烷烃混合物在Cu-BTC中的吸附与分离

用巨正则系综Monte Carlo (GCMC)和构型导向Monte Carlo (CBMC)相结合的方法模拟了298 K下甲烷-乙烷-丙烷体系以及正丁烷-异丁烷体系在1,3,5-苯三甲酸铜(II) (Cu-BTC)中的吸附行为. 结果表明, Cu-BTC对丙烷以及异丁烷的吸附分离都有较好的选择性. 通过我们发展的“材料剖面成像”方法研究了烷烃混合物在Cu-BTC中不同压力下的吸附位点, 从而进一步分析了烷烃混合物在Cu-BTC中的分离性能. 结果发现, 在吸附过程中主要存在着两种效应, 即能量效应和尺寸效应的竞争. 在甲烷-乙烷-丙烷体系中, 较高压力下, 由于尺寸效应的影响, 丙烷主要吸附在主孔道中, 而对甲烷和乙烷组分, 能量效应占主导地位, 从而导致乙烷主要吸附在四面体孔内, 甲烷则主要吸附在三角形孔窗外. 在正丁烷-异丁烷体系中, 能量效应起主导作用, 从而使异丁烷主要吸附在四面体孔内, 而正丁烷主要吸附在主孔道中.

Adsorption and Separation of Alkane Mixtures in Cu-BTC

Grand canonical ensemble Monte Carlo (GCMC) and configurational-bias Monte Carlo (CBMC) techniques were combined to simulate the adsorption behavior of methane-ethane-propane and n-butane-i-butane mixtures at 298 K in copper(II) benzene-1,3,5-tricarboxylate (Cu-BTC). The simulation results demonstrate that for the methane-ethane-propane mixtures propane is preferentially adsorbed, and the amount adsorbed of propane increases to a maximum and then decreases with increasing the pressure, whereas the shorter alkanes are almost not adsorbed at lower pressures and the amount adsorbed increases progressively and exceeds propane as the pressure increases. The selectivity of Cu-BTC to propane increases as the molar fraction of shorter chain components in the gas phase increases. As to the n-butane-i-butane mixtures, i-butane is adsorbed preferentially, the amounts adsorbed of both linear and branched alkanes in-crease with increasing the pressure and the amount of i-butane is greater than that of n-butane, the selectivity to i-butane is increased as the molar fraction of n-butane increases in the gas phase. Furthermore, the adsorp-tion sites of alkane mixtures at various pressures were investigated to understand the adsorption and separa-tion capabilities of Cu-BTC by mCT (Computer Tomography for materials) technique. The adsorption com-petition between the energy effect and the size effect has been found in the adsorption process. It indicates that at higher pressures propane mainly occupies the main channels due to the size effect while for methane and ethane the energetically favored ethane occupies the tetrahedron-shaped pockets leaving methane locat-ing at the outer sides of the triangular windows. As to the n-butane-i-butane mixtures, the energy effect is preferential to the size effect, therefore, i-butane mainly occupies the tetrahedral pockets while n-butane is located in the main channels.