Environment-friendly synthetic ammonia production process

Abstract

The present application belongs to the technical field of synthetic ammonia production, and particularly relates to an environmentally-friendly synthetic ammonia production process. The present application adopts 6.5MPa aerospace furnace semi-waste pot gasification technology, cooperates with CaO-Fe2O3-K2CO3 composite combustion improver and optimizes oxygen-coal ratio to realize efficiency increase from the source, adopts isothermal shift system to realize accurate conversion of CO, adopts activated carbon-molecular sieve composite adsorbent in four-tower PSA system, and realizes deep purification in combination with cryogenic separation. In the ammonia synthesis link, a carbon nanotube loaded ruthenium-based catalyst is taken as the core, the carbon nanotube is subjected to plasma treatment to form a defect site, the ultrasonic standing wave is used to drive accurate loading of ruthenium ions, supercritical CO2 reduction is used to control the size of ruthenium particles, nitrogen-doped carbon shell is combined with K + Limited enhancement of electron transfer significantly improves the catalytic activity of the catalyst, and the hydrogen-nitrogen ratio is optimized in combination with green hydrogen, thereby effectively improving the single-pass conversion rate and the yield of the product.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthetic ammonia production, and particularly relates to an environmentally-friendly synthetic ammonia production process. BACKGROUND

[0002] As one of the core products of modern chemical industry, synthetic ammonia is a basic raw material in the fields of fertilizers, medicines, dyes and explosives, and its production scale and technical level are directly related to agricultural safety and industrial development. However, the traditional synthetic ammonia process has long been plagued by problems such as high energy consumption, high pollution and large carbon emissions.

[0003] In the traditional coal-to-synthetic ammonia process, some small and medium-sized devices still use fixed gasification technology, which has problems such as low gasification temperature, incomplete reaction, and the production of by-products such as tar and phenols. These by-products not only increase the load of the subsequent purification process, but also easily cause equipment blockage and catalyst poisoning, and the treatment of organic matter such as tar requires additional energy consumption, further increasing production costs. In addition, in the traditional gasification process, there is a lack of regulation of high-efficiency combustion improvers, the coal coke reaction activation energy is high, and the oxygen-coal ratio is not reasonable, resulting in low effective gas yield per raw material coal and serious energy waste. In the shift process of crude synthetic gas, some old plants still use Fe-Cr catalysts and single-stage shift, which has problems such as insufficient CO conversion rate and high steam consumption; while modern devices use sulfur-tolerant Co-Mo catalysts, but still need to optimize the steam / CO ratio to reduce energy consumption. In the purification process, the traditional PSA system has limited efficiency in removing trace organic sulfur (such as COS) and inert gases (such as CH4), and needs subsequent deep purification. In addition, the service life of the adsorbent is shortened due to sulfur penetration or micropore blockage, and the adsorbent is easily poisoned or blocked by sulfur.

[0004] Therefore, it is urgent to develop a new synthetic ammonia process with low carbon, low pressure and high raw material tolerance. SUMMARY

[0005] The purpose of the present application is to provide an environmentally-friendly synthetic ammonia production process to solve the existing problems.

[0006] The present application is realized by the following technical solutions:

[0007] An environmentally-friendly synthetic ammonia production process comprises the following steps:

[0008] S1, the raw coal is dried and crushed to 80-120 mesh, 1-3% of the mass fraction of the composite combustion improver is added and uniformly mixed, and then the oxygen with a purity of ≥99.6% is sent into a 6.5MPa pressure grade aerospace furnace semi-waste pot gasifier at an oxygen-coal ratio of 1:0.8-1 to perform gasification treatment, to generate a crude synthesis gas;

[0009] S2, the crude synthesis gas is sent into a sulfur-tolerant isothermal shift system after dust removal by a Venturi scrubber, and two-stage isothermal shift is performed under the action of a Co-Mo catalyst to control the CO content at the outlet ≤0.6%;

[0010] S3, the crude synthesis gas treated in step S2 is sent into a four-tower PSA system to remove CO2 and sulfides under the conditions of an operating pressure of 2-3MPa and an adsorption temperature of 40-60℃, to obtain H2 and N2 mixed gas, which is then sent into a deep cooling separation system to perform rectification purification under the conditions of -180℃ and 0.5-1MPa, to obtain refined gas;

[0011] S4, green hydrogen is added to the refined gas above, the hydrogen-nitrogen ratio is adjusted to 2.8-3:1, the mixture is pressurized to 15MPa by a compressor, and then sent into an ammonia synthesis tower to synthesize ammonia under the action of a carbon nanotube supported ruthenium-based catalyst.

[0012] Further, the composite combustion improver in step S1 is CaO-Fe2O3-K2CO3, and the mass ratio of the three is 6:3:1.

[0013] The temperature of the gasification treatment is 1400-1600℃, and the gasification time is 4-6s.

[0014] Further, the specific parameters of the two-stage isothermal shift in step S2 are as follows:

[0015] First-stage shift: the catalyst type is K8-11, the operating temperature is 240-280℃, the steam / CO ratio is 1.8-2.2, and the outlet CO concentration is ≤3%;

[0016] Second-stage shift: the catalyst type is QDB-04, the operating temperature is 200-220℃, the steam / CO ratio is 1.2-1.5, and the outlet CO concentration is ≤0.6%.

[0017] Further, the four-tower PSA system in step S3 uses an activated carbon-molecular sieve composite adsorbent, and the adsorption cycle is 60-90s.

[0018] Further, the preparation of the activated carbon-molecular sieve composite adsorbent includes the following steps:

[0019] S3-1, the activated carbon: 13X molecular sieve: rice husk diatom = 3:7:2 mass ratio, according to 1:5~7 solid-liquid ratio into deionized water, stirring and mixing 2% of the total mass of the raw material cellulase, enzymatic reaction at 45~55℃, 100~200rpm stirring speed for 4~5h, then in-50℃, vacuum degree 10Pa under vacuum freeze drying 10~12h, dried through 80 mesh sieve to get adsorbent matrix;

[0020] S3-2, the adsorbent matrix and chitosan-lignin mixed solution according to 9:1 mass ratio mixing, stirring to form a uniform plasticity mud, using screw extrusion molding machine, through the diameter of 3mm circular die extrusion molding, cutting machine into length of 5~8mm strip-shaped adsorbent body, natural drying;

[0021] S3-3, the body is placed in DBD plasma reactor, helium is imported, plasma treatment is carried out;

[0022] S3-4, preparation of 0.5~0.6mol / L Ce(NO3)3 solution, the plasma treated body is immersed in the solution, ultrasonic immersion for 30~40min, after completion, take out and drain, then dry at 70~80℃ for 4~5h, then placed in the tube furnace, under N2 atmosphere, with 2~3℃ / min to 400℃, keep warm for 2~3h, then naturally cooled to room temperature.

[0023] Further, the mass ratio of chitosan to lignin in the chitosan-lignin mixed solution in step S3-2 is 1:1, and the solid content is 20%.

[0024] Further, the amount of helium imported in step S3-3 is 50~60mL / min, the power is controlled to 500W during plasma treatment, and the treatment time is 20~25min.

[0025] Further, the green hydrogen in step S4 is hydrogen produced by electrolysis of water, and the hydrogen purity is ≥99.99%.

[0026] Further, the preparation of carbon nanotube supported ruthenium-based catalyst in step S4 includes the following steps:

[0027] S4-1, the multi-walled carbon nanotubes are placed in a DBD plasma reactor, and Ar / O2 mixed gas is imported for plasma treatment;

[0028] S4-2, the multi-walled carbon nanotubes after plasma treatment are ultrasonically dispersed into ethanol to prepare a 0.1g / mL multi-walled carbon nanotube suspension;

[0029] RuCl3·3H2O was dissolved in ethanol to prepare a 0.1 mol / L ruthenium precursor solution, and 0.5 wt% HCOOH was added as a reduction promoter;

[0030] S4-3, the multi-walled carbon nanotube suspension and the ruthenium precursor solution are pumped into the Y-shaped microchannel of the microfluidic reactor, the flow rate ratio is 1:3 (CNT (carbon nanotube) liquid: ruthenium liquid), directional mixing is carried out under laminar flow state, a 1MHz ultrasonic standing wave field is turned on, the amplitude is set to 10μm, the ruthenium ions are precisely adsorbed on the defect sites of the multi-walled carbon nanotubes by using the standing wave pressure node, the residence time of the mixed solution in the microchannel is controlled to be 120~130s, and the adsorption rate of the ruthenium ions is ensured to reach 99%;

[0031] S4-4, the CNT-ruthenium precursor mixture loaded by the microfluidic is transferred to a supercritical CO2 reaction kettle, supercritical CO2 is introduced after sealing, the pressure in the kettle is increased to 15MPa, the temperature is controlled at 40℃, the reduction reaction is carried out under the supercritical CO2 atmosphere for 1.5~2.5h, then the pressure is reduced to normal pressure at a speed of 0.5MPa / min, the solid product Ru / CNTs is collected, and vacuum drying is carried out at 55~65℃ for 2~3h;

[0032] S4-5, the Ru / CNTs after vacuum drying is dispersed in ethanol, KNO3 and pyrrole monomer are added, stirring is carried out for 30~40min, then 0.1mol / L FeCl3 solution is added dropwise to initiate polymerization, and room temperature reaction is carried out for 2~3h to form poly-pyrrole-K + The CNTs are coated with a thin film;

[0033] The coated sample is transferred to a tube furnace, heated to 600℃ at a rate of 5℃ / min under an argon atmosphere (flow rate 40mL / min), and held for 1.5~2.5h, the polypyrrole is carbonized to form a nitrogen-doped carbon shell, and K + The K is confined in the carbon shell.

[0034] Further, the volume ratio of Ar to O2 in the Ar / O2 mixed gas during the plasma treatment in step S4-1 is 95:5;

[0035] The gas flow rate is controlled to be 40~50mL / min, the power is 300W, and the treatment time is 20~30min.

[0036] Further, three waste treatments and resource recycling are further included: the gasified waste residue is treated by vitrification and used as a building material raw material; waste water is treated by three-stage flash evaporation-double membrane method to realize closed loop circulation; CO2 desorbed by the PSA system directly obtains product gas with a purity of ≥99.9%; and the deactivated catalyst is subjected to solvent extraction to recover active components.

[0037] Compared with the prior art, the present application has the following advantages:

[0038] The application adopts 6.5MPa space furnace semi-waste pot gasification technology, cooperates with CaO-Fe2O3-K2CO3 composite combustion improver and optimizes oxygen-coal ratio, realizes efficiency from the source, the composite combustion improver realizes sulfur fixation through CaO, Fe2O3 reduces the coal coke reaction activation energy, K2CO3 catalyzes the carbon-CO2 reaction, cooperates to improve the coal conversion rate, the 1400~1600℃ ultrahigh temperature makes the macromolecules such as tar and phenol fully split, avoids the subsequent equipment blockage, and the raw coal utilization rate is high. The application realizes the accurate conversion of CO by adopting the isothermal shift system, the first stage utilizes K8-11 high activity to rapidly convert most of CO, the second stage deeply converts the remaining CO through QDB-04 low temperature activity, the four-tower PSA system adopts the activated carbon-molecular sieve composite adsorbent, and realizes deep purification in combination with cryogenic separation. In the ammonia synthesis link, the carbon nanotube loaded ruthenium-based catalyst is taken as the core, the carbon nanotube is treated by plasma to form a defect site, the ultrasonic standing wave drives the accurate loading of ruthenium ions, the supercritical CO2 reduction controls the ruthenium particle size, the nitrogen-doped carbon shell cooperates with K + The limited enhancement of electron transfer significantly improves the catalytic activity of the catalyst, and the hydrogen-nitrogen ratio is optimized in combination with green hydrogen, the single-pass conversion rate is effectively improved, and the yield of the product is improved. DETAILED DESCRIPTION

[0039] In order to further explain the application, the following specific examples are combined for illustration.

[0040] Example 1

[0041] An environment-friendly synthetic ammonia production process comprises the following steps:

[0042] S1, the raw coal is dried and crushed to 80 meshes, 1% of the composite combustion improver CaO-Fe2O3-K2CO3 (the mass ratio of the three is 6:3:1) is added and uniformly mixed, then the oxygen with a purity of ≥99.6% is sent into the 6.5MPa pressure grade space furnace semi-waste pot gasification furnace at an oxygen-coal ratio of 1:0.8 for gasification treatment, 1400℃ is treated for 4s, and the crude synthesis gas is generated;

[0043] S2, the crude synthesis gas is dusted by a Venturi scrubber, enters a sulfur-tolerant isothermal shift system, and is subjected to two-stage isothermal shift under the action of a Co-Mo catalyst, and the CO content at the outlet is controlled to be ≤0.6%;

[0044] The specific parameters of the two-stage isothermal shift are as follows:

[0045] The first-stage shift: the catalyst type is K8-11, the operating temperature is 240℃, the steam / CO ratio is 1.8, and the outlet CO concentration is ≤3%;

[0046] Second stage shift: catalyst model is QDB-04, operating temperature is 200 DEG C, steam / CO ratio is 1.2, outlet CO concentration is less than or equal to 0.6%;

[0047] S3, the crude synthetic gas treated in step S2 is introduced into a four-tower PSA system, and CO2 and sulfides are removed under the conditions of an operating pressure of 2-3 MPa and an adsorption temperature of 40 DEG C to obtain H2 and N2 mixed gas, which is then introduced into a cryogenic separation system, and refined gas is obtained by rectification purification under the conditions of -180 DEG C and 0.5 MPa;

[0048] The adsorption cycle is 60 s by using activated carbon-molecular sieve composite adsorbent;

[0049] The preparation of the activated carbon-molecular sieve composite adsorbent comprises the following steps:

[0050] S3-1, activated carbon, 13X molecular sieve and rice husk diatom are mixed in a mass ratio of 3:7:2, and then added into deionized water in a solid-liquid ratio of 1:5, stirred and mixed, then 2% of cellulase based on the total mass of raw materials is added, and enzymatic hydrolysis is carried out at 45 DEG C and a stirring speed of 100 rpm for 4 h, followed by vacuum freeze drying at -50 DEG C and a vacuum degree of 10 Pa for 10 h, and then the adsorbent matrix is obtained by sieving through an 80-mesh sieve;

[0051] S3-2, the adsorbent matrix is mixed with a chitosan-lignin mixed solution (the mass ratio of chitosan to lignin in the chitosan-lignin mixed solution is 1:1, and the solid content is 20%) in a mass ratio of 9:1, stirred until a uniform plastic mud is formed, then extruded into a strip-shaped adsorbent blank with a length of 5 mm by using a screw extrusion molding machine through a circular mold with a diameter of 3 mm, and naturally air-dried;

[0052] S3-3, the blank is placed in a DBD plasma reactor, helium gas is introduced at a flow rate of 50 mL / min, the power is controlled at 500 W, and the blank is treated for 20 min;

[0053] S3-4, a 0.5 mol / L Ce(NO3)3 solution is prepared, the blank treated by plasma is immersed in the solution, ultrasonic immersion is carried out for 30 min, then taken out and drained, then dried at 70 DEG C for 4 h, then placed in a tube furnace, heated to 400 DEG C at a rate of 2 DEG C / min under N2 atmosphere, kept for 2 h, and then naturally cooled to room temperature;

[0054] S4, green hydrogen (hydrogen produced by electrolysis of water, hydrogen purity ≥ 99.99%) is added to the above refined gas, the hydrogen-nitrogen ratio is adjusted to 2.8:1, and then the mixture is sent into an ammonia synthesis tower after being pressurized to 15 MPa by a compressor, and ammonia is synthesized under the action of a carbon nanotube supported ruthenium-based catalyst;

[0055] The preparation of the carbon nanotube loaded ruthenium-based catalyst comprises the following steps:

[0056] S4-1, the multi-walled carbon nanotubes are placed in a DBD plasma reactor, and Ar / O2 mixed gas is introduced for plasma treatment, the volume ratio of Ar and O2 in the Ar / O2 mixed gas is 95:5, the gas flow rate is controlled at 40 mL / min, the power is 300 W, and the treatment time is 20 min;

[0057] S4-2, the multi-walled carbon nanotubes after plasma treatment are ultrasonically dispersed in ethanol to prepare a 0.1 g / mL multi-walled carbon nanotube suspension;

[0058] RuCl3·3H2O is dissolved in ethanol to prepare a 0.1 mol / L ruthenium precursor solution, and 0.5 wt% HCOOH is added as a reduction promoter;

[0059] S4-3, the multi-walled carbon nanotube suspension and the ruthenium precursor solution are pumped into a Y-shaped microchannel of a microfluidic reactor, the flow rate ratio is controlled at 1:3 (CNT liquid: ruthenium liquid), directional mixing is carried out in a laminar flow state, a 1 MHz ultrasonic standing wave field is turned on, the amplitude is set at 10 μm, the ruthenium ions are precisely adsorbed on the defect sites of the multi-walled carbon nanotubes by using the standing wave pressure node, and the residence time of the mixed solution in the microchannel is controlled at 120-130 s, so that the adsorption rate of the ruthenium ions reaches 99%;

[0060] S4-4, the CNT-ruthenium precursor mixture after microfluidic loading is transferred to a supercritical CO2 reactor, supercritical CO2 (density 0.8 g / cm 3 ) is introduced after sealing, the pressure in the reactor is increased to 15 MPa, the temperature is controlled at 40℃, the reaction is carried out for 1.5 h, the pressure is reduced to normal pressure at a speed of 0.5 MPa / min, the solid product is collected, and vacuum drying is carried out at 55℃ for 2 h;

[0061] S4-5, the reduced Ru / CNTs are dispersed in ethanol, KNO3 and pyrrole monomer are added, stirring is carried out for 30 min, 0.1 mol / L FeCl3 solution is added dropwise to initiate polymerization, room temperature reaction is carried out for 2 h, and a poly-pyrrole-K + film coated CNTs are formed;

[0062] The coated sample is transferred to a tube furnace, heated to 600℃ at a rate of 5℃ / min under an argon atmosphere (flow rate 40 mL / min), and held for 1.5 h, the poly-pyrrole is carbonized to form a nitrogen-doped carbon shell, and K + is confined in the carbon shell.

[0063] Example 2

[0064] An environmentally friendly synthetic ammonia production process comprises the following steps:

[0065] S1, the raw coal is dried and crushed to 80 mesh, 2% of the mass fraction of the composite combustion improver CaO-Fe2O3-K2CO3 (the mass ratio of the three is 6:3:1) is added and uniformly mixed, then the purity is ≥99.6% oxygen is sent into the 6.5MPa pressure grade aerospace furnace semi-waste pot gasification furnace according to the oxygen-coal ratio 1:0.9, 1500℃ treatment for 5s, to generate crude synthesis gas;

[0066] S2, the crude synthesis gas is treated by the Venturi scrubber, enters the sulfur-tolerant isothermal shift system, and is subjected to two-stage isothermal shift under the action of Co-Mo catalyst, and the CO content at the outlet is controlled to be ≤0.6%;

[0067] The specific parameters of two-stage isothermal shift are as follows:

[0068] The first stage shift: the catalyst type is K8-11, the operating temperature is 260℃, the steam / CO ratio is 2, and the outlet CO concentration is ≤3%;

[0069] The second stage shift: the catalyst type is QDB-04, the operating temperature is 210℃, the steam / CO ratio is 1.3, and the outlet CO concentration is ≤0.6%;

[0070] S3, the crude synthesis gas treated in step S2 is introduced into a four-tower PSA system, CO2 and sulfides are removed under the conditions of operating pressure 2.5MPa and adsorption temperature 50℃, H2 and N2 mixed gas is obtained, and then introduced into a cryogenic separation system, refined gas is obtained under the conditions of-180℃ and 0.7MPa;

[0071] The adsorption cycle of the activated carbon-molecular sieve composite adsorbent is 60-90s;

[0072] The preparation of the activated carbon-molecular sieve composite adsorbent includes the following steps:

[0073] S3-1, the activated carbon: 13X molecular sieve: rice husk diatom = 3:7:2 mass ratio, is added to deionized water according to the solid-liquid ratio of 1:6, stirred and mixed, then 2% of the total mass of the raw material cellulase is added, the enzyme hydrolysis reaction is carried out at 50℃ and 150rpm stirring speed for 4.5h, then vacuum freeze drying is carried out at-50℃ and vacuum degree 10Pa for 11h, and the adsorbent matrix is obtained after drying and passing through 80 mesh screen;

[0074] S3-2, the adsorbent base and chitosan-lignin mixed solution (the mass ratio of chitosan to lignin in the chitosan-lignin mixed solution is 1:1, and the solid content is 20%) are mixed according to a mass ratio of 9:1, stirred to form a uniform plastic mud, and then extruded into a 6mm long strip-shaped adsorbent blank by using a screw extrusion molding machine and a 3mm diameter circular mold, and naturally air-dried;

[0075] S3-3, the blank is placed in a DBD plasma reactor, helium gas is introduced, the amount of helium gas introduced is 55mL / min, the power is controlled at 500W, and the treatment time is 22min;

[0076] S3-4, a 0.55mol / L Ce(NO3)3 solution is prepared, the plasma-treated blank is immersed in the solution, ultrasonic immersion is performed for 35min, after completion, the blank is taken out and drained, then dried at 75℃ for 4.5h, then placed in a tube furnace, heated to 400℃ at a rate of 2.5℃ / min under N2 atmosphere, and then naturally cooled to room temperature after holding for 2.5h;

[0077] S4, green hydrogen (hydrogen produced by electrolysis of water, hydrogen purity ≥99.99%) is added to the above refined gas, the hydrogen / nitrogen ratio is adjusted to 2.9:1, and then sent into an ammonia synthesis tower after being pressurized to 15MPa by a compressor, and ammonia is synthesized under the action of a carbon nanotube supported ruthenium-based catalyst;

[0078] The preparation of the carbon nanotube supported ruthenium-based catalyst comprises the following steps:

[0079] S4-1, the multi-walled carbon nanotubes are placed in a DBD plasma reactor, and Ar / O2 mixed gas is introduced for plasma treatment, the volume ratio of Ar to O2 in the Ar / O2 mixed gas is 95:5, the gas flow rate is controlled at 45mL / min, the power is 300W, and the treatment time is 25min;

[0080] S4-2, the plasma-treated multi-walled carbon nanotubes are ultrasonically dispersed in ethanol to prepare a 0.1g / mL multi-walled carbon nanotube suspension;

[0081] RuCl3·3H2O is dissolved in ethanol to prepare a 0.1mol / L ruthenium precursor solution, and 0.5wt% HCOOH is added as a reduction promoter;

[0082] S4-3, the multi-walled carbon nanotube suspension and the ruthenium precursor solution are pumped into the Y-shaped microchannel of the microfluidic reactor respectively, the flow rate ratio is 1:3 (CNT solution: ruthenium solution), directional mixing is carried out under laminar flow state, the 1MHz ultrasonic standing wave field is turned on, the amplitude is set to 10μm, the ruthenium ions are precisely adsorbed on the defect sites of the multi-walled carbon nanotubes by using the standing wave pressure node, the residence time of the mixed solution in the microchannel is controlled to be 125s, and the ruthenium ion adsorption rate reaches 99%;

[0083] S4-4, the microfluidic loaded CNT-ruthenium precursor mixture is transferred to a supercritical CO2 reaction kettle, after sealing, supercritical CO2 (density 0.8g / cm 3 ) is introduced, the pressure in the kettle is increased to 15MPa, the temperature is controlled at 40℃, after 2h of reaction, the pressure is reduced to normal pressure at a speed of 0.5MPa / min, the solid product is collected, and vacuum drying is carried out at 60℃ for 2.5h;

[0084] S4-5, the above reduced Ru / CNTs are dispersed in ethanol, KNO3 and pyrrole monomer are added, after stirring for 35min, 0.1mol / L FeCl3 solution is added dropwise to initiate polymerization, and the reaction is carried out at room temperature for 2.5h to form poly-pyrrole-K + film coated CNTs;

[0085] The coated sample is transferred to a tube furnace, heated to 600℃ at a rate of 5℃ / min under an argon atmosphere (flow rate 40mL / min), and kept for 2h, the poly-pyrrole is carbonized to form a nitrogen-doped carbon shell, and K + is confined in the carbon shell.

[0086] Example 3

[0087] An environment-friendly synthetic ammonia production process, comprising the following steps:

[0088] S1, the raw coal is dried and crushed to 120 mesh, 3% of the composite combustion improver CaO-Fe2O3-K2CO3 (the mass ratio of the three is 6:3:1) is added and uniformly mixed, then the mixture is sent into a space furnace semi-waste pot gasifier of 6.5MPa pressure grade together with oxygen with purity ≥99.6% at an oxygen-coal ratio of 1:1 for gasification treatment, treated at 1600℃ for 6s to generate crude synthesis gas;

[0089] S2, after the crude synthesis gas is dedusted by a Venturi scrubber, it enters a sulfur-tolerant isothermal shift system, and two-stage isothermal shift is carried out under the action of Co-Mo catalyst, and the CO content at the outlet is controlled to be ≤0.6%;

[0090] The specific parameters of the two-stage isothermal shift are as follows:

[0091] First stage shift: catalyst type K8-11, operating temperature 280℃, steam / CO ratio 2.2, outlet CO concentration ≤3%;

[0092] Second stage shift: catalyst type QDB-04, operating temperature 220℃, steam / CO ratio 1.5, outlet CO concentration ≤0.6%;

[0093] S3, the crude synthetic gas treated in step S2 enters a four-tower PSA system under the conditions of an operating pressure of 3 MPa and an adsorption temperature of 60℃ to remove CO2 and sulfides, and H2 and N2 mixed gas is obtained, which then enters a cryogenic separation system to be refined and purified under the conditions of -180℃ and 1 MPa, and refined gas is obtained;

[0094] An activated carbon-molecular sieve composite adsorbent is used, and the adsorption cycle is 90s;

[0095] The preparation of the activated carbon-molecular sieve composite adsorbent includes the following steps:

[0096] S3-1, activated carbon: 13X molecular sieve: rice hull diatom = 3:7:2 in mass ratio, is added to deionized water at a solid-liquid ratio of 1:7, is stirred and mixed, then 2% of cellulase based on the total mass of the raw materials is added, and enzymatic hydrolysis is carried out at 55℃ and a stirring speed of 200 rpm for 4-5h, followed by vacuum freeze drying at -50℃ and a vacuum degree of 10 Pa for 12h, and then the adsorbent matrix is obtained by sieving through an 80-mesh sieve after drying;

[0097] S3-2, the adsorbent matrix is mixed with a chitosan-lignin mixed solution (the mass ratio of chitosan to lignin in the chitosan-lignin mixed solution is 1:1, and the solid content is 20%) at a mass ratio of 9:1, and is stirred until a uniform plastic mud is formed, and then is extruded into a strip-shaped adsorbent blank with a length of 8mm by using a screw extrusion molding machine and passing through a circular mold with a diameter of 3mm, and is naturally air-dried;

[0098] S3-3, the blank is placed in a DBD plasma reactor, helium gas is introduced at a flow rate of 60mL / min, the power is controlled at 500W, and the blank is treated for 25min;

[0099] S3-4, a 0.6mol / L Ce(NO3)3 solution is prepared, the blank treated by plasma is immersed in the solution, ultrasonic immersion is performed for 40min, the blank is taken out and drained after completion, then is dried at 80℃ for 5h, is placed in a tube furnace, is heated to 400℃ at a rate of 3℃ / min under a N2 atmosphere, is kept at 400℃ for 3h, and is naturally cooled to room temperature;

[0100] S4, green hydrogen (hydrogen produced by electrolysis of water, hydrogen purity ≥ 99.99%) is added to the refined gas, the hydrogen-nitrogen ratio is adjusted to 3:1, and the mixture is pressurized to 15 MPa by a compressor and then sent to an ammonia synthesis tower, where ammonia is synthesized under the action of a carbon nanotube-supported ruthenium-based catalyst;

[0101] The preparation of the carbon nanotube-supported ruthenium-based catalyst comprises the following steps:

[0102] S4-1, the multi-walled carbon nanotubes are placed in a DBD plasma reactor, and Ar / O2 mixed gas is introduced for plasma treatment, the volume ratio of Ar to O2 in the Ar / O2 mixed gas is 95:5, the gas flow rate is controlled at 50 mL / min, the power is 300 W, and the treatment time is 30 min;

[0103] S4-2, the multi-walled carbon nanotubes after plasma treatment are ultrasonically dispersed in ethanol to prepare a 0.1 g / mL multi-walled carbon nanotube suspension;

[0104] RuCl3·3H2O is dissolved in ethanol to prepare a 0.1 mol / L ruthenium precursor solution, and 0.5 wt% HCOOH is added as a reduction promoter;

[0105] S4-3, the multi-walled carbon nanotube suspension and the ruthenium precursor solution are pumped into a Y-shaped microchannel of a microfluidic reactor at a flow rate ratio of 1:3 (CNT liquid: ruthenium liquid), and directional mixing is carried out under laminar flow, a 1 MHz ultrasonic standing wave field is turned on, the amplitude is set to 10 μm, the ruthenium ions are precisely adsorbed on the defect sites of the multi-walled carbon nanotubes by using the standing wave pressure node, the residence time of the mixed solution in the microchannel is controlled at 130 s, and the ruthenium ion adsorption rate is ensured to reach 99%;

[0106] S4-4, the CNT-ruthenium precursor mixture after microfluidic loading is transferred to a supercritical CO2 reaction kettle, supercritical CO2 (density 0.8 g / cm 3 ) is introduced after sealing, the pressure in the kettle is increased to 15 MPa, the temperature is controlled at 40℃, and after 2.5 h of reaction, the pressure is reduced to atmospheric pressure at a rate of 0.5 MPa / min, the solid product is collected, and vacuum drying is carried out at 65℃ for 3 h;

[0107] S4-5, the reduced Ru / CNTs are dispersed in ethanol, KNO3 and pyrrole monomer are added, stirring is carried out for 40 min, 0.1 mol / L FeCl3 solution is added dropwise to initiate polymerization, and room temperature reaction is carried out for 3 h to form poly-pyrrole-K + thin film coated CNTs;

[0108] The coated sample is transferred to a tube furnace, heated to 600℃ at a rate of 5℃ / min under an argon atmosphere (flow rate 40 mL / min), and held for 2.5 h, and the poly-pyrrole is carbonized to form a nitrogen-doped carbon shell, and K+ confined in the carbon shell.

[0109] Comparative Example 1

[0110] Comparative Example 1 is compared with Example 2, no composite combustion improver is added in step S1, and other steps are the same as Example 2.

[0111] Comparative Example 2

[0112] Comparative Example 2 is compared with Example 2, the two-stage isothermal shift in step S2 is replaced by the first-stage shift, and the second-stage shift is omitted, and other steps are the same as Example 2.

[0113] Comparative Example 3

[0114] Comparative Example 3 is compared with Example 2, the activated carbon-molecular sieve composite adsorbent in step S3 is replaced by pure 13X molecular sieve, and other steps are the same as Example 2.

[0115] Comparative Example 4

[0116] Comparative Example 4 is compared with Example 2, in the preparation of carbon nanotube loaded ruthenium-based catalyst, step S4-1 is omitted, and other steps are the same as Example 2.

[0117] Test detection

[0118] 1. Detection method

[0119] Gas composition: H2, CO, CO2, N2 and CH4 contents are detected by gas chromatograph (Agilent 7890A);

[0120] Sulfide: H2S is measured by iodine quantity method, and COS is measured by gas chromatograph-sulfur chemiluminescence detector (GC-SCD);

[0121] Tar content: isopropanol absorption-weight method;

[0122] Ammonia conversion rate: dilute sulfuric acid absorption-acid-base titration method;

[0123] Carbon emission: carbon balance method is used to calculate the CO2 emission per unit of ammonia (kg / t).

[0124] 2. Detection results

[0125] The test comparison data are shown in Table 1 below.

[0126] Table 1 Comparison table of key performance and environmental protection index detection of each example and comparative example of the environmentally friendly synthetic ammonia production process

[0127] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Effective gas (H2+CO) content of the crude synthesis gas (%) 88.5 89.2 90.1 78.5 89.0 89.1 89.2 Raw syngas tar content (mg / m 3 ) 15.2 12.5 10.8 45.8 12.6 12.7 12.5 Shift outlet CO content (%) 0.58 0.52 0.49 0.55 2.8 0.53 0.52 PSA export CO2 removal rate (%) 99.1 99.3 99.5 99.2 99.3 92.5 99.3 PSA outlet sulfide removal rate (%) 99.8 99.9 99.9 99.8 99.9 95.2 99.9 Ammonia single-pass conversion rate (%) 24.8 25.6 26.2 24.2 23.8 25.5 19.3 Catalyst activity retention rate (after 100 h, %) 95.8 96.5 97.2 95.8 95.2 90.2 62.5 Unit ammonia CO2 emission (kg / t) 1280 1250 1230 1420 1320 1260 1255

[0128] From the above table 1, it can be concluded that the effective gas content in the crude synthesis gas of Comparative Example 1 is reduced by 12% and the tar content is increased by 266% without adding the composite combustion improver, which shows that the composite combustion improver can synergistically improve the gasification efficiency and reduce the generation of by-products; the ammonia single-pass conversion rate is reduced by 9.7% in Comparative Example 2 in which the secondary shift is omitted and the outlet CO is increased from 0.52% to 2.8%, which shows that the setting of two-stage shift can realize deep conversion of CO and effectively avoid the poisoning of the synthesis catalyst by CO; the CO2 removal rate is reduced from 99.3% to 92.5% and the sulfide removal rate is reduced from 99.9% to 95.2% in Comparative Example 3 in which the pure 13X molecular sieve is used to replace the composite adsorbent, which shows that the selectivity of the pure 13X molecular sieve to complex impurities is insufficient compared with the composite adsorbent; the ammonia single-pass conversion rate is reduced by 24.6% and the activity retention rate is reduced by 35.2% in Comparative Example 4 in which the carbon nanotube plasma treatment is omitted, which shows that the plasma treatment can enhance the anchoring effect of ruthenium ions and carbon nanotubes and has high activity.

[0129] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An environmentally friendly synthetic ammonia production process, characterized in that, Includes the following steps: S1. After drying the raw coal, crush it to 80~120 mesh, add 1~3% of composite combustion aid and mix evenly. Then, feed it into a 6.5MPa pressure-rated aerospace furnace semi-waste boiler gasifier with oxygen purity ≥99.6% at an oxygen-to-coal ratio of 1:0.8~1 for gasification treatment to generate crude syngas. The composite combustion aid is CaO-Fe2O3-K2CO3; S2. After the crude syngas is dedusted by a Venturi scrubber, it enters a sulfur-resistant isothermal shift system, where a two-stage isothermal shift is performed under the action of a Co-Mo catalyst, controlling the outlet CO content to ≤0.6%. The specific parameters of the two-stage isothermal transformation are as follows: First-stage conversion: catalyst type K8-11, operating temperature 240~280℃, steam / CO ratio 1.8~2.2, outlet CO concentration ≤3%; Second-stage conversion: catalyst type QDB-04, operating temperature 200~220℃, steam / CO ratio 1.2~1.5, outlet CO concentration ≤0.6%; S3. The crude syngas processed in step S2 is fed into a four-tower PSA system. CO2 and sulfides are removed under an operating pressure of 2-3 MPa and an adsorption temperature of 40-60℃ to obtain a mixed gas of H2 and N2. The gas is then fed into a cryogenic separation system and purified by distillation at -180℃ and 0.5-1 MPa to obtain refined gas. The four-tower PSA system uses activated carbon-molecular sieve composite adsorbent; The preparation of the activated carbon-molecular sieve composite adsorbent includes the following steps: S3-1. Add activated carbon, 13X molecular sieve, and rice husk diatomaceous earth in a mass ratio of 3:7:2 to deionized water at a solid-liquid ratio of 1:5~7. After stirring and mixing, add 2% of the total mass of cellulase and carry out enzymatic hydrolysis at 45~55℃ and 100~200rpm for 4~5h. Then freeze-dry under vacuum at -50℃ and 10Pa for 10~12h. After drying, pass through an 80-mesh sieve to obtain the adsorbent matrix. S3-2. Mix the adsorbent matrix with the chitosan-lignin mixed solution at a mass ratio of 9:1 and stir until a uniform and plastic slurry is formed. Use a screw extruder to extrude the material through a 3mm diameter circular mold. Cut the material into strip-shaped adsorbent blanks with a length of 5-8mm and let them air dry. S3-3. Place the billet in the DBD plasma reactor, introduce helium gas, and perform plasma treatment. S3-4. Prepare a 0.5~0.6mol / L Ce(NO3)3 solution, immerse the plasma-treated green body in the solution, and ultrasonically impregnate it for 30~40min. After completion, remove it and drain it. Then dry it at 70~80℃ for 4~5h. Then place it in a tube furnace and heat it to 400℃ at 2~3℃ / min under N2 atmosphere. Hold it at this temperature for 2~3h and then let it cool naturally to room temperature. S4. Add green hydrogen to the above refined gas, adjust the hydrogen-nitrogen ratio to 2.8~3:1, pressurize it to 15MPa by the compressor and send it to the ammonia synthesis tower to synthesize ammonia under the action of ruthenium-based catalyst supported by carbon nanotubes. The preparation of the carbon nanotube-supported ruthenium-based catalyst includes the following steps: S4-1. Place multi-walled carbon nanotubes in a DBD plasma reactor and introduce Ar / O2 mixed gas for plasma treatment. S4-2. The plasma-treated multi-walled carbon nanotubes were ultrasonically dispersed in ethanol to prepare a 0.1 g / mL multi-walled carbon nanotube suspension. RuCl3·3H2O was dissolved in ethanol to prepare a 0.1 mol / L ruthenium precursor solution, and 0.5 wt% HCOOH was added as a reduction promoter. S4-3. Pump the multi-walled carbon nanotube suspension and the ruthenium precursor solution into the Y-shaped microchannel of the microjet reactor, control the flow rate ratio of carbon nanotube liquid to ruthenium liquid to be 1:3, turn on the 1MHz ultrasonic standing wave field, set the amplitude to 10μm, and control the residence time of the mixture in the microchannel to be 120~130s. S4-4. The microfluidically loaded carbon nanotube-ruthenium precursor mixture was transferred to a supercritical CO2 reactor, sealed, and supercritical CO2 was introduced to raise the pressure inside the reactor to 15 MPa. The temperature was controlled at 40 °C. After the reduction reaction was carried out in the supercritical CO2 atmosphere for 1.5~2.5 h, the pressure was reduced to atmospheric pressure at a rate of 0.5 MPa / min. The solid product Ru / carbon nanotube was collected and vacuum dried at 55~65 °C for 2~3 h. S4-5. Disperse the vacuum-dried Ru / carbon nanotubes in ethanol, add KNO3 and pyrrole monomer, stir for 30-40 min, then add 0.1 mol / L FeCl3 solution dropwise to initiate polymerization. React at room temperature for 2-3 h to form polypyrrole-K + Thin-film coated carbon nanotubes; The coated sample was transferred to a tube furnace and heated to 600°C at a rate of 5°C / min under an argon atmosphere, and held at that temperature for 1.5–2.5 h. This carbonized the polypyrrole to form a nitrogen-doped carbon shell. + It is confined within a carbon shell.

2. The environmentally friendly synthetic ammonia production process according to claim 1, characterized in that, In step S1, the mass ratio of CaO, Fe2O3, and K2CO3 in the composite combustion aid is 6:3:

1. The temperature of the gasification process is 1400~1600℃, and the gasification time is 4~6s.

3. The environmentally friendly synthetic ammonia production process according to claim 1, characterized in that, The adsorption cycle of the four-tower PSA system described in step S3 is 60~90s.

4. The environmentally friendly synthetic ammonia production process according to claim 1, characterized in that, In step S3-2, the chitosan-lignin mixed solution has a chitosan to lignin mass ratio of 1:1 and a solid content of 20%.

5. The environmentally friendly synthetic ammonia production process according to claim 1, characterized in that, The helium gas flow rate in step S3-3 is 50~60 mL / min, the plasma treatment power is controlled at 500 W, and the treatment time is 20~25 min.

6. The environmentally friendly synthetic ammonia production process according to claim 1, characterized in that, The green hydrogen mentioned in step S4 is produced by electrolysis of water, and the hydrogen purity is ≥99.99%.

7. The environmentally friendly synthetic ammonia production process according to claim 1, characterized in that, In step S4-1, the volume ratio of Ar to O2 in the Ar / O2 mixed gas during plasma treatment is 95:

5. The gas flow rate was controlled at 40-50 mL / min, the power at 300 W, and the processing time at 20-30 min.