The measurement and modelling of vapour-liquid equilibria in ternary systems containing polar, cross-associating, and associating compounds
Date
2020-12
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: The accurate production of simple binary vapour liquid equilibria (VLE) data sets is time consuming and expensive, and the measurement of similar data sets for multi component systems is even more laborious and tricky. Therefore, generic thermodynamic models that can predict VLE behaviour accurately are required for the optimisation and design of many processes within industry. This is especially true for complex systems such as polar, associating, and cross-associating mixtures.For the majority of complex VLE mixtures, thermodynamic models incorporating binary interaction parameters (BIPs) are required for an accurate representation.Models in the perturbation theory equations of state (EoS) use pure component data to predict phase equilibria. In doing so, these models predict rather than correlate VLE and phase equilibria. Perturbation theory models such as CPA-GV, SAFT-VR-Mie-GV, and sPC-SAFT-GV have been proved accurate for the prediction of binary systems and assumed to be accurate for multicomponent systems. However, there is a need to systematically test the assumption that these models can accurately predict complex multicomponent mixtures with a similar accuracy that they do for binary systems. This study therefore produced carefully measured new equilibrium data on the ternary VLE of four systems, as well as the nine binary systems within the ternary systems. Each system contained 1-propanol and 2-butanone, with the third component being either one of three different C4 esters, or2-propanol. These data sets were then used to test and evaluate the applicability and accuracyof the aforementioned EoS.The data of the nine binary and the four-ternary isobaric VLE systems were produced at 101.3kPa with the use of a Gillespie type still. This still had experimental uncertainties in temperature of ± 0.62 K and pressure of ± 0.046 bar. The liquid and vapour samples were analysed using a GC and had experimental uncertainties of ±0.016 mole fraction. The experimental procedure with the Gillespie still and the GC analysis was verified using vapour pressure of the binary systems that occur in all four ternary systems, 1-propanol/2-butanone, and existing literature data. All VLE data were thermodynamically consistent, passing both the McDermott-Ellis and the L/W consistency tests.
The deviations from the ideal state in the ternary systems were found to correspond to similar deviations in the binary mixtures. This was further evidenced with distillation boundaries when two azeotropes existed (methyl propionate and propyl formate systems) with the 2-propanol system displaying the largest deviations from the ideal state, and the ethyl acetate system behaving the most ideal.
Accurate results were found for the binary modelling, with both the SAFT-VR-Mie-GV and sPC-SAFT-GV models being able to cope with the cross-association and the non-ideal nature of the systems, having AAD values for the nine binary systems of 0.614 K and 0.011 mole fraction and 0.589 Kand 0.011mole fraction, respectively. In the ternary systems, the two models that accurately predicted the binary systems also predicted the ternary systems accurately, with comparable results with NRTL and each other. The AAD values of the four ternary systems were 0.820 K and 0.015 mole fraction, and 0.720K and 0.017 mole fraction, respectively. This work therefore shows that the SAFT type models display strong potential to predict the vapour-liquid equilibria in ternary systems containing polar, non-associating and associating compounds.
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
AFRIKAANSE OPSOMMING: Raadpleeg teks vir opsomming
Description
Thesis (MEng)--Stellenbosch University, 2020.
Keywords
Propyl formate, UCTD, Liquid-liquid equilibrium, Binary vapor systems, Vapour liquid equilibria