Vapor-liquid equilibrium measurement data for the two binary systems carbon dioxide + nitrogen and carbon dioxide + oxygen

Abstract

This thesis presents new, accurate, isothermal vapor-liquid equilibrium (VLE) measurement data for the two binary systems carbon dioxide and nitrogen (CO2+N2) and carbon dioxide and oxygen (CO2+O2). These measurements contribute to meeting the demand for thermophysical property data for the CO2-rich mixtures that will be handled within carbon capture, transport and storage (CCS), the focus in this work being the conditioning and transport processes within the CCS chain. The thermophysical properties of pure CO2 are relatively well described by accurate equations of state and models. However, as a trade-off between the cost of capturing CO2 within CCS and the required purity of the captured CO2 has to be made, it is expected that different impurities will be present in the captured CO2 stream. These impurities can significantly affect the thermophysical behavior of the mixture compared to that of pure CO2, and impact how processes within the CCS chain should be designed and operated. Examples of these changes in behavior are the possibility for an increase in the minimum operating pressure to keep the mixture in dense phase during transport, and an increase in the required compressor work required to bring the mixture up to this pressure. In addition, the behavior of CO2 with impurities during depressurization of a pipeline, either as a planned operation or in the case of a pipeline rupture, differs from the behavior of pure CO2 in ways that can influence safety aspects of the operation. To be able to make safe and economic decisions of how to design and operate these parts of the CCS chain, knowledge about the thermophysical properties of the CO2-rich mixtures that will be handled is required. Several recent literature studies have revealed large gaps in the thermophysical data for these CO2-rich mixtures, and modeling efforts have been limited by the lack of data and the dubious accuracy of some of the existing data. The VLE measurements presented in this thesis contribute to achieving more knowledge about the thermophysical properties of CO2-rich mixtures. This can contribute to achieving the goal of the development of a reference equation of state for the mixtures handled within CCS, which has been identified by several authors as one of the hindrances for the development and realization of CCS. The measurements of the VLE of CO2+N2 were carried out to validate the experimental apparatus, as there existed significant amounts of data for this system, some of which were of high quality. Equations of state describing this system were also readily available for comparison. In addition to validating the apparatus, the measurement campaign also resulted in new data for several temperature and pressure states where no data could be found in the open literature. The VLE measurements of the CO2+O2 system cover six temperatures from close to the triple point temperature (216.59 K) to close to the critical temperature of pure CO2 (304.13 K), and range from the vapor pressure of pure CO2 to close to the mixture critical point at each temperature. The VLE measurements reconcile the inconsistencies in the literature data for this system, noted in several literature reviews and modeling efforts. The measurements significantly improve the thermodynamic data situation for this system, and form the basis for improving equations of state.