Nitrogen oxide reducing agent for ship and preparation method thereof

Abstract

The invention discloses a marine nitrogen oxide reducing agent and a preparation method thereof, and belongs to the technical field of marine nitrogen oxide reducing agents, the preparation method comprises the steps of hydrolytic crystallization, dissolution, filtration, fine filtration and ultrafiltration; the hydrolytic crystallization comprises the following steps: mixing industrial urea and tertiary water, stirring at 73-75 DEG C, cooling for the first time, adding dodecynediol polyoxyethylene ether, cooling for the second time, adding a mixed urea solution with the temperature of 62.5-64 DEG C, cooling for the third time, preserving heat, centrifuging, and collecting a precipitate; the nitrogen oxide reducing agent for the ship is produced by adopting the same production equipment as the nitrogen oxide reducing agent for the automobile, the problem of membrane pollution is not easy to occur in production, the production efficiency is high, the production input cost is low, the production energy consumption is low, and the prepared nitrogen oxide reducing agent for the ship meets the standard requirement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nitrogen oxide reducing agent for ships, in particular to a nitrogen oxide reducing agent for ships and a preparation method thereof. BACKGROUND

[0002] Nitrogen oxide is an important substance that destroys the environment and forms acid rain, and harms human health. According to statistics, global ships emit about 10-15 million tons of nitrogen oxide per year, accounting for a large proportion of the total global nitrogen oxide emissions, about 7-14%. In view of this, the International Maritime Organization and the Chinese government are increasingly concerned about the problem of nitrogen oxide pollution caused by ships and are constantly improving the control requirements for nitrogen oxide emissions from ships.

[0003] The International Convention for the Prevention of Pollution from Ships is an international convention formulated by the International Maritime Organization to protect the marine environment, which sets safety regulations for preventing and limiting ships from emitting oil and other harmful substances to pollute the ocean. At present, the relatively mature single technologies that can meet the third stage control standard requirements of the International Convention for the Prevention of Pollution from Ships Annex VI include selective catalytic reduction (SCR) technology, exhaust gas recirculation (EGR) technology and low-pressure injection liquefied natural gas (LNG) engine technology. Among them, the SCR technology has a wide range of applications, has less impact on the safety of the engine, and has been widely recognized by the industry. More and more ship companies choose to install SCR systems on newly built ship fuel engines.

[0004] SCR technology is a kind of tail gas aftertreatment technology based on the selective reduction of nitrogen oxide in tail gas with reducing agent to convert it into harmless nitrogen and water. SCR technology is the mainstream technology for reducing harmful substances such as nitrogen oxide in diesel engine exhaust gas, and is also an essential system to ensure that modern cars and ships strictly comply with emission regulations. Urea water solution has the advantages of safety, non-toxicity, easy storage and convenient preparation, and is widely used in SCR systems for diesel engines in cars and ships. When the mass fraction of urea in urea water solution is 32.5%, the crystallization temperature of urea water solution is the lowest, which is -11℃. In order to avoid crystallization at low temperatures and facilitate the injection of urea water solution into the tail gas pipeline at low temperatures, the nitrogen oxide reducing agent used in the SCR system for diesel engines in cars is mainly urea water solution with a mass fraction of 32.5%. Since the demand for reducing agent by the SCR system for diesel engines in ships is large, and the temperature in the engine room of the ship is high, it is not easy to cause crystallization problems. Therefore, the nitrogen oxide reducing agent used in the SCR system for diesel engines in ships is mainly urea water solution with a mass fraction of 40%.

[0005] In order to regulate the market of marine nitrogen oxide reducing agent, China issued GB / T 35176.1-2017 / ISO 186 11-1:2014 Ship and Offshore Technology Marine Nitrogen Oxide Reducing Agent AUS 40 on December 29, 2017, and implemented it on July 1, 2018. In this standard, the nitrogen oxide reducing agent used in marine SCR system is called "marine nitrogen oxide reducing agent AUS 40", and the urea content, density at 20°C, refractive index at 20°C, alkalinity, biuret content, aldehyde content, insoluble content, phosphate content, calcium content, iron content, magnesium content, sodium content and potassium content are regulated.

[0006] As an applicant for the production of automotive nitrogen oxide reducing agent (32.5% mass fraction urea aqueous solution), considering that both automotive nitrogen oxide reducing agent and marine nitrogen oxide reducing agent are high-purity urea aqueous solution, the main difference is that the mass concentration of urea in high-purity urea aqueous solution is increased from 32.5% to 40%, therefore, the applicant uses the same production equipment as the automotive nitrogen oxide reducing agent, and refers to the preparation method of the automotive nitrogen oxide reducing agent, first purifies the industrial urea by hydrolysis crystallization to remove water-soluble impurities in the industrial urea, then uses three-stage water to obtain a mass fraction of 40% urea aqueous solution, and then uses polyethylene filter screen for filtration, polypropylene filter core for fine filtration and polysulfone filter membrane for ultrafiltration to remove insoluble impurities in the industrial urea, to obtain marine nitrogen oxide reducing agent. However, according to the disclosure in Zhu Zongmin, China Petroleum Enterprises, May 2020, from the perspective of production and operation management, automotive nitrogen oxide reducing agent and marine nitrogen oxide reducing agent are two completely different products for users. When the applicant prepared marine nitrogen oxide reducing agent according to the above method and made simple adjustments to the preparation method on the original production equipment, the following problems were encountered: Problem 1: In the purification of industrial urea by hydrolysis crystallization, the applicant refers to the content disclosed in the process of preparing high-purity automotive urea by cooling crystallization. If the cooling rate is too fast, it will cause impurity liquid preservation and adsorption, and also cause the aspect ratio of the obtained urea crystal to be large and the size to be small, which is not conducive to the downstream process. Therefore, the cooling rate is adopted by the method of slow first and fast later. The slow cooling rate is 0.05℃ / min for the first 100min, then the cooling rate is 0.10℃ / min for 70min, and finally the cooling rate is 0.20℃ / min for 40min. The stirring speed is set to 300rpm during the cooling process. However, in this route, when the cooling rate is increased in the later stage, on the one hand, the solution system becomes unstable and is easy to nucleate, on the other hand, the supersaturation degree is increased, which promotes secondary nucleation, resulting in an increase in the number of urea crystals prepared and small crystal size, and also causes the particle size of the prepared urea crystals to be uneven. Since the production of automotive nitrogen oxide reducing agent is not continuous, after obtaining urea crystals by cooling crystallization, the urea crystals will be temporarily stored. However, according to the content disclosed in the article "Reasons for urea product caking and solutions" by Li Tongsheng in Guangdong Chemical Industry in April 1991, if the urea particles are uniform and the particle size is moderate, the amount of dust entrained in the product can be reduced. Therefore, if the obtained urea crystal particles are not uniform and there are a large number of small particle size urea particles, the problem of dust entrainment is more likely to occur, which further leads to a high content of insoluble substances in the urea aqueous solution prepared from the urea crystals. According to the content disclosed in the article "Study on high-efficiency concentration of urea aqueous solution by multi-effect membrane distillation" by Zhang Lili in Tianjin University in June 2012, when ultrafiltration is performed for a period of time, the membrane flux of the assembly decreases, causing membrane fouling problems. Especially as the urea content in the urea aqueous solution increases and the relative content of dust in the used urea crystals increases, membrane fouling problems are more likely to occur in ultrafiltration.

[0007] To solve this problem, through retrieval, the most commonly used methods are: Method 1: According to the content disclosed in the article "Process of preparing high-purity automotive urea by cooling crystallization" by Li Pan in Dalian University of Technology in June 2017, a slow cooling route is adopted, i.e. the cooling rate is controlled at 0.05℃ / min and the stirring speed is 300rpm, so as to obtain urea crystals with large crystal size and uniform particle size. However, due to the extension of the cooling time, the production efficiency is reduced.

[0008] Method 2: According to the content disclosed in the article "Study on high-efficiency concentration of urea aqueous solution by multi-effect membrane distillation" by Zhang Lili in Tianjin University in June 2012, in order to avoid membrane fouling, the membrane material can be selected according to the properties of the feed liquid, which has strong hydrophilicity and the membrane surface charge is consistent with the charge of the solute in the solution. However, changing the membrane material involves device modification, which increases the production investment cost.

[0009] Problem 2: According to the research on high-efficiency concentration of urea aqueous solution by multi-effect membrane distillation, as the concentration of urea increases, the viscosity of urea increases. Moreover, as the concentration of urea increases, the relative content of insoluble substances in urea aqueous solution also increases. According to the research progress on the causes and model representation of ultrafiltration membrane pollution, Chen Anwen and Shi Xiangyun, Guangdong Chemical Industry, September 2012, the increase in viscosity will affect the mass transfer efficiency, increase the resistance on the surface of the ultrafiltration membrane, and reduce the membrane flux. Further, the increase in the relative content of insoluble substances will also exacerbate the membrane pollution problem in ultrafiltration.

[0010] To solve this problem, the most commonly used method is to improve the temperature of ultrafiltration to reduce the viscosity of urea aqueous solution, as disclosed in the research on high-efficiency concentration of urea aqueous solution by multi-effect membrane distillation, Zhang Lili, Tianjin University, June 2012, but this will increase the energy consumption of production. Alternatively, a modifier with viscosity-reducing effect can be added to the urea aqueous solution, but as disclosed in the preparation and performance testing of organic amine type low-temperature diesel vehicle urea solution, Wu Xiaoman, Wang Weiwei, Xing Liqin, Shi Ruonan, Xuchang College Journal, August 2018, the commonly used modifier small molecule alcohol will increase the viscosity of urea aqueous solution, further exacerbating the membrane pollution problem. Other modifiers not only have safety problems, but also may affect the refractive index of the nitrogen oxide reducing agent for ships, further causing the prepared nitrogen oxide reducing agent for ships to not meet the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Ship and Marine Technology Ship Nitrogen Oxide Reducing Agent AUS 40 for refractive index. In addition, the applicant also tried to add non-ionic surfactant to the urea aqueous solution and then filter, fine filter and ultrafilter, as disclosed in the influence of non-ionic surfactant on the crystallization performance of diesel vehicle exhaust treatment fluid, Zhao Yang and Yan Feng, Tianjin University of Technology Journal, June 2023, the non-ionic surfactant adsorbed on the surface of insoluble substances to promote the dispersion of insoluble substances. Although this method can reduce the membrane clogging problem, the non-ionic surfactants in the membrane pollutants interact with each other, which will increase the viscosity of the membrane pollutants, and it is difficult to flush the ultrafiltration membrane when flushing. SUMMARY

[0011] To address the shortcomings of existing technologies, this invention provides a marine nitrogen oxide reducing agent and its preparation method. This invention uses the same production equipment as automotive nitrogen oxide reducing agents to produce marine nitrogen oxide reducing agents, which reduces the likelihood of membrane fouling during production, resulting in high production efficiency, low production input costs, and low energy consumption. The prepared marine nitrogen oxide reducing agent meets the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Marine and Marine Technology - Marine Nitrogen Oxide Reducing Agents AUS 40.

[0012] To solve the above technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a nitrogen oxide reducing agent for ships includes: hydrolysis crystallization, dissolution, filtration, fine filtration, and ultrafiltration; The hydrolysis crystallization process involves mixing industrial urea and tertiary water, stirring at 73-75°C, performing a first cooling, adding dodecaacetylenol polyoxyethylene ether, performing a second cooling, adding a mixed urea solution at 62.5-64°C, performing a third cooling, maintaining the temperature, centrifuging, and using the collected precipitate as purified urea. In the hydrolysis crystallization, the mass ratio of industrial urea to tertiary water is 725-730:270; When adding dodecynediol polyoxyethylene ether, the amount of dodecynediol polyoxyethylene ether added is 50-60 mg / L; The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The mass ratio of industrial urea to mixed urea solution is 725-730:100-102; The first cooling process involves cooling at a rate of 0.05℃ / min for 100-110 minutes. The second cooling process involves cooling at a rate of 0.10℃ / min for 60-70 minutes. The third cooling process involves cooling at a rate of 0.2℃ / min for 100-110 minutes. When stirring at 73-75℃, the stirring speed is 280-320 rpm and the stirring time is 30-60 min; The heat preservation time is 20-30 minutes; The centrifugation speed is 3500-4000 rpm, and the centrifugation time is 10-15 min. The method for preparing the mixed urea solution is as follows: polyethylene glycol 8000, urea and tertiary water are mixed and stirred at 73-75°C to obtain a composite urea solution. In the preparation of the mixed urea solution, the mass ratio of polyethylene glycol 8000, urea, and tertiary water is 5-5.2:65-65.8:30-31. When stirring at 73-75℃, the stirring speed is 300-350 rpm and the stirring time is 30-60 min; The dissolution process involves mixing purified urea, tertiary water, and a mixed surfactant solution, and stirring at 40-45°C to obtain an aqueous urea solution. In the dissolution process, the mass ratio of purified urea, tertiary water, and mixed surfactant solution is 40:50:10. When stirring at 40-45℃, the stirring speed is 200-400 rpm and the stirring time is 30-60 min; The method for preparing the mixed surfactant solution is as follows: dodecynediol polyoxyethylene ether, anhydrous ethanol and tertiary water are mixed and stirred at 60-65°C. The stirring speed of the reaction equipment is controlled at 300-350 rpm and stirred for 30-60 min to obtain the mixed surfactant solution. In the preparation of the mixed surfactant solution, the mass ratio of dodecynediol polyoxyethylene ether, anhydrous ethanol, and tertiary water is 1-1.1:10-12:1000-1100. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; When stirring at 60-65℃, the stirring speed is 300-350 rpm and the stirring time is 30-60 min; The filtration process involves using a bag filter to filter the urea solution, resulting in a filtered urea solution. In the filtration process, the filter screen used in the bag filter is a polyethylene filter screen, and the filtration accuracy of the polyethylene filter screen is 1μm. The fine filtration is performed by using a fine filtration device to finely filter the filtered urea aqueous solution to obtain a finely filtered urea aqueous solution. In the fine filtration process, the filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm. The ultrafiltration process involves using an ultrafiltration device to ultrafilter the finely filtered urea aqueous solution to obtain a nitrogen oxide reducing agent for marine use. In the ultrafiltration process, the filter membrane used in the ultrafiltration equipment is a polysulfone filter membrane; The filter membrane used in the ultrafiltration equipment has a filtration accuracy of 0.01 μm and a stable pure water flux of 100 L / (m²) at 25℃ and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.24-0.26 MPa; All the water in question meets the national standard GB / T 6682-2008.

[0013] A reducing agent for nitrogen oxides used in ships, prepared by the aforementioned method.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The preparation method of the marine nitrogen oxide reducing agent of the present invention, in the preparation process, according to the content disclosed in Zhao Yang and Yan Feng, Journal of Tianjin University of Technology, June 2023, uses nonionic surfactants to inhibit urea crystallization. However, the difference from the prior art is that the present invention adds nonionic surfactants in the hydrolysis crystallization step. According to the content disclosed in Xia Sen, Zhejiang University, April 2024, when inhibiting methionine crystallization, hydroxypropyl cellulose mainly inhibits methionine aggregation or cluster formation by adsorbing on the surface of methionine crystals and inhibiting methionine aggregation or cluster formation through steric hindrance. Hydroxypropyl cellulose has a stronger inhibitory effect on axial growth than radial growth, causing a decrease in the crystal aspect ratio. The applicant referenced this principle and added a nonionic surfactant, dodecaacetylene glycol polyoxyethylene ether, before increasing the cooling rate to inhibit seed crystal formation. Then, before further increasing the cooling rate, a mixed urea solution containing polyethylene glycol 8000 and urea was added. According to the published research in "Performance and Mechanism of NO2 Removal by Wet Washing Reduction of Polyethylene Glycol / Urea Composite Solution" by Cheng Junqi, Dalian Maritime University, June 2023, there is a binding force between polyethylene glycol and urea. The large molecular weight of polyethylene glycol 8000 leads to significant steric hindrance, further resulting in a high viscosity of the polyethylene glycol 8000 aqueous solution. Therefore, this invention first mixes polyethylene glycol 8000 with urea. The polyethylene glycol 8000 and urea are bound together by intermolecular forces to obtain a mixed urea solution. This mixed urea solution is then added to a hydrolysis crystallization system. Utilizing the interaction between polyethylene glycol 8000 and urea, it adsorbs onto the surface of urea crystals and preferentially grows radially where steric hindrance is relatively low. The pre-bound urea in polyethylene glycol 8000 promotes urea aggregation and crystal growth, thus ensuring uniform size and particle size of the urea crystals. Furthermore, the nonionic surfactant dodecynekyne glycol polyoxyethylene ether coated on the surface of the urea crystals and polyethylene glycol 8000 also have a synergistic effect, preventing urea from entraining dust. (2) The preparation method of the marine nitrogen oxide reducing agent of the present invention also includes a mixed surfactant solution. The mixed surfactant solution is composed of nonionic surfactant dodecynediol polyoxyethylene ether and anhydrous ethanol. According to the content disclosed in Xiao Danfeng, Wang Yongchang, Zhang Minghui, Zhang Chunyan. Collection of Oil Production Engineering. June 2018, there is an interaction force between ethanol and surfactant micelles. At high temperature, the thermal motion of ethanol is intensified, which can reduce the viscosity of surfactant. In the present invention, when the nonionic surfactant dodecynediol polyoxyethylene ether coats and disperses insoluble matter, a portion of ethanol is also bound. Therefore, when insoluble matter is adsorbed on the surface of ultrafiltration membrane to form membrane contaminants, some ethanol is also entrained in the membrane contaminants. At high temperature, the thermal motion of ethanol is intensified, which will reduce the concentration of membrane contaminants and contribute to the dissolution of membrane contaminants. (3) This invention uses the same production equipment as automotive nitrogen oxide reducing agents to produce marine nitrogen oxide reducing agents. The prepared marine nitrogen oxide reducing agent meets the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Marine and Marine Technology Marine Nitrogen Oxide Reducing Agents AUS 40, and its density at 20℃ is 1127-1132 kg / m³. 3 The refractive index at 20℃ is 1.3954-1.3958, alkalinity (based on NH3) is 0.12-0.13%, biuret content is 0.15-0.17%, aldehyde content is 3.1-3.5 mg / kg, insoluble matter content is 4.0-4.2 mg / kg, phosphate content is 0.22-0.24 mg / kg, calcium content is 0.12-0.13 mg / kg, iron content is 0.08-0.10 mg / kg, magnesium content is 0.13-0.15 mg / kg, sodium content is 0.08-0.09 mg / kg, and potassium content is 0.16-0.19 mg / kg. Moreover, it is not prone to membrane fouling during production, and the treatment of membrane pollutants is relatively easy. (4) The preparation method of the marine nitrogen oxide reducing agent of the present invention requires less time during hydrolysis and crystallization, and does not require heating in ultrafiltration, thus resulting in high production efficiency and low energy consumption; it does not require improvement of production equipment, thus resulting in low production input cost. Detailed Implementation

[0015] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0016] The Class III water used in Examples 1-2 and Comparative Examples 1-3 met the requirements for Class III water in the national standard GB / T 6682-2008.

[0017] The tertiary water used in Examples 1-2 and Comparative Examples 1-3 was from the same production batch and had a conductivity of 0.30 mS / m at 25°C.

[0018] The industrial urea used in Examples 1-2 and Comparative Examples 1-3 was from the same production batch, with a total nitrogen (N) content (on a dry basis) of 46.4%.

[0019] In Examples 1-2 and Comparative Examples 1-3, the density, refractive index at 20°C, alkalinity, biuret content, aldehyde content, insoluble matter content, phosphate content, calcium content, iron content, magnesium content, sodium content, and potassium content of the prepared marine nitrogen oxide reducing agent were tested according to the test methods specified in GB / T 35176.1-2017 / ISO 186 11-1:2014 Ships and Marine Technology Marine Nitrogen Oxide Reducing Agents AUS 40.

[0020] Example 1 A method for preparing a nitrogen oxide reducing agent for ships is as follows: Step 1: Hydrolysis and Crystallization Add 730g of industrial urea and 270g of tertiary water to the reaction equipment. Control the temperature inside the reaction equipment to 75℃ and the stirring speed to 300rpm. Stir for 30min, keeping the stirring speed constant. Cool for 100min at a cooling rate of 0.05℃ / min. Add dodecynediol polyoxyethylene ether, controlling the amount of dodecynediol polyoxyethylene ether added to be 50mg / L. Cool for 60min at a cooling rate of 0.10℃ / min. Add 100g of mixed urea solution at 64℃. Cool for 100min at a cooling rate of 0.2℃ / min. Hold for 20min. Transfer to a centrifuge. Control the centrifugation speed to 3500rpm and centrifuge for 10min. Use the collected precipitate as purified urea. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The method for preparing the mixed urea solution is as follows: 5g of polyethylene glycol 8000, 65g of urea and 30g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 75℃, the stirring speed of the reaction equipment is controlled to 300rpm, and the mixture is stirred for 30min to obtain the composite urea solution. Step 2: Dissolve Immediately add all the purified urea obtained in step 1, along with tertiary water and a mixed surfactant solution, into the reaction apparatus. Control the mass ratio of purified urea, tertiary water, and mixed surfactant solution to 40:50:10. Control the temperature inside the reaction apparatus to 40°C. Control the stirring speed of the reaction apparatus to 200 rpm. Stir for 30 minutes to obtain a urea aqueous solution. The method for preparing the mixed surfactant solution is as follows: 1g of dodecaacetylenic diol polyoxyethylene ether, 10g of anhydrous ethanol and 1000g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 60℃, the stirring speed of the reaction equipment is controlled to 300rpm, and the mixture is stirred for 30min to obtain the mixed surfactant solution. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; Step 3: Filtering The entire urea solution obtained in step 2 was filtered using a bag filter to obtain a filtered urea solution. The filter used in the bag filter is a polyethylene filter, and the filtration accuracy of the polyethylene filter is 1μm. Step 4: Fine filtration The urea aqueous solution obtained in step 3 was further filtered using a fine filtration device to obtain a finely filtered urea aqueous solution. The filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm; Step 5: Ultrafiltration The urea aqueous solution obtained in step 4 was subjected to ultrafiltration using an ultrafiltration device to obtain a nitrogen oxide reducing agent for ships. The ultrafiltration equipment uses a polysulfone membrane with a filtration accuracy of 0.01 μm and a stable pure water flux of 100 L / (m²) at 25°C and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.25 MPa.

[0021] This embodiment also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0022] The nitrogen oxide reducing agent for ships prepared in this embodiment has a density of 1132 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3958, the alkalinity (as NH3) is 0.13%, the biuret content is 0.17%, the aldehyde content is 3.5 mg / kg, the insoluble matter content is 4.2 mg / kg, the phosphate content is 0.24 mg / kg, the calcium content is 0.12 mg / kg, the iron content is 0.10 mg / kg, the magnesium content is 0.15 mg / kg, the sodium content is 0.08 mg / kg, and the potassium content is 0.16 mg / kg.

[0023] Comparative Example 1 A method for preparing a nitrogen oxide reducing agent for ships is as follows: The same preparation method as in Example 1 was used, except that the addition of dodecaacetylenic diol polyoxyethylene ether was omitted in step 1: hydrolysis crystallization.

[0024] The remaining technical solutions are the same as in Example 1.

[0025] This comparative example also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0026] The nitrogen oxide reducing agent for ships prepared in this comparative example has a density of 1135 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3961, the alkalinity (as NH3) is 0.12%, the biuret content is 0.19%, the aldehyde content is 3.3 mg / kg, the insoluble matter content is 12.7 mg / kg, the phosphate content is 0.27 mg / kg, the calcium content is 0.11 mg / kg, the iron content is 0.12 mg / kg, the magnesium content is 0.17 mg / kg, the sodium content is 0.09 mg / kg, and the potassium content is 0.16 mg / kg.

[0027] Comparative Example 2 A method for preparing a nitrogen oxide reducing agent for ships is as follows: The same preparation method as in Example 1 was used, except that the addition of the mixed urea solution was omitted in step 1: hydrolysis crystallization.

[0028] The remaining technical solutions are the same as in Example 1.

[0029] This comparative example also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0030] The nitrogen oxide reducing agent for ships prepared in this comparative example has a density of 1140 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3967, the alkalinity (as NH3) is 0.13%, the biuret content is 0.19%, the aldehyde content is 3.0 mg / kg, the insoluble matter content is 8.2 mg / kg, the phosphate content is 0.23 mg / kg, the calcium content is 0.12 mg / kg, the iron content is 0.12 mg / kg, the magnesium content is 0.16 mg / kg, the sodium content is 0.10 mg / kg, and the potassium content is 0.15 mg / kg.

[0031] Comparative Example 3 A method for preparing a nitrogen oxide reducing agent for ships is as follows: The same preparation method as in Example 1 was used, except that in step 2: the preparation method of the mixed surfactant solution was changed to: Add 1g of dodecaacetylenic diol polyoxyethylene ether and 1000g of tertiary water to the reaction equipment, control the temperature inside the reaction equipment to 60℃, control the stirring speed of the reaction equipment to 300rpm, stir for 30min, and obtain a mixed surfactant solution. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0.

[0032] The remaining technical solutions are the same as in Example 1.

[0033] This comparative example also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0034] The nitrogen oxide reducing agent for ships prepared in this comparative example has a density of 1141 kg / m³ at 20°C. 3 The refractive index at 20℃ is 1.3970, the alkalinity (as NH3) is 0.15%, the biuret content is 0.20%, the aldehyde content is 3.6 mg / kg, the insoluble matter content is 4.1 mg / kg, the phosphate content is 0.27 mg / kg, the calcium content is 0.13 mg / kg, the iron content is 0.12 mg / kg, the magnesium content is 0.16 mg / kg, the sodium content is 0.15 mg / kg, and the potassium content is 0.20 mg / kg.

[0035] Example 2 A method for preparing a nitrogen oxide reducing agent for ships is as follows: Step 1: Hydrolysis and Crystallization Add 730g of industrial urea and 270g of tertiary water to the reaction equipment. Control the temperature inside the reaction equipment to 75℃ and the stirring speed to 300rpm. Stir for 60min, keeping the stirring speed constant. Cool for 110min at a cooling rate of 0.05℃ / min. Add dodecynediol polyoxyethylene ether, controlling the amount of dodecynediol polyoxyethylene ether added to 60mg / L. Cool for 70min at a cooling rate of 0.10℃ / min. Add 102g of mixed urea solution at 62.5℃. Cool for 110min at a cooling rate of 0.2℃ / min. Hold at this temperature for 30min. Transfer to a centrifuge and centrifuge at 4000rpm for 15min. Use the collected precipitate as purified urea. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The method for preparing the mixed urea solution is as follows: 5.2g of polyethylene glycol 8000, 65.8g of urea and 31g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 75℃, the stirring speed of the reaction equipment is controlled to 350rpm, and the mixture is stirred for 60min to obtain the composite urea solution. Step 2: Dissolve Immediately add all the purified urea obtained in step 1, along with tertiary water and a mixed surfactant solution, into the reaction apparatus. Control the mass ratio of purified urea, tertiary water, and mixed surfactant solution to 40:50:10. Control the temperature inside the reaction apparatus to 45°C and the stirring speed of the reaction apparatus to 400 rpm. Stir for 60 minutes to obtain a urea aqueous solution. The method for preparing the mixed surfactant solution is as follows: 1.1g of dodecaacetylenic diol polyoxyethylene ether, 12g of anhydrous ethanol and 1100g of tertiary water are added to the reaction equipment, the temperature inside the reaction equipment is controlled to 65℃, the stirring speed of the reaction equipment is controlled to 350rpm, and the mixture is stirred for 60min to obtain the mixed surfactant solution. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; Step 3: Filtering The entire urea solution obtained in step 2 was filtered using a bag filter to obtain a filtered urea solution. The filter used in the bag filter is a polyethylene filter, and the filtration accuracy of the polyethylene filter is 1μm. Step 4: Fine filtration The urea aqueous solution obtained in step 3 was further filtered using a fine filtration device to obtain a finely filtered urea aqueous solution. The filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm; Step 5: Ultrafiltration The urea aqueous solution obtained in step 4 was subjected to ultrafiltration using an ultrafiltration device to obtain a nitrogen oxide reducing agent for ships. The ultrafiltration equipment uses a polysulfone membrane with a filtration accuracy of 0.01 μm and a stable pure water flux of 100 L / (m²) at 25°C and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.25 MPa.

[0036] This embodiment also provides a marine nitrogen oxide reducing agent prepared by the aforementioned preparation method.

[0037] The nitrogen oxide reducing agent for ships prepared in this embodiment has a density of 1127 kg / m³ at 20°C. 3The refractive index at 20℃ is 1.3954, the alkalinity (based on NH3) is 0.12%, the biuret content is 0.15%, the aldehyde content is 3.1 mg / kg, the insoluble matter content is 4.0 mg / kg, the phosphate content is 0.22 mg / kg, the calcium content is 0.13 mg / kg, the iron content is 0.08 mg / kg, the magnesium content is 0.13 mg / kg, the sodium content is 0.10 mg / kg, and the potassium content is 0.19 mg / kg.

[0038] The density, refractive index at 20°C, alkalinity, biuret content, aldehyde content, insoluble content, phosphate content, calcium content, iron content, magnesium content, sodium content, and potassium content of the marine nitrogen oxide reducing agents prepared in Examples 1-2 and Comparative Examples 1-3 all comply with the requirements of GB / T 35176.1-2017 / ISO 186 11-1:2014 Ships and Marine Technology - Marine Nitrogen Oxide Reducing Agents AUS 40. This indicates that the preparation methods of Examples 1-2 and Comparative Examples 1-3, after adding appropriate modifiers for adjustment, will not lead to the problem of the prepared marine nitrogen oxide reducing agents failing to meet the standard requirements. However, compared with the marine nitrogen oxide reducing agent prepared in Example 1, the marine nitrogen oxide reducing agent prepared in Comparative Examples 1-2 has a relatively higher insoluble content.

[0039] Experimental Example 1 In Examples 1-2 and Comparative Examples 1-3, step 2: dissolution was modified by changing the phrase "immediately add all the purified urea obtained in step 1 to the reaction equipment with tertiary water" to "after placing all the purified urea obtained in step 1 in an open environment at a temperature of 23±1℃ and a relative humidity of 55±2% for 2 days, it was then added to the reaction equipment with tertiary water." The insoluble content of the prepared marine nitrogen oxide reducing agent was then tested, and the results are as follows:

[0040] The results above show that after the purified urea was left exposed for 1 day, the content of insoluble matter in the marine nitrogen oxide reducing agent prepared in Comparative Examples 1-2 was significantly higher than that in Example 1, indicating that the purified urea prepared in Comparative Examples 1-2 was more likely to carry dust.

[0041] Experimental Example 2 Thirty batches of marine nitrogen oxide reducing agent were continuously prepared according to the preparation methods of Examples 1-2 and Comparative Examples 1-3, respectively. Before continuous preparation, the polyethylene filter screen, polypropylene filter element, and polysulfone filter membrane were replaced with new ones. During continuous preparation, the filter screen, filter element, and filter membrane were not replaced with new ones. After continuous preparation, the stable pure water flux of the polysulfone filter membrane at 25°C and 0.1 MPa was tested. The test results are as follows:

[0042] Then, the polysulfone filter membrane was soaked in hot water at 50℃ for 40 minutes, and the stable pure water flux of the polysulfone filter membrane at 25℃ and 0.1MPa was tested. The test results are as follows:

[0043] The results above show that, compared with the preparation method of Example 1, the preparation methods of Comparative Examples 1-2 are more prone to membrane fouling. In the preparation method of Comparative Example 3, the membrane flux is more difficult to recover after membrane fouling, indicating that the adhesion of membrane pollutants is stronger.

Claims

1. A method for preparing a nitrogen oxide reducing agent for ships, characterized in that, include: Hydrolysis crystallization, dissolution, filtration, fine filtration, ultrafiltration; The hydrolysis crystallization process involves mixing industrial urea and tertiary water, stirring at 73-75°C, performing a first cooling, adding dodecaacetylenol polyoxyethylene ether, performing a second cooling, adding a mixed urea solution at 62.5-64°C, performing a third cooling, maintaining the temperature, centrifuging, and using the collected precipitate as purified urea. The method for preparing the mixed urea solution is as follows: polyethylene glycol 8000, urea and tertiary water are mixed and stirred at 73-75°C to obtain a composite urea solution. The dissolution process involves mixing purified urea, tertiary water, and a mixed surfactant solution, and stirring at 40-45°C to obtain an aqueous urea solution. The method for preparing the mixed surfactant solution is as follows: dodecynediol polyoxyethylene ether, anhydrous ethanol and tertiary water are mixed and stirred at 60-65°C to obtain the mixed surfactant solution.

2. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the hydrolysis crystallization, the mass ratio of industrial urea to tertiary water is 725-730:270; When adding dodecynediol polyoxyethylene ether, the amount of dodecynediol polyoxyethylene ether added is 50-60 mg / L; The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0; The mass ratio of industrial urea to mixed urea solution is 725-730:100-102.

3. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the hydrolysis crystallization process, the first cooling is performed at a cooling rate of 0.05℃ / min for 100-110 minutes. The second cooling process involves cooling at a rate of 0.10℃ / min for 60-70 minutes. The third cooling process involves cooling at a rate of 0.2℃ / min for 100-110 minutes. The centrifugation speed is 3500-4000 rpm, and the centrifugation time is 10-15 min.

4. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the preparation of the mixed urea solution, the mass ratio of polyethylene glycol 8000, urea and tertiary water is 5-5.2:65-65.8:30-31.

5. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the dissolution process, the mass ratio of purified urea, tertiary water, and mixed surfactant solution is 40:50:

10.

6. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, In the preparation of the mixed surfactant solution, the mass ratio of dodecynediol polyoxyethylene ether, anhydrous ethanol, and tertiary water is 1-1.1:10-12:1000-1100. The CAS number of the dodecylene diol polyoxyethylene ether is 169117-72-0.

7. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, The filtration process involves using a bag filter to filter the urea solution, resulting in a filtered urea solution. In the filtration process, the filter used in the bag filter is a polyethylene filter, and the filtration accuracy of the polyethylene filter is 1μm.

8. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, The fine filtration is performed by using a fine filtration device to finely filter the filtered urea aqueous solution to obtain a finely filtered urea aqueous solution. In the fine filtration process, the filter element used in the fine filtration equipment is a polypropylene filter element, and the filtration accuracy of the polypropylene filter element is 0.25μm.

9. The method for preparing a marine nitrogen oxide reducing agent according to claim 1, characterized in that, The ultrafiltration process involves using an ultrafiltration device to ultrafilter the finely filtered urea aqueous solution to obtain a nitrogen oxide reducing agent for marine use. In the ultrafiltration process, the filter membrane used in the ultrafiltration equipment is a polysulfone filter membrane; The filter membrane used in the ultrafiltration equipment has a filtration accuracy of 0.01 μm; The filter membrane used in the ultrafiltration equipment has a stable pure water flux of 100 L / (m³) at 25°C and 0.1 MPa. 2 •h); The pressure during ultrafiltration is 0.24-0.26 MPa.

10. A marine nitrogen oxide reducing agent prepared by the preparation method according to any one of claims 1-9.

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