A method for purifying urea for use in vehicles

Abstract

The application discloses a kind of urea purification methods for vehicle, urea and reaction promoter are added in aqueous ethanol solution;After dissolving, heat to mixed solution boiling and keep warm reflux;The filtrate is stirred to room temperature to make urea crystallization precipitate;Separate urea crystalline and dry to obtain the urea solid after purification;The filtrate is recycled to continue to apply urea purification.The method improves the solubility of urea in aqueous ethanol solution after adding reaction promoter, improves the purification effect of urea, and the content of biuret in urea after purification is as low as 0.11%;The filtrate after purification is reused, which reduces the loss of incomplete crystallization urea, improves the purification yield of urea, and reduces the discharge of recrystallization wastewater, reduces the environmental pollution of urea purification, and further reduces the purification cost;Compared with prior art, the content of biuret is reduced to below 0.2%, which greatly reduces the discharge of recrystallization wastewater, reduces the environmental pollution of urea purification, and further reduces the purification cost;Aqueous ethanol solution is used instead of alcohol solution to purify urea, which further reduces the purification cost.

Description

Technical Field

[0001] This invention relates to a production process for automotive urea, and more particularly to a method for purifying automotive urea. Background Technology

[0002] With increasing emphasis on environmental sustainability, stricter requirements are being placed on vehicle exhaust emissions. Urea for vehicles, as a catalyst for removing nitrogen oxides (NOx) from diesel engine exhaust, is being used to address this issue. x It is reduced to pollution-free N2 and H2O. Currently, the purity of urea on the market is insufficient. Biuret, as one of the main impurities in urea, can cause scale buildup and blockage in the SCR system of diesel engines and near the urea nozzles if its content is too high, affecting the efficiency of exhaust gas treatment. Currently, the main purification methods for industrial urea are recrystallization, organic phase extraction, and multi-stage filtration membrane technology to remove impurities. Recrystallization is energy-intensive; for example, patent CN102442928A uses recrystallization to remove impurities, but reducing the biuret content to below 0.2% using this method is too energy-intensive, the crystallization process is difficult to control, the process cycle is long, and the cost of industrial application is increased. Organic phase extraction, as used in CN105237439A, uses methanol / ethanol thermal extraction for urea purification. However, because urea has limited solubility in pure small molecule alcohols, and excessively high temperatures can also lead to the formation of biuret, further... The increased purification costs, coupled with the fact that the selected organic reagents are hazardous chemicals posing flammable and explosive risks, and generating large amounts of gaseous pollutants, along with stricter process requirements, all contribute to a significant increase in costs and risks, making large-scale application difficult. The purification results using multi-stage filtration membrane technology are not ideal. Using a superfilter to filter the initial automotive urea solution yields a purified automotive urea solution, typically containing approximately 2.8% biuret. Further reducing the biuret content to below 0.2% requires consuming large amounts of water and generating substantial wastewater, making subsequent treatment difficult and hindering large-scale industrial production. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to reduce the biuret content in automotive urea and improve the catalytic efficiency of automotive urea, by providing a method for purifying automotive urea.

[0004] Technical solution: The present invention provides a method for purifying automotive urea, comprising the following steps:

[0005] (S1) Add urea and a reaction aid in an ethanol aqueous solution at a mass ratio of 10000:4.5-6;

[0006] (S2) Dissolve, heat to boiling point of the mixed solution and keep warm under reflux;

[0007] (S3) Stir the filtrate and cool it to room temperature to allow urea crystals to precipitate.

[0008] (S4) Filter to separate urea crystals and dry to obtain purified urea solid;

[0009] (S5) The filtrate from step (S4) is recycled and added to step (1) for continued application.

[0010] Furthermore, the co-reactant is one or more of cerium oxide, copper oxide, manganese dioxide, and titanium dioxide, and the mass ratio of the co-reactant cerium oxide, copper oxide, manganese dioxide, and titanium dioxide is 1:1:1:1.

[0011] Furthermore, the concentration of the ethanol solution is 15%-30%.

[0012] Furthermore, the mass ratio of the co-reactant to the aqueous ethanol solution is 1:500-1000.

[0013] Furthermore, in step (S2), the mixed solution is kept at a reflux temperature of 80-90°C for 2-3 hours.

[0014] Furthermore, in step (S4), the filtrate is replenished with ethanol once and then added back into the purification process, with the amount of ethanol replenished being the same as the original amount added.

[0015] Furthermore, the filtrate from step (S4) is recycled and reused in step (1) for 3 to 4 more times. After the filtrate is recycled 3 to 4 times, the mixed solution in step (S3) is cooled to 0°C to precipitate and recover urea crystals, and the remaining liquid is discarded.

[0016] Furthermore, the reaction aids added in step (S1) are recovered and reused in the purification process.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. After adding the co-reactant, the solubility of urea in the ethanol aqueous solution is improved, the purification effect of urea is improved, and the content of biuret in the purified urea is as low as 0.11%; 2. The filtrate after purification can be reused, which reduces the purification cost and reduces the loss of incompletely crystallized urea, thereby improving the urea purification yield; 3. Compared with the prior art, the content of biuret is reduced to below 0.2%, which greatly reduces the discharge of recrystallization wastewater, reduces the pollution of urea purification to the environment, and further reduces the purification cost; 4. Using ethanol aqueous solution instead of alcohol solution to purify urea further reduces the purification cost. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0020] like Figure 1 The diagram shows a urea purification process. Urea can be purified using different ratios of co-reactants and different concentrations of ethanol aqueous solution, following this method.

[0021] Example 1

[0022] (S1) Add 500 kg of urea granules, 300 kg of 15% ethanol aqueous solution, 75 g of copper oxide, 75 g of cerium oxide, 75 g of manganese oxide and 75 g of titanium dioxide into a closed mixing vessel.

[0023] (S2) Stir and heat until completely dissolved, then heat to 80°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0024] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0025] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0026] (S5) Continue to add 350 kg of urea granules to the mixing vessel, and add 300 kg of 15% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0027] (S6) Continue to add 350 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, and repeat (S4) to obtain purified urea solid.

[0028] Example 2

[0029] (S1) Add 500 kg of urea granules, 300 kg of 20% ethanol aqueous solution, 75 g of copper oxide, 75 g of cerium oxide, 75 g of manganese oxide and 75 g of titanium dioxide into a closed mixing vessel.

[0030] (S2) Stir and heat until completely dissolved, then heat to 80°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0031] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0032] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0033] (S5) Continue to add 300 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0034] (S6) Continue to add 300 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, repeat (S4) to obtain purified urea solid.

[0035] Example 3

[0036] (S1) Add 500 kg of urea granules, 300 kg of 30% ethanol aqueous solution, 75 g of copper oxide, 75 g of cerium oxide, 75 g of manganese oxide and 75 g of titanium dioxide into a closed mixing vessel.

[0037] (S2) Stir and heat until completely dissolved, then heat to 80°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0038] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0039] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0040] (S5) Continue to add 250 kg of urea granules to the mixing vessel, and add 300 kg of 30% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0041] (S6) Continue to add 250 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, and repeat (S4) to obtain purified urea solid.

[0042] Comparative Example 1

[0043] (S1) Add 500 kg of urea granules, 300 kg of 20% ethanol aqueous solution, 75 g of copper oxide, 75 g of manganese oxide and 75 g of titanium dioxide into a closed mixing vessel;

[0044] (S2) Stir and heat until completely dissolved, then heat to 90°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0045] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0046] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0047] (S5) Continue to add 300 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0048] (S6) Continue to add 300 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, repeat (S4) to obtain purified urea solid.

[0049] Comparative Example 2

[0050] (S1) Add 500 kg of urea granules, 300 kg of 20% ethanol aqueous solution, 75 g of cerium oxide, 75 g of manganese oxide and 75 g of titanium dioxide into a closed mixing vessel;

[0051] (S2) Stir and heat until completely dissolved, then heat to 90°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0052] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0053] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0054] (S5) Continue to add 300 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0055] (S6) Continue to add 300 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, repeat (S4) to obtain purified urea solid.

[0056] Comparative Example 3

[0057] (S1) Add 500 kg of urea granules, 300 kg of 20% ethanol aqueous solution, 75 g of copper oxide, 75 g of cerium oxide and 75 g of titanium dioxide into a closed mixing vessel;

[0058] (S2) Stir and heat until completely dissolved, then heat to 90°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0059] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0060] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0061] (S5) Continue to add 300 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0062] (S6) Continue to add 300 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, repeat (S4) to obtain purified urea solid.

[0063] Comparative Example 4

[0064] (S1) Add 500 kg of urea granules, 300 kg of 20% ethanol aqueous solution, 75 g of copper oxide, 75 g of cerium oxide and 75 g of manganese oxide into a closed mixing vessel;

[0065] (S2) Stir and heat until completely dissolved, then heat to 90°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0066] (S3) Filter out the reaction aid and put it back into step (1). Transfer the filtrate to the crystallization vessel, stir and cool to room temperature. Centrifuge to allow urea crystals to precipitate. Centrifuge the filtrate and put it back into step (1).

[0067] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0068] (S5) Continue to add 300 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0069] (S6) Continue to add 300 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, repeat (S4) to obtain purified urea solid.

[0070] Comparative Example 5

[0071] (S1) Add 500 kg of urea granules and 300 kg of 20% ethanol aqueous solution into a sealed mixing vessel;

[0072] (S2) Stir and heat until completely dissolved, then heat to 90°C until the mixed solution boils and shows significant reflux, then keep it at the temperature and reflux for 2 hours.

[0073] (S3) The filtrate is transferred to a crystallization vessel and stirred until it cools to room temperature. It is then centrifuged to allow urea crystals to precipitate. The centrifuged filtrate is then returned to step (1).

[0074] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0075] (S5) Continue to add 300 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0076] (S6) Continue to add 300 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, repeat (S4) to obtain purified urea solid.

[0077] Comparative Example 6

[0078] (S1) Add 400 kg of urea granules and 300 kg of 20% ethanol aqueous solution into a sealed mixing vessel;

[0079] (S2) Stir and heat until completely dissolved, then stir and heat to 60°C;

[0080] (S3) The filtrate is transferred to a crystallization vessel and stirred until it cools to room temperature. It is then centrifuged to allow urea crystals to precipitate. The centrifuged filtrate is then returned to step (1).

[0081] (S4) Separate the urea crystals and dry them to obtain purified urea solid;

[0082] (S5) Continue to add 200 kg of urea granules to the mixing vessel, and add 300 kg of 20% ethanol aqueous solution to step S1. Repeat (S2), (S3) and (S4) to obtain purified urea solid.

[0083] (S6) Continue to add 200 kg of urea granules to the mixing vessel, repeat (S2), adjust (S3) the temperature of the crystallization vessel to 0℃, and repeat (S4) to obtain purified urea solid.

[0084] The urea solid obtained after purification in the above examples and comparative examples was mixed with high-purity water at a mass ratio of 32.5:67.5 to prepare a urea standard solution. The urea content and biuret content of the urea solution were tested according to the methods described in Appendix A and Appendix C of GB29518-2013. The test results are detailed in Table 1. The urea purification yield of each example was calculated based on the urea crystal quality and urea feed amount, as shown in Table 2.

[0085] The experimental results in Table 1, comparing Comparative Examples 5 and 6, indicate that high-temperature reflux can promote the solubility of urea in organic solvents, but it also promotes the formation of biuret. The amount of urea treated with the same amount of solvent in Comparative Example 5 is higher than that in Comparative Example 6; however, the biuret content after purification is higher, with Comparative Example 5 containing 1.5 times the biuret content of Comparative Example 6. Comparing Examples 1-3 and Comparative Example 5, the addition of a co-reactant reduced the biuret content in the urea solution by 54%-77%. Furthermore, Table 2, comparing Examples 1 and 6, shows that with the same solvent used for urea purification, the amount of urea treated increased by 55% after adding the co-reactant, and the urea yield also improved. Therefore, after dissolving urea and adding a co-reactant, high-temperature reflux for a period of time improves the urea solubility while effectively inhibiting the formation of biuret, significantly improving the urea purification efficiency.

[0086] Table 1. Biuret content after urea purification under different process conditions

[0087]

[0088] Table 2. Urea yield under different purification conditions

[0089] Example Feed quantity (kg) Material received (kg) yield Example 1 1550 1410 90.97％ Example 2 1400 1299 92.79％ Example 3 1250 1185 94.80％ Comparative Example 1 1400 1287 91.93％ Comparative Example 2 1400 1294 92.43％ Comparative Example 3 1400 1289 92.07％ Comparative Example 4 1400 1297 92.64％ Comparative Example 5 1400 1289 92.07％ Comparative Example 6 1000 898 89.80％

[0090] Compared with Comparative Examples 1-4, the amount of co-catalyst reduced in Example 2 resulted in an increase in the biuret content in the purified urea. Copper oxide, manganese oxide, and cerium oxide act as co-reactants to inhibit the formation of biuret, and their reduced dosage leads to a relative increase in the biuret content in the urea. Titanium dioxide, on the other hand, has high dispersibility and mainly promotes the dispersion performance of co-reactants in the purification solvent. It also improves the dispersion performance of copper oxide, manganese oxide, and cerium oxide in the solvent, thus promoting their inhibition of biuret formation. The lack of titanium dioxide has a smaller impact on the biuret content in the purified urea compared to copper oxide, manganese oxide, and cerium oxide.

[0091] Compared with Examples 1-3, the yield and purification effect of urea increased with the increase of ethanol content in the purification solvent. However, because the solubility of urea decreased with the increase of alcohol content, the amount of urea processed per batch decreased and the solvent cost increased. Considering both the purification effect and the extraction cost, the biuret content in the purified urea of ​​Example 2 was less than 0.2% (0.15%), and the purification cost was significantly reduced compared to existing technologies that reduce the biuret content to below 0.2%, while also significantly reducing the amount of recrystallization water used.

Claims

1. A method for purifying automotive urea, characterized in that, Includes the following steps: (S1) Add urea and a reaction aid in an ethanol-water solution at a mass ratio of 10000:4.5-6; (S2) Dissolve, heat to boiling, and maintain the temperature under reflux; (S3) Stir the filtrate and cool it to room temperature to allow urea crystals to precipitate. (S4) Filter to separate urea crystals and dry to obtain purified urea solid; (S5) The filtrate from step (S4) is recycled and reused in step (1); The co-reactants are cerium oxide, copper oxide, manganese dioxide and titanium dioxide, and the mass ratio of cerium oxide, copper oxide, manganese dioxide and titanium dioxide is 1:1:1:1; The mass ratio of the co-reactant to the aqueous ethanol solution is 1:500-1000; In step (S2), the reflux temperature of the mixed solution is 80-90℃; In step (S2), the mixed solution is kept warm and refluxed for 2-3 hours.

2. The method for purifying automotive urea according to claim 1, characterized in that, The concentration of the ethanol aqueous solution is 15%-30%.

3. The method for purifying automotive urea according to claim 1, characterized in that, The filtrate from step (S4) is replenished with ethanol once and then added back into the purification process, with the amount of ethanol replenished being the same as the original amount added.

4. The method for purifying automotive urea according to claim 3, characterized in that, The filtrate in step (S4) is reused 3-4 times. After the filtrate is recycled 3-4 times, the mixed solution in step (S3) is cooled to 0°C to precipitate and recover urea crystals. The remaining liquid is discarded.

5. The method for purifying automotive urea according to claim 1, characterized in that, The auxiliary reactant added in step (S1) is recovered and then reintroduced into the purification process.

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