RU2180890C1 - Method for production of high-condensed ammonium polyphosphate - Google Patents

Abstract

FIELD: fire retardants. SUBSTANCE: preparation of high-condensed ammonium polyphosphate applicable as fire retardant constituent of fire-protective swelling coatings and when manufacturing fire-resistant structural materials involves heating ammonium orthophosphate/urea mixture (1:1 molar ratio) in presence of ammonium polyphosphate in ammonia gas atmosphere to form low-melting eutectic, which is then heated at rate 160-200 C/min to 230-240 C, during which period melt crystallizes, and then to 280-300 C, after which product is hold at this temperature to dehydrate at reduced pressure 0.52-1.29 kPa. Anhydrous product is cooled and crushed. Decomposition point of product is 275-285 C and its weight loss 0.22-0.05%. EFFECT: enhanced process efficiency and improved quality of product. 1 tbl

Description

 The invention relates to the technology of highly condensed ammonium polyphosphate, used as a flame retardant in flame retardant intumescent coatings and in the manufacture of fire-resistant structural materials.

The fire retardant efficiency of ammonium polyphosphates is due, in particular, to their thermal stability. The temperature of the onset of mass loss should not be lower than 210-220 ^o C, the weight loss should also be minimal (not more than 0.2%).

 The thermal stability of polyphosphates depends on the proportion of low molecular weight polyphosphates in the composition of the product, which reduce the temperature at which it begins to decompose.

 The smaller the proportion of low molecular weight polyphosphates in the product, the higher the temperature at which decomposition of the product begins, the more effective its fire retardant effect.

A known method of producing ammonium polyphosphate, comprising mixing ammonium orthophosphate with urea in a molar ratio of 1: (1-1.2), thermal dehydration of the mixture at 270-300 ^o C for 0.5-2 hours in an atmosphere of gaseous ammonia in the presence of polyphosphate ammonia taken in an amount of 0.8-1.4 parts by weight for 1 weight.h. mixtures (SU, 710927, С 01 В 25/28, 01/25/80).

 The main disadvantage of this method is the introduction into the reaction zone of additional ammonia taken in excess of ≥5%, which leads to the formation of significant quantities of low molecular weight ammonium polyphosphates in the finished product.

A known method of producing condensed ammonium polyphosphates (NH ₄ PO ₃ ) _{n = 10 -10000} , including sequential heating with constant stirring of phosphorus oxide (V) and ammonium orthophosphate first at 50-150 ^o With in the presence of ammonia for 5-15 minutes at a pressure 1-2 mbar, stirring the reaction mixture for 10-60 minutes without ammonia at normal pressure in a nitrogen atmosphere and then with ammonia for 1-3 hours under a pressure of 1-5 mbar less than normal, followed by heating the reaction product to 200-400 ^o With keeping at this temperature only hours (EP, 0088265 A1, C 01 B 25/40, 09/14/89).

 The disadvantage of this method is the multi-stage and complexity due to the use of phosphorus oxide (V) and an additional amount of ammonia, ≤20% higher than stoichiometric, the introduction of nitrogen into the reaction zone.

A known method of producing highly condensed ammonium phosphate chain structure, including heating the mixture at a speed of up to 150 deg./min, containing urea and ammonium orthophosphate with their molar ratio (1-1.2): 1 at 270-300 ^o With a feed rate of the mixture 95 -195 kg / h with constant stirring in a rotary drum furnace (RU, 2118940 C1, C 01 B 25/38, 09/20/98).

The disadvantages of the method include:
insufficient heating rate for the fastest crystallization of low molecular weight phosphates from the melt; crystallization time exceeds in this case 40 minutes; the proportion of low molecular weight polyphosphates in the finished product is 34.7%, respectively, and the temperature of the beginning of its thermal decomposition does not exceed 165 ^o C; the maximum productivity of the finished product is 33 kg / h.

The closest is a method for producing condensed ammonium polyphosphates, including sequential heating in the presence of ammonium polyphosphate with stirring of an equimolar mixture of ammonium orthophosphate and urea to 108-118 ^o С in an atmosphere of gaseous ammonia with melting of the eutectic mixture of monoammonium phosphate - urea, up to 230-240 ^o С with crystallization the melt in the form of a porous mass and up to 280-300 ^o With holding for several hours to obtain highly condensed ammonium polyphosphates (Grishina I.A., Grishina E.F. et al. Development and the process of obtaining a new fire retardant "Fakkor". Proceedings of the NIUIF, vol. 238, M., 1981, pp. 143-155).

в связи с чем температура начала термического разложения продукта соответствует 141^oС, при 210^oС продукт теряет 0,4% массы.The disadvantage of this method is the content in the finished product of a significant amount of polyphosphates with

in connection with which the temperature of the onset of thermal decomposition of the product corresponds to 141 ^o With at 210 ^o With the product loses 0.4% of the mass.

 The technical task of the proposed method is to increase the temperature of the onset of thermal decomposition of highly condensed ammonium polyphosphate, reduce weight loss, i.e. increase its fire retardant efficiency.

The stated technical problem is achieved due to the fact that the method includes heating in the presence of ammonium polyphosphate with mixing of ammonium orthophosphate and urea in a molar ratio of 1: 1 in an atmosphere of gaseous ammonia with the formation of a refractory eutectic, then up to 230-240 ^o C with a heating rate of the eutectic melt 160 -200 degrees / min, with crystallization of the melt, and up to 280-300 ^o With at the same speed, with exposure for dehydration of the reaction product, maintaining in the reaction zone a vacuum of 0.52-1.29 kPa, subsequent cooling and grinding products kta.

The formation of highly condensed ammonium polyphosphate from orthophosphate and urea consists of several stages proceeding in the reaction zone:
- melting of low-temperature eutectic monoammonium phosphate - urea, accompanied by significant heat absorption;
- dehydration of monoammonium phosphate with the formation of low molecular weight ammonium polyphosphates (degree of polymerization P _n <10) and their crystallization from eutectic;
- dehydration of low molecular weight polyphosphates with the formation of highly condensed ammonium polyphosphates (P _n = 400-1050);
- hydrolysis of urea due to the water released during dehydration with the release of ammonia into the gas phase;
- the limiting stage in energy consumption and productivity is the stage of crystallization of low molecular weight polyphosphates from the melt of the eutectic monoammonium phosphate - urea.

в готовом продукте.If the heating rate is insufficient (below 160 deg./min), the crystallization stage extends over time, and the zone of the liquid-phase state of the material increases along the length of the rotating apparatus. During slow crystallization, a significant layer of the skull forms, heat transfer conditions worsen, the process of thermal dehydration slows down, a significant amount of polyphosphates forms with

in the finished product.

 The rate of heating of the eutectic is regulated not only by the required rate of the limiting stage of crystallization of low molecular weight polyphosphates, but also by their further dehydration with the formation of highly condensed ammonium polyphosphate. Exceeding the heating rate above 200 deg./min leads to local overheating of the crystallizing mass and sub melts with the formation of polyphosphoric acids.

 The dehydration rate of low molecular weight ammonium polyphosphates is also significantly affected by rarefaction in the reaction zone, which helps to remove gaseous reaction products. Removing excess amounts of water vapor and ammonia from the reaction zone shifts the equilibrium of the condensation reaction towards the formation of high polymer products. The increase in vacuum above 1.29 kPa leads to increased dust removal of the product from the apparatus and is technically impractical. A vacuum below 0.52 kPa does not provide for the removal of the required amounts of gases, i.e. Helps slow down the dehydration process.

 Example 1

A mixture of ammonium orthophosphate - diammonium phosphate is supplied to a rotating reactor with convective heating by flue gases in accordance with GOST 8515-75 "Technical Diammonium Phosphate", which is white crystals with a size of less than 1 mm, with a bulk density of 0.8-1 t / m ³ in quantity 650 kg and granular urea in accordance with GOST 2081-75, grade A, grade 1, with a granule size of less than 3 mm with a bulk density of 0.71 t / m ³ in an amount of 350 kg. The molar ratio of ammonium orthophosphate and urea is 1: 1.17. The mixture of reagents is fed into the reactor at a speed of 100 kg / h. Ammonium polyphosphate is also fed into the reactor in the form of a fine gray powder with a particle size of less than 0.25 mm with a bulk density of 0.67-1.03 t / m ³ in an amount of 500 kg at a rate of 50 kg / h.

In the reaction zone of the reactor, the reagents are continuously mixed and subsequently heated. At 80 ^o С, diammonium phosphate decomposes to monoammonium phosphate with the release of gaseous ammonia, at 110 ^o С a low-melting eutectic of monoammonium phosphate and urea is formed, the melting of which is accompanied by partial dehydration of monoammonium phosphate. The reactions proceed with heat absorption; the endothermic thermal effect of the stage is 70.328 J. Structural water released during the dehydration of monoammonium phosphate causes decomposition of urea. This produces 440 nm ³ / h of reaction gases containing 60 vol.% Ammonia. In the reaction zone, a vacuum is constantly maintained using a 1.29 kPa smoke exhauster to remove excess water and ammonia vapors from the reaction sphere (which shifts the equilibrium of the condensation reaction of ammonium polyphosphates towards the formation of high polymer ammonium polyphosphate).

При 280^oС в течение 2 часов происходит термическая дегидратация продуктов реакции и образование высококонденсированного полифосфата аммония (п. ф.а.), который выгружают из реактора, охлаждают в бункере естественным путем и подвергают размолу на электромагнитном измельчителе до размера частиц менее 0,25 мм.Subsequent heating of the low-temperature eutectic melt to 230 ^° C and 280 ^° C occurs in an atmosphere of gaseous ammonia at a speed of 200 degrees. / min with fast crystallization from the eutectic of condensed ammonium phosphates with a degree of polymerization

At 280 ^{° C.} , thermal dehydration of the reaction products and the formation of highly condensed ammonium polyphosphate (p.p.a.) occur during 2 hours, which is discharged from the reactor, naturally cooled in a hopper and milled on an electromagnetic grinder to a particle size of less than 0.25 mm

полифосфат аммония содержит, мас.%: Р₂O₅общ. 72,30; Р₂О₅

3,26; доля п.ф.а.

4,50.The resulting highly condensed

ammonium polyphosphate contains, wt.%: P ₂ O ₅ total. 72.30; P ₂ O ₅

3.26; share p.ph.

4.50.

The temperature of the onset of decomposition is 285 ^{° C.} , the mass loss upon heating to this temperature is 0.05%.

Thermally stable up to 324 ^o С (deep endo effect on the derivatogram). The loss of mass at 324 ^o With is 1.0%.

 The table shows the operational parameters of the proposed method according to examples 1-3, control comparative examples 4-6 and the characteristics of the obtained highly condensed ammonium polyphosphate.

As follows from their data presented in the table, by the proposed method receive highly condensed ammonium polyphosphate with a higher temperature of the onset of decomposition of the product (275-285 ^o C) compared with the known method (141 ^o C). In this case, the weight loss is 0.05-0.22% (in the known method of 0.4%). These characteristics provide an increase in flame retardant efficiency p.p.a., obtained by the proposed method.

Claims (1)

A method of producing highly condensed ammonium polyphosphate, including heating in the presence of ammonium polyphosphate with mixing ammonium orthophosphate and urea in a molar ratio of 1: 1 in an atmosphere of gaseous ammonia with the formation of a low melting eutectic, then up to 230-240 ^o With crystallization of the melt and up to 280-300 ^o With with exposure for dehydration of the reaction product, its subsequent cooling and grinding, characterized in that the heating of the low-melting eutectic melt to 230-240 ^° C and 280-300 ^° C is carried out at a speed of 160-200 degrees. / min, in the reaction zone support a vacuum of 0.52-1.29 KPa.

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