CN111573621B - A method for producing hydrogen by hydrolysis - Google Patents

Abstract

The invention provides a method for producing hydrogen by hydrolysis. The method utilizes an aqueous solution of a neutral salt and a Mg-Mg ₂ NiH ₄ composite material to carry out a hydrolysis reaction to produce hydrogen. The hydrolysis hydrogen production method provided by the present invention improves the comprehensive hydrogen production performance of the magnesium-based composite material, especially significantly improves the hydrolysis kinetic performance, and can directly react after contacting an aqueous solution of a neutral salt at room temperature, and produce hydrogen within 20 seconds The volume can be as high as 845.1mL, the conversion rate can reach 94.7%, and the maximum hydrogen production rate is 6391mL g ^‑1 min ^‑1 , which can realize rapid real-time hydrogen production and real-time hydrogen supply, and is suitable for providing high-purity hydrogen sources for hydrogen-consuming equipment such as hydrogen fuel cells . At the same time, the hydrolysis hydrogen production method provided by the invention does not need noble metal elements, the raw material is cheap, the operation is simple and convenient, the hydrogen production efficiency is high, and it is beneficial to industrialization.

Description

A method for producing hydrogen by hydrolysis

Technical field:

The invention relates to the field of hydrogen production by hydrolysis, in particular to a method for hydrogen production by hydrolysis of magnesium-based composite materials.

Background technique:

In the field of new energy, hydrogen energy has the advantages of high calorific value, zero pollution, and recyclability, and is considered to be the energy source with the most potential to replace fossil fuels. strict requirements. The development of safe, efficient, cheap and rapid hydrogen production technology has become a research hotspot. Among many hydrogen production technologies, hydrolysis of light metals for hydrogen production has become a research hotspot of scholars at home and abroad in recent years.

Among the light metals, magnesium metal has abundant resources, low price, high theoretical hydrogen production capacity (921mL/g), mild reaction conditions, and environmentally friendly hydrolysis by-products, so it has great development potential and research value. However, as the reaction progresses, a dense passivation layer Mg(OH) ₂ film is formed to cover the surface of the unreacted magnesium particles, which hinders the further diffusion of water molecules into the particles, resulting in a sharp decrease in the hydrolysis kinetics and conversion rate. .

At present, the research on the problems of magnesium-based materials mainly focuses on the introduction of additives to prepare composite hydrolyzed materials. For example, Huang et al. (J. Power Sources 365 (2017) 273-281) reported a Mg-10wt.% MoS ₂ composite hydrogen production agent with a hydrogen production capacity of 759.1 mL/g in 1 min and a maximum hydrogen production rate of 3258 mL g ^-1 min ^-1 ; Liu et al. (Energy68(2014) 548-554) introduced AlCl ₃ into the Mg–LiBH ₄ system to enhance its hydrolysis kinetics; Xiao et al. (Int.J.Hydrogen Energy 44(2019) 1366-1373) introduced In to catalyze the hydrolysis of Mg during the ball milling process, and the conversion rate reached 93.0% within 20 min. The relevant reports at home and abroad are summarized in Table 1, which are characterized by sacrificing the theoretical hydrogen production capacity of the system to promote the kinetics of magnesium hydrolysis. A more ideal solution is how to significantly improve the hydrolysis kinetics of magnesium without significantly reducing the theoretical hydrogen production capacity of the system, which has very important research value and practical significance.

Table 1 Comparison of hydrolysis performance of different magnesium-based materials

^a The volume of hydrogen gas produced by hydrogen production from 1 g of the compound

Invention content:

The object of the present invention is to provide a method for producing hydrogen by hydrolysis in view of the deficiencies in the prior art. The hydrogen production method has the advantages of short reaction time, high hydrogen production capacity, and fast hydrogen production rate. It is also efficient and simple, does not require complicated equipment and procedures, is low in cost, and is safe and environmentally friendly.

The technical scheme of the present invention is: a method for producing hydrogen by hydrolysis, the specific steps of which are:

1) Weighing Mg, Mg ₂ NiH ₄ and grinding aid to form a mixed composite material for mechanical ball milling to obtain Mg-Mg ₂ NiH ₄ Composite solid powder; wherein Mg accounts for 80% of the total mass percentage of the mechanically mixed composite material %～98.8%, Mg ₂ NiH ₄ 0.2%～15%, grinding aid 1%～5%;

2) Mix the composite solid powder with an aqueous solution of a neutral salt for hydrolysis (Mg+2H ₂ O→Mg(OH) ₂ +H ₂ , Mg ₂ NiH ₄ +4H ₂ O→2Mg(OH) ₂ +Ni+ 4H ₂ ), producing hydrogen gas.

Preferably, the ball mill used in the above-mentioned mechanical ball mill includes a planetary ball mill; the ball mill is carried out under an inert atmosphere, including an argon atmosphere; the grinding aid is a carbon material, and the carbon material includes but is not limited to graphite; The ball to material mass ratio is 20-40:1; the speed of the ball mill is 250-500r/min; the time of the ball mill is 0.5-5h.

Preferably, the above-mentioned neutral salt aqueous solution is NaCl solution, KCl solution or K ₂ SO ₄ solution, etc., and the mass concentration of the neutral salt aqueous solution is 2%-5%.

Preferably, the mass-to-volume ratio of the composite solid powder to the aqueous solution of the neutral salt is 1:(50-200) g/mL.

It is preferable that the temperature of the said hydrolysis reaction is 10-50 degreeC.

Beneficial effect:

1) The present invention provides a portable on-line hydrolysis hydrogen production method with low price and excellent performance, which has the advantages of short reaction time, high hydrogen production capacity and fast hydrogen production rate, and the hydrogen production rate can reach as high as 845.1mL/g within 20 seconds , the conversion rate is 94.7%, and the maximum hydrogen production rate is 6391mL g ^-1 min ^-1 . It is not difficult to find by comparing the relevant domestic and foreign research data in Table 1 that the hydrolysis hydrogen production performance obtained by the hydrogen production method provided by the present invention has significant international competitiveness.

2) The obtained high-purity hydrogen can be directly fed into other hydrogen-consuming equipment such as hydrogen fuel cells without other processing, and can be quickly produced anytime and anywhere according to demand, and can be used immediately after production, reducing many problems in the process of hydrogen storage and transportation .

Description of drawings:

Fig. 1 is the _XRD spectrum of the Mg-10wt.% _Mg2NiH4 composite material that embodiment 1 makes;

Fig. 2 is the Mg-10wt.% _Mg2NiH4 composite _material that embodiment 1 and comparative example make and do not add _Mg2NiH4The hydrolysis kinetics curve of Mg in 3.5%NaCl solution at 30 _℃ ;

Fig. 3 is _the SEM backscattered electron imaging figure of the Mg-10wt.% _Mg2NiH4 composite material that embodiment 2 makes;

Fig. 4 is the hydrolysis kinetics curve of the Mg-10wt.% _Mg2NiH4 composite material that embodiment 2 makes in 3.5%NaCl solution at 30 ℃ _;

_Fig . 5 is the hydrolysis kinetics curve of the Mg-10wt.% _Mg2NiH4 composite material prepared in Example 5 in 3.5% NaCl solution at different temperatures (10°C-40°C);

Fig. 6 is the Arrhenius curve of the Mg-10wt.% Mg ₂ NiH ₄ composite material prepared in Example 5.

Detailed ways:

The technical solutions of the present invention will be described in further detail below in conjunction with specific embodiments and accompanying drawings, but the present invention is not limited thereto.

Example 1

In a glove box with 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite are uniformly mixed according to the mass ratio of 88:10:2, then put into a ball mill jar and place the ball mill jar in a high-energy planetary ball mill (QM-3SP2), the ball-to-material ratio is 30:1, the ball milling speed is 400r/min, run for 30 minutes and stop for 6 minutes alternately, and ball mill in an argon atmosphere for 0.5h; after the ball milling is completed, carry out in an argon atmosphere glove box The material was collected to obtain a sample powder with fine particles (record Mg-10wt.% Mg ₂ NiH ₄ , t0.5).

The XRD pattern of the sample powder obtained by ball milling is shown in Figure 1. It can be seen from Figure 1 that, except for the diffraction peaks of Mg and Mg ₂ NiH ₄ , there are no diffraction peaks of MgO and other substances in the curve, which proves that during the ball milling process, Mg and Mg ₂ NiH ₄ No chemical reaction occurred.

Take 0.1g of sample powder and 20mL of NaCl solution with a mass concentration of 3.5% for hydrolysis reaction at 30°C. The reaction time is 2.5 minutes, and 784.3mL/g of hydrogen gas is released, with a conversion rate of 87.9%; 748.9mL/g of hydrogen gas is released within 1 minute. g, the conversion rate is 83.9%, and the hydrolysis kinetics curve in the first minute is shown in the curve (a) in Fig. 2 .

comparative example

In a glove box with 0.1MPa argon atmosphere, Mg powder and graphite were uniformly mixed according to a mass ratio of 98:2, then loaded into a ball mill jar and placed in a high-energy planetary ball mill (QM-3SP2) to Ball-to-material ratio 30:1, ball milling speed 400r/min, run for 30 minutes and stop for 6 minutes alternately, ball mill in an argon atmosphere for 1 hour; after the ball milling is completed, take the material in an argon atmosphere glove box to obtain a fine sample powder (Remember Mg, t1).

Take 0.1g of sample powder and 20mL of 3.5% NaCl solution for hydrolysis reaction at 30°C. The reaction time is 35 minutes, and 610.2mL/g of hydrogen gas is released, with a conversion rate of 67.6%; 117.5mL/g of hydrogen gas is released within 1 minute , the conversion rate is 13.0%, and the hydrolysis kinetics curve in the first 1 minute is shown in the curve (b) in Fig. 2 .

The hydrolysis kinetics curve of the hydrolysis reaction of the composite solid powder in NaCl solution is shown in the curve (a) in Figure 2, as can be seen from the curve (a) in Figure 2, the hydrolysis performance is very excellent; Powder hydrolysis (curve (b)), the hydrolysis performance of the Mg-10wt.%Mg ₂ NiH ₄ composite material has been greatly improved.

Example 2

In a glove box with an argon atmosphere of 0.1MPa, Mg powder, Mg ₂ NiH ₄ powder and graphite are uniformly mixed according to the mass ratio of 88:10:2, then put into a ball mill jar and place the ball mill jar in a high-energy planetary ball mill (QM-3SP2), with ball-to-material ratio 30:1, ball milling speed 400r/min, running for 30 minutes and stopping for 6 minutes alternately, ball milling in argon atmosphere for 3h; The sample powder with fine particles was obtained (record Mg-10wt.% Mg ₂ NiH ₄ , t3).

The SEM backscattered electron image of the sample powder obtained by ball milling is shown in Figure 3. From Figure 3, it can be seen that the small bright-colored particles are Mg ₂ NiH ₄ , the gray flakes are Mg, and the Mg ₂ NiH ₄ particles are embedded on the surface of the Mg flakes.

Take 0.1g of sample powder and 10mL of NaCl solution with a mass concentration of 3.5% for hydrolysis reaction at 30°C. The reaction time is 20 seconds, 845.1mL/g of hydrogen gas is released, the conversion rate is 94.7%, and the maximum hydrogen production rate is 6391mL g ^{- 1} min ^-1 . The hydrolysis kinetic curve is shown in the curve in Fig. 4. From the curve in Fig. 4, it can be seen that the hydrogen production amount and kinetic performance of hydrolysis are further improved.

Example 3

In a glove box with an argon atmosphere of 0.1MPa, Mg powder, Mg ₂ NiH ₄ powder and graphite are uniformly mixed according to the mass ratio of 94.8:0.2:5, then put into a ball mill jar and place the ball mill jar in a high-energy planetary ball mill (QM-3SP2), with ball-to-material ratio 40:1, ball milling speed 250r/min, running for 30 minutes and stopping for 6 minutes alternately, ball milling in argon atmosphere for 5h; after ball milling, take out in an argon atmosphere glove box material to obtain a fine sample powder.

Take 0.1g of sample powder and 5mL of NaCl solution with a mass concentration of 2% for hydrolysis reaction at 30°C. The reaction time is 4 minutes, and 766.8mL/g of hydrogen gas is released. The conversion rate is 87.6%, and 460.4mL/g of hydrogen gas is released within 1 minute. g, the conversion rate is 52.6%. Compared with pure magnesium, only a small amount of Mg ₂ NiH ₄ can be added to significantly improve the hydrolysis kinetics of Mg.

Example 4

In a glove box with 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite are uniformly mixed according to the mass ratio of 80:15:5, put into a ball mill jar and place the ball mill jar in a high-energy planetary ball mill (QM-3SP2), with ball-to-material ratio 20:1, ball mill speed 500r/min, run for 30 minutes and stop for 6 minutes alternately, ball mill in argon atmosphere for 1h; after ball milling, take it out in an argon atmosphere glove box material to obtain a fine sample powder.

Take 0.1g sample powder and 20mL K ₂ SO ₄ solution with a mass concentration of 5% for hydrolysis reaction at 30°C. The reaction time is 50 seconds, 757.6mL/g of hydrogen gas is released, and the conversion rate is 88.2%.

Example 5

In a glove box with 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite are uniformly mixed according to the mass ratio of 88:10:2, then put into a ball mill jar and place the ball mill jar in a high-energy planetary ball mill (QM-3SP2), with ball-to-material ratio 30:1, ball milling speed 400r/min, running for 30 minutes and stopping for 6 minutes alternately, ball milling in argon atmosphere for 1h; after ball milling, take it out in an argon atmosphere glove box The sample powder with fine particles was obtained (record Mg-10wt.% Mg ₂ NiH ₄ , t1).

Take 0.1g sample powder and 10mL NaCl solution with a mass concentration of 3.5% for hydrolysis reaction at 10°C, 20°C, 30°C and 40°C respectively;

The hydrolysis reaction is carried out at a temperature of 10° C., the hydrolysis kinetics performance is excellent, the reaction time is 40 seconds, 830.3 mL/g of hydrogen gas is released, and the conversion rate is 93.1%.

The hydrolysis reaction is carried out at a temperature of 20° C., the hydrolysis kinetics performance is excellent, the reaction time is 35 seconds, 834.9 mL/g of hydrogen gas is released, and the conversion rate is 93.6%.

The hydrolysis reaction is carried out at a temperature of 30° C., the hydrolysis kinetics performance is excellent, the reaction time is 30 seconds, 832.8 mL/g of hydrogen gas is released, and the conversion rate is 93.4%.

The hydrolysis reaction is carried out at a temperature of 40° C., the hydrolysis kinetics performance is excellent, the reaction time is 30 seconds, 850.2 mL/g of hydrogen gas is released, and the conversion rate is 95.3%.

The hydrolysis kinetic curves of the sample powder prepared in Example 5 at temperatures of 10°C, 20°C, 30°C and 40°C with NaCl solution are shown in curves (a) to (d) in Figure 5, respectively. From the curves (a) to (d) in Figure 5, it can be seen that the hydrolysis kinetics performance is excellent; and the hydrolysis performance of the Mg-10wt.% Mg ₂ NiH ₄ composite material has been further improved with the increase of the hydrolysis temperature .

Calculate the reaction activation energy of this hydrolysis system according to the Arrhenius equation, the Arrhenius curve is as shown in Figure 6, as can be seen from Figure 6, its reaction activation energy has only 19.8kJ/mol, significantly reduces compared with pure magnesium, thus the hydrolysis provided by the present invention The hydrogen production method has the advantages of short reaction time, high hydrogen production capacity and fast hydrogen production rate.

Claims (5)

1. A method for preparing hydrogen by hydrolysis comprises the following specific steps:

1) Weighing Mg and Mg ₂ NiH ₄ Mixing with grinding aid to obtain mixed composite material, and ball milling to obtain Mg-Mg ₂ NiH ₄ Compounding a solid powder; wherein the Mg accounts for 80 to 98.8 percent of the total mass of the mechanical mixed composite material, and the Mg accounts for ₂ NiH ₄ 0.2-15 percent of grinding aid and 1-5 percent of grinding aid; wherein the grinding aid is a carbon material;

2) And mixing the composite solid powder with a water solution of neutral salt, and performing hydrolysis reaction to generate hydrogen.

2. The method of claim 1, wherein the mechanical ball milling is a planetary ball mill; the ball milling is carried out in an inert atmosphere; the mass ratio of ball materials subjected to ball milling is 20-40; the rotating speed of the ball milling is 250-500 r/min; the ball milling time is 0.5-5 h.

3. The method of claim 1, wherein the aqueous solution of neutral salt is NaCl solution, KCl solution or K ₂ SO ₄ The mass concentration of the solution and the water solution of neutral salt is 2-5%.

4. The method according to claim 1, wherein the feed liquid mass volume ratio of the composite solid powder to the neutral salt water solution is 1 (50-200) g/mL.

5. The method according to claim 1, wherein the temperature of the hydrolysis reaction is 10 to 50 ℃.

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