Benchtop pulsed field gradient (PFG) nuclear magnetic resonance (NMR) measurements of the intra-diffusion coefficient ($D_i^{\ast }$$D_i^{\ast }$) for binary gaseous mixtures are presented as a function of composition, for temperature and pressure conditions broadly relevant to industrial and geological processes. This required the design, construction, and application of a novel NMR-compatible sapphire sample cell. Measurements were performed for methane–nitrogen, methane-helium, and methane-hydrogen mixtures, with compositions down to 0.5 mol% methane that were resolvable in a reasonable time frame. Consequently, extrapolation to infinite dilution was enabled, with the resultant values of $D_i^{\ast }$$D_i^{\ast }$(x_i = 0) compared with relevant mutual diffusion coefficients (D₁₂) from both literature and as estimated using kinetic theory (Thorne-Enskog equation). In the case of methane-helium mixtures, agreement was overwhelmingly within experimental uncertainty across the temperature–pressure parameter space explored, whereas in the case of methane–nitrogen, the determined values of $D_i^{\ast }$$D_i^{\ast }$(x_i = 0) were slightly larger than D₁₂ data as predicted by kinetic theory. In the case of methane-hydrogen mixtures, simultaneous measurements of both methane and hydrogen intra-diffusion coefficients were possible. Agreement between $D_i^{\ast }$$D_i^{\ast }$(x_i = 0) and kinetic theory was comfortably within experimental uncertainty in the case of hydrogen but deviated in the case of methane.

中文翻译：

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气态二元混合物的内扩散系数测量


室内扩散系数 （Di∗二元气体混合物的 >$D_i^{\ast }$） 表示为成分的函数，用于与工业和地质过程广泛相关的温度和压力条件。这需要设计、构建和应用一种新型的 NMR 兼容蓝宝石样品池。对甲烷-氮气、甲烷-氦和甲烷-氢混合物进行了测量，其成分低至 0.5 mol% 的甲烷可在合理的时间范围内分离。因此，启用了对无限稀释的外推，结果值为 Di∗”>$D_i^{\ast }$（x = 0） 与文献中的相关互扩散系数 （D₁₂） 相比，并使用动力学理论（Thorne-Enskog 方程）估计。 在甲烷-氦混合物的情况下，在所探索的温度-压力参数空间内，在实验不确定性范围内绝大多数是一致的，而在甲烷-氮的情况下，Di&#x2217 的确定值;>$D_i^{\ast }$（x = 0） 略大于动力学理论预测的 D₁₂ 数据。在甲烷-氢混合物的情况下，可以同时测量甲烷和氢的内部扩散系数。Di∗>$D_i^{\ast }$（x = 0） 和动力学理论在氢气的情况下处于实验不确定性范围内，但在甲烷的情况下则偏离了。