Simultaneously tuning dense skin and porous substrate of asymmetric hollow fiber membranes for efficient purification of aggressive natural gas

Abstract

Highly permeable, selective, and stable asymmetric membranes are required to replace the traditional separation approaches for natural gas purification with higher energy efficiency and smaller footprints. Herein, we report on the design and engineering of defect‐free asymmetric hollow fiber membranes with a thin dense skin and highly porous substrate to effectively deal with aggressive natural gas. A crosslinkable polymer with rigid molecular structure and high molecular weight was synthesized for developing spinning dope with desirable solution properties. Phase separation behavior of the polymer was carefully controlled by systematic formulation of the dope composition and optimizing spinning conditions, thereby realizing simultaneously tuning dense skins and porous substrates of the spun asymmetric hollow fiber membranes. The crosslinked hollow fiber membrane, with well‐preserved delicate asymmetric nanostructures, exhibited unprecedentedly high and stable separation performance for long‐term processing extremely aggressive CO2/CH4 mixtures (with pressure up to 820 psi containing C6+ hydrocarbons), thereby showing great potential for practical application of natural gas purification. This work offers a new platform to create hollow fiber membranes with both high permeance and plasticization resistance in natural gas service. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1269–1280, 2019

Hydrocarbon separations by glassy polymer membranes

“…Formation of defect-free thin-skinned crosslinked polyimide hollow fiber membranes was reported showing outstanding plasticization resistance under highly aggressive natural gas feeds. [37,38] In addition to crosslinking, recent studies showed that plasticization resistance in 6FDA-polyimides can be enhanced by incorporating triptycene-based moieties in the diamine monomer. [95,96] Aromatic polyimides with bulky side groups have good solubility in organic solvents, and thus can be solution processed into asymmetric or composite films or hollow fibers with thin separation layers.…”

“…Successful formation of defect-free thin-skinned hollow fiber membranes were widely reported using a number of aromatic polyimides. [37,38,[97][98][99][100][101]…”

“…High fractional free volume (FFV) aromatic polyimides were introduced in the 1990s [ 35 ] and have replaced or competed with low‐FFV glassy polymers (e.g., polysulfone, cellulose acetate) for air separation, hydrogen recovery, and low‐pressure natural gas purification. [ 36 ] More recently, crosslinked aromatic polyimides and the so‐called microporous polymers (e.g., polymers of intrinsic microporosity [PIMs], thermally rearranged [TR] polymers) have emerged pushing the limits of gas separation membranes further toward aggressive natural gas purification [ 37,38 ] and postcombustion CO 2 capture. [ 39,40 ] Due to hydrocarbon separation's large economic impact, polymer membranes have been considered by the petrochemical industry for hydrocarbon separations as early as the 1980s.…”

Exclusive and fast water channels in zwitterionic graphene oxide membrane for efficient water–ethanol separation

“…To date, membrane technologies have been increasingly applied in a wide range of industrial separation processes, owing to their advantages of energy efficiency, ease of operation, compactness, and modularity 1‐5 . To accelerate the advancement of membrane technologies, it is essential to develop advanced membranes with high permeability and selectivity, and sufficient stability 6 . Recently, two‐dimensional (2D) membranes, constructed by the assembly of 2D nanosheets, have shown great prospects as the next‐generation membranes to tackle many challenging separation issues 7‐10 .…”

Molecularly Engineered 6FDA‐Based Polyimide Membranes for Sour Natural Gas Separation

“…6FDA‐2,4,6‐trimethyl‐1,3‐diaminobenzene (DAM): 3,5‐diaminobenzoic acid (DABA) polyimide, designated as 6FDA‐DAM:DABA (Figure S1), has been shown to be a versatile platform for sour natural gas . The presence of DAM moiety with bulky ‐CH 3 groups in the polymer backbone provides a high free volume by suppressing the polymer chain packing to enable high gas permeability.…”