RU2624108C1 - Method of obtaining composite membrane materials based on hydride-forming intermetallic compounds and polymeric binders - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: method of obtaining composite membrane materials for the separation of hydrogen from gas mixtures based on hydride-forming intermetallic compounds and polymeric binders is described, comprising mechanical activation treatment of hydride-forming intermetallic compound powder in ball mill, subsequent momentary joint mechanical activation hydride-forming intermetallic compound powder processing with addition of barrier polymer material with a 1-5 min duration, press of metal-polymer composite powders, and subsequent rolling of metal-polymer compact.

EFFECT: membrane with high selective hydrogen permeability, productivity and reliability is obtained.

2 tbl, 12 dwg, 2 ex

Description

The invention relates to the field of membrane technology, and in particular to a technology for the separation of pure hydrogen from hydrogen-containing gas mixtures. The obtained metal-polymer composite membrane materials based on hydride-forming intermetallic compounds and polymer binders are capable of freely absorbing and desorbing hydrogen with high selectivity without passivation (poisoning) by air or other harmful impurities of hydride-forming alloys inside the polymer matrix. It has the property of maintaining size and strength constant during operation while maintaining membrane properties.

A known method of producing membranes for hydrogen purification by magnetron sputtering of a target and condensation in vacuum, characterized in that a selective film of metal or its alloy is applied to a two-layer ceramic substrate of aluminum oxide having two levels of through porosity. The use of a ceramic porous substrate of Al ₂ O _{3 is} proposed as a substrate, and a metal alloy (Pd-6 at.% Ru) is used as a selective layer (Patent RU 2538577 C2. Published: 01/10/2015).

The disadvantages of this method, reducing the operational characteristics of the membrane: "open" selective layer, which is passivated by components contained in industrial hydrogen-containing gases; delamination of the selective metal layer as a result of various coefficients of thermal expansion and dilatation of ceramics and metal in the case of time-variable hydrogen saturation; the complexity of the technology, the presence of expensive platinum group metals.

In the patent [RU 2285748 C2. Published: 02/10/2006] a method for producing gas-separating composite membranes, functioning due to the selective diffusion of various gases through a thin metal film, which are used in devices for deep hydrogen purification from associated impurities, hydrogen separation from hydrogen-containing impurities, in microreactors, etc. is considered.

A method of manufacturing composite membranes based on thin metal films involves applying a thin film of palladium and alloys based on it onto a cleaned technological substrate, followed by separating the metal film from the substrate and transferring it to the membrane holder. As the substrate take plates of monocrystalline silicon of instrument quality, used for microelectronics. The film is applied by at least one of the methods of physical vacuum deposition, chemical vapor deposition, electrochemical or chemical deposition. The metal film is separated from the substrate by completely or partially dissolving the substrate in flotation-type solutions for a given metal film, and the membrane is formed by transferring the metal film to the membrane holder in an aqueous solution, followed by fixing the metal film to the holder. The film is fixed by diffusion welding.

The disadvantage of this method is the very complicated technology for the production of membranes. The process of removing an ultrathin film from a technological substrate leads to a deterioration in the quality of the film and significantly complicates the process. In addition, the need to ensure very low adhesion when applying the film to the technological substrate also affects the perfection of the film during its formation. It should also be noted the presence of expensive platinum group metals.

In the patent [RU 2521382 C1. Published: 06.27.2014] a method for manufacturing a membrane for hydrogen evolution from gas mixtures is considered, in which a layer of palladium or its alloys is applied to the membrane surface based on metals of group 5 (vanadium, niobium, tantalum) or their alloys. This method is characterized in that before applying palladium or its alloys, the membrane is recrystallized by heating it in vacuum or in an inert gas atmosphere to a temperature equal to 0.8-0.9 of the melting temperature of the membrane material.

The disadvantage of this method is that the used metals of group 5 have a high chemical activity on their surface, which is usually coated with dense films of oxides that quickly form when interacting with air, water vapor, etc. Oxide films radically reduce the dissolution and hydrogen evolution rates through the metal surface, making membranes less permeable to hydrogen.

The disadvantage inherent to all porous metal-based composite membranes is the diffusion of the substrate atoms into the selective layer, as well as the reverse process when hydrogen is transmitted at high temperatures, which leads to a decrease in the permeability and reliability of the membrane as a whole.

The technical result of the present invention is the development of a highly efficient and reliable method for creating selective composite membranes with high performance for hydrogen purification. And the exclusion of expensive materials when creating these membranes.

This technical result may have a solution due to the capabilities of the technology of mechanical activation processing (or other technologies used for coating), pressing and rolling.

A method of producing composite membrane materials for hydrogen evolution from gas mixtures based on hydride-forming intermetallic compounds and polymer binders, including mechanically activating the hydride-forming intermetallic compound powder in a ball mill, followed by a short-term joint mechanically activating the hydride-forming intermetallic compound powder with the addition of a barrier polymer material lasting 1-5 minutes pressing metal polymer s composite powders and subsequent rolling of metal-obtained compact, the compacting is carried out at a temperature of from 1.1-1.2 barrier resin melting temperature.

To clarify the invention, graphic images were presented.

Where the figure 1 shows a graph of the distribution of particles of LaNi ₅ in size after MA processing - 5 minutes

In figure 2 - the Microstructure of the particles of LaNi ₅ powder after MA processing - 5 minutes Magnification × 1000.

Figure 3 - Microstructure of the particles of IC LaNi ₅ coated with a polymer of PE (mass concentration of the filler 50%).

In figure 4 - the microstructure of the cross section of the composite metal-polymer membranes PE / LaNi ₅ with a mass concentration of filler: 70%.

The figure 5 - the microstructure of the cross section of the composite metal-polymer membranes PE / LaNi ₅ with a mass concentration of filler: 50%.

Figure 6 - Data of differential scanning calorimetry, when heating samples of membranes from pure PE and metal / polymer membrane PE / LaNi ₅ with a mass concentration of filler 50%.

Figure 7 - Graph of the distribution of TiFe particles in size after MHS - 120 minutes

Figure 8 - Microstructure of particles of TiFe powder after MHS - 120 minutes Magnification × 1000.

Figure 9 - Microstructure of particles of IC TiFe coated with a polymer of PTFE (mass concentration of the filler 50%).

Figure 10 - Microstructure of the cross section of composite metal-polymer membranes PTFE / TiFe with a mass concentration of filler: 70%.

Figure 11 - Microstructure of the cross section of composite metal-polymer membranes PTFE / TiFe with a mass concentration of filler: 50%.

Figure 12 - Data of differential scanning calorimetry, when heating samples of membranes from pure PTFE and metal-polymer membrane PTFE / TiFe with a mass concentration of filler 50%.

The technology includes:

1. Mechanical activation processing of hydride-forming intermetallic compounds.

Preliminary mechanical activation of LaNi ₅ for 5 minutes to simplify the procedure for activating interaction with hydrogen.

To reduce the activation temperature of the TiFe intermetallic compound, it must be obtained in the nanostructured state by means of mechanical activation treatment of the initial TiFe powder for 60 minutes. Obtaining IC TiFe with a crystallite size of 8-12 nm is necessary to reduce the activation temperature to 300 ° C. This temperature allows the activation of TiFe ICs in a PTFE matrix and will not lead to polymer melting or degradation.

2. Joint mechanical activation processing of the finished hydride-forming intermetallic powder with a binder polymer (freely passing hydrogen through it and preventing the passivation of IC by impurity gases and holding metal particles in its volume) for a short time (1-5 minutes), in a planetary ball activator, for encapsulation of particles powder intermetallic compounds in the polymer. The content of the binder polymer should correspond to 40-60 wt.% By weight of the metal powder. Or applying binder barrier coatings, other possible coating methods, to an already prepared hydride-forming powder.

3. Thermal pressing on a vulcanizing press, above the melting temperature of the polymer in the atmosphere of air, to obtain metal-polymer compacts.

4. Rolling on rollers in order to obtain a thinner membrane.

5. Carrying out the procedure for activation of interaction with hydrogen. The proposed method for the manufacture of metal-polymer composite membrane materials for the purification of hydrogen helps to maintain high activity when interacting with hydrogen hydride-forming compounds inside the polymer matrix, i.e. for a membrane, one activation procedure is sufficient to initiate interaction with hydrogen. Also, metal-polymer membranes are resistant to destruction (embrittlement) when exposed to hydrogen.

Example 1

The hydride-forming intermetallic powder LaNi ₅ was processed in a ball planetary mill (type AGO-2C) for 5 minutes (at the same time, the required dispersion of metal particles was achieved) in an argon atmosphere (Figure 1). Immediately after receiving the dispersed IC LaNi ₅ (Figure 2), polyethylene powder (PE), 10, 50 and 70 wt.% Was added to the mechanoreactors. Processing takes 1-5 minutes, while the treatment time is achieved by coating the polymer with metal particles (Figure 3).

The obtained metal-polymer composite powder was pressed on a vulcanizing press with a force of 2 MPa at a temperature of 140 ° C (which is higher than the melting temperature of the polymer) in an atmosphere of air. The resulting metal-polymer compact cools with the installation. After thermal pressing, the obtained sample was rolled on laboratory rollers at a temperature of 90 ° C, at which it is most malleable. Above this temperature, structural changes occur (it begins to melt) and at higher temperatures, various effects, such as the shape memory effect, occur. The thickness of the obtained membranes was 0.1-0.2 mm (Figure 4, 5). With an increase in polymer concentration, pore-free membranes that are uniform in thickness and density can be obtained.

The results of DSC analysis (Figure 6) showed that the metal-polymer membrane PE / LaNi _{5 is} stable to a temperature of 120 ° C. In the temperature range of 25-120 ° C, no pronounced thermal effects are observed associated with possible degradation effects of PE. This is confirmed by the absence on the DSC curve of any reactions (peaks) associated with the chemical interaction of the components.

DSC analysis data allows us to conclude that such composite membranes can operate up to a temperature of 120 ° C.

The main characteristic of the obtained metal-polymer composite membrane material - selectivity is presented in table 1.

The results obtained confirm that the optimal mass concentration of the filler is 40-60%. This is such a concentration at which the best ratio of permeability and selectivity for these membranes is achieved. At mass concentrations of 10 and 70%, a decrease in selectivity is observed compared to a concentration of 50%. A lower polymer content reduces the selectivity of the membrane material, and a larger one decreases the membrane permeability.

In the case of the highest concentration of filler in the composite material, this result can be associated with the presence of a large number of voids in the volume of the material through which impurity gases (O ₂ , N ₂ , CO ₂ , CH ₄ ) can pass. Whereas in the case of the lowest filler concentration in the composite material, the number of active centers that absorb hydrogen on themselves decreases, which leads to a decrease in the total selectivity of the membranes.

Example 2

The hydride-forming intermetallic powder TiFe was processed in a ball planetary mill (type AGO-2C) for a duration of 60 minutes. According to the estimate, the grinding energy intensity in the mechanical activator (mill) was about 15 W / g. Immediately after receiving the dispersed TiFe IC (Figure 7, 8), polytetrafluoroethylene powder (PTFE, grade FP-4), 10, 50, and 70 wt.% Was added to the mechanoreactors. The processing was carried out for 1-5 minutes, while the treatment time is achieved by coating the polymer with metal particles (Figure 9).

The obtained metal-polymer composite powder was pressed on a vulcanizing press with a press force of 4 MPa at a temperature of 370 ° C (above the melting point of the polymer) in an atmosphere of air. The resulting metal-polymer compact cools with the installation. After thermal pressing, the obtained sample was rolled on laboratory rollers at a temperature of 150 ° C. The thickness of the obtained membranes was 0.1-0.3 mm (Figure 10, 11). It can be noted that with an increase in polymer concentration, pore-free membranes and uniform in thickness and density were obtained.

The results of DSC analysis (Figure 12) showed that the metal-polymer membrane of PTFE / TiFe is stable up to a temperature of 300 ° C. In the temperature range of 25-300 ° C, there are no pronounced thermal effects associated with the possible degradation phenomena of PTFE. This is confirmed by the absence on the DSC curve of any reactions (peaks) associated with the chemical interaction of the components.

DSC analysis data allows us to conclude that such composite membranes can operate up to a temperature of 300 ° C.

The main characteristic of the obtained metal-polymer composite membrane material - selectivity is presented in table 2.

The results obtained confirm that the optimal mass concentration of the filler is 40-60%. This is such a concentration at which the best ratio of permeability and selectivity for these membranes is achieved. At mass concentrations of 10 and 70%, a decrease in selectivity is observed compared to a concentration of 50%. A lower polymer content reduces the selectivity of the membrane material, and a larger one decreases the membrane permeability.

In the case of the highest concentration of filler in the composite material, this result can be associated with the presence of a large number of voids in the volume of the material through which impurity gases (O ₂ , N ₂ , CO ₂ , CH ⁴ ) can pass. Whereas in the case of the lowest filler concentration in the composite material, the number of active centers that absorb hydrogen on themselves decreases, which leads to a decrease in the total selectivity of the membranes.

A comparison of the obtained membranes with the known ones shows that the use of the invention allows:

1. Increase selective gas permeability.

2. To increase the reliability of the composite membrane using a binder polymer that prevents surface passivation by impurity gases and embrittlement when interacting with hydrogen.

3. To control the phase composition and structure parameters of the filler.

Claims (1)

A method of producing composite membrane materials for hydrogen evolution from gas mixtures based on hydride-forming intermetallic compounds and polymer binders, comprising mechanically activating a powder of hydride-forming intermetallic compounds in a ball mill, followed by a short-term joint mechano-activation processing of powder of hydride-forming intermetallic compounds with the addition of a barrier polymer material of 1-5 min duration metal polymer extrusion composite powders and subsequent rolling of metal-obtained compact.

Images