CN104445062B - A kind of method that smooth thermochemical cycles decomposition water prepares hydrogen - Google Patents

Abstract

The present invention relates to photolysis water hydrogen, it is desirable to provide a kind of method that smooth thermochemical cycles decomposition water prepares hydrogen.The method that this kind of light thermochemical cycles decomposition water prepares hydrogen includes step: take zinc nitrate, deionized water, glacial acetic acid, absolute ethyl alcohol obtained solution A, take butyl titanate, absolute ethyl alcohol obtained solution B, solution A is poured into solution B stir to gel, colloid is dried after grinding to form fine powder, reheat roasting and prepare binary metal composite oxide, binary metal composite oxide with light source irradiate reaction after, heat and be passed through steam carry out reaction produce H₂.Photochemistry is joined together by the present invention with heat chemistry, titanium zinc binary metal composite oxide is utilized to resolve into the feature of metal suboxide and oxygen at normal temperatures and pressures through illumination, greatly reduce the temperature needed for the thermochemical cycles first step, improve cycling condition.

Description

A method for producing hydrogen by photothermochemical cycle decomposition of water

technical field

The invention relates to the field of hydrogen production by photolysis of water, in particular to a method for producing hydrogen by photothermochemical cycle decomposition of water.

Background technique

As a clean and efficient secondary energy carrier, hydrogen energy has the characteristics of rich sources, light weight, high calorific value, green environmental protection, and various utilization forms and storage methods. play an important role in the future energy landscape. The large-scale, efficient and low-cost production of hydrogen is the key problem that must be solved first. Hydrogen production from fossil fuels is the most important method at this stage, and the technology is relatively mature. This method relies on fossil fuels and emits carbon dioxide, and its subsequent development is limited. Biomass hydrogen production is rich in resources and sustainable development, but its low energy density and scattered resources still need to be overcome. As the compound with the most abundant hydrogen content on the earth, water can be produced by electrolysis, photolysis, pyrolysis, thermochemical cycle and other methods. The energy efficiency of hydrogen production by electrolysis of water is as high as 70%, but combined with the power generation efficiency of thermal power plants, the energy utilization efficiency is as low as 24-32%. However, it has good development prospects in combination with renewable energy power generation. Hydrogen production by photolysis of water is one of the best ways for photochemical conversion and storage of solar energy, which is of great significance. The low efficiency and cost of photoenergy conversion still need further research. Direct high-temperature pyrolysis of water to produce hydrogen has defects such as difficult material adaptation and difficult separation of hydrogen and oxygen, so it is currently not feasible. Compared with direct pyrolysis of water, the thermochemical method greatly reduces the reaction temperature, and has the advantages of high efficiency, low cost and zero carbon emissions, so it has good market development potential.

The thermochemical water splitting cycle based on the redox of metal oxides usually consists of two steps: the first step is the decomposition of metal oxides at high temperature to produce oxygen and metal elements or lower valence metal oxides; the second step is the metal oxides or Metal oxides with lower valences undergo hydrolysis reactions at lower temperatures to produce hydrogen. The whole process can be expressed as follows:

1/xMO ₂ → 1/x MO _2-x +1/2O ₂ (1);

1/xMO _{2 -x} +H ₂ O → 1/xMO ₂ +H ₂ (2).

The first decomposition reaction is a high-temperature heat-absorbing process, which usually requires a high reaction temperature (>1600°C), so solar concentrated high-temperature heat sources must be used to drive the reaction. The second-step hydrolysis reaction is an exothermic process, and its reaction temperature is relatively low. It is easy to see from formula (1) and formula (2): the total reaction of the whole process is H ₂ O→H ₂ +O ₂ .

It can be seen that the key problem of the two-step thermochemical cycle is that the decomposition reaction temperature in the first step is too high. Therefore, how to use new methods to improve the reaction conditions and reduce the decomposition temperature is very important.

Contents of the invention

The main purpose of the present invention is to overcome the deficiencies in the prior art and provide a new method for preparing hydrogen based on photothermochemical combined cycle decomposing water of titanium-zinc composite oxide. In order to solve the problems of the technologies described above, the solution of the present invention is:

A method for producing hydrogen by photothermochemical cyclic decomposition of water is provided, which specifically includes the following steps:

(1) Determine the value of x in the general formula Ti _x Zn _1-x O _1+x , and the value range of x is 0.1 to 0.9, and then according to the general formula Ti _x Zn _1-x O _1+x , zinc (Zn ) to titanium (Ti) molar ratio, weigh zinc nitrate Zn(NO ₃ ) ₂ ·6H ₂ O and butyl titanate Ti(OBu) ₄ ; then measure deionized water, add the weighed zinc nitrate to Dissolve in deionized water, and add an appropriate amount (4-6ml) of glacial acetic acid HAc to inhibit hydrolysis; then add absolute ethanol EtOH to obtain solution A;

Among them, the volume ratio of deionized water to butyl titanate is 3:10, that is, H ₂ O:Ti(OBu) ₄ is 3:10; the volume ratio of absolute ethanol EtOH to butyl titanate is 3:1, That is, EtOH:Ti(OBu) ₄ is 3:1;

(2) Add the butyl titanate weighed in step (1) into absolute ethanol EtOH to prepare solution B (and stir vigorously); wherein, the volume ratio of butyl titanate to absolute ethanol is 1:3 , that is, Ti(OBu) ₄ : EtOH is 1:3;

(3) Pour (slowly) solution A obtained in step (1) into solution B obtained in step (2) being stirred, and continue stirring at room temperature until gel;

(4) Dry the colloid obtained in step (3) at 110°C for 12 hours, grind it into a fine powder, then heat the fine powder to 500°C at a heating rate of 2°C/min, and then bake it in an air atmosphere 1 hour, made binary composite metal oxide;

(5) At normal temperature and pressure (0-500°C, 0.1MPa), place the binary composite metal oxide prepared in step (4) in a closed cavity, and use a light source to irradiate and react for 1-2 hours;

The chemical reaction in this step is as follows: 1/yTi _x Zn _1-x O _1+x → 1/y Ti _x Zn _1-x O _1+xy +1/2O ₂ ;

(6) heating the binary composite metal oxide loaded with light in step (5) to 500° C., and (slowly) feeding water vapor at a temperature of 500° C. to react;

The chemical reaction in this step is as follows: 1/y Ti _x Zn _1-x O _1+xy +H ₂ O→1/y Ti _x Zn 1- _x O _1+x +H ₂ .

In the present invention, the overall reaction of step (5) and step (6) is: H ₂ O→H ₂ +1/2O ₂ .

Compared with prior art, the beneficial effect of the present invention is:

1. Combining photochemistry and thermochemistry, using the characteristics of titanium-zinc binary composite metal oxides to decompose into low-valent metal oxides and oxygen under normal temperature and pressure, greatly reducing the first step of the thermochemical cycle. The required temperature improves the circulation conditions;

2. The interdoped metal oxide prepared by this method has higher photoreactivity and thermochemical properties than a single metal oxide;

3. The operation required by this method is simpler and more convenient, and the maximum heat source temperature of various methods such as two-step thermochemical cycle is higher (>1600°C), and solar energy concentration is generally used, while the maximum heat source temperature of this method is Low (<500°C), solar energy, nuclear energy and other various forms of heat sources can be used.

detailed description

Below in conjunction with specific embodiment the present invention is described in further detail:

Example 1

(1) According to the general formula Ti _x Zn _1-x O _1+x , where x=0.1, zinc nitrate Zn(NO ₃ ) ₂ ·6H ₂ O and butyl titanate Ti(OBu) ₄ are weighed according to the molar ratio, Then according to the volume ratio Ti(OBu) ₄ : H ₂ O is 10:3, add deionized water to Zn(NO ₃ ) ₂ ·6H ₂ O to dissolve, and add 4ml glacial acetic acid HAc to inhibit hydrolysis, and then according to the volume ratio Ti( OBu) ₄ : EtOH is 1:3 adding absolute ethanol EtOH to obtain solution A;

(2) Add absolute ethanol EtOH to the Ti(OBu) ₄ weighed in the previous step according to the volume ratio Ti(OBu) ₄ : EtOH is 1:3 to obtain solution B, and stir vigorously;

(3) Slowly pour the solution A obtained in the step (1) into the solution B obtained in the stirring step (2), and keep stirring at room temperature until it gels;

(4) Dry the colloid obtained in step (3) at 110°C for 12 hours, grind it into fine powder, heat it to 500°C at a heating rate of 2°C/min, and roast it in an air atmosphere for 1 hour to prepare A binary composite metal oxide is obtained.

(5) Place the binary composite metal oxide prepared in step (4) in a closed chamber at 0°C and 0.1 MPa, and use a light source to irradiate and react for 1 hour. The chemical reaction equation is:

1/yTi _x Zn _1-x O _1+x →1/y Ti _x Zn _1-x O _1+xy +1/2O ₂ (1)

(6) Heat the titanium-zinc composite metal oxide loaded with light in step (5) to 500° C., and slowly feed water vapor while maintaining a temperature of 500° C. The chemical reaction equation is:

1/y Ti _x Zn _1-x O _1+xy +H ₂ O → 1/y Ti _x Zn 1- _x O _1+x +H ₂ (2).

Example 2

(1) According to the general formula Ti _x Zn _1-x O _1+x , where x=0.5, zinc nitrate Zn(NO ₃ ) ₂ ·6H ₂ O and butyl titanate Ti(OBu) ₄ are weighed according to the molar ratio, According to the volume ratio Ti(OBu) ₄ : H ₂ O is 10:3, add deionized water to Zn(NO ₃ ) ₂ ·6H ₂ O to dissolve, and add 5ml glacial acetic acid HAc to inhibit hydrolysis, and then according to the volume ratio Ti( OBu) ₄ : EtOH is 1:3 adding absolute ethanol EtOH to obtain solution A;

(2) Add absolute ethanol EtOH to the Ti(OBu) ₄ weighed in the previous step according to the volume ratio Ti(OBu) ₄ : EtOH is 1:3 to obtain solution B, and stir vigorously;

(3) Slowly pour the solution A obtained in the step (1) into the solution B obtained in the stirring step (2), and keep stirring at room temperature until it gels;

(4) Dry the colloid obtained in step (3) at 110°C for 12 hours, grind it into fine powder, heat it to 500°C at a heating rate of 2°C/min, and roast it in an air atmosphere for 1 hour to prepare A binary composite metal oxide is obtained.

(5) At 250°C and 0.1 MPa, place the binary composite metal oxide prepared in step (4) in a closed cavity, and use a light source to irradiate and react for 1.5 hours. The chemical reaction equation is:

1/yTi _x Zn _1-x O _1+x →1/y Ti _x Zn _1-x O _1+xy +1/2O ₂ (1)

(6) Heat the titanium-zinc composite metal oxide loaded with light in step (5) to 500° C., and slowly feed water vapor while maintaining a temperature of 500° C. The chemical reaction equation is:

1/y Ti _x Zn _1-x O _1+xy +H ₂ O → 1/y Ti _x Zn 1- _x O _1+x +H ₂ (2).

Example 3

(1) According to the general formula Ti _x Zn _1-x O _1+x , where x=0.9, zinc nitrate Zn(NO ₃ ) ₂ ·6H ₂ O and butyl titanate Ti(OBu) ₄ are weighed according to the molar ratio, According to the volume ratio Ti(OBu) ₄ : H ₂ O is 10:3, add deionized water to Zn(NO ₃ ) ₂ ·6H ₂ O to dissolve, and add 6ml of glacial acetic acid HAc to inhibit hydrolysis, and then according to the volume ratio Ti( OBu) ₄ : EtOH is 1:3 adding absolute ethanol EtOH to obtain solution A;

(2) Add absolute ethanol EtOH to the Ti(OBu) ₄ weighed in the previous step according to the volume ratio Ti(OBu) ₄ : EtOH is 1:3 to obtain solution B, and stir vigorously;

(3) Slowly pour the solution A obtained in the step (1) into the solution B obtained in the stirring step (2), and keep stirring at room temperature until it gels;

(4) Dry the colloid obtained in step (3) at 110°C for 12 hours, grind it into fine powder, heat it to 500°C at a heating rate of 2°C/min, and roast it in an air atmosphere for 1 hour to prepare A binary composite metal oxide is obtained.

(5) Place the binary composite metal oxide prepared in step (4) in a closed cavity at 500°C and 0.1 MPa, and use a light source to irradiate and react for 2 hours. The chemical reaction equation is:

1/yTi _x Zn _1-x O _1+x →1/y Ti _x Zn _1-x O _1+xy +1/2O ₂ (1)

(6) Heat the titanium-zinc composite metal oxide loaded with light in step (5) to 500° C., and slowly feed water vapor while maintaining a temperature of 500° C. The chemical reaction equation is:

1/y Ti _x Zn _1-x O _1+xy +H ₂ O → 1/y Ti _x Zn 1- _x O _1+x +H ₂ (2).

Finally, it should also be noted that what is listed above are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and many variations are possible.

The present invention may be embodied in other specific forms without departing from the spirit and main characteristics of the invention. Therefore, no matter from which point of view, the above-mentioned embodiments of the present invention can only be considered as illustrations of the present invention rather than limiting the present invention. The claims indicate the scope of the present invention, but the above description does not indicate the scope of the present invention. Therefore, any changes within the meaning and scope equivalent to the claims of the present invention should be considered as being included in the claims. within the scope of the book.

Claims (2)

1. A method for preparing hydrogen by photothermochemical circulation decomposing water, is characterized in that, specifically comprises the following steps: (1) Determine the value of x in the general formula Ti _x Zn _1-x O _1+x , and the value range of x is 0.1 to 0.9, and then according to the general formula Ti _x Zn _1-x O _1+x , zinc (Zn ) to titanium (Ti) molar ratio, weigh zinc nitrate Zn(NO ₃ ) ₂ ·6H ₂ O and butyl titanate Ti(OBu) ₄ ; then measure deionized water, add the weighed zinc nitrate to Dissolve in deionized water, and add appropriate amount of glacial acetic acid HAc to inhibit hydrolysis; then add absolute ethanol EtOH to obtain solution A; Among them, the volume ratio of deionized water to butyl titanate is 3:10, that is, H ₂ O:Ti(OBu) ₄ is 3:10; the volume ratio of absolute ethanol EtOH to butyl titanate is 3:1, That is, EtOH:Ti(OBu) ₄ is 3:1; (2) Add the butyl titanate weighed in step (1) into absolute ethanol EtOH to prepare solution B; wherein, the volume ratio of butyl titanate to absolute ethanol is 1:3, that is, Ti(OBu ) ₄ : EtOH is 1:3; (3) Pour the solution A obtained in the step (1) into the solution B obtained in the stirring step (2), and continue stirring at room temperature until gelling; (4) Dry the colloid obtained in step (3) at 110°C for 12 hours, grind it into a fine powder, then heat the fine powder to 500°C at a heating rate of 2°C/min, and then bake it in an air atmosphere 1 hour, made binary composite metal oxide; (5) At a temperature of 0-500°C and a pressure of 0.1 MPa, place the binary composite metal oxide prepared in step (4) in a closed cavity, and use a light source to irradiate and react for 1-2 hours; The chemical reaction in this step is as follows: 1/yTi _x Zn _1-x O _1+x → 1/yTi _x Zn _1-x O _1+xy +1/2O ₂ ; (6) heating the binary composite metal oxide loaded with light in step (5) to 500° C., and feeding water vapor at a temperature of 500° C. to carry out the reaction; The chemical reaction in this step is as follows: 1/yTi _x Zn _1-x O _1+xy +H ₂ O→1/yTi _x Zn _1-x O _1+x +H ₂ . 2. A method for producing hydrogen by photothermochemical cycle decomposing water according to claim 1, characterized in that the total reaction of step (5) and step (6) is: _H2O → _H2 +1/2O ₂ .