Recycling method of industrial natural gas waste gas containing carbon dioxide

Abstract

The invention belongs to the technical field of environmental protection, and particularly relates to a recycling method of industrial natural gas waste gas containing carbon dioxide. The industrial natural gas waste gas containing carbon dioxide is sequentially subjected to dust removal through a dust remover, cooling, condensation and water removal through a condenser, nitrogen and sulfide removal through a photocatalytic purifier and oxygen removal through an oxygen removal tank, and purified waste gas is obtained after treatment; hydrazine hydrate and softened water are input into a premixer to be premixed, meanwhile, waste gas purification gas is introduced, and premixed liquid is obtained; an exhaust port of the premixer is connected with an absorption tank to absorb residual carbon dioxide, and then drying, collecting and compressing are performed to obtain nitrogen; and respectively pumping the premixed solution and a cyanamide aqueous solution into a Taylor-type tubular reactor, injecting a waste gas purification gas into the Taylor-type tubular reactor, and carrying out a reaction to obtain the aminoguanidine carbonate. According to the method, CO2 in the waste gas is recycled to produce an aminoguanidine carbonate product, high economic benefits are obtained, and nitrogen is provided for production after treatment.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a method for recycling and utilizing industrial natural gas waste containing carbon dioxide. Background Technology

[0002] Currently, factories use steam boilers to provide steam, hot water, and other heat sources for daily production, mainly by burning natural gas. The large amount of carbon dioxide produced by combustion is released into the atmosphere instead of being utilized in a high-value manner, which cannot generate economic benefits and will also lead to global warming.

[0003] Liquid amine absorption (commonly known as "amine washing") is currently the most mature and only commercially viable carbon dioxide capture technology. Essentially, it involves a reversible chemical reaction between acidic gas and an alkaline absorbent, forming unstable salts such as carbonates, bicarbonates, or carbamates that decompose and release CO2, thus achieving carbon capture and recovery. It is a widely used technology in natural gas processing, chemical industries, and coal-fired power plants. However, despite its maturity, liquid amine absorption suffers from several problems, including: high energy consumption, solvent degradation and loss, absorbent oxidative degradation, equipment corrosion, environmental impact, low efficiency for low-concentration CO2 capture, and high power generation costs. These are detailed below. (1) High energy consumption, solvent degradation and loss: This is the biggest obstacle restricting the large-scale application of amine absorption, especially for carbon capture and storage (CCS); Regeneration energy consumption is huge: The amine-rich solution after absorbing CO2 needs to be heated to 100-120°C to desorb pure CO2 and regenerate the solvent. This reboiler heating process requires a large amount of steam, resulting in extremely high energy consumption. Solvent degradation and loss: During high-temperature regeneration, amine molecules themselves decompose due to heat, generating a variety of degradation products; impurities such as oxygen (O2), sulfur dioxide (SO2), and nitrogen oxides (NOx) in the raw gas will undergo irreversible chemical reactions with the amine, generating degradation products such as thermally stable salts; all of these will lead to a reduction in effective components and the generation of by-products.

[0004] (2) Equipment corrosion and high cost: Amine solutions themselves and their degradation products (especially thermally stable salts) are corrosive to carbon steel equipment; Under high CO2 concentrations and high temperatures, corrosion problems are particularly severe in areas with high temperature and high CO2 concentration, such as regeneration towers and reboilers. Increased costs: To combat corrosion, critical equipment requires the use of more expensive corrosion-resistant materials (such as stainless steel) and the addition of costly corrosion inhibitors, which increases initial investment and maintenance costs.

[0005] (3) Environmental pollution: This process is not entirely "green" technology; it also causes environmental pollution. Chemical waste: Thermally stable salts and non-renewable solvents produced during degradation need to be treated as hazardous waste; improper disposal will pollute the environment. Potential air pollution: As mentioned earlier, volatile amines may enter the atmosphere. Some degradation products of amines (such as nitrosamines) are considered potentially carcinogenic, raising health concerns. Water consumption: The system's cooling, water washing, and other processes require a large amount of water resources; Amine absorption is currently the "main force" in carbon capture, but its inherent economic and technological shortcomings make it not a perfect solution. Therefore, a large number of studies at home and abroad are dedicated to finding more environmentally friendly, efficient and energy-saving technologies for recovering carbon dioxide-containing industrial natural gas waste gas. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention patent is to provide a method for recycling and utilizing carbon dioxide industrial waste gas, which improves economic efficiency, reduces carbon emissions, and has low energy consumption and low cost.

[0007] This invention provides a method for recovering and utilizing industrial natural gas containing carbon dioxide, comprising the following steps: (1) The industrial natural gas waste gas containing carbon dioxide is sequentially passed through a dust collector for dust removal, a condenser for cooling and condensation to remove water, a photocatalytic purifier for nitrogen and sulfides removal, and a deoxygenation tank for oxygen removal. After treatment, the waste gas is purified. (2) Hydrazine hydrate and softened water are fed into a premixer for premixing, and the waste gas purification gas obtained in step (1) is introduced at the same time to obtain a premixed liquid; the exhaust port of the premixer is connected to a sodium hydroxide absorption tank to absorb the remaining carbon dioxide, and then dried by a drying device. The dried gas is collected and compressed to obtain nitrogen. (3) The premixed liquid obtained in step (2) and the cyanamide aqueous solution are pumped into a Taylor tubular reactor respectively. The waste gas purification gas obtained in step (1) is injected into the Taylor tubular reactor to react and obtain aminoguanidine carbonate.

[0008] In step (2), the exhaust port of the premixer is connected to a sodium hydroxide absorption tank to absorb the remaining carbon dioxide. The absorbed gas is the carbon dioxide remaining in the unreacted waste gas purification gas. The dried gas is collected and compressed to obtain nitrogen, which can be recycled and reused for production.

[0009] We analyzed the exhaust gas from the natural gas boiler, and its main components are as follows: This invention utilizes the company's aminoguanidine project. Through extensive experimentation, it successfully recovered carbon dioxide from tail gas using aminoguanidine solution to prepare aminoguanidine carbonate, while simultaneously obtaining nitrogen. The invention first employs a suitable tail gas treatment method to remove impurities such as water vapor, nitrogen sulfides, and oxygen from natural gas tail gas that affect product quality and yield. Then, using an aminoguanidine solution, carbon dioxide in the tail gas is absorbed and reacted, yielding both aminoguanidine carbonate and industrial-grade nitrogen. This invention absorbs carbon dioxide from pretreated natural gas tail gas, simultaneously preparing economically valuable aminoguanidine carbonate and obtaining nitrogen for production needs—a multi-benefit approach.

[0010] Before purification, the CO2 content in the industrial natural gas exhaust gas is 9-15%. The purified exhaust gas obtained in step (1) of this invention mainly contains nitrogen and carbon dioxide, with nitrogen (80-90%) and carbon dioxide (10-20%) as the main components. After purification, the CO2 content in the gas is 10-20%, and SO2, NOx, CO, O2, and H2O are all <1 ppm. Separation of nitrogen and carbon dioxide requires special equipment. This invention does not require special equipment to completely separate nitrogen and carbon dioxide. Instead, it cleverly utilizes the company's aminoguanidine project to absorb carbon dioxide in the tail gas, thereby obtaining aminoguanidine carbonate and industrial nitrogen. The yield of aminoguanidine carbonate is still ≥95%, which is environmentally friendly, energy-efficient, and low-cost.

[0011] Preferably, the catalyst in the photocatalytic purifier is a titanium dioxide-based catalyst supported on 0.5-2 wt% metallic Cu, 1-3 wt% metallic Ni, and 5-10 at% non-metallic N. The purification conditions of the photocatalytic purifier are: visible LED light irradiation at 420-450 nm and a gas flow rate (GHSV) of 3000-5000 h⁻¹. -1 This ensures that the gas and catalyst are in full contact, thus effectively removing nitrogen sulfides.

[0012] Preferably, the Cu:Ni mass ratio is 1:2, and the N doping is 7 at%, which results in the best removal effect of nitrogen sulfides.

[0013] Preferably, in step (1), a mixed solution of sodium sulfite with a mass fraction of 2% and sodium bisulfite with a mass fraction of 2% is added to the deoxygenation tank. This mixed solution has the best effect on removing oxygen from the exhaust gas of the present invention.

[0014] Preferably, in step (3), the pH value of the reaction system is maintained between 5.0 and 5.5 during the reaction, and the reaction solution is cooled and crystallized to obtain the product aminoguanidine carbonate.

[0015] Preferably, step (2) is as follows: hydrazine hydrate and softened water are input into the premixer, and the waste gas purification gas obtained in step (1) is simultaneously introduced into the premixer. The pumping pressure of the waste gas purification gas is controlled between 0.10MPa and 0.15MPa, and the pH of the mixture is stabilized at 5.0 to 5.5. Premixing is performed, and a premixed liquid is obtained after premixing. The concentration of hydrazine hydrate is 80 to 81%, the mass ratio of hydrazine hydrate to softened water is 1.0:1.0 to 3.0, the premixing time is 2.5 to 5 hours, and the premixing temperature is 10 to 40°C. The exhaust port of the premixer is connected to a sodium hydroxide absorption tank to absorb the remaining carbon dioxide, and then dried by a drying device. The dried gas is collected and compressed to obtain nitrogen for production use.

[0016] Preferably, step (3) is as follows: the premixed liquid obtained in step (2) and the cyanamide aqueous solution are pumped into a Taylor tubular reactor respectively. The flow rate of the cyanamide aqueous solution in the Taylor tubular reactor is 3L~4L / min, the flow rate of the premixed liquid in the Taylor tubular reactor is 5L / min, the inner cylinder rotation speed of the Taylor tubular reactor is 500-1000 rpm, and the Taylor number (Ta) is ≥50. Waste gas purification gas injection ports are set at the inlet, middle and outlet of the Taylor tubular reactor respectively. Each injection port contains 3~5 air inlets (compared to 1 air inlet, 3~5 air inlets are set to make the waste gas purification gas more fully dispersed). The waste gas purification gas obtained in step (1) is injected into the Taylor tubular reactor through the air inlets by the pressure reducing valve. The pressure of the front injection port (the inlet injection port of the reactor) is set between 0.18~0.20MPa, and the pressure of the middle injection port (the middle injection port of the reactor) is set between 0.18~0.20MPa. The pressure is set between 0.15 and 0.17 MPa, and the pressure at the downstream inlet (reactor outlet inlet) is set between 0.10 and 0.13 MPa. The pH of the reaction system is maintained between 5.0 and 5.5, the total residence time of the reaction liquid is 2.5 to 5 hours, and the reaction temperature is 40 to 50°C. The resulting reaction liquid is rapidly cooled to 0 to 5°C at a rate of 10 to 20°C / min via a tubular heat exchanger and then enters a stainless steel reactor for crystallization. Crystallization takes place at 0 to 5°C for 1 to 3 hours. After crystallization, the liquid is filtered, washed, and dried to obtain the product aminoguanidine carbonate. The exhaust port of the Taylor tubular reactor is connected to the sodium hydroxide absorption tank in step two to absorb the remaining carbon dioxide, which is then dried by a drying device. The dried gas is collected and compressed to obtain nitrogen for production use.

[0017] While existing technologies disclose the direct reaction of hydrazine hydrate and cyanamide to produce aminoguanidine carbonate, this requires a 100% excess of cyanamide and yields only 80%-90%, resulting in high cost and low yield. Using purified industrial natural gas waste gas for the reaction further reduces yield and purity. This invention has found that directly reacting hydrazine hydrate and cyanamide releases a large amount of heat. Furthermore, the strong alkalinity of hydrazine hydrate causes cyanamide to polymerize into dicyandiamide, preventing the more expensive cyanamide from fully participating in the preparation of aminoguanidine, leading to low yield and high cost. Moreover, cyanamide exhibits poor stability under neutral / alkaline conditions and readily dimerizes into dicyandiamide. Industrial hydrazine hydrate operates at a pH between 8 and 9, at which point cyanamide is unstable and readily polymerizes into dicyandiamide. In this invention, hydrazine hydrate and softened water are first fed into a premixer via a proportioning pump for premixing and dilution. After premixing and dilution, the waste gas purification gas obtained in step (1) is pumped into the premixer. The pumping pressure of the waste gas purification gas obtained in step (1) is controlled between 0.10 MPa and 0.15 MPa. The CO2 flow rate is adjusted by online pH feedback to stabilize the pH of the mixture at 5.0 to 5.5 for premixing. The premixed liquid and the cyanamide aqueous solution are then pumped into a Taylor tubular reactor, and the waste gas purification gas obtained in step (1) is injected in stages for reaction. By first premixing the waste gas purified gas obtained in step (1) with hydrazine hydrate and softened water, and controlling the pH to be stable at 5.0~5.5, cyanamide can be stably present in the reaction system, which has the effect of improving yield and reducing side reactions. Then, a Taylor tubular reactor is used. By selecting a suitable waste gas purified gas injection method, cyanamide has high stability in this reaction system, avoiding polymerization into dicyandiamide. The same amount of cyanamide and hydrazine hydrate can be reacted to generate a certain amount of aminoguanidine carbonate, reducing the amount of high-cost cyanamide used, reducing production costs, and improving yield. Combined with Taylor vortex to enhance mass transfer, continuous reaction is achieved, improving product purity, yield and carbon dioxide utilization. The absorption of carbon dioxide in industrial natural gas waste gas by aminoguanidine solution is realized, and aminoguanidine carbonate with high product purity and yield is obtained.

[0018] Preferably, in step (2), the premixer is a pipeline reactor, the pumping pressure of the waste gas purification gas is controlled between 0.10MPa and 0.15MPa, and the pH of the mixed liquid is stable at 5.0~5.5. Under these conditions, the stability of cyanamide is enhanced, and the reaction of equal amounts of cyanamide and hydrazine hydrate can generate a quantitative amount of aminoguanidine carbonate. The hydrazine hydrate, cyanamide and dicyandiamide contained in the wastewater are all in trace amounts (all below 100ppm after testing), which greatly improves production efficiency and reduces production costs.

[0019] This invention utilizes three injection ports with varying pressures to ensure better participation of purified waste gas in the reaction, significantly improving carbon dioxide utilization. The pressure at the front injection port (reactor inlet) is set between 0.18 and 0.20 MPa, where carbon dioxide demand and consumption are highest. This higher pressure allows for greater carbon dioxide dissolution in the reaction solution, promoting the reaction. The pressure at the middle injection port (reactor midpoint) is set between 0.15 and 0.17 MPa to continue the reaction and improve conversion rate. The pressure at the rear injection port (reactor outlet) is set between 0.10 and 0.13 MPa to ensure sufficient reaction of unreacted products, further enhancing conversion rate and purity. This invention also employs continuous flow to suppress localized overreaction and maintains the pH of the reaction system between 5.0 and 5.5, thereby improving product purity and conversion rate.

[0020] The inner cylinder of a Taylor-type tubular reactor rotates at 500-1000 rpm, with a Taylor number (Ta) ≥ 50. The fluid transitions from laminar flow to Taylor vortex flow, forming periodic rotating vortex rings. This increases the gas-liquid or liquid-liquid contact area by 5-10 times, improving the dissolution rate of gases such as CO2 and increasing the mass transfer coefficient K. l The concentration of reactants is increased by more than 30%, resulting in a more uniform distribution of reactant concentrations, avoiding localized overconcentration or dead zones, and improving the yield.

[0021] The cooling and crystallization conditions are as follows: rapid cooling to 0-5°C at a rate of 10-20°C / min, followed by crystallization in a stainless steel reactor for 1-3 hours at 0-5°C. Existing processes suffer from uneven crystallization particle size across batches, low filtration efficiency, and difficulties in continuous crystallization and separation. This invention employs rapid cooling (10-20°C / min) of the obtained reaction liquid to 0-5°C via a tubular heat exchanger, combined with crystallization in a reactor. This achieves precise control of the crystal particle size at D50 = 40-50 μm, improving crystal particle uniformity and purity, and offering advantages in dissolution rate and stability.

[0022] Preferably, after crystallization, the liquid enters a three-in-one centrifugal washing and drying machine, and is stirred at a low speed of 10~20 r / min to ensure uniform distribution of the material. After feeding, the feed valve is closed and the filtrate outlet valve is opened. The pressure is gradually increased for filtration, with a pressure ≤0.3MPa. Water is added as the washing liquid, and the mixture is stirred at a speed of 20~30 r / min. When no liquid flows out of the outlet, the hot water inlet and outlet valves are opened first, and the vacuum valve is opened. Drying is carried out under vacuum. Before discharge, a sample is taken to test the drying loss, which is ≤1.0%. After passing the test, the product aminoguanidine carbonate is discharged.

[0023] Compared with the prior art, the present invention has the following advantages: (1) This invention studies and treats the exhaust gas of natural gas boilers, recovers CO2 from the exhaust gas and produces aminoguanidine carbonate products, which has achieved high economic benefits. After the exhaust gas discharged from the exhaust port in steps 2 and 3 is absorbed by liquid alkali and dried, nitrogen gas with high purity is obtained, which can provide nitrogen gas for production.

[0024] (2) This invention does not separate nitrogen and carbon dioxide through special treatment. Instead, it separates nitrogen and carbon dioxide by absorbing and utilizing carbon dioxide and then using the remaining nitrogen. The waste gas is purified by using a low-pressure premixing device and a low-pressure pipeline reactor to fully absorb and react carbon dioxide and discharge nitrogen.

[0025] (3) Addressing the problems of high energy consumption, solvent degradation and loss, equipment corrosion, high cost, and environmental impact associated with existing liquid amine absorption methods. This invention utilizes aminoguanidine absorption technology, which has the advantages of low energy consumption and avoids the disadvantages of solvent degradation and loss. This invention uses aminoguanidine to directly absorb carbon dioxide, thereby precipitating the product aminoguanidine carbonate. Unlike the amine absorption method, which requires a large amount of energy for carbon dioxide desorption, this invention solves the problem of high energy consumption and achieves energy saving and emission reduction. In addition, the carbon dioxide after tail gas treatment directly participates in the reaction to prepare aminoguanidine carbonate, without considering the degradation and loss of the main component, making it an environmentally friendly and economical carbon dioxide absorption method. This invention uses a pipeline reactor to absorb carbon dioxide to prepare aminoguanidine, which is non-corrosive and does not require expensive equipment investment and maintenance. The waste gas generated by this invention using aminoguanidine to absorb carbon dioxide is mainly wastewater, which can be treated by the factory's environmental protection equipment to meet emission standards. The small amount of solid waste generated is treated in compliance with regulations by qualified hazardous waste enterprises. The nitrogen generated after carbon dioxide absorption can be utilized without polluting the environment, making it green and environmentally friendly. The technological innovation of this invention is of great significance for achieving low-cost, high-efficiency, and green carbon capture.

[0026] (4) This invention can reduce the cost of CO2 raw materials; it can realize the integration of "carbon capture-reaction utilization" and reduce carbon emissions. Each ton of aminoguanidine product can absorb about 269.9 kg of waste gas CO2, reducing carbon emissions; compared with purchasing pure CO2, the production cost of this invention is reduced by about 35%.

[0027] (5) This invention utilizes carbon dioxide from waste gas in a reaction, and the discharged nitrogen gas, after drying, can be used in production. Overall energy consumption is reduced by 30%, and the total CO2 utilization rate is ≥95%. An additional 700~800 Nm³ of nitrogen is generated per ton of product. 3 To improve economic efficiency.

[0028] (6) Existing processes suffer from high batch operation risks associated with hydrazine hydrate (flammable and explosive) and cyanamide (highly toxic). This invention reduces exposure risks through a closed, continuous system. Cyanamide exhibits high stability in this reaction system, preventing polymerization into dicyanamide. It achieves the reaction of equal amounts of cyanamide and hydrazine hydrate to generate a fixed amount of aminoguanidine carbonate. The wastewater contains trace amounts of hydrazine hydrate, cyanamide, and dicyanamide (all below 100 ppm), significantly improving production efficiency and reducing production costs. This invention uses a pipeline reactor to react cyanamide and hydrazine hydrate, while simultaneously introducing purified waste gas in stages. This improves reaction efficiency, resulting in high product purity, high yield, and low cost. It also ensures that carbon dioxide in the purified waste gas fully participates in the reaction, avoiding waste, reducing emissions, and enhancing process safety and environmental friendliness. Attached Figure Description

[0029] Figure 1 This is the liquid chromatogram of the aminoguanidine carbonate prepared in Example 1; Figure 2 This is the mass spectrum of the aminoguanidine carbonate prepared in Example 1; Figure 3 This is a particle size distribution diagram of the aminoguanidine carbonate prepared in Example 1; Figure 4 This is a particle size distribution diagram of the aminoguanidine carbonate prepared in Comparative Example 9. Detailed Implementation

[0030] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0031] Example 1: Source of industrial natural gas containing carbon dioxide: steam boiler exhaust gas from Luning Pharmaceutical (CO2 15%, SO2 200 ppm, NOx 150 ppm, nitrogen 82%, oxygen 3%, water vapor trace amount negligible).

[0032] A method for recovering and utilizing industrial natural gas containing carbon dioxide includes the following steps: (1) The industrial natural gas waste gas containing carbon dioxide is sequentially passed through a dust collector for dust removal, a condenser for cooling and condensation to remove water, a photocatalytic purifier for nitrogen and sulfides removal, and a deoxygenation tank for oxygen removal. After treatment, the waste gas is purified. The catalyst in the photocatalytic purifier is a titanium dioxide-based catalyst supported on 1 wt% metallic Cu, 2 wt% metallic Ni, and 7 at% non-metallic N. The purification conditions of the photocatalytic purifier are: irradiation with visible LED light at 420-450 nm and a gas flow rate (GHSV) of 4000 h⁻¹. -1A mixed solution of sodium sulfite and sodium bisulfite with a mass fraction of 2% was added to the deoxygenation tank.

[0033] (2) Input 45 kg of hydrazine hydrate (concentration of 80%) and 90 kg of softened water into the premixer. At the same time, the waste gas purification gas obtained in step (1) is pumped into the premixer. The pumping pressure of the waste gas purification gas is controlled between 0.10 MPa and 0.15 MPa. The flow rate of the waste gas purification gas is adjusted by online pH feedback to stabilize the pH of the mixture at 5.0~5.5. Premixing is carried out for 4 hours and the premixing temperature is 30℃. After premixing, the premixed liquid is obtained. The exhaust port of the premixer is connected to the sodium hydroxide absorption tank to absorb the remaining carbon dioxide. Then, it is dried by the drying device. The dried gas is collected and compressed to obtain nitrogen for production use.

[0034] (3) The premixed liquid obtained in step (2) and 100 kg of 30% cyanamide aqueous solution were pumped into a Taylor tubular reactor respectively. The flow rate of the cyanamide aqueous solution in the Taylor tubular reactor was 3.5 L / min, and the flow rate of the premixed liquid in the Taylor tubular reactor was 5 L / min. The inner cylinder rotation speed of the Taylor tubular reactor was 800 rpm, and the Taylor number (Ta) was ≥50. Waste gas purification gas injection ports were set at the inlet, middle and outlet of the Taylor tubular reactor respectively. Each injection port contained 5 air inlets. The waste gas purification gas obtained in step (1) was injected into the Taylor tubular reactor through the air inlets by the pressure reducing valve. The pressure of the front injection port (the inlet injection port of the reactor) was set between 0.18 and 0.20 MPa, the pressure of the middle injection port (the middle injection port of the reactor) was set between 0.15 and 0.17 MPa, and the pressure of the rear injection port (the outlet injection port of the reactor) was set between 0.10 and 0.13 MPa. The reaction was maintained. The system's pH value is between 5.0 and 5.5, the total residence time of the reaction solution is 4 hours, and the reaction temperature is 45℃. The resulting reaction solution is rapidly cooled to 0℃ at a rate of 15℃ / min via a tubular heat exchanger and then introduced into a stainless steel reactor for crystallization. Crystallization takes place at 0℃ for 2 hours. After crystallization, the feed valve is opened to introduce the crystallized liquid into the tank of the three-in-one filter washing and drying machine. The mixture is stirred at a low speed of 15 r / min to ensure uniform material distribution. After feeding, the feed valve is closed, and the filtrate outlet valve is opened. Filtration is carried out by gradually increasing the pressure, which should be ≤0.3MPa. If air leakage is found in the filter cake, the agitator can be lowered for low-speed surface leveling. Washing liquid is introduced into the tank through the washing liquid inlet. After 50 kg of washing liquid has been introduced, the addition is stopped. The agitator is gradually and slowly lowered and stirred at a speed of 25 r / min for slurry stirring. When no liquid flows out of the outlet after pressure filtration, the hot water inlet and outlet valves are opened first, and the vacuum valve is opened for drying under vacuum. Before discharge, a sample is taken for drying loss test ≤1.0%. After passing the test, the material is ready to be discharged, and the product aminoguanidine carbonate is obtained after discharge.

[0035] The purified exhaust gas obtained after purification in step (1) of Example 1 contains 15-25% CO2, 75-85% nitrogen, and SO2, NOx, O2, and H2O are all <1 ppm; The liquid chromatogram of the aminoguanidine carbonate prepared in Example 1 is shown in Figure 1. Figure 1 The purity is 99.82%; the mass spectrum is shown below. Figure 2 [M+H]=75.1, which is the molecular weight of aminoguanidine; particle size distribution is shown in [reference needed]. Figure 3 The particle size distribution of aminoguanidine carbonate is uniform, with D50 between 40 and 50 μm, and the yield of aminoguanidine carbonate is 97%. The purity of the obtained nitrogen gas is 99.5%, and 0.9 tons / ton of nitrogen gas is produced as a byproduct.

[0036] Comparative Example 1: Comparative Example 1 is basically the same as Example 1, except that step (1) is not included. Untreated industrial natural gas containing carbon dioxide is used directly for the reaction, that is, the exhaust gas purification gas in steps (2) and (3) is replaced with untreated industrial natural gas containing carbon dioxide.

[0037] Comparative Example 1 had a yield of only 42% and a purity of 95.30%, with the product containing excessive sulfur impurities.

[0038] Comparative Example 2: Comparative Example 2 is basically the same as Example 1, except that the step of removing nitrogen and sulfur oxides by photocatalytic purifier is omitted in step (1).

[0039] Comparative Example 2 had a yield of 73% and a purity of 93.30%.

[0040] Comparative Example 3: Comparative Example 3 is basically the same as Example 1, except that the deoxygenation step in step (1) is removed.

[0041] Comparative Example 3 had a yield of 90% and a purity of 99.07%.

[0042] Comparative Example 4: Comparative Example 4 is basically the same as Example 1, except that the catalyst in the photocatalytic purifier is a titanium dioxide-based catalyst supported with 1 wt% metal V, 2 wt% metal W, and 7 at% non-metal N.

[0043] Comparative Example 4 had a yield of 84% and a purity of 98.60%.

[0044] Comparative Example 5 Comparative Example 5 is basically the same as Example 1, except that: in step (2), waste gas purification gas is not pumped into the premixer to keep the pH of the mixture stable between 7.0 and 7.5.

[0045] The aminoguanidine carbonate prepared in Comparative Example 5 had a yield of 46% and a purity of 94.50%.

[0046] Comparative Example 6 Comparative Example 6 is basically the same as Example 1, except that the pumping pressure of CO2 gas in step (2) is controlled at 0.050±0.005MPa and the pH of the mixture is stable between 6.2 and 6.5.

[0047] The aminoguanidine carbonate prepared in Comparative Example 6 had a yield of 79% and a purity of 98.50%.

[0048] Comparative Example 7 Comparative Example 7 is basically the same as Example 1, except that in step (2), only one exhaust gas purification gas injection port is set at the inlet of the Taylor tubular reactor. The injection port contains 5 air inlets and the pressure of the injection port is set between 0.18 and 0.20 MPa.

[0049] The aminoguanidine carbonate prepared in Comparative Example 7 had a yield of 76% and a purity of 96.20%.

[0050] Comparative Example 8 Comparative Example 8 is basically the same as Example 1, except that: in step (3), no waste gas is added to purify the gas, no product is precipitated, and aminoguanidine carbonate cannot be obtained.

[0051] Comparative Example 9 Comparative Example 9 is basically the same as Example 1, except that in step (3), the cooling rate of rapid cooling is 3℃ / min, the temperature is cooled to 20℃, and crystallization takes 3 hours.

[0052] The aminoguanidine carbonate prepared in Comparative Example 9 had a yield of 80.1% and a purity of 99.33%. The particle size distribution is shown in the figure. Figure 4 As can be seen, the crystal particle size is D50 = 87.51 μm. Comparative Example 8, due to its slow cooling rate and high crystallization temperature (20℃), has a low yield and low purity, resulting in a larger crystal particle size D50 and lower crystal particle uniformity.

Claims

1. A method for recovering and utilizing industrial natural gas waste gas containing carbon dioxide, characterized in that: Includes the following steps: (1) The industrial natural gas waste gas containing carbon dioxide is sequentially passed through a dust collector for dust removal, a condenser for cooling and condensation to remove water, a photocatalytic purifier for nitrogen and sulfides removal, and a deoxygenation tank for oxygen removal. After treatment, the waste gas is purified. (2) Hydrazine hydrate and softened water are fed into a premixer for premixing, and the waste gas purification gas obtained in step (1) is introduced at the same time to obtain a premixed liquid; the exhaust port of the premixer is connected to a sodium hydroxide absorption tank to absorb the remaining carbon dioxide, and then dried by a drying device. The dried gas is collected and compressed to obtain nitrogen. (3) The premixed liquid obtained in step (2) and the cyanamide aqueous solution are pumped into a Taylor tubular reactor respectively. The waste gas purification gas obtained in step (1) is injected into the Taylor tubular reactor to react and obtain aminoguanidine carbonate.

2. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 1, characterized in that: The catalyst in the photocatalytic purifier described in step (1) is a titanium dioxide-based catalyst supported on 0.5-2 wt% metallic Cu, 1-3 wt% metallic Ni, and 5-10 at% non-metallic N. The purification conditions of the photocatalytic purifier are: irradiation with visible LED light at 420-450 nm and a gas flow rate (GHSV) of 3000-5000 h⁻¹. -1 .

3. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 1, characterized in that: In step (1), a mixed solution of sodium sulfite and sodium bisulfite with a mass fraction of 2% is added to the deoxygenation tank.

4. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 1, characterized in that: In step (3), the pH value of the reaction system is maintained between 5.0 and 5.5 during the reaction.

5. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 1, characterized in that: Step (2) involves inputting hydrazine hydrate and softened water into a premixer, while simultaneously feeding the waste gas purification gas obtained in step (1) into the premixer. The pumping pressure of the waste gas purification gas is controlled between 0.10 MPa and 0.15 MPa, and the pH of the mixture is stabilized at 5.0 to 5.

5. Premixing is then performed, and a premixed liquid is obtained after premixing is completed.

6. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 5, characterized in that: In step (2), the concentration of hydrazine hydrate is 80-81%, the mass ratio of hydrazine hydrate to softened water is 1.0:1.0-3.0, the premixing time is 2.5-5 hours, and the premixing temperature is 10-40℃. The exhaust port of the premixer is connected to a sodium hydroxide absorption tank to absorb the remaining carbon dioxide, and then it is dried by a drying device. The dried gas is collected and compressed to obtain nitrogen.

7. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 1, characterized in that: Step (3) is as follows: The premixed liquid obtained in step (2) and the cyanamide aqueous solution are pumped into a Taylor tubular reactor respectively. Waste gas purification gas injection ports are set at the inlet, middle and outlet of the Taylor tubular reactor respectively. The waste gas purification gas obtained in step (1) is injected into the Taylor tubular reactor through the gas inlet through the pressure reducing valve. The pressure of the front injection port is set between 0.18 and 0.20 MPa, the pressure of the middle injection port is set between 0.15 and 0.17 MPa, and the pressure of the rear injection port is set between 0.10 and 0.13 MPa. The pH value of the reaction system is maintained between 5.0 and 5.

5. The obtained reaction liquid is cooled and crystallized by a tubular heat exchanger. After crystallization, the liquid is filtered, washed and dried to obtain the product aminoguanidine carbonate.

8. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 7, characterized in that: The flow rate of the cyanamide aqueous solution in the Taylor tubular reactor is 3-4 L / min, the flow rate of the premixed solution in the Taylor tubular reactor is 5 L / min, the rotational speed of the inner cylinder of the Taylor tubular reactor is 500-1000 rpm, and the Taylor number Ta≥50.

9. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 7, characterized in that: In step (3), each injection port contains 3 to 5 air inlets; the total residence time of the reaction liquid is 2.5 to 5 hours, and the reaction temperature is 40 to 50°C.

10. The method for recovering and utilizing carbon dioxide-containing industrial natural gas waste gas according to claim 7, characterized in that: In step (3), the cooling and crystallization conditions are as follows: rapidly cool to 0-5℃ at a rate of 10-20℃ / min, enter the stainless steel reactor for crystallization, and crystallize for 1-3 hours at 0-5℃.

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