本文是以分子動力學模擬甲烷與二氧化碳兩氣體混合物之分離行為，藉以奈米碳管薄膜(carbon nanotube membrane)模型探討之分離效果。所使用氣體間或氣體和碳管的勢能函數為Lennard Jones 12-6 potential，而二氧化碳和甲烷氣體分子都當成單一粒子。主要是探討二氧化碳與甲烷混合物的成分和壓力差對分離率和流率造成的影響，由模擬結果可以發現當壓力差的增加，會使兩氣體流率跟著上升，但是氣體容器甲烷莫耳分率較大的情況下，在高壓力差下會受到傳速較慢的二氧化碳進去較多的影響，使得甲烷流率趨緩。另外，對於純化甲烷氣體，氣體容器內甲烷莫耳分率必須在0.6到0.9之間，而當甲烷氣體的莫耳分率在0.7與0.3、壓力差大小為分別為40 bar與30 bar時，對甲烷和二氧化碳有最好的分離率，可以得到較好的分離效果。也就是說，在甲烷莫耳分率0.7、壓力差30 bar，利用奈米碳管薄膜分離天然氣，可以得最好的純化甲烷的效果，使能源利用得到最有效率的使用。

　　Molecular dynamics simulations are used to investigate transport and separation of CO2 and CH4 mixture in carbon nanotube. It is simulated in carbon nanotube membrane by molecular dynamics. The gas-gas and gas-carbon interactions were described using a Lennard-Jones 12-6 type potential, and two gases were represented as hard sphere. Our outcomes explore the performance of membrane for mixtures of CO2 and CH4 as a function of the composition of the feed gases and pressure gradient across carbon nanotube. The results indicate that as the pressure gradient increases for a fixed permeate pressure, the fluxes of two gas increase, but the CH4 flux increases slowly in high pressure gradient when the CH4 mole fraction is high. Because the many CO2 molecules which are less mobile flow into carbon nanotube in high pressure gradient, the CH4 flux increases slowly. We find that the work for purifying CH4 must be in a rage which is from 0.6 to 0.9 mole fraction of CH4. The CO2/CH4 mixture has the maximum and minimum separation factor at 0.3 mole fraction of CH4 and 40 bar of pressure gradient and 0.7 mole fraction of CH4 30 bar of pressure gradient, relatively and the minimum separation factor is optimum for purifying CH4. In other words, natural gas has best separation effect in carbon nanotube membrane at 0.7 mole fraction of CH4 and 30 bar of the pressure gradient. It offers advantages such as a low energy costs and environmental benignity.

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