Equilibrium and transport properties of CO₂+N2O and CO₂+NO mixtures. Molecular simulation and equation of state modelling study

In the present study, the thermodynamic behaviour and transport properties of CO₂ + N2O and CO₂ + NO mixtures have been investigated using molecular simulation and equation of state modelling. Molecular simulations were based on Monte Carlo and Molecular Dynamics calculations using force fields calibrated from pure component properties and no adjustment of mixture properties was performed. Original force fields were proposed for N2O, NO and N2O2 molecules. Special attention must be paid when studying nitric oxide containing systems because this compound can exist as a mixture of monomers (NO) and dimers (N2O2) under certain pressure and temperature conditions. Liquid-vapour coexistence properties of the reacting NO-N2O2 system were thus first investigated using combined reaction ensemble and Gibbs ensemble Monte Carlo methods. Using the new force fields proposed, phase compositions, phase densities and phase viscosities were determined for CO₂ + NO_x mixtures. Due to the strong similarities between carbon dioxide and nitrous oxide (Tc(CO₂) = 304.21 K; Tc(N2O) = 309.57 K; Pc(CO₂) = 7.38 MPa; Pc(N2O) = 7.24 MPa), the obtained thermodynamic and transport properties for a CO₂ + N2O mixture with 10 mol% of N2O are similar to pure CO₂ properties in the whole range of studied temperatures (273–293 K), in agreement with available experimental data. Calculations of CO₂ + NO equilibrium and transport properties were also performed at three different temperatures in the range of 253–273 K. At these temperatures, only the monomer form of the nitric oxide (NO) has to be accounted for. The performed calculations are pure predictions since no experimental data are available in the open literature for this system. For a mixture containing 10 mol% of NO, the simulation results show a decrease of the liquid densities and viscosities of 9% and 24% with respect to corresponding pure CO₂ values, respectively. The new pseudo-experimental data generated in this work were finally used to calibrate binary interaction parameters required in standard cubic equations of states. Both Peng-Robinson and Soave-Redlich-Kwong equations of state have been considered and after the regression, they display a decent match with experimental and pseudo-experimental data of the vapour-liquid equilibrium for the two studied mixtures.