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

自20世纪80年代以来，气体渗透膜在分离氢气和一氧化碳以及从哈伯-博世工艺的吹扫气体中回收氢气方面取得了成功。从那时起，气体渗透膜已应用于各种其他气体分离应用，其中天然气脱硫是迄今为止最大的应用。总的来说，目前大多数研究集中在室温和高温下的膜气体分离。人们对亚环境温度下的膜气体分离几乎一无所知。然而，潜在的应用是天然气处理，即从甲烷中去除氮和回收氦。这是最具挑战性的，目前是通过低温分离来完成的，需要大量的能量和大型的工艺设备。在所谓的膜混合工艺中，气体渗透膜与传统低温分离技术的结合有可能大大提高工艺性能。我们假设将膜气渗透系统与低温分离的各种组合进行集成分离将显着减少总能源需求和工艺设备尺寸。目前的气体渗透材料仅具有较低的CH4/N2选择性，在室温下不能有效地分离CH4/N2。尽管渗透速率会降低，但这个问题可以通过在亚环境温度下操作气体渗透模块来克服，从而提高CH4/N2的选择性。采用热集成技术对渗透阶段上游的原料气进行冷却，提高了分离过程的能效。此外，气体渗透伴随着焦耳-汤姆逊效应，导致气体通过膜的显著冷却。利用这种低温气流将进一步提高分离过程的能源效率。该项目的目标是确定和优化新的膜低温工艺，以去除氮气，并从天然气处理中的甲烷中回收氦气。可行的工艺方案将使人们获得新的天然气资源，否则这些资源将一直未被开发。

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.