CN111573620B - A modular hydrogen production method - Google Patents

Abstract

The invention belongs to the technical field of hydrogen production technology, and discloses a modular hydrogen production method. The method adopts a CuO-MgO cycle carrier to carry out a reaction-regeneration cycle. The methanol reactor uses methanol aqueous solution as a raw material, and at 200-300°C, High-purity hydrogen is produced through the synergistic cooperation of CuO‑MgO cycle carrier absorption and chemical chain methanol autothermal reforming reaction, accompanied by the generation of Cu and MgCO ₃ ; regeneration reactor, at 350‑450 °C, through By feeding oxygen or air, high-purity CO ₂ can be captured or CO ₂ and N ₂ mixed gas can be obtained, and at the same time, the regeneration of the CuO-MgO circulating carrier can be realized. The method of the present invention proposes to combine medium-low temperature CuO chemical chain circulation with MgO absorption-enhanced reforming, shortens the overall process, and provides a new method and approach for the high-purity hydrogen conversion of modularized methanol.

Description

A modular hydrogen production method

technical field

The invention belongs to the technical field of hydrogen production technology, and in particular relates to a modularized small-scale hydrogen production method.

Background technique

With the gradual depletion of fossil energy, hydrogen is considered to be the most environmentally friendly "ultimate energy" in the 21st century due to its high combustion calorific value, abundant resources, and no environmental pollution. Hydrogen energy is widely used in fuel cells, hydrogen vehicles, aerospace, fine chemical production, food processing and metal smelting, and its proportion in my country's terminal energy system will reach 10% or more. As a carrier of hydrogen energy, methanol has the characteristics of low carbon content, high energy density, low price, and convenient transportation and storage, making it an ideal hydrogen energy carrier.

At present, the main catalytic systems for methanol reforming reaction are CuO/ZnO/Al ₂ O ₃ , CuO/CeO ₂ /Al ₂ O ₃ , Cu/Fe/ZrO ₂ and other metal or metal oxide catalysts. However, the temperature required for these catalytic systems to achieve complete methanol conversion is high, and the high reaction temperature will promote the cracking reaction of methanol, resulting in an increase in the production of CO, reducing the purity of hydrogen, and complicating the hydrogen production process. The use of noble metal catalysts increases the cost of the reaction dramatically. The existing methanol conversion pathways mainly include methanol steam reforming reaction, methanol partial oxidation reaction, methanol autothermal reforming reaction and methanol cracking reaction. Among them, the content of CO produced by the methanol cracking reaction is relatively high, and although the theoretical hydrogen concentration of the methanol steam reforming reaction can reach more than 70vol.%, the reaction absorbs heat and cannot run stably by self-heating; while the partial oxidation of methanol and the autothermal reforming of methanol The concentration of hydrogen produced is low.

The product of the traditional methanol reforming process is a mixture of CO, CO ₂ and H ₂ , which needs to burn fuel to provide the heat required for the reforming reaction, and at the same time requires water-gas shift to convert CO into H ₂ , and then pass through the acid gas detachment device or pressure swing The adsorption device separates _CO2 to purify hydrogen, the overall process is long, the investment is high and energy consumption is high, and it is not suitable for small-scale modular distributed hydrogen production. Therefore, it is imperative to propose a new miniaturized methanol utilization technology that can not only solve the above problems, but also meet the needs of human beings for hydrogen energy development in the future.

Contents of the invention

The present invention aims to propose a modular hydrogen production method, which adopts CuO-MgO circulating carrier to absorb and enhance methanol chemical chain autothermal reforming to produce hydrogen, and realizes partial methanol production by regulating lattice oxygen activity and bulk phase migration ability in CuO Oxidation; through the absorption of _CO2 by MgO, the balance of CO water vapor shift reaction is promoted to move forward, and the preparation of ultra-high-purity hydrogen is realized. When the concentration of CO produced is lower than 50ppm, it can be used in proton exchange membrane fuel cells.

In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

A modular hydrogen production method, the method comprises the following steps:

1) Use CuO-MgO circulating carrier to carry out reaction-regeneration cycle, configure methanol aqueous solution, and preheat the configured methanol aqueous solution as a reactant to obtain a mixed gas of methanol and water vapor;

2) Pass the mixed gas of methanol and water vapor obtained in step 1) into the fuel reactor, the copper oxide participates in the partial oxidation and catalytic reforming of methanol, and at the same time, MgO absorbs CO ₂ to generate hydrogen and Cu-MgCO ₃ ;

3) Feed oxygen or air into the regeneration reactor to realize the regeneration of the CuO-MgO cycle carrier while capturing CO ₂ gas or obtaining CO ₂ and N ₂ mixed gas;

The step 2) and the step 3) are reciprocated to realize the autothermal reforming of methanol based on the chemical chain circulation mode.

Further, the CuO-MgO mass ratio of the CuO-MgO circulating support is 0.06-0.10.

Further, the MgO grain size of the CuO-MgO circulating support is 10-100 nm.

Further, the molar ratio of water to methanol in the methanol aqueous solution in step 1) is 0.3-1.0.

Further, the preheating temperature in the step 1) is 150-200°C.

Further, the reaction temperature in step 2) is 200-300°C.

Further, the reaction environment temperature in step 3) is 350-400°C.

Further, when the reaction in step 3) is carried out under an oxygen atmosphere, high-purity CO ₂ gas can be captured; when it is carried out under an air atmosphere, a mixed gas of N ₂ and CO ₂ is obtained.

The beneficial effects of the present invention are:

A modular hydrogen production method of the present invention is based on CuO-MgO circulating carrier absorption enhanced methanol chemical chain autothermal reforming to obtain high-purity hydrogen. As shown in Figure 1, the method includes a Cu-based chemical chain reforming process and an MgO-based absorption-enhanced reforming process, which is an organic combination of the two processes. The Cu-based chemical chain reforming process is shown in Figure 2. The copper-based oxygen carrier not only provides lattice oxygen to realize the autothermal reforming reaction of methanol, but also acts as a catalyst to catalyze methanol conversion, and the main product of methanol conversion is H ₂ and CO ₂ . The MgO-based absorption-enhanced reforming process is shown in Figure 3. As a medium-temperature absorbent, MgO participates in the absorption of _CO2 in the catalytic reforming process of methanol, and at the same time promotes the water-vapor shift reaction of CO gas. The final product is hydrogen, so Theoretically, hydrogen gas with a volume concentration of more than 99% can be obtained.

A modular hydrogen production method of the present invention, as shown in Figure 4, can realize self-heating operation through CuO-MgO carrier circulation, directly produce high-purity hydrogen, save equipment investment such as transformation and gas separation, greatly shorten the process, and can It is a highly integrated miniaturized distributed methanol hydrogen production device, suitable for the layout of hydrogen refueling stations and vehicle-mounted modular hydrogen production technology.

Relevant reaction models were built using ASPEN Plus software. Gibbs reactors were used for the fuel reactor and regeneration reactor, and the gas waste heat at the reactor outlet was used to preheat the aqueous methanol solution. The calculation results of ASPEN Plus system show that under the condition of waste heat utilization, the system can realize self-heating operation. The heat absorption and heat release of different reaction processes are analyzed as follows. In the fuel reactor, the steam reforming reaction of methanol is an endothermic reaction; the chemical reaction of magnesium oxide absorbing carbon dioxide is an exothermic reaction.

Methanol vapor reaction:

CH3OH+H2O _{→ CO2} + _3H2 (1)

_CO2 absorption reaction:

MgO+CO ₂ →MgCO ₃ (2)

In the regenerative reactor, the desorption of carbon dioxide by magnesium carbonate is an endothermic reaction; the reoxidation reaction of copper is an exothermic reaction. Therefore, the system is expected to achieve self-thermal equilibrium.

_CO2 desorption reaction:

MgCO ₃ →MgO+CO ₂ (3)

Cu-based oxygen carrier regeneration reaction:

2Cu+O ₂ →2CuO (4)

Under the premise of satisfying energy conservation and energy cascade utilization, the regenerative reactor is guaranteed to be in self-heating equilibrium, and the system can satisfy the self-heating balance. The feasible range after comprehensive consideration of heat distribution, _H2 concentration, CO concentration and other factors is shown in Fig. 5 . Therefore, it is preliminarily concluded that the absorption-enhanced methanol chemical chain reforming method can realize self-heating of the system, obtain high-purity hydrogen, and control the CO concentration at a low level.

In the regeneration reactor, if oxygen is used as the regeneration medium, high-purity CO ₂ gas can be captured while realizing the regeneration of the circulating carrier. The process is shown in reaction (3) and reaction (4). This process can not only realize the regeneration of the MgO-CuO cycle support for the next methanol conversion cycle, but also capture the carbon in methanol as _CO2 .

In addition to the methanol steam reforming reaction, methanol partial oxidation reaction, methanol cracking reaction and methanol autothermal reforming mentioned above, this patent proposes a new chemical chain methanol conversion method, that is, using the lattice oxygen [O] ² in CuO As an oxygen source, methanol autothermal reaction is realized, and the reaction process is as follows:

CH ₃ OH+[O] ^2- →CO ₂ +2H ₂ (5)

Description of drawings

Fig. 1 is a kind of modularized hydrogen production method provided by the present invention captures _CO in the process schematic diagram;

Fig. 2 is a Cu-based oxygen carrier chemical chain cycle diagram in a modular hydrogen production method provided by the present invention;

Fig. 3 is a Mg-based absorbent absorption enhancement cycle diagram in a modular hydrogen production method provided by the present invention;

Fig. 4 is a kind of modular hydrogen production method provided by the present invention captures _CO in the method flow chart;

Fig. 5 is the feasible interval after comprehensive consideration of heat distribution, _H2 concentration, CO concentration and other factors;

Fig. 6 Hydrogen concentration distribution diagram under different molar ratios of MgO/CH ₃ OH and CuO/CH ₃ OH;

Fig. 7 Distribution diagram of hydrogen atom utilization efficiency under different molar ratios of MgO/CH ₃ OH and CuO/CH ₃ OH;

Fig. 8 CO concentration distribution diagram under different molar ratios of MgO/CH ₃ OH and CuO/CH ₃ OH;

Figure 9 shows the distribution of methanol conversion under different molar ratios of MgO/CH ₃ OH and CuO/CH ₃ OH;

H under the flow rate of Fig. ₁₀ unit methanol Production rate changes trend graph with temperature;

Fig. 11 The trend graph of CO concentration and H atom utilization efficiency changing with temperature under the unit methanol flow rate;

Fig. 12 Distribution diagram of H ₂ production, CO concentration and H atom utilization efficiency under different H ₂ O/CH ₃ OH molar ratios;

Fig. 13 Heat distribution diagram of fuel reactor and regeneration reactor under different H ₂ O/CH ₃ OH molar ratios.

detailed description

Example 1:

1) Configure methanol aqueous solution with a water-alcohol ratio of 0.5, and use it as a reactant to preheat a mixture of methanol and water vapor at 150°C;

2) The preheated mixture of methanol and steam is passed into a fuel reactor at a temperature of 300° C., and the mass ratio of CuO to MgO is 0.06. Copper oxide participates in the partial oxidation and catalytic reforming of methanol, MgO participates in the absorption enhancement reaction of the methanol conversion process, and the CuO-MgO cycle carrier finally generates Cu-MgCO ₃ ;

3) Feed oxygen into the regeneration reactor at a temperature of 420°C to realize the regeneration of the CuO-MgO cycle carrier while capturing CO ₂ gas;

4) Such a cycle is repeated to realize the autothermal reforming of methanol based on the chemical chain circulation mode.

Example 2:

1) Configure an aqueous methanol solution with a water-alcohol ratio of 0.3, and use it as a reactant to preheat a mixture of methanol and water vapor at 180°C;

2) The preheated mixture of methanol and steam is passed into a fuel reactor at a temperature of 200° C., and the mass ratio of CuO to MgO is 0.08. Copper oxide participates in the partial oxidation and catalytic reforming of methanol, MgO participates in the absorption enhancement reaction of the methanol conversion process, and the CuO-MgO cycle carrier finally generates Cu-MgCO ₃ ;

3) Air is introduced into the regeneration reactor at a temperature of 450°C to realize the regeneration of the CuO-MgO circulating carrier and obtain the mixed gas of CO ₂ and N ₂ ;

4) Such a cycle is repeated to realize the autothermal reforming of methanol based on the chemical chain circulation mode.

Example 3:

1) Configure methanol aqueous solution with a water-alcohol ratio of 0.6, and use it as a reactant to preheat a mixture of methanol and water vapor at 200°C;

2) The preheated mixture of methanol and steam is passed into a fuel reactor at a temperature of 220° C., and the mass ratio of CuO to MgO is 0.07. Copper oxide participates in the partial oxidation and catalytic reforming of methanol, MgO participates in the absorption enhancement reaction of the methanol conversion process, and the CuO-MgO cycle carrier finally generates Cu-MgCO ₃ ;

3) Air is introduced into the regeneration reactor at a temperature of 350°C to realize the regeneration of the CuO-MgO circulating carrier and obtain the mixed gas of CO ₂ and N ₂ ;

4) Such a cycle is repeated to realize the autothermal reforming of methanol based on the chemical chain circulation mode.

Example 4:

1) Configure methanol aqueous solution with a water-alcohol ratio of 1.0, and use it as a reactant to preheat a mixture of methanol and water vapor at 160°C;

2) The preheated mixture of methanol and steam is passed into a fuel reactor at a temperature of 240° C., and the mass ratio of CuO to MgO is 0.10. Copper oxide participates in the partial oxidation and catalytic reforming of methanol, MgO participates in the absorption enhancement reaction of the methanol conversion process, and the CuO-MgO cycle carrier finally generates Cu-MgCO ₃ ;

3) Feed oxygen into the regeneration reactor with a temperature of 380°C to realize the regeneration of the CuO-MgO cycle carrier while capturing CO ₂ gas;

4) Such a cycle is repeated to realize the autothermal reforming of methanol based on the chemical chain circulation mode.

The hydrogen concentration, hydrogen atom utilization efficiency, carbon monoxide gas concentration and methanol conversion rate under different molar ratios of MgO/CH ₃ OH and CuO/CH ₃ OH were explored, and the calculation results are shown in Figure 6, Figure 7, Figure 8 and Figure 9, respectively. shown. In the hydrogen concentration distribution results, with the increase of the MgO/CH ₃ OH molar ratio, the hydrogen concentration increases significantly. When the MgO/CH ₃ OH molar ratio reaches about 1, the hydrogen concentration can reach 99%. As the MgO/CH ₃ OH molar ratio continues to increase, the theoretical hydrogen concentration can be higher. The utilization efficiency of H atoms is defined as the ratio of the number of H atoms in _H2 in the product to the number of H atoms provided by the reaction raw materials. As shown in Figure 7, the utilization efficiency of H atoms decreases linearly with the increase of _CuO /CH3OH molar ratio. This is because as the flow rate of CuO increases, more H atoms are converted into water, resulting in a decrease in the utilization efficiency of hydrogen atoms. When the molar ratio of CuO/CH ₃ OH is 0.7, the utilization efficiency of H atoms is about 70%. ; The analysis results of CO concentration distribution showed that the conversion of CO was favorable under the conditions of high CuO/CH ₃ OH molar ratio and high MgO/CH ₃ OH molar ratio, while low MgO/CH ₃ OH molar ratio and low CuO/CH ₃ The concentration of CO under the OH molar ratio can reach more than 0.5%, and this operating range should be avoided; exploring the influence of different CuO/CH ₃ OH and MgO/CH ₃ OH molar ratios on methanol conversion, it can be found that at a temperature of 220 ° C, The conversion rate of methanol tends to be completely converted, and the conversion rate of methanol can reach more than 99%.

Under the conditions of optimizing the molar ratios of MgO/CH ₃ OH and CuO/CH ₃ OH above, the ASPEN Plus software was used to explore the effects of different temperatures on the hydrogen production rate, CO concentration and H atom utilization efficiency. The results are shown in Figure 10 and Figure 11 Show. It can be found that the temperature has little influence on the yield of hydrogen, and a relatively high yield of hydrogen can also be obtained under low temperature conditions. This is due to the fact that the final reactions caused by the enhanced absorption are all in the direction of hydrogen production, so although the temperatures are different, the theoretical hydrogen yields are very close. According to Figure 11, it can be found that the high temperature will greatly increase the CO concentration, that is, the cracking reaction of methanol will occur. The effects of different H ₂ O/CH ₃ OH on the H ₂ yield, H atom utilization efficiency, CO concentration and system energy balance under the chemical looping methanol conversion method were explored, and the results are shown in Figure 12 and Figure 13. A high H ₂ O/CH ₃ OH molar ratio is beneficial to increase the hydrogen production rate and reduce the CO concentration, but the energy required by the system increases and the utilization efficiency of hydrogen atoms decreases. Therefore, there is a relatively good H ₂ O/CH ₃ The OH molar ratio range is 0.3-1.0, which ensures the optimal comprehensive performance of the system. Compared with the traditional methanol steam reforming technology, it has a lower H ₂ O/CH ₃ OH molar ratio, which saves the traditional process The water vapor shift and acid gas separation device shortens the process, so it is more conducive to system energy saving and miniaturized hydrogen production. Therefore, under the conditions of the water-alcohol ratio of 0.5 and the methanol conversion temperature of 300°C in this example, the obtained CO concentration is 0.2295%, and the H atom utilization efficiency is 60.587%. This embodiment can realize the autothermal conversion of methanol to produce high-purity hydrogen, and at the same time realize the cyclic regeneration of the CuO-MgO circulating carrier.

Although the preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are only illustrative and not restrictive. Those of ordinary skill in the art Under the enlightenment of the present invention, without departing from the purpose of the present invention and the scope of protection of the claims, personnel can also make specific changes in many forms, and these all belong to the protection scope of the present invention.

Claims (8)

1. A modular hydrogen production method, characterized in that, adopting CuO-MgO cycle carrier to carry out reaction-regeneration cycle; the method may further comprise the steps: 1) configuring an aqueous solution of methanol, and preheating the configured aqueous solution of methanol as a reactant to obtain a mixed gas of methanol and water vapor; 2) Pass the mixed gas of methanol and water vapor obtained in step 1) into the fuel reactor, the copper oxide participates in the partial oxidation and catalytic reforming of methanol, and at the same time, MgO absorbs CO ₂ to generate hydrogen and Cu-MgCO ₃ ; 3) Feed oxygen or air into the regeneration reactor to realize the regeneration of the CuO-MgO cycle carrier while capturing CO ₂ gas or obtaining CO ₂ and N ₂ mixed gas; The step 2) and the step 3) are reciprocated to realize the autothermal reforming of methanol based on the chemical chain circulation mode. 2. A modular hydrogen production method according to claim 1, characterized in that the mass ratio of CuO to MgO of the CuO-MgO circulating carrier is 0.06-0.10. 3. A modular hydrogen production method according to claim 1, characterized in that the MgO grain size of the CuO-MgO circulating carrier is 10-100 nm. 4. A modular hydrogen production method according to claim 1, characterized in that the molar ratio of water to methanol in the methanol aqueous solution in step 1) is 0.3-1.0. 5. A modular hydrogen production method according to claim 1, characterized in that the preheating temperature in step 1) is 150-200°C. 6. A modular hydrogen production method according to claim 1, characterized in that the reaction temperature in step 2) is 200-300°C. 7. A modular hydrogen production method according to claim 1, characterized in that the reaction environment temperature in step 3) is 350-400°C. 8. A modular hydrogen production method according to claim 1, characterized in that, when the reaction in step 3) is carried out under an oxygen atmosphere, high-purity _CO gas can be captured; When it is carried out, the mixture of N ₂ and CO ₂ is obtained.

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