Measurements and Modelling of Vapour–Liquid Equilibrium for (H2O + N2) and (CO2 + H2O + N2) Systems at Temperatures between 323 and 473 K and Pressures up to 20 MPa

Understanding the phase behaviour of (CO2 + water + permanent gas) systems is critical for implementing carbon capture and storage (CCS) processes, a key technology in reducing CO2 emissions. In this paper, phase behaviour data for (H2O + N2) and (CO2 + H2O + N2) systems are reported at temperatures from 323 to 473 K and pressures up to 20 MPa. In the ternary system, the mole ratio between CO2 and N2 was 1. Experiments were conducted in a newly designed analytical apparatus that includes two syringe pumps for fluid injection, a high-pressure equilibrium vessel, heater aluminium jacket, Rolsi sampling valves and an online gas chromatograph (GC) for composition determination. A high-sensitivity pulsed discharge detector installed in the GC was used to measure the low levels of dissolved nitrogen in the aqueous phase and low water levels in the vapour phase. The experimental data were compared with the calculation based on the γ-φ and SAFT-γ Mie approaches. In the SAFT-γ Mie model, the like parameters for N2 had to be determined. We also obtained the unlike dispersion energy for the (H2O + N2) system and the unlike repulsive exponent and dispersion energy for the (CO2 + N2) system. This was done to improve the prediction of SAFT-γ Mie model. For the (H2O + N2) binary system, the results show that the solubility of nitrogen in the aqueous phase was calculated better by the γ-φ approach rather than the SAFT-γ Mie model, whereas SAFT-γ Mie performed better for the prediction of the vapour phase. For the (CO2 + H2O + N2) ternary systems, both models predicted the experimental data for each phase with good agreement

Saturated Phase Densities of (CO2 + Methylcyclohexane) at Temperatures from (298 to 448) K and Pressures up to the Critical Pressure

This work reports saturated-phase densities for the CO2 + methylcyclohexane system at temperatures between 298 and 448 K and at pressures up to the critical pressure. The densities were measured with a standard uncertainty of <1.5 kg·m-3 and were fitted along isotherms with a recently developed nonlinear empirical correlation with an absolute average deviation (ΔAAD) of about 1.5 kg·m-3. This empirical correlation also allowed the estimation of the critical pressure and density at each temperature, and the obtained critical pressures were found to be in close agreement with previously published data. We also compare both our density data and vapor-liquid equilibrium (VLE) data from the literature with the predictions from two models: PPR-78 and SAFT-γMie. The results show that densities were predicted better with SAFT-γMie than with PPR-78, whereas PPR-78 generally performed better for VLE. This could indicate that some of the unlike parameters of SAFT-γMie could be further optimized

An industrial reference fluid for moderately high viscosity

In industrial practice, there is a demand for a reference standard for viscosity that is established for a readily available fluid to simplify the calibration of industrial viscometers for moderately high viscosities [(50 to 125) mPa · s]. Diisodecyl phthalate (DIDP) has been suggested as that reference fluid, and a number of studies of its properties have been carried out in several laboratories throughout the world, within the auspices of a project coordinated by the International Association for Transport Properties. That project has now progressed to the point where it is possible to collate the results of studies of the viscosity of the fluid by a number of different techniques, so as to lead to a proposed standard reference value which will be included in the paper. To support this recommended value, the various measurements conducted have been critically reviewed, and the sample purity and other factors affecting the viscosity have been studied. Density and surface tension measurements have also been performed. This paper does not describe the individual viscosity determinations carried out in independent laboratories because these are the subject of individual publications, but it does describe the ancillary studies conducted and their relevance to the viscosity standard. In addition, the paper contains recommended values for the viscosity of liquid DIDP. The samples of DIDP to which the recommended values refer are isomeric mixtures available commercially from certain suppliers, with a minimum purity by gas chromatography of 99.8 %. The recommended values result from a critical examination of all the measurements conducted to date and are supported by careful arguments dealing with the likely effects of the isomeric content of the sample as well as of other impurities. The proposed reference standard is intended particularly to serve an industrial need for a readily available calibration material with a viscosity close to that required in practical situations. To that end, the recommended value has an overall relative uncertainty of approximately 1 %. It is therefore not intended to supersede for the reference value for the viscosity of water at 20 °C, which is known much more accurately, but rather to complement it

Density and Phase Behavior of the CO2 + Methylbenzene System in Wide Ranges of Temperatures and Pressures

Knowledge of the thermophysical properties of CO2-hydrocarbon mixtures over extended ranges of temperature and pressure is crucial in the design and operation of many carbon capture and utilization processes. In this paper, we report phase behavior, saturated-phase densities, and compressed-liquid densities of CO2 + methylbenzene at temperatures between 283 K and 473 K and at pressures up to 65 MPa over the full composition range. The saturated-phase densities were correlated by a recently developed empirical equation with an absolute average relative deviation (ΔAARD) of ∼0.5%. The compressed-fluid densities were also correlated using an empirical equation with an ΔAARD value of 0.3%. The new data have been compared with the predictions of two equations of state: the predictive Peng–Robinson (PPR-78) equation of state and the SAFT-γ Mie equation of state. In both of these models, binary parameters are estimated using functional group contributions. Both models provided satisfactory representation of the vapor–liquid equilibrium and saturated-phase-density data, but the accuracy decreased in the prediction of the compressed-liquid densities where the ΔAARD was ∼2%. The isothermal compressibility and isobaric expansivity are also reported here and were predicted better with SAFT-γ Mie than with PPR-78. Overall, the comparisons showed that SAFT-γ Mie performs somewhat better than PPR-78, but the results suggest that further refinement of the SAFT-γ Mie parameter table are required