Mitchell Martha C, Gallo Marco, Nenoff Tina M
Department of Chemical Engineering, New Mexico State University, P.O. Box 30001, MSC 3805, Las Cruces, New Mexico 88003-8001, USA.
J Chem Phys. 2004 Jul 22;121(4):1910-6. doi: 10.1063/1.1766019.
Equilibrium molecular dynamics (MD) simulations of equimolar mixtures of hydrogen and methane were performed in three different titanosilicates: naturally occurring zorite and two synthetic titanosilicates, ETS-4 and ETS-10. In addition, single-component MD simulations and adsorption isotherms generated using grand canonical Monte Carlo simulations were performed to support the mixture simulations. The goal of this study was to determine the best membrane material to carry out hydrogen/methane separations. ETS-10 has a three-dimensional pore network. ETS-4 and zorite have two-dimensional pore networks. The simulations carried out in this study show that the increased porosity of ETS-10 results in self-diffusion coefficients for both hydrogen and methane that are higher in ETS-10 than in either ETS-4 or zorite. Methane only showed appreciable displacement in ETS-10. The ability of the methane molecules to move in all three directions in ETS-10 was demonstrated by the high degree of isotropy shown in the values of the x, y, and z components of the self-diffusion coefficient for methane in ETS-10. From our simulations we conclude that ETS-10 would be better suited for fast industrial separations of hydrogen and methane. However, the separation would not result in a pure hydrogen stream. In contrast, ETS-4 and zorite would act as true molecular sieves for separations of hydrogen and methane, as the methane would not move through membranes made of these materials. This was indicated by the near-zero self-diffusion coefficient of methane in ETS-4 and zorite.
在三种不同的钛硅酸盐中对等摩尔的氢气和甲烷混合物进行了平衡分子动力学（MD）模拟：天然的硅钛矿以及两种合成钛硅酸盐ETS - 4和ETS - 10。此外，还进行了单组分MD模拟以及使用巨正则蒙特卡罗模拟生成的吸附等温线，以支持混合物模拟。本研究的目的是确定用于氢气/甲烷分离的最佳膜材料。ETS - 10具有三维孔网络。ETS - 4和硅钛矿具有二维孔网络。本研究进行的模拟表明，ETS - 10孔隙率的增加导致氢气和甲烷的自扩散系数在ETS - 10中高于在ETS - 4或硅钛矿中的自扩散系数。甲烷仅在ETS - 10中表现出明显的置换。甲烷分子在ETS - 10中在所有三个方向上移动的能力通过ETS - 10中甲烷自扩散系数的x、y和z分量值所显示的高度各向同性得到证明。从我们的模拟中可以得出结论，ETS - 10更适合用于氢气和甲烷的快速工业分离。然而，这种分离不会产生纯氢气流。相比之下，ETS - 4和硅钛矿将作为氢气和甲烷分离的真正分子筛，因为甲烷不会通过由这些材料制成的膜。这由ETS - 4和硅钛矿中甲烷近乎零的自扩散系数表明。
