Method for preparing crystalline V-type ammonium polyphosphate with phosphoric acid

Abstract

The invention relates to a method for preparing crystalline V-type ammonium polyphosphate with phosphoric acid, comprising the following steps: dehydrating 85% phosphoric acid, adding melamine which functions as condensing agent to a reactor, continuously heating the reactor to 280-330 DEG C and the keeping the reactor at the 280-330 DEG C for 5-30 min, guiding dry ammonia gas to the reactor for ammonifying 15-60min by controlling the partial pressure of the dry ammonia gas at 0.02-0.04 MPa and the flow of the dry ammonia gas at 0.3-1.0 L / min, curing the product of reaction, crushing and discharging to obtain the product. The phosphoric acid and the melamine are used as the raw materials, and the molar ratio of the phosphoric acid to the melamine is 1:1 / 8-1 / 6. Detected by the X-ray diffraction, the product prepared by the method is the crystalline V-type ammonium polyphosphate. Compared with the method for preparing crystalline V-type ammonium polyphosphate with the ammonium phosphate, the method for preparing crystalline V-type ammonium polyphosphate with the phosphoric acid needs shorter time and lower reaction temperature, has stronger operability, uses the melamine as the condensing agent, produces the product of dry and white powder and ensures that the product has high yield and stable crystal form, are easy to crush and can be stored for a long time.

Description

【Technical field】 [0001] The invention relates to the technical field of ammonium phosphate, in particular to a method for preparing crystalline V-type ammonium polyphosphate by a phosphoric acid method. 【Background technique】 [0002] Crystalline APP has various crystal forms. Among the six known crystal forms, Type I and Type II APP have achieved large-scale industrial production; among the remaining crystal forms, Type III, Type VI and Type IV have no preparation methods, only crystalline Type V ammonium polyphosphate The preparation method has been reported. [0003] At present, the preparation methods of crystalline V-type ammonium polyphosphate mainly fall into two categories: using type I and type II APP as raw materials to realize crystal transformation under certain conditions and thermal condensation of ammonium phosphate. [0004] The literature (C.Y.Shen.et al.Journal of the American Chemical Society, 1969,91(1):62-67) pointed out that in the following temperat...

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Problems solved by technology

[0007] U.S. Patent No. 3,687,695 proposes to heat I-type, II-type APP and their mixture to 340-420°C, conduct heat treatment in a high ammonia-containing atmosphere, and then cool rapidly to obtain a new type of APP crystal form V, which transforms The condition is that the partial pressure of ammonia is at least 0.63MPa, and when the I-type structure is transformed into a V-type structure, it is cooled rapidly, and the cooling rate is higher than 50°C / min, especially at 250-350°C, the cooling rate is required to reach 75 ℃ / min, which can only be achieved by cooling with liquid nitrogen; this method needs to be quenched at high temperature, and the operating conditions are harsh, so it is not easy to realize

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