Seawater hydrogen production driven methane synthesis method based on microwave step-by-step catalysis

Abstract

The invention discloses a seawater hydrogen production driven methane synthesis method based on microwave step-by-step catalysis, and belongs to the technical field of seawater resource utilization and clean energy preparation. The method comprises the following steps: taking lignin carbon in series connection with nano nickel oxide as a catalyst, filling the upper layer of the nano nickel oxide with the lignin carbon, taking seawater as a reactant, pumping the seawater into a quartz tube by an independent water pump, enabling the seawater to pass through a carbon bed layer from top to bottom, and carrying out water gas reaction under the action of the lignin carbon on the upper layer to generate H2, CO and CO2; and carrying out methanation reaction under the catalysis of the lower-layer nano nickel oxide, so that CO is converted into CH4 from CO2 and H2. The product only contains a small amount of CO, the main products are CH4, H2 and CO2, the highest volume fraction of CH4 is 29.15%, the corresponding volume fraction of CO2 is 18.49%, the content of CO is 11.35%, and the content of H2 is 42%.

Description

Technical Field

[0001] The present invention belongs to the technical field of seawater resource utilization and clean energy preparation, and specifically relates to a method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis. Background Art

[0002] Methane (CH4) is the main component of natural gas and can be used as fuel for power generation, heating, and industrial raw material synthesis. Traditional methane production relies primarily on natural gas extraction and coal-to-gas processes, but these methods suffer from high resource consumption and carbon emissions. Therefore, the development of renewable, low-carbon methane production technologies has become a current research focus. Using seawater as a raw material presents several challenges, including:

[0003] High salinity and impurity interference: Seawater contains large amounts of inorganic salts such as sodium chloride, magnesium ions, and calcium ions. When used directly as a reaction medium, the salts can clog the catalyst pores and reduce the accessibility of active sites. Furthermore, dissolved organic matter (such as humic acid) and microorganisms in seawater compete with lignin char for adsorption, interfering with the water-gas reaction (CO + H2O → CO2 + H2).

[0004] Corrosion and reactor compatibility: Chloride ions in seawater accelerate the corrosion of reactor materials at high temperatures, especially damaging traditional metal reactors (such as stainless steel). Furthermore, the non-uniform dielectric loss characteristics of seawater in a microwave field can lead to localized overheating, exacerbating equipment losses.

[0005] There are technical bottlenecks in the simultaneous production of hydrogen and methanation. Specific issues include:

[0006] Reaction thermodynamic contradiction: The temperature requirements of the water-gas reaction (endothermic) and the methanation reaction (CO + 3H2 → CH4 + H2O, exothermic) conflict. Existing technologies often use fixed-bed reactors, which make precise temperature control difficult, resulting in low reaction efficiency. Research has shown that when the two reactions proceed simultaneously, the heat released by the methanation reaction can inhibit the endothermic water-gas reaction, reducing the overall yield.

[0007] Catalyst deactivation and poor selectivity: Lignin charcoal, as a multifunctional carrier, must simultaneously perform microwave absorption and hydrogen production catalysis. However, in seawater, its surface hydroxyl groups easily bind to salt, resulting in active site passivation. Furthermore, nickel-based catalysts are susceptible to sulfur poisoning (H2S generated by sulfate reduction in seawater) and carbon deposition in hydrogen-rich environments, reducing methane selectivity. Summary of the Invention

[0008] The present invention addresses the technical problem of providing a seawater-based hydrogen-driven methane synthesis method based on microwave-assisted step-by-step catalysis. Utilizing the selective heating properties of variable-frequency microwaves, the lignin charcoal and seawater undergo a water-gas reaction (C + H2O → CO + H2), generating hydrogen-rich gas. Subsequently, over the action of a nano-nickel oxide catalyst, the generated H2 further reacts with CO and CO2 in a methanogenic reaction to produce high-calorific value CH4.

[0009] Technical solution: In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis uses lignin carbon in series with nano-nickel oxide as a catalyst. The lignin carbon is filled on the upper layer of the nano-nickel oxide, and seawater is used as a reactant. A separate water pump pumps the seawater into a quartz tube. The seawater passes through the carbon bed from top to bottom. Under the action of the upper layer of lignin carbon, a water-gas reaction occurs to produce H2, CO and CO2. Under the catalysis of the lower layer of nano-nickel oxide, a methanation reaction occurs, converting CO, CO2 and H2 into methane.

[0011] The method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis has a microwave frequency of 4700-5700 MHz, a power of 100-200 W, and a temperature of 450-770°C.

[0012] The method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis has a microwave frequency of 4720-5525 MHz, a power of 100 W, and a temperature of 480-580°C.

[0013] In the method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis, the rate at which seawater is pumped into the quartz tube is 0.06 ml / min.

[0014] In the method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis, the filling mass ratio of lignin charcoal to nano-nickel oxide is 4:1.

[0015] In the method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis, the filling mass of lignin charcoal is 2 g, and the filling mass of nano-nickel oxide is 0.5 g.

[0016] In the method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis, the microwave frequency is 4720 MHz, the power is 100 W, and the reactor temperature is 480° C.

[0017] The method for producing hydrogen from seawater and driving methane synthesis based on microwave step-by-step catalysis has a microwave frequency of 5525 MHz, a power of 100 W, and a reactor temperature of 580°C.

[0018] The method for producing methane by driving hydrogen from seawater based on microwave-assisted step-by-step catalysis comprises the following steps:

[0019] The first step is to fill quartz wool in a quartz tube with an inner diameter of 8 mm, slowly put nano nickel oxide into the quartz tube, and fix it with quartz wool;

[0020] In the second step, the lignin charcoal is slowly loaded into the quartz tube so that it is located above the nano-nickel oxide and fixed with quartz wool;

[0021] The third step is to connect the quartz tube to the microwave reaction system, check the air tightness, and introduce nitrogen to purge the microwave reaction system and maintain the microwave reactor in an inert atmosphere;

[0022] The fourth step is to turn on the microwave power supply and input the variable frequency microwave into the microwave resonant cavity through the microwave feed port. The lignin charcoal absorbs microwaves of different frequencies and begins to heat up. The temperature change of the catalyst is detected in real time by an infrared thermometer and a thermal imager on the axial cross section of the quartz tube.

[0023] Step 5: After the reaction temperature is reached and remains stable, turn on the seawater pump to pump seawater into the quartz tube at a fixed rate to start the reaction;

[0024] Step 6: After the reaction is completed, collect the gaseous products.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] 1. Effectively alleviate the problems of high salinity and impurity interference: Through the hierarchical design of series catalysts, lignin charcoal as the upper catalyst preferentially adsorbs and decomposes organic matter and microorganisms in seawater, reducing their competitive adsorption on the active sites of the reaction; at the same time, the step-by-step catalytic strategy allows salt to be mainly retained in the upper carbon bed, avoiding clogging of the pores of the lower nano-nickel oxide, significantly improving the stability and accessibility of the catalyst in the seawater medium.

[0027] 2. Enhanced reactor compatibility and corrosion resistance: Using quartz tubes as reaction vessels, combined with the precise temperature control characteristics of variable frequency microwaves, avoids the chloride ion corrosion problem of traditional metal reactors in high-temperature seawater environments; the resonant matching of microwave frequency and the material's intrinsic frequency can evenly heat the reaction system, reduce equipment loss caused by local overheating, and extend the service life of the reactor.

[0028] 3. Inhibit catalyst deactivation and improve selectivity: The hydrophobic properties of lignin charcoal reduce the passivation effect of salt on surface hydroxyl groups. At the same time, the tandem catalytic design blocks the direct contact of sulfate in seawater with the underlying nano-nickel oxide catalyst, reducing the risk of sulfur poisoning. The low-temperature methanation activity of nano-nickel oxide inhibits the formation of carbon deposits, reducing the CO content in the product to 11.35% when the CH4 production is the highest, and significantly improving the methane selectivity.

[0029] 4. Breaking through the thermodynamic coupling limitations of reactions to achieve efficient conversion: Through a step-by-step catalytic strategy and dynamic regulation of variable-frequency microwaves, the upper lignin charcoal layer focuses on the water-gas reaction to produce hydrogen-rich syngas (H2, CO), while the lower layer of nano-nickel oxide simultaneously drives the methanation reaction. The two reactions form a synergistic pathway in independent catalytic regions, avoiding the mutual interference of endothermic and exothermic reactions in traditional processes and significantly alleviating thermodynamic contradictions. Experiments have shown that this method can increase the methane volume fraction to a maximum of 29.15%, while reducing the CO content to 11.35%, significantly improving the methane yield compared to traditional processes while reducing the formation of by-products.

[0030] 5. Efficient resource utilization and low carbon emissions: Improve energy efficiency and resource utilization: Directly use seawater as the water source, without pretreatment (such as desalination or distillation), saving 30%-40% of energy consumption in traditional processes; lignin charcoal is derived from biomass waste, realizing resource recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the result diagram of reaction products at different frequencies when the seawater rate is 0.06ml / min;

[0032] Figure 2 The graph shows the methane conversion rate at different frequencies. DETAILED DESCRIPTION

[0033] The present invention is further illustrated below with reference to specific examples. These examples are based on the technical solutions of the present invention and should be understood as merely illustrative and not intended to limit the scope of the present invention. The frequency conversion device used in these examples is the device disclosed in patent application publication number CN111117676A, entitled "A Microwave Continuous Frequency Modulation Synergistic Biomass Directed Depolymerization Device and Method of Use."

[0034] Methane conversion rate calculation formula:

[0035]

[0036] Among them, η CH4 is the methane conversion rate, are the volume fractions of CH4, CO, and CO2, respectively.

[0037] Example 1

[0038] In a microwave reactor, microwave power was set at 100W and frequency at 4720MHz. Lignocarbon and nano-nickel oxide were used in series to catalyze the water-gas reaction and water-gas shift reaction to produce hydrogen. The lignincarbon and nano-nickel oxide were filled in a 4:1 mass ratio, with a total mass of 2.5g. The lignincarbon was placed on top of the nano-nickel oxide. The seawater flow rate was 0.06ml / min. The specific implementation steps included:

[0039] The first step is to fill quartz wool in a quartz tube with an inner diameter of 8 mm, slowly put 0.5 g of nano nickel oxide into the quartz tube, and fill it with a small amount of quartz wool to fix it;

[0040] In the second step, after fixing the nano-nickel oxide with a small amount of quartz wool, 2g of lignin charcoal was slowly loaded into the quartz tube so that it was located above the nano-nickel oxide, and finally a small amount of quartz wool was added to fix it;

[0041] The third step is to connect the quartz tube to the microwave reaction system, check the air tightness, and introduce nitrogen to purge the microwave reaction system and maintain the microwave reactor in an inert atmosphere;

[0042] The fourth step is to turn on the microwave power supply and input the variable frequency microwave into the microwave resonant cavity through the microwave feed port. The lignin charcoal absorbs microwaves of different frequencies and begins to heat up. The temperature change of the catalyst is detected in real time by an infrared thermometer and a thermal imager on the axial cross section of the quartz tube.

[0043] Step 5: After the reaction temperature is reached and maintained stable, the seawater pump is turned on to pump seawater into the quartz tube at a fixed rate of 0.06 ml / min to control the hydrogen content and methane yield in the synthesis gas;

[0044] Step 6: After the reaction is completed, the gaseous products are collected using a gas sampling bag and analyzed offline in a gas chromatograph.

[0045] The infrared temperature of the reactor was 480° C., and the volume fractions of the gas components were H 2 : 56%, CO: 4%, CO 2 : 28%, and CH 4: 12%. In this embodiment, the methane conversion rate was 26.27%.

[0046] Example 2

[0047] In the microwave reactor, the microwave power was set to 100 W and the frequency was set to 5700 MHz. Other conditions and implementation steps were the same as those in Example 1.

[0048] The reactor infrared temperature was 770° C., and the gas composition was H 2 : 52%, CO : 43%, CO 2 : 2%, CH 4 : 1.7%. In this embodiment, the CH 4 conversion rate at this frequency and temperature was low, at 3.55%.

[0049] Example 3

[0050] In the microwave reactor, the microwave power was set to 100 W and the frequency was set to 5525 MHz. Other conditions and implementation steps were the same as those in Example 1.

[0051] The infrared temperature of the reactor was 580° C., and the gas composition was H 2 : 42%, CO: 11.35%, CO 2: 18%, CH 4: 29.15%. In this embodiment, the methane conversion rate was 49.41%.

[0052] Comparative Example 1

[0053] In the microwave reactor, the microwave power was set to 100 W and the frequency was set to 2450 MHz. Other conditions and implementation steps were the same as those in Example 1.

[0054] In this embodiment, the reaction system does not heat up and the reaction does not occur.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for producing methane from seawater by hydrogen driven by microwave step-by-step catalysis, characterized in that: Lignin carbon is connected in series with nano-nickel oxide as the catalyst. The lignin carbon is filled in the upper layer of nano-nickel oxide. Seawater is used as the reactant. A separate water pump pumps the seawater into the quartz tube. The seawater passes through the carbon bed from top to bottom. Water gas reaction occurs under the action of the upper layer of lignin carbon, and methanation reaction occurs under the catalysis of the lower layer of nano-nickel oxide.

2. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: The microwave frequency is 4700-5700 MHz, the power is 100-200 W, and the temperature is 450-770°C.

3. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: The microwave frequency is 4720-5525 MHz, the power is 100 W, and the temperature is 480-580°C.

4. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: Seawater was pumped into the quartz tube at a rate of 0.06 ml / min.

5. The method for producing methane from seawater by hydrogen driven by microwave step-by-step catalysis according to claim 1, characterized in that: The filling mass ratio of lignin charcoal to nano-nickel oxide is 4:

1.

6. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: The filling mass of the lignin charcoal is 2 g, and the filling mass of the nano-nickel oxide is 0.5 g.

7. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: The microwave frequency was 4720 MHz, the power was 100 W, and the reactor temperature was 480 °C.

8. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: The microwave frequency was 5525 MHz, the power was 100 W, and the reactor temperature was 580 °C.

9. The method for producing methane from seawater by hydrogen driven by microwave-assisted step-by-step catalysis according to claim 1, characterized in that: The following steps are involved: The first step is to fill quartz wool in a quartz tube with an inner diameter of 8 mm, slowly put nano nickel oxide into the quartz tube, and fix it with quartz wool; In the second step, the lignin charcoal is slowly loaded into the quartz tube so that it is located above the nano-nickel oxide and fixed with quartz wool; The third step is to connect the quartz tube to the microwave reaction system, check the air tightness, and introduce nitrogen to purge the microwave reaction system and maintain the microwave reactor in an inert atmosphere; The fourth step is to turn on the microwave power supply and input the variable frequency microwave into the microwave resonant cavity through the microwave feed port. The lignin charcoal absorbs microwaves of different frequencies and begins to heat up. The temperature change of the catalyst is detected in real time by an infrared thermometer and a thermal imager on the axial cross section of the quartz tube. Step 5: After the reaction temperature is reached and remains stable, turn on the seawater pump to pump seawater into the quartz tube at a fixed rate to start the reaction; Step 6: After the reaction is completed, collect the gaseous products.

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