Leszczynski Peter Jr, Lashkari Siamak, Kruczek Boguslaw
Department of Chemical and Biological Engineering, University of Ottawa, Ottawa, ON K1N 6N5, Canada.
Worley Chemetics, Burnaby, BC V5A 4T7, Canada.
Membranes (Basel). 2024 Jul 30;14(8):167. doi: 10.3390/membranes14080167.
The time-lag method is commonly used to determine membrane permeability, diffusivity and solubility in a single gas permeation experiment in a constant volume system. An unwritten assumption on which this method relies is that there is no resistance to gas accumulation in the downstream receiver of the system. However, this is not the case, even with the specially designed receiver used in this study when, in addition to tubing, the receiver utilizes an additional accumulation tank. The resistance to gas accumulation originates from a finite diffusivity (Knudsen diffusion) of gases in tubing, which are magnified by "resistance-free" accumulation tank(s). As a result of the resistance to gas accumulation, the time lag of the membrane is underestimated, which leads to an overestimation of gas diffusivity in the membrane. The experimentally predicted resistances in different configurations of the receiver, expressed by the difference in the time lag at two different receiver locations, were several times greater than the theoretically predicted values. A high molecular PPO membrane was used to demonstrate this effect. The time lags measured at different locations differed by as much as 30%. The diffusivity of nitrogen in a PPO of 4.04 × 10 m/s determined at the optimum configuration of the receiver is at least 50% lower than the literature-reported values.
时间滞后法通常用于在恒容系统的单一气体渗透实验中测定膜的渗透性、扩散系数和溶解度。该方法所依赖的一个未明确表述的假设是，系统下游接收器中气体积累不存在阻力。然而，实际情况并非如此，即便使用了本研究中专门设计的接收器，除了管道之外，该接收器还使用了一个额外的储气罐。气体积累的阻力源自气体在管道中的有限扩散率（克努森扩散），这种扩散率会因“无阻力”储气罐而放大。由于存在气体积累阻力，膜的时间滞后被低估，这导致膜中气体扩散率被高估。通过两个不同接收器位置的时间滞后差异表示的、在不同接收器配置下实验预测的阻力比理论预测值大几倍。使用一种高分子量的聚亚苯基氧化物（PPO）膜来证明这种效应。在不同位置测量的时间滞后相差高达30%。在接收器的最佳配置下测定的氮气在PPO中的扩散系数为4.04×10⁻¹⁰m²/s，至少比文献报道的值低50%。
