent, but is not required with ethane as solvent. An analysis of the operating range showed that a process using ethane is easier to control. Ethane as solvent is technically superior to carbon dioxide yet, depending on the exact process and location, costs, safety and logistics may favour the use of carbon dioxide.
The past decade has seen the development of high-performance epoxyacrylate coatings. Some of thes... more The past decade has seen the development of high-performance epoxyacrylate coatings. Some of these coatings are used exclusively as can coatings. To improve chemical resistance, emulsion polymerization in the presence of the dispersed epoxy resin can be conducted. Replicated factorial designs were designed to investigate some of the factors that contribute to the performance and stability of the epoxyacrylate coating. The factors investigated in this study were: the type and amount of neutralizing amine, the type of initiator, the presence or absence of salt, and the stirring speed of the impeller. The measured responses for the experimental design were particle size, particle size distribution, and conversion. It has been shown in this study that the type of amine used to neutralize the polyacrylic stabilizer significantly influenced the observed responses probably by acting as chain transfer agent during polymerization. The addition of salt significantly affected the observed responses by shielding the surface charges on the particle surface that impart stability to the latex through electrostatic repulsion. Stirring speed of the impeller and the type of initiator as factors in the range investigated do not influence the kinetics or the particle size and polydispersity to any great extent either on their own or in combination with other factors.
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Papers by Johannes Knoetze