CN103264988A - Method for producing hydrogen by reaction of aluminium and water catalyzed by aluminum hydroxide or oxide - Google Patents

Abstract

A method for generating hydrogen by reacting aluminum with water under the catalysis of aluminum hydroxide or oxides. The main content of the invention is to add a certain amount (10wt%~50wt%) of aluminum hydroxide or oxide powder with a micron or nanometer size into a closed container with a certain amount of water, and combine the added aluminum hydroxide or oxide with Water mix well. A certain amount of micron-sized pure aluminum (Al) powder is directly added to the closed container above containing the mixed solution of aluminum hydroxide or oxide and water. The pure aluminum (Al) powder in the above sealed container can continuously react with water and generate hydrogen at a normal temperature of 10°C to 40°C and a pressure of 0.04 atmospheres of vacuum to 1 atmospheres of ambient pressure. Among them, g-Al ₂ O ₃ and Al(OH) ₃ have a better effect on promoting the reaction of aluminum (Al) and water to produce hydrogen, and at the same time, the reaction speed of aluminum powder and water under vacuum conditions is faster than that under normal pressure conditions. quick. The main application of this invention is the hydrogen supply of mobile kilowatt-class fuel cells and the hydrogen supply of other small and medium-sized portable fuel cells.

Description

Method for generating hydrogen by reaction of aluminum and water under the catalysis of aluminum hydroxide or oxide

technical field

The invention relates to a process method for generating hydrogen by reacting pure aluminum powder with water under the catalysis of aluminum hydroxide or oxide. A fuel cell carried by a small, portable device provides the hydrogen source. The invention belongs to the technical field of chemistry and chemical engineering.

Background technique

 As people pay more and more attention to environmental changes, the research and development of efficient and clean energy technologies are getting more and more attention. Fuel cells are the core of clean energy technology, because fuel cells directly convert chemical energy into electrical energy and thus have high efficiency and low pollution. Hydrogen is an ideal fuel for fuel cells because the oxidation product of hydrogen is water, which is benign to the environment, and hydrogen has the characteristics of light weight and high energy density.

An important obstacle affecting the industrialization of hydrogen fuel cells is the transportation and storage of hydrogen. Because liquefied hydrogen requires a low temperature of -252 degrees Celsius (°C), compressing hydrogen to a weight ratio (>5 wt%) of hydrogen that can meet commercial requirements at room temperature requires a high pressure of about 700 atmospheres. None of these technologies are cost competitive for commercial operation. Therefore, people pay attention to hydrogen storage materials. The U.S. Department of Energy’s goal for the commercialization of hydrogen storage materials is that the weight ratio of hydrogen in hydrogen storage materials is 6.5% under the conditions of 0-100 degrees Celsius (°C) and 1-10 atmospheres. Although scientists from all over the world are looking for good hydrogen storage materials, the development of hydrogen storage materials is still relatively slow and there is no breakthrough, and there is no material that can meet the requirements of the US Department of Energy.

To solve the problem of hydrogen sources for fuel cells, people have recently turned their attention to hydrogen-producing materials. A characteristic of hydrogen-producing materials is that they can directly react with water to produce hydrogen, thereby providing hydrogen for fuel cells when needed, eliminating the problem of hydrogen storage and transportation. At present, the main research objects are metal hydrides, such as lithium hydride (LiH), sodium hydride (NaH), magnesium hydride (MgH ₂ ), sodium aluminum hydride (NaAlH ₄ ), lithium borohydride (LiBH ₄ ), sodium borohydride (NaBH ₄ ) and potassium borohydride (KBH ₄ ), etc. Considering various practical factors, only sodium borohydride (NaBH ₄ ) is currently commercialized. Therefore, as a hydrogen-generating material for portable applications, sodium borohydride (NaBH ₄ ) has been the most studied. The problem with using sodium borohydride (NaBH ₄ ) as a hydrogen-producing material is that sodium hydroxide (NaOH) must be used as a solution stabilizer, so there is a strong alkali pollution problem. At the same time, the use of sodium borohydride (NaBH ₄ ) as a hydrogen production material must use catalytic devices and catalysts to produce hydrogen, which will greatly increase the volume and cost of the system. Another current problem is that sodium borohydride (NaBH ₄ ) is expensive, about 55 US dollars per kilogram (US$55/kg), which affects the cost of use.

Another class of hydrogen-producing materials is metals. Although metal lithium (Li), sodium (Na) and potassium (K) can directly react with water and produce hydrogen, these alkali metals are expensive and the reaction products are strong alkalis that pollute the environment, so they have no commercial application value. But other metals such as iron (Fe) and aluminum (Al) are cheap and abundant on Earth, making them attractive as hydrogen-producing materials. In particular, metal aluminum (Al) not only has a light atomic mass, but also has a high electron density and a high amount of hydrogen produced by reacting with water. However, under normal temperature and pressure, the reactions of metallic iron (Fe) and aluminum (Al) with water are very slow and limited. Especially metal aluminum (Al), when exposed to an oxidizing environment, a passivated dense oxide protective film will be formed on its surface, therefore, the direct reaction between metal aluminum (Al) and water is difficult.

Contents of the invention

The purpose of this invention is to provide a new simple and cheap hydrogen production process, which can achieve the purpose of direct and complete reaction of aluminum (Al) and water to produce hydrogen under certain conditions.

The invention relates to a process for producing hydrogen by reacting pure aluminum powder with water under the catalysis of aluminum hydroxide or oxides, namely g-Al ₂ O ₃ , a-Al ₂ O ₃ or TiO ₂ , and is characterized in that it has The following process and steps:

a. Add a certain amount of micron or nanometer-sized aluminum hydroxide (Al(OH) ₃ ) or oxides, namely g-Al ₂ O ₃ , a-Al ₂ O ₃ or TiO ₂ powder, into a sealed container with a certain amount of water. container, and mix the added aluminum hydroxide or oxide with water;

b. Add a certain amount of micron-sized pure aluminum (Al) powder directly into the closed container above containing the mixed solution of aluminum hydroxide or oxide and water;

c. Under normal temperature and pressure or under normal temperature and vacuum conditions, that is, at 0.04 bar or 0.04 atmospheric pressure, the pure aluminum powder in the above-mentioned sealed container is continuously reacted with water to generate hydrogen; the reaction equation is:

Aluminum (Al) + water (3H ₂ O) → aluminum hydroxide (Al(OH) ₃ ) + hydrogen (3/2H ₂ ↑)

The weight percentage of aluminum hydroxide or oxide as a catalyst in the whole powder (aluminum powder + aluminum hydroxide or oxide) is 10 wt% to 50 wt%; the reaction temperature is 10°C to 40°C normal temperature, and the ambient pressure of the reaction ranges from a vacuum of 0.04 atmospheric pressure to a normal pressure of 1 atmospheric pressure.

The advantage of the inventive method is as follows:

(1) The present invention does not require special and harsh conditions, only a certain amount of aluminum hydroxide or oxide is added to the water, and the aluminum powder can react with water to produce hydrogen.

(2) It has a high hydrogen production capacity, and 1 kg of aluminum (Al) can produce 0.11 kg of hydrogen.

(3) Hydrogen can be produced without any acid or alkali, and the by-products of the reaction are chemically neutral and have no environmental pollution; and the by-products of the reaction can be reduced back to metal Al for recycling.

(4) The price of metal aluminum is relatively cheap, and the source of aluminum is abundant and easy to obtain; the cost of producing 1 kg of hydrogen from aluminum (Al) powder is about one-sixth of that of sodium borohydride (NaBH ₄ ).

Therefore, the use of aluminum powder to produce hydrogen has obvious advantages in the hydrogen supply of mobile kilowatt fuel cells and other small portable fuel cells.

Price advantage, and has the advantage of simple process equipment.

Description of drawings

Fig. 1 is the scanning electron microscope (SEM) photograph of powder used in the present invention: (a) the original aluminum (Al) powder that average size is 7.29 microns, (b) aluminum hydroxide (Al(OH) that average size is 2.5 microns ) ₃ ) powder, (c) nano g-Al ₂ O ₃ powder with a specific surface area of 190 m ² /g, (d) nano a-Al ₂ O ₃ powder with a specific surface area of 14.46 m ² /g, (e) Nano TiO ₂ powder with a specific surface area of 27.93 m ² /g.

Figure 2 shows the pure aluminum (Al) powder under normal temperature (25°C) and vacuum conditions of 0.04 atmospheric pressure (0.04bar) in the absence of a catalyst and the use of 28 wt% aluminum hydroxide (Al(OH) ₃ ) The hydrogen production rate (complete reaction rate) of the reaction between aluminum (Al) powder and water progresses with the reaction time. (Note: 28 wt% here refers to the weight percentage of aluminum hydroxide in the whole powder (aluminum powder + aluminum hydroxide), the amount of (aluminum powder + aluminum hydroxide) in the experiment is 1 gram, water The amount is 250 ml)

Figure 3 shows the pure aluminum (Al) powder under normal temperature (25°C) and 0.04 atmospheric pressure (0.04bar) vacuum conditions without catalyst and using 34 wt% g-Al ₂ O ₃ metal aluminum (Al) The hydrogen production rate (complete reaction rate) of the reaction between powder and water progresses with the reaction time. (Note: 34 wt% here refers to the weight percentage of g-Al ₂ O ₃ in the whole powder (aluminum powder + g-Al ₂ O ₃ ), in the experiment (aluminum powder + g-Al ₂ O ₃ ) The amount of water is 1g, the amount of water is 250ml)

Figure 4 shows the pure aluminum (Al) powder under the vacuum conditions of normal temperature (25°C) and 0.04 atmospheric pressure (0.04bar) in the absence of catalyst and the use of 39 wt% a-Al ₂ O ₃ metal aluminum (Al) The hydrogen production rate (complete reaction rate) of the reaction between powder and water progresses with the reaction time. (Note: 39 wt% here refers to the weight percentage of a-Al ₂ O ₃ in the whole powder (aluminum powder + a-Al ₂ O ₃ ), in the experiment (aluminum powder + a-Al ₂ O ₃ ) The amount of water is 1g, the amount of water is 250ml)

Figure 5 shows the pure aluminum (Al) powder under normal temperature (25°C) and 0.04 atmospheric pressure (0.04bar) vacuum conditions without a catalyst and using 40 wt% TiO ₂ Metal aluminum (Al) powder and water The reaction hydrogen production rate (complete reaction rate) progresses with the reaction time. (Note: 40 wt% here refers to the weight percentage of TiO ₂ in the whole powder (aluminum powder + TiO ₂ ), the amount of (aluminum powder + TiO ₂ ) in the experiment is 1 gram, and the amount of water is 250ml)

Figure 6 shows the pure aluminum (Al) powder under normal temperature (25°C) and normal pressure (1bar) or 0.04 atmospheric pressure (0.04bar) vacuum conditions under the condition of using 34 wt% g-Al ₂ O ₃ metallic aluminum (Al) The progress of the hydrogen production rate (complete reaction rate) of the powder and water reaction with the reaction time. (Note: 34 wt% here refers to the weight percentage of g-Al ₂ O ₃ in the whole powder (aluminum powder + g-Al ₂ O ₃ ), in the experiment (aluminum powder + g-Al ₂ O ₃ ) The amount of water is 1g, the amount of water is 250ml)

Figure 7 shows the pure aluminum (Al) powder under the vacuum conditions of normal temperature (25°C) and 0.04 atmospheric pressure (0.04bar) using g-Al ₂ O ₃ (12 wt%, 34 wt% , 54 wt%), the reaction hydrogen production rate (complete reaction rate) of metal aluminum (Al) powder and water progresses with the reaction time. (Note: In the experiment, the amount of (aluminum powder + g-Al ₂ O ₃ ) is 1 gram, and the amount of water is 250 ml).

Figure 8 is an X-ray diffraction diagram, wherein: a. the phase composition of pure aluminum (Al) powder reacted with water for 151 hours at normal temperature (25 ° C) and normal pressure (1 bar); b. at normal temperature (25 °C) and 0.04 atmospheric pressure (0.04bar) under vacuum conditions of pure aluminum (Al) powder and water phase composition after 119.3 hours of reaction; c. normal temperature (25°C) and 0.04 atmospheric pressure (0.04bar) vacuum Phase composition of pure (Al) powder after reacting with water for 32.4 hours under the condition of using 34 wt% g-Al ₂ O ₃ ; d. Normal temperature (25°C) and vacuum of 0.04 atmospheres (0.04bar) Phase composition of pure (Al) powder after reacting with water for 38.3 hours under the condition of using 39 wt% a-Al ₂ O ₃ ; e. Normal temperature (25°C) and vacuum of 0.04 atmosphere (0.04bar) Phase composition of pure (Al) powder after reacting with water for 29 hours under the condition of using 28 wt% Al(OH) ₃ ; f. Vacuum conditions at room temperature (25°C) and 0.04 atmosphere pressure (0.04bar) The phase composition of the pure (Al) powder after reacting with water for 39.8 hours using 40 wt% TiO ₂ is shown below.

Detailed ways

Specific embodiments of the present invention are now described in the following.

Embodiment one

The specific preparation process of this embodiment is as follows:

Get 250 milliliters (mL) deionized water and put into a sealed glass container of known volume, then add the aluminum hydroxide that is used to catalyze the reaction of aluminum and water, its addition is 28 wt%, stir evenly with glass rod, Then add metal aluminum (Al) powder, and then use a glass rod to stir all the powder and water evenly, and then seal the airtight glass container. If a vacuum is required, the air pressure in the airtight glass container is evacuated to a vacuum pressure of 0.04 atmospheres (0.04 bar), and then the experiment is started. Since the reaction of aluminum (Al) with water only produces hydrogen, we calculate the volume of hydrogen produced by recording the pressure change in the airtight glass container according to the ideal gas equation, and then calculate the total amount of hydrogen produced by the complete reaction of the added Al The complete reaction rate of metal aluminum (Al) powder and water changes with time, that is, the progress curve of hydrogen production.

Under the catalysis of aluminum hydroxide (Al(OH) ₃ ), the progress of the reaction of Al and water to produce hydrogen is shown in Figure 2; Pure aluminum (Al) powder will not react with water and produce hydrogen if there is no aluminum hydroxide within 45 hours, but when 28 wt% aluminum hydroxide (Al(OH) ₃ ) is added, pure aluminum ( Al) The powder will continuously react with water and generate hydrogen gas after a short (5.5 hours) induction period. After 29 hours, the Al reacted with water substantially completely.

Embodiment two

    The preparation process of this example is exactly the same as that of Example 1 above, except that 34 wt% g-Al ₂ O ₃ is used as the catalyst; under the catalysis of g-Al ₂ O ₃ , Al reacts with water to produce See Figure 3 for the progress; it shows that at room temperature (25°C) and under vacuum conditions of 0.04 atmospheric pressure (0.04bar), within 45 hours, if there is no g-Al ₂ O ₃ , the pure aluminum (Al) powder will does not react with water and generate hydrogen, _but when 34 wt% g- _Al2O3 is added, pure aluminum (Al) powder will continuously react with water and Hydrogen gas is produced. After 32.4 hours, the Al reacted with water substantially completely.

Embodiment three

The preparation process of this example is exactly the same as that of Example 1 above, except that 39 wt% a-Al ₂ O ₃ is used as a catalyst; under the catalysis of a-Al ₂ O ₃ , Al reacts with water to produce hydrogen The progress is shown in Figure 4; it shows that at normal temperature (25°C) and under the vacuum condition of 0.04 atmospheric pressure (0.04bar), if there is no a-Al ₂ O ₃ in the time of 45 hours, the pure aluminum (Al) powder will does not react with water to produce hydrogen _, but when 39 wt% a- _Al2O3 is added, pure aluminum (Al) powder will continuously react with water and produce hydrogen. After 38.3 hours, the Al reacted with water substantially completely.

Embodiment four

The preparation process of this example is exactly the same as that of Example 1 above, except that 39 wt% _TiO2 is used as the catalyst; the progress of the reaction of Al and water to produce hydrogen under the catalysis of _TiO2 is shown in Figure 5; Under normal temperature (25°C) and 0.04 atmospheric pressure (0.04bar) vacuum conditions, pure aluminum (Al) powder will not react with water and generate hydrogen if there is no TiO ₂ within 45 hours, but when adding With 40 wt% TiO ₂ , pure aluminum (Al) powder will continuously react with water and generate hydrogen gas after a short induction period (11.2 h). After 39.8 hours, the Al reacted with water substantially completely.

Experiments performed under other conditions and their results and comments

(1). The progress of the reaction of Al and water to produce hydrogen under the catalysis of g-Al ₂ O ₃ under different ambient pressures is shown in Figure 6; it shows normal temperature (25°C) normal pressure (1 bar) or normal temperature and 0.04 atmospheric pressure (0.04bar) vacuum condition, as long as g-Al ₂ O ₃ exists, pure aluminum (Al) powder will react with water continuously and generate hydrogen after a period of induction period. Of course, under vacuum conditions, the effect of adding g-Al ₂ O ₃ on promoting the reaction of aluminum (Al) and water to produce hydrogen is more obvious.

(2). Metal aluminum (Al) in the case of using g-Al ₂ O ₃ with different weight percentage ratios (12 wt%, 34 wt%, 54 wt%) under normal temperature and 0.04 atmospheric pressure (0.04bar) vacuum conditions The complete reaction rate of powder and water, that is, the progress of hydrogen production, is shown in Figure 7. It can be seen from FIG. 7 that the more the amount of oxide added, the more obvious the effect on promoting the reaction of aluminum (Al) and water to produce hydrogen. Of course, when the amount _of g- _Al2O3 added is 54 wt%, the effect of g- _Al2O3 on promoting the reaction of aluminum (Al) with water to produce _hydrogen seems to be close to saturation.

It can be seen from Figure 2-5 that g-Al ₂ o ₃ and Al(OH) ₃ It has a good effect on shortening the reaction induction period and promoting the reaction of aluminum (Al) and water to produce hydrogen.

Figure 8 shows that metal aluminum (Al) powder and water hardly react at normal temperature and pressure, and the added aluminum hydroxide (Al(OH) ₃ ) or oxides (g-Al ₂ O ₃ , a-Al ₂ O ₃ , TiO ₂ ) phase composition did not change before and after the reaction between aluminum (Al) powder and water, indicating that aluminum hydroxide (Al(OH) ₃ ) or oxide only produced hydrogen for the reaction of aluminum (Al) powder and water Play a catalytic role. From the reaction of aluminum (Al) powder and water to produce hydrogen, the by-product is bayerite (Al(OH) ₃ ), which shows that the reaction equation is:

Aluminum (Al) + water (3H ₂ O) → aluminum hydroxide (Al(OH) ₃ ) + hydrogen (3/2H ₂ ↑).

Claims (2)

1. a process of reacting with water to generate hydrogen under the catalysis of aluminum hydroxide or oxides, namely g-Al ₂ O ₃ , a-Al ₂ O ₃ or _TiO , is characterized in that it has the following The process and steps: a. Add a certain amount of micron or nanometer-sized aluminum hydroxide (Al(OH) ₃ ) or oxides, namely g-Al ₂ O ₃ , a-Al ₂ O ₃ or TiO ₂ powder, into a sealed container with a certain amount of water. container, and mix the added aluminum hydroxide or oxide with water; b. Add a certain amount of micron-sized pure aluminum (Al) powder directly into the closed container above containing the mixed solution of aluminum hydroxide or oxide and water; c. Under normal temperature and pressure or under normal temperature and vacuum conditions, that is, under 0.04 bar or 0.04 atmospheric pressure, the pure aluminum powder in the above-mentioned sealed container is continuously reacted with water to generate hydrogen; the reaction equation is: Aluminum (Al) + water (3H ₂ O) → aluminum hydroxide (Al(OH) ₃ ) + hydrogen (3/2H ₂ ↑). 2. as claimed in claim 1, under the catalysis of aluminum hydroxide or oxide, the process method of reacting aluminum powder and water to generate hydrogen is characterized in that aluminum hydroxide as catalyst is Al(OH) ₃ , oxide That is, g-Al ₂ O ₃ , a-Al ₂ O ₃ or TiO ₂ , the percentage by weight in the whole powder (aluminum powder + aluminum hydroxide or oxide) is 10 wt% to 50 wt%; the reaction The temperature is the normal temperature of 10 DEG C to 40 DEG C, and the ambient pressure of reaction is the normal pressure of the vacuum of 0.04 atmospheric pressure to 1 atmospheric pressure.

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