A method and device for pyrolyzing methane to produce hydrogen by coupling molten salt with a catalyst
By adopting the molten salt coupled catalyst process in methane pyrolysis hydrogen production technology, the problems of catalyst carbon deposition and high reaction temperature are solved, and efficient methane conversion and catalyst life extension are achieved.
Patent Information
- Application Number
- CN202410670158.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-12
- Publication Date
- 2025-06-24
- Estimated Expiration
- 2044-07-12
AI Technical Summary
The existing methane pyrolysis hydrogen production technology has the problem of catalyst carbon deposition and low reaction temperature, and carbon products contain metal impurities.
The molten salt coupled catalyst process is adopted, by adding a specific proportion of additives to the metal catalyst, partially dissolving the catalyst in the molten salt, forming a homogeneous liquid catalyst, reducing the reaction temperature and increasing the methane conversion rate, and at the same time, carbon is separated by flotation, extending the catalyst life.
Highly efficient methane conversion at lower temperatures (550-620℃), extending the catalyst life and reducing the content of metal impurities in carbon products.
Smart Images
Figure CN118637557B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of hydrogen production by pyrolysis of methane as a raw material, and specifically relates to a method and device for pyrolyzing methane to produce hydrogen by coupling molten salt with a catalyst. Background Art
[0002] Hydrogen is a clean energy carrier widely used in the fields of industry, energy and transportation. With the development of sustainable energy and the concern about carbon emissions, hydrogen, as a zero-emission energy medium, has received increasing attention and demand. Traditional hydrogen production methods mainly include steam methane reforming, coal gasification and water electrolysis. Methane is the main component of natural gas and the most common alkane compound. There are abundant methane resources globally, so using methane as a raw material for hydrogen has a rich resource basis.
[0003] Methane pyrolysis to produce hydrogen is a high-efficiency hydrogen production method. Under appropriate temperature and catalyst conditions, methane can be decomposed into hydrogen and solid carbon during the pyrolysis process without generating harmful gases such as carbon dioxide. Compared with traditional steam methane reforming for hydrogen production, methane pyrolysis to produce hydrogen can achieve zero-emission or low-emission hydrogen production. This is of great significance for reducing greenhouse gas emissions and addressing climate change. Due to the high activation energy of the methane pyrolysis reaction, early researchers used catalytic methane pyrolysis to reduce the activation energy of the reaction. Although the activation energy of the reaction was reduced from 422 kJ / mol to 96 kJ / mol, the carbon generated during the reaction was very likely to accumulate on the surface of the solid catalyst, causing the catalyst to deactivate. In recent years, the research has mainly focused on molten metal systems. Molten metal has a significant effect on preventing catalyst carbon deposition and deactivation, but there are also problems such as a relatively high reaction temperature (generally exceeding 1000 °C) and a relatively large content of metal impurities in the carbon products generated. Therefore, the present invention proposes a method and device for pyrolyzing methane to produce hydrogen by coupling molten salt with a catalyst to solve these problems. Summary of the Invention
[0004] Aiming at the problems existing in the prior art, the object of the present invention is to propose a method and device for pyrolyzing methane to produce hydrogen by coupling molten salt with a catalyst. The process and device of the present invention reduce the gas velocity through the bubbling of molten salt with methane gas, strengthen the heat transfer of the system, which is beneficial to the conversion of methane, and at the same time is beneficial to the separation of carbon by flotation, thereby prolonging the catalyst life. By adding a certain proportion of additives to the metal catalyst, the catalyst can be partially dissolved in the molten salt, thus forming a homogeneous liquid catalytic phase with the molten salt, strengthening the interaction between methane and the active sites on the catalyst surface, increasing the methane conversion rate while reducing the reaction temperature, so that the reaction can achieve a relatively high methane conversion rate at a relatively low temperature (550 - 620 °C).
[0005] The described process for producing hydrogen by pyrolyzing methane with a molten salt-coupled catalyst is characterized in that a homogeneous liquid catalyst formed by coupling molten salt and a catalyst is contained in a molten salt reactor, and the methane raw material gas is introduced into the molten salt reactor for pyrolysis reaction to generate hydrogen and solid carbon. The specific steps are as follows:
[0006] 1) Prepare the main catalyst. The preparation of the catalyst (taking Ni / Al2O3 as an example): Dissolve Ni(NO3)2·6H2O in deionized water, add γ-Al2O3, fully impregnate in a water bath at 70-80°C and 300-400 rpm, dry, grind, calcine in a muffle furnace at 450-550°C for 5-7 h, and then reduce in a hydrogen atmosphere to obtain Ni / Al2O3.
[0007] 2) Put the pre-prepared mixed salt and Ni / Al2O3 into an oven at 105°C for drying; first add the mixed salt to the reactor, set the reactor temperature to 430-450°C (heating at a rate of 5-15°C / min, and maintaining for 15-20 minutes when the temperature rises to the set temperature of 430-450°C), then add Ni / Al2O3 to the molten salt in the reactor and stir evenly; after the catalyst is evenly dispersed in the molten salt, then add NiO(NiCO3) and Li2O in a specific ratio to the catalyst to the molten salt successively. Specifically, first add NiO(NiCO3) to the molten salt, stir evenly, and then add Li2O to it, and keep stirring until the catalyst is dissolved in the molten salt to form a homogeneous liquid catalyst, and then set the reactor temperature to 550°C - 620°C;
[0008] 3) After the reactor temperature is stable at the set temperature, introduce N2 into the reactor to discharge air and create an inert atmosphere. Stop introducing N2 and change to introducing CH4 diluted with Ar (Ar:CH4 = 3-5:1, more preferably 4:1) into the reactor. During the reaction process, the composition of the product gas is analyzed in real time by an on-line gas chromatograph.
[0009] 4) After the reaction is completed, stop introducing CH4, turn off the heating switch of the reactor, open the reactor, extract the upper homogeneous phase of the molten salt from the reactor, and wash the obtained solid with water, pickling, and then water again, and filter to obtain solid carbon.
[0010] Furthermore, the added catalyst includes a main catalyst and a promoter. The main catalyst is one of Ni, Fe, Co, and Cu, and the promoter is composed of the corresponding metal oxide (carbonate) and Li2O. For example, when the main catalyst is Ni, the promoter is composed of NiO(NiCO3) and Li2O; the carrier is γ-Al2O3.
[0011] Furthermore, the mass ratios of the added NiO (NiCO3), Fe2O3 (Fe2(CO3)3), CoO (CoCO3), CuO (CuCO3) promoters to the corresponding 2 wt.% - 15 wt.% Ni / Al2O3, Fe / Al2O3, Co / Al2O3, Cu / Al2O3 catalysts are 2.5% - 19.1% (4.0% - 30.3%), 5.7% - 42.9% (5.2% - 39.1%), 2.5% - 19.1% (4.0% - 30.3%), 2.5% - 18.8% (3.9% - 29.2%), respectively.
[0012] Furthermore, the mass ratios of the added Li2O promoter to the 2 wt.% - 15 wt.% Ni / Al2O3, Fe / Al2O3, Co / Al2O3, Cu / Al2O3 catalysts are all 25% - 28.8%.
[0013] The mass percentage of Ni in Ni / Al2O3 is 2 wt.% - 15 wt.%;
[0014] The mass ratio of one or both of the aforementioned NiO and NiCO3 to Ni / Al2O3 is 2.5% - 30.3%. When only NiO is added, the mass ratio of NiO to Ni / Al2O3 is 2.5% - 19.1%. When only NiCO3 is added, the mass ratio of NiCO3 to Ni / Al2O3 is 4.0% - 30.3%;
[0015] The mass ratio of the aforementioned Li2O to Ni / Al2O3 is 25% - 28.8%.
[0016] When the cocatalyst is NiO and Li2O, Ni in the main catalyst Ni / Al2O3 will react with the added NiO promoter to form a strongly reducing sub-compound Ni2O, specifically as follows
[0017]
[0018] Meanwhile, the added Li2O will form LiAlO2 with the carrier Al2O3, promoting the dissolution of the catalyst in the molten salt.
[0019] When the cocatalyst is NiCO3 and Li2O, since NiCO3 is unstable at high temperatures, it will rapidly decompose into carbon dioxide and NiO with a relatively small particle size (60 nm) and uniform dispersion. Ni in the main catalyst Ni / Al2O3 reacts with NiO to form a strongly reducing sub-compound Ni2O, specifically as follows
[0020] NiCO3 → NiO + CO2
[0021]
[0022] The simultaneously added Li2O will react with the carrier Al2O3 to form LiAlO2, which promotes the dissolution of the catalyst in the molten salt.
[0023] The catalyst is partially dissolved in the molten carbonate, and the formed homogeneous liquid catalyst promotes the interaction between the methane feed gas and the catalyst active sites, improving the methane conversion rate. At the same time, the produced product carbon will float to the surface of the liquid catalyst, avoiding the deactivation of the catalyst due to carbon deposition and greatly improving the stability of the catalyst.
[0024] Furthermore, the used salt is a mixture of Li2CO3, Na2CO3 and K2CO3 with a mass ratio of 3:2 - 4:3 - 5 (further preferably 3:3:4).
[0025] The described device for producing hydrogen by pyrolyzing methane with a molten salt coupled catalyst is characterized by comprising a molten salt bubble cap reactor (1) filled with molten salt inside, a gas separator (12) and a temperature controller (6). In the molten salt bubble cap reactor (1), a bubble cap riser pipe (16) and a bubble cap (17) are arranged in the middle of the inner bottom wall. The bubble cap riser pipe (16) is above the molten salt liquid level, the bubble cap (17) is arranged outside the bubble cap riser pipe (16), there is a gap between the upper part of the bubble cap riser pipe (16) and the top end of the inner wall of the bubble cap (17). The bottom end of the bubble cap (17) is evenly provided with a number of exhaust tooth slots of the same height along the circumference, and the exhaust tooth slots are below the molten salt liquid level. An inlet pipe (11) is arranged on the left side of the bottom of the molten salt bubble cap reactor (1), and the inlet pipe (11) is connected to the feed gas and the carrier gas through a pipeline. The side part of the molten salt bubble cap reactor (1) is successively provided with a heating layer (3), a heat insulation layer (2) and an air heat insulation layer (5). An outlet (14) is arranged at the top of the molten salt bubble cap reactor (1). The temperature controller (6) includes a thermocouple (4) for measuring the temperature of the molten salt and a temperature control end (18) for controlling the temperature of the heating jacket.
[0026] Compared with the prior art, the beneficial effects obtained by the present invention are as follows:
[0027] 1) The present invention provides a process and device for producing hydrogen by pyrolyzing methane with a molten salt coupled catalyst. By adding a mixed auxiliary agent of a certain proportion of specific metal oxides (or corresponding carbonates) and Li2O to the metal catalyst, partial dissolution of the catalyst in the molten carbonate is achieved, enabling the original gas-solid interaction between the methane gas and the catalyst surface active sites to be transformed into a gas-liquid interaction, greatly increasing the methane conversion rate.
[0028] 2) The present invention utilizes the advantages of a molten salt system, such as high thermal conductivity, large heat capacity, and good thermal stability, to enhance the heat transfer of the system. By bubbling methane gas through the molten salt, the flow rate of the methane gas is reduced, the residence time of the methane gas in the molten salt layer is prolonged, and the methane conversion rate is increased. Compared with molten metal, the cooled salt is soluble in water, which is beneficial to the recovery of carbon products with lower impurity content.
[0029] 3) The pyrolysis reaction of the present invention is carried out in a molten salt medium. Since the density of carbon is smaller than that of the molten salt, the carbon generated during the pyrolysis process will continuously rise and finally reach the surface of the molten salt. The carbon is separated by flotation, thus solving the problem that carbon deposition on the catalyst surface deactivates the catalyst and greatly prolonging the service life of the catalyst. Description of the Drawings
[0030] Figure 1 Catalyst not dissolved in the molten salt
[0031] Figure 2 Catalyst dissolved in the molten salt to form a homogeneous liquid catalyst
[0032] Figure 3 Schematic diagram of the process flow of the molten salt coupled catalytic methane pyrolysis for hydrogen production constructed by the present invention
[0033] Figure 4 Schematic diagram of the structure of the molten salt coupled catalytic methane pyrolysis for hydrogen production reaction device constructed by the present invention
[0034] Figure 5 Schematic diagram of the structure of the molten salt bubble cap reactor constructed by the present invention
[0035] Reference numerals: 1 - molten salt bubble cap reactor, 2 - thermal insulation layer, 3 - heating layer, 4 - thermocouple, 5 - air insulation layer, 6 - temperature controller, 7 - N2 cylinder, 8 - CH4 cylinder, 9 - rotameter, 10 - regulating valve, 11 - inlet, 12 - gas separator, 13 - gas detection system, 14 - outlet, 15 - reactor cover, 16 - bubble cap riser, 17 - bubble cap, 18 - temperature control end. Detailed Embodiments
[0036] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.
[0037] Preparation example: 11.01 g of Ni(NO3)2·6H2O was dissolved in deionized water, 20 g of γ - Al2O3 was added, and the mixture was fully impregnated in a water bath at 75 °C and 350 rpm, dried, ground, calcined in a muffle furnace at 500 °C for 6 h, and then reduced under a hydrogen atmosphere to obtain 10 wt.% Ni / Al2O3.
[0038] Example 1: Preparation of Homogeneous Liquid Catalyst
[0039] Put the prefabricated mixed salt and 10wt.% Ni / Al2O3 catalyst into an oven at 105°C for drying; first add 150g of the mixed salt to the reactor, set the reactor temperature at 450°C, and let the reactor heat up at a rate of 10°C / min. When the temperature rises to the set temperature, keep it for 15 - 20 minutes, then add 10g of 10wt.% Ni / Al2O3 catalyst to the molten salt in the reactor and stir evenly; after the catalyst is evenly dispersed in the molten salt, add 1.27g of NiO (or 2.02g of NiCO3) to the molten salt and stir evenly. At this time, the catalyst cannot dissolve in the molten salt. As Figure 1 shown, then add 2.65g of Li2O to the molten salt and keep stirring until the catalyst dissolves in the molten salt to form a homogeneous liquid catalyst. As Figure 2 shown, then set the reactor temperature to 580°C.
[0040] Example 2: Pyrolysis of Methane Catalyzed by Pure Molten Salt
[0041] Adopt the Figure 3 shown process method and the Figure 4 structured device to conduct the methane pyrolysis reaction. First, dry 150g of the mixed salt (Li2CO3, Na2CO3, and K2CO3 with a mass ratio of 3:3:4) in an oven at 105°C for 4h to remove the moisture. Transfer the dried mixed salt to the reactor, install the reactor cover, set the reactor temperature, and let the reactor heat up at a rate of 10°C / min. When the temperature rises to 580°C and is kept for 15 - 20 minutes, introduce N2 into the reactor at a flow rate of 0.4L / min. After the air in the reactor is exhausted, stop introducing N2, and at the same time introduce the methane feed gas of 20vol.% CH4 - 80vol.% Ar into the reactor at a flow rate of 10mL / min. During the reaction process, the composition of the gas at the reactor outlet is detected in real time by on-line gas chromatography. Using the analysis results obtained by the chromatograph, the conversion rate of methane is calculated to be 5.8%. Continuous operation was carried out for 72h under the optimal conditions, and it was found that it could maintain a conversion rate of about 5% for 66h and then gradually decreased. After the reaction, turn off the reactor heating switch, open the reactor cover, extract the upper homogeneous phase of the molten salt from the reactor, and wash the obtained solid with water, pickling, and then water again. After filtration, 0.21g of solid carbon is obtained.
[0042] Example 3: Pyrolysis of Methane Catalyzed by Molten Salt Coupled with Ni / Al2O3
[0043] Adopt the Figure 3 shown process method and the Figure 4The device with the [[STRUCTURE]] is used for the methane pyrolysis reaction. First, 150 g of mixed salts (Li2CO3, Na2CO3, and K2CO3 with a mass ratio of 3:3:4) and 10 g of 10 wt.% Ni / Al2O3 catalyst are dried in an oven at 105 °C for 4 h to remove the moisture therein. The dried mixture is transferred to the reactor, the reactor cover is installed, and the reactor temperature is set so that the reactor heats up at a heating rate of 10 °C / min. When the temperature rises to 580 °C and is maintained for 15 - 20 minutes, N2 is introduced into the reactor at a flow rate of 0.4 L / min. After the air in the reactor is exhausted, the introduction of N2 is stopped. At the same time, a methane feed gas of 20 vol.% CH4 - 80 vol.% Ar is introduced into the reactor at a flow rate of 10 mL / min. During the reaction process, the composition of the gas at the reactor outlet is detected in real time by an on-line gas chromatograph. Using the analysis results obtained by the chromatograph, the conversion rate of methane is calculated to be 76.4%. The activity of the catalyst is detected for 72 h, and it is found that it can maintain a methane conversion rate of about 70% for 54 h and then gradually decreases. After the reaction is completed, the heating switch of the reactor is turned off, the reactor cover is opened, the upper homogeneous phase of the molten salt is extracted from the reactor, and the obtained solid is washed with water, pickled with acid, washed with water again, and 2.35 g of solid carbon is obtained after filtration.
[0044] Example 4: Pyrolysis of methane by molten salt coupled with catalyst
[0045] Adopt Figure 3 The process method shown and Figure 4 The device with the [[STRUCTURE]] is used for the methane pyrolysis reaction, except that the catalyst used is added with a specific proportion of NiO(NiCO3) and Li2O additives to strengthen the gas-liquid interaction and improve the conversion rate.
[0046] It should be noted that the specific "[[STRUCTURE]]" in the text needs to be filled with the actual structure information.First, the pre-prepared mixed salt (Li2CO3, Na2CO3, and K2CO3 with a mass ratio of 3:3:4) and 10 wt.% Ni / Al2O3 catalyst were placed in an oven at 105 °C for drying; first, 150 g of the mixed salt was added to the reactor, the reactor temperature was set at 450 °C, and the reactor was heated at a heating rate of 10 °C / min. When the temperature rose to the set temperature, it was maintained for 15 - 20 minutes. Then, 10 g of 10 wt.% Ni / Al2O3 catalyst was added to the molten salt in the reactor and stirred evenly; after the catalyst was evenly dispersed in the molten salt, 1.27 g of NiO (or 2.02 g of NiCO3) was added to the molten salt. After stirring evenly, 2.65 g of Li2O was added to the molten salt and continuously stirred until the catalyst was dissolved in the molten salt to form a homogeneous liquid catalyst. Finally, the reactor temperature was set to 580 °C. When the temperature stabilized at 580 °C, N2 was introduced into the reactor at a flow rate of 0.4 L / min. After the air in the reactor was exhausted, the introduction of N2 was stopped. At the same time, a methane raw gas of 20 vol.% CH4 - 80 vol.% Ar was introduced into the reactor at a flow rate of 10 mL / min. During the reaction process, the composition of the gas at the reactor outlet was detected in real time by an on-line gas chromatograph. Using the analysis results obtained by the chromatograph, the conversion rate of methane was calculated to be 92.5%. The activity of the catalyst was detected for 72 h, and it was found that it could maintain a methane conversion rate of about 90% for 69 h and then gradually decreased. After the reaction ended, the heating switch of the reactor was turned off, the reactor cover was opened, the upper homogeneous phase of the molten salt was extracted from the reactor, and the obtained solid was washed with water, pickled with acid, and washed with water again. After filtration, 3.85 g of solid carbon was obtained.
Claims
1. A method for producing hydrogen by thermal decomposition of methane using molten salt coupled catalyst, characterized in that: The following steps are involved: 1) Preparation of main catalyst; 2) Place the mixed salt and main catalyst in an oven to dry; first add the mixed salt to the reactor, set the reactor temperature to 430-450 °C, then add the main catalyst to the molten salt in the reactor and stir evenly; after the catalyst is evenly dispersed in the molten salt, add the co-catalyst to the molten salt and stir continuously until the catalyst is dissolved in the molten salt to form a homogeneous liquid catalyst, and then set the reactor temperature to 550 °C-620 °C; The main catalyst and the co-catalyst are one of the following combinations: The first combination: the main catalyst is Ni / Al2O3, and the co-catalyst is one or two of NiO and NiCO3 and Li2O; The second combination: the main catalyst is Fe / Al2O3, and the co-catalyst is one or two of Fe2O3, Fe2(CO3)3 and Li2O; The third combination: the main catalyst is Co / Al2O3, and the co-catalyst is one or two of CoO and CoCO3 and Li2O; The fourth combination: the main catalyst is Cu / Al2O3, and the co-catalyst is one or two of CuO and CuCO3 and Li2O; 3) After the reactor temperature stabilizes at the set temperature, N2 is introduced into the reactor, air is exhausted, the introduction of N2 is stopped, and CH4 diluted with Ar is introduced into the reactor instead. During the reaction, the composition of the product gas is analyzed in real time by an online gas chromatograph; 4) After the reaction is completed, stop introducing CH4, turn off the reactor heating switch, open the reactor, extract the upper homogeneous phase of the molten salt from the reactor, wash the obtained solid with water, acid, and water, and obtain solid carbon after filtering.
2. A method for producing hydrogen by thermal decomposition of methane using molten salt coupled catalyst, characterized in that: The following steps are involved: 1) Preparation of Ni / Al2O3 catalyst; 2) Put the mixed salt and Ni / Al2O3 into an oven for drying; first add the mixed salt to the reactor, set the reactor temperature to 430-450 ℃, then add Ni / Al2O3 to the molten salt in the reactor and stir evenly; after the catalyst is evenly dispersed in the molten salt, add one or two of NiO, NiCO3 and Li2O to the molten salt, stir continuously until the catalyst is dissolved in the molten salt to form a homogeneous liquid catalyst, and then set the reactor temperature to 550 ℃-620 ℃; 3) After the reactor temperature stabilizes at the set temperature, N2 is introduced into the reactor, air is exhausted, the introduction of N2 is stopped, and CH4 diluted with Ar is introduced into the reactor instead. During the reaction, the composition of the product gas is analyzed in real time by an online gas chromatograph; 4) After the reaction is completed, stop introducing CH4, turn off the reactor heating switch, open the reactor, extract the upper homogeneous phase of the molten salt from the reactor, wash the obtained solid with water, acid, and water, and obtain solid carbon after filtering.
3. The method for producing hydrogen by pyrolysis of methane using molten salt coupled catalyst according to claim 2, characterized in that: The mass percentage of Ni in Ni / Al2O3 is 2 wt.%-15 wt.%; The mass ratio of one or two of NiO and NiCO3 to Ni / Al2O3 is 2.5%-30.3%. When NiO is added, the mass ratio of NiO to Ni / Al2O3 is 2.5%-19.1%. When NiCO3 is added, the mass ratio of NiCO3 to Ni / Al2O3 is 4.0%-30.3%. The mass ratio of Li2O to Ni / Al2O3 is 25%-28.8%.
4. The method for producing hydrogen by pyrolysis of methane using molten salt coupled catalyst according to claim 2, characterized in that: In step 1), the catalyst Ni / Al2O3 is prepared, which specifically includes: Ni(NO3)2·6H2O was dissolved in deionized water, γ-Al2O3 was added, fully impregnated in a water bath at 70~80 ℃ and 300~400 rpm, dried, ground, calcined in a muffle furnace at 450~550 ℃ for 5~7 h, and then reduced in a hydrogen atmosphere to obtain Ni / Al2O3.
5. The method for producing hydrogen by pyrolysis of methane using molten salt coupled catalyst according to claim 2, characterized in that: In step 2), the mixed salt is a mixture of Li2CO3, Na2CO3 and K2CO3 in a mass ratio of 3:2~4:3~5.
6. The method for producing hydrogen by pyrolysis of methane using molten salt coupled catalyst according to claim 2, characterized in that: In step 2), the reactor temperature is set to 430-450 °C, specifically comprising: Increase the temperature at a rate of 5-15 ℃ / min, and when the temperature reaches the set temperature of 430-450 ℃, maintain it for 15-20 minutes.
7. The method for producing hydrogen by pyrolysis of methane using molten salt coupled catalyst according to claim 2, characterized in that: In step 2), one or two of NiO and NiCO3 and Li2O are added to the molten salt, specifically comprising: First add one or two of NiO and NiCO3 to the molten salt, stir evenly, and then add Li2O.
8. The method for producing hydrogen by pyrolysis of methane using molten salt coupled catalyst according to claim 2, characterized in that: In step 3), the volume ratio of Ar to CH4 is 3-5:1.