Method for purifying urea solution containing impurities by using modified zeolite

Abstract

The invention discloses a method for purifying an impurity-containing urea solution by using modified zeolite, and belongs to the field of urea purification. The method comprises the following steps: (1) preparing metal salt modified zeolite; and (2) mixing the urea solution containing impurities with the metal salt modified zeolite, and purifying to obtain the purified urea solution for vehicles. According to the purification method, the concentration of biuret and phosphate in the urea solution can be reduced, macromolecular substances in the solution can be intercepted through the porous structure of the calcium salt modified natural zeolite, meanwhile, the calcium-based modified zeolite can react with the phosphate to generate precipitates, the precipitates are attached among pores of the zeolite, and the purification effect is improved. And the cleanliness of the obtained urea solution for the vehicle can be improved, and scaling substances in a vehicle SCR system are reduced, so that the service life of the vehicle SCR system is prolonged.

Description

Technical Field

[0001] The invention relates to the field of urea purification, and in particular to a method for purifying a urea solution containing impurities by using modified zeolite. Background Art

[0002] During the use of automotive urea solution, a large amount of scaling will be generated to block the SCR system. Reducing the content of biuret in automotive urea solution can effectively alleviate this phenomenon. At present, the content of biuret in automotive urea solution on the market is generally between 0.25-0.3%. Even if it meets the national standard, obvious scaling will still occur. After driving 50,000 kilometers, the vehicle will begin to generate scaling, causing the vehicle to alarm and affecting the normal use of the vehicle. Reducing the content of biuret to below 0.2% can effectively reduce the generation of scaling and extend the service life of the vehicle.

[0003] The phosphate in the automotive urea solution will affect the activity of the SCR catalyst. Too high a phosphate content will reduce the activity of the SCR catalyst and shorten its service life.

[0004] At present, the purification of industrial urea granules is mainly based on recrystallization. However, while this method reduces the content of biuret and phosphate, it involves a heating and cooling process, which consumes too much energy. In addition, there are many uncontrollable factors in the recrystallization process, and the overall process cost is too high. At present, the purification of automotive urea on the market is mainly through multi-stage membrane filtration technology, but this technology can only filter out some insoluble impurities and macromolecular organic matter. The filtration efficiency of the main substances biuret and phosphate is relatively low. Generally, the content of biuret after filtration is 0.27%, and the content of phosphate is 0.45 mg / kg. If you want to continue to reduce the impurity content, you need to consume a large amount of organic solvents and perform liquid-liquid extraction. This method will not only produce a large amount of sewage, but also bring certain safety hazards, making it difficult to produce on a large scale. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a method for purifying a urea solution containing impurities by using modified zeolite, which has good purification effect, simple purification process, and is energy-saving and environmentally friendly.

[0006] Technical solution: The method for purifying a urea solution containing impurities by using modified zeolite of the present invention comprises the following steps:

[0007] (1) preparing metal salt modified zeolite;

[0008] (2) The impurity-containing urea solution and the metal salt-modified zeolite are mixed and purified to obtain a purified automotive urea solution.

[0009] Furthermore, in step (1), the preparation method of the metal salt modified zeolite is: placing natural zeolite in a metal salt solution for sufficient reaction and filtering; wherein the metal salt is a calcium salt, the pore size of the natural zeolite is 6-15A, and the mass concentration of the metal salt solution is 200-500g / L; the dosage ratio of the natural zeolite and the metal salt solution is 0.8-1.2g:1mL, preferably 1g:1mL.

[0010] Furthermore, in step (2), the impurities include biuret and phosphate, and the content of biuret in the urea solution is 0.26-0.34%; the content of phosphate in the urea solution is 0.3-0.45 mg / kg.

[0011] Furthermore, in step (2), the ratio of the impurity-containing automotive urea solution to the metal salt-modified zeolite is 50-70 mL: 1 g, preferably 60 mL: 1 g.

[0012] Furthermore, in step (2), the purification treatment is carried out under the conditions of: mixing thoroughly at 20-40° C. for 1-2 hours.

[0013] Furthermore, the method further comprises step (3): the metal salt modified zeolite obtained after the purification treatment is activated and then recycled.

[0014] Furthermore, the activation treatment is carried out by circulating washing with dilute hydrochloric acid and water; wherein the concentration of the dilute hydrochloric acid is 1-3 mol / L.

[0015] Principle of the invention: In the present invention, zeolite has a porous structure and has certain filtering performance after modification. The impurities (biuret and phosphate) in the automotive urea solution have a larger molecular formula than the urea molecule and can be retained by zeolite. The mechanism is mainly physical adsorption, including ion exchange and chemical precipitation. The surface of zeolite carries some hydroxide ions (OH-), which can form chemical bonds with cations in phosphate, so that phosphate is bound to the surface of zeolite.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) low energy consumption, simple process, and significantly lower cost compared with the prior art recrystallization; (2) no waste water is generated in the production process, and no loss occurs, thereby reducing costs; (3) the preparation process can not only significantly reduce the content of biuret and phosphate, but also remove some macromolecular organic matter and insoluble impurities; (4) the impurities in urea are reduced, which can delay the formation of scale in the vehicle post-treatment system, extend the service life of the vehicle, reduce the cost of vehicle use, and improve the cleanliness of the obtained vehicle urea solution, reduce the scale in the SCR system, thereby extending the service life of the vehicle SCR system. DETAILED DESCRIPTION

[0017] The present invention is further described below in conjunction with specific embodiments.

[0018] Example 1: The method for purifying a urea solution containing impurities using a modified zeolite provided in this example comprises the following steps:

[0019] (1) Preparation of calcium salt modified zeolite: 500 g of natural zeolite with a pore size of 15 Å was selected and dissolved in 500 mL of a calcium chloride solution with a concentration of 200 g / L, stirred for 30 min, and filtered to obtain calcium salt modified zeolite;

[0020] (2) 50 g of the calcium salt-modified zeolite obtained in step (1) is filled into a filtering tank, and then 3000 mL of a urea solution having a biuret content of 0.32% and a phosphate content of 0.45 mg / kg is added into the tank, the temperature is adjusted, and stirring is performed at room temperature to fully mix the urea solution and the calcium salt-modified zeolite, and then the temperature is raised to 40° C. and maintained for 1 hour to improve the filtration efficiency. Finally, the temperature is lowered to room temperature, and the filtrate is discharged from the filter tank at a rate of 1 L / min to obtain a purified automotive urea solution;

[0021] (3) The calcium salt modified zeolite after the purification treatment in step (2) is circulated and washed with 1 mol / L dilute hydrochloric acid and pure water to obtain the calcium salt modified zeolite that meets the use requirements and can be recycled again.

[0022] Example 2: The method for purifying a urea solution containing impurities using a modified zeolite provided in this example comprises the following steps:

[0023] (1) Preparation of calcium salt modified zeolite: 500 g of natural zeolite with a pore size of 15 Å was selected and dissolved in 500 mL of a calcium chloride solution with a concentration of 300 g / L, stirred for 30 min, and filtered to obtain calcium salt modified zeolite;

[0024] (2) 50 g of the calcium salt-modified zeolite obtained in step (1) is filled into a filter tank, and then 3000 mL of a urea solution having a biuret content of 0.32% and a phosphate content of 0.45 mg / kg is filled into the tank, the temperature is adjusted, and stirring is performed at room temperature to fully mix the urea solution and the calcium salt-modified zeolite, and then the temperature is raised to 40° C. and maintained for 1 hour to improve the filtration efficiency. Finally, the temperature is lowered to room temperature, and the filtrate is discharged from the filter tank at a rate of 1 L / min to obtain a purified automotive urea solution;

[0025] (3) The calcium salt modified zeolite after the purification treatment in step (2) is circulated and washed with 1 mol / L dilute hydrochloric acid and pure water to obtain the calcium salt modified zeolite that meets the use requirements and can be recycled again.

[0026] Comparative Example 1: The difference from Example 1 is that unmodified natural zeolite is used.

[0027] Comparative Example 2: The difference from Example 1 is that in step (1), the pore size of the natural zeolite is 50A.

[0028] Comparative Example 3: The difference from Example 1 is that in step (1), the pore size of the natural zeolite is 3A.

[0029] Comparative Example 4: The difference from Example 1 is that in step (1), the concentration of the calcium chloride solution is 1000 g / L.

[0030] Comparative Example 5: The difference from Example 1 is that in step (1), the usage ratio of natural zeolite and calcium chloride solution is 1000 g:500 mL.

[0031] Comparative Example 6: The difference from Example 1 is that in step (2), the usage ratio of calcium salt-modified zeolite to urea solution is 50 g:6000 mL.

[0032] The purified automotive urea solutions obtained in Example 1 and Example 2, Comparative Examples 1 to Comparative Examples 5 and the untreated urea solutions containing impurities were analyzed for content and performance. The results are shown in Table 1.

[0033] As shown in Table 1 below, the urea solution after the treatment of Example 1 and Example 2 can fully meet the various indicators in the national standard, and the content of biuret and phosphate can be reduced to the national standard requirements, which can improve the product quality. After the treatment of the comparative example 1 scheme, although there is a certain impurity removal and purification effect, the impurity removal rate is low. In comparative examples 2 and 3, the selected zeolite pore size is different from that of the embodiment, which will lead to incomplete removal of biuret and phosphate. The calcium solution content in comparative example 4 is high, which will lead to an increase in the calcium ion content in the urea solution, and there is a risk of unqualified. The modified zeolite in comparative examples 5 and 6 has a large relative processing capacity, and the urea solution processed is too much, and the purification effect is not obvious.

[0034] Table 1 Content and performance analysis of automotive urea solutions obtained from Example 1-Example 2 and Comparative Example 1-Comparative Example 5

[0035]

Claims

1. A method for purifying a urea solution containing impurities using a modified zeolite, characterized in that: The following steps are involved: (1) preparing metal salt modified zeolite; (2) The impurity-containing urea solution and the metal salt-modified zeolite are mixed and purified to obtain a purified automotive urea solution.

2. The method according to claim 1, characterized in that: In step (1), the preparation method of the metal salt modified zeolite is: placing natural zeolite in a metal salt solution for sufficient reaction and filtering to obtain the zeolite.

3. The method according to claim 2, characterized in that The metal salt is a calcium salt.

4. The method according to claim 2, characterized in that: The pore size of the natural zeolite is 6-15A.

5. The method according to claim 2, characterized in that: The mass concentration of the metal salt solution is 200-500 g / L; the usage ratio of the natural zeolite and the metal salt solution is 0.8-1.2 g:1 mL.

6. The method according to claim 1, characterized in that In step (2), the impurities include biuret and phosphate; the content of biuret in the urea solution is 0.26-0.34%; the content of phosphate in the urea solution is 0.3-0.45 mg / kg.

7. The method according to claim 1, characterized in that In step (2), the ratio of the impurity-containing automotive urea solution to the metal salt-modified zeolite is 50-70 mL: 1 g.

8. The method according to claim 1, characterized in that In step (2), the purification treatment conditions are: mixing thoroughly at 20-40°C for 1-2 hours.

9. The method according to claim 1, characterized in that: The method further comprises step (3): the metal salt modified zeolite obtained after the purification treatment is activated and then recycled.

10. The method according to claim 9, characterized in that The activation treatment method is: using dilute hydrochloric acid and water for cyclic flushing; wherein the concentration of the dilute hydrochloric acid is 1-3 mol / L.

Images