Carbon dioxide hydrogenation methanation-cracking carbon preparation series method

Abstract

The invention discloses a carbon dioxide hydrogenation methanation-cracking carbon preparation series method, which comprises the following steps: generating CH4 through a reaction of # imgabs0 # imgabs1 #, and realizing the production of a carbon material by adopting the technologies of condensation separation of CH4 and water vapor, CH4 cracking reaction of # imgabs2 #, cyclic utilization of hydrogen and the like. The process is composed of a carbon dioxide hydrogenation methanation reactor and a methane cracking reactor. In the methanation reactor, CO2 and H2 react under a low-temperature condition to generate CH4 and water vapor; cH4 and water vapor are separated by adopting a compressor condensation separation technology, and the separated CH4 is conveyed to a cracking reactor. In the methane cracking reactor, CH4 is cracked at a high temperature to generate H2 and a carbon nanomaterial, and then H2 is returned to the methanation reactor again. The separation of CH4 and water vapor at a relatively low temperature is realized in the tandem carbonization process through a low-temperature condensation technology; through low-temperature CO2 methanation and CH4 catalytic cracking, the content of CO2 is reduced, a high-quality carbon nanomaterial is obtained, and cyclic utilization of CO2 and H2 is realized.

Description

Technical Field

[0001] The invention relates to a carbon dioxide hydrogenation methanation-cracking carbon production series method, belonging to the technical field of combustion chemical industry and materials. Background Art

[0002] Carbon dioxide methanation technology is a process that converts carbon dioxide into a more valuable chemical methane. This technology can convert waste carbon dioxide into high-quality methane, thereby reducing greenhouse gas emissions and reducing dependence on fossil fuels. The core of this technology lies in the design and optimization of catalysts. New catalysts can increase the speed and selectivity of the reaction, greatly reduce energy consumption and reduce waste generation. Under certain pressure and temperature, carbon dioxide and hydrogen are converted into natural gas through reaction. Carbon dioxide methanation technology can utilize carbon dioxide as a resource, realize the recycling of carbon resources, and reduce pollution to the environment and excessive dependence on fossil fuels.

[0003] Methane catalytic cracking technology is a process that decomposes natural gas methane into more valuable chemicals. This technology converts methane into substances such as graphene, carbon nanotubes and hydrogen through a catalyst. This new catalyst can improve reaction efficiency, reduce temperature and pressure requirements, and reduce the generation of undesirable carbon byproducts and waste, thereby greatly improving catalytic efficiency. Methane catalytic cracking technology can effectively utilize methane in natural gas, reduce natural gas waste, and provide new ideas for energy transformation. At the same time, the materials such as graphene and carbon nanotubes produced by this technology have high value and broad application prospects, and can be used in many fields such as energy storage, sensors, and biomedicine. In recent years, with the research and development of new materials such as carbon nanotubes and graphene, methane catalytic cracking technology has rapidly become a hot research field. This technology has great application potential in sustainable energy and chemical manufacturing, and there is still broad room for development in the future.

[0004] The carbon dioxide hydrogenation methanation-cracking tandem carbon production method can achieve efficient energy utilization, reduce carbon emissions, and improve resource utilization efficiency. The hydrogen produced during the methane catalytic cracking process can be used in the carbon dioxide methanation reaction, thereby reducing energy consumption and improving reaction efficiency. In addition, the application of methane catalytic cracking technology to the carbon dioxide methanation reaction can also effectively reduce the temperature and pressure required for the catalytic synthesis of methane from carbon dioxide.

[0005] In summary, the carbon dioxide hydrogenation, methanation and cracking cascade carbon production method can achieve efficient utilization of resources and reduction of carbon emissions, and has important practical significance and far-reaching application prospects. Summary of the invention

[0006] In view of the problems of the existing carbon dioxide methanation-methane catalytic cracking, such as the difficulty in collecting and purifying carbon dioxide, high CH4 and H2O content, and limited synthesis gas quality, the present invention proposes a carbon dioxide hydrogenation methanation-cracking carbon production series method, which aims to reduce pollutant emissions and resource waste and realize comprehensive resource utilization. In addition, it also helps to improve the content and purity of carbon materials and prepare high-purity nanocarbon. Not only that, it is also conducive to the recycling of regenerated hydrogen.

[0007] The present invention is achieved by the following technical means:

[0008] A carbon dioxide hydrogenation methanation-cracking carbon production series method comprises the following steps:

[0009] Step 1): CO2 methanation

[0010] The mixed gas of CO2 and H2 is reacted in the presence of a catalyst to obtain a mixed gas containing CH4 and H2O;

[0011] Step 2): CH4, H2O condensation separation

[0012] Transmit CH4 and H2O to the condenser through pipelines, and condense and separate CH4 and H2O in the compressor by controlling the condenser parameters;

[0013] Step 3): CH4 catalytic cracking

[0014] The CH4 separated in step 2) is transported to a CH4 catalytic cracking reactor, and a CH4 catalytic cracking reaction is carried out in a fixed bed, a moving bed or a fluidized bed reactor to obtain high-purity hydrogen and carbon materials;

[0015] Step 4): H2 recycling

[0016] The high-purity hydrogen obtained from the methane cracking reaction is recycled to step 1).

[0017] Furthermore, in step 1), the molar ratio of CO2 to H2 is 1:2 to 1:4.

[0018] Furthermore, the CO2 methanation reaction conditions in step 1) are: reaction temperature 200°C to 350°C, reaction pressure 0.1MPa to 1MPa.

[0019] Furthermore, in the reaction gas of step 1), the reaction order of CO2 is between 0 and 1, and the reaction order of H2 is between 0.3 and 2.5.

[0020] Furthermore, the catalyst in step 1) is selected from a nickel-based catalyst or a palladium-based catalyst.

[0021] Furthermore, the nickel-based catalyst is selected from any one of the following: Ni / Al2O3, Ni / Y2O3, Ni / ZrO2, Ni / La2O3, Ni / CeO2.

[0022] Furthermore, the palladium-based catalyst is selected from any one of the following: Ru / Al2O3, Ru / Y2O3, Ru / ZrO2, Ru / La2O3, Ru / CeO2.

[0023] In the present invention, the catalyst may also be replaced by at least one of a noble metal catalyst, a transition metal catalyst, a metal catalyst, and a multi-metal catalyst.

[0024] Furthermore, in step 3), the CH4 catalytic cracking reaction temperature is 600°C to 1000°C.

[0025] Furthermore, the CH4 catalytic cracking reaction temperature is 650°C to 800°C.

[0026] The present invention reports for the first time that CO2 and H2 are subjected to a methanation reaction under a nickel-based catalyst, and further based on the coordinated control of the amount of catalyst used, the reaction temperature and the CO2 / H2 molar ratio during the treatment process, the product selectivity and conversion rate are optimized, and the concentration of carbon dioxide in the atmosphere is further reduced, which helps to alleviate the environmental problem of global warming, reduce pollutant emissions and resource waste, and achieve comprehensive utilization of resources. Moreover, it also helps to improve the content and purity of carbon materials, prepare high-purity nanocarbon, and achieve hydrogen recycling. The product is circulated to step 1) as a CO2 methanation reactant, and a carbon dioxide hydrogenation, methanation and cracking series carbon production cycle process is realized.

[0027] The technical solution of the present invention is that CO2 and H2 carry out CO2 methanation reaction under a nickel-based catalyst, and the coordinated control of the catalyst dosage, carbon dioxide flow rate, CO2 / H2 molar ratio and reaction pressure and temperature in the CO2 methanation reaction process is the key to achieving optimization of product selectivity and conversion rate and obtaining a high-purity CH4-H2O mixture; selecting suitable catalysts and reaction conditions for methane catalytic cracking reaction to achieve efficient and controllable chemical reaction is the key to obtaining high-purity carbon materials.

[0028] The beneficial effects of the present invention are:

[0029] 1. The present invention reports for the first time that the methanation reaction of H2 and CO2 under a nickel-based catalyst is helpful to achieve the optimization of product selectivity and conversion rate. Compared with H2 / CO2=2, the H2 / CO2 molar ratio is 4, and the CO2 conversion rate and CH4 selectivity increase by about 30% and 35%, respectively. In addition, in the CO2 methanation process, the CO2 conversion rate decreases with increasing temperature, and the CH4 selectivity increases with increasing H2 / CO2 ratio. When the H2 / CO2 ratio reaches 4, the selectivity reaches the maximum value, which is almost 1.

[0030] 2. Based on the methanation reaction of H2 and CO2 under a nickel-based catalyst in the present invention, compared with other catalyst methanation treatment processes, the present invention adopts a nickel-based catalyst, which has higher catalytic activity and low cost.

[0031] 3. Based on the treatment process of step 1) of the present invention, further through the coordinated control of the amount of catalyst, reaction temperature and CO2 / H2 molar ratio, a synergistic effect can be produced, which is conducive to the optimization of product selectivity and conversion rate, and further reduces the concentration of carbon dioxide in the atmosphere. The results show that when the ratio of H2 to CO2 is 4:1, the yield is up to 95%; when the reaction temperature is 300°C, the yield is up to 97%.

[0032] 4. Based on the treatment process of step 2) of the present invention, the product is purified and separated by further controlling the parameters such as condenser temperature, pressure, gas flow rate, cooling rate and cooling medium. The results show that the condenser temperature is usually set between 0°C and 10°C; the larger the volume flow, the better the separation effect, and the general gas flow is set at about 10mL / min; too fast condensation speed will cause methane to not be fully condensed, and too slow will reduce the condensation efficiency. In general experiments, the cooling rate is between 0.5°C / min and 2°C / min; choosing low-temperature cooling media such as mixed brine and dry ice water mixture is very helpful to improve the condensation effect.

[0033] 5. Based on the treatment process of step 3) of the present invention, by controlling the type, morphology and quality of the catalyst, the reaction temperature and pressure, and the CH4 gas flow rate, it is beneficial to improve the efficiency and selectivity of the catalytic cracking reaction and optimize the reaction rate. Not only that, it is also helpful to improve the content and purity of the carbon material, prepare high-purity nanocarbon, and use the catalyst to crack CH4 at a suitable temperature and pressure to generate reaction products such as carbon materials and hydrogen. The results show that when using Ni / Al2O3 catalyst, the most suitable reaction temperature is 900°C, and when using Co-Mo / Al2O3 catalyst, the most suitable reaction temperature is 800°C.

[0034] 6. Based on the carbon dioxide hydrogenation methanation-cracking series carbon production circulation system of the present invention, CO2-H2 can achieve effective adsorption, activation and dissociation on the catalyst material. The stable adsorption form of CO2 on the Ni (111) surface obtained by density functional theory calculation is a linear form, that is, the O atom of the CO2 molecule forms a Ni-O-Ni bridge bond with two adjacent Ni atoms on the Ni surface. At the same time, the adsorption energy of CO2 obtained by calculation is usually between 20-30 kJ / mol. On the nickel-based catalyst, the most stable adsorption site of CO2 is located on the surface of metallic nickel. For the CO2 molecule, the holes on the nickel surface can provide sufficient binding sites, so that the adsorption energy of CO2 adsorbed on the metallic nickel surface reaches the minimum value and becomes the most stable adsorption site. Therefore, the Ni-based catalyst used is more conducive to the activation and dissociation of CO2.

[0035] Based on the above analysis, it can be seen that the recycling of hydrogen based on the carbon dioxide hydrogenation, methanation and cracking cascade carbon production method is simple and easy to operate, with a high CO2 conversion rate, suitable for industrial applications, and can obtain high-quality carbon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a flow chart of the series connection method of the present invention.

[0037] Figure 2 X is the X of Example 1 (H2 / CO2 molar ratio is 4) CO2 Graph of the changes with temperature and pressure.

[0038] Figure 3 is the S of Example 1 (H2 / CO2 molar ratio is 4) CH4 Graph of the changes with temperature and pressure.

[0039] Figure 4 Example 2 (pressure is 1atm, 30atm) X CO2 Graph showing the changes with different H2 / CO2 ratios.

[0040] Figure 5 Example 2 (pressure 1atm, 30atm) S CH4 Graph showing the changes with different H2 / CO2 ratios. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the embodiments, comparative examples and accompanying drawings.

[0042] In the following cases, the H2:CO2 ratio is a molar ratio. CO2 and S CH4 Variations with temperature and pressure.

[0043] Example 1

[0044] Tested by experiment

[0045] 1) A mixture of H2 and CO2 (reaction pressure = 1, 10, 30, 100 atm, H2:CO2 = 4:1) was introduced into a CO2 methanation reactor and heated to 200°C at a heating rate of 20°C / min. In addition, the CO2 flow rate in the reaction gas was 10 mL / min and the H2 flow rate was 40 mL / min. The main products were methane and water vapor, containing a small amount of by-product CO. The relationship between the CO2 conversion rate and CH4 selectivity in the reaction gas and the temperature and pressure is shown in Figure 2 , Figure 3 shown.

[0046] 2) After the methanation is completed, the atmosphere of the temperature rise stage is switched to 100 vol% N2 with a flow rate of 40 mL / min, and the reactor is heated to 400°C, 600°C, and 800°C at a heating rate of 20°C / min to enter the high temperature reaction stage. At a high temperature of 800°C, the CO2 conversion rate and CH4 selectivity are reduced, and the product is a mixture of CO, CO2, and CH4.

[0047] During the temperature rise and methanation stages of the CO2 methanation reactor, the gas production was continuously collected to determine the trends of the yields of each gas component and the total gas yield with temperature. The results are shown in Figure 2 , Figure 3 When the ratio of CO2 to H2 is 1:4, higher pressure leads to higher CO2 conversion and higher CH4 selectivity. When the temperature reaches 300-350℃, the CO2 conversion and CH4 selectivity are close to 100%.

[0048] Embodiment 2:

[0049] Compared with Example 1, the only difference is that the H2 / CO2 molar ratio is different during the CO2 methanation process.

[0050] 1) A mixture of H2 and CO2 (reaction pressure = 1, 30 atm, H2:CO2 = 2, 4, 6) was introduced into a CO2 methanation reactor and heated to 200°C at a heating rate of 20°C / min. In addition, the CO2 flow rate in the reaction gas was 6.7, 10, 20 mL / min, and the H2 flow rate was 40 mL / min. The main products were methane and water vapor, containing a small amount of by-product CO. The relationship between the CO2 conversion rate and CH4 selectivity in the reaction gas and the change of temperature and pressure is shown in Figure 4 , Figure 5 shown.

[0051] 2) After the methanation is completed, the atmosphere of the temperature rise stage is switched to 100 vol% N2 with a flow rate of 40 mL / min, and the reactor is heated to 400°C, 600°C, and 800°C at a heating rate of 20°C / min to enter the high temperature reaction stage. At a high temperature of 600°C, the CO2 conversion rate and CH4 selectivity are reduced, and the product is a mixture of CO, CO2, and CH4.

[0052] During the temperature rise and methanation phase of the CO2 methanation reactor, the gas production was continuously collected, and the yield of each gas component and the total gas yield were determined as a function of temperature. The results are shown in Table 1. According to the results in Table 1, the CO2 conversion rate decreases with increasing temperature and increases with increasing H2 / CO2 ratio. A higher H2 to CO2 ratio generally results in a higher CO2 conversion rate and a higher CH4 selectivity. The H2 / CO2 ratio significantly affects the CH4 selectivity until the ratio reaches 4, at which point the selectivity reaches its maximum value of almost 1.

[0053] Table 1X CO2 and S CH4 Variations with temperature and pressure

[0054]

[0055]

[0056] Embodiment 3:

[0057] 1) 0.200 g Ni-Fe / Al2O3 catalyst and a CH4 and N2 mixed gas (20% CH4 / N2, 25 mL / min, SV=75000 mL / (h·g)) were introduced into a CH4 cracking reactor, and the temperature was raised to 800°C at a heating rate of 10°C / min, N2 was used as a carrier gas, and its flow rate was 20 mL / min, and CH4 was added to the carrier gas, wherein the CH4 flow rate was 5 mL / min. The main products were biochar and hydrogen.

[0058] 2) The atmosphere of the heating stage was switched to 100 vol% N2 with a flow rate of 20 mL / min, and the reactor was heated to 800°C at a heating rate of 10°C / min to enter the high-temperature reaction stage. Methane was cracked, and the product was a mixture of C and H2, and a small amount of CO was produced.

[0059] During the CH4 cracking reactor temperature rise and methane catalytic cracking stage, the gas production was continuously collected to determine the trend of CH4 conversion rate and carbon yield with temperature. The methane conversion rate increased with the increase of temperature; the carbon yield increased first and then decreased with the increase of temperature.

[0060] Embodiment 4:

[0061] Compared with Example 3, the only difference is that the catalyst Ni 3-xFe x The molar ratio of Ni-Fe in Al is different.

[0062] 1) 0.200 g Ni-Fe / Al2O3 catalyst and a mixed gas of CH4 and N2 (20% CH4 / N2, 25 mL / min, SV=75000 mL / (h·g), Ni 2.7 Fe 0.3 Al, Ni 2.4 Fe 0.6 Al, Ni 2.1 Fe 0.9 Al, Ni 1.8 Fe 1.2 A1) was introduced into a CH4 cracking reactor, and the temperature was raised to 800°C at a heating rate of 10°C / min, N2 was used as a carrier gas, and its flow rate was 20mL / min, and CH4 was added to the carrier gas, wherein the CH4 flow rate was 5mL / min. The main products were biochar and hydrogen.

[0063] 2) The atmosphere of the heating stage was switched to 100 vol% N2 with a flow rate of 20 mL / min, and the reactor was heated to 800°C at a heating rate of 10°C / min to enter the high-temperature reaction stage. Methane was cracked, and the product was a mixture of C and H2, and a small amount of CO was produced.

[0064] During the CH4 cracking reactor temperature rise and methane catalytic cracking stage, the gas production was continuously collected to determine the trend of CH4 conversion rate and carbon yield with temperature. The specific results are shown in Table 3. As the iron content increases, the initial CH4 conversion rate decreases slightly, and the carbon yield first increases and then decreases. As the reaction proceeds, the CH4 conversion first increases and then slowly decreases, and then drops sharply to zero. Ni 2.4 Fe 0.6 Al has the highest carbon yield, which is about twice that of Ni3Al.

[0065] Catalyst used Ni 3-x Fe x The Raman spectrum data of Al are shown in Table 3. Carbon graphitization degree I D / I G As the Fe content in the Ni-Fe alloy increases, it decreases significantly, from 1.49 (Ni3Al) to 1.18 (Ni 1.8 Fe 1.2 Al).

[0066] Table 2Ni 3-x Fe x Methane conversion and carbon yield over Al catalyst

[0067]

[0068] Table 3Ni3-x Fe x Graphitization degree of carbon on Al catalyst

[0069]

[0070] Comparative Example 1:

[0071] Compared with Example 3, the only difference is that the catalyst is Al2O3.

[0072] 1) 0.200 g of Al2O3 catalyst and a mixed gas of CH4 and N2 (20% CH4 / N2, 25 mL / min, SV=75000 mL / (h·g)) were introduced into a CH4 cracking reactor, and the temperature was raised to 800°C at a heating rate of 10°C / min, N2 was used as a carrier gas, and its flow rate was 20 mL / min, and CH4 was added to the carrier gas, wherein the CH4 flow rate was 5 mL / min. The main products were biochar and hydrogen.

[0073] 2) The atmosphere of the heating stage was switched to 100 vol% N2 with a flow rate of 20 mL / min, and the reactor was heated to 800°C at a heating rate of 10°C / min to enter the high-temperature reaction stage. Methane was cracked, and the product was a mixture of C and H2, and a small amount of CO was produced.

[0074] During the CH4 cracking reactor temperature rise and methane catalytic cracking stage, the gas production was continuously collected to determine the trend of CH4 conversion and carbon yield with temperature. The methane conversion increased with increasing temperature; the carbon yield first increased and then decreased with increasing temperature. Compared with the Ni-Fe / Al2O3 catalyst, the catalytic performance of the Al2O3 catalyst was greatly reduced.

[0075] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents, and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A carbon dioxide hydrogenation methanation-cracking carbon production series method, comprising the following steps: Step 1): CO2 methanation The mixed gas of CO2 and H2 is reacted in the presence of a catalyst to obtain a mixed gas containing CH4 and H2O; Step 2): CH4, H2O condensation separation Transmit CH4 and H2O to the condenser through pipelines, and condense and separate CH4 and H2O in the compressor by controlling the condenser parameters; Step 3): CH4 catalytic cracking The CH4 separated in step 2) is transported to a CH4 catalytic cracking reactor, and a CH4 catalytic cracking reaction is carried out in a fixed bed, a moving bed or a fluidized bed reactor to obtain high-purity hydrogen and carbon materials; Step 4): H2 recycling The high-purity hydrogen obtained from the methane cracking reaction is recycled to step 1).

2. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 1, wherein: In step 1), the molar ratio of CO2 to H2 is 1:2 to 1:

4.

3. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 1, wherein: Step 1) The CO2 methanation reaction conditions are: The reaction temperature is 200°C to 350°C, and the reaction pressure is 0.1MPa to 1MPa.

4. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 1, wherein: In the reaction gas of step 1), the reaction order of CO2 is between 0 and 1, and the reaction order of H2 is between 0.3 and 2.

5.

5. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 1, wherein: The catalyst in step 1) is selected from a nickel-based catalyst or a palladium-based catalyst.

6. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 5, wherein: The nickel-based catalyst is selected from any one of the following: Ni / Al2O3, Ni / Y2O3, Ni / ZrO2, Ni / La2O3, and Ni / CeO2.

7. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 5, wherein: The palladium-based catalyst is selected from any one of the following: Ru / Al2O3, Ru / Y2O3, Ru / ZrO2, Ru / La2O3, Ru / CeO2.

8. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 1, wherein: Step 3) The CH4 catalytic cracking reaction temperature is 600°C to 1000°C.

9. A carbon dioxide hydrogenation methanation-cracking carbon production series method according to claim 8, wherein: The CH4 catalytic cracking reaction temperature is 650°C to 800°C.

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