WO2025212927A1

WO2025212927A1 - Methods of synthesizing polyimide membranes for membrane-based gas separation and related compositions

Info

Publication number: WO2025212927A1
Application number: PCT/US2025/023011
Authority: WO
Inventors: Ruilan GUO; Agboola Suleiman; Tengfei Luo; Jiaxin XU; Meng JIANG; Joseph Emery; Gang Liu
Original assignee: University of Notre Dame
Current assignee: University of Notre Dame
Priority date: 2024-04-03
Filing date: 2025-04-03
Publication date: 2025-10-09
Anticipated expiration: 2026-10-03

Abstract

Methods for synthesizing polyimide membranes for membrane-based gas separation and related composition are described. The method comprises contacting a compound with an alicyclic diamine compound to form a polyimide membrane compound. The method comprises applying the polyimide membrane compound to a gas separation process. The polyimide membrane compound is configured to separate at least one of H₂/N₂, H₂/CH₄, O₂/N₂, CO₂/N₂, CO₂/CH₄, H₂/CO₂, N₂/CH₄, CO₂/N₂, or any combination thereof.

Description

METHODS OF SYNTHESIZING POLYIMIDE MEMBRANES FOR MEMBRANE-BASED GAS SEPARATION AND RELATED COMPOSITIONS

RELATED APPLICATIONS

[001] This application claims priority from provisional application No. 63/574,021 filed on April 3, 2024, and incorporated herein by reference in its entirety.

GOVERNMENT LICENSE RIGHTS

[002] This invention was made with government support under CBET2102592 awarded by the National Science Foundation (NSF). The government has certain rights in the invention.

FIELD

[003] The present disclosure relates to methods of synthesizing polyimide membranes for membrane-based gas separation and related compositions.

BACKGROUND

[004] Gas separation plays an important role in various industrial applications, including the purification of natural gas, the production of hydrogen, and the separation of oxygen and nitrogen from air. Traditional methods for gas separation often rely on cryogenic distillation or pressure swing adsorption.

SUMMARY

[005] Some embodiments relate to a method. The method comprises contacting a compound of the formula: where R is at least one of a (-) single bond, any combination thereof. In some embodiments, the compound is contacted with an alicyclic diamine compound to form a partially alicyclic polyimide (PAPI) membrane compound of the formula: where R is at least one of a (-) single bond, , or any combination thereof, and n is greater than 50. In some embodiments, the method comprises applying the partially alicyclic polyimide membrane compound to a gas separation process. In some embodiments, the partially alicyclic polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, H2/CO2, N2/CH4, CO2/N2, or any combination thereof.

[006] Some embodiments relate to a method. In some embodiments, the method comprises contacting a compound of the formula: where R is at least one of a (-) single bond, any combination thereof. In some embodiments, the compound is contacted with an aromatic diamine compound to form a polyimide membrane compound of the formula: where R is at least one of a (-) single bond, any combination thereof, and n is greater than 50. In some embodiments, the method comprises applying the polyimide membrane compound to a gas separation process. In some embodiments, the polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, or any combination thereof.

DRAWINGS

[007] FIGS. 1 A, 1 B, 1C, and 1 D are schematic diagrams of reactions of PAP Is, according to some embodiments. [008] FIG. 2A and 2B are schematic diagrams of reactions, according to some embodiments.

[009] FIG. 3 is a schematic diagram of ¹H NMR spectra for PAPIs, according to some embodiments.

[0010] FIG. 4 is a schematic diagram of the FTIR spectra of four PAPIs and two analog aromatic Pls, according to some embodiments.

[0011] FIG. 5 is a photograph of free-standing thin films of PAPIs, according to some embodiments.

[0012] FIGS. 6A and 6B are schematic diagrams of WAXS (Wide-angle X-ray scattering) profile of (a) partially alicyclic polyimides and (b) two analogue aromatic polyimides, according to some embodiments.

[0013] FIGS. 7A and 7B are schematic diagrams of (a) TGA of PAPIs and (b) the DSC of Trip-AATC, according to some embodiments.

[0014] FIGS. 8A, 8B, 8C, and 8D are schematic diagrams of Robeson’s upper bound performance of all six Pls relative to the commercial membranes for H2/CH4, H2/N2, CO2/CH4, and O2/N2, respectively, according to some embodiments.

[0015] FIGS. 9A, 9B, and 9C are schematic diagrams of Robeson’s upper bound performance of all six polyimides relative to the commercial membranes for H2/CO2, N2/CH4, and CO2/N2, respectively, according to some embodiments.

[0016] FIG. 10 is a schematic diagram of the parity plots (comparison between experimental values and prediction by GREA machine learning) of gas permeabilities for all six polyimide membranes, according to some embodiments.

DETAILED DESCRIPTION

[0017] Among those benefits and improvements that have been disclosed, other objects and advantages of this disclosure will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present disclosure are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the disclosure that may be embodied in various forms. In addition, each of the examples given regarding the various embodiments of the disclosure which are intended to be illustrative, and not restrictive.

[0018] Any prior patents and publications referenced herein are incorporated by reference in their entireties.

[0019] Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in one embodiment,” “in an embodiment,” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although it may. All embodiments of the disclosure are intended to be combinable without departing from the scope or spirit of the disclosure.

[0020] As used herein, the term "based on" is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of "a," "an," and "the" include plural references. The meaning of "in" includes "in" and "on."

[0021] As used herein, the term “contacting” refers to bringing two or more components into immediate or close proximity, or into direct contact.

[0022] Current gas separation methods involve high-performance aromatic polyimides (Pls) that have fluorine-containing moieties due to the fluorine-containing Pls increase in free volume, and strong C - F bond that contribute to thermal stability of the fluorine-containing Pls. The persistence of fluorinated compounds in the environment and bioaccumulation at the end-of-life of the fluorine-containing Pls can have an adverse effect on the environment. Existing polymeric membranes used as an alternative to the fluorine-containing Pls have limited thermal and mechanical stability, and suboptimal selectivity and permeability for certain gas pairs. The methods and compositions disclosed herein overcome these challenges.

[0023] The polyimides disclosed herein are at least one of a partially alicyclic polyimide, an aromatic polyimide, or any combination thereof. The polyimides can be selected using machine learning (ML) models.

[0024] In some embodiments, ML models can be trained to predict descriptions of atoms, functional groups, and bond connectivity in polymers that have thermal and chemical stability for membrane-base gas separations for processes such as hydrogen purification (H2/CH4, H2/N2), natural gas sweetening (CO2/CH4), and oxygen enrichment (O2/N2), etc.

[0025] In some embodiments, an advanced graph neural network (GNN) with graph rationalization enhanced by environment-based augmentations (GREA) are created to address the challenges of limited available data. In some embodiments, the advanced GNN with graph rationalization separates the polymer graph into two segments: a 'rationale subgraph' for supporting GNN decisions and an 'environment subgraph' considered as extraneous data. In some embodiments, the environment subgraph is merged with various rationale subgraphs to augment the data representation of polymers in a latent space. In some embodiments, to compensate for the sparse and unbalanced nature of the labeled data, 500-800 instances per gas, a semi-supervised approach named graph imbalanced regression (SGIR) is applied which effectively utilizes a larger pool of unlabeled data. In some embodiments, during training, the GREA method emphasizes features in the polymer graphs, enabling effective learning from limited data while reducing the risk of overfitting and enhancing the model’s applicability to new scenarios.

[0026] With ML models, PolyInfo, the most comprehensive polymer database, can be surveyed to predict the gas permeability of over 12,000 homopolymer candidates not previously labeled. The GREA model's predictions can be interpreted using the 'rationale' component. In some embodiments, the ML strategy addresses the common issues of small and skewed datasets encountered in material science research. Experimental validation of selected polymers was based on various criteria, including predicted performance relative to the 2008 Robeson upper bound line, nonfluorinated polyimides due to environmental considerations, unique structural characteristics such as alicyclic units, and practical factors like the availability and cost of commercial monomers, as well as the anticipated simplicity of synthesizing the polymers.

[0027] Some embodiments relate to a method for producing a partially alicyclic polyimide (PAPI) membrane compound. The method includes contacting a compound of the formula:

[0028] with an alicyclic diamine compound to form a partially alicyclic polyimide membrane compound of the formula:

[0031] n is greater than 50.

[0032] In some embodiments, the compound is at least one of 3, 3', 4,4'-

Benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA), triptycene dianhydride (Trip-DAn), pentiptycene dianhydride (Pent-DAn), or any combination thereof.

[0033] In some embodiments, the alicyclic diamine compound comprises a 1 - amino-3-aminomethyl-3,5,5-trimethylcyclohexane (AATC diamine). The AATC diamine can have the formula:

[0034] The method includes applying the partially alicyclic polyimide membrane compound to a gas separation process.

[0035] The partially alicyclic polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, H2/CO2, N2/CH4, CO2/N2, or any combination thereof.

[0036] In some embodiments, the contacting forms the polyimide membrane compound of the formula:

[0037] In some embodiments, the partially alicyclic polyimide membrane compound is 3,3',4,4'-Benzophenonetetracarboxylic 1 -amino-3-aminomethyl-3,5,5- trimethylcyclohexane (BT-AATC).

[0038] In some embodiments, the contacting forms the partially alicyclic polyimide membrane compound of the formula:

[0039] In some embodiments, the partially alicyclic polyimide membrane compound is 4,4'-(Hexafluoroisopropylidene) 1 -amino-3-aminomethyl-3,5,5- trimethylcyclohexane (6F-AATC).

[0040] In some embodiments, the contacting forms the partially alicyclic polyimide membrane compound of the formula:

[0041] In some embodiments, the partially alicyclic polyimide membrane compound is triptycene 1 -amino-3-aminomethyl-3,5,5-trimethylcyclohexane (Trip- AATC).

[0042] In some embodiments, the contacting forms the partially alicyclic polyimide membrane compound of the formula:

[0043] In some embodiments, the partially alicyclic polyimide membrane compound is pentiptycene 1 -amino-3-aminomethyl-3,5,5-trimethylcyclohexane (Pent- AATC).

[0044] In some embodiments, Trip-AATC and Pent-AATC, being polyimides, can be useful in microelectronics applications such as optical transparency, low charge-transfer-complex formations, reduced dielectric constants, or the like.

[0045] In some embodiments, the partially alicyclic polyimide membrane compound is 3,3’4,4’-biphenyltetracarboxylic 1 -amino-3-aminomethyl-3,5,5- trimethylcyclohexane (BP-AATC).

[0046] FIGS. 1 A, 1 B, 1 C, and 1 D are schematic diagrams of the reactions.

[0047] In some embodiments, the contacting proceeds in a presence of m- cresol for a time period of about 30 minutes to 4 hours at a temperature of about 60 °C to 100 °C.

[0048] In some embodiments, the contacting proceeds in a presence of m- cresol for a time period of about 30 minutes to 4 hours, or any range or subrange between 30 minutes and 4 hours. For example, in some embodiments, the contacting proceeds in a presence of m-cresol for a time period of about 1 hour to 3 hours, 30 minutes to 3 hours, 30 minutes to 2 hours, 30 minutes to 1 hour, 1 hour to 4 hours, 2 hours to 4 hours, or 3 hours to 4 hours.

[0049] In some embodiments, the contacting proceeds in a presence of m- cresol at a temperature of about 60 °C to 100 °C, or any range or subrange between 60 °C and 100 °C. For example, in some embodiments, the contacting proceeds in a presence of m-cresol at a temperature of about 70 °C to 90 °C, 60 °C to 90 °C, 60 °C to 80 °C, 60 °C to 70 °C, 70 °C to 100 °C, 80 °C to 100 °C, or 90 °C to 100 °C.

[0050] In some embodiments, after contacting, the method comprises heating the polyimide membrane compound to a temperature of about 150 °C to 300 °C for a time period of about 1 hour to about 3 hours.

[0051] In some embodiments, after contacting, the method comprises heating the polyimide membrane compound to a temperature of about 100 °C to 200 °C, or any range or subrange between 100 °C and 200 °C. For example, in some embodiments, after contacting, the method comprises heating the polyimide membrane compound to a temperature of about 120 °C to 180 °C, 140 °C to 1600 °C, 100 °C to 180 °C, 100 °C to 160 °C, 100 °C to 140 °C, 100 °C to 120 °C, 120 °C to 200 °C, 140 °C to 200 °C, 160 °C to 200 °C, or 180 °C to 200 °C.

[0052] In some embodiments, after contacting, the method comprises heating the polyimide membrane compound for a time period of about 1 hour to about 3 hours, or any range or subrange between 1 hour and 3 hours. For example, in some embodiments, after contacting, the method comprises heating the polyimide membrane compound for a time period of about 2 hours to 3 hours, or 1 hour to 2 hours.

[0053] In some embodiments, the method comprises contacting the polyimide membrane compound with ortho-dichlorobenzene for a time period of about 4 hours to 14 hours. For example, in some embodiments, the method comprises contacting the polyimide membrane compound with ortho-dichlorobenzene for a time period of about 5 hours to 13 hours, 6 hours to 12 hours, 7 hours to 1 1 hours, 8 hours to 10 hours, 4 hours to 12 hours, 4 hours to 10 hours, 4 hours to 8 hours, 4 hours to 6 hours, 6 hours to 14 hours, 8 hours to 14 hours, 10 hours to 14 hours, or 12 hours to 14 hours. [0054] In some embodiments, the polyimide membrane compound has a purity of 90% as measured by proton nuclear magnetic resonance (¹H-NMR). In some embodiments, the polyimide membrane compound has a purity of about 90% to 99.9% as measured by ¹H-NMR, or any range or subrange between about 90% and 99.9%. For example, in some embodiments, the polyimide membrane compound has a purity of about 91 % to 99%, 92% to 98%, 93% to 97%, 94% to 96%, 90% to 99%, 90% to 98%, 90% to 97%, 90% to 96%, 90% to 95%, 90% to 94%, 90% to 93%, 90% to 92%, 90% to 91 %, 91 % to 99.9%, 92% to 99.9%, 93% to 99.9%, 94% to 99.9%, 95% to 99.9%, 96% to 99.9%, 97% to 99.9%, 98% to 99.9%, or 99% to 99.9% as measured by ¹ H-NMR.

[0055] In some embodiments, the polyimide membrane compound is nonfluorinated.

[0056] Some embodiments relate to a method. The method includes contacting a compound of the formula:

[0057] with an aromatic diamine compound to form a polyimide membrane compound of the formula:

[0058] where: at least one of a (-) single bond, r any combination thereof, ater than 50. e embodiments, the compound is at least one of triptycene dianhydride (Trip-DAn), pentiptycene dianhydride (Pent-DAn), or any combination thereof.

[0062] In some embodiments, the aromatic diamine compound comprises 1 ,5- Diaminonaphthalene.

[0063] In some embodiments, the method includes the step of applying the polyimide membrane compound to a gas separation process. In some embodiments, the polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, H2/CO2, N2/CH4, and CO2/N2, or any combination thereof.

[0064] In some embodiments, the contacting forms the polyimide membrane compound of the formula:

[0065] In some embodiments, the polyimide membrane compound is triptycene 1 ,5-diaminoaphthalene (Trip-DANP).

[0066] In some embodiments, the contacting forms the polyimide membrane compound of the formula:

[0067] In some embodiments, the polyimide membrane compound is pentiptycene 1 ,5-diaminoaphthalene (Pent-DANP).

[0068] In some embodiments, Trip-DANP and Pent-DANP, being polyimides, can be useful in microelectronics applications such as optical transparency, low charge-transfer-complex formations, reduced dielectric constants, or the like.

[0069] FIG. 2A and 2B are schematic diagrams of the reactions.

[0070] In some embodiments, the contacting proceeds in a presence of 1 - Methyl-2-pyrrolidinone (NMP) for a time period of about 4 hours to 8 hours at room temperature to obtain a polyamic acid solution (PAA), or any range or subrange between about 4 hours to 8 hours. For example, in some embodiments, the contacting proceeds in a presence of NMP for a time period of about 5 hours to 7 hours, 4 hours to 7 hours, 4 hours to 6 hours, 4 hours to 5 hours, 5 hours to 8 hours, 6 hours to 8 hours, or 7 hours to 8 hours.

[0071] In some embodiments, the contacting comprises dissolving the polyimide membrane compound in the NMP.

[0072] In some embodiments, the contacting occurs at a temperature range of about 75 °C to 85 °C, or any range or subrange between about 75 °C to 85 °C. For example, in some embodiments, the contacting occurs at a temperature range of about 80 °C to 85 °C, or 70 °C to 80 °C.

[0073] In some embodiments, after contacting, the method comprises casting the polyamic acid solution on a glass plate. In some embodiments, the polyamic acid solution forms a PAA film. In some embodiments, the PAA film has a thickness of about 20 micrometers (pm) to 100 pm, or any range or subrange between 20 pm and 100 pm. For example, in some embodiments, the PAA film has a thickness of about 30 pm to 90 pm, 40 pm to 80 pm, 50 pm to 70 pm, 20 pm to 90 pm, 20 pm to 80 pm, 20 pm to 70 pm, 20 pm to 60 pm, 20 pm to 50 pm, 20 pm to 40 pm, 20 pm to 30 pm, 30 pm to 100 pm, 40 pm to 100 urn, 50 m to 100 pm , 60 urn to 100 urn, 70 urn to 100 pm, 80 pm to 100 pm, or 90 pm to 100 pm.

[0074] In some embodiments, the method further comprises heating the PAA film to a temperature range of about 10 °C to 500 °C, or any range or subrange between 10 °C to 500 °C. For example, in some embodiments, the heating occurs at a temperature range of about 50 °C to 450 °C, 100 °C to 400 °C, 150 °C to 350 °C, 200 °C to 300 °C, 10 °C to 450 °C, 10 °C to 400 °C, 10 °C to 350 °C, 10 °C to 300 °C, 10 °C to 250 °C, 10 °C to 200 °C, 10 °C to 150 °C, 10 °C to 100 °C, 10 °C to 50 °C, 50 °C to 500 °C, 100 °C to 500 °C, 150 °C to 500 °C, 200 °C to 500 °C, 250 °C to 500 °C, 300 °C to 500 °C, 350 °C to 500 °C, 400 °C to 500 °C, or 450 °C to 500 °C.

[0075] In some embodiments, as the temperature rises from about 10 °C to 500 °C, the temperature is held for 15 minutes at 10 °C, 180 °C, 210 °C, 250 °C, 350 °C, and 400 °C.

[0076] In some embodiments, the polyimide membrane compound is an aromatic polyimide.

[0077] Examples

[0078] Syntheses of Polymers

[0079] Polymers 6F-AATC, BP-AATC, Trip-AATC, and BT-AATC were synthesized by reacting 1 .7 g (9.98 mmol) of 5-amino-1 ,3,3-trimethyl cyclohexane methylamine (AATC) with a stoichiometric equal amount of dianhydride in 42 ml m- cresol at 11 .2 wt.% concentration in a flame-dried 3-neck flask fitted with a mechanical stirrer. The monomers, AATC and dianhydride underwent complete dissolution within

1 hour of the reaction at 70 °C. The dissolved monomers were then maintained at 90 °C for 3 h.

[0080] Then, the temperature was gradually raised to 200 °C within 2 hours prior to the addition of 10 ml ortho-dichlorobenzene. A Dean-Stark trap was then attached for azeotropic reflux to complete the imidization over another 12 hours at 200 °C. Fiber chunks of the polymers were obtained by precipitating the viscous solution into a 300 ml/300 ml water/ methanol mixture. The fiber chunks of the polymers indicated high molecular weight of the polymer. The polymer was then stirred in 500 ml methanol for 12 hours and in 500 ml methanol for 3 hours before the polymer was filtered and dried at 100 °C for 12 h in vacuo. The polymers were confirmed by proton nuclear magnetic resonance spectroscopy (¹H NMR) and Fourier transform infrared spectroscopy in attenuated total reflectance mode (ATR-FTIR).

[0081] Trip-DANP and BP-DANP were prepared using a modified thermal imidization procedure to obtain free-standing polymer films. The free-standing polymer films were tested in pressure-driven gas permeation equipment. 0.8030 g (5.076 mmol) of 1 ,5-diaminonaphthalene (DANP) was dissolved in 4 ml anhydrous 1 -Methyl-2- pyrrolidinone (NMP, > 99.5%) (anhydrous NMP) at 80 °C. An equimolar amount of the corresponding dianhydride and 1 1 ml anhydrous NMP was added to maintain 15 wt.% solid content while the temperature was maintained at 80 °C until complete dissolution of both monomers. Then, the reaction was left to continue at room temperature for another 4 hours to obtain a viscous polyamic acid (PAA) solution.

[0082] To achieve complete imidization and obtain thin films of the final polyimide, the PAA solution was diluted to 7.5 wt.% with anhydrous NMP, filtered with 0.45 pm Teflon filters, and cast on glass plates under an infrared lamp at about 60 °C for 24 hours. The PAA film was then dried at 150 °C under a vacuum for 12 hours, soaked in methanol for 3 hours, and dried again at 150 °C under a vacuum for 12 hours. Finally, the solvent-free PAA film was sandwiched between two porous ceramic plates and thermally imidized in a muffle furnace under nitrogen flow, where the temperature was ramped at 10 °C min^-1 to 180, 210, 250, 350, and 400 °C, maintaining 15 minutes at each temperature before cooling to room temperature at 10 °C min^-1. The fully imidized structure of the solvent-free films of the final polyimides and their respective PAAs were confirmed by Fourier transform infrared spectroscopy in attenuated total reflectance mode (ATR-FTIR).

[0083] Characterization Methods

[0084] A Bruker AVANCE III HD 500 MHz spectrometer was used to acquire the ¹H NMR spectra of the synthesized TPDAn monomer and all the AATC polymers (6F-AATC, BP-AATC, Trip-AATC, & BT-AATC) in deuterated solvents. For example, deuterated solvents include CDCh and DMSO-d6. The FTIR spectra of the polymer films were obtained using a mid-IR, Shimadzu IRXross FTIR integrated with a diamond QATR10 module (4500-400 cm^-1) in attenuated total reflection (ATR) mode having a resolution of 4 cm^-1 and 64 scans. Thermogravimetric analysis (TGA) was conducted using TA Instruments TGA Q500 ramped at 10 °C min^-1 from 100 to 600 °C under a 50 mL min ¹ nitrogen purge. Differential scanning calorimetry (DSC) analysis was performed using DSC Q2000 by TA Instruments in two heating cycles, where each cycle was ramped at 10 °C min^-1 to 400 °C and cooled at 10 °C min^-1. Wide-angle X- ray scattering (WAXS) was performed on all polymer films using a Malvern Panalytical X-ray diffractometer. Reflection mode by Cu Ko radiation (wavelength, A= 1 .54 A) was selected, with the current and voltage of the X-ray generator set to 40kV and 40 mA, respectively. In 29 ranging from 5 to 45°, a step increment of 0.02° and a scan speed of 7 s per step were assigned for all measurements. The observed diffraction peak maxima at 6 (°) were used to calculate the average cf-spacing, d (A), for each film, according to Bragg’s law, d=A/2 sin (6). The density of polymer films was determined at room temperature in deionized (DI) water from Mettler Toledo ML 204 analytical balance attached with a density kit. DI water was chosen due to its negligible absorption in hydrophobic films. The buoyancy method governs the density measurements, and the averaged density value over at least eight measurements was reported. The group contribution method was used to calculate the van der Waals specific volume, V_w (cm³g^-1), of the polymers.

[0085] Gas Permeation Tests

[0086] Pure gas permeation: Ultra-high pure gases from Airgas were used to measure the gas transport properties of all the polymers. Five light gases, H2, CH4, N2, O2, and CO2, were permeated at 35 °C and 3 bar using a constant-volume variablepressure method. Thin films of the polymers were mounted on aluminum duct tape with epoxy glue and protected on the backside with filter paper. The thin films were about 50 - 70 pm in thickness. The exposed film region was scanned with Imaged to measure the available area for gas permeation and then loaded into the gas cell with the sampler holder immersed in a deionized water bath for temperature control. The entire system, upstream and downstream sides, was degassed in vacuo for at least 12 hours before each gas permeation experiment. The upstream pressure for each gas permeation experiment was maintained at 30, 50, and 80 psig until a steady state increase in pressure vs. time in the downstream was achieved. The permeability for each gas was calculated using the expression below:

[0088] where P (Barrer, 1 Barrer = 10^-1°cm³ (STP) cm/(cm² s cmHg)) is the gas permeability, /is the film thickness (cm), Vd is the calibrated downstream volume (cm³),

Pup is the upstream pressure (psi), A is the effective film area

( ) are the steady-state pressure increments in downstream, and the leak rate leak of the system (cmHg/s), respectively; T is the test temperature (K), and R is the gas constant (0.278 cm³ cmHg/(cm³ (STP) K)).

[0089] The ideal selectivity (CTA/B) for two different gases, A (more permeable) and B, is defined as the ratio of pure gas permeability of the two gases and is calculated as

[0091] The estimated lag time was used to calculate the apparent diffusion coefficient D (cm²s^-1) in the equation below, where I is the film thickness (cm), and the tiag is the lag time. While the solubility coefficient, S (cm³ (STP)/cm³ atm), can be obtained using the relationship

[0094] Mixed gas permeation: Mixed gas permeation was measured at 35 °C using a gas chromatograph for concentration detection for binary compositions of 50:50 and 20:80 CO2:CH4. Helium was the sweep gas. The total feed pressure varied between 3 and 14 bars, the stage cut was less than 1 %, and the total feed flow rate was 450 cm³ (STP) min^-1. The feed compositions were achieved using mixed flow controllers, and the composition of permeate gas mixtures was analyzed using a 3000 Micro GC, Inficon Inc. gas chromatograph (Syracuse, NY) equipped with a thermal conductivity detector.

[0095] The test films were prepared similarly to the pure gas measurement. The test sample was loaded into the gas cell and exposed to the mixture at the test temperature for a few hours before testing at various pressures. The feed composition was set using mixed flow controllers, whereas the sweep gas, Helium, flows the permeate into the gas chromatography for the analysis of each gas composition, and the permeability of each gas was determined by:

[0097] Where S_F = flowrate of the sweep gas, A = membrane area, I = membrane thickness, and x_Sweep are the mole fractions of component A and the sweep gas in the permeate stream respectively, while x_2A is the mole fraction of A in the feed gas. The mixed gas selectivity was calculated as the ratio of their mixed gas permeabilities.

[0098] Gas transport properties of polymers can be directly linked to the polymers microstructure development. Wide-angle X-ray scattering experiment was used to determine the inter- and intra-chain spacing by computing the d-spacing using Bragg’s relation, n = 2d sin 0, where 9 = the diffraction angle, d = d-spacing, A = wavelength of irradiation, n = 1 . The fractional free volume (FFV) was calculated using the group contribution theory and the polymer’s density based on Archimedes’ principle, FFV = 1 — 1.3pV_w, where p is the measured membrane density (g/cm³), and V_w is the van der Waals specific volume of the polymers (cm³g^-1).

[0099] RESULTS AND DISCUSSION

[00100] Polymer Synthesis and Membrane Fabrication

[00101] Polymer Synthesis and Structural Characterization: FIG. 3 is a schematic diagram of ¹H NMR for PAPIs. As shown in FIG. 3, PAPIs 6F-AATC, BP- AATC, and BT-AATC had a ¹H NMR 6 (CDCI3,) 8.18-8.13 (m, 4H, Hj.k) 8.03-7.97 (m, 2H, Hi), 5.00-4.24 (m, 1 H, H_d), 3.55 (s, 2H, Ht), 1 .05-0.98 (8, 9H, Hg ). Trip-AATC had a similar peak position as 6F-AATC, BP-AATC, and BT-AATC, with additional protons due to the triptycene unit. As shown in FIG.1 , Trip-AATC had a ¹H NMR 8 (CDCI3,) 5.5 (s, 2H, H3) and 8.18-8.13 (m, 10H, HI ,2,4,). Trip-DANP and BP-DANP could not be analyzed with ¹ H NMR because of Trip-DANP and BP-DANP insolubility in deuterated solvents.

[00102] FIG. 4 is a schematic diagram the FTIR of four PAPIs and two analogue aromatic Pls. FIG. 4 shows sharp peaks around the 2900-3015 cm^-1 region, likely corresponding to -CH stretching vibrations, and there are also distinct peaks around 1395 - 1465 cm ¹, indicating CH2 and CH3 bending. The peaks confirm the alicyclic component of the polyimide. All six polymers, 6F-AATC, BP-AATC, BT-AATC, Trip- AATC, Trip-DANP, and BP-DANP, display sharp peaks near 1 100 cm^-1 (C-N stretching), 1780cm^-1 (C=O symmetrical stretching), 1716cm^-1 (C=O asymmetrical stretching), 1375cm^-1 (C-N-C stretching), and 735cm^-1 (imide deformation ring) which are typical for polyimides.

[00103] The -C(CFs)2- moiety was observed around 1260-1210, & 1 180cm^-1. Trip-DANP and BP-DANP were fully imidized, as shown by the absence of -COOH and -CONH bands on the FT-IR.

[00104] Membrane Fabrication

[00105] Thin films having a thickness of about 50 pm to 70 pm of 6F-AATC, BP- AATC, Trip-AATC, and BT-AATC were obtained by solution casting on a circular glass plate using chloroform as the casting solvent. 1 .6 % w/v of the polymer solution was cast at room temperature under nitrogen flow for 48 - 72 hours, enabling slow evaporation of the solvent. The free-standing films were dried in vacuo for 12 hours at 180 °C.

[00106] FIG. 5 is a photograph of free-standing thin films of PAPIs on a circular glass plate. As shown in FIG. 5, the PAPIs, 6F-AATC, Trip-AATC, and BP-AATC are transparent, or colorless. BT-AATC is not transparent as shown. Transparent thin films were expected for polyimides from alicyclic monomers, due to the lower electronic conjugation by the alicyclic moiety. Ortho linkages lead to steric hindrance, which can lead to nonplanar conformation between the imide ring and the diamine moiety, lowering the charge-transfer complex formation. This decrease in chain interactions can reduce the T_g and improve the transparency of the films.

[00107] Microstructure Characterization and Thermal Properties

[00108] Table 1 shows the PAPIs (6F-AATC, Trip-AATC, BP-AATC, and BT- AATC) are less dense than the aromatic Pls (Trip-DANP and BP-DANP). The PAPIs lower densities attribute to a lower chain packing efficiency due to the presence of substituent methylene and methyl groups acting as spacers, thus disrupting the loosely packed molecular chains within the polymer matrix. The denser Trip-DANP and BP-DANP have more efficient packing of polymer chains due to stronger chain transfer complexes, thus reducing free volume elements for gas transport. FFV in Table 1 shows a downward trend from 6F-AATC to BP-DANP The partially alicyclic polyimides display higher FFV than the aromatic polymides, a linear trend to densities. [00109] Table 1. Physical and thermal properties of the PAPIs and the two analogue aromatic Pls

[00110] FIG. 6 is a schematic diagram of wide-angle X-ray scattering (WAXS) of (a) partially alicyclic Pls and (b) two analogue aromatic Pls. As shown in FIG. 6, the PAPIs (6F-AATC, Trip-AATC, and BP-AATC) except BT-AATC, have two peaks corresponding to complex amorphous structures or multiple phases within the polymer. The complex amorphous structures affect the path gases take when diffusing through the PAPIs, potentially reducing gas transport if the path becomes more tortuous, as with the aromatic polyimides. As shown in FIG. 4 and Table 1 , for lower angles, the higher d-spacings correspond to larger unit cells or more loosely packed chains. The partially alicyclic polyimides display sharper peak with higher intensities, with higher d-spacing values than the aromatic polyimides, Trip-DANP and BP-DANP, with broader peaks corresponding to more amorphous regions. The characteristics of the partially alicyclic polyimides are afforded further chain disruptions by the pendant methylene and methyl groups in the partially alicyclic polyimides. The presence of the alicyclic unit in the polymer backbone correspond to a relatively higher degree of crystallinity. Trip-AATC and Trip-DANP have a similar peak with a d-spacing around 7 A due to the triptycene unit as shown in other triptycene-containing polymers.

[00111] Trip-AATC had a d-spacing of 0.4 A more than Trip-DANP and a correspondingly higher area under the curve than Trip-DANP. Trip-DANP had larger unit cells than BP-DANP or more loosely packed chains than BP-DANP. More loosely packed chains are due to the methylene and methyl groups attached to the cyclohexane in the polymer backbone. A similar trend was observed between BP- AATC and BP-DANP. The PAPIs have higher interchain distances than the aromatic Pls. The broadness and low intensity of the peaks are due to the inflexible naphthalene unit favoring very tight chain packing. The inflexible naphthalene unit contributed the PAPIs very low gas transport properties and the highly rigid backbone that resulted in extremely high decomposition temperature, indetectable glass transition temperature, and insolubility in common organic solvents.

[00112] Thermal Properties:

[00113] The aromatic Pls had a non-detectable glass transition temperature (Tg) due to their highly rigid backbone structures. The naphthalene-containing Pls have undetectable T_g due to the very stiff naphthalene backbone. The insolubility of the polymers in common organic solvents necessitated solid-state thermal imidization for the polymer synthesis. The high rigidity benefited the size-sieving of small gas molecules. The T_g influenced gas transport properties with the transition from a brittle, glassy state to a more flexible, rubbery state. Above T_g, the polymers allowed more segmental mobility that facilitated gas transport. The PAPIs had a high T_g ranging from 272 to 31 1 °C that indicated the PAPIs had higher chain mobility, facilitating more gas diffusion. FIGS. 7A and 7B are schematic diagrams of the TGA of PAPIs. As shown in FIGS. 7A, the PAPIs had high decomposition temperatures (Td), 450 - 480 °C, at 5% weight loss, while the aromatic polymers had higher decomposition temperatures by about 100 °C, as shown in FIG. 7B. The thermal properties of the PAPIs are advantageous for gas separation processes occurring at elevated temperatures because the polymers maintain structural integrity at elevated temperatures and retain their performance. The microstructure and thermal properties of the non-fluorinated BP-AATC, Trip-AATC, AND BT-AATC are very similar to the fluorinated 6F-AATC with comparable gas separation performance.

[00114] Gas T ransport Properties [00115] Table 2 shows that gas permeability across the polymers decreases with an increase in the kinetic diameter of the permeating gases, in the following the order: H2 > CO2 > O2 > N2 > CH4. The trend indicated that smaller gases permeate more easily due to their lower kinetic diameters. The PAPIs, 6F-AATC, BP-AATC, Trip- AATC, and BT-AATC, exhibited higher permeabilities compared to aromatic Pls (Trip- DANP and BP-DANP). The PAPIs performance is attributed to higher FFV, facilitated by methylene and methyl pendant groups that disrupt chain packing, creating more diffusion paths. 6F-AATC was identified as the most permeable among the AATC- containing polymers, due to additional -C(CF3)2- units that further disrupt chain packing, thereby increasing the free volume. Conversely, BT-AATC showed the lowest permeability among the AATC-based polymers, comparable to that of the aromatic Pls (Trip-DANP and BP-DANP), due to the stronger electronic conjugation of the carbonyl group, enhancing chain transfer complexes (CTC), and reducing inter-chain distances. The BT-AATC trend was consistent with the yellow color (FIG. 5) compared to the other PAPIs (6F-AATC, Trip-AATC, BP-AATC) that were colorless. Additionally, Trip- AATC and Trip-DANP showed notably higher CO2 permeability than BP-AATC and BP-DANP, respectively, due to the presence of CC -philic ether groups in the triptycene units. The decreasing trend in O2, N2, and CPU permeabilities from 6F-AATC to BP-DANP, with AATC polymers showed at least twice the permeability of DANP polymers, aligned with the respective FFV measurements. The tight chain packing, due to higher CTC in DANP polymers, resulted in low permeabilities, especially for CH₄.

Table 2. Single gas permeability and ideal selectivity

[00116] FFV and molecular packing are important in determining the gas separation performance of polymers AATC-based polymers showed superior permeability due to the microstructure and free volume distribution.

[00117] The PAPIs displayed superior gas selectivity for hydrogen purification (H2/CH4 and H2/N2), biogas upgrading, and natural gas treatment to separate CO2 from CH4. Trip-DANP and BP-DANP displayed high selectivity for hydrogen production and purification applications due to low permeabilities for gases with larger kinetic diameters like N2 and CPU through these polymers.

[00118] BP-DANP exhibited superior O2/N2 selectivity of 17, suitable for air separation processes to produce nitrogen-enriched or oxygen-enriched streams. BP- DANP high selectivity is due to the polymer's free volume closely matching the kinetic diameter of O2 but being too small for N2 permeation. FIGS. 8A, 8B, 8C, 8D are schematic diagrams of the performance of all six Pls (BP-DANP, Trip-DANP, BP- AATC, Trip-AATC, 6F-AATC, BT-AATC) relative to the commercial membranes (H2/CH4, H2/N2, CO2/CH4, O2/N2). BP-DANP, Trip-DANP, BP-AATC, and Trip-AATC demonstrated performance above the 2008 upper bound line for hydrogen purification. While BP-DANP is above the 2008 tradeoff line for air (O2/N2) separation, Trip-DANP is above the 2008 tradeoff line for natural gas sweetening (CO2/CH4). The nonfluorinated Pls showed comparable performance to the fluorinated 6F-AATC, which confirmed the polymers can replace fluorinated gas separation polymers. FIGS. 9A, 9B, 9C, are schematic diagrams of the performance of all six Pls (BP-DANP, Trip- DANP, BP-AATC, Trip-AATC, 6F-AATC, BT-AATC) relative to the commercial membranes (H2/CO2, N2/CH4, CO2/N2).

[00119] Aromatic polyimides, Trip-DANP and BP-DANP, demonstrated superior selectivity compared to the PAPIs due to the aromatic polyimides CTC and the rigidity of their backbones, as measured by the undetectable glass transition temperature, which restricts gas diffusion. Trip-DANP and BP-DANP can be used in various gas separation applications. [00120] Table 3 describes polymers' gas diffusion and solubility. Except for CO2, the diffusion rates for O2, N2, and CPU decreased with the increasing kinetic diameter of the gases. The PAPIs had a higher diffusivity for O2, N2, and CO2, consistent with the permeability trends. In contrast, Trip-DANP and BP-DANP had lower O2 diffusivity and the lowest diffusivity for N2 and CO2, respectively. The lower diffusivity of aromatic polyimides, as evidenced by FFV and WAXS measurements, are due to tighter chain packing or stronger polymer chain interactions. The characteristic of aromatic polyimides enhanced the aromatic polyimides selectivity for certain gases, which confirmed that aromatic polyimides can be used in high-purity gas separation applications. The tetrahedral shape of methane contributes to the difficulty in diffusing through the aromatic polyimides more rigid structures than the other gases linear in shape. CO2 solubility trending differed, with the PAPIs displaying higher solubility, except for BT-AATC. The alicyclic segment in PAPIs, a stronger nucleophile, favored the sorption of CO2, an electrophile. PAPIs have lower interchain interactions and more dipole interactions between the gas molecules and the alicyclic segments in the polymer. Trip-AATC showed the highest CO2 solubility attributed to CO2-philic ether groups, aligning with its higher CO2 permeability.

[00121] Table 3. Diffusion and solubility coefficients of the PAPIs and the two analogue aromatic Pls

[00122] Mixed-gas permeation tests were performed using two feed compositions, 20:80 and 50:50 CO2/CH4 mol % for 6F-AATC, Trip-AATC, and BP- AATC. For both feed compositions, the CO2 permeabilities in mixed gas conditions with increasing pressures were consistent with pure gas measurements (Table 1 ). However, the gas chromatograph did not detect methane due to its extremely low permeability in all the polymers. Thus, CO2/CH4 selectivity could not be calculated.

[00123] The alicyclic segments in the non-fluorinated PAPIs, Trip-AATC and BP- AATC, significantly influenced the microstructure, processibility, and gas transport properties, resulting in a comparable performance to the fluorinated.

[00124] Comparison of Predicted and Experimental Gas Permeabilities

[00125] FIG. 10 is a schematic diagram of the parity plots of gas permeabilities for all six polymers. As shown in FIG. 10, there was a close match between the experiments and predictions for H2, CH4, N2, and O2 compared to CO2 for the polymers. The difference in the experimental and predicted for CO2 is due to CO2 separation attributable to the highly condensable nature of the gas as opposed to H2, CH4, N2, and O2, where diffusion is more dominant. The predicted gas permeabilities were not skewed towards the aromatic polyimides despite the training data being from all available literature data on gas separation membranes of aromatic polymers. The machine learning technique addresses the unlabeled and imbalanced data problem.

[00126] The ML-aided design of PAPIs with unique features substantiated by experimental validation demonstrated eco-friendly membrane-based gas separation polymers. The non-fluorinated PAPIs exhibited gas separation performance, robustness, and enhanced environmental compatibility for industrial applications.

[00127] The PAPIs exhibit processibility and high thermal stability and match the performance of fluorinated aromatic polyimides with minimized health and environmental consequences. The structure-property relationship of the polymers showed that incorporating alicyclic segments in polyimide membranes can be used in gas separation while promoting ecological sustainability and complying with tightening regulatory frameworks.

[00128] Any one or more of the embodiments disclosed herein shall be understood to be combinable without departing from the scope or spirit of the disclosure.

[00129] ASPECTS

[00130] Various Aspects are described below. It is to be understood that any one or more of the features recited in the following Aspect(s) can be combined with any one or more other Aspect(s).

Aspect 1 . A method comprising: contacting a compound of the formula:

R is at least one of a (-) single bond, -C(O)-, -C(CF3)2-, with an alicyclic diamine compound to form a partially alicyclic polyimide

(PAPI) membrane compound of the formula: where:

R is at least one of a (-) single bond, -C(O)-, -C(CF3)2-, r any combination thereof, and n is greater than 50; and applying the partially alicyclic polyimide membrane compound to a gas separation process, wherein the partially alicyclic polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, or any combination thereof.

Aspect 2. The method, according to Aspect 1 , wherein the alicyclic diamine compound comprises a 1 -amino-3-aminomethyl-3,5,5-trimethylcyclohexane (AATC) diamine.

Aspect s. The method according to any of Aspects 1 -2, wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula:

Aspect 4. The method according to any of Aspects 1 -3, wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula: Aspect s. The method according to any of Aspects 1 -4, wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula:

Aspect 6. The method according to any of Aspects 1 -5, wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula:

Aspect 7. The method according to any of Aspects 1 -6, wherein the contacting proceeds in a presence of m-cresol for a time period of about 30 minutes to 4 hours at a temperature of about 60 °C to 100 °C.

Aspect 8. The method according to any of Aspects 1 -7, wherein after contacting, the method comprises heating the partially alicyclic polyimide membrane compound to a temperature of about 100 °C to 200 °C for a time period of about 1 hour to about 3 hours.

Aspect 9. The method according to any of Aspects 1 -8, further comprises contacting the partially alicyclic polyimide membrane compound with orthodichlorobenzene for a time period of about 4 hours to 14 hours.

Aspect 10. The method according to any of Aspects 1 -9, wherein the partially alicyclic polyimide membrane compound has a purity of 99% as measured by ¹H-NMR.

Aspect 1 1. The method according to any of Aspects 1 -10, wherein the partially alicyclic polyimide membrane compound is non-flourinated.

Aspect 12. A method comprising: contacting a compound of the formula: with an aromatic diamine compound to form a polyimide membrane compound of the formula: where:

R is at least one of a (-) single bond, r any combination thereof, and n is greater than 50; and applying the polyimide membrane compound to a gas separation process, wherein the polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, or any combination thereof.

Aspect 13. The method according to Aspect 12, wherein the aromatic diamine compound comprises 1 ,5-Diaminonaphthalene.

Aspect 14. The method according to any one of Aspects 12-13, wherein the contacting forms the polyimide membrane compound of the formula:

Aspect 15. The method according to any one of Aspects 12-14, wherein the contacting forms the polyimide membrane compound of the formula: Aspect 16. The method according to any one of Aspects 12-15, wherein the contacting proceeds in a presence of 1 -Methyl-2-pyrrolidinone (NMP) for a time period of about 4 hours to 8 hours at room temperature to obtain a polyamic acid solution (PAA).

Aspect 17. The method according to any one of Aspects 12-16, wherein after contacting, the method comprises casting the polyamic acid solution on a glass plate, wherein the polyamic acid solution forms a PAA film.

Aspect 18. The method according to any one of Aspects 12-17, further comprises heating the PAA film to a temperature range of about 10 °C to 500 °C, wherein a temperature is held for 15 minutes at 10 °C, 180 °C, 210 °C, 250 °C, 350 °C, and 400 °C.

Aspect 19. The method according to any one of Aspects 12-18, is wherein the polyimide membrane compound is an aromatic polyimide.

Aspect 20. The method according to any one of Aspects 12-19, wherein the contacting proceeds under solid-state thermal imidization.

Claims

CLAIMS WHAT IS CLAIMED IS:

1 . A method comprising: contacting a compound of the formula: with an alicyclic diamine compound to form a partially alicyclic polyimide (PAPI) membrane compound of the formula: where: R is at least one of a (-) single bond, - any combination thereof, and n is greater than 50; and applying the partially alicyclic polyimide membrane compound to a gas separation process, wherein the partially alicyclic polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, H2/CO2, N2/CH4, CO2/N2, or any combination thereof.

2. The method of claim 1 , wherein the alicyclic diamine compound comprises a 1 - amino-3-aminomethyl-3,5,5-trimethylcyclohexane (AATC) diamine.

3. The method of claim 1 , wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula: where: n is greater than 50.

4. The method of claim 1 , wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula: where: n is greater than 50.

5. The method of claim 1 , wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula: where: n is greater than 50.

6. The method of claim 1 , wherein the contacting forms the partially alicyclic polyimide membrane compound of the formula: where: n is greater than 50.

7. The method of claim 1 , wherein the contacting proceeds in a presence of m- cresol for a time period of about 30 minutes to 4 hours at a temperature of about 60 °C to 100 °C.

8. The method of claim 7, wherein after contacting, the method comprises heating the partially alicyclic polyimide membrane compound to a temperature of about 100 °C to 200 °C for a time period of about 1 hour to about 3 hours.

9. The method of claim 8 further comprises contacting the partially alicyclic polyimide membrane compound with ortho-dichlorobenzene for about 4 hours to 14 hours.

10. The method of claim 1 , wherein the partially alicyclic polyimide membrane compound has a purity of 99% as measured by ¹H-NMR.

1 1. The method of claim 1 , wherein the partially alicyclic polyimide membrane compound is non-fluorinated.

12. A method comprising: contacting a compound of the formula: where:

R is at least one of a (-) single bond, any combination thereof, with an aromatic diamine compound to form a polyimide membrane compound of the formula: n is greater than 50; and applying the polyimide membrane compound to a gas separation process, wherein the polyimide membrane compound is configured to separate at least one of H2/N2, H2/CH4, O2/N2, CO2/N2, CO2/CH4, H2/CO2, N2/CH4, CO2/N2, or any combination thereof.

13. The method of claim 12, wherein the aromatic diamine compound comprises 1 ,5-diaminonaphthalene.

14. The method of claim 12, wherein the contacting forms the polyimide membrane compound of the formula: where: n is greater than 50.

15. The method of claim 12, wherein the contacting forms the polyimide membrane compound of the formula: where: n is greater than 50.

16. The method of claim 12, wherein the contacting proceeds in a presence of 1 - Methyl-2-pyrrolidinone (NMP) for a time period of about 4 hours to 8 hours at room temperature to obtain a polyamic acid solution (PAA).

17. The method of claim 16, wherein after contacting, the method comprises casting the polyamic acid solution on a glass plate, wherein the polyamic acid solution forms a PAA film.

18. The method of claim 17, further comprises heating the PAA film to a temperature range of about 10 °C to 500 °C, wherein a temperature is held for 15 minutes at 10 °C, 180 °C, 210 °C, 250 °C, 350 °C, and 400 °C.

19. The method of claim 12, wherein the polyimide membrane compound is an aromatic polyimide.

20. The method of claim 12, wherein the contacting proceeds under solid-state thermal imidization.