Vapor liquid equilibrium inside porous media

Preliminary analysis of the influence of porous medium on vapor-liquid equilibrium of binary mixtures was performed using a reduced form of Simplified Local Density theory developed by Rangarajan et al. (1995). Methane+n-octane was used as a model system. Density and composition profiles in equilibrium with a bulk fluid inside a porous medium (diameter >1nm) mere calculated. If the bulk fluid is a gas, a liquid film and sharp vapor-liquid interface is found near the wall. If the bulk fluid is a liquid, a densified liquid film concentrated in the heavier component can grow to substantial thickness. When the bulk fluid exist in two equilibrium vapor and liquid phases, only the liquid phase can exist in pores less than 10nm in diameter. The phase envelope inside a porous medium of about 10nm in diameter can be significantly smaller than that of the bulk fluid. The effect of the porous medium on vapor-liquid equilibrium is probably unimportant for macropores (>100nm). However, the influence of pores with diameter in the range of 1 to 10 nm can be quite substantial.