The present disclosure is directed to polymers for gas separation membranes. More specifically, the polymers include polymers based on a halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) for use in gas purification technologies.
Natural gas supplies 22% of the energy used worldwide, and makes up nearly a quarter of electricity generation. Further, natural gas is an important feedstock for the petrochemicals industry. According to the International Energy Agency (IEA), the worldwide consumption of natural gas is projected to increase from 120 trillion cubic feet (Tcf) in the year 2012 to 203 Tcf by the year 2040.
Raw, or unprocessed, natural gas is formed primarily of methane (CH4), however it may include significant amounts of other components, including acid gases (carbon dioxide (CO2) and hydrogen sulfide (H2S)), nitrogen, helium, water, mercaptans, and heavy hydrocarbons (C3+), among other components. These contaminants must be removed during gas processing in order to meet the standard pipeline specifications of sales gas. In particular, the removal of acid gases (CO2 and H2S) has been a significant research topic due to the problematic effects of acid gases on natural gas heating value, pipeline transportability, and pipeline corrosion in the presence of water.
Currently, the majority of gas processing plants remove CO2 and H2S from natural gas by absorption technology, such as amine adsorption. However, several drawbacks are associated with this technology, including energy usage, capital cost, maintenance requirements, and the like.
Embodiments described in examples herein provide a gas separation membrane including a polyimide polymer including a monomer having a structure including:
wherein when X1=X2, X1 and X2 are selected from F, Cl, Br, or I and wherein when X1 and X2 are different elements, X1 and X2 are independently selected from H, F, Cl, Br, or I.
Another embodiment described in examples herein provides a method for forming a gas separation membrane. The method includes obtaining a halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer and obtaining an dianhydride monomer. The halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer is reacted with the dianhydride monomer to form a polymer. The polymer is dissolved in a solvent to form a polymer solution. A film is formed from the polymer solution. The film is dried to form the gas separation membrane.
As separation technologies advance, the use of gas separation technologies based on polymeric membranes has been increasingly explored due to the potential for increased energy efficiency over current technologies, a small footprint, and a low capital cost. Although current membrane technologies do not outperform absorption systems, hybrid systems using absorption and membranes have proved to be a potentially attractive alternative. For membrane systems, it is desirable to have polymeric membranes with improved separation performance.
Polymeric membranes are thin semipermeable barriers that selectively separate some gas compounds from others. Generally, polymeric membranes do not operate as a filter, where small molecules are separated from larger ones through a medium with pores, rather it separates based on how well different compounds dissolve into the membrane and diffuse through it, for example, using a solution-diffusion model.
New membrane polymers and methods for synthesizing the polymers and forming membranes from the polymers are provided in examples herein. The polymers are based on halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) moieties. The membranes formed from these polymers are intended to improve the performance of polymeric membranes for use in natural gas separation application. The materials will enhanced the productivity, efficiency, and resistance to plasticization of the membranes at elevated operational conditions of pressure and temperature, during sweet and/or sour mixed-gas separation. This will reduce the capital expenditures (CAPEX) and operating expenditures (OPEX) of the membrane-based natural gas purification process.
Numerous polymeric membranes for gas separation have been developed in the decades, but few are currently commercialized for use in sour gas separation applications. Examples of polymeric materials used to form gas separation membranes include cellulose acetate (CA), polyimides (PI), and perfluoropolymers, such as polytetrafluoroethylene (PTFE), perfluorocycloalkene (PFCA), and the like. These polymeric materials are generally semi-crystalline polymers having a Tg of greater than about 100° C.
One of the main characteristics used for selection of the polymeric materials is the chemical structure. Various classes of polymers have been studied for use in gas separation membranes, such as sour mixed-gas separation. Materials that have been tested include polyimides and polyoxadiazoles. A successful candidate will form membranes with high CO2 and H2S permeability coefficients and high to moderate CO2/CH4 and H2S/CH4 selectivity coefficients, while withstanding the harsh chemical, physical, and thermal conditions encountered during the purification of natural gas.
One way of improving the membrane performance is by tailoring the properties of the polymeric material forming the membrane by to increase the dynamic free volume of the membrane by adding bulky groups or a heteroatom with larger size than carbon atom. Tailoring may also be used to improve the gas-polymer affinity by increasing the polarity within the polymer backbone.
This methodology can be used to allow the polymeric material to deal with each type of gas molecule in a distinct manner. For example, the dynamic free volume within the membrane matrix can separate the gas molecules based on the difference of their sizes (i.e., kinetic diameters, Dk) according to a kinetic phenomenon (i.e., rate of diffusion), since methane (Dk=3.80 Å, the main component of natural gas) is larger in size than the undesired existent impurities in natural gas (i.e., Dk=3.30 Å for CO2 and Dk=3.60 Å for H2S). Further, improving the gas-polymer affinity increases the solubility of polar gas molecules, such as H2S, or molecules containing polar bonds, such as CO2, to improve the permeation through the membrane matrix, while not influencing the transport of methane.
Halogen atoms, such as fluorine (F, atomic radii=64 pm; electronegativity=3.98), chlorine (Cl, atomic radii=99 pm; electronegativity=3.16), bromine (Br, atomic radii=114 pm; electronegativity=2.96) and iodine (I, atomic radii=133 pm; electronegativity=2.66) are known for their increased polarity and most are larger than carbon atoms (C, atomic radii=77 pm; electronegativity=2.55), with the exception of fluorine, which is smaller in size than carbon, but with much higher electronegativity. Thus, adding halogen atoms to the polymer backbone leads to fine-tune the diffusivity and solubility of gas molecules by increasing the dynamic free volume within the membrane matrix and the gas-polymer affinity, respectively. The techniques described herein improve the sweet and sour mixed-gas separation properties of polymeric membranes and their resistance to plasticization at elevated feed pressures, by developing new halogen-substituted CARDO-based polyimides
The prepared halogen-substituted CARDO moieties are reacted with a variety of dianhydride moieties to form polymer, such as homopolyimides, as shown in
The copolymerization is a synthetic methodology that aims to combine the gas permeation properties of two separate homopolymers into a single copolymer. The second diamine comonomer is chosen to complement the properties provided by the halogen-substituted CARDO-based homopolyimide to either improve the permeability or selectivity of the copolyimide membrane.
As described herein, for natural gas purification, it is useful to improve the permeability of impurities [such as carbon dioxide (CO2) and hydrogen sulfide (H2S)] and the membrane selectivities (CO2/CH4 and H2S/CH4) toward the main hydrocarbon constituting the natural gas; methane (CH4). In another aspect, it is desired to increase the plasticization resistance of polymeric membranes during high-pressure mixed-gas separation. The halogen polar groups are intended to form a dipole-dipole type interaction between the polymeric chains, which limits their mobility under harsh separation conditions of temperature and pressure. This strategy has proven to improve the permeation properties and plasticization resistance of the polymeric membranes during mixed-gas separation at high feed pressure.
As described herein, the synthetic methodology allows the preparation of a large variety of new polymers, including but not limited to, homopolymers, random copolymers, block copolymers, terpolymers, and so on. The polymers formed are used to prepare polymeric membranes with improved sweet or sour mixed-gas separations properties for natural gas purification application. The term sour means that the gas stream contains hydrogen sulfide (H2S), where membranes are prone to plasticization due to the high affinity of H2S molecules to polymeric materials due to the polar nature of H2S molecules. The changes can be implemented at every stage of the preparation of the polymer.
Materials
All materials listed in this work were used as received. Aniline (ACS reagent, ≥99.5%), sodium sulfite anhydrous (purity 98.0%), and toluene (ACS reagent, 99.5%) were purchased from Sigma-Aldrich, USA. 4,4′-(hexa-fluoroisopropylidene)diphthalic anhydride (6FDA, purity 99.0%), and m-cresol (purity 99.0%) were acquired from Alfa Aesar. 2,3,5,6-tetramethylbenzene-1,4-diamine (Durene; purity 98.0%), and 2,7-dibromo-9H-fluoren-9-one (purity >98.0%) were obtained from TCI America. Methanol (purity 98.0%), ethyl acetate (reagent grade), and N,N-dimethylacetamide (DMAc, reagent grade) were purchased from Fisher Scientific. Sodium hydroxide (purity ≥98.0%), and 2-propanol (purity ≥99.9%) were acquired from Fluka.
Characterization Techniques
Proton Nuclear Magnetic Resonance Spectroscopy (1H-NMR) The 1H-NMR spectra of the prepared polymers and monomers were recorded using a JEOL 500 MHz NMR spectrometer in deuterated chloroform (CHCl3-d) or dimethyl sulfoxide (DMSO-d6) accordingly.
Fourier Transform Infra-Red Spectroscopy (FTIR)
The Fourier Transform Infrared (FTIR) spectra were recorded using a Thermo Scientific Nicolet iS50 spectrometer in transmission mode. Samples could be of the form of powder solid or membrane.
Thermogravimetric Analysis (TGA) and Glass Transition Temperature (Tg)
The thermogravimetric analysis (TGA) plots and the differential scanning calorimetry (DSC) traces were performed using a NETZSCH STA 449 F3 Jupiter®. The TGA plots were recorded at a temperature range from 30° C. to 650° C. with a heating rate of 10° C./min under a nitrogen atmosphere. The glass transition temperature (Tg) was determined from the DSC traces over two consecutive cycles. Each cycle consists of heating the sample at a temperature range between 30° C. and 450° C., using a heating rate of 10° C./min under a nitrogen flow. The first run is aimed to clear the thermal history of the sample, and the Tg values were determined after the second cycle.
Syntheses of Monomers and Polymers
The reaction mixture was cooled down to 90° C., and the purple solid was treated with 10% sodium hydroxide until the pH was 14 then cooled down to 70° C. The stirring continued for 0.5 hour, then ethyl acetate was added and the organic layer was separated and washed with saturated sodium chloride, dried over MgSO4, filtered and evaporate to give the crude product as a purple solid. To purify the product, 50 mL of toluene and 5 mL of isopropanol are added for every 1 g of the crude product, and heat to reflux until the crude product is completely dissolved, then after cooling to 20° C., crystals form in the flask. After filtration, the solid phase was collected, and the solid phase was vacuum dried at 70° C. for 6 hours to afford the pure product 4,4′-(2,7-dibromo-9H-fluorene-9,9-diyl)dianiline (6.89 g, 13.61 mmol, 92% yield) as white solid. H NMR (500 MHz, DMSO-d6) δ 7.85 (d, J=8.1 Hz, 2H), 7.60-7.51 (dd, J1=8.5 Hz, J2=1.5 Hz, 2H), 7.42 (d, J=1.9 Hz, 2H), 6.73 (d, J=8.5 Hz, 4H), 6.44 (d, J=8.5 Hz, 4H), 5.01 (s, 4H).
The procedure of Example 3 was repeated using 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.676 g, 1.522 mmol) (6FDA), 2,3,5,6-tetramethylbenzene-1,4-diamine (0.250 g, 1.522 mmol) (Durene), m-cresol (8.00 ml), then 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.338 g, 0.761 mmol) (6FDA), and 4,4′-(2,7-dibromo-9H-fluorene-9,9-diyl)dianiline (0.385 g, 0.761 mmol) [CARDO(Br)], followed by m-cresol (8.00 ml) to afford 6FDA-Durene/6FDA-CARDO(Br) (2:1) (2.263 g, 1.492 mmol, 98% yield) as a white off powder. 1H NMR (500 MHz, DMSO-d6) δ 8.23-7.88 (m, 18H), 7.78 (s, 2H), 7.74 (s, 2H), 7.65 (d, J=7.4 Hz, 2H), 7.43 (d, J=7.5 Hz, 4H), 7.34 (d, J=7.0 Hz, 4H), 2.09 (s, 24H).
The procedure of Example 3 was repeated using 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.676 g, 1.522 mmol) (6FDA), 2,3,5,6-tetramethylbenzene-1,4-diamine (0.250 g, 1.522 mmol) (Durene) in m-cresol (4.6 ml), then 5,5′-(perfluoropropane-2,2-diyl)bis(isobenzofuran-1,3-dione) (0.225 g, 0.507 mmol) (6FDA), and 4,4′-(2,7-dibromo-9H-fluorene-9,9-diyl)dianiline (0.257 g, 0.507 mmol) [CARDO(Br)], followed by m-cresol (4.60 ml) to afford 6FDA-Durene/6FDA-CARDO(Br) (3:1) (2.263 g, 1.492 mmol, 98% yield) as a white off powder. 1H NMR (500 MHz, Chloroform-d) δ 8.12-7.81 (m, 24H), 7.62 (d, J=8.0 Hz, 2H), 7.57-7.48 (m, 4H), 7.35 (q, J=7.8 Hz, 8H), 2.14 (s, 36H).
Chemical Characterization
The various chemical structures of the compounds prepared in this disclosure were confirmed using 1H NMR in deuterated solvents. Examples of the spectra for these compounds are illustrated below. Further confirmation was provided by the results from FTIR analysis.
The FTIR spectra can also be used to qualitatively determine the molecular ratio of comonomers within the copolymer backbone. For example, the peak at 1511 cm−1 is attributed to the aromatic carbon-hydrogen bond (sp2 C—H) bending that mainly belongs to those of CARDO(Br) monomer, as can be seen from the FTIR spectrum of 6FDA-CARDO(Br) illustrated in
Thermal Properties
Density and Fractional Free Volume
The fractional free volume (FFV) values of membranes prepared from the studied polymers were calculated using the following equation:
where V is the specific volume and V0 is the occupied volume by the polymer. Note that V is the reciprocal of the polymer density and can be determined experimentally. The densities of the prepared polymers were measured using a Mettler Toledo XPE205 balance equipped with a density kit using cyclohexane (d=0.777 g/cm3) as the buoyant liquid at 20° C. The density values reported in Table 2 are the average values of at least five different measurements, with error values (standard deviation) below 5%. The occupied volume (V0) values were calculated from the van der Waals volumes (Vw) using Bondi's equation:
V
0=1.3×Vw (2)
The van der Waals volumes of copolymers were calculated from the individual Vw of the constituent homopolymers taking into consideration their different molar ratios in the copolymer backbone using the following equation:
V
w
=X
1
V
w
+X
2
V
w
, (3)
where X1 and X2 are the molar ratios, and Vw
For the durene:CARDO(Br) block copolymer series, the FFV increased with the increase of the molar ratio of durene in the copolymer backbone. For example, the FFV increased from 0.1855 for a durene:CARDO(Br) ratio of 1:1, to 0.2032 for a durene:CARDO(Br) ratio of 3:1. These results correlate to the gas permeation results in the next section.
Membrane Performance Test
Membrane Fabrication
The polymeric membranes were prepared using a solution casting method. Solutions with concentration of 3 wt. % polymer in N,N-dimethylformamide (DMF) were prepared. Then, 11 mL of the solution were filtered through a 0.45 μm PTFE filter to remove any possible solid impurities and poured into a leveled 5.5 cm diameter flat glass Petri dish. The casting dish was placed in a preheated oven at 85° C., under a gentle flow of nitrogen to allow a slow evaporation of the solvent. After 24 hours, the obtained membrane was further dried at 200° C. under vacuum for another 24 hours. The membrane was peeled off from the Petri dish by soaking in deionized water for a few minutes before peeling from the Petri dish. The membranes were then dried at 60° C. under vacuum for 6 hours. The thickness of the prepared membranes was determined to be in the range of 60-120 μm. For an individual membrane, the standard deviation of thickness uniformity was less than 3%. The formed membrane was cut using a 4 cm diameter cutter, to fit into the membrane cell of the gas permeation testing system.
Permeation Measurements
A mass flow meter 1914 measures the amount of permeate exiting the chamber 1908. A sample collector 1916 can be used to collect samples of permeate or retentate for analysis. A pressure transducer 1918 is used to measure the pressure of gas in the sample collector 1916. A carrier gas cylinder 1920 provides a carrier gas, such as helium, for a gas chromatograph 1922. The flow rate of the carrier gas is set by a needle valve 1923. After collection of a gas sample in the sample collector 1916, other valves are closed, and an actuated valve 1924 is opened to sweep the sample to the gas chromatograph 1922. A vacuum pump 1926 is used to pull a vacuum on the system before and between test runs.
Pure-Gas Permeation Measurement
The pure-gas permeation properties of the prepared polymeric membranes were measured using an in-house built constant volume/variable pressure permeation system. The membrane was placed in the permeation cell and subjected to a selected gas feed (i.e., He, N2, CH4 and CO2) for a specific time, to reach a permeation steady-state at a constant feed pressure of 100 psi and a temperature 22° C. The permeability coefficients (P) were calculated from the slope
the steady state (ss) of the permeate pressure (pp) versus time curve using the following equation:
where, Vd is the permeate tube volume (cm3), I is the membrane thickness (cm), pf is the gas feed pressure (cmHg), A is the membrane effective surface area (cm2), R is the universal gas constant (R=0.278 cm3·cmHg/cm3(STP)·K), T is the operational temperature (K),
is the steady-state pressure variation in the permeate tube (cmHg), and
is the leak rate of the system, which is usually very small and may be neglected. The permeability coefficient is expressed in Barrer, where 1 Barrer=10−10 cm3(STP)·cm/cm2·s·cmHg.
The ideal selectivity coefficient for two selected gases A and B is calculated from the ratio of their corresponding permeabilities (PA and PB) using the following expression:
The diffusivity coefficients D (cm2/s) of the gas penetrants were calculated by the time-lag method using the following expression:
where θ(s) is the time-lag determined from the pure-gas permeability measurement, and l (cm) in the membrane thickness. The solubility coefficient S (cm3(STP)/cm3·cmHg·) can be then calculated from the permeability and diffusivity coefficients using the following equation:
Results of Permeation Tests
The pure-gas permeation properties of membranes prepared from the studied polymers were determined using the permeation system 1900 in a constant-volume mode. For this study, four different pure gases were used: He, N2, CH4, and CO2. The polymeric membranes permeability and selectivity coefficients were calculated from the steady state of the pressure versus time curve, using a constant feed pressure of 100 psi and an operating temperature of 22° C. The obtained results are listed in Table 3. The permeability coefficients are listed in Barrer, where 1 Barrer=10−10 cm3 (STP) cm/cm2·s·cmHg.
The pure-gas permeation properties of 6FDA-CARDO(Br) homopolyimide show a moderate CO2 permeability of 80 Barrer and a relatively high CO2/CH4 selectivity of 27.5. These results are considered attractive to use the 6FDA-CARDO(Br) as a selectivity-enhancing segment in future copolymers. By comparing the gas permeation properties of 6FDA-CARDO(Br) to that of 6FDA-CARDO, we observe that the CO2 permeability increased by ˜35% in the case of 6FDA-CARDO(Br), while the CO2/CH4 selectivity dropped by only ˜9% due to the known permeability-selectivity trade-off for glassy polymers. These results demonstrate the benefit of adding halogen atoms to the 2 and 7 positions of the fluorenyl group of the CARDO moiety.
Further improvements can be gained by copolymerization. For example, copolymerization can be used employed to improve the mechanical properties of membranes, and their gas permeation properties, through the selection of comonomers that possess desired properties. Durene (2,3,5,6-tetramethylbenzene-1,4-diamine) and DAM (2,4,6-trimethylbenzene-1,3-diamine) are two potential comonomers known for forming membranes with good mechanical and gas permeation properties. Thus, a series of copolyimides containing durene:CARDO(Br) with various molar ratios 1:1, 2:1, and 3:1, and a DAM:CARDO(Br) molar ratio of 3:1 were prepared. These copolyimides formed mechanically stabled membranes and their pure-gas permeation properties were measured and listed in Table 3.
The pure-gas permeation studies for the durene:CARDO(Br) pair showed an increase in the pure CO2-permeability coefficients with an increasing molar ratio of the durene within the copolymer backbone. An increase in the FFV of the polymeric membrane matrix was also seen, as shown in the data of Table 2. For example, the pure CO2-permeability increased from 231 Barrer for a 1:1 molar ratio (FFV=0.1855) to 341 Barrer for a 2:1 molar ratio (FFV=0.1903), and 431 Barrer for a 3:1 molar ratio (FFV=0.2032).
In general, membranes prepared from glassy polymers suffer from permeability-selectivity trade-off, as shown in
In another example, replacing durene by DAM, with a DAM:CARDO(Br) equals to 3:1 to form the 6FDA-DAM/6FDA-CARDO(Br) (3:1) block copolyimide, afforded a membrane with slightly lower performance than the equivalent 6FDA-Durene/6FDA-CARDO(Br) (3:1). The pure CO2-permeability decreased to 378 Barrer with a similar CO2/CH4 selectivity of 20.5.
To better understand the separation process of the prepared membranes, the CO2 and CH4 diffusivity coefficients (in cm2/s) were measured using the time-lag method. The obtained results are listed in Table 4.
As shown, the diffusivity coefficients for both CO2 and CH4 for the series of durene:CARDO(Br) copolyimides showed an increase with an increase in the molar ratio of durene within the copolymers backbones. Since the permeability coefficient (P) is calculated from the product of diffusivity (D) and solubility (S) coefficients, the solubility coefficients of the prepared polymers were calculated using equation (7). The obtained solubility coefficients [in cm3(STP)/cm3·cmHg] are listed in Table 5.
The solubility coefficients for both CO2 and CH4 for the series of Durene:CARDO(Br) copolyimides showed an increase with an increase the molar ratio of Durene from 1:1 to 2:1 within the backbone of the copolymers. No further changes were seen when the molar ratio was increased to 3:1.
The CO2/CH4 diffusivity and solubility selectivity coefficients were calculated and the results are listed in Table 4 and Table 5, respectively. The CO2/CH4 diffusivity selectivity coefficients of the Durene:CARDO(Br) copolyimides were in the range of 1.53-1.97, while the CO2/CH4 selectivity coefficients were around 12, indicating that the separation through these polymeric membranes is solubility driven, which is in-line with the incorporation of the polar halogen group (i.e., bromine).
Mixed-Gas Permeation Measurement
Since natural gas is a mixture of different gases, it is desirable to measure the mixed-gas separation performance of the polymeric membranes. The permeation of gases through glassy polyimide membranes is affected by the presence of other gases in the flow. It is known that a small partial pressure of a condensable species such as CO2 in the feed gas can significantly reduce the permeability of a gas relative to its permeability individually. Therefore, the competition for Langmuir sorption sites for non-plasticized polymers will lead to a decrease of all penetrants permeabilities. Moreover, the selectivity coefficients may also decrease because of bulk flow and the change on the dynamic free volume (plasticization). Therefore, the permeability of a gas i in the mixed gas permeation process is given by:
Ptotal is derived from the permeability expression for mixed gas:
The selectivity coefficient (α*ij), which is the ability of a polymeric membrane to separate a binary feed gas mixture, is defined as follows:
where yi and yj are the mole fractions of gases i and j at the permeate side, and xi and xj are the mole fractions of gases i and j at the feed side.
To reflect the real properties of the membrane in the case of a non-ideal gas mixture, the modified expression of the selectivity (αi/jm,*) is represented by,
where P*i and P*j are the mixed gas permeability coefficients of components i and j determined by the fugacity driving force definition.
The mixed-gas separation performance of the prepared polymers were measured using a sweet gas mixture containing 10, 59, 30 and 1 vol. % of CO2, CH4, N2 and C2H6, respectively. The permeation measurements were recorded at different feed pressures (300-900 psi) with an increment of 200 psi at a fixed temperature of 22° C. The results obtained are listed in Table 6.
As a result of the decrease on the mixed-gas CO2 permeability coefficients with slight changes in mixed-gas CH4 permeability coefficients, the CO2/CH4 selectivity coefficients decreased when the pressure increased from 300 to 900 psi for all copolyimides, as shown in
Further, membranes prepared from 6FDA-DAM/6FDA-CARDO(Br) (3:1) were studied in a similar fashion to that of Durene/CARDO(Br) series using the same gas mixture composition and same testing conditions of pressure and temperature. The obtained data are listed in Table 6.
Embodiments described in examples herein provide a gas separation membrane including a polyimide polymer including a monomer having a structure including:
wherein when X1=X2, X1 and X2 are selected from F, Cl, Br, or I and wherein when X1 and X2 are different elements, X1 and X2 are independently selected from H, F, Cl, Br, or I.
In aspect the gas separation membrane includes a homopolymer of the structure:
wherein Ar1 includes an aromatic moiety or a bridging moiety.
In an aspect, the gas separation membrane includes a copolymer of the structure:
wherein Ar1 and Ar2 independently include aromatic moieties, bridging moieties, or both, and the ratio of n to m is between 3:1 and 1:3.
In an aspect, the gas separation membrane includes a random copolymer.
In an aspect, the gas separation membrane includes a block copolymer.
In an aspect, the gas separation membrane includes an oligomer of the structure:
wherein Ar1 includes an aromatic moiety or a bridging moiety.
In an aspect, the gas separation membrane includes a homopolymer of the structure:
In an aspect, the gas separation membrane includes a copolymer of the structure:
where the ratio between 1 and m is between 1:3 and 3:1.
In an aspect, the gas separation membrane includes a random copolymer.
In an aspect, the gas separation membrane includes a block copolymer.
In an aspect, the gas separation membrane includes a monomer of the structure:
wherein Ar4 includes an aromatic moiety or a bridging moiety
In an aspect, the gas separation membrane includes a monomer of the structure:
In an aspect, the gas separation membrane includes a monomer of the structure:
In an aspect, the gas separation membrane includes a monomer with the structure:
In an aspect, the gas separation membrane includes an oligomer with the structure:
Another embodiment described in examples herein provides a method for forming a gas separation membrane. The method includes obtaining a halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer and obtaining an dianhydride monomer. The halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer is reacted with the dianhydride monomer to form a polymer. The polymer is dissolved in a solvent to form a polymer solution. A film is formed from the polymer solution. The film is dried to form the gas separation membrane.
In an aspect, the halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer is formed by the reaction scheme:
wherein when X1=X2, X1 and X2 are selected from F, Cl, Br, or I and wherein when X1 and X2 are different elements, X1 and X2 are independently selected from H, F, Cl, Br, or I.
In an aspect, the halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer includes:
In an aspect, the halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer includes:
or any combinations thereof.
In an aspect, the halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer includes:
or any combinations thereof.
In an aspect, the dianhydride monomer includes:
or any combinations thereof,
In an aspect, the polymer is formed by heating the halogen-substituted 9,9-bis(4-aminophenyl)fluorene (CARDO) monomer, the dianhydride monomer, and an aromatic diamine.
In an aspect, the aromatic diamine comprises
or any combinations thereof.
Other implementations are also within the scope of the following claims.