System and method for preparing synthesis gas through methane self-heating thermocatalysis coupled photothermal catalysis cascade reforming

Abstract

The invention discloses a system and a method for preparing synthesis gas through methane self-heat-supply thermocatalysis coupled photothermal catalysis cascade reforming, and the method comprises the following steps: methane and oxygen are combusted in a combustion furnace, the generated high-temperature gas enters a first reactor after heat exchange, the temperature in the first reactor is maintained at 700-800 DEG C, the molar ratio of CH4 to CO2 is 1: (0.8-1.2), the temperature in the first reactor is maintained at 700-800 DEG C, and the temperature in the second reactor is maintained at 700-800 DEG C; carrying out a thermocatalytic dry reforming reaction; after the gas reacted in the first reactor is subjected to heat exchange through a second heat exchanger, the gas enters a second reactor, the temperature in the second reactor is maintained at 500-600 DEG C, the molar ratio of CH4 to CO2 is 1: (0.8-1.2), and a photo-thermal catalytic dry reforming reaction is carried out; high-temperature gas obtained after reaction in the second reactor enters a third heat exchanger for heat exchange and then enters a third reactor, the temperature in the third reactor is kept at 300-400 DEG C, the molar ratio of CH4 to H2O is 1: (0.8-1.2), and a second-stage photo-thermal catalytic reaction is carried out.

Description

Technical Field

[0001] The present invention belongs to the technical field of methane and carbon dioxide emission reduction, and specifically relates to a system and method for producing synthesis gas by methane self-heating thermal catalysis coupled with photothermal catalysis cascade reforming. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, ecological and environmental safety has received great attention from the state and the public. With the continuous acceleration of the pace of global industrialization, fossil fuels, especially oil and coal, are used in large quantities, and the CO2 generated by their thermal utilization is increasing day by day. How to efficiently utilize and transform CO2 has become an important issue of concern to society and the scientific community.

[0004] Methane is the main component of natural gas, oilfield gas, coalbed methane, biogas, and coke oven gas. my country has abundant natural gas and coalbed methane resources. Methane conversion to produce synthesis gas has become an effective way to utilize these high-quality hydrocarbon resources in a high-value manner. According to the different reforming media, it can be divided into steam reforming, partial oxidation, autothermal reforming, carbon dioxide reforming, and coupled reforming. Table 1 lists the typical methane reforming processes for preparing synthesis gas.

[0005] Table 1 Typical methane conversion process for producing synthesis gas

[0006]

[0007] The industrially applied methane synthesis gas process is methane steam reforming technology. The hydrogen-to-carbon ratio in the product is 3, which can provide hydrogen for ammonia synthesis and hydrogenation reactions, but is not conducive to methanol synthesis and Fischer-Tropsch reactions. The methane steam reaction is a strong endothermic reaction, requiring a high reaction temperature and a large amount of energy during the reaction. The manufacturing process and materials of the reactor are very high, and the equipment investment is huge. Secondly, the water gas conversion side reaction will also occur along with the steam reforming reaction: CO+H2O=CO2+H2, resulting in an increase in the CO2 content in the tail gas. The methane partial oxidation synthesis gas process uses the exothermic oxidation reaction of methane itself to promote the conversion of methane. However, the current methane partial oxidation synthesis gas process under catalytic conditions has not yet been industrialized. The main reason is that the reaction is difficult to control, and the catalyst has serious carbon deposition and sintering problems, which reduces the methane conversion rate and synthesis gas selectivity. Methane autothermal reforming can be considered as a special case of partial oxidation of methane. This process uses CO2, CO and H2O generated by the combustion of methane under non-catalytic conditions as reforming feed gas, and then reforms under catalytic conditions to generate synthesis gas. This process also has many disadvantages. The hot spot temperature of the catalyst bed makes the oxidation reaction difficult to control, and even leads to sintering and deactivation of the active components of the catalyst, which is one of the reasons that hinder the research and industrialization of methane catalytic oxidation reactions; there are also serious deactivation problems in the partial oxidation reaction of supported catalysts, and carbon deposition and Ni particle sintering lead to a decrease in methane conversion rate and synthesis gas selectivity. The preparation of synthesis gas by methane carbon dioxide reforming is a strong endothermic reaction, just like the steam reforming process. The hydrogen-carbon ratio of the synthesis gas in the methane carbon dioxide reforming product is about 1, which is an ideal raw material for Fischer-Tropsch synthesis and carbonyl synthesis. However, the process is currently affected by the water gas shift reaction, the hydrogen-carbon ratio of the synthesis gas is relatively low, and the carbon accumulation on the catalyst surface is serious.

[0008] Dry reforming DRM (CO2-CH4) technology has become an effective way to alleviate carbon emissions and strengthen the recycling of carbon resources, and has dual significance in terms of ecological environmental safety and economic benefits. CO2 and CH4 reforming to produce synthesis gas can not only simultaneously utilize and reduce two greenhouse gases, but also produce high-value fuels and chemicals. However, the use of traditional methods for CO2-CH4 dry reforming faces two major challenges. First, due to the high stability of CO and CH4 molecules and thermodynamic equilibrium limitations, a higher reaction temperature (>700℃) is required to obtain a more ideal synthesis gas yield, resulting in higher energy consumption for the reaction; secondly, high temperature will cause a large amount of carbon deposits to form on the catalyst surface, especially for non-precious metal catalysts, which are more likely to block their active metal sites, resulting in rapid deactivation of the catalyst. In addition, from the perspective of carbon balance, the energy required for high temperature is usually at the expense of producing CO2, which greatly reduces the effect of CO2 emission reduction. Summary of the invention

[0009] In view of the deficiencies in the prior art, the object of the present invention is to provide a system and method for producing synthesis gas by self-heating, thermal catalysis, coupled with photothermal catalysis, cascade reforming of methane.

[0010] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0011] In a first aspect, the present invention provides a system for producing synthesis gas by self-heating, thermal catalytic coupling, photothermal catalytic cascade reforming of methane, comprising a combustion furnace, a first heat exchanger, a first reactor, a second heat exchanger, a second reactor, a third heat exchanger and a third reactor connected in sequence;

[0012] All three reactors were filled with catalyst;

[0013] The second reactor and the third reactor are both photothermal reactors, and the shells of the reactors are light-transmitting panels;

[0014] The carbon dioxide source is connected to the first reactor, the second reactor and the third reactor through pipelines respectively, and the water vapor source is connected to the third reactor through a pipeline.

[0015] In some embodiments, the burner is connected to a methane source and an oxygen source.

[0016] The use of methane self-heating coupled with solar thermal catalysis provides a new solution for reactions that are severely limited by thermodynamic equilibrium. The coupling of light / thermal catalysts in the reaction of activating and converting thermodynamically stable CO2 and CH4 molecules shows unique advantages. However, how to effectively improve the conversion efficiency and energy efficiency of the reaction process and reduce the reaction energy consumption still poses great difficulties and challenges. Based on this, with the concept of reducing raw material costs, improving conversion efficiency, enhancing energy efficiency and improving anti-carbon deposition performance, a system and method for producing synthesis gas by methane self-heating thermal catalysis coupled with photothermal catalysis cascade reforming is provided.

[0017] In a second aspect, the present invention provides a method for producing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane, comprising the following steps:

[0018] Methane and oxygen are burned in a combustion furnace, and the generated high-temperature gas enters the first reactor after heat exchange, so that the temperature in the first reactor is maintained at 700-800°C, and CH4 and / or CO2 gas is added to the first reactor at the same time, so that the molar ratio of CH4 and CO2 is 1:0.8-1.2, and a thermal catalytic dry reforming reaction is carried out;

[0019] The gas after the reaction in the first reactor is heat exchanged in the second heat exchanger and then enters the second reactor, the temperature in the second reactor is maintained at 500-600° C., and CH4 and / or CO2 gas is added to the second reactor at the same time, so that the molar ratio of CH4 to CO2 is 1:0.8-1.2, and a photothermal catalytic dry reforming reaction is carried out;

[0020] The high-temperature gas after the reaction in the second reactor enters the third heat exchanger for heat exchange, and then enters the third reactor to maintain the temperature in the third reactor at 300-400°C. At the same time, CH4 and / or water vapor are added to the third reactor, and the molar ratio of CH4 to H2O is 1:0.8-1.2 to carry out a secondary photothermal catalytic reaction.

[0021] Since the gas produced by methane combustion is very hot, it can provide the required heat for the thermal catalytic dry reforming reaction after appropriate cooling. At the same time, the products of methane combustion are carbon dioxide and water. The carbon dioxide gas can be used as the raw material for the subsequent thermal catalytic dry reforming reaction, and the generated water vapor can be used as the raw material for the subsequent methane and water vapor photothermal catalytic reforming reaction.

[0022] Although the gas temperature after the thermal catalytic dry reforming reaction has decreased, it is still very high and can still provide heat for the subsequent first-level photothermal catalytic reaction; at the same time, the residual methane and / or carbon dioxide gas from the thermal catalytic dry reforming reaction can be used as raw materials for the subsequent first-level photothermal catalytic reforming reaction. Therefore, by connecting a first-level photothermal catalytic reforming reaction in series after the thermal catalytic dry reforming reaction, the excess gas raw material in the thermal catalytic dry reforming reaction can be controlled to ensure a higher conversion rate and reaction efficiency.

[0023] The gas temperature after the primary photothermal catalytic reforming reaction is 500-600°C, which can still provide heat for the secondary photothermal catalytic reaction of methane and water vapor. At the same time, the water vapor produced by methane combustion can be fully utilized to reduce the moisture content in the synthesis gas.

[0024] Through this process route, the heat self-supply of the methane and carbon dioxide dry reforming process can be achieved, and the cascade utilization of the heat of the high-temperature synthesis gas can be realized, which is beneficial to improving the economic benefits of the methane and carbon dioxide dry reforming.

[0025] In some embodiments, the molar ratio of CH4 to CO2 in the thermal catalytic dry reforming reaction is 1:1.

[0026] Preferably, in the primary photothermal catalytic reaction, the molar ratio of CH4 to CO2 is 1:1.

[0027] Preferably, in the secondary photothermal catalytic reaction, the molar ratio of CH4 to H2O is 1:1.

[0028] In some embodiments, the active component of the catalyst in the first reactor is a Ni-based single metal, a Ni-Ru bimetallic catalyst or a Ni-Pt bimetallic catalyst, and the carrier is Al2O3, MgAl2O4, hydrotalcite or MgO-MgAl2O3.

[0029] Further preferably, the mass percentage of the active components of the catalyst in the first reactor is 5%-15%; in the Ni-Ru bimetallic catalyst, the molar ratio of Ni to Ru is 4-12:1; in the Ni-Pt bimetallic catalyst, the molar ratio of Ni to Pt is 4-12:1.

[0030] In some embodiments, the catalyst in the second reactor and the third reactor is a Ni monometallic catalyst, a Ru-based monometallic catalyst or a Ni-Ru bimetallic catalyst, and the carrier is TiO2, SrTiO3, C3N4, hydrotalcite or ZnO.

[0031] Preferably, in the Ni-based monometallic catalyst, the mass percentage of Ni is 5%-15%, preferably 10-15%, and more preferably 12.5%;

[0032] Or, in the Ru-based monometallic catalyst, the mass percentage of Ru is 0.5%-3.0%;

[0033] Or, in the Ni-Ru bimetallic catalyst, the molar ratio of Ni to Ru is 1-12:1, preferably 4-12:1, and more preferably 4-6:1.

[0034] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0035] The present invention can realize the self-supply of heat in the methane carbon dioxide reforming process, realize the cascade utilization of the heat of the high-temperature synthesis gas, and improve the energy and economic efficiency of the methane carbon dioxide reforming.

[0036] In the process of preparing synthesis gas by methane reforming of the present invention, different catalysts are added to different reactors, and photothermal catalysis is used to effectively reduce the temperature of catalytic reforming, reduce energy consumption, and effectively prevent carbon deposition on the catalyst surface, thereby effectively alleviating catalyst blockage and extending the service life of the catalyst.

[0037] The advantages of this process are that it uses CH4 self-heating to achieve CH4-CO2 dry reforming by adjusting the ratio of reaction gases, ensuring that the H2 / CO ratio is 1, and utilizing the requirements of methane synthesis and Fischer-Tropsch reaction for synthesis gas; it uses photothermal coupling catalysis to reduce the reaction temperature of the entire process, greatly alleviating the agglomeration of active metals of the catalyst caused by high temperature, increasing the catalyst's resistance to carbon deposition and catalytic activity and stability, and also reducing the requirements for equipment materials; it reduces CO2 emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0039] Figure 1 This is a process flow chart of methane self-heating thermal catalytic coupled photothermal catalytic cascade reforming conversion to produce synthesis gas according to an embodiment of the present invention;

[0040] Figure 2 Graphs 1 and 2 show the CH4 conversion rate (a), CO2 conversion rate (b) and H2 / CO ratio (c) of different xNi / MgAl catalysts according to the embodiments of the present invention.

[0041] Figure 3 Graphs 1 and 2 show the CH4 conversion rate (a), CO2 conversion rate (b) and H2 / CO ratio (c) of different xRu / MgAl catalysts according to the embodiments of the present invention.

[0042] Figure 4 Graphs 1 and 2 show the CH4 conversion rate (a), CO2 conversion rate (b) and H2 / CO ratio (c) of different Ni-Ru / MgAl catalysts according to the embodiments of the present invention.

[0043] Figure 5 1 is a performance test diagram of the Ni6Ru1 / SrTiO3 catalyst in Example 5 of the present invention, wherein the methane dry reforming activity of the Ni6Ru1 / SrTiO3 catalyst in the photothermal and thermal catalytic processes (a) is the H2 yield; (b) is the CO yield; (c) is the H2 / CO ratio;

[0044] In the figure, 1-combustion furnace; 2-first heat exchanger; 3-first reactor; 4-second reactor; 5-third reactor. DETAILED DESCRIPTION

[0045] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0046] Example 1

[0047] A series of Ni-based single metal catalysts with different contents were prepared by gel sol method using MgAl(O) hydrotalcite as carrier. The specific preparation method is as follows: first, 1g P123 (polyethylene oxide) was added to 20ml deionized water and stirred at room temperature to dissolve, then hydrated nickel nitrate, 10.86g hydrated magnesium nitrate, and 6.11g hydrated aluminum nitrate were added in sequence, stirred evenly, then 5 drops of 6mol / L concentrated nitric acid were added, citric acid (the molar number of citric acid is 1.5 times the molar number of metal ions) was added, ultrasonic treatment was performed at 70W for 30min, stirring was performed at 60℃ until a sol was formed, and then the mixture was sealed and placed at room temperature for 3 days, and then calcined at 750℃ for 4 hours in air atmosphere with a heating rate of 2℃ / min. The catalyst was obtained after cooling to room temperature.

[0048] The catalytic performance of CH4+CO2 reforming was tested at 750℃, and the activity and stability of CH4-CO2 reforming catalyst were evaluated in a fixed-bed reactor at atmospheric pressure.

[0049] 300 mg of catalyst (40-60 mesh) and 1.5 g of quartz sand (40-60 mesh) were mixed evenly and placed in a quartz tube, and the quartz tube reactor was fixed in a heating furnace. A program temperature controller was used to control the temperature before the CH4-CO2 reforming reaction, and the temperature was programmed to reduce under H2 (30 mL / min) atmosphere, and the temperature was constant at 750°C for 120 min. Then the raw gas CH / CO=1, GHSV=80,000 mL / (g·h) was switched to react at 750°C.

[0050] The analysis was performed using Shanghai Haixin gas chromatograph (GC-950) (Ar as carrier gas, TDX-01 column), and the selectivity of the product and the conversion rate of the reactant were calculated using the external standard method. The chromatographic operating conditions were as follows: column furnace temperature 130°C, injection port temperature 120°C, thermal conductivity cell temperature: 100°C, vaporization chamber temperature: 150°C, current: 40A, carrier gas flow rate: 35mL / min, injection volume 1mL.

[0051] The catalytic results are as follows Figure 2 As shown, the % in the examples are all mass percentages. As the Ni content in the catalyst increases, the catalytic activity increases significantly, indicating that the Ni content is one of the important factors for improving the catalytic activity. Comparing the catalytic activity of the Ni / MgAl series, the catalytic activity of the 12.5% ​​Ni / MgAl catalyst is relatively good. For all catalysts, the conversion rate of CO2 is slightly higher than that of CH4, which is related to the reverse water gas shift reaction (RWGS: CO2+H2-H2O+CO), which consumes CO2 and produces CO at the same time, so the H2 / CO ratio is lower than the stoichiometric ratio of 1:1.

[0052] Example 2

[0053] A series of Ru-based single metal catalysts with different contents were prepared by a gel sol method using MgAl(O) hydrotalcite as a carrier. The specific preparation method is as follows:

[0054] In 20ml of deionized water, add 1g P123 and stir to dissolve at room temperature, then add hydrated ruthenium chloride, 10.86g hydrated magnesium nitrate, 6.11g hydrated aluminum nitrate in sequence, weigh the amount of ruthenium chloride added according to the calculation result, stir evenly, then add 5 drops of 6mol / L concentrated nitric acid, add citric acid (the molar number of citric acid is 1.5 times the molar number of metal ions), ultrasonicate at 70W for 30min, stir at 60℃ to form a sol, then seal and place at room temperature for 3 days, then roast at 750℃ in air atmosphere for 4 hours, with a heating rate of 2℃ / min. After cooling to room temperature, the catalyst sample can be obtained.

[0055] The catalytic performance of CH4+CO2 was tested at 750℃ using the same testing method as above.

[0056] The catalytic results are as follows Figure 3 As shown in the figure, for Ru-based single metal catalysts, as the mass percentage of Ru increases from 0.5% to 3.0%, the catalytic activity increases significantly, indicating that the Ru content is the main factor in improving the catalytic activity. Further increasing the Ru content to 4.0%, the initial conversion rate increases slightly, indicating that the promoting effect of the Ru content on the catalytic activity decreases. The decrease rate of CH4 conversion rate of the Ru-based single metal catalyst within 100h is within 2%, indicating that the Ru-based single metal catalyst has good catalytic activity and stability.

[0057] Example 3

[0058] A series of Ni-Ru bimetallic catalysts with different molar ratios of Ni and Ru were prepared by a gel sol method using MgAl(O) hydrotalcite as a carrier and a fixed Ni content of 2.5%wt. Specifically, 1g P123 was first added to 20ml of deionized water and stirred to dissolve at room temperature, and then hydrated ruthenium chloride, 0.32g hydrated nickel nitrate, 10.86g hydrated magnesium nitrate, and 6.11g hydrated aluminum nitrate were added in sequence to fix the Ni content at 2.5%wt. The corresponding mass of ruthenium chloride was added according to the molar ratio of nickel to ruthenium of 1:1, 2:1, 4:1, and 6:1, and the mixture was stirred evenly. Then, 5 drops of 6mol / L concentrated nitric acid were added, citric acid (the molar number of citric acid is 1.5 times the molar number of metal ions) was added, and ultrasound was applied at 70W for 30min, and stirred at 60°C to form a sol. The mixture was then sealed and placed at room temperature for 3 days, and then calcined at 750°C for 4 hours in an air atmosphere at a heating rate of 2°C / min. After cooling to room temperature, the catalyst sample was obtained.

[0059] In the above, when the molar ratio of nickel to ruthenium was 6:1 and the content of Ni was 2.5%wt, 0.049g of hydrated ruthenium chloride, 0.32g of hydrated nickel nitrate, 10.86g of hydrated magnesium nitrate, and 6.11g of hydrated aluminum nitrate were added;

[0060] When the molar ratio of nickel to ruthenium was 4:1 and the content of Ni was 2.5%wt, 0.073g of hydrated ruthenium chloride, 0.32g of hydrated nickel nitrate, 10.86g of hydrated magnesium nitrate, and 6.11g of hydrated aluminum nitrate were added;

[0061] When the molar ratio of nickel to ruthenium was 2:1 and the content of Ni was 2.5%wt, 0.147g of hydrated ruthenium chloride, 0.32g of hydrated nickel nitrate, 10.86g of hydrated magnesium nitrate, and 6.11g of hydrated aluminum nitrate were added;

[0062] When the molar ratio of nickel to ruthenium was 6:1 and the content of Ni was 2.5%wt, 0.294g of hydrated ruthenium chloride, 0.32g of hydrated nickel nitrate, 10.86g of hydrated magnesium nitrate, and 6.11g of hydrated aluminum nitrate were added.

[0063] The catalytic performance of CH4+CO2 was tested at 750°C, with the same reaction conditions as in Example 1, CH4 / CO2=1:1, pressure 0.1 MPa, total gas flow rate=120 mL / min, catalyst dosage 0.3 g. All catalysts were reduced in situ at 750°C in a H2 atmosphere for 120 min.

[0064] The catalytic results are as follows Figure 4 As shown in the figure, the pure Ni-based single metal catalyst experienced rapid deactivation. After 100 hours of reaction, the CH4 conversion rate dropped from 37.99% to 29.49%, a decrease of 22.37%. After adding Ru, the stability of the catalyst was improved to varying degrees. With the increase of the addition amount, the stability of the Ni-Ru bimetallic catalyst in the dry reforming reaction gradually increased, and the catalytic activity decrease rate gradually decreased. The decrease efficiency of the CH4 conversion rate within 100 hours was within 3%, which was enough to show that the Ni-Ru bimetallic catalyst had good catalytic activity and stability.

[0065] Example 4

[0066] like Figure 1 As shown, a system for producing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane comprises a combustion furnace 1, a first heat exchanger 2, a first reactor 3, a second heat exchanger, a second reactor 4, a third heat exchanger and a third reactor 5 connected in sequence;

[0067] The three reactors are filled with catalysts. The active component of the catalyst in the first reactor 3 is Ni monometallic, Ni-Ru bimetallic or Ni-Pt bimetallic catalyst, and the carrier is Al2O3, MgAl2O4 or MgO-MgAl2O3; the mass percentage of the active component of the catalyst in the first reactor 3 is 5%-15%; in the Ni-Ru bimetallic catalyst, the molar ratio of Ni to Ru is 4-12:1; in the Ni-Pt bimetallic catalyst, the molar ratio of Ni to Pt is 4-12:1;

[0068] The catalyst in the second reactor 4 and the third reactor 5 is a Ni monometallic catalyst, a Ru monometallic catalyst or a Ni-Ru bimetallic catalyst, and the carrier is TiO2, SrTiO3, C3N4 or ZnO. In the Ni monometallic catalyst, the mass percentage of Ni is 5%-15%; in the Ru monometallic catalyst, the mass percentage of Ru is 0.5%-3.0%; in the Ni-Ru bimetallic catalyst, the molar ratio of Ni to Ru is 12:1-4:1.

[0069] The second reactor 4 and the third reactor 5 are both photothermal reactors, and the shells of the reactors are light-transmitting panels;

[0070] The carbon dioxide source is connected to the first reactor 3, the second reactor 4 and the third reactor 5 through pipelines, respectively, and the water vapor source is connected to the third reactor 5 through a pipeline.

[0071] The burner is connected to a methane source and an oxygen source.

[0072] The first reactor 3 is provided with a temperature control feedback system, which forms feedback regulation with the first heat exchanger 2 at the front end to ensure that the first reactor 3 is maintained within the range of 700-800°C; the second reactor 4 is provided with a temperature control feedback system, which forms feedback regulation with the second heat exchanger at the front end to ensure that the second reactor 4 is maintained within the range of 500-600°C; the third reactor 5 is provided with a temperature control feedback system, which forms feedback regulation with the third heat exchanger at the front end to ensure that the third reactor 5 is maintained within the range of 300-400°C.

[0073] The second reactor 4 and the third reactor 5 are both photothermal reactors, and the shells of the reactors are light-transmitting quartz panels.

[0074] The filling method of the catalyst in the first reactor 3, the second reactor 4 and the third reactor 5 is dense phase filling in common filling.

[0075] Example 5

[0076] A method for reducing carbon emissions by reforming methane and CO2, using the system in Example 4, comprises the following steps:

[0077] The first stream of methane 100mL and oxygen 200mL are burned in the combustion furnace, and the generated high-temperature gas passes through the first heat exchanger and enters the first reactor. The first reactor is equipped with a temperature control feedback system, which forms feedback regulation with the first heat exchanger at the front end to ensure that the first reactor is maintained within the range of 700-800℃;

[0078] The gas after the first heat exchanger is extracted for component analysis, and the first valve is adjusted to add CH4 and / or CO2 gas to the reaction system so that the ratio of the two gases is 1:1. The thermal catalytic dry reforming reaction of CH4+CO2=2CO+2H2 is carried out through the first reactor.

[0079] The catalyst in the first reactor is a Ni-based single metal catalyst, the carrier is Al2O3, and the mass of the Ni-based single metal catalyst is 1.0 g.

[0080] The preparation method of Ni-based single metal catalyst is as follows: γ-Al2O3 nanoplate carrier sample is synthesized by hydrothermal method. First, 10g of aluminum isopropoxide is added to a 150mL three-necked flask, 50mL of deionized water is added to dissolve and vigorously stirred, and refluxed in a water bath at 80°C for 1h. After the white milky solution is cooled, it is transferred to an autoclave with a polytetrafluoroethylene liner and hydrothermally heated at 200°C for 20h. After naturally cooling to room temperature, the solution is centrifuged and the solid product is washed several times with deionized water. The centrifuged sample is dried at 110°C for 6h. Finally, the dried sample is placed in a corundum crucible and calcined at 700°C in a muffle furnace at a heating rate of 10°C / min for 2h. The γ-Al2O3 nanoplate carrier sample can be obtained.

[0081] The Ni / γ-Al2O3 nanoplate catalyst was prepared by the conventional isovolumetric impregnation method. First, 2.48g Ni(NO)2·6H2O was dissolved in deionized water, and then 5g of γ-Al2O3 nanoplate carrier was added to ensure that the mass fraction of Ni accounted for 10% of the catalyst mass. The sample was stirred continuously with a glass rod until its color was uniform. The sample was then allowed to stand at room temperature for 12 hours, and then dried at 110°C for 12 hours. The sample needed to be stirred from time to time during the heating process. After drying, the sample was naturally cooled to room temperature, and then the sample was heated to 500°C at a heating rate of 10°C / min and calcined for 4 hours to obtain the Ni / γ-Al2O3 nanoplate catalyst.

[0082] The temperature of the gas after the reaction is relatively high and contains a large amount of heat. After entering the second heat exchanger, it enters the second reactor. The second reactor is equipped with a temperature control feedback system, which forms feedback adjustment with the second heat exchanger at the front end to ensure that the second reactor is maintained in the range of 500-600℃. After coming out of the second heat exchanger, the gas composition is analyzed and CH4 and / or CO2 gas is added to the system according to the principle of a CH4:CO2 ratio of 1:1.

[0083] The second reactor is a photothermal reactor, which has a light-transmitting quartz panel and mainly carries out the photothermal catalytic reaction of CH2+CO2=2CO+2H2.

[0084] The main catalyst in the second reactor is a Ni-Ru bimetallic catalyst with a mass of 0.25 g. The molar ratio of Ni:Ru in the Ni-Ru bimetallic catalyst is 6:1, and the carrier is SrTiO3.

[0085] A Ni6Ru1 / SrTiO3 catalyst with a Ni:Ru molar ratio of 6:1 was prepared using a hydrothermal method, in which the nickel content was 5%wt. Then, 0.111g of RuCl3·3H2O and 0.61g of NiCl2·6H2O were dissolved in 20mL of deionized water and added to a hydrothermal kettle containing 3g of dry carrier SrTiO3 and 30mL of deionized water. Then, it was hydrothermally heated at 160°C for 24h. The resulting suspension was filtered and washed with deionized water and ethanol in turn to pH=7. After drying at 80°C for 8h and completely grinding, a solid powder was obtained, and the powder was reduced in hydrogen at a flow rate of 70mL / min at 600°C for 2h to obtain a Ni6Ru1 / SrTiO3 catalyst.

[0086] The performance of the Ni6Ru1 / SrTiO3 catalyst was tested using the following method:

[0087] An atmospheric fixed-bed reactor was used to evaluate the methane dry reforming performance of the catalyst. The reactor consists of a flat quartz tube with a length of 400 mm and an inner diameter of 3 mm. An appropriate amount of quartz wool was filled from bottom to top, and 500 mg of catalyst was mixed with an appropriate amount of quartz sand and filled into the catalyst bed to ensure uniform lighting and heating. The temperature of the catalyst bed was monitored using a K-type thermocouple inserted below the reactor. A 300W xenon lamp was used as the light source, and the light was directed to the catalyst in the quartz tube through the quartz window of the tube furnace. In order to prevent Ru from being exposed to oxidation in the air, the Ni6Ru1 / SrTiO3 catalyst sample was heated at 50 mL min - 1Reheating was performed under H2 atmosphere for 2 hours, reducing the temperature to 500°C, and then thermal and photothermal catalytic reactions were carried out. Then, heating was stopped and H2 was replaced by N2 until the temperature dropped to 150°C. Finally, the feed gas was passed into the quartz reaction tube. The dry reforming performance of methane was tested at 0.1MPa in the temperature range of 200-600°C. The reaction gas was analyzed on a column TDX-01 using a gas chromatograph equipped with a thermal conductivity detector and a flame ionization detector.

[0088] The performance test data of Ni6Ru1 / SrTiO3 catalyst can be found in Figure 5 In (a), (b) and (c), it can be seen from (a) and (b) that in the thermal catalytic process, the catalyst only generates H2 and CO at 350°C; while in the photothermal catalytic process, the products H2 and CO are generated at 200°C. The yields of H2 and CO in the photothermal catalytic process are 9.9 times and 7.9 times of the products of the thermal catalytic process at the same temperature, respectively. The higher yield under light confirms that the photocatalytic process helps to reduce the activation reaction temperature of CO2 and CH4 and increase the synthesis gas yield. The product yields of the photothermal catalytic and thermal catalytic processes both increase significantly with increasing temperature, but since DRM is a strongly endothermic reaction, high temperature is conducive to the reaction and has a greater impact on the reaction, while the effect of light on the reaction gradually decreases, and the gap between the two gradually narrows. However, even if the temperature rises to 600°C, the yields of H2 and CO in the photothermal process are 1.5 and 1.4 times of those in the thermal catalytic process, respectively, indicating that light promotes the reaction at high temperatures.

[0089] As shown in (c), the stoichiometric ratio of CO2 and CH4 is 1:1, and since no other products are observed, equal amounts of CO and H2 are produced. The higher CO yield may be due to the reverse water gas shift (RWGS) reaction, which refers to the reaction of CO2 with H2 to produce CO and H2O (CO2+H2=CO+H2O), which is widely used in DRM. It is the most important side reaction in DRM because it consumes H2 and produces CO, so the yield of H2 is lower than that of CO. As can be seen from Figure (c), the ratio of H2 to CO increases with increasing temperature, and at any temperature, the ratio of H2 to CO in the photothermal process is higher than that in the thermal catalytic process. The higher H2 to CO ratio indicates that the introduction of light helps to increase the H2 ratio, light helps the generation of H2, and the introduction of light reduces the occurrence of the RWGS reaction.

[0090] After two dry reformings of CH4+CO2, the high-temperature gas enters the third heat exchanger and then the third reactor. The third reactor is equipped with a temperature control feedback system, which forms feedback regulation with the third heat exchanger at the front end to ensure that the third reactor is maintained in the range of 300-400°C. After coming out of the third heat exchanger, the gas composition is analyzed and CH4 and / or H2O water vapor is added to the system according to the principle of a CH4:H2O ratio of 1:1.

[0091] The third reactor is a photothermal reactor, which has a light-transmitting quartz panel and mainly performs the photothermal catalytic reaction of CH4+H2O=CO+3H2. The main catalyst is a Ru-based monometallic catalyst, the mass of the catalyst is 0.25g, the mass percentage of Ru in the Ru-based monometallic catalyst is 2.0%, and the carrier is g-C3N4.

[0092] The Ru-based monometallic catalyst was prepared by placing 0.03 of RuCl3·3H2O and 20g of urea in an agate mortar and mixing them thoroughly. The mixture was calcined at 550°C for 2 hours to produce a 2%Ru / g-C3N4 photocatalyst, the component of which came from the thermal condensation of urea.

[0093] In the synthesis gas flowing out of the third reactor, the molar ratio of CO and H2 is about 1:1, the molar percentage of CO is about 47%; the molar percentage of H2 is about 47%; the molar percentage of methane is about 3%; the molar percentage of carbon dioxide is about 3%; the main uses of the synthesis gas are suitable for synthesizing methanol and as a raw gas for the Fischer-Tropsch reaction.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for producing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane, characterized in that: It comprises a combustion furnace, a first heat exchanger, a first reactor, a second heat exchanger, a second reactor, a third heat exchanger and a third reactor which are connected in sequence; All three reactors were filled with catalyst; The second reactor and the third reactor are both photothermal reactors, and the shells of the reactors are light-transmitting panels; The carbon dioxide source is connected to the first reactor, the second reactor and the third reactor through pipelines respectively, and the water vapor source is connected to the third reactor through a pipeline.

2. The system for producing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 1 is characterized in that: The burner is connected to a methane source and an oxygen source.

3. A method for producing synthesis gas by self-heating thermal catalytic coupled photothermal catalytic cascade reforming of methane, characterized in that: The steps include: Methane and oxygen are burned in a combustion furnace, and the generated high-temperature gas enters the first reactor after heat exchange, so that the temperature in the first reactor is maintained at 700-800°C, and CH4 and / or CO2 gas is added to the first reactor at the same time, so that the molar ratio of CH4 and CO2 is 1:0.8-1.2, and a thermal catalytic dry reforming reaction is carried out; The gas after the reaction in the first reactor is heat exchanged in the second heat exchanger and then enters the second reactor, the temperature in the second reactor is maintained at 500-600° C., and CH4 and / or CO2 gas is added to the second reactor at the same time, so that the molar ratio of CH4 to CO2 is 1:0.8-1.2, and a photothermal catalytic dry reforming reaction is carried out; The high-temperature gas after the reaction in the second reactor enters the third heat exchanger for heat exchange, and then enters the third reactor to maintain the temperature in the third reactor at 300-400°C. At the same time, CH4 and / or water vapor are added to the third reactor, and the molar ratio of CH4 to H2O is 1:0.8-1.2 to carry out a secondary photothermal catalytic reaction.

4. The method for preparing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 3, characterized in that: In the thermal catalytic dry reforming reaction, the molar ratio of CH4 and CO2 is 1:

1.

5. The method for preparing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 4, characterized in that: In the primary photothermal catalytic reaction, the molar ratio of CH4 and CO2 is 1:

1.

6. The method for producing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 5, characterized in that: In the secondary photothermal catalytic reaction, the molar ratio of CH4 and H2O is 1:

1.

7. The method for preparing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 3, characterized in that: The active component of the catalyst in the first reactor is a Ni-based monometallic catalyst, a Ni-Ru bimetallic catalyst or a Ni-Pt bimetallic catalyst, and the carrier is Al2O3, MgAl2O4, hydrotalcite or MgO-MgAl2O3.

8. The method for preparing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 7, characterized in that: The mass percentage of active components of the catalyst in the first reactor is 5%-15%; in the Ni-Ru bimetallic catalyst, the molar ratio of Ni to Ru is 4-12:1; in the Ni-Pt bimetallic catalyst, the molar ratio of Ni to Pt is 4-12:

1.

9. The method for preparing synthesis gas by self-heating, thermal catalysis and photothermal catalysis cascade reforming of methane according to claim 3, characterized in that: The catalyst in the second reactor and the third reactor is a Ni-based monometallic catalyst, a Ru-based monometallic catalyst or a Ni-Ru bimetallic catalyst, and the carrier is TiO2, SrTiO3, C3N4, hydrotalcite or ZnO.

10. The method for producing synthesis gas by self-heating, thermal catalytic coupled with photothermal catalytic cascade reforming of methane according to claim 9, characterized in that: In the Ni-based monometallic catalyst, the mass percentage of Ni is 5%-15%, preferably 10-15%, and more preferably 12.5%; Or, in the Ru-based monometallic catalyst, the mass percentage of Ru is 0.5%-3.0%; Or, in the Ni-Ru bimetallic catalyst, the molar ratio of Ni to Ru is 1-12:1, preferably 4-12:1, and more preferably 4-6:1.

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