RU2477704C2 - Method of producing highly compact hydrogen - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in motorcar, chemical, electronic and electrochemical industry, as well as hydrogen power engineering. First, nanoparticles of a metal catalyst - Pd, Pt, Ni, Ti, Fe, Co, Nb, Mo, Ta, W, Rh, Ru, Os, Ir, La, Mg and/or alloys thereof are placed in inter-fragment regions of carbon nanomaterial - graphite nanofibres or carbon nanotubes. The carbon nanomaterial is then cleaned from attached oxide-type functional groups by burning in an inert gas at 773 K. A layer of chemisorbed hydrogen with thermal desorption activation energy of about 1.2 eV is then formed on the inter-fragment surfaces and a layer of chemisorbed hydrogen with thermal desorption activation energy of about 2.5 eV is formed on graphene inner surfaces by holding the carbon nanomaterial in a current of gaseous molecular hydrogen at temperature of 773 K. Final hydrogenation of the carbon nanomaterial is carried out in a container at pressure, temperature and time of not more than 300 bar, 1000 K and 300 h, respectively, until obtaining 10 wt % or more of highly compact hydrogen with density in the order of 1 g/cm³ which is intercalated in the carbon nanomaterial.

EFFECT: invention reduces the pressure and temperature when producing highly compact hydrogen, enables to use simple, available and low power consumption equipment, and provides prolonged storage of hydrogen at room temperature.

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Description

1. The technical field to which the invention relates.

The invention relates to certain relevant areas of nanotechnology (B82B 3/00 - manufacturing or processing of nanostructures), technical physics and hydrogen energy. It can be used in the automotive, chemical, electronic, electrical and several other areas of technology.

2. The level of technology

As is known (see, for example, [1] V.L. Ginzburg. Physics and Astronomy. - M .: Nauka, 1980, p. 29; and [2] L. Schlapbach, A. Zuettel, P. Groening, P .Aabi. Hydrogen for modern materials and facilities, US Journal of Applied Physics A, 2001, Volume 72, pp. 245-253), at least three researchers' hopes are currently associated with hydrogen: 1) the thermonuclear reaction hydrogen synthesis; 2) the transmission of electricity with almost no loss in superconducting devices; 3) for secondary fuel, harmless to the environment - the so-called hydrogen energy.

All these hopes are attributed to a large extent to highly compact “megabar” hydrogen with a density of ~ 1 g / cm ³ achieved at megabar ~ 100 GPa and short-term “static” compression of the initial molecular hydrogen in special devices - the so-called diamond anvils (see, for example , [3] L.F. Vereshchagin, E.N. Yakovlev, and Yu.A. Timofeev, The Possibility of the Transition of Hydrogen to the Metallic State, Journal of the Russian Federation "Letters to JETP", 1975, Volume 21, Issue 3, p. 190- 193).

The diamond anvil [3], currently used by researchers for isothermal megabar short-term compression of molecular hydrogen (usually at cryogenic temperatures), the device is relatively simple. However, it costs about tens of thousands of US dollars. In addition, working with megabar hydrogen in such an installation is difficult and unsafe. Hydrogen is dissolved in the metal gasket existing in the installation, making it brittle - hydrogen embrittlement of the metal, and also enters into chemical reactions with the metal, forming brittle hydrides. Therefore, only short-term experiments are possible.

It is important to emphasize that during forced pressure relief in a diamond anvil, hydrogen reverses from a highly compact state to its initial gaseous state. Therefore, it is not possible to save highly compact “megabar” hydrogen in devices such as diamond anvils for a detailed stationary study of such hydrogen and its application in technology, in particular in automotive and space technology (as an efficient and environmentally friendly fuel).

A number of researchers believe that the study of high-compact “megabar” hydrogen using a diamond anvil [3] can lead to the development of a high-temperature (~ 300 K) superconductor, which can be the basis for new electrical engineering.

Megabar pressures are now also obtained by dynamically compressing molecular hydrogen under pulsed energy action, for example, using spherical geometry explosive devices (see, for example, [4] R.F. Trunin, V.D. Urlin, A.B. Medvedev, Dynamic Compression of Hydrogen Isotopes at Megabar Pressure, Journal of the Uspekhi Fizicheskikh Nauk, 2010, Volume 180, No. 6, pp. 605-622). [4] contains an analysis and systematization of a number of the most famous works on dynamic and static megabar compression of hydrogen.

To further advance in the field of studying and practical application of high-compact “megabar” hydrogen, it is obviously necessary to develop a fundamentally new method for producing such “megabar” hydrogen at room temperatures (~ 300 K), free from a number of disadvantages of the existing “static” and dynamic methods [3 , 4] short-term megabar compression of the initial molecular hydrogen, which is the subject of the present invention.

The claimed method differs from the methods [3, 4] by higher technical, technological and economic efficiency and safety and, in particular, provides the possibility of long-term storage (in special devices) of a high-compact “megabar” molecular hydrogen (at temperatures ~ 300 K) for a detailed study and practical use.

The technical result of the claimed invention is the technical effect of obtaining and long-term storage at temperatures of ~ 300 K of highly compact molecular hydrogen with a density of ~ 1 g / cm ³ corresponding to megabar (~ 100 GPa) compression of molecular hydrogen in special devices that are fundamentally different from special devices used in methods [3, 4], which eliminates a number of known disadvantages inherent in these methods [3, 4].

The reliability of the manifestation of the claimed technical result is based on the theoretical evidence and experimental information presented in the description.

As shown in the present invention, special devices for the production and long-term existence (or storage) of a highly compact “megabar” (~ 1 Mbar) molecular hydrogen with a density of ~ 1 g / cm ³ (at a temperature of ~ 300 K) can be created using modern carbon polygraphic nanomaterials, which, under certain conditions, have “mega-size” (~ 10 Mbar) elastic and strength properties (see, for example, [5] V.D. Blank, B. A. Kulnitsky, I. A. Perezhogin, Yu.L. .Alypevsky, D.V. Batov, N.V. Kazennov, Nanotube as a reaction cell. Deformation processes in nanotubes. "Materials Science", 2007, No. 1, pp. 42-48).

It should be emphasized that such a technical result of the present invention is absent in the known methods of hydrogen sorption storage in carbon polygraphic nanomaterials (sorbents). Note that the concept of sorption includes the processes of adsorption, absorption, chemisorption and capillary condensation of sorbate (hydrogen); see, for example, [6] “Chemical Encyclopedic Dictionary”, I.L. Knunyants, E.V. Vonsovsky and others, M .: Soviet Encyclopedia (1983), p. 536.

So, in the patent [7] of EP No. 1882522, class. СВВ 31/02, 2008, devoted to a method for storing hydrogen in a modified polygraphic, i.e. carbon, nanostructure, in the paragraphs of the description [0005], [0006], [0017], [0024], [0028] and [0029], hydrogen with high density and pressure is chemisorbed in the nanomaterial, but numerical values of density and pressure are not given hydrogen. The density values given in the description of [7] in Table 4 are 0.001-0.015 g / cm ³ . Such density values are three to two orders of magnitude lower than the density (~ 1 g / cm ³ ) obtained by megabar compression (at ~ 300 K) of molecular hydrogen [3, 4]. In addition, it should be noted that the state of hydrogen chemisorbed by carbon nanomaterial in the method [7], i.e. hydrogen bonded to carbon nanomaterial by strong covalent bonds [6] is fundamentally different from the highly compact molecular state of hydrogen in the methods [3, 4], i.e. states with a weak, so-called van der Waals physical interaction between molecules [6]. The final density of ~ 1 g / cm ³ (at ~ 300 K) and the molecular state of hydrogen subjected to megabar compression (in special devices) are essential features of the technical solution in the methods [3, 4], which are absent in the method [7]. The greatest value of the external pressure of molecular hydrogen gas, at which the nanomaterial was hydrogenated, in the method [7], given in the paragraph [0079] of the description, is 12 MPa, i.e. ~ 120 bar. In this case, the chemical potential of hydrogen chemisorbed by carbon nanomaterial corresponds to the chemical potential of gaseous molecular hydrogen at a pressure of ~ 120 bar and a hydrogenation temperature of the nanomaterial (~ 300 K), i.e. in the method [7] do not carry out megabar compression of molecular hydrogen.

In the patent [8] EP No. 1209119, class. С01В 3/00, 2002, devoted to the method for storing chemisorbed hydrogen in modified carbon polygraphic nanomaterials, in the paragraphs of the description [0016] and [0017], as well as in claims 2 and 4 of the formula, it is advisable to introduce a metal catalyst into carbon polygraphic nanomaterials, - at least one of the metals, alloys and compounds indicated in this patent capable of forming the so-called “reversible” hydrides in an amount corresponding to the composition of the “hybrid” metal catalyst — carbon. In the paragraphs of the description [0023] and [0024], a possible mechanism of chemical hydrogenation of the “hybrid” metal-catalyst-carbon system is considered up to the content of chemisorbed hydrogen corresponding to CH carbohydride. In paragraphs 6 and 12 of the formula, the highest value of the external pressure of molecular hydrogen gas, used in the patent for hydrogenation of the nanomaterial, is -13.8 MPa, i.e. ~ 140 bar, close to that for the above patent [7] EP No. 1882522.

In the above patents [7, 8], as in other well-known patents for the sorption storage of hydrogen in carbon nanomaterials, there is no technical result (effect) for the production and storage of highly compact “megabar” molecular hydrogen with a density of ~ 1 g / cm ³ (at ~ 300 K) corresponding to megabar compression of molecular hydrogen.

However, the above discussion shows that patents of the type [7, 8] (and especially the patent [7]) have more common features with the claimed invention than the works [3] and [4].

Therefore, as a prototype of the present invention, it seems appropriate to consider a patent [7] for the sorption storage of high-density hydrogen in carbon polygraphic nanomaterials, and consider works [3] and [8] as analogues.

3. Disclosure of invention

A fundamentally new method for producing highly compact molecular hydrogen with a density of ~ 1 g / cm ^{3 is} proposed.

In the inventive method, multilayer intercalation of highly compact molecular hydrogen (in an amount of ≥10 wt.%) Between graphene layers in carbon nanomaterials, for example, graphite nanofibers (see Fig. 1 from the Example of implementation, where microphotographs of dehydrated graphite nanofibers are presented, arrows indicate some of nanofields slotted between the graphene layers remaining after desorption nanofibres (care) are intercalated high density (~ 1 g / cm ³⁾ of molecular hydrogen in quant stve ~ 17 wt.%). To achieve this technical result, the complex of operations described below is carried out, which ultimately results in the occurrence of high local internal megabar stresses (pressures P * _{H2 (graph)} , expression (1)) in carbon nanomaterial (due to the energy of association of atomic hydrogen to molecular).

Using expression (1), the so-called “law of acting masses” is described for the transition of atomic hydrogen from the gas phase (in the surrounding hydrogenous atmosphere) to a highly compact molecular state in slit-like nanocavities (Fig. 1) between graphene layers in carbon nanomaterials (2 N _{( gas)} ⇔Н _{2 (graph)} ), presented in a form convenient for the relevant estimates:

где Р_Н(газ),

- равновесное и стандартное давления атомарного газообразного водорода соответственно,

where P _{N (gas)} ,

- equilibrium and standard pressure of atomic gaseous hydrogen, respectively,

- равновесная фугитивность (эффективное давление), отвечающая высококомпактному молекулярному состоянию интеркалированного водорода, и стандартное давление молекулярного водорода соответственно,

- equilibrium fugacity (effective pressure) corresponding to the highly compact molecular state of intercalated hydrogen, and standard molecular hydrogen pressure, respectively,

ΔH _(diss) , ΔS _(diss) - standard energy (enthalpy) and entropy of dissociation of molecular hydrogen gas, respectively (ΔH _(diss) ≈ 4.5 eV,

(ΔS _(diss) ≈ 0 (to a first approximation)),

ΔV is the corresponding change in the volume of material,

T is the temperature of the material,

k is the Boltzmann constant.

в углеродном наноматериале при технологичных температурах, не превышаюшх 1000 К, и реальных (для практического осуществления) давлений атомарного водорода P_H(газ) порядка нескольких паскалей.From here, megabar values of local stresses are obtained.

in carbon nanomaterial at technological temperatures not exceeding 1000 K, and real (for practical implementation) atomic hydrogen pressures P _{H (gas) of the} order of several pascals.

In the proposed method, carbon multilayer nanomaterials consisting of crystalline nanofragments of graphene layers are used as a material object — graphite nanofibres or carbon nanotubes, over which the following actions are performed:

conduct preliminary cleaning of carbon nanomaterial from the attached functional groups of the oxide type, for example, by annealing in an inert gas;

create a layer of chemisorbed hydrogen in carbon nanomaterial on interfragmental interfaces with an activation energy of thermal desorption of ~ 1.2 eV (see Fig. 2 and Fig. 3), capable of passing only atomic hydrogen into carbon nanomaterial at technologically advanced external pressures, temperatures and hydrogenation times, not exceeding 300 bar, 1000 K and 300 hours, respectively (Fig. 2 shows theoretical models of chemisorption of hydrogen atoms on graphite (in graphene and edge planes of the material), in model “F” the activation energy of thermal desodes the portion is ~ 2.5 eV (thermodesorption peak γ in Fig. 3), in the "H" model - ~ 1.2 eV (thermodesorption peak β in Fig. 3), in the "C, D" models - ~ 3.6 eV); (Fig. 3 shows the experimental curves (from the Example of implementation) of temperature-programmed desorption, the thermodesorption peak β (with activation energy ~ 1.2 eV) and the thermodesorption peak y (with activation energy ~ 2.5 eV), chemisorbed hydrogen from samples of graphite (polygraphic) nanofibers hydrogenated at 773 K in a stream of gaseous molecular hydrogen (curve 1), as well as at 300 K with a pressure of gaseous hydrogen of ~ 1 bar (curve 2));

create a layer of chemisorbed hydrogen on the graphene internal surfaces of the carbon nanomaterial with an activation energy of thermal desorption of ~ 2.5 eV (Fig. 2 and Fig. 3), which leads to weakening of cohesion between the graphene layers of the nanomaterial;

create, for example, through the catalytic atomization of hydrogen near the interfragmental interfaces of the carbon nanomaterial, the partial pressure of atomic hydrogen P _{H (gas) of the} order of several pascals (in accordance with expression (1));

when using catalytic hydrogen atomization as a preferred method, carbon nanomaterials are introduced into the interfragmental regions of carbon nanomaterial, for example, by a chemical or electrochemical method — at least one of the group of metals dissociatively absorbing hydrogen and including Pd, Pt, Ni, Ti, Fe, Co, Nb, Mo, Ta, W, Rh, Ru, Os, Ir, La, Mg and / or their alloys, in an amount necessary and sufficient to ensure the partial pressure of atomic hydrogen of the order of several pascals (in accordance with zheniem (1));

hydrogenation of such carbon nanomaterial from gaseous molecular hydrogen is carried out at external pressures, temperatures, and process times not exceeding 300 bar, 1000 K, and 300 h, respectively, up to achieving ≥10 wt% of highly compact molecular hydrogen internally into carbon nanomaterial with a density of ~ 1 g / cm ³ .

4. The implementation of the invention

Implementation example

A sample of ~ 1 g of graphite (polygraphic) nanofibers (with a fiber diameter of ~ 50 nm, a fiber length of ~ 5 μm and a specific surface of ~ 200 m ² / g) containing ~ 1 wt.% Inclusions of nanoparticles (size ~ 10-30 nm) a palladium catalyst is placed in a stainless steel container and incubated for 2 hours in a helium stream at 773 K (to clean the sorbent from the attached functional groups of the oxide type).

Then the carbon nanomaterial (sample) is kept in a flow of gaseous molecular hydrogen at a temperature of 773 K until the formation of chemisorbed hydrogen on interfragmental material interfaces in an amount of ~ 3 wt.%, Characterized by an activation energy of thermal desorption of ~ 1.2 eV (thermal desorption peak β in Fig. 3), as well as chemisorbed hydrogen on graphene planes (layers) of the material in an amount of ~ 5 wt.%, Characterized by an activation energy of thermal desorption of ~ 2.5 eV (thermal desorption peak γ in Fig. 3). A peak corresponding to the activation energy of thermal desorption of ~ 3.6 eV and a number of other thermal desorption peaks is also possible (Fig. 2).

Then, the final hydrogenation of such graphite nanofibers is carried out in a steel container at room temperature (~ 300 K) and a pressure of gaseous molecular hydrogen of ~ 10 MPa (~ 100 bar) for a time not exceeding 300 h, until intercalation into slot-like nanocavities in carbon nanomaterial ( Fig. 1) highly compact hydrogen with a density of ~ 1 g / cm ³ in an amount of ~ 17 wt.%.

The pressure of gaseous molecular hydrogen (~ 100 bar) in the container is removed, which leads to the departure of the intercalated highly compact molecular hydrogen from carbon nanomaterial (Fig. 1) in a time of ~ 10 min (at ~ 300 K).

It should be emphasized that this relaxation time of the process (~ 10 min) is orders of magnitude higher than the lifetime of the high-density state of hydrogen in dynamic and static methods (methods and installations) of external megabar compression of hydrogen [3, 4].

It should also be emphasized that if the pressure of gaseous molecular hydrogen (~ 100 bar) in the container is not removed, then highly compact molecular hydrogen intercalated into slot-like nanocavities in carbon nanomaterial (at ~ 300 K) can be stored for almost unlimited time. This allows for stationary studies of highly compact molecular hydrogen, as well as the use of such hydrogen in technology.

The density of highly compact molecular hydrogen (p _n ) intercalated into slit-like nanocavities (Fig. 1) in carbon nanomaterial is determined using the expressions:

where ρ _C = 2.3 g / cm ³ is the density of graphite defect-free nanofibers [2],

f _vH = 0.4 ± 0.1 - volume fraction of slit-like nanocavities in graphite

nanofibers, which is determined from Fig. 1,

ν _H , v _C is the volume of the carbon part of the sample and the volume of slit-like nanocavities in the sample (Fig. 1), respectively,

f _mH = 0.17 ± 0.01 is the mass fraction of molecular hydrogen intercalated into the slot-like nanocavities (Fig. 1), which is determined using the gravimetric method,

m _H , m _C is the mass of the carbon part of the sample (Fig. 1) and the mass of highly compact molecular hydrogen intercalated into slot-like nanocavities (Fig. 1), respectively.

This yields the value ρ _H = 0.7 ± 0.2 g / cm ³ , which in the case of comprehensive compression of molecular hydrogen at ~ 300 K corresponds (according to the data of [3, 4]) to megabar external pressures.

In the claimed invention (in the embodiment), the external pressure of molecular hydrogen gas (in a steel container) on the sample is ~ 10 MPa (~ 100 bar), the temperature of the sample is ~ 300 K, the time of desorption (desorption) from the sample of intercalated highly compact hydrogen (when removing pressure in the container) is ~ 10 min. This together provides a real opportunity to save highly compact hydrogen with a density of ~ 1 g / cm ^{3 for a} sufficient (almost unlimited) time and in sufficient quantity for its stationary study and technological use.

In the claimed invention (in the embodiment), a megabar internal pressure (voltage) is created that compresses molecular hydrogen in slit-like nanocavities in the sample (Fig. 1) due to the energy of association of atomic hydrogen into molecular (expression (1)).

This is confirmed by the processing of data on a certain “bloat” of slit-like nanocavities observed in microphotographs (Fig. 1) in their middle part, i.e. lenticular form of nanocavities in the sample. In this regard, estimates are made (using data [5] on the superhigh ~ 10 Mbar strength characteristics of graphene) of the internal stresses (pressures) necessary for such a mechanical "bloating" of slot-like nanocavities in carbon nanomaterial (Fig. 1), which give close to megabar values internal pressures (accurate to one or two orders of magnitude).

Claims (2)

1. A method of producing highly compact hydrogen, comprising producing hydrogen with a high density, characterized in that carbon multilayer nanomaterials consisting of nanofragments of graphene layers are used as a material object — graphite nanofibres or carbon nanotubes;
preliminary purification of carbon nanomaterial from attached functional groups of the oxide type is carried out by annealing it in an inert gas;
create a layer of chemisorbed hydrogen with an activation energy of thermal desorption of ~ 1.2 eV in carbon nanomaterial on its interfragmental interfaces;
create a layer of chemisorbed hydrogen on the graphene internal surfaces in nanofragments of carbon nanomaterial with an activation energy of thermal desorption of ~ 2.5 eV;
create, for example, by the catalytic atomization of hydrogen near the interfragmental interfaces of the carbon nanomaterial, the partial pressure of atomic hydrogen of the order of several pascals;
when hydrogen catalytic atomization is used as the preferred method, nanoparticles of a metal catalyst are introduced into the interfragmental regions of the carbon nanomaterial — at least one of the group of metals dissociatively absorbing hydrogen, including Pd, Pt, Ni, Ti, Fe, Co, Nb, Mo, Ta, W, Rh, Ru, Os, Ir, La, Mg and / or their alloys;
hydrogenation of such carbon nanomaterial from gaseous molecular hydrogen is carried out at external pressures, temperatures, and process times not exceeding 300 bar, 1000 K, and 300 h, respectively, up to reaching ≥10 wt% of highly compact hydrogen intercalated into carbon nanomaterial with a density of ~ 1 g / cm ³ . 2. The method according to claim 1, characterized in that graphite nanofibers containing ~ 1 wt.% Nanoparticles with a size of ~ 10-30 nm of a palladium catalyst are used as the starting carbon nanomaterial, over which the following actions are carried out:
withstand carbon nanomaterial for 2 hours in a helium stream at 773 K;
carry out chemisorption of hydrogen in carbon nanomaterial by soaking in a stream of gaseous molecular hydrogen at a temperature of 773 K, up to the formation of ~ 3 wt.% chemisorbed hydrogen in carbon nanomaterial, characterized by an activation energy of thermal desorption of ~ 1.2 eV, as well as the formation of ~ 5 wt. .% chemisorbed hydrogen, characterized by an activation energy of thermal desorption of ~ 2.5 eV;
they carry out the final hydrogenation of carbon nanomaterial in a container at room temperature ~ 300 K and a pressure of gaseous molecular hydrogen of ~ 10 MPa, or ~ 100 bar for a time not exceeding 300 h, until intercalation into carbon nanomaterial of ~ 17 wt.% highly compact molecular hydrogen with density ~ 1 g / cm ³ .

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