Fire retardant BDP production wastewater treatment method

Abstract

The invention belongs to the technical field of flame retardant wastewater treatment, and discloses a treatment method of flame retardant BDP wastewater. The method specifically comprises the following steps: (1) firstly, introducing carbon dioxide into the BDP wastewater, and carrying out a neutralization reaction; (2) evaporating and concentrating the BDP wastewater to obtain evaporation condensate water and evaporation mother liquor, and discharging the evaporation condensate water after COD (Chemical Oxygen Demand) is reduced; (3) cooling the evaporation mother liquor, introducing excessive carbon dioxide, and separating out generated sodium bicarbonate; and (4) carrying out solid-liquid separation to obtain wet salt and phenol-containing wastewater, drying the wet salt to obtain sodium bicarbonate, and rectifying the phenol-containing wastewater to prepare high-purity phenol. According to the method, phenol is recycled, meanwhile, sodium bicarbonate is a byproduct, after evaporation condensate water is subjected to biochemical degradation, the COD is lower than the nanotube emission standard of 500 mg / L, and the problems that BDP wastewater is large in pollution and solid waste is generated in the treatment process are solved.

Description

Technical Field

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

[0002] Bisphenol A-bis(diphenyl phosphate), referred to as BDP, is a halogen-free organophosphorus flame retardant, a type of halogen-free, low-smoke, low-toxic environmentally friendly flame retardant. The wastewater produced by BDP is mainly composed of sodium phenolate and sodium hydroxide, and also contains other low-fraction organic matter. The usual treatment method is to directly evaporate the wastewater to prepare sodium phenolate. Due to the high COD in the wastewater, the obtained sodium phenolate contains a large amount of viscous matter, the product purity is not high, and the remaining wastewater produces secondary pollution.

[0003] Therefore, how to realize the resource utilization of phenol, reduce the COD of BDP wastewater, and solve the problem of severe BDP wastewater pollution and solid waste generation during the treatment process are issues that technicians in this field urgently need to solve. Summary of the invention

[0004] In view of this, the present invention provides a method for treating wastewater produced by flame retardant BDP. According to the characteristics of the wastewater, a process technology of "neutralization of carbon dioxide - evaporation and concentration - cooling - oxidation of condensed water to remove COD - preparation of phenol from aqueous phenol" is proposed, which realizes the resource utilization of phenol and produces sodium bicarbonate as a by-product. After biochemical degradation, the COD of the evaporated condensed water is lower than the nanotube emission standard of 500 mg / L, which solves the problem of severe pollution of BDP wastewater and generation of solid waste in the treatment process.

[0005] In order to achieve the above object, the present invention provides a method for treating wastewater produced by 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 evaporated and concentrated to obtain evaporated condensed water and evaporated mother liquor, and the evaporated condensed water is degraded by a biochemical module to reduce COD before being discharged into a pipe;

[0008] (3) after the mother liquor is cooled, excess carbon dioxide is introduced, and the excess carbon dioxide generates sodium bicarbonate with low solubility and precipitates;

[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, which 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 technical scheme are as follows: according to the principle of neutralization reaction, the carbon dioxide introduced into the wastewater first reacts with sodium hydroxide to obtain sodium carbonate, and the excess carbon dioxide continues to react with sodium phenolate to generate 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 will precipitate during the evaporation process; if the pH value is less than 10, there will be excess carbon dioxide, and the excess carbon dioxide will react with sodium carbonate to generate sodium bicarbonate. During the evaporation process, the sodium bicarbonate will decompose into sodium carbonate and release carbon dioxide, which will affect the evaporation process.

[0012] Furthermore, there is no limit to the flow rate and speed of introducing carbon dioxide. The faster it is introduced, the faster the reaction is; the slower it is introduced, the slower the reaction is.

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

[0014] The beneficial effects of the above technical solution are as follows: after the mixed solution of phenol, sodium phenolate and sodium carbonate undergoes an evaporation process, the amount of evaporated water is 30%-40% of the mass of the liquid before evaporation. If the amount of evaporated water is too much, the sodium carbonate concentration is too high, resulting in the precipitation of sodium carbonate; if the amount of evaporated water is too little, the sodium carbonate concentration is 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 condensed water is <35°C.

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

[0017] Biochemical treatment of wastewater is a common and effective method to reduce chemical oxygen demand (COD). The principle is that microorganisms (mainly bacteria, fungi, etc.) in wastewater use organic matter in wastewater as a carbon source and energy source for growth, reproduction and metabolic activities. Microorganisms oxidize and decompose organic matter into carbon dioxide, water and new cell substances, thereby reducing COD in wastewater.

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

[0019] The use of biochemical modules to reduce wastewater COD has many significant advantages. First, the operating cost is low, which is mainly reflected in two aspects: energy consumption and reagent costs. In terms of energy consumption, it consumes less energy than other treatment methods; and in terms of reagent costs, there is no need to invest a lot of money to purchase various chemical agents. Second, the biochemical module is environmentally friendly. It relies on naturally existing microorganisms and their metabolic mechanisms in nature to play a role. The entire treatment process will not produce secondary pollution, and it is very beneficial for the ecosystem to maintain a good circulation state, which is in line with the concept of green environmental protection and sustainable development.

[0020] Although biochemical treatment has many advantages, it also has relatively strict requirements on the salt content in wastewater. Generally speaking, excessive salt content in wastewater will have a serious inhibitory or even fatal effect on the microorganisms involved in biochemical treatment. For example, in a high-salt environment, the osmotic pressure in the cells of bacteria, fungi and other microorganisms will be unbalanced, causing cell dehydration, which in turn affects the normal physiological metabolic activities of the microorganisms and may eventually cause their death. Therefore, in order to ensure that the biochemical treatment process can be carried out smoothly and effectively, the total dissolved solids (TDS) content in the wastewater is generally required to be less than 8000mg / L.

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

[0022] The beneficial effects of adopting the above technical scheme are as follows: due to the azeotropic formation of water and phenol, the condensed water contains a small amount of phenol and no inorganic salts, and can be discharged through a pipe after biochemical treatment to reduce COD; after the evaporation mother liquor is cooled, carbon dioxide is continued to be introduced, and the introduction of carbon dioxide is stopped when the pH value of the feed liquid is reduced to 8.0, and the carbon dioxide reacts with sodium carbonate to generate sodium bicarbonate with a smaller solubility, which is precipitated to obtain wet salt sodium bicarbonate.

[0023] Preferably, the purity of the carbon dioxide is the purity of industrial grade carbon dioxide, which is ≥ 99%.

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

[0025] The phenol-containing wastewater is extracted with an extractant to obtain an organic phase and an aqueous phase;

[0026] The organic phase enters a desolventizing tower to obtain an extractant and a phenol material, the extractant is returned to the extraction step, the phenol material is refined to obtain refined phenol and a heavy component in the bottom of the tower, and the heavy component in the bottom of the tower is returned to step (1);

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

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

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

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

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

[0032] The present invention creatively proposes the process technology of "carbon dioxide neutralization - evaporation concentration - cooling - condensed water oxidation to remove chemical oxygen demand (COD) - aqueous phenol to prepare phenol" to treat BDP wastewater. This method not only successfully realizes the resource extraction of phenol, but also produces a valuable product, sodium bicarbonate. At the same time, after the evaporated condensed water is treated with biochemical degradation, its chemical oxygen demand (COD) can reach the nanopipe emission standard of less than 500 mg / L. This achievement effectively solves the thorny problem of high pollution level of BDP wastewater and the generation of solid waste in the process of treating such wastewater. This method uses carbon dioxide as raw material, which has a wide source and low price, and in the entire process of process implementation, it can also help solve related problems in carbon cycle, which can be said to kill multiple birds with one stone and has significant environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0034] Figure 1 Schematic diagram of the BDP wastewater treatment process flow.

[0035] Figure 2 Schematic diagram of the aqueous phenol refining process. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0037] The water quality parameters of BDP wastewater are as follows

[0038] project pH COD(mg / L) Sodium phenolate (g / L) Sodium hydroxide (g / L) Numeric >14 190000 43.87 50.09

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

[0040] Phenol-containing wastewater enters the bottom of the extraction tower, and the extractant toluene enters the top of the extraction tower through the extractant buffer tank for extraction operation. The organic phase is extracted from the top of the extraction tower and enters the organic phase buffer tank. The water phase is extracted from the bottom of the extraction tower and enters the water phase buffer tank. The organic phase enters the middle of the desolventizing tower. The organic phase at the top of the desolventizing tower is extracted to the extractant buffer tank for recycling. The materials in the bottom of the desolventizing tower enter the refining tower to refine phenol. The phenol product is obtained at the top of the refining tower, and the heavy component discharge device in the bottom of the tower goes to the previous neutralization process; the water phase in the water phase buffer tank enters the top of the stripping tower, and the gas phase at the top of the stripping tower returns to the extractant buffer tank for recycling. The wastewater from the stripping tower bottom is discharged from the device and returned to the system to go to the previous neutralization process.

[0041] Example 1

[0042] The water quality composition of BDP wastewater is shown in the table above. Carbon dioxide gas with a purity of 99% is introduced until the pH of the solution drops to 10.5, then the introduction of carbon dioxide is stopped. The wastewater is heated and evaporated at a temperature of 99°C. The quality of the evaporated condensed water is controlled and the evaporation is stopped when the amount of condensed water is 33% of the mass of the original solution. The COD in the condensed water is 1800 mg / L and the phenol content is 0.8 g / L. The condensed water is discharged after biochemical treatment. After the evaporated concentrated liquid is cooled to room temperature of 25°C, carbon dioxide is continued to be introduced until the pH reaches 8.0, then the introduction of carbon dioxide is stopped and the liquid is separated into solid-liquid separation to obtain sodium bicarbonate wet salt, which is then dried to obtain solid sodium bicarbonate. The liquid phase of the solid-liquid separation is layered, and the upper layer is returned to mix with the raw material and enter the neutralization process; the lower layer goes to the phenol refining process, such as Figure 2 As shown, the extractant is toluene, and the supplementary amount is 7.5% of the mass of the waste water entering the extraction tower; the waste water entering the distillation process has a phenol content of 17.5%, a sodium bicarbonate content of 3.5%, and a water content of 79%; the purity of the phenol obtained by distillation is ≥99.5%, and the mother liquor of the stripping tower and the refining tower is returned to the neutralization process.

[0043] Example 2

[0044] The water quality composition of BDP wastewater is shown in the table above. Carbon dioxide gas with a purity of 99% is introduced until the pH of the solution drops to 10.8, then the introduction of carbon dioxide is stopped. The wastewater is heated and evaporated at an evaporation temperature of 100°C. The quality of the evaporated condensed water is controlled. Evaporation is stopped when the amount of condensed water is 35% of the mass of the original solution. The COD in the condensed water is 1750 mg / L and the phenol content is 0.77 g / L. The condensed water is discharged after biochemical treatment. After the evaporated concentrated liquid is cooled to room temperature of 25°C, carbon dioxide is continued to be introduced until the pH reaches 8.0, then the introduction of carbon dioxide is stopped, and the feed liquid is separated into solid-liquid separation to obtain sodium bicarbonate wet salt, which is then dried to obtain solid sodium bicarbonate. The liquid phase of the solid-liquid separation is layered, and the upper layer is returned to mix with the raw material and enter the neutralization process; the lower layer goes to the phenol refining process, such as Figure 2As shown, the extractant is toluene, and the supplementary amount is 5% of the mass of the waste water entering the extraction tower; the waste water entering the distillation process has a phenol content of 18.1%, a sodium bicarbonate content of 3.7%, and a water content of 78.2%; the purity of the phenol obtained by distillation is ≥99.5%, and the mother liquor of the stripping tower and the refining tower is returned to the neutralization process.

[0045] Example 3

[0046] The water quality composition of BDP wastewater is shown in the table above. Carbon dioxide gas with a purity of 99% is introduced until the pH of the solution drops to 10, then the introduction of carbon dioxide is stopped. The wastewater is heated and evaporated at an evaporation temperature of 98°C. The quality of the evaporated condensed water is controlled. Evaporation is stopped when the amount of condensed water is 40% of the mass of the original solution. The COD in the condensed water is 1820 mg / L and the phenol content is 0.82 g / L. The condensed water is discharged after biochemical treatment. After the evaporated concentrated liquid is cooled to room temperature of 25°C, carbon dioxide is continued to be introduced until the pH reaches 8.0, then the introduction of carbon dioxide is stopped, and the feed liquid is separated into solid-liquid separation to obtain sodium bicarbonate wet salt, which is then dried to obtain solid sodium bicarbonate. The liquid phase of the solid-liquid separation is layered, and the upper layer is returned to mix with the raw material and enter the neutralization process; the lower layer goes to the phenol refining process, such as Figure 2 As shown, the extractant is toluene, and the supplementary amount is 5% of the mass of the waste water entering the extraction tower; the waste water entering the distillation process has a phenol content of 19.0%, a sodium bicarbonate content of 3.5%, and a water content of 77.5%; the purity of the phenol obtained by distillation is ≥99.5%, and the mother liquor of 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. Take 1.4L of wastewater sample, adjust the pH to 8.0 with 20% concentrated hydrochloric acid, and then evaporate the wastewater directly. At 110℃, 1000g of condensate is obtained by evaporation. The COD of the condensate is 80000mg / L, the conductivity is 60μs / cm, and a mixture of viscous mother liquor and impure salts is obtained. The condensate has low conductivity and can be discharged through pipes after biochemical treatment; the impure salts and viscous mother liquor are difficult to separate, which is harmful to the environment and requires high hazardous waste treatment costs.

[0049] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one 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 present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to 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: The following steps are involved: (1) First, carbon dioxide is introduced into the BDP wastewater to cause a neutralization reaction; (2) evaporating and concentrating the BDP wastewater to obtain evaporation condensate and evaporation mother liquor, wherein the evaporation condensate is discharged after reducing COD; (3) after the evaporated mother liquor is cooled, excess carbon dioxide is introduced to generate sodium bicarbonate for precipitation; (4) After solid-liquid separation, wet salt and liquid phase are obtained, and the wet salt is dried to obtain sodium bicarbonate; after oil-water separation of the liquid phase, phenol-containing wastewater is obtained, which enters the distillation process to prepare high-purity phenol.

2. A method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that: In step (1), the endpoint pH value of the neutralization reaction is 10-11.

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 evaporation concentration is ≥98° C., and the amount of evaporated water is 30%-40% of the mass of the BDP wastewater before evaporation.

4. The method for treating wastewater from the production of flame retardant BDP according to claim 1, characterized in that: In step (2), the water temperature of the evaporated condensed water is less than 35°C.

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

0.

6. 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%.

7. 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: The phenol-containing wastewater is extracted with an extractant to obtain an organic phase and an aqueous phase; The organic phase enters a desolventizing tower to obtain an extractant and a phenol material, the extractant is returned to the extraction step, the phenol material is refined to obtain refined phenol and a heavy component in the bottom of the tower, and the heavy component in the bottom of the tower is returned to step (1); The aqueous phase enters the stripping tower to obtain a tower top gas phase and tower bottom waste water, the tower top gas phase is returned to the extraction process, and the tower bottom waste water is returned to step (1).

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

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

10. The 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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