RU2803726C2 - Method for obtaining gas separation membranes for hydrogen-containing mixtures based on surface fluorined polybenzodioxane - Google Patents

Abstract

FIELD: gas separation membranes.

SUBSTANCE: invention is related to the field of creating gas separation polymer membranes intended for separation of hydrogen from gas mixtures containing carbon dioxide, methane, and nitrogen. A method for producing gas separation membranes for hydrogen-containing mixtures based on a surface fluorinated polybenzodioxane polymer with internal microporosity PIM-1 consists of synthesis of a PIM-1 polymer based on polybenzodioxane in a reaction medium of dimethyl sulfoxide, with a mass average molecular weight Mw=75000 Da and a number average molecular weight Mn=25000 Da, obtaining a solution of the PIM-1 polymer in chloroform with a concentration of 5% at room temperature, pouring this solution onto the substrate, evaporating the solvent by keeping it under vacuum to constant weight, separating the resulting membrane from the substrate, surface fluoridation of the membrane on one side with elemental fluorine in a preliminarily perfluorodecalin saturated with fluorine, while perfluorodecalin is saturated with fluorine by bubbling it with a mixture of gases consisting of 10% fluorine and 90% nitrogen with a mixture flow rate of 0.5 ml/sec.

EFFECT: expanding the arsenal of methods for producing gas separation membranes from surface fluorinated polybenzodioxane, which have high selectivity and permeability parameters with a simple and economical method for their production.

1 cl, 5 dwg, 6 tbl, 13 ex

Description

The invention relates to the field of creating gas separation polymer membranes intended for the separation of hydrogen from gas mixtures containing carbon dioxide, methane, and nitrogen.

Hydrogen is currently used as a reagent in various chemical and technological processes and, as an environmentally friendly fuel, can be used as an energy source in internal combustion engines, fuel cells and other devices [1]. The transition of modern industry to environmentally friendly hydrogen energy poses the challenge of developing cost-effective processes for separating hydrogen from industrial gas streams. Hydrogen-containing gas mixtures in industry are obtained in petrochemical processes from synthesis gas (steam reforming of methane, gasification of coal, cellulose, polymer waste, pulp and paper and waste processing industries, etc. with an additional stage of carbon monoxide conversion by water gas reaction), methane pyrolysis and other hydrocarbons, as well as from biogas of hydrogen-synthesizing bacteria. Industrial gas mixtures, as a rule, require the purification of hydrogen from accompanying gases, such as carbon dioxide, carbon monoxide, methane, nitrogen, etc. To separate these mixtures, cryogenic, adsorption, absorption methods can be used, however, membrane methods for separating gases are of greatest interest mixtures due to their advantages: compactness, modularity of production, low energy consumption. The key element of the membrane installation is a membrane module with a selective layer, for which it is most advisable to use membranes based on polymer materials that have the best ratios of selectivity and permeability for hydrogen-containing gas vapors (H ₂ -CO ₂ , H ₂ -CH ₄ , H ₂ - CO, H ₂ -N ₂ ). These include polymers that form upper boundaries on the corresponding Robson diagrams (dependences of selectivity for a gas pair on the permeability coefficient of a more permeable gas in logarithmic coordinates) [2]. Among the polymers of various classes that determine the upper limits for gas pairs H ₂ -CO ₂ , H ₂ -CH ₄ and H ₂ -N ₂ , fluorinated and perfluorinated polymers, as well as polybenzodioxane (PIM-1), are often found. Thus, for a pair of gases O ₂ -N ₂ out of 11 polymers that determine the upper limit, 1 fluorine-containing and PIM-1, for a pair of gases CO ₂ -CH ₄ out of 16 polymers that determine the upper limit, 6 fluorine-containing and PIM-1, for a pair He-CH gases ₄ out of 11, defining the upper limit of polymers, 3 fluorinated and 6 perfluorinated, for a pair of N ₂ -CH gases ₄ out of 19, defining the upper limit of polymers, 2 fluorinated and 11 perfluorinated, for a He-CO pair ₂ out of 12, defining the upper limit of polymers, 2 fluorinated and 8 perfluorinated, and for the He-H pair, ₂ out of 12 defining the upper limit of polymers, 1 fluorinated and 11 perfluorinated [3]. Thus, the introduction of fluorine into the polymer structure is an important design element leading to an improved combination of permeability and selectivity. However, as a rule, fluorine-containing polymers are not industrial. The exceptions are perfluorinated polymers of the brands Nafion, Cytop, Hyflon AD and Teflon AF, but the multi-stage nature of their synthesis and the high cost of monomers lead to the high cost of polymers. To introduce fluorine into the structure of polymers, chemical modification of the near-surface layer of the polymer membrane through direct fluorination is often used. The use of gas-phase fluorination [4] is associated with a number of disadvantages: high heat generation, which often leads to destruction of the polymer and poor controllability of the process depending on the fluorine concentration and fluorination time [5], deterioration of the gas separation characteristics of membranes over time [6], for highly permeable polymers associated with fast processes physical aging [7,8]. To eliminate these shortcomings, Pashkevich D.S. et al. in [9] proposed a method for liquid-phase fluorination of 1,1,1,2-tetrafluoroethane and methane in a perfluorinated liquid – perfluorodecalin. In [10-13], attractive gas transport parameters were obtained for a number of industrially produced polymers. However, the most significant effects were previously observed during gas-phase fluorination of highly permeable polytrimethylsilylpropine [14], the data for which are located near the upper boundaries of the Robson diagrams [15].

The closest to the proposed solution in terms of the set of essential features and the achieved result (prototype) is the gas separation membrane and the method for its production described in [16]. The polybenzodioxane polymer PIM-1 was synthesized according to a method known from [17], in which 5,5 ⁰ ,6,6 ⁰ -tetrahydroxy-3,3,3 ⁰ ,3 ⁰ -tetramethyl-1,1 ⁰ -spirobisindan (3, 40 g, 10.0 mmol) and 2,3,5,6-tetrafluoroterephthalonitrile (2.00 g, 10.0 mmol) were added to a 100 ml three-neck round bottom flask, previously purged with argon, then N was also added, N ⁰ - dimethylacetamide (18.0 ml) and stirred until a clear solution formed. The solution was then heated in an oil bath at 150 °C, after which potassium carbonate powder K ₂ CO ₃ (3.50 g, 25.4 mmol) was added in portions over 5 min. The solution became viscous and a light yellow suspension formed. Three portions of toluene (2 ml each) were then added after 10 min and the whole was stirred for an additional 15 min. The viscous polymer was poured into methanol (200 ml), after which a yellow precipitate formed. The precipitate was redissolved in chloroform and precipitated with methanol twice, and then dried in a vacuum oven at 120 °C for 12 h. The result was the polymer PIM-1 with a yield of 96%. M _n = 34·10 ⁴ Yes; PDI =2.22. Membranes were formed from the resulting PIM-1 powder. For this purpose, PIM-1 powder was dissolved in chloroform with a concentration of 2–3 wt. %, after which the solution was filtered through a 0.45 mm hydrophobic PTFE filter into a flat Petri dish. The solvent was then slowly evaporated over two days at room temperature. As a result, transparent yellow isotropic films were obtained. Fresh membranes were prepared by incubating in methanol for 12 h and then dried in a vacuum oven at 120°C for 12 h. The membranes were then fluorinated in a 50 mL chemical reactor immersed in a water bath (25°C). The gas in the reactor was first pumped out with a vacuum pump and then filled with a fluorine nitrogen mixture F ₂ /N ₂ (5/95) at a rate of 200 ml/min to a pressure of 4 bar. To obtain different degrees of fluorination, PIM-1 films were kept in the reactor for different times (1, 5, 10, 30 min). Fluorinated PIM-1 membranes turned out to be insoluble in common solvents.

The resulting membranes had good gas separation properties for helium gas mixtures, but were not effective enough for hydrogen-containing gas mixtures. Also, a significant disadvantage of gas-phase fluorination used in the prototype is the large exothermic effect, which can transform the reaction into combustion or explosion mode. To prevent this effect, direct gas-phase fluorination is carried out at low temperatures and with strong dilution of fluorine with an inert gas (helium, nitrogen, argon).

To eliminate the above disadvantages, the task was set to create a safe technology for producing a fluorinated polymer membrane for separating multicomponent hydrogen-containing gas mixtures.

The technical result of the claimed invention is to expand the arsenal of methods for producing gas separation membranes from surface fluorinated polybenzodioxane, which have high selectivity and permeability parameters with a simple and cost-effective method for their production.

The technical result is achieved by the fact that in the proposed method for producing gas separation membranes for hydrogen-containing mixtures, the PIM-1 polymer based on polybenzodioxane is synthesized in the reaction medium of dimethyl sulfoxide, with a mass average molecular weight Mw = 75,000 Da and a number average molecular weight Mn = 25,000 Da, obtaining a solution of PIM-1 polymer in chloroform with a concentration of 5% at room temperature, pouring this solution onto the substrate, evaporating the solvent by keeping it under vacuum to constant weight, separating the resulting membrane from the substrate, surface fluoridation of the membrane on one side with elemental fluorine in an environment of perfluorodecalin pre-saturated with fluorine , while perfluorodecalin is saturated with fluorine by bubbling it with a mixture of gases consisting of 10% fluorine and 90% nitrogen with a mixture flow rate of 0.5 ml/sec.

Carrying out fluorination of PIM-1 films in the environment of perfluorodecalin (perfluorinated liquid with a boiling point of 142 ° C) allows you to effectively remove the heat released during the reaction process, and thereby makes it possible to carry out direct fluorination at room and elevated temperatures, expands the range of variation of fluorine concentration in the fluorinating agent mixture and fluoridation time.

The invention is illustrated by the following drawings.

Fig. 1 - Schematic diagram of the Barotron barometric installation for individual gases. In the figure the numbers indicate: 1,4,6,7,8,11 - valves; 2.10 - pressure sensors; 3.9 - containers with calibrated volumes; 5 - membrane cell; 12,13 - air thermostat with related elements; 14 - vacuum system.

Fig. 2 – Schematic diagram of a barometric installation for gas mixtures.

In the figure the numbers indicate: 15 - gas preparation unit; 16 - helium cylinder; 17- tee; 18.28 - 6-way valve; 19 - membrane cell; 20.31 - detector; 21,22,23 - pressure sensors; 24 - fine adjustment valve; 25 – 4-way valve; 26,27 – chromatograms; 29 – comparison column; 30 – working column.

Fig. 3 - Robson diagram for a pair of gases H ₂ /CH ₄ . Data are presented for samples PIM-1 (control) subjected to surface fluorination for 15 min (F-1, F-2), 30 min (F-3, F-4), 45 min (F-5, F-6 ), 60 min (F-7, F-8). The filled symbol corresponds to the original PIM-1 polymer; half-filled symbols correspond to ideal selectivity and permeability data for individual gases; open symbols correspond to separation factor and permeability data for mixtures of gases. The crossed out symbols correspond to literature data [16] for PIM-1 films with different fluorination times (FPIM-1 – 1 min, FPIM-5 – 5 min, FPIM-10 – 10 min, FPIM-30 – 30 min).

Fig. 4 - Robson diagram for a pair of gases H ₂ /CO ₂ . Data are presented for samples PIM-1 (control) subjected to surface fluorination for 15 min (F-1, F-2), 30 min (F-3, F-4), 45 min (F-5, F-6 ), 60 min (F-7, F-8). The filled symbol corresponds to the original PIM-1 polymer; half-filled symbols correspond to ideal selectivity and permeability data for individual gases; open symbols correspond to separation factor and permeability data for mixtures of gases. The crossed out symbols correspond to literature data [16] for PIM-1 films with different fluorination times (FPIM-1 – 1 min, FPIM-5 – 5 min, FPIM-10 – 10 min, FPIM-30 – 30 min).

Figure 5 - Robson diagram for a pair of gases H ₂ /N ₂ . Data are presented for PIM-1 (control) samples subjected to surface fluorination for 15 min (F-1, F-2), 30 min (F-3, F-4), 45 min (F-5, F-6 ), 60 min (F-7, F-8). The filled symbol corresponds to the original PIM-1 polymer; half-filled symbols correspond to ideal selectivity and permeability data for individual gases; open symbols correspond to separation factor and permeability data for mixtures of gases. The crossed out symbols correspond to literature data [16] for PIM-1 films with different fluorination times (FPIM-1 – 1 min, FPIM-5 – 5 min, FPIM-10 – 10 min, FPIM-30 – 30 min).

The inventive method was carried out as follows.

To obtain a polybenzodioxane polymer with internal microporosity, 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindan (TTSBI, 97%) from TCI Europe NV was used. (Belgium) and 2,3,5,6-tetrafluoroterephthalonitrile (TFTN, 99%) from P&M (Russia), K ₂ CO ₃ (Akrus, >99.5%) which was pre-dried at 160°C, as well as dimethyl sulfoxide (DMSO, 99%), tetrahydrofuran (THF, ≥99.0%), methanol (≥99.0%) and chloroform (99.0%) from Sigma-Aldrich, which were used without preliminary purification.

We took 1.0210 g (3 mmol) TTSBI, 0.6003 g (3 mmol) TPTPH, 1.6000 g (12 mmol) _K2CO3 , 8 ml _DMSO and 2 ml toluene, which were loaded into the flask in a flow of argon at room temperature. Then the flask with the reaction mixture, while stirring with a conventional stirrer, was placed in an ultrasonic bath (“Elmasonic S10H”) preheated to 60–80°C with constant ultrasonic treatment (37 kHz) for 5 hours. After this time, 30 ml was added to the reaction mixture deionized water and heating continued for another 30 minutes with simultaneous ultrasonic treatment to transfer all inorganic salts into solution. The very fine yellow polymer powder PIM-1 was isolated by filtration on a Schott filter. Residues of inorganic salts and DMSO were removed by subsequent extraction of PIM-1 powder in a Soxhlet apparatus with an equal-volume ethanol–water mixture. After vacuum drying, the yield of PIM-1 was almost quantitative and amounted to 99%.

The polymer was further purified from the low molecular weight part by reprecipitation from a 5% solution in chloroform into a volume of THF equal to the volume of chloroform. After reprecipitation, the polymer yield was 96%, weight-average molecular weight M _w = 75,000 Da, number-average molecular weight M _n = 25,000 Da.

Homogeneous films with a thickness of 100-200 μm were prepared from the polybenzodioxane obtained in the described manner. To do this, a 5% solution of the PIM-1 polymer in distilled chloroform at room temperature was poured onto a cellophane film, the film was removed from the substrate, and then kept under vacuum to constant weight to evaporate the solvent.

A film of polybenzodioxane PIM-1 for comparison (control sample) was prepared in a reactor for surface fluorination without the use of a fluorinating mixture of gases. A PIM-1 film was installed in the membrane holder, and the holder was secured in a fluoroplastic glass (hereinafter referred to as the reactor), which already contained perfluorodecalin (PFD). The PPD was stirred for 30 minutes using a magnetic stirrer. Thus, the surface layer of the PIM-1 film was saturated with PPD. After 30 minutes, the membrane holder was removed from the beaker and the PIM-1 film was taken out. The remaining FPD on the surface of the film was carefully shaken off, and then the PIM-1 film was placed between two filter paper disks,

Surface fluoridation of PIM-1 was carried out according to the following procedure. A mixture of gases was bubbled through a fluoroplastic beaker filled with PPD for 60 minutes: 10% fluorine and 90% nitrogen at a mixture flow rate of 0.5 ml/sec. This flow rate was determined using a flow meter. Turn on the magnetic stirrer. After a specified time, the supply of the gas mixture was closed. Next, we proceeded to treat the membranes in FPD saturated with fluorine. The PIM-1 sample was placed in a holder and installed in a reactor with an FPD in such a way that surface liquid-phase fluorination occurred on one side. The supply of the fluorine-nitrogen mixture to the reactor was turned on and the magnetic stirrer was simultaneously put into operation. The gas flow rate was 0.5 ml/sec. After 15 minutes of treatment, the gas supply was closed and the magnetic stirrer was turned off. The PIM-1 sample was removed from the reactor and dried using filter paper. Next, this experiment on surface fluoridation of PIM-1 with a fluorine-nitrogen mixture was carried out for 30, 45, 60 minutes. A total of 8 PIM-1 films were fluorinated; for each fluorination time, the experiment was carried out for two films. Next, all samples in plastic bags were placed in a desiccator and vacuumed for 15 minutes. The need for this procedure was due to the presence of excess PPD on the surface of the membranes.

Measurements of the gas separation properties of membranes for individual gases (hydrogen, nitrogen, carbon dioxide, methane) were carried out by the Deines-Barrera method [20] using the Barotron installation [21] (Fig. 1) with capacitive pressure sensors in the range from 1 to 3 atm at 22+ /-2ºС. Submembrane pressure did not exceed 12 mm Hg. (0.016 atm).

Measurements of the gas separation properties of membranes for gas mixtures were carried out on model gas mixtures at atmospheric pressure with the possibility of determining their concentration in the retentate and permeate flow in a gas separation unit [22] (Fig. 2) with chromatographic detection. Previously, calibration was carried out for individual gases on small volumes (0.5 - 32 µl) using a dosing device to determine the gas concentration in the permeate and on large volumes (125, 530, 1006 µl) to determine the gas concentration in the retentate. Chromatographic analysis was carried out at a detector temperature of 150 °C, a column temperature of 100 °C, a carrier gas (He) flow rate of 50 ml/min, a packed metal column length of 200 cm, an internal diameter of 3 mm, adsorbent - activated carbon, detector - DTP. To avoid an increase in the degree of hydrogen selection by more than 1%, the flow rate of the mixture was varied from 60 to 130 ml/min. The sample was introduced using a 6-way dosing tap; the volume of the loop (dose) was 1.006 ml.

The permeability coefficient of component A in the mixture was found using the formula:

,

Where

P _A – gas permeability coefficient [cm ³ (n.s.) cm/cm ² s cm Hg];

l – film thickness [cm];

∆ p – pressure difference between permeate and retentate [cm Hg];

T – cell temperature [K];

S – membrane surface area [cm ² ];

p _atm – atmospheric pressure [cm Hg];

ω _A – mole fraction of the componentA in permeate;

– permeate volumetric velocity [cm³/With];

1 Barrer = 10 ¹⁰ cm ³ (n.s.) cm/cm ² s cm Hg.

The separation factor SF was calculated as follows: ,

Where – the ratio of the concentrations of hydrogen and gas C _x (CO ₂ , N ₂ or CH ₄ ) in the permeate, – the ratio of their concentrations in the retentate.

Model gas mixtures were prepared in a cylinder. Mixtures of the following composition were obtained: H ₂ /CO ₂ (65/35), H ₂ /CH ₄ (36/64), H ₂ /N ₂ (60/40).

Examples of practical implementation of the method.

Example 1. Determination of permeability and ideal selectivity for a pair of gases H ₂ and CH ₄ .

A film of polybenzodioxane PIM-1 for comparison (control sample) was prepared in a reactor for surface fluorination without the use of a fluorinating mixture. Namely, the PIM-1 film was placed in perfluorodecalin and kept for 30 min. Then dried and vacuumed. Surface fluorinated films F-1 – F-8 were obtained according to the method described above; the fluorination times of the films are indicated in Table. 1.

The PIM-1 film was placed in the cell of the Barotron installation (Fig. 1) and the transport parameters of hydrogen and methane were measured by the Deines-Barrer method. The experimental temperature was 22±2°C. The measurement results are summarized in Table 1.

From Table 1 it can be seen that the selectivity or ideal separation factor α(H ₂ /CH ₄ ) = P (H ₂ )/ P (CH ₄ ) for films F-1, F-2 increased slightly as a result of fluorination from 15.1 to 19.7; F-3, F-4 increased as a result of fluoridation by 37 times from 15.1 to 568; F-5, F-6 increased as a result of fluoridation by 29 times from 15.1 to 433; F-7, F-8 increased as a result of fluoridation by 74 times from 15.1 to 1114.

As can be seen from Fig. 3 on the Robson diagram for the H ₂ /CH ₄ pair, points PIM-1, F-1, F-2 are located above the “upper limit” of 2008 in the region of highly permeable polymers; points F-3, F-4, F-5, F-8 are located above the “upper limit” of 2015, F-6, F-7 are located near the “upper limit” of 2015.

Table 1.

Sample t (min),
fluoridation duration l(µm), film thickness Р _H2 /P _СH4 , atm P _H2 , Barrer P _CH4 , Barrer α(H ₂ /CH ₄ ),
selectivity PIM-1 - 78.4±1.7 1.19/1.18 1779 118 15.1 F-1 15 87.0±1.1 1.13/1.15 1876 95 19.7 F-2 15 96.0±5.8 1.09/1.11 1773 99 17.9 F-3 thirty 89.1±4.9 1.11/1.09 1192 2.1 568 F-4 thirty 94.6±1.4 1.13/1.14 741 1.6 463 F-5 45 96.2±3.3 1.12/1.09 559 1.3 433 F-6 45 90.6±2.2 1.25/1.18 462 1.4 340 F-7 60 71.2±2.7 1.12/1.16 414 1.3 319 F-8 60 99.4±1.4 1.11/3.12 457 0.41 1115 FPIM-1[16] 1 - 1/1 500 0.82 610 FPIM-5[16] 5 - 1/1 326 0.20 1630 FPIM-10[16] 10 - 1/1 479 0.65 737 FPIM-30[16] thirty - 1/1 540 1.3 415

Example 2. Determination of permeability and ideal selectivity for gas vapor H₂ and CO₂. The gas permeability of fluorinated film membranes PIM-1 and F-1 – F-8 was determined using the installation shown in Figure 1. The experimental temperature was 22±2°C. The surface fluoridation technique is presented above. The measurement results are presented in Table 2.

From Table 2 it can be seen that the selectivity (or ideal separation factor) α(H ₂ /СO ₂ ) = P (H ₂ )/ P (СO ₂ ) increased slightly as a result of fluorination for F-1, F-2 from 0.76 to 1.02 ; F-3, F-4 increased as a result of fluoridation by an order of magnitude from 0.76 to 7.3; F-5, F-6 increased as a result of fluoridation by 14 times from 0.76 to 11; F-7, F-8 increased as a result of fluoridation by 22.4 times from 0.76 to 17.

As can be seen from Figure 4 on the Robson diagram for the H ₂ /CO ₂ pair, points PIM-1, F-1, F-2 are located in the general cloud of points in the region of highly permeable polymers; points F-3, F-4, F-5, F-6, F-7, F-8 are located much higher than the “upper limit” of 2008.

Table 2.

Sample t (min),
fluoridation duration l(µm), film thickness P _H2 /P _CO2 , atm P _H2 , Barrer P _CO2 , Barrer α(H ₂ /CO ₂ ),
selectivity PIM-1 - 78.4±1.7 1.19/1.18 1779 2328 0.76 F-1 15 87.0±1.1 1.13/1.15 1876 1832 1.0 F-2 15 96.0±5.8 1.09/1.04 1773 2181 0.81 F-3 thirty 89.1±4.9 1.11/1.02 1192 215 5.5 F-4 thirty 94.6±1.4 1.13/1.06 741 102 7.3 F-5 45 96.2±3.3 1.12/0.94 559 60 9.3 F-6 45 90.6±2.2 1.25/1.12 462 42 eleven F-7 60 71.2±2.7 1.12/1.17 414 55 7.5 F-8 60 99.4±1.4 1.11/1.08 457 27 17 FPIM-1[16] 1 - 1/1 500 40 13 FPIM-5[16] 5 - 1/1 326 22 15 FPIM-10[16] 10 - 1/1 479 thirty 16 FPIM-30[16] thirty - 1/1 540 85 6

Example 3. Determination of permeability and ideal selectivity for a pair of gases H ₂ and N _2.

The gas permeability of film membrane polymers PIM-1 and F-1 – F-8 was determined using the installations shown in Figure 1. The surface fluoridation technique is presented above. The experiment temperature was 22±2°C. The measurement results are presented in Table 3.

From Table 3 it can be seen that the selectivity (or ideal separation factor) α(H ₂ /N ₂ ) = P (H ₂ )/ P (N ₂ ) for F-1, F-2 increased slightly as a result of fluorination from 18.3 to 22.3 ; F-3, F-4 increased as a result of fluoridation by an order of magnitude from 18.3 to 239; F-5, F-6 increased as a result of fluoridation by 17 times from 18.3 to 310 F-7, F-8 increased as a result of fluoridation by 28 times from 18.3 to 515.

As can be seen from Fig.5. on the Robson diagram for the H ₂ -N pair, ₂ PBD points, F-1, F-2, F-7, are located above the “upper limit” of 2008 in the area of highly permeable polymers, F-3, F-4, F-5, F-6, F-8 are located above the “upper limit” of 2015.

Table 3.

Sample t (min),
fluoridation duration l(µm), film thickness P _H2 /P _CO2 , atm P _H2 ,
Barrer P _N2 ,
Barrer α(H ₂ /N ₂ ),
selectivity PIM-1 - 78.4±1.7 1.19/1.18 1779 97 18 F-1 15 87.0±1.1 1.13/1.11 1876 84 22 F-2 15 96.0±5.8 1.09/1.09 1773 90 20 F-3 thirty 89.1±4.9 1.11/1.10 1192 6.5 183 F-4 thirty 94.6±1.4 1.13/1.09 741 3.1 239 F-5 45 96.2±3.3 1.12/1.10 559 1.8 311 F-6 45 90.6±2.2 1.25/1.11 462 1.7 270 F-7 60 71.2±2.7 1.12/1.18 414 2.2 190 F-8 60 99.4±1.4 1.11/1.08 457 0.89 515 FPIM-1[16] 1 - 1/1 500 2.0 250 FPIM-5[16] 5 - 1/1 326 0.88 370 FPIM-10[16] 10 - 1/1 479 2.4 200 FPIM-30[16] thirty - 1/1 540 3.2 169

Example 4. Determination of permeability and vapor separation factor of gases H ₂ and CH _4.

The gas permeability of the film membrane polymers PIM-1 and F-1 – F-8 was determined using a gas chromatographic installation (Fig. 2). The surface fluoridation technique is presented above. The temperature of the experiment was 22±2°C. The film was placed in the cell of a chromatographic installation and the transport parameters of a model mixture of hydrogen and methane, in the ratio H ₂ /CH ₄ - 36/64%, were measured using the method described above. Based on the area data of the H ₂ /CH ₄ chromatogram, the following values were found for film F-2: P (H ₂ ) = 2701 Barrer, P (CH ₄ ) = 159 Barrer; for film F-4: P (H ₂ ) = 364 Barrer, P (CH ₄ ) = 2.5 Barrer; for film F-5: P (H ₂ ) = 251 Barrer, P (CH ₄ ) = 2.0 Barrer, for film F-8: P (H ₂ ) = 209 Barrer, P (CH ₄ ) = 1.8 Barrer.

Thus, the separation factor α(H ₂ /CH ₄ ) = P (H ₂ )/ P (CH ₄ ) varies in the range of 17-143.

As can be seen from Figure 3 on the Robson diagram for the pair H₂-CH₄ point F-2 is above the 2008 “upper limit” in the area of high-permeability polymers, and points F-4, F-5, F-8 are located above the 2008 “upper limit”, but the separation factor H₂/CH₄amounts to 115-143, which is several times less than the ideal selectivity. The relative error was 20%.

Table 4 - Permeability coefficients P [Barrer] and selectivity α, separation factor SF of the studied polymer samples.

Sample l(µm), film thickness Р _H2 /P _СH4 , atm Selection rate,% _H2 - _CH4 FR _H2 - _{CH4 αP} H ₂ CH ₄ P ( _H2 ) P ( _CH4 ) P ( _H2 ) P ( _CH4 ) F-2 96.0±5.8 0.46/0.80 0.87 0.05 2701 159 16.7 1773 99 17.9 F-4 94.6±1.4 0.41/0.71 0.26 0.002 364 2.5 143 741 1.6 463 F-5 96.2±3.3 0.41/0.73 0.16 0.001 251 2.0 125 559 1.3 433 F-8 99.4±1.4 0.41/0.72 0.15 0.001 209 1.8 115 457 0.41 115

Example 5. Determination of permeability and vapor separation factor of gases H ₂ and CO _2.

The gas permeability of the film membrane polymers PIM-1 and F-1 – F-8 was determined using a gas chromatographic installation (Fig. 2). The surface fluoridation technique is presented above. The temperature of the experiment was 22±2°C. The film was placed in the cell of a chromatographic installation and the transport parameters of a model mixture of hydrogen and carbon dioxide, in the ratio H ₂ /CO ₂ - 65/35%, were measured using the method described above. Based on the area of the H ₂ /CO ₂ chromatogram, the following values were found for the F-2 film: P (H ₂ ) = 2160 Barrer, P (CO ₂ ) = 3549 Barrer; for film F-4: P (H ₂ ) = 418 Barrer, P (CO ₂ ) = 71 Barrer; for film F-5: P (H ₂ ) = 224 Barrer, P (CO ₂ ) = 51 Barrer; for film F-8: P (H ₂ ) = 194 Barrer, P (CO ₂ ) = 29 Barrer.

Thus, the separation factor α(H ₂ /СO ₂ ) = P (H ₂ )/ P (СO ₂ ) varies in the range from 0.60 to 6.7.

As can be seen from Fig.4. on the Robson diagram for the pair H₂-CO₂ point F-2 is in the region of highly permeable polymers, and points F-4, F-5, F-8 are located above the “upper limit” of 2008, but the separation factor H₂/CO₂ is 4.4-6.7, which less than ideal selectivity.

Table 5 - Permeability coefficients P [Barrer] and selectivity α, separation factor SF of the studied polymer samples.

Sample l(µm), film thickness Р _H2 /P _СH4 , atm Selection rate,% H ₂ -CO ₂ SF H ₂ -CO _{2 αP} H ₂ CO ₂ P ( _H2 ) P ( _CO2 ) P ( _H2 ) P ( _CO2 ) F-2 96.0±5.8 0.89/0.47 0.76 1.24 2160 3549 0.60 1773 2181 0.81 F-4 94.6±1.4 0.75/0.40 0.28 0.05 418 71 5.8 741 102 7.3 F-5 96.2±3.3 0.74/0.40 0.15 0.033 224 51 4.4 559 60 9.3 F-8 99.4±1.4 0.74/0.40 0.13 0.02 194 29 6.7 457 27 16.9

Example 6. Determination of permeability and vapor separation factor of gases H ₂ and N _2.

The gas permeability of the film membrane polymers PIM-1 and F-1 – F-8 was determined using a gas chromatographic installation (Fig. 2). The surface fluoridation technique is presented above. The temperature of the experiment was 22±2°C. The film was placed in the cell of a chromatographic installation and the transport parameters of a model mixture of hydrogen and nitrogen were measured, in the ratio H₂/N₂ – 60/40% using the method described above. According to the chromatogram areas for mixture H₂/N₂ permeability values were found for the original film F-2:R(H₂) = 2675 Barrer,R(N₂) = 52 Barrer; for film F-4:R(H₂) = 479 Barrer,R(N₂) = 3.3 Barrer; for film F-5:R(H₂) = 226 Barrer,R(N₂) = 3.6 Barrer; for F-8 film:R(H₂) = 190 Barrer,R(N₂) = 3.7 Barrer.

Thus, the separation factor α(H ₂ /N ₂ ) = P (H ₂ )/ P (N ₂ ) varies in the range from 49 to 146.

As can be seen from FIG. 5 on the Robson diagram for the H ₂ -N ₂ pair, point F-2 is located much higher than the “upper limit” of 2008 in the region of highly permeable polymers; point F-4 is much higher than the “upper limit” of 2008; point F-5 is at the “upper limit” of 2008; point F-8 is between the “upper limits” of 1991 and 2008. The relative error was 20%.

Table 6 - Permeability coefficients P and selectivity α, separation factor SF of the studied polymer samples.

Sample l(µm), film thickness Р _H2 /P _СH4 , atm Degree of selection,% _H2 - _N2 SF _H2 - _{N2 αP} H ₂ N ₂ P ( _H2 ) P ( _N2 ) P ( _H2 ) P ( _N2 ) F-2 96.0±5.8 0.89/0.47 0.93 0.02 2675 52 50 1773 90 19.7 F-4 94.6±1.4 0.67/0.45 0.27 0.002 479 3.3 146 741 3.1 239 F-5 96.2±3.3 0.69/0.46 0.15 0.002 226 3.6 62 559 1.8 311 F-8 99.4±1.4 0.70/0.47 0.13 0.003 190 3.7 49 457 0.89 515

Thus, the presented experimental data on permeability and separation factor for hydrogen-containing mixtures (H ₂ /CH ₄ , H ₂ /CO ₂ , H ₂ /N ₂ ) show that the surface fluorinated membranes of polybenzodioxane PIM-1 obtained by the claimed method can be successfully used for the separation of hydrogen-containing mixtures of gases formed, in particular, after steam reforming of methane, pyrolysis of methane, gasification of coal, cellulose, polymer industry waste, as well as from biogas of hydrogen-synthesizing bacteria.

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Claims (1)

A method for producing gas separation membranes for hydrogen-containing mixtures based on a surface fluorinated polybenzodioxane polymer with internal microporosity PIM-1, including the synthesis of a PIM-1 polymer based on polybenzodioxane in a reaction medium of dimethyl sulfoxide, with a mass average molecular weight Mw=75000 Da and a number average molecular weight Mn=25000 Da , obtaining a solution of the PIM-1 polymer in chloroform with a concentration of 5% at room temperature, pouring this solution onto the substrate, evaporating the solvent by keeping it under vacuum to constant weight, separating the resulting membrane from the substrate, surface fluoridation of the membrane on one side with elemental fluorine in a pre-saturated environment perfluorodecalin fluorine, while perfluorodecalin is saturated with fluorine by bubbling it with a mixture of gases consisting of 10% fluorine and 90% nitrogen with a mixture flow rate of 0.5 ml/sec.