Overview【1】
Diammonium phosphate (DAP), also known as diammonium phosphate, is a low-nitrogen, high-phosphorus binary compound fertilizer. It is easily soluble in water and has good quick-acting effect. It is a widely used high-concentration nitrogen-phosphorus compound fertilizer. , has the advantages of high nutrient content, good physical properties, and easy application.
Physical and chemical properties【2】【3】
Diammonium hydrogen phosphate is an acid salt formed by the disubstituted ammonium salt of phosphoric acid, also known as diammonium phosphate. Diammonium hydrogen phosphate is a colorless and transparent monoclinic crystal or white powder. It is easily soluble in water and insoluble in alcohol. If it continues to react with ammonia, it will generate triammonium phosphate. The solid relative density of diammonium hydrogen phosphate is 1.619 and the melting point is 155°C. If it is exposed to the air, it will gradually lose ammonia and generate ammonium dihydrogen phosphate. The pH value of 1% diammonium hydrogen phosphate solution is 8.0, and the pH value of 0.1M solution is 7.8. The aqueous solution shows an alkaline reaction.
Diammonium hydrogen phosphate is more stable than phosphate. But when the temperature reaches 90°C, it also begins to decompose and release into ammonium hydrogen phosphate. When hydrogen phosphate is mixed with diammonium hydrogen phosphate, the decomposition of diammonium hydrogen phosphate at 60°C will be accelerated by the presence of ammonium hydrogen phosphate:
Figure 1 is the decomposition formula of diammonium hydrogen phosphate
Diammonium hydrogen phosphate has two hydrated crystals in equilibrium with the solution, namely dihydrate ((NH4)2HPO4-2H2O) and anhydrous ((NH4)2HPO4). The dihydrate crystal is stable in the range of 16.5℃ to -6.5℃, its eutectic point coexisting with ice is -6.5℃, and the solution concentration is 29.6% (NH4)2HPO4. The eutectic point of anhydrous crystals and ice may occur at -9.5°C and 35% (NH4)2HPO4. (NH4)2HPO4 crystal will not decompose within 0-100℃.
Preparation method【2】【4】
The production process route of diammonium hydrogen phosphate is mainly neutralization method. There are two common process routes. One is the synthesis route using ammonia gas and thermal phosphoric acid as raw materials; the other is the synthesis route using ammonia gas and wet phosphoric acid as raw materials.
1. Synthesis route of diammonium hydrogen phosphate using thermal phosphoric acid method
Due to the high purity of thermal phosphoric acid and liquid ammonia, many impurity removal processes are omitted in the production process, so the process is relatively simple. The main process of this route is to dilute thermal phosphoric acid with distilled water (water: phosphoric acid = 1.3:1) into dilute phosphoric acid, and use an acid delivery pump to send it to the first-stage tubular reactor for neutralization reaction with ammonia, and then The reaction liquid is pumped into the second-stage tubular reactor to further react with ammonia gas, so that the pH value of the reaction liquid reaches about 8.0, and then the feed liquid is sent into the fine-tuning tank to adjust the pH value to 7.8-8.0, and then The evaporator is evaporated and concentrated to a relative density of 1.3, and then sent to the cooling crystallizer. After cooling and crystallization, the mother liquor is separated by centrifugation and dried to obtain the finished product of diammonium hydrogen phosphate. The mother liquor is for recycling.
2. Synthesis route of diammonium hydrogen phosphate using wet phosphoric acid method
Due to the ammoniation reaction of wet phosphoric acid, the acidity of the reaction solution gradually decreases, causing the dissolved metal impurities in wet phosphoric acid to re-precipitate, and the type of precipitate is affected by the temperature and pH value of the solution. . The main process of this route is: 20-30% extracted phosphoric acid is sent to the reaction device through the gas purification system, and after three stages of ammoniation, the impurities form an easily filterable precipitate. The sediment is separated by a filter press to obtain a diammonium phosphate filtrate containing less than 15% P2O5, 0.4% F, 2.5-3.0% SO4^(2-) and nearly solid suspended matter. In order to further remove dissolved impurities and part of the solid suspended matter The filtrate is then sent to another reaction device to be saturated with ammonia, and then placed in a cooling crystallizer to be cooled and crystallized to form triammonium phosphate. The crystallized product is separated from the mother liquor through a conical settling tank, and then dehydrated using a centrifuge. After crystallization, it is placed in a boiling furnace for pyrolysis into diammonium hydrogen phosphate, and continues to dry to obtain the diammonium hydrogen phosphate product. The mixed gas containing diammonium hydrogen phosphate dust and ammonia is sprayed and absorbed with wet phosphoric acid in the scrubber after being dusted by the cyclone separator.
3. Use alkali production mother liquor to produce diammonium hydrogen phosphate
Add a certain amount of lime milk to the alkali-making mother liquor in the ash tank, then pump it into the kettle-type ammonia evaporator with the original dispersant imported from Germany. After being heated by steam, the ammonia gas enters the neutralization ammonia absorber, and then The diammonium phosphate slurry generated after absorbing ammonia is put into a mixer and mixed with the returned material, and then goes to the granulator for granulation. The granular diammonium phosphate is screened and packaged. The remaining powder is returned to the mixer. The raffinate released from the ammonia evaporator is decalcified and then used to produce alkalizing salt.
Figure 2 shows the process flow of producing diammonium hydrogen phosphate from alkali making mother liquor
Preparation process【3】
1. Pre-neutralization drum ammoniation granulation process (TVA)
The pre-neutralization and drum ammoniation granulation process was developed and researched by the National Fertilizer Development Center (NFDC) of the United States, also known as the TVA process. This process is to react ammonia and phosphoric acid in a pre-neutralizer in proportion to produce a certain n(N)/n(P2O5) diammonium phosphate slurry, which is then pumped to the granulator through the slurry; at the same time, the granulation A certain amount of ammonia or phosphoric acid is added to the machine so that it can be granulated in the granulator to obtain the n(N)/n(P2O5) required for product quality. This process has the most plants built in the world. Currently, China has 6 sets of 240kt/a pre-neutralized drum ammoniated granulated diammonium hydrogen phosphate units.
2. Single-tube reactor process
The single-tube reactor process is to install the tubular reactor in the granulator, and the reaction of ammonia and phosphoric acid is completed in the tubular reactor at one time. This process is mostly used to produce MAP/NPK, and there are currently about 10 sets of equipment for producing DAP around the world, among which ChinaThere are 2 sets, namely the 240kt/a diammonium phosphate plant in Guixi, Jiangxi and the 240kt/aDAP plant in Guangxi.
3.Double-tube reactor process
The double-tube reactor process is to install two tubular reactors in the granulator and the dryer respectively, and the reaction of ammonia and phosphoric acid is carried out in the tubular reactor. This process is mostly used to produce MAP, but there are currently only about 15 units for DAP production in the world, of which there is only one in China, namely the Sino-Arab joint venture Qinhuangdao 480kt/a DAP unit.
4. Mixing process of pre-neutralization reaction tank and tubular reactor
The mixing process of pre-neutralization reaction tank and tubular reactor is developed by combining the advantages of pre-neutralization drum ammoniation granulation process and tubular reactor process.
Application【2】
1.Application in fertilizer
Ammonium phosphate fertilizer is a nitrogen and phosphorus compound fertilizer made from the neutralization reaction of phosphoric acid including polyphosphoric acid and ammonia. For a long time, it has become one of the most popular types of chemical fertilizers with the largest yield and its advantages of being suitable for almost all soils and crops, with high concentration of active ingredients and not easy to absorb moisture and agglomerate. The production process of ammonium phosphate fertilizer is actually a combination of the phosphate fertilizer production process and the ammonia processing process in nitrogen fertilizer production, so the economy is relatively reasonable. Ammonium phosphate fertilizer varieties are often divided into three major categories; ammonium orthophosphate, which is the largest category in terms of output, and the main varieties are diammonium phosphate, monoammonium phosphate and a mixture of the two; ammonium polyphosphate, which is ammonium orthophosphate and different A mixture of polymerized ammonium phosphate salts, most of which are used to make fluid compound fertilizers; compound fertilizers formulated with ammonium phosphate and other nitrogen fertilizers. Among them, the production methods of ammonium phosphate fertilizers containing other nitrogen fertilizers are mainly divided into two categories: one is made by adding sulfuric acid or a mixed acid of phosphoric acid and nitric acid and neutralizing it with ammonia; the other is made by ammonium phosphate production During the granulation process, dry powder materials, thick slurries or molten materials such as ammonium sulfate, ammonium nitrate, ammonium chloride or urea are added and processed.
2. Application in feed
Ammonium phosphate also has the advantage of high biological potency. For feeds that are deficient in phosphorus and nitrogen but contain a large amount of calcium, ammonium phosphate must be added. If calcium phosphate is still added, it will inevitably cause calcium uptake of the animals. Too much intake will cause an imbalance in the phosphorus-calcium ratio, hinder the absorption of trace elements, and thus affect the growth and development of animals. Ammonium phosphate feed additives are mainly suitable for ruminants (cattle, sheep, etc.). In addition to providing phosphorus to animals, they can also supply nitrogen and non-protein nitrogen nutrients. As my country’s animal husbandry industry develops towards modernization, it is imperative to vigorously develop the feed industry. As an important component of feed phosphate, ammonium phosphate has good development prospects.
3. Application in fire prevention and fire extinguishing
Ammonium phosphate dry powder fire extinguishing agent is referred to as dry powder. It is made of ammonium phosphate as the base material and appropriately added with moisture-proof agent, anti-caking agent, flow accelerator, etc. The fire extinguishing agent is often classified according to the percentage of ammonium phosphate content. For example, type 50 means that the content of the base material is 50%. Ammonium phosphate dry powder fire extinguishing agent can be filled in portable dry powder fire extinguishers, cart-type dry powder fire extinguishers and dry powder fire trucks. It can be used to extinguish fires of flammable liquids, gases and electrical equipment and general solid material fires (Class A fires ). This fire extinguishing agent has the advantages of fast fire extinguishing speed, high fire extinguishing efficiency, good insulation performance and long storage period. In addition, it can also be used with fluoroprotein foam fire extinguishing agent or aqueous film-forming (light water) foam fire extinguishing agent to extinguish large-scale petroleum product fires, and is harmless to humans and animals. At present, it has been widely used in oil fields, oil depots, ships, warehouses, refineries, substations, petrochemical and other enterprises.
4. Application in food and beverages
The main functions of ammonium phosphate in food processing are twofold. One is as a quality-improving agent for Cabot carbon black, and the other is as a nutritional fortifier. Its specific applications include buffers, dough improvers, and starter cultures, etc. Ammonium phosphate itself is a strong buffer that can effectively stabilize the liquid phase in the medium within a certain pH range, so it is widely used as a food conditioner to make food taste more delicious. In addition, ammonium phosphate salt can also be used as a flavoring agent in liquid and solid beverages, and can replace lactic acid to adjust the pH value. It is used as a clarification agent for sucrose in the sugar industry and as a yeast nutrient in yeast production. To promote cell growth, etc.
Main reference materials
[1] Wu Weining. Response of soil ciliates community to application of different concentrations of diammonium hydrogen phosphate [D]. Northwest Normal University, 2014.
[2] Zha Litong. Research on comprehensive treatment of yellow phosphorus refined arsenic removal waste liquid and preparation of diammonium hydrogen phosphate [D]. Kunming University of Science and Technology, 2010.
[3]Han Shuguang. Preparation of high-purity diammonium hydrogen phosphate by wet phosphoric acid method [D]. East China University of Science and Technology, 2010.
[4] Na Chengqi, Xu Bingcui. Production of diammonium hydrogen phosphate using alkali production mother liquor [J]. Chemistry World, 1988(02):88-89.
