CN102633736B - Method for synthesizing cyanic acid or melamine by utilizing ammonia gas and carbon dioxide - Google Patents

Abstract

The invention relates to a method for synthesizing cyanic acid or melamine by utilizing ammonia gas and carbon dioxide. The method comprises the following steps: directly reacting by taking ammonia gas and carbon dioxide as raw materials or taking ammonium bicarbonate, ammonium carbonate and ammonium carbamate as the raw materials in the presence of a catalyst or no catalyst under the conditions that the temperature is 200-300 DEG C and the pressure is 0-30MPa to obtain a cyanic acid or melamine product. By using the method disclosed by the invention, a series of problems during the synthesis process of urea are avoided, synthesis production cycle energy consumption, consumption of manpower and physical resources of cyanic acid or melamine are reduced, and production cost is lowered.

Description

Utilize ammonia and carbon dioxide to synthesize the method for cyanuric acid or melamine

technical field

The invention relates to a method for synthesizing cyanuric acid and melamine, which belongs to the technical field of chemical industry.

technical background

Both cyanuric acid and melamine belong to triazine heterocyclic compounds, and both are important chemical products that have developed rapidly in my country in recent years. The structural formulas of cyanuric acid (a) and melamine (b) are as follows:

Cyanuric acid, also known as isocyanuric acid or cyanuric acid, is a widely used synthetic intermediate, such as synthetic resins, flame retardants, herbicides, etc. Cyanuric acid as a raw material for synthetic resins involves medicine, pesticides , coatings, textiles, light industry and other fields. The synthesis process route of cyanuric acid generally has the following types:

1 Phosgene reacts with ammonia:

6COCl ₂ +6NH ₃ →2C ₃ N ₃ H ₃ O ₃ +12HCl

2 Trimerization of cyanate:

3HOCN →C ₃ N ₃ H ₃ O ₃

3 hydrocyanic acid oxidation:

6HCN+3O ₂ →2C ₃ N ₃ H ₃ O ₃

4 Hydrolysis of cyanuric chloride:

C ₃ N ₃ H ₃ Cl ₃ +3H ₂ O→C ₃ N ₃ H ₃ O ₃ +3HCl

5 Urea pyrolysis:

3CO(NH ₂ ) ₂ →C ₃ N ₃ H ₃ O ₃ +3NH ₃

The first four of the above synthetic process routes have the disadvantages of high toxicity of raw materials, complicated process or high cost, and it is difficult to realize large-scale industrial production. The production method of cyanuric acid is generally all to be synthetic (route 5) with urea as raw material at present.

As the raw material for the synthesis of melamine-formaldehyde resin, melamine, together with urea-formaldehyde resin (UF) and phenolic resin (PF), is known as the three major wood adhesives. It can also be used to synthesize cross-linking agents, finishing agents, color-fixing agents, flocculants, etc., and are widely used. In wood, plastic, paint, paper, textile, leather, electrical and pharmaceutical industries.

The production of melamine is currently based on urea as a raw material, with alumina, silica gel, silica-alumina gel, etc. as catalysts, at a temperature of 380-450 ° C, under high pressure, low pressure or normal pressure conditions.

Chinese patent document CN102295615A (CN201110196920.1) provides a method for synthesizing melamine at low temperature, including using urea condensates such as urea, biuret or cyanuric acid as raw materials, and feeding ammonia gas at 150-300°C to keep ammonia The gas partial pressure is 0-50MPa, and the melamine is obtained by direct reaction under the condition of adding a catalyst or not adding a catalyst. When a catalyst is added, the preferred catalyst is ammonium chloride or ammonium sulfate, and the amount of the catalyst is 1-5 wt% of the mass of the raw material. In the process of synthesizing melamine, ammonia and CO ₂ are not released, so that the consumption of raw materials is greatly reduced, and the reaction temperature is low, so that the equipment is simplified, the energy consumption is reduced, and the pollution is reduced. The present invention is a further improvement based on the applicant's patent application.

Contents of the invention

In order to solve many practical problems existing in the prior art cyanuric acid, melamine production process, reduce the production cost of cyanuric acid, melamine, the present invention proposes a kind of synthetic method of cyanuric acid, melamine, directly with ammonia Gas and carbon dioxide are used as raw materials to synthesize cyanuric acid or melamine, which simplifies the process route and reduces the cost.

Technical scheme of the present invention is as follows:

A method for synthesizing cyanuric acid and melamine is characterized in that ammonia and carbon dioxide are mainly used as raw materials, or ammonium bicarbonate, ammonium carbonate or ammonium carbamate are used as raw materials at a temperature of 200-300 ° C and a pressure of 0 -30MPa, react under the condition of adding catalyst or not adding catalyst, and directly synthesize cyanuric acid or melamine products;

In terms of the moles of ammonia and carbon dioxide, ammonia in the raw materials used: carbon dioxide reaction molar ratio=(0.5-1.2): 1, the reaction gets cyanuric acid;

In terms of the moles of ammonia and carbon dioxide, ammonia in the raw materials used: when the carbon dioxide reaction molar ratio=(2.0-4.5): 1, the reaction gets melamine;

When ammonium bicarbonate, ammonium carbonate or ammonium carbamate is used as raw material, ammonia or carbon dioxide may need to be added to meet the above molar ratio of ammonia and carbon dioxide.

According to the present invention, ammonium bicarbonate can be directly used in the synthesis of cyanuric acid; by additionally adding ammonia, the melamine product can be obtained when ammonia: carbon dioxide reaction molar ratio in the reaction system = (2.0-4.5): 1.

According to the present invention, ammonium carbonate and ammonium carbamate can be directly used in the synthesis of melamine; by additionally adding carbon dioxide, ammonia in the reaction system: when the molar ratio of carbon dioxide reaction=(0.5-1.2): 1, melamine can be obtained Acid products.

According to the invention, when a catalyst is added, the preferred catalyst is ammonium chloride or ammonium sulphate. The dosage of the catalyst is 1-5wt% of the raw material mass. The addition of catalyst can shorten the reaction time and increase the content of reaction products.

According to the present invention, preferably, when no catalyst is added, the reaction is carried out at 200-300° C. under a pressure of 1-30 MPa for 10-60 minutes. Most preferably, when no catalyst is added, the reaction is carried out at 230-250° C. under a pressure of 20 MPa for 10-40 minutes.

According to the present invention, preferably, when adding the catalyst, at 220-270° C., keep the reaction pressure at 5-25 MPa, add ammonium chloride or ammonium sulfate catalyst accounting for 1-5 wt% of the raw material mass, and react for 1-30 minutes. Most preferably, when the catalyst is added, the reaction is carried out for 10-20 minutes at 200-210° C. and a reaction pressure of 10-20 MPa.

According to the present invention, preferably, the crude cyanuric acid obtained by the reaction is purified with 20% aqueous sulfuric acid at a purification temperature of 80-100° C., and dried to obtain pure white solid cyanuric acid with a content ≥ 98 wt%.

According to the present invention, preferably, the crude melamine obtained by the reaction is washed with pure water at 40-80° C., filtered 1-2 times, and dried to obtain pure white solid melamine with a content ≥ 98 wt%. Most preferably, it is purified with pure water at 60-80°C.

According to the present invention, when ammonia and carbon dioxide are used as raw materials, examples 1, 3, 4, and 7 are used as specific preferred solutions.

According to the present invention, when using ammonium bicarbonate, ammonium carbonate, ammonium carbamate as raw material, take embodiment 2,5,6 as specific preferred scheme.

The synthesis of cyanuric acid of the present invention is on reaction mechanism, no longer carries out the process that urea condensation generates cyanuric acid, but is raw material by ammonia gas and carbon dioxide, or the reactant of ammonia gas and carbon dioxide such as ammonium bicarbonate etc. As a raw material, it can be directly reacted under high temperature and high pressure to obtain cyanuric acid. In terms of reaction mechanism, the synthesis of melamine of the present invention no longer decomposes cyanic acid under high temperature into cyanamide and carbon dioxide reaction, but uses ammonia and carbon dioxide as raw materials, or the reactants of ammonia and carbon dioxide such as ammonium carbonate or amino Ammonium formate can be directly reacted under high temperature and high pressure to obtain melamine. By controlling different ammonia-carbon ratios in the reaction system, cyanuric acid or melamine can be prepared respectively.

The inventive method has changed the process of first synthesizing urea by ammonia and carbon dioxide, and then synthesizing cyanuric acid or melamine, and proposes a new method for directly synthesizing cyanuric acid or melamine. Under a certain temperature and pressure, cyanuric acid or melamine can be obtained directly with or without a catalyst, which avoids the need to adopt certain technical measures to strictly control the by-product biuret in the process of synthesizing urea from ammonia and carbon dioxide. At the same time, it greatly reduces the production cycle, energy consumption, manpower and material consumption of the target product synthesized by the two-step process in the past, and reduces the production cost. It is a green production method of cyanuric acid or melamine; in addition, this The synthesis of cyanuric acid in the inventive method is still a relatively good carbon dioxide capture and storage technology, which can convert carbon dioxide into an important chemical product, cyanuric acid, and has important application value.

The process of synthesizing cyanuric acid or melamine in the method of the present invention is a gas-solid phase or multiphase reaction, and its reaction speed is related to the heating rate and the amount of catalyst added. Since the reaction product exists in the solid form in the reaction system, a high-purity product can be obtained through simple purification. According to the present invention, the content of the reacted cyanuric acid or melamine is ≥95%, and the yield is ≥95%, and the content of the purified cyanuric acid or melamine is ≥98%, and the yield is ≥95%.

The present invention surprisingly finds that it is more advantageous to obtain cyanuric acid and melamine directly from ammonia and carbon dioxide in industrial production under high temperature and high pressure. React with carbon dioxide to directly synthesize cyanuric acid, which avoids the invalid circulation of ammonia in the existing urea as raw material synthesis process and saves a lot of production costs. It is a green synthesis route of cyanuric acid and a simpler method suitable for industrial production. Straightforward process method.

Detailed ways

The present invention will be further described below in conjunction with the examples, but not limited thereto. The present invention will be further described below in conjunction with the examples, but not limited thereto. The content percentage involved in the embodiment is the mass percentage, and the sulfuric acid aqueous solution concentration is the mass percentage. Wherein, embodiment 1-3 is the synthesis description of cyanuric acid, and embodiment 4-7 is the synthesis description of melamine.

Embodiment 1. take ammonia, carbon dioxide as raw material synthetic cyanuric acid, reaction formula is:

3CO ₂ +3NH ₃ →C ₃ N ₃ H ₃ O ₃ +3H ₂ O

According to the molar ratio of n(NH ₃ ):n(CO ₂ )=0.8:1, feed 440g of ammonia gas and 1040g of carbon dioxide into the reactor, keep the reaction pressure of the system at 20.0MPa at 240-250°C, and react for 10min; The reaction product is mainly white cyanuric acid (C ₃ N ₆ H ₃ O ₃ ) solid, with a content of 95%, and after purification, the content is 98%, and the yield is 95%;

Embodiment 2. take ammonium bicarbonate as raw material synthetic cyanuric acid, and reaction formula is:

3NH ₄ HCO ₃ →C ₃ N ₃ H ₃ O ₃ +6H ₂ O

Add 670g of ammonium bicarbonate into the reactor, keep the system reaction pressure at 20.0MPa at 230-250°C, and react for 5min; the reaction product is mainly white cyanuric acid (C ₃ N ₆ H ₃ O ₃ ) solid, with a content of 95.2%, the content after purification is 98.5%, and the yield is 95%.

Embodiment 3. take ammonia and carbon dioxide as raw material to synthesize cyanuric acid under catalytic conditions, and the reaction formula is:

According to the reaction amount of n(NH ₃ ):n(CO ₂ )=1.1:1, add 440g of ammonia gas, 1040g of carbon dioxide and 50g of ammonium chloride into the reactor, heat to 200-210°C, and keep the system reaction pressure at 15.0 MPa, reacted for 15 minutes; the reaction product was mainly white cyanuric acid (C ₃ N ₆ H ₃ O ₃ ) solid, with a content of 96%, and after purification, the content was 99%, and the yield was 96%.

Embodiment 4. take ammonia, carbon dioxide as raw material synthetic melamine, reaction formula is:

3CO ₂ +6NH ₃ →C ₃ N ₆ H ₆ +6H ₂ O

According to the reaction molar ratio of n(NH ₃ ):n(CO ₂ )=2.2:1, add 585g of ammonia and 695g of carbon dioxide into the reactor, keep the reaction pressure of the system at 20.0MPa at 230-250°C, and react for 40min; The reaction product is mainly white melamine (C ₃ N ₆ H ₆ ) solid, with a content of 95%, and after purification, the content is 98%, and the yield is 95%.

Embodiment 5. take ammonium carbonate as raw material synthetic melamine, reaction formula is:

3(NH ₄ ) ₂ CO ₃ →C ₃ N ₆ H ₆ +9H ₂ O

Add 570g of ammonium carbonate to the reactor, keep the system reaction pressure at 20.0MPa at 230-250°C, and react for 30min; the reaction product is mainly white melamine (C ₃ N ₆ H ₆ ) solid, with a content of 95.5%, and the purified content It was 98.5%, and the yield was 95%.

Embodiment 6. take ammonium carbamate as raw material synthetic melamine, and reaction formula is:

3NH ₂ COONH ₄ →C ₃ N ₆ H ₆ +6H ₂ O

Add 710g of ammonium carbamate (methylammonium) into the reactor, heat to 230-240°C, keep the system reaction pressure at 10.0MPa, and react for 30min; the reaction product is mainly white melamine (C ₃ N ₆ H ₆ ) solid, with a content of 95%, the content after purification is 98%, and the yield is 96%.

Embodiment 7. take ammonia and carbon dioxide as raw material to synthesize melamine under catalytic conditions, and the reaction formula is:

According to the reaction amount of n(NH ₃ ):n(CO ₂ )=2.2:1, add 585g of ammonia gas, 695g of carbon dioxide and 55g of ammonium chloride into the reactor, and keep the system reaction pressure at 15.0MPa at 200-210°C , and reacted for 20 minutes; the reaction product was mainly white melamine (C ₃ N ₆ H ₆ ) solid, with a content of 96%, and after purification, the content was 99%, and the yield was 96%.

The product obtained by the method of the invention is cyanuric acid or melamine with a content of more than 95%, and the by-product content is very small, and can be directly used in industrial production without purification treatment. If a pure product is required, it can be purified by existing purification methods. The product cyanuric acid purification method of the present invention is to adopt 20% sulfuric acid aqueous solution, heat 80-100 ℃, wash, filter and purify 1-2 times, and obtain pure cyanuric acid. The method for purifying the melamine product of the present invention is to use pure water, heat at 40-80°C, wash, filter and purify for 1-2 times to obtain pure melamine.

Claims (7)

1. A synthetic method of cyanuric acid or melamine is characterized in that taking ammonia and carbon dioxide as raw material or taking ammonium bicarbonate, ammonium carbonate or ammonium carbamate as raw material, at temperature 200-300 ℃, pressure 0- 30MPa, add catalyst or react under the condition of not adding catalyst, and directly synthesize cyanuric acid or melamine products; In terms of the moles of ammonia and carbon dioxide, ammonia in the raw materials used: carbon dioxide reaction molar ratio=(0.5-1.2): 1, the reaction gets cyanuric acid; In terms of the moles of ammonia and carbon dioxide, ammonia in the raw materials used: when the carbon dioxide reaction molar ratio=(2.0-4.5): 1, the reaction gets melamine; When ammonium bicarbonate, ammonium carbonate or ammonium carbamate is used as raw material, ammonia or carbon dioxide may need to be added to meet the above molar ratio of ammonia and carbon dioxide. 2. the synthetic method of cyanuric acid or melamine as claimed in claim 1 is characterized in that when adding catalyzer, described catalyzer is ammonium chloride or ammonium sulfate. 3. the synthetic method of cyanuric acid or melamine as claimed in claim 1 or 2 is characterized in that when adding catalyzer, the consumption of described catalyzer is the 1-5wt% of raw material quality. 4. the synthetic method of cyanuric acid or melamine as claimed in claim 1 is characterized in that when not adding catalyst, at 200-300 ℃, pressure is 10-30MPa, reacts 10-60min. 5. the synthetic method of cyanuric acid or melamine as claimed in claim 3 is characterized in that when adding catalyzer, at 220-270 ℃, keep reaction pressure and be 5-25MPa, react 1-30min. 6. the synthetic method of cyanuric acid or melamine as claimed in claim 1 is characterized in that the product cyanuric acid crude product obtained by reaction is purified with 20% sulfuric acid aqueous solution, 80-100 ℃ of purifying temperature, dry, obtain white Pure solid cyanuric acid, content ≥ 98wt%. 7. the synthetic method of cyanuric acid or melamine as claimed in claim 1 is characterized in that the product melamine crude product obtained by reaction is washed with 40-80 ℃ of pure water, filtered 1-2 times, and dried to obtain white solid melamine Pure product, content ≥ 98wt%.