阅读说明：本技术 一种石灰氮的合成方法 (Method for synthesizing lime nitrogen ) 是由 高鹏 张宁 安敬瑞 崔卫华 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,具体涉及一种石灰氮的合成方法,本发明方法以氧化钙、氨基甲酸铵为原料,通过煅烧制得石灰氮,且煅烧过程中通入含氨气体。本发明在煅烧过程中通入含氨气体,有效减少了氨基甲酸铵的分解,降低了反应温度,提高了收率,避免了最终产品中副产物的夹杂,保证了产物中有效成分氰胺化钙的有效含量。反应无废弃物产生,具有很高的环保价值,大大降低了生产成本,适合工业化生产。(The invention belongs to the technical field of chemical industry, and particularly relates to a method for synthesizing lime nitrogen. According to the invention, ammonia-containing gas is introduced in the calcining process, so that the decomposition of ammonium carbamate is effectively reduced, the reaction temperature is reduced, the yield is improved, the inclusion of byproducts in the final product is avoided, and the effective content of the effective component calcium cyanamide in the product is ensured. No waste is generated in the reaction, the method has high environmental protection value, greatly reduces the production cost and is suitable for industrial production.)

1. The method is characterized in that calcium oxide and ammonium carbamate are used as raw materials, the lime nitrogen is prepared by calcining, and ammonia-containing gas is introduced in the calcining process.

2. The method for synthesizing lime nitrogen according to claim 1, wherein the ammonia-containing gas is a gas with an ammonia gas content of more than 40%, and can be derived from ammonia gas or liquid ammonia or a mixed gas containing ammonia gas.

3. The method for synthesizing lime nitrogen according to claim 1, which is characterized by comprising the following specific steps:

(1) a first calcination stage: the following reactions occur: 2NH₂COONH₄+CaO→Ca(OCN)₂+2NH₃+3H₂O；

The specific process is as follows: uniformly mixing calcium oxide and ammonium carbamate, placing the mixture in a high-temperature reaction furnace, continuously introducing ammonia-containing gas to keep the system pressure at 0-3MPa, reacting at the temperature of 100 ℃ and 150 ℃ for 2-4h, and continuously heating after the reaction is finished;

(2) a second calcination stage: the following reactions occur: ca (OCN)₂→CaCN₂+CO₂；

The specific process is as follows: and continuously introducing ammonia-containing gas to keep the system pressure at 0-3MPa, heating to 800 ℃ for reaction for 4-8h, and cooling to room temperature under the nitrogen atmosphere after the reaction is finished to obtain the high-quality lime nitrogen.

4. The method for synthesizing lime nitrogen according to claim 3, wherein the molar ratio of calcium oxide: ammonium carbamate-1: 2-8.

5. The method for synthesizing lime nitrogen according to claim 3, wherein the system pressure is maintained at 0-1MP during the steps (1) and (2).

6. The method for synthesizing lime nitrogen according to claim 5, wherein the system pressure is maintained at 0.1-0.5MP during the steps (1) and (2).

Technical Field

The invention belongs to the technical field of chemical industry, and particularly relates to a method for synthesizing lime nitrogen.

Background

Lime nitrogen, also known as calcium cyanamide, is a raw material for producing cyanamide, dicyandiamide, thiourea and carbendazim, and can be used as a metal heat treatment agent in steel operation and a base fertilizer in agriculture. At present, the consumption of lime nitrogen for producing cyanamide and dicyandiamide in China accounts for 60% of the total consumption of lime nitrogen, the consumption of lime nitrogen for producing thiourea and carbendazim accounts for about 35% of the total consumption of lime nitrogen, and the consumption of lime nitrogen for the agricultural field only accounts for about 5% of the total consumption of lime nitrogen.

At present, the synthesis method of lime nitrogen is that calcium carbide is crushed and then evenly mixed with fluorite and return lime, the mixture is ground into calcium carbide powder by a ball mill, the calcium carbide powder enters a nitriding furnace and reacts with nitrogen at the high temperature of 1000 ℃, lime nitrogen is generated after 42 to 48 hours, and clinker is taken out and crushed and finely crushed by a tube mill to prepare the finished product of calcium cyanamide. The prior production process has the defects of high energy consumption, high cost and large pollution. Therefore, the synthesis process which is economical, cheap, simple and safe to operate and free of pollution is selected, and the synthesis process has great economic value.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for synthesizing lime nitrogen, which solves the problems of high production cost, large energy consumption, large pollution and the like in the prior art.

The method takes calcium oxide and ammonium carbamate as raw materials, high-quality lime nitrogen is prepared by calcining, and ammonia-containing gas is introduced in the calcining process.

The ammonia-containing gas refers to gas with the ammonia gas volume percentage of more than 40%, and can be derived from ammonia gas or liquid ammonia or mixed gas containing ammonia gas.

The method comprises the following specific steps:

(1) a first calcination stage: the following reactions occur: 2NH₂COONH₄+CaO→Ca(OCN)₂+2NH₃+3H₂O；

The specific process is as follows: uniformly mixing calcium oxide and ammonium carbamate, placing the mixture in a high-temperature reaction furnace, continuously introducing ammonia-containing gas to keep the system pressure at 0-3MPa, reacting at the temperature of 100 ℃ and 150 ℃ for 2-4h, and continuously heating after the reaction is finished;

(2) a second calcination stage: the following reactions occur: ca (OCN)₂→CaCN₂+CO₂；

The specific process is as follows: and continuously introducing ammonia-containing gas to keep the system pressure at 0-3MPa, heating to 800 ℃ for reaction for 4-8h, and cooling to room temperature under the nitrogen atmosphere after the reaction is finished to obtain the high-quality lime nitrogen product.

In the first calcining stage, the reaction is difficult to occur due to too low temperature, and the decomposition of ammonium carbamate is accelerated due to too high temperature, so that the calcining temperature is controlled at 100-150 ℃ and the reaction lasts for 2-4 h.

In the second stage of the burning, the temperature is too low, the reaction is slow, and the temperature is too high, so that the energy consumption is wasted, and therefore, the burning temperature is controlled at 500-800 ℃, and the reaction lasts for 4-8 h.

In the whole calcining reaction process, the amount of ammonium carbamate is too low, and the reaction is insufficient; too high an amount of ammonium carbamate is wasteful, and therefore, in terms of molar ratio of pure substances, calcium oxide: ammonium carbamate-1: 2-8.

The ammonia-containing gas is continuously introduced in the whole calcining reaction process, and the inventor finds that the introduction of the ammonia-containing gas can inhibit the decomposition of the ammonium carbamate to a certain degree through experiments, so that the yield is improved, and the reaction temperature is reduced to a certain degree. In addition, the ammonia-containing gas can take away the water generated in the system in time, and the generated product CaCN is avoided₂It can be decomposed with water to increase yield. Other products generated in the reaction process of the invention are discharged in a gas form, and the excessive ammonium carbamate can be decomposed into the gas form and discharged in the second-stage sintering section, thereby ensuring the CaCN in the products₂An effective amount of (a).

In the whole calcining stage, the pressure is controlled to be 0-3MPa by controlling the introduction of ammonia-containing gas, the pressure is too low, the concentration of the ammonia-containing gas is too low, and the effect of inhibiting the decomposition of ammonium carbamate is poor; the pressure is too high, the reaction at high temperature of more than 500 ℃ has potential danger, and the requirement on the high-temperature pressure resistance of equipment is high.

The system pressure will have a certain effect on promoting the reaction, but for the pressure resistance and safety of the equipment, the system pressure is preferably kept between 0 and 1MP during the steps (1) and (2), and more preferably kept between 0.1 and 0.5 MP.

In conclusion, ammonia-containing gas is introduced in the calcining process, so that the decomposition of ammonium carbamate is effectively reduced, the reaction temperature is reduced, the yield is improved, the inclusion of byproducts in the final product is avoided, the effective content of the effective component calcium cyanamide in the product is ensured to be far higher than the purity (about 60%) of the calcium cyanamide in the currently marketed lime nitrogen, the energy consumption is low, the production cost is low, and the finally obtained product has high quality.

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.