阅读说明：本技术 一种二步法制备水溶性聚磷酸铵的方法 (Method for preparing water-soluble ammonium polyphosphate by two-step method ) 是由 周凌翔 王国栋 张勇 马克猛 龙文恒 于 2021-03-17 设计创作，主要内容包括：本发明公开了一种二步法制备水溶性聚磷酸铵的方法,涉及水溶性聚磷酸铵生产技术领域。将熔融磷酸一铵和熔融尿素送入反应釜中反应,得到酸性聚磷酸铵熔融液；将聚磷酸熔融液送入捏合反应器,与固体尿素二次反应,得到聚磷酸铵半成品；将聚磷酸铵半成品冷却、破碎后得到水溶性聚磷酸铵产品；反应过程汇总尾气经风机送入洗涤塔中洗涤达标后排放。制备方法分两步进行,一次反应在较高温度下进行得到多聚合度分布的聚磷酸铵熔融体,二次反应在较低温度下进行,进一步提高聚合率,得到加工性能好的聚磷酸铵。尿素分二次投入,降低了聚合反应剧烈程度,限制尿素用量,降低生产成本,优化了现有的返料工艺路线,缩短了装置流程。(The invention discloses a method for preparing water-soluble ammonium polyphosphate by a two-step method, and relates to the technical field of water-soluble ammonium polyphosphate production. Feeding molten monoammonium phosphate and molten urea into a reaction kettle for reaction to obtain acidic ammonium polyphosphate molten liquid; feeding the polyphosphoric acid molten liquid into a kneading reactor, and carrying out secondary reaction with solid urea to obtain an ammonium polyphosphate semi-finished product; cooling and crushing the ammonium polyphosphate semi-finished product to obtain a water-soluble ammonium polyphosphate product; and tail gas gathered in the reaction process is sent into a washing tower through a fan to be washed and discharged after reaching the standard. The preparation method is carried out in two steps, wherein the first reaction is carried out at a higher temperature to obtain the ammonium polyphosphate fused mass with the distribution of multiple polymerization degrees, and the second reaction is carried out at a lower temperature to further improve the polymerization rate and obtain the ammonium polyphosphate with good processing performance. The urea is added twice, so that the intensity of polymerization reaction is reduced, the urea consumption is limited, the production cost is reduced, the existing material returning process route is optimized, and the device flow is shortened.)

1. A method for preparing water-soluble ammonium polyphosphate by a two-step method is characterized by comprising the following steps:

a. feeding molten monoammonium phosphate and molten urea into a reaction kettle respectively through a feeder according to a molar ratio of 1: 0.1-0.4, and reacting at the temperature of 200-260 ℃ and the pressure of 0.05-0.25 MPa for 1-6 h to obtain an acidic ammonium polyphosphate molten liquid;

b. feeding the polyphosphoric acid molten liquid into a kneading reactor under the action of the pressure of a reaction kettle, and carrying out secondary reaction with solid urea at the temperature of 120-180 ℃ for 0.2-2 h to obtain an ammonium polyphosphate semi-finished product;

c. cooling and crushing the ammonium polyphosphate semi-finished product to obtain a water-soluble ammonium polyphosphate product;

d. and tail gas gathered in the reaction process is sent into a washing tower through a fan to be washed and discharged after reaching the standard.

2. The method for preparing water-soluble ammonium polyphosphate according to the two-step method of claim 1, which is characterized in that: and in the step b, the mol ratio of the ammonium polyphosphate molten liquid to the solid urea is 1: 0.1-0.2.

3. The method for preparing water-soluble ammonium polyphosphate according to the two-step method of claim 1, which is characterized in that: and b, continuously feeding molten monoammonium phosphate into a melting tank from a monoammonium phosphate raw material in the step a, wherein the melting temperature is 185-215 ℃, and the residence time in the melting tank is 0.5-2.0 h.

4. The method for preparing water-soluble ammonium polyphosphate according to the two-step method of claim 3, which is characterized in that: the melting tank is provided with a heat-conducting oil heating coil and a heat-insulating jacket.

5. The method for preparing water-soluble ammonium polyphosphate according to the two-step method of claim 1, which is characterized in that: and b, continuously feeding the molten urea in the step a into a melting tank from a urea raw material, wherein the melting temperature is 130-150 ℃, and the residence time in the melting tank is 0.5-2.0 h.

6. The method for preparing water-soluble ammonium polyphosphate according to the two-step method, which is characterized by comprising the following steps: the melting tank is provided with a low-pressure saturated steam coil pipe and a heat-preserving jacket.

Technical Field

The invention relates to the technical field of water-soluble ammonium polyphosphate production, and particularly relates to a method for preparing water-soluble ammonium polyphosphate by a two-step method.

Background

Ammonium polyphosphate (APP for short) is a polyphosphate containing nitrogen and phosphorus, has white powder appearance, and has two forms of crystallization and amorphousness, and the general formula is (NH)₄)_n+2P_nO_3n+1(n.gtoreq.2). When n is 2-20, the compound is water-soluble and is used as an agricultural fertilizer; when n is more than 20, the flame retardant is insoluble APP, can be heated and decomposed at high temperature to form a polyphosphoric acid hard shell covering a combustion surface, releases ammonia gas, water vapor and other non-combustible gases to prevent combustion, and is mainly used as a flame retardant in the industries of fireproof coatings, wood, plastics, fibers and the like.

In foreign countries, ammonium polyphosphate has been widely used in the field of agricultural production, particularly in developed countries in the united states and europe. Ammonium polyphosphate, which was reported to be used as a fertilizer in the us developed in the last 60 th century, was reacted with ammonia gas at high temperature in a tubular reactor by a thermal method or a wet method to produce an ammonium polyphosphate solution.

The ammonium polyphosphate is researched and started late in China, mainly is ammonium polyphosphate with high polymerization degree, and the application of the ammonium polyphosphate is mainly flame retardant. In recent years, ammonium polyphosphate gradually enters the production fields of compound fertilizers, liquid fertilizers and the like. Ammonium polyphosphate is produced by a plurality of methods, and the common methods for producing water-soluble ammonium polyphosphate mainly comprise a phosphoric acid-urea condensation method and an ammonium phosphate-urea condensation method.

The patent CN108002357A discloses a production method of a high-water-solubility ammonium polyphosphate solid, industrial phosphoric acid with 72-76% of phosphorus pentoxide by mass fraction, liquid ammonia and gas ammonia are used as raw materials, a high-temperature molten material is prepared through a tubular neutralization polycondensation reaction and a further neutralization polycondensation reaction of a polymerization kettle, then a water-solubility ammonium polyphosphate finished product return material is added, and the high-water-solubility ammonium polyphosphate solid is prepared through cooling and crushing. The method has the defects that the cost of industrial phosphoric acid is high, the prepared high-temperature molten material is viscous and easy to absorb moisture, the property is poor after direct cooling, and 2-3 times of ammonium polyphosphate returning material needs to be provided to promote cooling and crystallization of the molten material. Not only is the material returning flow increased, but also in the actual production, the melt is easy to be bonded and returned to form a large material in the mixing and cooling process, which is not beneficial to the stability of the product quality and the process control.

Patent CN105503276B discloses a preparation method of full water-soluble solid ammonium polyphosphate, which comprises melting ammonium dihydrogen phosphate to obtain molten slurry, adding urea into the prepared slurry, stirring to react to obtain reaction slurry, adding the reaction slurry into water-soluble solid ammonium polyphosphate to complete the reaction to obtain polymerized cured substance, pulverizing the cured substance, and sealing and packaging to obtain water-soluble ammonium polyphosphate. The reaction slurry prepared by the method is also viscous, and needs to be added with 2-3 times of ammonium polyphosphate returning charge to promote cooling and crystallization of a molten material, and the deficiency of the reaction slurry is the same as CN 108002357A.

The patent CN105967164A discloses a method for preparing water-soluble ammonium polyphosphate with high polymerization rate, which comprises the steps of adding monoammonium phosphate and urea into a reaction kettle according to a certain proportion, stirring, heating to control the temperature to be 110-. The method can directly obtain ammonium polyphosphate with better processing performance, and has the defects of high urea consumption and lower reaction temperature, the obtained ammonium polyphosphate takes ammonium pyrophosphate as the main component, and the ammonium phosphate of trimerization and above is rarely distributed.

Aiming at the problems, the invention adopts monoammonium phosphate as a raw material, utilizes a two-step method to prepare the water-soluble ammonium polyphosphate, optimizes the process flow and obtains the water-soluble ammonium polyphosphate product with good processing performance, wide polymerization degree distribution and relatively low cost.

Disclosure of Invention

The invention aims to provide a method for preparing water-soluble ammonium polyphosphate by a two-step method, which solves the problems of high raw material consumption and less ammonium phosphate distribution of trimerization and above in the product in the existing preparation method.

In order to solve the technical problems, the invention adopts the following technical scheme: a method for preparing water-soluble ammonium polyphosphate by a two-step method is characterized by comprising the following steps:

a. feeding molten monoammonium phosphate and molten urea into a reaction kettle respectively through a feeder according to a molar ratio of 1: 0.1-0.4, and reacting at the temperature of 200-260 ℃ and the pressure of 0.05-0.25 MPa for 1-6 h to obtain an acidic ammonium polyphosphate molten liquid;

b. feeding the polyphosphoric acid molten liquid into a kneading reactor under the action of the pressure of a reaction kettle, and carrying out secondary reaction with solid urea at the temperature of 120-180 ℃ for 0.2-2 h to obtain an ammonium polyphosphate semi-finished product;

c. cooling and crushing the ammonium polyphosphate semi-finished product to obtain a water-soluble ammonium polyphosphate product;

d. and tail gas gathered in the reaction process is sent into a washing tower through a fan to be washed and discharged after reaching the standard.

The further technical scheme is that the mol ratio of the ammonium polyphosphate molten liquid to the solid urea in the step b is 1: 0.1-0.2.

The further technical scheme is that in the step a, molten monoammonium phosphate is continuously fed into a melting tank from a monoammonium phosphate raw material, the melting temperature is 185-215 ℃, and the residence time in the melting tank is 0.5-2.0 h.

The further technical proposal is that the melting tank is a melting tank with a heat-conducting oil heating coil and a heat-preserving jacket.

The further technical scheme is that in the step a, the molten urea is continuously fed into a melting tank from a urea raw material, the melting temperature is 130-150 ℃, and the residence time in the melting tank is 0.5-2.0 h.

The further technical proposal is that the melting tank is provided with a low-pressure saturated steam coil and a heat-preserving jacket.

The reaction mechanism is as follows:

nNH₄H₂PO₄+CO(NH₂)₂→(NH₄)_nH₂P_nO_3n+1+CO₂+2NH₃+(n-1)H₂O (1)

2NH₄H₂PO₄+CO(NH₂)₂→(NH₄)₄P₂O₇+CO₂ (2)

the method comprises the following steps that firstly, monoammonium phosphate and urea react at a high temperature to generate an acidic ammonium polyphosphate melt (reaction formula 1) with multiple polymerization degrees distributed, and the ammonium polyphosphate melt and the urea further react at a low temperature to generate ammonium pyrophosphate (reaction formula 2), wherein the main reaction in the step is that unpolymerized monoammonium phosphate in the ammonium polyphosphate melt reacts with the urea to improve the physical property of the ammonium polyphosphate, so that the ammonium polyphosphate with good processing performance is obtained.

Compared with the prior art, the invention has the beneficial effects that: the method has simple process and step-by-step control of the reaction process, namely, the first reaction is carried out at higher temperature to obtain acidic ammonium polyphosphate fused mass with multi-polymerization degree distribution, and the second reaction is carried out at lower temperature to further improve the polymerization rate and obtain the ammonium polyphosphate with good processing performance. The method limits the dosage of urea, reduces the production cost and prepares the ammonium polyphosphate product with excellent performance. The urea is added twice, so that the intensity of polymerization reaction is reduced, the existing material returning process route is optimized, the device flow is shortened, and the method has obvious guiding significance for large-scale device construction.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Example 1

Melting monoammonium phosphate in a melting tank with a heat-conducting oil heating coil and a heat-insulating jacket, melting urea in the melting tank with a low-pressure saturated steam coil and the heat-insulating jacket, and maintaining the temperature of the monoammonium phosphate melting tank at 200 ℃ and the urea melting temperature at 135 ℃ to ensure that the melting liquid has good fluidity.

According to the weight ratio of monoammonium phosphate: and (3) uniformly and stably feeding the monoammonium phosphate molten liquid and the urea molten liquid into a reaction kettle for polymerization reaction according to the urea molar ratio of 1: 0.2. Controlling the reaction temperature to be 250 ℃, the pressure to be 0.05MPa and the reaction time to be 4.0h to obtain the acidic ammonium polyphosphate molten solution.

Feeding the ammonium polyphosphate molten liquid into a kneading reactor under the action of the pressure of a reaction kettle, wherein the weight ratio of the ammonium polyphosphate molten liquid: the solid urea is reacted for the second time under the conditions that the molar ratio of the solid urea is 1:0.15, the reaction temperature is 120 ℃ and the reaction time is 2.0 h. And after the reaction is finished, obtaining a powdery or blocky ammonium polyphosphate semi-finished product, cooling and crushing to obtain a powdery water-soluble ammonium polyphosphate product, wherein the product indexes are shown in tables 1 and 2.

Example 2

Melting monoammonium phosphate in a melting tank with a heat-conducting oil heating coil and a heat-insulating jacket, melting urea in the melting tank with a low-pressure saturated steam coil and the heat-insulating jacket, and maintaining the temperature of the monoammonium phosphate melting tank at 215 ℃ and the urea melting temperature at 130 ℃ to ensure that the melting liquid has good fluidity.

According to the weight ratio of monoammonium phosphate: and (3) uniformly and stably feeding the monoammonium phosphate molten liquid and the urea molten liquid into a reaction kettle for polymerization reaction according to the urea molar ratio of 1: 0.1. Controlling the reaction temperature at 260 ℃, the pressure at 0.10MPa and the reaction time at 6.0h to obtain the acidic ammonium polyphosphate molten solution.

Feeding the ammonium polyphosphate molten liquid into a kneading reactor under the action of the pressure of a reaction kettle, wherein the weight ratio of the ammonium polyphosphate molten liquid: the solid urea is reacted for the second time under the conditions that the molar ratio of the solid urea is 1:0.2, the reaction temperature is 160 ℃ and the reaction time is 1.5 h. And after the reaction is finished, obtaining a powdery or blocky ammonium polyphosphate semi-finished product, cooling and crushing to obtain a powdery water-soluble ammonium polyphosphate product, wherein the product indexes are shown in tables 1 and 2.

Example 3

Melting monoammonium phosphate in a melting tank with a heat-conducting oil heating coil and a heat-insulating jacket, melting urea in the melting tank with a low-pressure saturated steam coil and the heat-insulating jacket, and maintaining the temperature of the monoammonium phosphate melting tank at 210 ℃ and the urea melting temperature at 140 ℃ so as to ensure that the melting liquid has good fluidity.

According to the weight ratio of monoammonium phosphate: and (3) uniformly and stably feeding the monoammonium phosphate molten liquid and the urea molten liquid into a reaction kettle for polymerization reaction according to the urea molar ratio of 1: 0.3. Controlling the reaction temperature at 220 ℃, the pressure at 0.15MPa and the reaction time at 2.0h to obtain the acidic ammonium polyphosphate molten solution.

Feeding the ammonium polyphosphate molten liquid into a kneading reactor under the action of the pressure of a reaction kettle, wherein the weight ratio of the ammonium polyphosphate molten liquid: the solid urea is reacted for the second time under the conditions that the molar ratio of the solid urea is 1:0.15, the reaction temperature is 140 ℃ and the reaction time is 1.0 h. And after the reaction is finished, obtaining a powdery or blocky ammonium polyphosphate semi-finished product, cooling and crushing to obtain a powdery water-soluble ammonium polyphosphate product, wherein the product indexes are shown in tables 1 and 2.

Example 4

Melting monoammonium phosphate in a melting tank with a heat-conducting oil heating coil and a heat-insulating jacket, melting urea in the melting tank with a low-pressure saturated steam coil and the heat-insulating jacket, and maintaining the temperature of the monoammonium phosphate melting tank at 190 ℃ and the urea melting temperature at 133 ℃ to ensure that the melting liquid has good fluidity.

According to the weight ratio of monoammonium phosphate: and (3) uniformly and stably feeding the monoammonium phosphate molten liquid and the urea molten liquid into a reaction kettle for polymerization reaction according to the urea molar ratio of 1: 0.4. Controlling the reaction temperature at 200 ℃, the pressure at 0.2MPa and the reaction time at 1.0h to obtain the acidic ammonium polyphosphate molten solution.

Feeding the ammonium polyphosphate molten liquid into a kneading reactor under the action of the pressure of a reaction kettle, wherein the weight ratio of the ammonium polyphosphate molten liquid: the solid urea is reacted for the second time under the conditions that the molar ratio of the solid urea is 1:0.1, the reaction temperature is 180 ℃ and the reaction time is 0.5 h. And after the reaction is finished, obtaining a powdery or blocky ammonium polyphosphate semi-finished product, cooling and crushing to obtain a powdery water-soluble ammonium polyphosphate product, wherein the product indexes are shown in tables 1 and 2.

TABLE 1 index analysis results of ammonium polyphosphate prepared by the method of the present invention

	Example 1	Example 2	Example 3	Example 4
					Total P2O5% by weight	65.58	64.37	65.78	65.67
Total N%	13.43	14.40	14.62	14.10
					Total nutrient%	79.01	78.77	80.4	79.77
Polymerization ratio%	97.38	95.62	96.65	96.89
					Average degree of polymerization	3.17	3.07	3.84	3.24

TABLE 2 ammonium polyphosphate polymerization degree distribution made by the method of the present invention

As can be seen from tables 1 and 2, in the water-soluble ammonium polyphosphate product prepared by the method, the content of ammonium polyphosphate more than trimerization is more than 60 percent, and the advantage of high content of ammonium phosphate more than trimerization is as follows: (1) the higher the polymerization degree, the longer the chain structure, the slower the hydrolysis rate and the more durable the fertilizer effect; (2) the longer the chain structure is, the more weakly acidic protons substituted by metal ions can be provided, and the chelating ability is stronger. Under the same condition, the chelating capacity of the ammonium polyphosphate with the polymerization degree of 3-5 is 2-3 times of that of 1.5-2.

The ammonium polyphosphate prepared by the method has the average polymerization degree of 3-5, is uniform in polymerization degree distribution, has the polymerization rate of more than 95%, can be dissolved in 100g of water at normal temperature by more than 145g, and has excellent agricultural application value. The content of ammonium polyphosphate phosphorus (calculated by phosphorus pentoxide) prepared by the method reaches more than 64 percent, the total nutrient reaches more than 78 percent, and the ammonium polyphosphate phosphorus is a water-soluble formula fertilizer raw material with excellent performance and provides nutrient space for adding other elements. The fertilizer effect of the ammonium polyphosphate prepared by the method is good, the ammonium polyphosphate prepared by the method is mixed with the traditional diammonium phosphate and then applied to a corn field test, and the result shows that the yield of diammonium phosphate added with the mixed ammonium polyphosphate is increased by 8-10% compared with that of diammonium phosphate.

Although the invention has been described herein with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts or arrangements within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts or arrangements, other uses will also be apparent to those skilled in the art.