Hydrogen purification system and purification method for fuel cells

Abstract

This invention relates to the field of hydrogen purification, and discloses a hydrogen purification system and method for fuel cells. The system includes: a catalytic unit, a heat exchange unit, and an electrochemical hydrogen pump connected in sequence; wherein, the catalytic unit is used to remove CO and CO2 from the hydrogen-containing feed gas to obtain crude hydrogen; the heat exchange unit is used to exchange heat and saturate water on the crude hydrogen to obtain a saturated gas; the electrochemical hydrogen pump is used to separate and purify the saturated gas in a charging state to obtain purified hydrogen. The hydrogen purification system for fuel cells provided by this invention can effectively purify hydrogen-containing feed gas, that is, it can significantly improve the hydrogen yield while meeting the hydrogen quality requirements for fuel cells (hydrogen purity ≥ 99.97%).

Description

Technical Field

[0001] This invention relates to the field of hydrogen purification technology, and specifically to a hydrogen purification system and method for fuel cells. Background Technology

[0002] Currently, the hydrogen refueling stations for fuel cells in my country undergoing demonstration operation meet the following standards for fuel cell hydrogen: H2 ≥ 99.97%, CO2 ≤ 2 ppm, CO ≤ 0.2 ppm, CH4 ≤ 2 ppm, O2 ≤ 5 ppm, H2O ≤ 5 ppm, and N2 ≤ 100 ppm. The CO impurity content in industrial pure hydrogen and high-purity hydrogen does not meet the requirements for fuel cell hydrogen, necessitating deep CO removal. Currently, the main methods for CO removal from hydrogen are PSA and TSA methods, which have high equipment and operating costs.

[0003] Furthermore, if CO in high-purity hydrogen is purified to below 0.2 ppm using pressure swing adsorption, the resulting hydrogen yield is too low, and the purification cost increases. Therefore, there is an urgent need to provide a new purification technology to meet the hydrogen quality requirements for fuel cells. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of low hydrogen yield and increased purification cost in the existing hydrogen purification technology, and to provide a hydrogen purification system and method for fuel cells. This system can significantly improve the hydrogen yield while ensuring a hydrogen purity of ≥99.97%, which meets the hydrogen quality requirements for fuel cells.

[0005] To achieve the above objectives, a first aspect of the present invention provides a hydrogen purification system for fuel cells, the system comprising: a catalytic unit, a heat exchange unit, and an electrochemical hydrogen pump connected in sequence; wherein,

[0006] The catalytic unit is used to remove CO and CO2 from the hydrogen-containing feed gas to obtain crude hydrogen.

[0007] The heat exchange unit is used to exchange heat and saturate water in the crude hydrogen gas to obtain saturated gas;

[0008] The electrochemical hydrogen pump is used to separate and purify the saturated gas in a charging state to obtain purified hydrogen.

[0009] A second aspect of the present invention provides a method for purifying hydrogen for fuel cells. The method includes: catalytically removing CO and CO2 from a hydrogen-containing feed gas to obtain crude hydrogen; then introducing the crude hydrogen into a heat exchange unit for heat exchange and water saturation to obtain a saturated gas; then introducing the saturated gas into an electrochemical hydrogen pump, and separating and purifying the saturated gas during the charging process of the electrochemical hydrogen pump to obtain purified hydrogen.

[0010] Through the above technical solutions, the hydrogen purification system for fuel cells provided by this invention can effectively purify hydrogen-containing feed gas, that is, it can significantly improve the hydrogen yield while meeting the hydrogen quality requirements for fuel cells (hydrogen purity ≥ 99.97%). For example, when using the purification system and method of Example 1 of this invention to purify hydrogen-containing feed gas, the hydrogen yield reaches 90% while meeting the hydrogen quality requirements for fuel cells, i.e., a hydrogen purity of 99.999%. However, when using the purification system and method of Comparative Example 3, i.e., pressure swing adsorption, to purify hydrogen-containing feed gas, the hydrogen recovery rate is only 60.02% while meeting the hydrogen quality requirements for fuel cells, i.e., a hydrogen purity of 99.99948%. Furthermore, the purification method provided by this invention has a simple process flow, high reliability, convenient operation, easy implementation, and low purification cost. Attached Figure Description

[0011] Figure 1 This is a process flow diagram of a preferred embodiment of the present invention for purifying hydrogen for fuel cells.

[0012] Explanation of reference numerals in the attached figures

[0013] 1. Catalytic unit; 2. Heat exchange unit; 3. Electrochemical hydrogen pump Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] Existing technologies typically employ pressure swing adsorption (PSA) units, i.e., multiple PSA tanks, to remove impurities from hydrogen-containing feed gas through PSA adsorption, thereby obtaining pure hydrogen. However, obtaining pure hydrogen through PSA leads to excessively low hydrogen yield. To address this issue, the inventors of this invention discovered that by first passing the hydrogen-containing feed gas into a catalytic unit, CO and CO2 in the feed gas are converted into CH4, which is harmless to the fuel cell stack, under the action of a methanation catalyst, crude hydrogen is obtained. This crude hydrogen is then passed into a heat exchange unit for heat exchange and water saturation, resulting in a saturated gas. Finally, an electrochemical hydrogen pump further purifies the saturated gas by removing inert and difficult-to-remove weakly polar gas molecules such as N2, Ar, He, and CH4, thereby obtaining hydrogen that meets the standards for fuel cell vehicles.

[0016] As previously described, a first aspect of the present invention provides a hydrogen purification system for fuel cells, the system comprising: a catalytic unit, a heat exchange unit, and an electrochemical hydrogen pump connected in sequence; wherein,

[0017] The catalytic unit is used to remove CO and CO2 from the hydrogen-containing feed gas to obtain crude hydrogen.

[0018] The heat exchange unit is used to exchange heat and saturate water in the crude hydrogen gas to obtain saturated gas;

[0019] The electrochemical hydrogen pump is used to separate and purify the saturated gas in a charging state to obtain purified hydrogen.

[0020] In some embodiments of the present invention, preferably, the electrochemical hydrogen pump includes a gas inlet, an impurity gas outlet, and a hydrogen outlet, wherein the gas inlet is used to introduce the saturated gas into the electrochemical hydrogen pump, the impurity gas outlet is used to discharge the separated and purified impurity gas, and the hydrogen outlet is used to discharge the purified hydrogen. In the present invention, the gas inlet and the impurity gas outlet are disposed on the anode of the electrochemical hydrogen pump, and the hydrogen outlet is disposed on the cathode of the electrochemical hydrogen pump.

[0021] In some embodiments of the present invention, preferably, the catalytic unit is filled with a methanation catalyst to convert CO and CO2 in the hydrogen-containing feed gas into CH4. In this invention, by setting up a catalytic unit to convert CO and CO2 in the hydrogen-containing feed gas into CH4, CO and CO2 can be effectively prevented from entering the electrochemical hydrogen pump, thus avoiding the poisoning effect of CO and CO2 on the catalyst layer.

[0022] In some embodiments of the present invention, preferably, the methanation catalyst comprises a support and an active component supported on the support, wherein the content of the support is 20-95 wt% and the content of the active component is 5-80 wt% based on the total weight of the methanation catalyst.

[0023] The present invention has a wide range of choices for the support and active components. Preferably, the support is selected from at least one of Al2O3, SiO2 and ZrO2, and the active component is selected from at least one of Ni, Co, Cu, Fe and Mo.

[0024] The present invention does not impose any particular limitation on the structure of the electrochemical hydrogen pump. Preferably, the electrochemical hydrogen pump includes an anode, a cathode, and a proton exchange membrane.

[0025] The present invention does not impose any particular limitation on the structure of the anode or cathode, and can be a conventional choice in the art. Preferably, the anode or cathode includes a gas diffusion layer and a catalyst layer.

[0026] The present invention has a wide range of options for the proton exchange membrane. Preferably, the proton exchange membrane is a Nafion membrane or a PBI membrane.

[0027] The present invention does not have any particular limitation on the catalyst layer. Preferably, the catalyst layer is composed of a Pt catalyst or a Pt-Rh catalyst.

[0028] In this invention, the heat exchange unit is used to contact the crude hydrogen gas with water for heat exchange and water saturation, ensuring that it meets the saturated gas requirements of the electrochemical hydrogen pump and that the temperature of the saturated gas meets the gas temperature required for charging the electrochemical hydrogen pump. In this invention, water has the functions of heat exchange and humidification for the crude hydrogen gas. This invention does not impose any particular limitation on the equipment used in the heat exchange unit; any conventional choice in the art is acceptable, as long as it can achieve water saturation and heat exchange for cooling. In this invention, the gas temperature required for charging the electrochemical hydrogen pump is preferably 60-160°C.

[0029] According to a preferred embodiment of the present invention, the hydrogen purification system for fuel cells includes: a catalytic unit, a heat exchange unit, and an electrochemical hydrogen pump connected in sequence. The electrochemical hydrogen pump includes an anode, a cathode, and a proton exchange membrane. Both the anode and cathode are composed of a gas diffusion layer and a catalytic layer. The anode has a gas inlet and an impurity gas outlet, and the cathode has a hydrogen outlet. By employing the purification system provided by the present invention, hydrogen-containing feed gas can be continuously purified, achieving high purity hydrogen with a high yield. Simultaneously, the electrochemical hydrogen pump of the present invention can also pressurize hydrogen while purifying it to reduce downstream compression costs, thereby achieving a dual function of hydrogen purification and pressurization, saving energy.

[0030] A second aspect of the present invention provides a method for purifying hydrogen for fuel cells. The method includes: catalytically removing CO and CO2 from a hydrogen-containing feed gas to obtain crude hydrogen; then introducing the crude hydrogen into a heat exchange unit for heat exchange and water saturation to obtain a saturated gas; then introducing the saturated gas into an electrochemical hydrogen pump, and separating and purifying the saturated gas during the charging process of the electrochemical hydrogen pump to obtain purified hydrogen.

[0031] The hydrogen purification method for fuel cells of this invention can be summarized as follows: First, CO and CO2 in the hydrogen-containing feed gas are catalytically removed to obtain crude hydrogen. Then, the crude hydrogen is introduced into a heat exchange unit for heat exchange and water saturation to meet the saturation gas requirements of the electrochemical hydrogen pump, and to ensure that the temperature of the saturated gas meets the gas temperature required for charging the electrochemical hydrogen pump. The saturated gas is then introduced into the electrochemical hydrogen pump. During charging, impurity gases on the anode cannot pass through the proton exchange membrane and are thus discharged from the electrochemical hydrogen pump, while hydrogen loses electrons and gains protons at the anode, i.e., H2 (anode) → 2H2O. + +2e -Subsequently, under the influence of an applied voltage, protons pass through the proton exchange membrane to the cathode. At the cathode, the protons recombine with electrons transferred through the external circuit to generate hydrogen gas, H₂. + +2e - →H2 (cathode), that is, in this process, hydrogen is first oxidized at the anode and then reduced at the cathode to obtain purified hydrogen.

[0032] In some embodiments of the present invention, preferably, the catalytic removal temperature is 20-400°C, more preferably 150-300°C. Under this preferred condition, it is more advantageous to convert CO and CO2 into CH4, thereby achieving the removal of CO and CO2.

[0033] In some embodiments of the present invention, preferably, the charging conditions include a voltage of 0.05-3V, more preferably 1-2V.

[0034] In some embodiments of the present invention, there is no particular limitation on the hydrogen-containing feed gas. Preferably, the hydrogen-containing feed gas contains 10-99.7 wt% H2, 0-90 wt% N2, 0-90 wt% CH4, 0-20 wt% CO, 0-20 wt% CO2 and 0-10 wt% Ar.

[0035] According to a preferred embodiment of the present invention, hydrogen-containing feed gas is introduced into a hydrogen purification system for fuel cells for hydrogen purification. The specific process flow is as follows: Figure 1 As shown:

[0036] Hydrogen-containing feed gas is introduced into catalytic unit 1. At a temperature of 150-300℃, under the action of a methanation catalyst, CO and CO2 in the hydrogen-containing feed gas are converted into CH4 to obtain crude hydrogen gas. Then, the crude hydrogen gas is introduced into heat exchange unit 2 to exchange heat and saturate with water, ensuring it meets the saturation gas requirements of electrochemical hydrogen pump 3 and that the saturated gas temperature meets the gas temperature required for charging electrochemical hydrogen pump 3. The saturated gas is then introduced into the anode of electrochemical hydrogen pump 3 through a gas inlet. When charging with a voltage of 1-2V, other impurity gases on the anode cannot pass through the proton exchange membrane (Nafion membrane or PBI membrane) and are discharged from the impurity gas outlet. Meanwhile, the hydrogen gas on the anode passes through the gas diffusion layer and is ionized into H2O under the action of the catalytic layer. + It reaches the cathode through the proton exchange membrane (Nafion membrane or PBI membrane), and H on the cathode + Under the action of the catalyst layer, it recombines into H2, and then is discharged from the hydrogen outlet through the gas diffusion layer.

[0037] The present invention will be described in detail below through embodiments. Unless otherwise specified, all raw materials used in the following embodiments are commercially available.

[0038] The purity of H2, CO2, CO, CH4, N2 and Ar was determined by Fourier transform infrared spectroscopy (FTIR)-gas chromatography (GC-PHID).

[0039] Hydrogen yield % = (molar amount of hydrogen obtained / molar amount of hydrogen in feed gas) × 100%.

[0040] The composition and content of the hydrogen-containing feed gas are shown in Table 1.

[0041] Table 1

[0042]

[0043]

[0044] Example 1

[0045] According to such Figure 1 The process flow shown is for the separation and purification of hydrogen gas. Specifically, hydrogen-containing feed gas 1 is introduced into catalytic unit 1. At a temperature of 300℃, under the action of a methanation catalyst (72wt% Al2O3 and 28wt% Ni), CO and CO2 in the hydrogen-containing feed gas 1 are converted into CH4 to obtain crude hydrogen gas. Then, the crude hydrogen gas is introduced into heat exchange unit 2 to contact with water for heat exchange and water saturation, so that it meets the saturation gas requirements of electrochemical hydrogen pump 3, and the temperature of the saturated gas meets the gas temperature required for charging electrochemical hydrogen pump 3, which is 110℃. Then, the above-mentioned saturated gas is introduced into the anode of electrochemical hydrogen pump 3 through the gas inlet. When charging with a voltage of 1.0V, other impurity gases on the anode cannot pass through the proton exchange membrane (PBI membrane at 110℃) and are discharged from the impurity gas outlet. However, the hydrogen gas on the anode passes through the gas diffusion layer and is ionized into H2O under the action of the catalyst layer (composed of Pt catalyst). + It passes through the proton exchange membrane (PBI membrane at 110℃) to reach the cathode, where H... + The hydrogen is recombine into H2 under the action of the catalytic layer (composed of Pt catalyst), and then discharged from the hydrogen outlet through the gas diffusion layer. The purity and yield of the obtained hydrogen are listed in Table 2.

[0046] Example 2

[0047] According to such Figure 1The process flow shown is for the separation and purification of hydrogen gas. Specifically, hydrogen-containing feed gas 2 is introduced into catalytic unit 1. At a temperature of 200℃, under the action of a methanation catalyst (72wt% Al2O3 and 28wt% Ni), CO and CO2 in the hydrogen-containing feed gas 2 are converted into CH4 to obtain crude hydrogen gas. Then, the crude hydrogen gas is introduced into heat exchange unit 2 to contact with water for heat exchange and water saturation, so that it meets the saturated gas requirements of electrochemical hydrogen pump 3, and the temperature of the saturated gas meets the gas temperature required for charging electrochemical hydrogen pump 3, i.e., 100℃. Then, the above-mentioned saturated gas is introduced into the anode of electrochemical hydrogen pump 3 through the gas inlet. When charging with a voltage of 1.5V, other impurity gases on the anode cannot pass through the proton exchange membrane (PBI membrane at 120℃) and are discharged from the impurity gas outlet, while the hydrogen gas on the anode passes through the gas diffusion layer and is ionized into H2O under the action of the catalyst layer (composed of Pt catalyst). + It passes through the proton exchange membrane (PBI membrane at 120℃) to reach the cathode, where H... + The hydrogen is recombine into H2 under the action of the catalytic layer (composed of Pt catalyst), and then discharged from the hydrogen outlet through the gas diffusion layer. The purity and yield of the obtained hydrogen are listed in Table 2.

[0048] Example 3

[0049] According to such Figure 1 The process flow shown is for the separation and purification of hydrogen gas. Specifically, hydrogen-containing feed gas 3 is introduced into catalytic unit 1. At a temperature of 250°C, under the action of a methanation catalyst (72wt% Al2O3 and 28wt% Ni), CO and CO2 in the hydrogen-containing feed gas 3 are converted into CH4 to obtain crude hydrogen gas. Then, the crude hydrogen gas is introduced into heat exchange unit 2 to contact with water for heat exchange and water saturation, so that it meets the saturated gas requirements of electrochemical hydrogen pump 3, and the temperature of the saturated gas meets the gas temperature required for charging electrochemical hydrogen pump 3, i.e., 80°C. Then, the above-mentioned saturated gas is introduced into the anode of electrochemical hydrogen pump 3 through the gas inlet. When charging with a voltage of 2.0V, other impurity gases on the anode cannot pass through the proton exchange membrane (Nafion membrane at 80°C) and are discharged from the impurity gas outlet. However, the hydrogen gas on the anode passes through the gas diffusion layer and is ionized into H2O under the action of the catalyst layer (composed of Pt catalyst). + It passes through the proton exchange membrane (Nafion membrane at 80°C) to reach the cathode, where H... + The hydrogen is recombine into H2 under the action of the catalytic layer (composed of Pt catalyst), and then discharged from the hydrogen outlet through the gas diffusion layer. The purity and yield of the obtained hydrogen are listed in Table 2.

[0050] Comparative Example 1

[0051] The method of Example 1 is the same, except that there is no heat exchange unit and electrochemical hydrogen pump. The hydrogen-containing feed gas 1 is introduced into the catalytic unit 1 for catalytic removal. Other operations are the same as in Example 1. The purity and yield of the obtained hydrogen are listed in Table 2.

[0052] Comparative Example 2

[0053] Two pressure swing adsorption (PSA) units connected in series were used to purify the hydrogen-containing feed gas 1. The first PSA unit (comprising two adsorption towers filled with molecular sieves and activated carbon adsorbent in a 1:1 mass ratio) removed most of the impurity gases. The second PSA unit (also consisting of two adsorption towers filled with molecular sieves and activated carbon adsorbent in a 1:1 mass ratio) further removed gases such as CO2, CO, CH4, N2, and Ar, thus obtaining pure hydrogen. The purity and yield of the obtained hydrogen are listed in Table 2.

[0054] Table 2

[0055]

[0056] Note: In purity, "%" represents weight percentage and "ppm" represents weight ppm.

[0057] As can be seen from the results in Table 2, the purification system and method provided by this invention can purify hydrogen-containing feed gas by utilizing catalytic-electrochemical coupling, so that the obtained hydrogen can meet the hydrogen standard for fuel cells (hydrogen purity ≥ 99.97%) while achieving a hydrogen yield of over 90%.

[0058] However, when using a catalytic unit alone or a traditional multi-tower pressure swing adsorption method to purify hydrogen-containing feed gas, it is not possible to simultaneously meet the requirements of high yield and high purity.

[0059] This demonstrates that, compared with existing technologies, the purification system and method provided by this invention can significantly improve the hydrogen yield while meeting the hydrogen quality requirements for fuel cells.

[0060] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A hydrogen purification system for fuel cells, characterized in that, The system comprises: a catalytic unit, a heat exchange unit, and an electrochemical hydrogen pump connected in sequence; wherein, The catalytic unit is used to remove CO and CO2 from the hydrogen-containing feed gas to obtain crude hydrogen. The heat exchange unit is used to exchange heat and saturate water in the crude hydrogen gas to obtain saturated gas; The electrochemical hydrogen pump is used to separate and purify the saturated gas in a charging state to obtain purified hydrogen.

2. The system according to claim 1, wherein, The electrochemical hydrogen pump includes a gas inlet, an impurity gas outlet, and a hydrogen outlet. The gas inlet is used to introduce the saturated gas into the electrochemical hydrogen pump, the impurity gas outlet is used to discharge the impurity gas obtained from the separation and purification, and the hydrogen outlet is used to discharge the purified hydrogen.

3. The system according to claim 1 or 2, wherein, The catalytic unit is filled with a methanation catalyst to convert CO and CO2 in hydrogen-containing feed gas into CH4.

4. The system according to claim 3, wherein, The methanation catalyst includes a support and an active component supported on the support. Based on the total weight of the methanation catalyst, the content of the support is 20-95 wt%, and the content of the active component is 5-80 wt%.

5. The system according to claim 4, wherein, The support is selected from at least one of Al2O3, SiO2 and ZrO2; And / or, the active component is selected from at least one of Ni, Co, Cu, Fe and Mo.

6. The system according to any one of claims 1, 2, 4 and 5, wherein, The electrochemical hydrogen pump includes an anode, a cathode, and a proton exchange membrane.

7. The system according to claim 6, wherein, The anode or cathode includes a gas diffusion layer and a catalyst layer; And / or, the proton exchange membrane is a Nafion membrane or a PBI membrane.

8. The system according to claim 7, wherein, The catalyst layer is composed of a Pt catalyst or a Pt-Rh catalyst.

9. The system according to claim 3, wherein, The electrochemical hydrogen pump includes an anode, a cathode, and a proton exchange membrane.

10. The system according to claim 9, wherein, The anode or cathode includes a gas diffusion layer and a catalyst layer; And / or, the proton exchange membrane is a Nafion membrane or a PBI membrane.

11. The system according to claim 10, wherein, The catalyst layer is composed of a Pt catalyst or a Pt-Rh catalyst.

12. A method for purifying hydrogen for fuel cells, characterized in that, The method includes: catalytically removing CO and CO2 from the hydrogen-containing feed gas to obtain crude hydrogen; then introducing the crude hydrogen into a heat exchange unit for heat exchange and water saturation to obtain saturated gas; then introducing the saturated gas into an electrochemical hydrogen pump, and separating and purifying the saturated gas during the charging process of the electrochemical hydrogen pump to obtain purified hydrogen.

13. The method according to claim 12, wherein, The temperature for catalytic removal is 20-400℃.

14. The method according to claim 13, wherein, The temperature for catalytic removal is 150-300℃.

15. The method according to any one of claims 12-14, wherein, The charging conditions include a voltage of 0.05-3V.

16. The method according to claim 15, wherein, The charging conditions include a voltage of 1-2V.

17. The method according to any one of claims 12-14 and 16, wherein, The hydrogen-containing feed gas contains 10-99.7 wt% H2, 0-90 wt% N2, 0-90 wt% CH4, 0-20 wt% CO, 0-20 wt% CO2 and 0-10 wt% Ar.

18. The method according to claim 15, wherein, The hydrogen-containing feed gas contains 10-99.7 wt% H2, 0-90 wt% N2, 0-90 wt% CH4, 0-20 wt% CO, 0-20 wt% CO2 and 0-10 wt% Ar.

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