Browsing by Author "Gowda, Rajesh"
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- ItemPhase equilibrium of limonene, p-cymene, indane, butylbenzene and 1,2,3-trimethylbenzene at subatmospheric conditions(Stellenbosch : Stellenbosch University, 2018-03) Gowda, Rajesh; Schwarz, C. E.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH SUMMARY: Waste tyre pyrolysis has long been seen as a suitable solution to the growing issue of accumulation of waste tyres in our environment. The pyrolysis of waste tyres produces three useful products, namely gas (~15 %), char (~35 %) and oil (~50 %), which can be used as fuel in various processes or as a feedstock for chemicals, one such chemical being limonene. Limonene is an extremely useful chemical and contributes to a number of industries ranging from household chemical production to aromatherapy. The extraction of this chemical from tyrederived oil (TDO) could have positive financial benefits to the waste tyre pyrolysis industry and thereby motivate the recycling of tyres through pyrolysis rather than incineration for fuel. A significant issue faced with the recovery of limonene from waste tyres however, is that a pure fraction is difficult to obtain due to fact that there are other compounds in the TDO that boil at similar temperatures to limonene itself, including p-cymene, indane, 1,2,3-trimethylbenzene and butylbenzene. Although a significant amount of literature is available on the pyrolysis process of waste tyres, not much is available on the purification of limonene from the TDO and there is a lack of data in the literature for the concerned compounds vapour-liquid equilibrium (VLE) data. This study therefore focuses on the experimental determination of the VLE data between limonene, p-cymene, indane, butylbenzene and 1,2,3-trimethylbenzene, at subatmospheric conditions. A setup in which phase equilibrium could be obtained was therefore required to be built as no setup was available for this study. Part of the capabilities required by the setup included accurate pressure measurement and control, accurate temperature measurement and disturbance-free sampling capabilities. The type of setup chosen was a vapour and liquid recirculation still that uses a Cottrell pump to achieve vapour-liquid equilibrium from a boiling feed. The VLE still was constructed using publicly available literature, after which its functional capabilities were commissioned. The experimental methodology was verified through measurement of isobaric VLE for relevant binary systems available in literature, namely ethanol/1-butanol at 101.3 kPa and n-decane/2-heptanone, n-decane/3-heptanone and n-nonane/pentanol at 40 kPa. Experiments were conducted under Argon environments at 40 kPa in an effort to reduce compound degradation. Additional compound degradation trials conducted at 40 kPa for the experimental systems, limonene/p-cymene, limonene/indane, limonene/butylbenzene, p-cymene/butylbenzene and limonene/1,2,3-trimethylbenzene/p-cymene/indane indicated a maximum operation time of 4 hours. This can be used as an indication of the maximum total residence time suitable for an industrial operation involving these compounds if operating at pressures below 40 kPa. Experimental accuracies, encompassing temperature, pressure and analysis effects, were found to be +/- 0.32 K in terms of temperature and +/- 0.0102 mole fraction in terms of composition. Pure fractions of indane and 1,2,3-trimethylbenzene could not be procured, thereby limiting the compositional range for which data could be obtained for systems including these compounds. The experimental results showed that barely any separation was present in the two binary systems, limonene/p-cymene and limonene/indane, with low relative volatilities for p-cymene and indane (relative to limonene) respectively, in the regions that separation was present. Both systems contained azeotropes – limonene/p-cymene at about 0.25 – 0.30 mole fraction limonene and ~416.2 K and limonene/indane at ~0.55 mole fraction limonene and ~415.9 K. However, only the limonene/indane azeotrope is definite due to the limonene/p-cymene system having a slightly narrower temperature range. The binary systems of limonene/butylbenzene and p-cymene/butylbenzene showed slightly better separation without the presence of azeotropes and with slightly higher relative volatilities for limonene and p-cymene (relative to butylbenzene) respectively. However, measuring this data proved difficult on the newly built still and had to be performed on the existing, additional Pilodist VLE still. This is due to there being insufficient mixing between the mixing and heating chambers of the constructed still for systems involving butylbenzene. Boiling regimes for these systems were noted to be irregular and included sudden vaporisations of the feed coinciding with drops in the measured vapour temperature of ~2 K. Furthermore, the quarternary system of limonene/1,2,3-trimethylbenzene/p-cymene/indane showed that purification of limonene from 1,2,3-trimethylebenzene would be difficult to realise on an industrial scale. All experimentally obtained data, verification and new, were found to be thermodynamically consistent according to the McDermott-Ellis consistency test. Additionally, vapour pressure data for limonene, p-cymene and butylbenzene were also obtained. Finally, the experimentally obtained phase equilibrium data were regressed with the NRTL, Wilson and UNIQUAC activity coefficient models using the Data Regression System by Aspen Plus®. The ability of the models to regress the experimental data were determined through visual comparison and descriptive statistics (AAD and AARD values). Comparisons showed that the Wilson activity coefficient model best describes the overall behaviour of the binary systems with the NRTL model proving better for that of the quarternary system. Nevertheless, all three relevant models do manage to describe the VLE behaviour fairly well. Furthermore, all the correlative models were compared with the predictive UNIFAC model, which showed that the UNIFAC model could not accurately predict the binary systems’ behaviours.