RU2782623C1 - Metal-organic coordination polymer for accumulating natural gas, methane and method for production thereof - Google Patents

Abstract

FIELD: polymers.

SUBSTANCE: invention relates to a method for producing a metal-organic coordination polymer for accumulating natural gas, methane. Method includes the stage of synthesis, consisting of an interaction of equimolar quantities of aluminium nitrate crystalline hydrate and trimesic acid dissolved in an aprotic polar organic solvent with a boiling point above 80 °C, taken in an amount equimolar or excess to the reagents, wherein the aluminium nitrate crystalline hydrate solution is heated to a temperature of 110 °C; the trimesic acid solution is heated to a temperature of 80 to 110 °C; the heated trimesic acid solution is added to the heated aluminium nitrate solution drop by drop while stirring intensively, at a rate of 5 to 15% vol. per minute; the mixture of solutions is heated to a temperature of 140 °C, held until sol is formed; said sol is polymerised at 100 to 150 °C for 2 to 3 days until a metal-organic coordination polymer with a gel structure is formed, and the activation stage consisting of repeated washing of the synthesised metal-organic coordination polymer with a gel structure under conditions of a vacuum with a pressure drop of at least 90 kPa with an aprotic polar organic solvent used at the stage of synthesis, heated to a temperature of 40 to 60 °C; drying for up to 24 hours first under standard conditions, then at a temperature of 100 to 150 °C, followed by thermal evacuation for up to 6 hours at a temperature of 120 to 300 °C and a residual pressure up to 0.26 kPa. Said activation stage ends when the mass of the metal-organic coordination polymer with a gel structure is stabilised. Also proposed is a metal-organic coordination polymer for accumulating natural gas, methane.

EFFECT: possibility of reducing the material consumption of the process by using the same solvent at the stages of synthesis and activation, shortening the time of production of a polymer gel characterised by the presence of active meso- and micropores, allow the gel to be applied as a base in various adsorption processes, including those in natural gas storage systems.

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Description

SUBSTANCE: group of inventions relates to a technology for the preparation of organometallic polymers, namely, to an organometallic polymer based on aluminum ions coordinated by trimesic acid ligands, which is synthesized by the solvothermal method and can be used for gas accumulation, in particular in systems for storing and transporting natural gas, methane.

Organometallic polymers or, as they are also called organometallic structures, represent a class of porous adsorbents consisting of metal ions or clusters coordinated by polyorganic ligands (linkers). A wide variety of organic ligands, combined with various metal cations, has resulted in a huge variety of potential porous materials with a wide range of porous surface properties and chemically controlled structures that have been critically evaluated over time for applications including gas storage and separation. The patent (US No. 7202385, IPC C07C 41/03; C07C 43/11; C08G 18/28; C08G 65/26; C08G 65/28) shows most of the structures described in the literature, which illustrates the variety of currently existing organometallic polymers.

Organometallic polymers are characterized by unique structural and energy characteristics, incl. regular crystalline structure, high specific surface area (up to 10,000 m ² /g) and a large volume of micropores, often exceeding those of zeolites and activated carbons, and are used as highly efficient adsorbents, for example, for gas storage and separation [T.A. Makal, JR Li, W. Lu, H.-C. Zhou Methane storage in advanced porous materials, Chem. soc. Rev. 2012. V. 41. P. 7761-7779].

To create high-performance organometallic polymers that can be used in gas storage and transportation systems, they must have not only appropriate adsorption characteristics, but also temperature stability.

The most famous and widespread organometallic polymer with the potential for storage and separation of gases, including methane [Tsivadze A.Yu., Aksyutin O.E., Ishkov A.G., Fomkin A.A., Menshikov I.E. , Pribylov A.A., Isaeva V.I., Kustov L.M., Shkolin A.V., Strizhenov E.M. Adsorption of methane on the metal-organic frame structure MOF-199 at high pressures in the region of supercritical temperatures, Physicochemistry of the surface and protection of materials. 2016. V. 52. No. 1. pp. 24-29.] [Baichuan Sun, Sibnath Kayal, Anutosh Chakraborty, Study of HKUST (Copperbenzene-l,3,5-tricarboxylate, Cu-BTCMOF)-1 metalorganic frameworks for CH ₄ adsorption: An experimental Investigation with GCMC ( grandcanonical Monte-carlo) simulation, Energy (2014), 1-9] is MOF-199 belonging to the HKUST-1 family, for example, patent (US 9925516, IPC B01D 53/02; B01J 20/22; B01J 20/28 ). However, the structure of MOF-199 has insufficient thermal stability, which is determined by the strength of metal-ligand bonds, since in the case of MOF-199, a divalent copper cation Cu(II) is used. This problem can be solved by replacing the divalent copper cation with another cation with higher valence values.

The use of the trivalent aluminum cation Al(III) is the most preferable for the task at hand, since aluminum-based organometallic polymers have high temperature stability and mechanical strength, a developed volume of micropores for gas accumulation, and a relatively low production cost, for example, in comparison with similar mechanical properties with organometallic polymers based on zirconium Zr(IV) or titanium Ti(IV).

Among the methods for the synthesis of organometallic polymers, there are, as a rule, modifications of the two most well-known methods: solvothermal, for example, [RU 2457213 C1, IPC C07F 11/00, publ. 27.07.2012] and under the influence of microwaves, for example, patent [RU 2578599 C1, IPC C08F 293/00, B01J 32/00].

The solvothermal method, partially described in RF 2457213, includes mixing the initial components, in particular, chromium(III) nitrate and terephthalic acid in an aqueous solution when heated. Heating is carried out in a closed volume at a rate of 11.5°/min to 220°C, followed by exposure.

A method for obtaining a coordination polymer under the influence of microwaves, for example, in RU 2578599, consists in mixing an aluminum salt of the composition AlCl ₃ × 6H ₂ O and an organic 2-amino-1,4-benzenedicarboxylic acid in the presence of a mixture of water and a polar organic solvent taken at mass ratio 1:1÷5, respectively. Then the resulting reaction mixture is heated at atmospheric pressure and at a temperature of 120-130°C under the influence of microwave radiation with a power of up to 200 W. As a polar organic solvent, a solvent with a boiling point above 130° C., capable of being heated effectively under microwave radiation conditions, such as dimethyl sulfoxide, N,N'-dimethylformamide or N,N'-diethylformamide, is used.

The disadvantage of the described approaches is that they make it possible to obtain non-activated organometallic polymers, which require a laborious selection of activation modes to remove solvent residues while maintaining the structure of the material in order to use them as gas sorbents.

The closest in essence and the achieved result is the method [US 9878906 B2, IPC SW 3/00, B01D 53/02, publ. 01/30/2018], which includes interaction with stirring and a pressure of not more than 2 bar (absolute), at least one metal compound with at least one, at least, bidentate organic compound, which can be coordinated with the metal in the presence of a non-aqueous organic solvent, selected from DMF, DEF and NMP to form a porous organometallic structure where the metal is Mg, Ca, Be, Sr, Ga or Al and an organic compound which has at least two atoms selected from oxygen, sulfur or nitrogen, through which the organic compound can be coordinated with the metal, where at least one bidentate organic compound is a di-, tri - or tetracarboxylic acid. The reaction is carried out without additional base, while the formed organometallic framework is additionally calcined at a temperature above 250°C. Example 13 of this invention is closest to the result we achieve. It carries out the synthesis of an organometallic framework polymer with a solvent N,N'-dimethylformamide, which consists in the fact that 7.8 g of trimesic acid (VTS) and 22.9 g of Al(NO ₃ ) ₃ *9H ₂ O are dissolved in 520.5 g of N,N'-dimethylformamide at 130°C and incubated for 4 days with stirring the resulting suspension, which is filtered by washing with N,N'-dimethylformamide twice with a volume of 100 ml and methanol four times with a volume of 100 ml. Then the filter with the substance deposited on it is dried by thermal vacuum drying at a temperature of 200°C for 16 hours. The formed powder of the organometallic framework is calcined for activation at 330°C in a muffle furnace with air purge at a flow rate of 100 l/h for 3 days. In this case, the heating rate of the furnace is 75 deg/hour. The resulting aluminum-based organometallic framework polymer has a Langmuir specific surface area of 1791 m ² /g.

The objective of this group of inventions was to develop a method for the synthesis of an organometallic coordination polymer with the structure of an organometallic gel, based on aluminum ions coordinated by trimesic acid ligands, having a developed nanopore surface and increased thermal stability, which makes it possible to use the resulting organometallic gel as an adsorbent in gas transportation and storage systems. , in particular, natural gas, methane.

The technical result to be achieved by the group of inventions is:

- creation and preservation of the gel structure of the synthesized organometallic coordination polymer;

- increasing its thermal stability;

- reduction of material and energy costs for production by reducing the time of synthesis and the use of one solvent at the stage of synthesis and washing.

The technical result is achieved due to the fact that in the method for obtaining an organometallic coordination polymer for the accumulation of natural gas, methane, including a synthesis stage consisting of the interaction of equimolar amounts of aluminum nitrate crystal hydrate and trimesic acid dissolved in an aprotic polar organic solvent with a boiling point above 80°C , taken in an equimolar or excess amount to the reagents, while the solution of aluminum nitrate crystal hydrate is heated to 110 ° C, the trimesic acid solution is heated to a temperature of 80-110 ° C, the heated trimesic acid solution is added dropwise with vigorous stirring to the heated aluminum nitrate solution with speed 5-15% vol. per minute, the mixture of solutions is heated to 140°C at a rate of 10-15°C per hour, kept until a sol is formed, which is placed in an autoclave and kept at a temperature of 100-150°C for 2-3 days until an organometallic coordination polymer with a gel structure, and an activation step consisting of washing the synthesized organometallic coordination polymer with a gel structure with an aprotic polar organic solvent heated to 40-60 ° C, used in the synthesis stage, using a vacuum-generating filter system at a pressure drop of at least 90 kPa, drying at room temperature, drying in an oven at 100-150°C, installation in a thermal vacuum chamber at 120-300°C and a residual pressure of up to 0.26 kPa, the activation stage is completed upon stabilization of the mass of the organometallic coordination polymer with a gel structure.

Organometallic coordination polymer with a gel structure for accumulating natural gas, methane, having thermal stability at temperatures of at least 500 ° C, containing pores with an effective inner diameter of 0.75-0.80 nm, specific surface area from 1300 to 1700 m ² /g, micropore volume 0.5-0.6 cm ³ /g, total pore volume 1.0-1.8 cm ³ /g.

The group of inventions is illustrated by tables and illustrations:

Table 1 - Chemical composition of the surface of the synthesized organometallic gel, where: Wt - weight percent, At - atomic percent;

Table 2 - Parameters of the porous structure of the synthesized samples of organometallic gel, where: V ₀ - specific volume of micropores, cm ³ /g; E ₀ - characteristic energy of nitrogen adsorption, kJ/mol; D is the effective inner diameter of micropores, nm; E is the characteristic adsorption energy of benzene, kJ/mol; S _BET - specific surface area according to the BET method, m ² /g; V _s - total pore volume, cm ³ /g; S _me - area of mesopores, m ² /g; V _me - volume of mesopores, cm ³ /g.

Fig. 1 - Photograph of scanning electron microscopy of the obtained sample of an organometallic coordination polymer with a gel structure;

Fig. 2 - IR spectra of the synthesized organometallic coordination polymer with a gel structure - solid line, aluminum-based organometallic polymer (prototype) - dotted line.

Fig. 3 - X-ray diffraction patterns of the synthesized organometallic coordination polymer with a gel structure - top line, aluminum-based organometallic polymer (prototype) - bottom line.

Fig. 4 - Thermogravimetric curves: solid line - synthesized sample of an organometallic coordination polymer with a gel structure; dotted line - organometallic polymer based on aluminum (prototype).

Fig. 5 - Isotherm of adsorption-desorption of nitrogen at 77 K on the sample (1). Light symbols - adsorption. Dark symbols - desorption.

Fig. 6 - Skeleton model of a fragment of the synthesized organometallic coordination polymer, where D is the effective inner diameter of the micropore.

The proposed group of inventions is implemented as follows.

Example 1

Trimesic acid (1,3,5-benzenetricarboxylic acid (Н ₃ ВТС)) and aluminum nitrate crystal hydrate Al(NO ₃ ) ₃ ⋅9H ₂ O were dissolved in the organic solvent N,N'-dimethylformamide in a molar ratio of 1:1 (1 mol acids per 1 mol of solvent, and 1 mol of salt per 1 mol of solvent). The resulting solutions were heated, aluminum salt solution to 110°C, trimesic acid solution to 80°C. Then, the heated trimesic acid solution was added dropwise, at a rate of 5-15% rpm, to the aluminum salt solution, with vigorous stirring with a magnetic stirrer, gradually raising the temperature of the reaction mixture to 140°C, and kept until a sol was formed (solution thickened) . The resulting sol was placed in an analytical autoclave with a tight screw cap and a fluoroplastic insert, after which it was sent to an oven, where synthesis was carried out at a temperature of 100°C with gradual heating to 140°C, and kept for another two days. Activation was carried out as follows: the resulting precipitate of the organometallic gel (MOG) was separated from the mother liquor by thermal vacuum filtration (desorption of solvent molecules), namely, repeatedly under vacuum, at a pressure drop of at least 90 kPa, washed with a solvent - N,N'-dimethylformamide, volume of 150 ml, heated to a temperature of 60°C. Next, the precipitate was dried first under standard conditions, then in an oven at a temperature of 100°C, with a rise to 140°C for 20 hours, and kept at 140°C for another 4 hours. In this drying mode, surface water is first removed (at 100 °C), then internal unbound (100-140°C), which allows stabilizing the framework of the synthesized MOG. The resulting MOG sample was activated to remove internal bound (crystal hydrate) water and solvent to the maximum in a thermal vacuum chamber at a temperature of 200°C, a residual pressure of up to 0.26 kPa (2 mm Hg) to constant weight (about 6 hours).

The obtained sample is an organometallic coordination polymer (MOCP) based on aluminum ions coordinated by trimesic acid ligands, has a gel structure and surface chemical composition indicated in Table 1. Its physicochemical properties are confirmed by the data of the analysis results shown in: FIG. 2 shows the absorption characteristic of the material in the IR spectrum, FIG. 3 - diffractogram, Fig. 4 - thermogravimetric curve, FIG. 5 - adsorption isotherms. A photograph of scanning electron microscopy of the obtained sample of MOF with a gel structure (Fig. 1) shows the presence of crystals of various sizes and a small amount of amorphous phase between them, which indicates the heterogeneity of the molecular weight distribution of the resulting polymer due to the reduction, compared with the prototype, of its time synthesis. The choice of special activation conditions for the maximum removal of both the free and bound liquid phase contributes to the preservation of the pore structure, provides acceptable strength and thermal stability of the MOF (Fig. 4). Under the conditions of high aerodynamic loading that a natural gas accumulator is subjected to during operation, such characteristics are preferable, which explains the advantages of the resulting polymer gel structure for the designated intended use, over highly crystalline, hard but brittle MOSF structures.

Absorption bands of the IR spectrum of the synthesized MOSF, Fig. 2, observed in the range 663-766 cm ^-1 , correspond to vibrations of bonds in the benzene ring and outside the plane of the aromatic ring. Bands appearing between 827-1153 cm ^-1 refer to symmetric and asymmetric bending vibrations O-C=O. Intense absorption peaks at 1368, 1445 and 1640 cm ^-1 are associated with deformation vibrations of C-O bonds, asymmetric and symmetric C=O types, respectively, in the -COOH group (in trimesic acid). Such characteristics also indicate the formation of MOFs of the claimed chemical composition.

The results of the analysis of thermal stability of the synthesized MOF with a gel structure, presented in Fig. 4 allowed us to establish that its thermal decomposition occurs at temperatures above 500°C. This indicates an increased thermal stability of the obtained polymer in comparison with the known organometallic coordination polymers based on aluminum cations coordinated with trimesic acid ligands.

Analysis of the parameters of the porous structure of the synthesized sample (1) (see Table 2) of an organometallic gel according to the isotherm of standard nitrogen vapor at a temperature of minus 196.15°C (77 K), Fig. 5 was carried out by the BET method and the theory of volumetric filling of micropores. The adsorption isotherm has a form characteristic of micro-mesoporous adsorbents. On FIG. Figure 6 shows a wireframe model of an organometallic gel (MOG) fragment, schematically illustrating its geometry and pore characteristics.

Example 2

It differs from example 1 in that the trimesic acid solution was heated to 110°C, then poured into a solution of aluminum nitrate crystal hydrate with stirring at a rate of 1 ml/min. The stage of synthesis was carried out at an increase in temperature from 100 to 120°C and then kept at a temperature of 120°C for another 60 hours. The stage of drying in an oven was carried out at a temperature of 100°C with gradual heating to 120°C. Kept in a thermal vacuum chamber at 120°C. The results of the analysis of the porous structure of the obtained sample of organometallic gel (2) are presented in table 2.

Example 3

It differs from example 1 in that trimesic acid and aluminum nitrate crystalline hydrate were dissolved in an organic solvent diethyl sulfoxide in a molar ratio of 1:2 (1 mol of acid per 2 mol of solvent, and 1 mol of salt per 2 mol of solvent). The synthesis step was carried out at a temperature increase from 100 to 150°C and then kept at a temperature of 150°C for another 48 hours. The drying step in an oven was carried out at a temperature of 100°C and gradually heated to 130°C. Kept in a thermal vacuum chamber at 250°C. The results of the analysis of the porous structure of the obtained sample of organometallic gel (3) are presented in Table 2.

Example 4

It differs from example 1 in that diethylformamide was used as a solvent, the synthesis stage was carried out at a temperature of 120°C for 60 hours. The drying stage in an oven was carried out at a temperature of 100°C with gradual heating to 120°C. Kept in a thermal vacuum chamber at 300°C. The results of the analysis of the porous structure of the obtained sample of organometallic gel (4) are presented in Table 2.

Example 5

It differs from example 1 in that the synthesis stage was carried out at a temperature of 130°C with an increase in temperature to 140°C and then kept at a temperature of 140°C for another 48 hours, and the activation stage was carried out by solvent filtration with dimethyl sulfoxide heated to a temperature of 40°C, drying in an oven was carried out at 100°C with heating to 140°C, kept in a thermal vacuum chamber at 160°C. The results of the analysis of the porous structure of the obtained sample of organometallic gel (5) are presented in Table 2.

The proposed group of inventions makes it possible to obtain an organometallic coordination polymer with a gel structure, with a developed inner surface consisting of micro- and mesopores, which, in comparison with similar materials, has a higher thermal stability, and the drying and activation parameters contribute to the maximum preservation of the pores obtained at the synthesis stage. characteristics, which generally indicates the achievement of the claimed technical result.

Claims (2)

1. A method for producing an organometallic coordination polymer for the storage of natural gas, methane, which includes a synthesis stage consisting of the interaction of equimolar amounts of aluminum nitrate crystal hydrate and trimesic acid dissolved in an aprotic polar organic solvent with a boiling point above 80 ° C, taken in equimolar or excess to the reagents, while the solution of hydrated aluminum nitrate is heated to a temperature of 110°C, the solution of trimesic acid is heated to a temperature of 80-110°C, the heated solution of trimesic acid is added dropwise with vigorous stirring to the heated solution of aluminum nitrate at a rate of 5-15 % about. per minute, the mixture of solutions is heated to a temperature of 140°C, kept until a sol is formed, which is polymerized at a temperature of 100–150°C for 2–3 days until an organometallic coordination polymer with a gel structure is formed, and an activation stage consisting of repeated washing of the synthesized an organometallic coordination polymer with a gel structure under vacuum at a pressure drop of at least 90 kPa with an aprotic polar organic solvent heated to a temperature of 40-60 ° C, used at the stage of synthesis, drying up to 24 hours, first under standard conditions, then at a temperature of 100-150 ° C, thermal vacuum up to 6 hours at a temperature of 120-300°C and a residual pressure of up to 0.26 kPa, while the activation stage is completed when the mass of the organometallic coordination polymer with the gel structure is stabilized. 2. Organometallic coordination polymer for the storage of natural gas, methane, obtained by the method according to p. surface from 1300 to 1700 m ² /g, micropore volume 0.5-0.6 cm ³ /g, total pore volume 1.0-1.8 cm ³ /g.

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