阅读说明：本技术 一种利用工业湿法净化磷酸制造食品级磷酸二氢钠的方法 (Method for preparing food-grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid ) 是由 吴正奇 许琦 徐歆 李摇摇 姚其凤 吴龙 李倩 陈小强 于 2018-08-09 设计创作，主要内容包括：本发明公开了一种利用工业湿法净化磷酸制造食品级磷酸二氢钠的方法：⑴加水稀释：取工业湿法净化磷酸于耐酸容器中加纯水搅拌稀释；⑵中和反应与脱氟硫：加入脱氟硫剂和氢氧化钠搅拌反应,膜过滤得精密过滤的中和液；⑶氧化脱砷、微碱性脱重金属与膜过滤：调节中和液的pH至微碱性、加入氧化剂、加热、冷却、膜过滤,得精密过滤的微碱性脱重金属和氧化脱砷液；⑷pH调节与浓缩：用磷酸调整pH值并浓缩,得磷酸二氢钠浓缩液；⑸降温结晶：浓缩液转入结晶设备内,搅拌、冷却、结晶、固液分离,得磷酸二氢钠湿结晶；⑹结晶干燥：湿结晶干燥至产品要求水分,得食品级磷酸二氢钠产品。方法易行,成本低,纯度高,砷和重金属离子脱除充分,溶解性能好。(A process for preparing food-class sodium dihydrogen phosphate from industrial wet-purified phosphoric acid includes such steps as diluting ⑴ with water, adding pure water to acid-proof container, stirring, diluting, neutralizing ⑵, adding defluorinating agent and sodium hydroxide, stirring, membrane filtering to obtain the neutralized liquid, oxidizing ⑶ to remove arsenic, slightly alkaline, removing heavy metal and membrane filtering, regulating pH value to slightly alkaline, adding oxidant, heating, cooling, membrane filtering to obtain concentrated liquid, regulating ⑷ pH value, concentrating, regulating pH value with phosphoric acid to obtain concentrated sodium dihydrogen phosphate, cooling ⑸, cooling, crystallizing, cooling, solid-liquid separation to obtain wet sodium dihydrogen phosphate crystal, drying ⑹, drying wet crystal, and drying.)

1. A method for preparing food-grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid is characterized by comprising the following steps:

⑴ adding water to dilute the phosphoric acid, placing the phosphoric acid into an acid-proof container, adding water with the mass multiple of 0.5-3.1 times of the phosphoric acid under the condition of stirring to obtain a dilute phosphoric acid solution with the mass percentage concentration of 20.7-56.7%, and continuously stirring to obtain a dilute phosphoric acid solution for industrial wet purification;

⑵ neutralization reaction and defluorination and desulfurization, namely, putting phosphoric acid diluent ⑴ into an acid-resistant container, adding defluorination and desulfurization agent with the mass fraction of 0.1-1% of the phosphoric acid diluent under the condition of stirring, continuously stirring to ensure that the defluorination and desulfurization agent are fully dissolved and fully reacted with fluoride ions and sulfate radicals in the phosphoric acid diluent purified by the industrial wet method to obtain a reaction mixture, neutralizing the reaction mixture by using sodium hydroxide solution with the mass percentage concentration of 20-50% under the condition of stirring until the pH value is 3.8-4.8, and continuously stirring to obtain a neutralization solution, controlling the temperature of the neutralization solution to be 20-60 ℃, and precisely filtering the neutralization solution by using membrane filtration equipment to obtain the precisely filtered neutralization solution for later use;

⑶, oxidizing to remove arsenic, slightly alkaline to remove heavy metal and membrane filtering, under the condition of continuous stirring, adjusting the pH of the neutralized liquid obtained by precise filtering with ⑵ to 7.0-8.0 by using a sodium hydroxide solution with the mass percentage concentration of 20-50%, adding an oxidant with the mass fraction of 0.1-4% of the neutralized liquid, heating the mixture and maintaining the temperature to the temperature required by arsenic oxidation, refluxing, preserving heat and oxidizing for 0.5-8 hours under the condition of stirring, then opening cooling water to reduce the temperature of the mixture to 20-60 ℃, continuously stirring for 0.5-10 hours, and precisely filtering the mixture by using membrane filtering equipment to obtain the slightly alkaline to remove heavy metal and the oxidized arsenic-removing liquid for later use;

⑷, adjusting and concentrating the pH of the ⑶ obtained alkalescent heavy metal removal and arsenic removal liquid to 3.7-4.6 by phosphoric acid under the condition of continuous stirring to obtain sodium dihydrogen phosphate solution, and concentrating the sodium dihydrogen phosphate solution to 45-65% by mass percent by a forced circulation vacuum concentration method under the conditions of a vacuum degree of 0.8-0.99 MPa and a temperature of 70-110 ℃ to obtain sodium dihydrogen phosphate concentrated solution for later use;

⑸ cooling crystallization, transferring the ⑷ sodium dihydrogen phosphate concentrated solution into crystallization equipment, after crystallizing sodium dihydrogen phosphate within the temperature range of a sodium dihydrogen phosphate crystallization metastable zone for 1-25 hours, cooling the temperature to-5-10 ℃ at a cooling speed of 1-10 ℃/hour, continuing crystallization for 1-50 hours until no crystallization is generated, performing solid-liquid separation on the crystallization mixture to obtain wet sodium dihydrogen phosphate crystals and a crystallization mother solution of sodium dihydrogen phosphate, and performing concentration-crystallization or concentration-spray drying on the crystallization mother solution of sodium dihydrogen phosphate to obtain agricultural grade sodium dihydrogen phosphate which is used as agricultural sodium phosphate fertilizer, and taking wet sodium dihydrogen phosphate crystals for standby;

⑹ drying the crystal, drying the ⑸ wet crystal of sodium dihydrogen phosphate with hot air under normal pressure until the product requires moisture, cooling and packaging to obtain food grade sodium dihydrogen phosphate product, wherein the temperature of the material in the whole process is controlled to be less than or equal to 120 ℃.

2. The method for preparing food grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid according to claim 1, wherein the industrial wet-process purified phosphoric acid obtained in step ⑴ is defluorinated, desulfurized, extracted, re-extracted and purified wet-process phosphoric acid with a mass percentage concentration of 85%, and the mass of the wet-process purified phosphoric acid is superior, first-class and qualified products according to HG/T4069-2008 "industrial wet-process purified phosphoric acid", and the water has an electrical conductivity of less than 10^-3s/m reverse osmosis process pure water, ion exchange process pure water, and distillation condensation process pure water.

3. The method of claim 1, wherein the defluorinating agent used in step ⑵ is analytically or chemically pure barium carbonate or barium bicarbonate, the sodium hydroxide is analytically or chemically pure solid sodium hydroxide, and the membrane filtration device comprises a silicon carbide membrane module in the form of a honeycomb briquette type inner tube membrane with a pore size of 1, 0.5, 0.1 or 0.04 μm.

4. The method for preparing food-grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid according to claim 1, wherein the sodium hydroxide in step ⑶ is analytically or chemically pure solid sodium hydroxide, the oxidants are analytically or chemically pure hydrogen peroxide (hydrogen peroxide) and bleaching powder, the temperature required by arsenic oxidation is 50-100 ℃, and the membrane material of the membrane filtration equipment is silicon carbide, the membrane component is a honeycomb coal type inner tubular membrane, and the size of the membrane pores is 1, 0.5, 0.1 or 0.04 μm.

5. The method as claimed in claim 1, wherein the phosphoric acid obtained in step ⑷ has a purity of analytically pure, chemically pure and food grade, and a concentration of 75% by mass and 85% by mass.

6. The method for producing food grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid according to claim 1, wherein the temperature range of the metastable zone of sodium dihydrogen phosphate crystals in the step ⑸ is 5-35 ℃.

7. The method for producing food grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid as claimed in claim 1, wherein the required water content in step ⑹ is less than or equal to 2% by weight.

Technical Field

The invention relates to the technical field of food additive processing, in particular to a method for preparing food-grade sodium dihydrogen phosphate by industrial wet-process purified phosphoric acid.

Background

Sodium dihydrogen phosphate is an important chemical raw material and is widely applied to industrial departments such as biological fermentation, food, medicine, feed, chemical industry, agriculture and the like. The production method of sodium dihydrogen phosphate mainly includes a neutralization method, an extraction method, an ion exchange method, a double decomposition method, a direct method, a crystallization method, an electrolytic method, and the like, and the main production method is the neutralization method. Phosphoric acid can be classified into wet-process phosphoric acid obtained by acidifying phosphate ore as a raw material and hot-wet-process phosphoric acid obtained by burning pure phosphorus as a raw material according to the source of the phosphoric acid used, and thus sodium dihydrogen phosphate can be classified into hot-process sodium dihydrogen phosphate and wet-process sodium dihydrogen phosphate, wherein the hot-process sodium dihydrogen phosphate has high purity but high cost; according to the purity, the sodium dihydrogen phosphate can be divided into industrial grade, agricultural grade and food grade, wherein the quality standard of the food grade sodium dihydrogen phosphate is highest. Food grade sodium dihydrogen phosphate is typically produced from hot process phosphoric acid via a neutralization process.

The method has the advantages that the method has abundant phosphate ore resources in China, industrial-grade wet-process phosphoric acid and phosphate represented by sodium dihydrogen phosphate are prepared by using the phosphate ore as a raw material, the technology is mature, the cost is low, the product quality is stable, but the impurity content is high, the purity is low, and the requirement of food grade cannot be met. In contrast, the production of phosphoric acid by a thermal process and phosphates represented by sodium dihydrogen phosphate from phosphorus has a high cost, although the technology is mature, the product quality is stable, the purity is high, the impurity content is low, and the requirement of food grade can be met. Therefore, how to utilize abundant phosphate rock resources in China to prepare food-grade phosphoric acid and phosphate represented by sodium dihydrogen phosphate through wet-process phosphoric acid is economically important and urgent in demand.

The core problem to be solved for preparing the food-grade sodium dihydrogen phosphate is prepared from wet-process phosphoric acid (comprising a diluted phosphoric acid semi-finished product with the mass percentage concentration of 20-50% and industrial wet-process purified phosphoric acid with the mass percentage concentrations of 75% and 85%), and comprises the following steps: a. how to separate a small amount of toxic elements such as lead, cadmium, mercury and arsenic in industrial wet-process phosphoric acid to ensure that the product meets the necessary sanitary and safety requirements of food additives; b. how to separate fluorine, iron, calcium and other conventional elements in the industrial wet-process phosphoric acid to ensure that the product reaches the corresponding quality limit index; c. how to separate solid particles, pigment particles and the like in industrial wet-process phosphoric acid to ensure that each index of a product reaches corresponding quality requirements. A large number of researchers at home and abroad research the process technology for preparing food-grade phosphoric acid by refining and purifying wet-process phosphoric acid and preparing food-grade phosphate represented by sodium dihydrogen phosphate by taking the wet-process phosphoric acid as a raw material, and a batch of new processes, new technologies and new achievements are brought forward. For example, Hubei Sanning chemical company develops a new technology which is mainly characterized by extracting wet phosphoric acid from melamine, back-extracting and sodium chloride sodium treatment to obtain food-grade sodium dihydrogen phosphate, and is industrialized. Chinese patent CN201210473441.4 discloses a preparation method of sodium dihydrogen phosphate dodecahydrate; chinese patent CN201510606518.4 discloses a method for preparing sodium dihydrogen phosphate by separating impurities through ammoniation by using wet-process phosphoric acid; chinese patent CN200910102800.3 discloses a method for preparing food-grade sodium dihydrogen phosphate by directly neutralizing and concentrating dilute phosphoric acid; chinese patent CN200910028905.9 discloses a method for co-producing high-purity formic acid and sodium dihydrogen phosphate by the reaction of calcium formate and superphosphoric acid; chinese patent CN86101186.4 discloses a method for preparing sodium dihydrogen phosphate by an "association-displacement" method; US7601319 discloses a process for the production of sodium dihydrogen phosphate.

How to remove toxic and harmful components in industrial wet-process purified phosphoric acid and improve the purity of sodium dihydrogen phosphate with high efficiency and low cost to meet the requirement of food additives on sanitation and safety is a core technical problem of preparing food-grade sodium dihydrogen phosphate by industrial wet-process purified phosphoric acid and is also a fundamental development direction for improving economic benefits in the wet-process phosphoric acid industry.

Disclosure of Invention

Aiming at the defects that the sodium dihydrogen phosphate prepared by industrial wet-process purified phosphoric acid cannot meet the food-grade requirement and the prior art has, the invention aims to provide the preparation method of the food-grade sodium dihydrogen phosphate, which has the advantages of low cost, high purity, sufficient removal of arsenic and heavy metal ions, high sanitary safety, simple and convenient process, high raw material utilization rate, good dissolving performance and mechanized production.

The technical concept of the invention is as follows: the method comprises the steps of utilizing the salting-out effect that sulfate ions and fluoride ions in industrial wet-process purified phosphoric acid are easier to generate barium fluosilicate and barium sulfate precipitates and sodium dihydrogen phosphate under the weak acid condition and simultaneously carrying out defluorination and desulfurization, arsenite can be oxidized into insoluble arsenate, heavy metal ions generate insoluble precipitates under the neutral alkali condition, phosphoric acid is neutralized into sodium dihydrogen phosphate and sodium dihydrogen phosphate with high solubility, the solubility of the sodium dihydrogen phosphate and the sodium dihydrogen phosphate is obviously changed along with the temperature, adding water to the industrial wet-process purified phosphoric acid for dilution, adding a defluorination and debaterization agent and membrane filtration after neutralization and simultaneously carrying out defluorination and desulfurization on filtrate, oxidizing dearsenization and precipitation of the heavy metal ions by using an oxidant under the weak alkaline condition, and obtaining the food-grade sodium dihydrogen phosphate through pH adjustment, concentration, crystallization and drying.

In order to achieve the purpose, the invention adopts the following technical measures:

a method for preparing food-grade sodium dihydrogen phosphate by using industrial wet-process purified phosphoric acid comprises the following steps:

⑴ adding water to dilute the phosphoric acid, placing the phosphoric acid into an acid-proof container, adding water with the mass multiple of 0.5-3.1 times of the phosphoric acid under the condition of stirring to obtain a dilute phosphoric acid solution with the mass percentage concentration of 20.7-56.7%, and continuously stirring to obtain the diluted phosphoric acid solution for industrial wet purification.

The industrial wet-process phosphoric acid purification comprises defluorination and desulfurizationAnd wet-process phosphoric acid which is subjected to extraction-back extraction purification treatment and has a mass percentage concentration of 85 percent, wherein the mass of the wet-process phosphoric acid is superior, first-class and qualified products which meet the requirements of HG/T4069 + 2008 industrial wet-process purified phosphoric acid; the water refers to the conductivity of less than 10^-3s/m reverse osmosis process pure water, ion exchange process pure water, and distillation condensation process pure water.

Preferably, the industrial wet-process purified phosphoric acid is subjected to defluorination, desulfurization and extraction-back extraction purification treatment, and has a mass percentage concentration of 85%, and the mass of the industrial wet-process purified phosphoric acid is a first-class product and a qualified product which meet the requirements of HG/T4069-2008 industrial wet-process purified phosphoric acid; the water refers to the conductivity of less than 10^-3s/m reverse osmosis pure water.

⑵ neutralization reaction and defluorination and desulfurization, namely, putting phosphoric acid diluent ⑴ into an acid-resistant container, adding defluorination and desulfurization agent with the mass fraction of 0.1-1% of the phosphoric acid diluent under the condition of stirring, continuously stirring to ensure that the defluorination and desulfurization agent are fully dissolved and fully reacted with fluoride ions and sulfate radicals in the phosphoric acid diluent purified by the industrial wet method to obtain a reaction mixture, neutralizing the reaction mixture by using sodium hydroxide solution with the mass percentage concentration of 20-50% under the condition of stirring until the pH value is 3.8-4.8, continuously stirring to obtain a neutralization solution, controlling the temperature of the neutralization solution to be 20-60 ℃, and precisely filtering the neutralization solution by using membrane filtration equipment to obtain the precisely filtered neutralization solution for later use.

The defluorination and desulfurization agent is analytically pure or chemically pure barium carbonate and barium bicarbonate; the sodium hydroxide is analytically pure or chemically pure solid sodium hydroxide; the membrane filtration equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 1, 0.5, 0.1 and 0.04 mu m.

Preferably, the defluorination and desulfurization agent is analytically pure barium carbonate and barium bicarbonate; the sodium hydroxide is analytically pure solid sodium hydroxide; the membrane filtering equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 0.1 and 0.04 mu m.

⑶ oxidizing and dearsenifying, slightly alkaline heavy metal removing and membrane filtering, under the condition of continuously stirring, adjusting the pH value of the neutralized liquid obtained by the precise filtering with 20-50% by mass of sodium hydroxide solution, adjusting the pH value of the neutralized liquid obtained by ⑵ to 7.0-8.0, adding oxidant with the mass fraction of 0.1-4% of the neutralized liquid, heating the mixture to the temperature required by arsenic oxidation and maintaining the temperature, refluxing, preserving heat and oxidizing for 0.5-8 hours under the condition of stirring, then opening cooling water to reduce the temperature of the mixture to 20-60 ℃, continuously stirring for 0.5-10 hours, and precisely filtering the mixture by membrane filtering equipment to obtain the slightly alkaline heavy metal removing and the oxidized dearsenifying liquid for later use.

The sodium hydroxide is analytically pure or chemically pure solid sodium hydroxide; the oxidant is analytically pure or chemically pure hydrogen peroxide (hydrogen peroxide) and bleaching powder; the temperature required by the arsenic oxidation is 50-100 ℃; the membrane filtration equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 1, 0.5, 0.1 and 0.04 mu m.

Preferably, the sodium hydroxide is analytically pure solid sodium hydroxide; the oxidant is analytically pure or chemically pure hydrogen peroxide (hydrogen peroxide); the temperature required by the arsenic oxidation is 70-95 ℃; the membrane filtering equipment has the membrane material of silicon carbide, the membrane component is a honeycomb briquette type inner tubular membrane, and the sizes of membrane pores are 0.1 and 0.04 mu m.

⑷ adjusting and concentrating the pH of the ⑶ obtained alkalescent heavy metal and arsenic removal liquid to 3.7-4.6 with phosphoric acid under the condition of continuous stirring to obtain sodium dihydrogen phosphate solution, and concentrating the sodium dihydrogen phosphate solution to 45-65% by mass percentage concentration by a forced circulation vacuum concentration method under the conditions of a vacuum degree of 0.8-0.99 MPa and a temperature of 70-110 ℃ to obtain sodium dihydrogen phosphate concentrated solution for later use.

The purity of the phosphoric acid is analytically pure, chemically pure and food grade, and the mass percentage concentration of the phosphoric acid is 75% and 85%.

Preferably, the phosphoric acid is food-grade phosphoric acid with a mass percentage concentration of 85%.

⑸ cooling crystallization, transferring the concentrated solution of sodium dihydrogen phosphate ⑷ into crystallization equipment, crystallizing sodium dihydrogen phosphate within the temperature range of a metastable zone of the sodium dihydrogen phosphate crystallization for 1-25 hours, cooling to-5-10 ℃ at a cooling rate of 1-10 ℃/hour, continuously crystallizing for 1-50 hours until no crystal is generated, performing solid-liquid separation on the crystallized mixture to obtain wet crystals of sodium dihydrogen phosphate and a crystallization mother liquor of sodium dihydrogen phosphate (the crystallization mother liquor of sodium dihydrogen phosphate is concentrated-crystallized or concentrated-spray dried to obtain agricultural grade sodium dihydrogen phosphate which is used as agricultural sodium phosphate fertilizer), and taking wet crystals of sodium dihydrogen phosphate for standby.

The temperature range of the sodium dihydrogen phosphate crystal metastable zone is 5-35 ℃.

Preferably, the temperature range of the sodium dihydrogen phosphate crystal metastable zone is 5-20 ℃.

⑹ drying the crystals, drying the ⑸ wet crystals of sodium dihydrogen phosphate by hot air at normal pressure until the moisture content of the product is required, cooling and packaging to obtain the food grade sodium dihydrogen phosphate product, and controlling the temperature of the materials in the whole process of the step to be less than or equal to 120 ℃.

The required moisture content is less than or equal to 2 percent by mass.

Preferably, the water requirement is less than 2% in percentage by mass.

Compared with the prior art, the method has the advantages and beneficial effects that:

1. the method mainly solves the separation of tiny solid particles (including pigments) in industrial wet-process purified phosphoric acid by filtering through a silicon carbide film with strong acid resistance, realizes the precipitation and precipitation of main impurities with high contents of fluorine, sulfur and the like in wet-process diluted phosphoric acid by neutralizing to subacidity, solves the technical problems and difficulties of removing toxic and harmful arsenic, lead, cadmium and other heavy metals in the wet-process diluted phosphoric acid by oxidizing dearsenification, alkalescence deaddition and film filtering, and mainly achieves the technical effects of separating impurities, removing toxic and harmful substances and improving the purity of sodium dihydrogen phosphate so that the product meets the food-grade quality requirement. Compared with the prior art, the invention is characterized in that the prior art can only utilize industrial wet-process purified phosphoric acid to prepare the industrial grade sodium dihydrogen phosphate, and the invention realizes the technical breakthrough of directly preparing the food grade sodium dihydrogen phosphate by utilizing the industrial wet-process purified phosphoric acid.

2. Through the technical treatment of the invention, the removal rate of insoluble impurities in industrial wet-process purified phosphoric acid is 100 percent, the removal rate of pigments is more than 95 percent, and the appearance is clear and transparent; the removal rate of main impurities such as fluorine ions, sulfur ions (sulfate ions) and the like is more than 99 percent; the removal rate of toxic and harmful substances such as arsenic, lead, cadmium and the like is more than 99.99 percent; the phosphoric acid retention rate is more than 99.5 percent. Through determination, the obtained food-grade sodium dihydrogen phosphate is white crystalline powder or granules, and all indexes of the food-grade sodium dihydrogen phosphate meet or exceed the requirements of national food safety standard GB25564-2010 food additive sodium dihydrogen phosphate.

3. Low cost, high purity, sufficient removal of arsenic and heavy metal ions, high sanitary safety, simple and convenient process, high utilization rate of raw materials, good solubility, mechanized production and suitability for large-scale and small-scale production.

Drawings

FIG. 1 is a process flow diagram for producing food grade sodium dihydrogen phosphate from industrial wet-purified phosphoric acid.

Detailed Description

The applicant shall now describe the process of the present invention in further detail with reference to specific examples.