Shift of the azeotropic point of binary Lennard–Jones mixtures confined in a slit-like pore

Abstract

The Gibbs ensemble Monte Carlo simulation is used to investigate the vapor–liquid phase behavior of a binary Lennard–Jones mixture confined in a slit-like pore at reduced temperature T* = 1.0. Our simulation program is tested by comparing the simulated phase diagram with the previous simulation results from various methods. Then phase diagrams of a binary asymmetric Lennard–Jones mixture confined in the slit-like pores are investigated by varying the pore width and fluid–pore wall interaction. The asymmetric system studied exhibits azeotropic behavior. The pore walls are symmetric but selective to the two components. The simulated results indicate that both the pore width and interactions between fluid and the pore wall have significant influence on the vapor–liquid phase diagram for the binary Lennard–Jones mixture. When the interaction energy parameter between component 1 and the pore wall is fixed, the azeotropic point is shifted from the bulk azeotropic composition to component 2-rich side of the phase diagram as the interaction strength between component 2 and the pore wall is increased. In the meantime, both the azeotropic pressure and the relative volatility increase significantly. As the pore becomes narrower, it is found that the azeotropic pressure increases significantly while the azeotropic composition remains almost unchanged. The phase selectivity decreases as the pore becomes narrower in the whole range of composition. All the simulated results suggest that the azeotropic point of a binary mixture can be shifted or even be removed by the confinement and the relative volatility for vapor–liquid equilibria can be changed greatly by changing the pore width or fluid–pore wall interactions.