A method for synthesizing ammonia using a co-loaded porous carbon catalyst based on heavy bio-oil

Abstract

The present application relates to the technical field of distributed mild ammonia synthesis, and particularly relates to a method for synthesizing ammonia by using a Co-loaded porous carbon catalyst based on heavy bio-oil. The method uses industrial waste, i.e. heavy bio-oil, to synthesize a cascade porous carbon-based Co catalyst (Co-PBs) by means of co-catalytic pyrolysis. Cobalt, on one hand, acts as a pyrolysis catalyst to promote the pyrolysis of heavy bio-oil, forming a porous biochar framework with a larger surface area. On the other hand, co-catalytic pyrolysis leads to more uniform loading of cobalt, which, as a plasma-assisted ammonia synthesis catalyst, further promotes the adsorption of free radicals and the dissociation of NH3, enhancing the performance of ammonia synthesis. Due to the enhancement of mass transfer rate and the more uniform distribution of transition metal active sites, Co-PBs exhibit a plasma-assisted ammonia synthesis rate as high as 1.605 mmol / g·h. Meanwhile, the extremely high stability of Co-PBs enables it to maintain stable performance in 24 cycles and 40h long-time reactions, showing its great application potential.

Description

Technical Field

[0001] This invention relates to the field of distributed mild ammonia synthesis technology, and more particularly to a method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil. Background Technology

[0002] Ammonia is an extremely important chemical raw material and one of the world's most produced inorganic materials. It also possesses unique advantages such as high hydrogen storage density (17.7 wt%), clean and efficient production, and renewability, making it a highly promising new zero-carbon fuel and hydrogen storage material. However, the traditional ammonia synthesis method—the Haber-Bosch process—requires temperatures as high as 500°C and pressures of 150-300 bar. The centralized Haber process consumes 2% of global energy annually and emits over 420 million tons of CO2. Therefore, in recent years, an increasing number of emerging green and low-carbon ammonia synthesis technologies have been developed, such as photocatalytic ammonia synthesis, electrochemical ammonia synthesis, chemical looping ammonia synthesis, and biological nitrogen fixation. Plasma-assisted ammonia synthesis technology can couple with distributed renewable energy sources to synthesize ammonia through a zero-carbon process at ambient temperature and pressure. Theoretically, it has a higher rate than the Haber process and is considered a green ammonia synthesis process with enormous application potential. Plasma-assisted ammonia synthesis only requires a small plasma generator and can be well coupled with renewable energy sources such as solar and wind power. On-site reaction in remote areas can also avoid energy consumption during industrial product transportation. Currently, widely used catalysts include Al2O3, SiO2, mesoporous molecular sieves, and organometallic frameworks. They share the characteristics of abundant porous structures and large specific surface areas, which can enhance the mass transfer performance of free radicals and increase the number of active sites. However, their drawbacks include the difficulty in controlling the pore structure to enhance plasma-assisted ammonia synthesis. Furthermore, these materials are expensive and prone to structural collapse and deactivation under prolonged strong electric fields. Heavy bio-oil, a waste product from biomass pyrolysis, can serve as an ashless source for carbon synthesis, offering the advantage of removing the original biomass framework structure, and its framework structure is easily controllable. On the other hand, current solutions for utilizing heavy bio-oil face many challenges; therefore, converting bio-oil into valuable carbon materials is a potential way to utilize this waste. Using heavy bio-oil, a byproduct of biodiesel production from biomass pyrolysis, as a raw material, a Co-supported porous carbon catalyst based on heavy bio-oil was prepared for plasma-assisted ammonia synthesis. This not only avoids the cost and environmental hazards of its catalytic cracking process but also provides an effective strategy for future green ammonia synthesis processes. Summary of the Invention

[0003] Purpose of the invention: The present invention aims to provide a method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil.

[0004] Technical solution: The present invention provides a method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil. Ammonia is synthesized by plasma-assisted synthesis. The Co-supported porous carbon catalyst is added to the plasma-assisted ammonia synthesis reactor, and N2 and H2 are transported to the plasma-assisted ammonia synthesis reactor to react and synthesize ammonia. The Co-supported porous carbon catalyst is prepared by the following steps: (1) mixing Co source and heavy bio-oil to obtain material A; (2) pre-carbonizing material A and then grinding it into powder to obtain powder B; (3) mixing powder B with alkali, grinding the mixture evenly, and then carbonizing the resulting product to obtain powder C. Powder C is the Co-supported porous carbon catalyst.

[0005] Furthermore, ammonia is synthesized via plasma-assisted synthesis. A Co-supported porous carbon catalyst is added to the plasma-assisted ammonia synthesis reactor, and N2 and H2 are transported to the plasma-assisted ammonia synthesis reactor to react and synthesize ammonia.

[0006] Furthermore, the temperature for ammonia synthesis is 200-400℃.

[0007] Furthermore, N2 and H2 are fed into the plasma-assisted ammonia synthesis reactor at a flow rate of 1:7 to 7:1.

[0008] Further, in step (1), the Co source is Co(NO3)2·6H2O, and the mass ratio of Co(NO3)2·6H2O to heavy bio-oil is 1:10~20.

[0009] Furthermore, in step (2), the pre-carbonization conditions are to raise the temperature to 500-550°C at a rate of 5-10°C / min under an inert gas atmosphere and maintain it for 1-1.5 hours for pre-carbonization.

[0010] Furthermore, in step (3), the alkali is NaOH, and the amount of NaOH added is 1-3 times the mass of powder B.

[0011] Furthermore, in step (3), the carbonization conditions are to raise the temperature to 800-850°C at a rate of 5-10°C / min under an inert gas atmosphere and maintain it for 2-2.5 hours.

[0012] Further, in step (3), powder C is washed several times with acid solution and water respectively to remove salt and impurities from powder C. The resulting product is dried to obtain a Co-supported porous carbon catalyst.

[0013] Furthermore, in step (4), the acid solution is an HCl solution.

[0014] This invention utilizes heavy bio-oil, an industrial waste, to synthesize a cascaded porous carbon-based Co catalyst (Co-PBs) via co-catalytic pyrolysis. Cobalt acts as a pyrolysis catalyst, promoting the pyrolysis of heavy bio-oil and forming a porous biochar framework with a larger surface area. Furthermore, co-catalytic pyrolysis results in a more uniform cobalt loading, which, as a plasma-assisted ammonia synthesis catalyst, further promotes the adsorption of free radicals and the dissociation of NH3, enhancing the performance of ammonia synthesis. Due to the enhanced mass transfer rate and more uniform distribution of transition metal active sites, Co-PBs exhibit a plasma-assisted ammonia synthesis rate as high as 1.605 mmol / g·h. Simultaneously, the extremely high stability of Co-PBs allows it to maintain stable performance over a long reaction period of 24 cycles and 40 h, demonstrating its significant application potential.

[0015] Beneficial Effects: Compared with the prior art, the present invention has the following significant advantages: The present invention prepares a Co-supported porous carbon catalyst via co-catalytic pyrolysis and applies it to the field of plasma-assisted ammonia synthesis. The Co-supported porous carbon material prepared by the present invention has a loose and porous hollow carbon framework structure, which is beneficial to enhancing its mass transfer performance, resulting in more free radicals being able to contact the active sites, thus increasing the rate of ammonia synthesis;

[0016] The ammonia synthesis rate of the Co-supported porous carbon material used in this invention reaches 1.605 mmol / g·h, which exceeds that of Co-supported porous biochar materials prepared by direct loading and impregnation methods. At the same time, it greatly simplifies the catalyst preparation process. Co serves as both a pyrolysis catalyst and an active metal for plasma-assisted ammonia synthesis, which is a "two birds with one stone" strategy.

[0017] The plasma-assisted ammonia synthesis method using Co-supported porous carbon materials in this invention exhibits high stability, with the ammonia synthesis rate remaining almost unchanged within 40 hours.

[0018] The plasma-assisted ammonia synthesis method using Co-loaded porous carbon materials in this invention was compared over 24 cycles. It was found that the ammonia synthesis rate stabilized at a high value after the 5th cycle and did not decrease further, thus exhibiting good cyclicity. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation process of the Co-supported porous carbon material described in this invention.

[0020] Figure 2 This is a scanning electron microscope image of the Co-supported porous carbon material described in this invention.

[0021] Figure 3This is the plasma-assisted ammonia synthesis reaction and testing apparatus described in this invention.

[0022] Figure 4 This is a comparison of the ammonia synthesis rate between the Co-supported porous carbon material described in this invention and commercial materials.

[0023] Figure 5 The ammonia synthesis rate of the Co-supported porous carbon material described in this invention under different gas ratios.

[0024] Figure 6 The ammonia synthesis rate of the Co-supported porous carbon material described in this invention at different temperatures.

[0025] Figure 7 The change in the ammonia synthesis rate of the Co-supported porous carbon material described in this invention during a long reaction of 40 hours.

[0026] Figure 8 This refers to the change in the ammonia synthesis rate of the Co-supported porous carbon material described in this invention over 24 cyclic reaction cycles. Detailed Implementation

[0027] like Figure 1 As shown, this embodiment of the invention provides a method for preparing a Co-supported porous carbon catalyst based on heavy bio-oil, comprising the following steps:

[0028] (1) Mix Co source and heavy bio-oil to obtain material A; preferably, the Co source is Co(NO3)2·6H2O, and the mass ratio of Co(NO3)2·6H2O to heavy bio-oil is 1:10~20.

[0029] (2) Material A is pre-carbonized and then ground into powder to obtain powder B; wherein, the pre-carbonization conditions are to heat to 500~550℃ at a rate of 5-10℃ / min under an inert gas atmosphere and maintain it for 1~1.5h for pre-carbonization.

[0030] (3) Powder B is mixed with alkali, and the mixture is ground evenly. The resulting mixture undergoes secondary carbonization under an inert gas atmosphere, with the temperature increased to 800-850℃ at a rate of 5-10℃ / min and maintained for 2-2.5 hours. The resulting product is ground into powder C. Powder C is washed several times with acid solution and water to remove salts and impurities. The product is then dried to obtain Co-supported porous carbon catalysts (Co-PBs).

[0031] Preferably, the alkali is NaOH, and the amount of NaOH added is 1-3 times the mass of powder B.

[0032] The heavy bio-oil used in this embodiment of the invention is composed of 10% acid, 55% phenol, 10% ketone, 5% aldehyde, 15% ester, and 5% alcohol, wherein the contents of C and O are 58% and 36%, respectively.

[0033] Example 1

[0034] This embodiment provides a method for preparing a Co-supported porous carbon catalyst based on heavy bio-oil, comprising the following steps:

[0035] (1) Add 0.5g Co(NO3)2·6H2O and 10g heavy bio-oil to a beaker; stir thoroughly for 5 minutes at room temperature to obtain material A;

[0036] (2) Place material A in a quartz boat, heat it to 500°C at a rate of 5°C / min in an Ar atmosphere in a tube furnace and hold it for 1 hour for pre-carbonization, then cool it naturally to room temperature and grind it into powder B.

[0037] (3) Mix powder B with 3 times the mass of NaOH, grind evenly and place in an alumina boat, and heat to 800℃ at a rate of 10℃ / min in an Ar atmosphere in a tube furnace and hold for 2h, then cool naturally to room temperature and grind into powder C.

[0038] (4) Wash the powder C with 2 mol / L HCl solution and distilled water 6 times each to remove salt and impurities;

[0039] (5) The obtained sample was dried at 100℃ for 12h to obtain Co-supported porous carbon catalyst.

[0040] The preparation flow chart of the above Co-supported porous carbon material is as follows: Figure 1 As shown, porous biochar material with extremely high specific surface area and excellent pore structure was successfully synthesized through three processes: pre-carbonization, secondary carbonization, and neutralization and cleaning.

[0041] Surface morphology such as Figure 2 As shown, the material exhibits a loose and porous hollow carbon skeleton structure, which is beneficial to enhancing its mass transfer performance, resulting in more free radicals being able to contact the active sites, thus increasing the rate of ammonia synthesis.

[0042] Example 2

[0043] This embodiment provides a method for preparing a Co-supported porous carbon catalyst based on heavy bio-oil, comprising the following steps:

[0044] (1) Add 0.5g Co(NO3)2·6H2O and 5.0g heavy bio-oil to a beaker; stir thoroughly for 5 minutes at room temperature to obtain material A;

[0045] (2) Place material A in a quartz boat, heat it to 500°C at a rate of 5°C / min in an Ar atmosphere in a tube furnace and hold it for 1 hour for pre-carbonization, then cool it naturally to room temperature and grind it into powder B.

[0046] (3) Mix powder B with 3 times the mass of NaOH, grind evenly and place in an alumina boat, and heat to 800℃ at a rate of 10℃ / min in an Ar atmosphere in a tube furnace and hold for 2h, then cool naturally to room temperature and grind into powder C.

[0047] (4) Wash the powder C with 2 mol / L HCl solution and distilled water 6 times each to remove salt and impurities;

[0048] (5) The obtained sample was dried at 100℃ for 12h to obtain Co-supported porous carbon catalyst.

[0049] Example 3

[0050] This embodiment provides a method for preparing materials for a plasma-assisted ammonia synthesis method using a Co-supported porous carbon catalyst prepared from heavy bio-oil.

[0051] Includes the following steps:

[0052] (1) Add 0.5g Co(NO3)2·6H2O and 10g heavy bio-oil to a beaker; stir thoroughly for 5 minutes at room temperature to obtain material A;

[0053] (2) Place material A in a quartz boat, heat it to 550°C at a rate of 10°C / min in an Ar atmosphere in a tube furnace and hold it for 1.5h for pre-carbonization, then cool it naturally to room temperature and grind it into powder B.

[0054] (3) Mix powder B with 1 times the mass of NaOH, grind evenly and place in an alumina boat, and heat to 850℃ at a rate of 5℃ / min in an Ar atmosphere in a tube furnace and hold for 2.5h, then cool naturally to room temperature and grind into powder C.

[0055] (4) Wash the powder C with 2 mol / L HCl solution and distilled water 6 times each to remove salt and impurities;

[0056] (5) The obtained sample was dried at 100℃ for 12h to obtain Co-supported porous carbon catalyst.

[0057] Example 4

[0058] This embodiment provides a plasma-assisted ammonia synthesis method using a Co-supported porous carbon catalyst prepared based on heavy bio-oil.

[0059] The plasma-assisted ammonia synthesis apparatus in this invention is as follows: Figure 3 As shown, nitrogen and hydrogen are thoroughly mixed before entering the reactor. The plasma power is controlled by a power generator and a voltage regulator. The amount of synthesized ammonia is determined using a dilute sulfuric acid solution and a conductivity meter. The specific steps include the following:

[0060] (1) Connect the high-voltage electrode in the plasma-assisted ammonia synthesis reactor to a high-voltage power supply;

[0061] (2) Wrap a stainless steel mesh around the outside of the reactor as a low-voltage electrode and ground it;

[0062] (3) A fixed microporous substrate carrying catalyst powder is provided at the bottom of the high voltage electrode, and the Co-supported porous carbon-based material prepared in Example 1 is filled into the fixed microporous substrate.

[0063] (4) Heat the reactor to 200°C using a tubular furnace;

[0064] (5) N2 and H2 are fed into the reactor in a 1:1 ratio to react and synthesize ammonia, wherein the flow rates of N2 and H2 are both 50 ml / min;

[0065] (6) The amount of synthesized ammonia was determined by using a dilute sulfuric acid solution and a conductivity meter.

[0066] Example 5

[0067] This embodiment provides the application of the Co-supported porous carbon catalysts prepared in Examples 1 and 2 in ammonia synthesis. The effect of different catalysts on the ammonia synthesis effect was investigated: ammonia was synthesized according to the steps described in Example 4, with Co / Al2O3 being a commercially available 5% by mass porous alumina catalyst, and the ratio of N2 to H2 in step (5) set to 1:1.

[0068] The results are as follows Figure 4 As shown, the ammonia synthesis rate of the Co-supported porous carbon material used in Example 1 of this invention reaches 1.605 mmol / g·h, which exceeds the mass fraction of 10% Co-supported porous biochar material. At the same time, it greatly simplifies the catalyst preparation process. Co serves as both a pyrolysis catalyst and an active metal for plasma-assisted ammonia synthesis, which is a "two birds with one stone" strategy.

[0069] The effect of different H2 and N2 ratios on ammonia synthesis was investigated: Ammonia was synthesized according to the steps described in Example 3, and the inlet gas flow rates of H2 and N2 were adjusted to achieve H2:7, 2:6, 3:5, 4:4, 5:3, 6:2, and 7:1 ratios, respectively, and ammonia was finally synthesized. The results are as follows: Figure 5As shown, the ammonia synthesis rate was measured as a function of the H2 to N2 ratio, reaching its maximum value at a ratio of 1:1.

[0070] The effect of different heating temperatures on the ammonia synthesis effect was investigated: Ammonia was synthesized according to the steps described in Example 3, with heating temperatures of 50, 100, 200, 300, and 400 degrees Celsius in step (4). The results are as follows: Figure 6 As shown, the plasma ammonia synthesis rate was measured as a function of temperature, and the rate of increase with temperature was fastest before 200℃.

[0071] The above measurement results show that the plasma-assisted ammonia synthesis method using Co-supported porous carbon materials in this application has a much higher rate than commonly used methods, demonstrating its potential for industrial application.

[0072] Example 6

[0073] Stability and recyclability of a plasma-assisted ammonia synthesis method based on a Co-supported porous carbon catalyst prepared from heavy bio-oil

[0074] Includes the following steps:

[0075] (1) Connect the high-voltage electrode in the plasma-assisted ammonia synthesis reactor to a high-voltage power supply;

[0076] (2) Wrap a stainless steel mesh around the outside of the reactor as a low-voltage electrode and ground it;

[0077] (3) A fixed microporous substrate supporting catalyst powder is provided at the bottom of the high voltage electrode, and Co-loaded porous carbon-based material is filled into the fixed microporous substrate;

[0078] (4) Heat the reactor to 200°C using a tubular furnace;

[0079] (5) N2 and H2 are fed into the reactor at a flow rate of 50 ml / min to react and synthesize ammonia;

[0080] (6) The amount of synthesized ammonia was determined by using a dilute sulfuric acid solution and a conductivity meter.

[0081] The stability of the plasma-assisted ammonia synthesis method based on Co-supported porous carbon materials in this invention within 40 hours is as follows: Figure 7 As shown, the ammonia synthesis rate remains almost unchanged within 40 hours when using Co-supported porous carbon material as a catalyst, demonstrating its application value as an industrial catalyst.

[0082] The plasma-assisted ammonia synthesis method based on Co-supported porous carbon catalyst prepared from heavy bio-oil in this invention achieves the following ammonia synthesis rate over 24 cycles: Figure 8As shown, after the 5th cycle, the ammonia synthesis rate can stabilize at a high value and will not decline further, demonstrating its great potential for future industrial applications.

[0083] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil, characterized in that, Ammonia is synthesized by plasma-assisted synthesis. Co-supported porous carbon catalyst is added to the plasma-assisted ammonia synthesis reactor, and N2 and H2 are transported to the plasma-assisted ammonia synthesis reactor to react and synthesize ammonia. The Co-supported porous carbon catalyst is prepared by the following steps: (1) Co source and heavy bio-oil are mixed to obtain material A; (2) Material A is pre-carbonized and then ground into powder to obtain powder B. The pre-carbonization conditions are to heat to 500-550 ℃ at a rate of 5-10 ℃ / min under an inert gas atmosphere and maintain it for 1-1.5 h; (3) Powder B is mixed with NaOH. The amount of NaOH added is 1-3 times the mass of powder B. The mixture after grinding is carbonized. The carbonization conditions are to heat to 800-850 ℃ at a rate of 5-10 ℃ / min under an inert gas atmosphere and maintain it for 2-2.5 h. The carbonized product is ground into powder C, which is the Co-supported porous carbon catalyst.

2. The method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil according to claim 1, characterized in that, Ammonia is synthesized via plasma-assisted synthesis. A Co-supported porous carbon catalyst is added to the plasma-assisted ammonia synthesis reactor, and N2 and H2 are transported to the reactor to react and synthesize ammonia.

3. The method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil according to claim 1, characterized in that, The temperature for ammonia synthesis is 200-400℃.

4. The method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil according to claim 1, characterized in that, N2 and H2 are fed into the plasma-assisted ammonia synthesis reactor at a flow rate of 1:7 to 7:

1.

5. The method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil according to claim 1, characterized in that, In step (1), the Co source is Co(NO3)2·6H2O, and the mass ratio of Co(NO3)2·6H2O to heavy bio-oil is 1:10~20.

6. The method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil according to claim 1, characterized in that, In step (3), powder C is washed several times with acid solution and water to remove salt and impurities from powder C. The resulting product is dried to obtain a Co-supported porous carbon catalyst.

7. The method for synthesizing ammonia using a Co-supported porous carbon catalyst based on heavy bio-oil according to claim 1, characterized in that, In step (4), the acid solution is an HCl solution.

Images