CN111573621A - A kind of method of producing hydrogen by hydrolysis - Google Patents

Abstract

The invention provides a method for producing hydrogen by hydrolysis, which utilizes the hydrolysis reaction of an aqueous solution of neutral salt and a Mg-Mg ₂ NiH ₄ composite material to produce hydrogen. The hydrolysis hydrogen production method provided by the 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 with an aqueous solution of neutral salt at normal temperature, and produce hydrogen within 20 seconds The amount 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 precious metal elements, the raw material price is low, the operation is simple and convenient, and the hydrogen production efficiency is high, which is favorable for industrialization.

Description

A kind of method of producing hydrogen by hydrolysis

Technical field:

The invention relates to the field of hydrogen production by hydrolysis, in particular to a method for producing hydrogen 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, especially the development of hydrogen-consuming equipment such as hydrogen fuel cells. strict requirements. The development of safe, efficient, cheap and fast hydrogen production technology has become a research hotspot. Among the many hydrogen production technologies, light metals for hydrogen production by hydrolysis are the research hotspots of scholars at home and abroad in recent years.

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

At present, the research on the problems of magnesium-based materials mainly focuses on the preparation of composite hydrolyzed materials by introducing additives. For example, Huang et al. (J.Power Sources 365(2017) 273-281) reported a Mg-10wt.%MoS2 composite _hydrogen -producing agent with a hydrogen production capacity of 759.1mL/g in 1min and a maximum hydrogen production rate of 3258mL g ⁻¹ min ⁻¹ ; Liu et al. (Energy68(2014) 548-554) Introducing AlCl3 into the Mg _{– LiBH4} system to enhance its hydrolysis kinetics; Xiao et al. (Int.J.Hydrogen Energy 44(2019) 1366-1373) In the process of ball milling, In was introduced to catalyze the hydrolysis of Mg, and the conversion rate reached 93.0% within 20 min. The relevant reports at home and abroad are summarized in Table 1, which are all characterized by sacrificing the theoretical hydrogen production capacity of the system to promote the kinetic performance of magnesium hydrolysis. A more ideal solution is how to significantly improve the hydrolysis kinetics of magnesium without significantly reducing the theoretical hydrogen production of the system, which has very important research value and practical significance.

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

^a The volume of hydrogen gas obtained from the hydrogen production of 1 g of the complex

Invention content:

The purpose of the present invention is to provide a method for producing hydrogen by hydrolysis in view of the deficiencies of the prior art. The hydrogen production method has the advantages of short reaction time, high hydrogen production amount, and fast hydrogen production rate, and at the same time, it is efficient and convenient, 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 kind of method for producing hydrogen by hydrolysis, and its concrete steps are:

1) Weigh Mg, Mg ₂ NiH ₄ and a grinding aid to form a mixed composite material for mechanical ball milling to obtain a Mg-Mg ₂ NiH ₄ composite solid powder; wherein Mg accounts for 80% of the total mass 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 neutral salt to carry out a hydrolysis reaction (Mg+2H ₂ O→Mg(OH) ₂ +H ₂ ,Mg ₂ NiH ₄ +4H ₂ O→2Mg(OH) ₂ +Ni+ 4H ₂ ), producing hydrogen.

Preferably, the ball mill used in the above-mentioned mechanical ball milling includes a planetary ball mill; the ball milling is carried out in 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 mass ratio of balls to material is 20-40:1; the rotating speed of the ball mill is 250-500r/min; the time of the ball-milling is 0.5-5h.

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

Preferably, the mass-to-liquid 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 effects:

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 amount and fast hydrogen production rate, and the hydrogen production amount can be as high as 845.1 mL/g within 20 seconds , the conversion rate was 94.7%, and the maximum hydrogen production rate was 6391 mL g ^-1 min ^-1 . It is not difficult to find by comparing the relevant research data at home and abroad in Table 1, the hydrogen production performance obtained by hydrolysis obtained by the hydrogen production method provided by the present invention has significant competitiveness in the world.

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

Description of drawings:

Fig. 1 is the XRD pattern of the Mg-10wt.%Mg ₂ NiH ₄ composite material prepared in Example 1;

Figure 2 is a graph showing the hydrolysis kinetics of Mg-10wt.%Mg ₂ NiH ₄ composites prepared in Example 1 and Comparative Example and Mg without Mg ₂ NiH ₄ in 3.5% NaCl solution at 30°C;

3 is a SEM backscattered electron imaging image of the Mg-10wt.%Mg ₂ NiH ₄ composite material prepared in Example 2;

Figure 4 is a graph showing the hydrolysis kinetics of the Mg-10wt.%Mg ₂ NiH ₄ composite prepared in Example 2 in a 3.5%NaCl solution at 30°C;

Figure 5 is a graph showing the hydrolysis kinetics of the Mg-10wt.%Mg ₂ NiH ₄ composite prepared in Example 5 in 3.5% NaCl solution at different temperatures (10°C to 40°C);

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

Detailed ways:

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

Example 1

In a glove box under 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite were uniformly mixed in a mass ratio of 88:10:2, then put into a ball mill jar and placed in a high-energy planetary ball mill In (QM-3SP2), the ball-to-material ratio is 30:1, the ball milling speed is 400 r/min, the operation is alternately performed for 30 minutes and then stopped for 6 minutes, and the ball is milled in an argon atmosphere for 0.5h; Take the material to obtain a sample powder with fine particle size (referred to as 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 in addition to 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 Mg and Mg ₂ NiH ₄ are in the process of ball milling. No chemical reaction occurred.

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

Comparative ratio

In a glove box under 0.1MPa argon atmosphere, Mg powder and graphite were uniformly mixed in a mass ratio of 98:2, put into a ball mill jar, and the ball mill jar was placed in a high-energy planetary ball mill (QM-3SP2). The ball-to-material ratio is 30:1, the ball milling speed is 400 r/min, the operation is alternately performed for 30 minutes and then stopped for 6 minutes, and the ball is milled in an argon atmosphere for 1 hour; (Note Mg, t1).

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

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

Example 2

In a glove box under 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite were uniformly mixed in a mass ratio of 88:10:2, then put into a ball mill jar and placed in a high-energy planetary ball mill In (QM-3SP2), the ball-to-material ratio is 30:1, the ball milling speed is 400 r/min, the operation is alternately performed for 30 minutes and then stopped for 6 minutes, and the ball is milled for 3 hours in an argon atmosphere; , to obtain a sample powder with fine particles (referred to as 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. It can be seen from Figure 3 that the small bright 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 0.1 g of the sample powder and 10 mL of NaCl solution with a mass concentration of 3.5% at 30 ° C for hydrolysis reaction, the reaction time is 20 seconds, 845.1 mL/g of hydrogen is released, the conversion rate is 94.7%, and the maximum hydrogen production rate is 6391 mL g ^{- 1} min ^-1 . The hydrolysis kinetic curve is shown in the curve in Figure 4. From the curve in Figure 4, it can be seen that the amount of hydrogen produced by hydrolysis and the kinetic performance are further improved.

Example 3

In a glove box of 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite were uniformly mixed according to the mass ratio of 94.8:0.2:5, then put into a ball mill jar and placed in a high-energy planetary ball mill In (QM-3SP2), the ball-to-material ratio is 40:1, the ball milling speed is 250 r/min, the operation is alternately performed for 30 minutes and then stopped for 6 minutes, and the ball is milled for 5 hours in an argon atmosphere; to obtain sample powder with fine particles.

Take 0.1 g of sample powder and 5 mL of NaCl solution with a mass concentration of 2% at 30 ° C for hydrolysis reaction, the reaction time is 4 minutes, 766.8 mL/g of hydrogen is released, the conversion rate is 87.6%, and 460.4 mL/g of hydrogen is released within 1 minute. g, the conversion was 52.6%. Compared with pure magnesium, only a small amount of Mg ₂ NiH ₄ is 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 were uniformly mixed in a mass ratio of 80:15:5, then put into a ball mill jar and placed in a high-energy planetary ball mill In (QM-3SP2), the ball-to-material ratio is 20:1, the ball milling speed is 500 r/min, the operation is alternately performed for 30 minutes and then stopped for 6 minutes, and the ball is milled for 1 h in an argon atmosphere; to obtain sample powder with fine particles.

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

Example 5

In a glove box under 0.1MPa argon atmosphere, Mg powder, Mg ₂ NiH ₄ powder and graphite were uniformly mixed in a mass ratio of 88:10:2, then put into a ball mill jar and placed in a high-energy planetary ball mill In (QM-3SP2), the ball-to-material ratio is 30:1, the ball milling speed is 400 r/min, the operation is alternately performed for 30 minutes and then stopped for 6 minutes, and the ball is milled for 1 h in an argon atmosphere; The sample powder with fine particle size was obtained (denoted as Mg-10wt.%Mg ₂ NiH ₄ , t1).

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

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

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

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

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

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

The reaction activation energy of the hydrolysis system is calculated according to the Arrhenius equation. The Arrhenius curve is shown in Figure 6. It can be seen from Figure 6 that the reaction activation energy of the hydrolysis system is only 19.8 kJ/mol, which is significantly lower than that of pure magnesium. The hydrogen production method has the advantages of short reaction time, high hydrogen production amount and fast hydrogen production rate.

Claims (5)

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

1) weighing Mg and Mg₂NiH₄Mixing with grinding aid to obtain mixed composite material, and ball milling to obtain Mg-Mg₂NiH₄Compounding 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 for₂NiH₄0.2-15 percent of grinding aid and 1-5 percent of grinding aid;

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 grinding aid is a carbon material; the mass ratio of ball materials for ball milling is 20-40: 1; 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 K₂SO₄The 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 aqueous solution of the neutral salt is 1 (50-200) g/mL.

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

Images