Method and device for recovering phosphate ester compounds in wastewater

Abstract

The invention provides a method and a device for recovering phosphate ester compounds in wastewater, and belongs to the technical field of wastewater recovery. The method for recovering the phosphate ester compounds in the wastewater comprises the following steps: 1) mixing the wastewater and an electrolyte, and adjusting the pH value to 7.5-9 to obtain a mixed material; 2) carrying out extraction or adsorption regeneration on the obtained mixed material to obtain an extraction solution containing the phosphate ester compound or a regeneration solution containing the phosphate ester compound; 3) distilling the extraction liquid containing the phosphate ester compound or the regeneration liquid containing the phosphate ester compound to obtain the phosphate ester compound; the phosphate ester compound is tris (2-cyanoethyl) phosphite ester or tris (2-cyanoethyl) phosphate ester. According to the method provided by the invention, the tris (2-cyanoethyl) phosphite or tris (2-cyanoethyl) phosphate in the wastewater can be effectively recovered, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater recovery, and in particular relates to a method for recovering phosphate compounds in wastewater and a device used therein. Background Art

[0002] Phosphate compounds and nitrile compounds are commonly used additives for lithium-ion electrolytes, and have a significant effect on improving the high voltage performance, high temperature performance and cycle performance of lithium-ion batteries. Studies have found that tris(2-cyanoethyl)phosphate and tris(2-cyanoethyl)phosphite can be used as additives for high-voltage lithium-ion battery electrolytes to improve the high temperature performance and cycle performance of batteries.

[0003] Both tris(2-cyanoethyl)phosphate and tris(2-cyanoethyl)phosphite will generate a large amount of wastewater during the production and synthesis process, and a certain amount of products will remain in the wastewater. The prices of tris(2-cyanoethyl)phosphate and tris(2-cyanoethyl)phosphite are high. Therefore, recycling tris(2-cyanoethyl)phosphate and tris(2-cyanoethyl)phosphite in the wastewater has extremely high economic value. Summary of the invention

[0004] The invention provides a method for recovering phosphate compounds in wastewater and a device used therefor. The method provided by the invention can effectively recover tris(2-cyanoethyl)phosphate and tris(2-cyanoethyl)phosphite in wastewater, thereby reducing production costs.

[0005] In order to achieve the above object, the present invention provides a method for recovering phosphate compounds in wastewater, comprising the following steps:

[0006] 1) mixing the wastewater and the electrolyte, adjusting the pH to 7.5-9, and obtaining a mixed material;

[0007] 2) extracting or regenerating the obtained mixed material to obtain an extract containing phosphate ester compounds or a regenerated liquid containing phosphate ester compounds;

[0008] 3) distilling the extract containing the phosphate ester compound or the regenerated liquid containing the phosphate ester compound to obtain the phosphate ester compound;

[0009] The phosphate compound is tris(2-cyanoethyl)phosphite or tris(2-cyanoethyl)phosphate.

[0010] Preferably, the wastewater in step 1) is wastewater generated from the preparation of tris(2-cyanoethyl)phosphate or tris(2-cyanoethyl)phosphite; and the wastewater temperature is controlled at 0-25°C.

[0011] Preferably, the electrolyte in step 1) includes one or more of sodium chloride, potassium chloride, potassium nitrate, sodium nitrate, potassium sulfate and sodium sulfate.

[0012] Preferably, the amount of electrolyte added in step 1) is 1% to 50% of the mass of the wastewater.

[0013] Preferably, in step 1), an alkaline solution is used to adjust the pH, and the alkaline solution includes one or more of an aqueous sodium hydroxide solution, a potassium hydroxide solution, an ammonia solution, a sodium carbonate solution, a potassium carbonate solution, a sodium bicarbonate solution and a potassium bicarbonate solution.

[0014] Preferably, the extraction agent used for extraction in step 2) includes one or more of dichloromethane, chloroform, toluene, butanone and methyl isobutyl ketone.

[0015] Preferably, the temperature during extraction in step 2) is 0-100° C., and the mass ratio of wastewater to extractant is 1:0.1-100.

[0016] Preferably, in step 2), resin is used for adsorption, and after obtaining the resin for adsorbing phosphate compounds, regeneration is performed using a regeneration liquid.

[0017] Preferably, the regeneration liquid includes one or more of acetonitrile, acetone, cyclohexane, toluene and N-methylpyrrolidone; the volume ratio of the regeneration liquid to the resin is 0.5 to 100:1.

[0018] Preferably, the pressure during distillation in step 3) is 10Pa-500Pa and the temperature is 50-100°C.

[0019] The present invention provides a device for recovering phosphate compounds in wastewater as described in any one of the above, comprising:

[0020] Reactor, pH adjustment kettle, extraction device and molecular distillation device;

[0021] The discharge port of the preparation kettle is connected to the feed port of the pH adjusting kettle; the discharge port of the pH adjusting kettle is connected to the material feed port of the extraction device; the extractant discharge port of the molecular distillation device is connected to the extractant feed port of the extraction device; the extractant discharge port of the extraction device is connected to the feed port of the molecular distillation device.

[0022] Preferably, the extraction device comprises a first extraction device, a second extraction device and a third extraction device;

[0023] The discharge port of the preparation kettle is connected to the feed port of the pH adjusting kettle; the discharge port of the pH adjusting kettle is connected to the material feed port of the first extraction device; the wastewater discharge port of the first extraction device is connected to the material feed port of the second extraction device; the wastewater discharge port of the second extraction device is connected to the material feed port of the third extraction device; the extractant discharge port of the molecular distillation device is connected to the extractant feed port of the third extraction device; the extractant discharge port of the third extraction device is connected to the extractant feed port of the second extraction device; the extractant discharge port of the second extraction device is connected to the extractant feed port of the first extraction device; the extractant discharge port of the first extraction device is connected to the feed port of the molecular distillation device.

[0024] The present invention provides a device for recovering phosphate compounds in wastewater as described in any one of the above, comprising:

[0025] Preparation kettle, pH adjustment kettle, first adsorption regeneration device, second adsorption regeneration device and molecular distillation device;

[0026] The discharge port of the preparation kettle is connected to the feed port of the pH adjusting kettle; the discharge port of the pH adjusting kettle is respectively connected to the feed ports of the first adsorption regeneration device and the second adsorption regeneration device; the upper material discharge ports of the first adsorption regeneration device and the second adsorption regeneration device are respectively connected to the feed port of the molecular distillation device; the regeneration liquid discharge port of the molecular distillation device is respectively connected to the regeneration liquid feed ports of the first adsorption regeneration device and the second adsorption regeneration device.

[0027] Compared with the prior art, the advantages and positive effects of the present invention are:

[0028] The method for recovering tris(2-cyanoethyl)phosphite and tris(2-cyanoethyl)phosphate from wastewater provided by the present invention includes adding electrolyte to wastewater and then recovering tris(2-cyanoethyl)phosphite and tris(2-cyanoethyl)phosphate by extraction or adsorption, thereby greatly increasing the recovery amount and reusing them for production, thereby effectively improving product revenue and reducing the pollution of wastewater to the environment.

[0029] The method provided by the invention has mild reaction conditions, simple operation process and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A diagram of a production unit for recovering phosphate compounds from wastewater by extraction;

[0031] Figure 2 A diagram of a production unit for recovering phosphate compounds from wastewater by adsorption;

[0032] Among them, 1-preparation kettle, 2-pH adjustment kettle, 3-first extraction device, 4-second extraction device, 5-third extraction device, 6-molecular distillation device, 7-first adsorption regeneration device, 8-second adsorption regeneration device. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] The present invention provides a method for recovering phosphate compounds in wastewater, comprising the following steps:

[0035] 1) mixing the wastewater and the electrolyte, adjusting the pH to 7.5-9, and obtaining a mixed material;

[0036] 2) extracting or regenerating the obtained mixed material to obtain an extract containing phosphate ester compounds or a regenerated liquid containing phosphate ester compounds;

[0037] 3) distilling the extract containing the phosphate ester compound or the regenerated liquid containing the phosphate ester compound to obtain the phosphate ester compound;

[0038] The phosphate compound is tris(2-cyanoethyl)phosphite or tris(2-cyanoethyl)phosphate.

[0039] The present invention mixes wastewater and electrolyte, adjusts the pH to 7.5-9, and obtains a mixed material. In the present invention, the wastewater is preferably wastewater produced by preparing tris(2-cyanoethyl)phosphate or tris(2-cyanoethyl)phosphite. In the present invention, the temperature of the wastewater is preferably controlled at 0-25°C. In the present invention, if the wastewater temperature is too high, it will cause part of the tris(2-cyanoethyl)phosphite or tris(2-cyanoethyl)phosphate to decompose, while if it is too low, it will require additional energy consumption to adjust the temperature. It is understandable that the temperature specified in the present application is the optimal temperature.

[0040] In the present invention, the electrolyte preferably includes one or more of sodium chloride, potassium chloride, potassium nitrate, sodium nitrate, potassium sulfate and sodium sulfate; the amount of the electrolyte added is preferably 1% to 50% of the mass of the wastewater, and more preferably 20% to 40%. In the present invention, the addition of electrolyte can reduce the solubility of tris(2-cyanoethyl)phosphite and tris(2-cyanoethyl)phosphate in water, and improve the subsequent extraction or adsorption efficiency. In the present invention, it is preferred to use an alkaline solution to adjust the pH, and the alkaline solution preferably includes one or more of sodium hydroxide aqueous solution, potassium hydroxide solution, ammonia water, sodium carbonate solution, potassium carbonate solution, sodium bicarbonate solution and potassium bicarbonate solution, and more preferably sodium hydroxide aqueous solution, sodium carbonate aqueous solution or sodium bicarbonate aqueous solution. In the present invention, a certain amount of alkaline solution is added to the wastewater to control the pH at 7.5 to 9, so that the by-product (the product of the hydrolysis of Cl on the monosubstituted and disubstituted to OH) becomes a sodium salt to reduce the solubility of the by-product in the extractant. If the pH is too high, the product may decompose. It can be understood that the pH range defined in the present application is the optimal range.

[0041] After obtaining the mixed material, the present invention extracts or regenerates the obtained mixed material by adsorption to obtain an extract containing phosphate compounds or a regeneration liquid containing phosphate compounds. In the present invention, the extractant for extraction preferably includes one or more of dichloromethane, chloroform, toluene, butanone and methyl isobutyl ketone. The temperature during extraction is preferably 0 to 100°C, more preferably 5 to 40°C, and the mass ratio of wastewater to extractant is preferably 1:0.1 to 100, more preferably 1:3 to 10. In the present invention, it is preferred to use resin for adsorption, and then use regeneration liquid for regeneration after obtaining the resin that adsorbs phosphate compounds. In the present invention, the regeneration liquid preferably includes one or more of acetonitrile, acetone, cyclohexane, toluene and N-methylpyrrolidone; the volume ratio of the regeneration liquid to the resin is preferably 0.5 to 100:1, more preferably 2 to 8:1.

[0042] After obtaining the extract containing phosphate ester compounds or the regeneration liquid containing phosphate ester compounds, the present invention distills the extract containing phosphate ester compounds or the regeneration liquid containing phosphate ester compounds to obtain phosphate ester compounds. In the present invention, the pressure during distillation is preferably 10Pa to 500Pa, and the temperature is preferably 50 to 100°C.

[0043] The method for recovering tris(2-cyanoethyl)phosphite and tris(2-cyanoethyl)phosphate from wastewater provided by the present invention includes adding electrolyte to wastewater and then recovering tris(2-cyanoethyl)phosphite and tris(2-cyanoethyl)phosphate by extraction or adsorption, thereby greatly increasing the recovery amount and reusing them for production, thereby effectively improving product revenue and reducing the pollution of wastewater to the environment.

[0044] like Figure 1 As shown, the present invention provides a device for recovering phosphate compounds in wastewater described in any one of the above items, comprising:

[0045] Reactor 1, pH regulating kettle 2, extraction device and molecular distillation device 6;

[0046] The discharge port of the preparation kettle 1 is connected to the feed port of the pH adjusting kettle 2; the discharge port of the pH adjusting kettle 2 is connected to the material feed port of the extraction device; the extractant discharge port of the molecular distillation device 6 is connected to the extractant feed port of the extraction device; the extractant discharge port of the extraction device is connected to the feed port of the molecular distillation device 6.

[0047] In the present invention, in order to fully extract, it is preferred to use a multi-stage extraction method for extraction.

[0048] In the present invention, the extraction device comprises a first extraction device 3, a second extraction device 4 and a third extraction device 5;

[0049] The discharge port of the preparation kettle 1 is connected to the feed port of the pH adjusting kettle 2; the discharge port of the pH adjusting kettle 2 is connected to the material feed port of the first extraction device 3; the wastewater discharge port of the first extraction device 3 is connected to the material feed port of the second extraction device 4; the wastewater discharge port of the second extraction device 4 is connected to the material feed port of the third extraction device 5; the extractant discharge port of the molecular distillation device 6 is connected to the extractant feed port of the third extraction device 5; the extractant discharge port of the third extraction device 5 is connected to the extractant feed port of the second extraction device 4; the extractant discharge port of the second extraction device 4 is connected to the extractant feed port of the first extraction device 3; the extractant discharge port of the first extraction device 3 is connected to the feed port of the molecular distillation device 6.

[0050] In the present invention, a multi-stage extraction device is used for extraction. During operation, the mixed material and the extractant enter the multi-stage extraction device in a reverse contact manner. That is, the decomposed wastewater enters from the first extraction device 3, and the extractant enters from the third extraction device 5.

[0051] The present invention provides a device for recovering phosphate compounds in wastewater as described in any one of the above, comprising:

[0052] It includes a preparation kettle 1, a pH adjustment kettle 2, a first adsorption regeneration device 7, a second adsorption regeneration device 8 and a molecular distillation device 6;

[0053] The discharge port of the preparation kettle 1 is connected to the feed port of the pH adjusting kettle 2; the discharge port of the pH adjusting kettle 2 is respectively connected to the feed ports of the first adsorption regeneration device 7 and the second adsorption regeneration device 8; the upper material discharge ports of the first adsorption regeneration device 7 and the second adsorption regeneration device 8 are respectively connected to the feed port of the molecular distillation device 6; the regeneration liquid discharge port of the molecular distillation device 6 is respectively connected to the regeneration liquid feed ports of the first adsorption regeneration device 7 and the second adsorption regeneration device 8.

[0054] The device for recovering phosphate compounds in wastewater provided by the present invention is provided with a first adsorption regeneration device 7 and a second adsorption regeneration device 8. When the first adsorption regeneration device 7 is regenerated, the second adsorption regeneration device 8 is adsorbed, thereby enabling continuous production.

[0055] When working (normal continuous operation), first open the connecting pipeline between the pH adjusting kettle 2 and the first adsorption regeneration device 7, and the connecting pipeline between the molecular distillation device 6 and the second adsorption regeneration device 8. Close the connecting pipeline between the pH adjusting kettle 2 and the second adsorption regeneration device 8, and the connecting pipeline between the molecular distillation device 6 and the first adsorption regeneration device 7. The mixed material transferred from the pH adjusting kettle 2 is transferred to the first adsorption regeneration device 7 to contact with the resin for adsorption, and at the same time, the regeneration liquid separated in the molecular distillation device 6 is transferred to the second adsorption regeneration device 8. The tris(2-oxyethyl) phosphate adsorbed in the resin is separated from the resin and dissolved in the regeneration liquid. The regeneration liquid dissolved with tris(2-cyanoethyl) phosphate is transferred to the molecular distillation device 6 again for molecular distillation, and tris(2-cyanoethyl) phosphate and the regeneration liquid are separated to obtain the product tris(2-cyanoethyl) phosphate. When the resin and regeneration liquid in the first adsorption regeneration device 7 are mixed for regeneration, the connecting pipeline between the pH adjusting kettle 2 and the first adsorption regeneration device 7 is closed, and the connecting pipeline between the pH adjusting kettle 2 and the second adsorption regeneration device 8 is opened, and the mixed material transferred out of the pH adjusting kettle 2 is transferred into the second adsorption regeneration device 8 for adsorption and regeneration.

[0056] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0057] The production equipment in Examples 1 to 4 and Comparative Examples 1 to 2 is as follows Figure 1 shown.

[0058] The production equipment in Example 5 is as follows Figure 2 shown.

[0059] The wastewater used in each embodiment and comparative example is the wastewater generated when producing tris(2-cyanoethyl)phosphate, wherein tris(2-cyanoethyl)phosphate is produced by the method disclosed in CN117164619A. The mass concentration of 3-hydroxypropionitrile in the wastewater is 1.8%, and the mass concentrations of tris(2-cyanoethyl)phosphate, di(2-cyanoethyl)phosphate, and (2-cyanoethyl)phosphate are 1.6%, 2.2%, and 2.6%, respectively.

[0060] Example 1

[0061] The wastewater enters the preparation kettle at a rate of 100g / min, and potassium nitrate enters the preparation kettle at a rate of 20g / min. The outlet temperature of the wastewater from the preparation kettle is controlled at 20°C. The wastewater from the preparation kettle enters the pH adjustment kettle, and NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 7.5.

[0062] The mixed material enters from the material feed port of the first extraction device, and the extractant dichloromethane enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to dichloromethane is 1:10, and the extraction temperature is controlled at 0°C. The content of tris(2-cyanoethyl)phosphate in the wastewater after extraction is 0.0033%, and the content of tris(2-cyanoethyl)phosphate in dichloromethane is 0.133%.

[0063] The extracted dichloromethane was transferred to a molecular distillation device for molecular distillation. The dichloromethane inlet temperature was 90° C., the reaction pressure was 20 Pa, and 1.764 g of tris(2-cyanoethyl)phosphate with a purity of 90.5% was obtained per minute at the bottom of the molecular distillation.

[0064] Example 2

[0065] The wastewater enters the preparation kettle at a rate of 100g / min, and sodium sulfate enters the preparation kettle at a rate of 20g / min. The outlet temperature of the wastewater from the preparation kettle is controlled to be 10°C. The wastewater from the preparation kettle enters the pH adjustment kettle, and NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 9;

[0066] The mixed material enters from the material feed port of the first extraction device, and the extractant toluene enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to toluene is 1:6, and the extraction temperature is controlled at 10°C. The content of tri(2-cyanoethyl) phosphate in the waste water after extraction is 0.054%, and the content of tri(2-cyanoethyl) phosphate in toluene is 0.213%.

[0067] The extracted toluene was transferred to a molecular distillation device for molecular distillation. The toluene inlet temperature was 90° C., the reaction pressure was 10 Pa, and 1.630 g of tris(2-cyanoethyl)phosphate with a purity of 94.2% was obtained per minute at the bottom of the molecular distillation.

[0068] Example 3

[0069] The wastewater enters the preparation kettle at a rate of 100g / min, and sodium chloride enters the preparation kettle at a rate of 5g / min. The outlet temperature of the wastewater from the preparation kettle is controlled to be 20°C. The wastewater from the preparation kettle enters the pH adjustment kettle, and NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 9;

[0070] The mixed material enters from the material feed port of the first extraction device, and the extractant toluene enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to toluene is 1:6, and the extraction temperature is controlled at 20°C. The content of tri(2-cyanoethyl) phosphate in the waste water after extraction is 0.063%, and the content of tri(2-cyanoethyl) phosphate in toluene is 0.243%.

[0071] The extracted toluene was transferred to a molecular distillation device for molecular distillation. The toluene inlet temperature was 50° C., the reaction pressure was 300 Pa, and 1.699 g of tris(2-cyanoethyl)phosphate with a purity of 90.3% was obtained per minute at the bottom of the molecular distillation.

[0072] Example 4

[0073] The wastewater enters the preparation kettle at a rate of 100 g / min, and sodium chloride enters the preparation kettle at a rate of 5 g / min. The temperature of the wastewater outlet of the preparation kettle is controlled to be 20°C. The wastewater from the preparation kettle enters the pH adjustment kettle. NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 7.5. The outlet of the preparation kettle is connected to the wastewater inlet of the multi-stage centrifugal extraction device.

[0074] The mixed material enters from the material feed port of the first extraction device, and the extractant butanone enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to butanone is 1:8, and the extraction temperature is controlled at 20°C. The content of tris(2-cyanoethyl)phosphate in the waste water after extraction is 0.0042%, and the content of tris(2-cyanoethyl)phosphate in toluene is 0.190%.

[0075] The extracted butanone was transferred to a molecular distillation device for molecular distillation. The butanone inlet temperature was 90° C., the reaction pressure was 30 Pa, and 1.773 g of tris(2-cyanoethyl)phosphate with a purity of 90.0% was obtained per minute at the bottom of the molecular distillation.

[0076] Example 5

[0077] The wastewater enters the preparation kettle at a rate of 100 g / min, and potassium nitrate enters the preparation kettle at a rate of 8 g / min. The outlet temperature of the wastewater from the preparation kettle is controlled to be 0°C. The wastewater from the preparation kettle enters the pH adjustment kettle, and NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 7.5.

[0078] The mixed material and the resin are mixed for adsorption, and the volume ratio of the mixed material to the resin is 1:5. The resin adsorbed with tri(2-cyanoethyl)phosphate is mixed with acetonitrile to regenerate the resin. The volume ratio of the resin to acetonitrile is 1:5. Tri(2-cyanoethyl)phosphate is separated from the resin and dissolved in the regeneration liquid, and the content of tri(2-cyanoethyl)phosphate in the regeneration liquid is 0.0638%.

[0079] The regenerated liquid was transferred to a molecular distillation device for molecular distillation. The material inlet temperature was 90° C., the reaction pressure was 20 Pa, and 1.781 g of tris(2-cyanoethyl)phosphate with a purity of 89.6% was obtained per minute at the bottom of the molecular distillation.

[0080] Comparative Example 1

[0081] The wastewater enters the pH adjusting kettle at a speed of 100g / min, and the wastewater temperature is controlled at 20°C. The wastewater from the preparation kettle enters the pH adjusting kettle, and NaOH solution is added dropwise to the pH adjusting kettle to control the pH to 7.5. The outlet of the preparation kettle is connected to the wastewater inlet of the multi-stage centrifugal extraction device;

[0082] The mixed material enters from the material feed port of the first extraction device, and the extractant dichloromethane enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to dichloromethane is 1:10, and the extraction temperature is controlled at 0°C. The content of tris(2-cyanoethyl)phosphate in the wastewater after extraction is 0.0012%, and the content of tris(2-cyanoethyl)phosphate in dichloromethane is 0.148%.

[0083] The extracted dichloromethane was transferred to a molecular distillation device for molecular distillation. The dichloromethane inlet temperature was 90° C., the reaction pressure was 20 Pa, and 1.541 g of tris(2-cyanoethyl)phosphate with a purity of 90.2% was obtained per minute at the bottom of the molecular distillation.

[0084] From the comparison between Example 1 and Comparative Example 1, it can be seen that not adding electrolyte leads to a decrease in the extraction rate of tris(2-cyanoethyl)phosphate, thereby reducing the recovery amount of tris(2-cyanoethyl)phosphate.

[0085] Comparative Example 2

[0086] The wastewater enters the preparation kettle at a rate of 100 g / min, and sodium chloride enters the preparation kettle at a rate of 5 g / min. The temperature of the wastewater outlet of the preparation kettle is controlled to be 80°C. The wastewater from the preparation kettle enters the pH adjustment kettle. NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 9. The outlet of the preparation kettle is connected to the wastewater inlet of the multi-stage centrifugal extraction device;

[0087] The mixed material enters from the material feed port of the first extraction device, and the extractant toluene enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to toluene is 1:6, and the extraction temperature is controlled at 25°C. The content of tri(2-cyanoethyl) phosphate in the waste water after extraction is 0.0027%, and the content of tri(2-cyanoethyl) phosphate in toluene is 0.079%.

[0088] The extracted toluene was transferred to a molecular distillation device for molecular distillation. The toluene inlet temperature was 50° C., the reaction pressure was 300 Pa, and 0.58 g of tris(2-cyanoethyl)phosphate with a purity of 82.7% was obtained per minute at the bottom of the molecular distillation.

[0089] From the comparison between Example 3 and Comparative Example 2, it can be seen that the wastewater temperature is too high, which causes some tris(2-cyanoethyl)phosphate to decompose, thereby affecting the recovery amount and purity of tris(2-cyanoethyl)phosphate.

[0090] Comparative Example 3

[0091] The wastewater enters the preparation kettle at a rate of 100 g / min, and sodium chloride enters the preparation kettle at a rate of 5 g / min. The temperature of the wastewater outlet of the preparation kettle is controlled to be 20°C. The wastewater from the preparation kettle enters the pH adjustment kettle. NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 7. The outlet of the preparation kettle is connected to the wastewater inlet of the multi-stage centrifugal extraction device;

[0092] The mixed material enters from the material feed port of the first extraction device, and the extractant butanone enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to butanone is 1:8, and the extraction temperature is controlled at 20°C. The content of tris(2-cyanoethyl)phosphate in the wastewater after extraction is 0.0087%, and the content of tris(2-cyanoethyl)phosphate in butanone is 0.189%.

[0093] The extracted butanone was transferred to a molecular distillation device for molecular distillation. The butanone inlet temperature was 90° C., the reaction pressure was 30 Pa, and 2.497 g of tris(2-cyanoethyl)phosphate with a purity of 63.7% was obtained per minute at the bottom of the molecular distillation.

[0094] From the comparison between Example 4 and Comparative Example 3, it can be seen that as the pH decreases, some by-products change from ionic state to molecular state, are easily adsorbed by the extractant, and the product purity is low.

[0095] Comparative Example 4

[0096] The wastewater enters the preparation kettle at a rate of 100 g / min, and sodium sulfate enters the preparation kettle at a rate of 20 g / min. The temperature of the wastewater outlet of the preparation kettle is controlled to be 10°C. The wastewater from the preparation kettle enters the pH adjustment kettle, and NaOH solution is added dropwise to the pH adjustment kettle to control the pH to 12. The outlet of the preparation kettle is connected to the wastewater inlet of the multi-stage centrifugal extraction device;

[0097] The mixed material enters from the material feed port of the first extraction device, and the extractant toluene enters from the extractant feed port of the third extraction device. The mass ratio of the mixed material to toluene is 1:6, and the extraction temperature is controlled at 10°C. The content of tri(2-cyanoethyl) phosphate in the waste water after extraction is 0.0016%, and the content of tri(2-cyanoethyl) phosphate in toluene is 0.0264%.

[0098] The extracted toluene was transferred to a molecular distillation device for molecular distillation. The toluene inlet temperature was 90° C., the reaction pressure was 10 Pa, and 0.16 g of tris(2-cyanoethyl)phosphate with a purity of 98.3% was obtained per minute at the bottom of the molecular distillation.

[0099] From the comparison between Example 2 and Comparative Example 4, it can be seen that excessive addition of NaOH solution and high pH result in decomposition of most of the tris(2-cyanoethyl)phosphate, thereby affecting the recovery of the tris(2-cyanoethyl)phosphate.

[0100] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for recovering phosphate compounds in wastewater, characterized in that: The steps include: 1) mixing the wastewater and the electrolyte, adjusting the pH to 7.5-9, and obtaining a mixed material; 2) extracting or adsorbing and regenerating the obtained mixed material to obtain an extract containing phosphate ester compounds or a regenerated liquid containing phosphate ester compounds; 3) distilling the extract containing the phosphate ester compound or the regenerated liquid containing the phosphate ester compound to obtain the phosphate ester compound; The phosphate compound is tris(2-cyanoethyl)phosphite or tris(2-cyanoethyl)phosphate.

2. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: The wastewater in step 1) is wastewater generated by preparing tris(2-cyanoethyl)phosphate or tris(2-cyanoethyl)phosphite; the temperature of the wastewater is controlled at 0-25°C.

3. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: The electrolyte in step 1) includes one or more of sodium chloride, potassium chloride, potassium nitrate, sodium nitrate, potassium sulfate and sodium sulfate.

4. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: The amount of electrolyte added in step 1) is 1% to 50% of the mass of the wastewater.

5. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: In step 1), an alkaline solution is used to adjust the pH, and the alkaline solution includes one or more of a sodium hydroxide aqueous solution, a potassium hydroxide solution, an ammonia solution, a sodium carbonate solution, a potassium carbonate solution, a sodium bicarbonate solution and a potassium bicarbonate solution.

6. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: The extractant used for extraction in step 2) includes one or more of dichloromethane, chloroform, toluene, butanone and methyl isobutyl ketone.

7. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: The temperature during extraction in step 2) is 0-100° C., and the mass ratio of wastewater to extractant is 1:0.1-100.

8. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: In step 2), resin is used for adsorption, and after the resin for adsorbing phosphate compounds is obtained, it is regenerated using regeneration liquid.

9. The method for recovering phosphate compounds in waste water according to claim 8, characterized in that: The regeneration liquid includes one or more of acetonitrile, acetone, cyclohexane, toluene and N-methylpyrrolidone; the volume ratio of the regeneration liquid to the resin is 0.5-100:

1.

10. The method for recovering phosphate compounds in wastewater according to claim 1, characterized in that: The pressure during distillation in step 3) is 10Pa-500Pa and the temperature is 50-100°C.

11. A device for recovering phosphate compounds in waste water according to any one of claims 1 to 10, characterized in that: include: Reactor, pH adjustment kettle, extraction device and molecular distillation device; The discharge port of the preparation kettle is connected to the feed port of the pH adjusting kettle; the discharge port of the pH adjusting kettle is connected to the material feed port of the extraction device; the extractant discharge port of the molecular distillation device is connected to the extractant feed port of the extraction device; the extractant discharge port of the extraction device is connected to the feed port of the molecular distillation device.

12. The device according to claim 11, characterized in that The extraction device comprises a first extraction device, a second extraction device and a third extraction device; The discharge port of the preparation kettle is connected to the feed port of the pH adjusting kettle; the discharge port of the pH adjusting kettle is connected to the material feed port of the first extraction device; the wastewater discharge port of the first extraction device is connected to the material feed port of the second extraction device; the wastewater discharge port of the second extraction device is connected to the material feed port of the third extraction device; the extractant discharge port of the molecular distillation device is connected to the extractant feed port of the third extraction device; the extractant discharge port of the third extraction device is connected to the extractant feed port of the second extraction device; the extractant discharge port of the second extraction device is connected to the extractant feed port of the first extraction device; the extractant discharge port of the first extraction device is connected to the feed port of the molecular distillation device.

13. A device for recovering phosphate compounds in waste water according to any one of claims 1 to 10, characterized in that: include: Preparation kettle, pH adjustment kettle, first adsorption regeneration device, second adsorption regeneration device and molecular distillation device; The discharge port of the preparation kettle is connected to the feed port of the pH adjusting kettle; the discharge port of the pH adjusting kettle is respectively connected to the feed ports of the first adsorption regeneration device and the second adsorption regeneration device; the upper material discharge ports of the first adsorption regeneration device and the second adsorption regeneration device are respectively connected to the feed port of the molecular distillation device; the regeneration liquid discharge port of the molecular distillation device is respectively connected to the regeneration liquid feed ports of the first adsorption regeneration device and the second adsorption regeneration device.

Images