Monitoring the Diffusivity of Light Hydrocarbons in a Mixture by Magic Angle Spinning Pulsed Field Gradient NMR: Methane/Ethane/Ethene in ZIF-8
Monitoring the Diffusivity of Light Hydrocarbons in a Mixture by Magic Angle Spinning Pulsed Field Gradient NMR: Methane/Ethane/Ethene in ZIF-8
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DOI：
10.1021/acs.jpcc.7b09335
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发表时间：
2017-11-16
影响因子：
3.7
通讯作者：
Stepanov, Alexander G.
中科院分区：
文献类型：
--
作者：
Dvoyashkina, Nina;Freude, Dieter;Stepanov, Alexander G.
采用H-1魔角旋转脉冲场梯度（MAS PFG）NMR测量了吸附在ZIF-8金属有机骨架（MOF）微孔中的轻烃甲烷、乙烷和乙烯的三组分混合物的扩散系数。结果表明，在313 K时，混合物中的扩散系数按乙烷<乙烯<甲烷的顺序增加，自扩散系数D的变化范围从乙烷的0.22 × 10 ~（-10）m ~（2）s ~（-1）到甲烷的1.96 × 10 ~（-10）m ~（2）s ~（-1）。从乙烷到甲烷的扩散率增加的这种趋势类似于单个烃的趋势。得出的结论是，烃与ZIF-8框架的侧壁的相互作用影响的流动性，而不是分子间的烃的相互作用。当分子克服连接相邻笼的窗口的能垒时，后者对分子不起作用。混合物中碳氢化合物扩散系数的活化能E-a按以下顺序增加：甲烷（E-a = 2.4 kJ mol（-1））<乙烯（E-a = 7.2 kJ mol（-1））<乙烷（E-a = 11.5 kJ mol（-1））。在最低研究温度（273 K）下，甲烷的扩散系数比乙烷和乙烯的扩散系数分别大13.3和2.2倍，而乙烯和乙烷的扩散系数相差5.8倍。这一发现为在ZIF-8上分离三种研究的烃提供了可能性。
H-1 magic angle spinning pulsed field gradient (MAS PFG) NMR was applied for the measurement of the diffusivities in a three-component mixture of the light hydrocarbons methane, ethane, and ethene, which were absorbed in the micropores of ZIF-8 metal-organic framework (MOF). It has been found that diffusivity in the mixture increases in the order ethane < ethene < methane with variance of self-diffusion coefficients D from 0.22 X 10(-10) m(2) s(-1) for ethane to 1.96 x 10(-10) m(2) s(-1) for methane at 313 K. This tendency in increasing of diffusivity from ethane to methane is similar to the tendency for individual hydrocarbons. It is concluded that the interaction of a hydrocarbon with the micropore wall of the ZIF-8 framework influences the mobility rather than the intermolecular hydrocarbon interaction. The latter plays no role for the molecules, when they overcome the energy barrier of the window connecting neighbor cages. The activation energies E-a for diffusivity of the hydrocarbons in mixture increases in the order methane (E-a = 2.4 kJ mol(-1)) < ethene (E-a = 7.2 kJ mol(-1)) < ethane (E-a = 11.5 kJ mol(-1)). At the lowest studied temperature (273 K) D of methane is larger than D of ethane and ethene by 13.3 and 2.2 times, correspondingly, while the diffusivities of ethene and ethane differ by 5.8 times. This finding offers the possibility for separation of the three studied hydrocarbons on ZIF-8.