Bubble points and densities of H2 (up to ∼ 5%) in CO2-rich binary systems

Franklin Okoro, Friday Junior Owuna, Antonin Chapoy, Pezhman Ahmadi, Rod Burgass

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Abstract

In this study, experimental measurements of the bubble points of binary mixtures containing varying concentrations of CO2 (99.5 %, 99 %, 98.5 %,98 %, and ∼ 95 %) with hydrogen (H2) were made. These measurements were carried out from low temperatures (240.20 K) up to 294.84 K (with uncertainties of 0.14 K) using the constant composition expansion method. The experimental data were used to validate two thermodynamic models - the Peng-Robinson and Multi-Fluid Helmholtz Energy Approximation Equation of state (PR-EoS and MFHEA-EoS). From the results, the presence of H2 in CO2 at concentrations between 0.5 and 5 % caused a significant (∼19–980 %) positive deviation from the phase behaviour of CO2 stream compared to that of pure CO2. This effect intensified with higher concentrations of H2 and decreased with rising temperatures. Both models demonstrated good agreement with the experimental bubble point data, exhibiting <4 % average deviation for the system. Notably, the PR-EoS outperformed the MFHEA-EoS, showing <3 % average deviation. Densities of CO2 (99.5 %) with H2 were measured at 278.14, 298.34, 323.55, and 348.40 K and pressures up to 35 MPa. While the densities of CO2 (94.99 %) with H2 were measured at 278.06, 288.13, 298.26, and 323.53 K and pressures up to 35 MPa using a vibrating tube densimeter which was calibrated using water and hydrogen. For the 99.5 % CO2 binary mixture, the average absolute relative deviations (AARD) of the model predictions were 0.09 % and 0.26 % against MFHEA and PR EoS respectively. The AARD of the model predictions for the 94.99 % CO2 were 0.33 % and 1.49 % with MFHEA and PR EoS respectively. Furthermore, even at low concentrations (0.5 %), the presence of H2 led to a substantial reduction (>35 %) in the density of the mixture compared to that of pure CO2 at lower pressure conditions with this effect becoming more pronounced at higher temperatures and concentrations of H2. Both models predicted the densities of the system well (with <2 % deviations from the experimental data), though MFHEA-Eos was more accurate with <0.4 % maximum relative deviation (MaxRD) for all the data points.
Original languageEnglish
Article number114321
JournalFluid Phase Equilibria
Volume592
Early online date3 Jan 2025
DOIs
Publication statusE-pub ahead of print - 3 Jan 2025

Keywords

  • Bubble point
  • CCUS
  • CO
  • Constant-composition expansion
  • Density
  • EoS
  • H

ASJC Scopus subject areas

  • General Chemical Engineering
  • General Physics and Astronomy
  • Physical and Theoretical Chemistry

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