Abstract
To provide a suitable absorbent for the carbon dioxide (CO2) compression-absorption refrigeration (CAR) system and promote the development of this system, the viscosities of CO2 + 1-ethyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate ([emim][FAP]) and CO2 + 1-hexyl-3-methylimidazolium tris(perfluoroethyl)trifluorophosphate ([hmim][FAP]) mixtures at vapor-liquid equilibrium were measured within the temperatures of 303.15–343.15 K and pressures of 1–10 MPa. The effects of CO2 solubility, pressure, temperature and ionic liquid structure on the mixture viscosity were investigated. The results showed that the mixture viscosity decreased with the increase of pressure and temperature. The longer the cationic alkyl chain of ionic liquid was, the larger the viscosities of ionic liquid and the corresponding mixture after absorbing CO2 were. But the mixture viscosity was less affected by the ionic liquid structure with the increase of temperature and pressure. The dissolution of CO2 could effectively reduce the mixture viscosity, to below 5.5 cP at most. Considering the CO2 absorption performance of ionic liquid and the viscosity of corresponding mixture, [hmim][FAP] is more suitable for the CO2 CAR system. In addition, to accurately predict the mixture viscosity within a certain working conditions for subsequent theoretical research of this system, an improved Grunberg equation was obtained by correlating the measured data and introducing the pressure factor. The overall average relative deviation between the calculated and measured data was 9.33%. The equation can be used to calculate the viscosity of the above CO2-ionic liquid mixtures.
Published Version
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