Anti-crystallization urea solution for vehicles and method for preparing the same

Abstract

The present application belongs to the technical field of vehicle exhaust treatment, and particularly relates to an anti-crystallization urea solution for vehicles and a preparation method thereof. The composition comprises the following components: high-purity urea, anti-crystallization additives and deionized water. The present application uses a full-ammonium system formula and a light process chain to synergistically inhibit crystallization: a micro-dose of ammonium salt is introduced at the formula end to selectively adsorb crystal faces, reduce the growth rate, prolong the induction period and weaken the adhesion; ammonium carbamate / ammonium bicarbonate is used to provide trace free ammonia and mild buffering to promote the preferential hydrolysis / ammonolysis of isocyanic acid, thereby reducing high-melting-point phases such as cyanuric acid at the source; an ammonia-type strong acid cation resin terminal polishing removes heterogeneous nucleation sites such as calcium, magnesium, iron and copper, and is combined with vacuum degassing, absolute value microfiltration and low-temperature short-time crystallization induction and re-filtration in a closed loop to simultaneously reduce the nucleation rate, crystal growth and by-phase generation, reduce nozzle / mixer evaporation-re-crystallization and freeze-thaw insolubles, and stabilize atomization and ammonia-tail gas mixing.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of vehicle exhaust treatment, and particularly relates to an anti-crystallization urea solution for vehicles and a preparation method thereof. BACKGROUND

[0002] As the core reducing agent of the selective catalytic reduction (SCR) system to achieve high-efficiency denitration, the 32.5% urea aqueous solution of the urea solution for vehicles (AdBlue / DEF) exposes a serious functional failure risk in low-temperature environment (below-20℃) and vehicle frequent start-stop working conditions: low-temperature freezing crystallization leads to urea pump and nozzle blockage, and the thermal cycle in the start-stop process aggravates the local water evaporation of the solution, promotes the concentration of the residual liquid to form hard crystalline deposits. More seriously, urea will decompose to produce isocyanic acid (HNCO) intermediates in the high-temperature injection stage, and the active substance is easy to have side reactions with trace water, ammonia or metal ions in the system to generate stubborn insoluble substances such as biuret and cyanuric acid; at the same time, metal ions such as calcium, magnesium and iron from production equipment or storage containers act as crystal nucleus inducers, significantly reduce the crystallization barrier and accelerate the impurity deposition chain reaction. The three mechanisms (low-temperature phase change crystallization, isocyanic acid derived side reaction, metal ion catalytic nucleation) work together to cause filter screen blockage, sensor failure and injection precision degradation, and finally trigger the SCR system failure and vehicle torque limiting operation. The current industry solutions have the following defects: the electric heating device can only delay low-temperature crystallization but cannot inhibit isocyanic acid side reactions, and greatly increases energy consumption; the traditional alcohol / ammonium salt additives can reduce the freezing point, but will promote the generation of isocyanic acid at high temperature, and at the same time introduce additional metal ions to aggravate nucleation and deposition. The existing technology has always failed to break through the bottleneck of the synergistic regulation of low-temperature stability, side reaction inhibition and metal impurity passivation, resulting in serious lack of reliability of the urea solution for vehicles in severe working conditions. Therefore, based on the above defects, it is extremely necessary to develop a new type of anti-crystallization urea solution. SUMMARY

[0003] In view of the defects of the prior art, the purpose of the present application is to provide an anti-crystallization urea solution for vehicles and a preparation method thereof. In order to solve the crystalline deposition, isocyanic acid side reaction and metal ion induced nucleation in low-temperature and start-stop working conditions, the present application uses the full ammonium system formula and light process chain to synergistically inhibit crystallization: a small amount of polyaspartic acid ammonium salt / poly-maleic acid ammonium salt is introduced into the formula end to selectively adsorb crystal faces, reduce growth rate, prolong induction period and weaken adhesion; ammonium carbamate / ammonium bicarbonate provides trace free ammonia and mild buffering to promote isocyanic acid to preferentially hydrolyze / ammonolysis, and to reduce high-melting-point phases such as cyanuric acid at the source; on the process end, an ammonia type strong acid cation resin is used for terminal polishing to remove calcium, magnesium, iron and copper and other heterogeneous nucleation sites, and is matched with vacuum degassing, absolute value microfiltration and low-temperature short-time crystallization induction and re-filtration closed loop synergy to simultaneously reduce nucleation rate, crystal growth and by-product phase generation, reduce nozzle / mixer evaporation and re-crystallization and freeze-thaw insoluble substances, and stabilize atomization and ammonia and tail gas mixing.

[0004] The technical effect of the present application is realized by the following technical scheme: an anti-crystallization vehicle urea solution, which comprises the following components: high-purity urea, an anti-crystallization additive, and deionized water.

[0005] Preferably, the mass fraction of the high-purity urea is 32.5%;

[0006] Preferably, the anti-crystallization additive comprises the following components: a polycarboxylic acid ammonium salt and a volatile ammonium salt.

[0007] Preferably, the polycarboxylic acid ammonium salt is any one or more of a polyammonium aspartate and a polymaleate ammonium salt; further preferably, the polyammonium aspartate and the polymaleate ammonium salt are prepared in a ratio of 2.5:1; and the volatile ammonium salt is any one of ammonium bicarbonate and ammonium carbamate; further preferably, the volatile ammonium salt is ammonium carbamate.

[0008] Preferably, in the polycarboxylic acid ammonium salt, the molecular weight of the polyammonium aspartate is between 2 and 5 kDa; and the molecular weight of the polymaleate ammonium salt is between 1 and 3 kDa.

[0009] Preferably, the addition amount of the polycarboxylic acid ammonium salt is 5-30 ppm.

[0010] Preferably, the addition amount of the volatile ammonium salt is 30-60 ppm.

[0011] Another aspect of the present application provides a preparation method of an anti-crystallization vehicle urea solution, which specifically comprises the following steps:

[0012] S101: Circulatingly washing the liquid receiving equipment with deionized water, 0.1% ammonia water overnight, replacing the deionized water until the electric conductivity is less than or equal to 5 µS / cm, and cleaning the equipment;

[0013] S102: Adding deionized water to the equipment to reach a target liquid level of 95%, controlling the temperature to be 15-25 ℃, and nitrogen sealing; slowly adding urea, stirring, and circulating through a 5 μm safety filter to remove large particles;

[0014] S103: Under the condition of nitrogen sealing, adding a polycarboxylic acid ammonium salt mother liquor to step S102, stirring for 10-15 min, then adding a volatile ammonium salt mother liquor, and stirring for another 10-15 min to obtain a mixed solution;

[0015] S104: the mixed solution of step S103 is added into the ammonia type SAC resin, circulating at a linear speed of 1-3 BV / h for 30-60 min, removing resin powder through a 0.2 μm filter, adjusting the refractive index / density to 32.5% based on 20°C, vacuum degassing, 0.1-0.2 μm filtration, jacket cooling to-5 to-8°C, incubating for 30-60 min, re-filtering through a 0.1 μm filter to retain induced microcrystals, warming to 15-20°C, and obtaining a urea solution;

[0016] Preferably, in step S101, the liquid receiving device material is preferably any one of polypropylene / high density polyethylene / polyvinylidene fluoride / polytetrafluoroethylene; it should be noted that the necessary stainless steel parts are made of 316L and are acid pickled and passivated, and the contact time is shortened;

[0017] Preferably, in step S103, the polycarboxylic acid ammonium salt mother liquor is prepared by adding polycarboxylic acid ammonium salt into deionized water, adding 1-5% ammonia water dropwise to adjust to pH 8.5-9.5 to completely dissolve, and 0.2 μm filtration;

[0018] Preferably, in step S103, the volatile ammonium salt mother liquor is prepared by adding volatile ammonium salt into 4°C deionized water, dissolving uniformly, and 0.2 μm filtration;

[0019] Preferably, in step S104, the vacuum degassing parameters are: pressure 20-90 mbar, time 10-30 min;

[0020] Preferably, in step S104, the ammonia type SAC resin is an ammonia type strong acid cation resin.

[0021] The beneficial effects of the present application are as follows:

[0022] The present application cooperates with the micro-dosage formulation of the full ammonium system and the simple and industrialized process chain to reduce the probability of crystallization and deposition. On the formulation level, poly-aspartic acid ammonium salt or poly-maleic acid ammonium salt is used as a threshold type crystal face regulator. By selectively adsorbing on the key growth surface of the crystal, the equivalent interface energy is improved and the step migration rate is reduced. The crystal growth of urea and its related deposition phase is changed from rapid densification to slow and loose morphology. The crystallization induction period is prolonged, and the secondary adhesion is weakened, which is more easily dissolved by subsequent airflow and heat cycle. At the same time, ammonium carbamate or ammonium bicarbonate provides a small amount of free ammonia and a mild buffer at a low dose, changes the competitive reaction path of isocyanic acid in a low-temperature wet wall environment, promotes its hydrolysis and ammonolysis rather than self-trimerization to form cyanuric acid, and reduces the generation of stubborn deposition from the chemical precursor level. The above two types of functional molecules use ammonium ions as cations, do not introduce sodium, potassium and metal elements, and are compatible with the thermal decomposition products and selective catalytic reduction system, avoiding the potential adverse effects of common complexing agents, alcohols or surfactants on the catalyst, particulate filter and concentration sensor. The process level used in the present application no longer relies on high-strength chemical complexing, but uses an ammonia type strong acid cation resin to polish the solution at the end, preferentially exchanges and removes trace metal ions such as calcium, magnesium and iron and hardness sources, significantly reducing the density of heterogeneous nucleation sites, while replenishing the cationic environment with ammonium ions to maintain chemical consistency with the post-processing system. Vacuum degassing and low-permeation headspace control further reduce the fluctuations of dissolved carbon dioxide and free ammonia, inhibit the ion strength drift and slow generation of carbonate side phases during the storage period, and maintain a stable pH and ion background during the delivery and filling stages. The synergistic system used in the present application forms a coherent closed loop in mechanism. The threshold polymer reduces the crystal growth dynamics, the buffer source changes the intermediate chemical direction, the resin polishing reduces the heterogeneous nucleation sites, the degassing stabilizes the solution thermodynamic boundary, and the microfiltration and crystal induction interception weakens the solid seed cycle. Each link targets different control variables but has the same goal. The inhibition effect on nucleation rate and crystal growth rate after superposition is much greater than that of any single measure. And all chemical modifications are centered on the ammonium system, with extremely low ion strength increment and complete pyrolysis path. The ammonia supply and catalytic materials within the SCR reaction window will not be subject to additional toxic burden. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are only a part of the present application, and other drawings can also be obtained by those skilled in the art without creating any inventive labor.

[0024] Figure 1 is the urea solution crystallization time result diagram of examples 1-3 and comparative examples 1-3 of the present application;

[0025] Figure 2 Figure 1 is a graph of the results of the weight of insoluble matter in the urea solution of Examples 1-3 and Comparative Examples 1-3 of the present application in the cyclic freeze-thaw test;

[0026] Figure 3 Figure 2 is a graph of the results of the deposition test of the urea solution of Examples 1-3 and Comparative Examples 1-3 of the present application. DETAILED DESCRIPTION

[0027] The technical solutions of the present application will be described in detail below with reference to the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application; based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. It should be noted that, unless otherwise specified, the raw materials involved in the present application are purchased through conventional commercial channels.

[0028] Example 1: An anti-crystallization urea solution for vehicles, which comprises the following components: high-purity urea, anti-crystallization additives, and deionized water; the mass fraction of the high-purity urea is 32.5%; the raw materials of the anti-crystallization additives include: polyammonium carboxylate and volatile ammonium salt; the polyammonium carboxylate is polyammonium aspartate and polyammonium maleate prepared in a ratio of 2.5:1; the total addition amount of the polyammonium aspartate and the polyammonium maleate is 15 ppm; the volatile ammonium salt is ammonium carbamate; the addition amount of the ammonium carbamate is 40 ppm.

[0029] The preparation of the anti-crystallization urea solution for vehicles includes the following steps:

[0030] S101: Circulatingly rinse the high-density polyethylene liquid receiving equipment with deionized water, 0.1% ammonia water overnight, replace the deionized water until the electrical conductivity is ≤5 µS / cm, and clean the equipment;

[0031] S102: Add deionized water to the equipment to the target liquid level of 95%, control the temperature at 20℃, and nitrogen seal; slowly add urea, stir, and circulate through a 5 μm safety filter to remove large particles;

[0032] S103: Under the condition of nitrogen sealing, add the polyammonium carboxylate stock solution to step S102, stir for 12 min, then add the volatile ammonium salt stock solution, and stir for another 12 min to obtain a mixed solution;

[0033] S104: The mixed solution of step S103 is added to the ammonia type SAC resin, circulated at a linear speed of 2BV / h for 50min, removed through a 0.2μm filter core to remove resin fine powder, adjusted to 32.5% with a refractive index / density at a 20°C basis, vacuum degassed at a pressure of 50mbar for 20min, filtered through a 0.1μm filter, jacketed to -6°C, incubated for 50min, re-filtered through a 0.1μm filter core to trap induced microcrystals, warmed to 18°C, and a urea solution is obtained;

[0034] The polycarboxylic acid ammonium salt mother liquor is prepared by adding polycarboxylic acid ammonium salt and polymaleic acid ammonium salt into deionized water, adding 3% ammonia water dropwise to adjust to pH 9, completely dissolving, and filtering through a 0.2μm filter.

[0035] The volatile ammonium salt mother liquor is prepared by adding carbamate into 4°C deionized water, dissolving uniformly, and filtering through a 0.2μm filter.

[0036] Example 2: An anti-crystallization vehicle urea solution, which comprises the following components: high-purity urea, anti-crystallization additives, and deionized water; the mass fraction of the high-purity urea is 32.5%; the anti-crystallization additives comprise the following raw materials: polycarboxylic acid ammonium salt and volatile ammonium salt; the polycarboxylic acid ammonium salt is polymaleic acid ammonium salt; the addition amount of the polymaleic acid ammonium salt is 5ppm; the volatile ammonium salt is ammonium bicarbonate; and the addition amount of the ammonium bicarbonate is 60ppm.

[0037] The preparation of the anti-crystallization vehicle urea solution comprises the following steps:

[0038] S101: The high-density polyethylene liquid receiving equipment is washed with deionized water, 0.1% ammonia water is added overnight, deionized water is replaced until the electrical conductivity is ≤5μS / cm, and the equipment is cleaned;

[0039] S102: Deionized water is added to the equipment to a target liquid level of 95%, the temperature is controlled at 25°C, and it is nitrogen sealed; urea is slowly added, stirred, and circulated through a 5μm safety filter to remove large particles;

[0040] S103: Under nitrogen sealing, the polycarboxylic acid ammonium salt mother liquor is added to step S102, stirred for 10min, then the volatile ammonium salt mother liquor is added, stirred for another 10min, and a mixed solution is obtained;

[0041] S104: The mixed solution of step S103 is added to the ammonia type SAC resin, circulated at a linear speed of 2BV / h for 50min, removed through a 0.2μm filter core to remove resin fine powder, adjusted to 32.5% with a refractive index / density at a 20°C basis, vacuum degassed at a pressure of 50mbar for 20min, filtered through a 0.1μm filter, jacketed to -6°C, incubated for 50min, re-filtered through a 0.1μm filter core to trap induced microcrystals, warmed to 18°C, and a urea solution is obtained;

[0042] The polycarboxylic acid ammonium salt mother liquor is prepared by adding polycarboxylic acid ammonium salt into deionized water, completely dissolving by adding 1% ammonia water to adjust pH to 8.5, and filtering with 0.2 μm;

[0043] The volatile ammonium salt mother liquor is prepared by adding ammonium bicarbonate into 4°C deionized water, dissolving uniformly, and filtering with 0.2 μm.

[0044] Example 3: An anti-crystallization vehicle urea solution, which comprises the following components: high-purity urea, anti-crystallization additives, and deionized water; the mass fraction of the high-purity urea is 32.5%; the raw materials of the anti-crystallization additives comprise: polycarboxylic acid ammonium salt and volatile ammonium salt; the polycarboxylic acid ammonium salt is polyaspartic acid ammonium salt; the addition amount of the polyaspartic acid ammonium salt is 30 ppm; the volatile ammonium salt is ammonium bicarbonate; and the addition amount of the ammonium bicarbonate is 30 ppm.

[0045] The preparation of the anti-crystallization vehicle urea solution comprises the following steps:

[0046] S101: The high-density polyethylene liquid connection equipment is cleaned by circulating flushing with deionized water, 0.1% ammonia water overnight, and deionized water replacement to a conductivity of ≤5 μS / cm;

[0047] S102: Deionized water is added to the equipment to a target liquid level of 95%, the temperature is controlled at 15°C, and nitrogen sealing is performed; urea is slowly added, stirred, and circulated through a 5 μm safety filter to remove large particles;

[0048] S103: Under the condition of nitrogen sealing, the polycarboxylic acid ammonium salt mother liquor is added to step S102, stirred for 15 min, then the volatile ammonium salt mother liquor is added, stirred for another 15 min, and a mixed solution is obtained;

[0049] S104: The mixed solution of step S103 is added to the ammonia type SAC resin, circulated at a linear speed of 1 BV / h for 60 min, filtered through a 0.2 μm filter to remove resin fines, adjusted to 32.5% with a refractive index / density at a 20°C basis, vacuum degassed at a pressure of 20 mbar for 10 min, filtered with 0.1 μm, jacketed to a temperature of -5°C for 60 min, filtered again through a 0.1 μm filter to trap induced microcrystals, warmed to 20°C, and a urea solution is obtained;

[0050] The polycarboxylic acid ammonium salt mother liquor is prepared by adding polyaspartic acid ammonium salt into deionized water, completely dissolving by adding 5% ammonia water to adjust pH to 9.5, and filtering with 0.2 μm;

[0051] The volatile ammonium salt mother liquor is prepared by adding ammonium bicarbonate into 4°C deionized water, dissolving uniformly, and filtering with 0.2 μm.

[0052] Comparative Example 1: The process parameters of this comparative example are consistent with those of Example 1, the only difference being that the addition of the polycarboxylic acid ammonium salt mother liquor in step S103 is omitted, i.e., no polyaspartic acid ammonium salt / polymaleic acid ammonium salt is added, and the remaining operation procedures are performed according to Example 1.

[0053] Comparative Example 2: The process parameters of this comparative example are consistent with those of Example 1, the only difference being that the addition of the volatile ammonium salt mother liquor in step S103 is omitted, i.e., no ammonium carbamate / ammonium bicarbonate is added, and the remaining operation procedures are performed according to Example 1.

[0054] Comparative Example 3: The process parameters of this comparative example are consistent with those of Example 1, the only difference being that the polishing step of the ammonia type strong acid cation resin in step S104 is omitted, i.e., it directly enters the refraction adjustment step, and the remaining operation procedures are performed according to Example 1.

[0055] Performance test: The content of biuret, insoluble matter and metal ions of the urea solution for vehicle in Examples 1-3 and Comparative Examples 1-3 was tested according to the standards GB 29518-2013 Appendix C, E, G, and the nitrogen oxide conversion rate was tested according to HJ 451-2008 “Environmental Protection Product Technical Requirements for Diesel Vehicle Emission Aftertreatment Device”. The test results are shown in Table 1.

[0056] Table 1. Performance index results of urea solution in Examples 1-3 and Comparative Examples 1-3

[0057]

[0058] Based on the results in Table 1, Comparative Example 1 did not add polyaspartic acid ammonium salt crystal face regulator, and the urea solution after preparation still contained free-growing primary crystal nuclei. The lack of threshold polymer resulted in a decrease in interfacial energy and an increase in step migration rate, and the crystals quickly densified during isothermal residence and thermal cycling, resulting in a significantly higher insoluble content than the examples. When the droplets repeatedly evaporate or redissolve on the nozzle and mixer wall, the loose and fragile crystals are converted into a hard and adherent layer, the spray plume is blocked, the ammonia and exhaust gas mixing uniformity decreases, the ammonia concentration distribution at the inlet of the SCR catalyst is distorted, and the nitrogen oxide conversion rate in the durability test is slightly lower than that of the examples. Comparative Example 2 retains the crystal face regulator but omits the ammonium carbamate buffer, and the isocyanic acid cannot be hydrolyzed or ammonolysis in time in the low temperature zone, and the deposition amount of cyanuric acid and polyurea family increases with the cycle. These high-melting-point by-products are often needle-shaped or flaky and are intercalated between urea crystals, forming a porous network structure. Although there is little difference in early insoluble testing, the by-products are converted into a dense and hard shell after sintering by the gas flow in the nozzle heat section, hindering subsequent thermal decomposition and ammonia transport. Because the degree of by-product deposition covering active sites is slightly lower than that of Comparative Example 1, the NO XThe conversion rate decline was between the two examples, but still significantly lower than that of the example. Comparative Example 3 used all the additives in the formulation, but removed the ammonia-type strong acidic cation exchange resin polishing. Hardness ions and trace amounts of iron and copper were retained in the solution, becoming heterogeneous nucleation centers, shortening the supersaturation induction period and promoting the migration of crystal size distribution to larger particle sizes. The insoluble matter and metal ion residues were significantly increased. The generated crystals intertwined with metal oxides or hydroxides, resulting in stronger adhesion and greater cleaning difficulty. The higher Ca-Mg background also increased the risk of surface ashing after urea pyrolysis, potentially poisoning the catalytic coating and leading to NO X The conversion efficiency was reduced to a minimum. A comprehensive comparison shows that the examples, through a triple synergistic approach of crystal suppression, precursor suppression, and physical nucleation, simultaneously reduced nucleation density, crystal growth rate, and byproduct formation, achieving the lowest insoluble matter, the lowest metal residue, and the highest nitrogen oxide conversion rate.

[0059] Anti-crystallization test: 100 mL of sample (urea solution of Examples 1-3 and Comparative Examples 1-3) was placed in a -11°C constant temperature bath, and the transmittance was recorded by laser scattering once every 15 min; the time when the first visible crystals appeared was recorded, and the results are as follows. Figure 1 As shown; 100 mL of the same batch of sample was frozen at -20°C for 6 h and then thawed at 25°C for 6 h, recorded as 1 cycle, and 10 cycles were performed; finally, the insoluble matter was filtered and weighed (0.45 µm filter membrane), and the results are as follows. Figure 2 As shown; 100 mL of the same batch of samples were processed using a small electrically heated nozzle (200°C) and a pressure pump, with the parameters set as follows: spray for 3 seconds + pause for 30 seconds as one cycle, for a total of 1000 cycles; the deposit mass at the nozzle orifice was weighed, and the results are as follows. Figure 3 As shown.

[0060] based on Figure 1 , Figure 2 and Figure 3 The results showed that, in Comparative Example 1, which did not add polyaspartic acid ammonium salt, the urea primordial crystal nuclei lacked an interfacial barrier layer during the formulation stage, resulting in decreased interfacial energy, increased step migration rate, and a significantly shortened crystal nucleation time. During thermal cycling, rapidly densified insoluble clusters repeatedly adhered to the nozzle and mixer walls as they evaporated or redissolved, leading to a significantly higher nozzle orifice deposition rate than in the Example. This resulted in atomized feather compression, deteriorated ammonia / tail gas mixing uniformity, and distorted ammonia concentration distribution at the SCR inlet, which was reflected in the durability test as NO. XThe conversion rate dropped below 90%. Comparative Example 2 retained the crystal face regulator but omitted the ammonium carbamate weak buffer, and the isocyanic acid was difficult to hydrolyze or ammonolysis in time in the low temperature zone, which can lead to the continuous generation of cyanuric acid and polyurea side phases and the formation of needle-shaped or scaly porous networks between loose urea crystals, and the insoluble matter was sintered into a hard shell deposit after being blown by the gas flow in the hot section of the nozzle, and the adhesion and density increased synchronously. Comparative Example 3 retained the weak buffer and crystal face regulator in the formula, and cancelled the polishing of the ammonium type strong acidic cation resin, which can lead to the hardness ions and trace iron and copper not being removed, the density of the solution heterogeneous nucleation significantly increased, the induction period shortened significantly, and the crystal particle size distribution migrated to large particle size; the insoluble matter and metal residues simultaneously increased, the generated crystals and metal oxides / hydroxides were intertwined, the adhesion was the strongest, the nozzle deposition amount doubled compared with the baseline and was difficult to redissolve. The examples, under the synergistic effect of crystal face retardation, precursor buffer and physical denucleation, simultaneously lengthened the nucleation induction period, inhibited the generation of high melting point side phases and significantly reduced metal heterogeneous nucleation, formed a closed loop inhibition of the three kinetic paths of crystallization, and finally obtained the lowest insoluble matter and the lowest deposition.

[0061] While embodiments of the present application have been shown and described with reference to particular embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the present application, which is defined by the appended claims and their equivalents.

Claims

1. An anti-crystallized urea solution for vehicles, characterized by, The composition comprises the following components: high-purity urea, anti-crystallization additive and deionized water; the mass fraction of the high-purity urea is 32.5%; the composition of the anti-crystallization additive comprises the following components: polycarboxylic acid ammonium salt and volatile ammonium salt; The polycarboxylic acid ammonium salt is any one or more of polyammonium aspartate and polyammonium maleate; The volatile ammonium salt is any one of ammonium bicarbonate and ammonium carbamate; The molecular weight of the polyammonium aspartate is between 2 and 5 kDa; the molecular weight of the polyammonium maleate is between 1 and 3 kDa; The addition amount of the polycarboxylic acid ammonium salt is 5-30 ppm; The addition amount of the volatile ammonium salt is 30-60 ppm; The preparation of the anti-crystallization automotive urea solution specifically comprises the following steps: S101: The liquid connection equipment is washed with deionized water, ammonia water is added overnight, deionized water is used to replace and reduce the electric conductivity, and the equipment is cleaned; S102: Deionized water is added to the equipment, the temperature is controlled, and nitrogen sealing is performed; urea is slowly added, stirred, and circulated through a security filter to remove large particles; S103: Under the condition of nitrogen sealing, the polycarboxylic acid ammonium salt mother liquor is added to step S102, stirred, then the volatile ammonium salt mother liquor is added, stirred again, and a mixed solution is obtained; S104: The mixed solution of step S103 is added to an ammonia type SAC resin, linear speed circulation treatment is performed, a filter core is used to remove resin fine powder, the refractive index is adjusted, vacuum degassing is performed, filtration is performed, jacket cooling is performed, heat preservation is performed, the filter core is used for filtration again to trap induced microcrystals, the temperature is adjusted, and urea solution is obtained.

2. An anti-crystallized urea solution for vehicles according to claim 1, characterized in that, In step S103, the polycarboxylic acid ammonium salt mother liquor is prepared by adding polycarboxylic acid ammonium salt to deionized water, adding 1-5% ammonia water dropwise to adjust to pH 8.5-9.5 to completely dissolve, and 0.2 μm filtration.

3. An anti-crystallized urea solution for vehicles according to claim 2, characterized in that, In step S103, the volatile ammonium salt mother liquor is prepared by adding volatile ammonium salt to 4 ℃ deionized water, dissolving uniformly, and 0.2 μm filtration.

4. An anti-crystallized urea solution for vehicles according to claim 3, characterized in that, In step S104, the vacuum degassing parameters are: pressure 20-90 mbar, time 10-30 min.

Images