Method for preparing urea catalytic liquid for vehicle

Abstract

The invention relates to a method for preparing urea catalytic liquid for a vehicle, which comprises the following steps: (1) preparing purified water of which the conductivity is below 10 mu s/em and the resistivity is between 16 and 19 MOmega cm by utilizing a two-step method; (2) adding the purified water prepared in the step (1) into raw material urea, and stirring and heating the mixture to between 50 and 70 DEG C, and performing absorption treatment on the obtained urea solution by using activated carbon so as to enable the specific gravity of the urea solution to reach 1.18-1.20; and (3) preparing solution of which the crystalline urea accounts for 25 to 40 weight percent by adding the purified water prepared in the step (1) into the crystalline urea obtained in the step (2), and filtering the solution by using a superfine film once more so as to obtain the required catalytic liquid containing the urea. The impurity content of the catalytic liquid (particularly the content of biuret) prepared by the method fully meets requirements of the standard.

Description

technical field [0001] The invention relates to a preparation method of a catalytic liquid for removing nitrogen compounds in automobile tail gas, in particular to a preparation method of a urea catalytic liquid for automobiles. Background technique [0002] High-purity urea vehicle catalytic liquid is a reducing agent used to remove nitrogen oxides in automobile exhaust. In the special catalytic reactor on the automobile, nitrogen oxides can be effectively converted into non-polluting nitrogen and water vapor In order to meet the automobile exhaust emission standards. [0003] In the past, the recrystallization method was used to purify urea, but the temperature of the crystallization liquid was not controlled. Generally, the temperature of the crystallization liquid in production was above 70°C. Since urea would generate biuret above 70°C, the biuret impurity content exceeded 0.3 % standard (the biuret content standard is ≤0.3%, which is an international standard requirem...

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Problems solved by technology

[0003] In the past, the recrystallization method was used to purify urea, but the temperature of the crystallization liquid was not controlled. Generally, the temperature of the crystallization liquid in production was above 70°C. Since urea would generate biuret above 70°C, the biuret impurity content exceeded 0.3 % standard (the biuret content standard is ≤0.3%, which is an international standard requirement and a domestic industry standard. If the biuret content exceeds the standard, the vehicle exhaust emission level will not meet the Euro IV emission standard)