Carbon molecular sieve membrane from a microporous spirobisindane-based polyimide precursor with enhanced ethylene/ethane mixed-gas selectivity

Abstract

Ethylene is typically produced by steam cracking of various hydrocarbon feedstocks. The gaseous products are then separated in a demethanizer followed by a deethanizer unit and finally sent to a C 2 splitter for the final purification step. Cryogenic distillation of ethylene from ethane is the most energy-intensive unit operation process in the chemical industry. Therefore, the development of more energy-efficient processes for ethylene purification is highly desirable. Membrane-based separation has been proposed as an alternative option for replacement or debottlenecking of C 2 splitters but current polymer membrane materials exhibit insufficient mixed-gas C 2 H 4 /C 2 H 6 selectivity (<7) to be technically and economically attractive. In this work, a highly selective carbon molecular sieve (CMS) membrane derived from a novel spirobisindane-based polyimide of intrinsic microporosity (PIM-6FDA) was developed and characterized. PIM-6FDA showed a single-stage degradation process under an inert nitrogen atmosphere which commenced at $480 C. The CMS formed by pyrolysis at 800 C had a diffusion/ size-sieving-controlled morphology with a mixed-gas (50% C 2 H 4 /50% C 2 H 6 ) ethylene/ethane selectivity of 15.6 at 20 bar feed pressure at 35 C. The mixed-gas ethylene/ethane selectivity is the highest reported value for CMS-type membranes to date.

Hydrocarbon separations by glassy polymer membranes

“…Koros and coworkers developed a family of covalently crosslinked polyimides with enhanced F I G U R E 6 Deconvoluting diffusion and sorption contributions to hydrocarbon permeation in diffusion-selective glassy polymers. [24,60,[75][76][77][78][79][80][81] (a) Diffusivity (D A )versus sorption coefficient (S A ) and (b) diffusion selectivity (D A /D B ) versus sorption selectivity (S A /S B ). Hollow points: aromatic polyimides, solid points: microporous polymers (A: ethylene, propylene, butadiene; B: ethane, propane, n-butane) plasticization resistance by esterification (using 1,3-propanediol [92] or polyethylene glycol [93] as crosslinking agents) or decarboxylation reaction [94] of carboxylic acid-containing polyimides ( Figure 9).…”

A Review on the Progress in Nanoparticle/C Hybrid CMS Membranes for Gas Separation

“…In recent years, the gas permeability of pure CMS membranes has been greatly improved by use of high-performance CMS membrane precursors [93,94,95,96,97]. Research and attention on hybrid CMS membranes is less than before.…”

Synthesis and characterization of new spirobisindane‐based poly(imide)s: Structure effects on solubility, thermal behavior, and gas transport properties

“…In recent years, some research groups focused on the design of new PIs, based on monomers that inhibit interchain packing and limit the free rotation of the imide ring along the polymer backbone, which create microporosity. This new class of polymers, the PIs of intrinsic microporosity ( PIM‐PIs ), has properties of both families, the PIMs microporosity and solubility, and the PIs synthetic versatility . PIM‐PIs structure is based on diamine and dianhydrides monomers with packing‐disrupting units, such as spirocenters and bridged bicycles, while bulky substituents, close to the amino group, hinder the imide ring free rotation and promote structural rigidity, these factors affect the stacking of the polymer chains …”