Novel Method for Characterization of Gas Separation Membranes

分离过程是世界能源消耗总量的主要贡献者。目前仅在美国就有超过40，000个蒸馏塔在运行，占全球能源使用量的11%。采用能源密集度较低的蒸馏方法，可以大大减少用于分离的能源。 气体分离膜是有吸引力的，因为它们不需要热驱动力并且不涉及吸附剂来分离混合物。自20世纪80年代以来，它们已被广泛用于各种工业应用，与低温蒸馏，吸收和吸附竞争。然而，它们在全球分离市场中的份额仍然相当小。限制该技术的主要挑战是膜的渗透性和选择性之间的权衡。克服这一挑战需要改进膜材料的性能。热重排（TR）聚合物和固有微孔聚合物（PIM）的最新发展有助于推动权衡路线，但气体分离膜需要更多的进展，以增加其在全球分离市场的份额。膜材料开发的关键方面是准确表征其气体传输系数，如扩散系数、溶解度系数和渗透系数。这些传输系数在动态膜气体渗透测试（也称为时滞测试）中测定。 本研究的目的是开发一种表征气体分离膜的新方法，该方法依赖于准确监测由于气体分子在高压下进入膜而引起的压力衰减。与依赖于监测由于气体分子从膜中出现而引起的压力升高的传统方法不同，新方法将允许在整个测试期间在膜的渗透侧保持气体的零浓度。后者是时滞分析的关键假设，这在当前最先进的测试系统中是固有地违反的。新方法需要建立新一代的膜测试系统，将允许更准确地确定膜中的气体传输特性，并更好地理解膜中发生的传输机制。最终，在气体分离膜的这些最基本方面的进展将有助于它们在现有市场中变得更具竞争力，例如炼厂气纯化、合成气比例调节、酸性气体纯化、氮气富集和脱水，以及使它们在其他应用中具有吸引力，包括从天然气中分离氮气和从烟道气中捕获二氧化碳。

Separation processes are a major contributor to the total energy consumed in the world. Over 40,000 of the distillation columns currently in operation in the United States alone are responsible for 11% of the global energy usage. Implementation of less energy-intensive competitors of distillation could bring a huge reduction in the energy used for separation. Gas separation membranes are attractive because they do not require a thermal driving force and do not involve sorbents to separate mixtures. Since the 1980s they have become widely used in various industrial applications, competing with cryogenic distillation, absorption, and adsorption. Nevertheless their share in the global separation market remains rather insignificant. The main challenge that limits this technology is a tradeoff between permeability and selectivity of the membranes. Overcoming this challenge requires improvements in properties of membrane materials. Recent developments in thermally rearranged (TR) polymers and polymers of intrinsic microporosity (PIMs) have helped to push the tradeoff line up, but more progress is needed for gas separation membranes to increase their share of the global separation market. The key aspects in the development of membrane materials is the accurate characterization of their gas transport coefficients, such as diffusion, solubility and permeability coefficients. These transport coefficients are determined in a dynamic membrane gas permeation test, also referred to as a time-lag test. The objective of this research is to develop a new method for characterization of gas separation membranes, which relies on accurate monitoring of pressure decay due to gas molecules entering the membrane at high pressure. Unlike the conventional method, which relies on monitoring of pressure rise due to gas molecules emerging from the membrane, the new method will allow to maintain a zero concentration of the gas at the permeate-side of the membrane during the entire test. The latter is the key assumption of the time-lag analysis, which is inherently violated in the current state-of-the-art testing systems. The new method, which will require building a new generation of membrane testing systems, will allow for the more accurate determination of gas transport properties in membranes, and the better understanding of transport mechanism taking place in membranes. Ultimately, the progress in these most fundamental aspects of gas separation membranes will help them to become more competitive in the already existing markets such as refinery gas purification, syngas ratio adjustment, acid gas purification, nitrogen enrichment and dehydration, as well as making them attractive in other applications including separation of nitrogen from natural gas and capture of carbon dioxide from flue gases.