The Peng Robinson Equation of State (PR EoS) for liquid-vapour equilibrium is extended to model the solid-vapour (sublimation) and solid-liquid (melting) phase equlibria for carbon dioxide (CO2). The sublimation behaviour is modelled through the re-formulations of the empirically based analytical expressions for the two temperature dependent parameters, and in the PR EoS. The melting phase behaviour on the other hand is modelled by the coupling of the original and the extended PR EoS and equalisation of solid and liquid phase fugacities. Analytical expressions derived based on the extended PR EoS are used to determine thermodynamic and phase equilibrium derivative properties for solid/vapour CO2. These include internal energy, enthalpy, heat capacity, thermal expansion and isothermal compressibility coefficients as well as the adiabatic speed of sound. In most cases good agreement with the available experimental data is obtained covering the pressure and temperature ranges 0.1 – 100 MPa and 100 – 300 K. A pressure/temperature phase equilibrium diagram for solid-liquid-vapour CO2 is constructed to demonstrate the overall performance and the limitations of the two EoS as compared to the experimental data spanning the triple point up to 100 MPa pressure. It is shown that the application of the PR EoS along the CO2 sublimation line gives rise to significant errors.

An extended Peng‐Robinson equation of state for carbon dioxide solid‐vapor equilibrium

Solid–liquid–vapor phases of water and water–carbon dioxide mixtures using a simple analytical equation of state

A recent study by Eggeman and Chaffin (2005), which showed large discrepancies in CO2 freeze-out conditions as predicted by several commercial simulators, prompted a reexamination of using the TBS equation of state for phase equilibrium calculations involving solids. Salim and Trebble (1994) had previously presented a methodology for extending the Trebble-Bishnoi-Salim (TBS) equation of state (Salim, 1990) to calculations involving a solid phase. In this study, the CO2 freeze-out conditions in CO2/CH4 and CO2/C2H6 mixtures are calculated from the TBS equation of state, and it is shown that they provide a better data fit than the traditional Poynting correction method. Furthermore, since the use of an equation of state in SLE/SVE calculations does not require the explicit assumption of a pure solid phase, the model was assessed for its ability to correlate CO2 gas hydrate equilibrium conditions. Gas hydrates were simply treated as an impure solid phase, and it was seen that the predictions of gas hydrate e...

Prediction of CO2 freeze-out conditions and CO2 hydrate formation conditions with a single equation of state

This study explores the effects of interaction softness on the transport properties of simple fluids in which the particles interact via the potential, ϕ(r)
				=
				e(r/σ)−n, with n in the range 6–1152. Molecular dynamics simulation has been used to compute the self-diffusion coefficient, D, the shear viscosity ηs, bulk viscosity ηb, and the thermal conductivity, λ, over a wide packing fraction range. A number of semi-empirical formulae for these transport coefficients have been tested against this data. It was found that the transport coefficients were proportional to the exponential of the two-body component of the entropy. The quality of agreement was best for D and worst for the thermal conductivity. A cell model for the fluid based on the simulated mean square force was not successful in correlating the diffusion coefficient data over the wide range of n. We also consider several variants on the Stokes–Einstein relationship, which provide an informative insight into the global behaviour of (mainly) the self-diffusion coefficient and shear viscosity.

Transport coefficients of soft sphere fluids

The cell theory of Lennard-Jones and Devonshire is re-analysed and it is found that, in addition to the critical point originally reported for the 12-6 potential (and widely quoted in standard textbooks), the model exhibits a further critical point. The latter is shown to be actually a more appropriate candidate for liquid-gas criticality than the original critical point.

The Lennard-Jones-Devonshire cell model revisited

In this paper the potential energy of the Lennard-Jones and Devonshire (LJD) model has been corrected to increase its PVT prediction abilities The correction of potential energy is done in two ways (i) taking the coordination number as a function of temperature and volume to improve the second virial prediction ability and (ii) taking pair correlation effects into account to improve the phase transition prediction ability The results of calculations indicate improvement both on PVT behavior in the above range of variation especially on the phase transition prediction ability in solid–liquid and vapor–liquid regions

Ebrahim Ahmadnia

Papers

Improvement on Lennard-Jones–Devonshire theory for predicting liquid–solid phase transition