A synthesis method for producing dicyandiamide by urea method
Patent Information
- Application Number
- CN202410566078.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-09
- Publication Date
- 2026-11-03
AI Technical Summary
The existing calcium carbide method for producing dicyandiamide suffers from pollution problems, limited raw material sources, high energy consumption, and poor product purity, thus limiting the production of dicyandiamide and necessitating a new production method.
The method for producing dicyandiamide using the urea process involves reacting urea with water under high temperature and pressure to generate melamine, followed by reacting melamine with hydrogen under a catalyst to generate dicyandiamide. The finished product is obtained by heating and crystallizing, and then washing with pure water, thus achieving gas recovery and recycling.
It achieves low-cost production without calcium impurities, maintains a balanced element ratio, meets green chemical requirements, and improves product purity and raw material utilization efficiency.
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Figure CN123026534A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of dicyandiamide production technology, specifically relating to a synthesis method for producing dicyandiamide using the urea process. Background Technology
[0002] Dicyandiamide (DICY or DCD), also known as cyanoamine, is a dimer of cyanamide and a cyanoguanidine derivative. Its chemical formula is C₂H₄N₄. Dicyandiamide is a white crystalline powder, soluble in water, alcohols, ethylene glycol, and dimethylformamide, but practically insoluble in ethers and benzene. It is stable when dry.
[0003] Cyanamide, dicyandiamide, and melamine are all cyanamide compounds. Current technology utilizes calcium carbide to produce calcium cyanamide through a high-temperature nitridation reaction. Calcium cyanamide is then carbonized in water to produce monocyanamide, which is primarily used to polymerize dicyandiamide. Previously, melamine was polymerized from dicyandiamide in a high-temperature, high-pressure, closed reactor. However, with the rise of the urea industry, a method for producing melamine using inexpensive urea was successfully implemented, severing the industrial link between dicyandiamide and melamine. Currently, in the chemical industry, monocyandiamide, dicyandiamide, and melamine are completely unrelated. As pollution problems from the calcium carbide method become increasingly prominent, raw material sources are limited, and the inherent problems of high energy consumption and poor product purity persist, the calcium carbide method for producing monocyandiamide and dicyandiamide is facing increasing constraints. Therefore, the synthesis technology of producing monocyandiamide and dicyandiamide using the urea method is receiving more and more attention.
[0004] Therefore, it is necessary to propose a synthetic method for producing dicyandiamide using the urea process, in order to at least partially solve the problems existing in the prior art.
[0005] The information disclosed above in this background section is only for enhancing the understanding of the background section of this invention, and therefore may include prior art that is not known to those skilled in the art. Summary of the Invention
[0006] The purpose of this invention is to provide a method for synthesizing dicyandiamide using the urea process, in order to solve the problems mentioned in the background art.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] A method for synthesizing dicyandiamide using the urea process, comprising:
[0009] Step 1: React urea with water under high temperature and high pressure, and obtain melamine solid by crystallization separation;
[0010] Step 2: Melamine and hydrogen are reacted in the presence of a catalyst to obtain a mixed solution containing dicyandiamide;
[0011] Step 3: Heating the solution until the dicyandiamide is completely dissolved, then gradually lowering the temperature to allow the dicyandiamide to gradually crystallize out of the solution;
[0012] Step 4: Filter the crystallized precipitate, wash the dicyandiamide crystals with pure water, and dry them to obtain the finished dicyandiamide product.
[0013] Preferably, in step one, the initial reaction conditions are: reaction temperature 180℃~200℃, reaction pressure 10MPa~20MPa, and continuous reaction for 1h~2h. During this process, urea hydrolyzes to generate ammonia and ammonium cyanate. Then, the reaction pressure is adjusted to 20MPa~30MPa, and the reaction continues for 2h~4h under the same temperature conditions. During this process, ammonia and ammonium cyanate react to generate melamine.
[0014] Preferably, in step one, ammonia gas is introduced into the reactor during the initial reaction to promote the hydrolysis of urea. The concentration of ammonia gas can be between 5% and 10%. The main function of introducing ammonia gas is to adjust the pH value of the reaction and promote the hydrolysis of urea. After adjusting the reaction pressure, ferric chloride can be added as a catalyst to improve the reaction efficiency.
[0015] Preferably, in step two, the reaction temperature is 150℃~250℃, the reaction pressure is 20MPa~30MPa, nickel is used as a catalyst to promote the reaction, and other metal catalysts such as rhodium can also be selected.
[0016] Preferably, in step two, the molar flow rate of hydrogen is determined based on the molar ratio of melamine to hydrogen. The molar amount of melamine is obtained by measuring the melamine sample obtained in step one. From the reaction process of melamine and hydrogen, the molar ratio of melamine to hydrogen to complete the hydrogenation reaction is 1:6. Therefore, the flow rate of hydrogen should be set under the condition of satisfying the hydrogenation reaction.
[0017] Preferably, in step three, the generated gas is collected during the heating process because heating causes some hydrogen in the solution to enter the gas, and these gases need to be treated before being released to the outside. After the dicyandiamide is completely dissolved, the unreacted melamine in the mixed solution is removed by filtration.
[0018] Preferably, in step four, the filtrate produced by filtration is distilled and the generated gas is collected. The gas is then purified by an adsorbent to recover the hydrogen present in the filtrate, and the recovered hydrogen can be recycled.
[0019] Preferably, in step four, the purified water is water that has been distilled or reverse osmosis treated, and the washing process is repeated multiple times to ensure thorough cleaning. Filter paper or a filter is used to separate the washed dicyandiamide crystals from the water, the crystals are collected, and excess water is discharged.
[0020] Compared with the prior art, the beneficial effects of the present invention are:
[0021] This invention uses urea as a raw material to first react and generate melamine, and then uses melamine as a raw material to produce dicyandiamide. This changes the existing production approach, is inexpensive, and does not contain impurities such as calcium. The gases used in the reaction process are recovered, separated, and recycled. In the chemical reaction of melamine to dicyandiamide, the C / H / N elements are converted in equal proportions, with neither excess nor deficient elements, thus meeting the requirements of green chemical industry.
[0022] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description
[0023] Figure 1 This is a flowchart of the synthesis method for a real-time example of the present invention. Detailed Implementation
[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0025] Example 1:
[0026] Please see Figure 1 As shown, a method for synthesizing dicyandiamide using the urea process includes:
[0027] Step 1: React urea and water at 180℃~200℃ and 10MPa~20MPa for 1h~2h. Then adjust the reaction pressure to 20MPa~30MPa and continue the reaction for 2h~4h. After crystallization and separation, melamine solid is obtained.
[0028] Step 2: Melamine is reacted with hydrogen at 150℃~250℃, 20MPa~30MPa and with a nickel catalyst to obtain a mixed solution containing dicyandiamide.
[0029] Step 3: Heating the solution until the dicyandiamide is completely dissolved, then gradually lowering the temperature to allow the dicyandiamide to gradually crystallize out of the solution;
[0030] Step 4: Filter the crystallized precipitate, wash the dicyandiamide crystals with pure water, and dry them to obtain the finished dicyandiamide product. Distill the filtrate and collect the generated gas. Purify the gas with an adsorbent to recover the hydrogen gas present in the filtrate.
[0031] In step one, ammonia is introduced into the reactor during the initial reaction to promote the hydrolysis of urea. After adjusting the reaction pressure, ferric chloride can be added as a catalyst to improve the reaction efficiency.
[0032] In step two, the molar flow rate of hydrogen is determined based on the molar ratio of melamine to hydrogen, and the molar amount of melamine is obtained by measuring the melamine sample obtained in step one.
[0033] In step two, the hydrogenation reaction generates ammonia, which is mixed with the hydrogen used. After the hydrogen supply is stopped, the hydrogen containing ammonia is separated. The separated ammonia, after being processed by a certain reaction method, can be used as part of the ammonia supplied in step one to reduce ammonia consumption.
[0034] In step three, the gas generated during the heating process is collected, and after the dicyandiamide is completely dissolved, the unreacted melamine in the mixed solution is removed by filtration.
[0035] In step four, the purified water used is water that has been distilled or reverse osmosis treated, and the process is repeated multiple times during rinsing to ensure thorough cleaning.
[0036] Detailed operating procedures:
[0037] Urea and water were added to the No. 1 high-pressure reactor for reaction. Ammonia gas, preheated to the same temperature, was continuously introduced. After a period of reaction, the ammonia gas was stopped and the reaction pressure was adjusted. A catalyst was selected to continue the reaction according to the reaction situation. After the reaction was completed, the reaction solution was passed into a three-in-one filter to obtain melamine crystals through crystallization and filtration.
[0038] Melamine crystals and nickel catalyst were added to the No. 2 high-pressure reactor, and hydrogen was continuously introduced to carry out the hydrogenation reaction, so as to obtain a mixed solution containing dicyandiamide.
[0039] Stop the flow of hydrogen gas, heat the mixed solution containing dicyandiamide until the dicyandiamide is completely dissolved, collect the gas generated during the heating process, and slowly cool it to allow the dicyandiamide to gradually crystallize out.
[0040] The solution is filtered using a three-in-one filter, then washed with pure water to remove residual impurities, and dried in a well-ventilated place or in a low-temperature oven to obtain pure dicyandiamide.
[0041] Example 2:
[0042] Add 150g of 99% urea and 100g of water to a high-pressure reactor. Continuously introduce ammonia gas at 180℃~200℃ and 10MPa~20MPa. After reacting for 1h~2h, adjust the reaction pressure to 20MPa~30MPa and continue reacting for 2h~4h. After the reaction is completed, use a three-in-one filter to crystallize and separate melamine crystals.
[0043] The obtained melamine crystals and nickel catalyst were successively added into a new high-pressure reactor. Hydrogen gas was continuously introduced at a molar ratio of melamine to hydrogen of 1:6 to carry out the hydrogenation reaction, and a mixed solution containing dicyandiamide was obtained.
[0044] Stop the flow of hydrogen gas, heat the mixed solution containing dicyandiamide until the dicyandiamide is completely dissolved, collect the gas generated during the heating process, and slowly cool it to allow the dicyandiamide to gradually crystallize out.
[0045] Dicyandiamide crystals are obtained by filtering with a three-in-one filter, then washed with pure water to remove residual impurities, and dried in a well-ventilated place or in a low-temperature oven to obtain pure dicyandiamide product.
[0046] The dry weight of the sample after drying in Example 2 was 203.2 g; the content was analyzed to be 96.15%.
[0047] As can be seen from the above, this invention uses urea as a raw material to first react and generate melamine, and then uses melamine as a raw material to produce dicyandiamide. This changes the existing production approach, is inexpensive, and does not contain impurities such as calcium. The gas used in the reaction process is recovered, separated, and recycled. In the chemical reaction of melamine to dicyandiamide, the C / H / N elements are converted in equal proportions, with neither excess nor deficient elements, thus meeting the requirements of green chemical industry.
[0048] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0049] The accompanying drawings of the embodiments disclosed in this invention only involve the structures involved in the embodiments disclosed in this invention. Other structures can refer to general designs. In the absence of conflict, the same embodiment and different embodiments of this invention can be combined with each other.
[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for synthesizing dicyandiamide using the urea process, characterized in that, include: Step 1: React urea with water under high temperature and high pressure, and obtain melamine solid by crystallization separation; Step 2: Melamine and hydrogen are reacted in the presence of a catalyst to obtain a mixed solution containing dicyandiamide; Step 3: Heating the solution until the dicyandiamide is completely dissolved, then gradually lowering the temperature to allow the dicyandiamide to gradually crystallize out of the solution; Step 4: Filter the crystallized precipitate, wash the dicyandiamide crystals with pure water, and dry them to obtain the finished dicyandiamide product.
2. The method for synthesizing dicyandiamide using the urea process according to claim 1, characterized in that: In step one, the initial reaction conditions are: reaction temperature 180℃~200℃, reaction pressure 10MPa~20MPa, continuous reaction for 1h~2h, then the reaction pressure is adjusted to 20MPa~30MPa, and the reaction continues for 2h~4h under the same temperature conditions.
3. The method for synthesizing dicyandiamide using the urea process according to claim 2, characterized in that: In step one, ammonia is introduced into the reactor during the initial reaction to promote the hydrolysis of urea. After adjusting the reaction pressure, ferric chloride can be added as a catalyst to improve the reaction efficiency.
4. The method for synthesizing dicyandiamide using the urea process according to claim 3, characterized in that: In step two, the reaction temperature is 150℃~250℃, the reaction pressure is 20MPa~30MPa, and nickel is used as a catalyst to promote the reaction.
5. The method for synthesizing dicyandiamide using the urea process according to claim 4, characterized in that: In step two, the molar flow rate of hydrogen is determined based on the molar ratio of melamine to hydrogen, and the molar amount of melamine is obtained by measuring the melamine sample obtained in step one.
6. The method for synthesizing dicyandiamide using the urea process according to claim 5, characterized in that: In step three, the gas generated during the heating process is collected, and after the dicyandiamide is completely dissolved, the unreacted melamine in the mixed solution is removed by filtration.
7. The method for synthesizing dicyandiamide using the urea process according to claim 6, characterized in that: In step four, the filtrate produced by filtration is distilled and the generated gas is collected. The gas is then purified by an adsorbent to recover the hydrogen present in the filtrate.
8. The method for synthesizing dicyandiamide using the urea process according to claim 7, characterized in that: In step four, the purified water used is water that has been distilled or reverse osmosis treated, and the process is repeated multiple times during rinsing to ensure thorough cleaning.