Low temperature membrane gas separation for nitrogen removal and helium recovery from natural gas

自20世纪80年代以来，气体渗透膜成功地操作以分离氢气和一氧化碳以及从Haber-Bosch工艺的吹扫气体中回收氢气。从那时起，气体渗透膜已应用于各种其它气体分离应用中，其中天然气脱硫是迄今为止最大的应用。一般来说，今天的大多数研究集中在室温和高温下的膜气体分离。人们对低于环境温度下的膜气体分离几乎一无所知。然而，一个潜在的应用是天然气处理，即从甲烷中去除氮气和回收氦气。这是最具挑战性的，目前通过需要大量能量和大型工艺设备的低温分离来完成。气体渗透膜和传统的低温分离技术在所谓的膜混合过程中的组合具有显著改善过程性能的潜力。我们假设，进行集成分离与膜气体渗透系统在各种组合与低温分离将显着降低总的能量需求和工艺设备的尺寸。现有技术的气体渗透材料仅固有低的CH 4/N2选择性，这对于在室温下的CH 4/N2分离是无效的。即使渗透速率将较低，该问题也可以通过在低于环境温度下操作气体渗透模块来克服，这导致增加的CH 4/N2选择性。在气体渗透阶段上游的原料气的冷却可以通过热集成来完成，这提高了分离过程的能量效率。此外，气体渗透伴随着焦耳-汤姆逊效应，导致渗透通过膜的气体的显著冷却。利用这种低温气流将进一步提高分离过程的能量效率。拟议项目的目标是确定和优化新的膜低温工艺，以去除氮气并在天然气处理中从甲烷中回收氦气。可行的工艺方案将使人们能够获得新的天然气资源，否则这些资源将无法勘探。

Gas permeation membranes operate successfully since the 1980s to separate hydrogen and carbon monoxide as well as recover hydrogen from purge gases of the Haber-Bosch process. Since that time gas permeation membranes have been applied in various other gas separation applications, where natural gas sweetening is by far the largest application today. In general most research today focusses on membrane gas separation at room temperature and at elevated temperatures. Almost nothing is known about membrane gas separation at sub-ambient temperatures. A potential application however is in natural gas treatment, i.e. the removal of nitrogen and the recovery of helium from methane. It is most challenging and is currently done by cryogenic separation demanding enormous amounts of energy and large process equipment. The combination of gas permeation membranes and conventional cryogenic separation technology in so-called membrane hybrid processes has the potential to drastically improve the process performance. We hypothesize that performing an integrated separation with a membrane gas permeation system in various combination with cryogenic separation will significantly reduce the total energy demand and the process equipment size. State of the art gas permeation materials inherent only low CH4/N2 selectivities which are not efficient for CH4/N2 separation at room temperature. Even though the permeation rates will be lower, this problem can be overcome by operating the gas permeation modules at sub-ambient temperature which results in increased CH4/N2 selectivities. The cooling of the raw gas upstream of the gas permeation stage can be done by heat integration which enhances the energy efficiency of the separation process. Furthermore, gas permeation is accompanied by the Joule-Thomson effect resulting in significant cooling of the gas permeating through the membrane. Taking advantage of this low temperature gas stream would further increase the energy efficiency of the separation process. The objective of the proposed project is to identify and optimize new membrane-cryogenic processes to remove nitrogen and to recover helium from methane in natural gas treatment. Viable process scenarios will give access to new natural gas resources that would otherwise remain unexplored.