CN100361981C - A method and device for refining cyanuric acid at room temperature - Google Patents

Abstract

The invention relates to a method and a device for refining cyanuric acid at room temperature, belonging to the technical field of chemical industry. The method of refining cyanuric acid is to first place sulfuric acid or hydrochloric acid in the reactor, add crude cyanuric acid under stirring conditions, and then apply ultrasonic waves to the reactants in the reactor for a certain period of time. In the device for refining cyanuric acid, the ultrasonic generator is placed in the reactor, and is evenly distributed along the inner wall of the reactor, and the ultrasonic generator is driven by the external power supply of the reactor. The stirring paddle is placed at the bottom of the reactor, and the stirring paddle is driven by a motor outside the reactor. The discharge valve is placed at the bottom of the reactor. The ultrasonic generator can also be placed on the outer wall of the bottom of the reactor. The method and device of the present invention have the advantages of shortening the refining time of cyanuric acid, reducing equipment corrosion and prolonging equipment life. The whole production process is simple, safe and reliable, saves energy, has high production efficiency, and has good economic and social benefits.

Description

A method and device for refining cyanuric acid at room temperature

technical field

The invention relates to a method and a device for refining cyanuric acid at room temperature, belonging to the technical field of chemical industry.

Background technique

Since Scherer invented the synthesis of cyanuric acid from urea in 1776, it has developed into an important fine chemical intermediate. Cyanuric acid has a triazine structure and is prone to reactions such as addition, substitution, and condensation. It is an important chemical product. Nearly 500 downstream products of cyanuric acid have been developed using it as a raw material. They are widely used in chemical industry, light industry, Machinery, electrical appliances, textiles, agriculture, daily use and other fields. There are more than 20 production plants in my country with an annual output of about 100,000 tons.

At present, the solid-phase method is mainly used in China to produce cyanuric acid, that is, urea (or ammonium chloride with catalyst) is condensed and reacted at 250-300°C to produce crude cyanuric acid, and its cyanuric acid content is generally 60-80%, and impurities For urea, biuret, triuret, ammonium amide, etc., the content of cyanuric acid products is required to be above 98%, which requires refining the crude cyanuric acid to meet the quality requirements.

The refining technology of cyanuric acid mainly uses sulfuric acid or hydrochloric acid to reconvert the ammonium in the crude product into cyanuric acid and remove other impurities.

U.S. Patent No. 2,768,167 points out that when producing melamine, the by-products of ammeline and ammeline are difficult to separate from melamine, so their mixture is concentrated and heated in an acidic aqueous solution until the temperature reaches When the temperature is above 165°C, a conversion rate of over 90% can be obtained to generate cyanuric acid. The acid used is preferably sulfuric acid, and hydrochloric acid is also acceptable, but the use of hydrochloric acid will bring more serious equipment corrosion problems. The amount of sulfuric acid is: the three substituents of melamine are all amino groups, and 3/2 mole of sulfuric acid is needed per mole of material; ammeline contains two amino groups, and 1 mole of sulfuric acid is needed per mole of material; Contains an amino group, and 1/2 mole of sulfuric acid is required for each mole of material. The concentration of free acid directly controls the reaction speed, and the reaction speed is more suitable when the concentration of sulfuric acid is 5%-20%. The minimum reaction temperature should be above 150°C. At this time, the heating must ensure the pressure, otherwise the water will volatilize; when the reaction temperature is lower than 165°C, the reaction speed increases slowly, and when it is higher than this temperature, the reaction speed is rapid When it reaches 175°C to 180°C, it is very attractive from the perspective of industrial scale. The best reaction speed appears at 200°C, but if the temperature is too high, the cost will increase rapidly.

Melamine, ammeline and ammeline are also the by-products of cyanuric acid produced by direct pyrolysis of urea. raw materials. The digestion of crude cyanuric acid with sulfuric acid is the refining method that is usually matched with the direct pyrolysis of solid-phase urea to produce cyanuric acid.

The acid boiling reaction is all batch operation, and the representative reaction formula is:

C ₃ N ₃ NH ₂ (OH) ₂ +H ₂ O → (HCNO) ₃ +NH ₃

C ₃ N ₃ (NH ₂ ) ₂ OH+2H ₂ O→(HCNO) ₃ +2NH ₃

C ₃ N ₃ (NH ₂ ) ₃ +3H ₂ O → (HCNO) ₃ +3NH ₃

2NH ₃ +H ₂ SO ₄ → (NH ₄ ) ₂ SO ₄

When heated to a certain temperature, the amide is converted into cyanuric acid, and the generated ammonia reacts with sulfuric acid to form ammonium sulfate, which breaks the balance of the conversion reaction and makes the conversion reaction proceed in the positive direction. In the case of a sufficient amount of sulfuric acid, the conversion reaction is complete Carried out, all the amides are converted into cyanuric acid to achieve the refining effect.

The earliest acid cooking reactions were carried out under normal pressure. Under a certain acid concentration, the maximum heating temperature can only reach 105°C. No matter how high the temperature is, a large amount of water will evaporate, so the reaction time is relatively long. It takes 3 to 4 hours. European patent EPA0124710 carried out a high-temperature acid boiling experiment. When the heating temperature reaches 160°C, the reaction needs to be carried out for 90 minutes; when the heating temperature reaches 170°C, the reaction needs to be carried out for 40 minutes; When the heating temperature reaches 200°C, the reaction needs to be carried out for 5-8 minutes. Moreover, as the heating temperature increases, the operating pressure of the system also gradually increases.

The currently widely used refining process is: crush the crude cyanuric acid (about 60 mesh), put it in an enamel kettle and make a 20% to 30% slurry with sulfuric acid, refine it under boiling conditions for 4 to 8 hours, and cool the refined solution , After filtering, washing and drying, cyanuric acid with a purity greater than 98% can be obtained.

The above processes can be divided into normal pressure and high pressure processes. The high-pressure process has a short reaction time and is easy to realize continuous production. However, due to its high reaction temperature, the equipment material is difficult to meet the corrosion requirements or the investment is large, and there is no industrial application in China; the atmospheric pressure process is a technology commonly used in China, and its main problems The reason is that the temperature is high, about 105°C, which causes serious corrosion of the equipment. Even the enamel reaction kettle has a service life of only about one year, and the reaction time is long, and the cyanuric acid is easy to decompose, which reduces the product yield, so the production efficiency of the equipment is low. , higher energy consumption.

Contents of the invention

The purpose of the present invention is to propose a method and device for refining cyanuric acid at room temperature, using ultrasonic waves for refining cyanuric acid to shorten the reaction time and lower the reaction temperature, so as to achieve the goals of simple, safe, efficient and energy-saving production process.

The method for normal temperature refining cyanuric acid that the present invention proposes comprises the following steps:

(1) the sulfuric acid that concentration is 15～25% or the hydrochloric acid that concentration is 4～10% is placed in reaction kettle, adds crude product cyanuric acid under stirring condition, and the weight ratio of adding is: crude product cyanuric acid: sulfuric acid solution Or hydrochloric acid solution=1:1.5～1:2.5;

(2) Applying ultrasonic waves to the reactants in the reactor, the ultrasonic frequency is 20-80KHz, the ultrasonic sound intensity is 0.2-10W/cm ² , and the reaction time is 30-120 minutes.

The crude product cyanuric acid in the above method has a cyanuric acid content of 60-95%.

The device for purifying cyanuric acid at room temperature that the present invention proposes comprises a reaction kettle, an ultrasonic generator, a power supply, a discharge valve, a motor and a stirring paddle. The ultrasonic generator is placed in the reaction kettle, distributed evenly along the inner wall of the reaction kettle, and the ultrasonic generator is driven by the external power supply of the reaction kettle. The stirring paddle is placed at the bottom of the reactor, and the stirring paddle is driven by a motor outside the reactor. The discharge valve is placed at the bottom of the reactor.

Another structure of the device for refining cyanuric acid at room temperature proposed by the present invention includes a reactor, an ultrasonic generator, a power supply, and a discharge valve; the ultrasonic generator is placed on the outer wall of the bottom of the reactor, and cloth, the ultrasonic generator is driven by a power supply; the discharge valve is placed at the bottom of the reactor.

The method and device for refining cyanuric acid at normal temperature proposed by the present invention have the advantages of shortening the refining time of cyanuric acid, reacting at normal temperature, greatly reducing corrosion to equipment, and thus greatly prolonging equipment life. Moreover, the reaction at room temperature does not require steam heating, which can save energy. The device is suitable for the refining process of cyanuric acid. The whole production process is simple, safe and reliable, saves energy, has high production efficiency, and has good economic and social benefits.

Description of drawings

Fig. 1 is a structural schematic diagram of a refining device proposed by the present invention.

Fig. 2 is a schematic diagram of another structure of the device of the present invention.

In Fig. 1 and Fig. 2, 1 is a reactor, 2 is an ultrasonic generator, 3 is a power supply, 4 is a discharge valve, 5 is a motor, 6 is a stirring paddle, and 7 is a reactor.

Detailed ways

The method for purifying cyanuric acid at room temperature proposed by the present invention, at first, put sulfuric acid with a concentration of 15 to 25% or hydrochloric acid with a concentration of 4 to 10% in the reactor, add crude product cyanuric acid under stirring conditions, and the added weight The ratio is: crude cyanuric acid: sulfuric acid solution or hydrochloric acid solution = 1: 1.5 ~ 1: 2.5; then apply ultrasonic waves to the reactants in the reactor, the ultrasonic frequency is 20 ~ 80KHz, and the ultrasonic sound intensity is 0.2 ~ 10W/cm ² , The reaction time is 30 to 120 minutes.

The crude product cyanuric acid in the above method has a cyanuric acid content of 60-95%.

The device for refining cyanuric acid at room temperature that the present invention proposes has a structure as shown in Figure 1, including a reactor 1, an ultrasonic generator 2, a power supply 3, a discharge valve 4, a motor 5 and a stirring paddle 6. Ultrasonic generators 2 are placed in the reactor 1 and distributed evenly along the inner wall circumference of the reactor, and the ultrasonic generators 2 are driven by a power supply 3 outside the reactor. The stirring paddle 6 is placed at the bottom of the reactor 1, and the stirring paddle 6 is driven by the motor 5 outside the reactor. The discharge valve 4 is placed at the bottom of the reactor 1 .

Another structure of the device for refining cyanuric acid at room temperature proposed by the present invention, as shown in FIG. 2 , includes a reactor 7, an ultrasonic generator 2, a power supply 3 and a discharge valve 4. Ultrasonic generators 2 are placed on the bottom outer wall of the reactor 7 and distributed uniformly along the bottom of the reactor. The ultrasonic generators 2 are driven by a power supply 3 . A discharge valve 4 is placed at the bottom of the reactor 7 .

The working principle of the method of the present invention is: the refining process of cyanuric acid is an acid-base reaction process in essence, and the acid-base reaction can be completed quickly at normal temperature and pressure, but the process speed of refining under normal pressure is very slow, indicating that its reaction process is traditional quality control. Ultrasonic waves are sound waves with a frequency greater than 20kHz, and their main functions in the refining process of cyanuric acid are mechanical action and cavitation. During the propagation of ultrasonic waves in the medium, it causes the alternating compression and stretching of the medium particles. Although the vibration displacement and velocity of the particle do not change much, its acceleration is quite large (10 ⁴ m/s ² ). Such a large acceleration can significantly increase the permeability of the acid solution into the crude cyanuric acid particles, strengthen the mass transfer process, and thus strengthen the reaction process. However, the most important reason for ultrasonic enhancement of refining reaction is the cavitation effect generated by ultrasonic waves. Ultrasonic cavitation refers to the activation of micro-bubble nuclei in solution under the action of sound waves, which manifests as a series of dynamic processes such as oscillation, growth, shrinkage and even collapse of the nuclei. According to different manifestations, cavitation can have two forms: steady-state cavitation and transient cavitation. Steady-state cavitation occurs under the action of lower sound intensity, and the cavitation bubble oscillates in the medium in a nonlinear manner for several cycles. During the oscillation process, the microflow around the cavitation bubble has a greater impact on other particles in the solution. The tangential force is conducive to the penetration of acid liquid into the interior of crude cyanuric acid particles. Low-intensity ultrasound can not only form a microflow around the crude cyanuric acid particles, but also make the crude cyanuric acid particles produce intragranular circulation, thereby improving the permeability of the particles. Ultrasonic action can increase the mass transfer process without increasing the temperature of the medium, which is the main mechanism of ultrasonic enhanced refining reaction. Transient cavitation occurs under the action of strong sound intensity, and gas (steam) bubbles are rapidly generated, grown, compressed, and collapsed within one sound wave cycle. Studies have shown that when the transient cavitation collapses, local hot spots above 5000K can be formed, and the pressure can reach hundreds or even thousands of atmospheres. With the release of high pressure, a powerful shock wave (homogeneous) or a high-speed jet (heterogeneous) will be formed in the solution. In the refining reaction, this powerful impingement flow can effectively reduce and eliminate the retardation layer between the particles and the acid solution, thereby increasing the mass transfer rate. At the same time, the impact flow produces a physical shear force on the crude cyanuric acid particles, causing them to deform, rupture, and release the contents, which greatly accelerates the reaction process.

Below are the embodiments of the inventive method:

Example 1

Select crude cyanuric acid with a content of 65%, mix the crude cyanuric acid with sulfuric acid with a concentration of 20%, and the ratio of the ingredients is 1:2, when the ultrasonic frequency is 30KHz, the sound intensity is 0.5W/ ^cm It is refined for 40 minutes at room temperature, and the content of the cyanuric acid product after filtering, washing and drying is greater than 98%.

Example 2

Select crude cyanuric acid with a content of 75%, mix the crude cyanuric acid with sulfuric acid with a concentration of 25%, the proportioning ratio is 1:1.7, and the ultrasonic frequency is 50KHz, the sound intensity is 2W/cm ² , and the temperature is Refining at room temperature for 30 minutes, after filtering, washing and drying, the content of the cyanuric acid product is greater than 98%.

Example 3

Select crude cyanuric acid with a content of 85%, mix the crude cyanuric acid with 5% hydrochloric acid, the proportioning ratio is 1:2, and the ultrasonic frequency is 80KHz, the sound intensity is 5W/cm ² , and the temperature is Refining at room temperature for 50 minutes, after filtering, washing and drying, the content of the cyanuric acid product is greater than 98%.

Example 4

Select crude cyanuric acid with a content of 70%, mix the crude cyanuric acid with 8% hydrochloric acid, the proportioning ratio is 1:2.3, and the ultrasonic frequency is 20KHz, the sound intensity is 0.2W/cm ² , the temperature It is refined for 70 minutes at room temperature, and the content of the cyanuric acid product after filtering, washing and drying is greater than 98%.

Claims (2)

1. the method for a refining cyanuric acid under normal temperature is characterized in that this method comprises following each step:

(1) be that 15～25% sulfuric acid or concentration are that 4～10% hydrochloric acid places in the reactor with concentration, under agitation condition, add the acid of crude product cyanogen urea, the weight ratio that adds is: the acid of crude product cyanogen urea: sulphuric acid soln or hydrochloric acid soln=and 1: 1.5～1: 2.5, in the acid of described crude product cyanogen urea, the content of cyanogen urea acid is 60～95%;

(2) reactant in the reactor is applied ultrasonic wave, ultrasonic frequency is 20～80KHz, the ultrasonic wave sound intensity 0.2～10W/cm ², the reaction times is 30～120 minutes.

2. the device of a refining cyanuric acid under normal temperature is characterized in that this device comprises reactor, ultrasonic generator, power supply, discharge valve; Described ultrasonic generator places the reactor bottom outer wall, and uniform along the bottom of reactor, ultrasonic generator is by power drives; Described discharge valve places reactor bottom.