HELIUM RECOVERY BY PERMEATION

Highly efficient helium purification through a dual-membrane system: insights from molecular dynamics simulations

Almost all helium is resourced from natural gas reservoirs. Hence, it is essential to develop new efficient technologies to recover helium from natural gas. In this work, we propose a novel dual membrane system, consisting of C2N (M1) and graphdiyne (M2) membranes, to separate and purify helium from a ternary gas mixture of He/N2/CH4. In this regard, we performed molecular dynamics (MD) simulations to investigate the separation performance of the proposed system. Here, we explored the effect of applied pressure (up to 2 MPa) and the feed composition on the separation performance. The simulation results revealed that in the designed system, the M1 membrane allows He and N2 to diffuse through and prevents CH4 from crossing even at an applied pressure gradient. Next, the M2 membrane only allows He to transfer through and prevents N2 from crossing even at the applied pressure gradient. As a result, the dual membrane system showed a high He permeance of 2.5 × 106 GPU and ultrahigh He selectivity. In addition, the suggested dual membrane system could separate three components simultaneously at the applied pressure of 2 MPa, which implies the outstanding performance of the system. We also analyzed the density map, the van der Waals interactions, and the potential of the mean force calculations to better understand the permeation of gas species across the designed system.

High-Performance Polybenzimidazole Membranes for Helium Extraction from Natural Gas

Increasing helium use in research and production processes necessitates separation techniques to secure sufficient supply of this noble gas. Energy-efficient helium production from natural gas is still a big challenge. Membrane gas separation technology could play an important role. Herein, a novel poly( p-phenylene benzobisimidazole) (PBDI) polymeric membrane for helium extraction from natural gas with low He abundance is reported. The membranes were fabricated by a facile interfacial polymerization at room temperature. The thin and defect-free membrane structure was manipulated by the confined polymerization of monomers diffusing through the interface between two immiscible liquids. Both He/CH₄ selectivity and He permeance are competitive over those of other commercial perfluoropolymers. Even at low He content of 1%, separation performance of the PBDI membrane transcended the current upper bound. The unprecedented selectivity (>1000) together with the excellent stability (∼360 h) endows PBDI membranes with a great potential for energy-efficient industrial recovery and production of this precious He resources from reservoirs with low abundance.

High-Pressure Aging of Asymmetric Torlon® Hollow Fibers for Helium Separation from Natural Gas

Membrane separation for helium extraction from natural gas gained increased interest recently. Several vendors offer membrane elements for helium extraction, although data on their performance and operating experience are unpublished. The aim of this work was to obtain and study the separation performance of asymmetric hollow-fiber membrane element from commercial polyamide-imide Torlon®, in conditions close to the industrial process of helium extraction from natural gas. A membrane element with an active area of 0.177 m2, a helium permeance of 100 l(STP)/(m2·h·bar), and a selectivity α(He/CH4) = 340 was produced. This corresponds to a selective layer thickness of 82.3 nm, which was confirmed by SEM and resistance model calculations. The obtained membrane element was employed to decrease the concentration of helium in its binary mixture with methane from 0.4% to 0.05%. A relationship of separation characteristics from transmembrane pressure is also presented. At 70 bar and a stage cut of 2.7%, the feed flow rate was 0.16 m3(STP)/h, which yielded a helium permeate concentration of 14.7%. At 80 bar, a decrease in permeance to 60 l(STP)/(m2·h·bar) and in selectivity to 240 was observed. It was shown that the main reason for aging was the increased support resistance, due to a partial compaction of pores with a radius of less than 15 nm.

Review of Membranes for Helium Separation and Purification

Membrane gas separation has potential for the recovery and purification of helium, because the majority of membranes have selectivity for helium. This review reports on the current state of the research and patent literature for membranes undertaking helium separation. This includes direct recovery from natural gas, as an ancillary stage in natural gas processing, as well as niche applications where helium recycling has potential. A review of the available polymeric and inorganic membranes for helium separation is provided. Commercial gas separation membranes in comparable gas industries are discussed in terms of their potential in helium separation. Also presented are the various membrane process designs patented for the recovery and purification of helium from various sources, as these demonstrate that it is viable to separate helium through currently available polymeric membranes. This review places a particular focus on those processes where membranes are combined in series with another separation technology, commonly pressure swing adsorption. These combined processes have the most potential for membranes to produce a high purity helium product. The review demonstrates that membrane gas separation is technically feasible for helium recovery and purification, though membranes are currently only applied in niche applications focused on reusing helium rather than separation from natural sources.