A method for treating wastewater from production of a flame retardant BDP

Abstract

The present application belongs to the technical field of waste water treatment of flame retardant, and discloses a kind of processing method of flame retardant BDP waste water.It is specifically disclosed that (1) first, carbon dioxide is introduced into BDP waste water to generate neutralization reaction; (2) then, BDP waste water is evaporated and concentrated to obtain evaporated condensate water and evaporation mother liquor, and the evaporated condensate water is discharged after reducing COD; (3) the evaporation mother liquor is cooled and then excess carbon dioxide is introduced to generate sodium bicarbonate precipitation; (4) after solid-liquid separation, wet salt and phenol-containing waste water are obtained, the wet salt is dried to obtain sodium bicarbonate, and the phenol-containing waste water enters the rectification process to prepare high-purity phenol. The phenol resource is realized, and sodium bicarbonate is produced as a byproduct. The evaporated condensate water is discharged after biochemical degradation, with COD lower than 500 mg / L, which meets the pipe discharge standard, and solves the problems of BDP waste water pollution and solid waste generated during the treatment process.

Description

A method for treating wastewater from the production of flame retardant BDP Technical Field

[0001] This invention relates to the field of flame retardant wastewater technology, and more specifically to an environmentally friendly treatment method for flame retardant BDP (bisphenol A-bis(diphenyl phosphate)) wastewater. Background Technology

[0002] Bisphenol A-bis(diphenyl phosphate), abbreviated as BDP, is a halogen-free organophosphorus flame retardant, a type of environmentally friendly flame retardant that is halogen-free, low-smoke, and low-toxicity. BDP production wastewater mainly consists of sodium phenolate and sodium hydroxide, and also contains other low-fraction organic compounds. The usual treatment method is direct evaporation of the wastewater to produce sodium phenolate. However, due to the high COD in the wastewater, the resulting sodium phenolate contains a large amount of viscous substances, resulting in low product purity, and the remaining wastewater causes secondary pollution.

[0003] Therefore, how to realize the resource utilization of phenol, reduce the COD of BDP wastewater, and solve the problems of high pollution and solid waste generation in the treatment process of BDP wastewater are urgent issues that need to be addressed by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a method for treating wastewater from the production of flame retardant BDP. Targeting the characteristics of the wastewater, a process technology of "carbon dioxide neutralization - evaporation and concentration - cooling - COD removal by condensate oxidation - preparation of phenol from hydrous phenol" is proposed. This achieves the resource utilization of phenol, while simultaneously producing sodium bicarbonate as a byproduct. After biochemical degradation, the COD of the evaporation condensate is below the municipal discharge standard of 500 mg / L, solving the problems of high pollution from BDP wastewater and the generation of solid waste during the treatment process.

[0005] To achieve the above objectives, the present invention provides a method for treating wastewater from the production of flame retardant BDP, comprising the following steps:

[0006] (1) First, carbon dioxide is introduced into the BDP wastewater to cause a neutralization reaction and reduce the concentration of sodium phenolate in the wastewater;

[0007] (2) The BDP wastewater is then evaporated and concentrated to obtain evaporated condensate and evaporated mother liquor. The evaporated condensate is degraded by a biochemical module to reduce COD before being discharged into the sewer system.

[0008] (3) After the mother liquor is cooled, excess carbon dioxide is introduced. When there is excess carbon dioxide, sodium bicarbonate with low solubility is precipitated.

[0009] (4) After solid-liquid separation, wet salt and liquid phase are obtained. The wet salt is dried to obtain sodium bicarbonate. After oil-water separation of the liquid phase, phenol-containing wastewater is obtained and enters the distillation process to prepare high-purity phenol.

[0010] Preferably, in step (1), the endpoint pH value of the neutralization reaction is 10-11.

[0011] The beneficial effects of adopting the above technical solution are as follows: According to the principle of neutralization reaction, the carbon dioxide introduced into the wastewater first reacts with sodium hydroxide to produce sodium carbonate. The excess carbon dioxide continues to react with sodium phenolate to produce phenol and sodium carbonate. At this time, the pH value of the solution needs to be controlled at 10-11. If the pH value is greater than 11, too much sodium phenolate will remain, and it will precipitate during the evaporation process. If the pH value is less than 10, there is excess carbon dioxide. The excess carbon dioxide reacts with sodium carbonate to produce sodium bicarbonate. During the evaporation process, sodium bicarbonate decomposes into sodium carbonate and releases carbon dioxide, which affects the evaporation process.

[0012] Furthermore, there are no restrictions on the flow rate and speed of carbon dioxide introduction; a faster flow results in a faster reaction, and a slower flow results in a slower reaction.

[0013] Preferably, in step (2), the evaporation and concentration temperature is ≥98℃, and the amount of water evaporated is 30%-40% of the mass of BDP wastewater before evaporation.

[0014] The beneficial effects of adopting the above technical solution are as follows: After the evaporation process, the water content of the mixed solution of phenol, sodium phenolate, and sodium carbonate is 30%-40% of the mass of the solution before evaporation. If too much water is evaporated, the sodium carbonate concentration will be too high, causing sodium carbonate to precipitate; if too little water is evaporated, the sodium carbonate concentration will be too low, which is not conducive to the subsequent precipitation of sodium bicarbonate.

[0015] Preferably, in step (2), tap water can be used for condensation, and the water temperature of the evaporated condensate is <35℃.

[0016] Preferably, in step (2), the degradation of the biochemical module specifically involves:

[0017] Biological wastewater treatment is a common and effective method for reducing chemical oxygen demand (COD). The principle is that microorganisms (mainly bacteria and fungi) in the wastewater utilize organic matter as a carbon and energy source for growth, reproduction, and metabolic activities. These microorganisms oxidize and decompose organic matter into carbon dioxide, water, and new cellular material, thereby reducing the COD in the wastewater.

[0018] The beneficial effects of using the biochemical module are:

[0019] Using biochemical modules to reduce COD in wastewater offers several significant advantages. Firstly, it boasts low operating costs, primarily in terms of energy and reagent costs. Compared to other treatment methods, it consumes significantly less energy; and in terms of reagent costs, it eliminates the need for substantial investments in various chemical agents. Secondly, biochemical modules are environmentally friendly. They rely on naturally occurring microorganisms and their metabolic mechanisms to function, ensuring the entire treatment process does not generate secondary pollution and is highly conducive to maintaining a healthy ecosystem cycle, aligning with the principles of green environmental protection and sustainable development.

[0020] While biological treatment offers numerous advantages, it also imposes strict requirements on the salinity of wastewater. Typically, excessively high salinity in wastewater can severely inhibit or even kill the microorganisms involved in the biological treatment process. Microorganisms such as bacteria and fungi experience osmotic pressure imbalances within their cells in high-salt environments, leading to cell dehydration and affecting their normal physiological and metabolic activities, potentially ultimately causing their death. Therefore, to ensure the smooth and effective implementation of the biological treatment process, the total dissolved solids (TDS) content in the wastewater is generally required to be less than 8000 mg / L.

[0021] Preferably, in step (3), the final pH value of the mother liquor after evaporating excess carbon dioxide is 8.0.

[0022] The beneficial effects of adopting the above technical solution are as follows: Since water and phenol undergo azeotropy, the condensate contains a small amount of phenol and no inorganic salts. It can be treated biochemically to reduce COD before being discharged into the pipeline. After the mother liquor is cooled, carbon dioxide is continuously introduced. When the pH value of the feed liquid drops to 8.0, the introduction of carbon dioxide is stopped. Carbon dioxide reacts with sodium carbonate to generate sodium bicarbonate with low solubility and precipitates out to obtain wet sodium bicarbonate.

[0023] Preferably, the purity of the carbon dioxide is the same as that of industrial-grade carbon dioxide, with a purity ≥ 99%.

[0024] Preferably, in step (4), the specific steps of the distillation process include:

[0025] Phenolic wastewater was extracted using an extractant to obtain an organic phase and an aqueous phase;

[0026] The organic phase enters the desolventizing tower to obtain the extractant and phenol material. The extractant is returned to the extraction process. The phenol material is refined to obtain refined phenol and heavy components from the bottom of the tower. The heavy components from the bottom of the tower are returned to step (1).

[0027] The aqueous phase enters the stripping tower to obtain the top gas phase and the bottom wastewater. The top gas phase is returned to the extraction process, and the bottom wastewater is returned to step (1).

[0028] Preferably, since water and phenol are azeotropic, toluene needs to be added as an extractant during the distillation process.

[0029] Preferably, the amount of toluene added is 5%-10% of the mass of the phenol-containing wastewater.

[0030] Preferably, the purity of the high-purity phenol is ≥99.5%.

[0031] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] This invention creatively proposes a process technology for treating BDP wastewater: "carbon dioxide neutralization—evaporation and concentration—cooling—condensate oxidation to remove chemical oxygen demand (COD)—hydrous phenol to produce phenol." This method not only successfully achieves the resource-based extraction of phenol but also produces sodium bicarbonate as a valuable byproduct. Simultaneously, after biochemical degradation treatment, the COD of the evaporation condensate reaches below 500 mg / L, meeting the municipal emission standard. This achievement effectively solves the thorny problems of high pollution levels in BDP wastewater and the generation of solid waste during its treatment. This method uses carbon dioxide as a raw material, which is widely available and inexpensive. Furthermore, the entire process helps address related issues in carbon cycling, offering multiple benefits and demonstrating significant environmental and economic advantages. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0034] Figure 1 is a schematic diagram of the BDP wastewater treatment process.

[0035] Figure 2 is a schematic diagram of the refining process of aqueous phenol. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The water quality parameters of BDP wastewater are shown in the table below.

[0038] The values ​​for the following items are: pH, COD (mg / L), sodium phenolate (g / L), and sodium hydroxide (g / L): >1419000043.8750.09 surface

[0039] The distillation process flow is shown in Figure 2:

[0040] Phenolic wastewater enters the bottom of the extraction tower. Toluene, the extractant, enters the top of the extraction tower via the extractant buffer tank for extraction. The organic phase collected from the top of the extraction tower enters the organic phase buffer tank, while the aqueous phase collected from the bottom of the extraction tower enters the aqueous phase buffer tank. The organic phase enters the middle of the desolventizing tower. The organic phase at the top of the desolventizing tower is collected back to the extractant buffer tank for recycling. The material at the bottom of the desolventizing tower enters the refining tower to purify the phenol. Phenol product is obtained at the top of the refining tower, and the heavy components at the bottom of the tower are discharged from the device to the preceding neutralization process. The aqueous phase in the aqueous phase buffer tank enters the top of the stripping tower, and the vapor phase at the top of the stripping tower is returned to the extractant buffer tank for recycling. The wastewater from the bottom of the stripping tower is discharged from the device and returned to the system to the preceding neutralization process.

[0041] Example 1

[0042] The composition of the BDP wastewater is shown in the table above. 99% pure carbon dioxide gas was introduced until the solution pH dropped to 10.5, at which point the carbon dioxide introduction was stopped. The wastewater was heated and evaporated at 99℃. The mass of the condensate was controlled, and evaporation was stopped when the condensate volume reached 33% of the original solution mass. The COD in the condensate was 1800 mg / L, and the phenol content was 0.8 g / L. The condensate underwent biological treatment before being discharged. After the concentrated evaporation liquid was cooled to room temperature (25℃), carbon dioxide was introduced again until the pH reached 8.0, at which point the carbon dioxide introduction was stopped. The liquid and solid were then separated to obtain wet sodium bicarbonate, which was dried to obtain solid sodium bicarbonate. The liquid phase from the solid-liquid separation is divided into layers. The upper layer is returned to be mixed with the raw materials and enters the neutralization process; the lower layer is sent to the phenol refining process, as shown in Figure 2. The extractant is toluene, and the replenishment amount is 7.5% of the mass of the wastewater entering the extraction tower. The wastewater entering the distillation process contains 17.5% phenol, 3.5% sodium bicarbonate, and 79% water. The phenol obtained from the distillation has a purity of ≥99.5%. The mother liquor from the stripping tower and the refining tower is returned to the neutralization process.

[0043] Example 2

[0044] The composition of the BDP wastewater is shown in the table above. 99% pure carbon dioxide gas was introduced until the solution pH dropped to 10.8, at which point the carbon dioxide introduction was stopped. The wastewater was heated and evaporated at 100℃. The mass of the condensate was controlled, and evaporation was stopped when the condensate volume reached 35% of the original solution mass. The COD in the condensate was 1750 mg / L, and the phenol content was 0.77 g / L. The condensate underwent biological treatment before being discharged. After the concentrated evaporation liquid was cooled to room temperature (25℃), carbon dioxide was introduced again until the pH reached 8.0, at which point the carbon dioxide introduction was stopped. The solid and liquid were then separated to obtain wet sodium bicarbonate, which was dried to obtain solid sodium bicarbonate. The liquid phase from the solid-liquid separation is divided into layers. The upper layer is returned to be mixed with the raw materials and enters the neutralization process; the lower layer is sent to the phenol refining process, as shown in Figure 2. The extractant is toluene, and the replenishment amount is 5% of the mass of the wastewater entering the extraction tower. The wastewater entering the distillation process contains 18.1% phenol, 3.7% sodium bicarbonate, and 78.2% water. The phenol obtained from the distillation has a purity of ≥99.5%. The mother liquor from the stripping tower and the refining tower is returned to the neutralization process.

[0045] Example 3

[0046] The composition of the BDP wastewater is shown in the table above. 99% pure carbon dioxide gas was introduced until the solution pH dropped to 10, at which point the carbon dioxide introduction was stopped. The wastewater was heated and evaporated at 98℃. The mass of the condensate was controlled, and evaporation was stopped when the condensate volume reached 40% of the original solution mass. The COD in the condensate was 1820 mg / L, and the phenol content was 0.82 g / L. The condensate underwent biological treatment before being discharged. After the concentrated evaporation liquid was cooled to room temperature (25℃), carbon dioxide was introduced again until the pH reached 8.0, at which point the carbon dioxide introduction was stopped. The liquid and solid were then separated to obtain wet sodium bicarbonate, which was dried to obtain solid sodium bicarbonate. The liquid phase from the solid-liquid separation is divided into layers. The upper layer is returned to be mixed with the raw materials and enters the neutralization process; the lower layer is sent to the phenol refining process, as shown in Figure 2. The extractant is toluene, and the replenishment amount is 5% of the mass of the wastewater entering the extraction tower. The wastewater entering the distillation process contains 19.0% phenol, 3.5% sodium bicarbonate, and 77.5% water. The phenol obtained from the distillation has a purity of ≥99.5%. The mother liquor from the stripping tower and the refining tower is returned to the neutralization process.

[0047] Comparative Example 1

[0048] The composition of BDP wastewater is shown in the table above. A 1.4L wastewater sample was taken, and the pH was adjusted to 8.0 with 20% concentrated hydrochloric acid. The wastewater was then directly evaporated at 110℃, yielding 1000g of condensate. The condensate had a COD of 80000mg / L and a conductivity of 60μs / cm. A viscous mother liquor and a mixture of miscellaneous salts were also obtained. The condensate, with its low conductivity, can be discharged into the sewer system after biological treatment. However, the resulting miscellaneous salts and viscous mother liquor are difficult to separate, posing a significant environmental hazard and requiring expensive hazardous waste treatment.

[0049] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for treating wastewater from the production of flame retardant BDP, characterized in that, Includes the following steps: (1) First, carbon dioxide is introduced into the BDP wastewater to cause a neutralization reaction. The final pH value of the neutralization reaction is 10-11. (2) The BDP wastewater is then evaporated and concentrated to obtain evaporation condensate and evaporation mother liquor. The evaporation condensate is discharged after reducing COD. (3) After the evaporation mother liquor is cooled, excess carbon dioxide is introduced to generate sodium bicarbonate. (4) After solid-liquid separation, wet salt and liquid phase are obtained. The wet salt is dried to obtain sodium bicarbonate. After oil-water separation of the liquid phase, phenol-containing wastewater is obtained and enters the distillation process to prepare high-purity phenol.

2. The method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that, In step (2), the evaporation and concentration temperature is ≥98℃, and the amount of water evaporated is 30%-40% of the mass of BDP wastewater before evaporation.

3. The method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that, In step (2), the temperature of the evaporated condensate is <35℃.

4. The method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that, In step (3), the final pH value of the mother liquor after evaporating excess carbon dioxide is 8.

0.

5. The method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that, The purity of the carbon dioxide is ≥99%.

6. The method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that, In step (4), the specific steps of the distillation process include: extracting phenol-containing wastewater with an extractant to obtain an organic phase and an aqueous phase; the organic phase enters a desolventizing tower to obtain an extractant and phenol material; the extractant is returned to the extraction process; the phenol material is refined to obtain refined phenol and a bottom heavy component; the bottom heavy component is returned to step (1); the aqueous phase enters a stripping tower to obtain a top gas phase and bottom wastewater; the top gas phase is returned to the extraction process; and the bottom wastewater is returned to step (1).

7. The method for treating wastewater from the production of flame retardant BDP according to claim 6, characterized in that, The extractant is toluene.

8. The method for treating wastewater from the production of flame retardant BDP according to claim 7, characterized in that, The amount of toluene added is 5%-10% of the mass of the phenol-containing wastewater.

9. A method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that, The purity of the high-purity phenol is ≥99.5%.

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