Doctoral Degrees (Chemical Engineering)

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Browsing Doctoral Degrees (Chemical Engineering) by browse.metadata.advisor "Cripwell, Jamie Theo"

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    Developing the s-SAFT-γ Mie equation of state toward nonaqueous alkanolamine-based carbon capture systems
    (Stellenbosch : Stellenbosch University, 2024-03) Schulze-Hulbe, Alexander; Cripwell, Jamie Theo; Burger, Andries Jacobus; Stellenbosch University. Faculty of Engineering. Dept. of Chemical Engineering. Process Engineering.
    ENGLISH ABSTRACT: Decarbonizing industrial processes is imperative for mitigating the harmful effects of climate change. A promising route to decarbonization lies in developing nonaqueous alkanolamine-based carbon capture processes. However, there is a very wide range of nonaqueous formulations to choose from, and little available thermodynamic data. Accordingly, an apt starting point for assessment of nonaqueous alkanolamine-based carbon capture is the development of a predictive thermodynamic modeling tool which captures the salient phenomena of these systems. The Statistical Associating Fluid Theory (SAFT) equations of state (EoSs) present a fundamental approach to thermodynamic modeling. Combining these EoSs with the group-contribution (GC) approach provides these rigorous models with considerable predictive capabilities. This renders GC-approach SAFT EoSs particularly useful in the data-scarce context of nonaqueous alkanolamine-based carbon capture. Accordingly, the main aim of this work was to develop structural SAFT-γ Mie (“s-SAFT-γ Mie”), a stateof- the-art GC-approach SAFT EoS, toward a description of alkanolamine solvent/CO2/organic cosolvent systems. This presents the first instance in which the predictive capabilities of a GC-approach EoS are extended to nonaqueous alkanolamine-based carbon capture systems. However, myriad approaches can be followed in developing parameters for GC-approach EoSs. This renders parameterization challenging, thus presenting an obstacle to industrial implementation of these models. To facilitate use of GC-approach EoSs, a further aim of this work was to illustrate how GCapproach EoSs can be parameterized for nonaqueous alkanolamine-based carbon capture systems using a systematic and consistent approach. Transferable s-SAFT-γ Mie group interaction parameters were developed from the ground up for primary and secondary alcohols, as well as primary amines. The model exhibited robust capabilities in modelling these components as well as their mixtures with n-alkanes. However, results for linear alkanolamines indicate that s-SAFT-γ Mie’s generalizability comes at the expense of quantitative accuracy. In the process of developing these parameters, a novel and generalizable approach was devised to account for the effect of changing hydroxyl group position in secondary alcohols. This further developed s-SAFT- γ Mie’s capabilities in distinguishing between the properties of isomers, an important characteristic for solvent/cosolvent screening purposes. s-SAFT-γ Mie further provided qualitatively accurate descriptions for a wide range of organic cosolvents with a single parameter set. This broadly generalizable modeling approach can be extended to components for which little or no reliable data are available, highlighting its value to carbon capture process designers. The parameters thus developed were transferred to CO2-containing mixtures. Pertinently, s-SAFT-γ Mie provided qualitatively accurate descriptions of CO2 solubility in polyethylene glycols, which are important components for nonaqueous carbon capture. Regarding alkanolamine solvent/CO2/organic cosolvent systems, s-SAFT-γ Mie was capable of qualitatively reproducing the effects of temperature, liquid-phase composition as well as organic cosolvent chain length on CO2 solubility. This holds for lower pressures, where CO2 solubility is driven by chemical absorption, as well as higher pressures, where CO2 is dissolved by physical absorption. These robust predictive capabilities render s-SAFT-γ Mie well-suited to comparing CO2 solubility in several alkanolamine solvent/organic cosolvent formulations, highlighting its potential future use within the context of a solvent/cosolvent screening tool.
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    Extending SAFT-VR Mie to the global phase behaviour of CO2 and its mixtures
    (Stellenbosch : Stellenbosch University, 2022-04) Smith, Sonja Almi Milé; Schwarz, Cara Elsbeth; Cripwell, Jamie Theo; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: Understanding the phase behaviour of CO2-containing mixtures is important for many industrial processes, amongst others supercritical fluid fractionation and enhanced oil recovery. These mixtures are complicated by the CO2 quadrupole moment, and, because these processes are often conducted near CO2’s critical point, critical phenomena. These characteristics make thermodynamic modelling of CO2-containing systems challenging. Many equations of state (EoSs) with firm theoretical foundations have been developed. The Statistical Associating Fluid Theory, or SAFT EoS, is rooted in statistical mechanics where macroscopic properties are calculated by considering the energy contributions of molecular interactions. The SAFT with Variable Range Mie-potential (SAFT-VR Mie) model was the focus of this project, because it is arguably the most advanced of the SAFT-variants and shows promise as a holistic predictive tool. The industrially relevant Cubic Plus Association (CPA) model was included for comparative purposes. The overarching aim of this project was to improve the predictive modelling of CO2- containing mixtures, thereby developing a single model that describes the global phase behaviour of these mixtures. To achieve this, the models’ descriptions of quadrupolar interactions and of the critical region needed improvement. To account for quadrupolar interactions, SAFT-VR Mie (VRM) and CPA were extended with the quadrupolar terms of Gross (G) and Larsen & coworkers (L), and three new models were proposed: VRM-G, VRM-L, and CPA-G. CPA extended with the Larsen quadrupolar term was developed in previous work (Bjørner & Kontogeorgis, Fluid Phase Equilibria 2016;408:151􀀀69), and is called qCPA. The quadrupolar models were evaluated by modelling the phase equilibria of binary mixtures containing CO2 or benzene + n-alkanes, 1-alkanols, water, or esters. The quadrupolar models’ improvements are most pronounced in the CO2 + n-alkane systems. The quadrupolar models predict these systems’ phase behaviour accurately at subcritical conditions, and offer improved qualitative descriptions at supercritical conditions. In the CO2 + 1-alkanol systems, good predictions are obtained when accounting for both quadrupolar and cross-association interactions. A single set of CO2 association parameters, determined from a sensitivity analysis, were used to predict the VLE behaviour of CO2 + 1-alkanol mixtures ranging from ethanol to 1-decanol. There is still room for improvement, specifically regarding the water- and ester mixtures. In the water mixtures, the additional quadrupolar terms do not improve the descriptions of the nonpolar models. To obtain good qualitative descriptions of the phase boundaries, the cross-association description is the most important. In the ester mixtures, the polar models do not capture the balance between dipolar, quadrupolar, and dipole-quadrupole interactions adequately. Based on the results for the CO2 + n-alkane and CO2 + 1-alkanol mixtures, VRM-G and qCPA were identified as the best quadrupolar model options in SAFT-VR Mie and CPA, respectively. These models are based in mean-field theory, and therefore cannot describe the critical region. To this end, VRM-G and qCPA were treated with renormalisation corrections, yielding VRM-G + RG and qCPA + RG. Both models improve the description of pure component properties in and around the critical region, without losing accuracy outside the critical region. The RG-models were extended to mixtures using the isomorphism approach and applied to binary n-alkane and CO2 + n-alkane systems. qCPA + RG only offers significant improvement for the more symmetric systems; this improvement, however, does not worsen prediction of binary VLE outside the critical region. In VRM-G + RG, remarkable predictions of the critical loci are obtained without binary interaction parameters. VRM-G + RG also describes the phase behaviour of these systems outside the critical region accurately, thus achieving the overarching aim of developing a global model for CO2-containing mixtures. The following contributions stem from this research: 1. The development of VRM-G and VRM-L, published in Journal of Chemical & Engineering Data 2020;65(12):5778 􀀀 5800; 2. The development of CPA-G, published in Fluid Phase Equilibria 2021;528:112848; 3. The development of VRM-G + RG.