Urea solution for diesel vehicle and preparation method thereof

Abstract

The invention relates to a urea solution for a diesel vehicle and a preparation method of the urea solution in the technical field of vehicle tail gas treatment. The urea solution comprises a urea aqueous solution and a surfactant, the preparation method of the urea solution for the diesel vehicle comprises the following steps: determining the addition amount of the surfactant in the urea solution according to the number of WHTC hot test particles and the crystal mass of the urea solution; and mixing the urea aqueous solution and the surfactant in proportion to form the urea solution. According to the urea solution prepared through the preparation method of the urea solution for the diesel vehicle, the number of particles can be controlled, and meanwhile crystallization can be reduced.

Description

Technical Field

[0001] The present application relates to the technical field of vehicle exhaust treatment, and in particular to a urea solution for diesel vehicles and a preparation method thereof. Background Art

[0002] After the urea aqueous solution used in the selective catalytic reduction (SCR) system is sprayed out by the urea nozzle, it is first decomposed into ammonia when the exhaust temperature is above 180°C, and then reacts with NOx gas under the action of the catalyst to generate nitrogen and water, thereby achieving the purpose of reducing exhaust pollutants.

[0003] However, in the actual reaction process of urea, some undecomposed urea and byproducts such as cyanuric acid will be deposited in the post-treatment mixer and management, and eventually form block crystals. If the crystal size is large, it will seriously affect the urea hydrolysis process and cause a significant increase in exhaust resistance. After adding surfactants to the urea solution, the surface tension of urea droplets is reduced, which is beneficial to the atomization and dispersion of urea droplets and helps to inhibit the formation of crystals.

[0004] The National VI emission regulations have strict restrictions on the number of engine particulate emissions, but urea will produce a large amount of particulate matter such as ammonia salts under high temperature conditions, and the number of urea particles will increase significantly after adding surfactants to the urea solution.

[0005] To this end, the present invention is proposed. Summary of the invention

[0006] In view of the problems existing in the background technology, the present application provides a urea solution for diesel vehicles and a preparation method thereof. The urea solution prepared by the preparation method can control the number of particles while reducing crystallization.

[0007] According to one aspect of the present invention, a method for preparing a urea solution for a diesel vehicle is provided, wherein the urea solution comprises an aqueous urea solution and a surfactant, and the preparation method comprises the following steps: determining the amount of the surfactant added to the aqueous urea solution according to the number of WHTC hot test particles and the crystal quality of the urea solution; and mixing the aqueous urea solution and the surfactant in proportion to form a urea solution.

[0008] In some embodiments of the present invention, determining the amount of the surfactant added to the urea aqueous solution includes: preparing urea solution samples with different surfactant mass fractions, and the surfactant mass fractions of all urea solution samples are increased from 0% by a set difference; then performing a WHTC hot cycle emission test on all urea solution samples to obtain the number of WHTC hot test particles of each urea solution sample; and selecting the first 1200s of the WHTC cycle of each urea solution sample as the basic working condition, and running the cycle 30 times. After the cycle is completed, the residual crystals are weighed to obtain the crystal mass of each urea solution sample; and then selecting the urea solution sample with the corresponding surfactant mass fraction according to the particle number limit of the WHTC hot cycle emission test and the requirements for the crystal quality.

[0009] In some embodiments of the present invention, the set difference is 0.05%~0.15%.

[0010] In some embodiments of the present invention, the particle number limit of the WHTC hot cycle emission test is 6×10 11 # / kWh.

[0011] In some embodiments of the present invention, the components of the urea solution are mixed by stirring with high-pressure air.

[0012] In some embodiments of the present invention, the mixing time is 40-60 min.

[0013] In some embodiments of the present invention, the components of the urea solution are mixed uniformly at room temperature.

[0014] According to another aspect of the present invention, a urea solution prepared by the method for preparing the urea solution for diesel vehicles is provided.

[0015] The embodiment of the present application provides a method for preparing a urea solution for a diesel vehicle. The method for preparing a urea solution for a diesel vehicle, based on the relationship between the surfactant concentration and the surface tension, the number of particles and the crystal quality of the urea solution, uses urea solution samples with different surfactant mass fractions and cooperates with a WHTC hot cycle emission test to accurately obtain the WHTC hot test particle number and crystal quality of each urea solution sample, and then compares the WHTC hot test particle number and crystal quality of each urea solution sample with the required values, thereby obtaining a surfactant mass fraction that meets the requirements, that is, determining the amount of surfactant added to the urea aqueous solution, thereby achieving the purpose of reducing crystallization and controlling the particle number to meet the emission requirements, ensuring the performance of the engine, and being very environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the following detailed description of the preferred embodiment.The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application.

[0017] Figure 1 It is a relationship diagram between surfactant concentration and surface tension, particle quantity and crystal quality in the urea solution of the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will easily recognize multiple non-critical parameters, which can be changed or modified, and the results are substantially the same.

[0019] If no specific technology or conditions are specified in the examples, the technology or conditions described in the literature in this field or the product instructions are used. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased through regular channels. The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available products unless otherwise specified.

[0020] Surfactants are a class of chemical products that can reduce the surface tension of a liquid when present in a solution at low concentrations.

[0021] The present application discloses a method for preparing a urea solution for a diesel vehicle. The urea solution includes a urea aqueous solution and a surfactant. The preparation method includes the following steps: The amount of surfactant added to the urea aqueous solution is determined based on the number of particles and crystal quality of the urea solution in the WHTC hot test.

[0022] The urea aqueous solution and the surfactant are mixed in proportion to form a urea solution.

[0023] It should be understood that the urea aqueous solution in the present invention refers to a solution in which the solute is urea and the solvent is ultrapure water.

[0024] By using the preparation method in the technical solution, the amount of surfactant added to the urea aqueous solution is determined based on the WHTC hot test particle number and crystal quality of the urea solution, thereby achieving the purpose of reducing crystallization and controlling the particle number to meet emission requirements, ensuring the performance of the engine, and being very environmentally friendly.

[0025] In some embodiments of the present invention, determining the amount of surfactant added to the urea aqueous solution comprises the following steps: Urea solution samples with different surfactant mass fractions were prepared, and the surfactant mass fractions of all urea solution samples were increased from 0% according to the set difference.

[0026] Then, a WHTC hot cycle emission test was performed on all urea solution samples to obtain the number of WHTC hot test particles of each urea solution sample; and the first 1200s of the WHTC cycle of each urea solution sample was selected as the basic operating condition, and the cycle was run 30 times. After the cycle was completed, the residual crystals were weighed to obtain the crystal mass of each urea solution sample.

[0027] Then, according to the particle number limit of the WHTC hot cycle emission test and the requirements for crystallization quality, a urea solution sample with a corresponding surfactant mass fraction is selected.

[0028] By using urea solution samples with different surfactant mass fractions and cooperating with the WHTC (transient condition) hot cycle emission test, the WHTC hot test particle number and crystal mass of each urea solution sample can be accurately obtained. Then, the WHTC hot test particle number and crystal mass of each urea solution sample are compared with the required values ​​to obtain the surfactant mass fraction that meets the requirements. The operation is simple and convenient. Based on this experimental data, urea solutions that meet specific requirements can be accurately prepared.

[0029] Furthermore, the set difference in the present invention may be 0.05% to 0.15%, for example, the set difference may be 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, etc.

[0030] Furthermore, a larger set difference can be used to find a surfactant mass fraction range that preliminarily meets the requirements, such as setting a difference of 0.15%, and then a smaller set difference can be used to more accurately locate the surfactant mass fraction, such as setting a difference of 0.05%, so as to reduce the number of experiments and improve efficiency.

[0031] The particle number limit of the WHTC hot cycle emission test is 6×10 11 # / kWh.

[0032] Specifically, the WHTC hot cycle emission test can be carried out in accordance with the emission regulations GB 17691-2018. During the test, the urea injection amount remains the same. The particle number limit of the present invention is 6×10 11 # / kWh (6E+11 # / kWh) is the particle number limit for the WHTC hot cycle emission test in GB17691-2018.

[0033] It should be noted that in other implementations, a more stringent particle number limit may be selected depending on different standards.

[0034] In some embodiments of the present invention, the components of the urea solution are mixed by agitation with high-pressure air.

[0035] Furthermore, the mixing time is 40-60 min.

[0036] Furthermore, the components of the urea solution are mixed uniformly at room temperature.

[0037] The invention also discloses a urea solution prepared by the method for preparing the urea solution for diesel vehicles. The urea solution comprises a urea aqueous solution and a surfactant.

[0038] In some embodiments of the present invention, the surfactant may be selected from fatty alcohol polyoxyethylene ethers.

[0039] In other embodiments, other surfactants that can reduce the surface tension of the urea solution can be applied to the configuration method proposed in the present invention.

[0040] The present invention also provides the following experimental examples and test results.

[0041] It should be noted that the relationship between the surfactant concentration and the surface tension, the number of particles and the crystal quality in the urea solution of the present invention is as follows: Figure 1 As shown in the figure, when the surfactant concentration is less than M2, the surface tension of the urea droplets decreases rapidly as the surfactant concentration increases; when the surfactant concentration is greater than M2, the surface tension of the urea droplets basically does not change as the surfactant concentration increases; when the urea injection amount is the same, the number of particles and the crystal quality change trend with the surfactant concentration is similar to the surface tension. In order to reduce the crystal quality, the surfactant concentration is set to M2 for the best effect, but the number of particles at this time greatly exceeds the regulatory limit, so the surfactant concentration should be lower than M1.

[0042] Specifically, the urea solution used in this experimental example meets the requirements of GB 29518-2013, and the mass fraction of urea is 32.5%; the surfactant is fatty alcohol polyoxyethylene ether.

[0043] Different doses of fatty alcohol polyoxyethylene ether were added to the urea solution at room temperature, and the mixture was stirred with high-pressure air for 40 to 60 minutes. The preparation results are shown in Table 1. Experimental examples are numbered A to I, with mass concentrations ranging from 0% to 0.8% and a concentration interval of 0.1%; among them, Experimental examples B to I all meet the requirements of GB 29518-2013.

[0044] Table 1 Test results of different concentrations of surfactant urea solution

[0045] On the engine test bench, the WHTC hot cycle emission test was carried out in accordance with the emission regulations GB 17691-2018, and the urea injection amount remained the same during the test. The particle number limit for the WHTC hot cycle emission test in GB 17691-2018 is 6E+11# / kWh. The particle number results of urea solutions numbered A~I are shown in Table 1.

[0046] The first 1200s of the WHTC cycle was selected as the basic working condition, and the cycle was run 30 times. After the cycle was completed, the residual crystals were weighed. The crystal quality results are shown in Table 1.

[0047] From the test results in Table 1, it can be seen that as the concentration of fatty alcohol polyoxyethylene ether surfactant increases, the number of particles in the WHTC hot test increases rapidly at first, and then changes slightly after Scheme F; the crystal quality decreases rapidly at first, and then changes slightly after Scheme G. If the minimum crystal quality is pursued, Experimental Example F is the best formulation, but at this time the number of particles in the WHTC hot test has greatly exceeded the regulatory requirements.

[0048] Since the number of particles in the WHTC hot test is a mandatory requirement of emission regulations, the concentration of fatty alcohol polyoxyethylene ether surfactant in this experimental example should be less than 0.4%, preferably should not exceed 0.3%, and Experimental Example D can be selected as the final formula of the urea solution.

[0049] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for preparing a urea solution for a diesel vehicle, characterized in that: The urea solution comprises a urea aqueous solution and a surfactant; The preparation method comprises the following steps: Determining the amount of the surfactant added to the urea aqueous solution according to the WHTC hot test particle quantity and crystal quality of the urea solution; The urea aqueous solution and the surfactant are mixed in proportion to form a urea solution.

2. The preparation method according to claim 1, characterized in that: The determination of the amount of the surfactant added to the urea aqueous solution includes: Prepare urea solution samples with different surfactant mass fractions, and the surfactant mass fractions of all urea solution samples increase from 0% according to the set difference; Then, a WHTC hot cycle emission test was performed on all urea solution samples to obtain the number of WHTC hot test particles of each urea solution sample; and the first 1200s of the WHTC cycle of each urea solution sample was selected as the basic working condition, and the cycle was run 30 times. After the cycle was completed, the residual crystals were weighed to obtain the crystal mass of each urea solution sample; Then, according to the particle number limit of the WHTC hot cycle emission test and the requirements for crystallization quality, a urea solution sample with a corresponding surfactant mass fraction is selected.

3. The preparation method according to claim 2, characterized in that: The set difference is 0.05%~0.15%.

4. The preparation method according to claim 2, characterized in that The particle number limit of the WHTC hot cycle emission test is 6×10 11 # / kWh.

5. The preparation method according to claim 1, characterized in that: The components of the urea solution are stirred and mixed by high-pressure air.

6. The preparation method according to claim 5, characterized in that: The mixing time is 40-60 min.

7. The preparation method according to claim 1, characterized in that: The components of the urea solution are mixed uniformly at room temperature.

8. A urea solution prepared by the method for preparing a urea solution for diesel vehicles according to any one of claims 1 to 7.

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