CN109455685B - Method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate - Google Patents
Method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate Download PDFInfo
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- CN109455685B CN109455685B CN201811618894.5A CN201811618894A CN109455685B CN 109455685 B CN109455685 B CN 109455685B CN 201811618894 A CN201811618894 A CN 201811618894A CN 109455685 B CN109455685 B CN 109455685B
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- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/30—Alkali metal phosphates
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Abstract
The invention discloses a method for producing sodium dihydrogen phosphate and sodium chloride products by purifying a byproduct crude product sodium pyrophosphate of phosphorus-containing salt-containing wastewater such as glyphosate mother liquor and the like. The oxidative assistant is used for improving the dispersibility of the crude sodium pyrophosphate mixed solution and the special use method of the process water is used for improving the viscosity of the slurry and improving the crystallization effect. Sodium orthophosphate and sodium chloride are extracted by using solubility differences of sodium pyrophosphate, hydrolysate thereof and sodium chloride in crude sodium pyrophosphate under different temperatures, pH value conditions and the action of an auxiliary agent. The production process has the advantages of high dissolution speed, excellent product quality, small wastewater amount, greatly reduced environmental protection treatment cost, reaction advantage, environmental protection advantage, quality advantage and cost advantage.
Description
Technical Field
The invention belongs to the technical field of three-waste treatment production, and particularly relates to a method for refining crude sodium pyrophosphate obtained by burning or high-temperature oxidizing high-sodium chloride phosphorus-containing wastewater such as glyphosate mother liquor, which is particularly suitable for refining crude sodium pyrophosphate obtained by burning or high-temperature oxidizing glyphosate mother liquor by a glycine method or an IDA method.
Background
The treatment of the glyphosate mother liquor is an industrial problem, and the glyphosate mother liquor produced by the glycine method or the IDA method has the characteristics of high COD, high TP, high salt, complex components and difficult degradation, and has great treatment difficulty and high cost. At present, the mainstream mother liquor treatment process adopts an oxidation method to degrade the mother liquor and recover phosphorus elements, mainly comprises an incineration method, a high-temperature oxidation method, a medium-temperature oxidation method, a low-temperature oxidation method and the like, and sodium chloride and phosphate are recovered by a membrane separation technology or evaporation concentration in the mother liquor treatment process. For example: membrane separation to recover sodium chloride, glyphosate and other substances, evaporation concentration to recover glyphosate and sodium chloride, directional conversion of concentrated mother liquor to recover sodium pyrophosphate, catalytic oxidation of mother liquor to recover phosphate, etc. Each method has advantages and disadvantages, a plurality of major glyphosate manufacturers respectively adopt different treatment processes, and most enterprises carry out combined treatment on glyphosate mother liquor by the processes. At present, the Xingfa group, the Xinan chemical industry, the Shandong Runfeng and other companies all have devices for producing sodium pyrophosphate by directionally converting concentrated mother liquor, the main content of the obtained crude sodium pyrophosphate is 40-85%, the content of sodium chloride is 3-35% according to different treatment processes of various enterprises, and impurities such as sodium carbonate, sodium bicarbonate, sodium sulfite, sodium bisulfite, organic phosphorus and the like are also contained. For the route, no matter the membrane treatment desalting process or the evaporation concentration desalting process is adopted, the finally obtained sodium pyrophosphate crude product contains high sodium chloride, the product has many impurities, color difference, peculiar smell, low main content, poor quality, low market price and limited application occasions, and further purification is needed to improve the main content and the quality.
The treatment of the glyphosate mother liquor is an industrial problem, and in order to really make the environment-friendly treatment of the glyphosate mother liquor, the organization of the national ministry of industry and informatization in 2014-2017 develops part 1 of the industrial salt of the glyphosate byproduct: sodium chloride, part 2 of the industrial salt by-produced from glyphosate: crude sodium pyrophosphate, "part 3 of glyphosate byproduct Industrial salt: disodium hydrogen phosphate industry Standard solicits for comments. At present, the crude sodium pyrophosphate products produced by most manufacturers by the existing processes cannot meet the standard, so the crude sodium pyrophosphate products are urgently required to be solved, and the purification of the crude sodium pyrophosphate products is trendy.
Some companies refine crude sodium pyrophosphate to obtain sodium pyrophosphate, but in the production process, the problems of slow dissolution of the crude sodium pyrophosphate, high viscosity of a dissolving solution, low treatment capacity, large wastewater amount, high cost and poor product quality exist, and the residual quantity of sodium chloride and organic phosphorus in a phosphate product is large and the quality is poor. For example, CN206915770U is a system for purifying phosphorus resources after advanced treatment of glyphosate mother liquor. CNIO68098llA a method for preparing sodium pyrophosphate by using crude sodium pyrophosphate and CN106882781A a method for decolorizing crude sodium pyrophosphate during purification production of sodium pyrophosphate products to directly refine and extract sodium pyrophosphate, and the problems of slow dissolution of crude sodium pyrophosphate, large viscosity of a dissolving solution, small device processing capacity and high sodium chloride content in sodium pyrophosphate products also exist in the process of treating crude sodium pyrophosphate. Therefore, a new process method needs to be developed by combining material characteristics.
Disclosure of Invention
The method for producing sodium orthophosphate and sodium chloride by purifying crude sodium pyrophosphate provided by the invention has the advantages that in the refining process of the crude sodium pyrophosphate,
the orthophosphate and the sodium chloride are separated by utilizing the characteristics of different solubilities of various components and hydrolysate in the crude sodium pyrophosphate under different temperature and pH value conditions and under the action of an auxiliary agent. The orthophosphate may be produced specifically as sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, or a mixture of sodium dihydrogen phosphate and disodium hydrogen phosphate, or a mixture of disodium hydrogen phosphate and trisodium phosphate, specifically a hydrated product of the sodium phosphate salt, according to the market demand, and may be achieved by adjusting temperature, pH, and the like. Phosphoric acid and oxidizing substances are used as auxiliary agents for treatment, the dissolution, hydrolysis and crystallization of the by-product crude sodium pyrophosphate are promoted, the crystallization effect is improved by changing the viscosity of slurry while impurities are removed, and the quality of sodium orthophosphate and sodium chloride is improved. Firstly, sodium chloride is filtered and extracted from mixed slurry obtained after the dissolution and hydrolysis of crude sodium pyrophosphate, and then orthophosphate is extracted from filtrate. Then refining the extracted sodium chloride crude product and orthophosphate crude product respectively. And returning filtrate B obtained in the process of separating orthophosphate by the filtering device B to the hydrolysis kettle for recycling.
In the traditional glyphosate mother liquor treatment process, the mother liquor generated in the refining process of crude sodium pyrophosphate is generally sleeved in devices such as a glyphosate mother liquor mvr evaporation device, a multi-effect evaporation device and the like for evaporation concentration desalination, and the desalted mother liquor is incinerated to form a large circulation. In the production process of the method, the mother liquor after phosphate purification is circularly used for dissolving crude sodium pyrophosphate, water entering the system is finally brought out in the form of sodium orthophosphate hydrate, sodium chloride in the crude product is continuously separated out through enrichment and crystallization instead of desalting and dewatering by reusing an evaporation and concentration process, so that the consumption of fresh water and the generation of wastewater are greatly reduced, and the steam consumption, the cost and the environment-friendly treatment pressure are reduced.
A method for producing sodium dihydrogen phosphate and sodium chloride products by purifying crude sodium pyrophosphate comprises the following steps:
(1) Material preparation and salting out: mixing crude sodium pyrophosphate and water in a hydrolysis kettle, dropwise adding phosphoric acid to control the pH value of the mixed material to be in the range of 0.5-4.5, adding an oxidizing auxiliary agent, and stirring at 70-120 ℃ for 5-60min to dissolve and hydrolyze the crude sodium pyrophosphate;
preferably, the pH is in the range of 4.0 to 4.5.
(2) And (3) recovering a sodium chloride product: discharging and filtering the slurry in the hydrolysis kettle in the step (1) while the slurry is hot to obtain a sodium chloride product and filtrate; and (3) discharging the hydrolysis kettle slurry while the hydrolysis kettle slurry is hot, and filtering to obtain a sodium chloride product and a filtrate, wherein the filtrate mainly comprises water, sodium dihydrogen phosphate and sodium chloride, and the filtrate sodium dihydrogen phosphate and the sodium chloride are both saturated and reach a neutral state.
And washing the filter residue A (namely sodium chloride) by using the hot filtrate B2 preheated by the heat exchanger and heated by the heater, and recycling the obtained washing liquid A to the hydrolysis kettle for recycling. The obtained sodium chloride product reaches the glyphosate byproduct industrial salt: sodium chloride "standard.
The sodium chloride product is taken out as a product or further goes to a sodium chloride deep refining device for further purification. Preferably, washing liquid or filtrate in the process of purifying the sodium chloride product by the sodium chloride deep refining device returns to the hydrolysis kettle for reuse.
Further preferably, hydrochloric acid or an alcohol solution of hydrogen chloride is used as an extraction agent to extract and refine the obtained sodium chloride product, the pH value of the refined sodium chloride product is adjusted to be neutral by using a small amount of liquid alkali, and the quality of the sodium chloride product is superior to that of glyphosate byproduct industrial salt: according to the standard of sodium chloride, the glyphosate residual quantity is reduced to be within 0.02 percent (mass ratio), and the total phosphorus is reduced to be within 0.08 percent.
Preferably, the hydrochloric acid after leaching is reused in the glyphosate mother liquor post-treatment process for adjusting the pH value of the mother liquor and recovering the leached phosphorus, and the rest impurities after leaching are oxidized with the mother liquor.
Preferably, the alcohol solution after leaching is evaporated to recover alcohol, the obtained phosphorus-containing concentrated solution is subjected to deoxidation and recovery, and the recovered alcohol is recycled.
The hydrochloric acid is reused in the glyphosate mother liquor post-treatment process, is used for adjusting the pH value of the mother liquor, simultaneously recovers the leached phosphorus, and oxidizes the rest impurities along with the mother liquor.
The alcohol is one or more of methanol, ethanol, propanol, isopropanol and butanol.
(3) Recovering sodium dihydrogen phosphate products: cooling the filtrate obtained in the step (2), mixing the filtrate with alkali in a mixer, controlling the pH value of the mixed solution to be in the range of 4.0-7.0 to generate sodium dihydrogen phosphate, filtering impurities by a filter, then sending the mixture to a crystallization kettle, adding water and sodium dihydrogen phosphate crystals into the crystallization kettle when the temperature of the slurry is reduced to 30-90 ℃, then cooling and crystallizing at the temperature of 0-30 ℃ for 2-8h to precipitate sodium dihydrogen phosphate dihydrate, and filtering and separating the slurry after sufficient crystallization to obtain the sodium dihydrogen phosphate dihydrate product.
And (4) the mother liquor obtained after separating the sodium dihydrogen phosphate in the step (3) is a cold saturated phosphate solution, the sodium chloride content of the mother liquor is close to saturation, the mother liquor returns to the dissolving kettle for recycling, and crude sodium pyrophosphate is continuously dissolved.
The crude sodium pyrophosphate is a crude sodium pyrophosphate product obtained by burning or high-temperature oxidizing phosphorus-containing sodium chloride-containing wastewater such as glyphosate mother liquor, N-phosphonomethyl iminodiacetic acid mother liquor and the like, is a mixture of gray, grey-white or grey-black powder, block and particle, mainly comprises sodium pyrophosphate and sodium chloride, has the main content of 40-85 percent of sodium pyrophosphate, the content of 3-40 percent of sodium chloride and the total organic carbon of about 0.2 percent, and also contains impurities such as sodium carbonate, sodium bicarbonate, sodium sulfite, sodium bisulfite, organic phosphorus and the like. The pH value of the water solution is about 10.0.
The mass ratio of the crude sodium pyrophosphate to the water is 1: (0.5-2.0). The water is process water, and the process water is filtrate obtained after the crystallization kettle slurry is filtered, and process water in the processes of washing and refining sodium chloride and sodium dihydrogen phosphate.
The addition amount of the oxidizing auxiliary agent in the step (2) is 0.005-2.5% of the mass of the crude sodium pyrophosphate.
The oxidizing auxiliary agent in the step (2) is any one or a combination of sodium perchlorate, sodium chlorate, sodium chlorite and sodium hypochlorite. The preferable scheme is that the oxidizing auxiliary agent is a mixture of sodium chlorate and sodium hypochlorite, and the mass ratio of the oxidizing auxiliary agent to the mixture is 1: (0.2-1.2).
In the step (3), the alkali is one or a combination of sodium hydroxide, sodium carbonate and sodium bicarbonate.
The mass ratio of the water to the crude sodium pyrophosphate is (0-5) to 1. (ii) a The weight of the sodium dihydrogen phosphate crystals is 0.05-0.2% of the crude sodium pyrophosphate. Preferably 0.1%.
The crude sodium pyrophosphate is a crude sodium pyrophosphate product obtained by burning or oxidizing phosphorus-containing sodium chloride-containing wastewater such as glyphosate mother liquor and the like at high temperature.
(4) Mother liquor is recycled:
the mother liquor (i.e., filtrate B) contains about 60% of water, about 30% of sodium chloride, and about 10% of phosphate. And the cold filtrate B exchanges heat with the hot filtrate A through a heat exchanger, goes to a process water storage tank, is further heated through a heater and returns to the dissolving kettle for recycling, and crude sodium pyrophosphate is continuously dissolved.
(5) Preferred conditions
Preferably, hot filtrate B2 which is preheated by a heat exchanger and heated by a heater is used for washing filter residue A (namely sodium chloride), and the obtained washing liquid A is recycled to the hydrolysis kettle for recycling.
Preferably, the washing liquid or filtrate in the process of purifying the orthophosphate product by the washing device B and the orthophosphate deep refining device returns to the hydrolysis kettle for reuse.
In the content, the invention also provides a device for producing sodium dihydrogen phosphate and sodium chloride by purifying the crude sodium pyrophosphate, wherein the bottom of the hydrolysis kettle is connected with the filter A; the filtering device A is connected with the heat exchanger, the heat exchanger is connected with the mixer, the mixer is connected with the filter C, the filter C is connected with the crystallization kettle, the crystallization kettle is connected with the filter B, the filter B is connected with the washing device B, and the washing device B is connected to the phosphate deep refining device. The filter B and the washing device B are respectively connected with a heat exchanger through pipelines, the heat exchanger is connected with a heater through a connecting water storage tank, and the heater is connected to the hydrolysis kettle.
The bottom of the filter A is connected with a washing device A through a pipeline, one path of the washing device A is connected to a sodium chloride deep refining device (13), and the other path is connected to a heat exchanger (4).
The washing device A is connected to a connecting pipeline between the heater and the hydrolysis kettle through a pipeline.
The technical scheme of the invention has the following beneficial effects:
1. the reaction advantage and the energy-saving advantage are obvious. The method has the advantages of high speed of dissolving and hydrolyzing the crude sodium pyrophosphate, thorough reaction, large treatment capacity in unit time and great improvement on the productivity of the monomer device. Can be completely dissolved in only 5-20min, and the dissolving time is greatly shortened compared with the traditional process.
2. Has good economic and environmental protection benefits. Mother liquor (namely filtrate B of a filtering device B in the attached drawing of the specification) after the sodium dihydrogen phosphate is purified from the crude sodium pyrophosphate can be recycled, water in process water used for dissolving and hydrolyzing the crude sodium pyrophosphate is combined with the sodium pyrophosphate (hydrolysis reaction and hydration reaction), water added into the system is finally extracted out of the system in the form of orthophosphate combined water, only a small amount of concentrated water is periodically discharged, and water resources in the recycled process water are recycled. And simultaneously, sodium chloride in the crude sodium pyrophosphate is precipitated due to saturation to realize separation. Therefore, the amount of waste water in the refining and purifying process is reduced by more than 92 percent compared with other processes of extracting phosphate by wet catalytic oxidation and the like. The method can improve the purity of the orthophosphate to the maximum extent and reduce the output of the wastewater, and has outstanding environmental protection benefit and good economical efficiency.
3. The method can recover sodium chloride products, recover chlorine resources and reduce the discharge amount of chlorine-containing waste liquid and waste residues. The method has the advantages that the cost for recovering the sodium chloride is far lower than that for recovering the sodium chloride by using an evaporation concentration method, and the quality is good.
4. The orthophosphate and sodium chloride products obtained by the method have few impurities and high purity. (1) The method uses phosphoric acid to accelerate the dissolution of the sodium pyrophosphate crude product, does not introduce new anion impurities, and simultaneously removes the anion impurities such as carbonate, bicarbonate radical, sulfite radical, sulfate radical and the like generated in the incineration process of waste water such as glyphosate mother liquor and the like, and the removal of sulfide reduces the peculiar smell of the product. (2) The method uses oxidizing auxiliary agent to burn residual TOC, COD and NH in mother liquor 3 N is oxidized and removed, whitening and peculiar smell removing effects are achieved, meanwhile, colloid dispergation in a mixed system is promoted, material particles are fully dispersed, the viscosity of material liquid is reduced, the crystallization effect is good, a synergistic effect is further generated under the effects, and the obtained orthophosphate crystals and sodium chloride crystals are high in purity. (3) Because the mother liquor after the orthophosphate is purified by the crude sodium pyrophosphate is returned to the system again for recycling, the washing water quantity is increased, the purity of the sodium dihydrogen phosphate is increased, and the sodium chloride and the non-orthophosphoric acid are recycled within the limit of the acceptable range of the wastewaterThe characteristic impurity indexes such as substances and the like are obviously improved. (4) The mother liquor after sodium chloride purification returns to the system again for recycling, so that the washing water quantity is increased as much as possible and the purity of sodium chloride is increased within the limit of the acceptable range of wastewater. (5) The content of chloride in the sodium dihydrogen phosphate recovered by the method is as low as 0.10%, and compared with the level of chloride of about 1% obtained by the traditional processes of companies such as south Tong Jiangshan, hubei Xingfa and the like, the index of residual chloride is greatly reduced.
5. The phosphorus residue in the sodium chloride product is very low, the glyphosate reaches within 0.05 percent, and the total phosphorus reaches within 0.15 percent. Meanwhile, the phosphorus element is recovered more thoroughly. Further preferably, the glyphosate residue is reduced to be within 0.02% (mass ratio) and the total phosphorus is reduced to be within 0.08% when the obtained sodium chloride product is subjected to extraction and refining by using an alcoholic solution or an alcoholic solution of hydrochloric acid or hydrogen chloride.
Because the mother liquor after the sodium phosphate is purified by the crude sodium pyrophosphate is returned to the system again for recycling, the washing water quantity is increased as much as possible within the limit of acceptable wastewater, the sodium chloride quality is improved, and the loss of the sodium phosphate is reduced.
Drawings
FIG. 1 is a process flow diagram for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate, wherein the process flow diagram comprises a hydrolysis kettle 1, a filter A2, a material washing device A3, a heat exchanger 4, a water storage tank 5, a mixer 6, a filter C7, a crystallization kettle 8, a filter B9, a material washing device B10, a phosphate deep refining device 11, a heater 12 and a sodium chloride deep refining device 13.
Detailed Description
Example 1
Method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate
In the technical scheme, the mother liquor after sodium dihydrogen phosphate crystallization has high sodium dihydrogen phosphate content and large phosphoric acid consumption, but the comprehensive cost is also advantageous because the hydration amount of the sodium dihydrogen phosphate is small and the mother liquor is recycled. The process scheme is particularly suitable for enterprises with devices matched with pentasodium phosphate and hexametaphosphate.
1. Preparing materials: during initial start-up, crude sodium pyrophosphate and water were mixed in a ratio of 1:1 in a hydrolysis kettle (hydrolysis tank), and dropwise adding phosphoric acid to control the pH value of the mixed material to be 3.5.
In the continuous operation process, the crude sodium pyrophosphate and process water (filtrate B2, washing liquid A from the washing device A and other process water in the implementation step) are mixed according to the ratio of 1:1 in a hydrolysis kettle (hydrolysis tank), and dropwise adding phosphoric acid to control the pH value of the mixed material to be 3.5.
After the crude sodium pyrophosphate is partially dissolved, adding a mixture of oxidizing auxiliary agents sodium chlorate and sodium hypochlorite into a hydrolysis kettle (hydrolysis tank) for oxidation and sol reaction, wherein the addition amount of the auxiliary agents is 0.015 percent of the mass of the crude sodium pyrophosphate; after the addition of the auxiliary agent, the solution viscosity is reduced, and the dissolving speed is further improved; stirring at 90 deg.C for 30min to dissolve and hydrolyze crude sodium pyrophosphate;
the oxidizing auxiliary agent is sodium chlorate and sodium hypochlorite according to a mass ratio of 1: 1.
2. Salting out: along with the dissolution of the crude product, the contents of phosphate and sodium chloride in the mixed solution are gradually increased, the sodium chloride is saturated firstly because the solubility is relatively low, and when the crude product is continuously put into the system, the sodium chloride is continuously crystallized and separated out, and the content of the phosphate is continuously improved.
3. And (3) recovering a sodium chloride product: discharging while hot, and filtering to obtain filtrate A and filter residue A. The filter residue A is a crude sodium chloride product, and the sodium chloride product is obtained by washing the materials and can also be sent to a sodium chloride deep refining device for further purification. The sodium pyrophosphate and the sodium chloride in the filtrate A are saturated to reach a neutral state.
4. And (3) recovering an orthophosphate product:
and (3) exchanging heat between the hot filtrate A and the cold filtrate B1 through a heat exchanger, mixing the hot filtrate A and the cold filtrate B with alkali sodium hydroxide in a mixer to obtain a solution A2, and controlling the pH value of the mixed solution A2 to be 6.5 to gradually generate sodium dihydrogen phosphate. The solution A2 is filtered by a filter C to remove a small amount of impurities and then is sent to a crystallization kettle.
When the temperature of the slurry is reduced to 55-60 ℃, adding a proper amount of water and sodium dihydrogen phosphate crystals into a crystallization kettle, wherein the mass ratio of the crystallization water to the crude sodium pyrosulfate is 1. In the cooling process, the solubility of the sodium dihydrogen phosphate is rapidly reduced to reach a supersaturated state, and sodium dihydrogen phosphate crystals are continuously separated out. The solubility of the sodium chloride in the mixed solution is less reduced along with the temperature, so the sodium chloride is remained in the slurry mother liquor and is not separated out.
And (3) filtering and separating the fully crystallized slurry by a filter B to obtain a filter residue B, namely a sodium dihydrogen phosphate product (sodium dihydrogen phosphate dihydrate). The obtained sodium dihydrogen phosphate can also be sent to a deep refining device for further purification.
5. Mother liquor is recycled:
the mother liquor (i.e., filtrate B) contains about 60% of water, about 30% of sodium chloride, and about 10% of phosphate. And the cold filtrate B exchanges heat with the hot filtrate A through a heat exchanger, goes to a process water storage tank, is further heated through a heater and returns to the dissolving kettle for recycling, and crude sodium pyrophosphate is continuously dissolved.
Preferably, hot filtrate B2 which is preheated by a heat exchanger and heated by a heater is used for washing filter residue A (namely sodium chloride), and the obtained washing liquid A is recycled to the hydrolysis kettle for recycling.
Preferably, the washing liquid or filtrate in the process of purifying the orthophosphate product by the washing device B and the orthophosphate deep refining device returns to the hydrolysis kettle for reuse.
Preferably, washing liquid or filtrate in the process of purifying the sodium chloride product by the sodium chloride deep refining device returns to the hydrolysis kettle for reuse.
Table 1: crude sodium pyrophosphate hydrolysate and sodium chloride solubility data
Example 2
A device for producing sodium pyrophosphate and sodium chloride by purifying crude sodium pyrophosphate is characterized in that the bottom of a hydrolysis kettle 1 is connected with a filter A2; filter equipment A2 is connected with heat exchanger 4, and heat exchanger 4 is connected with blender 6, and blender 6 is connected with filter C7, and filter C7 is connected with crystallization kettle 8, and crystallization kettle 8 is connected with filter B9, and filter B9 is connected with washing material device B10, washes material device B10 and is connected to pyrophosphate degree of depth refining plant 11.
The filter B9 and the washing device B10 are respectively connected with the heat exchanger 4 through pipelines, the heat exchanger 4 is connected with the heater 12 through the connecting water storage tank 5, and the heater 12 is connected to the hydrolysis kettle 1.
The bottom of the filter A2 is connected with a washing device A3 through a pipeline, one path of the washing device A3 is connected to a sodium chloride deep refining device 13, and the other path is connected to a heat exchanger 4.
The heater 12 is connected to the washing device A3 via a line.
The hydrolysis kettle 1 is provided with a pyrophosphoric acid crude product inlet pipeline, a phosphoric acid pipeline, an auxiliary agent pipeline, a water pipeline and a steam pipeline.
And water inlet pipelines are arranged on the material washing device A3 and the material washing device B10.
The crystallization kettle 8 is provided with a crystallization water pipeline.
Claims (5)
1. A method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate is characterized in that:
(1) Material preparation and salting out: mixing crude sodium pyrophosphate and water in a hydrolysis kettle, dropwise adding phosphoric acid to control the pH value of the mixed material to be in the range of 0.5-4.5, adding an oxidizing auxiliary agent, and stirring at 70-120 ℃ for 5-60min to dissolve and hydrolyze the crude sodium pyrophosphate, wherein the crude sodium pyrophosphate is a crude sodium pyrophosphate product which is obtained by burning glyphosate mother liquor and PMIDA mother liquor phosphorus-containing sodium chloride wastewater and contains sodium pyrophosphate and sodium chloride as main components, is a gray, grey-white or grey-black powdery, blocky and granular mixture, contains the sodium pyrophosphate and the sodium chloride as main components, contains 40-85% of sodium pyrophosphate, 3-35% of sodium chloride and 0.1-0.3% of total organic carbon, and also contains sodium carbonate, sodium bicarbonate, sodium sulfite, sodium bisulfite and organic phosphorus impurities, and the pH value of an aqueous solution of the mixture is 9.5-10.55;
(2) And (3) recovering a sodium chloride product: discharging and filtering the slurry in the hydrolysis kettle in the step (1) while the slurry is hot to obtain a sodium chloride product and a filtrate A;
(3) Recovering sodium dihydrogen phosphate products: cooling the filtrate A in the step (2), mixing the filtrate A with alkali in a mixer, controlling the pH value of the mixed solution to be in the range of 4.0-7.0 to generate sodium dihydrogen phosphate, filtering impurities out by a filter, then conveying the mixture to a crystallization kettle, adding water and sodium dihydrogen phosphate crystals into the crystallization kettle when the temperature of slurry is reduced to 30-90 ℃, then cooling and crystallizing at the temperature of 0-30 ℃ for 2-8h to precipitate sodium dihydrogen phosphate dihydrate, filtering and separating the slurry after full crystallization to obtain a sodium dihydrogen phosphate dihydrate product and a filtrate B, wherein the alkali is sodium chlorate and sodium hypochlorite according to the mass ratio of 1:0.2-1.2 of a mixture; the mass ratio of the added water to the crude sodium pyrophosphate in the raw material is (0-5): 1; the weight of the sodium dihydrogen phosphate crystal is 0.05-0.2% of the produced sodium dihydrogen phosphate;
and the cold filtrate B exchanges heat with the hot filtrate A through a heat exchanger, goes to a process water storage tank, is further heated through a heater and returns to the dissolving kettle for recycling, and crude sodium pyrophosphate is continuously dissolved.
2. The method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate according to claim 1, which is characterized in that: the mass ratio of the crude sodium pyrophosphate to the water in the step (1) is 1: (0.5-2.0).
3. The method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate according to claim 1, wherein the steps of: the addition amount of the oxidizing auxiliary agent in the step (1) is 0.005-2.5% of the mass of the crude sodium pyrophosphate.
4. The method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate according to claim 1, which is characterized in that: the oxidizing auxiliary agent in the step (1) is any one or a combination of more of sodium perchlorate, sodium chlorate, sodium chlorite and sodium hypochlorite.
5. The method for producing sodium dihydrogen phosphate and sodium chloride by purifying crude sodium pyrophosphate according to claim 1, wherein the steps of: when the temperature of the slurry solution is reduced to 40-50 ℃, water and sodium dihydrogen phosphate crystals are added.
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| CN108328591B (en) * | 2018-03-12 | 2020-02-18 | 江西金龙化工有限公司 | Method for recycling and comprehensively utilizing glyphosate mother liquor and utilizing boiler flue gas energy |
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