方解石纳米孔隙内二氧化碳毛细凝聚的分子模拟

Molecular Simulation of Carbon Dioxide Capillary Condensation in Nanopores

在二氧化碳地质封存、增产非常规油气以及孔隙材料表征测量方面,纳米孔隙中二氧化碳相态的准确预测具有重要意义。然而,由于纳米尺度下毛细力、分离压等作用力占据主导因素,流体在孔隙中的相行为与体相流体存在根本不同。已有实验和模拟表明,Kelvin毛细凝聚理论无法预测特征尺度10nm下的,孔隙内流体凝聚压力与体相饱和蒸气压的偏离程度。本文利用分子模拟方法,研究了孔径范围为0.83-8.0nm的方解石纳米孔隙中二氧化碳毛细凝聚。结果表明,微孔(小于2nm)中二氧化碳受吸附层影响,凝聚压力远低于体相饱和蒸气压,介孔(2〜50nm)中二氧化碳受壁面影响,凝聚压力仍低于体相饱和蒸气压,且受孔径影响显著,并获得了纳米孔隙中二氧化碳相态随压力的变化规律。

Phase state of carbon dioxide in nanopores has significant influence on the carbon sequestration,enhancing unconventional resources and pore size distribution measurement.Considering capillary force and disjoining pressure are dominated factors in nanoscale,the phase behavior of fluids in nanopores is different from bulk state.Based on the developed capillary condensation theory,it has been demonstrated by simulation and experiments,that the shift between condensation pressure of fluids in nanopores and saturation pressure of bulk fluids could not be predicted by theorical approach when pore size is less than 10 nm.However,molecular simulation is convenient and has the advantage of accuracy,could give an alternative method to research the fluid condensation in nanoscale pores.In this work,molecular simulation of carbon dioxide condensation in calcite nanopores has been conducted,give an insight into the different kinds of phase state and capillary condensation of carbon dioxide in calcite slit nanopores with pore width in 0.83 nm~8.0 nm.The results show that,adsorption layer in micropores(less than 2 nm) is dominated and the condensation pressure of carbon dioxide in micropores is much lower than bulk saturation pressure,carbon dioxide in mesopores(2~50 nm) is influenced by solid wall and the condensation pressure is also lower than bulk saturation pressure and affected by pore width.