The Effect of Functional Groups on the Phase Behavior of Carbon Dioxide Binaries and Their Role in CCS.

Sergiu Sima,Catinca Secuianu

doi:10.3390/molecules26123733

Sergiu Sima, Catinca Secuianu

Open Access

https://doi.org/10.3390/molecules26123733

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Abstract

In recent years we have focused our efforts on investigating various binary mixtures containing carbon dioxide to find the best candidate for CO2 capture and, therefore, for applications in the field of CCS and CCUS technologies. Continuing this project, the present study investigates the phase behavior of three binary systems containing carbon dioxide and different oxygenated compounds. Two thermodynamic models are examined for their ability to predict the phase behavior of these systems. The selected models are the well-known Peng–Robinson (PR) equation of state and the General Equation of State (GEOS), which is a generalization for all cubic equations of state with two, three, and four parameters, coupled with classical van der Waals mixing rules (two-parameter conventional mixing rule, 2PCMR). The carbon dioxide + ethyl acetate, carbon dioxide + 1,4-dioxane, and carbon dioxide + 1,2-dimethoxyethane binary systems were analyzed based on GEOS and PR equation of state models. The modeling approach is entirely predictive. Previously, it was proved that this approach was successful for members of the same homologous series. Unique sets of binary interaction parameters for each equation of state, determined for the carbon dioxide + 2-butanol binary model system, based on k12–l12 method, were used to examine the three systems. It was shown that the models predict that CO2 solubility in the three substances increases globally in the order 1,4-dioxane, 1,2-dimethoxyethane, and ethyl acetate. CO2 solubility in 1,2-dimethoxyethane, 1.4-dioxane, and ethyl acetate reduces with increasing temperature for the same pressure, and increases with lowering temperature for the same pressure, indicating a physical dissolving process of CO2 in all three substances. However, CO2 solubility for the carbon dioxide + ether systems (1,4-dioxane, 1,2-dimethoxyethane) is better at low temperatures and pressures, and decreases with increasing pressures, leading to higher critical points for the mixtures. By contrast, the solubility of ethyl acetate in carbon dioxide is less dependent on temperatures and pressures, and the mixture has lower pressures critical points. In other words, the ethers offer better solubilization at low pressures; however, the ester has better overall miscibility in terms of lower critical pressures. Among the binary systems investigated, the 1,2-dimethoxyethane is the best solvent for CO2 absorption.

Highlights

Correlating experimental data on a limited range of pressures, temperatures, and compositions is the preferred method by many research groups, efforts were dedicated to analyzing the phase behavior of systems using a global approach [17,18,19,20,21,22,23,34,35,37,38,39,42]
As in type I phase behavior, type II phase behavior is characterized by a continuous liquid–vapor (LV) critical curve extending between the critical points of the pure components, and by a liquid–liquid (LL) critical curve intersecting the three-phase liquid–liquid–vapor equilibrium line (LLV) in an upper critical endpoint (UCEP) [43,44]
1,4-dioxane are isomers, the behavior of the carbon dioxide mixture seems to be dictated are isomers, the behavior of the carbon dioxide mixture seems to be dictatedby bythe thecritical critical properties of pure components, which in this case are more similar between ethyl properties of pure components, which in this case are more similar between ethylacetate acetate and and1,2-dimethoxyethane, 1,2-dimethoxyethane,as as well wellas asthe the linear linearstructures

Summary

Introduction

CCS costs could be decreased in circumstances where industrial operations produce large amounts of CO2 gas streams or even pure CO2 , but they remain a barrier to its application Many studies in this area have concentrated almost entirely on the creation of improved sorbents with enhanced CO2 capacity and/or lower regeneration heat. The alternative is the use of equations of state (EoS) models, that are the most widely used method for correlating and/or predicting phase equilibria and mixture properties, even though they have their known limitations [24]. The model system we selected isfor the can be obtained based on a well-documented carbon dioxide containing system other if experimental data are available for latter.

Compound

Modelling

Results and Discussion

P–T fluid phase diagrams for carbon

Conclusions