Developing the s-SAFT-γ Mie equation of state toward nonaqueous alkanolamine-based carbon capture systems
Date
2024-03
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Stellenbosch : Stellenbosch University
Abstract
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.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (PhD)--Stellenbosch University, 2024.