CN113651725A - System and method for preparing dicyandiamide by reusing melamine tail gas - Google Patents
System and method for preparing dicyandiamide by reusing melamine tail gas Download PDFInfo
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- CN113651725A CN113651725A CN202110913454.8A CN202110913454A CN113651725A CN 113651725 A CN113651725 A CN 113651725A CN 202110913454 A CN202110913454 A CN 202110913454A CN 113651725 A CN113651725 A CN 113651725A
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- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C277/00—Preparation of guanidine or its derivatives, i.e. compounds containing the group, the singly-bound nitrogen atoms not being part of nitro or nitroso groups
- C07C277/08—Preparation of guanidine or its derivatives, i.e. compounds containing the group, the singly-bound nitrogen atoms not being part of nitro or nitroso groups of substituted guanidines
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Abstract
The invention particularly relates to a system and a method for preparing dicyandiamide by reusing melamine tail gas. The method comprises the following steps: introducing a part of melamine tail gas into a crystallizer through a cold air compressor, introducing a part of melamine tail gas into a reactor, simultaneously introducing a small amount of carbon dioxide, reacting to obtain cyanamide gas, filtering the cyanamide gas containing solid impurities through a filter-1, polymerizing in a polymerization reactor to obtain dicyandiamide gas, filtering the solid impurities contained in the dicyandiamide gas through a filter-2, cooling and crystallizing in the crystallizer with the melamine tail gas as process cold air, collecting dicyandiamide solid in a trap, reusing a part of gas as process gas, and reusing a part of gas as process tail gas after treatment. The dicyandiamide solid obtained by the method realizes simple process flow, environmental protection, high raw material utilization rate, byproduct steam, low energy consumption and cost saving on the basis of ensuring high product quality and purity.
Description
Technical Field
The invention relates to the technical field of dicyandiamide preparation, in particular to a system and a method for preparing dicyandiamide by reusing melamine tail gas.
Background
Dicyandiamide, also known as dicyandiamide, dicyandiamide (a dimer of cyanamide, also a cyano derivative of guanidine), of the formula (NH)2CN)2. Dicyandiamide is generally a white crystal in the form of needles, diamonds, scales or powders, having a melting point of 205 ℃.
The existing dicyandiamide preparation method is to hydrolyze calcium cyanamide to obtain calcium cyanamide hydrogen suspension, remove calcium hydroxide filter residue through vacuum filtration, and introduce carbon dioxide into the filtrate to precipitate calcium in the form of calcium carbonate to obtain cyanamide liquid. Polymerizing under alkaline condition, filtering, cooling, crystallizing, separating and drying to obtain dicyandiamide. The equation is as follows:
2CaCN2+2H2O→Ca(HCN2)2+Ca(OH)2
Ca(HCN2)2+CO2+H2O→2NH2CN+CaCO3
2NH2CN→(NH2CN)2
the main factors influencing the quality index of dicyandiamide in the existing lime nitrogen process technology are calcium oxide, calcium hydroxide, calcium carbonate and other impurities contained in the product. The lime nitrogen method has long production process flow and high equipment cost, can generate a large amount of waste residues and waste water, causes serious environmental pollution and large cost, and simultaneously needs a large amount of cooling water to control temperature in the lime nitrogen hydrolysis decalcification process, and can cause great waste of energy consumption and water resources.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a system and a method for preparing dicyandiamide by reusing melamine tail gas, which have the advantages of low energy consumption, simple process flow, environmental protection and low equipment cost. The method has the advantages that the dicyandiamide product prepared by the processes of reaction, polymerization and the like of the melamine tail gas does not contain any calcium-containing impurities, the quality influence factor of the calcium impurities in the lime nitrogen method on the dicyandiamide can be solved, the method is simple in process flow compared with the lime nitrogen method, waste residues and waste water are not generated, the raw material utilization rate is high, the product purity is high, steam can be generated as a byproduct, the cost is reduced, a large amount of cooling water is not needed in the production flow for temperature control, the water resource consumption can be reduced, the tail gas is repeatedly utilized in the system in the process of preparing the dicyandiamide by the melamine tail gas, the cost can be reduced, and the energy consumption can be reduced.
In order to achieve the above purpose, the specific technical scheme of the invention is as follows:
the system for preparing dicyandiamide by reusing melamine tail gas comprises a reactor, a filter-1, a polymerization reactor, a filter-2, a crystallizer and a catcher, wherein the reactor is sequentially connected with the filter-1, the polymerization reactor, the filter-2, the crystallizer and the catcher through pipelines;
the reactor is connected with a flue gas system;
the process cold air is connected with the crystallizer through a cold air compressor;
the trap is connected with the crystallizer through a cold gas compressor or connected with the reactor through a compressor.
As a better embodiment in the application, the polymerization reactor is provided with a water feeding port and a steam outlet, water enters the polymerization reactor through the water feeding port, and steam generated by the polymerization reactor is connected with the outside through the steam outlet.
As a better embodiment in the application, impurity discharge ports are arranged on the filter-1 and the filter-2, so that the impurities can be conveniently discharged.
As a preferred embodiment in the present application, the method for preparing dicyandiamide by recycling melamine off-gas using the above system comprises the following steps:
firstly, introducing a part of melamine tail gas serving as process cold air into a crystallizer through a cold air compressor, introducing a part of melamine tail gas into a reactor, simultaneously introducing a small amount of carbon dioxide gas into the reactor, and reacting the melamine tail gas and the carbon dioxide gas in the reactor to obtain cyanamide gas; introducing the cyanamide gas into a filter-1, filtering the solid impurities carried out, and introducing into a polymerization reactor;
introducing the cyanamide gas into the polymerization reactor, and polymerizing in the polymerization reactor to obtain dicyandiamide gas; the dicyandiamide gas enters a filter-2, and solid impurities brought out are filtered and then sent into a crystallizer;
mixing the process cold air and dicyandiamide gas in a crystallizer through a cold air compressor, cooling and crystallizing, allowing the gas carrying dicyandiamide crystals to enter a trap to complete gas-solid separation, collecting to obtain dicyandiamide solid, and reusing a part of the separated gas as process gas and a part of the separated gas as process tail gas after treatment.
As a preferred embodiment in this application, in step (i), the melamine off-gas contains carbon dioxide: 30-70%, ammonia: 20-60% and the balance of a small amount of isocyanic acid and nitrogen; the temperature of the melamine tail gas is 120-240 ℃.
As a better implementation mode in the application, in the step (i), a fluidized bed reactor or a fixed bed reactor is selected as a reactor for the melamine tail gas reaction, and the temperature of the reactor is controlled to be 600-850 ℃.
As a better implementation mode in the application, in the step (i), a reactor is connected with a flue gas system, and heat is provided by using high-temperature flue gas.
As a preferred embodiment in this application, in step two, the polymerization reactor temperature is controlled to 150 ℃ to 350 ℃.
In the second step, as a preferred embodiment of the present application, the heat generated in the polymerization reaction in the polymerization reactor is absorbed by water, and the heat is removed by changing the water into steam.
In step (c), a part of the gas separated by the trap is compressed and pressurized by a cold gas compressor and then enters a crystallizer for reuse or is pressurized by a compressor and then enters a reactor for reuse.
Compared with the prior art, the positive effects of the invention are as follows:
according to the invention, tail gas emitted by the existing melamine device is used as a raw material to prepare dicyandiamide, the melamine tail gas has a certain temperature, and is not required to be preheated, so that the consumption of heat energy can be reduced, the melamine tail gas is directly used as the raw material, the treatment process of the melamine tail gas can be reduced, ammonia and carbon dioxide in the tail gas can be simultaneously utilized, the requirement of green production is met, and meanwhile, the transportation cost and the raw material cost in the raw material transportation process can be reduced by utilizing the tail gas emitted by the existing melamine device.
In the polymerization process of preparing dicyandiamide from dicyandiamide in the polymerization reaction process, a large amount of heat is generated, water can be introduced into the polymerization reactor by using a pipeline to absorb the heat, so that the water is changed into steam to be discharged, the corrosion to equipment and the damage to the polymerization process caused by overhigh temperature in the polymerization reactor are avoided, the heat is utilized, and the heat loss is reduced.
And thirdly, the melamine tail gas is used as process cold air to enter a crystallizer, and dicyandiamide gas from a polymerization reactor is cooled and crystallized to be reused, so that the raw material cost is reduced. Melamine tail gas carries dicyandiamide solid to enter a trap, after gas-solid separation, a part of gas is treated and reused as process tail gas, a part of gas can selectively enter a crystallizer to be reused as process cold air, and meanwhile, a small amount of dicyandiamide powder brought out of the trap can be brought into the crystallizer to be recycled; the pressure of the compressor can be selected to enter the reactor to be reused as raw materials, and simultaneously, a small amount of dicyandiamide powder taken out can be taken into the reactor to be recycled, so that the utilization rate of the raw materials reaches 90-99%, and the pollution to the environment can be avoided.
The method has the advantages that the dicyandiamide is prepared by recycling the melamine tail gas, the problem of waste residues generated in the existing lime nitrogen method can be effectively solved, the green and environment-friendly effects are achieved, the treatment process of the waste residues is reduced, calcium-containing impurities such as calcium oxide and calcium hydroxide are avoided, and the purity of the dicyandiamide product is 98-99.5%.
Drawings
FIG. 1 is a schematic flow chart of a process for preparing dicyandiamide by a lime nitrogen method.
Fig. 2 is a schematic flow chart of the process for preparing dicyandiamide by reusing melamine off-gas in embodiment 1 of the present invention.
Fig. 3 is a schematic flow chart of the process for preparing dicyandiamide by reusing melamine off-gas in embodiment 2 of the present invention.
Detailed Description
The system for preparing dicyandiamide by reusing melamine tail gas comprises: the device comprises a filter-1, a polymerization reactor, a filter-2, a crystallizer and a catcher, wherein the reactor is sequentially connected with the filter-1, the polymerization reactor, the filter-2, the crystallizer and the catcher through pipelines;
the reactor is connected with a flue gas system;
the process cold air is connected with the crystallizer through a cold air compressor;
the trap is connected with the crystallizer through a cold gas compressor or connected with the reactor through a compressor.
The polymerization reactor is provided with a water feeding port and a steam outlet, water enters the polymerization reactor through the water feeding port, and steam generated by the polymerization reactor is connected with the outside through the steam outlet;
impurity discharge ports are formed in the filter-1 and the filter-2, so that impurities can be conveniently discharged.
The method for preparing dicyandiamide by reusing melamine tail gas comprises the following steps:
firstly, introducing a part of melamine tail gas from a melamine device into a crystallizer through a cold air compressor as process cold air, introducing a part of the melamine tail gas into a reactor, simultaneously introducing a small amount of carbon dioxide gas into the reactor, and reacting the melamine tail gas and the small amount of carbon dioxide gas in the reactor to obtain cyanamide gas. The cyanamide gas enters a filter-1, solid impurities brought out are filtered, and then the filtered solid impurities are introduced into a polymerization reactor.
Introducing the cyanamide gas into the polymerization reactor, and polymerizing in the polymerization reactor to obtain the dicyandiamide gas. The dicyandiamide gas enters a filter-2, and solid impurities brought out are filtered and then sent into a crystallizer.
Mixing the process cold air and dicyandiamide gas in a crystallizer through a cold air compressor, cooling and crystallizing, allowing the gas carrying dicyandiamide crystals to enter a trap to complete gas-solid separation, collecting to obtain dicyandiamide solid, and reusing a part of the separated gas as process gas and a part of the separated gas as process tail gas after treatment.
Preferably, in the step (i), the melamine off-gas contains carbon dioxide: 30-70%, ammonia: 20-60 percent, the balance being a small amount of isocyanic acid and nitrogen, and the temperature of the melamine tail gas being 120-240 ℃.
Preferably, in the step (i), the reactor for the melamine tail gas reaction can be a fluidized bed reactor or a fixed bed reactor, and the temperature of the reactor is controlled to be 600-850 ℃.
Preferably, in the step (i), the reactor is connected with a flue gas system, and heat can be provided by using high-temperature flue gas.
Preferably, in the step (II), the temperature of the polymerization reactor is controlled to be between 150 and 350 ℃.
Preferably, in the step (ii), the heat in the polymerization reaction in the polymerization reactor may be absorbed by water, and the water is changed into steam to perform heat removal.
Preferably, in the third step, a part of the gas separated by the trap is compressed and pressurized by a cold gas compressor and then enters a crystallizer for reuse or is pressurized by a compressor and then enters a reactor for reuse.
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It is to be noted that the features in the following embodiments and examples may be combined with each other without conflict.
It should be noted that, in order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
Example 1:
the process flow diagram of the method for preparing dicyandiamide by reusing melamine tail gas is shown in fig. 2, the tail gas contains 52% of carbon dioxide, 47% of ammonia, and the balance of a small amount of isocyanic acid and nitrogen by volume percentage, and the sum of the total volume percentage is 100%.
The melamine tail gas with the temperature of about 190 ℃ is divided into two parts, wherein one part is used as process cold air and is introduced into a crystallizer through a cold air compressor, the other part is introduced into a fluidized bed reactor, a small amount of carbon dioxide gas is introduced into the fluidized bed reactor, the reactor is connected with a flue gas system, heat is provided by high-temperature flue gas, the temperature of the flue gas is controlled to be 700 ℃, and the melamine tail gas reacts in the reactor to obtain the cyanamide gas. The mass ratio of the melamine tail gas as a reaction raw material to the cold air in the process is 1: 2.6. The cyanamide gas enters a filter-1, solid impurities brought out are filtered, and then the filtered solid impurities are introduced into a polymerization reactor.
The cyanamide gas is introduced into the polymerization reactor, the heat in the polymerization process can be absorbed by water, the water is changed into steam to transfer heat, the temperature of the polymerization reactor is controlled at 240 ℃, and the cyanamide is polymerized to obtain the dicyandiamide gas. The dicyandiamide gas enters a filter-2, and solid impurities brought out are filtered and then sent into a crystallizer.
After the process cold air passing through the cold air compressor and the dicyandiamide gas are mixed, cooled and crystallized in the crystallizer, the gas carries the dicyandiamide crystals to enter the trap to complete gas-solid separation, dicyandiamide solid is obtained by collection, a part of the separated gas is used as the process cold air, compressed and pressurized by the cold air compressor to enter the crystallizer for reuse, and a part of the separated gas is used as the process tail gas for reuse after treatment.
Example 2
The process flow schematic diagram of the method for preparing dicyandiamide by reusing melamine tail gas is shown in fig. 3. the tail gas contains 52 percent of carbon dioxide, 47 percent of ammonia, and the balance of a small amount of isocyanic acid and nitrogen by volume percentage, and the sum of the total volume percentage is 100 percent.
The melamine tail gas with the temperature of 190 ℃ is divided into two parts, wherein one part is used as process cold air and is introduced into a crystallizer through a cold air compressor, the other part is introduced into a fluidized bed reactor, a small amount of carbon dioxide gas is introduced into the fluidized bed reactor, the reactor is connected with a flue gas system, heat is provided by using high-temperature flue gas, the temperature of the melamine tail gas is controlled to be 700 ℃, the mass ratio of the melamine tail gas as a reaction raw material to the process cold air is 1:4.5, and the melamine tail gas is reacted in the reactor to obtain the cyanamide gas. The cyanamide gas enters a filter-1, solid impurities brought out are filtered, and then the filtered solid impurities are introduced into a polymerization reactor.
The cyanamide gas is introduced into the polymerization reactor, the heat in the polymerization process can be absorbed by water, the water is changed into steam to transfer heat, the temperature of the polymerization reactor is controlled at 200 ℃, and the dicyanamide is polymerized to obtain the dicyandiamide gas. The dicyandiamide gas enters a filter-2, and solid impurities brought out are filtered and then sent into a crystallizer.
After the process cold air passing through a cold air compressor and the dicyandiamide gas are mixed, cooled and crystallized in a crystallizer, the gas carries the dicyandiamide crystals to enter a trap to complete gas-solid separation, dicyandiamide solid is obtained by collection, a part of the separated gas is used as process gas, is pressurized by the compressor and enters a reactor for reuse, and a part of the separated gas is used as process tail gas for reuse after treatment.
The specific results of comparing the process parameters and the cost of the example 1 and the example 2 with those of the existing lime nitrogen method are shown in the following table:
the foregoing basic embodiments of the invention and their various further alternatives can be freely combined to form multiple embodiments, all of which are contemplated and claimed herein. In the scheme of the invention, each selection example can be combined with any other basic example and selection example at will. Numerous combinations will be known to those skilled in the art. The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The system for preparing dicyandiamide by reusing melamine tail gas is characterized by comprising a reactor, a filter-1, a polymerization reactor, a filter-2, a crystallizer and a catcher, wherein the reactor is sequentially connected with the filter-1, the polymerization reactor, the filter-2, the crystallizer and the catcher through pipelines;
the reactor is connected with a flue gas system;
the process cold air is connected with the crystallizer through a cold air compressor;
the trap is connected with the crystallizer through a cold gas compressor or connected with the reactor through a compressor.
2. The system of claim 1, wherein: the polymerization reactor is provided with a water inlet and a steam outlet, water enters the polymerization reactor through the water inlet, and steam generated by the polymerization reactor is connected with the outside through the steam outlet.
3. The system of claim 1, wherein: impurity discharge ports are arranged on the filter-1 and the filter-2, so that impurities can be conveniently discharged.
4. Method for the preparation of dicyandiamide by means of the recycling of melamine off-gas with the system according to any of claims 1 to 3, characterized in that it comprises the following steps:
firstly, introducing a part of melamine tail gas serving as process cold air into a crystallizer through a cold air compressor, introducing a part of melamine tail gas into a reactor, simultaneously introducing a small amount of carbon dioxide gas into the reactor, and reacting the melamine tail gas and the carbon dioxide gas in the reactor to obtain cyanamide gas; introducing the cyanamide gas into a filter-1, filtering the solid impurities carried out, and introducing into a polymerization reactor;
introducing the cyanamide gas into the polymerization reactor, and polymerizing in the polymerization reactor to obtain dicyandiamide gas; the dicyandiamide gas enters a filter-2, and solid impurities brought out are filtered and then sent into a crystallizer;
mixing the process cold air and dicyandiamide gas in a crystallizer through a cold air compressor, cooling and crystallizing, allowing the gas carrying dicyandiamide crystals to enter a trap to complete gas-solid separation, collecting to obtain dicyandiamide solid, and reusing a part of the separated gas as process gas and a part of the separated gas as process tail gas after treatment.
5. The method for preparing dicyandiamide by reusing melamine tail gas according to claim 4, wherein: in the step I, the melamine tail gas contains carbon dioxide: 30-70%, ammonia: 20-60% and the balance of a small amount of isocyanic acid and nitrogen; the temperature of the melamine tail gas is 120-240 ℃.
6. The method for preparing dicyandiamide by reusing melamine tail gas according to claim 4, wherein: in the first step, the reactor for the reaction of the melamine tail gas is a fluidized bed reactor or a fixed bed reactor, and the temperature of the reactor is controlled to be 600-850 ℃.
7. The method for preparing dicyandiamide by reusing melamine tail gas according to claim 4, wherein: in the first step, a reactor is connected with a flue gas system, and heat is provided by using high-temperature flue gas.
8. The method for preparing dicyandiamide by reusing melamine tail gas according to claim 4, wherein: in the second step, the temperature of the polymerization reactor is controlled to be 150-350 ℃.
9. The method for preparing dicyandiamide by reusing melamine tail gas according to claim 4, wherein: in the second step, the heat in the polymerization reaction in the polymerization reactor is absorbed by water, and the water is changed into steam to remove the heat.
10. The method for preparing dicyandiamide by reusing melamine tail gas according to claim 4, wherein: in the third step, part of the gas separated by the catcher is compressed and pressurized by a cold gas compressor and then enters a crystallizer for reuse or is pressurized by a compressor and then enters a reactor for reuse.
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| CN202110913454.8A CN113651725A (en) | 2021-08-10 | 2021-08-10 | System and method for preparing dicyandiamide by reusing melamine tail gas |
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| CN202110913454.8A CN113651725A (en) | 2021-08-10 | 2021-08-10 | System and method for preparing dicyandiamide by reusing melamine tail gas |
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2721786A (en) * | 1952-04-19 | 1955-10-25 | American Cyanamid Co | Preparation of cyanamide |
| CN101862577A (en) * | 2009-06-12 | 2010-10-20 | 河南骏化发展股份有限公司 | Method for reclaiming melamine tail gas |
| CN112521313A (en) * | 2020-12-16 | 2021-03-19 | 四川金象赛瑞化工股份有限公司 | System and process for producing dicyandiamide by melamine |
-
2021
- 2021-08-10 CN CN202110913454.8A patent/CN113651725A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2721786A (en) * | 1952-04-19 | 1955-10-25 | American Cyanamid Co | Preparation of cyanamide |
| CN101862577A (en) * | 2009-06-12 | 2010-10-20 | 河南骏化发展股份有限公司 | Method for reclaiming melamine tail gas |
| CN112521313A (en) * | 2020-12-16 | 2021-03-19 | 四川金象赛瑞化工股份有限公司 | System and process for producing dicyandiamide by melamine |
Non-Patent Citations (1)
| Title |
|---|
| 汪多仁: "《绿色农药与化肥中间体》", 30 April 2009 * |
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