RU2069164C1 - Method of hydrogen production - Google Patents

Abstract

FIELD: methods of hydrogen production and storing with usage of hydride-forming sorbents, method is used in autonomous sources of hydrogen production. SUBSTANCE: hydrogen-bearing composition is formed from mixture of taken in stoichiometric ratio of hydrides powders with metals or hydrates, metal components of which are capable to form intermetallic compounds and locally ignite them. EFFECT: improved process. 2 cl

Description

 The invention relates to space rocket and aviation technology, in particular to methods for storing and producing hydrogen using hydride-forming sorbents, and can be used as a stand-alone source of hydrogen both in the field and on board the aircraft.

A known method of producing hydrogen, implemented in a hydrogen generator, including a chamber filled with metal hydride, to ensure the operation of which requires the supply of heat stimulating the desorption of hydrogen [1]
The disadvantage of this method is that to obtain hydrogen to the hydride, it is necessary to supply sufficiently large heat fluxes per unit time, which, taking into account the thermal conductivity of the hydride and the limited possibility of electric heaters, is rather difficult.

 The closest in technical essence and the achieved result is a method for producing hydrogen [2] which consists in endothermic decomposition of a metal hydride matrix placed in a reaction vessel. The hydride matrix has a shape corresponding to the configuration of the inner shell of the vessel, and such dimensions that it fills most of the internal volume of the vessel. The matrix has a large number of evenly distributed perforations, in each of which there is a chemical heat source for the decomposition of hydride. Each chemical heat source contains an initiator, and on the outer surface of the vessel there is a means for actuating the specified initiator.

In the known method for the evolution of hydrogen from the hydride matrix, it is also necessary to supply heat sufficient to decompose the hydride. As a rule, the chemical heat source mentioned is almost equal in mass to the mass of the hydride matrix. So, for example, to obtain hydrogen by separating it from NaBH ₄ (the most hydrogen-intensive hydride used), 1 kg of which contains 0.1182 kg of H ₂ , the termite composition (BaO ₂ + Al) must be taken as much as NaBH ₄ . Thus, to obtain 0.1182 kg of H ₂ , 2 kg of a mixture of hydride and thermite composition used as a chemical source of heat is required. When producing hydrogen by decomposition of hydrides such as LiH, NaH, TiH _{2, it is} also necessary to have high temperatures at which these hydrides decompose, respectively, 1138 K, 703 K, 1193 K. This when using chemical heat sources also leads to high energy consumption, and accordingly, and to large weight and size characteristics. In addition, due to the low thermal conductivity of hydrides, the time to reach the set temperatures is quite long.

 The objective of the invention is to reduce energy consumption and reduce the duration of the process for producing hydrogen.

 The problem is achieved in that in accordance with the method of producing hydrogen by supplying heat to a hydrogen-containing composition based on metal hydrides or intermetallic compounds, according to the invention, a sample formed from a mixture of hydride powders with metals or hydrides taken in a stoichiometric ratio is placed in an oxygen-free medium whose components are capable of forming intermetallic compounds and locally ignite it. The formed sample is preheated to a temperature of 323-773 K.

 The process of producing hydrogen from this mixture is based on the use of internal chemical energy of the starting reagents forming intermetallic compounds, which is the most advantageous organization of the process of hydrogen evolution from hydrides from a thermal point of view.

 Some of the features that distinguish this technical solution from the known one are not new, however, the combination of all the distinguishing features in comparison with the prototype and analogues makes it possible to obtain a qualitatively new method for producing hydrogen, which can significantly reduce energy consumption during the process and accelerate the process for producing hydrogen. This allows us to conclude that the technical solution has novelty and differences.

 The essence of the method is as follows.

 The hydrogen-containing composition is formed from at least a metal and metal hydride or from two different hydrides, the metals of which have a significant chemical agent, have the same crystal lattice and close atomic radii, and are able to form intermetallic chemical compounds between themselves. A significant amount of heat is released, especially in the reaction with the formation of intermetallic compounds with the presence of a covalent or ionic component. This heat is enough to liberate hydrogen from hydrides.

The process of producing hydrogen by the proposed method can be represented as follows:
Me _m H _x + Me _n H _y __ → Me _m Me _n + H _{x + y}
The synthesis of intermetallic compounds Me _m Me _n are called high-temperature self-propagating synthesis (SHS) and can take place both in the thermal explosion mode and in the layer-by-layer combustion mode.

 The thermal explosion mode is characterized by the course of the reaction in the entire volume of the reaction system; in the combustion mode, the chemical reaction after its local initiation spontaneously moves through the substance in the form of a narrow zone. For the self-propagating reaction to occur both in the thermal explosion mode and in the combustion mode, there are critical conditions: the high exotherm of the reaction rate from temperature.

 Thus, from hydrides, the metals of which can form intermetallic compounds by the SHS method, hydrogen can be separated out with minimal energy consumption.

 The implementation of the proposed method for producing hydrogen can be demonstrated by the following examples.

1. Take a mixture of powders of hydride Ti, H ₂ and Al with a dispersion of (50-100) 10 ^-6 and in a stoichiometric ratio according to the equation:
TiH ₂ + Al __ → TiAl + H ₂
From the mixture obtained, a tablet is pressed into a porosity of ≈40% with a diameter of (15-20) 10 ^-3 m and a length of (20-30) 10 ^-3 m. Having placed the tablet in a sealed reactor, a vacuum of 1.3 • 10 ^{- is} created in it using a pump ^{. 6} MPa. Then, after pre-heating the mixture to a temperature of 573 K using a tungsten filament, pressed into one of the ends of the tablets, the mixture is ignited. After local initiation of the exothermic reaction of the formation of the TiAl intermetallic compound, its front spontaneously moves along the compressed tablet. A significant amount of hydrogen is released. So, in the case of the formation of the TiAl intermetallic compound, 1 kg of the mixture will release 0.0256 kg of hydrogen. In the case of the formation of TiAl ₃ by reaction:
TiH ₂ + 3Al __ → TiAl ₃ + H ₂
kg of the mixture will give 0.0149 kg of H ₂ . In the case of using 1 kg of a mixture of hydrides TiH ₂ and AlH ₃ during the formation of the intermetallic compound TiAl according to the equation:
2TiH ₂ + 2AlH ₃ __ → 2TiAl + 5H ₂
0.063 kg of hydrogen will be released.

In the formation of the intermetallic compound TiAl ₃ according to the equation:
TiH ₂ + 3AlH ₃ __ → TiAl ₃ + 5.5H ₂
0.069 kg of H ₂ will be released from 1 kg of the mixture.

For comparison, it should be noted that the temperature of thermal decomposition of TiH ₂ in accordance with the prototype method is 1073-1273 K.

2. In the case of using a mixture of LiH and AlH _{3, the} mixture is ignited without preliminary heating. In the formation of intermetallic compounds LiAl, according to the equation
LiH + AlH ₃ _ → LiAl + 2H ₂
1 kg of the mixture will give off 0.1055 kg of hydrogen.

When hydrogen is released from LiH by thermal decomposition (T _decomp. 1138 K) using a thermite composition, the amount of hydrogen produced will be ≈ 0.052 kg.

When producing hydrogen by decomposing NaBH ₄ (T _decomp. 600 K) using a thermite composition, for example, a BaO + Al mixture which is taken in a ratio of 1: 1 hydride, has 1 kg of a mixture of NaBH ₄ hydride and a thermite composition in which NaBH _{4 is} contained 50% will release 0.0591 kg of hydrogen.

 It should be noted that upon receipt of 10 l of hydrogen at a pressure of 150 atm, using the decomposition of reversible metal hydrides in standard designs with heating to specified temperatures through the wall, the process duration is 180 250 s.

 When using the proposed method for producing the same amount of hydrogen at the same pressure, the duration of the process for producing hydrogen, in accordance with the reaction rate of formation of intermetallic compounds, is 3 8 s.

 Proposed in the inventive method, the temperature range of the preheating of various mixtures corresponds to the temperature interval for the formation of intermetallic compounds for metal components included in a particular mixture.

 Thus, the proposed method allows to obtain hydrogen by separating it from metal hydrides through the use of internal chemical energy released during the formation of intermetallic compounds in the mode of self-propagating high-temperature synthesis, significantly reducing energy consumption and reducing the duration of the process.

 As shown by the calculations and the obtained experimental data, this significantly improves the operational parameters of the process compared with the thermal decomposition of metal hydrides.

Claims (2)

 1. A method of producing hydrogen by decomposing a hydride-containing composition by heating through an initiator, characterized in that a sample is formed in an oxygen-free medium formed from a mixture of hydride powders with metals or hydrides taken in a stoichiometric ratio, the metal components of which can form intermetallic compounds by reaction self-propagating high-temperature synthesis, and for its implementation as an initiator use a filament brought up to the sample.  2. The method according to claim 1, characterized in that the formed sample is preheated to 323-773K.