Phase Equilibria for Carbon Capture and Storage

Abstract

Carbon dioxide (CO2) is an important material in many industries but is also representing more than 80% of greenhouse gases (GHGs). Anthropogenic carbon dioxide accumulates in the atmosphere through burning fossil fuels (coal, oil, and natural gas) in power plants and energy production facilities, and solid waste, trees, and other biological materials. It is also the result of certain chemical reactions in different industry (e.g., cement and steel industries). Carbon capture and storage (CCS), among other options, is an essential technology for the cost-effective mitigation of anthropogenic CO2 emissions and could contribute approximately 20% to CO2 emission reductions by 2050, as recommended by International Energy Agency (IEA). Although CCS has enormous potential in numerous industries and petroleum refineries due their large CO2 emissions, a significant impediment to its utilization on a large scale remains both operating and capital costs. It is possible to reduce the costs of CCS for the cases where industrial processes generate pure or rich CO2 gas streams, but they are still an obstacle to its implementation. Therefore, significant interest was dedicated to the development of improved sorbents with increased CO2 capacity and/or reduced heat of regeneration. However, recent results show that phase equilibria, transport properties (e.g., viscosity, diffusion coefficients, etc.) and other thermophysical properties (e.g., heat capacity, density, etc.) could have a significant effect on the price of the carbon. In this context, we focused our research on the phase behavior of physical solvents for carbon dioxide capture. We studied the phase behavior of carbon dioxide and different classes of organic substances, to illustrate the functional group effect on the solvent ability to dissolve CO2. In this chapter, we explain the role of phase equilibria in carbon capture and storage. We describe an experimental setup to measure phase equilibria at high-pressures and working procedures for both phase equilibria and critical points. As experiments are usually expensive and very time consuming, we present briefly basic modeling of phase behavior using cubic equations of state. Phase diagrams for binary systems at high-pressures and their construction are explained. Several examples of phase behavior of carbon dioxide + different classes of organic substances binary systems at high-pressures with potential role in CCS are shown. Predictions of the global phase diagrams with different models are compared with experimental literature data.

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

“…The carbon dioxide + 2-butanol system is a type II phase diagram [ 43 , 44 ] since it exhibits liquid–liquid immiscibility [ 45 ]. As a function of two independent variables, phase diagrams show the domains occupied by the various phases of a system, the boundaries that distinguish these areas, and the special points of the system [ 43 , 44 , 46 ]. 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, but also 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 ].…”