CN103601165A - Method for changing crystal morphology of ammonium dihydrogen phosphate by using additive - Google Patents

Abstract

A method for changing the crystal form of ammonium dihydrogen phosphate by using additives. The raw material ammonium dihydrogen phosphate has a purity of more than 95%. Ammonium dihydrogen phosphate: water is mixed in a ratio of 30-85:100 in parts by mass, and organic carboxylic acid or Carboxylate additive, stir evenly, heat the solution to 45-65°C to dissolve, and use the cooling crystallization method to cool down to 5-35°C; after washing, filtering, and drying, rod-shaped ammonium dihydrogen phosphate crystals are obtained. The rod-shaped ammonium dihydrogen phosphate crystal prepared by the method of the present invention has a quadrangular pyramid at both ends, the average radial particle size of the crystal is 0.6-1.2 mm, the axial particle size is 3-5 mm, the product purity is over 99.5%, and the crystal product has high strength and flowability. Good performance, easy to filter and dry, improve the application value of ammonium dihydrogen phosphate products.

Description

Method for changing the crystal form of ammonium dihydrogen phosphate by using additives

technical field

The invention belongs to the technical field of crystallization in the chemical engineering industry, and in particular relates to an additive and a method for changing the crystal form of ammonium dihydrogen phosphate.

Background technique

Ammonium dihydrogen phosphate, the English name is ammonium dihydrogen phosphate, also known as monoammonium phosphate, is a white crystal; the molecular formula is NH ₄ H ₂ PO ₄ , the relative molecular weight is 115.03, and it will decompose into ammonium metaphosphate (NH ₄ PO ₃ ), which can be made by reacting ammonia water and phosphoric acid. Ammonium dihydrogen phosphate is easily soluble in water, slightly soluble in ethanol, and insoluble in acetone. Ammonium dihydrogen phosphate is mainly used as a fertilizer and a fire retardant for wood, paper, and fabrics, as well as pharmaceuticals and ruminant feed additives.

The document Physica B-Condensed Matter404(2009)8-11:1611-1616 mentions that oxalic acid with a concentration of 1%-5% is added to a saturated aqueous solution of monoammonium phosphate (37.4g/100g water) at 20°C, and the state Evaporate slowly for 20 days under low temperature, and spontaneously grow to obtain crystals. The product is 3-5 monoammonium phosphate crystals with a particle size of about 3mm in a 250mL solution. This method is to grow crystals under the condition of standing in the laboratory, relying on the natural evaporation of water, the evaporation rate is greatly affected by the external environment, the evaporation rate is slow, the preparation cycle is too long, the crystal shape of the product is not perfect, the process yield is low, and it is not convenient for large-scale production. Scale application.

Patent CN101654235B proposes to dissolve agricultural monoammonium phosphate with pure water, add oxidant, decolorizer and biological flocculant, filter, heat to 70-80°C and concentrate for 180-240 minutes until microcrystals appear, and then cool down to After drying at 25°C, monoammonium phosphate crystals are obtained, and the particle size is only about 0.2mm. The raw material quality of this process is relatively poor, the operation steps are loaded down with trivial details and the time is long, and the product is finely broken.

Chinese patent 200910263800.1 uses phosphoric acid and ammonia water for neutralization reaction and then naturally cools to room temperature to obtain crystals. The purity requirements for raw phosphoric acid are relatively high, and the preparation process equipment is complicated, involving neutralization reactors, tubular reactors, neutralization tanks, and spraying. Granulator. Chinese patent 200910102880.2 utilizes wet-process phosphoric acid neutralization reaction, concentrates the monoammonium phosphate slurry by secondary heating, granulates, dries, crushes and sieves into granular monoammonium phosphate products. The yield of this method is low, and the product is an agglomerate of crystals with poor gloss and easy to contain impurities. The purity is only about 98%, and it is only used as an agricultural chemical fertilizer. The production process consumes a lot of energy and the equipment is complicated. Patent CN101538027A uses a single-tube one-step neutralization-drum granulation process to produce granular monoammonium phosphate, which requires more equipment and high temperature and high pressure energy consumption. Patent CN1174812A selects wet-process phosphoric acid as a raw material, and sprays and dries to obtain monoammonium phosphate particles. Due to incomplete evaporation during the spraying process, the water content of the particles is as high as 3%.

Currently commercially available ammonium dihydrogen phosphate crystallization products are irregular in shape, as shown in Figure 1. The main particle size is 0.2-0.4 mm, the crystal is finely divided, the surface is rough, and the crystal plane is incomplete, which affects the purity, bulk density, fluidity, etc. of the product. performance. When ammonium dihydrogen phosphate is used as a fertilizer, due to the small particle size and low bulk density of the powdered product, it is easy to be blown away with the wind after being sprinkled into the field, which reduces the fertilizer effectiveness. In order to improve its particle size and specific gravity and be suitable for agricultural use, granulation technology is generally used to process it into spherical agglomerated particles with a larger specific gravity, but the granulation itself does not change the crystal form of ammonium dihydrogen phosphate and does not improve product purity. When ammonium dihydrogen phosphate is used as a fire retardant for wood and fabrics and in the pharmaceutical industry, its crystal form, including crystal appearance, particle size, fluidity, purity, etc., is generally required to play a better role.

Contents of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a method for using additives to change the crystal form of ammonium dihydrogen phosphate, further reducing the cost of preparation and difficulty in operation, and adopting additives to obtain the rod-shaped crystal form of ammonium dihydrogen phosphate, the crystal size is large , Regular shape, smooth surface, complete crystal surface, easy to filter, product purity over 99.5%.

The present invention uses additives to change the crystal form of ammonium dihydrogen phosphate. The raw material ammonium dihydrogen phosphate has a purity of more than 95%. Mix ammonium dihydrogen phosphate: water at a ratio of 30-85:100 in parts by mass, and add organic carboxylic acid or Carboxylate additive, stir evenly, heat the solution to 45-65°C to dissolve, use the cooling crystallization method, cool down to 5-35°C; wash, filter, and dry to obtain rod-shaped ammonium dihydrogen phosphate crystals.

The organic carboxylic acid additive is selected from organic dicarboxylic acids, organic tricarboxylic acids or organic tetracarboxylic acids.

The organic dicarboxylic acid is selected from succinic acid or malonic acid, the organic tricarboxylic acid is selected from citric acid or nitrilotriacetic acid, and the organic tetracarboxylic acid is selected from ethylenediamine One of tetraacetic acid or pyromellitic acid.

The carboxylate additive is selected from sodium carboxylate or potassium carboxylate.

The sodium carboxylic acid salt is selected from disodium edetate, sodium citrate or disodium malonate, and the potassium carboxylic acid salt is selected from potassium pyromellitic acid, potassium nitrilotriacetate or citric acid One of the potassium.

The addition amount of the organic carboxylic acid or carboxylate additive is 500-10000ppm.

The cooling rate is 2-20°C/h.

Adding a small amount of organic carboxylic acid or carboxylate additive in the cooling crystallization process of ammonium dihydrogen phosphate changes the physical and chemical environment of its crystal growth, especially the surface charge distribution of the crystal and the solid-liquid interfacial tension, thus affecting the interaction of different crystal planes. The growth rate reduces the overall growth rate of the crystal. The tetrahedral PO ₄ in the crystal is connected to the NHO bond and the NH ₄ group, and the excess hydrogen bond distorts the lattice of the NH ₄ ion, thereby controlling the crystal morphology. The method mainly controls the growth rate of the (101) crystal plane and the (100) crystal plane, promotes the lateral growth of the crystal, inhibits the vertical growth, and obtains a thick rod-shaped ammonium dihydrogen phosphate crystal.

The invention provides a method for changing the crystal form of ammonium dihydrogen phosphate through additives. The crystal form is rod-shaped, and the two ends of the crystal are pyramid-shaped. The average radial grain size of the crystal is 0.6-1.2mm, and the axial grain size is 3-5mm. The surface is smooth and clean, the crystal plane is complete, the product purity reaches more than 99.5%, and the single mass yield of the process is 36% to 69%. The obtained ammonium dihydrogen phosphate has large crystal particles, is easy to filter and dry, reduces the entrainment and residue of mother liquor, has high crystal purity, good gloss, good fluidity, high crystal strength, and is convenient for packaging and transportation, improving the product quality of ammonium dihydrogen phosphate. application value.

Description of drawings

Figure 1: Commercially available ammonium dihydrogen phosphate crystal magnified 40 times electron microscope photo;

Fig. 2: Example 1 ammonium dihydrogen phosphate crystal magnified 30 times electron micrograph;

Figure 3: 30 times magnified electron micrograph of the ammonium dihydrogen phosphate crystal in Example 2.

Detailed ways

The following examples describe the present invention in detail:

Example 1:

Take 30g of ammonium dihydrogen phosphate with a purity of 98%, 100g of deionized water, add 500ppm ethylenediaminetetraacetic acid, and stir evenly. The solution was heated to 45°C to dissolve, and the cooling crystallization method was adopted at a cooling rate of 2°C/h, and the temperature was lowered to 5°C. After washing, filtering and drying, rod-shaped ammonium dihydrogen phosphate crystals were obtained. The process quality yield is 35.8%, the product purity reaches 99.9%, the average radial particle size of the crystal is 0.84mm, and the axial particle size is 4.15mm. The electron microscope photo of the product is shown in Figure 2.

Example 2:

Take 70g of ammonium dihydrogen phosphate with a purity of 97.2%, 100g of deionized water, add 10000ppm nitrilotriacetic acid, stir evenly, continue to heat the solution to 60°C, and adopt the cooling crystallization method with a cooling rate of 6°C/h to 20°C. After washing, filtering and drying, rod-shaped ammonium dihydrogen phosphate crystals were obtained. The process quality yield is 62.42%, the product purity reaches 99.7%, the average radial particle size of the crystal is 1.00mm, and the axial particle size is 3.18mm. The electron microscope photo of the product is shown in Figure 3.

Example 3:

Take 60g of ammonium dihydrogen phosphate with a purity of 96%, 100g of deionized water, add 2000ppm succinic acid, and stir evenly. The solution was heated to 58°C to dissolve, and the cooling crystallization method was adopted at a cooling rate of 12°C/h, and the temperature was lowered to 10°C. After washing, filtering and drying, rod-shaped ammonium dihydrogen phosphate crystals were obtained. The process quality yield is 69.13%, the product purity reaches 99.6%, the average radial particle size of the crystal is 0.64mm, and the axial particle size is 4.03mm.

Example 4:

Take 70g of ammonium dihydrogen phosphate with a purity of 95.5%, 100g of deionized water, add 5000ppm potassium pyromellitic acid, stir well, continue to heat the solution to 65°C, adopt cooling crystallization method, the cooling rate is 20°C/h, and cool down to 30°C ℃. After washing, filtering and drying, rod-shaped ammonium dihydrogen phosphate crystals were obtained. The process quality yield is 55.72%, the product purity is 99.5%, the average radial particle size of the crystal is 1.16mm, and the axial particle size is 4.85mm.

Example 5:

Take 85g of ammonium dihydrogen phosphate with a purity of 95%, 100g of deionized water, add 8000ppm sodium citrate, stir evenly, continue to heat the solution to 65°C, and use the cooling crystallization method with a cooling rate of 10°C/h to 35°C. After washing, filtering and drying, rod-shaped ammonium dihydrogen phosphate crystals were obtained. The process quality yield is 60.78%, the product purity reaches 99.6%, the average radial particle size of the crystal is 1.00mm, and the axial particle size is 3.44mm.

The preparation method disclosed and proposed in the present invention to change the crystal form of ammonium dihydrogen phosphate by using additives can be realized by those skilled in the art by referring to the contents of this article and appropriately changing raw materials, process parameters and other links. The methods and products of the present invention have been described through preferred implementation examples, and those skilled in the art can obviously make changes or appropriate changes and combinations to the methods and products described herein without departing from the content, spirit and scope of the present invention to realize The technology of the present invention. In particular, it should be pointed out that all similar substitutions and modifications will be obvious to those skilled in the art, and they are all considered to be included in the spirit, scope and content of the present invention.

Claims (8)

1. A method for changing the crystal form of ammonium dihydrogen phosphate by using additives, which is characterized in that: the purity of the raw material ammonium dihydrogen phosphate is more than 95%, and ammonium dihydrogen phosphate: water is mixed in a ratio of 30 to 85:100 in parts by mass , add organic carboxylic acid or carboxylate additive, stir evenly, heat the solution to 45-65°C to dissolve, adopt cooling crystallization method, cool down to 5-35°C; after washing, filtering and drying, dihydrogen phosphate in rod form is obtained ammonium crystals. 2. The preparation method according to claim 1, characterized in that, the organic carboxylic acid additive is selected from organic dicarboxylic acids, organic tricarboxylic acids or organic tetracarboxylic acids. 3. preparation method as claimed in claim 2 is characterized in that, described organic dicarboxylic acid is selected from the one in succinic acid or malonic acid, and organic tricarboxylic acid is selected from citric acid or ammonia tricarboxylic acid One of acetic acid, one of organic tetracarboxylic acid selected from ethylenediaminetetraacetic acid or pyromellitic acid. 4. preparation method as claimed in claim 1 is characterized in that, described carboxylate additive is selected from carboxylate sodium salt or carboxylate potassium salt. 5. preparation method as claimed in claim 4 is characterized in that, described carboxylic acid sodium salt is selected from the one in disodium edetate, sodium citrate or disodium malonate, potassium carboxylate The salt is selected from potassium pyromellitic acid, potassium nitrilotriacetate or potassium citrate. 6. The preparation method according to claim 1, characterized in that, the addition amount of the organic carboxylic acid or carboxylate additive is 500-10000ppm. 7. The preparation method according to claim 1, characterized in that, the cooling rate is 2-20°C/h. 8. The preparation method as claimed in claim 1, characterized in that, the rod-shaped ammonium dihydrogen phosphate crystal obtained has two ends in the shape of a quadrangular pyramid, the average radial grain size of the crystal is 0.6-1.2 mm, and the axial grain size is 0.6 mm. 3~5mm.

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