阅读说明：本技术 一种正压吸收二氧化碳生产单氰胺的方法 (Method for producing cyanamide by positive pressure absorption of carbon dioxide ) 是由 张超 梁万根 刘冠宏 崔卫华 张宁 曹斌 于 2019-11-06 设计创作，主要内容包括：本发明属于化工技术领域,尤其涉及一种正压吸收二氧化碳生产单氰胺的方法。向合成釜中加入母液,通入二氧化碳,控制釜内压力0.2～1.0MPa,按比例投加石灰氮,控制合成釜内温度≤30℃,PH≤8.5,投料完成后,继续通二氧化碳并保温一段时间,然后进行泄压、放料、过滤,获得单氰胺产品。本申请通过改进单氰生产工艺,以正压吸收二氧化碳生产单氰胺,提高反应效率,降低二氧化碳单耗。(The invention belongs to the technical field of chemical industry, and particularly relates to a method for producing cyanamide by positively-pressuring absorption of carbon dioxide. Adding mother liquor into a synthesis kettle, introducing carbon dioxide, controlling the pressure in the kettle to be 0.2-1.0 MPa, adding lime nitrogen according to the proportion, controlling the temperature in the synthesis kettle to be less than or equal to 30 ℃ and the PH to be less than or equal to 8.5, after the feeding is finished, continuously introducing the carbon dioxide, keeping the temperature for a period of time, and then performing pressure relief, discharging and filtering to obtain a cyanamide product. The method improves the single cyanogen production process, absorbs carbon dioxide at positive pressure to produce the single cyanamide, improves the reaction efficiency and reduces the unit consumption of the carbon dioxide.)

1. The method for producing cyanamide by positively absorbing carbon dioxide is characterized by comprising the following steps: adding mother liquor into a synthesis kettle, introducing carbon dioxide, controlling the pressure in the kettle to be 0.2-1.0 MPa, adding lime nitrogen according to a proportion, controlling the temperature in the synthesis kettle to be less than or equal to 30 ℃ and the PH to be less than or equal to 8.5, after the feeding is finished, continuously introducing the carbon dioxide, keeping the temperature for a period of time, and then performing pressure relief, discharging and filtering to obtain a cyanamide product; the mother solution is cyanamide solution or water washing water or industrial water obtained by washing cyanamide slag with water.

2. The method for producing cyanamide by absorbing carbon dioxide under positive pressure according to claim 1, wherein the mass percentage of cyanamide in the cyanamide solution is 5-9%.

3. The method for producing cyanamide by absorbing carbon dioxide under positive pressure according to claim 1, wherein the mass ratio of the cyanamide aqueous solution mother liquor to the lime nitrogen is 2-6: 1.

4. The method for producing cyanamide by absorbing carbon dioxide under positive pressure according to claim 1 or 3, wherein the content of available nitrogen in lime nitrogen is not less than 20%.

5. The method for producing cyanamide by absorbing carbon dioxide under positive pressure according to claim 1, wherein the ratio of the lime nitrogen feeding speed t/h to the carbon dioxide flux t/h is 0.5-3.0: 1.

6. The method for producing cyanamide by positively-pressuring absorption of carbon dioxide according to claim 1, wherein the pressure in the kettle is controlled to be 0.5 to 1.0 MPa.

7. The method for producing cyanamide by absorbing carbon dioxide under positive pressure according to claim 1, wherein the temperature in the synthesis kettle is controlled to be 20-25 ℃.

8. The method for producing cyanamide by positively-pressuring absorption of carbon dioxide according to claim 1, wherein the holding time is 0-45 min.

9. The method for producing cyanamide by positive pressure absorption of carbon dioxide as claimed in claim 8, wherein the holding time is 10-20 min.

10. The method for producing cyanamide by positive pressure absorption of carbon dioxide as claimed in claim 9, wherein the holding time is 15 min.

Technical Field

The invention belongs to the technical field of chemical industry, and particularly relates to a method for producing cyanamide by positively-pressuring absorption of carbon dioxide.

Background

Cyanamide is a medical raw material and an intermediate, is mainly used for producing cytarabine hydrochloride, 3-amino-5-hydroxy 1, 2, 4-triazole and the like, is also an organic synthetic raw material, such as producing cyanuramide, dicyandiamide, methyl carbamate and the like, and further producing medicines of barbituric acid, sulfonamides, various guanidine salts, pesticide-diclofop, carbendazim, creatine and the like. The cyanamide can be used as a plant growth regulator in agriculture, has insecticidal and bactericidal effects, is a good dormancy terminator particularly in the production of cherries and grapes, can bring about early flowering and fruiting, increase the yield and change the fruit meat quality.

The physicochemical properties of the product are as follows: the crystal cyanamide is unstable, is colorless crystalline solid, is rhombic, colorless, is easy to damp and has a melting point of 42 ℃. It is soluble in water, ethanol, diethyl ether and benzene, insoluble in ethylene oxide, and can volatilize with water vapor and be toxic. The 50.0% water solution is colorless liquid with specific weight of 1.0724, and cyanamide has high solubility in water, weak acidity and complete mutual solubility with water at 43 deg.C. 30.0% of cyanamide is obtained by adding acid into the aqueous suspension of calcium cyanamide, is an important organic synthesis intermediate, is especially widely applied to the synthesis of medicines and pesticides, and can be used as a plant growth regulator.

In the existing process for synthesizing cyanamide, the inside of a synthesis kettle is under slight negative pressure, a large amount of carbon dioxide is not reacted and is discharged as tail gas, the utilization rate of the carbon dioxide is low, the reaction efficiency is low, and the unit consumption of the carbon dioxide is high.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for producing cyanamide by absorbing carbon dioxide at positive pressure, which changes the inside of a synthesis kettle into positive pressure absorption, improves the utilization rate of carbon dioxide, improves the reaction rate, reduces the unit consumption of carbon dioxide, and can reduce the unit consumption of carbon dioxide by more than 30 percent by adopting positive pressure absorption compared with micro-negative pressure synthesis of cyanamide.

The method specifically comprises the following steps:

adding mother liquor into a synthesis kettle, introducing carbon dioxide, controlling the pressure in the kettle to be 0.2-1.0 MPa, adding lime nitrogen according to the proportion, controlling the temperature in the synthesis kettle to be less than or equal to 30 ℃ and the PH to be less than or equal to 8.5, after the feeding is finished, continuously introducing the carbon dioxide, keeping the temperature for a period of time, and then performing pressure relief, discharging and filtering to obtain a cyanamide product.

The mother solution is a cyanamide solution or water washing water or industrial water obtained by washing cyanamide slag, wherein the cyanamide solution can be a cyanamide aqueous solution, or a cyanamide solution obtained after a cyanamide synthesis process is used (a small amount of dicyandiamide and the like may be contained in the cyanamide solution), and the mass percentage of the cyanamide in the cyanamide solution is preferably 5-9%.

Under normal temperature and normal pressure, the solubility of carbon dioxide in water is 0.878L/Kg (water), and at 0.2MPa and 20 ℃, the solubility can reach 1.72L/Kg (water), and at 1.0MPa and 20 ℃, the solubility at 20 ℃ is 7.85L/Kg (water). Preferably, the pressure in the kettle is controlled to be 0.5-1.0 MPa.

In the process of synthesizing the cyanamide, the pH of the feed liquid needs to be kept neutral or weakly acidic. In general, in the synthesis process, the pH can be reduced to about 6 at the lowest level due to the characteristics of the feed liquid, so the bottom line is not required. However, if the pH is too high, generally above 9, the pH will start to polymerize in large amounts to form dicyandiamide, and if the temperature is too high, the dicyandiamide content will increase, and if the temperature and the pH are not appropriate, the danger index will be increased, and the yield of the dicyandiamide will be reduced, so that the temperature in the synthesis kettle will be controlled to be less than or equal to 30 ℃ and the pH will be less than or equal to 8.5. More preferably, the temperature in the synthesis vessel is controlled to 20 to 25 ℃.

Preferably, the content of the available nitrogen of the lime nitrogen is more than or equal to 21%, and the mass ratio of the mother liquor to the lime nitrogen is 2-6: 1. If the solid-liquid ratio in the synthesis kettle is too high, the mass of the lime nitrogen/the mass of the mother liquor are too high, so that the feed liquid in the synthesis kettle is too viscous, the solubility of carbon dioxide is reduced, the reaction is slow, and the reaction time is prolonged. If the solid-to-liquid ratio is too low, the yield of cyanamide per kettle is affected.

Preferably, the ratio of the lime nitrogen feeding speed (t/h) to the carbon dioxide flux (t/h) is 0.5-3.0: 1. Therefore, the lime nitrogen fed in can be ensured to react immediately, the loss of effective nitrogen is reduced, and the yield of the cyanamide is improved. The larger the carbon dioxide flux, the lower this ratio, but too low a ratio, a large amount of carbon dioxide is wasted without participating in the reaction. The ratio of lime nitrogen feeding speed (t/h) to carbon dioxide flux (t/h) is preferably 1-2: 1, and more preferably 1.2-1.8: 1.

Preferably, the heat preservation time is 0-45 min, so that the residual lime nitrogen in the synthesis kettle can be completely reacted. The preferable heat preservation time is 10-20min, and more preferably 15min, so that the energy consumption can be reduced while the complete reaction is ensured.

The method improves the production process of the cyanamide, and replaces the existing micro-negative pressure process for synthesizing the cyanamide with the process for synthesizing the cyanamide by positive pressure absorption. The cyanamide is synthesized by positive pressure absorption, the utilization rate of carbon dioxide is improved, the reaction rate is improved, and the unit consumption of carbon dioxide is reduced.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.