Homogeneous electro-catalysis chain type low-temperature methanol preparation method for biological natural gas

Abstract

The invention discloses a homogeneous electro-catalysis chain type low-temperature methanol preparation method for biological natural gas. The method comprises the following steps: S1, constructing a PtII / PtIV redox cycle system, and forming a homogeneous electro-catalysis system by using acidic solution coordination ions as a reaction medium; s2, the biogas is introduced into a homogeneous electro-catalysis system, and a Pt II complex is adopted to generate a Pt II-methyl intermediate through an oxidative addition reaction; s3, oxidizing the Pt II-methyl intermediate into a PtIV-CH3 compound through a Pt IV complex, and reducing, eliminating and releasing methanol to regenerate a Pt II complex; s4, PtII species accumulated in the reaction are regenerated into PtIV through electrochemical cathode reduction, methanol is prepared through closed-loop circulation of the catalyst, and unreacted biogas is combusted to supply heat to other steps in the system while the unreacted biogas is subjected to circular reaction. The concentration of the methanol product obtained by the method provided by the invention is as high as 99.8%, and the method has the advantages of simple and convenient process, low cost, cleanness, high efficiency and wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical fields of renewable energy utilization, new materials and environmental protection, and in particular to a method for preparing methanol from biogas in a homogeneous electrocatalytic chain at low temperature. Background Art

[0002] Biomass energy includes crop straw, livestock and poultry manure, forestry residues, and domestic waste. It is the world's fourth largest energy source after coal, oil, and natural gas. It has the characteristics of large quantity, wide distribution, low pollution, and carbon neutrality. It is also the only renewable carbon source. Replacing high-carbon-emission fossil energy with biomass and realizing the upgrading and transformation of carbon-based green new energy is an important trend in future development. The biochemical conversion of wet-based biomass into biogas through microbial fermentation is an effective way to realize the utilization of biomass resources. It has the advantages of mild conditions and wide adaptability of raw materials, but there are still key challenges in practical application. The source of biogas is mainly distributed, with low energy density and unit calorific value. The transportation process involves the construction of pipelines, compressed gas cylinders, liquefied transportation, etc., which is costly. There are many restrictions on storage, transportation, and use, and there is also the risk of gas leakage.

[0003] Further converting biogas into green methanol can effectively solve the above-mentioned bottleneck problem. Compared with gaseous fuels, green methanol has significant advantages as a liquid fuel. Methanol can be stably stored at room temperature and pressure, avoiding the technical difficulties of high-pressure storage of liquefied natural gas (LNG) or compressed natural gas (CNG). Compared with gas transportation, its lower limit of explosion concentration is higher and its safety is better. In addition, methanol is an important basic chemical raw material that can be used to synthesize chemical products such as formaldehyde, acetic acid, and olefins. It can also be used as a hydrogen energy storage medium and directly used as a fuel cell or to replace traditional fuel. Therefore, the development of bio-based low-carbon green methanol is of great significance for my country to reduce carbon emissions and promote green energy transformation, and the prospects are broad.

[0004] Natural gas-to-methanol technology primarily involves reforming to produce syngas and pressurizing syngas to produce methanol. This process is mature, but it suffers from issues such as high temperature and energy consumption, a complex reaction pathway, catalyst deactivation, and numerous byproducts. Chinese invention patent CN115779581A discloses a purification device for natural gas-to-methanol production, which improves the purification of harmful impurities from methanol gas. Chinese utility model patent ZL201220634819.X discloses a novel natural gas-to-methanol system that effectively addresses the issue of non-condensable gas generated in the pre-tower of the distillation system in existing natural gas-to-methanol systems and cannot be reused. Chinese invention patent ZL202110672554.6 discloses a biogas-to-methanol process. Based on an electrically heated converter, the syngas separated from the upper portion of the crude methanol separator is split into streams and returned to the syngas compressor inlet and the feed heat exchanger inlet, recovering the useful gas from the syngas and streamlining the process. Furthermore, methane-to-methanol production also involves methods such as photothermal catalysis and partial oxidation. Chinese invention patent ZL202210664264.1 discloses a photothermal catalyst for direct conversion of methane to methanol, its preparation method, and its application. Chinese invention patent ZL202411151127.3 provides a method for direct oxidation of methane to methanol using oxygen, and its application.

[0005] None of the above patents involve a method for producing methanol from biogas using homogeneous electrocatalytic chain at low temperature. This problem needs to be solved urgently. Summary of the Invention

[0006] The present invention solves the problems of complex natural gas methanol production process, high energy consumption and low product selectivity in the prior art. The present invention provides a method for directly producing methanol from biogas at low temperature electrocatalysis, thereby realizing efficient and clean production of liquid fuel from biogas.

[0007] The present invention is achieved through the following technical solutions:

[0008] The object of the present invention is to provide a method for producing methanol from biogas in a homogeneous electrocatalytic chain at low temperature, comprising the following steps:

[0009] S1. Construction of homogeneous electrocatalytic system: Using water-soluble platinum complex to construct Pt Ⅱ / Pt Ⅳ A redox cycle system uses acidic solution coordination ions as reaction media to stabilize platinum species, forming a homogeneous electrocatalytic system; the homogeneous electrocatalytic system involves a Pt-based cathode material, an inert anode material, a Pt(IV)-containing acidic electrolyte, and a separated ion exchange membrane;

[0010] S2. Biogas activation: The pretreated biogas is introduced into the homogeneous catalytic system. Ⅱ The complex generates Pt through oxidative addition reactionⅡ - Activation of biogas using methyl intermediates;

[0011] S3, methanol oxidation generation: through the system Pt Ⅳ The complex Pt Ⅱ -Methyl intermediate is oxidized to high-valent Pt Ⅳ -CH3 complex, followed by release of methanol and regeneration of Pt via reductive elimination Ⅱ complex;

[0012] S4. Electrochemical regeneration and circulation: The Pt accumulated in the reaction is regenerated by the electrochemical anode. Ⅱ Species regeneration to Pt Ⅳ The Pt-based catalytic electrode material acts as the catalytic electrode, while hydrogen or oxygen is evolved at the anode, achieving a closed-loop catalyst cycle to produce methanol. Unreacted biogas reacts in a cyclic reaction and is burned to provide heat for other steps in the system. The burner for this cyclic heat supply operates at a temperature of 800-900°C.

[0013] Preferably, in step S1, Pt Ⅱ The complex is PtCl4 2- 、[Pt(NO2)2Cl2] 2- or its derivatives, Pt Ⅳ The complex is PtCl6 2- , [PtO2Cl2] 2- or its derivatives.

[0014] Construction of homogeneous electrocatalytic system: using Pt Ⅱ Complex PtCl4 2- 、[Pt(NO2)2Cl2] 2- or its derivatives as methane activation catalysts, Pt Ⅳ Complex PtCl6 2- , [PtO2Cl2] 2- Or its derivatives are used as oxidants, dissolved in acidic aqueous solution, using carbon-based anode materials to form a homogeneous catalytic system, the reaction medium uses hydrochloric acid or sulfuric acid system acidic electrolyte, pH value 1-3, Cl - 、NO3 - The platinum species is stabilized by isocoordinating ions, with an ion concentration of 0.1-1.5 mol / L. The reaction temperature is controlled at 30-80°C, more preferably 50-60°C.

[0015] Preferably, the reaction medium in the homogeneous electrocatalytic system in step S1 is an acidic electrolyte of hydrochloric acid or sulfuric acid system with a pH value of 1-3, and the coordination ion Cl - or NO3 - To stabilize the platinum species, the concentration of the coordination ions is 0.1-1.5 mol / L.

[0016] Preferably, the specific conditions of step S2 are: biogas partial pressure 0.5-2.0 MPa, Pt Ⅱ Concentration 0.05-0.2mol / L, chloride ion concentration 0.5-1.5mol / L, temperature 40℃-80℃, activation time 10-60 minutes.

[0017] In step S2, biogas activation: the pretreated biogas enters the electrochemical reaction unit through the bubbling reactor, and the PtⅡ complex reacts with methane through an oxidative addition reaction to generate a Pt-methyl intermediate (Pt-CH3), thereby activating the biogas. The reaction formula is:

[0018] PtCl4 2- +CH4→PtCl3(CH3) - +HCl+Cl - (1)

[0019] Preferably, the specific conditions of step S3 are: Pt Ⅳ / Pt Ⅱ The molar ratio is 1:1-2:1, the oxidation reaction time is 20-60 minutes, and the pH value is 1.5-2.5 to inhibit excessive oxidation products.

[0020] Methanol is oxidized in step S3: Pt Ⅳ species as oxidants, Pt Ⅱ -CH3 intermediate is converted into high-valent Pt Ⅳ -CH3 complex, followed by release of methanol and regeneration of Pt via reductive elimination Ⅱ Species, the reaction formula is:

[0021] [PtCl3(CH3)] - +PtCl6 2- +H2O→2[PtCl4] 2- +CH3OH+H + +Cl - (2)

[0022] Pt(IV) oxidation of Pt Ⅱ The essence of the process of -CH3 to methanol is the synergistic effect of the oxidative addition of Pt(II) and the reduction elimination of CO bond formation. The mechanism is as follows:

[0023] (a) Oxidative addition:

[0024] Pt(IV) species (such as PtCl6 2- ) acts as an oxidant to attack the electron-rich Pt Ⅱ -CH3 intermediate ([PtCl3(CH3)] - ). Reaction formula: [PtCl3(CH3)]- +PtCl6 2- →[Cl3Pt-CH3-PtCl5] 2- +Cl -

[0025] The chlorine ligand (Cl - ) as a leaving group, making PtCl6 2- Converted to electrophilic [PtCl5] - [PtCl5] - with [PtCl3(CH3)] - σ-bond metathesis occurs, the Pt(II)-C bond breaks, and a Pt(IV)-C bond (i.e., a high-valent Pt IV -CH3), and simultaneously generate a double platinum core intermediate (containing Pt IV -CH3 and Pt II unit).

[0026] (b) Nucleophilic attack and hydrolysis to release methanol:

[0027] Water (or OH) in the system - ) acts as a nucleophile to attack the high-valent Pt IV -CH3 in the methyl carbon atom, triggering CO bond formation and reductive elimination. Reaction formula: [Pt IV Cl3(CH3)] + +H2O→[Pt II Cl3] - +CH3OH+H +

[0028] The oxygen atom of H2O attacks the carbon of -CH3 with nucleophilicity, forming a tetrahedral transition state. IV The center undergoes a 2-electron reduction (from +4 to +2), releasing CH3OH and ultimately releasing Pt II species.

[0029] Preferably, the specific conditions of step S4 are: cathode potential -0.3 to 0.2 V, current density 20-80 mA / cm 2 The electrolysis time is synchronized and carried out continuously with step S2 and step S3.

[0030] Electrochemical regeneration and circulation in step S4: In a strong oxidizing environment (high potential, acidic medium), the Pt accumulated in the reaction is oxidized by electrochemical anodic oxidation. Ⅱ Species regeneration to Pt Ⅳ At the same time, hydrogen or oxygen is released at the anode to realize the closed-loop cycle of the catalyst to produce methanol. The unreacted biomass natural gas re-enters the activation step for cyclic reaction while part of the tail gas is burned for heat. The reaction formula is:

[0031] 2Pt 2+ +2H2O→2Pt 4+ +4e - +O2+4H + (3)

[0032] Simplify: Pt 2+ →Pt 4+ +2e -

[0033] Preferably, the anode potential is >1.0 V vs. RHE.

[0034] Preferably, the Pt-based catalytic electrode material described in step S4 is prepared by artificial intelligence machine learning combined with microwave-assisted polyol reduction. The catalytic electrode preparation proposed in the present invention involves constructing an electrode element superstructure model using deep neural network, random forest and gradient boosting decision tree machine learning methods.

[0035] Further preferably, the preparation method of the Pt-based catalytic electrode material described in step S4 comprises the following steps: dissolving H2PtCl6 and a transition metal salt in ethylene glycol with a pH value of 8.9-9.3, adding PVP as a morphology directing agent, and reacting under microwave radiation at 180°C-230°C for 30-60 minutes to obtain a multifunctional nanocomposite material; dissolving PVDF in NMP to obtain a PVDF / NMP solution, mixing the nanocomposite material and the conductive carbon black powder evenly, and slowly adding the mixture to the stirring PVDF / NMP solution until a uniform composite material slurry is formed, activating the graphene layer of the carbon cloth with concentrated nitric acid, and then impregnating the composite material slurry, rolling it into a thin layer, and annealing it to obtain the Pt-based catalytic electrode material.

[0036] The method for preparing a Pt-based catalytic electrode material comprises the following steps: dissolving chloroplatinic acid (HPtCl) and a selected transition metal salt (such as NiCl, CoCl, or FeCl) in ethylene glycol, and adjusting the pH of the mixed solution to 8.9-9.3 using an alkaline solution (such as a NaOH or KOH solution in ethylene glycol or water). High-molecular-weight polyvinylpyrrolidone (PVP, molecular weight ≈ 55 kDa) is added as a morphology-directing agent and stabilizer. The amount of PVP added is 1-5 times the combined mass of the platinum and transition metal. The mixed solution is placed in a microwave reactor and subjected to microwave heating at 180°C-230°C for 30-60 minutes. During this process, the metal ions are reduced by ethylene glycol (concentration 5-15 mol / L), and a Pt-based multifunctional nanocomposite is formed under the control of PVP. After the reaction is completed, the mixture is cooled to room temperature, the product is separated by filtration, and repeatedly washed with ethanol and deionized water to remove residual ethylene glycol, PVP, and ionic byproducts. The mixture was dried in a vacuum oven at 60° C. for 12 hours to obtain a dry multifunctional nanocomposite material.

[0037] The mass ratio of dried multifunctional nanomaterial, conductive carbon black (Vulcan XC-72R), and polyvinylidene fluoride (PVDF) (binder) should be within the following range: 70%–85%: 10%-20%: 5%-15%. Dissolve the weighed PVDF powder in the organic solvent N-methylpyrrolidone (NMP) to create a 5-10wt% PVDF / NMP solution. Continuously stir magnetically until the PVDF is completely dissolved, forming a transparent or translucent viscous solution. Pre-grind and mix the nanocomposite powder and conductive carbon black powder until thoroughly mixed. Slowly add the mixture to the stirring PVDF / NMP solution and continue stirring vigorously for 30-120 minutes until a uniform, stable slurry is formed without noticeable graininess.

[0038] After the carbon cloth is activated with concentrated nitric acid to form a graphene layer, it is directly impregnated with the composite material slurry to ensure that the slurry fully penetrates into the interior of the carbon cloth fibers and covers its surface. The coated carbon cloth is preliminarily dried at 60°C-80°C for 10-30 minutes to remove most of the NMP solvent. The electrode material after preliminary drying is rolled using a roller press. Rolling is performed multiple times under an appropriate pressure (5-20MPa) to enhance the bonding strength between the composite material layer and the carbon cloth substrate, reduce the contact resistance, and form a dense, uniform, and catalytically active thin layer of a certain thickness. Preferably, a 0.2mm thin layer is rolled under a pressure of 10MPa. The rolled electrode material is placed in a tube furnace (or muffle furnace) and annealed under an inert atmosphere (high-purity N2 or Ar). A heating program is set (such as heating at a rate of 2-5°C / min) and kept at 250°C-350°C for 1-3 hours. Preferably, annealing is performed at 320°C in an Ar atmosphere for 2 hours. After rolling and annealing, the Pt-based catalytic electrode material is obtained.

[0039] More preferably, the transition metal in the transition metal salt is cobalt or nickel, the molar ratio of platinum to transition metal is 1 / 1-3 / 1, and the amount of PVP added is 1-5 times the sum of the mass of platinum and transition metal. The cobalt or nickel salt is Co(NO3)2 or NiCl2.

[0040] Preferably, the pretreatment step of the biogas pretreated in step S1 is specifically: allowing the biogas to absorb H2S and CO2 through a NaOH solution, the reaction temperature is 30°C-50°C, and the pH value of the NaOH solution is 9-10.

[0041] Preferably, the method further comprises step S5, a separation system: using membrane separation technology or distillation to separate the methanol product in the liquid phase, with the product concentration exceeding 99%. The present invention adopts an industrial-grade nanofiltration membrane separation system (polyimide composite nanofiltration membrane), a liquid-phase methanol-water solution (methanol concentration 70-85%, temperature 45-50°C, transmembrane pressure difference 3.5-4.0MPa, methanol recovery rate ≥92%, product purity 99.3%). Alternatively, a vacuum distillation method is adopted, with the product purity reaching up to 99.8%.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] (1) The biogas homogeneous electrocatalytic chain-type low-temperature methanol production technology provided by the present invention realizes the low-temperature and efficient production of methanol from biogas and the cyclic regeneration of precious metal catalysts, solving the bottleneck problems of difficult liquefied storage and transportation of biogas and harsh conditions and complex processes for conventional methanol synthesis. It has the advantages of simple operation, low cost, cleanliness and high efficiency.

[0044] (2) The method proposed in the present invention enables biogas to achieve a comprehensive methanol conversion rate of more than 80% at 30°C-80°C, and the product concentration after methanol separation exceeds 99%. Electrochemical regeneration replaces chemical oxidants, and there is no by-product pollution. The deactivation problem of heterogeneous catalysts is avoided through the homogeneous system. Hydrogen can also be co-produced (hydrogen evolution mode) for use as energy or chemical raw materials. The process is simple, economical, and has a wide range of application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a schematic flow chart of a method for producing methanol from biogas in a homogeneous electrocatalytic chain at low temperature. DETAILED DESCRIPTION

[0046] The present invention will be described in further detail below with reference to the examples. These examples are intended to illustrate the present invention only and are not intended to limit the scope of the present invention. Experimental methods in the following examples, where specific conditions are not specified, generally follow conventional conditions in the art or conditions recommended by the manufacturer; raw materials and reagents used, unless otherwise specified, are considered to be commercially available through conventional markets.

[0047] A method for producing methanol from biogas in a homogeneous electrocatalytic chain at low temperature, comprising the following steps:

[0048] S1. Pretreatment process: After the biogas is pretreated with desulfurization and decarbonization, high-concentration biogas is obtained;

[0049] S2. Catalytic electrode preparation: Pt-based catalytic electrode materials were constructed based on artificial intelligence machine learning combined with microwave-assisted polyol reduction, with a reaction temperature range of 30°C to 80°C.

[0050] S3. Construction of electrocatalytic system: Using water-soluble platinum (Pt) complex, construct Pt Ⅱ / Pt Ⅳ The redox cycle system, as the core electrocatalytic system, stabilizes the platinum species by using acidic solution coordination ions as reaction media;

[0051] S4. Biogas activation: The purified biogas enters the electrocatalytic system through the bubbling reactor. Ⅱ The complex reacts with methane through an oxidative addition reaction to generate Pt Ⅱ -Methyl intermediate (Pt-CH3), activated biogas, the reaction formula is:

[0052] PtCl4 2- +CH4→PtCl3(CH3) - +HCl+Cl - (1)

[0053] S5, methanol oxidation generation: through the system Pt Ⅳ Species (complex) acts as an oxidant to oxidize the Pt-CH3 intermediate to a high-valent Pt Ⅳ -CH3 complex, followed by release of methanol and regeneration of Pt via reductive elimination Ⅱ Species (complex), the reaction formula is:

[0054] PtCl3(CH3) - +PtCl6 2- →2 PtCl4 2- +CH3OH+HCl (2)

[0055] S6. Electrochemical regeneration and recycling: Pt accumulated in the reaction is reduced by electrochemical cathode Ⅳ Species regeneration to Pt Ⅱ At the same time, hydrogen or oxygen is released at the anode to realize the closed-loop cycle of the catalyst to produce methanol. The unreacted biomass natural gas re-enters the activation step for cyclic reaction. At the same time, part of the tail gas is burned by the burner to provide heat. The reaction formula is:

[0056] PtCl6 2- +2e - →PtCl4 2- +2Cl - (3)

[0057] S7. Separation system: Membrane separation technology or distillation is used to separate the methanol product in the liquid phase, and the product concentration exceeds 99%.

[0058] In the following preferred embodiment, in step S1, biogas is subjected to wet synergistic desulfurization and decarbonization, H2S and CO2 are absorbed by NaOH, the reaction temperature is 30°C-50°C, and the pH value is 9-10.

[0059] The following preferred embodiments include: step S2, where a Pt-based catalytic electrode material is constructed based on artificial intelligence machine learning combined with a microwave-assisted polyol reduction method, with a reaction temperature range of 30°C to 80°C; the machine learning method involves deep neural networks, random forests, and gradient boosting decision tree machine learning methods; the microwave-assisted polyol reduction method involves H2PtCl6 and a transition metal salt (Co(NO3)2, NiCl2, etc.), a Pt:Co atomic ratio of 1 / 1-3 / 1, PVP as a morphology directing agent (MW=55kDa), and a reaction under microwave irradiation at 180°C-230°C for 30-60 minutes, with a pH value of 8.9-9.3. The PVDF binder accounts for 8%-10% of the composite material slurry, and the carbon cloth is activated with concentrated nitric acid and then impregnated with the composite material slurry.

[0060] The preparation method of a Pt-based catalytic electrode material comprises the following steps: dissolving chloroplatinic acid (HPtCl) and a selected transition metal salt (such as NiCl, CoCl, or FeCl) in ethylene glycol. The pH of the mixed solution is adjusted to 8.9-9.3 using an alkaline solution (such as a NaOH or KOH solution in ethylene glycol or water). High-molecular-weight polyvinylpyrrolidone (PVP, molecular weight ≈ 55 kDa) is added as a morphology-directing agent and stabilizer. The amount of PVP added is 1-5 times the combined mass of the platinum and transition metal. The mixed solution is placed in a microwave reactor and heated under microwave irradiation at 180°C-230°C for 30-60 minutes. During this process, the metal ions are reduced by ethylene glycol (concentration 5-15 mol / L), and a Pt-based multifunctional nanocomposite is formed under the control of PVP. After the reaction is completed, the mixture is cooled to room temperature, the product is separated by filtration, and repeatedly washed with ethanol and deionized water to remove residual ethylene glycol, PVP, and ionic byproducts. The mixture was dried in a vacuum oven at 60° C. for 12 hours to obtain a dry multifunctional nanocomposite material.

[0061] The mass ratio of dried multifunctional nanomaterial, conductive carbon black (Vulcan XC-72R), and polyvinylidene fluoride (PVDF) (binder) should be within the following range: 70%–85%: 10%-20%: 5%-15%. Dissolve the weighed PVDF powder in the organic solvent N-methylpyrrolidone (NMP) to create a 5-10wt% PVDF / NMP solution. Continuously stir magnetically until the PVDF is completely dissolved, forming a transparent or translucent viscous solution. Pre-grind and mix the nanocomposite powder and conductive carbon black powder until thoroughly mixed. Slowly add the mixture to the stirring PVDF / NMP solution and continue stirring vigorously for 30-120 minutes until a uniform, stable slurry is formed without noticeable graininess.

[0062] After the carbon cloth is activated with concentrated nitric acid to form a graphene layer, it is directly impregnated with the composite material slurry to ensure that the slurry fully penetrates into the interior of the carbon cloth fibers and covers its surface. The coated carbon cloth is preliminarily dried at 60°C-80°C for 10-30 minutes to remove most of the NMP solvent. The electrode material after preliminary drying is rolled using a roller press. Rolling is performed multiple times under an appropriate pressure (5-20MPa) to enhance the bonding strength between the composite material layer and the carbon cloth substrate, reduce the contact resistance, and form a dense, uniform, and catalytically active thin layer of a certain thickness. Preferably, a 0.2mm thin layer is rolled under a pressure of 10MPa. The rolled electrode material is placed in a tube furnace (or muffle furnace) and annealed under an inert atmosphere (high-purity N2 or Ar). A heating program is set (such as heating at a rate of 2-5°C / min) and kept at 250°C-350°C for 1-3 hours. Preferably, annealing is performed at 320°C in an Ar atmosphere for 2 hours. After rolling and annealing, the Pt-based catalytic electrode material is obtained.

[0063] More preferably, the transition metal in the transition metal salt is cobalt or nickel, the molar ratio of platinum to transition metal is 1 / 1-3 / 1, and the amount of PVP added is 4-5 times the sum of the mass of platinum and transition metal. The cobalt or nickel salt is Co(NO3)2 or NiCl2.

[0064] The following embodiment is preferred, in step S3, Pt Ⅱ Complex PtCl4 2- 、[Pt(NO2)2Cl2] 2- or its derivatives as methane activation catalysts, Pt Ⅳ Complex PtCl6 2- , [PtO2Cl2] 2- Or its derivatives are used as oxidants, dissolved in an acidic aqueous solution containing chloride ions to form a homogeneous catalytic system. The reaction medium uses hydrochloric acid or sulfuric acid system acidic electrolyte, pH value 1-3, Cl - 、NO3 - The platinum species is stabilized by isocoordinating ions with an ion concentration of 0.1-1.5 mol / L. The reaction temperature is controlled at 30°C-80°C.

[0065] The following embodiment is preferred, in step S4, Pt Ⅱ The complex generates Pt-methyl intermediate through oxidative addition reaction to activate biogas. The biogas partial pressure is 0.5-2.0MPa. Pt Ⅱ Concentration: 0.05-0.2mol / L, chloride ion concentration: 0.5-1.5mol / L, temperature: 40℃-80℃, activation time 10-60 minutes.

[0066] The following embodiment is preferred, in step S5, the system Pt Ⅳ Species oxidize the Pt-CH3 intermediate to high-valent Pt Ⅳ -CH3 complex, followed by release of methanol and regeneration of Pt via reductive elimination Ⅱ Species, Pt Ⅳ / Pt Ⅱ Molar ratio 1:1-2:1, oxidation reaction time: 20-60 minutes, pH value 1.5-2.5.

[0067] The following embodiment is preferred, in step S6, the Pt accumulated in the reaction is reduced by electrochemical cathode Ⅳ Species regeneration to Pt Ⅱ At the same time, hydrogen or oxygen is released at the anode to realize the closed-loop cycle of the catalyst to produce methanol. The unreacted biomass natural gas is recycled and part of the tail gas is burned to provide heat. The cathode potential is -0.3 to 0.2V and the current density is 20-80mA / cm 2The exhaust gas combustion heating temperature is 800℃-900℃.

[0068] In the following preferred embodiment, in the separation step S7, a nanofiltration membrane separation system and an AI-driven membrane separation system with dynamic optimization of transmembrane pressure are used to purify the methanol product at a temperature of 45°C-50°C and a transmembrane pressure difference of 3.5-4.0 MPa.

[0069] Example 1

[0070] A method for producing methanol from biogas in a homogeneous electrocatalytic chain at low temperature, comprising the following steps:

[0071] S1. Pretreatment process: Biogas is pretreated by wet desulfurization and decarbonization, with H2S and CO2 absorbed by NaOH, the reaction temperature is 30℃, and the pH value is 9.

[0072] S2. Catalytic Electrode Preparation: A catalytic electrode was prepared using a microwave-assisted polyol reduction method. H2PtCl6 and Co(NO3)2 were dissolved in ethylene glycol at a predetermined atomic ratio (Pt:Co atomic ratio = 2 / 1). PVP (polyvinylpyrrolidone) was added as a morphology-directing agent (MW = 55 kDa) in an amount four times the combined mass of platinum and Co. The reaction was carried out under microwave irradiation at 200°C for 40 min. A multifunctional nanocomposite was obtained by controlling the pH value (8.9), the reducing agent concentration, and the cooling rate. Specifically, the mixed solution was placed in a microwave reactor and subjected to microwave heating at 200°C for 40 min. During this process, the metal ions were reduced by ethylene glycol (concentration 5-15 mol / L), and a Pt-based multifunctional nanocomposite was formed under the control of PVP. After the reaction was completed, the mixture was cooled naturally to room temperature, and the product was isolated by filtration and repeatedly washed with ethanol and deionized water to remove residual ethylene glycol, PVP, and ionic byproducts. The product was then dried in a vacuum oven at 60°C for 12 hours to obtain a dry multifunctional nanocomposite.

[0073] Prepare a 75%:15%:10% mass ratio of dried multifunctional nanomaterial, conductive carbon black (Vulcan XC-72R), and polyvinylidene fluoride (PVDF) (binder). Dissolve the weighed PVDF powder in the organic solvent N-methylpyrrolidone (NMP) to create an 8wt% PVDF / NMP solution. Magnetic stirring is continued until the PVDF is completely dissolved, forming a transparent or translucent viscous solution. Pre-grind and mix the nanocomposite powder and conductive carbon black powder at a mass ratio of 5:1. Slowly add the mixture to the stirring PVDF / NMP solution and continue stirring vigorously for 30-120 minutes until a uniform, stable slurry with no noticeable graininess is formed.

[0074] After the carbon cloth is activated with concentrated nitric acid to form a graphene layer, it is directly impregnated with the composite material slurry to ensure that the slurry fully penetrates into the carbon cloth fibers and covers its surface. The coated carbon cloth is preliminarily dried at 70°C for 20 minutes to remove most of the NMP solvent. The electrode material after preliminary drying is rolled using a roller press. Rolling is performed multiple times under appropriate pressure (10MPa) to form a 0.2mm thin layer to enhance the bonding strength between the composite material layer and the carbon cloth substrate, reduce contact resistance, and form a dense, uniform and catalytically active thin layer with a certain thickness. The rolled electrode material is placed in a tube furnace and annealed under the protection of an inert atmosphere (high-purity N2). A heating program is set (e.g., heating at a rate of 5°C / min) and kept at 320°C for 2 hours. After rolling and annealing, a Pt-based catalytic electrode material is obtained.

[0075] S3. Construction of electrocatalytic system: Pt Ⅱ The complex is PtCl4 2- , Pt Ⅳ The complex uses PtCl6 2- , dissolves in an acidic aqueous solution containing chloride ions to form PtCl4 2- / PtCl6 2- Homogeneous catalytic system. The reaction medium uses hydrochloric acid, pH value 1.5, Cl - Ion concentration: 1.0 mol / L. Reaction temperature: 50°C.

[0076] S4, Biogas Activation: The purified biogas enters the electrochemical reaction unit through the bubbling reactor, Pt Ⅱ The complex reacts with methane through an oxidative addition reaction to generate Pt Ⅱ -Methyl intermediate (Pt-CH3), activated biogas, methane partial pressure: 0.5MPa, Pt Ⅱ Concentration: 0.1 mol / L (PtCl4 2- Calculation), chloride ion concentration: 1.0 mol / L, temperature: 50°C, activation time: 20 minutes.

[0077] S5, methanol oxidation generation: through the system Pt Ⅳ Species act as oxidants to oxidize the Pt-CH3 intermediate to high-valent Pt Ⅳ -CH3 complex, followed by release of methanol and regeneration of Pt via reductive elimination Ⅱ Complex, Pt Ⅳ / Pt Ⅱ The molar ratio was 1:1, the oxidation reaction time was 20 min, and the pH value was 1.5 to inhibit excessive oxidation products.

[0078] S6. Electrochemical regeneration and recycling: Pt accumulated in the reaction is reduced by electrochemical cathode ⅡSpecies regeneration to Pt Ⅳ At the same time, hydrogen or oxygen is released at the anode to realize the closed-loop cycle of the catalyst to produce methanol. The cathode potential is -0.3V and the current density is 30mA / cm 2 The electrolysis time is synchronized and carried out continuously with step S4 and step S5.

[0079] S7. Methanol separation: Membrane separation technology is used to separate the methanol product in the liquid phase. The methanol in the liquid aqueous solution is separated by an industrial-grade polyimide composite nanofiltration membrane system. The temperature is 45°C, the transmembrane pressure difference is 3.5 MPa, and the product purity is 99.3%.

[0080] The implementation results show that the single-pass conversion rate of biogas to methanol is 12.3%, the methanol recovery rate is 87.5%, the purity of the separated product is 99.3%, and the cycle stability is 200h.

[0081] Example 2

[0082] Based on Example 1, Examples 2-6 were carried out with different implementation conditions. The implementation methods were the same as in Example 1 and will not be described in detail here. The corresponding implementation conditions and implementation results are listed in Table 1.

[0083] Table 1

[0084]

[0085]

[0086] The above-mentioned Example 1 is for the basic reaction parameters of low-temperature chain electrocatalytic production of methanol from biogas. Examples 2-6 respectively provide the reaction parameters of high-activity type, low-temperature energy-saving type, high-pressure rapid type, low-concentration resource type, and intelligent optimization type. Example 2 improves the conversion rate and methanol yield based on Example 1; Example 3 adapts to low-temperature conditions, reduces overall energy consumption, and is suitable for distributed production; Example 4 can effectively increase the reaction rate, with a fuel single-pass conversion rate of 21.5%, but with increased Pt material consumption; Example 5 is suitable for low-grade biogas, which can effectively reduce overall costs; Example 6 achieves full process automation, with a methanol yield increased to 94.5%, a methanol purity of 99.7% after membrane separation, and reduced catalyst loss. Each example has the following common characteristics: NaOH wet desulfurization pretreatment is used, the catalytic electrode is prepared by microwave-assisted polyol reduction, the carbon cloth substrate is activated by concentrated nitric acid, the circulating system exhaust is burned for heat, and energy self-balance is achieved. Methanol selectivity is monitored by online chromatography / mass spectrometry to prevent excessive oxidation. Each embodiment is suitable for scenarios with different scales (centralized / distributed), raw material qualities, and energy efficiency requirements through parameter combination optimization.

[0087] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for producing methanol from biogas in a homogeneous electrocatalytic chain at low temperature, characterized in that: The steps include: S1. Construction of homogeneous electrocatalytic system: Using water-soluble platinum complex to construct Pt Ⅱ / Pt Ⅳ The redox cycle system uses acidic solution coordination ions as reaction media to stabilize platinum species and form a homogeneous electrocatalytic system; S2. Biogas activation: The pretreated biogas is introduced into the homogeneous electrocatalytic system. Ⅱ The complex generates Pt through oxidative addition reaction Ⅱ - Activation of biogas using methyl intermediates; S3, methanol oxidation generation: through the system Pt Ⅳ The complex Pt Ⅱ -Methyl intermediate is oxidized to high-valent Pt Ⅳ -CH3 complex, followed by release of methanol and regeneration of Pt via reductive elimination Ⅱ complex; S4. Electrochemical regeneration and circulation: The Pt accumulated in the reaction is regenerated by the electrochemical anode. Ⅱ Species regeneration to Pt Ⅳ Pt-based catalytic electrode materials are used as catalytic electrodes to realize the closed-loop cycle of catalyst to produce methanol. While the unreacted biogas is cyclically reacted, it is burned to provide heat for other steps in the system.

2. The method according to claim 1, characterized in that In step S1, Pt Ⅱ The complex is PtCl4 2- 、[Pt(NO2)2Cl2] 2- or its derivatives, Pt Ⅳ The complex is PtCl6 2- , [PtO2Cl2] 2- or its derivatives.

3. The method according to claim 1 or 2, characterized in that In step S1, the reaction medium in the homogeneous electrocatalytic system is an acidic electrolyte of hydrochloric acid or sulfuric acid system with a pH value of 1-3, and the coordination ion Cl is used. - or NO3 - To stabilize the platinum species, the concentration of the coordination ions is 0.1-1.5 mol / L.

4. The method according to claim 1, wherein The specific conditions of step S2 are: biogas partial pressure 0.5-2.0 MPa, Pt Ⅱ Concentration 0.05-0.2mol / L, chloride ion concentration 0.5-1.5mol / L, temperature 40℃-80℃, activation time 10-60 minutes.

5. The method according to claim 1 or 4, characterized in that The specific conditions of step S3 are: Pt Ⅳ / Pt Ⅱ The molar ratio is 1:1-2:1, the oxidation reaction time is 20-60 minutes, and the pH value is 1.5-2.

5.

6. The method according to claim 1 or 4, characterized in that The specific conditions of step S4 are: cathode potential -0.3 to 0.2 V, current density 20-80 mA / cm 2 The electrolysis time is synchronized and carried out continuously with step S2 and step S3.

7. The method according to claim 1, characterized in that The Pt-based catalytic electrode material described in step S4 is prepared by artificial intelligence machine learning combined with microwave-assisted polyol reduction method.

8. The method according to claim 7, characterized in that The preparation method of the Pt-based catalytic electrode material described in step S4 specifically includes the following steps: dissolving H2PtCl6 and a transition metal salt in ethylene glycol with a pH value of 8.9-9.3, adding PVP as a morphology directing agent, and reacting under microwave radiation at 180°C-230°C for 30-60 minutes to obtain a multifunctional nanocomposite material; dissolving PVDF in NMP to obtain a PVDF / NMP solution, mixing the nanocomposite material and conductive carbon black powder evenly, and slowly adding the mixture to the stirring PVDF / NMP solution until a uniform composite material slurry is formed, activating the graphene layer of carbon cloth with concentrated nitric acid, and then impregnating the composite material slurry, rolling it into a thin layer, and annealing it to obtain the Pt-based catalytic electrode material.

9. The method according to claim 8, characterized in that The transition metal in the transition metal salt is cobalt or nickel, the molar ratio of platinum to the transition metal is 1 / 1-3 / 1, and the added amount of PVP is 1-5 times the sum of the masses of platinum and the transition metal.

10. The method according to claim 1, characterized in that The pretreatment step of the biogas pretreated in step S2 is specifically as follows: the biogas is allowed to absorb H2S and CO2 through a NaOH solution, the reaction temperature is 30°C-50°C, and the pH value of the NaOH solution is 9-10.

Images