CN107441669B

CN107441669B - Method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue by heterogeneous catalysis

Info

Publication number: CN107441669B
Application number: CN201610373976.2A
Authority: CN
Inventors: 张涛; 唐盛伟; 梁斌; 龚海
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2016-05-31
Filing date: 2016-05-31
Publication date: 2020-05-29
Anticipated expiration: 2036-05-31
Also published as: CN107441669A

Abstract

The invention relates to a method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue under heterogeneous catalysis, which adopts active alumina or pseudo-boehmite as a catalyst, hydrolyzes under self-pressure in a closed pressure vessel at the temperature of 190-240 ℃, and can decompose melamine, cyanuric acid or melamine OAT waste residue into ammonia and carbon dioxide, wherein the main components of the melamine OAT waste residue are melamine, ammeline, ammelide and cyanuric acid. Meanwhile, ammonia and carbon dioxide generated by hydrolysis are raw material gases for producing urea, and can be co-produced with a urea device, so that the method provides an effective resource recycling method, and is suitable for the current industrial enterprises for producing melamine.

Description

Method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue by heterogeneous catalysis

Technical Field

The invention relates to a method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue by heterogeneous catalysis, belonging to the technical field of solid waste treatment and circular economy.

Background

Melamine is used as an important chemical intermediate and is widely applied to synthesis of plastics, water-soluble coatings, adhesives, fibers and flame retardants. The global demand for melamine is around 200 million tons in 2015 and is increasing every year. In the process for producing melamine by a high-pressure method, melamine OAT waste residues can be generated, the yield is quite large, if the waste residues cannot be reasonably treated, certain influence on the environment can be certainly caused, and meanwhile, the utilization rate of chemical resources can be reduced. The main components of the melamine OAT waste residue are melamine, ammeline, ammelide and cyanuric acid, which are all nitrogen-containing compounds containing triazine rings, are very stable under general conditions and are difficult to degrade by a general physical or chemical method. At present, the industrial method adopts a high-temperature high-pressure hydrolysis method, does not use a catalyst, and directly decomposes the melamine OAT waste residue into ammonia and carbon dioxide at 285 ℃ and 8.5MPa, wherein the ammonia and the carbon dioxide are also raw material gases for producing urea. The method realizes the green cycle production of the melamine, but the higher hydrolysis temperature and pressure of the method lead the operation energy consumption to be higher, have strict requirements on equipment and influence the application and popularization of the process. Therefore, the method of catalytic hydrolysis is adopted, the reaction temperature is reduced, and the operation cost and equipment investment of the hydrolysis reaction are reduced, so that the method has important practical value for the utilization of melamine OAT.

In addition to the high-temperature high-pressure hydrolysis method described above, other studies have been made on the utilization of melamine OAT slag, but none of them have been commercialized. One approach is to separate the various components of the OAT for use, such as by adjusting the pH to separate the melamine in the OAT [ WO:0136397a1], but with the process consuming a significant amount of acid and base and only recovering the melamine therein; separation can also be carried out according to the difference of sublimation points of each component, but the energy consumption is higher [ Saito s. Sublimatographicalnalysis; sublimographic separation of melamine, aggregate and cyclic acid [ J ]. Japan analysis, 1978,27: 321-. Another method is to use the waste melamine OAT slag to prepare other products, such as sulfonated amino resin or cyanuric acid, but the OAT component is complex, the prepared product has low effective component and complex process [ Lahalih SM, Absihalabi M.recovery of colloidal free resins and their conversion to useful products [ J ]. Ind EngChem Res.1989,28(4): 500-504; EP:0124710,1984; US 4963674.1990; cones, plum, et al, use the solid waste discharged from melamine production to prepare a melamine environment [ J ]. environmental engineering, 2003,21(4):4-44 ].

The method adopts the active alumina or the pseudo-boehmite as the catalyst, can hydrolyze the melamine, the cyanuric acid or the melamine OAT waste residue into ammonia and carbon dioxide under the condition of lower temperature, and effectively overcomes the defects of the traditional high-temperature high-pressure hydrolysis method.

Disclosure of Invention

Compared with the prior art for industrially treating the OAT waste residue, the method has the beneficial effects that the reaction temperature of the traditional industrial hydrolysis process is reduced, so that the energy consumption and the over-high requirement on equipment are reduced, and the high-efficiency, green and environment-friendly recovery and utilization of solid waste are realized. The specific technical scheme is as follows:

the method comprises the steps of placing a solution or suspension containing melamine, cyanuric acid or melamine OAT waste residue into a high-pressure reaction kettle, keeping a certain liquid-solid ratio, using active alumina or pseudo-boehmite as a catalyst at 190-240 ℃, and continuously stirring and reacting for 1-10 hours under the pressure of a system, so that the melamine, cyanuric acid or melamine OAT waste residue can be hydrolyzed into ammonia and carbon dioxide.

The process conditions are that the concentration of melamine, cyanuric acid or melamine OAT waste residue is 0.05 g/L-20 g/L, the mass ratio of the added active alumina or pseudo-boehmite catalyst is 0.1-10%, the reaction temperature is 190-240 ℃, and the reaction time is 1-10 h.

The method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue by heterogeneous catalysis adopts the reaction principle as follows: under the catalytic action of activated alumina or pseudo-boehmite, the amino groups on triazine rings of melamine, ammeline and ammelide are gradually replaced by hydroxyl groups, ammelic acid is finally generated, and ammelic acid is further hydrolyzed into ammonia and carbon dioxide. The reaction process is shown in figure 1.

Drawings

FIG. 1 is a diagram of the hydrolysis pathway of melamine, ammeline, ammelide, ammelic acid to ammonia and carbon dioxide in a stepwise manner under the catalytic action of activated alumina or pseudo-boehmite.

Detailed Description

To better illustrate the invention, the following examples are given:

example 1

The initial concentration of melamine is 0.67g/L, the mass ratio of the added activated alumina is 3.8%, the reaction temperature is 220 ℃, the reaction time is 5 hours, the degradation rate of the melamine is 99.8% and the yield of ammonia and carbon dioxide is 96.1% by detecting the solution after the reaction.

Example 2

The initial concentration of melamine is 2.4g/L, the mass ratio of the added pseudoboehmite is 4.6%, the reaction temperature is 200 ℃, the reaction time is 7 hours, and the degradation rate of the melamine is 93.2% and the yield of ammonia and carbon dioxide is 91.7% by detecting the solution after the reaction.

Example 3

The initial concentration of cyanuric acid is 0.67g/L, the mass ratio of the added activated alumina is 3.8%, the reaction temperature is 220 ℃, the reaction time is 2 hours, the degradation rate of cyanuric acid is 98.4% and the yield of ammonia and carbon dioxide is 97.5% by detecting the solution after the reaction.

Example 4

The initial concentration of cyanuric acid is 5.0g/L, the mass ratio of added pseudoboehmite is 1.2%, the reaction temperature is 190 ℃, the reaction time is 6 hours, the degradation rate of cyanuric acid is 99.1% and the yield of ammonia and carbon dioxide is 98.4% by detecting the solution after the reaction.

Example 5

The initial concentration of the melamine OAT waste residue is 16.67g/L, the mass ratio of the added activated alumina is 3.6%, the reaction temperature is 220 ℃, the reaction time is 7 hours, and the solution after the reaction is detected, so that the degradation rate of the melamine OAT waste residue is 93.4%, and the yield of ammonia and carbon dioxide is 92.0%.

Example 6

The initial concentration of the melamine OAT waste residue is 10.0g/L, the mass ratio of the added pseudo-boehmite is 2.8%, the reaction temperature is 200 ℃, the reaction time is 8 hours, and the solution after the reaction is detected, so that the degradation rate of the melamine OAT waste residue is 91.7%, and the yield of ammonia and carbon dioxide is 90.4%.

Example 7

The initial concentration of the melamine OAT waste residue is 20.0g/L, the mass ratio of the added activated alumina is 7.9%, the reaction temperature is 240 ℃, the reaction time is 6 hours, and the solution after the reaction is detected, so that the degradation rate of the melamine OAT waste residue is 94.7%, and the yield of ammonia and carbon dioxide is 92.5%.

Claims

1. A method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residues through heterogeneous catalysis is characterized in that a certain amount of melamine, cyanuric acid or melamine OAT waste residues are placed in a closed pressure-resistant container containing water, activated alumina or pseudo-boehmite is used as a catalyst, the temperature is heated to 190-240 ℃, the self pressure of a system is kept, heating and stirring are continuously carried out for 1-10 hours until the melamine, cyanuric acid or melamine OAT waste residues are hydrolyzed into ammonia and carbon dioxide, and the certain amount refers to the concentration of the melamine, cyanuric acid or melamine OAT waste residues being 0.05-20 g/L.

2. The method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue under heterogeneous catalysis as claimed in claim 1, wherein the heterogeneous phase is a liquid-solid catalytic system.

3. The method for hydrolyzing melamine, cyanuric acid or melamine OAT waste residue under heterogeneous catalysis as claimed in claim 1, wherein the mass ratio of the added active alumina or pseudo-boehmite catalyst is 0.1% -10%.