Browsing by Author "Narasigadu, Caleb."

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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).
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.
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).
Investigation of perfluorocarbons as potential physical solvents for flue gas cleaning.
(2017) Tshibangu, Mulamba Marc.; Ramjugernath, Deresh.; Narasigadu, Caleb.; Coquelet, Christophe.
Abstract available in PDF file.
Phase equilibrium investigation of the water and acetonitrile solvent with heavy hydrocarbons.
(2006) Narasigadu, Caleb.; Ramjugernath, Deresh.; Naidoo, Paramespri.; Raal, Johan David.
Thermodynamics plays an important role for separation processes in chemical industries. Phase equilibrium is of special interest in chemical engineering as separation processes such as distillation and extraction involve phase contacting. The main focus of this research was the measurement of new phase equilibrium data for acetonitrile and water with heavy hydrocarbons that included: heptanoic acid, 1-nonanol, dodecane and 1-dodecene. Hence, binary vapour-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE) and vapour-liquid-liquid equilibrium (VLLE) data were investigated. The VLE and VLLE data were measured with the modified apparatus of Raal (Raal and Miihlbauer, 1998). The modification, undertaken by Ndlovu (2005), enabled measurement for VLLE systems. Isothermal binary VLE data for the (nonanol + 1-dodecene) system at 403.15 K was measured and VLLE data for the systems (acetonitrile + 1-dodecene) at 343.15 K, and (nonanol + water) at 353.15 K were investigated. The LLE data were measured with the modified apparatus of Raal and Brouckaert (1992). The modification, introduced by Ndlovu (2005), improved thermal insulation and the sampling procedures. Binary LLE data for the systems (acetonitrile + 1-dodecene) at 1 atm and (water + 1-nonanol) at 1 atm were measured. Furthermore, ternary data at 323.15 K and 1 atm were also measured for the systems containing water + acetonitrile with the each of the following components: heptanoic acid, 1-nonanol, dodecane and 1-dodecene. The experimental VLE data were regressed using two different methods: the combined method and the direct method. For the combined method, the second virial coefficients were calculated from the methods of Pitzer and Curl (1957) and Tsonopoulos (1974). The activity coefficients were calculated using three local-composition based activity coefficients models: the model of Wilson (1964), the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Anderson and Prausnitz (1978). For the direct method, the equation of state of Stryjek and Vera (1986) and the alpha function of Twu et al. (1991) in the equation of state of Peng and Robinson (1976) were employed. In addition, the mixing rules of Wong and Sandler (1992) and Twu and Coon (1996) were utilised. Furthermore, the point test of Van Ness et al. (1973) and the direct test of Van Ness (1995) were employed to test the thermodynamic consistency of the experimental VLE data measured in this work. The experimental binary LLE data were regressed using the three-suffix Margules model, Van Laar (1910) model and the NRTL model of Renon and Prausnitz (1968) to obtain the temperature dependence of the model parameters. The experimental ternary LLE data were subjected to a two part correlation: the tie-line correlation and the binodal curve correlation. The tie-lines were correlated with the NRTL model of Renon and Prausnitz (1968) and the modified UNIQUAC model of Anderson and Prausnitz (1978). The binodal curves were correlated with the Hlavaty (1972) equation, B-density function equation of Letcher et al. (1989) and the log y equation of Letcher et al. (1986).
Phase equilibrium studies of NFM and toluene with heavy hydrocarbons and the conceptual process design of an aromatics recovery unit.
(2017) Brijmohan, Nivaar.; Narasigadu, Caleb.; Ramjugernath, Deresh.
Distillation and extraction are commonly employed phase separation techniques, and improved efficiency and cost reduction in these large-scale processes are motivating factors behind thermodynamic equilibrium investigations. This first objective of the research undertaken was phase equilibrium studies of two ternary systems comprising of a heavy hydrocarbon and toluene, with the suitability of NFM as an extraction solvent investigated, due to its good selectivity and heat stability (Xia et al., 2008). The other objective was the development and simulation of a conceptual process design using Aspen Plus V8.4 to demonstrate the separation and recovery of aromatics using NFM, and to make a comparison to an existing process in terms of energy and cost efficiency. Ternary liquid-liquid equilibrium (LLE) phase compositions were generated for the systems n-nonane (1) + toluene (2) + NFM (3), as well as n-decane (1) + toluene (2) + NFM (3). The measurements were conducted at 303.15 K, 323.15 K, and 343.15 K for each system. The modified apparatus of Raal and Brouckaert (1992) was used, with the latest modifications to the cell incorporating an adjustable temperature sleeve and magnetic stirrer (Narasigadu et al., 2014). The uncertainty in temperature of each cell was 0.02 and 0.01 respectively. Composition uncertainty was minimized by ensuring that phase composition samples were within 1% of the repeatability error for the average absolute deviation of at least 3 samples taken. Samples were analysed using gas chromatography. The ternary systems measured in this work were modelled in terms of the NRTL model (Renon and Prausnitz, 1968) and the UNIQUAC model (Abrams and Prausnitz, 1975). Calculated RMSD values were between 0.002 and 0.02 for both models, indicating that the models represented the data satisfactorily, with the NRTL model displaying superior representation due to lower RMSD values compared to UNIQUAC. The effectiveness of using NFM an alternative solvent to extract toluene from a mixture containing n-nonane and n-decane was evaluated by determining the distribution coefficient, selectivity, and separation factor. A process design simulation was developed using Aspen Plus V8.4 for the separation of benzene, toluene, ethylbenzene and xylene (BTEX) isomers from a hydrocarbon mixture using NFM as the ABSTRACT ii solvent. Process conditions and column specifications were optimized by investigating numerous unit configurations and running sensitivity analyses on these parameters. The aim was to target a recovery of at least 99% aromatics, which was achieved. A sequence of columns was used to effect the aromatics recovery, consisting of a counter-current liquid-liquid extraction column, followed by four distillation columns in series. The simulation results indicated that the process would consume at least 11 kcal/kg extract less energy than the sulfolane process. This manifests as lower heating and steam requirements, resulting in reduced costs of at least R19 million per annum.