Device and method for preparing natural gas by electrochemical reduction of domestic waste cracking gas

Abstract

The present invention discloses a device and method for preparing natural gas by electrochemically reducing cracked gas of domestic waste, and specifically relates to the technical field of post-treatment of domestic waste. The device comprises a cracking gasification synthesis tower, a plasma tower and an electrochemical methanation reactor; wherein an electrolysis device is arranged in the electrochemical methanation reactor, and the electrolysis device is sequentially provided with a cathode electrode, a diaphragm and an anode electrode from the inside to the outside; after the gas obtained by cracking the domestic waste in the cracking gasification synthesis tower is processed by the plasma tower, the gas enters from the cathode electrode of the electrolysis device to carry out an electrochemical reduction reaction, and after the reaction is completed, the by-products are collected from the outlet of the anode electrode and returned to the cracking gasification synthesis tower to continue the reaction; pure methane is released and collected from the outlet of the cathode electrode. The present invention integrates the anode, the diaphragm and the cathode into a whole, and is a coaxial structure, which has the technical advantages of low internal resistance, fast ion penetration and transfer, small mass transfer resistance, high current efficiency, firm structure, safety and reliability, and long service life.

Description

Technical Field

[0001] The invention relates to the technical field of domestic waste post-treatment, and in particular to a device and method for preparing natural gas by utilizing electrochemical reduction of domestic waste cracking gas. Background Art

[0002] There are two methods for disposing urban domestic waste: traditional landfill and incineration, and the recently developed pyrolysis gasification method. Due to the preciousness of urban land, landfill is not suitable for disposing large amounts of urban waste, so incineration is widely used. However, incineration is usually accompanied by secondary pollution such as dioxins and fly ash, which poses serious environmental safety risks. In recent years, pyrolysis gasification has been used to convert organic waste into combustible synthesis gas, namely CO, H 2 etc., which attracted widespread attention.

[0003] Thermal cracking gasification method, such as Chinese patent CN111704934A, a thermal cracking heavy oil device using pulverized coal and petroleum coke gasification, includes a coupling reactor and a fractionation tower, petroleum coke, pulverized coal, air and water undergo gasification reaction and release heat in the coupling reactor, and there is a thermal cracking reaction unit in the coupling reactor, so that the heavy oil absorbs the heat of the gasification reaction in the thermal cracking reaction unit to undergo a thermal cracking reaction, and then the oil gas and petroleum coke are separated by a separator, the petroleum coke is sent to the coupling reactor, and the generated oil gas is sent to the fractionation tower to separate the chemical products. However, this method also has some disadvantages: CO in the synthesis gas is toxic, which brings certain safety risks to production, storage and transportation.

[0004] The biological method uses the metabolism of microorganisms to convert organic waste into natural gas methane, namely CH 4 ; Chinese patent CN105907793A, a method for producing methane in a straight-cylinder organic waste anaerobic fermentation treatment system, when the fermented raw materials ferment in the fermentation pipeline to produce biogas, the biogas accumulates in the gas storage plate, and as the biogas pressure gradually increases, the biogas liquid in the fermentation pipeline will be squeezed to flow to the feed pipe, the discharge pipe, and the turbulent flow interval, and the biogas liquid level in the feed pipe, the discharge pipe, and the turbulent flow interval will gradually rise. When the biogas liquid level in the turbulent flow interval reaches the exhaust pipe at the end of the feed pipe and the drain pipe at the end of the discharge pipe, the biogas liquid in the turbulent flow interval will flow into the water pressure room through the exhaust pipe at the end of the feed pipe and the drain pipe at the end of the discharge pipe. Although the obtained methane has high purity, the microbial metabolism is slow, the production cycle is long, the efficiency is low, the operating cost is high, and the economic value is low.

[0005] In industry, for CO, H 2The catalytic synthesis of methane is also a mature process and has been widely used. Chinese patent CN106944072A, a method for preparing a highly efficient isothermal coal-based synthesis gas to methane catalyst, solves the problem of the inability to achieve both stability and production cost in existing methane catalysts. The technical solution includes the following steps: (1) dissolving a water-soluble alkali metal or alkaline earth metal salt in water, impregnating the carrier under ultrasound assistance, and then drying and calcining in steps to obtain the modified carrier M 1 / Support; (2) dissolving nickel nitrate and rare earth metal salt in an aqueous solution, adding carrier M 1 / Support obtains a suspension, adds an alkaline solution to the suspension under stirring and ultrasound assistance to control its pH value for precipitation; (3) the precipitate is filtered, washed, dried step by step, and calcined to obtain the catalyst NiM 2 / M 1 / Support, the mass content of the active component NiO is 5-35%, the mass content of alkali metal or alkaline earth metal oxide is 0.5-10%, the mass content of rare earth metal oxide is 0.5-10%, and the balance is carrier. However, due to the complicated production process, high purity requirements for raw materials, and the complex composition of organic waste, a small amount of S or Cl will poison the NiO-based catalyst and make it ineffective; at the same time, because NiO is reduced to metal elements by electrons in a reducing atmosphere, it loses its activity and has no catalytic effect. Finally, the NiO-based catalyst will react with CO and even H 2 The nickel-based catalyst becomes ineffective due to the reaction; this requires oxidation resurrection and regeneration. Such repeated deactivation and regeneration will result in a short catalyst life and high cost, and its operating efficiency is very low, so it is rarely used in waste disposal.

[0006] Traditional electrochemical methods require an electrolyte solution as a medium for proton transfer, which limits the process development of electrolysis in the gas phase. Summary of the invention

[0007] To this end, the present invention provides a device and method for preparing natural gas by electrochemical reduction of domestic waste cracking gas to solve the above-mentioned problems.

[0008] The electrochemical reduction method has the advantage of high purity of the prepared product comparable to the biological transformation method, but also has the advantages of fast reaction, high efficiency, safety and reliability similar to the catalytic synthesis method. Its biggest advantage is that it can realize unit operation and the equipment is simple.

[0009] In view of the defects of traditional garbage disposal methods, the present invention adopts the electrochemical reduction method to achieve efficient conversion and utilization of domestic garbage. The present invention is a bold innovation in the electrolysis device. It integrates the anode electrode, electrolyte membrane (diaphragm), and cathode electrode together, and uses porous electrodes to construct a multi-dimensional super strong channel for protons, which not only reduces the internal resistance, but also improves its kinetic efficiency, so that both electron conduction and proton transfer can be carried out efficiently and quickly, breaking through the limitations of the catalytic method that requires continuous regeneration and other harsh operating conditions, thereby achieving the conversion of CO, CO 2 Direct conversion into natural gas CH 4 New technology.

[0010] The electrode of the present invention is always in an active state due to the in-situ regeneration of the catalyst coated on the electrode under the action of the electric field, and the catalyst has a long service life and high efficiency.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] According to one aspect of the present invention, a device for preparing natural gas by electrochemically reducing pyrolysis gas of domestic waste is provided, the device comprising a pyrolysis gasification synthesis tower, a plasma tower and an electrochemical methanation reactor;

[0013] Wherein, an electrolysis device is arranged in the electrochemical methanation reactor, and the electrolysis device is provided with a cathode electrode, a diaphragm and an anode electrode in sequence from the inside to the outside;

[0014] The gas obtained from the cracking and gasification synthesis tower after cracking domestic waste is treated by the plasma tower, and then the gas enters the cathode electrode of the electrolysis device for electrochemical reduction reaction. After the reaction is completed, the by-products are collected from the anode electrode outlet and returned to the cracking and gasification synthesis tower to continue the reaction; pure methane is released and collected from the cathode electrode outlet.

[0015] Furthermore, the cathode electrode, the diaphragm and the anode electrode are all made of porous material structures.

[0016] Furthermore, the cathode electrode comprises nickel foam, ceramic foam or mesoporous foamed glass; wherein the nickel foam, ceramic foam or mesoporous foamed glass is filled with polyvinyl alcohol gel or polyethylene glycol gel, and after being filled, it is used as an initial material, one side of the initial material is covered with a diaphragm material, and after being tightly bonded to the diaphragm; sintering is performed to remove the filled polyvinyl alcohol gel or polyethylene glycol gel, thereby obtaining a porous basic cathode electrode material covered with a diaphragm.

[0017] Furthermore, the material of the diaphragm is selected from ZrO 2 、Al 2 O 3 、MgO、Re 2 O 3 、MnO2 A sol-gel liquid composed of at least two components; the sol-gel liquid is deposited on one side of the cathode electrode by an impregnation method, and then after sintering, the diaphragm and the cathode electrode are tightly bonded to form a diaphragm-cathode basic electrode material; the diaphragm-cathode basic electrode is an anode electrode on the other side of the diaphragm.

[0018] Generally speaking, the thinner the diaphragm is, the more conducive it is to ion penetration. In order to take into account the strength of the diaphragm, the thickness is usually between 1 micron and 1 millimeter.

[0019] Furthermore, the basic cathode electrode material covered with the diaphragm is electrolessly plated with NiO, Al 2 O 3 、MgO、Re 2 O 3 , PbO 2 At least two components.

[0020] Furthermore, the anode electrode is adhered to the other side of the diaphragm in the base cathode electrode material covered with the diaphragm, and is first chemically plated with Pb(NO 3 ) 2 The conductive coating of the precursor is then plated with a mixed solution by electroplating; wherein the mixed solution is composed of MnO 2 , CuO, graphite, and carbon black are mixed to finally form a coaxially arranged electrode system in which the anode electrode, diaphragm, and cathode electrode are tightly bonded together.

[0021] Furthermore, the device is also provided with a solid-liquid separator and a sulfur recovery device. The solid-liquid separator is connected to the plasma tower and is used for solid-liquid separation, and the solid enters the sulfur recovery device.

[0022] Furthermore, the plasma tower is composed of a positive electrode and a negative electrode, and the positive electrode and the negative electrode are coaxially arranged; wherein the negative electrode is a metal mesh structure, the mesh structure material is a mesh metal material, the positive electrode is a tubular structure, and the tube wall is drilled with small holes arranged in an array to form a nozzle, and water vapor is ejected from the nozzle and evenly distributed between the positive electrode and the negative electrode; the mesh negative electrode arranged in the plasma tower also has the function of a gas-liquid separator, the gas enters the electrochemical methanation reactor from the upper outlet to react, and the liquid and the solid colloid solution accompanying the liquid flow downward along the mesh negative electrode and the tube wall to the solid-liquid separator behind the tower (the temperature of this part can be set to room temperature);

[0023] In the plasma tower, H 2 S. NH 3 In the plasma tower, the strong oxidizing free radicals generated in the presence of water vapor decompose into H 2 and S, H2 and N 2 Among them, the solid S is mixed with the liquid and flows to the solid-liquid separator at the bottom of the tower, enters the sulfur recovery device, and obtains solid S.

[0024] According to another aspect of the present invention, a method for preparing natural gas by electrochemically reducing domestic waste cracking gas is provided, the method comprising:

[0025] Step 1: Preparation of cathode electrode-diaphragm-anode electrode

[0026] Nickel foam, ceramic foam or mesoporous foamed glass is filled with polyvinyl alcohol gel or polyethylene glycol gel (to block the holes in the nickel foam, ceramic foam or mesoporous foamed glass). After being filled, it is used as the initial material. One side of the initial material is covered with a diaphragm material and tightly bonded to the diaphragm. Sintering is performed to remove the filled polyvinyl alcohol gel or polyethylene glycol gel to form a solid porous diaphragm layer, thereby obtaining a porous basic cathode electrode material covered with a diaphragm. The cathode electrode and the diaphragm on the basic cathode electrode material covered with a diaphragm are both porous, and the cathode electrode has good conductivity, and the diaphragm is electrically insulating;

[0027] During sintering, the polyvinyl alcohol gel or polyethylene glycol gel in the pores will be naturally removed due to the high temperature, and the original pores of the foam nickel or foam ceramic-mesoporous foam glass will be restored. This step completes the production of the diaphragm.

[0028] The diaphragm material is selected from ZrO 2 、Al 2 O 3 、MgO、Re 2 O 3 、MnO 2 A bonded body composed of a mixture of at least two components;

[0029] The base cathode electrode material covered with a diaphragm is electrolessly plated with NiO, Al 2 O 3 、MgO、Re 2 O 3 , PbO 2 At least two components;

[0030] The anode electrode is prepared on the other side of the diaphragm in the basic cathode electrode material covered with the diaphragm; specifically, the anode electrode is firstly electrolessly plated with Pb(NO 3 ) 2 The conductive coating of the precursor is then plated with a mixed solution by electroplating; wherein the mixed solution is composed of MnO 2 , CuO, graphite, and carbon black are mixed to form a coaxially arranged electrode system in which the anode electrode, the diaphragm, and the cathode electrode are tightly bonded together;

[0031] In this system, the anode electrode has porosity and good conductivity, and the anode electrode-diaphragm-cathode electrode has porosity and strong ion permeability;

[0032] Step 2: Synthesis of methane

[0033] The gas obtained from the cracking and gasification synthesis tower after cracking domestic waste is treated by the plasma tower, and the gas enters the cathode electrode of the electrolysis device. The oxygen obtained at the anode electrode is its by-product, and an electrochemical reduction reaction is carried out. After the reaction is completed, the by-product is collected from the anode electrode outlet and returned to the cracking and gasification synthesis tower to continue the reaction; pure methane is released and collected from the cathode electrode outlet.

[0034] Furthermore, in step 1, the mixed solution is composed of MnO 2 , CuO, graphite and carbon black.

[0035] Furthermore, in the step 1, the basic integrated electrode including the cathode electrode, the separator and the anode electrode is aged at 300° C.-400° C. to form a basic electrode with a porous structure.

[0036] The function of the anode is to release oxygen efficiently, making CO and CO 2 The oxygen in the reaction can be quickly separated. After the oxygen is removed, the equilibrium reaction will make the entire reaction tilt towards the direction of methanation, accelerating the reaction rate. Therefore, the electrochemical methanation method of the present invention has a higher yield and reaction rate than the catalytic method, and also has a higher output. In addition, the electrochemical methanation method can simultaneously take away the water and heat generated in the reaction process, accelerating the reaction process, which is also not available in the existing catalytic methane production technology.

[0037] The integrated electrode of the present invention includes NiO, Al 2 O 3 、MgO、Re 2 O 3 , PbO 2 The cathode electrode is composed of nickel foam, ceramic foam or mesoporous foam glass with catalytic effect, containing ZrO 2 、Al 2 O 3 、MgO、Re 2 O 3 、MnO 2 At least two of the membranes adapted for oxygen ion transport are provided, comprising MnO 2, CuO, graphite, carbon black and other high oxygen evolution anode electrodes with mixed catalytic effects are integrated into an integrated electrode. The electrode made by the method of the present invention has the characteristics of a porous anode electrode, a microporous selective ion diaphragm, and a porous or mesoporous cathode electrode. There is no gap between the electrode and the diaphragm, and it has good conductivity and high ion / proton penetration. The integrated electrode of the present invention belongs to a gas electrode and is suitable for high temperature, gas phase reaction electrochemistry.

[0038] In the present invention, in the electrochemical methanation reactor, the composition of the catalyst and the reaction conditions are adjusted to promote the conversion of carbon monoxide (CO) and carbon dioxide (CO 2 ) and hydrogen (H 2 ) reacts to form methane (CH 4 ).

[0039] Reaction temperature: 300-350℃; pressure 0.2-1MPa, with high CO / CO 2 The conversion rate and CH 4 selectivity.

[0040] The present invention has the following advantages:

[0041] The present invention adopts the electrochemical reduction method to treat domestic waste, which can not only achieve the methane purity comparable to the biological conversion method, but also achieve the advantages of fast reaction, high efficiency, safety and reliability similar to the catalytic synthesis method, and can also realize the characteristics of unit operation and simple equipment, and the final methane product obtained is of higher quality.

[0042] The embodiments of the present invention innovate the integration of diaphragms and electrodes to address the defects of existing electrochemistry, integrating the anode electrode, ion-selective diaphragm, and cathode electrode into a whole, with no gaps between the anode-diaphragm-cathode, so that the electronic conduction resistance (internal resistance) is minimized. At the same time, the anode electrode, cathode electrode, and diaphragm are all made of porous material structures, with no gaps between the electrodes and the diaphragm, so that proton / ion transfer is extremely short, and can be multi-dimensional, multi-channel, and barrier-free, increasing its conductivity and high permeability of ions / protons, and achieving the maximum reaction rate.

[0043] The novel electrode of the present invention is an integrated electrode having a highly porous anode electrode, a microporous ion-selective diaphragm, and a porous or mesoporous cathode electrode. The electrolysis device made of the anode-diaphragm-cathode forms a coaxial structure, which is firm, safe, reliable, and has a long service life. The anode-diaphragm-cathode three-in-one structure of the present invention has good electronic conductivity, easy ion penetration, small mass transfer resistance, and high efficiency. Due to the porosity of the electrode, it is equivalent to the integration of many layers of electrodes, so the electrode has a large specific surface area, a very large effective area, and a higher electrolysis efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the implementation methods of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings in the following description are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0045] The structures, proportions, sizes, etc. illustrated in this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with the technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantial technical significance. Any structural modification, change in proportion or adjustment of size shall still fall within the scope of the technical contents disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0046] Figure 1 A schematic diagram of electron movement in a cathode-diaphragm-anode electrode provided by the present invention;

[0047] Figure 2 A flow chart of a device for preparing natural gas by electrochemical reduction of domestic waste cracking gas provided in Example 1 of the present invention;

[0048] Figure 3 An enlarged detail diagram of an electrolysis device provided in an electrochemical methanation reactor provided in Example 1 of the present invention;

[0049] In the figure: 1- cathode electrode, 2- diaphragm, 3- anode electrode. DETAILED DESCRIPTION

[0050] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] The traditional electrolytic cell has a large internal resistance due to the large electrode spacing, and it is necessary to increase the additional voltage for molecular dissociation to achieve the purpose of electrolysis, which makes the electrolysis energy consumption high and the cost high. In addition, since traditional electrodes all use metal conductive electrodes, the dense electrodes hinder the transfer of protons, resulting in low reaction rate, poor effect, and low yield. The embodiments of the present invention innovate the integration of diaphragms and electrodes to address these defects, integrating the anode electrode, ion-selective diaphragm, and cathode electrode into a whole, with the anode-diaphragm-cathode closely adjacent to each other without gaps, so that the electronic conduction resistance (internal resistance) is minimized. At the same time, the anode electrode, cathode electrode, and diaphragm all use porous material structures, so that the proton / ion transfer is extremely short-distance, multi-dimensional, multi-channel, and barrier-free, achieving the maximum reaction rate.

[0052] Principle: Figure 1 shown.

[0053] The method of the present invention mainly relies on the action of electrochemical catalysts, and the cathode electrocatalysts NiO, Al 2 O 3 、MgO、Re 2 O 3 , PbO 2 The methanogenic reaction is mainly concentrated at the cathode electrode. Adjusting the composition of the catalyst and the reaction conditions promotes the conversion of carbon monoxide (CO) and carbon dioxide (CO 2 ) and hydrogen (H 2 ) reacts to form methane (CH 4 ).

[0054] The specific surface area between the cathode chamber (cathode electrode) - diaphragm - anode chamber (anode electrode) is very large, which is not only conducive to the rapid penetration of ions, but also because the reactants need to be transferred and adsorbed on the electrode surface to obtain the conduction of electrons to react chemically, the large electrode area means that more molecules react at the same time, which leads to higher efficiency and greater output:

[0055] 1. The mixed gas enters the cathode chamber for reaction. After the DC power supply is turned on, the negative electrode - The reaction conducted to the cathode electrode is CO 2 +e - →CO+O 2- ; O formed 2- Since the cathode electrode repels each other but is attracted by the anode electrode, the electrons are transferred through the diaphragm into the anode electrode and released. - Then, O is released in the anode chamber. 2 Reaction, at the anode O 2- Given e - The oxygen is returned to the cathode through the current limiter for the next round of reaction, and the generated oxygen is collected at the anode outlet and then enters the cracking gasification synthesis tower to participate in the reaction;

[0056] Similarly, CO loses O after gaining electrons. 2- ;CO 2 、O in CO 2- After the loss, it is replenished by hydrogen, thus generating methane;

[0057] At the cathode, the apparent reaction equation is as follows:

[0058] CO + H 2 → CH 4 + H 2 O;

[0059] CO 2 + H 2 → CH 4 + H 2 O;

[0060] Under the action of the electric field, the O generated on the cathode 2- Migrate to the anode chamber through the diaphragm, so there is no H in the cathode chamber 2 O production. This makes the electrochemical method more efficient, with greater yield and reaction speed than the catalytic method;

[0061] At the anode, the O 2- Release electrons to react: O 2- -e - → O 2 ; Get oxygen;

[0062] 2. After the generated water vapor is energized by direct current, H 2 O→H + +O 2- , O 2- The cathode electrode enters the anode electrode (anode chamber) through the diaphragm to react. 2- Given e - Back to the cathode, O 2- -e - →O 2 The generated oxygen is collected at the anode outlet and then enters the cracking gasification synthesis tower to participate in the reaction; H + +e - →H 2 , further providing hydrogen for methane synthesis;

[0063] H 2 O→ H 2 + O 2 ;

[0064] The reaction principle of producing sulfur from hydrogen in a plasma tower:

[0065] H 2 S→H2 +S;

[0066] NH 3 →H 2 +N 2 .

[0067] Example 1

[0068] This embodiment provides a device for preparing natural gas by electrochemically reducing domestic waste cracking gas, such as Figure 2 As shown:

[0069] The device comprises a cracking gasification synthesis tower, a crude synthesis gas storage tank, a plasma tower, an electrochemical methanation reactor, a water separation tank, a solid-liquid separator and a sulfur recovery device;

[0070] Wherein, the plasma tower is provided with a gas-liquid separator;

[0071] An electrolysis device is provided in the electrochemical methanation reactor. Figure 3 As shown, the electrolysis device is provided with a cathode electrode 1, a diaphragm 2 and an anode electrode 3 in sequence from the inside to the outside;

[0072] The gas obtained after the cracking and gasification synthesis tower cracks the domestic waste is first stored in the crude synthesis gas storage tank, and then the gas is prepared to enter the gas-liquid separator for plasma tower treatment. After gas-liquid separation, the gas enters the cathode electrode 1 of the electrolysis device, and the oxygen obtained by the anode electrode is its by-product. After the DC power supply is powered on, an electrochemical reduction reaction is carried out. After the reaction is completed, the by-product is collected from the outlet of the anode electrode 2 and returned to the cracking and gasification synthesis tower to continue the reaction; pure methane is released from the cathode electrode outlet and enters the water separation tank to remove water vapor and then collected. The purity of the obtained methane can be >99%;

[0073] The positive and negative electrodes in the plasma tower stimulate water molecules to produce hydroxyl radicals under the ionization effect, making NH 3 and H 2 S decomposition, the equation is as follows: H 2 S→H 2 +S; NH 3 →H 2 +N 2 The hydrogen is merged into the synthesis gas, and the liquid after gas-liquid separation enters the solid-liquid separator for solid-liquid separation. After the solid is separated, it enters the sulfur recovery device for recovery, and the liquid enters the water treatment unit for treatment and can be discharged.

[0074] The cathode electrode 1, the separator 2 and the anode electrode 3 are all made of porous material structures.

[0075] Example 2

[0076] This embodiment provides a method for preparing natural gas by electrochemically reducing domestic waste cracking gas using the device of embodiment 1:

[0077] Step 1: Preparation of cathode electrode-diaphragm-anode electrode

[0078] Select nickel foam as the cathode, fill the nickel foam with polyvinyl alcohol gel until all pores are filled, and prepare the diaphragm material containing ZrO 2 、Al 2 O 3 Prepare a sol-gel solution, and deposit the sol-gel solution on one side of the nickel foam filled with polyvinyl alcohol gel by an impregnation method, and then dry (150°C, 24h) and sinter (400-600°C, 6h) it to achieve a dense structure at the nanoscale, that is, to obtain a basic electrode material with a film layer and a cathode electrode without any cracks on the surface. During the impregnation process, measure and calculate the deposition amount so as to calculate the thickness of the diaphragm;

[0079] On the side not covered with the diaphragm, NiO and Al are chemically plated. 2 O 3 obtaining a cathode electrode layer and a separator layer;

[0080] On the other side of the base electrode material film layer, Pb(NO 3 ) 2 The conductive coating of the precursor is then electroplated with MnO 2 A mixed solution consisting of CuO, graphite and carbon black forms an anode electrode layer;

[0081] The cathode electrode layer, the separator layer and the anode electrode layer are aged at 300° C.-400° C. to form an integrated electrode with a porous structure.

[0082] Step 2: Synthesis of methane

[0083] The gas obtained by cracking the domestic waste in the cracking gasification synthesis tower (the oxygen content is controlled not to be higher than 10%) is first stored in the crude synthesis gas storage tank (the crude synthesis gas contains carbon monoxide (CO) and carbon dioxide (CO 2 ) and hydrogen (H 2 ) ratios are approximately 35%, 45%, and 20% respectively. At the beginning of the preparation, the crude synthesis gas is stored in the crude synthesis gas storage tank and enters the gas-liquid separator for treatment in the plasma tower. After gas-liquid separation, the gas enters the cathode electrode 1 of the electrolysis device for electrochemical reduction reaction (reaction conditions: temperature 320°C, pressure 0.5MPa). After the reaction is completed, the by-products are collected from the outlet of the anode electrode 2 and returned to the cracking gasification synthesis tower to continue the reaction (the oxygen-containing (O)) is measured at the outlet of the anode chamber. 2 ) concentration is 35% and carbon dioxide (CO 2) concentration is 65%); pure methane is released from the cathode electrode outlet into the water separation tank to remove water vapor and then collected. The purity of the obtained methane can be > 99%;

[0084] The liquid after gas-liquid separation enters the solid-liquid separator for solid-liquid separation. After solid separation, it enters the sulfur recovery device for recovery. The liquid enters the water treatment unit for treatment and can be discharged.

[0085] In this embodiment, the thickness of the diaphragm is about 50 microns. At the above 320°C, CO 2 The conversion rate is as high as 90.9% and CH 4 The selectivity is as high as 99.0%.

[0086] Example 3

[0087] This embodiment provides a method for preparing natural gas by electrochemically reducing domestic waste cracking gas using the device of embodiment 1:

[0088] Step 1: Preparation of cathode electrode-diaphragm-anode electrode

[0089] Select nickel foam as the cathode, fill the nickel foam with polyvinyl alcohol gel until all pores are filled, and prepare the diaphragm material containing ZrO 2 、Al 2 O 3 、MgO、Re 2 O 3 、MnO 2 Prepare a sol-gel solution, and deposit the sol-gel solution on one side of the nickel foam filled with polyvinyl alcohol gel by an impregnation method, and then dry (150°C, 24h) and sinter (400-600°C, 6h) it to achieve a dense structure at the nanoscale, that is, to obtain a basic electrode material with a film layer and a cathode electrode without any cracks on the surface. During the impregnation process, measure and calculate the deposition amount so as to calculate the thickness of the diaphragm;

[0090] Chemically plate ZrO on the side not covered with the diaphragm 2 、Al 2 O 3 、MgO、Re 2 O 3 、MnO 2 obtaining a cathode electrode layer and a separator layer;

[0091] On the other side of the base electrode material film layer, Pb(NO 3 ) 2 The conductive coating of the precursor is then electroplated with MnO 2 A mixed solution consisting of CuO, graphite and carbon black forms an anode electrode layer;

[0092] The cathode electrode layer, the separator layer and the anode electrode layer are aged at 300° C.-400° C. to form an integrated electrode with a porous structure.

[0093] Step 2: Synthesis of methane

[0094] The gas obtained by cracking the domestic waste in the cracking gasification synthesis tower (the oxygen content is controlled not to be higher than 10%) is first stored in the crude synthesis gas storage tank (the crude synthesis gas contains carbon monoxide (CO) and carbon dioxide (CO 2 ) and hydrogen (H 2 ) ratios are approximately 35%, 45%, and 20%, respectively. At the beginning of the preparation, the crude synthesis gas is stored in the crude synthesis gas storage tank and enters the gas-liquid separator of the plasma tower for gas-liquid separation. The gas enters from the cathode electrode 1 of the electrolysis device, and the anode electrode introduces carbon dioxide (as a diluent gas for oxygen production) to carry out electrochemical reduction reaction (reaction conditions: temperature 320°C, pressure 0.5MPa). After the reaction is completed, the by-products are collected from the outlet of the anode electrode 2 and returned to the cracking gasification synthesis tower to continue the reaction (the oxygen (O) content is measured at the outlet of the anode chamber). 2 ) concentration is 32% and carbon dioxide (CO 2 ) concentration is 68%); pure methane is released from the cathode electrode outlet into the water separation tank to remove water vapor and then collected. The purity of the obtained methane can be > 99%;

[0095] The liquid after gas-liquid separation enters the solid-liquid separator for solid-liquid separation. After solid separation, it enters the sulfur recovery device for recovery. The liquid enters the water treatment unit for treatment and can be discharged.

[0096] In this embodiment, the thickness of the diaphragm is about 50 microns. At the above 320°C, CO 2 The conversion rate is as high as 95.9% and CH 4 The selectivity is as high as 99.0%.

[0097] Example 4

[0098] The electrolysis device of the present invention can be directly used to electrolyze water to produce hydrogen and oxygen. If the main purpose of urban garbage is to generate heat or electricity (heat or electricity), most of the combustible components have been burned out and there is no carbon monoxide, then the electrolysis device of the present invention can be used to electrolyze water to obtain pure hydrogen.

[0099] This embodiment provides a method for preparing hydrogen by electrochemically reducing domestic waste cracking gas using the device of embodiment 1:

[0100] Step 1 is the same as step 1 of Example 2.

[0101] Step 2: Synthesis of Hydrogen

[0102] The gas obtained by cracking the domestic waste in the pyrolysis gasification synthesis tower (the oxygen content is controlled not to be higher than 10%) is first stored in the crude synthesis gas storage tank. After the preparation starts, the crude synthesis gas is stored in the crude synthesis gas storage tank and enters the gas-liquid separator for plasma tower treatment. After gas-liquid separation, the crude synthesis gas contains carbon monoxide (CO) and carbon dioxide (CO 2 ) and hydrogen (H 2 ) ratios are approximately 35%, 42%, and 23% respectively. About 38% of the gas is separated by pressure swing adsorption to obtain carbon dioxide (CO 2 The remaining refined synthesis gas contains approximately 90% combustible components. The refined synthesis gas is injected into a low-speed gas generator to generate electricity, and the generated electricity is supplied to the electrolysis device;

[0103] The separation of 38% of carbon dioxide (CO 2 ) The gas is introduced into the anode chamber to dilute the oxygen produced by the anode. After dilution, the oxygen at the outlet of the anode electrode 2 returns to the cracking gasification synthesis tower to continue the reaction;

[0104] The cathode electrode introduces water vapor into the cathode electrode 1 of the electrolysis device to carry out an electrochemical hydrogen production reaction (reaction conditions: temperature 320°C, pressure 0.5MPa). After the reaction is completed, the concentration measured at the cathode chamber outlet is as high as 92.0% hydrogen and 8% water vapor;

[0105] In the experiment of this embodiment, the crude synthesis gas is subjected to pressure transformation and refining to obtain a higher concentration of combustible gas, which is injected into a low-speed gas generator to directly generate electricity, and the generated electricity is used to compensate for the power supply of this experiment. In this embodiment, the gas with 8% water vapor can be removed through a subsequent water separation tank (hydrogen-water separation tank) to obtain pure hydrogen. The experiment shows that the synthesis gas produced by domestic waste can be converted into a pure hydrogen production process.

[0106] The byproduct oxygen and diluent carbon dioxide are both useful reactants required by the cracking gasification synthesis tower. Oxygen as a combustion aid can increase the furnace temperature (air is not used here because nitrogen in the air will dilute the combustible components in the synthesis gas, reduce the combustion calorific value, and cause subsequent separation difficulties), and carbon dioxide can accelerate the generation rate and output of combustible gas. This is because CO 2 Reforming with C in the cracking furnace produces more CO and can reduce carbon deposition. The reaction formula is:

[0107] CO 2 + C→ 2CO ;

[0108] In addition to compensating for the electricity consumption of the electrolysis device, the electricity generated by the gas generator can be exported for commercial purposes.

[0109] Example 5

[0110] This embodiment provides a method for preparing purified methane by electrochemically reducing pyrolysis gas of domestic waste using the device of embodiment 1:

[0111] Steps 1 and 2 of this embodiment are exactly the same as those of embodiment 2;

[0112] Step 3: Purification of methane

[0113] The methane mixed gas obtained in Example 2 was first cooled to 23°C at 7.5 MPa to remove CO 2 and H 2 O;

[0114] Then, in the autoclave expansion tank, the gas pressure is rapidly reduced to 5 MPa through a capillary tube and the temperature is maintained at -82°C. 4 The liquefied CO2 is returned to the electrochemical reaction tower and converted into pure CH4 4 natural gas.

[0115] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A device for preparing natural gas by electrochemical reduction of domestic waste cracking gas, characterized in that: The device comprises a cracking gasification synthesis tower, a plasma tower and an electrochemical methanation reactor; Wherein, an electrolysis device is arranged in the electrochemical methanation reactor, and the electrolysis device is provided with a cathode electrode, a diaphragm and an anode electrode in sequence from the inside to the outside; The gas obtained by the cracking gasification synthesis tower after cracking the domestic waste is processed by the plasma tower to convert the impurities H2S and NH3 into hydrogen. The gas enters the cathode electrode of the electrolysis device and undergoes an electrochemical reduction reaction. After the reaction is completed, the by-products are collected from the anode electrode outlet and returned to the cracking gasification synthesis tower to continue the reaction; pure methane is released and collected from the cathode electrode outlet; The cathode electrode, the diaphragm and the anode electrode all adopt porous material structures; The plasma tower is composed of a positive electrode and a negative electrode, and the positive electrode and the negative electrode are coaxially arranged; wherein the negative electrode is a metal mesh structure, the mesh structure material is a mesh metal material, the positive electrode is a tubular structure, and a nozzle is formed by drilling small holes arranged in an array on the tube wall, and water vapor is sprayed from the nozzle and evenly distributed between the positive electrode and the negative electrode; the mesh negative electrode arranged in the plasma tower also has the function of a gas-liquid separator, and the gas enters the electrochemical methanation reactor from the upper end outlet to react, and the liquid and the solid colloid solution accompanying the liquid flow downward along the mesh negative electrode and the tower wall to the solid-liquid separator behind the tower; In the plasma tower, H2S and NH3 are decomposed into H2 and S, H2 and N2 under the action of strong oxidizing free radicals generated in the presence of water vapor; solid S is mixed with liquid and flows to the solid-liquid separator at the bottom of the tower and enters the sulfur recovery device to obtain solid S; The cathode electrode comprises foamed nickel, foamed ceramic or mesoporous foamed glass; wherein the preparation method is as follows: the foamed nickel, foamed ceramic or mesoporous foamed glass is filled with polyvinyl alcohol gel or polyethylene glycol gel, and after being filled, it is used as an initial material, a diaphragm material is added to one side of the initial material, and after being tightly bonded to the diaphragm, sintering is performed, and after sintering, the filled polyvinyl alcohol gel or polyethylene glycol gel is removed to obtain a porous basic cathode electrode material covered with a diaphragm; The diaphragm material is a bonded body composed of a mixture of at least two components selected from ZrO2, Al2O3, MgO, Re2O3, and MnO2; The base cathode electrode material covered with a diaphragm is chemically plated with at least two components of NiO, Al2O3, MgO, Re2O3, and PbO2 on the non-diaphragm side; The anode electrode is adhered to the other side of the diaphragm in the basic cathode electrode material covered with the diaphragm, and is first chemically plated with a conductive coating using Pb(NO3)2 as a precursor, and then electroplated with a mixed solution; wherein the mixed solution is composed of a mixture of MnO2, CuO, graphite, and carbon black, and finally forms a coaxially arranged electrode system in which the anode electrode, diaphragm, and cathode electrode are tightly bonded together.

2. The device for preparing natural gas by electrochemical reduction of domestic waste cracking gas according to claim 1, characterized in that: The diaphragm material is deposited on one side of the cathode electrode by an impregnation method, and after sintering treatment, the diaphragm and the cathode electrode are tightly bonded to form a diaphragm-cathode basic electrode material.

3. The device for preparing natural gas by electrochemical reduction of domestic waste cracking gas according to claim 2, characterized in that: The thickness of the diaphragm is between 1 micrometer and 1 millimeter.

4. The device for preparing natural gas by electrochemical reduction of domestic waste cracking gas according to claim 1, characterized in that: The positive and negative electrodes in the plasma tower excite water molecules under the action of ionization to produce hydroxyl free radicals to decompose NH3 and H2S to obtain H2 and N2, H2 and S respectively; the hydrogen is merged into the synthesis gas, and the liquid after gas-liquid separation enters the solid-liquid separator for solid-liquid separation. After the solid separation, it enters the sulfur recovery device for recovery, and the liquid enters the water treatment unit for treatment and can be discharged.

5. A method for preparing natural gas by electrochemical reduction of domestic waste cracking gas, characterized in that: The device for preparing natural gas by electrochemically reducing cracked gas from domestic waste as claimed in claim 1 comprises: Step 1, preparation of cathode electrode-diaphragm-anode electrode: Filling polyvinyl alcohol gel or polyethylene glycol gel with nickel foam, foam ceramic or mesoporous foamed glass is used as the initial material after being fully filled, and a diaphragm material is covered on one side of the initial material, and sintered after being tightly bonded to the diaphragm. After sintering, the filled polyvinyl alcohol gel or polyethylene glycol gel is removed to obtain a porous basic cathode electrode material covered with a diaphragm; The diaphragm material is a bonded body composed of a mixture of at least two components selected from ZrO2, Al2O3, MgO, Re2O3, and MnO2; The base cathode electrode material covered with a diaphragm is chemically plated with at least two components of NiO, Al2O3, MgO, Re2O3, and PbO2 on the non-diaphragm side; The anode electrode is prepared on the other side of the diaphragm in the basic cathode electrode material covered with the diaphragm; specifically, a conductive coating layer with Pb(NO3)2 as a precursor is firstly chemically plated, and then a mixed solution is plated by electroplating; wherein the mixed solution is composed of a mixture of MnO2, CuO, graphite and carbon black, and finally a coaxially arranged electrode system is formed in which the anode electrode, the diaphragm and the cathode electrode are tightly bonded together; Step 2, synthesis of methane: The gas obtained from the cracking and gasification synthesis tower after cracking domestic waste is treated by the plasma tower, and then the gas enters the cathode electrode of the electrolysis device for electrochemical reduction reaction. After the reaction is completed, the oxygen obtained at the anode electrode is its by-product, which is collected from the anode electrode outlet and returned to the cracking and gasification synthesis tower for further reaction; pure methane is released and collected from the cathode electrode outlet.

6. The method for preparing natural gas by electrochemical reduction of domestic waste cracking gas according to claim 5, characterized in that: In the step 1, the mixed solution is composed of MnO2, CuO, graphite and carbon black.

7. The method for preparing natural gas by electrochemical reduction of domestic waste cracking gas according to claim 5, characterized in that: In the step 1, a basic integrated electrode including a cathode electrode, a separator and an anode electrode is aged at 300° C. to 400° C. to form an electrolysis device with a porous structure.

8. The method for preparing natural gas by electrochemical reduction of domestic waste pyrolysis gas according to claim 5, characterized in that: In the step 2, the electrochemical reduction reaction temperature is 300-350° C. and the pressure is 0.2-1 MPa.

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